## Bit error performance of QPSK

#### As predicted earlier, the bit error rate performance for QPSK is theoretically identical to that for BPSK. If the carrier reference is not perfectly phase coherent, however, not only will the wanted signal output voltage of each detector fall, but each detector will suffer cross-talk from the orthogonal symbols and the performance will be degraded even further. QPSK thus has lower tolerance to phase jitter in the carrier recovery process than BPSK. The major attraction of QPSK is that it allows the modem designer that opportunity to recover the bandwidth efficiency of a binary baseband data stream in a bandpass modulation format, without sacrificing BER performance. |

#### Maximum bandwidth efficiency (QPSK) = 2 bits/second/Hz

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