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Communications, IEEE Transactions on

Issue 10 • Date October 2011

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Displaying Results 1 - 25 of 32
  • Table of contents

    Publication Year: 2011 , Page(s): c1 - c4
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  • [Staff list]

    Publication Year: 2011 , Page(s): c2
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  • The Universality of Generalized Hamming Code for Multiple Sources

    Publication Year: 2011 , Page(s): 2641 - 2647
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (238 KB) |  | HTML iconHTML  

    We consider zero-error Slepian-Wolf coding for a special kind of correlated sources known as Hamming sources. Moreover, we focus on the design of codes with minimum redundancy (i.e., perfect codes). As shown in a prior work by Koulgi et al., the design of a perfect code for a general source is very difficult and in fact is NP-hard. In our recent work, we introduce a subset of perfect codes for Hamming sources known as Hamming Codes for Multiple Sources (HCMSs). In this work, we extend HCMSs to generalized HCMSs, which can be proved to include all perfect codes for Hamming sources. To prove our main result, we first show that any perfect code for a Hamming source with two terminals is equivalent to a Hamming code for asymmetric Slepian Wolf coding (c.f. Lemma 2). We then show that any multi-terminal (of more than two terminals) perfect code can be transformed to a perfect code for two terminals (c.f. Lemma 3) and to a perfect code with an asymmetric form (c.f. Lemma 4). Equipped with these results, we prove that every perfect Slepian-Wolf code for Hamming sources is equivalent to a generalized HCMS. View full abstract»

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  • New Representations for the Gaussian Class Multivariate Weibull Distribution with Constant Correlation and Applications

    Publication Year: 2011 , Page(s): 2648 - 2653
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (250 KB) |  | HTML iconHTML  

    Novel single-integral representations for the multivariate probability density functions (PDFs) and cumulative distribution functions (CDFs) of the Gaussian class Weibull distribution are derived. The solutions are expressed in terms of familiar mathematical functions which are available in common mathematical software. The well known equal (constant) correlation model is considered. A special linear transformation of independent Gaussian random variables is used to generate correlated Weibull random variables. The advantage of the new representation is that only a single integral computation is needed to compute a N-dimensional distribution. The new representation of the CDF is used for the performance evaluation of a selection diversity combiner operating in equally correlated Weibull fading channels. The new PDF representation is also used for an analysis of the moments of the output signal-to-noise ratio of an equal-gain diversity combiner operating in equally correlated Weibull fading channels. View full abstract»

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  • A New Formula for the BER of Binary Modulations with Dual-Branch Selection over Generalized-K

    Publication Year: 2011 , Page(s): 2654 - 2658
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (230 KB) |  | HTML iconHTML  

    Error performance is one of the main performance measures and the derivation of its closed-form expression has proved to be quite involved for certain communication systems operating over composite fading channels. In this letter, a unified closed-form expression, applicable to different binary modulation schemes, for the bit error rate of dual-branch selection diversity based systems undergoing independent but not necessarily identically distributed generalized-K fading is derived in terms of the extended generalized bivariate Meijer G-function. View full abstract»

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  • Flexible Spectrum Access for Opportunistic Secondary Operation in Cognitive Radio Networks

    Publication Year: 2011 , Page(s): 2659 - 2664
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (420 KB) |  | HTML iconHTML  

    In this letter a Discrete-Time Markov Chain (DTMC) framework is adopted to capture the effect of flexible spectrum channelization for the opportunistic access of secondary users (SUs) in a primary-secondary shared spectrum scenario. Two implementation alternatives are proposed: a fixed channelization scheme (FCS) and an adaptive channelization scheme (ACS). Moreover, service-type characterization of SUs is also addressed by defining time vs. volume based services. Results indicate the suitability of the ACS over the FCS. View full abstract»

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  • Frame Synchronization of Coded Modulations in Time-Varying Channels via Per-Survivor Processing

    Publication Year: 2011 , Page(s): 2665 - 2670
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (250 KB) |  | HTML iconHTML  

