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	<channel>
		<title><![CDATA[ Wireless Communications, IEEE Transactions on - new TOC ]]></title>
		<link>http://ieeexplore.ieee.org</link>
		<description>TOC Alert for Publication# 7693 </description>
		<year>2009</year>
		<month>November </month>
		<day>06</day>
		<item>
			<title><![CDATA[IEEE Transactions on Wireless Communications]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288917]]></link>
			<description><![CDATA[ ]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288917]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>c1</startPage>
			<endPage>c1</endPage>
			<fileSize>105</fileSize>
			<authors><![CDATA[]]></authors>
		</item>
		<item>
			<title><![CDATA[Distributed Space-Time Trellis Codes for a Cooperative System]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288918]]></link>
			<description><![CDATA[In this paper, we propose a novel distributed spacetime trellis code (DSTTC) structure, and analyze its error performance in both slow and quasi-slow Rayleigh fading channels. The protocol adopted is decode-and-forward (DAF) with a single relay between the source and destination. Both scenarios with perfect and imperfect decoding at the relay are investigated. For imperfect decoding at the relay node, we consider an equivalent one-hop link model for the source-relay-destination path, and use it to modify the maximum likelihood detection metric by taking into account the equivalent signal-to-noise ratio (SNR) of the link model. The upper bounds of pairwise error probability (PEP) are derived for slow and quasi-slow Rayleigh fading channels, and the DSTTC design criteria are formulated accordingly. Based on the proposed design criteria, new DSTTCs are constructed by computer search. Simulation results demonstrate the superiority of the designed codes.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288918]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4897</startPage>
			<endPage>4905</endPage>
			<fileSize>266</fileSize>
			<authors><![CDATA[Yuan, J.;Chen, Z.;Li, Y.;Chu, L.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Interference Mitigation Using Uplink Power Control for Two-Tier Femtocell Networks]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288919]]></link>
			<description><![CDATA[This paper proposes two interference mitigation strategies that adjust the maximum transmit power of femtocell users to suppress the cross-tier interference at a macrocell base station (BS). The open-loop and the closed-loop control suppress the cross-tier interference less than a fixed threshold and an adaptive threshold based on the noise and interference (NI) level at the macrocell BS, respectively. Simulation results show that both schemes effectively compensate the uplink throughput degradation of the macrocell BS due to the cross-tier interference and that the closed-loop control provides better femtocell throughput than the open-loop control at a minimal cost of macrocell throughput.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288919]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4906</startPage>
			<endPage>4910</endPage>
			<fileSize>306</fileSize>
			<authors><![CDATA[Han-Shin Jo;Cheol Mun;June Moon;Jong-Gwan Yook;]]></authors>
		</item>
		<item>
			<title><![CDATA[Blind Adaptive Constrained MOE Receiver for Uplink MC-CDMA Systems with Real Signaling in Multi-Cell Environments]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288920]]></link>
			<description><![CDATA[A blind adaptive constrained minimum output energy (MOE) receiver has been proposed for the uplink multicarrier code-division multiple access (MC-CDMA) system in a multicell environment when some users, including the desired user, employ real-valued modulation such as binary phase-shift keying (BPSK) or amplitude-shift keying (ASK). Since the imaginary part of residual interference at the filter output does not affect the decision of the desired user¿s data in this case, the proposed receiver has been designed to perfectly eliminate the real part of residual in-cell interference using the information of the spreading sequence and to reduce the real part of residual intercell interference by minimizing the constrained output energy. Results of analysis and simulation show that the proposed blind adaptive algorithm converges faster and has a higher steadystate signal-to-interference and noise ratio (SINR) than those of conventional schemes.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288920]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4911</startPage>
			<endPage>4915</endPage>
			<fileSize>331</fileSize>
			<authors><![CDATA[Bangwon Seo;Hyung-Myung Kim;]]></authors>
		</item>
		<item>
			<title><![CDATA[Bit Error Rate of TH-BPSK UWB Receivers in Multiuser Interference]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288921]]></link>
			<description><![CDATA[It is well known that the Gaussian distribution is not an accurate model for approximating the probability density function (PDF) of the multiple access interference (MAI) in timehopping UWB (TH-UWB) systems. An exact theoretical model which explains the key features of the PDF of the MAI in THUWB systems is discussed. These features, which can be precisely anticipated by the proposed model include impulses, singularities, and the tail behaviour in the distribution of the MAI. The model reveals in quantitative terms why a Gaussian approximation for the MAI in TH-UWB systems is highly imprecise even in an environment with a large number of independent interferers. Based on the model obtained for the PDF of the MAI and exploiting the maximum a posteriori (MAP) receiver design rule, the optimal attainable BER performance of binary TH-UWB receivers in additive white Gaussian noise channels is numerically determined. The performances of some recently proposed UWB receivers are benchmarked against the optimal performance showing that some of them achieve near-optimal performance.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288921]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4916</startPage>
			<endPage>4921</endPage>
			<fileSize>290</fileSize>
			<authors><![CDATA[Hosseini, I.;Beaulieu, N.C.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Probability-Based Optimization of Inter-Sensing Duration and Power Control in Cognitive Radio]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288922]]></link>
			<description><![CDATA[Probability-based strategies are proposed in this letter to determine the optimal inter-sensing duration and power control for cognitive radio (CR). With utilization of the statistics of licensed band occupancy, appropriate inter-sensing duration is determined to capture the recurrence of spectrum opportunity in time when the licensed signal is detected, or to achieve the maximum spectrum efficiency under a certain level of interference with licensed communication when the licensed signal is declared absent. Transmit power is varied dynamically according to the non-interfering probability at each sample so as to increase the transmission rate and decrease the interference power.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288922]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4922</startPage>
			<endPage>4927</endPage>
			<fileSize>311</fileSize>
			<authors><![CDATA[Xiangwei Zhou;Jun Ma;Li, G.Y.;Young Hoon Kwon;Soong, A.C.K.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Joint Source/Relay Precoder Design in Nonregenerative Cooperative Systems Using an MMSE Criterion]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288923]]></link>
			<description><![CDATA[This paper considers transmitter precoding in an amplify-and-forward cooperative system where multiple antennas are equipped at the source, the relay, and the destination. Existing methods for the problem only consider the design of the relay precoder. To further improve the performance, we include the source precoder into the design. Using a minimum-meansquare- error (MMSE) criterion, we propose a joint source/relay precoder design method, taking both the direct and relay links into account. It is shown that the MMSE is a highly nonlinear function of the precoding matrices, and a direct minimization is not feasible. To facilitate analysis, we propose to design the precoders toward first diagonalizing the MSE matrix of the relay link. This imposes certain structural constraints on both precoders that allow us to derive an analytically tractable MSE upper bound. By conducting minimization with respect to this bound, the solution can be obtained by an iterative water-filling technique.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288923]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4928</startPage>
			<endPage>4933</endPage>
			<fileSize>265</fileSize>
			<authors><![CDATA[Fan-Shuo Tseng;Wen-Rong Wu;Jwo-Yuh Wu;]]></authors>
		</item>
		<item>
			<title><![CDATA[Performance Analysis of Soft-Bit Maximal Ratio Combining in Cooperative Relay Networks]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288924]]></link>
			<description><![CDATA[In digital cooperative relaying, signals from the source-destination and relay-destination links are combined at the destination to achieve spatial diversity. These signals may not necessarily belong to the same modulation scheme due to the varying channel qualities of the two links. Recently, we have proposed the ¿soft-bit maximum ratio combiner¿ (SBMRC) as a low complexity diversity combining scheme for signals with different modulation levels. SBMRC exhibits BER performance that is very close to the optimal maximum likelihood detector (MLD), but with much reduced complexity. In this paper, we revisit SBMRC and provide tight lower bound for the BER performance. Since SBMRC has BER performance slightly inferior to MLD, the derived lower bound can also be used as a good approximation for the BER performance of MLD.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288924]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4934</startPage>
			<endPage>4939</endPage>
			<fileSize>312</fileSize>
			<authors><![CDATA[Sediq, A.B.;Yanikomeroglu, H.;]]></authors>
		</item>
		<item>
			<title><![CDATA[On Joint Fine Time Adjustment and Channel Estimation for OFDM Systems]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288925]]></link>
