Sets of rate-compatible universal turbo codes nearly optimized over various rates and interleaver sizes
A method and apparatus for Turbo encoding uses a set of rate-compatible Turbo Codes optimized at high code rates and derived from a universal constituent code. The Turbo Codes have rate-compatible puncturing patterns. The method comprises: encoding a signal at a first and second encoder using a best rate 1/2 constituent code universal with higher code rates, the first encoder and the second encoder each producing a respective plurality of parity bits for each information bit; puncturing the respective plurality of parity bits at each encoder with a higher rate best puncturing patterns; and puncturing the respective plurality of parity bits at each encoder with a lower rate best puncturing pattern. In a variation, the best rate 1/2 constituent code represents a concatenation of polynomials 1+D 2 +D 3 (octal 13) and 1+D+D 3 (octal 15), D a data bit. A Turbo Encoder is provided which has hardware to implement the method.
1. A method of encoding signals, the method comprising:
generating a first set of parity bits using a constituent code based on received information bits;
interleaving the information bits;
generating a second set of parity bits using another constituent code based on the interleaved information bits, wherein the constituent codes are universally adapted to accommodate a variety of interleaver depths and Turbo code rates;
puncturing the sets of parity bits according to one of the code rates; and
outputting a coded signal based on the punctured parity bits.
2. A method according to claim 1 , wherein the constituent codes exhibit a rate of 1/2 and have a transfer function of G(D) =[1, (1+D+D 3 )/(1+D 2 +D 3 )], D denoting unit delay in presentation of the information bits for generation of the parity bits.
3. A method as claimed in claim 1 , wherein the constituent codes exhibit a rate of 1/3 and have a transfer function of G(D)=[1, (1+D+D 3 )/(1+D 2 +D 3 ), (1+D+D 2 +D 3 )/(1+D 2 +D 3 )], D denoting unit delay in presentation of the information bits for generation of the parity bits.
4. A method according to claim 1 , further comprising:
selecting a candidate system rate for the constituent codes;
evaluating performance of all possible Turbo code rates formed by the constituent codes according to a first interleaver depth and a plurality of test patterns;
determining a subgroup of candidate pairs of constituent codes, wherein other interleaver depths are applied to the subgroup; and
determining the universal constituent codes from the subgroup yielding best performance for the interleaver depths.
5. A computer-readable medium bearing instructions for encoding signals, the instructions, being arranged, upon execution, to cause one or more processors to perform the method of claim 1 .
6. An encoder comprising:
a first constituent encoder configured to generate a first set of parity bits using a constituent code based on received information bits;
an interleaver configured to interleave the information bits;
a second constituent encoder configured to generate a second set of parity bits using another constituent code based on the interleaved information bits, wherein the constituent codes are universally adapted to accommodate a variety of interleaver depths and Turbo code rates; and
logic for puncturing the sets of parity bits according to one of the code rates, wherein a coded signal is output based on the punctured parity bits.
7. An encoder according to claim 6 , wherein the constituent codes exhibit a rate of 1/2 and have a transfer function of G(D)=[1, (1+D+D 3 )/(1+D 2 +D 3 )], D denoting unit delay in presentation of the information bits for generation of the parity bits.
8. An encoder as claimed in claim 6 , wherein the constituent codes exhibit a rate of 1/3 and have a transfer function of G(D)=[1, (1+D+D 3 )/(1+D 2 +D 3 ), (1+D+D 2 +D 3 )/(1+D 2 +D 3 )], D denoting unit delay in presentation of the information bits for generation of the parity bits.
9. An encoder according to claim 6 , wherein a candidate system rate is selected for the constituent codes, and performance of all possible Turbo code rates formed by the constituent codes is evaluated according to a first interleaver depth and a plurality of test patterns, a subgroup of candidate pairs of constituent codes being determined, wherein other interleaver depths are applied to the subgroup, and the universal constituent codes are determined from the subgroup yielding best performance for the interleaver depths.
10. A method of decoding encoded signals, the method comprising:
receiving an encoded signal encoded by a Turbo encoder, a first set of parity bits being generated using a constituent code based on received information bits, a second set of parity bits being generated using another constituent code based on interleaving the information bits, wherein the constituent codes are universally adapted to accommodate a variety of interleaver depths and Turbo code rates, and the sets of parity bits are punctured according to one of the code rates; and
iteratively decoding the encoded signal to output a decoded signal based the universal constituent codes.
11. A method according to claim 10 , wherein the constituent codes exhibit a rate of 1/2 and have a transfer function of G(D)=[1, (1+D+D 3 )/(1+D 2 +D 3 )], D denoting unit delay in presentation of the information bits for generation of the parity bits.
12. A method as claimed in claim 10 , wherein the constituent codes exhibit a rate of 1/3 and have a transfer function of G(D)=[1, (1+D+D 3 )/(1+D 2 +D 3 ), (1+D+D 2 +D 3 )/(1+D 2 +D 3 )], D denoting unit delay in presentation of the information bits for generation of the parity bits.
13. A method according to claim 10 , wherein a candidate system rate is selected for the constituent codes, and performance of all possible Turbo code rates formed by the constituent codes is evaluated according to a first interleaver depth and a plurality of test patterns, a subgroup of candidate pairs of constituent codes being determined, wherein other interleaver depths are applied to the subgroup, and the universal constituent codes are determined from the subgroup yielding best performance for the interleaver depths.
14. A computer-readable medium bearing instructions for decoding encoded signals, the instructions, being arranged, upon execution, to cause one or more processors to perform the method of claim 10 .
15. A receiver for processing coded signals, the receiver comprising:
a Turbo encoder configured to encode a signal at a first and second encoder using a universal constituent code optimized based on a plurality of interleaver depths and Turbo code rates, the first encoder and the second encoder each producing at least one parity bit, the Turbo encoder being further configured to determine a sequence of bits to transmit based on the universal constituent code; and
a modulator configured to modulate the sequence of bits according to a predetermined modulation scheme.
16. A receiver according to claim 15 , wherein the modulation scheme includes one of a Code Division Multiple Access (CDMA) and Time Division Multiple Access (TDMA).