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Communications Letters, IEEE

Issue 5 • Date May 2009

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Displaying Results 1 - 25 of 28
  • IEEE Communications Letters - Cover

    Page(s): c1 - c2
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    Freely Available from IEEE
  • Enhanced SNR estimates from direct-sequence spread-spectrum demodulator statistics

    Page(s): 289 - 291
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (189 KB) |  | HTML iconHTML  

    Demodulator statistics are used in a binary direct-sequence spread-spectrum receiver to improve the performance of a well-known signal-to-noise ratio (SNR) estimate for ratios of the binary symbol energy to one-sided noise density that are below approximately 7 dB. The new estimate requires no pilot symbols, training sequences, data symbol decisions, or channel measurements, and it can be obtained prior to decoding. View full abstract»

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  • Security flaw of authentication scheme with anonymity for wireless communications

    Page(s): 292 - 293
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (117 KB) |  | HTML iconHTML  

    Recently, Wu et al. discussed some security flaws of enhanced authentication scheme with anonymity for wireless environments proposed by Lee et al. and showed how to overcome the problems regarding anonymity and backward secrecy. However, in the paper, we will show that Wu et al.'s improved scheme still did not provide user anonymity as they claimed. View full abstract»

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  • Analysis of cognitive radio spectrum access with finite user population

    Page(s): 294 - 296
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (193 KB) |  | HTML iconHTML  

    A new loss model for cognitive radio spectrum access with finite user population are presented, and exact solution for the model and its approximation for computation scalability are given. Our model provides the investigation of the delay performance of a cognitive radio system. We study the delay performance of a cognitive radio system under various primary traffic loads and spectrum band allocations. View full abstract»

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  • A simple adaptive optimization scheme forIEEE 802.11 with differentiated channel access

    Page(s): 297 - 299
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (301 KB) |  | HTML iconHTML  

    This letter proposes an adaptive scheme to optimize the system throughput of IEEE 802.11 with differentiated channel access ability. Due to the difficulty of estimating the number of active stations and that approaches based on the estimation may not converge reported in previous research, the proposed scheme is developed to maximize the system throughput without the requirement of station number information while providing service differentiation among different traffic classes. Specially, the scheme is simple to implement and it only requires to measure the time the channel is in idle and collision states separately. Performance evaluation results show that the scheme is effective in achieving near to the theoretical maximum system throughput. View full abstract»

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  • Asymptotic performance analysis of amplify-and-forward cooperative networks in a nakagami-m fading environment

    Page(s): 300 - 302
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (210 KB) |  | HTML iconHTML  

    This letter analyzes the performance of repetition-based cooperative wireless networks using amplify-and forward relaying. The network consists of a source, R parallel relays, and a destination, and the channel coefficients are distributed as independent, non-identical, Nakagami-m. The approximated average symbol error rate (SER) is investigated. For sufficiently large SNR, this letter derives a close-form average SER when m is an integer. The simplicity of the asymptotic results provides valuable insights into the performance of cooperative networks and suggests means of optimizing them. We also use simulation to verify the analytical results. Results show that the derived error rates are tight approximations particularly at medium and high SNR. View full abstract»

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  • On the impact of mobility and soft vertical handoff on voice admission control in loosely coupled 3G/WLAN networks

    Page(s): 303 - 305
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (262 KB) |  | HTML iconHTML  

    Loose coupling between 3G and WLAN ensures flexibility and openness. However, providing an ubiquitous mobile voice service in a loosely coupled 3G/WLAN network requires both packet-level and call-level quality of service (QoS) guarantees using soft vertical handoff (SVHO) and call admission control (CAC). In this paper, we evaluate the impact of both SVHO and WLAN mobility on call blocking and dropping probabilities rederived for the integrated network. For this purpose, we propose a new multi-region mobility model that accurately estimate these probabilities under a resource-efficient dynamic threshold SVHO compared to a standard static-threshold SVHO. Results show us that the resource-efficient SVHO blocks and drops much less voice calls than the static one when very low mean and high variability of multi-mode mobile station velocities are noticed. Therefore, resource-efficient SVHO implementations are highly recommended in these mobility environments. View full abstract»

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  • Multi-neighbor random key pre-distribution: a probabilistic analysis

    Page(s): 306 - 308
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (193 KB) |  | HTML iconHTML  

    In this study, to obtain stronger connectivity, we propose and analyze a scheme extended by random key predistribution (RKP), which can work only in highly dense networks and require path construction. We propose a multi-neighbor random key pre-distribution scheme that releases these strong constraints. Accordingly, an establishment protocol and a probabilistic analysis in terms of dependency overhead are presented. We have made use of the measure of dependence to derive the exact value of the key connectivity probability. View full abstract»

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  • A simple detect-and-forward scheme in fading channels

    Page(s): 309 - 311
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (177 KB) |  | HTML iconHTML  

    In this letter, we introduce and analyze a detect-and-forward scheme for cooperative communications over fading channels based on the transmission of partial source-relay channel state information. The proposed scheme is simple to implement and its efficiency is demonstrated through constrained capacity calculation and throughput evaluation based on practical coding schemes. View full abstract»

