Showing papers in "IEEE Communications Letters in 2000"
TL;DR: Suboptimal strategies for combining partial transmit sequences that achieve similar performance but with reduced complexity are presented.
Abstract: Orthogonal frequency-division multiplexing (OFDM) is an attractive technique for achieving high-bit-rate wireless data transmission. However, the potentially large peak-to-average power ratio (PAP) has limited its application. Recently, two promising techniques for improving the PAP statistics of an OFDM signal have been proposed: the selective mapping and partial transmit sequence approaches. Here, we present suboptimal strategies for combining partial transmit sequences that achieve similar performance but with reduced complexity.
896 citations
TL;DR: The sphere decoding (SD) algorithm is applied to the lattice sphere packing representation of a multi-antenna system and the algebraic space-time (ST) codes and yields a huge improvement over the well-known V-BLAST detection algorithm.
Abstract: We explore the lattice sphere packing representation of a multi-antenna system and the algebraic space-time (ST) codes. We apply the sphere decoding (SD) algorithm to the resulted lattice code. For the uncoded system, SD yields, with small increase in complexity, a huge improvement over the well-known V-BLAST detection algorithm. SD of algebraic ST codes exploits the full diversity of the coded multi-antenna system, and makes the proposed scheme very appealing to take advantage of the richness of the multi-antenna environment. The fact that the SD does not depend on the constellation size, gives rise to systems with very high spectral efficiency, maximum-likelihood performance, and low decoding complexity.
853 citations
TL;DR: Two timing offset estimation methods for orthogonal frequency division multiplexing (OFDM) systems as modifications to Schmidl and Cox's method are presented and both have significantly smaller estimator variance in both channel conditions.
Abstract: Two timing offset estimation methods for orthogonal frequency division multiplexing (OFDM) systems as modifications to Schmidl and Cox's method (see IEEE Trans. Commun., vol.45, p.1613-21, 1997) are presented. The performances of the timing offset estimators in additive white Gaussian noise channel and intersymbol interference channel are compared in terms of estimator variance obtained by simulation. Both proposed methods have significantly smaller estimator variance in both channel conditions.
473 citations
TL;DR: Although space-time block codes provide full diversity at low computational costs, it is shown that they incur a loss in capacity because they convert the matrix channel into a scalar AWGN channel whose capacity is smaller than the true channel capacity.
Abstract: Space-time block codes are a remarkable modulation scheme discovered recently for the multiple antenna wireless channel. They have an elegant mathematical solution for providing full diversity over the coherent, flat-fading channel. In addition, they require extremely simple encoding and decoding. Although these codes provide full diversity at low computational costs, we show that they incur a loss in capacity because they convert the matrix channel into a scalar AWGN channel whose capacity is smaller than the true channel capacity. In this letter the loss in capacity is quantified as a function of channel rank, code rate, and number of receive antennas.
428 citations
TL;DR: This work proposes new trellis codes found through systematic code search that achieve the theoretically maximal diversity gain and improved coding gain compared to known codes.
Abstract: Space-time coded modulation has been shown to efficiently use transmit diversity to increase spectral efficiency. We propose new trellis codes found through systematic code search. These codes achieve the theoretically maximal diversity gain and improved coding gain compared to known codes.
405 citations
TL;DR: This letter proposes a burst assembly mechanism that can reduce the traffic autocorrelation or degree of self-similarity, and at the same time keep the delay due to burst formation limited at the network edges.
Abstract: In this letter we consider burst switching for very high speed routing in the next generation Internet backbone. In this scenario, Internet protocol (IP) packets to a given destination are collected in bursts at the network edges. We propose a burst assembly mechanism that can reduce the traffic autocorrelation or degree of self-similarity, and at the same time keep the delay due to burst formation limited at the network edges.
356 citations
TL;DR: It is found that an antenna separation of 4 wavelengths between nearest neighbors in a linear base array of dually polarized antennas allows one to achieve 80% of the capacity attainable in the uncorrelated antenna case.
Abstract: As the base station is usually placed above local clutter, the angular spectrum incident on the base is narrow, inducing correlation among base antenna signals, which reduces the capacity of a multiple transmit and receive antenna systems. In this work the general expression for link capacity is derived, when there is correlation among receive antennas and among transmit antennas. It is found that an antenna separation of 4 wavelengths between nearest neighbors in a linear base array of dually polarized antennas allows one to achieve 80% of the capacity attainable in the uncorrelated antenna case.
304 citations
TL;DR: A simulation study of a cellular system using multiple-input multiple-output (MIMO) antenna techniques along with adaptive modulation and aggressive frequency reuse shows how much MIMO systems outperform systems with receive-diversity-only when noise dominates.
