Adaptive demodulation method of high-order qam modulation symbols based on log-likelihood ratio threshold

Abstract

The invention discloses a log-likelihood-ratio-threshold-based adaptive demodulation method for a high-order QAM modulation symbol. A sending terminal employs fixed-order high-order square quadrature amplitude modulation (QAM) and ratio-free error correction coding; a receiving terminal calculates an absolute value of a log-likelihood ratio of each bit in a received symbol and the absolute value of the log-likelihood ratio is compared with a preset log-likelihood ratio threshold value; a bit having the absolute value of the log-likelihood ratio larger than the preset log-likelihood ratio threshold value is demodulated; and otherwise, the bit is deleted. Under the circumstance that the length of the codon inputted by a decoder for ratio-free error correction and coding is fixed, a method for calculating a log-likelihood ratio demodulation threshold is provided, wherein the required decoding and error code performances are realized. According to the method provided by the invention, the modulation order number is not limited; the method is applied to all square QAM satellites; and the spectrum effectiveness changes with the change of the channel condition under the circumstance that error correction coding and modulation schemes are not adjusted at the sending terminal, so that the transmission capability of the channel is utilized fully.

Description

technical field [0001] The invention belongs to the fixed modulation and coding method at the sending end in the field of information communication. The receiving end comprehensively considers the decoding link of channel coding, and adjusts the demodulation threshold of the logarithmic likelihood ratio according to the current channel condition to perform adaptive demodulation of the received symbols and realize the rate Adaptive adjustment. Background technique [0002] Adaptive Modulation and Coding (AMC) technology is one of the link adaptive technologies in the communication system. Although this technology can adapt to channel characteristic fluctuations and improve spectrum utilization, the overhead of feedback is large, and the feedback control The complexity is high, and at the same time, the channel state information error caused by the feedback delay may lead to deviations in the AMC setting. For wireless communication systems with rapidly changing channels, this...

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Problems solved by technology

The first type of method needs to determine the area where each received symbol is located to determine the demodulated bits. The computational complexity of demodulation is high, especially when high-order modulation constellations are used, and the existing literature does not give the use of orders above 16. The scheme for delimiting the decision-making area during modulation; the second type of method needs to calculate the preset demodulation threshold. Although this method has low complexity in demodulation, the relevant literature only gives a modulation order of up to 16 When the demodulation threshold is calculated, there is no threshold calculation scheme for higher-order modulation, which limits the use of high-order modulation constellations, and accordingly limits the ability to adapt to channel changes

On the other hand, in the relevant literature of these two ADMs, there is no research on the design and performance analysis of ADM schemes combined with rateless coding.

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