SCMA with LDPC FEC Coding for NOMA Systems
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Solution Overview
Problem
Conventional multiple access schemes, such as CDMA, require large bandwidth expansion and equal power levels for all users, making them complex and inefficient for diverse terminal types and channel environments, especially in low SNR conditions.
Innovation Solution
The implementation of a scrambled coded multiple access (SCMA) scheme combined with low density parity check (LDPC) forward error correction (FEC) coding, which allows for a broad range of code rates and distinguishes between terminals using unique scrambling signatures, enabling simultaneous sharing of a wireless channel without the need for equal power levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional CDMA multiple access scheme is used, then multiple users can share common bandwidth, but large bandwidth expansion factor is required and all signals must be of equal power making the system complicated
Solution Approach 1:
The patent changes the fundamental parameters of the multiple access scheme by transitioning from orthogonal CDMA with equal power requirements to non-orthogonal multiple access with unequal power levels. This allows different users to transmit at different power levels simultaneously without requiring large bandwidth expansion, thereby reducing system complexity while maintaining multiple user access capability
Solution Approach 2:
The patent inverts the conventional approach by allowing signals to interfere with each other (non-orthogonal) rather than preventing interference (orthogonal). Instead of requiring equal power levels and large bandwidth expansion to separate users, the system allows unequal power levels and uses interference management techniques at the receiver to separate users, thereby simplifying the system
2Reliability
If conventional error coding for single-user systems is used in multi-user NOMA systems, then coding gain is achieved, but the coding is not optimized for multi-user interference environments
Solution Approach 1:
The patent applies local quality by optimizing the error correction code specifically for the multi-user NOMA environment rather than using generic single-user codes. The LDPC code is designed with specific properties (such as degree distributions) that are tailored to handle the characteristics of multi-user interference and power-domain multiplexing, thereby achieving both reliability and multi-user adaptability
3Reliability
If high code rate FEC encoding is used in CDMA systems, then coding gain is achieved, but bandwidth expansion requirements increase
Solution Approach 1:
The patent changes the operating parameters by using non-orthogonal multiple access with power domain separation instead of orthogonal CDMA with bandwidth expansion. This allows the system to achieve link closure through optimized power allocation and LDPC coding without requiring large bandwidth expansion factors, thereby reducing the quantity of bandwidth resource consumed
Data Source
AI summary
A multiple access scheme is provided. A first communications terminal encodes a first data stream using a forward error correction (FEC) code, and scrambles the encoded first data stream based on a first scrambling signature. A second communications terminal encodes a second data stream using the FEC code, and scrambles the encoded second data stream based on a second scrambling signature. The first scrambling signature and the second scrambling signature are used, respectively, by the first terminal and the second terminal to distinguish the first encoded data stream from the second encoded data stream as respectively originating from the first terminal and the second terminal in a multiple access scheme, whereby the first encoded data stream and the second encoded data stream simultaneously share a wireless communications channel. The FEC code is a low density parity check (LDPC) code configured with a data node degree of two or three.