Mobile Fading Channels Research Articles

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.

On the performance of error control coding with diversity for mobile channels

Upper bounds on the bit error probability are applied to evaluate the error performance of coded systems over non-interleaved and partially interleaved Rician fading mobile channels. The correlation between successive received symbols is exploited to bound the error performance. The bound allows useful evaluation of coding gains on realistic communication systems without going into lengthy computer simulations. By further defining the maximum energy degradation factors, compact upper bounds are expressed in a similar way as on the fully interleaved or memoryless channels. The maximum energy degradation factors are computed for a wide variety of mobile channel conditions. These factors give an interesting evaluation of the fading conditions and may be used to design coded communication systems on mobile channels. Furthermore, independent space or frequency diversity may be taken into account in these bounds and it is shown that the energy degradation due to correlation is independent of this added independent diversity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of 16-APSK modulation in AWGN and Rayleigh fading channel

The error probability for fully differential 16-APSK in a Rayleigh fading channel has been evaluated theoretically and through the use of extensive computer simulation. The optimum ring ratio and detection thresholds have been determined and the results indicate that 16-APSK can be considered as a potential candidate for spectrally efficient digital transmission over practical mobile fading channels.

Error bounds for trellis-coded MPSK on a fading mobile satellite channel

Analytical performance bounds are presented for trellis-coded MPSK, transmitted over a satellite-based land mobile channel. Upper bounds are evaluated using the well-known transfer function bounding technique, and lower bounds are achieved through knowledge of exact pairwise error probabilities. In order to analyze practical trellis-codes (four or more states), the uniform properties displayed by a certain class of trellis-codes are exploited, enabling the encoder transfer function to be obtained from a modified state transition diagram, having no more states than the encoder itself. Monte Carlo simulation results are presented in confirmation of all performance bounds and indicate a general weakness in the transfer function upper bounds. A new asymptotically tight upper bound is derived based on a simple modification to the standard transfer function bound, and results are presented for the four- and eight-state trellis-codes in Rician and Rayleigh fading. >

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

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. >

Teletext reception in mobile Rician fading channel with maximal ratio combining

The performance of teletext reception in a mobile environment has been evaluated, considering maximal ratio combining in a Rician fading channel. The performance is measured in terms of bit error probability and average number of errors per page. Enhanced quality is observed using the maximal ratio combining technique.

A new method for phase synchronization and automatic gain control of linearly modulated signals on frequency-flat fading channels

An optimal phase synchronization and automatic gain control (AGC) scheme for coherent reception of linearly modulated signals on frequency-flat mobile fading channels is presented. The channel model and receiver performance are described. It is shown that using the technique allows the irreducible error floors (due to random FM) known from the noncoherent methods to be practically eliminated. Depending on the fastness of the fading, large power gains over the noncoherent methods are achieved. Unfavorable analog signal processing and/or the high bandwidth inefficiency of the FDM-pilot coherent methods are also avoided.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Direct-sequence spread-spectrum parallel acquisition in a fading mobile channel

A parallel acquisition scheme for direct-sequence spread-spectrum systems is proposed, and its mean acquisition time performance is analyzed in both nonfading and Rayleigh-fading environments. An expression for the mean acquisition time is derived in terms of the probabilities of detection, missing, and false alarm. These parameters are first analyzed for a typical AWGN (additive white Gaussian noise) channel, then the Rayleigh-fading channel encountered in a typical UHF or microwave land mobile radio channel is studied. The channel is assumed frequency nonselective, and the effect of data modulation and code Doppler is not considered. The performance of the parallel system is compared to the corresponding serial system, and it is shown that a significant improvement can be achieved. >

Modified scatterer distribution model for fast fading mobile communication channel

Recent measurements of fast-fading power variation in a mobile communication channel showed significantly lower levels than predicted by classical theory. Two model modifications were tested : reduction of scatterers' number, and a limited sector distribution of the scatterers. The second modification offers a good explanation of the experimental results

Convolutionally interleaved PSK and DPSK trellis codes for shadowed, fast fading mobile satellite communication channels

