Bluetooth - IEEE 802-15-1
WiFi dominates the WLAN market and Bluetooth dominates the WPAN market. Although it has its critics Bluetooth wireless technology has matured into the most widely supported WPAN wireless standard available. Applications ranging from PC peripherals, mobile phones, cars, medical devices use Bluetooth and the applications within consumer, industrial and enterprise markets continue to grow rapidly.
The main features of Bluetooth 2.0 technology are low cost (<$2 per unit) and small size. The latest generation of devices have maximum achievable data rate of 3Mbps and although the standard range is 10m it is possible to extend the range to 100m with the use of additional amplification.
Bluetooth operates in the 2.4GHz industrial, scientific and medical (ISM) radio band which it subdivides into 79 communication channels. A robust and secure connection is ensured using an agile frequency-hopping scheme and short packets. Devices avoid interference from external signals, such as microwave ovens and radio transmitters, by hopping to a new frequency after transmitting or receiving a packet. Frequency hopping simply means that the channel used for sending and receiving data is changed after each packet and the channel change is called a ‘hop’. Channel hopping is necessary to meet the statutory restrictions imposed on ISM band usage but it does have advantages. Any spurious interference is short-lived and a packet that fails to reach its destination can be resent at the next frequency (packets are acknowledged in Bluetooth). Frequency hopping gives a basic base level of security because the channel hop sequence must be known in order to successfully receive messages – eavesdropping is therefore very difficult. Obviously, connected devices must somehow agree upon the channel hopping sequence as part of the communication process.
The Bluetooth specification defines a master-slave relationship between devices and when two or more devices connect an ad-hoc network called a piconet is formed. As shown in Figure 2, within a piconet one device operates in master mode and all other devices, up to maximum of seven, operate in slave mode. Devices within the same piconet share the same channel. Given that a maximum of seven slaves are allowed within the piconet, each device is identifiable by a 3-bit active device address. When devices come within range they automatically exchange addresses, capability details and establish a link. A master device sends its own unique 48-bit device address (similar to an Ethernet address) and the value of its internal clock. Slaves use this data to calculate the frequency-hopping sequence which guarantees synchronisation because the slaves use the same algorithm with the same initial values so they always arrive at the same hop sequence as the master device.
A master is the only device that initiates connections, however, once a link is established, a slave may request a master/slave switch and become the master. Communication takes place between the master and a slave: Slaves are not allowed to communicate directly.
Bluetooth Piconets and Scatternets
Multiple piconets with overlapping coverage areas form a scatternet and slaves may participate in different piconets on a time-division multiplex basis. Additionally, a device may be a master in one piconet and a slave in another or it may be a slave in more than one piconet.
Bluetooth Low Energy (BLE) 4.0
As its name suggests this version of Bluetooth targets low power and it is targeted at consumer and peripherals market. The basic specifications - range 100m, modulation frequency hopping spread spectrum (FHSS) - are unchanged but power consumption has been reduced significantly due largely to reductions in data rate, connection time and changes to the protocol. Only point-to-point and star connections are allowed: no piconets or scatternets.
| Bluetooth 2.0 | BLE | |
|---|---|---|
| Range | 100m | 100m |
| Power consumption | 1W | 0.01 - 0.5W |
| Data rate | 1–3 Mbit/s | 1 Mbit/s |
| Latency | 100ms | 6ms |
Bluetooth is mature and widely used technology that will certainly be a player in the low power networking arena. Its rapid rise to prominence in the marketplace for healthcare, fitness, security and home entertainment is clear evidence that supports this assertion.
Bluetooth