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Communications Letters, IEEE

Issue 1 • Date Jan. 2003

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Displaying Results 1 - 15 of 15
  • Subchip multipath delay estimation for downlink WCDMA system based on Teager-Kaiser operator

    Publication Year: 2003 , Page(s): 1 - 3
    Cited by:  Papers (13)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (234 KB) |  | HTML iconHTML  

    Accurate detection and estimation of overlapping fading multipath components is vital for many communication systems, particularly for positioning technologies. Traditional approaches used for channel estimation generally fail in estimating closely-spaced multipath components in code-division multiple access (CDMA) systems. Here, we present a highly efficient technique for asynchronous downlink WCDMA multipath delay estimation with subchip resolution capability based on nonlinear Teager-Kaiser operator concept. The behavior of this technique is influenced considerably by the pulse shape waveform. Both rectangular and root raised cosine pulse shaping filters are considered. View full abstract»

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  • Spreading code construction for CDMA

    Publication Year: 2003 , Page(s): 4 - 6
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (382 KB) |  | HTML iconHTML  

    In this letter, we use the well-known Walsh-Hadamard codes to construct larger sets of linearly dependent codes such that their matrix of correlations is band-diagonal. Optimal detection for systems employing these spreading codes can be efficiently accomplished by a trellis decoder. Analysis and simulation show that with a processing gain of N, up to 2N users can be accommodated without much performance degradation. This proposed approach is quite general and larger code set can be constructed analogously. View full abstract»

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  • Interference-oriented carrier assignment in wireless communications

    Publication Year: 2003 , Page(s): 7 - 9
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (269 KB) |  | HTML iconHTML  

    A carrier assignment problem, suitable for engineering the complex interference conditions of 2.5G and broadband fixed wireless access wireless environments, is addressed. The objective function minimizes the interference levels imposed by the carrier allocation, while the constraints assign the carriers required per cell and prevent unacceptable interference situations. The problem is formally stated and mathematically formulated. Solutions, adhering to the genetic algorithm and the simulated annealing paradigms, are discussed and indicative results are presented. View full abstract»

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  • Performance comparisons of dynamic resource allocation with/without channel de-allocationin GSM/GPRS networks

    Publication Year: 2003 , Page(s): 10 - 12
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB) |  | HTML iconHTML  

    In this letter, we analyzed and compared the performance of dynamic resource allocation with/without channel de-allocation in GSM/GPRS networks. It is quite known that dynamic resource allocation allows communication systems to utilize their resources more efficiently than the traditional fixed allocation schemes. In GPRS, multiple channels may be allocated to a user to increase the transmission rate. In the case when there are no free channels in the system, some of these channels may be de-allocated to serve higher priority calls. The results show that with channel de-allocation mechanism, the voice blocking probability can be greatly reduced, especially at high GPRS traffic load. Besides, the scheme with channel de-allocation mechanism can achieve higher channel utilization. View full abstract»

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  • Polarization of received signals for wideband wireless communications in a heavy rainfall region

    Publication Year: 2003 , Page(s): 13 - 14
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (167 KB) |  | HTML iconHTML  

    Wireless fixed network access offers many advantages such as scalability and ease of deployment in low population density areas. However, its coverage is greatly affected by rainfall. In this letter, we study the effects of rain attenuation on the radio channel in a heavy rainfall region for wideband signals in the 10-40-GHz frequency range. We conclude that although a lower frequency of <10 GHz is more affected by multipath due to a longer wavelength, it is still optimal in a heavy rainfall region due to high losses associated with higher frequency signals. In addition, for a path of over 1.5 km, the difference in horizontal and vertical polarization becomes significant. View full abstract»

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  • Bit error outage for diversity reception in shadowing environment

    Publication Year: 2003 , Page(s): 15 - 17
    Cited by:  Papers (42)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (323 KB) |  | HTML iconHTML  

    This letter addresses the problem of evaluating the bit error outage (BEO), i.e., the outage probability defined in terms of bit error probability, in a Rayleigh fading and shadowing environment. We consider coherent detection of binary phase-shift keying with maximal ratio combining (MRC). As an example application, the BEO in a log-normal shadowing environment is analyzed and the improvement in terms of BEO due to MRC is quantified in different shadowing environments. View full abstract»

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  • Modeling Bluetooth piconet performance

    Publication Year: 2003 , Page(s): 18 - 20
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (322 KB) |  | HTML iconHTML  

    The performance of a single Bluetooth piconet is analyzed using the theory of M/G/1 queues with vacations. Analytical results for probability distributions of packet access time and service cycle time are derived. Two scheduling policies are modeled and compared: exhaustive service was found to perform better, but limited service does not incur the risk of starvation. A hybrid scheme known as k-limited scheduling is shown to provide a reasonable tradeoff between performance and fairness. Results were confirmed through simulations. View full abstract»

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  • Unitary nonuniform space-time constellations for the broadcast channel

    Publication Year: 2003 , Page(s): 21 - 23
    Cited by:  Papers (2)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (267 KB) |  | HTML iconHTML  

