Performance Bounds of Concatenated Polar Coding Schemes

TL;DR

This paper analyzes the performance bounds of concatenated polar coding schemes over BMS channels, deriving error exponents, bounds, and approximations, and comparing them with simulation results for practical codes.

Contribution

It introduces new bounds on error rates and exponents for concatenated polar codes, including finite blocklength approximations and capacity-based bounds.

Findings

Small gap between normal approximation and actual error rate for BCH-polar codes over Gaussian noise.

Derived bounds help in understanding the rate split for outer codes in concatenated schemes.

Improved finite blocklength bounds using channel dispersions.

Abstract

A concatenated coding scheme over binary memoryless symmetric (BMS) channels using a polarization transformation followed by outer sub-codes is analyzed. Achievable error exponents and upper bounds on the error rate are derived. The first bound is obtained using outer codes which are typical linear codes from the ensemble of parity check matrices whose elements are chosen independently and uniformly. As a byproduct of this bound, it determines the required rate split of the total rate to the rates of the outer codes. A lower bound on the error exponent that holds for all BMS channels with a given capacity is then derived. Improved bounds and approximations for finite blocklength codes using channel dispersions (normal approximation), as well as converse and approximate converse results, are also obtained. The bounds are compared to actual simulation results from the literature. For the cases considered, when transmitting over the binary input additive white Gaussian noise channel, there was only a small gap between the normal approximation prediction and the actual error rate of concatenated BCH-polar codes.