Title :
An adaptive modulation scheme for simultaneous voice and data transmission over fading channels
Author :
Alouini, Mohamed-Slim ; Tang, Xiaoyi ; Goldsmith, Andrea J.
Author_Institution :
Dept. of Electr. Eng., California Inst. of Technol., Pasadena, CA, USA
fDate :
5/1/1999 12:00:00 AM
Abstract :
We propose a new adaptive modulation technique for simultaneous voice and data transmission over fading channels and study its performance. The proposed scheme takes advantage of the time-varying nature of fading to dynamically 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 M-ary amplitude modulation (M-AM) on the I channel for data. For favorable channel conditions, most of the power is allocated to high rate data transmission on the I channel. The remaining power is used to support the variable-power voice transmission on the Q channel. As the channel degrades, the modulation gradually reduces its data throughput and reallocates most of its available power to ensure a continuous and satisfactory voice transmission. The scheme is intended to provide a high average spectral efficiency for data communications while meeting the stringent delay requirements imposed by voice. We present closed-form expressions as well as numerical and simulation results for the outage probability, average allocated power, achievable spectral efficiency, and average bit error rate (BER) for both voice and data transmission over Nakagami-m fading channels. We also discuss the features and advantages of the proposed scheme. For example, in Rayleigh fading with an average signal-to-noise 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
Keywords :
Rayleigh channels; adaptive modulation; amplitude modulation; error statistics; integrated voice/data communication; land mobile radio; personal communication networks; phase shift keying; time-varying channels; BER; BPSK; I channel; M-AM; Nakagami-m fading channels; PCS; Q channel; Rayleigh fading; SNR; adaptive modulation; average allocated power; average bit error rate; average signal-to-noise ratio; channel conditions; closed-form expressions; data communications; data throughput; delay requirements; fixed-rate binary phase shift keying; high average spectral efficiency; inphase channel; mobile communications; outage probability; performance; quadrature channel; simulation results; simultaneous voice/data transmission; time-varying fading; transmitted power allocation; variable-power voice transmission; variable-rate M-ary amplitude modulation; Amplitude modulation; Binary phase shift keying; Bit error rate; Closed-form solution; Data communication; Degradation; Delay; Fading; Phase modulation; Throughput;
Journal_Title :
Selected Areas in Communications, IEEE Journal on