Showing papers in "IEEE Communications Letters in 2001"
TL;DR: Improved algorithms are developed to construct good low-density parity-check codes that approach the Shannon limit very closely, especially for rate 1/2.
Abstract: We develop improved algorithms to construct good low-density parity-check codes that approach the Shannon limit very closely. For rate 1/2, the best code found has a threshold within 0.0045 dB of the Shannon limit of the binary-input additive white Gaussian noise channel. Simulation results with a somewhat simpler code show that we can achieve within 0.04 dB of the Shannon limit at a bit error rate of 10/sup -6/ using a block length of 10/sup 7/.
1,642 citations
TL;DR: This letter investigates the MIMO channel capacity in correlated channels using the exponential correlation matrix model and proves that, for this model, an increase in correlation is equivalent to a decrease in signal-to-noise ratio (SNR).
Abstract: Multiple-input multiple output (MIMO) communication architecture has recently emerged as a new paradigm for wireless communications in rich multipath environment, which has spectral efficiencies far beyond those offered by conventional techniques. The channel capacity of the MIMO architecture in independent Rayleigh channels scales linearly as the number of antennas. However, the correlation of a real-world wireless channel may result in a substantial degradation of the MIMO architecture performance. In this letter, we investigate the MIMO channel capacity in correlated channels using the exponential correlation matrix model. We prove that, for this model, an increase in correlation is equivalent to a decrease in signal-to-noise ratio (SNR). For example, r=0.7 is the same as 3-dB decrease in SNR.
842 citations
TL;DR: A criterion for selecting the optimal antenna subset when linear, coherent receivers are used over a slowly varying channel and use of the post-processing SNRs of the multiplexed streams whereby the antenna subset that induces the largest minimum SNR is chosen.
Abstract: Future cellular systems will employ spatial multiplexing with multiple antennas at both the transmitter and receiver to take advantage of large capacity gains. In such systems it will be desirable to select a subset of available transmit antennas for link initialization, maintenance or handoff. We present a criterion for selecting the optimal antenna subset when linear, coherent receivers are used over a slowly varying channel. We propose use of the post-processing SNRs (signal to noise ratios) of the multiplexed streams whereby the antenna subset that induces the largest minimum SNR is chosen. Simulations demonstrate that our selection algorithm also provides diversity advantage thus making linear receivers useful over fading channels.
722 citations
TL;DR: An extension of SLM is proposed, which employs scrambling and refrains from the use of explicit side information in the receiver, and focuses on orthogonal frequency-division multiplexing (OFDM) in this letter.
Abstract: Selected mapping (SLM) peak-power reduction is distortionless as it selects the actual transmit signal from a set of alternative signals, which all represent the same information. The specific signal generation information needs to be transmitted and carefully protected against bit errors. Here, me propose an extension of SLM, which employs scrambling and refrains from the use of explicit side information in the receiver. Some additional complexity and nearly vanishing redundancy is introduced to achieve markedly improved transmit signal statistics. Even though SLM is applicable with any modulation, we concentrate on orthogonal frequency-division multiplexing (OFDM) in this letter.
475 citations
TL;DR: The proposed source decoder utilizes iterative schemes, and performs well even when the correlation between the sources is not known in the decoder, since it can be estimated jointly with the iterative decoding process.
Abstract: We propose the use of punctured turbo codes for compression of correlated binary sources. Compression is achieved because of puncturing. The resulting performance is close to the theoretical limit provided by the Slepian-Wolf (1973) theorem. No information about the correlation between sources is required in the encoding process. The proposed source decoder utilizes iterative schemes, and performs well even when the correlation between the sources is not known in the decoder, since it can be estimated jointly with the iterative decoding process.
425 citations
TL;DR: It is shown that the instantaneous envelope power function can be transformed into a linear sum of Chebyshev polynomials and the roots of the derivative of EPF can be obtained by solving a polynomial.
Abstract: A procedure for computing the continuous-time peak-to-average power ratio (PAR) of an orthogonal frequency-division multiplexing (OFDM) signal, with binary phase-shift keying (BPSK) subcarriers, is developed. It is shown that the instantaneous envelope power function (EPF) can be transformed into a linear sum of Chebyshev polynomials. Consequently, the roots of the derivative of EPF can be obtained by solving a polynomial. Using the procedure to evaluate the difference between the continuous-time and discrete-time PAR, it is shown that an oversampling factor of four is accurate.
