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Efficient Enumeration of Minimum Weight Codewords for Pre-Transformed Polar Codes


מושגי ליבה
An efficient algorithm is proposed to determine the number of minimum weight codewords of general pre-transformed polar codes, significantly reducing the computational complexity compared to state-of-the-art methods.
תקציר

The paper presents an improved algorithm for counting the minimum weight codewords of pre-transformed polar codes (PTPCs). Key highlights:

  1. The proposed algorithm eliminates all redundant visits of nodes in the search tree, reducing the computational complexity from state-of-the-art algorithms typically by several orders of magnitude. This allows the minimum distance properties to be directly considered in the code design of PTPCs.

  2. The algorithm supports arbitrary upper-triangular precoding, not just convolutional precoding. It represents the message sets as binary trees and computes their intersection efficiently.

  3. Numerical results are provided for very long codes, such as pre-transformed Reed-Muller (RM) codes with N=524288, for which only probabilistic estimates existed previously.

  4. Optimal convolutional polynomials for polarization-adjusted convolutional (PAC) codes are listed, minimizing the number of minimum weight codewords.

The paper first introduces the necessary background on polar codes and pre-transformed polar codes. It then presents the proposed algorithm for enumerating minimum weight codewords of PTPCs, exploiting the underlying structure of polar codes. The algorithm's complexity is analyzed and compared to prior work. Finally, the results demonstrate the significant complexity reduction and provide optimal precoder designs for PAC codes.

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סטטיסטיקה
The minimum distance of a pre-transformed polar code P(I,T) is lower bounded as dmin(P(I,T)) ≥ dmin(P(I)) = wmin. The number of codewords with weight dmin = 2^(n-r) of a pre-transformed polar code P(I,T) with RM(r,n) rate-profile I is lower bounded as Admin_LB(r) = 2^(r * (sum(alpha=0 to r) sum(beta=alpha to r) 2^(alpha+beta))).
ציטוטים
"The proposed algorithm eliminates all redundant visits of each coset in the search tree and is therefore significantly less complex." "The algorithm is demonstrated for randomly pre-transformed Reed–Muller (RM) codes and polarization-adjusted convolutional (PAC) codes. Further, we design optimal convolutional polynomials for PAC codes with this algorithm, minimizing the number of minimum weight codewords."

שאלות מעמיקות

How can the proposed algorithm be extended to enumerate higher-order weight distributions of pre-transformed polar codes

The proposed algorithm for enumerating minimum-weight codewords of pre-transformed polar codes can be extended to enumerate higher-order weight distributions by modifying the tree intersection process. To enumerate higher-order weight distributions, we need to consider weight distributions beyond just the minimum weight codewords. This can be achieved by expanding the tree intersection algorithm to track and count codewords of various weights, not just the minimum weight. By incorporating additional nodes and branches in the tree structure to represent different weight levels, we can traverse the tree to identify and count codewords with weights higher than the minimum weight. The algorithm can be adapted to keep track of the number of codewords at each weight level, providing a comprehensive analysis of the weight distribution of pre-transformed polar codes.

What are the potential applications of the minimum weight codeword enumeration beyond code design, e.g., in the context of error analysis or decoding performance

The enumeration of minimum weight codewords in pre-transformed polar codes has implications beyond code design. It can be utilized in error analysis and decoding performance evaluation in various communication systems. Error Analysis: By knowing the number of minimum weight codewords, we can assess the error-correcting capabilities of the code. Understanding the distribution of codewords of different weights helps in predicting the error patterns that the code can effectively correct. This information is crucial in designing robust communication systems that can handle different error scenarios. Decoding Performance: The enumeration of minimum weight codewords can also impact decoding algorithms. Decoders can be optimized based on the weight distribution information to improve decoding efficiency and accuracy. By considering the distribution of codewords, decoding algorithms can be tailored to handle specific weight ranges more effectively, leading to enhanced overall performance. System Reliability: Knowing the number of minimum weight codewords allows for a better assessment of system reliability. It helps in evaluating the probability of decoding errors and aids in designing error detection and correction mechanisms to enhance system reliability.

What insights can be gained by analyzing the structure and properties of the optimal convolutional polynomials for PAC codes identified in this work

Analyzing the structure and properties of the optimal convolutional polynomials for PAC codes identified in this work provides valuable insights into the performance and design of polar codes. Decoding Efficiency: Optimal convolutional polynomials play a crucial role in the decoding process of PAC codes. By analyzing these polynomials, we can gain insights into the decoding efficiency of the codes. Understanding the structure of the polynomials can help in developing more efficient decoding algorithms tailored to the specific characteristics of the code. Error Correction Capability: The properties of the optimal convolutional polynomials directly impact the error correction capability of PAC codes. By studying these properties, we can assess the code's ability to correct errors and optimize the code design for enhanced error correction performance. Code Design Optimization: The analysis of optimal convolutional polynomials guides the design optimization process for PAC codes. By identifying the key properties that contribute to minimizing the number of minimum weight codewords, we can refine the code design to achieve better overall performance in terms of error correction and decoding efficiency.
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