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Communications Letters, IEEE

Issue 5 • Date May 2010

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Displaying Results 1 - 25 of 43
  • IEEE Communications Letters - Cover

    Publication Year: 2010 , Page(s): c1
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    Freely Available from IEEE
  • Adaptive bayesian beamforming with sidelobe constraint

    Publication Year: 2010 , Page(s): 369 - 371
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB) |  | HTML iconHTML  

    The conventional Bayesian beamformer suffers substantial performance degradation, when the true direction-of-arrival is deterministic and is not included in the priori. In this letter, we propose a method with sidelobe constraint to improve the robustness of the Bayesian beamforming method. Support vector machine is used to obtain the weights. Numerical results show that the proposed beamformer can improve the Bayesian beamforming performance, and can output a relatively higher signal-to-noise-plus-interference ratio even when the desired direction-of-arrival is not included in the Bayesian priori region. View full abstract»

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  • Half-duplex gaussian interference channel with transmitter and receiver cooperation

    Publication Year: 2010 , Page(s): 372 - 374
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (266 KB) |  | HTML iconHTML  

    We propose an achievable region and capacity outer bound for half-duplex Gaussian interference channel with both transmitter (TX) and receiver (RX) cooperation. We show the significant improvement in achievable region compared to either TX or RX cooperation alone. Further, we quantify the sum rate increase with respect to the cooperation channel gain. View full abstract»

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  • Symbol error probability of cross QAM in rayleigh fading channels

    Publication Year: 2010 , Page(s): 375 - 377
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (206 KB) |  | HTML iconHTML  

    The exact symbol error probability (SEP) of cross-quadrature amplitude modulation (QAM) in Rayleigh flat fading channels has been derived. The closed-form SEP expression obtained contains only elemental functions. View full abstract»

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  • Exact analytical expression of schmidl-cox signal detection performance in AWGN

    Publication Year: 2010 , Page(s): 378 - 380
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (190 KB) |  | HTML iconHTML  

    In this letter we investigate the performance of Schmidl-Cox signal detection, a widely used approach in practical OFDM systems whose performance is usually evinced by resorting to Gaussian approximations. We show that, by a slight modification of the normalization factor, we are able to derive a basically equivalent approach whose performance can be expressed in exact analytical form. A particularly simple expression is found for the false alarm probability, allowing system designers a straightforward selection of optimal parameters. View full abstract»

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  • A simplified greedy algorithm for joint scheduling and beamforming in multiuser MIMO OFDM

    Publication Year: 2010 , Page(s): 381 - 383
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (178 KB) |  | HTML iconHTML  

    We consider a cellular system using frequency division duplexing and orthogonal frequency division multiplexing (OFDM), where the base station has multiple antennas and each mobile terminal feeds back a quantized version of the channel state information. For downlink transmission, the base station performs joint scheduling and beamforming with the objective of maximizing the system throughput. In this letter, we propose an iterative (in the user selection) beamforming algorithm which exploits approximated orthogonality conditions of the scheduled users. By simulation results it is seen that new approach outperforms existing scheduling techniques in terms of outage throughput with similar or lower complexity. View full abstract»

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  • A novel approach toward source-to-sink distance estimation in wireless sensor networks

    Publication Year: 2010 , Page(s): 384 - 386
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB) |  | HTML iconHTML  

    Estimation of the Euclidean distance between a source node and a sink node by using the hop-counts between them is an interesting research problem in WSNs (wireless sensor networks). In this paper, we propose a novel source-to-sink distance estimation method based on the observation that the neighbors of a sink can have different hop-counts relative to the same source. The proposed method not only uses the hop-count information of a sink, but also exploits the hop-count information of the sink's neighbors. Simulation results show that the proposed method outperforms other well-known hop-count-based source-to-sink distance estimation methods. View full abstract»

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  • Reliability-based hybrid MMSE/subspace-max-log-APP MIMO detector

    Publication Year: 2010 , Page(s): 387 - 389
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (307 KB) |  | HTML iconHTML  

