Three level delta modulation
The basic concept of three-level delta modulation (TLDM) is to quantize the error signal of a delta modulator into three levels instead of the usual two levels as in ordinary DM. A TLDM system must be able to transmit three different signals, corresponding to three possible states of the quantizer, whereas the ordinary DM system has to transmit only two signals. The problem of transmitting these signals over a noisy channel is examined, where the input signal is band-limited Gaussian noise. Two parameters that can be adjusted to optimize the performance of the system with respect to quantizing noise are considered: step size and quantizer threshold setting. The effect of additive channel noise on the performance of a TLDM system is assessed in terms of baseband transmission, probability of error, FSK and PSK transmission, transmission bandwidth, and baseband pulse transmission. It is concluded that TLDM can provide a 5 to 6 dB improvement in quantizing signal to noise ratio over ordinary DM for band-limited Gaussian signals. This improvement can be achieved without increasing the channel bandwidth and with an increase in system threshold of less than 2 dB.