Showing papers on "Channel state information published in 1998"
TL;DR: This paper describes the statistical models of fading channels which are frequently used in the analysis and design of communication systems, and focuses on the information theory of fading channel, by emphasizing capacity as the most important performance measure.
Abstract: In this paper we review the most peculiar and interesting information-theoretic and communications features of fading channels. We first describe the statistical models of fading channels which are frequently used in the analysis and design of communication systems. Next, we focus on the information theory of fading channels, by emphasizing capacity as the most important performance measure. Both single-user and multiuser transmission are examined. Further, we describe how the structure of fading channels impacts code design, and finally overview equalization of fading multipath channels.
2,017 citations
TL;DR: A minimum mean-square-error (MMSE) channel estimator is derived, which makes full use of the time- and frequency-domain correlations of the frequency response of time-varying dispersive fading channels and can significantly improve the performance of OFDM systems in a rapid dispersion fading channel.
Abstract: Orthogonal frequency-division multiplexing (OFDM) modulation is a promising technique for achieving the high bit rates required for a wireless multimedia service. Without channel estimation and tracking, OFDM systems have to use differential phase-shift keying (DPSK), which has a 3-dB signal-to-noise ratio (SNR) loss compared with coherent phase-shift keying (PSK). To improve the performance of OFDM systems by using coherent PSK, we investigate robust channel estimation for OFDM systems. We derive a minimum mean-square-error (MMSE) channel estimator, which makes full use of the time- and frequency-domain correlations of the frequency response of time-varying dispersive fading channels. Since the channel statistics are usually unknown, we also analyze the mismatch of the estimator-to-channel statistics and propose a robust channel estimator that is insensitive to the channel statistics. The robust channel estimator can significantly improve the performance of OFDM systems in a rapid dispersive fading channel.
1,039 citations
TL;DR: Very high diversity orders can be achieved and this results in an almost Gaussian performance over the fading channel, this multidimensional modulation scheme is essentially uncoded and enables one to trade diversity for system complexity, at no power or bandwidth expense.
Abstract: The increasing need for high data-rate transmissions over time- or frequency-selective fading channels has drawn attention to modulation schemes with high spectral efficiency such as QAM. With the aim of increasing the "diversity order" of the signal set we consider multidimensional rotated QAM constellations. Very high diversity orders can be achieved and this results in an almost Gaussian performance over the fading channel, This multidimensional modulation scheme is essentially uncoded and enables one to trade diversity for system complexity, at no power or bandwidth expense.
1,030 citations
TL;DR: An iterative decoding algorithm for any product code built using linear block codes based on soft-input/soft-output decoders for decoding the component codes so that near-optimum performance is obtained at each iteration.
Abstract: This paper describes an iterative decoding algorithm for any product code built using linear block codes. It is based on soft-input/soft-output decoders for decoding the component codes so that near-optimum performance is obtained at each iteration. This soft-input/soft-output decoder is a Chase decoder which delivers soft outputs instead of binary decisions. The soft output of the decoder is an estimation of the log-likelihood ratio (LLR) of the binary decisions given by the Chase decoder. The theoretical justifications of this algorithm are developed and the method used for computing the soft output is fully described. The iterative decoding of product codes is also known as the block turbo code (BTC) because the concept is quite similar to turbo codes based on iterative decoding of concatenated recursive convolutional codes. The performance of different Bose-Chaudhuri-Hocquenghem (BCH)-BTCs are given for the Gaussian and the Rayleigh channel. Performance on the Gaussian channel indicates that data transmission at 0.8 dB of Shannon's limit or more than 98% (R/C>0.98) of channel capacity can be achieved with high-code-rate BTC using only four iterations. For the Rayleigh channel, the slope of the bit-error rate (BER) curve is as steep as for the Gaussian channel without using channel state information.
