By Topic

Communications, IEEE Transactions on

Issue 6 • Date June 2011

Filter Results

Displaying Results 1 - 25 of 32
  • Table of contents

    Page(s): c1 - c4
    Save to Project icon | Request Permissions | PDF file iconPDF (62 KB)  
    Freely Available from IEEE
  • [Staff list]

    Page(s): c2
    Save to Project icon | Request Permissions | PDF file iconPDF (58 KB)  
    Freely Available from IEEE
  • Filter and Nested Lattice Code Design for MIMO Fading Channels with Side-Information

    Page(s): 1489 - 1494
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (206 KB) |  | HTML iconHTML  

    Linear-assignment Gel'fand-Pinsker coding (LA-GPC) is a coding technique for channels with interference known only at the transmitter, where the known interference is treated as side-information (SI). As a special case of the LA-GPC, dirty paper coding has been shown to be able to achieve the optimal interference-free rate for SI channels with perfect channel state information at the transmitter (CSIT). In the cases where only the channel distribution information at the transmitter (CDIT) is available, LA-GPC also has good (sometimes optimal) performance in a variety of fast and slow fading SI channels. In this letter, we design filters in the nested lattice based coding to make it achieve the same rate performance as the LA-GPC in multiple-input multiple-output (MIMO) channels. Compared with the random Gaussian codebooks used in previous works, our resultant coding schemes have algebraic structures and can be implemented in practical systems. Simulations in slow-fading channels are provided, and near interference-free error performance is obtained. The proposed coding schemes can serve as the fundamental building blocks to achieve the promised rate performance of MIMO Gaussian broadcast channels with CDIT or perfect CSIT. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Comment on "An Exact Performance Analysis of MRC/OSTBC over Generalized Fading Channels"

    Page(s): 1495 - 1496
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (118 KB) |  | HTML iconHTML  

    In this comment, it is shown that the semi-numerical algorithm for computation of the ergodic channel capacity, which has been suggested in the paper cited by the headline above, can be replaced by a closed-form solution - either based on generalized hypergeometric functions or, in a more concise and elegant approach, on Meijer's G-function. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optimized Differential GFSK Demodulator

    Page(s): 1497 - 1501
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (277 KB) |  | HTML iconHTML  

    Gaussian frequency shift keying (GFSK) is a promising digital modulation scheme. The design of simple and high-performance receivers for GFSK systems is a challenging task. In this letter, we develop an optimized differential GFSK demodulator and investigate the phase wrapping issue in its implementation. Simulation results show bit-error-rate (BER) performance improvement in comparison with conventional differential demodulators in both AWGN and flat fading channels. We also compare our proposed demodulator with other existing alternatives in terms of BER performance. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An Optimized SDE Model for Slotted Aloha

    Page(s): 1502 - 1508
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (233 KB) |  | HTML iconHTML  

    We consider a stochastic differential equation (SDE) model of slotted Aloha with the retransmission probability as the associated parameter. We formulate the problem in both (a) the finite horizon and (b) the infinite horizon average cost settings. We apply the algorithm of for the first setting, while for the second, we adapt a related algorithm from that was originally developed in the simulation optimization framework. In the first setting, we obtain an optimal parameter trajectory that prescribes the parameter to use at any given instant while in the second setting, we obtain an optimal time-invariant parameter. Our algorithms are seen to exhibit good performance. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Post-Scheduling SINR Mismatch Analysis for Multiuser Orthogonal Random Beamforming Systems

    Page(s): 1509 - 1513
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (206 KB) |  | HTML iconHTML  

    In this letter, we analyze the post-scheduling SINR mismatch of a multiuser orthogonal random beamforming (ORBF) system. The mismatch probability is derived for a Gaussian broadcast channel with M transmit antennas and K single-antenna users. Numerical results are shown to be identical to theoretical results. The probability analysis enables us to calculate the minimum number of users to satisfy a target mismatch probability. Another way to use the mismatch probability is to control CQI mismatch handling mechanisms. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Per-Tone Transmit Antenna Selection with Phase Precoding for OFDM

