Digitally Assisted Transmitter Enhancement Techniques for Millimeter Wave Radio Systems

Wireless communication has become an integral part of life in a modern society. The data to be transmitted is modulated on radio frequency carrier signals for transmission where the bandwidth of the signal to be transmitted increases proportional to the speed at which the data is intended to be transmitted. The present generation cellular wireless communication systems employ channel bandwidths as wide as 20 MHz in multipole bands between 800 MHz and 3.5 GHz with digitally modulated multi-carrier transmission schemes and hybrid access schemes in time, frequency and spatial domains. The radio spectrum has stretched to occupy multiple bands below to meet the demand for volume and speed of the data to be communicated. Indoor short range wireless communications of present generation employ channel bandwidths as wide as 160 MHz and transmit at powers lesser than a tenth of that transmitted by cellular systems and employ similar access schemes as cellular wireless systems. There has been a similar evolution in the area of wireless communications through satellites. Next generation wireless communication systems such as 5G and High-Throughput-Satellite systems in the millimetre wave bands have promised a step increase in data rates in the order of several gigabits per second operating multiple frequency bands over and above those in use at present. This necessitates design of state of the art mm-wave transceivers capable of operating in millimetre wave bands with instantaneous bandwidths of several hundreds of MHz. The cost and complexity of implementation of the radio transmission system increases rapidly as the bandwidths increase. This work investigates digital enhancement techniques to enhance performance of wideband radio frequency transmitters. A section of the work focusses on characterizing wideband impairments in radio frequency hardware and mitigating them through digital signal processing. Another section devises digital signal processing operations to jointly enhance power efficiency in radio frequency transmitters along with providing an additional tier of security to the information being transmitted.The third section focusses on methods of transmission of wideband modulated signals by seamlessly interleaving multiple radio frequency transceivers of relatively narrow bandwidths in the frequency domain thereby presenting an architecture for scalable bandwidth transmitters. Overall this thesis presents innovative techniques to mitigate limitations in radio frequency hardware that hinder wideband operation and schemes to construct scalable bandwidth transceivers with scope to reuse legacy radio frequency hardware for next generation communication systems in part or whole