Research On The CMA For The Quadrature Amplitude Modulation Signals

In the field of wireless communications, There are many factors that can affect the quality of communication, one of the most important is the intersymbol interference. In order to solve the effects of this kind of interference, Need effective equilibrium technology. Traditional equalization technology because of the need to send a certain length of training sequence was limited, The first is to take up a certain number of spectrum, Followed by some of the communication process are not allowed to send the training sequence in advance, so the traditional technique of balanced promotion by real communication constraints, Blind equalization technology because don’t need to send ahead of training sequence and favor, The technology only according to the received signal at the receiving end of a variety of statistical information can automatically adjust the balance parameters. Constant modulus algorithm(CMA) is a kind of blind equalization technology, Which makes use of the modulus value of signal information, To automatically adjust the tap coefficient of equalizer, Then let the balance after signal as far as possible close to the original signal, CMA algorithm for signal with constant modulus value balance effect is better, Because of its simple calculation and good convergence effect can also be used for low order QAM signal,But for high-order QAM signal is balanced, Due to the limitations of the cost function, There are larger error rate and slower convergence speed.Because the QAM system is a common by amplitude and phase modulation, the CMA algorithm adopted signal amplitude information only. So when CMA algorithm is directly used in QAM system, Creates a phase rotation, The multimode algorithm(MMA) can solve the problem of phase rotation.Multimode algorithm(MMA) is an improved of CMA algorithm, But its ber and convergence speed performance needs to be improved, This paper on the basis of MMA algorithm, Using the ideas of constellation matching, An improved algorithm of MMA, the simulation results show that the new algorithm has lower bit error rate and faster convergence speed.Because the CMA algorithm steady-state error is big, And v.Weerackody and s.a.Kassam sign constant modulus algorithm(Sign-CMA) steady-state error is small, Effectively resist known-plaintext attack and, But the convergence speed is slow, Aiming at the shortcomings of the Sign-CMA algorithm, This paper proposes a dual-mode equalization algorithm for QAM signal, This algorithm can get rid of disadvantages of poor channel phase rotation, Less steady residual error of the CMA algorithm, Than Sign-CMA algorithm of bit error tate is low.