    Page(s): 1514 - 1518
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (222 KB) |  | HTML iconHTML  

    If antenna selection in OFDM is done on a per-tone basis, the frequency domain can be exploited to achieve very good performance. However this means that the channel after antenna selection will have discontinuities in the frequency domain. In this paper we present a novel phase precoding that ensures that the channel after antenna selection is smooth enough in the frequency domain for advanced channel estimation. We analyse its performance and show that it is robust to channel estimation and reciprocity errors. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Error-Rate Performance Analysis of Incremental Decode-and-Forward Opportunistic Relaying

    Page(s): 1519 - 1524
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (242 KB) |  | HTML iconHTML  

    In this paper, we investigate an incremental opportunistic relaying scheme where the selected relay chooses to cooperate only if the source-destination channel is of an unacceptable quality. In our study, we consider regenerative relaying in which the decision to cooperate is based on a signal-to-noise ratio (SNR) threshold and takes into account the effect of the possible erroneously detected and transmitted data at the best relay. We derive a closed-form expression for the end-to-end bit-error rate (BER) of binary phase-shift keying (BPSK) modulation based on the exact probability density function (PDF) of each hop. Furthermore, we evaluate the asymptotic error performance and the diversity order is deduced. We show that performance simulation results coincide with our analytical results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Relay Selection from a Battery Energy Efficiency Perspective

    Page(s): 1525 - 1529
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (850 KB) |  | HTML iconHTML  

    The battery nonlinearity has never been considered for energy analysis in relay networks. In this letter, we adopt the realistic nonlinear battery model, apply the battery energy consumption results in to general relay networks, investigate the optimum and suboptimum energy allocation solutions for relaying transmission, and establish the relay selection criterion from the battery energy efficiency perspective. Our analyses and comparisons show that relaying does not always increase the system energy efficiency. We further establish closed-form conditions that can be easily checked to determine whether the relay transmission is preferable to the direct transmission. Numerical examples are also presented to verify these results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Hybrid ARQ Protocol for Multi-Antenna Multicasting Using a Common Feedback Channel

    Page(s): 1530 - 1542
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (558 KB) |  | HTML iconHTML  

    Wireless multicasting (also called common information broadcasting) is a technique where a common information message is transmitted to multiple users. This is typically accomplished by having the basestation broadcast out a signal representing this message. In this paper, we consider a multicasting scheme where the basestation transmits the multicasting signal without any a-priori knowledge of the users' channel state information. In this set-up, a hybrid automatic repeat request (ARQ) control is employed to improve the reliability of multicasting communication. In most hybrid ARQ set-ups, each user is usually allocated a dedicated feedback channel to tell the basestation if the previously transmitted signal was correctly decoded. However, dedicated feedback channels waste significant uplink resources, especially when the number of users is large. To mitigate this problem, we consider a negative acknowledgement (NACK) based hybrid ARQ control where the failed users are allowed to transmit the NACK signal (which is assumed to be the same for all users) through a common channel while the other users remain silent. We consider the effect of feedback error and multicasting signal decoding error on our hybrid ARQ system performance as the number of users grows large. Specifically, it is shown that the throughput performance of the proposed hybrid ARQ scheme using repetition retransmission is not severely degraded relative to the throughput performance of the noiseless feedback case. In addition, we show that the performance improvement obtained by replacing repetition encoding with incremental redundancy becomes insignificant for the large number of users asymptote. On the other hand, it is shown that the improvement provided by incremental redundancy is significant when some of the users are allowed to fail to decode the message. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Turbo Coded Noncoherent Space-Time Modulation Using Information-Bearing Pilots and Spatial Multiplexing

    Page(s): 1543 - 1554
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (588 KB) |  | HTML iconHTML  

