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Showing papers in "IEEE Communications Letters in 1998"


Journal ArticleDOI
TL;DR: The characteristics of impulse radio using a modulation format that can be supported by currently available impulse signal technology are described and analytical estimates of its multiple- access capability under ideal multiple-access channel conditions are given.
Abstract: Impulse radio, a form of ultra-wide bandwidth (UWB) spread-spectrum signaling, has properties that make it a viable candidate for short-range communications in dense multipath environments. This paper describes the characteristics of impulse radio using a modulation format that can be supported by currently available impulse signal technology and gives analytical estimates of its multiple-access capability under ideal multiple-access channel conditions.

2,377 citations


Journal ArticleDOI
TL;DR: This work investigates, through extensive computer simulations, the effects of clipping and filtering on the performance of OFDM, including the power spectral density, the crest factor, and the bit-error rate.
Abstract: Orthogonal frequency division multiplexing (OFDM) is an attractive technique for wireless communication applications. However, an OFDM signal has a large peak-to-mean envelope power ratio, which can result in significant distortion when passed through a nonlinear device, such as a transmitter power amplifier. We investigate, through extensive computer simulations, the effects of clipping and filtering on the performance of OFDM, including the power spectral density, the crest factor, and the bit-error rate. Our results show that clipping and filtering is a promising technique for the transmission of OFDM signals using realistic linear amplifiers.

1,341 citations


Journal ArticleDOI
TL;DR: A significant improvement over the performance of the binary codes is found, including a rate 1/4 code with bit error probability <10/sup -5/ at E/sub b//N/sub 0/=0.2 dB.
Abstract: Gallager's (1962) low-density binary parity check codes have been shown to have near-Shannon limit performance when decoded using a probabilistic decoding algorithm. We report the empirical results of error-correction using the analogous codes over GF(q) for q>2, with binary symmetric channels and binary Gaussian channels. We find a significant improvement over the performance of the binary codes, including a rate 1/4 code with bit error probability <10/sup -5/ at E/sub b//N/sub 0/=0.2 dB.

1,284 citations


Journal ArticleDOI
TL;DR: The results show that an ultra-wide bandwidth signal does not suffer multipath fading, and the robustness of the UWB signal in multipath is quantified through cumulative distribution functions of the signal quality in various locations of the building.
Abstract: The results of an ultra-wide bandwidth (UWB) signal propagation experiment, using bandwidth in excess of 1 GHz, performed in a typical modern office building are presented. The robustness of the UWB signal in multipath is quantified through cumulative distribution functions of the signal quality in various locations of the building. The results show that an UWB signal does not suffer multipath fading.

612 citations


Journal ArticleDOI
TL;DR: A quasi-analytical experimental analysis is described in this paper to quantify the tradeoff between energy capture and diversity level in a RAKE receiver using measured received waveforms obtained from ultrawide bandwidth signal propagation experiments.
Abstract: A quasi-analytical experimental analysis is described in this paper to quantify the tradeoff between energy capture and diversity level in a RAKE receiver using measured received waveforms obtained from ultrawide bandwidth signal propagation experiments.

551 citations


Journal ArticleDOI
TL;DR: A simple analytical model is presented to compute the saturation throughput performance in the presence of a finite number of terminals and in the assumption of ideal channel conditions, which shows that the model is extremely accurate in predicting the system throughput.
Abstract: To satisfy the emerging need of wireless data communications, the IEEE is currently standardizing the 802.11 protocol for wireless local area networks. This standard adopts a CSMA/CA medium access control protocol with exponential backoff. We present a simple analytical model to compute the saturation throughput performance in the presence of a finite number of terminals and in the assumption of ideal channel conditions. The model applies to both basic and request-to-send/clear-to-send (RTS/CTS) access mechanisms. Comparison with simulation results shows that the model is extremely accurate in predicting the system throughput.

