Multimode receiver architecture

Abstract

A radio receiver comprising a compensator arranged to compensate for intersymbol interference in a signal received at the receiver and a configurator arranged to configure the compensator, wherein the compensator comprises a programmable filter and the configurator is capable of configuring the filter in a first mode to operate as an ISI equaliser or in a second mode to implement a RAKE finger set.

The invention claimed is: 
     
       1. A radio receiver, comprising:
 a radio frequency (RF) front end configured to convert a radio signal received at the radio receiver to a baseband signal at a first oversampling rate; 
 a downsampling unit configured to downsample the baseband signal from the first oversampling rate to a second oversampling rate; 
 a filter configured to produce a filtered signal by filtering the baseband signal at the second oversampling rate using configurable filter coefficients; 
 a symbol rate conversion unit configured to convert the filtered signal to a symbol-rate signal; 
 a channel estimation unit configured to calculate a channel impulse response estimate based on the baseband signal at the second oversampling rate; 
 a minimum mean-square error (MMSE) weights calculation unit configured to calculate a first set of filter coefficients for minimum mean-square error (MMSE) equalization, the first set of filter coefficients being based on the channel impulse response estimate; 
 a finger determination unit configured to identify a set of RAKE finger positions based on the baseband signal at the first oversampling rate; and 
 a maximum ratio combining (MRC) weights calculation unit configured to calculate a second set of filter coefficients based on the channel impulse response estimate and the set of RAKE finger positions, the second set of filter coefficients causing the filter in conjunction with symbol rate conversion unit to operate as a RAKE receiver, 
 wherein the filter uses the first set of filter coefficients as the configurable filter coefficients during a first mode and uses the second set of filter coefficients as the configurable filter coefficients during a second mode. 
 
     
     
       2. A radio receiver according to  claim 1 , wherein, in the second mode, the radio receiver is operable to time align and combine several multipath components of the radio signal for collective conversion from chip rate to symbol rate. 
     
     
       3. A radio receiver according to  claim 1 , wherein calculation of the second set of filter coefficients in the MRC weights calculation unit includes mapping each finger position in the set of RAKE finger positions onto the channel impulse response estimate. 
     
     
       4. A radio receiver according to  claim 3 , wherein calculation of the second set of filter coefficients in the MRC weights calculation unit further includes, for each finger position in the set of RAKE finger positions, calculating the complex conjugate of the channel impulse response estimate value that has been mapped to that finger position. 
     
     
       5. A radio receiver according to  claim 1 , that is compatible with Wideband Code Division Multiple Access (WCDMA). 
     
     
       6. A radio receiver according to  claim 1 , wherein conversion of the filtered signal to the symbol-rate signal in the symbol rate conversion unit includes despreading the filtered signal. 
     
     
       7. A radio receiver according to  claim 6 , wherein conversion of the filtered signal to the symbol-rate signal in the symbol rate conversion unit further includes descrambling the filtered signal. 
     
     
       8. A radio receiver according to  claim 1 , wherein calculating the first set of filter coefficients in the MMSE weights calculation unit includes matrix inversion. 
     
     
       9. A radio receiver according to  claim 1 , wherein the filter is a finite impulse response (FIR) filter and the configurable filter coefficients are tap weights. 
     
     
       10. A method for use in a radio receiver, the method comprising
 converting a received radio signal to a baseband signal at a first oversampling rate; 
 downsampling the baseband signal from the first oversampling rate to a second oversampling rate; 
 filtering the baseband signal at the second oversampling rate using configurable filter coefficients to produce a filtered signal, the filtering using a first set of filter coefficients as the configurable filter coefficients during a first mode and using a second set of filter coefficients as the configurable filter coefficients during a second mode; 
 converting the filtered signal to a symbol-rate signal; 
 calculating a channel impulse response estimate based on the baseband signal at the second oversampling rate; 
 calculating the first set of filter coefficients for minimum mean-square error (MMSE) equalization, the first set of filter coefficients being based on the channel impulse response estimate; 
 identifying a set of RAKE finger positions based on the baseband signal at the first oversampling rate; and 
 the second set of filter coefficients based on the channel impulse response estimate and the set of RAKE finger positions, the second set of filter coefficients causing the filtering in conjunction with the converting to provide RAKE receiver processing. 
 
     
     
       11. A method according to  claim 10 , wherein, in the second mode, the method is operable to time align and combine several multipath components of the radio signal for collective conversion from chip rate to symbol rate. 
     
     
       12. A method according to  claim 10 , wherein calculating the second set of filter coefficients includes mapping the each finger position in the set of RAKE finger positions onto the channel impulse response estimate. 
     
     
       13. A method according to  claim 12 , wherein calculating the second set of filter coefficients further includes, for each finger position in the set of RAKE finger positions, calculating the complex conjugate of the channel impulse response estimate value that has been mapped to that finger position. 
     
     
       14. A method according to  claim 10 , wherein the method is compatible with Wideband Code Division Multiple Access (WCDMA). 
     
     
       15. A method according to  claim 10 , wherein converting the filtered signal to the symbol-rate signal includes despreading the filtered signal. 
     
     
       16. A method according to  claim 15 , wherein converting the filtered signal to the symbol-rate signal further includes descrambling the filtered signal. 
     
     
       17. A method according to  claim 10 , wherein calculating the first set of filter coefficients includes matrix inversion. 
     
     
       18. A method according to  claim 10 , wherein the filtering is finite impulse response (FIR) filtering and the configurable filter coefficients are tap weights.