Showing papers on "Channel state information published in 1995"
18 Jun 1995
TL;DR: By examining the bit error-rate with antipodal signalling, it is shown that an increase in capacity over a perfectly-power controlled (Gaussian) channel can be achieved, especially if the number of users is large, and the inherent diversity in multiuser communications over fading channels is shown.
Abstract: We consider a power control scheme for maximizing the information capacity of the uplink in single-cell multiuser communications with frequency-flat fading, under the assumption that the users attenuations are measured perfectly. Its main characteristics are that only one user transmits over the entire bandwidth at any particular time instant and that the users are allocated more power when their channels are good, and less when they are bad. Moreover, these features are independent of the statistics of the fading. Numerical results are presented for the case of single-path Rayleigh fading. We show that an increase in capacity over a perfectly-power controlled (Gaussian) channel can be achieved, especially if the number of users is large. By examining the bit error-rate with antipodal signalling, we show the inherent diversity in multiuser communications over fading channels.
2,265 citations
25 Jul 1995
TL;DR: The authors present the MMSE and LS estimators and a method for modifications compromising between complexity and performance and the symbol error rate for a 18-QAM system is presented by means of simulation results.
Abstract: The use of multi-amplitude signaling schemes in wireless OFDM systems requires the tracking of the fading radio channel. The paper addresses channel estimation based on time-domain channel statistics. Using a general model for a slowly fading channel, the authors present the MMSE and LS estimators and a method for modifications compromising between complexity and performance. The symbol error rate for a 18-QAM system is presented by means of simulation results. Depending upon estimator complexity, up to 4 dB in SNR can be gained over the LS estimator.
1,647 citations
TL;DR: A modification of the Viterbi decoding algorithm (VA) for binary trellises which uses a priori or a posteriori information about the source bit probability for better decoding in addition to soft inputs and channel state information is proposed.
Abstract: Source and channel coding have been treated separately in most cases. It can be observed that most source coding algorithms for voice, audio and images still have correlation in certain bits. Transmission errors in these bits usually account for the significant errors in the reconstructed source signal. This paper proposes a modification of the Viterbi decoding algorithm (VA) for binary trellises which uses a priori or a posteriori information about the source bit probability for better decoding in addition to soft inputs and channel state information. Analytical upper bounds for the BER of convolutional codes for this modified VA (APRI-VA) are given. The algorithm is combined with the soft output viterbi algorithm (SOVA) and an estimator for the residual correlation of the source bits to achieve source-controlled channel decoding for framed source bits. The description is simplified by an algebra for the log-likelihood ratio L(u)=log(P(u=+1)/P(u=-1)) which allows a clear definition of the "soft" values of source-, channel-, and decoded bits as well as a simplified description of the traceback version of the SOVA. Applications are given for PCM transmission and the full rate GSM speech codec. For an PCM coded oversampled bandlimited Gaussian source transmitted over Gaussian and Rayleigh channels with convolutional codes the decoding errors are reduced by a factor of 4 to 5 when the APRI-SOVA is used instead of the VA. A simple dynamic Markov correlation estimator is used. With these receiver-only modifications the channel SNR in a bad mobile environment can be lowered by 2 to 4 dB resulting in the same voice quality. Further applications are briefly discussed. >
476 citations
TL;DR: The coherent reception of direct sequence-code division multiple access (DS-CDMA) signals in a multipath fading channel is considered and the channel model assumes independent paths with Nakagami fading statistics is considered, which is a reasonable model for a frequency-selective fading channel.
Abstract: The coherent reception of direct sequence-code division multiple access (DS-CDMA) signals in a multipath fading channel is considered. The channel model assumes independent paths with Nakagami fading statistics; this model includes the Rayleigh channel os a special case and is a reasonable model for a frequency-selective fading channel. The bit error rate (BER) performance of a RAKE receiver under various multipath fading conditions is derived and evaluated. The results indicate that over 50 users may access the channel (assuming 127 chips per bit) simultaneously under typical fading conditions, and can achieve an uncoded BER of 0.01 with an average received signal-to-noise ratio per bit of 10 dB. >
386 citations
TL;DR: In this paper, the impact of channel estimation errors on the performance of a multichannel DFE was analyzed for a coherent receiver with a decision-feedback equalizer operating on a Rayleigh fading channel under a suitable adaptive algorithm.
