Pulse or digital communications – Receivers – Interference or noise reduction
Reexamination Certificate
1999-12-22
2001-10-09
Pham, Chi (Department: 2631)
Pulse or digital communications
Receivers
Interference or noise reduction
C375S285000, C375S229000
Reexamination Certificate
active
06301315
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to methods and apparatus for symbol estimation and a receiver.
2. Description of Related Art
As digital wireless communication systems are deployed around the world, the importance of providing clear and cost-effective communication services increases. Various obstacles include mitigating the effects of inter symbol interference (ISI) and co-channel interference (CCI) which result when transmitted signals travel along several paths to one or more intended receivers. When the difference in path lengths are relatively small, the multiple signal images arrive at almost the same time. However, as the difference in path lengths increase, the multiple signal images can appear as echoes of the transmitted signal and give rise to ISI and CCI.
Currently, ISI and CCI multipath time dispersion is mitigated by using some form of equalization, such as linear equalization (LE), decision feedback equalization (DFE), maximum likelihood sequence estimation (MLSE), and the minimum mean square linear equalization (MMSE-LE) with MLSE equalization providing the best performance.
Digital equalizers work by taking periodic samples of the received multiple signal images and removing the destructive components which are disbursed over a period of time. However, as the length of time covered by an equalizer increases, the required complexity and processing power of the maximum likelihood equalizer becomes prohibitive. Therefore, the time period covered by an equalizer, or response time, is often truncated to be less than the impulse response time of the transmitted signal, which degrades the performance of the maximum likelihood equalizer. Accordingly, there is a need for systems and methods that better equalized signals with ISI using a truncated response time.
SUMMARY OF THE INVENTION
The present invention provides systems and methods for mitigating interference on a received signal by providing an equalizer having a truncated response time preceded by a linear filter which compensates for the truncated response time. The invention also provides methods and systems for mitigating the interference on a received signal by providing a receiver having a filter and equalizer with a truncated response time followed by a symbol mapping technique that takes advantage of noise correlation produced by the equalizer by adjusting symbol mapping boundaries accordingly.
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patent: 6115435 (2000-09-01), Harada et al.
Simon Haykin, An Introduction to Analog and Digital Communications, published 1989 by Willey & Son, Inc., pp. 250-251.
AT&T Corp.
Pham Chi
Phu Phuong
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