LDPC Block Length Selection for OFDM Packet Packing
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Solution Overview
Problem
In wireless communications systems, particularly in OFDM transmission, the selection of LDPC block size is challenging due to performance degradation from using too small a codeword or increased transmission time and power consumption from using too large a codeword, especially when packet lengths do not match exactly with available codewords, leading to inefficient air interface usage.
Innovation Solution
A method to determine the number of available bits in a minimum number of OFDM symbols and calculate the integer number of LDPC codewords and their length using the formula Navbits=(NCBPS*(1+USTBC))*ceil(Npld/(NCBPS*R*(1+USTBC))), with USTBC indicating the use of STBC, and referencing a table to select optimal codeword lengths and numbers based on available bits, thereby maximizing coding gains while minimizing OFDM symbols.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a smaller codeword is used, then transmission time is reduced, but coding gains are degraded and performance deteriorates
Solution Approach 1:
The patent implements dynamic selection of LDPC block sizes (multiple block sizes including 648, 1296, 1944, and 2592 bits) based on the actual data payload size. This allows the system to adaptively choose the optimal codeword length for each transmission, maximizing coding gains when possible while minimizing transmission time when data size permits, thereby resolving the contradiction between transmission time and coding performance.
2Reliability
If a larger codeword is used, then coding gains are improved, but transmission time increases and power consumption rises
Solution Approach 1:
The system dynamically selects from multiple LDPC block sizes (648, 1296, 1944, 2592 bits) based on the data payload size and transmission requirements. This dynamic adaptation allows the system to use larger codewords only when the data size justifies the coding gains, avoiding unnecessary increases in transmission time and power consumption, thus resolving the contradiction between coding gains and transmission efficiency.
3Reliability
If a larger codeword is used, then coding gains are improved, but power consumption increases
Solution Approach 1:
The patent implements dynamic selection of LDPC block sizes based on actual transmission needs and data payload size. By choosing the minimum necessary block size that provides adequate coding gains for the given data, the system avoids the excessive power consumption associated with always using larger codewords, while still maintaining reliability when needed.
4Device complexity
If fixed LDPC block sizes are used, then implementation is simplified, but air interface efficiency is reduced due to mismatch with variable packet lengths
Solution Approach 1:
The patent extends the set of available LDPC block sizes from fixed options to multiple dynamic options (648, 1296, 1944, 2592 bits). This allows the system to dynamically match the codeword size to the packet length, significantly improving air interface efficiency by reducing the need for padding and retransmissions, while maintaining manageable implementation complexity through standardized block size options.
Data Source
AI summary
A transmitter determines a number of available bits (Navbits) in a minimum number of orthogonal frequency division multiplex (OFDM) symbols in which a data field of a packet may fit, by Navbits=(NCBPS*(1+USTBC))*ceil(Npld/(NCBPS*R*(1+USTBC))), where USTBC equals 1 when Space-Time Block Code (STBC) is used and 0 otherwise, where Npld=LENGTH*8+16, where NCBPS is the number of coded bits per symbol, where R is the code rate, and where LENGTH is a number of bytes in a Physical Layer Convergence Protocol (PLCP) PLCP Service Data Unit (PSDU); and determines an integer number of Low-Density Parity-Check Code (LDPCC) codewords to be transmitted, NCW, and the length of the codewords to be used, LLDPC, from information capable of being expressed in a table format.