Showing papers on "Channel state information published in 1994"
TL;DR: Results show that the degradation in performance with correlation in an adaptive array that combats fading and suppresses interference is only slightly larger than that for combating fading alone, i.e., with maximal ratio combining.
Abstract: In this paper, we investigate the effect of correlations among the fading signals at the antenna elements of an adaptive array in a digital wireless communication system. With an adaptive array, the signals received by multiple antennas are optimally weighted and combined to suppress interference and combat desired signal fading. Previous results for flat and frequency-selective fading assumed independent fading at each antenna. Here, we present a model of local scattering around a mobile where the received multipath signals arrive at the base station within a given beamwidth, and derive a closed-form expression for the correlation as a function of antenna spacing. Results show that the degradation in performance with correlation in an adaptive array that combats fading and suppresses interference is only slightly larger than that for combating fading alone, i.e., with maximal ratio combining. This degradation is small even with correlation as high as 0.5. >
635 citations
Book•
30 Apr 1994
TL;DR: This work describes how the MPSK Signal Set over a Rayleigh Fading Channel became Reliable and Unreliable, and the techniques used to derive these Symbols and their encoding and decoding techniques.
Abstract: Preface. 1. Fading Channel Modeling. 2. Digital Transmission over Fading Channels. 3. Convolutional Codes. 4. Bandwidth-Efficient Coded-Modulation Schemes. 5. Trellis-Coded Modulation Schemes for Fading Channels. 6. Reed-Solomon Codes. 7. RS-Coded MPSK Schemes for Fading Channels. 8. Differential Detection of Coded-Modulation Schemes on a Fading Channel. 9. Performance of Coded Modulation Schemes on Shadowed Rician Fading Channels. 10. Quadrature Pulse-Overlapping Modulation Techniques. Appendix A: Calculation of the Chernoff Factors for Rician and Rayleigh Fading Channels. Appendix B: Calculation of the Transition Probabilities for the MPSK Signal Set over a Rayleigh Fading Channel. Appendix C: Encoding and Decoding Techniques for RS Codes Using Fourier Transform. Appendix D: Derivation of the Probability of Correct Decision for Reliable and Unreliable MPSK Symbols. References. Index.
209 citations
TL;DR: In this article, the authors derived metrics for maximum-likelihood differential detection of uncoded and trellis coded MPSK and QAM transmitted over Rayleigh and Rician fading channels.
Abstract: This paper derives metrics for maximum-likelihood differential detection of uncoded and trellis coded MPSK and QAM transmitted over Rayleigh and Rician fading channels. Receiver structures based on these metrics are proposed and their error probability performance analyzed and/or simulated. The results represent a generalization of the notion of multiple symbol differential detection, previously introduced by the authors for MPSK over an AWGN, to the fading channel and other modulations. For the coded cases, ideal interleaving/deinterleaving is assumed and furthermore the presence or absence of channel state information. An interesting side result is that for a constant envelope modulation transmitted over a fading channel with unknown but rapidly-varying phase error (the other extreme to the slowly-varying phase error case normally assumed for differential detection), under certain practical assumptions, it is shown that the optimum receiver is of the limiter-discriminator type. >
206 citations
TL;DR: All of the packet combining schemes discussed in this paper provide improved throughput and reliability performance relative to that provided by the standard type-I hybrid-ARQ or EEC systems.
Abstract: Type-I hybrid-ARQ protocols can be used to construct powerful adaptive rate algorithms through the use of packet combining techniques. In this paper several packet combining schemes are presented for use in conjunction with the Viterbi decoder over stationary and time-varying channels. The first technique presented is an averaged diversity combiner, which is shown to be identical in performance to an interleaved code combiner over an AWGN channel. The averaged diversity combiner is then generalized to make use of packet weights based on either ideal channel state information or weights derived from side information generated by the Viterbi decoder. It is shown that the weighted diversity combiner using decoder side information performs almost as well as the system using ideal channel state information. All of the packet combining schemes discussed in this paper provide improved throughput and reliability performance relative to that provided by the standard type-I hybrid-ARQ or EEC systems. This performance improvement is obtained at the expense of negligible to moderate modifications to the transmitter and receiver. Performance bounds are derived for each of the combining schemes and their tightness verified through simulation results. >
132 citations
31 Oct 1994
TL;DR: A statistical, time varying, dispersive, wireless vector channel model which is based on the physical propagation environment is developed and shown to be consistent with the known characteristics of the wireless communication channel.
