Definition and Function
Channel coding allows for error correction by adding redundancy bits at the transmitter end and is a core technology for improving wireless transmission reliability. Wireless channels are subject to fading, interference, multipath, and other adverse factors, making raw data prone to errors during transmission. By introducing check information, channel coding enables the receiver to detect and correct a certain number of errors, thereby achieving a lower bit error rate under the same signal-to-noise ratio.
Shannon's theorem indicates that, at a given channel capacity, there exist theoretically error-free transmission schemes, and channel coding is the key method to approach this limit. From the Turbo codes of the 3G era and their continued optimization in 4G, to LDPC codes for data channels and Polar codes for control channels in 5G, every advancement in coding technology has significantly enhanced the spectral efficiency and reliability of mobile communications.
Main Coding Types
Turbo Code
Main coding for 3G/4G, close to Shannon limit, iterative decoding has high complexity
LDPC Code
Used in 5G data channels, high throughput, parallel decoding, suitable for large data blocks
Polar Code
5G control channel adoption, short code performance is excellent, Huawei-led standard
Convolutional code
Traditional scheme, 2G/early systems, Viterbi decoding
Comparison of coding characteristics
| Coding Type | Applicable scenarios | Code Length Characteristics | Complexity |
|---|---|---|---|
| Turbo | 3G/4G Data and Control | Medium and Long Codes Preferred | High (Iteration) |
| LDPC | 5G Data Channel | Long Code Preferred | Medium (Parallel) |
| Polar | 5G Control Channel | Short code advantage | Low (SCL) |
| Convolutional code | 2G/legacy system | Any | Low |
5G coding selection logic
5G eMBB scenarios have high throughput and low latency requirements for data channels. The parallel decoding feature and long code performance of LDPC codes make them the preferred choice. Control channels carry critical signaling, with small data volumes but extremely high reliability requirements. Polar codes approach the Shannon limit in short code scenarios and have low decoding latency, making them suitable for latency-sensitive services like URLLC. This "data LDPC + control Polar" combination is the technological consensus reached after intense debates in the 5G standards.
Considerations for IoT scenarios
IoT devices mostly use standards such as NB-IoT, LTE-M, LTE Cat.1, etc., with the underlying layer still relying on Turbo or simplified coding. For weak coverage and low-power scenarios, coding gain directly affects link budget and battery life. Choosing the appropriate coding scheme, number of repetitions, and modulation order is key to balancing reliability and efficiency.
SimtoLink's IoT SIM cards and module solutions all operate on cellular networks using advanced channel coding. Whether it is the deep coverage of NB-IoT, the medium-rate transmission of Cat.1, or future new standards like 5G RedCap, channel coding is the fundamental support for ensuring reliable data transmission. In scenarios such as smart metering, vehicle terminals, and industrial sensors, SimtoLink relies on the operator network's coding and retransmission mechanisms to ensure that IoT devices can still report data stably under weak signal conditions, reducing the repeated transmissions and power waste caused by transmission errors.