Showing papers on "Channel state information published in 1991"

The land mobile satellite communication channel-recording, statistics, and channel model

Abstract: The communication channel between the MARECS satellite at 26 degrees W and a cruising van was measured and recorded in European areas exhibiting satellite elevations from 13 to 43 degrees . Different environments and mobile antennas were tested. The results of an extensive statistical evaluation include spectra of the fading amplitude; probability density, and distribution of the received signal power; and the percentage of time for fade and nonfade periods. Based on the physical phenomena of multipath fading and signal shadowing, an analog model of the land mobile satellite channel which can readily be used for software and hardware fading simulation is developed. The most important parameter of this model is the time-share of shadowing. The Rice factor which characterizes the channel during unshadowed periods, can vary from 3.9 to 18.1 dB. Block error probability density, error gap distribution, and block error probability are discussed. >

Computer models for fading channels with applications to digital transmission

Abstract: The authors describe computer models for Rayleigh, Rician, log-normal, and land mobile satellite fading channels. All computer models for the fading channels are based on the manipulation of a white Gaussian random process. This process is approximated by a sum of sinusoids with random phase angle. These models compare very well with analytical models in terms of their probability distribution of envelope and phase of the fading signal. For the land mobile satellite fading channel, results of level crossing rate and average fade duration are given. These results show that the computer models can provide a good coarse estimate of the time statistic of the faded signal. Also, for the land mobile satellite fading channel, the results show that a 3-pole Butterworth shaping filter should be used with the model. An example of the application of the land mobile satellite fading channel model to predict the performance of a differential phase-shift keying signal is described. >

Bit error probabilities MDPSK over the nonselective Rayleigh fading channel with diversity reception

Abstract: Data transmission using M-ary differential phase shift keying (MDPSK) over the nonselective Rayleigh fading channel with diversity reception is considered. While previous studies on error probability mostly assume no fading fluctuation, the author considers, exclusively, the case in which the fading process fluctuates from one symbol interval to the next. Exact bit error probability results for 2, 4, and 8 DPSK as well as tight upper bounds are derived. Some applications of the results are discussed. >

Optimal detection of digital data over the nonselective Rayleigh fading channel with diversity reception

Abstract: Based on the criterion of minimum symbol error probability, an analysis is made of symbol-by-symbol detection of a sequence of digital data transmitted using linear suppressed-carrier modulation over L independent diversity channels with AWGN (additive white Gaussian noise) and slow nonselective Rayleigh fading. The optimal receiver is derived, but is found to be difficult to implement in practice because of its exponential growth in complexity as a function of sequence length. Suboptimal decision-feedback approximations are then suggested which are linear and readily implementable and can be integrated as generalized differentially coherent receivers. The exact bit error probabilities of these suboptimal receivers are obtained. Tight upper bounds on these error probabilities are also obtained which show simply how they behave as a function of signal-to-noise ratio and order of diversity. A main conclusion of this work is that optimal data detection on a fading channel should be performed using MMSE (minimum mean squared error) estimates of the quadrature amplitudes of the channel fading processes as a coherent reference. >

Throughput estimation of ARQ protocols for a Rayleigh fading channel using fade- and interfade-duration statistics

Abstract: Error detection combined with automatic repeat request retransmission is used to provide reliable digital data transmission over a communication channel. The throughput for a system using go-back-N or selective-repeat protocols with Rayleigh fading in both directions of transmission is approximated by using fade- and interfade-duration statistics of a multipath channel. Results indicate that for a slow-fading channel (e.g. fading rate=1.34 Hz), the throughput of go-back-N is only slightly inferior to that of selective-repeat, mainly due to the burstiness of the channel bit errors. >

An investigation of channel estimation and equalization techniques for moderately rapid fading HF-channels

Abstract: Two basic schemes of channel estimation/prediction and decision-feedback equalization (DFE) for moderately rapid fading dispersive HF-channels are investigated. Simulation results show that non-adaptive adjustment of DFE coefficients by direct calculation from the estimated channel impulse response has the potential of being significantly more robust channel time variations than a DFE employing adaptive coefficient tracking. Receiver performance is now limited by the quality of the channel estimate rather than the equalizer's adaptive algorithm. An optimized state-of-the-art adaptive estimator/predictor featuring individual adaptation of channel coefficients is shown to recover part of the potential performance gain. >