    In this letter, an optimum frame synchronizer is proposed for coded modulations in channels with uncertainties. Coded modulations include various frame synchronization scenarios, e.g., convolutionally coded transmissions and nonlinear modulations with memory. Frame synchronization is proposed as a maximum a posteriori probability estimation implemented using trellis path search for Markov chain decoding. In addition, time-varying uncertainties such as frequency offset and phase noise are jointly estimated via per-survivor processing as frame synchronization proceeds. The proposed frame synchronizer exploits the coding gain of coded modulations to achieve better performance than conventional frame synchronizers. We show that the resulting frame synchronizer consists of a correlation term and two data correction terms. Numerical results show that the proposed frame synchronizer is robust to uncertainties at the receiver and it exhibits improved performance. View full abstract»

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  • Energy Efficiency Analysis of Some Cooperative and Non-Cooperative Transmission Schemes in Wireless Sensor Networks

    Publication Year: 2011 , Page(s): 2671 - 2677
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (300 KB) |  | HTML iconHTML  

    We compare the energy efficiency of some transmission schemes in wireless sensor networks. By constraining the system to end-to-end throughput requirements, we assume that the nodes in multi-hop and cooperative schemes operate at a spectral efficiency which is twice that of the single-hop transmission. By taking into account the energy consumption of the RF circuitry, we show that cooperation may be considerably more energy efficient than non-cooperative schemes even in small transmission ranges, specially if a feedback channel is available. View full abstract»

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  • MIMO Relaying: Distributed TAS/MRC in Nakagami-m Fading

    Publication Year: 2011 , Page(s): 2678 - 2682
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (300 KB) |  | HTML iconHTML  

    We develop a unified framework for the symbol error rate (SER) of distributed transmit antenna selection with receiver maximal-ratio combining (TAS/MRC) in multiple-input multiple-output (MIMO) relay networks. We focus on nonregenerative relaying with NS, NR, and ND antennas at the source, relay, and destination, respectively. We consider the general fading scenario of Nakagami-m fading with distinct m fading parameters in the source-to-relay and the relay-to-destination links. We present new analytical expressions for the statistics of the end-to-end signal-to-noise ratio (SNR). Specifically, we derive exact expressions and first order expansions for the cumulative distribution function and moment generating function of the end-to-end SNR. Based on these, we derive new closed-form expressions for the asymptotic SER under M-ary phase-shift keying (M-PSK) and M-ary quadrature amplitude modulation (M-QAM). Our asymptotic solutions accurately identify the diversity order and the array gain as two key design components of the network. View full abstract»

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  • Effective Informed Dynamic Scheduling for Belief Propagation Decoding of LDPC Codes

    Publication Year: 2011 , Page(s): 2683 - 2691
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (604 KB) |  | HTML iconHTML  

    The simultaneous flooding scheduling is popular for Low-Density Parity-Check (LDPC) Belief Propagation (BP) decoding. Non-simultaneous sequential scheduling is superior to the flooding scheduling, and asynchronous dynamic scheduling has better FER performance than the sequential scheduling. However, all strategies encounter the trouble of locating the error variable node. This paper proposes an informed dynamic scheduling strategy, which utilizes the instability of the variable node and the residual of the variable-to-check message to locate the message to be updated first. The informed dynamic scheduling overcomes the trapping sets effectively. This paper also designs an informed dynamic scheduling strategy with adaptivity to pass more messages in parallel, which effectively postpones the influence of cycles in the Tanner graph. In some sense, the strategy lengthens cycles. Simulation results show that the two informed dynamic scheduling strategies outperform other algorithms. View full abstract»

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  • On BICM Receivers for TCM Transmission

    Publication Year: 2011 , Page(s): 2692 - 2702
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (479 KB) |  | HTML iconHTML  

    Recent results have shown that the performance of bit-interleaved coded modulation (BICM) using convolutional codes in nonfading channels can be significantly improved when the interleaver takes a trivial form (BICM-T), i.e., when it does not interleave the bits at all. In this paper, we give a formal explanation for these results and show that BICM-T is, in fact, the combination of a TCM transmitter and a BICM receiver. To predict the performance of BICM-T, a new type of distance spectrum for convolutional codes is introduced, analytical bounds based on this spectrum are developed, and asymptotic approximations are presented. It is shown that the free Hamming distance of the code is not the relevant optimization criterion for BICM-T. Asymptotically optimal convolutional codes for different constraint lengths are tabulated and BICM-T is shown to offer asymptotic gains of about 2 dB over traditional BICM designs based on random interleavers. The asymptotic gains over uncoded transmission are found to be the same as those obtained by Ungerboeck's one-dimensional trellis-coded modulation (1D-TCM), and therefore, in nonfading channels, BICM-T is shown to be as good as 1D-TCM. View full abstract»