    We propose a new class of unitary space-time matrix constellations that have nonuniform error performance. Such codes are important for transmission over a broadcast, or point-to-multipoint, communication channel and when scalable source coding is used. Our new codes can be encoded differentially and are based entirely on phase-shift keying. Analytical design criteria are discussed and a simulation result is presented to exemplify the designs. View full abstract»

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  • A push mechanism for GPRS supporting private IP addresses

    Publication Year: 2003 , Page(s): 24 - 26
    Cited by:  Papers (4)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (211 KB) |  | HTML iconHTML  

    The General Packet Radio Service (GPRS) provides a packet switched data service for mobile users. However, the existing GPRS specification does not provide the push mechanism and it is difficult to support GPRS services such as call termination (incoming call) for wireless voice over IP (VoIP). Based on the short message service, this paper proposes a push mechanism for GPRS supporting private IP addresses. Our approach does not need to modify the existing GPRS structure. View full abstract»

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  • Effect of keyholes on the symbol error rate of space-time block codes

    Publication Year: 2003 , Page(s): 27 - 29
    Cited by:  Papers (24)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (355 KB) |  | HTML iconHTML  

    In multiple-input multiple-output (MIMO) fading environments, degenerate channel phenomena, so-called keyholes or pinholes, may exist under realistic assumptions where a MIMO channel has uncorrelated spatial fading between antenna arrays but a rank-deficient transfer matrix. In this letter, we analyze the average symbol error rate (SER) of orthogonal space-time block codes (STBCs) with M-PSK and M-QAM constellations over keyhole channels. View full abstract»

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  • Pilot embedding for joint channel estimation and data detection in MIMO communication systems

    Publication Year: 2003 , Page(s): 30 - 32
    Cited by:  Papers (45)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB) |  | HTML iconHTML  

    A novel pilot-aided joint channel estimation and data detection method for MIMO communication systems is proposed. Unlike, conventional methods where pilots are time-multiplexed with data symbols, a pilot-embedding method where low-level pilots are transmitted concurrently with the data is used to obtain an initial estimate of the channel such that a turbo decoding process can be started. The soft information obtained from the turbo decoder is subsequently used to improve channel estimates. View full abstract»

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  • Fast adaptive arithmetic code for large alphabet sources with asymmetrical distributions

    Publication Year: 2003 , Page(s): 33 - 35
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (303 KB) |  | HTML iconHTML  

    We address the problem of constructing an adaptive arithmetic code in the case where the source alphabet is large and there are lots of different symbols with equal counts of occurrence. For an alphabet of N symbols and r distinct symbol weights we describe a code for which the number of operations needed for encoding and decoding is equal to clogr+c/sub 1/ instead of clogN+c/sub 2/ as in previous arithmetic codes, c, c/sub 1/, c/sub 2/ are constants. When r is small relative to N-which is the case for most practical coding problems on large alphabets-the encoding and decoding speed of the suggested code will be substantially greater than with known methods. View full abstract»

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  • Binary sequences with low aperiodic autocorrelation for synchronization purposes

    Publication Year: 2003 , Page(s): 36 - 38
    Cited by:  Papers (12)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    An evolutionary algorithm is used to find three sets of binary sequences of length 49-100 suitable for the synchronization of digital communication systems. Optimization of the sets are done by taking into consideration the type of preamble used in data frames and the phase-lock mechanism of the communication system. The preamble is assumed to be either a pseudonoise (PN) sequence or a sequence of 1s. There may or may not be phase ambiguity in detection. With this categorization, the first set of binary sequences is optimized with respect to aperiodic autocorrelation which corresponds to the random (PN) preamble without phase ambiguity case. The second and third sets are optimized with respect to a modified aperiodic autocorrelation for different figures of merit corresponding to the predetermined preamble (sequence of 1s) with and without phase ambiguity cases. View full abstract»

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  • Loss probability behavior of Pareto/M/1/K queue

    Publication Year: 2003 , Page(s): 39 - 41
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (286 KB) |  | HTML iconHTML  

    In this letter, we investigate the queue behavior with Pareto interarrival and exponential service time distribution. By numerical analysis and simulations, we analyze the asymptotic and the exact loss probabilities of GI/M/1/K to show the big discrepancy between the asymptotic and the actual loss probability and propose a model for the loss probability of Pareto/M/1/K as a function of the buffer size K and the geometric parameter. View full abstract»

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  • A remedy for performance degradation of TCP Vegas in asymmetric networks

    Publication Year: 2003 , Page(s): 42 - 44
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (235 KB) |  | HTML iconHTML  

    Many previous studies have indicated that TCP Vegas outperforms TCP Reno. This letter shows that in asymmetric networks in which the bottleneck is on the reverse path rather than on the forward path, Vegas underutilizes the available bandwidth on the forward path by a large margin. A solution that makes use of the TCP timestamp option can effectively restore the throughput on the forward path. 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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Editor-in-Chief
George K. Karagiannidis
Aristotle University of Thessaloniki
Greece