Guest Editors' Introduction: Digitally Enhanced Wireless Transceivers

h CURRENT AND NEXT-GENERATION electronic systems and devices such as automotive electronics, portable and handheld devices, computers, sensor networks, and biomedical implant devices, increasingly rely on wireless communication. The massive and relatively inexpensive digital processing resources available in modern semiconductor technologies open new opportunities for digitally intensive wireless system design. The partial or entire replacement of analog, mixed-signal, and RF functions by digital or digitally assisted functions is a recent trend in wireless transceiver design to improve performance, enhance testability, and reduce form factor. Digital PLLs and modulators, digital-RF transceivers, digitally assisted power amplifiers, digitally assisted data converters, among others have been demonstrated recently. In addition, communication functions based on digital building blocks open opportunities for new radio and subsystem architectures. Technology scaling and dense integration have resulted in increased device variability and vulnerability to aging effects which in many instances has a negative impact on production yield and longterm reliability. Beyond the requirements of testing for quality control, the idea of calibrating a wireless system as part of the test procedure to recover yield loss has been coined recently. Toward this end, digitally-assisted RF ICs can now integrate sophisticated autonomic calibration procedures (also regarded as self-healing or self-tuning) aiming at optimizing performance metrics in the presence of process and environmental variations. The above-mentioned technology trends must be developed coherently across all layers of the communication system with the ultimate objective of designing wireless devices that are flexible, resilient and affordable as a whole. These requirements are particularly challenging for emerging networking applications such as machine-to-machine communications. This special issue of IEEE DESIGN & TEST OF COMPUTERS provides an overview of the challenges, current practice, and future research directions of digitally enhanced wireless systems. In ‘‘Digital and Digitally Enhanced Wireless Transceivers: Evolution and Future Directions,’’ R. Staszewski revisits the digitization journey of wireless systems and the motivations that have driven this research field, reviews state-of-the-art solutions, and offers insights for future developments. In ‘‘Digitally Intensive Receiver Design: Opportunities and Challenges,’’ R. Nanda and D. Markovic describe a directsampling receiver which provides a wide range of runtime adaptability by varying parameters such as sample rate, filter order, and interpolation factor. In ‘‘Mixed-Signal SoCs with in situ Self-Healing Circuitry,’’ C. Maxey et al. discuss the goals and recent achievements of the HEALICs program. The program’s aim is to enhance wireless systems with sensors, actuators, and mixed-signal control loops in order to improve their performance yield. In ‘‘Dual-Control Self-Healing Architecture for HighPerformance Radio SoCs,’’ C. Chien et al. discuss a self-healing 60 GHz transceiver architecture which