Compare LDPC and Polar codes used in 5G NR.

5G NR uses LDPC for data and Polar codes for control channels. LDPC (Low-Density Parity-Check): Sparse parity-check matrix enables parallel decoding. 5G uses quasi-cyclic LDPC with base graphs (BG1 for large blocks, BG2 for small). Iterative belief propagation decoding with excellent performance at moderate-high SNR. Better for larger block sizes (>500 bits). Polar codes: Based on channel polarization; some bit channels become reliable, others unreliable. Frozen bits placed on unreliable channels. Successive cancellation (SC) decoding is basic; SC List (SCL) with CRC improves performance. Better for small block sizes and low latency. Both approach Shannon limit within ~0.5 dB. LDPC has lower decoding latency for high throughput; Polar has more flexible rate matching.