    In this paper, we present a turbo coded space-time modulation scheme for noncoherent block fading channels, where neither the transmitter nor the receiver knows the channel state information. The turbo coded bits are divided into two parts which are respectively transmitted through information-bearing pilots and spatial multiplexing (SM). Since this approach effectively increases the cardinality of the set of possible transmit (space-time) signal matrices, a large rate gain can be obtained without increasing the modulation order, as shown through achievable-rate analysis. At the receiver, an iterative detection-decoding algorithm is performed cooperatively among the turbo decoder, the coherent demapper for the SM, and the noncoherent demapper for the information-bearing pilots through the help of the proposed signal matrix detector, which enables these two demappers to utilize the channel information inherent in all the received symbols within the same fading block. Compared to the previous work in the literature, the proposed scheme can provide advantages in both error performance and complexity. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Future Simplification of Procedure for Decoding Nonsystematic Reed-Solomon Codes Using the Berlekamp-Massey Algorithm

    Page(s): 1555 - 1562
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (273 KB) |  | HTML iconHTML  

    It is well-known that the Euclidean algorithm can be used o find the systematic errata-locator polynomial and the errata-evaluator polynomial simultaneously in Berlekamp's key equation that is needed to decode a Reed-Solomon (RS) codes. In this paper, a simplified decoding algorithm to correct both errors and erasures is used in conjunction with the Euclidean algorithm for efficiently decoding nonsystematic RS codes. In fact, this decoding algorithm is an appropriate modification to the algorithm developed by Shiozaki and Gao. Based on the ideas presented above, a fast algorithm described from Blahut's classic book is derivated and proved in this paper to correct erasures as well as errors by replacing the Euclidean algorithm by the Berlekamp-Massey (BM) algorithm. These facts lead to significantly reduce the decoding complexity of the proposed RS decoder. In addition, computer simulations show that this simple and fast decoding technique reduces the decoding time when compared with existing efficient algorithms including the new Euclidean-algorithm-based decoding approach proposed in this paper. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Cooperation via Trellis Pruning

    Page(s): 1563 - 1569
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB) |  | HTML iconHTML  

    This paper introduces a new approach to cooperative communications. Consider two partner nodes that cooperate to convey their data to a common destination, each transmitting not only its own "local" data but also acting as a relay for its partner, thereby effecting spatial diversity. In the proposed scheme, each partner multiplexes local data with relayed data and convolutionally encodes the resulting bitstream prior to transmission; the other partner then uses its knowledge of the relayed data to prune edges from the code trellis, thereby decoding at a lower (and more robust) rate. The destination observes two copies of each source's data - one transmitted as local information, the other transmitted as relayed information - and employs iterative decoding to recover the same. The resulting performance is superior to that of cooperation schemes based on time sharing - for example, a gain of 4.1 dB is observed at a frame-error rate of 10-3 with memory M = 3 codes - as well as schemes employing the newer algebraic superposition approach of Xiao et al., with trellis pruning enjoying an advantage of 0.55 dB to 1.04 dB over algebraic superposition, depending on M. The new approach requires some additional decoding complexity at each partner node, but the decoding complexity at the destination node is kept constant. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Precise BER Computation for Binary Data Detection in Bandlimited White Laplace Noise

    Page(s): 1570 - 1579
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (405 KB) |  | HTML iconHTML  

    Investigation into the characteristics and behaviours of Laplace noise is of crucial importance for evaluating the performance of communication systems operating in impulsive noise, as well as for ultra-wideband wireless systems operating in the presence of multi-user interference. The bit error rate performances of a binary data communication system operating in the presence of additive bandlimited white Laplace noise is analyzed theoretically. A theoretical expression for the average bit error rate is derived using the Beaulieu series for the optimal soft-limiting detector and the matched-filter detector when arbitrary pulse shapes are used. The bit error rate performance of a reduced complexity version of the optimal detector, the hard-limiting detector, and a reduced complexity version of the matched-filter detector, the sum-of-samples detector, are also analyzed. The analytical expressions for the bit error rate are validated by numerical examples. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Intermodulation Distortion in Multicarrier Satellite Systems: Analysis and Turbo Volterra Equalization

