Providing reliable service to users close to the edge between cells remains a
challenge in cellular systems, even as 5G deployment is around the corner.
These users are subject to significant signal attenuation, which also degrades
their uplink channel estimates. Even joint detection using base station (BS)
cooperation often fails to reliably detect such users, due to near-far power
imbalance, and channel estimation errors. Is it possible to bypass the channel
estimation stage and design a detector that can reliably detect cell-edge user
signals under significant near-far imbalance? This paper shows, perhaps
surprisingly, that the answer is affirmative -- albeit not via traditional
multiuser detection. Exploiting that cell-edge user signals are weak but {\em
common} to different base stations, while cell-center users are unique to their
serving BS, this paper establishes an elegant connection between cell-edge user
detection and canonical correlation analysis (CCA) of the associated space-time
baseband-equivalent matrices. It proves that CCA identifies the common subspace
of these matrices, even under significant intra- and inter-cell interference.
The resulting mixture of cell-edge user signals can subsequently be unraveled
using a well-known algebraic signal processing technique. Interestingly, the
proposed approach does not even require that the signals from the different
base stations are synchronized -- the right synchronization can be
automatically determined as well. Experimental results demonstrate that the
proposed approach achieves order of magnitude BER improvements compared to
`oracle' multiuser detection that assumes perfect knowledge of the cell-center
user channels.

本文旨在探究绕过信道估计阶段并设计出一种可靠地检测在重要的近 - 远功率失衡下的细胞边缘用户信号的探测器，使用多基站联合检测往往不能可靠地检测到这些信号，而这种探测器可以通过基于典范相关分析的方法识别这些基带等效矩阵的公共子空间从而实现。

通过规范相关分析可靠检测未知的小区边缘用户

Reliable Detection of Unknown Cell-Edge Users Via Canonical Correlation  Analysis

We consider the downlink of a multi-cell system with multi-antenna base
stations and single-antenna user terminals, arbitrary base station cooperation
clusters, distance-dependent propagation pathloss, and general "fairness"
requirements. Base stations in the same cooperation cluster employ joint
transmission with linear zero-forcing beamforming, subject to sum or per-base
station power constraints. Inter-cluster interference is treated as noise at
the user terminals. Analytic expressions for the system spectral efficiency are
found in the large-system limit where both the numbers of users and antennas
per base station tend to infinity with a given ratio. In particular, for the
per-base station power constraint, we find new results in random matrix theory,
yielding the squared Frobenius norm of submatrices of the Moore-Penrose
pseudo-inverse for the structured non-i.i.d. channel matrix resulting from the
cooperation cluster, user distribution, and path-loss coefficients. The
analysis is extended to the case of non-ideal Channel State Information at the
Transmitters (CSIT) obtained through explicit downlink channel training and
uplink feedback. Specifically, our results illuminate the trade-off between the
benefit of a larger number of cooperating antennas and the cost of estimating
higher-dimensional channel vectors. Furthermore, our analysis leads to a new
simplified downlink scheduling scheme that pre-selects the users according to
probabilities obtained from the large-system results, depending on the desired
fairness criterion. The proposed scheme performs close to the optimal
(finite-dimensional) opportunistic user selection while requiring significantly
less channel state feedback, since only a small fraction of pre-selected users
must feed back their channel state information.

该研究旨在探讨多基站系统下行链路的多天线基站和单天线用户终端、任意基站合作集群、距离相关传播路径损耗和一般的 “公平性” 要求，并提出了一种新的简化下行调度方案，根据所需的公平性标准预先选择用户，其性能接近有限维机会用户选择的最优方案，同时需要明显较少的信道状态反馈。