Abstract: A coherent receiver with a decision-feedback equalizer (DFE) operating on a Rayleigh fading channel under a suitable adaptive algorithm is considered. In the analysis of a DFE, a common assumption is that the receiver has perfect knowledge of the channel impulse response. However, this is not the case in practice, and for a rapidly fading channel, errors in channel tracking can become significant. We analyze theoretically the impact of these errors on the performance of a multichannel DFE. The expressions obtained for the achievable average MPSK bit error probabilities depend on the estimation error covariance. In order to specify this matrix, we focus on a special case when a Kalman filter is used as an optimal channel estimator. In this case, the probability of bit error can be assessed directly in terms of channel fading model parameters, the most interesting of which is the fading rate. Our results show the penalty imposed by imperfect channel estimation, as well as the fading-induced irreducible error rates. >
117 citations
TL;DR: Two analytical methods for determining the packet error rate in the non-interleaved Rayleigh fading channel are presented and it is shown that the convolutional code with intra packet interleaving is least sensitive to slow fading.
Abstract: Two analytical methods for determining the packet error rate in the non-interleaved Rayleigh fading channel are presented. The first method is an exact evaluation of the packet error rate, whereas the second method is based on a k-state digital channel model. The fading model is a nonfrequency selective Rayleigh fading with a first-order low pass spectrum for the quadrature fading components. The analytical methods are complemented by simulations. The influence of the fading bandwidth on the packet error rate and the packet throughput is discussed. Block codes as well as convolutional codes are considered. The results show that without forward error correction the throughput for slow fading is higher than for fast fading. With forward error correction the packet error rate is sensitive to the fading bandwidth. Furthermore it is shown that the convolutional code with intra packet interleaving is least sensitive to slow fading. >
83 citations
TL;DR: Novel 2-D TCM schemes that attain diversity of order two even for a trellis structure that includes parallel paths with one symbol per edge are developed and assessed via computer simulation for some representative TCM-QAM schemes.
Abstract: The design of trellis coded modulation (TCM) schemes for QAM constellations to counteract simultaneous flat fading and additive white Gaussian noise (AWGN) is considered. Motivated by the results of Divsalar and Simon (see IEEE Trans. Commun., vol.36, p.1004, 1988), and incorporating some recent ideas from Boulle and Belfiore (1992), we develop novel 2-D TCM schemes that attain diversity of order two even for a trellis structure that includes parallel paths with one symbol per edge. An algorithm is described that transforms codes designed for the AWGN channel into codes that achieve significant gains over flat fading channel, while preserving their coding gain over AWGN channel. Their performance is assessed via computer simulation for some representative TCM-QAM schemes under the assumption of uncorrelated fading and perfect channel state information (CSI). Finally, the effects of finite interleaving as well as imperfect CSI on code performance are investigated. >
54 citations
23 Oct 1995
TL;DR: This paper proposes a method, based on dynamic programming, to compute the rate-distortion performance for a given channel and source realization, and shows how the rates changes with end-to-end delay and feedback delay.
Abstract: Video transmission over wireless links is an emerging application which involves a time-varying channel. In this paper we propose that rate control algorithms should be used at the video encoders, along with models of the channel behavior, to improve the performance of such systems. Rather than letting information be lost as the channel conditions change, in our scheme channel state information is fed back to the encoder. We propose a method, based on dynamic programming, to compute the rate-distortion performance for a given channel and source realization. We show how the rate-distortion performance changes with end-to-end delay and feedback delay.
54 citations
TL;DR: Simulation results demonstrate that these algorithms can track adequately the severe fading fluctuations encountered on a Rayleigh channel and that their superiority over DPSK becomes impressive with fast fading.