A new 4-state 8PSK TCM scheme for fast fading, shadowed mobile radio channels

Abstract: The design of a 4-state, rate-2/3, 8PSK trellis-coded modulation (TCM) code, based on the design criteria for fading channels, is presented. To evaluate and compare the performance of this code with the other 4-state 8PSK TCM schemes presented in the literature, computer simulation is performed for a shadowed Rician fading channel. The simulation results show the superiority of the scheme for bit-error probabilities of 10/sup -3/ or less. This makes the code a suitable choice for both speech and data transmission over mobile fading channels. >

Performance of direct-sequence spread spectrum multiple-access systems in mobile radio

Abstract: The performance of coherent directsequence spread-spectrum multiple-access (DS/SSMA) communications over different mobile radio channels is investigated. Analytical techniques and numerical methods were used for a channel having a number of resolvable, discrete Rayleigh fading paths, while simulations were employed for transmissions over urban mobile radio channels. We found that even a flat Rayleigh fading channel caused a severe degradation in system performance compared with the additive white Gaussian noise channel, and that the system was unusable even for a few users when a wideband urban mobile radio channel was used. By transmitting a sounding sequence of chip length Ns = 511 to allow the receiver to estimate the channel impulse response, spreading the symbol over N = 127 chips, and on deploying fifth-order combinative space diversity equipped with adaptive correlation diversity of Kβ = 1.0 (CD/ACD), we were able to obtain a residual probability of bit error PR of less than 10−3 for 10 users, in spite of the urban mobile radio channel having 19 resolvable fading paths. By increasing N to 511 and deploying fifth-order maximal-ratio-combining (MRC) space diversity, a PR of 4 × 10−5 for 20 users was achieved when the radio channel consisted of 10 resolvable independent Rayleigh fading paths.

Fading channel simulator

Abstract: Fading channel effects on a transmitted communication signal are simulated with both frequency and time variations using a channel scattering function to affect the transmitted signal. A conventional channel scattering function is converted to a series of channel realizations by multiplying the square root of the channel scattering function by a complex number of which the real and imaginary parts are each independent variables. The two-dimensional inverse-FFT of this complex-valued channel realization yields a matrix of channel coefficients that provide a complete frequency-time description of the channel. The transmitted radio signal is segmented to provide a series of transmitted signal and each segment is subject to FFT to generate a series of signal coefficient matrices. The channel coefficient matrices and signal coefficient matrices are then multiplied and subjected to inverse-FFT to output a signal representing the received affected radio signal. A variety of channel scattering functions can be used to characterize the response of a transmitter-receiver system to such atmospheric effects.

Signal decoding method using both signal and channel state information

Abstract: Multilevel angle modulated information is decoded through integral use of channel state information. In a Viterbi Algorithm Trellis Code Modulation decoder (213), channel state information indicating temporal reliability of received symbols is utilized, along with the received symbol information and the Trellis Coding rules themselves, to facilitate a most probable symbol determination. The channel state information may be received signal strength indication information. The latter can be additionally processed by, for example, time delay compensation (401), normalization (403), morphological erosion (404), linearization (406), and/or through static channel detection (408).

Adaptive trellis coded modulation for mobile communications

Abstract: An adaptive scheme for trellis coded modulation of multiple phase shift keying (MPSK) signals, called adaptive trellis coded MPSK (ATCMPSK), is proposed for the Rayleigh fading channel. The adaptive scheme is based on varying the coding/modulation (codulation) rate according to channel conditions. Slow fading and ideal channel information at the receiver are assumed. It is shown that ATCMPSK results in a considerable improvement in bit error rate (BER) performance of MPSK signals under fading. >

Channel interpolation for digital mobile radio communications

Abstract: Digital cellular radio (DCR) communications occur over a fading multipath channel. In the case of low bit-rate, narrowband communications, a fast adaptive algorithm is required to track the rapid time variations in the DCR channel. The authors demonstrate the feasibility of a novel block-adaptive strategy which computes the time-varying channel impulse response (CIR) by interpolating a set of CIR estimates obtained through periodic training. Furthermore, they have discovered that channel tracking is limited by the CIR estimation noise rather than by the CIR interpolation. >

Fading memory and necessity of the small gain theorem

Abstract: The authors consider fading memory for nonlinear time-varying systems and associated problems of robust stability. They establish notation, state some preliminary results, and consider the fading memory property. Uniform and pointwise fading memory are defined. The focus is on the differences between pointwise and uniform fading memory, and conditions are provided for an operator to have pointwise fading memory. Previous results showing that the small-gain theorem is necessary for robust stability of fading memory nonlinear systems are generalized. These results are applied to a robust stabilization problem. Conditions are presented under which a closed-loop system exhibits fading memory. >