466 citations


Journal ArticleDOI
TL;DR: Two blind carrier offset estimation algorithms are presented by exploiting the intrinsic structure information of OFDM signals to offer the accuracy of super resolution subspace methods, viz., MUSIC and ESPRIT, without involving computationally intensive subspace decompositions.
Abstract: While multipath induced phase rotations can be dealt with by differential encoding in orthogonal frequency division multiplexing (OFDM) communications, the loss of orthogonality due to the carrier offset must be compensated before discrete Fourier transform (DFT)-based demodulation can be performed. In this letter, we present a high-performance/low-complexity blind carrier offset estimation algorithm by exploiting intrinsic structure information of OFDM signals. The algorithm offers the accuracy of a super resolution subspace method, viz. MUSIC, without involving computationally intensive subspace decompositions.

404 citations


Journal ArticleDOI
Ana Garcia Armada1, Miguel Calvo
TL;DR: This letter analyzes the phase noise effects on an orthogonal frequency division multiplexing (OFDM) signal and its dependence with the sub-carrier spacing and pilot-based channel estimation is analyzed.
Abstract: This letter analyzes the phase noise effects on an orthogonal frequency division multiplexing (OFDM) signal and its dependence with the sub-carrier spacing. Pilot-based channel estimation, which has been suggested as a means of combating the channel effects, can also correct the phase noise effects under some circumstances, which are investigated.

213 citations


Journal Article
TL;DR: In this paper, a new iterative decoding (ID) scheme for bit-interleaved coded modulation (BICM) is proposed, where the bit-metric generation at the demodulator is optimized with the soft-output feedback from the convolutional decoder.
Abstract: A new iterative decoding (ID) scheme is suggested for bit-interleaved coded modulation (BICM). The bit-metric generation at the demodulator is optimised with the soft-output feedback from the convolutional decoder. Computer simulation results indicate that BICM-ID, with a few iterations, significantly outperforms conventional trellis coded modulation and is therefore another promising technique to achieve large coding gain without bandwidth expansion.

210 citations


Journal ArticleDOI
TL;DR: This novel approach to fading channel prediction is combined with transmitter signal optimization to mitigate the effects of "deep fades", which severely limit the performance of mobile radio systems.
Abstract: In wireless communication systems, the direct signal and the reflected signals form an interference pattern resulting in a received signal given by the sum of these components. They are distinguished by their Doppler shifts at the mobile. Since the parameters associated with these components are slowly varying, the fading coefficients can be accurately predicted far ahead. This novel approach to fading channel prediction is combined with transmitter signal optimization to mitigate the effects of "deep fades", which severely limit the performance of mobile radio systems. This capability will potentially help to reduce power requirements for wireless channels and improve the system performance.

204 citations


Journal ArticleDOI
TL;DR: It is shown that after a proper simple modification, the soft-output Viterbi algorithm (SOVA) proposed by Hagenauer and Hoeher (1989) becomes equivalent to the max-log-maximum a posteriori (MAP) decoding algorithm.
Abstract: It is shown that after a proper simple modification, the soft-output Viterbi algorithm (SOVA) proposed by Hagenauer and Hoeher (1989) becomes equivalent to the max-log-maximum a posteriori (MAP) decoding algorithm. Consequently, this modified SOVA allows to implement the max-log-MAP decoding algorithm by simply adjusting the conventional Viterbi algorithm. Hence, it provides an attractive solution to achieve low-complexity near-optimum soft-input soft-output decoding.

Journal ArticleDOI
TL;DR: An iterative decoder structure is presented, which combines channel equalization and turbo decoding, and results are presented for a rate 1/2 turbo code with binary phase-shift keying modulation, transmitted over an intersymbol interference channel having severe frequency distortion.
Abstract: In this letter, the subject of turbo coding in the presence of an intersymbol interference channel is investigated. An iterative decoder structure is presented, which combines channel equalization and turbo decoding. At each iteration extrinsic information from the channel detector is fed into the turbo decoders, and then their extrinsic information is fed back to the channel detector. Simulation results are presented for a rate 1/2 turbo code with binary phase-shift keying (BPSK) modulation, transmitted over an intersymbol interference (ISI) channel having severe frequency distortion. The performance is about 0.8 dB from the ISI channel capacity at a bit-error rate of 10/sup -5/.