Abstract: New algorithms are proposed to implement coherent detection of PSK signals transmitted over frequency-flat Rayleigh channels. Channel gain estimates are derived both from known symbols multiplexed with the data stream and from tentative data decisions. The performance of these algorithms is assessed by computer simulation with uncoded and trellis-coded modulation. Comparisons are also made with differentially coherent detection (DPSK) and with perfect coherent detection (corresponding to ideal knowledge of the fading process). Simulation results demonstrate that these algorithms can track adequately the severe fading fluctuations encountered on a Rayleigh channel and that their superiority over DPSK becomes impressive with fast fading.
48 citations
01 Jan 1995
TL;DR: In urban areas, cellular radio signals are subject to Rayleigh fading, which results in rapid changes in the channel gain, which can lead to large variations in channel gain for TDMA-systems without the possibility of frequency hopping.
Abstract: In urban areas, cellular radio signals are subject to Rayleigh fading, which results in rapid changes in the channel gain. For TDMA-systems without the possibility of frequency hopping, this can ca ...
34 citations
01 Oct 1995
TL;DR: The authors developed the probability of bit error for the asynchronous DS-CDMA by modelling the multiple access interference (MAI) as aGaussian process, as well as an improved Gaussian process.
Abstract: The authors analyse the performance of uncoded and coded asynchronous DS-CDMA systems over multipath fading channels. The fading-channel model adopted is a general one; by varying the parameters it is possible to model Rician or Rayleigh fading. Using these fading models, the authors developed the probability of bit error for the asynchronous DS-CDMA by modelling the multiple access interference (MAI) as a Gaussian process, as well as an improved Gaussian process. For coded systems, they investigated the effect of bit-to-bit dependence, due to the MAI, and fading within a codeword on the computation of the probability of bit error.
Journal Article•
TL;DR: A detection technique for continuous phase modulation (CPM) that employs decision feedback carrier recovery and adaptive channel estimation and shows a substantial reduction of the error floor relative to that of differential detection.
Abstract: Differential detection techniques, which are commonly used in fast fading environments, are characterized by an irreducible error rate that increases with fading rate. The main source of this error floor is the phase error introduced by the multiplicative fading process. The paper describes a detection technique for continuous phase modulation (CPM) that employs decision feedback carrier recovery and adaptive channel estimation. This receiver was evaluated by software simulation and the results show a substantial reduction of the error floor relative to that of differential detection. Furthermore, in additive white Gaussian noise (AWGN) channels, the adaptive nature of the receiver allows it to perform close to ideal coherent detection of differentially encoded phase shift keying (DE-CPSK). >
TL;DR: Capacity and power control issues are considered for urban CDMA microcells that operate on channels characterized by log-normal shadowing and Nakagami fading, and it is shown that the reverse channel is relatively insensitive, and the forward channel very sensitive, to shadow and fading variations.
Abstract: Capacity and power control issues are considered for urban CDMA microcells that operate on channels characterized by log-normal shadowing and Nakagami fading. The effects of fading on the desired and interfering signals, variations in the shadow standard deviation, imperfect power control, and the required E_b / N_o for satisfactory link operation are investigated. It is shown that the reverse channel is relatively insensitive, and the forward channel very sensitive, to shadow and fading variations. Power control error is shown to significantly degrade reverse channel capacity. Two biased forward channel power control strategies are introduced to enhance existing unbiased balancing forward channel power control algorithms.
09 May 1995
TL;DR: This scheme relies on a multiuser Viterbi algorithm that incorporates an adaptive estimation of the overall channel impulse responses, given by the convolution of the signature sequences of the users and corresponding physical channels impulse responses.
Abstract: Multiuser detection in code division multiple access systems usually requires either knowledge of the transmitted signature sequences and channel state information or use of a known training sequence for adaptation. We develop a scheme that can be employed for the joint adaptive blind multiuser identification and detection in asynchronous CDMA systems. This scheme relies on a multiuser Viterbi algorithm that incorporates an adaptive estimation of the overall channel impulse responses, given by the convolution of the signature sequences of the users and corresponding physical channels impulse responses. Once the overall channel responses are estimated, the blind multiuser detection algorithm performs like the maximum-likelihood sequence estimator. Results are provided to illustrate the convergence of the blind multiuser approach, near-far resistance and sensitivity to the algorithm initialization.
