Wireless body area networks (WBAN) play a key role in the future of e-Health. In response, IEEE sets up working group 802.15.6 to standardize WBAN schemes. Of all existing standard proposals, the 2.4GHz proposal is the most mature and ready for mass production. However, as e-Health WBAN applications are often mission/life critical, people are concerned with the reliability (particularly, coexistence reliability) of this proposal. This study evaluates the 2.4GHz proposal under WiFi/Bluetooth interference in the context of medical multi-parameter monitoring. The authors conclude that WiFi poses a major threat to such application scenario, while Bluetooth does not.
Top1. Introduction
Healthcare has become a major concern for many countries across the globe. For example, the United States' healthcare expenditure surpassed US$2.3 trillion in 2008, which is 16.2% of the nation's GDP (National Health Care Expenditures Data, 2010); and China is facing the severe challenge of aging, as a consequence of long-lasting one-child policy (Kaneda, 2006).
To curb the healthcare crisis, medical devices and systems must be upgraded to expand capabilities, increase efficiency, improve safety, and enhance convenience. One enabling technology to these goals is wireless body area networks (WBAN).
A key application of WBAN is multi-parameter monitoring (i.e., monitoring multiple vital signs). For instance, during operation or intensive care, a patient must be attached with multiple electrodes to simultaneously monitor various vital signs: electrocardiography (ECG), electroencephalography (EEG), temperature, 
level, oxygen level, blood pressure, etc.. In many cases, the patient must be plugged with these electrodes for hours, days, or even longer durations (e.g., 
monitoring in intensive care unit (ICU)).
Goldman (2009) investigated the drawbacks of using wired electrodes instead of wireless electrodes in multi-parameter monitoring settings. According to his investigation, the wires of electrodes can literally tie a patient to the bed. Even worse, a small movement of the patient may stretch the wires, causing electrodes to fall off. This can be at least annoying to the patient and care givers, and sometimes can even cause lethal ramifications. In contrast, replacing wired electrodes with WBAN wireless electrodes will not only make the patient more comfortable, but also reduce the probability that electrodes fall off. This idea, which we call WBAN multi-parameter monitoring, is illustrated by Figure 1.
Figure 1. Multi-parameter monitoring through WBAN
Same as wired monitoring, in Figure 1, the patient is attached with various types of electrodes, e.g., twelve ECG electrodes, one oxygen level electrode, one blood pressure electrode, one respiration electrode, etc. But unlike the wired case, all electrodes connect to the monitor through wireless. The monitor and all electrodes form a WBAN. The monitor plays the role of base station, while the electrodes play the role of clients. We call the wireless links from the base station to clients the downlinks, while the wireless links from clients to base station the uplinks.
Researchers and engineers have spent a lot of efforts to build WBANs. CodeBlue is a famous wireless sensor network solution for healthcare (Georgios, 2007). MobiHealth and UbiMon also contribute to regulate a ubiquitous wireless monitoring environment for wearable sensors (Halteren, 2004; Imperial College, 2011). Recently, IEEE 802.15.6 Task Group begins to define guidelines for wireless body area networks, focusing on low power, small size and light weight (Reichman, 2009).