Journal ArticleDOI
TL;DR: Frequency-domain correlative coding with correlation polynomial F(D)=1-D in OFDM mobile communication systems to compress the intercarrier interference caused by channel frequency errors shows that such a simple coding method enhances system CIR by 3.5 dB, without reducing the bandwidth efficiency.
Abstract: This study considers the use of frequency-domain correlative coding with correlation polynomial F(D)=1-D in OFDM mobile communication systems to compress the intercarrier interference caused by channel frequency errors. A theoretical expression of carrier-to-interference power ratio (CIR) has been derived. It shows that such a simple coding method enhances system CIR by 3.5 dB, without reducing the bandwidth efficiency.

Journal ArticleDOI
TL;DR: A novel near-optimal receiver for the detection of signals in symmetric /spl alpha/-stable noise is introduced which is very close to the locally optimum receiver and is significantly better than the performance of previously suggested sub-optimum receivers.
Abstract: There has been great interest in symmetric /spl alpha/-stable distributions which have proved to be very good models for impulsive noise. However, most of the classical non-Gaussian receiver design techniques cannot be extended to the symmetric /spl alpha/-stable noise case since these techniques require an explicit compact analytical form for the probability density function (PDF) of the noise distribution which /spl alpha/-stable distributions do not possess. A new analytical representation has been suggested for the symmetric /spl alpha/-stable PDF which is based on scale mixtures of Gaussians. Based on this new analytical representation, this paper introduces a novel near-optimal receiver for the detection of signals in symmetric /spl alpha/-stable noise. The performance of the new receiver is very close to the locally optimum receiver and is significantly better than the performance of previously suggested sub-optimum receivers. The new technique has important potential in radar, sonar, and other applications.

Journal ArticleDOI
TL;DR: A procedure for generating two equal power Rayleigh-fading envelopes with any desired cross-correlation coefficient to aid researchers in simulating correlated fading envelopes, which can be used to study the impact of correlation on the performance of diversity systems.
Abstract: A procedure for generating two equal power Rayleigh-fading envelopes with any desired cross-correlation coefficient is given. Having this ability will aid researchers in simulating correlated fading envelopes, which can be used to study the impact of correlation on the performance of diversity systems.

Journal ArticleDOI
TL;DR: A new form of the Marcum (1950) Q-function is presented that has both computational and analytical advantages and enables simple upper and lower bounds to be found analogous to the Chernoff bound on the Gaussian Q- function.
Abstract: A new form of the Marcum (1950) Q-function is presented that has both computational and analytical advantages. The new form is particularly useful in simplifying and rendering more accurate the analysis of the error probability performance of uncoded and coded partially coherent, differentially coherent, and noncoherent communication systems in the presence of fading. It also enables simple upper and lower bounds to be found analogous to the Chernoff bound on the Gaussian Q-function.

Journal ArticleDOI
TL;DR: A linearly constrained constant modulus approach for the blind suppression of multiuser interferences in direct-sequence code division multiple access systems outperforms existing blind approaches because it only requires a rough estimate of the desired user code and timing.
Abstract: This article presents a linearly constrained constant modulus approach for the blind suppression of multiuser interferences in direct-sequence code division multiple access systems. The method performs the same as minimum mean square error receivers and outperforms existing blind approaches because it only requires a rough estimate of the desired user code and timing.

Journal ArticleDOI
TL;DR: A ready-to-implement ARQ scheme with packet combining with analytical description of the scheme in random error channel shows excellent agreement with simulation results and an upper bound for type-II schemes is defined.
Abstract: In an automatic repeat request (ARQ) scheme, a packet is retransmitted if it gets corrupted due to transmission errors caused by the channel. Here we describe a ready-to-implement ARQ scheme with packet combining. An analytical description of the scheme in random error channel shows excellent agreement with simulation results. An upper bound for type-II schemes is defined. For smaller packet sizes, throughput of the proposed scheme is sufficiently close to the upper bound till a very high bit error rate.

Journal ArticleDOI
TL;DR: It is concluded that it is indeed theoretically possible to use the RPLC to solve the local loop problem in a second, fixed line telephone network.
Abstract: Based on the results of an extensive measurement campaign executed in the city of Amsterdam, the Netherlands, a channel model for the residential power line channel (RPLC) used as a digital communications channel is presented. From this model bounds for the channel capacity of such a channel used under European regulations are calculated. It is concluded that it is indeed theoretically possible to use the RPLC to solve the local loop problem in a second, fixed line telephone network.