970 citations
07 Jun 1998
TL;DR: A minimum mean-square-error (MSE) channel estimator is derived, which makes full use of the time- and frequency-domain correlations of the frequency response of time-varying dispersive fading channels and can significantly improve the performance of OFDM systems in a rapid dispersion fading channel.
Abstract: Orthogonal frequency division multiplexing (OFDM) modulation is a promising technique for achieving the high-bit-rates required for a wireless multimedia service. Without channel estimation and tracking, OFDM systems have to use differential phase-shift keying (DPSK), which has a 3 dB signal-to-noise ratio (SNR) loss compared with coherent phase-shift keying (PSK). To improve the performance of OFDM systems by using coherent PSK, we investigate robust channel estimation for OFDM systems. We derive a minimum mean-square-error (MSE) channel estimator, which makes full use of the time- and frequency-domain correlations of the frequency response of time-varying dispersive fading channels. Since the channel statistics are usually unknown, we also analyze the mismatch of the estimator to channel statistics and propose a robust channel estimator that is insensitive to the channel statistics. The robust channel estimator can significantly improve the performance of OFDM systems in a rapid dispersive fading channel.
675 citations
16 Aug 1998
TL;DR: It is shown that variable-rate coding is not needed to achieve capacity and, even when the CSIT is not perfect, the capacity achieving power allocation is of the waferfilling type.
Abstract: We study the capacity of some channels whose conditional output probability distribution depends on a state process independent of the channel input and where channel state information (CSI) signals are available both at the transmitter (CSIT) and at the receiver (CSIR). When the channel state and the CSI signals are jointly independent and identically distributed (i.i.d.), the channel reduces to a case studied by Shannon (1958). In this case, we show that when the CSIT is a deterministic function of the CSIR, optimal coding is particularly simple. When the state process has memory, we provide a general capacity formula and we give some more restrictive conditions under which the capacity has still a simple single-letter characterization, allowing simple optimal coding. Finally, we turn to the additive white Gaussian noise (AWGN) channel with fading and we provide a generalization of some results about capacity with CSI for this channel. In particular, we show that variable-rate coding (or multiplexing of several codebooks) is not needed to achieve capacity and, even when the CSIT is not perfect, the capacity achieving power allocation is of the waferfilling type.
545 citations
05 Oct 1998
TL;DR: The effect of fading correlations in multi-element antenna (MEA) communication systems is investigated and it is shown that the MEA capacity can be expressed as the sum of the capacities of several subchannels, whose gains are affected by the fading correlation.
Abstract: We investigate the effect of fading correlations in multi-element antenna (MEA) communication systems. The enormous capacity of an MEA system can potentially be reduced by fading correlation. To model the narrowband Rayleigh-fading multipath environment, we propose an abstract model. Using this model, the fading statistics can be determined from the geometrical parameters of the MEA and the multipath environment. This, model allows us to directly observe how the choice of antenna geometry affects capacity. We show that the MEA capacity can be expressed as the sum of the capacities of several subchannels, whose gains are affected by the fading correlation. As the fading correlation becomes higher, the disparity between the gains of these subchannels becomes larger and as a result some of the subchannels do not convey information at any significant rate.
510 citations
TL;DR: It is shown that successive decoding is optimal, and the optimal decoding order and power allocation can be found explicitly as a function of the fading states; this is a consequence of an underlying polymatroid structure that is exploited.
Abstract: For pt.I see ibid., vol.44, no.7, p.2796-815 (1998). In multiaccess wireless systems, dynamic allocation of resources such as transmit power, bandwidths, and rates is an important means to deal with the time-varying nature of the environment. We consider the problem of optimal resource allocation from an information-theoretic point of view. We focus on the multiaccess fading channel with Gaussian noise, and define two notions of capacity depending on whether the traffic is delay-sensitive or not. In the present paper, we introduce a notion of delay-limited capacity which is the maximum rate achievable with delay independent of how slow the fading is. We characterize the delay-limited capacity region of the multiaccess fading channel and the associated optimal resource allocation schemes. We show that successive decoding is optimal, and the optimal decoding order and power allocation can be found explicitly as a function of the fading states; this is a consequence of an underlying polymatroid structure that we exploit.
