Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
2001-02-14
2004-12-28
Ha, Dac V. (Department: 2634)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S146000, C370S335000, C370S441000, C370S479000
Reexamination Certificate
active
06836504
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to communication systems, and more particularly, to a method and apparatus for spreading symbols in a communication system.
BACKGROUND OF THE INVENTION
In current Code Division, Multiple Access (CDMA) communication systems, data to be transmitted is repeated within a frame based on a transmission rate. More particularly, voice encoded data exits a voice encoder (vocoder) at a particular transmission rate and is convolutionally encoded. As symbols exit the convolutional encoder, they are repeated a number of times, with the number being based on the current transmission rate. The result of simultaneously repeating symbols in such a way is to make the data rate over the air interface constant irrespective of the transmission rate. This is illustrated in FIG.
1
. As shown, convolutional encoder
112
encodes input data bits
110
at a fixed encoding rate of one data bit to two data symbols (i.e., rate ½) such that convolutional encoder
112
outputs data symbols
114
at twice the input data rate. In this case, the input bit “0” was convolutionally encoded resulting in symbol “01”. The output of encoder
112
is input into symbol repeater
116
, where it is repeated a number of times based on the transmission rate (i.e., full, half, quarter, or eighth). In this particular example, the symbol was repeated once, indicating half-rate transmission.
One of the primary problems with the current transmission scheme is that the data repetition used for sub-rate transmission (particularly in the case of eighth-rate frames) results in a false determination of the transmission rate by the receiver. More particularly, because each symbol is repeated a number times, it is possible to generate very long strings of zeros. These strings of zeros are easily decodable by the full-rate decoder and have been observed to cause very low Symbol Error Rates (SERs) resulting in the frame falsely being decoded as a full-rate frame. Therefore a need exists for a method and apparatus for transmission within a communication system that reduces falsing within a communication system.
REFERENCES:
patent: 5751761 (1998-05-01), Gilhousen
patent: 6091760 (2000-07-01), Giallorenzi et al.
patent: 6122310 (2000-09-01), Ziemer et al.
patent: 6625136 (2003-09-01), Niegel et al.
patent: 2343346 (2000-05-01), None
patent: WO 99/45669 (1999-09-01), None
patent: WO 00/05831 (2000-02-01), None
Hetherington Mark
Morgan William K.
Proctor Lee
Wong Naisum
Ha Dac V.
May Steven A.
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