By means of random multiple access (RMA), there is a prevailing tendency for massive machine-type terminals to have access into networks without numerous signaling interactions and frequent resource scheduling. Being one of the promising techniques to fulfill this requirement, sparse code multiple access (SCMA) is anticipated to notably broaden connections for the communication system. However, when applying RMA in the SCMA uplink, as massive terminals would randomly transmit their packets in an uncoordinated way, it is quite possible for some terminals to share an identical codebook so as to introduce the codebook collision problem. In this case, an indefinite number of terminals with possible codebook collisions would competitively share a same block of channel resources, resulting in an overloading status and deteriorated performance. To deal with this problem, we illustrate first the potential utilization of codebook collisions for RMA and propose then a partial Gaussian tree approximation (PGTA) detector to relieve heavy computational burden due to overloading conditions. With approximate decomposition of likelihood functions that has rarely been discussed, the proposed PGTA detector with proper message passing rules is able to approach the performance of a traditional message passing detector with considerably lower complexity.

中文翻译：

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具有码本冲突的面向随机多路访问的SCMA上行链路的部分高斯树近似（PGTA）检测器

借助于随机多路访问（RMA），大型机器型终端普遍存在无需大量信令交互和频繁资源调度即可访问网络的趋势。作为满足此要求的有前途的技术之一，稀疏代码多路访问（SCMA）有望显着拓宽通信系统的连接。然而，当在SCMA上行链路中应用RMA时，由于大型终端将以不协调的方式随机地发送其分组，因此某些终端很有可能共享相同的码本，从而引入了码本冲突问题。在这种情况下，无限数量的具有可能的码本冲突的终端将竞争性地共享相同的信道资源块，从而导致过载状态和性能下降。为了解决这个问题，我们首先说明了RMA密码本冲突的潜在利用，然后提出了部分高斯树近似（PGTA）检测器，以减轻由于过载情况造成的繁重计算负担。通过很少讨论的似然函数的近似分解，所提出的具有适当消息传递规则的PGTA检测器能够以相当低的复杂性接近传统消息传递检测器的性能。