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Communications Letters, IEEE

Issue 7 • Date July 2001

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Displaying Results 1 - 15 of 15
  • Optimum discrete-power adaptive QAM scheme for Rayleigh fading channels

    Publication Year: 2001 , Page(s): 281 - 283
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (81 KB) |  | HTML iconHTML  

    In this letter, the utilization of a finite number of power levels per constellation in adaptive QAM schemes for flat fading channels is analyzed. Assuming a maximum target BER, the optimum switching thresholds in order to maximize the spectral efficiency are found for Rayleigh fading. Both analysis and simulation results show that a small number of power levels per constellation allows to obtain a good compromise between high spectral efficiency and low feedback information rate. View full abstract»

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  • Hybrid channel adaptive handover scheme for non-GEO satellite diversity based systems

    Publication Year: 2001 , Page(s): 284 - 286
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (47 KB) |  | HTML iconHTML  

    This article presents an improved hybrid handover scheme, which is proposed for the satellite component of UMTS. The scheme is channel adaptive and is generic as it can operate in soft and hard handover. The handover algorithm uses different power thresholds to add/drop a highest and second highest satellite and uses dual satellite diversity only under critical channel conditions. The analysis includes the simulation of a LEO constellation and the elevation-dependent satellite channel. Based on the channel time series the hybrid scheme shows improved performance when compared to existing handover schemes and is less bandwidth demanding than continuous diversity. View full abstract»

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  • On estimating the RMS delay spread from the frequency-domain level crossing rate

    Publication Year: 2001 , Page(s): 287 - 289
    Cited by:  Papers (21)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (88 KB) |  | HTML iconHTML  

    It is shown that the level crossing rate (LCR) of a Rayleigh distributed stochastic process is proportional to the second centralized moment of the normalized power spectrum of the underlying complex Gaussian process. This proportionality factor is independent of the power spectrum. The relation can be applied for estimating the RMS delay spread of time-dispersive (frequency-selective) radio channels from swept-frequency power measurements, where the RMS delay spread is proportional to the LCR in the frequency-domain, independent of the channel impulse response. View full abstract»

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  • Comments on "Closed-form analysis of linearly constrained CMA-based blind multiuser detector"

    Publication Year: 2001 , Page(s): 290 - 291
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (35 KB) |  | HTML iconHTML  

    We point out that the proof of global convergence of LCCM detector is incorrect in the paper by Tang et al. (see ibid., vol.4, no.9, p.273-76, 2000). According to propositions presented in the paper by Xu and Feng (see Electron. Lett., vol.36, no.2, p.171-72, 2000), we further analyze the conditions for global convergence of LCCM detector, and give the low bound of constraint on the power of desired user. View full abstract»

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  • Training sequence versus cyclic prefix-a new look on single carrier communication

    Publication Year: 2001 , Page(s): 292 - 294
    Cited by:  Papers (98)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (63 KB) |  | HTML iconHTML  

    Orthogonal frequency-division multiplexing (OFDM), with the help of a cyclic prefix, enables low complexity frequency domain equalization, but suffers from a high crest factor. Single carrier with cyclic prefix (SC-CP) has the same advantage with similar performance, but with a lower crest factor and enhanced robustness to phase noise. The cyclic prefix is overhead, so we put more information in it by implementing this cyclic prefix as a training sequence (TS). This new training aided frequency domain equalized single carrier (TASC) scheme offers us additional known symbols and enables better synchronization and (potentially) channel estimation, with the same performance as SC-CP. View full abstract»

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  • Time delay compensation in power controlled cellular radio systems

    Publication Year: 2001 , Page(s): 295 - 297
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (62 KB) |  | HTML iconHTML  

    Transmission power control is an important means to manage the radio resources in wireless communications. The performance, however may be reduced due to time delays as in any controlled system. Most controllers to date are designed without considering time delays, which may result in oscillatory or unstable systems. To overcome these problems, time delay compensation (TDC) is introduced. The main idea is to adjust the measurements [e.g., signal-to-interference ratio (SIR)] to include the effects of issued but not yet applied power control commands. TDC thereby improves the stability and performance of an arbitrary power control algorithm. The benefits are illustrated by simulations using some popular power control algorithms. View full abstract»

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  • Resource reservation with pointer forwarding schemes for the mobile RSVP

    Publication Year: 2001 , Page(s): 298 - 300
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (71 KB) |  | HTML iconHTML  

    We propose a pointer forwarding scheme for the mobile resource reservation protocol (MRSVP) to reduce the resource reservation cost on the wireless Internet. We show that the pointer forwarding scheme could significantly degrade the reservation cost when a mobile host performs locality movement. View full abstract»

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  • Improved 8- and 16-state space-time codes for 4PSK with two transmit antennas

    Publication Year: 2001 , Page(s): 301 - 303
    Cited by:  Papers (42)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (117 KB) |  | HTML iconHTML  

