Challenges in multi-mode transmitter design

The future of wireless communication can be considered as plethora of heterogeneous systems operating together with current and legacy technologies. One view point of Fourth generation wireless communication is the seamless integration of wide variety of systems (Cellular -- GSM, GPRS, EDGE, UMTS and WLAN) for efficient service provision. Unfortunately, conventional GSM/GPRS transmitter architectures are designed to deliver constant-envelope half-duplex signals and have little in common with UMTS architectures, which generate envelope-varying full-duplex signals. Also, OFDM shows its high sensitiveness to non-linear effects, so it requires more linear amplification than other modulation schemes. Multi-carrier modulated signal has a very large peak power, so the influence of non-linear amplifier becomes large. Increase in peak power leads to input signal saturation, which leads to non-linear amplitude distortion and that leads to out of band radiation and degradation of BER. As a result, combining these transmitters within one multimode handset can be an expensive proposition.

This paper explores and proposes several possible architectures for implementing multi-mode multi-band transmitters which provides all the necessary functionality for both linear and non-linear modulation schemes. There are a number of different architectures that can be employed to implement a multi-mode transmitter. However, the trade-offs between power consumption, linearity, baseband complexity and implementation issues have resulted in a favoured architecture for supporting both non-linear and linear modulation.