1.0E-04 1.0E-05 Eb/No (dB) Figure 7.17 BPSK, QPSK, 8-PSK and 16-PSK BER performance locked to (or is 'in-phase' with) the transmitter's carrier reference phase. The quadrature axis is a reference axis which is perpendicular to the in-phase axis. QPSK, 8-PSK, and 16-PSK multi-phase modulation schemes facilitate transmission of multiple number of bits at any transmission time interval (QPSK: 2 bits; 8-PSK: 3 bits; and 16-PSK: 4 bits). In effect they enable the transmitter to speak two, three or four times as fast. Multi-PSK techniques are efficient in supporting transmission of more data bits. However, similar to multi-level ASK they too suffer from relatively poor error performance. Again, maintain a similar detection boundary the distance between two signal constellation points needs to be increased. This results in a higher level of required SNR for the same BER performance. The BER performance of BPSK, QPSK, 8-PSK and 16-PSK are compared in Figure 7.17. Note that 8-PSK systems require 3 dB higher transmission power (twice as much) compared with BPSK/QPSK for the same BER of 10-3. The BPSK and QPSK performances are identical. QPSK can be considered as two BPSK systems superimposed on top of each other, with an orthogonal (90°) phase shift. Since each system behaves as a BPSK and does not interfere with the other, the overall performance is the same as a BPSK system. BPSK and QPSK modulation schemes are the most efficient in terms of utilised power. Figure 7.18 compares BPSK and 2-ASK systems. As can be seen a 2-ASK system requires 3dB more power for a similar BER performance of 10-3. QPSK and 8-PSK are commonly used Digital Modulation 1.0E+00 1.0E-01 1.0E-02 2-ASK 1.0E-03 1.0E-04 1.0E-05 Eb/No (dB) Figure 7.18 BPSK and 2-ASK BER performance in wireless telecommunications standards, in particular QPSK is used in the 3G WCDMA (Wideband Code Division Multiple Access) standard and 8-PSK in the 2G EDGE [Enhanced Data Rates for Global System for Mobile Communications (GSM) Evolution] standard where power utilisation e