			<description><![CDATA[This paper addresses training-sequence-based joint fine time adjustment and channel estimation for orthogonal frequency-division multiplexing systems. The proposed approach first derives an optimized threshold that adapts to the channel statistic and the signal-to-noise ratio. Then a practical suboptimal threshold is presented to avoid the estimation of the channel statistic. The suboptimal threshold requires no pre-simulations and performs as well as the optimal one. For performance analysis, the probability of perfect fine time adjustment given a particular threshold is also derived. The theoretical results agree well with the simulation results in both Rayleigh and Ricean channels.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288925]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4940</startPage>
			<endPage>4944</endPage>
			<fileSize>230</fileSize>
			<authors><![CDATA[Chin-Liang Wang;Hung-Chin Wang;]]></authors>
		</item>
		<item>
			<title><![CDATA[Cooperative Decode-and-Forward Relaying for Secondary Spectrum Access]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288926]]></link>
			<description><![CDATA[We propose a two-phase protocol based on cooperative decode-and-forward relaying for a secondary system to achieve spectrum access along with a primary system. The primary and secondary systems comprise of a transmitter-receiver pair, PT-PR and ST-SR, respectively. In the first transmission phase, PT transmits the primary signal to PR, which is also received by ST and SR, where it is decoded. At ST, the primary signal is regenerated and linearly combined with the secondary signal by assigning fractions &#x003B1; and (1¿&#x003B1;) of the available power to the primary and secondary signals respectively. This combined signal is then broadcasted by ST in the second transmission phase. We show that as long as ST is located within a critical radius from PT, there exists a threshold value for &#x003B1; above which the outage probability of the primary system will be equal to or lower than the case without spectrum sharing. We also determine the outage probability achieved by the secondary system. Theoretical and simulation results confirm the efficiency of the proposed spectrum sharing scheme.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288926]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4945</startPage>
			<endPage>4950</endPage>
			<fileSize>373</fileSize>
			<authors><![CDATA[Han, Y.;Pandharipande, A.;Ting, S.H.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Variance-Reduced Partial Parallel Interference Cancellation for MC-CDMA Uplink Systems]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288927]]></link>
			<description><![CDATA[In this paper, we present an improved version of partial parallel interference cancellation (PPIC), called variancereduced PPIC (VRPPIC), for multicarrier code division multiple access uplink systems. The VRPPIC detector is a combination of the PPIC receiver and a new bit estimator, where a simplified realization is derived for the main PPIC operations and soft decisions from PPIC are linearly combined by the bit estimator using appropriate weighting factors (derived from the PPIC weighting factors) to reduce the conditional variance of the final signal estimate. Also, we derive an optimal weighting factor (OWF) selection algorithm for VRPPIC based on minimizing a monotonically increasing conditional variance function. The derived OWFs for all the interference cancellation stages are equal and can easily be obtained from a linear function of the number of active users. Simulation results show that VRPPIC with the proposed OWFs significantly outperforms VRPPIC (or PPIC) with randomly selected weighting factors in multipath Rayleigh fading channels.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288927]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4951</startPage>
			<endPage>4956</endPage>
			<fileSize>279</fileSize>
			<authors><![CDATA[Chin-Liang Wang;Chang-Chen Chu;Chih-Chiang Wu;]]></authors>
		</item>
		<item>
			<title><![CDATA[An Efficient Adaptive Distributed Space-Time Coding Scheme for Cooperative Relaying]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288928]]></link>
			<description><![CDATA[A non-regenerative dual-hop wireless system based on distributed Alamouti space-time coding is considered. It is assumed that each relay retransmits an appropriately scaled space-time coded version of its received signal. The main goal of this paper is to find a scaling function for each relay to minimize the outage probability. In the high Signal-to-Noise Ratio (SNR) regime for the relay-destination link, it is shown that a threshold-based scaling function (i.e., the relay remains silent if its channel gain with the source is less than its predetermined threshold) is optimum from the outage probability point of view. Numerical results demonstrate a dramatic performance improvement as compared to the case that the relay stations forward their received signals with full power even for finite SNR scenarios.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288928]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4957</startPage>
			<endPage>4962</endPage>
			<fileSize>252</fileSize>
			<authors><![CDATA[Abouei, J.;Bagheri, H.;Khandani, A.K.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Amplify-and-Forward Cooperative OFDM with Multiple-Relays: Performance Analysis and Relay Selection Methods]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288929]]></link>
			<description><![CDATA[In this paper, we investigate a cooperative system with multiple relays and amplify-and-forward relaying over frequency-selective channels. To extract the available multipath diversity, we employ orthogonal frequency division multiplexing (OFDM) with precoding. Through the derivation of pairwise error probability (PEP), we demonstrate that PEP is not a simple exponential function of the signal-to-noise ratio (SNR), but it includes a term that involves some power of logarithm of the SNR. If that term is ignored, the diversity order is given by the summation of the channel length in the direct link and the minimum of channel lengths in each relaying link confirmed by simulation results. Based on the PEP expression, we also propose two relay selection strategies; one is on a per-subcarrier basis and the other is on an all-subcarrier basis. Our simulation results indicate that both strategies result in performance improvements although the per-subcarrier method performs better.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288929]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4963</startPage>
			<endPage>4968</endPage>
			<fileSize>275</fileSize>
			<authors><![CDATA[Ding, Y.;Uysal, M.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Frequency-Domain Bit-Flipping Equalizer for Wideband MIMO Channels]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288930]]></link>
			<description><![CDATA[We propose a low-complexity equalizer whose performance approaches that of the optimal maximum-likelihood estimators in wideband multiple-input multiple-output (MIMO) channels. The proposed algorithm makes use of a bit-flipping refinement procedure preceded by a frequency-domain equalizer and is based on local-optima searching algorithms. Through performance evaluations, it is demonstrated that the proposed equalizer can perform well when a large number of diversity branches are available in severely dispersive fading channels.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288930]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4969</startPage>
			<endPage>4973</endPage>
			<fileSize>464</fileSize>
			<authors><![CDATA[Koike-Akino, T.;Devroye, N.;Tarokh, V.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Error Performance of Digital Modulation Schemes with MRC Diversity Reception over &#x003B7;-&#x003BC; Fading Channels]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288931]]></link>
			<description><![CDATA[This paper provides exact-form expressions for the average symbol error probability (ASEP) of various digital modulation schemes with maximal ratio combining (MRC) diversity over L independent, not necessarily identically distributed (n.i.d.) &#x003B7;-&#x003BC; fading channels. The derived expressions are given in terms of the Lauricella and Appell hypergeometric functions and include several others available in the literature such as those for Nakagami-m and Hoyt. General asymptotic ASEP expressions are also derived for all the considered modulation schemes which provide useful insights regarding the factors affecting the performance of the considered system.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288931]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4974</startPage>
			<endPage>4980</endPage>
			<fileSize>800</fileSize>
			<authors><![CDATA[Peppas, K.;Lazarakis, F.;Alexandridis, A.;Dangakis, K.;]]></authors>
		</item>
		<item>
			<title><![CDATA[A Novel Uplink MIMO Transmission Scheme in a Multicell Environment]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288932]]></link>
			<description><![CDATA[Uplink multiple-input multiple-output (MIMO) transmission scheme is developed for time division duplex (TDD) systems in a multicell environment. We propose a precoding scheme that maximizes the total achievable rate and works in the decentralized manner with only locally available channel state information (CSI) at each transmitter. We first establish and solve a decentralized optimization problem for the case of multiple-input single-output (MISO) channels, introducing a new precoding design metric called signal to generated interference plus noise ratio (SGINR). By extending the result to general MIMO channels, we propose an SGINR-based precoding scheme where the number of transmit streams is selected adaptively to the surrounding environments. Simulation results confirm that the proposed precoding scheme offers significant throughput enhancement in multicell environments.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288932]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4981</startPage>
			<endPage>4987</endPage>
			<fileSize>746</fileSize>
			<authors><![CDATA[Byong Ok Lee;Hui Won Je;Oh-Soon Shin;Kwang Bok Lee;]]></authors>
		</item>
		<item>
			<title><![CDATA[Space-Time Codes for Multiple Access Systems with Low MMSE Decoding Complexity]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288933]]></link>
