Spatial Division Multiplexing (SDM) Technology: Application of Spatial Multiplexing in Multi-Antenna Systems

# 1. Introduction

## 1.1 Overview of Space Division Multiplexing Technology
Space Division Multiplexing (SDM) is a technique that utilizes the physical space for information transmission. By multiplexing signals in the spatial dimension, it enables independent transmission between multiple users or streams. SDM technology is widely applied in multi-antenna systems, significantly enhancing system capacity and spectral efficiency.

## 1.2 Advantages and Challenges of Multi-antenna Systems
Multi-antenna systems leverage spatial and spectral diversity to notably improve signal coverage, data transfer rates, and system reliability. However, these systems also face challenges such as antenna selection, interference management, and increased complexity.

## 1.3 Research Background and Motivation
With the rapid development of mobile communications and wireless networks, how to improve system capacity, spectral efficiency, and coverage has become a hot topic of current research. Against this backdrop, SDM technology, as an important optimization tool for multi-antenna systems, has attracted widespread attention and research.

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# 2. Fundamentals of Space Division Multiplexing Technology

Space Division Multiplexing (SDM) is a technology that utilizes spatial resources for data transmission, mainly applied in multi-antenna systems. In traditional multi-antenna systems, antennas operate independently of each other, while SDM technology utilizes the independence in space dimensions to transmit different data streams through distinct spatial channels, thereby increasing the system's transmission capacity and performance.

#### 2.1 Principles and Basic Concepts of SDM
SDM technology exploits the spatial independence between antennas to enable simultaneous transmission by multiple users within limited spectral resources. By weighting and combining signals from different antennas, it is possible to separate and transmit different user signals, thereby improving the system's spectral utilization efficiency.

#### 2.2 Operating Principles of Multi-antenna Systems
Multi-antenna systems use spatial diversity and spatial multiplexing to enhance system capacity and coverage. By using multiple antennas to receive signals from different transmission paths and combining them using statistical characteristics, the multipath effect caused by signal transmission paths can be effectively suppressed, and the system's reception performance can be improved.

#### 2.3 Comparison of SDM with Traditional Multi-antenna Systems
Traditional multi-antenna systems mainly rely on spatial diversity to enhance system reliability and coverage, while SDM technology places more emphasis on utilizing spatial multiplexing to increase system capacity and spectral efficiency. SDM technology enables multi-antenna systems to achieve higher data transfer rates between users and higher system capacity under the same frequency bands and bandwidth conditions.

# 3. Applications of SDM Technology in Multi-antenna Systems

SDM technology has a wide range of applications in multi-antenna systems and can optimize system performance through antenna selection algorithms, power control algorithms, and scheduling algorithms.

#### 3.1 Antenna Selection Algorithms Based on SDM
In multi-antenna systems, SDM technology can be used to select different antennas to maximize system throughput or minimize transmission interference. SDM technology achieves multi-user signal transmission in space by assigning different resource blocks or carriers to different antennas. The antenna selection algorithm can select the best antenna for communication based on the user's location and channel state information.

Below is a Python example code for an antenna selection algorithm based on SDM:

def antenna_selection(users, antennas, channel