数字通信第5章加性高斯白噪声的最佳接收机ppt课件.ppt

第5章加性高斯白噪声信道的最佳接收机,.1 受加性高斯白噪声恶化信号的最佳接收机,相关解调器,结 论,最佳AWGN接收机的实现形式,5.2 无记忆调制的最佳接收机性能分析,二进制调制的错误概率,1、2PAM2、正交信号,Binary signals,Exercises5-4, 5-8,M=2, equals to the antipodal signalsk increase by one, 4dB SNR is requiredUse Gray coding,Use Gray coding,4PSK and 4QAM are comparableWhen M4, M-ary QAM is better than M-ary PSK,The pdf of first correlation is,The rest of correlation,The probability of correct decision is,For each term,The correct decision,Symbol error rate,For the bit error rate,Orthogonal signals,M-ary biorthogonal signals,Constructed from M/2 orthogonal signals,Demodulation: Use M/2 orthogonal cross correlation or matched filters,Tx: s1(t),Cross correlation,The sign used to determine s(t) or -s(t) was transmitted,The correct decision for s1(t) r1 0r1 rm=nm,Thus, -r1 nmr1, correct,The probability of correct decision is,Biorthogonal signals,Differential PSK,The received signal is compared with phase of the preceding signalno carrier information needed,No noise, - k-k-1No noise, - rkr*k is independent of carrier phase,Error probability estimation of DPSK,Assumption: k-k-1=0,- compared with nk-1 and nk,x, y are the uncorrelated Gaussian random variable , N0,Similar to PSKnoise is twice largerDPSK has 3 dB poorer performance,Binary PSK and DPSK- less than 3dB differencesPb get smaller, differences becomes small,BPSK & 4PSK have the same BER4 phase DPSK worse than 2 phase DPSK,数字调制方式的比较,带宽和频带利用率（归一化数据速率R/W）给定的错误概率情况下，R/W和比特SNR的关系曲线带宽受限区域功率受限区域信道容量限,5.5 有线和无线通信系统性能分析,本节内容,再生中继器无线通信中链路预算分析,