In the third generation cellular radio system, a variable spreading factor (VSF) and a multi-code (MC) schemes are adopted to support multirate data transmission. Although these schemes affect the statistics of intercell interference and therefore the spectral efficiency, their precise impact is not completely understood. In this letter, a closed-form solution for the moments of the reverse link intercell interference is derived and the spectral efficiency is calculated from the solution. It is shown that the intercell interference gives a bad effect to the spectral efficiency as the portion of high rate user in a cell is increased.

This paper introduces an improved multistage parallel interference cancellation (PIC) technique that uses the reverse-link synchronous transmission technique (RLSTT) to improve the estimation of data at the initial stage. Because the subtraction of an interfering signal based on an incorrect bit decision quadruples the interference power for that signal, the relatively high decision bit error rate (BER) may lead to a poor cancellation or even a higher BER at the following stages. The RLSTT is a robust approach which takes into account the fact the tentative decision at the earlier stages is less reliable than the following stages and makes the earlier cancellation more reliable. The analysis demonstrates that a better transmission performance can be achieved by using the RLSTT at the initial stage of PIC.