An adaptive modulation scheme for simultaneous voice and data transmissionover fading channels

We propose a new adaptive modulation technique for simultaneous voice and d ata transmission over fading channels and study its performance. The propos ed scheme takes advantage of the time-varying nature of fading to dynamical ly allocate the transmitted power between the inphase (I) and quadrature (Q ) channels. It uses fixed-rate binary phase shift keying (BPSK) modulation on the Q channel for voice, and variable-rate Mary amplitude modulation (M- AM) on the I channel for data. For favorable channel conditions, most of th e power is allocated to high rate data transmission on the I channel. The r emaining power is used to support the variable-power voice transmission on the Q channel, As the channel degrades, the modulation gradually reduces it s data throughput and reallocates most of its available power to ensure a c ontinuous and satisfactory voice transmission. The scheme is intended to pr ovide a high average spectral efficiency for data communications while meet ing the stringent delay requirements imposed by voice. We present closed-fo rm expressions as well as numerical and simulation results for the outage p robability, average allocated power, achievable spectral efficiency, and av erage bit error rate (BER) for both voice and data transmission over Nakaga mi-m fading channels. We also discuss the features and advantages of the pr oposed scheme. For example, in Rayleigh fading with an average signal-to-no ise ratio (SNR) of 20 dB, our scheme is able to transmit about 2 Bits/s/Hz of data at an average BER of 10(-5) while sending about 1 Bit/s/Hz of voice at an average BER of 10(-2).