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Communications Letters, IEEE

Issue 7 • Date July 2007

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Displaying Results 1 - 25 of 28
  • IEEE Communications Letters - Table of contents

    Publication Year: 2007 , Page(s): C1 - C2
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    Freely Available from IEEE
  • Comments on "Power and Spectrally Efficient Four-Dimensional Super-Orthogonal WCDMA Building Blocks for Next Generation Wireless Applications"

    Publication Year: 2007 , Page(s): 561
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (42 KB) |  | HTML iconHTML  

    The modulation scheme proposed in [1] contrary to the authors' claims provides neither amplitude constancy nor gain in resource utilization. View full abstract»

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  • Greedy Anti-Void Routing Protocol for Wireless Sensor Networks

    Publication Year: 2007 , Page(s): 562 - 564
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (174 KB) |  | HTML iconHTML  

    The unreachability problem (i.e. the so-called void problem) which exists in the greedy routing algorithms has been studied for the wireless sensor networks. However, most of the current research work can not fully resolve the problem (i.e. to ensure the delivery of packets) within their formulation. In this letter, the greedy anti-void routing (GAR) protocol is proposed, which solves the void problem by exploiting the boundary finding technique for the unit disk graph (UDG). The proposed rolling-ball UDG boundary traversal (RUT) is employed to completely guarantee the delivery of packets from the source to the destination node. The proofs of correctness for the proposed GAR protocol are also given at the end of this letter. View full abstract»

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  • BPSK Bit Error Outage over Nakagami-m Fading Channels in Lognormal Shadowing Environments

    Publication Year: 2007 , Page(s): 565 - 567
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (100 KB) |  | HTML iconHTML  

    In this letter, we address the problem of finding a tractable expression for the bit-error outage (BEO) defined as the probability to observe a given average bit error rate (BER) over a fading channel in a shadowing environment. Our contribution is two-fold: (1) a simple yet tight approximation of the bit error probability (BEP) for binary phase shift keying (BPSK) over a frequency-flat Nakagami-m fading channel is derived, which (2) facilitates the derivation of a tight lower bound of the BEO in presence of lognormal shadowing in closed form. Theoretical results are corroborated by means of simulation results, confirming the tightness of the bounds. View full abstract»

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  • Estimating the Ergodic Capacity of Log-Normal Channels

    Publication Year: 2007 , Page(s): 568 - 570
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB) |  | HTML iconHTML  

    In this paper, we first provide a very accurate estimation of the capacity of a single-input single-output system operating in a log-normal environment. Then, hinging on the fact that the sum of log-normal Random Variables (RV) is well approximated by another log-normal RV, we apply the obtained results to find the capacity of Maximum Ratio Combining and Equal Gain Combining in a log-normal environment. The capacity in an interference-limited environment is also investigated in this paper. The analytical expressions obtained match perfectly the capacity given by simulations. View full abstract»

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  • On Capacity and Fairness of Quality-Based Channel-State Reporting with Different Thresholds in Non-Identical Rayleigh Fading Channels

    Publication Year: 2007 , Page(s): 571 - 573
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB) |  | HTML iconHTML  

    The quality-based channel-state reporting (QBR) that prevents the users with signal strength below a threshold from sending feedback induces a fairness problem in non-identically distributed fading channels. This letter extends QBR so as to achieve a fair throughput among users to whom different values of the threshold are assigned. With numerical investigation, the proposed extension is shown to achieve both multiuser diversity and a near absolute fairness where all the users have the same individual throughput. View full abstract»

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  • Stable Topology Control for Mobile Ad-Hoc Networks

    Publication Year: 2007 , Page(s): 574 - 576
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (141 KB) |  | HTML iconHTML  

