11-12-2012, 01:42 PM
Bluetooth Technology Overview
[attachment=43346]
Basics of Bluetooth
Bluetooth is a short-range radio technology that enables wireless connectivity between mobile devices. Design-wise, the three main goals for Bluetooth were: small size, minimal power consumption, and low price. The technology was designed to be simple, and the target was to have it become a de facto standard in wireless connectivity.
Bluetooth radio operates in the unlicensed ISM band at 2.4 GHz [Core, p.19]. In some countries, this band is reserved for military use, but these countries have now begun freeing that band for general use. The maximum gross data rate is 1 Mbps [Core, p.41].
The range of Bluetooth depends on the power class of the radio. Most devices are expected to use the class 2 radio that provides 0 dBm nominal output power, resulting in a range of up to 10 meters in an obstacle-free environment. This range is sufficient for cable-replacement applications. When a longer range is needed (e.g., in access points), a more powerful radio (class 1) can be used. Larger power consumption is not a problem if the device is a piece of fixed equipment. With mobile devices such as mobile phones, power-consumption issues are crucial and therefore class 2 is the only feasible option.
Air Interface
Piconet and Scatternet
The Bluetooth network is called a piconet. In the simplest case it means that two devices are connected (see Figure 2a). The device that initiates the connection is called a master and the other devices are called slaves. The majority of Bluetooth applications will be point-to-point applications. Bluetooth connections are typically ad hoc connections, which means that the network will be established just for the current task and then dismantled after the data transfer has been completed.
A master can have simultaneous connections (point-to-multipoint) to up to seven slaves (see Figure 2b). Then, however, the data rate is limited. One device can also be connected in two or more piconets. The set-up is called scatternet (see Figure 2c). A device can, however, only be a master to one piconet at a time. Support for hold, park, or sniff mode is needed for a device to be part of the scatternet. In these modes a device does not actively participate in a piconet, leaving time for other activities such as participating in another piconet, for example.
Frequency Hopping
Bluetooth technology uses a frequency hopping technique, which means that every packet is transmitted on a different frequency. In most countries, 79 channels can be used. With a fast hop rate (1600 hops per second), good interference protection is achieved. Another benefit is a short packet length. If some other device is jamming the transmission of a packet, the packet is resent in another frequency determined by the frequency scheme of the master. This scenario is depicted in Figure 3 where packets of device 1 (colored packets) and device 2 (banded packets) are trying to use the same frequency. Note that this case only refers to situations where there are two or more simultaneous active piconets or a non-Bluetooth device using the same frequency in range.
Links and Packets
The Asynchronous Connectionless (ACL) links are defined for data transmission, primarily packet data. They support symmetrical and asymmetrical packet-switched connections. Multi-slot packets use the ACL link type and can reach the maximum data rate of 723 kbps in one direction and 57.6 kbps in the other direction. The master controls the ACL link bandwidth and decides how much of the bandwidth a slave can use in a piconet. Broadcast messages are supported in the ACL link, i.e., from the master to all slaves in the piconet [Whitepaper1, p.12].
The Synchronous Connection Oriented (SCO) links support symmetrical, circuit-switched, point-to-point connections and are therefore primarily used for voice traffic. Two consecutive time slots at fixed intervals are reserved for an SCO link [Whitepaper1, p.12]. The SCO link reserves every sixth slot for a transmitting channel and the subsequent slot for a receiving channel, so there can be up to three simultaneous SCO links. The data rate for SCO links is 64 kbps [Core, p.58].
[attachment=43346]
Basics of Bluetooth
Bluetooth is a short-range radio technology that enables wireless connectivity between mobile devices. Design-wise, the three main goals for Bluetooth were: small size, minimal power consumption, and low price. The technology was designed to be simple, and the target was to have it become a de facto standard in wireless connectivity.
Bluetooth radio operates in the unlicensed ISM band at 2.4 GHz [Core, p.19]. In some countries, this band is reserved for military use, but these countries have now begun freeing that band for general use. The maximum gross data rate is 1 Mbps [Core, p.41].
The range of Bluetooth depends on the power class of the radio. Most devices are expected to use the class 2 radio that provides 0 dBm nominal output power, resulting in a range of up to 10 meters in an obstacle-free environment. This range is sufficient for cable-replacement applications. When a longer range is needed (e.g., in access points), a more powerful radio (class 1) can be used. Larger power consumption is not a problem if the device is a piece of fixed equipment. With mobile devices such as mobile phones, power-consumption issues are crucial and therefore class 2 is the only feasible option.
Air Interface
Piconet and Scatternet
The Bluetooth network is called a piconet. In the simplest case it means that two devices are connected (see Figure 2a). The device that initiates the connection is called a master and the other devices are called slaves. The majority of Bluetooth applications will be point-to-point applications. Bluetooth connections are typically ad hoc connections, which means that the network will be established just for the current task and then dismantled after the data transfer has been completed.
A master can have simultaneous connections (point-to-multipoint) to up to seven slaves (see Figure 2b). Then, however, the data rate is limited. One device can also be connected in two or more piconets. The set-up is called scatternet (see Figure 2c). A device can, however, only be a master to one piconet at a time. Support for hold, park, or sniff mode is needed for a device to be part of the scatternet. In these modes a device does not actively participate in a piconet, leaving time for other activities such as participating in another piconet, for example.
Frequency Hopping
Bluetooth technology uses a frequency hopping technique, which means that every packet is transmitted on a different frequency. In most countries, 79 channels can be used. With a fast hop rate (1600 hops per second), good interference protection is achieved. Another benefit is a short packet length. If some other device is jamming the transmission of a packet, the packet is resent in another frequency determined by the frequency scheme of the master. This scenario is depicted in Figure 3 where packets of device 1 (colored packets) and device 2 (banded packets) are trying to use the same frequency. Note that this case only refers to situations where there are two or more simultaneous active piconets or a non-Bluetooth device using the same frequency in range.
Links and Packets
The Asynchronous Connectionless (ACL) links are defined for data transmission, primarily packet data. They support symmetrical and asymmetrical packet-switched connections. Multi-slot packets use the ACL link type and can reach the maximum data rate of 723 kbps in one direction and 57.6 kbps in the other direction. The master controls the ACL link bandwidth and decides how much of the bandwidth a slave can use in a piconet. Broadcast messages are supported in the ACL link, i.e., from the master to all slaves in the piconet [Whitepaper1, p.12].
The Synchronous Connection Oriented (SCO) links support symmetrical, circuit-switched, point-to-point connections and are therefore primarily used for voice traffic. Two consecutive time slots at fixed intervals are reserved for an SCO link [Whitepaper1, p.12]. The SCO link reserves every sixth slot for a transmitting channel and the subsequent slot for a receiving channel, so there can be up to three simultaneous SCO links. The data rate for SCO links is 64 kbps [Core, p.58].