399 citations
AT&T1
TL;DR: An Alamouti-like scheme for combining space-time block-coding with single-carrier frequency-domain equalization with significant diversity gains at low complexity over frequency-selective fading channels is proposed.
Abstract: 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.
389 citations
TL;DR: Asymptotic analysis reveals that both moment-based estimators for the K parameter of Rice fading distribution are nearly asymptotically efficient, and that there is a compromise between the computational simplicity and the statistical efficiency of these two estimators.
Abstract: We study the statistical performance of two moment-based estimators for the K parameter of Rice fading distribution, as less complex alternatives to the maximum-likelihood estimator. Our asymptotic analysis reveals that both estimators are nearly asymptotically efficient, and that there is a compromise between the computational simplicity and the statistical efficiency of these two estimators. We also show, by Monte Carlo simulation, that the fading correlation among the envelope samples deteriorates the performance of both estimators. However, the simpler estimator, which employs the second and the fourth moments of the signal envelope, appears to be more suitable for real-world applications.
334 citations
TL;DR: This work presents an architecture that is optimal, in the sense of maximum link spectral efficiency, inThe presence of spatially colored interference, and compares it, under various propagation conditions, to other adaptive-antenna techniques with equal number of antennas.
Abstract: Previous information theory results have demonstrated the enormous capacity potential of wireless communication systems with multiple transmit and receive antennas. To exploit this potential, a number of space-time architectures have been proposed which transmit parallel data streams, simultaneously and on the same frequency, in a multiple-input multiple-output fashion. With sufficient multipath propagation, these different streams can be separated at the receiver. Mostly, these space-time schemes have been studied only in the presence of spatially white noise. We present an architecture that is optimal, in the sense of maximum link spectral efficiency, in the presence of spatially colored interference. We evaluate this new architecture and compare it, under various propagation conditions, to other adaptive-antenna techniques with equal number of antennas.
313 citations
TL;DR: A probabilistic data association (PDA) method for multiuser detection over synchronous code-division multiple-access (CDMA) communication channels and computer simulations show that the system usually converges within three to four iterations, and the resulting probability of error is very close to that of the optimal maximum-likelihood (ML) detector.
Abstract: A probabilistic data association (PDA) method is proposed in this letter for multiuser detection over synchronous code-division multiple-access (CDMA) communication channels. PDA models the undecided user signals as binary random variables. By approximating the inter-user interference (IUI) as Gaussian noise with an appropriately elevated covariance matrix, the probability associated with each user signal is iteratively updated. Computer simulations show that the system usually converges within three to four iterations, and the resulting probability of error is very close to that of the optimal maximum-likelihood (ML) detector. Further modifications are also presented to significantly reduce the computational cost.
219 citations
TL;DR: A novel ISI-free pulse is presented that has smaller maximum distortion, a more open receiver eye, and a smaller probability of error in the presence of symbol timing error than the Nyquist pulse for the same excess bandwidth.
Abstract: A novel ISI-free pulse is presented that has smaller maximum distortion, a more open receiver eye, and a smaller probability of error in the presence of symbol timing error than the Nyquist pulse for the same excess bandwidth.
TL;DR: This new training aided frequency domain equalized single carrier (TASC) scheme offers additional known symbols and enables better synchronization and (potentially) channel estimation, with the same performance as SC-CP.
Abstract: 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.
TL;DR: It is proven that, depending on the criterion chosen to reduce the interference, the receiver operations of the V-BLAST system are fundamentally equivalent to either a zero-forcing (ZF) or a minimum-mean-square-error (MMSE) GDFE.
Abstract: This letter shows that the receiver processing of the Vertical Bell Labs Layered Space-Time (V-BLAST) architecture may he viewed as a generalized decision feedback equalizer (GDFE) as applied to a multiple-input-multiple-output (MIMO) channel. It is proven that, depending on the criterion chosen to reduce the interference, the receiver operations of the V-BLAST system are fundamentally equivalent to either a zero-forcing (ZF) or a minimum-mean-square-error (MMSE) GDFE.
TL;DR: A novel estimation algorithm based on maximum-likelihood principles and the generalized Akaike information criterion are proposed for orthogonal frequency-division multiplexing access technique.
Abstract: The orthogonal frequency-division multiplexing access technique has been attracting considerable interest especially for wireless local area networks (WLANs). We consider the joint estimation of the symbol timing, the channel length and the channel-impulse response. A novel estimation algorithm based on maximum-likelihood principles and the generalized Akaike information criterion are proposed. We provide simulation results to illustrate the performance of our proposed algorithm.
