Real-time communication for embedded wireless networks

In recent decades, computer systems have been embedded into physical environments for automated real-time monitoring and control. This trend will continue, and even expand, to improve and secure our quality of life in many areas such as defense, emergency rescue, biosensing, pervasive computing, and assisted living. Analyzing application scenarios such as (1) cooperative mobile robots for rescue activities and (2) wireless sensor networks for surveillance/biosensing, some important observations can be made. First, the system requires end-to-end real-time performance to ensure emergency response within bounded delay; second, mobility and ease of deployment are mandatory requirements in the described scenarios; hence, wired backbone or wireless links with infrastructure are not viable options. Finally, the described applications are mainly event driven and the runtime workload is dynamic, hence, real-time data flows need to be established on demand, they require bounded delay, low jitter, and guaranteed data throughput. Since timeliness is a property tightly related to the way each shared resource (such as the wireless medium) is managed at a low level, this chapter will first cover protocols and challenges related to the medium access control (MAC) layer, followed by an overview of a light-weight real-time communication architecture (RAP), a delay-sensitive network-layer protocol (SPEED), and a notion of network capacity to quantify the ability of the network to transmit information in time.