    Page(s): 1580 - 1590
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1262 KB) |  | HTML iconHTML  

    The urgent objective of transmitting high data rates over satellite, coupled with the challenge to maximize satellite mass efficiency, has necessitated that multiple carriers share the same transponder high-power amplifier (HPA). This paper presents analytical framework that characterizes the resulting intermodulation distortion (IMD) by utilizing Volterra series representation to account for the memory within the carrier itself and those associated with other carriers. Also provided is analytical evaluation of nonlinear IMD which involves computing statistical averages of higher-order products of Volterra series containing complex-valued symbols from multiple carriers. Using this theoretical characterization, novel algorithms are developed to overcome IMD in highly distortion-limited environments by employing the powerful Turbo equalization method with linear minimum mean-squared error criterion. Further, the solution is adaptive so compensation does not require prior knowledge of the HPA characteristics and can be rapidly responsive to variations in the environment. Through extensive simulations, it is shown that the proposed multicarrier analysis and Turbo Volterra techniques can be used to substantially remove IMD resulting from operating the nonlinear transponder HPA, shared by multiple carriers, near saturation. By applying more iterations of joint equalization and decoding, the solution can approach the ideal performance when feeding back correct decisions. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • ZF Detectors over Correlated K Fading MIMO Channels

    Page(s): 1591 - 1603
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB) |  | HTML iconHTML  

    This paper provides a systematic characterization of Zero-Forcing (ZF) detectors over multiple-input multiple-output (MIMO) channels that experience both small and large-scale fading. In particular, we consider the generic K distribution (Rayleigh/gamma distribution) to model the composite fading fluctuations and also assume the general case of semi-correlated small-scale fading. In the following, novel exact analytical expressions for the achievable sum rate are derived, followed by asymptotic expressions in the high and low Signal-to-Noise ratio (SNR) regimes. In these limiting cases, two common and insightful affine expansions are studied followed by new, closed-form upper and lower bounds on the sum rate that remain tight for all SNRs. In the second part of the paper, we present exact tractable expressions along with first-order expansions for the symbol error rate (SER) and outage probability; we also quantify the performance of ZF detectors in terms of diversity order and array (or coding) gain. The implications of the model parameters on the ZF detector performance are investigated via Monte-Carlo simulations which also validate the theoretical analysis. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Decision-Feedback Differential Detection in Impulse-Radio Ultra-Wideband Systems

    Page(s): 1604 - 1611
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (372 KB) |  | HTML iconHTML  

    In this paper we present decision-feedback differential detection (DF-DD) schemes for autocorrelation-based detection in impulse-radio ultra-wideband (IR-UWB) systems, a signaling scheme regarded as a promising candidate in particular for low-complexity wireless sensor networks. To this end, we first discuss ideal noncoherent sequence estimation and approximations thereof based on block-wise multiple-symbol differential detection (MSDD) and the Viterbi algorithm (VA) from the perspective of tree-search/trellis decoding. Exploiting relations well-known from tree-search decoding, we are able to derive the novel decision-feedback differential detection (DF-DD) schemes. A comprehensive comparison with respect to performance and complexity of the presented schemes in a typical IR-UWB scenario reveals-along with novel insights in techniques for complexity reduction of the sphere decoder applied for MSDD- that sorted DF-DD achieves close-to-optimum performance at very low, and in particular constant receiver complexity. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On Cubic Metric Reduction in OFDM Systems by Tone Reservation

    Page(s): 1612 - 1620
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (500 KB) |  | HTML iconHTML  

