Pulse or digital communications – Equalizers – Automatic
Patent
1996-06-27
1999-02-09
Pham, Chi H.
Pulse or digital communications
Equalizers
Automatic
375229, 375231, H04K 102, H04L 2503
Patent
active
058704310
ABSTRACT:
The finite impulse response (FIR) filter is implemented as a table using read-only memory (ROM). The FIR filter table stores a pre-calculated output filter value for each permissible combination of input values to be filtered. Streams of input values are successively shifted into the table and corresponding output values are successively output. In an exemplary implementation, the FIR filter is employed within a digital cellular telephone for use in smoothing a digital signal to be transmitted. The size of the required FIR filter table is minimized by exploiting constraints imposed upon the signal to be filtered and by exploiting linearity and symmetry within the filter itself. More specifically, the telephone employs a data burst randomizer to provide a data signal composed of sequences of null or 0 values and sequences of antipodal values (+1's and -1's). Hence, the permissible input combinations for the FIR filter include only patterns containing either all antipodal signals, all null signals, leading antipodal signals followed by trailing null signals, or leading null signals followed by trailing antipodal signals. The FIR filter look up is configured to exploit these limitations on the input streams yielding a look up table having relatively few entries. Method and apparatus implementations are disclosed.
REFERENCES:
patent: 4551816 (1985-11-01), Hyatt
patent: 5369606 (1994-11-01), Hessel
patent: 5535150 (1996-07-01), Chaing
patent: 5566101 (1996-10-01), Kodra
patent: 5579124 (1996-11-01), Aijala et al.
patent: 5586068 (1996-12-01), Rakid
Black Peter J.
Easton Kenneth D.
Bayard Emmanuel
Edmonston Brian S.
English Sean
Miller Russell B.
Pham Chi H.
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