Subscriber unit and method for variable forward error correction (FEC) decoding
View Patent ↗The present invention provides for making code rate adjustments and modulation type adjustments in a pseudonoise (PN) encoded CDMA system. Coding rate adjustments may be made by changing the number of information bits per symbol, or Forward Error Code (FEC) coding rate. A forward error correction (FEC) block size is maintained at a constant amount. Therefore, as the number of information bits per symbol are increased, an integer multiple of bits per epoch is always maintained. The scheme permits for a greater flexibility and selection of effective data rates providing information bit rates ranging from, for example, approximately 50 kilobits per second to over 5 mega bits per second (Mbps) in one preferred embodiment.
1. A subscriber unit comprising:
a forward error correction (FEC) decoder configured to:
receive a plurality of data blocks, wherein each of the plurality of data blocks is a fixed size and each of the plurality of data blocks is encoded with a respective FEC code having a respective FEC code rate; and
to FEC decode the plurality of data blocks using the respective FEC code for each of the plurality of data blocks to generate a plurality of decoded segments, wherein each of the plurality of decoded segments is a variable number of data bits based on the respective FEC code rates.
2. The subscriber unit of claim 1 , further comprising:
a controller configured to select a FEC code rate and to signal the selected FEC code rate to the FEC decoder.
3. The subscriber unit of claim 2 , further comprising:
a segment disassembler configured to generate a data frame based on the plurality of decoded segments.
4. The subscriber unit of claim 1 , further comprising:
a demodulator configured to demodulate a received signal and to generate the plurality of data blocks.
5. The subscriber unit of claim 4 , wherein the demodulator is configured to demodulate the received signal using a Quadrature Phase Shift Keying (QPSK) modulation scheme.
6. The subscriber unit of claim 4 , wherein the demodulator is configured to demodulate the received signal using a Quadrature Amplitude Modulation (QAM) modulation scheme.
7. A method for use in a subscriber unit, the method comprising:
receiving a plurality of data blocks, wherein each of the plurality of data blocks is a fixed size and each of the plurality of data blocks is encoded with a respective error correction code having a respective FEC code rate; and
FEC decoding the plurality of data blocks using the respective FEC code for each of the plurality of data blocks to generate a plurality of decoded segments, wherein each of the plurality of decoded segments is a variable number of data bits based on the respective FEC code rates.
8. The method of claim 7 , further comprising:
generating a data frame based on the plurality of decoded segments.
9. The method of claim 7 , further comprising:
demodulating a received signal to produce the plurality of data blocks.
10. The method of claim 9 , wherein the demodulating uses a Quadrature Phase Shift Keying (QPSK) modulation scheme.
11. The method of claim 9 , wherein the demodulating uses Quadrature Amplitude Modulation (QAM) modulation scheme.