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  • On a buffering hypothesis in 802.11 analytic models

    Page(s): 312 - 314
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (220 KB) |  | HTML iconHTML  

    Using detailed statistical analysis of data taken from simulations and test-bed experiments, we have recently reported the inappropriateness of a queue-decoupling approximation that has been implicitly adopted by many distinct authors to incorporate queueing behavior in analytic models of finite load 802.11 networks. In the present paper we show that this flawed hypothesis leads to network throughput prediction errors in the presence of stations with asymmetric offered loads. We suggest that care should be taking in drawing deductions from models that adopt this hypothesis and that further modeling innovation is necessary. View full abstract»

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  • Antenna location design for generalized distributed antenna systems

    Page(s): 315 - 317
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (241 KB) |  | HTML iconHTML  

    A squared distance criterion for antenna location design in generalized distributed antenna systems (GDAS) is proposed to maximize the cell averaged ergodic capacity. The criterion requires the antenna port locations minimize the expectation of the squared distance between a randomly distributed user and the nearest antenna port. This is equivalent to codebook design in vector quantization. For uniform user distribution, we can easily derive analytical expressions for antenna locations. For more general user distribution, we can obtain numerical results using the codebook design algorithm. Applying the proposed criterion to circular-layout GDAS with uniform user distribution and linear cell with non-uniform user distribution, we achieve near optimal performance. View full abstract»

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  • Contention free inter-cellular slot reservation

    Page(s): 318 - 320
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (197 KB) |  | HTML iconHTML  

    A distributed reservation protocol tailored for cellular wireless networks is presented that facilitates contention free inter-cellular slot allocation and reservation. While reserved slots are protected from inter-cell interference by a busy burst enabled reservation protocol, collisions due to simultaneously accessed unreserved slots by neighboring cells are mitigated by means of resource partitioning patterns. Shifting these partitioning patterns over time allows each cell to successively probe all slots. This ensures that full frequency reuse is maintained, in the way that all cells may utilize the entire frequency band. In effect a contention free inter-cellular slot allocation policy is established that in a distributed manner dynamically controls the spatial reuse, in terms of concurrently accessed radio resources by neighboring cells. View full abstract»

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  • Primary network cognition with spatial diversity signature

    Page(s): 321 - 323
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    The identification of primary networks improves efficiency in dynamic spectrum access. We propose a spatial diversity signature for the primary signal detection, which exploits the structure of space-time or space-frequency codeword based on Alamouti scheme. The signature pattern informs the secondary user which network transmits the primary signal and enables to maintain an experiential database for each primary network. The proposed scheme provides reliable detection and network identification performance over frequency-selective fading channels in low signal-to-noise ratio regimes, without sacrificing the data rate of primary system. View full abstract»

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  • Asymptotic spectral behavior of spectrally precoded OFDM signal with arbitrary input statistics

    Page(s): 324 - 326
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    In this letter, we study the asymptotic spectral behavior of the spectrally precoded orthogonal frequency-division multiplexing (SP-OFDM) signal with arbitrary input statistics. It is shown that all constraints and spectral precoders previously developed for SP-OFDM with independent and identically distributed and zero-mean data provide fast decaying spectral sidelobes for SP-OFDM with arbitrary input statistics. View full abstract»

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  • Sidelobe suppression in NC-OFDM systems using constellation adjustment

    Page(s): 327 - 329
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (269 KB) |  | HTML iconHTML  

    In this letter, a new method for sidelobe suppression in non-contiguous orthogonal frequency division multiplexing (NC-OFDM) systems is proposed. Unlike the conventional approach, sidelobes are suppressed by iteratively adjusting the constellation points for the subcarriers that are close to the edges of the used bandwidth. The constellation points corresponding to the maximum sidelobe suppression are chosen for transmission. Simulation results show that the proposed algorithm yields good performance improvement in terms of sidelobe suppression, and does not have a significant impact on the peak-to-average power ratio (PAPR). View full abstract»

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  • Performance analysis of linear receivers in a MIMO relaying system

    Page(s): 330 - 332
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB) |  | HTML iconHTML  

    We investigate the performance of linear receivers in a cooperative system which consists of a source, a decode-and-forward (DF) relay and a destination that are all multi-antenna nodes. The relay uses zero-forcing (ZF) equalization whereas the destination employs maximum ratio combining (MRC) as well as ZF techniques. Considering that perfect channel state information is available at the relay and destination, and the fading is Rayleigh, we derive a closed-form approximate expression for the outage probability of the post-receiver signal-to-noise ratio (SNR) of each data stream at the destination and analyze the diversity order. The validity of the outage probability expression is confirmed with the numerical results. View full abstract»

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  • A geometric approach for turbo decoding of reed-solomon codes in QAM modulation schemes

    Page(s): 333 - 335
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    This work studies the turbo decoding of Reed-Solomon codes in QAM modulation schemes for additive white Gaussian noise channels (AWGN) by using a geometric approach. Considering the relations between the Galois field elements of the Reed-Solomon code and the symbols combined with their geometric dispositions in the QAM constellation, a turbo decoding algorithm, based on the work of Chase and Pyndiah, is developed. Simulation results show that the performance achieved is similar to the one obtained with the pragmatic approach with binary decomposition and analysis. View full abstract»

