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摘要
This work proposed the linear minimum mean square error ( LMMSE) space- time receivers for synchronous multi- rate direct sequence code devision multiple access ( DS/ CDMA) systems. The performance of the proposed receivers is analyzed. The high- rate ( HR) LMMSE space- time receiver with combining technique can provide essentially the same performance for low- rate ( LR) users as LR LMMSE space- time receiver while eliminate the time delay for the HR users. The performance of the proposed multi- rate LMMSE space- time receivers are studied in the context of two multi- rate access methods: multi- code ( MC) access where high data rate users multiplex their information streams onto multiple codes, and variable spreading length ( VSL) access where signature sequences of different lengths are assigned to users with different data rates. Through the simulation results, we show that: ( a) the proposed multi- rate LMMSE space- time receivers are optimum near- far resistant; ( b) the proposed multi- rate LMMSE space- time receivers have a clear performance improvement compared to the time only LMMSE dual rate receiver; ( c) there is a performance gain of the proposed multi- rate LMMSE space- time receivers compared to the multi- rate decorrelating space- time receiver when near- far ratio ( NFR) is low; ( d) The performance difference between MMSE combining and MRC in multi- rate system is much more pronounced than in single- rate system. Simulations also show that the VSL access method is more robust than MC access method considering changing rate- ratio in multi- rate systems.
- 出版日期2003-11
