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Communications Letters, IEEE

Issue 1 • Date Jan. 2004

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Displaying Results 1 - 25 of 31
  • Table of contents

    Publication Year: 2004 , Page(s): 01
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    Freely Available from IEEE
  • IEEE Communications Letters Society Information

    Publication Year: 2004 , Page(s): 0_2
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  • A new class of signal constellations for differential unitary space-time modulation (DUSTM)

    Publication Year: 2004 , Page(s): 1 - 3
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB) |  | HTML iconHTML  

    In this letter, a new class of signal constellations is proposed for differential unitary space-time modulation with multiple transmit antennas. In the proposed method, a rotation matrix is introduced to design signal constellations with large diversity product which is a primary property for signal constellations to have good performance in high signal to noise ratio (SNR). View full abstract»

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  • Approaching the capacity of multiple access channels using interleaved low-rate codes

    Publication Year: 2004 , Page(s): 4 - 6
    Cited by:  Papers (30)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB) |  | HTML iconHTML  

    We show that the capacity of a Gaussian multiple access channel can be approached by interleaved low-rate codes together with a simple chip-by-chip iterative decoding strategy. Based on a rate ≈ 1/69 code and with a total of 35 simultaneous users (the aggregate rate ≈ 1/2), performance of BER=10-5 is observed at Eb/N0 ≈ 1.4 dB, which is close to the corresponding capacity limit (Eb/N0 ≈ 0 dB). View full abstract»

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  • On the equivalence of linear MMSE chip-level equalizer and generalized RAKE

    Publication Year: 2004 , Page(s): 7 - 8
    Cited by:  Papers (10)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (89 KB) |  | HTML iconHTML  

    Several linear equalization schemes have been proposed for the downlink of direct-sequence code-division multiple-access systems. Previous numerical performance evaluation of such algorithms showed the equivalence of the linear minimum mean-square error chip-level equalizer and a slightly modified version of the generalized RAKE. In this letter, we establish this equivalence analytically. View full abstract»

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  • A CPCH access method for prioritized services in W-CDMA

    Publication Year: 2004 , Page(s): 9 - 11
    Cited by:  Papers (2)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (128 KB) |  | HTML iconHTML  

    Common packet channel (CPCH) access is an efficient approach to support packet data transmissions in a wideband code-division multiple-access (W-CDMA) system. This letter introduces a simple access control method for CPCH, which results in higher throughput. This method also provides prioritized services for different traffic classes. Each traffic class is assigned a distinct transmit permission probability that is determined at the new call initiation stage based on the status of CPCH channel occupancy. The differentiated service qualities, which correspond to different transmit permission probabilities, are evaluated in terms of packet blocking rates. The overall system performance is also evaluated in terms of normalized throughput. View full abstract»

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  • BER performance of multiple-antenna OFCDM with imperfections

    Publication Year: 2004 , Page(s): 12 - 14
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    This letter investigates the performance degradation due to the imperfect parameters in orthogonal frequency- and code-division multiplexing (OFCDM) systems with multiple antennas. For the performance evaluation, the average bit error rate (BER) expression is generalized to the multiple-antenna case in the presence of the channel estimation error and frequency offset. Derived results show that the multiple-antenna OFCDM systems experience a severe BER degradation regardless of the number of users. View full abstract»

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  • On a hybrid beamforming/space-time coding scheme

    Publication Year: 2004 , Page(s): 15 - 17
    Cited by:  Papers (3)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    A multiple transmit antenna system based on hybrid beamforming and space-time coding technologies is examined. The reduction factor of the required transmitted energy achievable by the use of hybrid scheme is quantified for any given outage capacity. We show that although a sole space-time coding configuration is superior asymptotically (i.e., for extremely low outage requirements), a hybrid beamforming/space-time coding configuration can be a more effective solution for modest outage requirements. It may provide a useful design guideline for wireless systems, especially for the downlink where multiple transmit antenna scheme is feasible. View full abstract»