			<description><![CDATA[We study a class of space-time codes constructed by linear dispersion encoding that allow low-complexity linear minimum mean square error (MMSE) decoding for a multiple access system. Considering that the information symbols are drawn from square QAM constellations, we optimize rate-one spacetime code designs with MMSE decoding to achieve minimum bit error rate (BER) for any channel realization. In addition, the performance is further improved with a simple MMSE successive interference cancellation (MMSE-SIC) method. Simulation results compare the proposed design with existing rate-one designs and show that simple rate-one circulant designs are also good candidates for deployment in multiple access systems.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288933]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4988</startPage>
			<endPage>4992</endPage>
			<fileSize>214</fileSize>
			<authors><![CDATA[Fu-Te Hsu;Hsuan-Jung Su;]]></authors>
		</item>
		<item>
			<title><![CDATA[A Multilevel Coded Modulation Approach for Hexagonal Signal Constellation]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288934]]></link>
			<description><![CDATA[We propose a new coded modulation called hexagonal shell modulation (HSM). The HSM has a signal constellation composed of shell-like tiling of hexagons and thus has a lower peak-to-average power ratio (PAR) than a standard square quadrature amplitude modulation (QAM) with comparable bandwidth efficiency and minimum Euclidean distance. The main challenge is that HSM has a non-power-of-two number of constellation points, and thus assignment of binary information to HSM is not straightforward. We resolve this by applying a multilevel coded modulation (MLC) scheme where a ternary set partitioning combined with binary-input ternary-output (BITO) turbo codes is employed to fully exploit the property of the nonpower- of-two constellation points. Throughout this letter, we focus on an 18-ary HSM with the information rate of 3 bit/symbol as a specific example. It is shown that this system outperforms the standard square 16-QAM with the same rate when PAR is constrained.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288934]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4993</startPage>
			<endPage>4997</endPage>
			<fileSize>279</fileSize>
			<authors><![CDATA[Tanahashi, M.;Ochiai, H.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Adaptive Beamforming with Dimension Reduction in Spatially Correlated MISO Channels]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288935]]></link>
			<description><![CDATA[In this paper, we propose an adaptive beamforming scheme that generates the beam weight using dominant eigenvectors of the spatial covariance matrix. The number of eigenvectors used for the generation of beam weight is determined to maximize the signal-to-noise ratio (SNR) for given feedback constraints (e.g., the amount of feedback information and feedback delay). It is shown that the conventional limited feedback beamforming and eigen-beamforming are special cases of the proposed scheme. Simulation results show that the proposed beamforming scheme can effectively be applied to spatially correlated channels.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288935]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>4998</startPage>
			<endPage>5002</endPage>
			<fileSize>221</fileSize>
			<authors><![CDATA[Jae-Yun Ko;Yong-Hwan Lee;]]></authors>
		</item>
		<item>
			<title><![CDATA[Relay Selection for Secure Cooperative Networks with Jamming]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288936]]></link>
			<description><![CDATA[This paper deals with relay selection in cooperative networks with secrecy constraints. The proposed scheme enables an opportunistic selection of two relay nodes to increase security against eavesdroppers. The first relay operates as a conventional mode and assists a source to deliver its data to a destination via a Decode-and-Forward strategy. The second relay is used in order to create intentional interference at the eavesdropper nodes. The proposed selection technique jointly protects the primary destination against interference and eavesdropping and jams the reception of the eavesdropper. The new approach is analyzed for different complexity requirements based on instantaneous and average knowledge of the eavesdropper channels. In addition an investigation of an hybrid security scheme which switches between jamming and non-jamming protection is discussed in the paper. It is proven that an appropriate application of these two modes further improves security. The enhancements of the proposed selection techniques are demonstrated analytically and with simulation results.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288936]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5003</startPage>
			<endPage>5011</endPage>
			<fileSize>523</fileSize>
			<authors><![CDATA[Krikidis, I.;Thompson, J.S.;Mclaughlin, S.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Minimum Bit Error Rate Multiuser Transmission Designs Using Particle Swarm Optimisation]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288937]]></link>
			<description><![CDATA[We consider the downlink of a multiuser system equipped with multiple antennas transmitting to multiple singleantenna mobile receivers. Particle swarm optimisation (PSO) is invoked to solve the constrained nonlinear optimisation problem for the minimum bit error rate (MBER) multiuser transmitter (MUT). The proposed PSO aided symbol-specific MBER-MUT and average MBER-MUT schemes provide improved performance in comparison to the conventional minimum mean-squareerror MUT scheme, while imposing a reduced complexity compared to the state-of-the-art sequential quadratic programming based symbol-specific MBER-MUT and average MBER-MUT schemes, respectively.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288937]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5012</startPage>
			<endPage>5017</endPage>
			<fileSize>269</fileSize>
			<authors><![CDATA[Yao, W.;Chen, S.;Tan, S.;Hanzo, L.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Anti-Collision Backscatter Sensor Networks]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288938]]></link>
			<description><![CDATA[Sensor collision (interference) is studied in a large network of low bit-rate sensors that communicate via backscatter, i.e. modulate the reflection of a common carrier transmitted by a central reader. Closed-form analysis is provided, quantifying sensor collision (interference) in high-density, backscatter sensor networks (BSN), as a function of number of tags and aggregate bandwidth. Analysis is applicable to a broad class of sensor subcarrier modulations, propagation environments and reader antenna directivity patterns. It is discovered that anti-collision performance in high-density backscatter sensor networks is feasible provided that appropriate modulation is used at each sensor. That is due to the round-trip nature of backscatter communication as well as the extended target range, which both impose stringent requirements on spectrum efficiency, not easily met by all modulations. Furthermore, aggregate bandwidth savings for given anti-collision performance are quantified, when simple division techniques on subcarrier (modulating) frequency and space (via moderately directive hub antenna) are combined.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288938]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5018</startPage>
			<endPage>5029</endPage>
			<fileSize>755</fileSize>
			<authors><![CDATA[Bletsas, A.;Siachalou, S.;Sahalos, J.N.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Leveraging Multi-AP Diversity for Transmission Resilience in Wireless Networks: Architecture and Performance Analysis]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288939]]></link>
			<description><![CDATA[With the increasing development of IEEE 802.11 based Wireless Local Area Network (WLAN) devices, large-scale multi-cell WLANs with a high density of users and access points (APs) have emerged widely in various hotspots. Providing resilient data transmission has been a primary challenge for scaling the WLANs because the high density of users and APs results in too many collisions. In this paper, we analyze and point out the defect of the single association mechanism defined in IEEE 802.11 on transmission reliability from a network perspective. Then, we propose a "multi-AP" architecture with which a MAC layer device called an AP Controller (AC) is employed to enable each user to associate and cooperate with multiple APs. In this way, the users can benefit from the diversity effect of multipaths with independent collisions and transmission errors. This paper concentrates on the theoretical analysis of performance comparison between the proposed "Multi-AP" architecture and that in IEEE 802.11. Extensive simulation results show that the proposed "multi-AP" architecture can obtain much better performance in terms of the throughput per user and the total throughput, and the performance gain is position dependent. Moreover, the unfairness issue in traditional WLANs due to capture effect can be alleviated properly in the "multi-AP" framework.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288939]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5030</startPage>
			<endPage>5040</endPage>
			<fileSize>575</fileSize>
			<authors><![CDATA[Zhu, Y.;Zhang, Q.;Niu, Z.;Zhu, J.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Precoder Design for Non-Regenerative MIMO Relay Systems]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288940]]></link>
			<description><![CDATA[This paper studies the precoder design for a 3- node non-generative MIMO relay channel, taking the direct link transmission into consideration. We first look into the scenario where precoding is only performed at the relay. Our analytical approach enables a relay precoding design to achieve better ergodic capacity than the precoding design to achieve a lower bound of the capacity reported in earlier works. We next propose an iterative algorithm to perform joint precoding design at both the source and the relay. To reduce the computation complexity of the iterative algorithm, a two-step algorithm is then developed. Our numerical results show that under some circumstances, capacity gain can be achieved by performing precoding at both the source and the relay compared to the case where precoding is performed at the relay only. The efficiency of the proposed two-step algorithm is verified since it achieves roughly identical capacity as the iterative joint precoding scheme.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288940]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5041</startPage>