Using a model from the literature, the performance of convolutionally interleaved phase-shift-keying (PSK) and differential phase-shift-keying (DPSK) trellis codes for digital speech transmission over shadowed mobile satellite communication channels is determined by computer simulation. First the characteristics of fading channels are examined and analyzed in terms of the probability distributions of amplitude, phase, and burst errors. A statistical method, using a histogram approach, is utilized along with the simulations of fading channels to generate these probability distributions. A test for channel burst error behavior is presented. A periodic convolutional interleaver/deinterleaver to be used with trellis coding to combat slow fading in digital, shadowed mobile satellite channels is designed. This interleaver ha less than half the time delay for the same bit error performance than a block interleaver. The results show that the periodic convolutional interleaver provides considerable improvement in the error and time delay performance of mobile satellite communication channels for up to average shadowing conditions as compared to other techniques. >

On the use of repetition coding with binary digital modulations on mobile channels

Repetition, diversity, and single-error-correcting codes are examined for use with binary modulation techniques over a mobile communication fading channel. Both bit-error performance and bandwidth efficiency are considered for phase-shift keyed, differential phase-shift keyed, and frequency-shift keyed modulations. The error-correction capability of repetition coding is considered, and optimum repetition is found. M-tuple diversity with maximum-ratio-combining is then compared with repetition coding both with a single-error-correcting code and without coding. It is found that a minimum of a 10 dB signal-to-noise power ratio is required for an improved performance with repetition code or diversity. The repetition code is about 3 dB inferior to optimal diversity. An optimized design of moderate complexity and bandwidth expansion can be reached with twofold diversity and three repetitions as an inner layer of coding concatenated with an outer single-error-correcting code. >

The performance of trellis coded multilevel DPSK on a fading mobile satellite channel

The performance of a trellis-coded multilevel differential phase-shift keying (DPSK) modulation over a mobile satellite channel characterized by additive white Gaussian noise (AWGN) and slow Rician fading is presented. Both the optimum and Gaussian (suboptimum) decoding metrics are considered, with performance results given only for the latter. Analytical results (upper bounds on bit error rate) are obtained wherever possible and illustrated by several numerical examples. Also given are simulation results which are more indicative of the exact system performance. Comparisons with results previously obtained for coherent detection of the same coded modulations are presented. >

Trellis Coded Modulation for 4800-9600 bits/s Transmission Over a Fading Mobile Satellite Channel

The combination of trellis coding and MPSK signaling with the addition of asymmetry to the signal set is discussed with regard to its suitabllity as a modulation/coding scheme for the fading mobile satellite channel. For MPSK, introducing nonuniformity (asymmetry) into the spacing between signal points in the constellation buys a further improvement in performance over that achievable with trellis coded symmetric MPSK, all this without increasing the average or peak power, or changing the bandwidth constraints imposed on the system. Whereas previous contributions have considered the performance of trellis coded modulation transmitted over an additive white Gaussian noise (AWGN) channel, the emphasis in this paper is on the performance of trellis coded MPSK in the fading environment. The results will be obtained by using a combination of analysis and simulation. It will be assumed that the effect of the fading on the phase of the received signal is fully compensated for either by tracking it with some form of phase-locked loop or with pilot tone calibration techniques. Thus, our results will only reflect the degradation due to the effect of the fading on the amplitude of the received signal. Also, we shall consider only the case where interleaving/deinterleaving is employed to further combat the fading. This allows for considerable simplification of the analysis and is of great practical interest. Finally, the impact of the availability of channel state information on average bit error probability performance is assessed.

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.

High-reliability data transmission to mobile vehicles

The design for an adaptive-rate data transmission system providing very reliable two-way data transmission over a fading mobile channel is outlined and measurements are presented. A single u.h.f. or v.h.f. carrier is required. Operation with practical fading has been tested using a recording of variations in mobile-channel gain in conjunction with a hardware simulation of the system. The tests show that an error probability of 10−10 can readily be achieved. For operation in 12.5 kHz bandwidth, four-phase keying at 10 kbauds is proposed. In this case the system will provide a mean data rate in each direction of 1.8 kbit/s with the mean power of the fading signal 7 dB above the receiver noise. With increasing received power the mean data rate in each direction tends to 4.8 kbit/s. These rates can be doubled by interleaving an identical scheme operating on a second carrier frequency.