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Communications Letters, IEEE

Issue 8 • Date Aug. 2003

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Displaying Results 1 - 21 of 21
  • Differential space-time-frequency modulation over frequency-selective fading channels

    Publication Year: 2003 , Page(s): 349 - 351
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (393 KB) |  | HTML iconHTML  

    We present a differential space-time-frequency (DSTF) modulation scheme for systems with two transmit antennas over frequency-selective fading channels. The proposed DSTF scheme employs a concatenation of a spectral encoder and a differential encoder/mapper, which are designed to yield the maximum spatio-spectral diversity and significant coding gain. To reduce the decoding complexity, the differential encoder is designed with a unitary structure that decouples the maximum likelihood (ML) detection in space and time; meanwhile, the spectral encoder utilizes a linear constellation decimation (LCD) coding scheme that encodes across a minimally required set of subchannels for full diversity and, hence, incurs the least decoding complexity among all full-diversity codes. View full abstract»

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  • Combined transmit and receive antenna diversity for WCDMA in multipath fading channels

    Publication Year: 2003 , Page(s): 352 - 354
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (453 KB) |  | HTML iconHTML  

    We analyze the performance of various receiver antenna diversity combining schemes in combination with transmit diversity on the downlink of a WCDMA system. The analytical framework developed can handle an arbitrary number of transmit and receive antennas, as well as the study on the effect of dissimilar received signal strengths at the mobile handset on the average symbol error rate performance of a multitude of digital modulation schemes. View full abstract»

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  • Data aggregation and dilution by modulus addressing in wireless sensor networks

    Publication Year: 2003 , Page(s): 355 - 357
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB) |  | HTML iconHTML  

    DADMA is a distributed data aggregation and dilution technique for sensor networks where nodes aggregate/dilute sensed data by following the rules given in an SQL statement. Our test results show that DADMA reduces the number of transmitted packets 60% on the average. View full abstract»

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  • A dynamic anchor-cell assisted paging with an optimal timer for PCS networks

    Publication Year: 2003 , Page(s): 358 - 360
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (253 KB) |  | HTML iconHTML  

    An intra location area (intra-LA) location update (LU) scheme is proposed to increase paging accuracy for PCS networks. In the proposed scheme, each mobile terminal (MT) has a valid/invalid anchor-cell, which may be dynamically changed. A MT updates its anchor-cell information only when the status is changed, i.e., from the valid to the invalid or vice versa. Therefore, the intra-LA LU cost is minimized. Whenever the MT enters a cell, a timer is set. The MT realizes that the entered cell is its current anchor-cell if the timer expires before leaving the cell. An analytical model is proposed, and the optimal time threshold is derived explicitly. View full abstract»

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  • Capacity of MIMO systems with closely spaced antennas

    Publication Year: 2003 , Page(s): 361 - 363
    Cited by:  Papers (46)  |  Patents (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB) |  | HTML iconHTML  

    Wide-band radio channel measurements at 5.2 GHz with four transmit and four receive antennas at variable element spacing are reported, aiming to evaluate the potential of compact antenna arrays at mobile terminals. We show that, for an element spacing d<0.5/spl middot//spl lambda/ (down to 0.2/spl middot//spl lambda/), the link capacity is not smaller than that for much larger d. This is explained by the observation that mutual coupling changes the radiation patterns of closely spaced antenna elements, individually. Compact multi-antenna terminals may thus become practical. View full abstract»

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  • Capacity of RAKE reception with energy randomization

    Publication Year: 2003 , Page(s): 364 - 366
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (382 KB) |  | HTML iconHTML  

    We consider a RAKE receiver for coherent binary orthogonal signaling over a frequency selective multipath Rayleigh fading channel. The receiver uses maximal-ratio combining such that the weight estimation errors are not independent of the additive noise. We find the capacity-achieving energy randomization scheme with two energy levels for the cases of imperfect and perfect channel estimates. We observe that the capacity-achieving probability gets closer to 1/2 with increase in the number of paths. We also show that the capacity is higher if channel estimates are perfect and that the channel estimation errors have more pronounced effect on the capacity at low signal-to-noise ratios. View full abstract»

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  • A parallel shuffled paging strategy under delay bounds in wireless systems

    Publication Year: 2003 , Page(s): 367 - 369
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (342 KB) |  | HTML iconHTML  