Journal ArticleDOI
TL;DR: It is shown that the optimum multiuser detection problem for a synchronous code-division multiple access (CDMA) system is equivalent to the minimum capacity cut problem in a related network and an optimumMultiuser Detection algorithm with polynomial computational complexity for a certain class of signature sequences is proposed.
Abstract: The optimum multiuser detection problem was shown to be NP-hard, i.e., its computational complexity increases exponentially with the number of users (Verdu 1986, 1989). In this letter, we show that the optimum multiuser detection problem for a synchronous code-division multiple access (CDMA) system is equivalent to the minimum capacity cut problem in a related network and propose an optimum multiuser detection algorithm with polynomial computational complexity for a certain class of signature sequences. The minimum cut problem is solvable in polynomial time if the capacities of the links not incident to source and sink are nonnegative. This condition in the optimum detection problem is equivalent to all cross correlations between the signature sequences of the users being negative. One example of such a set of signature sequences is obtained when shifted versions of the maximal length sequences (or m-sequences) are used. In this case the cross correlation between users i and j is given as /spl Gamma//sub ij/=-1/G for all i,j, where G is the processing gain.

Journal ArticleDOI
TL;DR: Simulations show that the detector is limited by the theoretical channel capacity at low signal-to-noise ratio (SNR) and asymptotically achieves single user performance at high SNR.
Abstract: A multiuser detection algorithm, applicable to asynchronous users having the same signaling waveform and power levels, is presented. Users are assumed to employ forward error correction coding but with different pseudorandom interleaving. The algorithm is derived from iterative techniques for cross-entropy minimization, similar to turbo decoding. Simulations show that the detector is limited by the theoretical channel capacity at low signal-to-noise ratio (SNR) and asymptotically achieves single user performance at high SNR.

Journal ArticleDOI
TL;DR: The estimation range can be greatly extended without sacrificing the estimation accuracy and a simple technique is indicated to measure the Doppler bandwidth, which allows the algorithm to operate in an adaptive manner in a time-varying environment.
Abstract: A data-aided feedforward algorithm has been proposed by Kuo and Fitz (see IEEE Trans. Commun., vol.45, p.1412-26, 1997) for carrier frequency estimation in M-ary phase-shift keying (PSK) transmissions over frequency-flat Rayleigh fading channels. Its accuracy is very good but the estimation range may be limited under certain operating conditions. Also, its application requires a knowledge of the Doppler bandwidth. We show that the estimation range can be greatly extended without sacrificing the estimation accuracy and a simple technique is indicated to measure the Doppler bandwidth. This allows the algorithm to operate in an adaptive manner in a time-varying environment.

Journal ArticleDOI
TL;DR: An extremely compact new formula is presented that is extraordinarily similar to its counterpart for M-ary phase shift keying (MPSK) that simplifies the error probability expressions in other situations such as nonorthogonal signaling, maximum-likelihood differential detection of DPSK with block-by-block detection, and Gray coding of MDPSK.
Abstract: This article presents an extremely compact new formula for the symbol error probability in M-ary differential phase shift keying (MDPSK) that is extraordinarily similar to its counterpart for M-ary phase shift keying (MPSK). This result follows from a new form for a generic error probability associated with the phase angle between two vectors perturbed by Gaussian noise. The new form also leads to a new expression for the Marcum Q-function. As special cases, the generic error probability is noted to also contain MPSK, CPFSK, and digital FM. Finally, it is pointed out that the generic error probability simplifies the error probability expressions in other situations such as nonorthogonal signaling, maximum-likelihood differential detection of DPSK with block-by-block detection, and Gray coding of MDPSK.

Journal ArticleDOI
TL;DR: Using an alternate representation of the Marcum Q-function, an expression for the bivariate Rayleigh cumulative distribution function is found in the form of a single integral with finite limits and an integrand composed of elementary functions.
Abstract: Using an alternate representation of the Marcum Q-function, an expression for the bivariate Rayleigh cumulative distribution function is found in the form of a single integral with finite limits and an integrand composed of elementary functions. This result has advantage over previous forms of the same CDF which involve the Marcum Q-function itself or are expressed as infinite series of products of integrals.

