Bluetooth, HiperLan, IEEE 802.11 comparison

It is clear that medical devices and medical information management products will benefit from the advantages provided by Bluetooth wireless technology. And although Bluetooth certainly presents new challenges to the medical device industry, the benefits stand to be quite significant in both current and future use models for medical products.

Among other technologies HIPERLAN will offer high data rates and relative high throughput even without any infrastructure in the network. This opens basically new applications to wireless data communications. Compared to the growth in for example the number of Internet nodes, which has risen from virtually nothing in 1986 to over 1.4 Millions in 1993, the potential number of HIPERLAN nodes is even higher. Radio-based LANs are doing to portables what they should be: truly movable.

The Bluetooth standard is becoming more and more of a short time network between devices for a small amount of information. The major difference is the data rates of the different technologies. First Bluetooth runs at a much slower data rate than 802.11. Bluetooth has a maximum capacity of 1 Mbps. This is compared to the, now standard, 802.11b which runs up to 11 Mbps. The first 802.11 standard also only ran at 1 Mbps.

The reason for the different data rates between the technologies lies in the Physical and Data layers. The Physical Layer of Bluetooth has very little transmitter power at the antenna, as opposed to the 'high' output power of an 802.11 Transceiver. The output power of a Bluetooth transmitter is 1 mW, whereas the output power of 802.11 is 1 W. The modulation technique has something to do with the data rate also. Bluetooth using GFSK (Gaussian Frequency Shift Keying) as opposed to CCK (Complementary Code Keying) in 802.11

This also leads to the transmission type. Bluetooth uses what is called Frequency Hopping and 802.11b uses what is called DSSS (Direct Sequence Spread Spectrum). Frequency hopping could cause delays in the transmission and the only way to prevent this is to slow down the information exchange. Therefore only 1 packet is sent on 1 hop frequency. But, in the case of a larger packet, it could be spread out over a maximum of 5 time slots (or the equivalent of missing 5 hop frequencies). In the DSSS case, the CDMA allows the signal to be spread out over a large frequency range and make all other users look like noise to the destination. This allows for higher data rates and more users.

Another difference is the usage, Bluetooth is being used for device to device data transfer. This allows devices such as PDA's, Notebooks, Cell Phones, Printers and Fax machines to talk to each other, on the fly. This is to avoid time consuming 'access' procedures for a wired network, as well as the cost of wiring the access points for communicating with these devices. This is appealing to the business traveler who needs to set up the printer in the hotel room and print from the Notebook computer. It can be done seamlessly and without any trouble to the user. The devices take care of all the trouble, from security settings and encryption to connecting and disconnecting. The only real trouble to the user is the set up of the printer and Notebook. The use of 802.11 has become more of an access point for a computer to get on a wired backbone. This is the direction that the developers have been taking in the past few years. 802.11 does have the ability to create ad-hoc networks, but that isn't the way many people have decided to use it.
The security of each is different too. Bluetooth uses a combination of 4 LFSR's (Linear Feedback Shift Registers) to encrypt data at the physical layer. Bluetooth also has the very high frequency hoping rate which also aids in keeping data secure. This unfortunately has drawbacks too. The hopping pattern is sent on every packet sent out to a device, so if someone was so inclined, all that would be needed to determine the hopping pattern would be to capture one packet. There is also a key code word that is generated at initialization of the two devices, again helping aid in security. Most of the security is taken care of at the software level for Bluetooth. There is no need for users to setup anything. IEEE 802.11 has access points that act as a hub in a wired network, and thus don't have much security at the physical layer. The problem with this is that the hub sends all packets to every device connected to it in a wired network. The same holds true for a 802.11 access point. The 'hub' sends all packets to every user in the vicinity, and if the data wasn't meant for that computer, it is ignored. This is a big security issue if a malicious user would happen to want to listen to the network. IEEE 802.11 standard has an optional encryption capability. This is implemented by embedding RC4 security algorithm in the data layer. But this brings out another security issue, by storing the 'passwords' on the computers and at the access points. This does encrypt the transmissions though.
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