    We present an algorithm which is a flexible and scalable trade-off both in complexity and performance between unbiased MMSE and Max-Log-APP MIMO detection. In a first step, LLRs are generated based on linear detection (Max-Log per stream). A predefined number of LLRs is chosen as 'reliable' based on LLR magnitude. For the remaining 'unreliable' subspace we compute the joint Max-Log-APP solution. The algorithm contains unbiased MMSE detection as well as full Max-Log-APP detection as special cases and is suited for iterative detection-decoding. View full abstract»

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  • Optimal joint source and relay beamforming for MIMO relays with direct link

    Publication Year: 2010 , Page(s): 390 - 392
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (186 KB) |  | HTML iconHTML  

    In this letter, we investigate the optimal structure of the source precoding matrix and the relay amplifying matrix for non-regenerative multiple-input multiple-output (MIMO) relay communication systems with the direct source-destination link. We show that both the optimal source precoding matrix and the optimal relay amplifying matrix have a beamforming structure. Based on this structure, an iterative joint source and relay beamforming algorithm is developed to minimize the mean-squared error (MSE) of the signal waveform estimation. Numerical example demonstrates an improved performance of the proposed algorithm. View full abstract»

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  • Error analysis for fingerprint-based localization

    Publication Year: 2010 , Page(s): 393 - 395
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (294 KB) |  | HTML iconHTML  

    In this paper, we derive the theoretical error Probability Density Function (PDF) and Region of Confidence (RoC) conditioned on the on-line signal parameter vector, for a generalized fingerprint-based localization system. As the computations of these terms require the exact expression of the joint PDF for both the device location and the on-line signal parameter vector, which is often not available practically, we propose to approximate this joint PDF by Nonparametric Kernel Density Estimation techniques using the training fingerprints. View full abstract»

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  • Relay selection and power allocation for cooperative network based on energy pricing

    Publication Year: 2010 , Page(s): 396 - 398
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (266 KB) |  | HTML iconHTML  

    In this letter, we propose a relay selection and power allocation scheme for decode-and-forward (DF) cooperative network based on energy pricing. Modeling the nodes of the network as energy sellers, we can derive the optimal power allocation solution between the source node and the relay node by graphic method intuitively and select the optimal relay node according to minimum cost (MIC) criteria. Simulation results show that the lifetime of the cooperative network can be significantly prolonged using the proposed scheme compared with other schemes. View full abstract»

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  • Multiple output selection-LAS algorithm in large MIMO systems

    Publication Year: 2010 , Page(s): 399 - 401
    Cited by:  Papers (13)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (253 KB) |  | HTML iconHTML  

    We present a low-complexity algorithm for detection in large MIMO systems based on the likelihood ascent search (LAS) algorithm. The key idea in our work is to generate multiple possible solutions or outputs from which we select the best one. We propose two possible approaches to achieve this goal and both are investigated. Computer simulations demonstrate that the proposed algorithm, Multiple Output Selection-LAS, which has the same complexity order as that of conventional LAS algorithms, is superior in bit error rate (BER) performance to LAS conventional algorithms. For example, with 20 antennas at both the transmitter and receiver, the proposed MOS-LAS algorithm needs about 4 dB less SNR to achieve a target BER of 10-4 for 4-QAM. View full abstract»

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  • A computationally efficient near-optimal algorithm for capacity-maximization based joint transmit and receive antenna selection

    Publication Year: 2010 , Page(s): 402 - 404
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (237 KB) |  | HTML iconHTML  

    This letter presents a computationally efficient joint transmit and receive antenna selection (EJTRAS) algorithm based on a modification of the selection criterion in [1]. We show that the modification allows us to reduce the algorithm's computational complexity by a factor of L, where L is the number of selected antennas without sacrificing the performance. Nearoptimal outage and ergodic capacity can therefore be attained with significantly lower complexity as verified by the extensive computer simulations. View full abstract»

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  • Performance analysis of IEEE 802.16m sleep mode for heterogeneous traffic

