The Aironet 340 and 350 series APs were tested by a two-step approach. In the first step, one AP was connected directly with the server that was not connected to the campus Ethernet backbone. In the second step, the AP was assigned a public Internet Protocol (IP) address and connected to the Ethernet backbone in the Susan Mott Webb Nutrition (Webb) Building at the University of Alabama at Birmingham. The IP address was assigned to an AP through either HyperTerminal or a Web console using a Web browser. An administrator ID and password were then created to enhance the Web console security. The client computer required a type II PCMCIA (Personal Computer Memory Card International Association) card slot. Every client needed a functional IP address to become associated with the AP. The Wired Equivalent Privacy (WEP) keys were enabled for both the AP and the clients to ensure two-way authentication.

The coverage of the WLAN was found to highly structure dependent. The floor of the Webb building measures about 60 by 25 meters. A single Aironet 340 AP was unable to cover the entire floor with a "good" link status. This was achieved using two (more powerful) Aironet 350 APs. Achieving the "excellent" link status on the floor required the use of the S2406P (Cushcraft) patch antenna. The wireless clients associated with the AP had a "fair" or "good" status one floor up and one floor down from the floor where the AP was located. There was a small area outside the 5-floor building in which the clients could associate with the AP with a "poor" status.

In order to test the feasibility of implementing an isolated LAN around a patient's home, we chose a two-story house with the layout shown in Figure 1. Two simulated scenarios were tested: one with an ambulance parked on the street next to the house (Figure 1A and 1C), and the other with the ambulance parked next to the house in its parking lot (Figure 1B and 1D). Two connection modes under each scenario were also tested: one mode used the AP-client connection (Figure 1A and 1B) and the other used a peer-to-peer connection without the AP (Figure 1C and 1D). The link statuses both inside and outside the house were at least "good", and some of the area close to the AP in both scenarios had "excellent" coverage. This suggested that an ambulance with a patch antenna could communicate at a reasonable rate with handheld devices operating inside the patient's home, through either an AP or a direct peer-to-peer connection.

To quantify the baseline signal strength, one Aironet 350 AP was tested in the open area: "excellent", "good", "fair", and "poor" link statuses were obtained within 10, 25, 50, and 100 feet (~4, 10, 20, and 39 meters), respectively. As shown in Table 1A, the file transfer rate for a 10-MB file was 224–2,000 kbps, depending on the distance. Interestingly, higher rates were reached for files of size 10–100 MB.

We chose Ipaq Pocket PCs as PDAs due to their relatively large amount of RAM compared to other PDAs, and a cellular phone (Motorola) as alternative data transmission device when the PDA was outside the WLAN coverage (to simulate the scenario when a long-range antenna, such as a yagi antenna (Cisco), is not available). The transfer rates for single files of different sizes are summarized in Table 3A. The faxing speed through the phone did not appear to be correlated with the file size, since a 50-fold difference in file size resulted in a 30% difference in the time needed to complete the file transmission. The reason is unknown, and should be further investigated.

A Cisco V3 ACS was used to improve the security of the network 13. As shown in Figure 2, the Active Directory facility of a Windows 2000 Server was used as a network access server to communicate with the ACS for authentication, authorization, and accounting (AAA) 14. The ACS was able to control client access to the network through the AAA process.

When managing a WLAN with many clients, there are often insufficient public IP addresses. The solution is to use either the Dynamic Host Configuration Protocol (DHCP) or a private LAN with a Network Address Translation (NAT) server. DHCP services are not easily managed and sometimes create security challenges to network administrators in determining the user's identity. A private LAN seems to be a better solution and more applicable in most ER environments where many wireless clients may transmit at same times, thus maintaining relatively high-speed connections. Figure 3 shows a private LAN with a NAT server that was configured and tested. All wireless clients were centrally managed through an ACS server. The file transfer rates were similar to those achieved with public IP addresses under similar conditions (data not shown).

Health-care organizations have traditionally been slow in accepting WLAN technology in clinical practice. One of the major concerns has been its cost 1516, followed by security 17181920, although the benefits of WLANs have been demonstrated in many fields including telemedicine 21. The cost of a simple WLAN like the one tested here was calculated (Table 4).

