Filter weight estimation device with update at HSDSCH symbol rate, for a symbol level equaliser
A filter weight estimation device (D), for an equaliser of a communication receiver, comprises i) a tap delay line connected to N branches each comprising a descrambler (DS 1 -DSN) and a despreader (DE 1 -DEN), for despreading received signals, corresponding to one or more available multiplexed channels associated with different channelization codes, with a reference code equal to the sum of all the channelization codes associated to the available multiplexed channels, Ë) an adaptive filter (AF) comprising N input filter taps respectively connected to the N branches and a regression input and arranged to estimate the sum of the symbols outputted by the despreaders (DE 1 -DEN) and associated to each available channel, said symbol sum constituting a pseudo-symbol estimate defining a reference symbol estimate (rs), and to implement a mechanism of a LMS type to deliver a chosen number of filter weights (fi), iË) a quantiser (SM) arranged to quantise the reference symbol estimate (rs) to estimate a desired reference symbol (d), and iv) an error computation module (AM) for subtracting the reference symbol estimate (rs) from the desired reference symbol (d) to output an error signal (e) feeding the regression input.
1. A filter weight estimation device for an equalizer of a communication receiver, comprising:
a tap delay line connected to N branches each comprising a descrambler and a despreader, for despreading received signals, corresponding to at least one available multiplexed channel associated with a channelization code, with a reference code to output a symbol, where N is an integer;
an adaptive filter comprising N input filter taps respectively connected to said N branches and a regression input and arranged to output a reference symbol estimate; and
an error computation module for subtracting said reference symbol estimate from a desired reference symbol to output an error signal that is fed to said regression input,
wherein each despreader is arranged to despread the received signals with said reference code equal to a vector sum of all the channelization codes that have been used into a base station to spread different groups of user symbols associated to the different multiplexed channels,
wherein said adaptive filter is arranged to estimate a symbol sum by said despreaders and associated to each available multiplexed channel, and arranged to implement a mechanism of a least mean square type to deliver a chosen number of filter weights,
wherein said symbol sum constitutes a pseudo-symbol estimate defining said reference symbol estimate, and
wherein said adaptive filter further comprises a multilevel quantizer arranged to quantize said reference symbol estimate in order to estimate said desired reference symbol.
2. The filter weight estimation device according to claim 1 , wherein said filter weight estimation device is arranged to process said received signals corresponding to the available multiplexed channels of a HSDSCH type and each associated to a 16 chips long channelization code.
3. The filter weight estimation device according to claim 1 , wherein said adaptive filter is of a type chosen in a group comprising at least a least mean square type and a normalized least mean square type, in order to realize a linear minimum mean-squared error filter.
4. The filter weight estimation device according to claim 1 , wherein said multilevel quantizer is arranged to make maximum a posteriori decision, based on a priori probabilities, in order to estimate said reference symbol estimate.
5. The equalizer of claim 1 , wherein said equalizer comprising said filter weight estimation device; and a data filtering stage comprising a linear filter provided with the filter weights by said filter weight estimation device, fed with said received signals and arranged to equalize said received signals with a delay equal to a chosen number of chips in order to output a total chip sequence estimate.
6. The equalizer according to claim 5 , wherein said data filtering stage comprises said linear filter fed with said received signals and arranged to output said total chip sequence estimate, a descrambler arranged for descrambling said total chip sequence estimate with a chosen scrambling code to output a descrambled total chip sequence estimate, and at least one despreader arranged for despreading said descrambled total chip sequence estimate with the corresponding channelization code associated to a user channel in order to output user symbols.
7. A communication equipment comprising the communication receiver according to claim 1 .
8. The communication equipment according to claim 7 , wherein said communication equipment constitutes a mobile telephone.