Fading Mobile Radio Channels Research Articles

Channel Correlation Analysis by Exploiting Temporal‐Spectral‐Spatial Information

This paper deals with the modeling, analysis, and measurement of a Small scale fading (SSF) mobile radio channel. The physics of SSF are first reviewed to reveal the generating mechanisms of channel selectivity. A stochastic channel model is then derived as a function of time, antenna array displacement and frequency, which falls in the category of tapped delay line model. Specifically, the taps can be represented as a combination of a possible line of sight or dominant reflected path and a Gaussian distributed component comprised of unresolvable scattered paths. After that, general analytical solutions are provided for the 3D temporal-spectral-spatial correlations of SSF via the exploitation of channel statistical properties. We show that this function can be expressed as the product of three low order temporal, spectral and spatial correlations individually under appropriate assumptions on the associated wireless propagation environment. This will definitely facilitate the derivations of the closed form expression regarding the correlation function of SSF. From engineering perspective, this analysis can be utilized to develop network correlation maps for example. Finally, out field measurement results verify the validity of our theoretical analysis.

Building Solfware for Simulating Fading mObile Radio Channel in mobile Telecommunications.

Building Solfware for Simulating Fading mObile Radio Channel in mobile Telecommunications.

Stochastic modelling of Rice fading channels with temporal, spatial and spectral correlation

A statistical characterisation of a small-scale fading mobile radio channel is presented and a fading simulator for the simulation of multiple input-multiple output multicarrier systems is introduced. The derivation of the equivalent lowpass channel as a function of time, transmit and receive antenna positions and subcarrier frequency, leads to a tapped delay-line model with time, space and frequency-selective taps. The taps are modelled as a sum of a deterministic line-of-sight or dominant scattered path and a zero-mean Gaussian part composed of a number of unresolvable scattered paths, and are therefore Rice fading. The Gaussian parts can have the desired temporal and spatiospectral correlations generated by time-correlation shaping filtering and a space-frequency correlation transformation, respectively. The structure and details of the simulator are presented, and the simulator is shown to achieve good accuracy while retaining a reasonable computational complexity.

A complementary codes pilot-based transmitter diversity technique for OFDM systems

This letter presents a complementary codes pilot-based space-time block code/orthogonal frequency division multiplex (STBC/OFDM) system. In this system, a pair of complementary codes transmitted in a pre-defined order with the OFDM data signals is used as the pilot signals in a two-antenna transmitter diversity system, and used to estimate the channels for optimal data detection at the receiver side. A complete receiver architecture has been designed and Monte Carlo simulations have been used to verify the performance of the system in mobile radio fading channels.

Regular paper section: A new wcdma transmit power control technique

In this paper a new Transmit Power Control (TPC) scheme is proposed for SINR-based fast PC algorithms using frcquency-mutiplexed pilot symbols on the uplink of a WCDMA Rayleigh fading mobile radio channel with multi-path. The performance of various PC techniques is evaluated by means of Monte Carlo computer simulation. The WCDMA modem considered includes different coding schemes and a matched filter RAKE combining receiver. The objective is to investigate the effects of the number of resolvable propagation paths, the antenna diversity reception scheme employed and the coding scheme used on the performance of the fast power controlled WCDMA receiver in a Rayleigh fading single-cell environment. The results obtained indicate that the unbalanced PC algorithms outperform the conventional balanced PC algorithms. It is also theoretically proved that the unbalanced PC algorithms have better tracking ability than the conventional PC algorithms.

Deterministic channel modeling and long range prediction of fast fading mobile radio channels

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.

ARQ error control for fading mobile radio channels

In this paper, we study the correlation properties of the fading mobile radio channel. Based on these studies, we model the channel as a one-step Markov process whose transition probabilities are a function of the channel characteristics. Then we present the throughput performance of the Go-Back-N and selective-repeat automatic repeat request (ARQ) protocols with timer control, using the Markov model for both forward and feedback channels. This approximation is found to be very good, as confirmed by simulation results.

ADAPTIVE EQUALIZATION WITH RLS‐MLSE ASSISTED BY FEC BLOCK CODING FOR FADING MOBILE RADIO CHANNELS

In this paper, we propose an adaptive maximum-likelihood (ML) sequence estimator with RLS channel estimation, which is assisted by forward error control (FEC) coding. The reliable symbols reconstructed in the FEC decoder are used as the feedback signal to the RLS channel estimator. The scheme is compared with decision feedback equalization (DFE) with RLS algorithm, which is assisted by FEC coding. Computer simulations show that in frequency-selective fast fading mobile radio channels, the proposed scheme performs better at moderate Doppler frequencies. It is suitable for four-phase modulation data transmission at the rate of several 10 kb/s in 900 MHz band or in the 1800 MHz band.

A reception scheme switching between equalization and differential detection in frequency‐selective fading mobile radio channels—delay‐spread detection and adaptive reception control

AbstractA new reception scheme in which an adaptive equalization‐linear reception circuit and delay detectionlimiter reception circuit are switched optimally on a frequency‐selective fading mobile radio channel with a varying delay spread is proposed. First, the two‐path frequency selective fading propagation model is classified into a fixed delay model and time‐varying delay model in which delay varies according to Markov process. Next, a receiver state model suitable for these propagation models is proposed. the receiver consists of three states: (i) limiter amplifier and delay detection; (ii) linear amplifier and equalizer; and (iii) linear amplifier and baseband delay detection. In addition, a delay spread sensor detecting the delay wave component ratio for state transitions is proposed.Finally, various characteristics have been clarified by computer simulations. It has been clarified that the ratio for selecting adaptive equalization under flat fading can be less than 0.4 and 50 percent with one symbol delay frequency‐selective fading in a delay‐fixed model, and characteristics are infiuenced by the time constant of the processing in a delay transition model.

