| 摘要 |
In a digital time-shared transmission system, a receiver receives a signal whose symbol rate is lower than the channel bandwidth of the system. A correlating and sampling circuit receives a baseband signal, samples the signal a number of times with each symbol time, performs channel correlation, generates a channel estimate and samples down the once sampled signal to an observed signal with two values for each symbol time. A channel equalizer executes a fractional viterbi algorithm which utilizes two delta-metric values for each state transition and generates estimated symbols. A channel estimating filter receives a symbol sequence of alternating zero-value symbols and the estimated symbols and generates an estimated signal. The channel estimating filter is adapted with the aid of an error signal and the filter delivers a channel estimate to the channel equalizer. Weighting factors are generated with the aid of the error signal and the two aforementioned delta-metric values are co-weighted to a common delta-metric value with the aid of weighting factors, this common delta-metric value being used to generate the estimated symbols. The use of the weighting factors improves the metric calculation and enables the channel estimating filter and the channel equalizer to be relatively simple. The insertion of the zero-value symbols simplifies the generation of the weighting factors and the adaptation of the channel estimating filter. |
