Time Division Multiple Access (TDMA) Technology: Principles and Applications of Time-Sliced Multiple Access Communication

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### 1.2 Development of TDMA Technology

Time Division Multiple Access (TDMA), a multiple access technology widely used in wireless communication systems, allocates resources by dividing time into multiple slots, allowing multiple users to communicate on the same frequency. Here is a detailed overview of the development of TDMA technology:

#### 1.2.1 Early Development (1960s)

- **Background**: In the 1960s, with the increasing demand for wireless communication, traditional Frequency Division Multiple Access (FDMA) and Code Division Multiple Access (CDMA) gradually revealed their limitations, especially in terms of spectral efficiency and user capacity.
- **TDMA Concept**: Researchers began exploring the allocation of time as a resource, thus proposing the concept of TDMA. At that time, TDMA was mainly used in military and satellite communication fields.

#### 1.2.2 Early Commercialization (1970s)

- **First-Generation Mobile Communication**: In the 1970s, TDMA technology was introduced into the first-generation mobile communication systems, particularly during the establishment of the GSM (Global System for Mobile Communications) standard in Europe.
- **GSM Standard**: The establishment of the GSM standard in 1982 marked the commercialization of TDMA technology. The GSM system adopted TDMA technology, dividing each channel into multiple time slots, thereby allowing multiple users to share the same frequency.

#### 1.2.3 Technological Maturity (1980s to 1990s)

- **GSM Promotion**: The GSM system quickly spread in Europe and other regions, becoming one of the most widely used mobile communication standards globally. The successful application of TDMA technology significantly increased the capacity of mobile communication networks.
- **Various Variants**: With technological advancements, multiple TDMA-based variants emerged, such as IS-136 (North American TDMA standard) and PDC (Japanese Personal Digital Cellular).

#### 1.2.4 Integration with Other Technologies (2000s)

- **Emergence of 3G Technology**: Entering the 21st century, with the development of 3G technology, TDMA was combined with other technologies, such as CDMA and OFDM, to form more complex multiple access schemes.
- **TD-SCDMA**: China proposed TD-SCDMA (Time Division-Synchronous Code Division Multiple Access) in the 3G standard, a product of the combination of TDMA and CDMA, aimed at improving spectral efficiency.

#### 1.2.5 Modern Development (2010s to Present)

- **LTE and 5G**: Although LTE (Long-Term Evolution) and 5G primarily use OFDM technology, TDMA still plays an important role in certain scenarios, especially in the Internet of Things (IoT) and Low-Power Wide Area Networks (LPWAN).
- **Emerging Applications**: TDMA technology has received renewed interest in some emerging applications, such as smart grid and intelligent transportation systems, where TDMA can effectively manage communication between devices.

## 1.3 Application Areas of TDMA Technology

TDMA technology is widely used in mobile communication and wireless local area networks. In mobile communication, TDMA technology is used to implement voice calls and data transmission. TDMA technology in wireless local area networks can provide high-speed wireless network connections, supporting multiple users' simultaneous internet access.

Furthermore, TDMA technology is applied in aerospace, military communication, and other fields to meet the demands for high spectral efficiency and interference resistance. With the advent of the 5G era, TDMA technology will continue to play a significant role and, by integrating with other multiple access technologies, drive innovation and progress in communication technology.

# 2. Principles of Time-Division Multiple Access Communication

## TDMA Schematic

**TDM: Divides the channel into N time slots and transmits N parallel data streams.**

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The essence of OFDM is that the sending end uses data to be modulated to weight a series of complex exponential signals, synthesizing a complex signal, which is transmitted through IQ modulation. The receiving end recovers the complex signal through IQ demodulation, calculates the weighting coefficients, which are the Fourier coefficients, and thus obtains the modulated data.

In actual communication systems, IDFT (Inverse Discrete Fourier Transform) is generally used to implement baseband OFDM modulation, and DFT is used to implement baseband OFDM demodulation.

Using IDFT for baseband OFDM modulation: By IDFT, N parallel frequency domain sample data are transformed into N parallel time domain sample data, which are then converted from parallel to serial and from digital to analog, resulting in the OFDM baseband modulation signal. Finally, the real and imaginary parts are modulated onto the radio frequency carrier through IQ modulation.

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According to Shannon's formula, increasing the bandwidth B can lower the requirement for the signal-to-noise ratio without changing the channel capacity.

How to implement spreading and despreading:

Spreading: The input bit stream is multiplied by the spreading code, converting the low-speed bit stream into a high-speed chip stream.

Despreading: The high-speed chip stream is multiplied by the despreading code (identical to the spreading code), summed, and if the result is positive, it is judged as 0; if negative, it is judged as 1, thus restoring the original bit stream.

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*[W_{0}^{64}](***: Used for spreading of the pilot channel;
![W_{32}^{64}](***: Used for spreading of the synchronization channel;
![W_{1}^{64} \sim W_{7}^{64}](***: Used for spreading of the paging channel, can also be used as traffic channels;
Other Walsh codes: Used for spreading of the forward FCH and SCH channels.

**The chip rate in the CDMA system is 1.2288Mchip/s**

**The CDMA system uses an m-sequence with a period of 2^15-1=32676 for pilot communication (pilot communication) The following is the principle of pilot communication:**

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2. **Channel Allocation**: Each user is allocated one or more slots for communication. Different