Channel estimation is the main hurdle to reaping the benefits promised by the intelligent reflecting surface (IRS), due to its absence of ability to transmit/receive pilot signals as well as the huge number of channel coefficients associated with its reflecting elements. Recently, a breakthrough was made in reducing the channel estimation overhead by revealing that the IRS-BS (base station) channels are common in the cascaded user-IRS-BS channels of all the users, and if the cascaded channel of one typical user is estimated, the other users' cascaded channels can be estimated very quickly based on their correlation with the typical user's channel \cite{b5}. One limitation of this strategy, however, is the waste of user energy, because many users need to keep silent when the typical user's channel is estimated. In this paper, we reveal another correlation hidden in the cascaded user-IRS-BS channels by observing that the user-IRS channel is common in all the cascaded channels from users to each BS antenna as well. Building upon this finding, we propose a novel two-phase channel estimation protocol in the uplink communication. Specifically, in Phase I, the correlation coefficients between the channels of a typical BS antenna and those of the other antennas are estimated; while in Phase II, the cascaded channel of the typical antenna is estimated. In particular, all the users can transmit throughput Phase I and Phase II. Under this strategy, it is theoretically shown that the minimum number of time instants required for perfect channel estimation is the same as that of the aforementioned strategy in the ideal case without BS noise. Then, in the case with BS noise, we show by simulation that the channel estimation error of our proposed scheme is significantly reduced thanks to the full exploitation of the user energy.
翻译:频道估计是获取智能反射表面(IRS)所承诺的好处的主要障碍,原因是它缺乏传输/接收实验信号的能力,以及与其反射元素相关的频道系数数量巨大。最近,在减少频道估计管理费方面,取得了突破,显示所有用户的级联用户-IRS-BS(基地台)频道是常见的。如果对一个典型用户的级联频道进行估算,其他用户的级联频道可以根据其与典型用户频道的关联性快速估算。然而,这一战略的一个局限性是用户能源的浪费,因为许多用户在典型用户频道估计时需要保持缄默。在本文件中,通过观察用户的级联用户-IRS-BS(基地台)频道在所有级联至BS天线的所有级联频道中都是常见的。基于这一发现,我们提议在上链接通信中采用新型双阶段的频道估计协议协议。具体而言,BSS的典型用户战略在BS级联路段期间需要大幅保持静电路段的预估测算。