After collecting all patient data at a patient's home, the data must ultimately be transferred to the ER. This involves two critical synchronization steps: (1) from the patient's home to a server on the ambulance, and (2) from the ambulance to the ER (while in transit or upon arrival). Here the WLAN was employed for both of these steps, using Microsoft Briefcase and Windows Workgroups. Automatic synchronization with the destination server and batch synchronization were desired. The ultimate objective is, however, to link the two synchronization steps using a long-range antenna that reaches up to 25 miles (e.g., a yagi antenna from Cisco). This would significantly shorten the time needed to transfer data from a patient's home to the ER, since the data will reach a ER WLAN earlier. We are currently performing the associated experiments. We also tested the use of a cellular phone and other types of PDA (e.g., a Palm Pilot) with network capabilities in transmitting a small (up to 50 MB) but critical file. The results suggested that cellular phones or PDAs with network cards can be effective alternatives to the use of a long-range antenna to transmit data from a patient's home to the ER.

EKG data are considered very valuable in the early detection, early intervention, and possibly better outcome of heart attack patients 9. The use of a wearable device with sensors to monitor specific physiological signals and communicate with a personal server has been reported 22. Land-based telephone lines have also been employed to transmit EKG data and for monitoring by clinical personnel 23. In our study, we showed that files up to 5–10 MB (the size of a typical high-quality digitalized EKG image) could be transferred using FTP or other file transfer methods within minutes. Handheld devices such as a Pocket PC and cellular phone may be useful in transmitting EKG files when the ambulance is still at the patient's home, as shown in Table 3. The time required to transmit a file is proportional to its size in the case of a Pocket-PC-to-laptop transfer, but this was found not to be the case between a cellular phone and a fax machine. The reason for this discrepancy is unknown, and needs to be further investigated. The use of a long-range antenna may ultimately be needed to increase the transmission capacity and speed.

The WLAN operates at 2.42 GHz with an output power of 100 mW, which may pose a risk of interference with medical devices using similar frequencies. Previous studies have shown that a WLAN may interfere with medical devices in close proximity 24 but is unlikely to be interfered with by such devices 25. Further studies are needed to clearly address the possibility. In another study, infrared modems exhibited a similar performance to a wired system even in an electrically noisy environment 26, indicating that infrared wireless connectivity can be safely and effectively used in operating rooms. These studies suggest that a WLAN can be acceptable for use in prehospital settings if careful interference testing is conducted.

The major concern over a WLAN is its security 17181920, especially when personal information is involved. It has been reported that the open-air clear-text transmission of WEP keys and MAC addresses increases network vulnerability 13272829. One approach to minimizing the risk is to control the access of remote and/or wireless clients through the Remote Access Dial-in User Service and AP management using the Extensible Authentication Protocol. The regulation by the Healthcare Insurance Portability and Accountability Act may further delay an organization's decision to adopt WLAN technology, although both the Institute of Electrical and Electronic Engineering (IEEE) 802.3 and the OpenAir standard specifications offer security protection (these are the two major standards in the unlicensed commercial 2.4-GHz WLAN market). According to our experiences, the following steps are required to implement a secure WLAN. First, anonymous access should be disabled and the Service Set Identifier of an AP and data encryption key (WEP key) should be enabled. Secondly, a Web console should be used to designate an administrator and manage APs and clients. Thirdly, an ACS server such as Cisco Secure ACS should be implemented to work with Active Directory in order to offer both device- and user-dependent AAA services. Digital certificates should be applied whenever possible for mutual authentication to protect sensitive information through secure server access and secure Web access. In addition, the physical security of the APs, client, and server computers can never be overemphasized.

The IEEE 802.11 specification addresses both the physical and MAC layers (Orthner, personal communication), and the OpenAir 2.4 interface standard is derived from the Wireless LAN Interoperability Forum 29 and needs to be interoperable with the IEEE 802.11 standards. The 5-GHz band WLAN standard (IEEE 802.11a) will become more popular once its cost decreases and the required components become more widely available. The use of standardized compliant devices facilitates communication and interoperability.

The present study was mainly based on the Windows operating system and Cisco wireless products. IEEE 802.11a products for the next generation of WLANs are emerging quickly from various vendors. Hence the stability, compatibility, and interoperability with other vendors require further evaluation. Although currently it is relatively expensive to implement a WLAN using this new protocol, the prices and capabilities are expected to improve within the near future.