Abstract: We describe a simulation study of a cellular system using multiple-input multiple-output (MIMO) antenna techniques along with adaptive modulation and aggressive frequency reuse. We show for the case of 3 transmit and 3 receive antennas, how much MIMO systems outperform systems with receive-diversity-only when noise dominates. When co-channel interference from surrounding cells dominates, the differences shrink, as do the absolute numbers. We quantify these reductions for the specific cases studied, and discuss further areas of research.
266 citations
TL;DR: This letter addresses the problem of dimensioning fiber delay lines for optical buffers in a network scenario where packets are asynchronous and of variable length by providing a simple analytical model to dimension the basic time unit of the fiber delay line, as the crucial parameter that determines the queueing performance.
Abstract: This letter addresses the problem of dimensioning fiber delay lines for optical buffers in a network scenario where packets are asynchronous and of variable length. The focus is placed on providing a simple analytical model to dimension the basic time unit of the fiber delay line, as the crucial parameter that determines the queueing performance.
191 citations
TL;DR: A new technique for secure information transmission in a mobile environment that uses the short term reciprocity of the radio channel so that information is intelligible only to an intended receiver.
Abstract: A new technique for secure information transmission in a mobile environment is described. This technique uses the short term reciprocity of the radio channel so that information is intelligible only to an intended receiver. The exchange of information does not require the availability of a common secure key between two users; however, the proposed technique can also be used for cryptographic key agreement between two users.
184 citations
TL;DR: Simulations comparing the new technique with other well known stopping criteria show that the proposed SDR scheme achieves similar performance in terms of the bit error rate, frame error rate (FER), and the average number of iterations, while requiring lower complexity.
Abstract: This article proposes a simple stopping criterion for turbo decoding that extends the existing sign change ratio (SCR) technique. The new sign difference ratio (SDR) criterion counts the sign differences between the a priori information and the extrinsic information. Unlike the SCR, it requires no extra data storage. Simulations comparing the new technique with other well known stopping criteria show that the proposed SDR scheme achieves similar performance in terms of the bit error rate (BER), frame error rate (FER), and the average number of iterations, while requiring lower complexity. A GENIE scheme is included as the limit of all possible stopping criteria.
TL;DR: In this article, a frequency offset compensation method for OFDM-FDMA, that can correct offsets after the DFT via circular convolution, is proposed as an alternative to the direct method that corrects frequency offsets by multiplying the complex exponents of the offset estimates before DFT.
Abstract: A frequency offset compensation method for OFDM-FDMA, that can correct offsets after the DFT via circular convolution, is proposed as an alternative to the direct method that corrects frequency offsets by multiplying the complex exponents of the offset estimates before the DFT. In contrast to the direct method whose complexity increases proportional to the number of users, the computational load of the proposed scheme decreases as the number of users increases. It is shown that the proposed method is simpler to implement than the direct method when the number of users is greater than two. Furthermore, the former can outperform the latter, because a frequency offset compensation for one user after the DFT does not affect the data of other users. Computer simulation results demonstrate the advantage of the proposed method.
TL;DR: This letter investigates a communication strategy for digital ultra-wide bandwidth impulse radio, where the separation between the adjacent pulses is chaotic arising from a dynamical system with irregular behavior, by numerically simulating its operation in the presence of noise and filtering.
Abstract: In this letter we investigate a communication strategy for digital ultra-wide bandwidth impulse radio, where the separation between the adjacent pulses is chaotic arising from a dynamical system with irregular behavior. A pulse position method is used to modulate binary information onto the carrier. The receiver is synchronized to the chaotic pulse train, thus providing the time reference for information extraction. We characterize the performance of this scheme in terms of error probability versus E/sub b//N/sub 0/ by numerically simulating its operation in the presence of noise and filtering.
TL;DR: Two algorithms for estimating the integer part of the carrier-frequency offset are derived based on the observation of two consecutive OFDM symbols, one of which is blind.
Abstract: In orthogonal frequency division multiplexing systems, the carrier-frequency offset can be divided into two parts: (1) an integer one-multiple of the subcarrier spacing 1/T and (2) a fractional one-less than 1/2T in amplitude. Some schemes proposed in the literature can only recover the fractional part. We derive two algorithms for estimating the integer part. They are based on the observation of two consecutive OFDM symbols. The first algorithm exploits pilot symbols multiplexed with the data, the other is blind.
TL;DR: Four signal-to-noise ratio (SNR) estimators for quaternary phase-shift keying (QPSK)-like signaling are proposed and examined and the results show that the estimators based on the inverse of the SNR perform better than the estimator based onThe SNR.
Abstract: Four signal-to-noise ratio (SNR) estimators for quaternary phase-shift keying (QPSK)-like signaling are proposed and examined. Two are based on receiver statistics directly related to the SNR while two others are based on receiver statistics inversely related to the SNR. The results show that the estimators based on the inverse of the SNR perform better than the estimators based on the SNR.
