Strong Intersymbol Interference Research Articles

Simulated performance of an acoustic modem using phase-modulated signals in a time-varying, shallow-water environment

Underwater acoustic modems using coherent modulation, such as phase-shift keying, have proven to efficiently exploit the bandlimited underwater acoustical communication channel. However, the performance of an acoustic modem, given as maximum range and data and error rate, is limited in the complex and dynamic multipath channel. Multipath arrivals at the receiver cause phase distortion and fading of the signal envelope. Yet, for extreme ratios of range to depth, the delays of multipath arrivals decrease, and the channel impulse response coherently contributes energy to the signal at short delays relative to the first arrival, while longer delays give rise to intersymbol interference. Following this, the signal-to-multipath ratio (SMR) is introduced. It is claimed that the SMR determines the performance rather than the signal-to-noise ratio (SNR). Using a ray model including temporal variations of the shallow-water environment, the performance of the acoustic modem may be estimated. Simulations indicate that optimum performance is not necessarily found at receiver depths yielding the maximum total signal level, since the SMR may correspondingly be low due to strong intersymbol interference. [Work sponsored by the Danish Technical Research Council.]

Performance of non-coherent digital equalisersin DECT systems

The performance, in terms of bit error rate, of various data detectors at the output of a 1 bit differential demodulator for DECT receivers, is evaluated assuming static channels. The relevant result is that a one-tap decision feedback equaliser with an optimised threshold value yields a similar performance to the much more complex Viterbi algorithm. Moreover, in the presence of channels with a strong intersymbol interference, the decision feedback equaliser gains more than 2 dB in terms of SNR at BER 10/sup 3/ with respect to the threshold detector.

A Decision-feedback Receiver for Channels with Strong Intersymbol Interference

This paper deals with the problem of equalizing channels containing strong intersymbol interference. Typical of such channels are those of digital magnetic recording systems and data communication systems with partial-response signaling. First we discuss reasons that a conventional receiver with a linear equalizer cannot efficiently compensate for distortion in such channels. We then present a new receiver configuration in which the equalizer and quantizer are embedded in an inverse filter circuit that eliminates major intersymbol interference components. This configuration allows us to use a simple iteration algorithm to adaptively adjust the equalizer. Application of the scheme to digital magnetic recording data is discussed as an illustrative example.