501 citations
TL;DR: The theory and practice of a new advanced modem technology suitable for high-data-rate wireless communications and its performance over a frequency-flat Rayleigh fading channel are presented and it is concluded that STCM can provide significant SNR improvement over simple delay diversity.
Abstract: This paper presents the theory and practice of a new advanced modem technology suitable for high-data-rate wireless communications and presents its performance over a frequency-flat Rayleigh fading channel. The new technology is based on space-time coded modulation (STCM) with multiple transmit and/or multiple receive antennas and orthogonal pilot sequence insertion (O-PSI). In this approach, data is encoded by a space-time (ST) channel encoder and the output of the encoder is split into N streams to be simultaneously transmitted using N transmit antennas. The transmitter inserts periodic orthogonal pilot sequences in each of the simultaneously transmitted bursts. The receiver uses those pilot sequences to estimate the fading channel. When combined with an appropriately designed interpolation filter, accurate channel state information (CSI) can be estimated for the decoding process. Simulation results of the proposed modem, as applied to the IS-136 cellular standard, are presented. We present the frame error rate (FER) performance results as a function of the signal-to-noise ratio (SNR) and the maximum Doppler frequency, in the presence of timing and frequency offset errors. Simulation results show that for a 10% FER, a 32-state eight-phase-shift keyed (8-PSK) ST code with two transmit and two receive antennas can support data rates up to 55.8 kb/s on a 30-kHz channel, at an SNR of 11.7 dB and a maximum Doppler frequency of 180 Hz. Simulation results for other codes and other channel conditions are also provided. We also compare the performance of the proposed STCM scheme with delay diversity schemes and conclude that STCM can provide significant SNR improvement over simple delay diversity.
445 citations
TL;DR: It is shown that a Markov approximation for the block error process is a good model for a broad range of parameters, and the relationship between the marginal error rate and the transition probability is largely insensitive to parameters such as block length, degree of forward error correction and modulation format.
Abstract: We investigate the behavior of block errors which arise in data transmission on fading channels. Our approach takes into account the details of the specific coding/modulation scheme and tracks the fading process symbol by symbol. It is shown that a Markov approximation for the block error process (possibly degenerating into an identically distributed (i.i.d.) process for sufficiently fast fading) is a good model for a broad range of parameters. Also, it is observed that the relationship between the marginal error rate and the transition probability is largely insensitive to parameters such as block length, degree of forward error correction and modulation format, and depends essentially on an appropriately normalized version of the Doppler frequency. This relationship can therefore be computed in the simple case of a threshold model and then used more generally as an accurate approximation. This observation leads to a unified approach for the channel modeling, and to a simplified performance analysis of upper layer protocols.
277 citations
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.
16 Aug 1998
TL;DR: This work model time-varying channels as finite-state Markov channels and determine their capacity as a function of the feedback delay assuming perfect channel state information at the receiver, and applies the result to derive power control strategies to maximize the capacity for finite- state additive Gaussian noise channels and log-normal shadow fading channels.
Abstract: While feedback does not increase the capacity of memoryless channels, the capacity of time-varying channels with feedback can be increased by exploiting the structure in the channel variations. Feedback information from the receiver is usually available at the transmitter only after some time delay. The capacity increase due to feedback depends on the feedback delay relative to the channel decorrelation time. We model time-varying channels as finite-state Markov channels and determine their capacity as a function of the feedback delay assuming perfect channel state information at the receiver. We apply the result to derive power control strategies to maximize the capacity for finite-state additive Gaussian noise channels and log-normal shadow fading channels.
TL;DR: This paper is a tutorial on the calculation of error probabilities for fading channels through the evaluation of the Laplace transform Φ Δ (s) of the probability density function of the difference A between the metrics of two competing signal sequences.