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  • Error Rate for PSK and QAM Modulations for Non-Ideal OFDM Systems with Noisy Channel Estimates and Receive Diversity

    Publication Year: 2011 , Page(s): 2703 - 2715
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (494 KB) |  | HTML iconHTML  

    This paper characterizes the SER for a non-ideal OFDM system with either M-PSK or M-QAM constellations operating over a frequency-selective, time-varying, Rayleigh fading channel. The imperfections that we consider are inter-carrier interference (ICI) and/or inter-symbol interference (ISI), imperfect time and frequency synchronization, and noisy channel estimates. We consider an MRC receiver with L diversity branches. We present SER characterizations with and without ISI, and show that the effect of ISI, especially for higher order modulation schemes, e.g., 8PSK and above, can be very severe, irrespective of the number of diversity branches. View full abstract»

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  • Diversity Gain Regions for MIMO Fading Broadcast Channels

    Publication Year: 2011 , Page(s): 2716 - 2728
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (574 KB) |  | HTML iconHTML  

    In wireless communication systems, users with heterogeneous information content constrain the network by having different reliability requirements. In this paper an information-theoretic framework is proposed to study communication systems which provide heterogeneous reliabilities for the users. This is done by defining individual probabilities of error for the users in the network and obtaining their fundamental tradeoffs. Using this framework, a system can be realized, which can provide a tradeoff of reliabilities among the users for a fixed vector of users' rates. This adds a completely new dimension to the performance tradeoff in such networks, which is beyond what is given by the conventional performance versus rate tradeoff in single-user systems. Although this is a very general concept and can be applied to any multi-terminal communication system, in this paper we consider multiple-input multiple-output (MIMO) fading broadcast channel. In particular, we quantify the reliability tradeoff by introducing the notion of diversity gain region (DGR), which specifies the set of diversity gain vectors that are simultaneously achievable by the users for a fixed vector of users' multiplexing gains. We show the existence of a tradeoff among the users' diversity gains by deriving inner and outer bounds for the DGR. View full abstract»

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  • Soft-In Soft-Out DFE and Bi-Directional DFE

    Publication Year: 2011 , Page(s): 2729 - 2741
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (446 KB) |  | HTML iconHTML  

    We design a soft-in soft-out (SISO) decision feedback equalizer (DFE) that performs better than its linear counterpart in turbo equalizer (TE) setting. Unlike previously developed SISO-DFEs, the present DFE scheme relies on extrinsic information formulation that directly takes into account the error propagation effect. With this new approach, both error rate simulation and the extrinsic information transfer (EXIT) chart analysis indicate that the proposed SISO-DFE is superior to the well-known SISO linear equalizer (LE). This result is in contrast with the general understanding today that the error propagation effect of the DFE degrades the overall TE performance below that of the TE based on a LE. We also describe a new extrinsic information combining strategy involving the outputs of two DFEs running in opposite directions, that explores error correlation between the two sets of DFE outputs. When this method is combined with the new DFE extrinsic information formulation, the resulting "bidirectional" turbo-DFE achieves excellent performance-complexity tradeoffs compared to the TE based on the BCJR algorithm or on the LE. Unlike turbo LE or turbo DFE, the turbo BiDFE's performance does not degrade significantly as the feedforward and feedback filter taps are constrained to be time-invariant. View full abstract»

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  • Linear Diversity Combining on Nakagami-0.5 Fading Channels

    Publication Year: 2011 , Page(s): 2742 - 2752
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (390 KB) |  | HTML iconHTML  

