【正文】 n and QPSK modulation was pared with simulation by MATLAB. The experiment proves that 16QAM modulation and demodulation is not only easy to achieve but also better to perform. Keywords:16QAM。 modulation。 demodulation。 BER 1. Introduction When the data ratetobandwidth ratio is greater than 2bit / s,we can consider this modulation is the standard for highfrequency modulation. In the same band, M 2 the MARY modulation with a greater rate of information transmission than M = 2 binary modulation. However, the MARY modulation are able 石家莊鐵道大學(xué)四方學(xué)院畢業(yè)設(shè)計(jì) 43 to raise the data ratetobandwidth ratio, they usually at the cost of reducing its power utilization. Because of with the value of M increasing in the signal vector diagram the minimum distance between signal points will be reduced accordingly. So when the signal was damaged by noise and interference, the error probability of received signal will increase. In the 1960s put forward a joint amplitude and phase modulation (APM) [also known as amplitude phase shift keying (APK)] and attracted people’s attention. This is because this kind of modulation pare with conventional Mary modulation it not only has a high data ratetobandwidth ratio but also has good power utilization which had developed rapidly. The socalled a joint phase and amplitude modulation is the amplitude and phase of carrier was changed with the two independent baseband signal’s changing.[1,2] principle of 16QAM modulation and demodulation In the orthogonal modulation circuit, the slip of the two orthogonal carrier was bilateral suppression carrier amplitude modulated by the amplitude discrete baseband signals, QAM signals can be received. MQAM signal can be expressed as: S(t) = Σxkg(t kTs) cos wct .∑ ykg(t kTs)sin wct .It is the sum of 2 branchs 石家莊鐵道大學(xué)四方學(xué)院畢業(yè)設(shè)計(jì) 44 modulated orthogonal carrier signal. In the circuit, the orthogonal carrier sin wct can be obtained by carrier coswct phaseshifted π / (t) stands for the system impulse response units, xk, yk respectively express the kvalue of the symbol of 2way multilevel signals transmitted, Ts is symbol duration, Wc is the carrier angular frequency. Ideally, the carrier states of 16QAM can modulate 4b signal. 16QAM provides 16 states,every 4b signal can express one state,each 16QAM symbols cycle transmits 4b signal. According to the constellation map and the receiving carrier signal amplitude and phase, demodulator can determine the information of the sending side. 16QAM adopt the orthogonal with the projection on I coordinate modulating carrier amplitude, the projection on Q coordinates modulating orthogonal carrier add 2 amplitude modulated signals is required phasemodulation signal. The input data sequences through Serial/Parallel conversion and transform into two road I and using rectangular constellation chart, the level code of 2 road orthogonal signal use 2 bits signal for representation, namely the L = 24 level conversion,the output value of I and Q two way for 0,1,2, constellation mapping pletes converting a digital sequence 石家莊鐵道大學(xué)四方學(xué)院畢業(yè)設(shè)計(jì) 45 consisting of 0,1,2,3 to a digital sequence consisting of 3,1,1, corresponding relations as follows: 00 —— +3， 01 —— +1， 10 —— 1,11 —— , I road value for 4 levels, namely x = 177。 1, 177。 3. Q value method is exactly the same way to the I 2 4 level conversion and constellation mapping, forming xk , yk . In order to restrain the outofband radiation of already tuning signals, xk , yk may through the preset lowpass filter system, then respectively multiply with orthogonal 2 road carriers, forming 2 road ASK modulated signals, Lastly, two road ASK modulated signals together can get different amplitude and phase of already adjustable QAM output signal. At the receiving end,divide the modulated signal into 2 road and multiply by the local recoveried orthogonal carrier respectively then through lowpass filter in order to get off times x(t), y(t)frequency ponents to get . After that,according to the local restored clock to do multilevel judgment, 16QAM with x = 177。2, 177。 for judgment level,af ter judgement,we can get a group data consisting of x = 177。1, 177。3. 16QAM constellation inverse mapping pletes converting 177。1, 177。3 to 0 ， 1 ， 2 ， 3, its corresponding relationship is the same as the constellation chart mapping. Then after 42 level conversion and Parallel/Serial 石家莊鐵道大學(xué)四方學(xué)院畢業(yè)設(shè)計(jì) 46 conversion we can get output data sequence. The whole principle is shown in Figure 1.[1,2,4,5] parison of 16QAM、 BPSK and QPSK modulation performance QPSK is short for Quadrature Phase Shift modulation can modulate 2 bits signal in each symbols cycle,use four different carrier phase(0,90176。,180176。,270176。or 45176。,135176。 ,225 176。 ,315 176。 )to characterize digital ,we can group the input binary digital sequences,two bits of each group, then use four different carrier phase to characterize them. BPSK is short for Binary Phase Shift modulation use two different carrier phase to characterize digital information, each symbol cycle transfer one bit we have understood the modulation principle of 16QAM,QPSK and we want to pare the performance of several modulation mode,there are two primary performance index: bit error rate and data ratetobandwidth used MATLAB to program the BER of 16QAM in case of SNR=1,[3]after simulation we can get the result of changed the value of SNR,we may get different value of , we can also simulate the BER of QPSK,BPSK modulation in different condition of ,We draw the relationships between SNR and BER for the three kinds of 石家莊鐵道大學(xué)四方學(xué)院畢業(yè)設(shè)計(jì) 47 modulation,they as shown in Figure 2. In an ideal situation, we know BPSK modulation bandwidth utilization is 1 bit /( Hzs . ) ,QPSK modulation bandwidth utilization is 2 )/( Hzsbit . ,16QAM modulation band