5.1: Introduction

In the history of wireless communication, radar, and sensor systems there have been many standards and different types of systems. Following the development of the main cellular radio systems is a good proxy for the evolution of nearly all RF systems. Mobile radio up to and including 1G cellular radio was essentially analog with only simple signaling using tones or FSK modulation. There were many incompatible mobile radio and 1G systems as little thought was given to worldwide interoperability and radio companies were content with proprietary standards.

The situation continued with 2G cellular radio as there were many incompatible 2G systems with each only able to support one modulation method. Most of the radio functionality was in the analog hardware but VLSI was starting to become mature and it was possible to do limited error correction coding. At the basestation there was enough computing power to dynamically manage interference and implement simple system-level optimization. In the evolution to 3G there were many proposals all exploiting the increasing capability of VLSI. With the introduction of 3G, communication providers enforced the adoption of a single word-wide standard. Perhaps ‘single’ is a stretch as there were still several variations of the 3G implementation but a core set of standards supporting worldwide connectivity was adopted.

The path forward was becoming unmanageable so following the introduction of 3G an international consortium focused on developing a strategy to support cellular communications that was more capable and upwards compatible.

For the first time, with 4G a large number of modulation methods were supported with most of the modulation and demodulation functionality implemented in a DSP unit called the baseband processor. Changing modulation and demodulation formats was a simple procedure of running different code. This is software-defined radio with analog circuitry implementing just the translation from an analog baseband signal, really a modulated signal on a low-frequency intermediate frequency carrier, to the high-frequency RF signal. Modulation by the baseband data produced the baseband analog signal with the baseband processor implementing a digital version of an analog modulation format. With 5G additional capability is provided with the 4G standard becoming a subset of the 5G standard.

for RF hardware. This is particularly important as the actual performance required of hardware is often not directly related to the specifications developed by system designers. For example, one of the most important characteristics of digital radio systems is the bit error rate (BER). The BER is a quantity that cannot be determined until the components of a system are integrated. Thus in the design of subsystems, indirect measures such as intermodulation distortion (IMD) (referring to the generation of spurious signals when discrete tones are applied to a subsystem) are specified. The relationship between IMD and BER is weak. Clearly higher IMD tends to indicate a higher BER for the same technology, but the relative performance of different technologies cannot be evaluated this way. Thus an essential system design problem is developing sufficient and tractable criteria that enable subsystems to be locally designed and optimized, leading to an overall optimized system.