Abstract: In a wireless communication environment, multipath propagation and mobile user motion result in a dispersive time-varying communication channel. In order to analyze the performance of wireless communication systems, it is necessary to define models which reasonably approximate the time varying impulse response of the radio channel. Many widely accepted scalar channel (single antenna) statistical models have been reported. In order to analyze performance for real time adaptive antenna array techniques, it is necessary to extend existing scalar channel statistical models to the vector channel (multiple antenna) case. The paper develops a statistical, time varying, dispersive, wireless vector channel model which is based on the physical propagation environment. The model is shown to be consistent with the known characteristics of the wireless communication channel. Antenna pattern interference rejection as a function of update rate is presented as an application example for the vector channel model. >
105 citations
TL;DR: The authors investigate the achievable error probabilities over the correlated Rician channel, employing coherent detection and ideal side information on the realization of the fading processes at the receiver to enhance the insight to the effect of the basic parameters governing the performance.
Abstract: The correlated Rician channel is a useful model for a slowly fading channel, in which the complex fading process is composed of two quadrature Gaussian processes with a given autocorrelation function. For slow fading the correlation between adjacent symbols is relatively high. The authors investigate the achievable error probabilities over the channel, employing coherent detection and ideal side information on the realization of the fading processes at the receiver. An underlying decoding delay constraint which precludes the use of (ideal) interleaving is assumed. Coded BPSK performance is addressed both with and without the piecewise constant approximation (according to which the fading value remains constant during the symbol duration). For the latter case, that is no piecewise constant approximation, the analysis relies on the Fredholm determinant associated with the fading process autocorrelation function. The authors focus on the exponentially correlated channel. The "worst case" pairs of codewords are identified. The exponential behavior of the error probability with random coding (and i.i.d. Gaussian inputs) is analyzed, and the behavior of the cut-off rate and capacity is addressed. The results enhance the insight to the effect of the basic parameters governing the performance and these are examined in view of previous works and compared to relevant performance results for the block-fading channel model. >
72 citations
TL;DR: The asymptotic efficiencies of multiuser detectors designed for the Gaussian channel when employed over the Rician fading channel are obtained, thereby quantifying the loss in performance incurred by these mismatched detectors.
Abstract: Synchronous code division multiple access (CDMA) data transmission over a non-selective Rician fading channel is considered, where the faded signal components arrive at the receiver in synchronism with the specular signal component. Under the assumption that the fading parameters are uncorrelated, this fading CDMA channel is shown to be equivalent to a Gaussian CDMA channel over which a modified signal set is employed. A fading counterpart of the multiuser asymptotic efficiency performance measure is defined. The asymptotic efficiencies of the optimum, decorrelating, and conventional detectors designed for the fading channel are derived. The conventional detector, which has low complexity, is shown to degrade rapidly in near-far environments. The optimal detector for the fading channel exhibits a significant improvement in performance but at the price of a computational complexity that increases exponentially with the number of users. The linear decorrelating detector for the fading case is optimally near-far resistant. The asymptotic efficiencies of multiuser detectors designed for the Gaussian channel when employed over the Rician fading channel are also obtained, thereby quantifying the loss in performance incurred by these mismatched detectors. >
57 citations
08 Jun 1994
TL;DR: An adaptive coding system that adjusts the rate allocation according to actual channel conditions and shows that the objective and the subjective speech quality of the adaptive coders are superior than their non-adaptive counterparts.