			<endPage>5049</endPage>
			<fileSize>383</fileSize>
			<authors><![CDATA[Mo, R.;Chew, Y.H.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Intelligent RFID Tag Detection Using Support Vector Machine]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288941]]></link>
			<description><![CDATA[RFID Tag detection/recognition is one of the most critical issues for successful deployment of RFID systems in diverse applications. The main factors influencing tag detection by RFID reader antenna include tag position, relative position of reader, read field length, etc. In this paper, we analyze the characteristics of tag detection for a carton box object on a wooden pallet by an experimental approach based on tag signal strength, and we propose a method for predicting detection related directly to the strength of tag signal using an intelligent machine learning technique called support vector machine (SVM). The use of the proposed method is able to save time and cost by quick prediction of tag detection. Extensive experiments showed that the proposed approach can predict tag recognition for a carton box object with an accuracy at 95% for various reader heights and read field lengths. The proposed approach is effective for determining the best tag detection influencing factor conditioned on the target object with the help of detectability prediction.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288941]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5050</startPage>
			<endPage>5059</endPage>
			<fileSize>429</fileSize>
			<authors><![CDATA[Minho Jo;Hee Yong Youn;Hsiao-Hwa Chen;]]></authors>
		</item>
		<item>
			<title><![CDATA[A Comprehensive Framework for Performance Analysis of Dual¿Hop Cooperative Wireless Systems with Fixed¿Gain Relays over Generalized Fading Channels]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288942]]></link>
			<description><![CDATA[In the present contribution, we propose a comprehensive framework for the analysis of cooperative dual¿hop wireless systems over generalized fading channels, which use an Amplify and Forward (AF) relaying mechanism with blind and semi¿blind relays. In particular, the proposed framework provides either exact results or very accurate bounds for computing the Moment Generating Function (MGF) of the end¿ to¿end Signal¿to¿Noise Ratio (SNR) for various fading channel models typically encountered in real propagation environments. Furthermore, with the help of the MGF¿based approach for performance analysis of wireless systems over fading channels, we will show that important performance indexes can be easily derived from the MGF. With respect to previous published articles on the matter, the main contribution of the paper is twofold: i) by relying on the properties of the Meijer¿G function, either exact expressions or accurate bounds for the MGF of the end¿to¿end SNR are provided, and ii) the analysis encompasses the vast majority of fading channel models. Numerical and simulation results will be compared to substantiate the analytical derivation.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288942]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5060</startPage>
			<endPage>5074</endPage>
			<fileSize>732</fileSize>
			<authors><![CDATA[Renzo, M.D.;Graziosi, F.;]]></authors>
		</item>
		<item>
			<title><![CDATA[A Graph Theory Based Opportunistic Link Scheduling for Wireless Ad Hoc Networks]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288943]]></link>
			<description><![CDATA[Taking advantage of the independent fading channel conditions among multiple wireless users, opportunistic transmissions schedule the user with the instantaneously best condition and thus increase the spectrum utilization efficiency of wireless networks. So far, most proposed opportunistic scheduling policies for ad hoc networks exploit local multiuser diversity, i.e., each transmitter selects its best receiver independently. However, due to co-channel interference, the decisions of neighboring transmitters are highly correlated. Furthermore, the neighboring links without a common sender also experience independent channel fading. Taking the contention relationship and the channel diversity among links into account, we extend the concept of multi-user diversity to a more generalized one, by which a set of senders cooperatively schedule the instantaneously and globally best out-going links, thus the spatial diversity of the channel variation can be further exploited. In this paper, we formulate the opportunistic scheduling problem with fairness requirements into an optimization problem and present its optimal solution, i.e., the optimal scheduling policy. We also propose GOS, a distributed Graph theory based and Opportunistic Scheduling algorithm, which modifies IEEE 802.11 protocol to implement the optimal scheduling policy. Theoretical analysis and simulation results both verify that our implementation achieves higher network throughput and provides better fairness support than the existing algorithms.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288943]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5075</startPage>
			<endPage>5085</endPage>
			<fileSize>463</fileSize>
			<authors><![CDATA[Chen, Q.;Zhang, Q.;Niu, Z.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Unipolar Space-Time Codes with Reduced Decoding Complexity for TH-UWB with PPM]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288944]]></link>
			<description><![CDATA[In this paper, we consider the problem of Space- Time (ST) coding with unipolar Pulse Position Modulations (PPM) and propose a novel ST code that satisfies a large number of construction constraints rendering it superior to the existing PPM encoding schemes. In particular, the proposed 2 ÿ 2 code achieves a full transmit diversity order while transmitting at a rate of 1 PPM-symbol per channel use. The proposed scheme can be associated with M-ary PPM constellations for all even values of M without introducing any constellation expansion. This renders the proposed scheme suitable for low cost carrier-less Ultra-Wideband (UWB) systems where information must be conveyed only by the time delays of the modulated sub-nanosecond pulses without introducing any amplitude amplifications or phase rotations. Finally, the proposed scheme can be associated with a reduced complexity optimal Maximum-Likelihood (ML) decoder that takes the structure of the proposed code into consideration in order to simplify the decoding procedure. We also propose a simple diversity-preserving suboptimal decoder that requires approximately half the number of multiplications compared to the ML decoder. Possible extensions to transmitters equipped with three antennas are also discussed in situations where a certain number of feedback bits is available.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288944]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5086</startPage>
			<endPage>5095</endPage>
			<fileSize>378</fileSize>
			<authors><![CDATA[Abou-Rjeily, C.;Bkassiny, M.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Distributive Subband Allocation, Power and Rate Control for Relay-Assisted OFDMA Cellular System with Imperfect System State Knowledge]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288945]]></link>
			<description><![CDATA[In this paper, we consider distributive subband, power and rate allocation for a two-hop downlink transmission in an orthogonal frequency-division multiple-access (OFDMA) cellular system with fixed relays which operate in decode-andforward strategy. We take into account of the penalty of packet errors due to imperfect CSIT and system fairness by considering weighted sum goodput as our optimization objective. Based on the cluster-based architecture, we obtain a fast-converging distributive solution with only local imperfect CSIT by using decomposition of the optimization problem. To further reduce the signaling overhead and computational complexity, we propose a reduced feedback distributive solution, which can achieve asymptotically optimal performance for large number of users with arbitrarily small feedback overhead per user.We also derive asymptotic average system throughput so as to obtain useful design insights.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288945]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5096</startPage>
			<endPage>5102</endPage>
			<fileSize>508</fileSize>
			<authors><![CDATA[Ying Cui;Vincent K. N. Lau;Rui Wang;]]></authors>
		</item>
		<item>
			<title><![CDATA[Impact of Node Density on Throughput and Delay Scaling in Multi-Hop Wireless Networks]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288946]]></link>
			<description><![CDATA[This paper studies the impact of node density on the end-to-end throughput and delay in multi-hop wireless networks. In existing work, each packet is most assumed to be relayed through one cell at each hop and the hop progress is approximated by the square root of a cell area, which does not correspond to the actual hop progress in the real network. In this paper, we calculate the hop progress by taking into account the effect of node density (i.e., the number of nodes within the transmission range of each node), and obtain the required hop count for a multi-hop path. Based on the result, we further discuss the scaling relations between node density and throughput and delay in multi-hop wireless networks. The effects of power control on the scaling relations are also examined. The results show that the impact of node density on the throughput and delay scaling is significant. Specifically, with a larger node density, the required hop count is reduced, resulting in exponential growth of the throughput. However, larger node density incurs more contentions among neighboring nodes. Consequently, it causes linear degradation in throughput. With our model, this trade-off is readily observed.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288946]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5103</startPage>
			<endPage>5111</endPage>
			<fileSize>839</fileSize>
