Pulse or digital communications – Equalizers – Automatic
Patent
1993-09-20
1996-04-30
Coles, Sr., Edward L.
Pulse or digital communications
Equalizers
Automatic
375341, 375348, 375229, 455 512, H03H 730, H04B 100
Patent
active
055132154
ABSTRACT:
In a simulcast communication system, a method and apparatus for compensating differences in propagation time, lack of synchronization in transmitters, and multipath fading to recover data transmitted to a receiving device. In a simulcast communication system(26) that comprises a plurality of transmitters (32), a receiver (36) includes a digital signal processor (DSP) (86) that processes a demodulated received signal to adaptively compensate for changes in the channel through which a multipath signal is propagated from the transmitters to the receiver. In one embodiment, the DSP comprises a decision feedback equalizer. An error signal is produced by the equalizer through a comparison of the estimated symbols with symbols most likely transmitted, for use in updating filter coefficients used by the equalizer in processing the received signal. Alternatively, in a linear adaptive equalizer, reference or pilot symbols transmitted with the data symbols are used to determine the error signal. Another embodiment implements a Viterbi algorithm to make decisions of the most likely data symbols in response to estimates of the channel impulse response. Further, a hybrid embodiment combines the Viterbi decoder with a bi-directional decision feedback equalizer that produces forward and reverse estimates of the sequence of data symbols. The Viterbi decoder selects between the forward and reverse sequences based upon channel impulse response estimates to dynamically compensate for varying channel conditions. Using any one of these embodiments, a linear modulated signal can be decoded to recover the data transmitted, even though the received signal has been degraded by propagation in a multipath fading channel. The same techniques are also disclosed as applicable to constant envelope modulated transmissions in a simulcast system.
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Ho Paul K.
Marchetto Robert F.
Stewart Todd A.
Coles Sr. Edward L.
Glenayre Electronics, Inc.
Nguyen Madeleine A-V
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