Pilot-Based Unsourced Random Access With a Massive MIMO Receiver, Interference Cancellation, and Power Control
Pilot-Based Unsourced Random Access With a Massive MIMO Receiver, Interference Cancellation, and Power Control
复制标题
具有大规模 MIMO 接收器、干扰消除和功率控制的基于导频的无源随机接入
DOI：
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发表时间：
2021
影响因子：
16.4
通讯作者：
G. Caire
中科院分区：
文献类型：
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作者：
Alexander Fengler;O. Musa;P. Jung;G. Caire
研究了具有多接收天线的瑞利块衰落AWGN信道上的无源随机接入问题。具体来说，我们处理慢衰落场景，其中相干块长度与活跃用户数量相比较大，并且消息可以在单个衰落相干块中传输。无源随机访问是指一种未经授权的随机访问形式，其中用户被限制使用相同的码本，因此是先验的不可区分的。接收方必须恢复已发送消息的列表直至排列。在本文中，我们提出了一种基于将用户消息分成两部分的方法。首先，一小块比特从普通的“导频”码本中选择一个相对较短的码字。然后用高斯信道的标准分组码对剩余的消息位进行编码。接收机利用多测量向量近似消息传递（MMV-AMP）算法从导频部分估计活跃用户信道，然后利用估计的信道进行相干最大比合并（MRC）对第二部分进行解码。我们对所提出的方案提供了一个精确的封闭形式近似分析。此外，我们分析了在用户组上执行连续干扰消除时的MRC解码，在复杂性和性能之间取得了有吸引力的权衡。最后，考虑到大规模随机访问的独特性质，我们研究了功率控制策略的影响。作为副产品，我们还提出了MMV-AMP算法的扩展，该算法允许通过在MMV-AMP算法的每一步执行最大似然估计将路径损失系数视为确定性未知数。
We consider the unsourced random access problem on a Rayleigh block-fading AWGN channel with multiple receive antennas. Specifically, we treat the slow fading scenario where the coherence blocklength is large compared to the number of active users and a message can be transmitted in a single fading coherence block. Unsourced random access refers to a form of grant-free random access where users are constrained to use the same codebook and therefore are a priori indistinguishable. The receiver must recover the list of transmitted messages up to permutations. In this paper, we propose an approach based on splitting the user messages into two parts. First, a small block of bits selects a relatively short codeword from a common “pilot” codebook. Then the remaining message bits are encoded by a standard block code for the Gaussian channel. The receiver makes use of a multiple measurement vector approximate message passing (MMV-AMP) algorithm to estimate the active user channels from the “pilot” part, and then uses the estimated channels to perform coherent maximum ratio combining (MRC) to decode the second part. We provide an accurate closed-form approximated analysis of the proposed scheme. Furthermore, we analyze the MRC decoding when successive interference cancellation is performed over groups of users, striking an attractive tradeoff between complexity and performance. Finally, we investigate the impact of power control policies, taking into account the unique nature of massive random access. As a byproduct, we also present an extension of the MMV-AMP algorithm which allows pathloss coefficients to be treated as deterministic unknowns by performing maximum likelihood estimation in each step of the MMV-AMP algorithm.