			<authors><![CDATA[Jia-Chun Kuo;Wanjiun Liao;Ting-Chao Hou;]]></authors>
		</item>
		<item>
			<title><![CDATA[Nonquiet Primary User Detection for OFDMA-Based Cognitive Radio Systems]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288947]]></link>
			<description><![CDATA[Cognitive radio (CR) is one of the most promising solutions to the scarcity of radio spectrum. In CR systems, the channel sensing technique to detect the appearance of a primary user (PU) directly affects the performances of both CR user and PU. In this paper, we propose a nonquiet channel sensing scheme for the orthogonal frequency division multiple access (OFDMA)- based CR systems. The proposed nonquiet PU detection scheme is based on the reasoning that a CR user can detect the PU even though the signal transmitted from other CR user interferes with the detection, if the interference power is sufficiently low. Since the interference power decreases as the channel condition between the transmitter and receiver CR users gets worse, the proposed scheme regards the sensing results with deeper channel fading as more reliable, given that the received signal power from PU is unknown. We design a linear combining scheme which integrates multiple sensing results to obtain spectral, temporal, and spatial diversity gain. We also suggest a system-wide PU detection mechanism based on the proposed combining scheme. The simulation results show that the proposed scheme can detect the appearance of PU effectively while achieving high utilization of the CR system.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288947]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5112</startPage>
			<endPage>5123</endPage>
			<fileSize>819</fileSize>
			<authors><![CDATA[Jeong, S.S.;Jeong, D.G.;Jeon, W.S.;]]></authors>
		</item>
		<item>
			<title><![CDATA[A Design for an EXIT Chart Based Scheduling and Rate Control for Multi-User MIMO Systems]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288948]]></link>
			<description><![CDATA[This paper proposes a scheduling and adaptive rate control scheme for multi-user multiple-input multiple-output (MIMO) systems in the uplink, designed to improve system throughput in single-carrier broadband wireless systems exploiting a frequency domain soft canceller with minimum mean square error (FD-SC/MMSE) turbo equalizer. Aiming at the reduction of computational burden involved in the scheduling and adaptive rate control while maintaining high throughput efficiency, scheduling including a stream selection is first conducted in the base station (BS) based on the expected signal to noise power ratio (SNR) under an assumption that the turbo receiver is converged. The BS then conducts a coding rate optimization for each scheduled stream to maximize the throughput efficiency. A main contribution is to reveal a mechanism that the convergence property is controlled to maximize the throughput efficiency by a prediction of the iterative behavior based on extrinsic information transfer (EXIT) trajectory which is predicted from channel transfer functions and a window control proposed in this paper. Computer simulation confirms that the achievable average system throughput can be significantly improved by the proposed scheme.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288948]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5124</startPage>
			<endPage>5132</endPage>
			<fileSize>1007</fileSize>
			<authors><![CDATA[Obata, H.;Ibi, S.;Sampei, S.;]]></authors>
		</item>
		<item>
			<title><![CDATA[A Universal Encoding Scheme for MIMO Transmission Using a Single Active Element for PSK Modulation Schemes]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288949]]></link>
			<description><![CDATA[A universal scheme for encoding multiple symbol streams using a single driven element (and consequently a single radio frequency (RF) frontend) surrounded by parasitic elements (PE) loaded with variable reactive loads, is proposed in this paper. The proposed scheme is based on creating a MIMO system by expanding the far-field of a compact parasitic array into an orthogonal set of angular functions (basis). Independent information streams are encoded by means of angular variations of the far-field in the wavevector domain, rather than spatial variations as usually happens in conventional MIMO systems. The array can spatially multiplex the input streams by creating all the desired linear combinations (for a given modulation scheme) of the basis functions. The desired combinations are obtained by projecting the ratio of the symbols to be spatially multiplexed on the ratio of the basis functions¿ weights (complex coefficients), which is a function of the currents induced on the PE within the antenna domain, and controlled by the independent reactive loadings.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288949]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5133</startPage>
			<endPage>5142</endPage>
			<fileSize>1469</fileSize>
			<authors><![CDATA[Alrabadi, O.N.;Papadias, C.B.;Kalis, A.;Prasad, R.;]]></authors>
		</item>
		<item>
			<title><![CDATA[A Two-Level Medium Access Framework for Exploiting Multi-User Diversity in Multi-Rate IEEE 802.11 Wireless LANs]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288950]]></link>
			<description><![CDATA[Fast rate adaptation has long been recognized as an effective way to improve the PHY-layer data rate of wireless networks. However, in random access wireless networks such as IEEE 802.11 wireless LANs, MAC-layer throughput is dominated by stations with the lowest transmission rates, resulting in an underutilization of spectrum bandwidth. In this paper, we propose a novel two-level medium access framework, referred to as Two-Level MAC, to solve the aforementioned problem and to significantly improve system spectrum efficiency through the exploitation of multiuser diversity. The key idea of Two-Level MAC is to introduce a second level of deterministic channel access on top of the traditional IEEE 802.11 DCF protocol. By doing so, higher priority is granted to high-rate stations in a fully distributed manner. Meanwhile, collisions among potential contending stations are drastically reduced. Through analysis, we show how such Two-Level MAC can be optimized to achieve the maximum system throughput. The superiority of the proposed protocol is verified through analyses and extensive simulations.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288950]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5144</startPage>
			<endPage>5154</endPage>
			<fileSize>491</fileSize>
			<authors><![CDATA[Da Rui Chen;Ying Jun Zhang;]]></authors>
		</item>
		<item>
			<title><![CDATA[Fountain Code Design for Data Multicast with Side Information]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288951]]></link>
			<description><![CDATA[Fountain codes are a robust solution for data multicasting to a large number of receivers which experience variable channel conditions and different packet loss rates. However, the standard fountain code design becomes inefficient if all receivers have access to some side information correlated with the source information. We focus our attention on the cases where the correlation of the source and side information can be modelled by a binary erasure channel (BEC) or by a binary input additive white Gaussian noise channel (BIAWGNC). We analyse the performance of fountain codes in data multicasting with side information for these cases, derive bounds on their performance and provide a fast and robust linear programming optimization framework for code parameters. We demonstrate that systematic Raptor code design can be employed as a possible solution to the problem at the cost of higher encoding/decoding complexity, as it reduces the side information scenario to a channel coding problem. However, our results also indicate that a simpler solution, non-systematic LT and Raptor codes, can be designed to perform close to the information theoretic bounds.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288951]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5155</startPage>
			<endPage>5165</endPage>
			<fileSize>1046</fileSize>
			<authors><![CDATA[Sejdinovic, D.;Piechocki, R.J.;Doufexi, A.;Ismail, M.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Maximum Channel Throughput via Cooperative Spectrum Sensing in Cognitive Radio Networks]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288952]]></link>
			<description><![CDATA[In cognitive radio networks, the secondary (unlicensed) users need to find idle channels via spectrum sensing for their transmission. Cooperative spectrum sensing (CSS) is a promising technology in spectrum sensing with an admirable performance. In CSS, multiple secondary users individually sense the idle channels and send their decisions to the network center, and then the center will do a final decision. In this paper, we focus on the optimal sensing settings of the CSS to maximize the channel throughput under some constraints on the interference to cognitive radio network. Particularly, we consider two scenarios in this paper. In the first scenario, only one channel is sensed at one time, and we aim at maximizing an individual channel capacity. Some simple algorithms are also derived to calculate the optimal solution for the first scenario. In the second scenario, multiple channels are jointly sensed simultaneously, and our objective is to maximize the overall channel capacity. We prove that the optimization problem in the second scenario can be converted into a convex-optimization problem, which can be solved efficiently and reliably. Simulation results show a significant improvement of the channel capacity by using the proposed optimal CSS in cognitive radio networks.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288952]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5166</startPage>
			<endPage>5175</endPage>
			<fileSize>445</fileSize>
			<authors><![CDATA[Shen, J.;Jiang, T.;Liu, S.;Zhang, Z.;]]></authors>
		</item>
		<item>
			<title><![CDATA[New PAPR-Preserving Mapping Methods for Single-Carrier FDMA with Space-Frequency Block Codes]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288953]]></link>