Abstract: This paper is a tutorial on the calculation of error probabilities for fading channels.The method we advocate is centered on the evaluation of the Laplace transform Φ Δ (s) of the probability density function of the difference A between the metrics of two competing signal sequences. In some cases, knowledge of the function Φ Δ (s) allows one to determine error probabilities exactly in closed form, or asymptotically as the signal-to-noise ratio grows to infinity. The general technique that we describe here allows their computation in numerical form to any desired degree of accuracy. Coded as well as uncoded transmission can be considered in this unified framework. For illustration's sake, some examples of calculations are provided for frequency-flat slow-fading channels in which coherent detection is used, and the channel state information is perfect, or unavailable, or obtained from a noisy pilot tone.
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.
16 Aug 1998
TL;DR: It is shown that successive decoding is optimal, and the optimal decoding order and power allocation can be found explicitly as a function of the fading states; this is a consequence of an underlying polymatroid structure that is exploited.
Abstract: We consider the multi-access, white-noise, fading channel, and introduce a notion of delay-limited capacity, which is the maximum rate achievable with delay independent of how slow the fading is. We characterize the delay-limited capacity region and the associated optimal power allocation schemes. We show that successive decoding is optimal, and the optimal decoding order and power allocation can be found explicitly as a function of the fading states; this is a consequence of an underlying polymatroid structure that we exploit.
08 Nov 1998
TL;DR: This paper applies and modify the ROOT-MUSIC algorithm to model and further predict the complex fading process and concludes that the proposed approach may find many applications to improve a system's performance under fast fading situations.
Abstract: Fast fading is a major difficulty for wireless systems operating at higher and higher carrier frequencies. As suggested by the Jakes (1974) fading simulation model, fading processes due to multipath propagation can be, by nature, modeled in baseband as a combination of multiple complex superimposed sinusoids. In this paper, starting with the observation of a flat faded and noise corrupted baseband modulated signal, we apply and modify the ROOT-MUSIC algorithm to model and further predict the complex fading process. The modeling/prediction performance is evaluated by both simulated and real-world fading data. It is shown that short-term prediction is feasible, and we conclude that the proposed approach may find many applications to improve a system's performance under fast fading situations.
05 Oct 1998
TL;DR: Two new detection methods for the simple transmit diversity scheme proposed by Alamouti are presented, requiring no channel state information at either the transmitter or the receiver.
Abstract: We present two new detection methods for the simple transmit diversity scheme proposed by Alamouti (see IEEE Journal on Selected Areas of Communications, Special Issue on Signal Processing for Wireless Communications, 1998). The new detection schemes require no channel state information at either the transmitter or the receiver. Using 2 transmit antennas and 1 receive antenna, the scheme provides a diversity order of two. Simulations have been included to show that the scheme has almost a 3 dB penalty compared to coherent detection.
Patent•
23 Mar 1998TL;DR: In this paper, a channel quality estimator determines and evaluates the bit error rate (BER) of a signal on a control channel and estimates the quality of the traffic channel based on the QoS of the control channel signal.
Abstract: A method and apparatus for effectively monitoring quality of a traffic channel in a communication, and in response, modifying transmission coding or data transmission rates, or both, improves communication quality and increases data transfers rates in digital wireless communication systems. A channel quality estimator determines and evaluates the bit error rate (BER) of a signal on a control channel and estimates the quality of the traffic channel based on the quality of the control channel signal. Accordingly, the processing and control circuitry of either a mobile station or base station adjusts the error correction applied to traffic channel transmissions. The traffic channel data transmission rate may also be modified based on the control channel signal quality.
01 Jun 1998
TL;DR: Difficulties in using the Suzuki PDF to predict system behaviour, in particular bit error rate (BER), are presented, and the use of the generalised gamma PDF is recommended.