    One of the major drawbacks of multicarrier modulation is the large envelope fluctuations which either requires an inefficient use of high power amplifiers (HPAs) or decreases the system performance. Peak-to-average power ratio (PAPR) is the best known measure of the envelope fluctuations and is widely employed to design multicarrier systems. However, recently, another metric known as cubic metric (CM), is being considered in several multicarrier systems since it can predict HPA power de-rating more accurately. In this paper tone reservation (TR) technique, originally used for PAPR-reduction, is reformulated to reduce CM. We first simplify CM to define the objective function, denoted as objective CM (OCM). Then we demonstrate that OCM is convex and formulate TR for CM-reduction as an unconstrained convex optimization problem. The solution to this problem is found by means of an iterative algorithm which approaches the optimal solution with few steps. In this paper a low-complexity suboptimal algorithm capable of approaching the optimum with sufficient accuracy is also proposed. Simulation results show that for similar computational complexity, the performance of CM-reduction is superior to that of PAPR-reduction both in terms of bit error rate and out-of-band leakage. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High-SNR Performance of MIMO Multi-Channel Beamforming in Double-Scattering Channels

    Page(s): 1621 - 1631
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB) |  | HTML iconHTML  

    This paper investigates the symbol error rate (SER) performance of the multiple-input multiple-output (MIMO) multi-channel beamforming (MB) in the general double-scattering channel. We derive an asymptotic expansion on the marginal eigenvalue distribution of the MIMO channel matrix, and apply the result to get an approximate expression on the average SER at high signal-to-noise ratio (SNR). Two parameters pertaining to the SER, i.e., the diversity gain and the array gain, are analyzed. Our results show that it suffices for the double-scattering channel to have only limited scatterers, if the same diversity gain as the Rayleigh channel is desired; however, once the number of scatterers is below a certain level, the array gain in the double-scattering channel will vary with the SNR logarithmically. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Stability and Distributed Power Control in MANETs with Per Hop Retransmissions

    Page(s): 1632 - 1643
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (485 KB) |  | HTML iconHTML  

    In the current work the effects of hop-by-hop packet loss and retransmissions via ARQ protocols are investigated within a Mobile Ad-hoc NET-work (MANET). A success probability function is related to each link, which can be controlled by power and rate allocation. The expression for the network's stability region is initially derived where the success function plays a critical role. The investigation considers functions with specific properties which are shown to be satisfied for various expressions of the success probability related to different modulation and coding schemes as well as outage events. A Network Utility Maximization problem (NUM) with stability constraints is further formulated which decomposes into the input rate control and the scheduling problem. Under certain assumptions the latter is relaxed to a simpler form. This allows application of supermodular game theory and the algorithmic approach in is adapted to include the family of success functions of interest. It is shown finally that interference measurements per node drastically reduce the amount of information exchange required for solving the scheduling problem. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Power Allocation in Spectrum Sharing Cognitive Radio Networks with Quantized Channel Information

    Page(s): 1644 - 1656
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (477 KB) |  | HTML iconHTML  

    We consider a wideband spectrum sharing system where a secondary user can access a number of orthogonal frequency bands each licensed to a distinct primary user. We address the problem of optimum secondary transmit power allocation for its ergodic capacity maximization subject to an average sum (across the bands) transmit power constraint and individual average interference constraints on the primary users. The major contribution of our work lies in considering quantized channel state information (CSI) (for the vector channel space consisting of all secondary-to-secondary and secondary-to-primary channels) at the secondary transmitter as opposed to the prevalent assumption of full CSI in most existing work. It is assumed that a central entity called a cognitive radio network manager has access to the full CSI information from the secondary and primary receivers and designs (offline) an optimal power codebook based on the statistical information (channel distributions) of the channels and feeds back the index of the codebook to the secondary transmitter for every channel realization in real-time, via a delay-free noiseless limited feedback channel. A modified Generalized Lloyds-type algorithm (GLA) is designed for deriving the optimal power codebook, which is proved to be globally convergent and empirically consistent. An approximate quantized power allocation (AQPA) algorithm is presented, that performs very close to its GLA based counterpart for large number of feedback bits and is significantly faster. We also present an extension of the modified GLA based quantized power codebook design algorithm for the case when the feedback channel is noisy. Numerical studies illustrate that with only 3-4 bits of feedback per band, the modified GLA based algorithms provide secondary ergodic capacity very close to that achieved by full CSI and with only as little as 4 bits of feedback per band, AQPA provides a comparable performance, thus making it an attractive choice for prac- - tical implementation. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multi-Hop Coherent Free-Space Optical Communications over Atmospheric Turbulence Channels

