无线通信原理与应用-ch4.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 参见PPT.27 * * * * * * * * Cont. * Cont. * Cont. * Cont. * Cont. * * * * * * . * * * * * * * * * * * * * * * * * * * * * * MPSK Spectrum and Bandwidth The null-null RF bandwidth is equal to Cont. * Cont. * M-ary Quadrature Amplitude Modulation (QAM) QAM Signal both the amplitude and phase of the carrier varing not constant distance between possible symbol states. M-ary QAM signal where is the energy of the signal with the lowest amplitude, and and are a pair of independent integers chosen according to the location of the particular signal point * QAM Constellation Cont. * The Comparison of MQAM Constellation and MPSK Cont. * QAM BER The average probability of error in AWGN channel for M-ary QAM, using coherent detection, is Cont. * The power spectrum and bandwidth efficiency of QAM modulation is identical to M-ary PSK modulation. In terms of power efficiency, QAM is superior to MPSK. Cont. * Outline Digital Modulation Linear Modulation-BPSK、DPSK、QPSK、 QPSK Constant Envelope Modulation-FSK, MSK, GMSK Combined Modulation Technique-QAM Spread Spectrum Modulation Technique Modulation Performance in Fading Channels * Spread Spectrum Modulation Concept Spread Spectrum Modulation Concept transmission bandwidth is several orders of magnitude greater than the minimum required signal bandwidth. spread spectrum signals are pseudorandom and have noise-like properties when compared with the digital information data. The spreading waveform is controlled by a pseudo- noise (PN) sequence which is a binary sequence. * Spread Spectrum Modulation Properties Interference rejection capability: multi-access interference (MAI)、narrowband interference Resistance to multipath