Error-rate performance of block-coded M-ary modulation and hard decision decoding systems on rayleigh fading channel

Abstract: Error rates of block-coded MPSK and/or MQAM systems with hard-decision decoding are evaluated theoretically on the Rayleigh fading channel characterizing the land mobile channel. BCH codes are employed as the block codes and analysis is carried out both for nondiversity reception and for dual MRC diversity reception. It is shown that on the Rayleigh fading channel, in contrast to the AWGN channel, BCH-coded MPSK systems can achieve significant coding gain compared to uncoded BPSK even in the hard-decision decoding case without changing spectral efficiency. It is shown also that diversity reception is needed for sufficient large coding gain in higher spectral efficiency. Moreover, it is suggested that the code length longer than a threshold is necessary for large coding gain under the given number of multilevel modulation and given spectral efficiency.

Soft decision decoding for bandwidth efficient RS coded MPSK schemes over a Rayleigh fading channel

Abstract: The authors consider the performance of the bandwidth-efficient RS (Reed-Solomon) coded MPSK schemes using soft-decision decoding over a Rayleigh fading channel. For the short codes it is practical to perform soft-decision decoding by introducing a trellis structure and using the Viterbi algorithm. The authors carried out upper bound analysis and computer simulation for Viterbi decoding of two short RS-coded 8PSK (phase shift keying) schemes, namely, RS

Analysis of decision-aided DPSK in the presence of multipath fading

Abstract: A decision-aided DPSK receiver scheme is proposed, which can achieve channel equalization using data symbols alone (i.e. no additive reference information is required). It makes use of the fact that for a typical irreducible error rate of 1%, 99% of the received symbols are correctly demodulated. Using this information to remove the modulation from the incoming radio signal effectively results in the recovery of unmodulated carrier component subject to the multiplicative channel distortion. Filtering this regenerated carrier signal to extract the channel information and minimizing noise results in a signal representative of system distortion (assuming flat fading), which can be used to effectively cancel most of the fading distortion on the incoming signal and thereby reduce the irreducible error floor significantly. >

Performance evaluation of a hybrid spread spectrum system in a hostile land mobile radio channel

Abstract: A performance evaluation is presented for a hybrid (direct-sequence frequency-hopped) spread-spectrum (SS) operating in a hostile jamming cellular mobile radio environment. The effects of a barrage jammer, Rayleigh fading, and log-normal shadowing on the system performance are discussed. Probability of error expressions for a hybrid BDPSK (binary differential phase shift keying) SS are derived in terms of the channel parameters. The results are compared to those obtained for the same system without fading and shadowing. For a given probability of error, the performance is worse for the case of Rayleigh fading compared to the case of additive white Gaussian noise only. Severe performance degradation is also observed, primarily as a result of fading in a mobile radio channel. Consequently, in order to achieve a high performance level, diversity should be used to reduce the effect of shadowing and fast fading. >

Probability density of the power spectrum transfer function for a two-path and three-path factory radio channel

Abstract: Channel parameters are obtained from a recent channel model which was developed from experimental factory data. The model shows that the average number of signals with relatively large amplitudes (not less than 10% of the largest signal present in the data) is three or less. Since most channel degradations result from large amplitude signals which cause severe fading, it is reasonable to find the fading statistics for channels with a few paths. In particular, the distribution of the power spectrum of the transfer function derived here can be used to design a reliable multiple-access communication system operating over such a multipath fading channel. >

Reduced complexity short-block data detection techniques for fading time-dispersive channels

Abstract: The achievement of reliable digital communications over fading channels with severe time-dispersion is considered. Two short-block data detection techniques based on linear and nonlinear decision-directed estimation principles are investigated. Short alternating blocks of data and training symbols are used. The training blocks are useful for both channel tracking and data block detection. In contrast to the recursive symbol-by-symbol equalization approaches usually used, each data block is detected as a unit. Previous restrictions imposed on short-block detection schemes have been removed, resulting in reduced complexity algorithms and higher throughput efficiency. Performance is presented for QPSK (quadrature phase shift keying) type signaling using a Rayleigh fading channel model with severe time-dispersion. >

On the Applicability of FEC-Coding on Rayleigh Fading Channels in Inter-Vehicle Communication

Abstract: This paper deals with the applicability of FEC coding in short range mobile radio networks for inter vehicle communication where sender and receiver are in motion. A propagation model is introduced which is composed of free path propagation loss for the mean received power added by a Rayleigh distributed short term fading. Evaluations of the statistical channel behaviour are the basis for investigations of suitable FEC codes. We investigate several FEC-codes with different coderates. We will show that the word error probability can be reduced significantly.