Abstract: Probability distribution functions (PDFs) are discussed for characterising narrowband fading processes in mobile radio communications. In particular, the effects of short-term channel variations (fast fading), and longer term channel variations (shadow fading) are discussed in relation to commonly used PDFs. A channel model is proposed to represent the mixture of these processes, and is shown to be well represented by the Suzuki PDF. Difficulties in using the Suzuki PDF to predict system behaviour, in particular bit error rate (BER), are presented, and the use of the generalised gamma PDF is recommended. It is shown that this PDF represents channel behaviour as well as the Suzuki PDF, and that it is much more convenient for BER prediction. The accuracy of BER prediction using this PDF is demonstrated by computer simulation of digital radio transmission over Suzuki fading channels.
TL;DR: An enhanced version of the access protocol to take advantage of the memory in the fading channel behavior is proposed and analyzed and the Markovian-fading channel model is shown to provide better performance results than the i.i.d. channel model.
Abstract: The throughput performance of a wireless media access protocol taking into account the effect of correlated channel fading, capture, and propagation delay is analyzed. For efficient access on the uplink (mobile-to-base-station link), the protocol makes use of the uplink channel status information which is conveyed to the mobiles through a busy/idle flag broadcast on the downlink (base-station-to-mobile link). A first-order Markov model is used to describe the correlation in the packet success/failure process on a Rayleigh-fading channel. The analytical results obtained through the first-order Markov approximation of the channel are compared to those obtained from an independent and identically distributed (i.i.d.) channel model. The Markovian-fading channel model is shown to provide better performance results than the i.i.d. channel model. Simulations show that a first-order Markov approximation of the Rayleigh-fading process is quite accurate. An enhanced version of the access protocol to take advantage of the memory in the fading channel behavior is proposed and analyzed. The effect of retransmission of erroneous data packets and propagation delay on the throughput is also analyzed. It is shown that the access protocol with an error detect (ED) feature is efficient in slow fading (e.g., pedestrian user speeds), whereas a retransmission protocol is more efficient in fast fading (e.g., vehicular user speeds).
TL;DR: This work considers the problem of still image transmission over time-varying channels with the channel state information (CSI) available at (1) receiver only and (2) both transmitter and receiver being informed about the state of the channel, and quantifies the effect of CSI availability on the performance.
Abstract: We explore joint source-channel coding (JSCC) for time-varying channels using a multiresolution framework for both source coding and transmission via novel multiresolution modulation constellations. We consider the problem of still image transmission over time-varying channels with the channel state information (CSI) available at (1) receiver only and (2) both transmitter and receiver being informed about the state of the channel, and we quantify the effect of CSI availability on the performance. Our source model is based on the wavelet image decomposition, which generates a collection of subbands modeled by the family of generalized Gaussian distributions. We describe an algorithm that jointly optimizes the design of the multiresolution source codebook, the multiresolution constellation, and the decoding strategy of optimally matching the source resolution and signal constellation resolution "trees" in accordance with the time-varying channel and show how this leads to improved performance over existing methods. The real-time operation needs only table lookups. Our results based on a wavelet image representation show that our multiresolution-based optimized system attains gains on the order of 2 dB in the reconstructed image quality over single-resolution systems using channel optimized source coding.
Patent•
AT&T1
TL;DR: In this article, a robust channel estimator that is insensitive to the channel statistics is provided, which can significantly improve the performance of a multicarrier system such as an OFDM modulation system in a rapid dispersive fading channel.
Abstract: A method and apparatus provide channel estimation for multicarrier systems. A minimum mean-square-error (MMSE) channel estimator makes full use of time-and frequency-domain correlations of the frequency response of time-varying dispersive fading channels. A robust channel estimator that is insensitive to the channel statistics is provided. The robust channel estimator can significantly improve the performance of a multicarrier system such as an orthogonal frequency division multiplexing (OFDM) modulation system in a rapid dispersive fading channel. In addition, the estimation process can employ a new reference generator which can select the source of the reference signal as being a decoded or undecoded signal depending on the correction success rate of the decoder.
