Frozen-Bit Jammer Steering (FB-JS): Mitigating Multi-Band Channel Erasures in 5G Polar Codes

Abstract

The mathematical properties of the polar coding make it a code capable of achieving capacity limits under Successive-Cancellation List (SCL) decoding, and, therefore, the polar coding schemes have been universally accustomed to the 5G New Radio (NR) specification for protecting the transmissions over the control channels. In today's environment, however, the wireless transceivers are subjected to multi-band deterministic jamming and narrow-band pulsed interference in hostiles or co-existence spectrum environments. The traditional channel-domain mitigation techniques are based on global scrambling or chaotic interleaving which randomize the burst erasures. This paper shows that classical uniform interleavers cause severe soft-value LLR contamination across recursive decoding trees. Classical interleavers achieve this by distributing erasures uniformly over the code structure, and so destroy the natural isolation of error-free sub-trees and contaminate the soft-value updates at recursive check-nodes, which makes path metric discrimination very difficult in the SCL engine. In order to mitigate this structural weakness in the context of strict hardware limitations, Frozen-Bit Jammer Steering (FB-JS) external interleaving framework is proposed, which operates as a 3GPP-compatible external permuter transparent to standardized silicon cores. Instead of being able to scramble bit sequences everywhere, the proposed FB-JS engine makes use of the fact that the standardized 5G NR polar matrix is asymmetric by nature. It maps only the first, frozen-bit-rich, coordinates of the polar codeword to the slots of the multi-band interference. This way, simulations show that the targeted jamming channels are fully neutralized, without the need to redesign hardcoded silicon reliability sequences. Without requiring dynamic reallocation of hardcoded frozen bit sets in silicon ASICs/FPGAs, the proposed engine prevents recursive LLR degradation during decoding. Simulation results confirm that FB-JS successfully isolates targeted jamming erasures and maintains baseline-equivalent error performance under heavy multi-band interference, providing a resilient, low-complexity physical-layer defense for tactical 5G/6G communication networks.