Shortwave Short-term Blind Equalization Algorithms

High Frequency (HF) communication is a kind of communication which mainlyrelies on reflecting by the ionosphere. In recent years, many countries re-focused on HFcommunication because of its low transmit power, long-range transmission and goodinvulnerability characteristics. Equalization technique is widely used in HFcommunication because the inter-symbol interference (ISI) exists in HF propagationcritically affects the quality of communication. Due to no need to send trainingsequence, blind equalization technique becomes a hot research, which not onlyimproves the transmission efficiency, but also applies in the blind receiving in HFcommunication. Burst technique is more and more used in HF communication, butblind equalization technique in the short-time burst condition is backward.In this paper, we researched blind equalization technique in the short-time burst HFcondition and finished the work as follows:(1) The features of HF channel are introduced and then the influence on datatransmission in HF is analyzed. After this, we research the Watterson simulation modelof HF channel and discuss the selection of HF channel model in the short-time burstcondition.(2) The principle of constant modulus algorithm (CMA) is introduced, and then weanalyze the performance of CMA by step-size, the decline of HF channel and AWGN.We modify the CMA through variable step-size and dual-mode algorithms to solve theproblems of CMA: slow rate of convergence and large steady-state error afterconvergence.(3) The necessity of blind equalizing in the short-time burst condition isdemonstrated. We point out that the data-reusing method is the key of applying thetraditional CMA to the short-time burst processing. We combine the approach ofcircularly reusing data vector string with CMA, and then get a new algorithm which canprocess the short-time burst signal. The simulation result indicates that the modifiedalgorithm can effectively equalize the received short-time burst HF signal. (4) Joint blind equalization and modulation recognition algorithm is introduced.For the problem that the dispersion constant in CMA needs to know modulation type,several solution algorithms are analyzed and compared. At last, we point out the futureresearch on this problem.