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Communications Letters, IEEE

Issue 8 • Date Aug. 2008

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Displaying Results 1 - 22 of 22
  • IEEE Communications Letters - Cover

    Publication Year: 2008 , Page(s): C1 - C2
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    Freely Available from IEEE
  • Spatial modulation: optimal detection and performance analysis

    Publication Year: 2008 , Page(s): 545 - 547
    Cited by:  Papers (134)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (233 KB) |  | HTML iconHTML  

    In this letter, we derive the optimal detector for the so-called spatial modulation (SM) system introduced by Mesleh et al. in (Mesleh, 2006). The new detector performs significantly better than the original (~ 4 dB gain), and we support our results by deriving a closed form expression for the average bit error probability. As well, we show that SM with the optimal detector achieves performance gains (~ 1.5 - 3 dB) over popular multiple antenna systems, making it an excellent candidate for future wireless communication standards. View full abstract»

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  • A new sub-optimal decoder for quasi-orthogonal space-time block codes

    Publication Year: 2008 , Page(s): 548 - 550
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (175 KB) |  | HTML iconHTML  

    This letter addresses the sub-optimal decoding of quasi-orthogonal space-time block codes. First, decoding using a simple linear receiver is considered in terms of the complexity versus error performance trade off. A new Chase-type sub- optimal decoding algorithm is proposed using the inner products in the metric expression as reliability measures. View full abstract»

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  • How to tune VoIP codec selection in WLANs?

    Publication Year: 2008 , Page(s): 551 - 553
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (189 KB) |  | HTML iconHTML  

    In IEEE 802.11e-based WLANs, link adaptation mechanisms, which choose the transmission rate of each node, provoke unexpected and random variations on the effective channel capacity. When these changes are towards lower bit-rates, inelastic flows, such as VoIP, can suffer from sudden congestion, which results on higher packet delays and losses. A VoIP codec selection algorithm has been proposed as a solution to this issue, which is triggered both by channel rate changes as well as in combination with a call admission control mechanism. The results show that an important improvement in terms of hotspot capacity for VoIP calls can be achieved by choosing the VoIP codec adaptively in a multi-rate scenario. By defining a new grade of service-related parameter, Qmacr, which captures the tradeoff between dropping and blocking probabilities and perceived speech quality, the codec selection algorithm can be tuned to achieve maximum capacity without severely penalizing any of those variables, and hence satisfying both technical and user quality requirements. View full abstract»

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  • Characterizing the traffic distribution in linear wireless sensor networks

    Publication Year: 2008 , Page(s): 554 - 556
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    In a multi-hop wireless sensor network (WSN), the traffic load is not evenly distributed over the nodes. For example, the sensors which are one hop away from the sink relay the whole network traffic. This imbalanced traffic distribution can degrade the network lifetime and functionality. Here, an analysis is proposed to characterize the traffic load distribution over a randomly deployed linear WSN. The effect of the number of nodes and their distribution over the network is taken into account and the results are verified through computer simulation. View full abstract»

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  • Comparison of two SNR-based feedback schemes in multiuser dual-hop amplify-and-forward relaying networks

    Publication Year: 2008 , Page(s): 557 - 559
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (362 KB) |  | HTML iconHTML  

    In this letter, we investigate amplify-and-forward relaying where a source is communicating with the best user through an intermediate relay that covers multiple users. To reduce the amount of feedback that is needed to select the best user, we consider two kinds of SNR-threshold based channel quality information (CQI) reporting: end-to-end SNR based reporting (ETE-R) and second-hop quality based reporting (SH-R). We derive the probability density function (pdf) and the cumulative density function (cdf) of the SNR received at the best user in Rayleigh fading channels, and compare the average capacity, the average number of feedback users and the feedback outage probability of the two reporting schemes, respectively. Numerical results show that SH-R can achieve the same capacity as an ideal full feedback system when the number of users is large while it reduces the amount of feedback greatly, but ETE-R provides relatively poor performance. View full abstract»

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  • Novel interference cancellation methods for BS-CDMA in uplink broadband mobile communication systems

    Publication Year: 2008 , Page(s): 560 - 562
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB) |  | HTML iconHTML  

    A single-carrier block-spread CDMA (BS-CDMA) system was proposed to offer multi-user interference (MUI) robustness and complexity reduction. However, perfect MUI elimination in BS-CDMA requires channels to be stationary within the block spreading duration which is not always applicable in high-rate mobile communication system. This letter proposes two novel interference cancellation methods to reduce the MUI arising from such scenario by using mobility condition to determine the detection ordering. Simulation results show that the proposed techniques offer significant performance improvement in a realistic multi-user multi-path environment. View full abstract»

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  • A simple model for nonsaturated IEEE 802.11 DCF networks

    Publication Year: 2008 , Page(s): 563 - 565
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (269 KB) |  | HTML iconHTML  