			<description><![CDATA[Innovative mapping schemes for Space-Frequency Block Codes (SFBC) which are compatible with the structure of Single-Carrier Frequency Division Multiple Access (SC-FDMA) systems are introduced. We first show that existing space-time and space-frequency block codes lack flexibility in terms of framing or cause a degradation of the signal envelope properties when combined with SC-FDMA. Then, we present an Alamoutibased orthogonal code designed for 2 transmit antennas that makes use of an innovative mapping in the frequency domain to preserve the low envelope properties of SC-FDMA. Next, an extension of this concept to a quasi-orthogonal code for 4 transmit antennas is presented and analyzed. We prove the good performance of the proposed schemes over multiple-input multiple-output (MIMO) channels both in static and in highmobility scenarios.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288953]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5176</startPage>
			<endPage>5186</endPage>
			<fileSize>563</fileSize>
			<authors><![CDATA[Ciochina, C.;Castelain, D.;Mottier, D.;Sari, H.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Distributed Transmit Power Allocation for Multihop Cognitive-Radio Systems]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288954]]></link>
			<description><![CDATA[In this paper, we consider a relay-assisted wideband cognitive-radio (CR) system under the assumption that the frequency band chosen by the CR relay network for unlicensed spectrum usage overlaps with one or more bands dedicated to primary (e.g., licensed) narrowband links. Our objective is to optimize the performance of the CR system while limiting the interference in direction of the primary receivers, without requiring any adaptation of the transmitted signal spectra at the cognitive nodes. To this end, we study appropriate transmit power allocation (TPA) strategies among the cognitive relays. We first investigate the optimal centralized (OC) TPA solution and show that it can be formulated as a linear program. Since the OC-TPA solution requires a considerable amount of information exchange between the cognitive nodes, we develop two distributed TPA schemes, namely (i) a fully decentralized (FD) TPA scheme and (ii) a distributed feedback-assisted (DFA) TPA scheme. The FD-TPA scheme aims at maximizing the output signal-tointerference- plus-noise ratio (SINR) at the destination node of the CR network according to a best-effort strategy. It requires neither feedback information from the destination node nor an exchange of channel state information between the cognitive relays. The DFA-TPA scheme, on the other hand, utilizes feedback information from the destination node, in order to achieve a predefined target output SINR value, while minimizing the overall transmit power spent by the relays. Analytical and simulationbased performance results illustrate that notable performance improvements compared to non-cooperative transmission (i.e., without relay assistance) are achieved by the proposed schemes, especially when more than two hops are considered. In particular, the proposed distributed TPA schemes typically perform close to the OC-TPA solution.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288954]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5187</startPage>
			<endPage>5201</endPage>
			<fileSize>595</fileSize>
			<authors><![CDATA[Mietzner, J.;Lampe, L.;Schober, R.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Distributed Energy Efficient Spectrum Access in Cognitive Radio Wireless Ad Hoc Networks]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288955]]></link>
			<description><![CDATA[In this paper, energy efficient spectrum access is considered for a wireless cognitive radio ad hoc network, where each node is equipped with cognitive radio, has limited energy, and the network is an OFDMA system operating on time slots. In each slot, the users with new traffic demand will sense the spectrum and locate the available subcarrier set. Given the data rate requirement and maximal power limit, a constrained optimization problem is formulated for each individual user to minimize the energy consumption per bit over all selected subcarriers, while avoid introducing harmful interference to the existing users. Because of the multi-dimensional and non-convex nature of the problem, a fully distributed subcarrier selection and power allocation algorithm is proposed by combining an unconstrained optimization method with a constrained partitioning procedure. Due to the non-cooperative behavior among new users, they will execute distributed power control to manage the co-channel interference when needed. Simulation results demonstrate that the proposed scheme performs tightly to the global optimal solution. In addition, the comparison between the proposed energy efficient allocation scheme and the well established rate or power efficient allocation algorithms is carried out to demonstrate the advantage of the proposed scheme in terms of network lifetime.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288955]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5202</startPage>
			<endPage>5213</endPage>
			<fileSize>842</fileSize>
			<authors><![CDATA[Gao, S.;Qian, L.;Vaman, D.R.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Transmission Control with Imperfect CSI in Channel-Aware Slotted ALOHA Networks]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288956]]></link>
			<description><![CDATA[The impact of imperfect channel state information (CSI) on the transmission control of channel-aware slotted ALOHA networks is studied in this work. By taking into consideration the statistics of the channel estimation error to maximize the achievable stable throughput, we obtain the optimal transmission control policy that determines the transmission probability, rate, and power that should be adopted under different channel states. Specifically, with imperfect CSI, we find that high transmission probabilities should be assigned to channel states that allow for high probability of successful transmission (which may be affected by the estimation errors), but rate allocation must be performed more conservatively (compared to the case with perfect CSI) in order to avoid transmission errors due to imprecise channel estimates. The policies are first developed for single carrier systems and then extended to multicarrier systems with maximum per-user power constraints. The asymptotic maximal stable throughput is analyzed for both the single and multiple carrier systems as the number of users goes to infinity. We observe that, with error in the channel estimate, the proposed transmission control policy that takes into consideration the error statistics may significantly increase the throughput compared to strategies that are derived under the perfect CSI assumption.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288956]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5214</startPage>
			<endPage>5224</endPage>
			<fileSize>592</fileSize>
			<authors><![CDATA[Shu-Hsien Wang;Hong, Y.-W.P.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Asymptotic Optimality for Distributed Spectrum Sharing using Bargaining Solutions]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288957]]></link>
			<description><![CDATA[Recent studies on spectrum usage reveal poor utilization, both spatially and temporally. Opportunistic use of licensed spectrum while limiting interference to primary users can enhance spectrum reuse and provide orders of magnitude improvement in available channel capacity. This calls for spectrum sharing protocols that are dynamic, flexible, and efficient, in addition to being fair to end users. We employ cooperative game theory to address the opportunistic spectrum access problem. Specifically, we develop a game-theoretic model to analyze a scenario in which nodes in a wireless network seek to agree on a fair and efficient allocation of spectrum. First, we show that in high interference environments, the utility space of the game is non-convex, making certain optimal allocations unachievable with pure strategies. To mitigate this, we show that as the number of channels available increases, the utility space approaches convexity, thereby making optimal allocations achievable with pure strategies. Second, by comparing and analyzing three bargaining solutions, we show that the Nash Bargaining Solution achieves the best tradeoff between fairness and efficiency, using a small number of channels. Finally, we develop a distributed algorithm for spectrum sharing that is general enough to accomodate non-zero disagreement points, and show that it achieves allocations reasonably close to the Nash Bargaining Solution.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288957]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5225</startPage>
			<endPage>5237</endPage>
			<fileSize>736</fileSize>
			<authors><![CDATA[Suris, J.E.;Dasilva, L.A.;Han, Z.;Mackenzie, A.B.;Komali, R.S.;]]></authors>
		</item>
		<item>
			<title><![CDATA[The RF-Chain Limited MIMO System¿Part I: Optimum Diversity-Multiplexing Tradeoff]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288958]]></link>
			<description><![CDATA[The large gain promised by the multi-input multioutput (MIMO) technology comes with a cost. In particular, multiple analog radio frequency (RF) chains, which are expensive and power consuming, are required at both the transmitter and receiver sides. On the other hand, the antennas connecting to the RF chains are less expensive. Hence, one engineering compromise is to implement more antennas than RF chains and to use only a subset of them based on some antenna selection (AS) algorithm. An interesting question therefore arises: given a RF chain limited MIMO system, what is the fundamental performance gain by adding more antennas? In this two-part paper, we answer this question by using the diversity-multiplexing (D-M) gain tradeoff metric. Consider a Rayleigh fading channel with M<sub>t</sub>) antennas and L<sub>t</sub> (L<sub>t</sub> &#x02A7D; M<sub>t</sub>) RF chains at the transmitter while M<sub>r</sub> antennas and L<sub>r</sub> (L<sub>r</sub> &#x02A7D; M<sub>r</sub>) RF chains at the receiver. We obtain the fundamental D-M tradeoff as a function of M<sub>t</sub>, M<sub>r</sub>, and min(L<sub>r</sub>, L<sub>t</sub>). Referring to the special case where L<sub>t</sub> = M<sub>t</sub>) and L<sub>r</sub> = M<sub>r</sub> as the RF unlimited system (or full system) and RF limited system (or pruned system) otherwise, we prove that the pruned system with optimal channel-dependent AS has the same D-M tradeoff as the full system if the multiplexing gain is less than some integer threshold P, while it suffers from some diversity gain loss for multiplexing gains larger than P. In particular, if min(L<sub>r</sub>, L<sub>t</sub>) = K = min(M<sub>r</sub>, M<sub>t</sub>), then P = K, i.e. the D-M tradeoffs of the pruned system and the full system are the same. Moreover, this result can be extended to more general fading channels such as Nakagami channel. A fast and D-M tradeoff-optimal AS algorithm is proposed as a byproduct of our analysis. Index Terms?Antenna selection, dive-
