Maximizing data rate by adjusting codes and code rates
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 FEC decode a plurality of data blocks, wherein each of the plurality of data blocks is a fixed size and encoded with an error correction code, and to strip redundant FEC code bits from the plurality of data blocks and generate a plurality of decoded segments based on the plurality of data blocks, wherein each of the decoded segments is a variable number of data bits; and
a controller configured to select a decoding rate and to signal the selected decoding rate to the FEC decoder.
2. The subscriber unit of claim 1 , wherein the FEC decoder is configured to decode each of the plurality of data blocks based on the selected decoding rate.
3. The subscriber unit of claim 2 , wherein a size of each of the plurality of decoded segments is based on the selected decoding rate.
4. The subscriber unit of claim 1 , further comprising:
a segment disassembler configured to generate a data frame based on the plurality of decoded segments.
5. The subscriber unit of claim 1 , further comprising:
a demodulator configured to demodulate a received signal and to generate the plurality of data blocks.
6. The subscriber unit of claim 5 , wherein the demodulator is configured to demodulate the received signal using a Quadrature Phase Shift Keying (QPSK) modulation scheme.
7. The subscriber unit of claim 5 , wherein the demodulator is configured to demodulate the received signal using a Quadrature Amplitude Modulation (QAM) modulation scheme.
8. A method for use in a subscriber unit, the method comprising:
forward error correction (FEC) decoding a plurality of data blocks including stripping redundant FEC code bits from the plurality of data blocks, wherein each of the plurality of data blocks is a fixed size and encoded with an error correction code;
generating a plurality of decoded segments based on the plurality of data blocks, wherein each of the plurality of decoded segments is a variable number of data bits; and
selecting a decoding rate, wherein a size of each of the plurality of decoded segments is based on the decoding rate.
9. The method of claim 8 , wherein the decoding is performed based on the selected decoding rate.
10. The method of claim 9 , wherein a size of each of the plurality of decoded segments is based on the selected decoding rate.
11. The method of claim 8 , further comprising:
generating a data frame based on the plurality of decoded segments.
12. The method of claim 8 , further comprising:
demodulating a received signal to produce the plurality of data blocks.
13. The method of claim 12 , wherein the demodulating uses a Quadrature Phase Shift Keying (QPSK) modulation scheme.
14. The method of claim 12 , wherein the demodulating uses Quadrature Amplitude Modulation (QAM) modulation scheme.