TL;DR: This method, numerical in nature, enables researchers to simulate correlated fading envelopes for use in the study of the impact of correlation on diversity system performance and theStudy of multicarrier CDMA (MC-CDMA), where the number of carriers notably exceeds the degree of system diversity.
Abstract: A procedure for generating N Rayleigh fading envelopes with any desired covariance matrix is given. This method, numerical in nature, enables researchers to simulate correlated fading envelopes, for use in: (1) the study of the impact of correlation on diversity system performance and (2) the study of multicarrier CDMA (MC-CDMA), where the number of carriers notably exceeds the degree of system diversity.
TL;DR: The theoretical and simulation results indicate that an estimation of the SNR is not necessary from a practical point of view and this setup is aligned with decoder implementation aspects of future mobile communication systems.
Abstract: Theoretically, it is necessary to estimate the SNR when using a MAP of the log-MAP constituent decoder. The effect of an SNR mismatch on the bit error rate performance of turbo-codes and the design of good variance estimators have been addressed by several authors. In this letter we study the SNR sensitivity of turbo-decoding with log-MAP and max-log-MAP constituent decoders respectively for AWGN and Rayleigh fading channels. Our theoretical and simulation results indicate that an estimation of the SNR is not necessary from a practical point of view. Our setup is aligned with decoder implementation aspects of future mobile communication systems.
TL;DR: The symbol error probability for coherent detection of several types of M-ary modulation schemes is derived using maximal ratio combining and is made analytically tractable by transforming the correlated physical diversity branches into independent virtual branches.
Abstract: We derive the symbol error probability for coherent detection of several types of M-ary modulation schemes using maximal ratio combining. We consider Nakagami fading channels, where the instantaneous signal-to-noise ratios of the diversity branches are not necessarily independent or identically distributed. The proposed problem is made analytically tractable by transforming the correlated physical diversity branches into independent virtual branches.
TL;DR: In this article, the performance of 2D wavelength hopping/time spreading CDMA systems is limited by the occurrence of the beat noise between the components of the signal and the multiple user interference.
Abstract: The system performance of 2-D wavelength hopping/time spreading CDMA systems is found to be limited by the occurrence of the beat noise between the components of the signal and the multiple user interference. The variance of the noise is determined and the probability of error is calculated for a general system employing asymmetric prime-hop sequences. A comparison with an idealized system neglecting the beat noise reveals that the system performance is seriously affected by the beat noise.
TL;DR: In this contribution, the performance of the inverse normalized variance, Tolparev-Polyakov, and the Lorenz estimators have been compared through Monte Carlo simulation, and it has been observed that the inverse stabilized variance estimator is superior to the others over a broad range of m values.
Abstract: Nakagami distribution has proven useful for modeling the multipath faded envelope in wireless channels. The shape parameter of the Nakagami distribution, known as the m parameter, can be estimated in different ways. In this contribution, the performance of the inverse normalized variance, Tolparev-Polyakov, and the Lorenz estimators have been compared through Monte Carlo simulation, and it has been observed that the inverse normalized variance estimator is superior to the others over a broad range of m values.
TL;DR: A general recursive algorithm for the efficient and accurate computation of the bit error rate (BER) of square-shaped M-QAM constellations over additive white Gaussian noise (AWGN) channels is derived using Gray coded bit mapping.
Abstract: A general recursive algorithm for the efficient and accurate computation of the bit error rate (BER) of square-shaped M-QAM constellations over additive white Gaussian noise (AWGN) channels is derived. We take advantage of the relationship amongst different square-shaped M-QAM constellations using Gray coded bit mapping.
AT&T1
TL;DR: This letter describes an efficient bit allocation algorithm for digital subscriber loop modems that use discrete multi-tone technology that computes the optimum bit allocation profile within all constraints and requires fewer computations than the conventional "water-filling" approach.
Abstract: This letter describes an efficient bit allocation algorithm for digital subscriber loop modems that use discrete multi-tone technology. The algorithm computes the optimum bit allocation profile within all constraints and requires fewer computations than the conventional "water-filling" approach. Conventional algorithms are unable to assign data bits to higher frequency bins over long loops with high level of interference due to the power spectrum mask limitation, even if the total power budget is not expended. We propose a novel scheme to distribute data over multiple bins at correspondingly reduced power in these, otherwise unpopulated bins.
TL;DR: This letter is concerned with a frequency offset estimation technique for OFDM based transmission systems that utilizes a repetitive signal structure inside of a OFDM symbol which is used to enlarge the range and increase the accuracy of offset estimation.
