Seventy Years of Radar and Communications: The Road from Separation to Integration

TL;DR

This paper reviews the historical evolution of radar and communications, highlighting their convergence into integrated sensing and communication systems and discussing future research directions from a signal processing perspective.

Contribution

It provides a systematic overview of R&C development, emphasizing the transition to ISAC and the associated signal processing frameworks and trends.

Findings

R&C have evolved from separate to integrated systems.

Technological trends include increased frequencies, bandwidths, and antenna arrays.

Future research directions in ISAC are discussed.

Abstract

Radar and communications (R&C) as key utilities of electromagnetic (EM) waves have fundamentally shaped human society and triggered the modern information age. Although R&C have been historically progressing separately, in recent decades they have been converging towards integration, forming integrated sensing and communication (ISAC) systems, giving rise to new, highly desirable capabilities in next-generation wireless networks and future radars. To better understand the essence of ISAC, this paper provides a systematic overview on the historical development of R&C from a signal processing (SP) perspective. We first interpret the duality between R&C as signals and systems, followed by an introduction of their fundamental principles. We then elaborate on the two main trends in their technological evolution, namely, the increase of frequencies and bandwidths, and the expansion of antenna arrays. We then show how the intertwined narratives of R&C evolved into ISAC, and discuss the resultant SP framework. Finally, we overview future research directions in this field.