Abstract: Although the mobile communication channels are time-varying, most systems allocate the combined rate between the speech coder and error correction coder according to a nominal channel condition. This generally leads to a pessimistic design and consequently an inefficient utilization of the available resources, such as bandwidth and power. This paper describes an adaptive coding system that adjusts the rate allocation according to actual channel conditions. Two types of variable rate speech coders are considered : the embedded coders and the multimode coders and both are based on code excited linear prediction (CELP). On the other hand, the variable rate channel coders are based on the rate compatible punctured convolutional codes (RCPC). A channel estimator is used at the receiver to track both the short term and the long term fading condition in the channel. The estimated channel state information is then used to vary the rate allocation between the speech and the channel coder, on a frame by frame basis. This is achieved by sending an appropriate rate adjustment command through a feedback channel. Experimental results show that the objective and the subjective speech quality of the adaptive coders are superior than their non-adaptive counterparts. Improvements of up to 1.35 dB in SEGSNR of the speech signal and up to 0.9 in informal MOS for a combined rate of 12.8 kbit/s have been found. In addition, we found that the multimode coders perform better than their embedded counterparts. >
34 citations
TL;DR: A general model for envelope correlation statistics of line-of-sight fading known as Nakagami-Rice fading is developed and can be applied to the analysis of correlation statistics in frequency and spatial domains for microcellular mobile radio, maritime and aeronautical mobile-satellite communications.
Abstract: Based on the theoretical method developed by Clarke for the analysis of correlation characteristics in Rayleigh fading conditions, we develop a general model for envelope correlation statistics of line-of-sight fading known as Nakagami-Rice fading. The model developed here has a considerable degree of univer- sality and can be applied to the analysis of correlation statistics in frequency and spatial domains for microcellular mobile radio, maritime and aeronautical mobile-satellite communications. Us- ing this model, we examine the frequency correlation statistics of two typical Nakagami-Rice fading environments.
34 citations
TL;DR: A general result is derived for the bit error rate (BER) of differential quadrature phase shift keying (DQPSK) for reception in slow fading and additive white Gaussian noise (AWGN).
Abstract: A general result is derived for the bit error rate (BER) of differential quadrature phase shift keying (DQPSK) for reception in slow fading and additive white Gaussian noise (AWGN). Fading models include Rayleigh, Rician, Nakagami and shadowed Rician, which describe a wide range of fading conditions encountered in mobile communications. Easily computable, the result is potentially useful in evaluating the BER of such systems.
33 citations
28 Nov 1994
TL;DR: A maximum likelihood decoder is derived for codewords transmitted over a noninterleaved Rayleigh flat fading channel, followed by an exact expression for the pairwise error event probability of such a decoder in the case of very slow fading.
Abstract: The majority of previous analytical studies of signal-space coding techniques (includes trellis and block codes) on the Rayleigh-fading channel have assumed ideal interleaving. The effect of finite interleaving on the performance of different coding schemes has been studied only by simulation In this paper we first derive a maximum likelihood (ML) decoder for codewords transmitted over a noninterleaved Rayleigh flat fading channel, followed by an exact expression for the pairwise error event probability of such a decoder. It includes phase shift keying (PSK), quadrature amplitude modulation (QAM) signal sets, trellis coded modulation (TCM) and block coded modulation (BCM) schemes, as well as coherent (ideal channel state information) and partially coherent (e.g., differential, pilot tone, etc.) detection. We derive an exact expression for the pairwise event probability in the case of very slow fading-i.e., the fading experienced by all the symbols of the codeword is highly correlated. We also show that the interleaving depth required to optimize code performance for a particular minimum fading bandwidth can be approximated by the first zero of the fading channel's auto-correlation function.
28 Nov 1994
TL;DR: The author presents analytical performance results for the coding technique, and compares it with built-in time diversity coded modulation, which assumes no channel information at the transmitter.
Abstract: Proposes a variable-rate coded modulation technique for narrowband fading channels, where channel state information is available to both the transmitter and receiver. The technique can be applied to either trellis or block codes. The basic premise is to adjust the size of the transmit signal constellation relative to the fade depth via power control. Specifically, channel coding gain is achieved through binary encoding and subset partitioning, while the size of the transmit constellation is adjusted to maximize the data rate. The author presents analytical performance results for the coding technique, and compares it with built-in time diversity coded modulation, which assumes no channel information at the transmitter.
01 May 1994
TL;DR: An optimal sequential decoding scheme for a joint source and channel coding system operating in the Rayleigh flat fading channel and it is found that sequential decoding significantly improves the system performance when a correlated source is transmitted.
