In this work we treat the unsourced random access problem on a Rayleigh block-fading AWGN channel with multiple receive antennas. Specifically, we consider the slowly fading scenario where the coherence block-length is large compared to the number of active users and the message can be transmitted in one coherence block. Unsourced random access refers to a form of grant-free random access where users are considered to be a-priori indistinguishable and the receiver recovers a list of transmitted messages up to permutation. In this work we show that, when the coherence block length is large enough, a conventional approach based on the transmission of non-orthogonal pilot sequences with subsequent channel estimation and Maximum-Ratio-Combining (MRC) provides a simple energy-efficient solution whose performance can be well approximated in closed form. Furthermore, we analyse the MRC step when successive interference cancellation (SIC) is done in groups, which allows to strike a balance between receiver complexity and reduced transmit powers. Finally, we investigate the impact of power control policies taking into account the unique nature of massive random access, including short message lengths, uncoordinated transmission, a very large amount of concurrent transmitters with unknown identities, channel estimation errors and decoding errors. As a byproduct we also present an extension of the MMV-AMP algorithm which allows to treat pathloss coefficients as deterministic unknowns by performing maximum likelihood estimation in each step of the MMV-AMP algorithm.
翻译:在这项工作中,我们处理Rayleigh 区块布满多个接收天线的AWGN 频道上无源随机访问问题。 具体地说,我们考虑一种缓慢淡化的设想,即一致性区块长度与活跃用户的数量相比很大,而且信息可以在一个一致性区块中传递。 无源随机访问是指一种无赠与随机访问的形式,用户被视为优先不可分,接收者回收了一个传送信息到变异的列表。 在这项工作中,当一致性区块长度足够大时,我们展示一种常规方法,其基础是传输非正反向试验序列的试点序列,随后的频道估计和最大拉迪奥-Combining(MRC)提供了一种简单的节能解决方案,其性能性能非常接近于封闭的形式。 此外,当用户被视为优先取消干扰(SICE)时,我们分析MRC的步步步,从而能够在接收方复杂和传输能力减弱之间取得平衡。 最后,我们调查了权力控制政策的影响,考虑到大规模随机访问的独特性质,包括短信息段段段次的传输机序和最大波段段段级估算,我们通过不协调的MLIMVDRVA进行不规则的大幅递解变变压。