Chip-equalised UMTS downlink for fast fading channels

TY - GEN

T1 - Chip-equalised UMTS downlink for fast fading channels

AU - White, G

AU - Zakharov, Y

AU - Burr, A

PY - 2004

Y1 - 2004

N2 - The 3(rd) generation of mobile communications networks, such as those based on WCDMA, will require high performance downlink receivers to maximise capacity. The Rake receiver, commonly proposed for WCDMA systems to counteract multipath channel effects, provides poor performance when there are a high number of active users per cell. This is due to loss of orthogonality between user spreading codes, which results in high levels of multiple access interference (MAI). Chip equalisation has been shown to suppress MAI by restoring the orthogonality of user codes prior to despreading. In this paper, we propose a simple system for chip equalisation of 3(rd) generation UNITS transmission frames in fast fading channels. FIR MMSE equalisation with common pilot channel estimation is used and slot-wise linear interpolation between equaliser tap coefficients provides a simple method for tracking the time-varying channel. The performance of the proposed system over a vehicular multipath timevariant channel is assessed by simulation. The benefits to system performance of UNITS-standard turbo coding and interleaving in the fast fading environment are studied. Performance is compared with the equivalent Rake receiver at each stage. It is shown that, despite increased sensitivity to channel estimation error relative to the Rake receiver, the proposed method can be used to achieve significant performance benefits in highly-loaded cells, even for high mobile terminal speed. Performance benefits are particularly marked where chip equalisation is used in conjunction with turbo coding and interleaving.

AB - The 3(rd) generation of mobile communications networks, such as those based on WCDMA, will require high performance downlink receivers to maximise capacity. The Rake receiver, commonly proposed for WCDMA systems to counteract multipath channel effects, provides poor performance when there are a high number of active users per cell. This is due to loss of orthogonality between user spreading codes, which results in high levels of multiple access interference (MAI). Chip equalisation has been shown to suppress MAI by restoring the orthogonality of user codes prior to despreading. In this paper, we propose a simple system for chip equalisation of 3(rd) generation UNITS transmission frames in fast fading channels. FIR MMSE equalisation with common pilot channel estimation is used and slot-wise linear interpolation between equaliser tap coefficients provides a simple method for tracking the time-varying channel. The performance of the proposed system over a vehicular multipath timevariant channel is assessed by simulation. The benefits to system performance of UNITS-standard turbo coding and interleaving in the fast fading environment are studied. Performance is compared with the equivalent Rake receiver at each stage. It is shown that, despite increased sensitivity to channel estimation error relative to the Rake receiver, the proposed method can be used to achieve significant performance benefits in highly-loaded cells, even for high mobile terminal speed. Performance benefits are particularly marked where chip equalisation is used in conjunction with turbo coding and interleaving.

M3 - Conference contribution

SN - 0-7803-8337-0

SP - 377

EP - 381

BT - 2004 IEEE 5TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS

PB - IEEE

CY - NEW YORK

T2 - 5th IEEE Workshop on Signal Processing Advances in Wireless Communications

Y2 - 11 July 2004 through 14 July 2004

ER -