    We propose a simple approximate model for a nonsaturated IEEE 802.11 DCF network. Our model is much simpler than others that have appeared in the literature. The main simplification we introduce is that the attempt rate in the nonsaturated setting can be approximated by scaling the attempt rate of the saturated setting with the probability of a packet arrival. We verify our model using ns-2 simulation and show that our MAC access delay result is the most accurate amongst related work, while our collision probability and throughput results achieve comparable accuracy to [1]. View full abstract»

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  • Robust L1-norm beamforming for phased array with antenna switching

    Publication Year: 2008 , Page(s): 566 - 568
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (217 KB) |  | HTML iconHTML  

    A beamforming method for estimation of the direction-of-arrival (DOA) and distance in the presence of impulsive noise using a phased array with antenna switching is proposed. The proposed robust beamformer is nonlinear in nature and uses the absolute value loss function. Experiment results demonstrate that the proposed method is satisfactorily verified using experimental data from the developed 24 GHz phased array system with antenna switching. View full abstract»

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  • Decoding the golden space-time trellis coded modulation

    Publication Year: 2008 , Page(s): 569 - 571
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (173 KB) |  | HTML iconHTML  

    This letter presents new techniques enabling low complexity implementation of a decoder for 2 times 2 MIMO using an inner space-time block code (STBC) concatenated with an outer trellis coded modulation (TCM). The receiver includes a Viterbi decoder and sphere decoders to compute branch metrics. We present a technique to reduce the number of sphere decoding processes at each step of the trellis still retaining maximum- likelihood (ML) frame-error rate (FER) performance as well as a sub-optimal technique to speed up the decoding, with a negligible FER performance loss. View full abstract»

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  • Soft-decision priority-first decoding algorithms for variable-length error-correcting codes

    Publication Year: 2008 , Page(s): 572 - 574
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (179 KB) |  | HTML iconHTML  

    Joint source-channel decoding has recently received extensive attention due to the rise in the applications of multimedia wireless communication. Based on a code trellis rather than on a code tree, this work presents a maximum a posteriori (MAP) soft-decision priority-first decoding algorithm and its approximations for variable-length error-correcting codes. Simulation results indicate that for the code with average codeword length 6.269 bits and free distance 3, under moderate signal-to-noise ratio, one of the proposed algorithms almost reaches the lowest decoding complexity, and has nearly the same performance on symbol error probability as the MAP decoding. View full abstract»

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  • Rate-compatible distributed arithmetic coding

    Publication Year: 2008 , Page(s): 575 - 577
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (132 KB) |  | HTML iconHTML  

    Distributed arithmetic coding has been shown to be effective for Slepian-Wolf coding with side information. In this letter, we extend it to rate-compatible coding, which is useful in presence of a feedback channel between encoder and decoder. The performance loss with respect to the original version is negligible. View full abstract»

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  • An efficient algorithm for ML decoding of raptor codes over the binary erasure channel

    Publication Year: 2008 , Page(s): 578 - 580
    Cited by:  Papers (9)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (186 KB) |  | HTML iconHTML  

    In this letter, we propose an efficient algorithm for maximum-likelihood decoding of Raptor codes used over the binary erasure channel. The algorithm is inspired by the decoding scheme suggested in the 3GPP multimedia broadcast/multicast services standard and is an improved version of it. View full abstract»

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  • Stability analysis of an improved min-sum decoder

    Publication Year: 2008 , Page(s): 581 - 583
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (183 KB) |  | HTML iconHTML  

    It has been shown that under min-sum (MS) decoding, scaling the messages at the output of check nodes can improve the performance of regular low-density parity-check (LDPC) codes. However, for irregular codes designed for the sum-product decoder, linear scaling can hinder the performance. The problem of code design for MS and linear scaling min-sum (LSMS) decoders have been recently investigated. It is shown that the gap to the capacity for LSMS codes is better than MS codes, but compared to sum-product codes the gap is still considerable. In this letter, a modified MS decoding is proposed and studied. We use the stability analysis of density evolution to show that the proposed method allows for a larger fraction of edges connected to degree-2 variable nodes than LSMS codes. Finally, by designing codes based on the modified method, we show that compared to MS and LSMS codes, a smaller gap to the capacity can indeed be achieved while the complexity of decoding remains essentially the same. View full abstract»

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  • Optimization of the wireless optical system with bessel pointing loss factor

    Publication Year: 2008 , Page(s): 584 - 586
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (203 KB) |  | HTML iconHTML  

    The performance of wireless optical communication systems is affected by transmitter sway. In this letter we develop a model that relates the bit error probability with the sway parameters. In the system considered, the transmitter is equipped with the diffraction-limited circular aperture which is uniformly illuminated and non-obscured. Accordingly, the far-field effect is described by the Bessel function of the first kind of order one. The optimization results are reported. View full abstract»

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  • Extended perfect difference codes for SAC optical CDMA PONs

    Publication Year: 2008 , Page(s): 587 - 589
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (233 KB) |  | HTML iconHTML  

