During the data transmission process, data collision is a problem that we have to solve. This phenomenon may cause data loss, error or delay, thus affecting the normal operation of the device and the integrity of the data. It is different from signal interference. Interference refers to the adverse effect of external factors or other signal sources on the signal being wirelessly transmitted, while data collision refers specifically to the situation where two or more devices send data at the same time, causing the signals to interfere with each other at the receiving end.
Common technical methods in wireless transmission usually include: carrier sense multiple access/collision avoidance (CSMA/CA), time division multiple access (TDMA), frequency division multiple access (FDMA), code division multiple access (CDMA) technology.
Carrier sense multiple access/collision avoidance (CSMA/CA) is a common method in wireless networks. Before sending data, the device first monitors whether the channel is idle to avoid conflicts as much as possible. When the channel is idle, the device will not send data immediately, but wait for a random period of time (called backoff time) before sending. If the channel is occupied by other devices during the waiting period, it will wait for a random period of time before trying again. In addition, the possibility of collision can be further reduced through the request to send/clear to send (RTS/CTS) mechanism. The sending device first sends an RTS signal, and the receiving device replies with a CTS signal after receiving it. After receiving the CTS signal, other devices know not to send data during this period of time, thereby avoiding conflicts.
This method is widely used in Wi-Fi networks. It effectively reduces data collisions and improves the performance of wireless networks. For example, in a home wireless network, when multiple devices (such as mobile phones, computers, smart appliances, etc.) need to communicate with the wireless router at the same time, the CSMA/CA mechanism can coordinate their transmission to ensure that data can be transmitted more stably.
Time Division Multiple Access (TDMA) technology is a time slot transmission method that divides the transmission time of the wireless channel into several time frames, and each time frame is further divided into multiple time slots. Each device is assigned a specific time slot for data transmission, which avoids collisions caused by different devices sending data at the same time. It's like on a road, the time is divided into different time periods by traffic lights, and only specific vehicles are allowed to pass in each time period.
In some wireless communication systems that require high real-time data transmission, such as the GSM (Global System for Mobile Communications) network, TDMA technology is used. It can ensure that each user (device) has exclusive access to the channel in its allocated time slot, and the reliability of data transmission is high, but the disadvantage is that the channel utilization may be limited to a certain extent, because if a device does not transmit data in its allocated time slot, this time slot will be wasted.
Frequency Division Multiple Access (FDMA) technology divides the total bandwidth of the wireless channel into multiple different frequency bands (sub-channels), and each device is assigned a specific frequency band for data transmission. In this way, different devices work on different frequency bands, just like dividing different channels in a wide river, and the ships (data) on each channel do not interfere with each other, thus avoiding data collisions.
The advantage of FDMA is that the technology is relatively simple, and signals in different frequency bands can be transmitted simultaneously without interfering with each other, but the disadvantage is that the spectrum utilization rate is relatively low, and there needs to be a certain protection band between different frequency bands to prevent interference between frequency bands, etc.
Code Division Multiple Access (CDMA) technology assigns a unique coding sequence to each device. When sending data, the device encodes the data with this coding sequence before sending it. At the receiving end, the original data is restored by decoding using the same coding sequence. The coding sequences of different devices are mutually orthogonal, which means that even if multiple devices send data at the same time, they can be distinguished at the receiving end by the coding sequence, as if each device is assigned a unique language, and the receiving end can recognize and understand each language, thereby extracting the data sent by the corresponding device.