    Topology control is the problem of adjusting the transmission parameters, chiefly power, of nodes in a Mobile Ad Hoc Network (MANET) to achieve a desired topology. Over the last several years, this problem has received much attention. Despite this work however, the stability of available techniques has not been studied. This paper presents the first control- theoretic investigation of topology control in MANETs. We take a simple representative fully distributed topology control algorithm called LINT and show that it is unstable under certain conditions. We then formulate LINT in a control-theoretic context, and derive a new mechanism called CLINT that is shown to be stable for a wide range of parameter variations. We compare the in- practice performance of LINT and CLINT using comprehensive simulations and show that CLINT provides a higher throughput. View full abstract»

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  • AMC-Based Transmission of Resource Allocation Messages for Short-Sized Packet Services

    Publication Year: 2007 , Page(s): 577 - 579
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (114 KB) |  | HTML iconHTML  

    We introduce a scheme that applies adaptive modulation and coding (AMC) to the transmission of resource allocation messages, and show that the AMC transmission of control messages reduces control overhead and is particularly effective for services with small-sized packets, such as VoIP. View full abstract»

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  • Analyzing Large Scale Real-World Wireless Multihop Network

    Publication Year: 2007 , Page(s): 580 - 582
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (98 KB) |  | HTML iconHTML  

    We present the results of analysis of Berlin's free multihop wireless network and provide topological, link reliability and traffic statistics we have captured from it. The network is relatively large compared with known wireless multihop networks and testbeds, and it had 316 participating nodes on the average. The observed properties are different from frequently used models: the network is connected but with low average node density, it has large number of bridges (some of them with very low quality of links) and the traffic distribution is highly asymmetrical. View full abstract»

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  • Peak Power Reduction in Closed-Loop MIMO-OFDM Systems via Mode Reservation

    Publication Year: 2007 , Page(s): 583 - 585
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (156 KB) |  | HTML iconHTML  

    This letter studies peak-to-average power ratio (PAPR) reduction for orthogonal frequency-division multiplexing (OFDM) signals in eigenbeamformed multiple antenna systems. The weak eigenmodes abandoned by the waterfilling allocation are intentionally filled in order to offset signal peaks in the time domain.Numerical results indicate that this method can significantly increase the efficiency of peak power constrained systems with no modification of the receiver required. View full abstract»

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  • Rate Optimization for 2D OFDM Relaying

    Publication Year: 2007 , Page(s): 586 - 588
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (91 KB) |  | HTML iconHTML  

    We solve optimal symbol dimensions for a recently introduced two-dimensional orthogonal frequency division multiplexing (2D OFDM) scheme with a two-dimensional cyclic prefix (2D CP). The 2D OFDM technique is shown to improve the rate of a wireless relaying system if the channel coherence time is at least nine times longer than the channel impulse response. Furthermore, feasibility and application scenarios of 2D OFDM are discussed using the parameters of terrestrial digital video broadcasting systems (DVB-T/H) as examples. View full abstract»

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  • Outage Probability of Selection Cooperation in the Low to Medium SNR Regime

    Publication Year: 2007 , Page(s): 589 - 597
    Cited by:  Papers (26)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (105 KB) |  | HTML iconHTML  

    Selection has been shown to be an effective and practical method of implementing cooperative diversity. However, the available analysis has largely focused on diversity order and the asymptotically high signal to noise ratio (SNR) regimes. We approximate the outage probability of selection cooperation for all SNR levels and arbitrary channel distributions. The approximations are significantly better than the available high-SNR approximations for practical values of outage probability. View full abstract»

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  • Clique Number vs. Chromatic Number in Wireless Interference Graphs: Simulation Results

    Publication Year: 2007 , Page(s): 592 - 594
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (72 KB) |  | HTML iconHTML  

    Interference due to transmissions by adjacent nodes in a multi-hop wireless network can be modeled using a unit disc graph (UDG). We investigate the reliability associated with using the clique number instead of the chromatic number of the UDG while computing the interference. In our extensive simulations with UDGs of random networks, we observed that the clique number and the chromatic number values were typically very close to one another and the maximum deviation was much less than the theoretical bounds. This implies very high reliability in the proposed approximation. View full abstract»