TL;DR: This letter presents a new algorithm for computing the phase factors that achieves better performance than the exhaustive search approach for PTS.
Abstract: The peak-to-average power ratio (PAR) of an orthogonal frequency-division multiplexing (OFDM) signal can be substantially larger than that of a single carrier system. Partial transmit sequence (PTS) combining can improve the PAR statistics of an OFDM signal. As PTS requires an exhaustive search over all combinations of allowed phase factors, the search complexity increases exponentially with the number of subblocks. In this letter, we present a new algorithm for computing the phase factors that achieves better performance than the exhaustive search approach.
TL;DR: Cramer-Rao lower bounds (CRLBs) are derived for the estimation of signal-to-noise ratio (SNR) of binary phase-shift keying and quaternary phase- shift keying modulated signals.
Abstract: We derive Cramer-Rao lower bounds (CRLBs) for the estimation of signal-to-noise ratio (SNR) of binary phase-shift keying (BPSK) and quaternary phase-shift keying (QPSK) modulated signals. The received signal is corrupted by additive white Gaussian noise (AWGN). The lower bounds are derived for non-data-aided estimation where the transmitted symbols are unknown at the receiver. The bounds are compared to those for data-aided estimations (known symbols at the receiver). It is shown that at low SNR there is a significant difference between the bounds for non-data-aided and data-aided estimations.
TL;DR: This work proposes a secure three-party EKE protocol without server public-keys, which is suitable for applications requiring secure communications between many light-weight clients (end users) and is impractical for some environments.
Abstract: Three-party key-exchange protocols with password authentication-clients share an easy-to-remember password with a trusted server only-are very suitable for applications requiring secure communications between many light-weight clients (end users); it is simply impractical that every two clients share a common secret. Steiner, Tsudik and Waidner (1995) proposed a realization of such a three-party protocol based on the encrypted key exchange (EKE) protocols. However, their protocol was later demonstrated to be vulnerable to off-line and undetectable on-line guessing attacks. Lin, Sun and Hwang (see ACM Operating Syst. Rev., vol.34, no. 4, p.12-20, 2000) proposed a secure three-party protocol with server public-keys. However, the approach of using server public-keys is not always a satisfactory solution and is impractical for some environments. We propose a secure three-party EKE protocol without server public-keys.
TL;DR: Maximum-likelihood estimation of the Nakagami (1960) m parameter is considered and two new estimators are proposed and examined and offer superior performance.
Abstract: Maximum-likelihood estimation of the Nakagami (1960) m parameter is considered. Two new estimators are proposed and examined. The sample mean and the sample variance of the new estimators are compared with the best reported estimator. The new estimators offer superior performance.
TL;DR: A data fusion model is presented for the enhanced accuracy of position estimates within wireless networks and is illustrated with several examples and concludes with recommendations for future research directions.
Abstract: The problem of position determination of a mobile user in a wireless network has been studied extensively-particularly in the context of military operations and emergency 911 service in cellular networks. The Global Positioning System (GPS) and network-based angle of arrival (AOA), time difference of arrival (TDOA), and time of arrival (TOA) techniques offer solutions to the position estimation problem. However, each method has limitations that prevent its adoption as a universal solution. Data fusion is a collection of methods and techniques for merging disparate types of information. We present a data fusion model for the enhanced accuracy of position estimates within wireless networks. We illustrate our model with several examples and conclude with recommendations for future research directions.
TL;DR: Simulation results and parameter comparison show that these STTC with a feedforward structure offer a better performance on fast fading channels than other known codes while maintaining a comparable performance on slow fading channels.
Abstract: New space-time trellis-coded modulation (STTC) which best satisfies the design criteria proposed by Tarokh, et al. (see IEEE Trans. Inform. Theory, vol.44, p.746-65, 1998) over fast fading channels are presented. STTC with a feedforward structure have been constructed by a systematic and exhaustive search. Simulation results and parameter comparison show that these codes offer a better performance on fast fading channels than other known codes while maintaining a comparable performance on slow fading channels.
TL;DR: The performance of packet-level media-independent forward error correction (FEC) schemes are computed in terms of both packet loss ratio and average burst length of multimedia data after error recovery.
