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

Frequency estimation in frequency-selective channels and its application to transmissions with antenna diversity = 주파수 선택적 페이딩 채널에서의 주파수 추정과 송신 다이버시티 시스템에의 응용

We estimate link reliabilities for IS-54/136 digital cellular handsets operating with or without an equalizer in urban, suburban, rural, and mountainous environments. We define the reliability of a user's receiver as the probability that the bit error rate (BER) is less than some specified value. The probability is taken over all mobile positions in a cell area and the BER is averaged over multipath fading. Using a range of tools for modeling and simulation of the digital cellular link (transmitter, channel, and receiver), we present an extensive set of results showing the influence of: (1) receiver structures (differential detection with no equalizer, differential detection with selection diversity, or coherent detection with a medium-complexity equalizer); (2) joint distribution of the channel's RMS delay spread and average signal-to-noise ratio (SNR) (this distribution is based on an environment-specific model reported previously); and (3) vehicle speed (0-200 km/h). In all simulations, we assumed a two-path Rayleigh fading channel characterized by: (1) the delay between paths and (2) the ratio of power received from the first path to that from the second path (the RMS delay spread relates to these two parameters). For typical cell sizes, we find that imposing an equalization requirement in IS-54/136 handsets is overly stringent in all environments, except mountainous areas. For these environments, achieving high reliability requires either equalization or other measures, such as smaller cells, directional base-station antennas, or dual-diversity handsets.

Link reliability for IS-54/136 handsets with different receiver structures

Techniques to reduce the effect of co-channel interference (CCI), intersymbol interference (ISI) and noise in a time-division multiple access (TDMA) radio cellular radio system will allow an increase in network capacity without a loss in quality of service. Two new analytical results have been derived and presented. The first result is the probability of error of a method for blind maximum likelihood (ML) data and channel estimation in the presence of noise. The second result is the mean square error of a displaced linear equalizer with infinite length on a time-varying channel in the presence of additive white Gaussian noise. These results provide measures of effectiveness of the blind maximum likelihood data and channel estimation method and the displaced linear equalizer used in the receiver. In order to achieve good system performance in a fast time-varying environment, a novel block adaptation with blind channel estimation strategy has been developed. It involves combinations of channel estimation and interpolation. With this strategy, in addition to the channel estimates obtained from known sequences in a TDMA time slot, channel estimates are obtained using small sequences of unknown data and the ML blind data and channel estimation method. The time-varying channel during

Equalization Techniques for TDMA Cellular Radio with Co-channel Interference

Blind adaptive detection using approximate oblique projector for synchronous DS/CDMA communication

An evaluation of a number of equalizers for frequency selective fading channels has appeared recently. Linear and decision feedback equalizers have been considered IS-54 digital cellular channels based on TDM concepts have delay spreads that result in at most one data symbol of overlap. Using a standard fading model, we find that a l&state sequence estimator, following a receive filter matched to the transmitter filter, provides excellent performance for delay spreads from zero to one symbol interval. It is superior to both linear and decision feedback equalizers in this application. Herein we assume perfect channel state information to establish ultimate performance. In practical application, at most three complex samples of the overall channel impulse that includes the receiver filter must be estimated. The frequency selective channel is a two-path model with time variation following standard Doppler variations for IS-54 channels. We present results for both root-raisedcosine filtered r/4-DQPSK and QPSK modulation formats..

16STATE NONLINEAR EQUALIZER FOR Is44 DIGITAL CELLULAR CHANNELS

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16STATE NONLINEAR EQUALIZER FOR Is44 DIGITAL CELLULAR CHANNELS