Several common methods of channel division

First of all, why divide the channel and the method of dividing the channel? What is faith? ? ?

Reason: The purpose of channel division is to effectively manage and utilize communication resources, so as to ensure that the communication between different users or devices can be carried out simultaneously without interfering with each other.

Multiple Access Link: It is a technology and protocol in which multiple users or devices share the same physical link for communication. Common channel division methods include  Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA)

1. Frequency Division Multiple Access (FDMA) : The frequency spectrum is divided into different sub-channels, and each user or terminal occupies an independent sub-channel for communication. Each sub-channel is independent in time and can support multiple users to communicate at the same time

2.  Time Division Multiple Access (TDMA): Time is divided into continuous time slots, and each user's data is placed in each time slot in a certain order for transmission. Each user occupies a channel in a different time slot for communication.

3. Code Division Multiple Access (CDMA): Use different spreading codes to encode user data, and transmit on different codes to realize parallel communication between multiple users. Each user recovers the original data by decoding its own spreading code.

4. 

 The code division multiplexing book is not very detailed, let's talk about it in detail

Code Division Multiple Access (CDMA) is a wireless communication technology that uses different spreading codes (Spreading Code) to encode user data and simultaneously transmit multiple user signals on the same frequency. CDMA implements parallel communication between multiple users by encoding and decoding user signals.

The following is a detailed explanation of CDMA:

1. Spreading Code:
   - CDMA uses spreading codes to encode user data. The spreading code is a low-speed sequence, which is operated bit by bit with the original data at the sending end, and converted into a high-speed spreading code element (chip). In this way, each user's data is spread over a wider bandwidth for transmission.
   - Different users use different spreading codes so that signals from each other can be distinguished. The spreading codes of each user are mutually orthogonal, that is, they have no cross interference in the vertical direction.

2. Sending end:
   - At the sending end, the original data is encoded by a spreading code to form a spreading signal. This spread spectrum signal contains user information and is sent to the receiver.
   - The sender will also mix its own signal with other signals to form an overall signal for wireless transmission.

3. Receiver:
   - At the receiver, the overall received signal contains the spread spectrum signals of multiple users.
   - The receiving end uses the same spreading code as the sending end to decode to separate the signals of different users.
   - The decoded signal is processed to extract user-specific raw data from it.

4. Advantages:
   - Strong anti-interference ability: Since the spreading codes of each user are mutually orthogonal, CDMA can effectively resist multipath fading, noise and interference from other users.
   - High capacity: CDMA allows multiple users to share the same frequency resource at the same time, realizing high-capacity parallel communication.
   - Flexibility: The number of users in a CDMA system can be dynamically increased or decreased, and the system can be flexibly adjusted according to requirements.

In general, CDMA uses spreading codes to encode and decode user data, enabling multiple users to transmit data in parallel on the same frequency. It has the advantages of strong anti-interference ability, high capacity and flexibility, and is widely used in modern wireless communication systems, such as CDMA2000 and WCDMA (Wideband CDMA).

 What is a channel?

A channel refers to a physical medium or a virtual communication path used to transmit and deliver information. It is the pathway through which information is transmitted from the sender to the receiver. In a communication system, a channel can be an actual physical medium (such as cable, optical fiber, air, etc.), or a logical virtual path.

In a simple communication system, a channel connects a sender and a receiver so that information can be exchanged between the two through the transmission of signals. The sender converts the information into an appropriate signal, which is then transmitted over a channel to the receiver, who then converts the signal back to the original information.

Channels can be unidirectional (supporting the transmission of information in one direction only) or bidirectional (supporting the transmission of information in both directions). The characteristics of the channel depend on the transmission medium and communication technology used, including bandwidth, signal-to-noise ratio, transmission rate, transmission delay, etc.

In digital communications, common channel types include wired channels (such as Ethernet, telephone lines), wireless channels (such as wireless local area networks, cellular networks), and satellite channels. Each channel has its specific transmission characteristics and scope of application.

In summary, a channel is a path or channel for information transmission and transmission, which connects the sender and the receiver, enabling information to be communicated between the two through signal transmission.