This paper proposes a flexible pilot assignment method to jointly optimize
the uplink and downlink data transmission in multi-cell Massive multiple input
multiple output (MIMO) systems with correlated Rayleigh fading channels. By
utilizing a closed-form expression of the ergodic spectral efficiency (SE)
achieved with maximum ratio processing, we formulate an optimization problem
for maximizing the minimum weighted sum of the uplink and downlink SEs subject
to the transmit powers and pilot assignment sets. This combinatiorial
optimization problem is solved by two sequential algorithms: a heuristic pilot
assignment is first proposed to obtain a good pilot reuse set and the data
power control is then implemented. Numerical results manifest that the proposed
algorithm converges fast to a better minimum sum SE per user than the
algorithms in previous works.

本文提出一种灵活的载波分配方法，能够联合优化具有相关瑞利衰落信道的多小区大规模多输入多输出系统中的上行和下行数据传输，在最小化加权上下行谱效率之和的约束下，通过利用最大比处理获得的符号误差率的闭式表达式进行优化问题的建模，并使用两种连续的算法来解决组合优化问题和功率控制。数值结果表明，所提出的算法比以前的算法更快地收敛到更好的用户最小和谱效率。

巨型 MIMO 系统中伴随空间相关性的上下行联合频谱效率提升的试点分配

Pilot Assignment for Joint Uplink-Downlink Spectral Efficiency  Enhancement in Massive MIMO Systems with Spatial Correlation

How to meet the demand for increasing number of users, higher data rates, and
stringent quality-of-service (QoS) in the beyond fifth-generation (B5G)
networks? Cell-free massive multiple-input multiple-output (MIMO) is considered
as a promising solution, in which many wireless access points cooperate to
jointly serve the users by exploiting coherent signal processing. However,
there are still many unsolved practical issues in cell-free massive MIMO
systems, whereof scalable massive access implementation is one of the most
vital. In this paper, we propose a new framework for structured massive access
in cell-free massive MIMO systems, which comprises one initial access
algorithm, a partial large-scale fading decoding (P-LSFD) strategy, two pilot
assignment schemes, and one fractional power control policy. New closed-form
spectral efficiency (SE) expressions with maximum ratio (MR) combining are
derived. The simulation results show that our proposed framework provides high
SE when using local partial minimum mean-square error (LP-MMSE) and MR
combining. Specifically, the proposed initial access algorithm and pilot
assignment schemes outperform their corresponding benchmarks, P-LSFD achieves
scalability with a negligible performance loss compared to the conventional
optimal large-scale fading decoding (LSFD), and scalable fractional power
control provides a controllable trade-off between user fairness and the average
SE.

本文提出了一种新的结构化大规模接入算法框架，包括一种初始接入算法、一种部分大尺度衰落解码策略、两种导频分配方案和一种分式功率控制策略，模拟结果表明，该框架在局部部分最小均方误差 (LP-MMSE) 和最大比例 (MR) 合并时提供了高的谱效率。

可扩展无线电脱耦大规模天线阵列的结构化大规模访问

Structured Massive Access for Scalable Cell-Free Massive MIMO Systems

In-band full-duplex (FD) operation is practically more suited for short-range
communications such as WiFi and small-cell networks, due to its current
practical limitations on the self-interference cancellation. In addition,
cell-free massive multiple-input multiple-output (CF-mMIMO) is a new and
scalable version of MIMO networks, which is designed to bring service antennas
closer to end user equipments (UEs). To achieve higher spectral and energy
efficiencies (SE-EE) of a wireless network, it is of practical interest to
incorporate FD capability into CF-mMIMO systems to utilize their combined
benefits. We formulate a novel and comprehensive optimization problem for the
maximization of SE and EE in which power control, access point-UE (AP-UE)
association and AP selection are jointly optimized under a realistic power
consumption model, resulting in a difficult class of mixed-integer nonconvex
programming. To tackle the binary nature of the formulated problem, we propose
an efficient approach by exploiting a strong coupling between binary and
continuous variables, leading to a more tractable problem. In this regard, two
low-complexity transmission designs based on zero-forcing (ZF) are proposed.
Combining tools from inner approximation framework and Dinkelbach method, we
develop simple iterative algorithms with polynomial computational complexity in
each iteration and strong theoretical performance guaranteed. Furthermore,
towards a robust design for FD CF-mMIMO, a novel heap-based pilot assignment
algorithm is proposed to mitigate effects of pilot contamination. Numerical
results show that our proposed designs with realistic parameters significantly
outperform the well-known approaches (i.e., small-cell and collocated mMIMO) in
terms of the SE and EE. Notably, the proposed ZF designs require much less
execution time than the simple maximum ratio transmission/combining.

该研究论文针对实现更高的无线电频谱和能量效率，提出了一种基于 in-band full-duplex 与 cell-free massive MIMO 的联合设计方案，优化了功控制、入口点和用户设备相关联和入口点选择，并结合零强制传输设计提高了计算效率及理论性能，并采用基于堆的导频分配算法来抵消导频污染。