    The Nakagami-0.5 distribution is an important special case of the Nakagami distribution as it represents a worst case fading scenario. This scenario is of particular significance for wireless applications with high quality of service requirements. The bit error probability (BEP) performances of three basic diversity combining schemes in Nakagami-0.5 fading are considered. It is shown that the error rate performances of dual branch equal gain and selection combining (SC) diversity are identical regardless of modulation format. It is also shown that L-branch maximal ratio combining diversity in Nakagami-0.5 fading has the same BEP performance as single branch reception in Nakagami-L/2 fading with L times the transmission power of each branch. A useful upper bound for the BEP of L-branch SC diversity in Nakagami-0.5 fading is also derived. The performance degradation for the worst case Nakagami-0.5 fading relative to Rayleigh fading can be as much as 24.6 dB for a dual-diversity receiver at target BEP of 10-6. The additional resources required to restore a specified performance level, as increased channel signal-to-noise ratio and as number of additional diversity branches, are quantified. It is concluded that worst case Nakagami channels can result in dramatically poorer performance than Rayleigh channels, making proper system design and evaluation essential to achieve a required transmission quality. View full abstract»

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  • Non-Coherent Detection for Two-Way AF Cooperative Communications in Fast Rayleigh Fading Channels

    Publication Year: 2011 , Page(s): 2753 - 2762
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (449 KB) |  | HTML iconHTML  

    Two-way cooperative communications are considered to improve the throughput of conventional one-way cooperative communications. For fast Rayleigh fading channels, we propose optimal and suboptimal non-coherent detectors for on-off keying (OOK) and frequency-shift keying (FSK) modulated two-way amplify-and-forward (AF) cooperative communications in this paper. In the proposed system, the relaying node combines the received signals from two nodes, amplifies them and retransmits the conjugate of the combined and amplified signals to the above-mentioned nodes. At the receivers of above-mentioned nodes, the optimal non-coherent detection is employed which is based on maximum likelihood rule. Since it involves integration operation, the optimal detector is simplified to a suboptimal detector which omits the real component of the relayed signal over the frequency which includes interference. The simulation results have shown that compared with the optimal detector, the proposed suboptimal detector reduces the receiver complexity at the expense of acceptable performance degradation. Furthermore, we have analytically studied the bit-error-rate performance upper and lower bounds of proposed non-coherent FSK modulated two-way AF cooperative communications. View full abstract»

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  • Gains in Error-Constrained Data Throughput from Extremely Fast Adaptation of Symbol Durations over Multi-Path Fading Channels: Coded and Uncoded Systems

    Publication Year: 2011 , Page(s): 2763 - 2775
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (710 KB) |  | HTML iconHTML  

    This paper quantitatively analyzes the gain in error-constrained data throughput due to the extremely rapid (symbol-by-symbol) adaptation of symbol durations. The analysis includes systems equipped with maximal ratio combining. For uncoded communication systems, we provide numerical results obtained from the analysis of theoretical throughput gains. For some coded communication systems with commonly used error correction codes, we provide numerical throughput gain results obtained from simulations. View full abstract»

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  • The κ-μ Extreme Distribution

    Publication Year: 2011 , Page(s): 2776 - 2785
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (935 KB) |  | HTML iconHTML  

    A number of realistic wireless applications can be found for which the propagated signal may experience extreme fading conditions. In particular, a recent work has reported on an experiment conducted within an enclosed environment where it has been shown that the fading conditions are indeed harsh, drastically departing from those predicted by traditional fading models. This paper investigates the κ-μ Extreme fading distribution, a member of the κ-μ fading model and obtained from it when its parameters reach their extreme values (κ → ∞ and μ → 0) for a fixed amount of fading. Field data reported elsewhere and collected in enclosed environment, along with other fading data collected by the authors' team, are used to compare the curve fit performance of the κ-μ Extreme model and the recently proposed Two-Ray distribution. The results show that the κ-μ Extreme distribution is flexible and suitable to model these scenarios. The performance of this new model is then explored in the three basic combining techniques, namely selection, maximum ratio, and equal gain, and a number of exact, closed-form formulas are obtained. Interestingly, it is shown that in extreme fading conditions, the selection combiner may outperform the equal gain combiner. View full abstract»

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  • SNR Estimation for M-ARY Non-Coherent Frequency Shift Keying Systems

    Publication Year: 2011 , Page(s): 2786 - 2795
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (421 KB) |  | HTML iconHTML  