    New space-time codes for 4PSK constellations, designed via a modified determinant criterion, send 2 b/s/Hz and show improved performance in quasi-static flat fading. View full abstract»

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  • Single-carrier frequency-domain equalization for space-time block-coded transmissions over frequency-selective fading channels

    Publication Year: 2001 , Page(s): 304 - 306
    Cited by:  Papers (156)  |  Patents (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (72 KB) |  | HTML iconHTML  

    We propose an Alamouti-like scheme for combining space-time block-coding with single-carrier frequency-domain equalization. With two transmit antennas, the scheme is shown to achieve significant diversity gains at low complexity over frequency-selective fading channels. View full abstract»

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  • Frame synchronization of convolutionally coded systems for packet transmission

    Publication Year: 2001 , Page(s): 307 - 309
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (74 KB) |  | HTML iconHTML  

    This letter proposes a decoder-assisted frame synchronization scheme for convolutionally encoded information packets. Rather than placing sync bits in a separate header, the sync bits are placed in a mid-amble and encoded as part of the information sequence, using the error correction encoder to resolve time ambiguities. This technique requires fewer bits for frame synchronization. The performance improvement over the conventional synchronization technique is explored via simulation. View full abstract»

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  • A matched filter approximation for SC/MMSE iterative equalizers

    Publication Year: 2001 , Page(s): 310 - 312
    Cited by:  Papers (21)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (84 KB) |  | HTML iconHTML  

    This letter proposes a new iterative ISI equalization algorithm that offers low computational complexity: order L/sup 2/ with channel memory length L. The proposed algorithm is an extension of Reynolds and Wang's SC/MMSE (soft canceler followed by MMSE filter) equalizer: approximations are used properly to reduce the computational complexity. It is shown that the approximations used in the proposed algorithm do not cause any serious performance degradations from the trellis-based iterative equalization algorithms. View full abstract»

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  • Improved design criteria and new trellis codes for space-time coded modulation in slow flat fading channels

    Publication Year: 2001 , Page(s): 313 - 315
    Cited by:  Papers (37)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (71 KB) |  | HTML iconHTML  

    The design criteria for space-time codes under slow flat Rayleigh fading environments are well known to be the rank criterion and the determinant criterion. However, the derivation of these two criteria is based on the assumption that the signal-to-noise ratio (SNR) is sufficiently high. Hence these criteria are loose when the SNR does not satisfy this assumption. In this letter, we consider this practical issue and derive tighter design criteria for moderate and low SNRs. Some new space-time trellis codes are found based on the new criteria through computer search. Simulation results show that these codes outperform existing codes under their designed SNR conditions. View full abstract»

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  • Analysis model of multiple input-queued switches with PIM scheduling algorithm

    Publication Year: 2001 , Page(s): 316 - 318
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (92 KB) |  | HTML iconHTML  

    In this letter, we propose a new analysis model of multiple input-queued switches that use the parallel iterative matching (PIM) scheduling algorithm under i.i.d Bernoulli traffic. Compared to the previous analysis models, our approach incurs very low computational complexity while maintaining good accuracy by employing a simple queueing model. Specifically, we model an input queue of the switch as a synchronous Geom/Geom/1/B queue with a service rate which is directly obtained from a PIM scheduling algorithm. We perform the simulation and verify the accuracy of our model. View full abstract»

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  • Calculating error-free seconds in xDSL systems corrupted by impulse noise

    Publication Year: 2001 , Page(s): 319 - 321
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (51 KB) |  | HTML iconHTML  

    An analytic approach to the calculation of error-free seconds in xDSL systems corrupted by impulse noise is outlined. The impulse noise is modeled by an n-state Markov renewal process. It is shown that lower and upper bounds can be calculated. A realistic estimate can also be obtained. Analytic results are compared with empirical results. View full abstract»

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  • A genetic local tuning algorithm for a class of combinatorial networks design problems

    Publication Year: 2001 , Page(s): 322 - 324
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (57 KB) |  | HTML iconHTML  

    Experimental evidences of many genetic algorithm (GA) researchers is that hybridizing a GA with a local search (LS) heuristic is beneficial. It combines the ability of the GA to widely sample a search space with a local search hill-climbing ability. This letter presents a genetic local search (GALS) mechanism applied on two stages on the initial genetic population. An elite nondominated set of solutions is selected, an intermediate population (IP) composed of the elite and the improved solutions by natural genetic operators is constructed and then a Nelder and Mead (1965) simplex downhill method (SDM) is applied to some solutions of the IP. Experimental results from solving a 20-nodes topology design and capacity assignment (TDCA) problem suggest that our approach provides superior results compared to four simple GA implementations found in the literature. View full abstract»

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George K. Karagiannidis
Aristotle University of Thessaloniki
Greece