rsity gain, fast algorithm, MIMO, Nakagami fading, outage probability, Rayleigh fading, spatial multiplexing gain, tradeoff.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288958]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5238</startPage>
			<endPage>5247</endPage>
			<fileSize>371</fileSize>
			<authors><![CDATA[Jiang, Y.;Varanasi, M.K.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Phoenix: Making Cooperation More Efficient through Network Coding in Wireless Networks]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288959]]></link>
			<description><![CDATA[This paper introduces a novel MAC protocol for wireless networks, called Phoenix, that employs ideas from Network Coding to enhance decode and forward cooperation. A relay is allowed to code data of its own together with a corrupted packet during a retransmission at no additional cost in bandwidth. Therefore, while in conventional cooperative protocols a node becomes a relay only to assist other terminals, with our proposal a cooperator can also serve its own traffic. We evaluate Phoenix¿s performance by means of a theoretical model and extensive simulation campaigns. We show that Phoenix is especially beneficial in multihop settings and interesting gains over benchmark protocols can be achieved.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288959]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5248</startPage>
			<endPage>5258</endPage>
			<fileSize>370</fileSize>
			<authors><![CDATA[Munari, A.;Rossetto, F.;Zorzi, M.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Opportunistic Spectrum Scheduling for Multiuser Cognitive Radio: A Queueing Analysis]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288960]]></link>
			<description><![CDATA[We develop a queueing analytic framework to study the data link layer quality-of-service performance measures for cognitive radio users in an infrastructure-based dynamic spectrum access environment. In order to allocate the available spectrum white spaces among the cognitive radio users in a spectrum overlay scenario, an opportunistic scheduling scheme is considered. The queueing model considers bursty traffic arrival pattern at the cognitive radio user ends, finite buffer size, activity of primary users (i.e., dynamic channel availability), and correlated channel fading. We present a step-by-step procedure to derive the delay distribution, average throughput, and packet loss rate for the cognitive radio users. The proposed framework facilitates cross-layer design for improved QoS experience in cognitive radio networks. Usefulness of the developed analytical model is demonstrated through example applications.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288960]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5259</startPage>
			<endPage>5269</endPage>
			<fileSize>648</fileSize>
			<authors><![CDATA[Rashid, M.M.;Hossain, Md.J.;Hossain, E.;Bhargava, V.K.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Spatial Spectrum Holes for Cognitive Radio with Relay-Assisted Directional Transmission]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288961]]></link>
			<description><![CDATA[Spectrum hole (SH) is defined as a spectrum band that can be utilized by unlicensed users, which is a basic resource for cognitive radio (CR) systems. Most of existing contributions detect SHs by sensing whether a primary signal is present or absent and then try to access them so that the CR and primary users use the spectrum band either at different time slots or in different geographic regions. In this paper, we propose a novel scheme with relays or directional relays for CR users to exploit new spectrum opportunity, called spatial SH. It can provide higher spectrum efficiency by coexistence of primary and CR users at the same region, time, and spectrum band. In particular, when the spectrum opportunity of a direct link from a CR transmitter to a CR receiver does not appear, our scheme may still establish the communication through indirect links, i.e., other CR users act as relay stations to assist the communication by using other spatial domains. Furthermore, we analyze the successful communication probabilities of CR users and demonstrate that the spectrum efficiency can be considerably improved by our scheme.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288961]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5270</startPage>
			<endPage>5279</endPage>
			<fileSize>1117</fileSize>
			<authors><![CDATA[Zhao, G.;Ma, J.;Li, G.Y.;Wu, T.;Kwon, Y.;Soong, A.;Yang, C.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Noncooperative Carrier Sense Game in Wireless Networks]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288962]]></link>
			<description><![CDATA[The performance of carrier sense multiple access (CSMA) wireless networks heavily depends on the level of spatial reuse, i.e., how many concurrent transmissions are allowed. Spatial reuse is primarily determined by physical carrier sense, and a key parameter for physical carrier sense is the carrier sense threshold. Our focus is on how to control the carrier sense threshold for improving network performance. We present a noncooperative game-theoretic framework, which leads to a fully distributed algorithm for tuning the carrier sense threshold. We introduce a utility function of each node, which is a nondecreasing concave function of the carrier sense threshold. A pricing function is further introduced to mitigate severe interference among nodes. The cost function is defined as the difference between the pricing and the utility functions. We prove that the noncooperative carrier sense game admits a unique Nash equilibrium (NE) under some technical conditions.We derive sufficient conditions that ensure the convergence of the synchronous and asynchronous update algorithms. Based on the analysis, we propose a fully distributed algorithm, entitled noncooperative carrier sense update algorithm (NCUA). Our simulation study indicates that NCUA outperforms standard CSMA with respect to the per-node throughput by 10¿50%.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288962]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5280</startPage>
			<endPage>5289</endPage>
			<fileSize>507</fileSize>
			<authors><![CDATA[Kyung-Joon Park;Hou, J.C.;Basar, T.;Hwangnam Kim;]]></authors>
		</item>
		<item>
			<title><![CDATA[Per-Node Based Optimal Power Control for Multi-Hop Cognitive Radio Networks]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288963]]></link>
			<description><![CDATA[Cognitive radio network (CRN) is a promising approach to improve spectrum efficiency for wireless networking. This paper investigates how to perform optimal power control on each node (or per-node based power control) in the network so as to optimize network performance. Per-node based power control is a difficult problem due to its large design space (i.e., interaction among the powers on different nodes in the network) and the coupling relationship between power control and upper layers (scheduling and routing). In this paper, we develop a formal mathematical model for joint power control, scheduling, and routing. We formulate a cross-layer optimization problem encompassing these three layers and develop a unified solution procedure based on branch-and-bound framework and convex hull relaxation. Using numerical results, we demonstrate the efficacy of the solution procedure and offer insights on the behavior of per-node based power control.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288963]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5290</startPage>
			<endPage>5299</endPage>
			<fileSize>460</fileSize>
			<authors><![CDATA[Shi, Y.;Hou, Y.T.;Zhou, H.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Opportunity Detection for OFDMA-Based Cognitive Radio Systems with Timing Misalignment]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288964]]></link>
			<description><![CDATA[Accurate detection of spectrum opportunities within the frequency band of an orthogonal frequency division multiple access (OFDMA) system carries critical importance for OFDMAbased cognitive radios. In this paper, we analyze the opportunity detection performances of energy detection and ESPRIT (estimation of signal parameters by rotational invariance techniques) algorithms in the presence of timing misalignments in uplink (UL) OFDMA. For the energy detector, the statistics of subcarrier power are derived considering timing misalignments, and they are verified through computer simulations. Using these statistics, which take inter-carrier-interference (ICI) effects into account, receiver operating characteristics (ROCs) of the energy detector receiver are obtained. It is shown that energy detection has a considerably better performance than ESPRIT, especially when the subcarrier assignment changes frequently. Moreover, a closed form expression is derived for the UL-OFDMA synchronization point that minimizes the ICI. Finally, it is shown that employing resource allocation blocks with larger sizes in the primary network yields better opportunities for the cognitive radio.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288964]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5300</startPage>
			<endPage>5313</endPage>
			<fileSize>732</fileSize>
			<authors><![CDATA[Sahin, M.E.;Guvenc, I.;Arslan, H.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Coverage in Multi-Antenna Two-Tier Networks]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288965]]></link>