    This paper considers how to estimate the average signal-to-noise ratio (SNR) for a communication system employing orthogonal non-coherent M-ARY frequency shift keying (NCMFSK), in white Gaussian noise (AWGN) and over both symbol-by-symbol fading channels and block fading channels. The proposed algorithm finds its application in a variety of applications including a cooperative transmission system, which is the main motivation behind this study. The maximum likelihood estimator and one using data statistics have been derived and simulated for various scenarios including data-aided, non-data aided and joint estimation using both the data and pilot sequences. We also derive the Cramer-Rao bound for the estimators in the case of Rayleigh fading channels. The results show that for a particular region of interest (e.g. high SNR or low SNR) and depending upon the availability of pilot sequence, a particular SNR estimation scheme is suitable. View full abstract»

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  • Iterative Sphere Detectors for Imperfect Channel State Information

    Publication Year: 2011 , Page(s): 2796 - 2807
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (482 KB) |  | HTML iconHTML  

    This manuscript presents an iterative detector based on a generalized Schnorr-Euchner enumeration for the case of imperfect channel state information. The detector determines the most contributive N∈{1,2} terms in each of the two log-sum-exponents. The objective function of the tree search is modified to account for (a) the channel estimation error variance and (b) the input a priories. Due to (a), the decomposition of the objective into the form used in conventional tree search is not possible. Moreover, both (a) and (b) invalidate the use of the progressive zigzag order. Because of this, a generalized Schnorr-Euchner enumeration is proposed where explicit sorting is done. Unlike the conventional tree search, the node weights are not computed in an additive way where the weight of a child node is the sum of the weights of the parent and the branch connecting them. The advantage of the proposed detectors compared to iterative channel estimation and decoding is that the repetition of the channel estimation and the QR decomposition is not needed. Also since they are based on the Schnorr-Euchner enumeration, they do not require an initial radius estimation and if channel estimation errors are small enough to be ignored, the search step becomes division- and square-root-free. View full abstract»

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  • Cooperation in Wireless Networks with Unreliable Channels

    Publication Year: 2011 , Page(s): 2808 - 2817
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (366 KB) |  | HTML iconHTML  

    In a distributed wireless system, multiple network nodes behave cooperatively towards a common goal. An important challenge in such a scenario is to attain mutual cooperation. This paper provides a non-cooperative game theoretic solution to enforce cooperation in wireless networks in the presence of channel noise. We focus on one-hop information exchange and model the packet forwarding process as a hidden action game with imperfect private monitoring. We propose a state machine based strategy to reach Nash Equilibrium. The equilibrium is proved to be a sequential one with carefully designed system parameters. Furthermore, we extend our discussion to a general wireless network scenario by considering how cooperation can prevail over collusion using evolutionary game theory. The simulation results are provided to back our analysis. In particular, network throughput performance is measured with respect to parameters like channel loss probability, route hop count, and mobility. Results suggest that the performance due to our proposed strategy is in close agreement with that of unconditionally cooperative nodes. Simulation results also reveal how the convergence of cooperation enforcement is affected by initial population share and channel unreliability. View full abstract»

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  • Performance Characterization of Ultrahigh SpeedOptically Amplified Spectral-Phase EncodedOCDMA Systems with Second-Harmonic-Generation Effect in Thin and Thick Crystal Receiver Structures

    Publication Year: 2011 , Page(s): 2818 - 2831
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB) |  | HTML iconHTML  