TL;DR: In this article, a matched filter bound (MFB) analysis is presented, in which the normalised Doppler rate is unrestricted, and thus applicable to OFDM signalling.
Abstract: A matched filter bound (MFB) analysis is presented, in which the normalised Doppler rate is unrestricted, and thus applicable to OFDM signalling. In contrast to the static channel case, the optimal matched filter receiver is shown to be time varying and the probability of error is shown to depend on the transmitted pulse shape.
TL;DR: A new formula is derived to determine the symbol error rate of MPSK scheme under Rician fading channels and the results are compared with a perfect carrier-referenced system.
Abstract: In order to combat the effects of channel fading, a pilot symbol-aided modulation based on fading time correlation has been proposed. In this paper we present results of analytical studies on this technique which were not included in previous works. We derive a new formula to determine the symbol error rate of MPSK scheme under Rician fading channels. The results are compared with a perfect carrier-referenced system. Computer simulations are also carried out to verify the analytical results. >
TL;DR: Simulation results show that the proposed subband multistage vector quantization coding technique, SB-MSVQ, is very robust to channel fading errors even at a very low channel power, whereas the baseline JPEG suffers fromChannel fading errors which are visually very annoying.
Abstract: A subband multistage vector quantization (SB-MSVQ) coding technique is proposed for wireless image communication. The Digital European Cordless Telecommunications (DECT) system has been used as a wireless communication environment. The impact of channel fading on the SB-MSVQ coding technique is investigated and its performance is compared with that of the baseline JPEG standard. Simulation results show that the proposed technique, SB-MSVQ, is very robust to channel fading errors even at a very low channel power, whereas the baseline JPEG suffers from channel fading errors which are visually very annoying. Due to the inherent structure of SB-MSVQ, the important low frequency information of an image is packed into a small portion of the encoded data. If this portion is received intact by the SB-MSVQ decoder, the overall quality degradation of the reconstructed image is marginal. >
06 Nov 1995
TL;DR: Through computer simulations, it is shown that the proposed system with (7,4) block code, 7-carriers and 7-antennas achieves 15 dB improvement in a slow fading channel compared with a time interleaving system.
Abstract: In this paper, we describe a prediversity (diversity at transmitter) scheme using coding, multi-carriers and multi-antennas designed for fading channels. Burst errors occur frequently in the Rayleigh flat fading mobile channel. To solve this kind of problem, the time interleaving technique has been utilized. However it can not deal with slow fadings, and has a long processing delay. Our proposal requires no time delay and provides a fixed BER characteristic not only for a slow fading but also for a fast fading channel. We derive an upper-bound for the BER. Through computer simulations, we show that the proposed system with (7,4) block code, 7-carriers and 7-antennas achieves 15 dB improvement in a slow fading channel (Doppler frequency f/sub D/=10 Hz) compared with a time interleaving system. As another application, we apply the pre-diversity technique to normal MPSK post-diversity system using trellis code.
17 Sep 1995
TL;DR: A maximum a posteriori (MAP) receiver using coherent detection is presented for binary PAM signals and a first order finite Markov chain model (HMM) that statistically characterizes the Nakagami-m fading process is used to aid the channel estimation.
Abstract: Signalling over Rayleigh fading channels can be classed as a general Gaussian problem. Optimal linear filtering can then be applied to jointly estimate the channel and detect the information sequence. For fading channels with non-Gaussian distributions, optimal linear filtering does not necessarily yield the best channel estimates. To exploit the channel memory, a first order finite Markov chain model (HMM) that statistically characterizes the Nakagami-m fading process is used to aid the channel estimation. Based on this, a maximum a posteriori (MAP) receiver using coherent detection is presented for binary PAM signals.
TL;DR: It is shown that the proposed error control scheme offers excellent throughput performance and the new scheme maintains its efficiency over a very broad range of signal-to-noise ratios.
