تجزیه و تحلیل عملکرد از فن آوری های بی سیم میزان کم برای کاربردهای پزشکی

In this article, we discuss what wireless technologies can be used for medical applications and how well they perform in a healthcare/hospital environment. We consider the emerging low-rate Wireless Personal Area Network technology as specified in the Institute of Electrical and Electronics Engineers 802.15.4 standard and evaluate its suitability to the medical environment. We focus on scalability issues and the need to support tens of communicating devices in a patient's hospital room. We evaluate the effect of packet segmentation and backoff parameter tuning to improve the overall network performance that is measured in terms of packet loss, goodput, and access delay. We also evaluate the performance of 802.15.4 devices under interference conditions caused by other 802.15.4 devices and by wireless local area networks using IEEE 802.11b.

In medicine, providing timely access to complete patient information is key to saving lives and improving the overall safety of the patient's care. While better recording and reporting systems have been developed to provide a wealth of healthcare data, the information remains fragmented and largely inaccessible. Even within hospitals and large medical groups, when patients see multiple providers in different settings, no one seems to have access to complete information. While many hospitals today are in the early stages of using data from all of the patient connected medical devices, connections are mainly based on the RS-232 port interfaces that are made permanently to stationary monitors. In addition to the wiring cost to plug more devices on the network, there are severe incompatibility issues where each device manufacturer defines its own data link communication method. Therefore, proprietary drivers have to be loaded every time a different device is plugged into the network, making it unrealistic to plug in mobile devices several times during the day. In this context, there is a need for a universal or even a wireless interface that provides connectivity, untethered access to information, and replaces the ‘hard-wired’ approach. Closing the gap on the network connectivity and scalability issues affecting the medical environment is poised to become a major effort in revamping the current healthcare system and making it more efficient. The Institute of Electrical and Electronics Engineers (IEEE) 1073 working group is currently developing standard specifications for medical device communication focusing on wireless technologies that are adequate for the clinical domain and the patient's bedside. The main objective for this effort is to develop a universal and interoperable interface for medical equipments that is (1) transparent to the end user, (2) easy to use and (3) quickly (re)configured. The purpose of the group is not so much to develop new technologies, but to evaluate the suitability of current available technologies in the medical space. In this article, we consider the IEEE 802.15.4-2003 standard [1] that is a likely candidate for low bit rate wireless personal area network (WPAN) applications, given the low bandwidth, low power requirement of most patient bedside devices. We evaluate the performance of a network consisting of several communicating devices in a patient's hospital room and stress the scalability and performance trade-offs that exist. Our objectives are to answer a number of questions concerning the performance and operation of a WPAN in a medical environment, for example the following: How many devices can be plugged into a WPAN? What is the performance achieved? What protocol parameters can be tuned to improve performance? The remainder of this article is organized as follows. Section 2 discusses the medical environment application requirements. In Section 3, we give a brief overview of the IEEE 802.15.4 protocol specifications. In Section 4, we consider scenarios to discuss performance trends and trade-offs. In Section 5, we expand our understanding of the performance of 802.15.4 by considering interference scenarios caused by multiple WPANs and a wireless local area network (WLAN). In Section 6, we offer some concluding remarks.

In this article, we investigate the use of the wireless technology described in the IEEE 802.15.4 standard specification for medical applications in support of multiple devices with different data rates. Our findings can be summarized as follows. The CSMA/CA mechanism built into the MAC protocol may limit the utilization of the medium. An aggregate data rate of 130% of the capacity from three transmitters leads to a goodput rate of little more than 50%. Furthermore, as the number of transmitters is increased to 16, the goodput rate drops to 5%. We explore two different avenues to alleviate this scalability problem. First, we explore moving beyond the legacy Ethernet interface, and defining a segmentation of the application framing structure into smaller chunks that fit into IEEE 802.15.4 MAC packets. This approach improves the goodput rate up to 90% for two/three transmitters, and 40% for 16 transmitters. An obvious side effect for this method is that the access delay can grow significantly, proportionally to the aggregate network load. Second, we look into tuning the backoff parameters that control the CSMA/CA mechanism. We observe that by increasing the transmission persistence, i.e. reducing the maximum number of CSMA/CA backoffs and the backoff exponent to 0, goodput is increased to 60 and 40% for two and 16 transmitters, respectively. The main disadvantage of transmission persistence is a transmission synchronization problem exhibited by the jagged pattern in the goodput curves. We verify that this synchronization is mainly due to the constant nature of the application traffic used and note that the behavior symptoms disappear for exponential packet generation distributions. In the area of interference we show that a WPAN sharing the same channel with another WPAN has no more interference effect than if all devices were using the same WPAN. However, WLAN interference is detrimental to a WPAN using 802.15.4. It is envisioned that if the penetration of WLAN continues at its current rate, then a WPAN using 802.15.4 will be incapacitated, unless the WLAN is idle most of the time or on a different channel. Choosing the optional sensing mechanism that detects any packet type for the 802.15.4 WPAN will improve its performance, but perhaps not enough to make a difference.