    In this paper we study and evaluate the performance of a spectral-phase encoded optical CDMA (SPE-OCDMA) system using advanced receiver structures based on second harmonic generation (SHG) effect imposed in a Thick or Thin crystal. This receiver structure is employed as the nonlinear pre-processor prior to the conventional low-speed photodetector. In our performance evaluation amplified spontaneous emission (ASE) of the optical amplifiers, receiver front end thermal noise and photodetector shot noise which are effective in low power conditions, and multiple access interference (MAI) noise which is the dominant source of noise in high power conditions in any coherent OCDMA communications system have been considered. We begin by studying the statistical behavior of Thick crystals in an optically amplified digital lightwave communication system in the context of a SPE-OCDMA communication system. The error probability for Thick crystal receiver structure is evaluated using Saddle-Point approximation. Furthermore, we obtain a closed form approximation for the probability density function (pdf) of the decision variable in SPE-OCDMA systems with Thin crystal SHG receiver. In this analysis, to obtain approximate probability density function, we employ Gram-Charlier expansion based on the corresponding first order moments of the decision variable. The first three moments are obtained in a closed form approximation and consequently a closed form expression for the error probability is obtained by integrating the approximated pdf of the decision variables for transmitting bit "1" and "0" in Thin crystal receiver structure. The precision of the approximation is verified by the Monte-Carlo simulation. Finally the performance of SPE-OCDMA network for both Thin and Thick SHG crystals are analytically evaluated and discussed for different number of interfering users and different code-lengths and different speed of the conventional photodetectors. We deduce that the performance of - - Thin SHG crystal receiver is more sensitive to the transmitted power level especially in low power conditions. It is concluded that in low power conditions where ASE, thermal and shot noises are the dominant noise sources, Thick SHG crystal receiver outperforms the Thin crystal receiver. However, in high power conditions where MAI noise is the most effective noise term, Thin SHG crystal receiver structure outperforms the Thick crystal receiver. View full abstract»

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  • Retrial Queuing Models of Multi-Wavelength FDL Feedback Optical Buffers

    Publication Year: 2011 , Page(s): 2832 - 2840
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB) |  | HTML iconHTML  

    Optical buffers based on Fiber Delay Lines (FDL) have been proposed for contention resolution in optical packet/burst switching systems. In this article, we propose a retrial queuing model for FDL optical buffers in asynchronous optical switching nodes. In the considered system, the reservation model employed is of post-reservation type and optical packets are allowed to re-circulate over the FDLs in a probabilistic manner. We combine the MMPP-based overflow traffic models of the classical circuit switching literature and fixed-point iterations to devise an algorithmic procedure to accurately estimate blocking probabilities as a function of various buffer parameters in the system when packet arrivals are Poisson and packet lengths are exponentially distributed. The proposed algorithm is both accurate and fast, allowing one to use the procedure to dimension optical buffers in next-generation optical packet switching systems. View full abstract»

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  • Optimum Power and Rate Allocation for Coded V-BLAST: Instantaneous Optimization

    Publication Year: 2011 , Page(s): 2841 - 2850
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (351 KB) |  | HTML iconHTML  

    Several instantaneous optimization strategies for rate and/or power allocation in the coded V-BLAST are studied analytically. Outage probabilities and system capacities of these strategies in a spatial multiplexing system are compared under generic settings. The conventional waterfilling algorithm is shown to be suboptimal for the coded V-BLAST and a new algorithm ("fractional water-filling") is proposed, which simultaneously maximizes the system capacity and minimizes the outage probability. Closed-form performance analysis of the considered algorithms is given, and the fractional water-filling algorithm is shown to attain the full MIMO channel diversity, significantly outperforming other strategies. Many of the results also apply to generic multi-stream transmission systems (e.g. spatial multiplexing on the channel eigenmodes, OFDM) or the systems relying on successive interference cancelation (multi-user detection, channel equalization). View full abstract»

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  • Joint Level 2 and 3 Dynamic Spectrum Management for Upstream VDSL

    Publication Year: 2011 , Page(s): 2851 - 2861
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB) |  | HTML iconHTML  

    Dynamic spectrum management (DSM) refers to a wide range of techniques for counteracting crosstalk in digital subscriber line (DSL) networks. DSM is categorized into three levels based on the degree of coordination among users. In this article, we investigate optimal joint level 2 and 3 DSM for upstream DSL. We will discuss the difficulties of finding the universally optimal solution and we propose an optimal algorithm, referred to as IF/MAC-OSB, under some practical and implementation assumptions for this problem. Using computer simulations, we show that IF/MAC-OSB is capable of increasing the user bit rates considerably compared to several other DSM techniques. The proposed algorithm involves using the minimum mean squared error (MMSE)-generalized decision feedback equalizer (GDFE) together with Lagrange dual optimization. We address several aspects of the problem including the optimal decoding order in the GDFE receiver, GDFE error propagation, and the computational complexity of the algorithm. We also study effects of channel model randomness and upstream power back-off utilization on the performance of the algorithm. View full abstract»

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Aims & Scope

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

 

 

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Meet Our Editors

Editor-in-Chief
Robert Schober
University of British Columbia