Abstract: A concatenated two-stage adaptive error control scheme with automatic repeat request (ARQ) has been developed which is especially suitable for severely fading channels and for a very broad range of signal-to-noise ratios. This new scheme uses two stages of adaptive coding: the inner code is a rate compatible binary block code which due to its short blocklength can be maximum likelihood decoded taking into account soft-decisions and channel state information. For retransmissions code combining can be used. The outer code is a Reed-Solomon code which is maximum-distance separable and can correct error bursts as well as erasures indicated by the inner decoder. No interleaving is necessary and no critical optimization of system parameters is required to adapt to different channels and signal-to-noise ratios. In the paper, the scheme is described in detail and its throughput efficiency is analyzed. Also, simulation results for the throughput in the Gaussian and in the Rayleigh channel are presented. It is shown that the proposed error control scheme offers excellent throughput performance. Compared to other schemes, the new scheme maintains its efficiency over a very broad range of signal-to-noise ratios. >
TL;DR: A simple, robust processing strategy, called the fading magnitude-integrate sample and dump (FM-ISD) processor, is proposed for use with limiter-discriminator detection of CPM signals in Rayleigh, fast fading channels.
Abstract: A simple, robust processing strategy, called the fading magnitude-integrate sample and dump (FM-ISD) processor, is proposed for use with limiter-discriminator detection of CPM signals in Rayleigh, fast fading channels. The FM-ISD processor is introduced as a simplification of an optimal estimator-correlator receiver. The performance is compared to a standard integrator processor and found to provide an improvement in performance for all values of signal-to-noise ratio. The FM-ISD processor is also shown to be robust to changes in modulation format, channel fading rate and pre-detection filter type. >
TL;DR: This paper presents a fundamental approach for deriving the bit error probability of BDPSK and QDPSK over the nonselective Rayleigh fading channel for a receiver with an arbitrary IF filter, and for a fading process with a small Doppler bandwidth compared to the symbol rate.
Abstract: This paper presents a fundamental approach for deriving the bit error probability of BDPSK and QDPSK over the nonselective Rayleigh fading channel for a receiver with an arbitrary IF filter, and for a fading process with an arbitrary Doppler spectrum with arbitrary Doppler bandwidth. The results generalize those published earlier which were restricted to matched filter reception and to a fading process with a small Doppler bandwidth compared to the symbol rate. This allows the error probability to be studied in the presence of varying degrees of ISI due to the bandlimitation of the received signal by the IF filter, and in the presence of fading fluctuations of various rates. The analytical approach presented is simple, and yet powerful in that it can handle the case of diversity reception. This is a great advantage over the alternative approach of using the distribution of the differential phase of the received signal over a symbol interval. The bit error probability results apply to both conventional BDPSK and QDPSK, as well as /spl pi//2-2DPSK and /spl pi//4-4DPSK, and allow the irreducible bit error probability as well as the SNR at which this irreducible value sets in to be studied as a function of the Doppler bandwidth and IF filter bandwidth. The computed results are applicable to the design of digital cellular mobile communication systems.
01 Jan 1995
TL;DR: The results show the penalty imposed by imperfect channel estimation, as well as the fading-induced irreducible error rates, in the special case when a Kalman filter is used as an optimal channel estimator.
Abstract: A coherent receiver with a decision-feedback equalizer (DFE) operating on a Rayleigh fading channel under a suitable adaptive algorithm is considered. In the analysis of a DFE, a common assumption is that the receiver has perfect knowledge of the channel impulse response. However, this is not the case in practice, and for a rapidly fading channel, errors in channel tracking can become significant. We analyze theoretically the impact of these errors on the performance of a multichannel DFE. The expressions obtained for the achievable average MPSK bit error probabilities depend on the estimation error covariance. In order to specify this matrix, we focus on a special case when a Kalman filter is used as an optimal channel estimator. In this case, the probability of bit error can be assessed directly in terms of channel fading model parameters, the most interesting of which is the fading rate. Our results show the penalty imposed by imperfect channel estimation, as well as the fading-induced irreducible error rates. >
TL;DR: The emphasis in this paper is on the performance of trellis coded M-ary QAM combined with PRS in the fading environment and the bit error probability upper bounds of the proposed 6QPR-TCM and 9QPR -TCM systems are better than their counterparts the 4QAM- TCM systems with 2 and 4 states, respectively, for SNR values greater than a threshold, which have the best error performances in the literature.
