A data detector is disclosed which includes a source of a data signal (5) representing a sequence of symbols. A maximum likelihood sequence detector (50), is coupled to the data signal source, and produces a most likely survivor sequence, which includes a plurality of symbols. A decision feedback equalizer (60) and a phase detector (70), controlling the timing of the sampling of the data signal, are made responsive to the most likely survivor sequence.

Data detection for partial response channels

To prevent a coefficient vector for a modulated wave candidate of repeated identical codes from diverging, an error calculating part (36) calculates the difference between a vector X(i) with elements of input signals x(i) at N successive times and a vector Y m (i) of N replica signals y m (i) received from a transversal filter (34) to obtain an error vector E m (i), the square of the norm of which is supplied to a maximum likelihood sequence estimating portion (31), when signal estimation is carried out. In addition, a code sequence candidate {a m } is produced and a corresponding modulated wave candidate s m is generated. The filter (34) calculates the inner product of the modulated wave candidate s m and the coefficient vector W m (i-1) corresponding to each state to produce y m (i). W m (i-1) of each state is updated to W m (i) using an inner product vector of a generalized inverse matrix produced from s m corresponding to the state transition selected by the estimating portion (31) and E m (i).

Adaptive demodulating method for generating replica and demodulator thereof

Cochannel interference is a major impairment that limits the capacity of microcellular radio systems. This paper proposes a trellis-coded cochannel interference canceller, which uses trellis-coded modulation with maximum likelihood sequence estimation of both the desired signal and cochannel interference. This technique permits operation even when the signal-to-interference ratio is 0 dB. Computer simulation results show that this technique significantly reduces the bit-error rate in microcellular systems with Nakagami-Rice fading, particularly when the average signal-to-interference ratio is 0 dB. However, the technique requires: (1) synchronization of the interference and the desired signal and (2) higher computational complexity than standard techniques.

Trellis-coded cochannel interference canceller for microcellular radio

The paper presents a Euclidean distance maximum likelihood sequence estimation (MLSE) receiver, based on the Viterbi algorithm (VA), suitable for fading and noisy communications channels, as that specified by the Group Special Mobiles (GSM). In a mobile cellular system, the fast varying channel characteristics, due to the fading and Doppler effects, require adaptive methods to update the channel coefficients to the MLSE receiver. The proposed technique continuously estimates the channel characteristics directly within the metric calculation of the VA. At each step of the VA, the sequence associated to the path with the best metric value (minimum-survivor method) among the survivor paths is used to update the channel estimate (employing conventional adaptive algorithms) throughout the entire informative sequence. However, the detection of the transmitted data sequence is performed by the VA only at the end of each burst. The proposed technique allows simpler receiver implementation and the simulation results show a good performance of this adaptive MLSE receiver in typical GSM environments.

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A continuously adaptive MLSE receiver for mobile communications: algorithm and performance

The invention includes method and apparatus for estimating channel impulse response and data in a signal transmitted over a channel in a communication system. The channel impulse response is estimated and then, using the estimated channel impulse response, the data in the signal is estimated. The output is then fed back to the channel impulse response estimator and the channel impulse estimation is repeated. The data estimation and channel impulse response estimation may be iterated a number of times. The channel impulse response estimating step uses correlative channel sounding.

Iterative channel estimation

The authors propose a novel adaptive equalization scheme which is a combination of the recursive least squares adaptive algorithm and maximum likelihood sequence estimation (RLS-MLSE). The performance of the scheme is demonstrated in frequency-selective fast fading mobile radio channels. RLS-MLSE employs a parallel estimation scheme in which the state of the channel is estimated by the Viterbi algorithm and the parameters of the channel impulse response are estimated by RLS. A simplified RLS algorithm and an extension to the diversity reception scheme are discussed. Computer simulations show that RLS-MLSE is suitable for 40-kb/s QPSK (quadrature phase shift keying) transmission in 900-MHz-band mobile radio systems, and that equalization with two-branch diversity operates up to a maximum Doppler frequency of 160 Hz. >

H. Suzuki

Papers

Adaptive equalization with RLS-MLSE for frequency-selective fast fading mobile radio channels