Future wireless communication services will require a reconfigurable transmitter capable of switching between several modulation techniques. Reconfigurability could be achieved by defining the transmitter in software. To adapt to different wireless standard, future radios have to be implemented in software. Software modem radios for 2 and 2.5 Generations have already been implemented (Jeffrey, 2002). In this paper, software defined transmitter capable of switching between Quadrature Phase Shift Keying (QPSK) and 8-Quadrature Amplitude Modulation (QAM) techniques has been implemented on a Digital Signal Processor (DSP) TMS320VC5416 platform. A single coupled standard quadrature recursive oscillator has been used in the design instead of two oscillators required for the two modulation schemes. This saves program memory. The results obtained are in accordance with the simulation and theoretical analysis.

Software Defined Radio (SDR) is a rapidly evolving technology, generating widespread interest in wireless communication. The fundamental idea of SDR is to replace most of the analogue signal processing modules in the transceivers with digital signal processing blocks in order to provide the advantage of flexibility through reconfiguration (Baudin et al., 1996). This will enable different air interfaces on a single generic hardware platform. For example, the same device can be used to get Global Position System (GPS) from satellite transmission, access the Internet by a wireless LAN, and send a print paper using Bluetooth air interface. A software radio is one that defines modulation, error correction and encryption, and exhibits some control over Radio Frequency (RF) hardware and can be reprogrammed.

This paper presents a software-defined transmitter capable of switching between Quadrature Phase Shift Keying (QPSK) and 8-Quadrature Amplitude Modulation (QAM) techniques. This has been achieved by using a common oscillator, which gives quadrature outputs at equal amplitudes. The oscillators have been implemented in software without using the lookup table approach to generate the sinusoid as reported in Glomez et al. (2006), where a PSK Modem has been implemented. The transmitter has been analyzed and simulated in Matlab, prior to being implemented on the Digital Signal Processor (DSP) board TMS320VC5416 of Texas Instruments.

Telecommunications Journal, Digital Signal Processor, DSP, Software Defined Radio, SDR, Wireless Communication, Global Position System, GPS, Satellite Transmission, Radio Frequency, Code Composure Studio, General Extension Language, GEL, Quadrature Amplitude Modulation, QAM.