Abstract: In order to improve the bandwidth efficiency and error performance, partial response signaling (PRS) and trellis coded modulation (TCM) are combined together. This method is named QPR-TCM. Whereas previous contributions have considered the performance of TCM transmitted over an additive white Gaussian noise (AWGN) channel, the emphasis in this paper is on the performance of trellis coded M-ary QAM combined with PRS in the fading environment. We only consider the case where interleaving/deinterleaving is employed to further combat the fading and assume that the ideal channel state information (CSI) is available. Analytical upper bounds are derived using the well known transfer function bounding technique, the bandwidth efficiencies are computed and the numerical results for several practical schemes are compared to each other. One interesting result is that when the combined system is used on a Rician fading channel, the bit error probability upper bounds of the proposed 6QPR-TCM and 9QPR-TCM systems are better than their counterparts the 4QAM-TCM systems with 2 and 4 states, respectively, for SNR values greater than a threshold, which have the best error performances in the literature. >
TL;DR: This paper extends the performance analysis of joint maximum-likelihood sequence estimation for trellis-coded modulation systems to general fading processes by considering the correlation function of the time-variant channel impulse response instead of assuming constant fading.
Abstract: In the literature the performance of joint maximum-likelihood sequence estimation for trellis-coded modulation systems was analyzed under the assumption that fading is so slow that the channel does not change during all error events. In this paper we extend the performance analysis to general fading processes by considering the correlation function of the time-variant channel impulse response instead of assuming constant fading. An easily evaluated closed-form upper bound is derived for the pairwise error probability. The bit error rate is then estimated by using a truncated union bound. Computer simulations show that our analytical results are good for all cases considered especially when diversity reception is used. >
17 May 1995
TL;DR: A first order vector Markov chain model is used to represent the frequency selective Rayleigh fading process and a suboptimum receiver based on the MarkovChain model is given.
Abstract: Multipath fading is a random process with memory. This memory can be exploited by using a Markov chain model and can be used in the estimation of the fading process. In the paper, a first order vector Markov chain model is used to represent the frequency selective Rayleigh fading process. A suboptimum receiver based on the Markov chain model is then given.
17 Sep 1995
TL;DR: New linear symbol-spreading strategies for efficient single- and multi-user communication in environments subject to fading due to time-varying multipath are introduced and significantly reduce the computation required to achieve a prescribed level of performance.
Abstract: New linear symbol-spreading strategies for efficient single- and multi-user communication in environments subject to fading due to time-varying multipath are introduced. For given power, bandwidth, and delay constraints, these new systems significantly reduce the computation required to achieve a prescribed level of performance. Several aspects of these systems and their performance are developed.
Patent•
27 Jun 1995TL;DR: In this paper, a functional unit (50) which produces a correlative estimate (h') of the coefficients of the channel impulse response, feeds another unit (52) which performs an iteration to obtain an improved estimate and optionally a channel state information signal (CSI).
Abstract: The method samples and stores the course of the training signal at the receiving end, at specific times. An estimated impulse response or transfer function of the channel is then deduced. The discrepancy between measured and calculated values is worked out and the estimate is varied in steps until the discrepancy is minimised. A functional unit (50) which produces a correlative estimate (h') of the coefficients of the channel impulse response, feeds another unit (52). This unit performs an iteration to obtain an improved estimate (h") and optionally a channel state information signal (CSI).
TL;DR: The performance of these combining methods in fading is compared with that in AWGN and multitone interference to determine which methods are effective against these degradations.
Abstract: Frequency hopping (FH) spread spectrum is a well known technique used in communications systems to provide protection against interference such as jamming. With fast FH (FFH) (one or more hops per transmitted data symbol), powerful and robust methods for diversity combining have been developed as an additional jamming countermeasure. These same techniques can be applied to reduce the effects of multiple access interference, and so can be considered for civilian CDMA applications. Although the performance of a FFH communications system can be degraded considerably by fading, few results exist which show the effects of fading on the diversity combining process. In this paper, both analytic and simulation results are presented for several diversity combining methods in a Rayleigh fading channel, which is often considered to be the worst case. The performance of these combining methods in fading is compared with that in AWGN and multitone interference to determine which methods are effective against these degradations.