Abstract: This letter is concerned with a frequency offset estimation technique for OFDM based transmission systems. The frequency estimation technique utilizes a repetitive signal structure inside of a OFDM symbol which is used to enlarge the range and increase the accuracy of offset estimation. Also, an averaged decision-directed channel estimation (ADDCE) technique suitable for burst data is proposed.
TL;DR: A direct-sequence code-division multiple access (DS/CDMA) concept which accommodates a higher number of users than the spreading factor N and a number of additional users at the expense of a small signal-to-noise ratio penalty.
Abstract: In this letter we introduce a direct-sequence code-division multiple access (DS/CDMA) concept which accommodates a higher number of users than the spreading factor N. Each of the available orthogonal spreading sequences of length N is assigned to one of the first N users which employ a common pseudonoise (PN) scrambling sequence. When the number of users K exceeds N, say K=N+M with M N. The proposed technique thus accommodates N users without any mutual interference and a number of additional users at the expense of a small signal-to-noise ratio penalty.
TL;DR: For applications which can tolerate delay, significant gain can be achieved with the proposed approach, and a relatively low complexity iterative decoding procedure is provided.
Abstract: In this letter, a new family of space-time codes is proposed. These codes employ a serially concatenated coding scheme with a standard space-time code as the outer code and a very simple rate-1 recursive code as the inner code. Adding this simple rate-1 recursive inner code does not decrease the bit rate and introduces only negligible complexity increase to the transmitter when compared to cases with standard space-time codes. An interleaver is embedded between the inner coder and the outer coder and the size of this interleaver determines the performance gain. We also provide a relatively low complexity iterative decoding procedure. For applications which can tolerate delay, significant gain can be achieved with the proposed approach.
TL;DR: A new multiple access concept which allows to accommodate more than N users on a channel of NW Hz bandwidth, where W Hz is the bandwidth of the individual user signals.
Abstract: We present a new multiple access concept which allows to accommodate more than N users on a channel of NW Hz bandwidth, where W Hz is the bandwidth of the individual user signals. It makes use of two sets of orthogonal signal waveforms, one for the first N users and one for the additional users. An iterative multistage detection technique is used to cancel interference between the two sets of users. At each stage of the detection process, the best estimate of the multiuser interference is synthesized using the decisions available from the previous stages, and this interference is subtracted from the user signals of interest before entering them to a threshold detector. The new concept is described using orthogonal code-division multiple access and time division multiple access as the two sets of signal waveforms, but we also briefly outline how it can be generalized to other orthogonal sets.
TL;DR: A learning automata-based time-division multiple-access protocol for broadcast networks, which is capable of operating efficiently under bursty traffic conditions, is introduced and the network performance is significantly improved.
Abstract: A learning automata-based time-division multiple-access protocol for broadcast networks, which is capable of operating efficiently under bursty traffic conditions, is introduced. According to the proposed protocol, the station which grants permission to transmit at each time slot is selected by means of learning automata. The learning automata update the choice probability of each station according to the network feedback information in such a way that it asymptotically tends to be proportional to the probability that this station is ready. In this manner, the number of idle slots is minimized and the network performance is significantly improved. Furthermore, the portion of the bandwidth assigned to each station is dynamically adapted to the station's needs.
TL;DR: It is shown that for comparable performance the new method can be implemented with much less quantization bits, which can lead to considerably lower decoding cost.
Abstract: This letter is concerned with the implementation issue of the sum-product algorithm (SPA) for decoding the low density parity check codes. It is shown that the direct implementation of the original form of SPA is sensitive to the quantization effect. We propose a parity likelihood ratio technique to overcome the problem. It is shown that for comparable performance the new method can be implemented with much less quantization bits, which can lead to considerably lower decoding cost.
TL;DR: A novel analytical framework in the discrete-time domain based on the FFT demodulation of a single OFDM symbol is proposed and previous methods are unify with some new results.
Abstract: We analyze the degradation of orthogonal frequency division multiplexing (OFDM) signals from time-variant distortions like carrier and sampling frequency offset, Doppler spread and oscillator phase noise. We propose a novel analytical framework in the discrete-time domain based on the FFT demodulation of a single OFDM symbol and unify previous methods with some new results. Exact definitions of the signal-to-subcarrier-interference ratio (SIR) and the effective signal-to-noise ratio (SNR) are given and evaluated for a HIPERLAN/2 system.
TL;DR: Widely linear structures for multiuser detection of code division multiple-access signals are proposed, which jointly elaborate the received signal and its complex conjugate, and significantly outperform the conventional linear ones.
Abstract: Widely linear structures for multiuser detection of code division multiple-access signals are proposed, which jointly elaborate the received signal and its complex conjugate. Computer simulations show that the new structures significantly outperform the conventional linear ones, in terms of suppression capability of both wideband multiple-access and narrowband interference.