Channel-Adaptive Modulation

Download

PDF Download (324Kb)

Description/Abstract

Packet Reservation Multiple Access (PRMA) assisted adaptive modulation suing 1,2 and 4 bit/symbol transmissions is proposed as an alternative to Dynamic Channel Allocation (DCA) in order to maximise the number of users supported in a traffic cell. The cell is divided in three concentric rings and in the central high Signal-to-Noise ratio (SNR) region 16-level Star Quadrature Amplitude Modulation (16-StQAM) is used, in the first ring Differential Quaternary Phase Shift Keying (DQPSK) is invoked, while in the outer ring Differential Phase Shift Keying (DPSK) is utilised. A channel SNR of about 7, 10 and 20 dB, respectively, was required in order to maintain a bit error ratio (BER) of about 1%, which can then be rendered error-free by the binary BCH error correction codes used. A 4.7 kbps Algebraic Code Excited Linear Predictive (ACELP) speech codec is favoured, which is protected by a quad-class source-sensitivity matched BCH coding scheme, yielding a total bit rate of 8.4 kbps. A GSM-like Voice Activity Detector (VAD) controls the PRMA-assisted adaptive system, which ensures a capacity improvement of a factor of 1.78 over PRMA aided binary schemes.