Journal ArticleDOI
TL;DR: Symbol-by-symbol maximum a posteriori decoding algorithms for nonbinary block and convolutional codes over an extension field GF(p/sup a/) are presented and meet all requirements needed for iterative decoding.
Abstract: Symbol-by-symbol maximum a posteriori (MAP) decoding algorithms for nonbinary block and convolutional codes over an extension field GF(p/sup a/) are presented. Equivalent MAP decoding rules employing the dual code are given which are computationally more efficient for high-rate codes. It is shown that these algorithms meet all requirements needed for iterative decoding as the output of the decoder can be split into three independent estimates: soft channel value, a priori term and extrinsic value. The discussed algorithms are then applied to a parallel concatenated coding scheme with nonbinary component codes in conjunction with orthogonal signaling.

Journal ArticleDOI
TL;DR: It is shown that the eigenvalues of the autocorrelation matrices of a pair of complementary sequences sum to a known constant.
Abstract: Estimating a channel impulse response using a known aperiodic sequence is considered. The problem can be reduced to minimizing the trace of the inverse of a Toeplitz matrix. An efficient algorithm for computing this trace is developed and optimal binary sequences up to length 32 are found and tabulated. The use of complementary sequences in this context is also investigated. It is shown that the eigenvalues of the autocorrelation matrices of a pair of complementary sequences sum to a known constant.

Journal ArticleDOI
TL;DR: The Viterbi algorithm (VA), which normally operates using a single trellis, can be optimally reformulated into a set of independent trellises for a special class of sparse intersymbol interference channels resulting in a suboptimal reduced complexity equalizer.
Abstract: The Viterbi algorithm (VA), which normally operates using a single trellis, can be optimally reformulated into a set of independent trellises for a special class of sparse intersymbol interference (ISI) channels. These independent trellises operate in parallel and have less overall complexity than a single trellis. This trellis decomposition can be applied to a more general class of sparse channels approximately resulting in a suboptimal reduced complexity equalizer.

Journal ArticleDOI
TL;DR: In this letter, O(rm+rnlog n) time algorithms for the most reliable quickest path problem and the quickest most reliable path problem are presented, where r is the number of different capacity values in the network.
Abstract: Let N=(V,E,c,l,p) be a network where V is the set of n vertices, E is the set of m edges, c(u,v)/spl ges/0 is the capacity of edge {u,v}, l(u,v)/spl ges/0 is the delay of edge {u,v}, p(u,v)/spl isin/[0,1] is the operational probability of edge {u,v}. In this letter, we present O(rm+rnlog n) time algorithms for the most reliable quickest path problem and the quickest most reliable path problem, where r is the number of different capacity values in the network.

Journal ArticleDOI
TL;DR: A suboptimal algorithm for modulation classification for classifying the modulation type of general M-ary phase-shifted keying signals is proposed and an asymptotic optimal classification algorithm is derived that is more effective.
Abstract: A suboptimal algorithm for modulation classification was proposed for classifying the modulation type of general M-ary phase-shifted keying (MPSK) signals. Yang and Soliman (see IEEE Trans. Aerosp. Electron. Syst., vol.33, no.1, p.38-45, 1997) approximated the phase probability density function of a received signal to be the Tikhonov function. Instead, we employ the exact phase density function and derive an asymptotic optimal classification algorithm. We show a structure of this proposed classifier for continuous wave (CW), binary phase-shift keying (BPSK), quaternary phase-shift keying (QPSK), and 8PSK. Besides, we give an example to demonstrate the capability of this algorithm and compare its performance to that in Yang and Soliman. It is shown that the performance is more effective.

Journal ArticleDOI
TL;DR: This letter proves that the frame-error rate (FER) of trellis codes with trell is actually a true upper bound, which may be useful to orientate the design of frame based transmission systems directly in terms of FER instead of the more common but less significant bit- error rate figure.
Abstract: The frame-error rate (FER) of trellis codes with trellis termination can be approximated by considering the length of the error events negligible with respect to the frame length. In this letter we prove that this approximation is actually a true upper bound. This may be useful to orientate the design of frame based transmission systems directly in terms of FER instead of the more common but less significant bit-error rate figure.