Variable rate QAM for mobile radio

Quadrature amplitude modulation (QAM) schemes which vary the number of modulation levels in accordance with the mobile radio fading channel variations are investigated. Important parameters considered are the fading rate and the block size used. We describe how the adaptive QAM modems can be employed and consider their use in a DECT-like TDD packet structure. System performance in the presence of cochannel interference is also considered. Simulations show that the variable rate system has about 5 dB improvement in channel SNR over a fixed 16-level QAM system for BER's between 10/sup -2/ and 10/sup -5/ and channel SNR's between 25 and 40 dB.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A coded 16 QAM scheme for fast fading mobile radio channels

An adaptive Viterbi algorithm, derived from a dynamic estimate of the fading channel is used for the decoding of a convolutional coded 16 QAM system in a mobile environment. The estimates are obtained by a sequence of known pilot symbols embedded in the data stream, and perform compensation for Rayleigh fading. The likelihood criterion in the Viterbi decoder is also modified by these channel estimates through a metric weighting function. We demonstrate through computer simulations, that our new technique achieves a BER improvement of 7-10 dB at P/sub e/=10/sup -3/ in a fast flat Rayleigh fading environment compared to an uncoded system. The BER performance of our new technique in a co-channel interference (CCI) controlled environment is also studied, and the results show that it may achieve a 40% to 85% improvement in capacity over the standard modem scheme for the new US digital cellular system, /spl pi//4-QPSK. >

Adaptive Bayesian decision feedback equalizer for dispersive mobile radio channels

The paper investigates adaptive equalization of time-dispersive mobile radio fading channels and develops a robust high performance Bayesian decision feedback equalizer (DFE). The characteristics and implementation aspects of this Bayesian DFE are analyzed, and its performance is compared with those of the conventional symbol or fractional spaced DFE and the maximum likelihood sequence estimator (MLSE). In terms of computational complexity, the adaptive Bayesian DFE is slightly more complex than the conventional DFE but is much simpler than the adaptive MLSE. In terms of error rate in symbol detection, the adaptive Bayesian DFE outperforms the conventional DFE dramatically. Moreover, for severely fading multipath channels, the adaptive MLSE exhibits significant degradation from the theoretical optimal performance and becomes inferior to the adaptive Bayesian DFE.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Differentially coherent detection technique for direct-sequence code acquisition in a Rayleigh fading mobile channel

A novel differentially coherent (DC) detection scheme for rapid code acquisition is proposed for a direct sequence (DS) spread-spectrum system being used to communicate over a fast Rayleigh fading mobile radio channel. The scheme processes the received signal at baseband using a complex differential detector with one-chip time delay and then performs a coherent partial correlation of the detector output with the product of a local DS code and its one-chip delayed phase to form a test sample. While still preserving the pseudo-noise attribute at its output, the differential detector is able to effectively suppress slowly fluctuating phase components due to fading and carrier frequency offset, thereby enhancing the in-sync correlation at the following correlator. The performance of this detection scheme is analysed based on a central-limit-theorem argument, and verified by simulation. Both serial and parallel acquisition systems employing the proposed DC detector are compared with the conventional parallel I-Q system by mean acquisition time performance. It is shown that the serial DC acquisition system significantly outperforms the parallel I-Q system in very fast Rayleigh fading environments.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Adaptive recursive least‐squares maximum‐likelihood sequence estimation with higher‐order state variable model of radio channels—adaptive performance improvement of rls‐mlse

AbstractSuperior tracking performance for fast fading mobile radio channels is obtained by extending channel models used in the adaptive recursive least squares maximum likelihood sequence estimation (RLS‐MLSE) derived from the theory of maximum likelihood signal estimation. Conventional adaptive maximum likelihood sequence estimators used the simple Markov model or random walk model to describe fluctuations of the impulse response of a frequency‐selective fading channel.In this paper, a second‐order Markov model that incorporates the first‐order time derivative of the impulse response is used. This higher‐order state variable approach improves the adaptability of the channel estimation algorithm and gives a significant improvement in signal transmission performance. Computer simulations show that the RLS‐MLSE based on this higher‐order state variable model yields good performance of 40 kbit/s QPSK with the maximum Doppler frequency up to 160 Hz.

Analysis of DPSK error rate due to multipath delay spread

The intersymbol interference (ISI) produced by multipath channel delay spread can be approximated as Gaussian noise. The equivalent average signal-to-noise power ratio (SNR) is defined. Very simple expressions for average bit error rate (BER) due to delay spread are derived for linear quaternary DPSK (QDPSK) transmission with differential detection over mobile radio Rayleigh fading channels.

Performance of access strategies for D-TASI over mobile radio fading channels

Demand Time Assigned Speech Interpolation (D-TASI) has been proposed as a means of more efficiently using the radio spectrum allocated to mobile radio systems. In the D-TASI system, the delay experienced in accessing the message channel in order to transmit a voice packet is a major obstacle to the practical implementation of the system.Access schemes for D-TASI are the subject of this paper. Three access schemes have been proposed and their theoretical models developed; computer software packages have also been developed to simulate the three proposed schemes—Aloha, Polling, and Table-driven. The probability of call blocking as a function of user population, voice channel traffic intensity and time-slot duration has been studied. It has been found that under fading conditions the Polling access scheme performs the best, closely followed by Slotted Aloha, The performance of the Table-driven scheme falls some way short of that of the other two schemes.

Data transmission over UHF fading mobile radio channels

Data transmission over UHF fading mobile radio channels

Data transmission over UHF fading mobile radio channels

Data transmission over UHF fading mobile radio channels

Data transmission over UHF fading mobile radio channels

Data transmission over UHF fading mobile radio channels