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  • Gallager's decoding algorithm Α over high order modulations

    Page(s): 336 - 338
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (290 KB) |  | HTML iconHTML  

    Gallager's decoding algorithm A (GDA) for low density parity check (LDPC) codes is of interest mainly due to its good performance with extremely low complexity. In this paper, we analyze GDA over 2m-ary pulse-amplitude modulation (2m-PAM). Firstly, we represent its average error probability by means of a recursion formula. We then define its threshold for additive white Gaussian noise (AWGN) channels and derive its stability condition. The bit-to-symbol mapping strategies have a strong influence on the performance of LDPC-coded modulation systems. Finally, we show that the bit-reliability mapping strategy proposed by Li and Ryan maximizes the threshold of the LDPC coded modulation system with GDA over Gray-mapped 2m-PAM in the AWGN channel. View full abstract»

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  • Interleaver optimization of convolutional turbo code for 802.16 systems

    Page(s): 339 - 341
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (221 KB) |  | HTML iconHTML  

    Convolutional turbo code (CTC) has been adopted as an optional channel coding scheme for wireless metropolitan area networks (WMAN) and digital video broadcasting (DVB) owing to its powerful error correction capability and flexibility. In spite of the fact that the internal interleaver of CTC mainly affects the characteristics of the code, interleaving parameters, especially for small and moderate block sizes, have not been fully optimized in terms of performance. In this paper, we investigate structural behavior of interleaving parameters and suggest several optimization methodologies for the CTC interleaver of 802.16 systems. Simulation shows that power gains up to 0.7 dB can be acquired at a target frame error rate of 10-5 by only substituting the newly optimized parameters for the current ones. View full abstract»

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  • Large girth quasi-cyclic LDPC codes based on the chinese remainder theorem

    Page(s): 342 - 344
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (339 KB) |  | HTML iconHTML  

    In this letter, we consider two problems associated with quasi-cyclic low-density parity-check (QC-LDPC) codes. The first is how to extend the code length of a QC-LDPC code without reducing the girth. The second is how to design a QCLDPC code with a prescribed girth easily. We deal with these two problems by using a combining method of QC-LDPC codes via the Chinese Remainder Theorem (CRT). Codes constructed with our proposed method have flexible code lengths, flexible code rates and large girth. Simulation results show that they perform very well with the iterative decoding. View full abstract»

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  • A proof of wavelength conversion not improving the lagrangian bound of the static RWA problem

    Page(s): 345 - 347
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB) |  | HTML iconHTML  

    The fact that wavelength conversion hardly improves the performance of static routing and wavelength assignment (RWA) in wavelength division multiplexing (WDM) networks has been observed in many previous studies. However, other than simulation results, until now there was no formal proof of such fact. In this paper, we formally prove that wavelength conversion does not improve the Lagrangian bound of the static RWA problem. View full abstract»

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  • Multivariate distributions for workload generation in video on demand systems

    Page(s): 348 - 350
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (271 KB) |  | HTML iconHTML  

    In this letter we present an analysis of workload in a real video on demand service with the objective of generating more accurate input data for simulation models. As well as statistically characterizing key aspects in the server workload of the multimedia system, we consider their statistical dependencies.We propose a procedure to generate multivariate distributions using normal copulas in the video on demand system. Results show that the proposed method fits exactly the statistical distributions to the empirical data and matches the real correlation coefficients matrix. View full abstract»

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  • Recursive formulas for the moments of queue length in the BMAP/G/1 queue

    Page(s): 351 - 353
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (145 KB) |  | HTML iconHTML  

    We present recursive formulas for the moments of the joint distribution of the queue length and the state of the underlying process in the BMAP/G/1 at the service completion and arbitrary time epochs. View full abstract»

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  • A capture-aware access control method for enhanced RFID anti-collision performance

    Page(s): 354 - 356
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (179 KB) |  | HTML iconHTML  

    This letter presents a novel anti-collision algorithm for radio frequency identification (RFID) systems that drastically improve throughput performance via an intelligent access control for capture inducement. In order to induce the capture, our protocol attempts to divide tags into multiple groups depending on received signal strength, and allow only a selected pair of groups to join the contention process, in which the outcome of contention is more likely to lead to capture due to a significant difference in their signal strengths. Numerical results show that our proposed algorithm significantly outperforms the existing approaches in terms of throughput. View full abstract»

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  • An improved ranging algorithm for ad-hoc relay networks over IEEE 802.16 OFDMA systems

    Page(s): 357 - 359
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (204 KB) |  | HTML iconHTML  

    We present a novel ranging scheme with a specific notification code to reduce the complexity of ranging detection while providing a sufficient ranging opportunity for small ranging success time (RST) in ad-hoc relay (AHR) networks over IEEE 802.16 OFDMA systems. Computational complexity and RST are analyzed. The simulation results show that the proposed scheme outperforms the conventional one and can be a good choice for ranging protocol in battery-powered AHR networks. View full abstract»

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George K. Karagiannidis
Aristotle University of Thessaloniki
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