RF Transmitter Architectures for Nomadic Multi-radio: A Review of the Evolution Towards Fully Digital Solutions

In this paper, a review of the major evolution steps of mobile transmitter architectures is summarized. We propose a classification and discuss about improvements and evolutions towards the full-digital solutions. This discussion is mandatory while the cognitive-radio concept implies the design of new structures for multi-radio front-ends. Technological process improvements, for example CMOS for high frequency, opens new possible solutions thanks to digitally based buildings blocks and functions. The conception of fully digital architectures is discussed in that idea. Our work in this domain is presented as a contribution in the study of transmitter architecture for multi-radio. Two ways are explored: (1) improvements of analog and digitized architectures, and (2) digital architectures. We present, in these two fields, a state of the art of published works and patents [US20130051440A1], [US20130084816A1], [US20120320957A1]. The Multiradio context drives us to redefine the important figures of merit for the architecture design, as seen in recent publications and patents such as [US20130049854A1], [US20130009710A1], [US8432219], [EP2541781A1]. The traditional efficiency/ linearity trade-off has to be considered with a mandatory frequency flexibility and power control ability, defined here as “power scale-ability”. These constraints made the conception of fully digital architectures attractive, thanks to the flexibility of digital systems. The first part of this paper will present the challenges of designing transmitter architectures for cellular and wireless local/extended area networks (WLAN and WIMAX for example), under the hypothesis of nomadic communication system. The design method in that context is consequently different from classical architecture design. In the second part, a classification of the RF transmitter architectures and their evolution are proposed. Evolution from linearization to linear architectures and introduction of digitized functions are presented, in that order. Solutions are appreciated differently, considering the multiple tradeoffs on efficiency, linearity, flexibility and complexity, while taking into account integration and realization (process).