    In sequential paging schemes, the paging process is considered on per user basis. When an incoming call arrives to a mobile terminal (MT), the associated location area is divided into several paging areas (PAs) and PAs are paged one by one until the MT is found. Even though sequential paging algorithms can reduce the paging cost compared to the blanket-paging scheme, they introduce extra and unnecessary delay due to the fact that, during each paging cycle, unpaged cells are idle and unused in terms of paging. In this letter, a simple parallel shuffled paging strategy is proposed to reduce delay and improve performance. In the proposed scheme, multiple MTs can be paged in difference PAs in parallel. Our study shows that the proposed scheme outperforms both the sequential paging and the blanket paging in terms of discovery rate and queueing delay. View full abstract»

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  • Multiuser diversity for a dirty paper approach

    Publication Year: 2003 , Page(s): 370 - 372
    Cited by:  Papers (107)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (263 KB) |  | HTML iconHTML  

    Multiuser diversity has attracted significant attention recently. In this letter, we propose a greedy algorithm based on QR decomposition of the channel and dirty paper precoding to exploit the multiuser diversity of the Gaussian vector broadcast channel. Simulations show the approach provides performance which is extremely close to a well-known upper bound on the sum rate. Further, exploiting multiuser diversity can provide large gain over approaches ignoring this resource. View full abstract»

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  • Measurement of keyhole effect in a wireless multiple-input multiple-output (MIMO) channel

    Publication Year: 2003 , Page(s): 373 - 375
    Cited by:  Papers (36)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (265 KB) |  | HTML iconHTML  

    It has been predicted theoretically that for some environments, the capacity of wireless multiple-input multiple-output systems can become very low even for uncorrelated signals; this effect has been termed "keyhole" or "pinhole." In this letter, we present the (to our knowledge) first measurement of this effect. The measurements are done in a controlled indoor environment, with transmitter and receiver in two adjacent rooms. One of the rooms is shielded, and propagation to the other room can occur only through a hole or a waveguide in the wall. We find that only the waveguide leads to an unambiguous keyhole, while a hole of the same size still allows multimodal propagation. Measurement of amplitude statistics also confirm theoretical predictions. View full abstract»

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  • Performance analysis of OFDMA uplink systems with symbol timing misalignment

    Publication Year: 2003 , Page(s): 376 - 378
    Cited by:  Papers (43)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (319 KB) |  | HTML iconHTML  

    This letter presents our investigation for the effect of symbol timing errors in orthogonal frequency-division multiple access (OFDMA) uplink systems. We express the symbol timing errors between users as the symbol timing misalignments with respect to the desired user. Then, we derive an explicit expression of the signal-to-noise ratio (SNR) as a function of the maximum value of the symbol timing misalignments. Analyses and simulation results show that, to achieve an SNR of 20 dB, the maximum value of the symbol timing misalignments must be less than the cyclic prefix duration plus 6.25% of the useful symbol duration. Based on the resulting SNR degradation, we evaluate the SNR gain with guard subcarriers in order to mitigate the effect of the symbol timing misalignments. View full abstract»

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  • A mobility measure for mobile ad hoc networks

    Publication Year: 2003 , Page(s): 379 - 381
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (261 KB) |  | HTML iconHTML  

    A mobility measure for mobile ad hoc networks is proposed that is flexible because one can customize the definition of mobility using a remoteness function. The proposed measure is consistent because it has a linear relationship to the rate at which links are established or broken for a wide range of mobility scenarios, where a scenario consists of the choice of mobility model, the physical dimensions of the network, the number of nodes. This consistency is the strength of the proposed mobility measure because the mobility measure reliably represents the link change rate regardless of network scenarios. View full abstract»

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  • Refinements to the packet error rate upper bound for Bluetooth networks

    Publication Year: 2003 , Page(s): 382 - 384
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (231 KB) |  | HTML iconHTML  

    The Bluetooth frequency hop sequence is uniformly distributed asymptotically but generally distributed otherwise. We present an upper bound on the Bluetooth packet error rate for single-slot packets that incorporates two inherent, short-term dependencies in the Bluetooth frequency hop sequence. First, the hop frequencies are chosen from a limited subset of the 79 Bluetooth frequencies that depends on past frequencies used. Second, subsequent packet frequency choices are usually selected from mutually exclusive subsets. Higher packet error rates result from these dependencies and from the limited range of the frequency hops. Our improved upper bound on the packet error rate allows more accurate Bluetooth performance analysis. View full abstract»

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  • Matrices analysis of quasi-orthogonal space-time block codes

    Publication Year: 2003 , Page(s): 385 - 387
    Cited by:  Papers (29)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB) |  | HTML iconHTML  

    In this paper, according to the analysis of existing transmission matrices of quasi-orthogonal space-time block codes (STBC), we generalize some of their characters and derive several new patterns to enrich the family of quasi-orthogonal STBC. View full abstract»

