[信息与通信]无线通信基础双语_教学课件_9.pptVIP

Only the basis function, , is needed to represent the BPSK signals. The most commonly used digital modulation techniques are M-ary phase shift keying (MPSK) such as differential quadrature phase shift keying (DQPSK), and minimum shift keying (MSK). In the second generation cellular system, North American IS-54 and Japanese PDC use π/4 shifted DQPSK (π/4-DQPSK), European GSM uses Gaussian filtered MSK (GMSK). In M-ary signaling, the mth waveform is represented as where or As each waveform represents l binary digits, we have Es=lEb and Ts=lTb, where Eb and Tb are the bit energy and bit duration, respectively With QPSK signaling, the symbols can take on four possible values, each corresponding to two bits. For , the modulated signal can be represented as: Letting Thus In the two-dimensional signal space defined by the orthogonal set , the QPSK signal can be represented by a point The signal constellation of QPSK for is shown Where 00 01 11 10 i q The boundaries of the decision regions are the That is, the optimum decision regions for the equally likely symbols are just the four quadrants. The decision rule is In order to minimize transmission bit error rate, the binary digits are assigned to the symbols in such a way that the adjacent symbols differ by only one binary digit. --Gray encoding 00 10 11 01 i q Gray mapping for QPSK with 7?/4 5?/4 3?/4 ?/4 0 t +1 -1 -1 -1 +1 +1 +1 -1 -1 +1 +1 -1 -1 +1 Q I +1 -1 +1 +1 -1 -1 -1 +1 -1 +1 i q -1 +1 +1 -1 I Q S/P ~ × × ∑ Transmitter NRZ{an} QPSK Signal MF MF 并/串 {an} DD DD Combined r(t) Carrier recovery a b Receiver I Q S/P ~ × × ∑ Transmitter NRZ{an} QPSK Signal an 1 0 1 1 0 1 0 0 2FSK switch Data switch reverse f1 f2 ∑ 2FSK Signal VCO FSK Signal {an} s s s BPFω1 BPFω2 Envelope Detector Envelope Detector Timing R