    In this letter, we present a new code family named the extended perfect difference codes (EPDC) suitable for passive optical network (PON) using compact SAC OCDMA encoder and decoder. Applying a mapping technique, we construct the EPDC, which not only still retain the cyclic property but also can provide flexible code length. Because of the cyclic property, the optical line terminal (OLT) needs only one arrayed waveguide grating (AWG) router to generate each user's codeword effectively. In addition, the decoder in each optical network unit (ONU) using fiber Bragg gratings (FBGs) and the EPDC is also designed. We analyze the system performance with the consideration of phase- induced intensity noise (PIIN) and thermal noise. The numerical result shows that the proposed code has higher transmission capacity than other SAC OCDMA codes. View full abstract»

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  • Traffic tree based burst scheduling in optical burst switching network

    Publication Year: 2008 , Page(s): 590 - 592
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (494 KB) |  | HTML iconHTML  

    Serializing bursts at the ingress node is an effective method to reduce burst loss in OBS networks. One of the key issues in the scheduling scheme is home channel assignment. In this letter, serialized burst traffic load (SBTL) is defined to evaluate the burst serializing degree according to the traffic tree model. A home channel assignment algorithm based on the optimization of total SBTL is proposed. Simulation is performed to verify the efficiency of the burst scheduling scheme for the proposed algorithm. The results show that the performance of the proposed algorithm is better than that obtained by greedy algorithm. View full abstract»

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  • A collision-aware wavelength assignment scheme for GMPLS based WDM networks

    Publication Year: 2008 , Page(s): 593 - 595
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (326 KB) |  | HTML iconHTML  

    In this paper, a new collision-aware wavelength assignment scheme called CAFF (collision-aware first fit) has been proposed for GMPLS based transparent WDM networks. CAFF assign a weight to each wavelength of the network links, which denotes the concurrent reservation probability. So the destination can select a wavelength with less collision probability according to the weight. Simulations are conducted to compare CAFF with a few existing schemes. Numerical results show that CAFF performs better in total blocking than the others under various traffic condition. View full abstract»

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  • Performance analysis of an optical packet switch with shared parametric wavelength converters

    Publication Year: 2008 , Page(s): 596 - 598
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (233 KB) |  | HTML iconHTML  

    Wavelength conversion capability has been shown to significantly improve the blocking performance of all-optical networks. In order to transport payloads that may be of different bit-rates and modulation formats, a transparent wavelength conversion method is desirable. Recently, parametric wavelength converters, that are capable of multi-channel wavelength conversion for heterogeneous optical services, have been experimentally demonstrated for optical circuits. In this letter, we analyse the performance of an asynchronous optical packet-switch (OPS) architecture that exploits such devices. A sensitivity analysis of the number of converters, as a function of the main switch design parameters, demonstrate a significant reduction in the number of converters when compared with architectures employing single- channel wavelength conversion. View full abstract»

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  • A software-based string matching algorithm for resource-restricted network system

    Publication Year: 2008 , Page(s): 599 - 601
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (290 KB) |  | HTML iconHTML  

    String matching is the most critical operation in network intrusion detection systems (NIDS) [1]. This paper proposes a novel memory-efficient string matching algorithm that only requires around 2% of the memory utilized in Aho-Corasick algorithm [2] but has more than 4 times the throughput of state-of-the-art algorithm with very limited memory resource. The proposed algorithm is flexible to fit different resource constraints and performance requirements. View full abstract»

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  • Design and analysis of contention-based request schemes for best-effort traffics in IEEE 802.16 networks

    Publication Year: 2008 , Page(s): 602 - 604
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    The IEEE 802.16 standard is designed to meet the need of metropolitan-area broadband wireless access. This work studies two collision-resolution requesting schemes for best-effort (BE) traffics in IEEE 802.16 networks. One is the exponential backoff scheme defined in the standard and the other is a piggyback mechanism enhanced by single-frame backoff, called the Request Piggyback (RPB) scheme. We analyze and compare their performance in terms of the request success probability and the packet delivery delay under Poisson traffic. The results show that the RPB scheme outperforms the exponential backoff scheme and can reduce request collision. View full abstract»

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  • Chord-zip: a chord-ring merger algorithm

    Publication Year: 2008 , Page(s): 605 - 607
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (237 KB) |  | HTML iconHTML  

    Distributed hash tables have been thoroughly examined in terms of robustness, topology-awareness and routing efficiency. However the dynamic composition of distributed hash tables has been neglected or has been dealt with only out of necessity. Future Internet networking envisions interaction and cooperation of autonomous networks, which often result in network (de)compositions where merging of distributed hash tables should be taken into consideration. Chord-Zip, a novel algorithm has been developed to efficiently and transparently handle the merging of Chord rings - a distributed hash table type - to their applications. View full abstract»

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IEEE Communications Letters  is aimed at satisfying the need for rapid dissemination of information, offering a vehicle for authors to expose their results to be used in future developments. This ensures early recognition of work. 

 

 

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George K. Karagiannidis
Aristotle University of Thessaloniki
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