The context refers to “any information that can be used to characterize the situation of an entity, where an entity can be a person, place, or physical object.” Radio context awareness is defined as the ability of detecting and estimating a system state or parameter, either globally or concerning one of its components, in a radio system for enhancing performance at the physical, network, or application layers. In this paper, we review the fundamentals of context awareness and the recent advances in the main radio techniques that increase the context awareness and smartness, posing challenges and renewed opportunities to added-value applications in the context of the next generation of wireless networks. 1. Introduction Modern wireless systems are required to manage radio resources in an effective and flexible manner in order to maximize the network capacity. Moreover, they are increasing their complexity and pervasiveness in the real world at several scales, giving rise to heterogeneous, more decentralized, and sophisticated systems. In this context, next generation radio systems are required to achieve high capacity, high reliability, flexibility, adaptivity, and full support to innovative applications and services that make use of the awareness of both the context and the surrounding environment. Therefore, collaboration, awareness, smartness, and adaptivity are the keywords of a trend that involves all the radio technologies, from wireless personal area networks (WPAN) to wireless metropolitan area networks/wide area networks (WMAN/WAN) and wireless regional area networks (WRAN) as depicted in Figure 1. Wireless sensor networks (WSN), whose radio technologies belong mainly to WPAN, play a fundamental role in the field of radio context awareness: these sensing networks are usually composed of a large number of low-power, inexpensive, and long-life nodes with sensing, computation, and wireless communication capabilities, and they can produce, with several degrees of performance and complexity, the features and the related applications that will be discussed in this paper. Figure 1: Current scenario of radio technologies and standards. Acronyms between square brackets are examples of tecnhologies based on the corresponding standards. As stated efficaciously in [1], context regards “any information that can be used to characterize the situation of an entity, where an entity is a person, place, or object that is considered relevant to the interaction between a user and an application, including the user and applications themselves.” Therefore, radio
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