A new approach to the estimation of radio link fading

Abstract: The need to predict the performance of digital microwave radio systems is introduced and the approach adopted by BT in the estimation of radio link fading for the outage prediction model is described. An examination of the limitations of fading laws given in the CCIR is made, and the need to separate composite fading into flat and selective components is identified. A simple method to perform this split is proposed and results from several links are presented. The certification of several radio performance prediction models submitted to the European Telecommunication Standards Institute is discussed. >

On Diversity Combining Techniques For DS-CDMA System Over Multipath Fading Channel

Abstract: Performance of DS-CDMA Cell-Site to Mobile communication link is evaluated, for several combining techniques at the receiver. Transmis- sion over the time variant multipath fading channel is treated as a link with a random number of diversity receptions. Performance of coded syS- tems with soft decision decoding is investigated. with and without Chan- nel State Information about the fading. Robustness of the proposed tech- niques for a different interference model is examined by simulation. sion. The channel model is based on Turin's model (l), with impulse response h(t) = Caj,G(t - zj).exp(j8,). The fading coefficients, {aJ) are Rayleigh distributed. {ej) and {T~} are the phases and delays respec- tively. Signal echoes amving via different paths are assumed to be com- pletely overlapping or resolved by more than the sequence correlation time. The number of paths rn is Binomially distributed, with parameters M.p, and the average received energy is constant. The channel is memoryless due to ideal interleaving. Interference is modeled as random sequences causing Gaussian noise. Perfect estimation of the paths random delays and phases is achieved by a strong pilot. Two classes of receivers are considered : 1. Receiver that uses Channel State Information (CSI) of paths fading. 2. Receiver that is not using the fading coefficients informa- tion (NCSI receiver). Several combining techniques are proposed for each class : (a) Combining all the received echoes (denoted All-Path), (b) combining the B strongest paths (Brnax) or (c) combining only the first jj paths that are stronger than a threshold T (called gth). The generalized cut-off rate Ro pursued by (2) is derived, as well as upper bounds on the error performance of these systems. Simulations results of convolutional codes with Viterbi decoding are compared to the bounds, and reveal the effects of changing the interference model to 2-level Laplace distributed interference. The maximum number of users per cell is found for a given receiving quality, using simulations and the Gaussian approximation. Channel State Information (CSI) Receivers m

On the performance of FSK signals with diversity in highly selective fading channels

Abstract: The effect of severe selective fading on the performance of orthogonal binary FSK signals when diversity reception is used is investigated. Detailed expressions are derived for the effect of multipath fading induced ISI that is limited to one adjacent pulse. Optimum noncoherent square law receivers are considered, and the analysis is carried out for four shapes of the fading delay power density spectrum, namely Gaussian, rectangular, triangular, and exponential. The results agree in the limit with previously published results based on the assumption of small degree of selectivity or near flat fading approximation. >

Multi-dimensional modulation codes for fading channel

Abstract: Some new codes are presented which have good performance on Rician fading channel with small decoding complexities A new M-way partition chain is proposed for the L x MPSK (L less than or equal to M) signal set which maximizes the intra-set distance of each subset at each partition level Based on this partition chain, a class of asymptotical optimum codes was found For M = 4, these codes have both large symbol distances and product distances Multi-level coding scheme allows to construct a code by hand such that the code meets some desired parameters, eg, symbol distance, product distance, etc In design of a multi-level code, all factors were considered which affect the performance and complexity of the code, such as, the decoding scheme, decoding complexity, and performance under the decoding scheme, eg, if the multi-stage decoding scheme is used, the performance degradation due to the suboptimum decoding is taken into consideration The performance for most of the presented codes was simulated on Rayleigh fading channel, and the results show that these codes have good performance with small decoding complexities

A technique for reducing computation in the simulation of communications systems operating on fading channels

Abstract: An application of importance sampling to reducing the run times of Monte Carlo simulations is described. It contains two contributions. First is a demonstration that biasing the simulation program to produce more fades can reduce the variance of the estimates of the BER. Second is an efficient method for creating channel gain sequences associated with fades, according to an arbitrarily specified fading spectrum. >