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  • A Control-Based Approach to Transport Channel Synchronization in UTRAN

    Publication Year: 2007 , Page(s): 595 - 597
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB) |  | HTML iconHTML  

    Transport channel synchronization in 3G access networks is currently based on a simple algorithm that tries to track the delay of the link by adding or subtracting a constant step. We propose an algorithm that improves the responsiveness of the system under abrupt delay changes, reducing frame losses. Our proposal is faster than the proportional tracking system upon which it is based and has delay-independent stability. View full abstract»

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  • Outage performance of mrt with unequal-power co-channel interference and channel estimation error

    Publication Year: 2007 , Page(s): 598 - 600
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (116 KB) |  | HTML iconHTML  

    In this letter we investigate the outage performance of maximal ratio transmission (MRT) with unequal-power co-channel interference (CCI) and channel estimation error. The exact expression for the outage probability is presented. Our results are applicable to the MRT systems with arbitrary numbers of transmit and receive antennas. View full abstract»

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  • Use of Different Acknowledgement Policies for Burst Transmission in Fiber-fed Wireless LANs

    Publication Year: 2007 , Page(s): 601 - 603
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (207 KB) |  | HTML iconHTML  

    The IEEE 802.11 e medium access control (MAC) for quality-of-service (QoS) support in 802.11 networks defines burst transmission and new acknowledgment (ACK) operations as optional mechanisms for increasing channel utilization. In this paper, we investigate how the performance of these new features is affected by the presence of fiber delay in high speed Wireless LAN (WLAN) over fiber networks. It is shown that the negative effect of the fiber delay on the throughput performance of the 802.11 MAC protocol can be significantly reduced when burst transmission is used with the block or the no ACK policies. View full abstract»

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  • A Transparent Failover Mechanism for a Mobile Network with Multiple Mobile Routers

    Publication Year: 2007 , Page(s): 604 - 606
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (213 KB) |  | HTML iconHTML  

    In a mobile network that is multihomed by multiple mobile routers, a mobile router that loses link connectivity can be replaced by the other mobile routers. We propose a transparent failover mechanism (TFM) to provide seamless Internet services to nodes in the mobile network, which is validated by implementing a real test-bed. Compared to the network mobility basic support protocol, TFM does not require the nodes attached to the failed mobile router to change their addresses, and hence has two advantages: (a) IP connectivity is maintained transparently, and (b) failover is quickly accomplished by avoiding the address re-configuration process in each node. View full abstract»

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  • LDPC Code Construction with Low Error Floor Based on the IPEG Algorithm

    Publication Year: 2007 , Page(s): 607 - 609
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (175 KB) |  | HTML iconHTML  

    We propose a modification on the improved progressive-edge-growth(IPEG) algorithm. Proposed modification increases the connectivity of variable nodes using extrinsic message degree of variable nodes, which results in reducing the small stopping sets. Through computer simulation, we confirm that the codes constructed by the proposed algorithm have lower error floor than those constructed by the original IPEG algorithm. View full abstract»

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  • Compensation Decoding of Space Time Frequency Block Codes

    Publication Year: 2007 , Page(s): 610 - 612
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (124 KB) |  | HTML iconHTML  

    A novel compensation decoding scheme for a given space time frequency linear block code is presented, exploiting the simplicity of zero forcing equalization, and special characteristics of the preceding matrix. The proposed decoding procedure is relatively simple and straightforward in comparison to maximum likelihood decoding (MLD) and sphere decoding (SD). The bit-error-rate performance of the proposed scheme is better than zero forcing decoding and close to MLD and SD for low to medium signal-to-noise ratio range. View full abstract»

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  • Robust Diversity-Combing Receivers for LDPC Coded FFH-SS with Partial-Band Interference

    Publication Year: 2007 , Page(s): 613 - 615
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (153 KB) |  | HTML iconHTML  