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  • Exact capacity distribution for dual MIMO systems in Ricean fading

    Publication Year: 2004 , Page(s): 18 - 20
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB) |  | HTML iconHTML  

    It is well known that multiple input multiple output (MIMO) systems offer the promise of achieving very high spectrum efficiencies (many tens of bit/s/Hz) in a mobile environment. The gains in MIMO capacity are sensitive to the type of channel encountered in the radio environment. To date most analytical work has concentrated on Rayleigh fading channels. Hence, in this letter we consider the capacity outage performance of MIMO systems in Ricean channels. Due to analytical complexity we concentrate on dual antenna systems (either two transmit or two receive antennas) and derive exact densities and distribution functions for the capacity. View full abstract»

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  • Impact of spatial correlation on the performance of orthogonal space-time block codes

    Publication Year: 2004 , Page(s): 21 - 23
    Cited by:  Papers (24)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB) |  | HTML iconHTML  

    We analyze the impact of transmitter and receiver spatial correlation on the performance of a multiple-input multiple-output (MIMO) system which applies an orthogonal space-time block code with no channel state information at the transmitter and perfect channel state information at the receiver. We derive a general formula for the bit error rate of a MIMO system with arbitrary number of transmit and receive antennas as a function of the correlation at the transmitter and the receiver. We prove that the diversity advantage is given by M·N if M is the rank of the transmit correlation matrix and N the rank of the receive correlation matrix, respectively. View full abstract»

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  • A novel sectional paging strategy for location tracking in cellular networks

    Publication Year: 2004 , Page(s): 24 - 26
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    In this letter, we propose a new paging technique, sectional paging, that reduces the paging cost while complying with the delay constraint for mobiles roaming with traceable patterns. Without having to install much additional complexity, the developed scheme predicts the likelihood of residence and assigns optimal paging boundaries. Thus while complying with the required delay constraints, quality-of-service (QoS) measures will not need to be sacrificed as a result of increasing the update threshold. Under the same network conditions and mobile characteristics, simulation results reveal that the usage of sectional paging is most suitable when the roaming pattern is either traceable or can be predicted with reasonable precision. View full abstract»

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  • Spare reservation and distributed release based multiple access for satellite multimedia services

    Publication Year: 2004 , Page(s): 27 - 29
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB) |  | HTML iconHTML  

    In this letter, we propose an efficient multiple access scheme for multimedia services in satellite networks, retransmission announced reservation multiple access (RARMA), in which resources are reserved according to the occasional demands by using spare reservation request and are released later by using a distributed release scheme. We analyze the throughput of RARMA, and show that our proposed scheme has a good throughput-delay characteristic through computer simulation. View full abstract»

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  • Considering spurious timeout in proxy for improving TCP performance in wireless networks

    Publication Year: 2004 , Page(s): 30 - 32
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB) |  | HTML iconHTML  

    In this letter, we introduce a new proxy that effectively prevents unnecessary retransmissions from flowing over a wireless link on a path with sudden delay. The proposed Spurious Timeout (STD) algorithm detects spurious timeout based on the data and acknowledge sequence number. It responses to spurious timeout by filtering duplicate acknowledgements that can cause spurious fast retransmission. Simulation results show that the proposed STD algorithm performs better than, or as well as, other end-to-end mechanisms. View full abstract»

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  • An integrated strategy for reducing location management cost

    Publication Year: 2004 , Page(s): 33 - 35
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (120 KB) |  | HTML iconHTML  

    In this letter, an integrated location information management strategy is proposed for mobile networks, where local anchor and replica are deployed to efficiently manage the location information of a mobile terminal (MT) based on its call and mobility characteristics. As an MT's user is roaming within the local signal transfer point (LSTP) region serving the user's home or workplace, the MT's location change is reported to a local anchor (LA)-the visitor location register (VLR) associated with the user's home or workplace. Meanwhile, the LA's location is replicated at several switches (called the replicas) originating relatively high call rates to the MT. As a result, the MT's home location register (HLR) needs to be accessed only when the MT changes its LSTP region or an incoming call for the MT is generated by a nonreplica originating switch. This is shown to reduce location tracking costs. View full abstract»