			<description><![CDATA[In two-tier networks ¿ comprising a conventional cellular network overlaid with shorter range hotspots (e.g. femtocells, distributed antennas, or wired relays) ¿ with universal frequency reuse, the near-far effect from cross-tier interference creates dead spots where reliable coverage cannot be guaranteed to users in either tier. Equipping the macrocell and femtocells with multiple antennas enhances robustness against the nearfar problem. This work derives the maximum number of simultaneously transmitting multiple antenna femtocells meeting a per-tier outage probability constraint. Coverage dead zones are presented wherein cross-tier interference bottlenecks cellular and femtocell coverage. Two operating regimes are shown namely 1) a cellular-limited regime in which femtocell users experience unacceptable cross-tier interference and 2) a hotspot-limited regime wherein both femtocell users and cellular users are limited by hotspot interference. Our analysis accounts for the per-tier transmit powers, the number of transmit antennas (single antenna transmission being a special case) and terrestrial propagation such as the Rayleigh fading and the path loss exponents. Single-user (SU) multiple antenna transmission at each tier is shown to provide significantly superior coverage and spatial reuse relative to multiuser (MU) transmission.We propose a decentralized carrier-sensing approach to regulate femtocell transmission powers based on their location. Considering a worst-case cell-edge location, simulations using typical path loss scenarios show that our interference management strategy provides reliable cellular coverage with about 60 femtocells per cell-site.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288965]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5314</startPage>
			<endPage>5327</endPage>
			<fileSize>938</fileSize>
			<authors><![CDATA[Chandrasekhar, V.;Kountouris, M.;Andrews, J.G.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Optimal Symbol Timing for OFDM Wireless Communications]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288966]]></link>
			<description><![CDATA[Orthogonal frequency division multiplexing (OFDM) has become a promising physical layer modulation technology for beyond 3G or 4G wireless communications due to effective inter-symbol interference mitigation for high speed data transmission. However, the timing of the OFDM symbol, i.e., the placement of the DFT collection window in a multi-path time dispersive channel remains an important and challenging issue in OFDM receiver design. An erroneous timing decision creates inter-symbol interference (ISI), inter-carrier interference (ICI), channel attenuation, and channel estimation error, which leads to a penalty on the collected OFDM symbol signal to noise ratio (SNR) resulting in an irreducible error floor. In this paper we quantify such effects and derive an optimal OFDM symbol timing solution in the sense of maximizing the signal to interference ratio (SIR) of the collected OFDM symbol. A practical timing algorithm, referred to as the equilibrium algorithm, is then developed to approximate the optimal timing decision. Compared with existing schemes in the literature, the proposed approach does not rely on explicit detection of individual channel paths or the delay spread boundary and therefore greatly reduces timing complexity. The equilibrium algorithm performs nearly as well as the optimal solution over a variety of channel delay spreads, is simple to implement, and is robust to channel estimation errors.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288966]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5328</startPage>
			<endPage>5337</endPage>
			<fileSize>823</fileSize>
			<authors><![CDATA[Wang, M.M.;Xiao, L.;Brown, T.;Dong, M.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Channel Estimation in OFDM Systems with Unknown Interference]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288967]]></link>
			<description><![CDATA[We investigate the problem of channel estimation in an orthogonal frequency-division multiplexing (OFDM) system plagued by unknown narrowband interference (NBI). Such scenario arises in many practical contexts, including cellular applications and emerging spectrum sharing systems, where coexistence of different types of wireless services over the same frequency band may result into remarkable co-channel interference. Estimation algorithms devised for conventional OFDM transmissions are expected to suffer from significant performance degradation in the presence of NBI. To overcome this difficulty, in the present work we follow a novel pilot-aided approach where the interference power on each pilot subcarrier is treated as a nuisance parameter which is averaged out from the corresponding likelihood function. The latter is then maximized in an iterative fashion according to the expectation-maximization (EM) principle or by applying the Jacobi-Newton algorithm. The resulting schemes have affordable complexity and are inherently robust to NBI. Their accuracy is investigated by means of computer simulations and compared with the relevant Cramer- Rao bound.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288967]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5338</startPage>
			<endPage>5347</endPage>
			<fileSize>566</fileSize>
			<authors><![CDATA[Morelli, M.;Moretti, M.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Integrated Energy Analysis of Error Correcting Codes and Modulation for Energy Efficient Wireless Sensor Nodes]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288968]]></link>
			<description><![CDATA[Optimizing energy consumption is a key objective in designing wireless sensor nodes. It has been shown earlier [1] that the node energy is strongly influenced by the modulation and the error correcting code (ECC) used. The utility of using ECC from an energy perspective is determined by the energy saving due to the ECC coding gain vis-a-vis the energy overhead of "redundant" bits and of encoding/decoding computation. Furthermore, the node energy varies with the change in errorcorrecting capability and code word length of a particular ECC as well as the modulation constellation size. The ECC coding gain is influenced by the constellation size. In this paper, the node energy variations with ECC and modulation parameters are analyzed for an energy optimal node design for the nodes operating in the additive white Gaussian noise channel. Based on this analysis, we compute the per information bit node energy and this is used to select an "optimal" ECC and modulation scheme pair. Our results show that the energy optimal ECC-modulation pair selected for some specific operating conditions could save as much as 50% energy. In nutshell, our work is targeted towards reducing the search space and finding an energy optimal ECCmodulation pair for the given environment and application.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288968]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5348</startPage>
			<endPage>5355</endPage>
			<fileSize>345</fileSize>
			<authors><![CDATA[Chouhan, S.;Bose, R.;Balakrishnan, M.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Characterization of Fading on Fixed Wireless Channels between 200 MHz and 2 GHz in Suburban Macrocell Environments]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288969]]></link>
			<description><![CDATA[Growing use of point-to-multipoint fixed wireless networks to support network access and SCADA applications in suburban macrocell environments has prompted regulators to re-allocate various bands between 200 MHz and 2 GHz to such applications. Links in such networks are usually obstructed by buildings and foliage and are classified as non-line-of-sight. Although it is well-known that such links are susceptible to fading caused by windblown trees and foliage, most past efforts to characterize fading on such links have focused on frequency bands at 1.9 GHz and above. Here, we show how signal fading in the 220, 850 and 1900 MHz bands vary with both distance and time-averaged wind speed in a representative macrocell environment. Based upon time-series of received signal strength collected in a typical macrocell environment with moderate foliage at locations between 1 and 4 km from a transmitting site located 80 m above ground level, we show that fading on such links is relatively severe at 1.9 GHz but decreases rapidly as the carrier frequency decreases. We have expressed our results in the form of a first-order simulation model. Additional data will be required to estimate standardized model parameters that can be applied to a broad range of environments.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288969]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5356</startPage>
			<endPage>5365</endPage>
			<fileSize>767</fileSize>
			<authors><![CDATA[Liou, A.;Sivertsen, K.N.;Arjmandi, P.;Viswanathan, G.;Diallo, B.;Lancashire, S.;Michelson, D.G.;]]></authors>
		</item>
		<item>
			<title><![CDATA[Energy Consumption and Message Delay Analysis of QoS Enhanced Base Station Controlled Dynamic Clustering Protocol for Wireless Sensor Networks]]></title>
			<link><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288970]]></link>
			<description><![CDATA[This paper proposes and analyzes a Quality of service enhanced Base station Controlled Dynamic Clustering Protocol (QBCDCP), suitable for the support of video and imaging traffic over resource constrained wireless sensor nodes. The protocol achieves energy efficiency through a rotating head clustering approach and delegation of energy-intensive tasks to a single high-power base station, while providing quality of service (QoS) support by including delay and bandwidth parameters in the route selection process. A Time Division Multiple Access (TDMA) scheme is used for intra- and intercluster communication, providing bandwidth reservation. Performance of QBCDCP is evaluated in terms of energy consumption and end-to-end image delay via analytical and discrete-event simulation techniques. Numerical results provide insights on the selection of network parameters such as number of clusters that improve the sensing node lifetime while maintaining high quality of service. The results also demonstrate the trade-off between end-to-end image delay and sensor node lifetime.]]></description>
			<pubDate><![CDATA[October  2009]]></pubDate>
			<guid><![CDATA[http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=5288916&arnumber=5288970]]></guid>
			<volume>8</volume>
			<issue>10</issue>
			<startPage>5366</startPage>
			<endPage>5374</endPage>
			<fileSize>688</fileSize>
			<authors><![CDATA[Fapojuwo, A.O.;Cano-Tinoco, A.;]]></authors>
		</item>
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