Abstract: The paper presents an optimal sequential decoding scheme for a joint source and channel coding system operating in the Rayleigh flat fading channel. The minimum mean-square error (MSE) between the original and the reconstructed source signals is used as the optimality criterion. The system being investigated consists of a vector quantizer (VQ) whose output indices are mapped directly into points in the modulation signal space. The modulation signal is then transmitted over a Rayleigh fading channel. A sequential decoder based on the Bayesian estimate is used to reconstruct the source signal from the received signal samples and from the channel state information (CSI). A recursive algorithm for implementing the Bayes receiver is introduced. Compared to the symbol by symbol decoding technique proposed earlier, it is found that sequential decoding significantly improves the system performance when a correlated source is transmitted. >
TL;DR: The proposed scheme incorporates the retransmission requests into the scoring of a statistical sequential inspection scheme proposed by E. Page in 1954 and is close to that of the ideal system with perfect channel state information.
Abstract: Improved performance of error control techniques over slowly varying channels can be realized by a system which adapts itself to changes in the channel conditions. Such action requires a method for monitoring the channel state and detecting a change in it. The frequency of retransmission requests in ARQ and type-I hybrid-ARQ error control strategies provides a natural source of channel state information. The proposed scheme incorporates the retransmission requests into the scoring of a statistical sequential inspection scheme proposed by E. Page in 1954. Each transmitted packet is scored based on the outcome of the decoding process (i.e., whether it is accepted or rejected). When the cumulative score crosses a decision boundary, the coding strategy is altered and the sequential inspection scheme is restarted using the same scoring routine with different weighting and boundary constants. In this way the channel encoder/decoder is able to alter its strategy and adapt itself to changes in the channel. The analysis of this system is based on the average run length of the tests in the various channel states. These values indicate the delay the system experiences in reacting to a change in the channel and the tendency the test has to terminate prematurely. These factors are a function of the test constants which are determined algorithmatically by maximizing the system throughput using the system reliability as a constraint. Results show that the performance of this system is close to that of the ideal system with perfect channel state information. >
18 Sep 1994
TL;DR: A computer simulation model for a land mobile radio fading channel that takes into consideration the effects caused by shadowing and can be considered as a deterministic model that approximates a stochastic process.
Abstract: In this paper a computer simulation model for a land mobile radio fading channel is presented. The model assumes non frequency-selective fading but takes into consideration the effects caused by shadowing. The simulation model is based on an efficient approximation of filtered white Gaussian noise by a finite sum of weighted sinusoids with equally distributed phases. Two completely different methods for the computation of the coefficients of the simulation model are discussed. The design of a fading channel model by one of the presented methods leads always to a simulation model that is completely determined for all time, and therefore, it can be considered as a deterministic model that approximates a stochastic process.
TL;DR: In this paper, the effect of receiver processing on the mitigation effect for wide-band DS/CDMA signals is investigated, and the effect is shown by a reduction of the coefficient of variation of the received power as a function of bandwidth spreading.
Abstract: Transmitting signals over multipath fading channels causes distortions and variations at the receiver. For narrow-band signals, the envelope of the received signal is well characterized by a Rayleigh random process. Rayleigh fading causes large variations in the signal envelope. For wide-band signals, the effect of Rayleigh fading is mitigated. The paper considers the effect of receiver processing on the mitigation effect for wide-band DS/CDMA signals. The mitigation effect is shown by a reduction of the coefficient of variation of the received power as a function of bandwidth spreading. The parameters chip rate, processing gain, and the number of multipath components tracked are investigated for their effect upon the mitigation-the mitigation effect is sensitive to combinations of these parameters. >
TL;DR: A Chernoff upper bound is derived for the pairwise error probability in the presence of an additive white Gaussian noise and a Rayleigh or Rice correlated fading and used to determine some indications in the design of optimum trellis coded modulation for correlated fading channels.
Abstract: We derive a Chernoff upper bound for the pairwise error probability in the presence of an additive white Gaussian noise and a Rayleigh or Rice correlated fading. The bound is useful for situations where perfect interleaving cannot be achieved. We use it to determine some indications in the design of optimum trellis coded modulation for correlated fading channels. >
01 Oct 1994
TL;DR: In this article, an extremely tight upper bound for symbol error probability for M-DPSK over a Rician channel, incorporating the effects of AWGN, fading bandwidth and fixed Doppler shift (for the line-of-sight component), was derived.