Abstract: The performance of packet-level media-independent forward error correction (FEC) schemes are computed in terms of both packet loss ratio and average burst length of multimedia data after error recovery The set of equations leading to the analytical formulation of both parameters are first given for a renewal error process Finally, the FEC performance parameters are computed for a Gilbert (1960) model loss process and compared to various experimental data
TL;DR: This paper presents a probabilistic treatment of the performance of a Bluetooth piconet under cochannel interference from otheretooth piconets, and an upper bound on the packet error rate of a link is given, as well as a lowerbound on the aggregated throughput of n collocated piconetry.
Abstract: This paper presents a probabilistic treatment of the performance of a Bluetooth piconet under cochannel interference from other Bluetooth piconets. An upper bound on the packet error rate of a link is given, as well as a lower bound on the aggregated throughput of n collocated piconets.
TL;DR: The average level crossing rate and average fade duration of the output signal envelope of a selection diversity combiner, operating on independent, but nonidentical fading input branch signals are derived.
Abstract: The average level crossing rate and average fade duration of the output signal envelope of a selection diversity combiner, operating on independent, but nonidentical fading input branch signals are derived. The exact closed-form results are valid for arbitrary diversity order, and are obtained for Rayleigh, Ricean, and Nakagami fading input signals.
TL;DR: In this letter, Doppler spread estimation in digital mobile radio systems is described and a maximum-likelihood approach is derived, and used to develop suboptimal approaches with lower complexity.
Abstract: In this letter, Doppler spread estimation in digital mobile radio systems is described. A maximum-likelihood approach is derived, and used to develop suboptimal approaches with lower complexity. The proposed algorithms rely on periodic channel estimation and can be used in both TDMA and CDMA systems.
TL;DR: This letter considers the problem of maximizing the number of lightpaths that may be established in a wavelength routed optical network (WRON), given a connection matrix, and develops algorithms based on solutions obtained by solving the LP-relaxation of the ILP formulation.
Abstract: In this letter, we consider the problem of maximizing the number of lightpaths that may be established in a wavelength routed optical network (WRON), given a connection matrix, i.e., a static set of demands, and the number of wavelengths the fiber supports. The problem of establishing all the connections of the connection matrix using the fewest number of wavelengths has been investigated in Banerjee and Mukherjee (1996) and Baroni et al. (1998). We call the former problem max-RWA (problem of maximizing the number of lightpaths) and the latter problem min-RWA (minimizing the number of wavelengths). In this letter, we only consider WRONs with no wavelength conversion capabilities. We formulate the max-RWA problem when no wavelength conversion is allowed as an integer linear programme (ILP) which may be solved to obtain an optimum solution. We hope to solve the ILP exactly for small size networks (few nodes). For moderately large networks (tens of nodes) we develop algorithms based on solutions obtained by solving the LP-relaxation of the ILP formulation. Results obtained for networks such as NSFNET and EONNET are presented.
TL;DR: 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 but these criteria are loose when the SNR does not satisfy this assumption.
Abstract: 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.
TL;DR: 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.
Abstract: 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.
TL;DR: This letter investigates the sensitivity of the iterative maximum a posteriori probability (MAP) decoder to carrier phase offsets and proposes simple carrier phase recovery algorithms operating within the iteratives MAP decoding iterations, requiring low hardware complexity.
Abstract: In this letter, we investigate the sensitivity of the iterative maximum a posteriori probability (MAP) decoder to carrier phase offsets and propose simple carrier phase recovery algorithms operating within the iterative MAP decoding iterations. The algorithms exploit the information contained in the extrinsic values generated within the iterative MAP decoder to perform carrier recovery, thus requiring low hardware complexity.
TL;DR: This article proves that both methods of identifying the channel in OFDM systems can achieve the same level of performance under certain conditions on the block length.
Abstract: Orthogonal frequency-division multiplex (OFDM) systems transmit data in blocks. The two simplest ways of identifying the channel in OFDM systems are to insert a training sequence between consecutive blocks or to insert pilot tones inside each block. This article proves that both methods can achieve the same level of performance under certain conditions on the block length.
TL;DR: A new message-passing schedule for the decoding of low-density parity-check (LDPC) codes is presented, designated "probabilistic schedule", which takes into account the structure of the Tanner graph of the code.
Abstract: We present a new message-passing schedule for the decoding of low-density parity-check (LDPC) codes. This approach, designated "probabilistic schedule", takes into account the structure of the Tanner graph (TG) of the code. We show by simulation that the new schedule offers a much better performance/complexity trade-off. This work also suggests that scheduling plays an important role in iterative decoding and that a schedule that matches the structure of the TG is desirable.