    Publication Year: 2010 , Page(s): 405 - 407
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (238 KB) |  | HTML iconHTML  

    We numerically analyze the performance of the emerging 802.16 m's sleep mode operation in order to gain a new insight regarding its power consumption and traffic transmission delay when a Mobile Station (MS) in the sleep mode is served with both non-realtime and realtime traffic simultaneously. We validate the analysis via the comparison with simulation results. View full abstract»

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  • Optimal data compression and forwarding in wireless sensor networks

    Publication Year: 2010 , Page(s): 408 - 410
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (267 KB) |  | HTML iconHTML  

    In this letter, we present a Linear Programming framework for modeling dynamic data compression and decompression in conjunction with flow balancing in wireless sensor networks. Using the developed framework, we investigated the sensor network lifetimes for different network sizes with various data compression and flow balancing strategies. Our results show that neither compressing all data nor avoiding data compression completely can achieve the longest possible network lifetime. Dynamic data transformation is shown to achieve significantly longer network lifetimes than the lifetimes obtained with the two pure strategies above. View full abstract»

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  • User selection and resource allocation algorithm with fairness in MISO-OFDMA

    Publication Year: 2010 , Page(s): 411 - 413
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB) |  | HTML iconHTML  

    The problem of user selection and resource allocation for the downlink of wireless systems operating over a frequency-selective channel is investigated. It is assumed that the Base Station (BS) uses many antennas, whereas a single antenna is available to each user. A suboptimal, but efficient algorithm is devised that is based on Zero Forcing (ZF) beamforming and on spatial correlation. The algorithm maximizes the sum of the users' data rates subject to constraints on total available power and proportional fairness among users' data rates. The main feature of it is the proportionality among users' data rates which is guaranteed as it is shown by simulations. View full abstract»

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  • Critical penetration for vehicular networks

    Publication Year: 2010 , Page(s): 414 - 416
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (645 KB) |  | HTML iconHTML  

    Feasibility of a cooperative vehicle-to-vehicle (V2V) system requires certain number of vehicles equipped with a communication device in order to carry out the information away from the origination. This way, we can deploy safety, traffic management and entertainment applications1. V2V uses both direct relaying (multihop forwarding over vehicles) and transport relaying (store and forward) in order to propagate the information. We introduce a closed mathematical formula for penetration of equipped vehicles in direct relaying which is dominant in dense scenarios and then simulate both direct and transport relaying to investigate further the critical penetration that is required to enable most of the applications. View full abstract»

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  • Measuring the connectivity of a cognitive radio ad-hoc network

    Publication Year: 2010 , Page(s): 417 - 419
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (542 KB) |  | HTML iconHTML  

    In Cognitive Radio Ad-Hoc Networks (CRAHN) the behavior of the primary users influences the secondary network connectivity and the relevant performance. The methodologies used to evaluate network connectivity have to be worked up to take into account this aspect. In this letter we propose the use of Laplacian matrix and its second smallest eigenvalue to measure the network algebraic connectivity of a CRAHN. We re-elaborate the Laplacian matrix in order to have in its second smallest eigenvalue a function of the primary users behavior expressed as an activity factor. In this way we are able to monitor the algebraic connectivity of CRAHNs. This metric can be a useful instrument for network planning, data routing and network maintenance. Performance results show how this methodology can be efficiently applied in this kind of networks. View full abstract»

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  • A simple pilot position detection technique for channel estimation of SC-FDE

    Publication Year: 2010 , Page(s): 420 - 422
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (222 KB) |  | HTML iconHTML  

    This letter investigates the frequency domain pilot multiplexing technique (FDPMT) for channel estimation of single-carrier frequency domain equalization (SC-FDE) and proposes a simple pilot position detection technique to blindly estimate the pilot positions in the frequency domain by using the noise subspace. Simulation results show that the proposed technique is robust to multipath fading channels with exponential power delay profile. View full abstract»

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  • BER analysis of direct conversion OFDM systems with MRC under channel estimation errors