Abstract: An extremely tight upper bound symbol error probability is developed for M-DPSK over a Rician channel, incorporating the effects of AWGN, fading bandwidth and fixed Doppler shift (for the line-of-sight component). In addition, the error probability has also been determined in the above channels with the use of post-detection diversity combining. The bounds are shown to be in excellent agreement with the exact solutions produced by previous authors using numerical computation techniques for both the Rician and Rayleigh fading channels. For the case of AWGN channel, the bound is reduced to that published elsewhere in the literature. The technique is also shown to be capable of formulating the exact fading bit error probability for both binary and quaternary DPSK.
08 Mar 1994
TL;DR: A new communications system based on the combination of Multitone transmission and Direct Sequence Sprectrum Spreading (DS/SS) that combines the DS/SS capabilities of combating multipath propagation by allowing diversity reception and the larger symbol duration of multitone systems, which is also favorable to combat the multipath effects.
Abstract: This paper proposes a new communications system based on the combination of Multitone transmission and Direct Sequence Sprectrum Spreading (DS/SS). This system combines the DS/SS capabilities of combating multipath propagation by allowing diversity reception, with the larger symbol duration of multitone systems, which is also favorable to combat the multipath effects. The performance of this system is investigated for a multipath, frequency selective, slowly Rician fading channel, and a suboptimal receiver based on matched filters. A model for the computation of the Bit Error Probability is derived for QPSK modulation of the orthogonal tones by the spread symbols. The system performance is investigated for selection diversity and maximal ratio combining (Rake reception). Then the influence of the number of tones is investigated for given bandwidth, bit rate and transmission power.
Patent•
AT&T1
TL;DR: In this paper, a system for inducing rapid fading in wireless communication systems, such as digital radio and television transmission, is described, where orthogonal polarization from antennas (30,32) combined with time varying offsets introduced by mixer (24) and oscillator (26) are combined to ensure rapid fading and result in improved signal reception at receiver antenna.
Abstract: A system for inducing rapid fading in wireless communication systems (10), such as digital radio and television transmission is described. Orthogonal polarization from antennas (30,32) combined with time varying offsets introduced by mixer (24) and oscillator (26) are combined to ensure rapid fading and result in improved signal reception at receiver antenna (35).
28 Nov 1994
TL;DR: In this article, an adaptive multiuser receiver for synchronous CDMA fading channels consists of an adaptive estimator of the fading distortion and the detector that utilizes so-obtained estimates.
Abstract: The optimal multiuser receiver for synchronous CDMA fading channels consists of an adaptive estimator of the fading distortion and the detector that utilizes so-obtained estimates High complexity of the optimal detector motivates the use of a decorrelating detector, whose performance is significantly improved through diversity The estimates of the complex fading processes are utilized both for maximal-ratio combining and carrier recovery To analyze the impact of channel estimation errors on the receiver performance, error probability of coherent decorrelating receiver is assessed directly in terms of the fading rate and the number of active users, showing the penalty imposed by imperfect channel estimation as well as fading-induced error probability floor The coherent receiver performance is compared to that of a differentially coherent receiver with equal gain combining
TL;DR: The effect of a specific fading correlation function derived for a mobile-to-mobile land communication channel on the performance of differentially coherent PSK and noncoherent FSK matched filter receivers is investigated.
Abstract: The effect of a specific fading correlation function derived for a mobile-to-mobile land communication channel on the performance of differentially coherent PSK and noncoherent FSK matched filter receivers is investigated. The bit error probability, irreducible error rate, and the degradation in signal-to-noise ratio (SNR) are specifically derived for each system. The effect of the fading bandwidth on the performance of the system is also investigated. >
01 Jan 1994
TL;DR: To analyze the impact of channel estimation errors on the receiver performance, error probability of coherent decorrelating receiver is assessed directly in terms of the fading rate and the number of active users, showing the penalty imposed by imperfect channel estimation as well as fading-induced error probability floor.