TL;DR: An efficient method to concurrently optimize a multiplicity of design variables for continuous selective-repeat (SR) and go-back-N (GBN) automatic repeat request (ARQ) strategies, both in noiseless and noisy feedback channels is outlined.
Abstract: This paper outlines an efficient method to concurrently optimize a multiplicity of design variables for continuous selective-repeat (SR) and go-back-N (GBN) automatic repeat request (ARQ) strategies, both in noiseless and noisy feedback channels. For these ARQ protocols, we adapt either the number of identical message blocks sent in each transmission (in the case of GBN scheme) or the number of copies of a block retransmitted to handle a NACKed codeword (for the SR protocol) dynamically to the estimated channel condition. The channel state information is obtained by counting the contiguous acknowledgment (ACK or NACK) messages. Exploiting the asymptotic properties of the steady state probability expressions, we show analytically that the optimum solution indeed lies in the infinite space. Subsequently, a simple expression to estimate the suboptimal design parameters is suggested. Our approach of minimizing the mean-square error function yields to a quantitative study of the appropriateness of the selected parameters. Exact analytical expressions that allows us to compute the throughput crossover probability between any two arbitrary multicopy transmission modes are derived. The results provide fundamental insights into how these key parameters interact and determine the system performance.
TL;DR: This paper focuses on the implementation and performance of a modified turbo decoder for the channel model of a slow frequency-hopped spread spectrum (FH-SS) system with partial band jamming and the calculation of branch transition probabilities inherent in the original turboDecoder.
Abstract: Turbo codes are investigated in a slow frequency-hopped spread spectrum (FH-SS) system with partial band jamming. In addition, full-band thermal noise is present. The channel model is that of a partial-band jammer in which a fraction of the frequency band is jammed and the remaining fraction is unjammed. This paper focuses on the implementation and performance of a modified turbo decoder for this model. We refer to the knowledge that each transmitted bit is jammed as channel state information. We consider cases of known or unknown channel state and variable number of bits per hop. Our approach is to modify the calculation of branch transition probabilities inherent in the original turbo decoder. For the cases with no side information and multiple bits per hop, we iteratively calculate channel state estimates. Analytical bounds are derived and simulation is performed for noncoherent demodulation. The performance of turbo codes is compared with a Reed-Solomon and a concatenated code comprised of a convolutional inner code and Reed-Solomon outer code.
18 May 1998
TL;DR: It is shown that channel interleaving is necessary on a correlated fading channel, and that the performance degrades as the product of fading bandwidth and symbol duration (BT/sub s/) decreases.
Abstract: This paper investigates the performance of a turbo coded system transmitting over correlated flat fading channels with channel interleaving and both perfect and estimated channel state information. We show that channel interleaving is necessary on a correlated fading channel, and that the performance degrades as the product of fading bandwidth and symbol duration (BT/sub s/) decreases. We consider both Rayleigh and Rician fading, and compare the performance of log-maximum a posteriori (log-MAP) and soft output Viterbi algorithm (SOVA) based decoding algorithms. It is shown that for fading channels, the performance of the log-MAP algorithm is considerably superior to that of the SOVA algorithm. A simple method for estimating the fading amplitudes and noise variance is proposed, and the impact of its use is investigated. It is shown that estimating the fades degrades the performance only slightly, and estimating the noise variance does not noticeably affect the performance.
TL;DR: A carrier-frequency offset estimator derived using maximum-likelihood techniques, designed for a digital space-diversity receiver, operating in a wide-band frequency-selective multipath fading channel, finds that, for most parameter configurations, there is approximately a factor of two improvement in the estimate error standard deviation when the antenna diversity is doubled.