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  • FFT-based hybrid antenna selection schemes for spatially correlated MIMO channels

    Publication Year: 2004 , Page(s): 36 - 38
    Cited by:  Papers (35)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB) |  | HTML iconHTML  

    In this letter, we address the antenna subset selection problem in spatially correlated multiple-input multiple-output (MIMO) channels. To reduce the severe performance degradation of the traditional antenna selection scheme in correlated channels, we propose to embed fast Fourier transform operations in the RF chains. The resulting system shows a significant advantage both for diversity schemes and for the capacity of spatial multiplexing, while requiring only a minor hardware overhead. View full abstract»

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  • Bit-error-rate performance of intra-chip wireless interconnect systems

    Publication Year: 2004 , Page(s): 39 - 41
    Cited by:  Papers (15)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB) |  | HTML iconHTML  

    This Letter evaluates the bit-error rate (BER) performance of a coherent binary phase-shift keying interconnect system operating on an intra-chip wireless channel at 15 GHz. Results show that the system performance degrades with the separation distance and the data rate. A high data rate at 2 Gb/s with a low BER<10-5 over the entire chip of size 20 × 20 mm can be achieved with the transmitted power of 10 dBm. View full abstract»

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  • Comparative performance evaluation of EDCF and EY-NPMA protocols

    Publication Year: 2004 , Page(s): 42 - 44
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (120 KB) |  | HTML iconHTML  

    Medium access represents one of the most critical building blocks regarding the performance of a wireless LAN. In this letter, we compare the performance of two well-known medium access control protocols specifically developed for the wireless environment, EDCF and EY-NPMA. To our knowledge, it is the first time that these two quality-of-service (QoS) aware medium access schemes are compared. Furthermore, we propose a novel scheme for medium access based on EY-NPMA, that demonstrates reduced overhead compared to the base protocol and better utilization of the common medium. The conclusions of this paper are based on extensive simulation trials. View full abstract»

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  • Exact BER analyses of Nakagami/Nakagami CCI BPSK and Nakagami/Rayleigh CCI QPSK systems in slow fading

    Publication Year: 2004 , Page(s): 45 - 47
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    A recent letter presented an approximate bit error rate (BER) analysis of coherent binary phase-shift keying (BPSK) in cochannel interference with Nakagami faded desired and interfering signals. Here, the exact BER of coherent nonreturn-to-zero (NRZ) BPSK with cochannel interference in Nakagami fading is derived showing that the approximate analysis may be inaccurate. The exact BER of NRZ quaternary PSK (QPSK) with Nakagami faded desired user signal and Rayleigh faded interfering signals is also derived. Slow fading, asynchronous timing and independent fading gains are assumed. View full abstract»

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  • Error probability of Q-ary symbol consisting of multiple channel symbols under Rayleigh fading

    Publication Year: 2004 , Page(s): 48 - 50
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB) |  | HTML iconHTML  

    Closed-form expressions for symbol error probabilities are derived for the case when modulation alphabet size M is smaller than symbol size Q. We consider slow Rayleigh fading channel where fading amplitudes and phases remain constant during one Q-ary symbol duration. An exact expression is obtained for noncoherent M-ary frequency-shift keyed (MFSK) modulation and the simple and accurate approximate expressions are obtained for M-ary phase-shift keyed (MPSK) and quadrature-amplitude modulation. Simulation results showed that the derived error probability are well agreed. View full abstract»

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  • A new class of carrier-hopping codes for code-division multiple-access optical and wireless systems

    Publication Year: 2004 , Page(s): 51 - 53
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (112 KB) |  | HTML iconHTML  