    Page(s): 1657 - 1663
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (363 KB) |  | HTML iconHTML  

    In this paper, we investigate multi-hop relaying as an efficient fading mitigation tool for coherent free-space optical (FSO) systems over atmospheric turbulence channels. We consider an FSO relaying system with decode-and-forward relay nodes and multiple heterodyne receivers with modal compensation. Based on a recently introduced statistical characterization for the combined effects of log-normal turbulence fading and modal compensation, we derive the outage probability and quantify the potential performance improvements through the derivation of diversity-multiplexing tradeoff (DMT) and diversity gain. Our outage analysis yields impressive power savings for multi-hop relaying even with a single-relay. In addition, the DMT analysis in practical signal-to-noise ratio (SNR) ranges demonstrates that multi-hop transmission scheme improves finite-SNR diversity gain throughout the range of the multiplexing gain. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dynamic Resource Allocation in Multi-Service OFDMA Systems with Dynamic Queue Control

    Page(s): 1664 - 1674
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (549 KB) |  | HTML iconHTML  

    We consider the problem of resource allocation in downlink OFDMA systems for multi service and unknown environment. Due to users' mobility and intercell interference, the base station cannot predict neither the Signal to Noise Ratio (SNR) of each user in future time slots nor their probability distribution functions. In addition, the traffic is bursty in general with unknown arrival. The probability distribution functions of the SNR, channel state and traffic arrival/density are then unknown. Achieving a multi service Quality of Service (QoS) while optimizing the performance of the system (e.g. total throughput) is a hard and interesting task since it depends on the unknown future traffic and SNR values. In this paper we solve this problem by modeling the multiuser queuing system as a discrete time linear dynamic system. We develop a robust H controller to regulate the queues of different users. The queues and Packet Drop Rates (PDR) are controlled by proposing a minimum data rate according to the demanded service type of each user. The data rate vector proposed by the controller is then fed as a constraint to an instantaneous resource allocation framework. This instantaneous problem is formulated as a convex optimization problem for instantaneous subcarrier and power allocation decisions. Simulation results show small delays and better fairness among users. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Cramer-Rao Lower Bounds of DOA Estimates from Square QAM-Modulated Signals

    Page(s): 1675 - 1685
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (447 KB) |  | HTML iconHTML  

    In this paper, we derive for the first time analytical expressions for the inphase/quadrature (I/Q) non-data-aided (NDA) Cramér-Rao lower bounds (I/Q NDA CRLBs) of the direction of arrival (DOA) estimates from square quadrature amplitude (QAM)-modulated signals corrupted by additive white circular complex Gaussian noise (AWCCGN) with any antenna configuration. Yet the main contribution embodied by this paper consists in deriving for the first time analytical expressions for the NDA Fisher information matrix (FIM) and then for the stochastic CRLB of the NDA DOA estimates in the case of square QAM-modulated signals. It will be shown that in the presence of any unknown phase offset (i.e., non-coherent estimation), the ultimate achievable performance on the NDA DOA estimates holds almost the same irrespectively of the modulation order. However, the NDA CRLBs obtained in the absence of the phase offset (i.e., coherent estimation) vary, in the high SNR region, from one modulation order to another. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

IEEE Transactions on Communications focuses on all telecommunications including telephone, telegraphy, facsimile, and point-to-point television by electromagnetic propagation.

 

 

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Robert Schober
University of British Columbia