Maximum likelihood block decision feedback estimation for CCK demodulation apparatus and method
A maximum likelihood CCK detector has a first subtractor which subtracts the contents of a pre-equalize register from a current symbol, and the output of this subtractor is coupled to a simple Fast Walsh Transform (FWT) with an iteration variable k. The output of the FWT is coupled to a second subtractor for subtracting a plurality of ICI corrections for all possible current symbols computed from the post-FWT domain value of the current CCK symbol and stored in post equalization registers. A post equalization register contains values computed from feedback filter coefficients determined during a packet preamble, where the feedback filter coefficients are provided to a reduced complexity post equalization value generator which populates the post equalization register using an iteration variable i.
1. A process for converting a symbol of length n symbol to a communication channel compensated decision feedback value, said process using a serial shift register, formed from a plurality flt_len of registers, each said register generating one of the output phases φ={1,j,−1,−j} from its output value, said process comprising:
a first step of loading a complete symbol value {c 1 ,c 2 , . . . , c nsymbol } into the first n symbol values of said shift register;
a second step of shifting the values of said shift register Nlength times, and for each shift operation, forming an output value by summing the product of each said channel_coefficient {C 1 ,C 2 , . . . , Cflt_len} multiplied by a respective shift register output phase {φ 1 ,φ 2 ,φ 3 , . . . , φflt_len}, where said channel coefficients {C 1 ,C 2 , . . . , Cflt_len} are derived from the characteristic of said communications channel which received said symbol;
a third step of providing said shifted output to a pre-equalization register where said pre-equalization register adds said shifted output to a subsequently received CCK symbol;
where said flt_len is greater than said n symbol .
2. The process of claim 1 where said channel coefficients are derived from a preamble part of a received packet.
3. The process of claim 1 where said n symbol is 8.
4. The process of claim 1 where said symbol is a CCK chip compatible with a CCK chip described in IEEE 802.11b.
5. The process of claim 1 where said symbol is one of 64 K symbols.
6. The process of claim 1 where the data rate of said CCK symbol is one of substantially 5.5 Mbps or substantially 11 Mbps.
7. The process of claim 1 where said symbol is a demodulated CCK symbol.
8. A process for converting a symbol of length n symbol to a communication channel compensated decision feedback value, said process using a serial shift register, formed from a plurality flt_len of registers, each said p register generating one of the output phases φ={1,j,−1,−j} from its output value, said process comprising:
a first step of loading a complete symbol value {c 1 ,c 2 , . . . , c nsymbol } into the first n symbol values of said shift register;
a second step of shifting the values of said shift register Nlength times, and for each shift operation, forming an output value by summing the product of each said channel_coefficient {C 1 ,C 2 , . . . , Cflt_len} multiplied by a respective shift register output phase {φ 1 ,φ 2 ,φ 3 , . . . , φflt_len}, where said channel coefficients {C 1 ,C 2 , . . . , Cflt_len} are derived from the characteristic of said communications channel which received said symbol, said characteristic determined during a preamble interval which precedes said symbols;
a third step of providing said shifted output to a pre-equalization register;
where said flt_len is greater than said n symbol .