# Challenges in Wireless System Integration as Enablers for Indoor Context Aware Environments
## 1 Introduction  
The evolution towards Smart Cities and by extension, Smart Regions, is driving the need of increasing user-environment interactivity levels. In this sense, Context Aware environments are foreseen as key elements in the control and regulation of the multiple systems which sustain Smart Cities, such as Intelligent Transportation Systems, Smart Health, Smart Grids, context-based marketing or e/open-Government, to name but a few [1; 2; 3; 4]. The benefits inherent to the use of Context Aware environments are mainly given by the reactive and in some instances proactive nature of these scenarios, in which multiple systems are capable of adapting to user needs as well as to the requirements of such systems. Large scale sensing capabilities as well as scalable communication networks with high mobility levels are compulsory in order to provide the required levels of interactivity within these environments. To this extent, multiple, massive transceiver deployments operating with a diverse array of communication system in a Heterogeneous Network mode are being considered in order toexploit the involved systems, as well as to provide a mechanism to gather and fuse data, which can be handled by upper-level business intelligence layers. Wireless communication systems spanning from Radio Frequency (RF) to millimeter wave spectrum are primarily adopted given their performance in terms of cost, size and coverage range. RF and microwave bands have been widely adopted, given the existence of multiple Industrial, Scientific and Medical bands, as well as by the massive deployment of Public Land Mobile Systems (mainly 3G and 4G) and wireless broadcast systems, such as radio and television services. In parallel, the progressive requirements in Internet-based connectivity given by the advent of the Internet of Things (IoT) renders forecasts in which by the next decade, the number of IP connected devices will increase by one to two orders of magnitude [5; 6; 7; 8; 9]. In order to comply with cost, energy and size restrictions, transceiver configurations and communication protocols must be kept simple and low cost. In parallel, requirements in relation with communication capabilities, in terms of bit rate, latency and Quality of Service (QoS) demands, must be met. Digital transmission systems employ adaptive modulation and coding schemes, coupled to other functionalities, such as time/space diversity or channel multiplexing, leading to time dependent communication channels. This later case requires the analysis of coverage/capacity relations, in order to guarantee adequate service values for overall communications (and hence, for the end systems within the Context Aware scenarios). The variability in channel characterization is given by multiple factors, such as user service demands (which can be time-dependent, as a function of the multiple services under consideration), user density, user location and user location variability, among others. The limiting factor is given by the total amount of interference experienced by each one of the transceivers within the system, as coverage/capacity relations are directly degraded as a function of overall spectral density values of interference within the bandwidth of operation. The advent of IoT conveys a relevant growth in wireless transceiver density. This condition is particularly relevant in the case of indoor scenarios, in which a large number of devices are embedded within the scenario (e.g., building automation systems, location and tracking systems, communication backup for home entertainment systems, etc.) and other non-structural transceivers, such as wearables from the users within the indoor environment are also present.