Method and state reduction in an equalizer
An equalizer apparatus comprises a first filter ( 406 ) having a first respective plurality of filter coefficients, a channel model filter ( 414 ) having a plurality of model filter coefficients, and an adaptive algorithm unit ( 416 ). The adaptive algorithm unit ( 416 ) is arranged to adapt at least a first predetermined number of the first respective plurality of filter coefficients and at least a second predetermined number of the plurality of model filter coefficients in response to an error signal (e) corresponding to a difference in filter output signals from the first filter and the channel model filters ( 406, 414 ). The adaptive algorithm unit ( 416 ) operates in accordance with a respective state channel estimation technique. The respective state channel estimation technique is adapted so as to reduce a number of states allocatable to at least one of the plurality of state-defining taps, thereby reducing an overall number of states definable associated with the plurality of state-defining taps. The channel model filter ( 414 ) is adapted a number of times corresponding to the reduced overall number of states.
1. An equaliser apparatus comprising:
a channel model filter having a plurality of model filter coefficients and a plurality of state defining taps; and
an adaptive algorithm unit configured to adapt at least a first predetermined number of the plurality of model filter coefficients in response to an error signal calculated using an output signal from the channel model filter; wherein,
the adaptive algorithm unit operates in accordance with a respective state channel estimation technique that is adapted to reduce a number of states that are allocatable to at least one of the plurality of state-defining taps, thereby reducing an overall number of states definable associated with the plurality of state-defining taps;
the number of states is reduced by reducing each digit of an octal number to a number represented by superstates, comprising at least one symbol; and
the channel model filter is adapted a number of times corresponding to the reduced overall number of states.
2. The apparatus as claimed in claim 1 , wherein a number of sub-superstates are allocated to each tap, independently of the other taps.
3. The apparatus as claimed in claim 2 , wherein the number of sub-superstates allocated to each tap is dependent on the power of each signal of the each tap.
4. The apparatus as claimed in claim 1 , further comprising at least one pre-filter having a respective plurality of pre-filter coefficients, wherein:
the adaptive algorithm unit is arranged also to adapt at least a second predetermined number of the respective plurality of pre-filter coefficients in response to the error signal; and
the error signal is calculated using at least one output signal from the at least one pre-filter and the output signal from the channel model filter.
5. The apparatus as claimed in claim 4 , wherein the channel model filter and the at least one pre-filter are adapted a number of times corresponding to the reduced overall number of states.
6. A terminal comprising the equaliser apparatus as claimed in claim 1 .
7. A system comprising at least one terminal as claimed in claim 6 .
8. A method of channel estimation for an equaliser apparatus comprising a channel model filter having a plurality of model filter coefficients and a plurality of state-defining taps, and an adaptive algorithm unit configured to adapt at least a first predetermined number of the plurality of model filter coefficients in response to an error signal calculated using an output signal from the channel model filter, wherein the adaptive algorithm unit operates in accordance with a respective state channel estimation technique, the method comprising the steps of:
reducing a number of states that are allocatable to at least one of the plurality of state-defining taps so as to reduce an overall number of states definable associated with the plurality of state-defining taps, wherein the number of states is reduced by reducing each digit of an octal number to a number represented by superstates, comprising at least one symbol; and
adapting the channel model filter a number of times corresponding to the reduced overall number of states.