Non data aided-error vector magnitude adaptive modulation method under fast time-varying channel

Abstract

The invention provides a non data aided-error vector magnitude (NDA-EVM) adaptive modulation method under a fast time-varying channel. The method comprises the steps of firstly, performing modulation by adopting QAM (Quadrature Amplitude Modulation), then estimating the coherence time of the channel by a receiving end, and collecting the statistics on the number of symbols sent within the coherence time; secondly, according to the data symbol of the current modulation order, calculating NDA-EVM values of all modulation orders and the bit error rate corresponding to the NDA-EVM of each modulation order under the current channel; and finally, under the condition of a specified bit error rate, selecting the current optimal modulation order, and returning to execute next modulation order adjustment. Compared with SNR-AM (Signal to Noise Ratio based-Adaptive Modulation) and DA-EVM-AM (Data Aided Error Vector Magnitude based-Adaptive Modulation), the NDA-EVM-AM method can improve the timeliness and accuracy of channel quality assessment and modulation order selection and then improve the spectrum efficiency of a system, wherein the spectrum efficiency can be improved to 0.82bit / s / Hz and 0.53bit / s / Hz to the highest degree.

Description

technical field [0001] The invention belongs to the technical field of communication, and in particular relates to a non-data-assisted error vector amplitude self-adaptive modulation method under fast time-varying channels. Background technique [0002] The high-speed movement of communication terminals makes the wireless channel present a fast time-varying characteristic, causing the spectrum utilization rate of the communication system to drop sharply, and even normal communication cannot be achieved. Adaptive modulation has the characteristics of enhancing transmission reliability and improving spectrum utilization, and is an effective way to solve this problem. The basic idea of ​​adaptive modulation is to evaluate the channel quality at the receiving end, feed back the estimation result to the sending end, and the sending end adjusts the modulation order of the transmitted data accordingly; the key issue is how to determine the physical quantity that accurately reflects...

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Problems solved by technology

The above method can effectively guarantee the spectrum utilization rate of the system under time-invariant channels or slow time-varying channels, but there are still the following problems when applied to fast time-varying channels: 1) The SNR counted at fixed time intervals cannot reflect channel changes in real time and accurately , resulting in wrong selection of modulation order; 2) In order to ensure the accuracy of SNR statistics, a large amount of auxiliary data needs to be used, which reduces the spectrum utilization; 3) It is necessary to frequently adjust the transmit power to compensate for the SNR loss caused by channel fading, and frequent power adjustments will cause Co-channel interference affects system stability

However, DA-EVM-AM is still unable to solve the problem of reduced spectrum utilization caused by a large amount of auxiliary data, and more importantly, none of the above-mentioned documents has given an effective engineering implementation plan

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