Improved Decoder Likelihoods for 3G Cellular Uplink over Asynchronous Multi-Path Fading Channels
Improved Decoder Likelihoods for 3G Cellular Uplink over Asynchronous Multi-Path Fading Channels
复制标题
DOI：
10.1109/vtcfall.2016.7881041
复制
发表时间：
2016-09
期刊：
影响因子：
--
通讯作者：
Shady O. Elbassiouny;A. Elezabi
中科院分区：
文献类型：
--
作者：
Shady O. Elbassiouny;A. Elezabi
预计在未来十年内仍将被广泛部署的3G系统采用直接序列码分多址（DS-CDMA）技术，该技术主要受到多址干扰（MAI）的影响。本文针对实际上行链路提出了改进的解码器对数似然比。基本思想是利用关于用户相互关联和衰落系数的知识来获得MAI的条件方差，而不是传统地假设它是具有固定方差的高斯分布。条件作用可能是基于用户的相互关系和/或信道衰落系数，并导致时间相关的方差。我们提出了芯片同步情况下的改进对数似然比，并推导了芯片异步多径衰落信道和提高余弦发射滤波器的对数似然比。我们的仿真框架采用3G标准的系统参数。正如预期的那样，同步用例的改进要大得多。然而，即使在蜂窝上行链路的实际情况下，由于illr的性能优势是显著接近3db。
3G systems, which are expected to still be widely deployed over the next decade, utilize Direct-Sequence Code-Division Multiple-Access (DS-CDMA) which suffers mainly from the Multiple Access Interference (MAI). This paper proposes improved decoder log-likelihood ratios for the practical uplink. The basic idea is to utilize knowledge about user cross-correlations and fading coefficients to obtain conditional variances for the MAI, rather than to conventionally assume it to be Gaussian with fixed variance. The conditioning may be on the users' cross-correlations and/or the channel fading coefficients and results in a time-dependent variance. We present improved log-likelihood ratios (ILLRs) for the chip synchronous case, and derive the ILLRs for the chip-asynchronous multi-path fading channel and the raised-cosine transmit filter. Our simulation framework applies system parameters from 3G standards. The improvements for the synchronous case are much larger, as expected. However, even in the practical case of cellular uplink, the performance advantage due to ILLRs is significant approaching 3 dB.