Polar Coding in 5G: Advantages and Disadvantages

This article explores the benefits and drawbacks of Polar Coding, a technology used in 5G networks for the control channel within the eMBB (Enhanced Mobile Broadband) service category.

What is Polar Coding?

• Polar codes are linear block error correction codes.
• They represent a coding system designed to achieve Shannon capacity, meaning they are provably capable of reaching the theoretical limits of data transmission.
• Invented by Erdal Arikan in 2009.
• Polar codes are implemented in 5G NR (New Radio) as control channels for the eMBB service, as defined by 3GPP standards. For data channels, 5G utilizes LDPC (Low-Density Parity-Check) codes.

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• Polar coding can be implemented as an encoder in the transmitter and a decoder in the receiver. The figure above illustrates a polar coding system with polar encoder and decoder modules.
• They can be implemented in various programming languages such as MATLAB, C, and C++.
• In MATLAB, the pencode() or systematic_pencode() functions are used as polar encoders. These are non-systematic polar encoders.
• The pdecode() or systematic_pdecode() functions serve as polar decoders in MATLAB, employing Successive Cancellation Decoding.

Polar coding can be applied to the modulation block in the following ways:

• Direct polarization
• Multi-level techniques (Multi-level coding and modulation)
• Polar lattices
• BICM (Bit interleaved coded modulation)

Several decoder types are used for polar codes:

• Maximum likelihood (ML)
• Successive cancellation (SC)
• Belief propagation (BP)
• List decoder
• List decoder with CRC
• Sphere-decoding

Benefits (Advantages) of Polar Coding

Here are the primary advantages of using Polar Coding:

• Modest Complexity: They offer manageable encoding/decoding complexity, denoted as O{n*log(n)}. This efficiency makes them suitable for many applications, including 5G wireless transceivers.
• Explicit Construction: Their design is clear and well-defined.
• Easy Implementation: Simple encoding and decoding algorithms facilitate straightforward implementation.
• High Hardware Efficiency: Polar codes offer efficient use of hardware resources.
• High Throughput in 5G: When used for channel coding, they have contributed to high throughput in 5G wireless networks. Huawei achieved 27 Gbps during 5G field trials.
• Suitable for Control Channels: They are well-suited for control channels where payload sizes are relatively small.

Drawbacks (Disadvantages) of Polar Coding

Despite their advantages, Polar Coding also has some limitations:

• SCD Performance: Polar coding typically uses Successive Cancellation Decoding (SCD), which can have poorer performance compared to LDPC and turbo coding techniques.
• Higher Latency: They can exhibit higher latency, denoted as O(N).
• Performance vs. Cost: While advanced decoders can improve performance, this often comes at a higher cost compared to LDPC, especially at finite N (block length).