    Carrier-hopping codes, a collection of two-dimensional (2-D) patterns with good correlation properties, find applications in frequency-hopping code-division multiple-access (CDMA) wireless and wavelength-hopping CDMA fiber-optic systems. This kind of codes were usually designed under the assumptions that one pulse per row is used in the 2-D patterns and the number of available carriers is the same as code weight. While the assumptions restrict code cardinality, there are scenarios in which the number of available carriers is more than the actual number of carriers needed in the patterns. To provide flexible code design without these assumptions, this letter reports a new family of carrier-hopping codes with expanded cardinality, while maintaining ideal correlation properties. The cardinality of the new codes is shown to be asymptotically optimal. View full abstract»

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  • On concatenated zigzag codes and their decoding schemes

    Publication Year: 2004 , Page(s): 54 - 56
    Cited by:  Papers (2)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB) |  | HTML iconHTML  

    In this letter, we show that a concatenated zigzag code can be viewed as a low-density parity-check (LDPC) code. Based on the bipartite graph representation for such a parallel-concatenated code, various sum-product based decoding algorithms are introduced and compared. The results show that the improved versions of sum-product algorithm exhibit better convergence rate while maintaining the essential parallel form. View full abstract»

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  • Improving belief propagation on graphs with cycles

    Publication Year: 2004 , Page(s): 57 - 59
    Cited by:  Papers (25)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB) |  | HTML iconHTML  

    In this letter, we propose two modifications to belief propagation (BP) decoding algorithm. The modifications are based on reducing the reliability of messages throughout the iteration process, and are particularly effective for short low-density parity-check codes, where the existence of cycles makes the original BP algorithm perform suboptimal. The proposed algorithms, referred to as "normalized BP" and "offset BP," reduce the absolute value of the outgoing log-likelihood ratio messages at variable nodes by using a multiplicative factor and an additive factor, respectively. Simulation results show that both algorithms perform more or less the same, and both outperform BP in error performance. View full abstract»

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  • A computational model for estimating blocking probabilities of multifiber WDM optical networks

    Publication Year: 2004 , Page(s): 60 - 62
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (112 KB) |  | HTML iconHTML  

    In this letter, we propose a computational model for calculating blocking probabilities of multifiber wavelength division multiplexing (WDM) optical networks. We first derive the blocking probability of a fiber based on a Markov chain, from which the blocking probability of a link is derived by means of conditional probabilities. The blocking probability of a lightpath can be computed by a recursive formula. Finally, the network-wide blocking probability can be expressed as the ratio of the total blocked load versus the total offered load. Simulation results for different fiber-wavelength configurations conform closely to the numerical results based on our proposed model, thus demonstrating the feasibility of our proposed model for estimating the blocking performance of multifiber WDM optical networks. View full abstract»

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  • Analysis of the SPEKE password-authenticated key exchange protocol

    Publication Year: 2004 , Page(s): 63 - 65
    Cited by:  Papers (6)  |  Patents (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (84 KB) |  | HTML iconHTML  

    In this letter, we show that for the SPEKE password-authenticated key exchange protocol, an adversary is able to test multiple possible passwords using a single impersonation attempt. In particular, when passwords are short Personal Identification Numbers (PINs), we show that a fully-constrained SPEKE is susceptible to password guessing attack. Our analysis contradicts the claim that the SPEKE protocol appears to be at least as strong as the Bellovin-Merritt EKE protocol. For EKE, an adversary can gain information about at most one possible password in each impersonation attempt. View full abstract»

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  • On throughput stabilization of network transport

    Publication Year: 2004 , Page(s): 66 - 68
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    A number of network applications require stable transport throughput for tasks such as control and coordination operations over wide-area networks. We present a window-based method that achieves stable throughput at a target level by utilizing a variation of the classical Robbins-Monro stochastic approximation algorithm. We analytically show the stability of this method under very mild conditions on the network, which are justified by Internet measurements. Our User Datagram Protocol (UDP)-based implementation provides stable throughput over the Internet under various traffic conditions. View full abstract»

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Aristotle University of Thessaloniki
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