Abstract: The optimal multiuser receiver for syn- chronous CDMA fading channels consists of an adaptive es- timator of the fading distortion and the detector that utilizes so-obtained estimates. High complexity of the optimal de- tector motivates the use of a decorrelating detector, whose performance is significantly improved through diversity. The estimates of the complex fading processes are utilized both for maximal-ratio combining and carrier recovery. To ana- lyze the impact of channel estimation errors on the receiver performance, error probability of coherent decorrelating re- ceiver is assessed directly in terms of the fading rate and the number of active users, showing the penalty imposed by imperfect channel estimat,ion as well as fading-induced error probability floor. The coherent receiver performance is com- pared to that of a differentially coherent receiver with equal gain combining. 1. Introductioii While multiuser detection has been analyzed thoroughly for both time-invariant and fading AWGN channels, little work has been reported on the underlying channel estimation is- sues in multiple-access fading channels. The impact of im- perfect channel estimates on multiuser receiver performance in rapidly fading channels is the subject of this paper. Recent results for the single-user case (l), (a) provide meth- ods for optimal receiver design based on statistical modeling of a fading process with memory. It is shown in (a) that the optimal receiver for a nonselective channel consists of an adaptive estimator of the fading distortion and a detec- tor which utilizes the entire received signal in detecting each symbol. While the optimal receiver is difficult to implement due to its complexity which is exponential in the symbol se- quence length, a suboptimal decision-directed receiver can be implemented instead. This receiver employs linear mini- mum mean-squared error (MMSE) estimation of the complex channel distortion, and uses the obtained estimates to per- form decision-directed carrier recovery via a planar filtering method (I). In multiple-access channels, the accuracy of fading chan- nel estimates is degraded due to the presence of multiple- access interference (MAI). A vector generalization of the op- timal receiver for nonselect,ive Rayleigh fading synchronous CDMA channels and its suboptimal, decision-direct,ed real- ization were presented in (3). Due to the quadratic detect,ion rule, even the decision-directed receiver has computational complexity exponential in the number of active users. Chan- nel estimation methods, designed especially for burst CDMA transmissions, were presented in (4). In this paper we propose an adaptive decision-directed coherent receiver with diversity reception for nonselective Rayleigh fading synchronous CDMA channels. The detection part of the receiver employs a low-complexity near-far re- sistant decorrelating detector whose complexity depends lin- early only on the number of users (5), (6). The detector utilizes the MMSE estimates of the fading processes as channel refer- ences for carrier recovery and diversity combining. For such a receiver, we quantify the effects of noisy estimates, caused by fading dynamics and MAI, on the multiuser receiver per- formance. The average error probability is determined by the values of the channel estimation error covariance matrix. In contrast to the approach taken in (3), where a diagonal struc- ture is imposed on the estimation error covariance matrix by assuming noiselessly observed past fading, no such constraints are required in the analysis presented. Gauss-Markov model- ing of a Rayleigh fading channel provides a method for calcu- lating the quasi-stationary error covariance of the Kalman fil- ter which is used as an optimal channel estimator. A differen- tially coherent receiver uses the same decorrelating technique and a simple, one-shot channel estimation. We compare the two receivers showing regions where each may be preferable, depending on the fading dynamics and MAI.
28 Nov 1994
TL;DR: Maximum-likelihood joint data and channel estimation with the so-called tap-variable step-size least mean square (TVSS-LMS) algorithm is proposed for the emerging Trans European Trunked RAdio (TETRA) and it is shown that the TVSS- LMS is suggested by a simplification of the more sophisticated Kalman channel predictor.
Abstract: Maximum-likelihood joint data and channel estimation with the so-called tap-variable step-size least mean square (TVSS-LMS) algorithm is proposed for the emerging Trans European Trunked RAdio (TETRA). It is shown that the TVSS-LMS is suggested by a simplification of the more sophisticated Kalman channel predictor. The different step sizes can be coarsely determined depending on the respective average channel tap power. Simulation results of a 16-state joint estimator show that for comparable complexity the TVSS-LMS considerably outperforms the conventional LMS in frequency-selective fast fading. Also in flat fading, where differential demodulation is near optimum for TETRA, the TVSS-LMS achieves almost the same bit error rate as a differential demodulation, while the conventional LMS experiences severe degradation.
