In a simulcast communication system (26), a method and apparatus for compensating differences in propagation time, lack of synchronization in transmitters, and multipath fading to recover data transmitted to a receiving device. In a simulcast communication system (26) that comprises a plurality of transmitters (32a, 32b, 32c), a receiver (36) includes a digital signal processor (DSP) (86) that processes a demodulated received signal to adaptively compensate for changes in the channel through which a multipath signal is propagated from the transmitters to the receiver. In one embodiment, the DSP comprises a decision feedback equalizer (300). An error signal is produced by the equalizer through a comparison of the estimated symbols with symbols most likely transmitted, for use in updating filter coefficients used by the equalizer in processing the received signal. Another embodiment implements a Viterbi algorithm to make decisions of the most likely data symbols in response to estimates of the channel impulse response. Using any one of these embodiments, a linear modulated signal can be decoded to recover the data transmitted, even though the received signal has been degraded by propagation in a multipath fading channel.

High speed simulcast system using adaptive compensation

Channel estimation is an integral part of standard adaptive receiver designs used in narrowband, digital wireless communication systems. In this tutorial paper, commonly used approaches to channel estimation are reviewed. Both time-invariant and time-varying channels are considered. For time-varying channels, both pilot symbol interpolation and data-directed channel tracking are considered. Applications include the Global System for Mobile communications, the Enhanced Data rates for Global Evolution system, and another Time-Division Multiple-Access system known as Telecommunications Industry Association/Electronics Industry Association/Interim Standard—136 (TIA/EIA/IS-136 or IS-136). Copyright © 2001 John Wiley & Sons, Ltd.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/wcm.14

Channel estimation in narrowband wireless communication systems

In the paper, a layered image transmission system is developed over cellular radio channels. The image coder is based on a multiresolution representation coupled with the ISO JPEG baseline coding standard. The multiresolution representation forms a pyramid in which information is layered in terms of different priorities that facilitates a more efficient use of forward error correction coding (FEC). After an error sensitivity analysis for different layers in an equalized mobile radio channel, an error control scheme based on block-interleaving and Bose-Chaudhuri-Hocquenghem (BCH) codes is proposed to minimize the effect of bursty channel errors on the picture quality degradation. Application of the new technique to the proposed Telecommunications Industry Association (TIA) Northern American digital cellular standard (IS-54) under different vehicle speeds with a signal-to-noise ratio of 22 dB is also investigated. Simulation results using a standard test image are presented to show the significant advantage of the proposed approach. >

Layered image transmission over cellular radio channels

Equalisation techniques for wireless channels, in particular for those encountered in mobile wireless communications, are examined. Equalisation is broadly defined to include reception techniques which estimate the state or response of the channel and then attempt to compensate for its effects. The paper considers equalisation techniques for fading dispersive channels which include both time and frequency selectivity. In addition, brief consideration is given to the problems of blind equalisation, techniques for dealing with fast fading channels and to the problem of joint equalisation and decoding. The paper does not attempt to provide in-depth analysis or performance results. Rather, the interested reader is referred to the extensive list of references.

Wireless channel equalisation

A soft decision decoder including an adaptive equalizer and a reliability information generator. The reliability information generator, receiving soft decision data and equalized square error from the adaptive filter, performs delay detection of the soft decision data, and then rotates the phase of the delay detected data so as to match the data to transmitted data components. The rotated data is weighted with the average value of the equalized square error to generate the reliability information for the soft decision Viterbi decoding. This makes it possible to obviate the exponential or logarithm calculations which are conventionally needed for generating the reliability information for carrying out the soft decision Viterbi decoding of the output of the adaptive equalizer, and hence to reduce the enormous amount of calculations and the size of hardware like DSP for performing the calculations.

Soft decision decoder

Issues encountered in the design of reliable narrowband time-division multiple access (TDMA) digital cellular mobile communication systems are considered. In particular, the problem of compensating for the harsh multipath fading environment in systems whose transmission bandwidth is commensurate with the coherence bandwidth of the fading channel is considered. A TDMA channel characterization parameter, the slot-normalized fade rate, is introduced, and an adaptive bidirectional equalization technique, which estimates the location of a deep fade within a time slot, is proposed. The simulation results show that the carrier-to-noise ratio requirement is only 15.5 dB when this equalization technique is used. This is achieved without diversity, and with low complexity. An equivalent equalized land mobile radio channel model and the analytical solution for the optimal bit likelihood calculation for pi /4-shift quadrature differential phase-shift keying (QDPSK) modulation are also derived under certain channel conditions. The results are used as soft decisions for the convolutional decoder. >

J.W. Ketchum

Papers

A soft-output bidirectional decision feedback equalization technique for TDMA cellular ratio