Abstract
Conventional wired body sensor networks have been used in hospitals over the last decade; however, the tethered operation restricts the mobility of the patients. In the scenario considered in this chapter, the signals collected from the patients’ bodies are wirelessly transmitted to a base station, and then delivered to a remote diagnosis centre through a communication infrastructure, enabling full mobility of the patient in the coverage area of the wireless network. Healthcare applications require the network to satisfy demanding requirements in terms of quality of service (QoS) and, at the same time, minimize the energy consumption of the sensor nodes. The traffic generated by data-intensive healthcare applications may lead to frequent collisions between sensor nodes and the consequent loss of data, if conventional MAC protocols for wireless sensor networks are used. Therefore, this chapter presents LPRT and CCMAC, two MAC protocols that intend to satisfy the QoS requirements of these applications, but differ in the wireless topology used. Experimental results for an implementation of the LPRT using an IEEE 802.15.4 compliant wireless sensor platform are presented, as well as simulation results comparing the performance of direct communication (between wireless body sensor nodes and the base station) with two other approaches relying on a cluster-based topology (similar to the one proposed by the authors of LEACH), which demonstrate the benefits of using a cluster-based topology on wireless healthcare applications.
Top1. Introduction
A body sensor network (BSN) consists of a group of sensors attached to a patient in order to acquire physiological data. Conventional wired BSNs have been used in hospitals over the last decades; however, these systems do not allow the patient to move around freely. Recent advances in wireless technologies are changing this scenario by enabling mobile and continuous monitoring of patients, even during their daily life activities. In such healthcare systems, the information sensed at the patient´s body is wirelessly transmitted to a base station, located no more than a few tens of meters away, and then delivered to a remote diagnosis centre through a communication infrastructure. These systems may require the monitoring of several bio-signals, such as electrocardiogram (ECG), heart rate, blood pressure, respiratory rate, pulse oximetry and temperature. Table 1 presents the electrical characteristics of the bio-signals commonly used in emergency medical care (Arnon et al., 2003; Paksuniemi et al., 2005).
Table 1. Bio-signals electrical characteristics
| Vital signal (Hz) | Freq. range (Hz) | Sampling rate (Hz) | Resolution (bit) |
| ECG (per lead) | 0.01…60-125 | 120-250 | 12 |
| Temperature | 0…0.1-1 | 0.2-2 | 12 |
| Oximetry | 0 … 30 | 60 | 12 |
| Blood pressure (BP) | 0 … 60 | 120 | 12 |
| Respiratory rate | 0.1 … 10 | 20 | 12 |
| Heart rate (HR) | 0.4 … 5 | 10 | 12 |
Key Terms in this Chapter
Body Sensor Network (BSN): A body sensor network consists of a group of sensors that form a network and are attached to a patient’s body in order to acquire physiological data.
Quality of Service (QoS): A set of characteristics of a network service that can be interpreted as representatives of its quality. It includes parameters and values such as data rates, acceptable delays, losses and errors.
Sensor Node: A sensor node is a device that possesses the capacity to gather sensor information from the environment, process the information and communicate with other nodes.
Wireless Sensor Network (WSN): A wireless sensor network consists of spatially distributed devices that communicate wirelessly and use sensors to cooperatively monitor physical conditions from the environment.
Base Station: A main transmitting and/or receiving station, often one which serves as a junction between wireless and wireline communication paths.
Transceiver: A transceiver is a communicating device that contains both a transmitter and a receiver.
Medium Access Control (MAC): In a layered network architecture, the layer that contains the set of functions that govern the access to the available medium.