Dynamic Spectrum Access (DSA): The Technical Principles of Flexible Spectrum Resource Allocation

# 1. Introduction

## 1.1 The Concept of Dynamic Spectrum Access Technology

Dynamic Spectrum Access (DSA) is a technology that manages and allocates radio spectrum resources through intelligent methods. Traditional methods of spectrum allocation are typically static, planned in advance by governments or operators for specific communication systems or service providers, resulting in low efficiency in the use of spectrum resources. DSA technology can effectively improve the utilization of spectrum resources by real-time sensing, selection, and sharing of unused or underutilized spectrum.

## 1.2 The Importance of Flexible Spectrum Resource Allocation

With the rapid development of wireless communication technology and the proliferation of wireless devices, the demand for spectrum resources continues to grow. However, traditional methods of spectrum allocation have many issues, such as spectrum waste, spectrum congestion, and spectrum monopolies. Therefore, the importance of flexible spectrum resource allocation is becoming increasingly significant. The introduction of DSA technology can achieve dynamic spectrum allocation and sharing, improving the utilization efficiency of spectrum resources to meet the needs of different wireless communication systems, and promoting innovation and development in wireless communication technology.

This is an excerpt from the introduction to dynamic spectrum access technology, and the following will continue to introduce traditional methods of spectrum allocation.

# 2. Traditional Methods of Spectrum Allocation

Traditional methods of spectrum allocation typically include Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA), all of which allocate different users in different times or frequencies.

### 2.1 Frequency Division Multiple Access (FDMA)

Frequency Division Multiple Access is a method that divides the available spectrum into multiple frequency bands, each user or device communicates on one frequency band. Each band is assigned to a user and can only be used exclusively by that user. The disadvantage of this method is that the spectrum utilization rate is low, as during certain periods some frequency bands may be idle.

# Code Example: Frequency Division Multiple Access
# Assume there are 4 users who need to communicate, divide the available spectrum into 4 frequency bands, each band is exclusively used by a user

# Spectrum division
frequency_bands = ['Band 1', 'Band 2', 'Band 3', 'Band 4']

# User communication
for user in range(4):
     print(f"User {user+1} is using {frequency_bands[user]} for communication")

# Run Results:
# User 1 is using Band 1 for communication
# User 2 is using Band 2 for communication
# User 3 is using Band 3 for communication
# User 4 is using Band 4 for communication

In this example, we assume there are 4 users who need to communicate. The available spectrum is divided into 4 frequency bands, and each user exclusively uses one band. Each user uses a frequency band for communication.

### 2.2 Time Division Multiple Access (TDMA)

Time Division Multiple Access is a method that divides time into multiple slots, and each user communicates in one slot. Users communicate according to a predetermined slot sequence, and each user can only transmit data in the slot assigned to it. The disadvantage of this method is that if the communication volume between users is unbalanced, spectrum utilization may be affected.

// Code Example: Time Division Multiple Access
// Assume there are 4 users who need to communicate, divide time into 4 slots, each user communicates in one slot

// Slot allocation
String[] time_slots = {"Slot 1", "Slot 2", "Slot 3", "Slot 4"};

// User communication
for (int user = 0; user < 4; user++) {
     System.out.println("User " + (user+1) + " is using " + time_slots[user] + " for communication");
}

// Run Results:
// User 1 is using Slot 1 for communication
// User 2 is using Slot 2 for communication
// User 3 is using Slot 3 for communication
// User 4 is using Slot 4 for communication

In this example, we assume there are 4 users who need to communicate. Time is divided into 4 slots, and each user is sequentially assigned to a slot for communication.

### 2.3 Code Division Multiple Access (CDMA)

Code Division Multiple Access is a multiple access method that uses coding technology. Each user has a unique coding sequence, and user data packets are encoded and transmitted simultaneously. The receiver uses the corresponding decoder to restore the data packets to their original data. This method has high spectrum utilization, but interference issues may arise when a large number of users communicate at the same time.

// Code Example: Code Division Multiple Access
// Assume there are 4 users who need to communicate, each user has a unique coding sequence, and data packets are transmitted simultaneously

// User coding
const user1_code = [1, -1, 1, -1];
const user2_code = [1, 1, -1, -1];
const user3_code = [-1, 1, 1, -1];
const user4_code = [-1, -1, -1, 1];

// Sending data packets
const data_packet = [0, 1, 0, 1];

// Simultaneously transmitting data packets
const transmitted_data = [];
for (let i = 0; i < 4; i++) {
     transmitted_data[i] = user1