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  • Exploiting error-control coding and cyclic-prefix in channel estimation for coded OFDM systems

    Publication Year: 2003 , Page(s): 388 - 390
    Cited by:  Papers (18)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (287 KB) |  | HTML iconHTML  

    OFDM systems typically use coding and interleaving across subchannels to exploit frequency diversity on frequency-selective channels. This letter presents a low-complexity iterative algorithm for blind and semi-blind joint channel estimation and soft decoding in coded OFDM systems. The proposed algorithm takes advantage of the channel finite delay-spread constraint and the extra observation offered by the cyclic-prefix. It converges within a single OFDM symbol and, therefore, has a minimum latency. View full abstract»

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  • An algorithm for construction of efficient fix-free codes

    Publication Year: 2003 , Page(s): 391 - 393
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (354 KB) |  | HTML iconHTML  

    We propose an algorithm for construction of fix-free codes, which involves a new codeword selection mechanism. Starting from the shortest codewords, the proposed algorithm selects fix-free codewords of any length i with respect to maximizing the number of available codewords of length i+1. Due to the increased fix-free codeword availability, the proposed algorithm constructs the codes of higher efficiency relative to the other algorithms in the literature. View full abstract»

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  • Hybrid symbol- and bit-based source-controlled channel decoding for MELP speech parameters

    Publication Year: 2003 , Page(s): 394 - 396
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (277 KB) |  | HTML iconHTML  

    A joint source channel coding (JSCC) scheme which exploits bit-level correlation as well as symbol-level correlation efficiently in a source-controlled channel decoding (SCCD) process is proposed and applied to the mixed-excitation linear prediction (MELP) parameters of speech. A modified BCJR algorithm is also proposed for use in the SCCD algorithm. Simulation results show that our proposed scheme performs better than other redundancy-based JSCC schemes such as bit-based SCCD, soft-bit speech decoding (SBSD) and iterative source-channel decoding. View full abstract»

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  • A waveband switching architecture and algorithm for dynamic traffic

    Publication Year: 2003 , Page(s): 397 - 399
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (257 KB) |  | HTML iconHTML  

    The proposed multi-granular optical cross-connect (MG-OXC) architecture and heuristic algorithm significantly reduce the number of used ports and hence the cost of an existing network, and also help in reducing the blocking probability of dynamic connection requests. View full abstract»

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  • Exploiting diversity in multimode fiber communications links via multisegment detectors and equalization

    Publication Year: 2003 , Page(s): 400 - 402
    Cited by:  Papers (4)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (210 KB) |  | HTML iconHTML  

    we propose diversity combination via optical multisegment detectors and electrical equalization techniques to mitigate the effects of intermodal dispersion in multimode fiber (MMF). With no equalization in MMF links, intermodal dispersion produces intersymbol interference (ISI) in the received optical signal that severely limits the achievable data transmission rates and fiber link lengths. Our quasi-simulated performance results (obtained with measured impulse responses) demonstrate that multisegment detection and equalization provide a low-cost and efficient solution to combat ISI and hence, to enhance the performance of MMF communications links. View full abstract»

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  • Asynchronous transmission WDM networks with performance efficiency improvement

    Publication Year: 2003 , Page(s): 403 - 405
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (237 KB) |  | HTML iconHTML  

    A network control architecture and a network interface unit for each station is introduced which restricts data channel collision and reduces the headers electronic processing bottleneck at each station for wavelength-division multiplexing (WDM) star-coupled photonic networks. Also we develop an analytic model for receiver collision analysis for performance measures evaluation. View full abstract»

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  • PD-RED: to improve the performance of RED

    Publication Year: 2003 , Page(s): 406 - 408
    Cited by:  Papers (41)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (311 KB) |  | HTML iconHTML  

    We propose a new active queue management (AQM) scheme to improve the performance of the well-known random early detection (RED) AQM. The new AQM is based on the proportional derivative (PD) control principle, and we call it PD-RED. In PD-RED we introduce minimal changes to RED. We demonstrate the improvement in performance of PD-RED over adaptive RED AQM by simulations. View full abstract»

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  • Optimal packet length scheduling for regulated media streaming

    Publication Year: 2003 , Page(s): 409 - 411
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (263 KB) |  | HTML iconHTML  

    We present, for a prerecorded stream, an algorithm to determine a packet length schedule that is optimal with respect to appropriate measures of distortion and quality smoothness, when the traffic is required to adhere to specified token bucket regulation constraints. View full abstract»

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Aristotle University of Thessaloniki
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