TL;DR: A novel adaptive channel precoder is proposed to improve the bit error rate performance of a personal wireless communication system, without increasing the complexity of the portable unit.
Abstract: A novel adaptive channel precoder is proposed to improve the bit error rate performance of a personal wireless communication system, without increasing the complexity of the portable unit. Consideration is given to a slowly fading channel with severe intersymbol interference.
02 Oct 1994
TL;DR: The paper presents an efficient method for estimating jammer parameters, based on an iterative clustering technique, applicable to slow frequency hopping PSK (SFH-PSK) systems corrupted by partial band (PB) jamming.
Abstract: It is well known that channel state information (CSI) can be used by the receiver to improve the BER performance of coded spread spectrum communications. Unfortunately, this information is generally not available, and has to be estimated by the receiver. The paper presents an efficient method for estimating jammer parameters, based on an iterative clustering technique. The approach presented is applicable to slow frequency hopping PSK (SFH-PSK) systems corrupted by partial band (PB) jamming. Simulations of the proposed method show that BER performance is, in most cases, very close to perfect CSI. >
04 Jul 1994
TL;DR: The performance of the two orthogonal multi-carrier CDMA systems is studied in nonfading and slowly nonselective fading channels and both systems provide an improved performance.
Abstract: Multi-carrier modulation techniques have been proposed for high bit rate services in fading channels. This paper presents two orthogonal multi-carrier CDMA systems. In one system the data bits are serial to parallel (S/P) converted to M branches where they are spread and modulated by orthogonal carriers. In the second system the data bits are transmitted in parallel with M orthogonal carriers (no S/P). We assumed a fixed available bandwidth. The performance of the two systems is studied in nonfading and slowly nonselective fading channels. Both systems provide an improved performance. System II over performs system I in the fading channel. >
TL;DR: Using an appropriate mathematical model for wideband frequency-selective fading channel, analytical results on the code-word error probability for a simple coding scheme and simulation results for more complex codes are presented.
Abstract: The transmission of frequency-hop spread-spectrum signals over a frequency-selective fading channel results in correlation between the amplitudes of signals that occupy different frequency slots. This correlation produces dependent errors among symbols transmitted at different frequencies. For a system that employs block coding, this dependence results in dependent errors, even if the code symbols are interleaved over the dwell intervals. Using an appropriate mathematical model for wideband frequency-selective fading channel, we present analytical results on the code-word error probability for a simple coding scheme and simulation results for more complex codes.
08 Mar 1994
TL;DR: The paper introduces some features of the CDMA-IC technique for the up-link (from mobile stations to base station) of a mobile radio system and describes a simple algorithm to generate the power list needed for the demodulation of the users' signals according to their received power.
Abstract: In a Code Division Multiple Access (CDMA) mobile radio communications system, interference from other users is one of the most critical drawbacks, and the Interference Cancellation (IC) technique is a method that, by exploiting orthogonal modulation properties, has been presented to reduce the effects and to increase the overall performance The paper introduces some features of the CDMA-IC technique for the up-link (from mobile stations to base station) of a mobile radio system and describes a simple algorithm to generate the power list needed for the demodulation of the users' signals according to their received power The use of non coherent reception has been investigated to avoid any channel estimation
28 Nov 1994
TL;DR: A coherent detection technique for binary continuous phase modulation (CPM), with modulation index of 1/2, operating in the Rayleigh flat fading channel is presented, based on the idea of inserting data dependent pilot symbols that forces the CPM signal to pass through known phase states periodically.
Abstract: We present in this paper a coherent detection technique for binary continuous phase modulation (CPM), with modulation index of 1/2, operating in the Rayleigh flat fading channel. The technique is based on the idea of inserting data dependent pilot symbols that forces the CPM signal to pass through known phase states periodically. When coupled with an appropriate front end filter and interpolation filter, very accurate channel state information (CSI) can be estimated at the receiver for fading compensation. Moreover, the accuracy of the CSI can be further refined by adopting a multiple-pass decoding approach. Finally, a precoding technique capable of essentially reducing the bit-error-rate (BER) by half is introduced.