    Publication Year: 2010 , Page(s): 423 - 425
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (358 KB) |  | HTML iconHTML  

    In this letter, we calculate an exact closed-form expression for the bit error rate (BER) of orthogonal frequency division multiplexing (OFDM) systems with direct conversion that employ maximal ratio combining (MRC) reception in multipath Rayleigh fading channels, using binary phase-shitf keying (BPSK) modulation. We assume a realistic system model where direct current (DC) offset, carrier frequency offset (CFO) and imperfect channel state information (ICSI) are simultaneously considered. Results show the appearance of an irreducible BER floor due to DC offset and ICSI. As a rule of thumb, we provide a simple expression for the maximum DC offset allowable in a direct conversion receiver. View full abstract»

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  • Combined bulk and per-tone transmit antenna selection in OFDM systems

    Publication Year: 2010 , Page(s): 426 - 428
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (257 KB) |  | HTML iconHTML  

    We present a modification of conventional transmit antenna selection schemes for OFDM systems by combining bulk and per-tone selection. We analyse the diversity and coding gains of the proposed approach with respect to symbol error and outage probability for uncoded systems, and show that these gains are identical to that which can be obtained by employing per-tone selection using all available antennas. This analysis leads to the surprising result that one can achieve optimal performance at high SNR relative to a per-tone selection system with M antennas by first selecting only two out of M antennas and performing per-tone selection on the chosen antennas. View full abstract»

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  • Fractional bit encoded spatial modulation (FBE-SM)

    Publication Year: 2010 , Page(s): 429 - 431
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB) |  | HTML iconHTML  

    In this Letter, we introduce fractional bit encoded (FBE)-spatial modulation (SM), which is a novel and more versatile SM scheme that allows the transmitter to be equipped with an arbitrary number of antennas. The solution is based on the theory of modulus conversion, and is especially useful for compact mobile devices where cost and space constraints pose fundamental limits on the achievable bit rate. Numerical results will show that FBE-SM can offer design flexibility and the desired trade-off in terms of attainable performance and capacity. View full abstract»

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  • Traffic-reduced precise ranging protocol for asynchronous UWB positioning networks

    Publication Year: 2010 , Page(s): 432 - 434
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (243 KB) |  | HTML iconHTML  

    This letter proposes a precise two-way ranging (TWR) protocol toward low traffic for asynchronous UWB positioning networks. The proposed TWR protocol pursuing instantaneous ranging update enables the estimation of clock frequency offset to achieve high ranging accuracy. Theoretical analysis and simulation results verify the performance. View full abstract»

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  • An efficient approximation for minimum latency broadcast in multi-channel multi-hop wireless networks

    Publication Year: 2010 , Page(s): 435 - 437
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    In this paper, we discuss the minimum latency broadcast problem (MLB) in multi-channel multi-hop wireless networks (MLB-MC). This problem is NP-hard since its special version, MLB in single-channel network (MLB-SC) is proved to be NP-hard . We design an efficient approximation for MLB-MC, analyze its approximation ratio, and evaluate its performance via numerical experiments. Furthermore, we give a general theorem as an upper bound to compare the performance between approximations for MLB-MC and MLB-SC. View full abstract»

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  • A quantitative analysis of the capacity of wireless mesh networks

    Publication Year: 2010 , Page(s): 438 - 440
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (201 KB) |  | HTML iconHTML  

    Evaluating wireless mesh network performances has become a specific challenge since the emergence of ubiquitous computing. In this article, we consider the network capacity as the performance measure and study its behaviour under two different interference models: (i) usual IEEE 802.11 MAC layer with acknowledgments at each hop, and (ii) block acknowledgments reported at the transport layer that can be included in the IEEE 802.16 standard. We derive a linear program modeling crosslayer characteristics of the wireless mesh network that is solved using column generation. We quantify the capacity gain induced by the move of the MAC acknowledgments into the transport layer, and show that a better load distribution is also obtained. View full abstract»

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Aristotle University of Thessaloniki
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