OFDM Packing and LDPC Framing for Variable-Length Constellation Shaping
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Solution Overview
Problem
Next-generation wireless local area networks (WLANs) face inefficiencies and throughput limitations due to the complexity of shaping encoding processes, particularly in Orthogonal Frequency-Division Multiple Access (OFDMA) channel allocation, where the number of bits transmitted is not fixed and the existing LDPC framing and OFDM packing procedures are hindered by the need for deterministic sequence lengths.
Innovation Solution
The implementation of a shaping encoder that modifies constellation point probabilities to generate a Gaussian-like distribution, allowing for efficient LDPC framing and OFDM packing by dynamically calculating the number of output bits, adding overhead bits as needed, and using repetition or puncturing to maintain a fixed relation between amplitude and parity bits, thereby addressing the variable output bit issue and improving throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If constellation shaping encoding is implemented to improve spectral efficiency and reduce shaping loss, then throughput and energy efficiency are improved, but the complexity of LDPC framing and OFDM packing increases due to variable output bit lengths
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing mapping tables that directly correlate input bit lengths to output bit lengths for different constellation sizes (e.g., QPSK, 16-QAM, 64-QAM, 256-QAM). This allows the system to determine the exact number of output bits before LDPC encoding begins, enabling proper framing and packing without dealing with variable lengths during the encoding process. The mapping tables are generated based on the constellation shaping encoder characteristics and stored for quick reference during transmission.
Solution Approach 2:
The patent implements dynamics by making the framing and packing process adaptive to different modulation and coding schemes. The system dynamically selects appropriate mapping tables based on the chosen constellation size and code rate, and adjusts the framing structure according to the specific input bit length. This dynamic adaptation allows the system to handle various throughput requirements while maintaining efficient resource utilization through constellation shaping.
2Loss of energy
If variable-length output bits from shaping encoder are used to achieve Gaussian distribution and shaping gain, then spectral efficiency improves, but deterministic sequence length requirement for OFDM packing is violated
Solution Approach 1:
The patent resolves this contradiction by performing preliminary calculation of the output bit length using pre-generated mapping tables before the actual encoding and packing processes. The mapping tables contain predetermined relationships between input bit lengths and output bit lengths for various constellation sizes, allowing the system to know the exact sequence length in advance. This preliminary determination enables the OFDM packing to proceed with deterministic sequence lengths while still utilizing variable-length output from the shaping encoder, as the packing structure can be appropriately configured based on the known output length.
3Adaptability or versatility
If overhead bits are added to accommodate variable output bit lengths, then framing flexibility improves, but transmission efficiency decreases due to increased overhead
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the overhead bit count based on the specific mapping between input and output bit lengths. Rather than using a fixed overhead structure, the system calculates the precise number of overhead bits needed for each framing instance based on the chosen constellation size, code rate, and input bit length. This parameter adaptation minimizes overhead while maintaining the necessary framing flexibility to handle variable-length shaped outputs.
Data Source
AI summary
An apparatus for a station (STA) configured for operating in a next-generation (NG) wireless local area network (WLAN) comprises the processing circuitry configured to modify probabilities of constellation points to generate a more Gaussian distribution. In these embodiments, for LDPC framing and OFDM packing, the transmitter circuitry may be configured to compute a number of output bits (bout) to be transmitted based on a number of payload bits (bin) at an output of a shaping encoder, a shaping rate (rshaping), and an overhead percent (Boverhead). A shaping gain of up to 1.53 dB may be achieved. A new shaping encoder is provided to address the issue that the number of bits is not fixed.