How is channel coding used in wireless communication?

1 What is channel coding?

Channel coding is a process that transforms the original data into a longer and more robust code that can withstand the errors and impairments caused by the wireless channel. Channel coding can be seen as a form of data protection that enhances the data's resilience and recoverability. Channel coding is usually done by adding extra bits, called parity bits, to the data, which can be used to detect and correct errors at the receiver. Channel coding can also involve rearranging or interleaving the data bits, which can reduce the impact of burst errors.

2 How does channel coding work?

Channel coding works by applying a mathematical function, called a code, to the data before transmitting it over the wireless channel. The code defines how the data bits are mapped to the code bits, and how the code bits are decoded back to the data bits at the receiver. The code also determines the rate and the performance of the channel coding. The rate is the ratio of the data bits to the code bits, and it reflects how much redundancy is added by the channel coding. The performance is the ability of the channel coding to reduce the error probability and increase the data reliability.

3 Why is channel coding important?

Channel coding is important because it enables wireless communication systems to achieve higher data rates, lower power consumption, and better quality of service. By adding redundancy and structure to the data, channel coding can improve the signal-to-noise ratio (SNR) and the bit error rate (BER) of the wireless channel, which means that more data can be transmitted and received with less errors and interference. Channel coding can also reduce the required transmit power, which can save battery life and extend the coverage of wireless devices. Moreover, channel coding can support different levels of data protection and quality, which can accommodate different types of wireless applications and services.

4 What are some examples of channel coding?

Channel coding is used in many wireless communication standards and technologies, such as cellular networks, Wi-Fi, Bluetooth, satellite communication, and radio broadcasting. Each system may use different types of channel codes depending on its design and requirements. Examples include block codes, which divide data into fixed-length blocks and add parity bits; convolutional codes, which use a sliding window to process data bits; turbo codes, which combine two or more convolutional codes and an interleaver; and low-density parity-check (LDPC) codes that use a sparse matrix to define the relationship between data bits and parity bits. All of these codes can provide better error correction than block codes, though they require varying levels of computational complexity and memory. LDPC codes have lower decoding complexity and latency than turbo codes.

5 How is channel coding used in GPRS?

GPRS, or General Packet Radio Service, is a wireless data service that operates on the GSM cellular network. GPRS allows users to access the internet and other data applications on their mobile devices. GPRS uses channel coding to optimize the data transmission and reception over the wireless channel. GPRS uses four coding and modulation schemes, called CS-1, CS-2, CS-3, and CS-4, which differ in their channel coding rate, modulation type, and data throughput. The coding and modulation schemes are selected dynamically based on the channel conditions and the user's data requirements. The table below summarizes the main features of the GPRS coding and modulation schemes.

| Scheme | Channel coding rate | Modulation type | Data throughput (kbps) |

| ------ | ------------------- | --------------- | ---------------------- |

| CS-1 | 1/2 | GMSK | 9.05 |

| CS-2 | 2/3 | GMSK | 13.4 |

| CS-3 | 3/4 | GMSK | 15.6 |

| CS-4 | 1 | 8-PSK | 21.4 |

As you can see, the lower the channel coding rate, the higher the redundancy and the lower the data throughput. The higher the modulation type, the higher the data throughput and the lower the robustness. GPRS uses a link adaptation mechanism to choose the most suitable coding and modulation scheme for each data transmission, based on the measured signal quality and the requested data rate. This way, GPRS can achieve the best trade-off between data speed and reliability over the wireless channel.

6 Here’s what else to consider

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