Abstract: This paper describes a carrier-frequency offset estimator derived using maximum-likelihood techniques. The estimator is designed for a digital space-diversity receiver, operating in a wide-band frequency-selective multipath fading channel. The estimator is suited to a burst-mode time-division-multiple-access system, because the estimate is formed in an open-loop manner, and relies on a training sequence normally used in burst-mode systems. The main advantage is that it does not require channel state information; rather, it only requires knowledge of the auto-correlation of the channel. Simulation results show the estimator to be unbiased over a wide frequency range. The normalized error standard deviation is shown to be 0.0015 across the frequency offset range for a receiver with four diversity branches, when the normalized channel delay spread is 0.1, the signal-to-noise ratio (SNR) is 10 dB, and the training sequence length is 23 symbols. It is found that, for most parameter configurations, there is approximately a factor of two improvement in the estimate error standard deviation when the antenna diversity is doubled.
TL;DR: The aim is the derivation of Cramer-Rao lower bounds for the joint estimation of all those channel parameters that impact signal detection, namely, carrier phase, carrier frequency offset, frequency rate of change, signal amplitude, fading power, and Gaussian noise power.
Abstract: The context of this paper is parameter estimation for linearly modulated digital data signals observed on a frequency-flat time-selective fading channel affected by additive white Gaussian noise. The aim is the derivation of Cramer-Rao lower bounds for the joint estimation of all those channel parameters that impact signal detection, namely, carrier phase, carrier frequency offset (Doppler shift), frequency rate of change (Doppler rate), signal amplitude, fading power, and Gaussian noise power. Time-selective frequency-flat fading is modeled as a low-pass autoregressive multiplicative distortion process. In particular, the important case of "slow" fading, with the multiplicative process remaining constant over the whole data burst, is specifically discussed. Asymptotic expressions of the bounds, valid for a large observed sample or for high signal-to-noise ratio (SNR), are also derived in closed form. A few charts with numerical results are finally reported to highlight the dependence of the bounds on channel status (SNR, fading bandwidth, etc.).
17 Feb 1998
TL;DR: F fading measurements gathered for the indoor propagation channel at 2.4 GHz are presented and a statistical analysis of the measurements was undertaken and the obtained fading distributions, level crossing rates, and average duration of fades are presented.
Abstract: To design efficient modulation and error control schemes for wireless local area networks, characterisation of signal fading is required. In this paper, we present fading measurements gathered for the indoor propagation channel at 2.4 GHz. A statistical analysis of the measurements was undertaken and the obtained fading distributions, level crossing rates, and average duration of fades are presented and discussed.
TL;DR: A channel estimation technique suitable for turbo codes is presented, which uses pilot symbols to obtain initial channel estimates, and refines the estimates after each iteration of the turbo decoder.
Abstract: Channel state information is required for the coherent detection and decoding of turbo codes transmitted over flat-fading channels. A channel estimation technique suitable for turbo codes is presented. The technique uses pilot symbols to obtain initial channel estimates, and refines the estimates after each iteration of the turbo decoder.
08 Sep 1998
TL;DR: This paper develops a model for channel mismatch errors, analyzes their distribution, and derive analytic expressions for the probability of error of the system in the presence of these errors, and shows an improvement in performance over the conventional multicarrier system designs.
Abstract: Most multicarrier system designs assume perfect knowledge of the transmission channel. However in practice, the accuracy in channel identification is limited either by errors in channel estimation or by variations in the channel once it had been estimated. When not accounted for, these channel mismatch errors degrade the performance of our system and can lead to unacceptably high bit error rates. In this paper, we extend the existing multicarrier design concepts to systems with imperfect channel knowledge. We assume a Rayleigh fading channel, and study the impact of errors due to variations in the transmission channel. We develop a model for these errors, analyze their distribution, and derive analytic expressions for the probability of error of our system in the presence of these errors. We then extend the existing loading algorithms, taking into account the channel mismatch errors, and show the improvement in performance over the conventional multicarrier system designs.