    Diversity-combining followed by min-sum decoding is proposed for mitigating partial-band interference in low-density parity-check (LDPC) coded frequency-hopping systems with diversity transmission. A new robust diversity-combining technique is derived based on the generalized maximum-likelihood ratio test (GMLRT). Simulations show that, among various diversity-combining techniques, the GMLRT, envelope self-normalizing and clipped-linear combining schemes are appealing for use in practice. View full abstract»

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  • Improving the Error Rate Performance of Turbo Codes using the Forced Symbol Method

    Publication Year: 2007 , Page(s): 616 - 618
    Cited by:  Papers (7)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (85 KB) |  | HTML iconHTML  

    This letter presents a method that significantly improves the error rate performance of turbo codes, especially in the error flare region, without changing the basic encoder structure. This method applies repeated decoding, with one or more symbols being forced to certain values, when an error is detected. This forces the decoder to output alternate sets of decisions that can then be checked for errors. The effectiveness of this method is demonstrated by its ability to lower the error flare by several orders of magnitude as soon as the error flare region is encountered. For the DVB-RCS 8-state, rate 1/2, double-binary turbo code and packets of 1504 information bits (MPEG-size), this method yields performance about 0.4 dB from the sphere-packing bound down to a packet error rate of 10-7. View full abstract»

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  • A Cross-Layered Network-Adaptive Video Streaming Using Sender-Driven Wireless Channel Monitoring

    Publication Year: 2007 , Page(s): 619 - 621
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (226 KB) |  | HTML iconHTML  

    In this letter, we propose a cross-layered network- adaptive video streaming system employing sender-driven wireless channel monitoring over a wireless LAN (WLAN). An intelligent sender with an embedded wireless access point (AP) estimates time-varying available bandwidth based on the observed transmission statistics of medium access control (MAC) and physical (PHY) layers. The estimated available bandwidth is then utilized to dynamically guide the network-adaptive control of temporally-scalable video flows. View full abstract»

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  • FIR Beamforming for Frequency-Selective Channels with Linear Equalization

    Publication Year: 2007 , Page(s): 622 - 624
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (112 KB) |  | HTML iconHTML  

    In this letter, we consider transmit beamforming with finite impulse response (FIR) filters for frequency-selective channels and simple linear equalization at the receiver. Since a closed-form solution for the optimum FIR beamforming filters (BFFs) does not seem to exist, an efficient numerical method for their recursive calculation is developed. Our numerical results show that for typical GSM/EDGE channels short FIR BFFs can closely approach the performance of the optimum infinite impulse response (IIR) BFFs derived in [1] and yield significant gains over single-antenna transmission. View full abstract»

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  • Accounting for link load correlation in the estimation of blocking probabilities in arbitrary network topologies

    Publication Year: 2007 , Page(s): 625 - 627
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (265 KB) |  | HTML iconHTML  

    In this paper, we discuss an efficient analytical framework that can accurately account for the link correlation in generic-topology circuit-switched networks. The model takes all active paths, as well as all free links, as independent objects on the network topology. Therefore, the actual sets of sequentially connected busy links (paths) and free links are seen as they appear in the network and the link correlation can be straightforwardly considered. Comparisons with results obtained from simulations show the excellent performance of the proposed analytical modeling for a variety of network topologies. View full abstract»

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  • Delay Sensitive Smoothed Round Robin (DS2R2) Scheduler for High-Speed Optical Networks

    Publication Year: 2007 , Page(s): 628 - 630
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB) |  | HTML iconHTML  

    Smoothed round robin (SRR) is an 0(1) scheduler that efficiently schedules flows based on flow granularity leading to short-term fairness. We propose DS2R2 - delay sensitive smoothed round robin scheduler that enhances SRR by adhering to delay constraints of flows. Scalability and performance issues of DS2R2 for high-speed optical networks are considered. 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
Greece