BLUETOOTH is a by now well-established communications standard for short-distance wireless connections. It replaces the many proprietary cables that connect one device to another with one universal short-range radio link. For instance, Bluetooth radio technology built into both the cellular telephone and the laptop would replace the cable used today to connect a laptop to a cellular telephone. Printers, desktops, fax machines, keyboards, joysticks and virtually any other digital device can be part of the Bluetooth system.
The Bluetooth radio technology also provides a universal bridge to existing data networks, a peripheral interface, and a mechanism to form small private ad hoc groupings of connected devices away from fixed network infrastructures
BRIEF HISTORY::
In 1995, the telecommunications and information technology industries recognized that a low-cost, low-power radio based cable replacement, or wireless link, would be feasible, thus eliminating the need for communication cables for short distances. Such a ubiquitous link would provide the basis for small portable devices to communicate together in an ad-hoc fashion.
Bluetooth technology has been designed to operate in noisy radio frequency environments, and uses a fast acknowledgement and frequency-hopping scheme to make the link robust, communication-wise. Bluetooth radio modules avoid interference from other signals by hopping to a new frequency after transmitting or receiving a packet. Compared with other systems operating in the same frequency band, the Bluetooth radio typically hops faster and uses shorter packets. This is because short packages and fast hopping limit the impact of microwave ovens and other sources of disturbances..
THE BASIC CONTROL SYSTEM BLOCK OF THIS SYSTEM
Functional parts of the Bluetooth system:
a radio unit
a link control unit
link management
software functions
SCO(synchronous, connection-oriented links)
How network connections are established?
Bluetooth supports both point-to-point and point-to-multi-point connections.
Several piconets (Piconet: a collection of devices connected via Bluetooth technology in an ad hoc fashion. A piconet starts with two connected devices, such as a portable PC and cellular phone, and may grow to eight connected devices All Bluetooth devices are peer units and have identical implementations. However, when establishing a piconet, one unit will act as a master for synchonization purposes, and the other(s) as slave(s) for the duration of the piconet connection.) can be established and linked together ad hoc, where each piconet is identified by a different frequency hopping sequence. All users participating on the same piconet are synchronized to this hopping sequence.
Before any connections in a piconet are created, all devices are in STANDBY mode. In this mode, an unconnected unit periodically "listens" for messages every 1.28 seconds. Each time a device wakes up, it listens on a set of 32 hop frequencies defined for that unit.
Once the signal is down-converted to the first IF, it can be filtered, amplified, sampled by an ADC, and subsequently digitally processed. Some designs rely here on analog IF filtering and much simpler analog FM-discriminator-based demodulator designs. After demodulation, there is a slicer, converting the FM-demodulated signal to a binary sequence
The connection procedure for a non-existent piconet is initiated by any of the devices, which then becomes master of the piconet thus created. (The one sending the data is the master)
INQUIRING AND PAGING
A connection is made by a PAGE message being sent if the address is already known, or by an INQUIRY message followed by a subsequent PAGE message, if the address is unknown.
In the initial PAGE state, the master unit will send a train of 16 identical page messages on 16 different hop frequencies defined for the device to be paged (slave unit). If no response, the master transmits a train on the remaining 16 hop frequencies in the wake-up sequence.
The maximum delay before the master reaches the slave is twice the wakeup period (2.56 seconds) while the average delay is half the wakeup period (0.64 seconds).
The INQUIRY message is typically used for finding Bluetooth devices, including public printers, fax machines and similar devices with an unknown address. The INQUIRY message is very similar to the page message, but may require one additional train period to collect all the responses.
A power saving mode can be used for connected units in a piconet if no data needs to be transmitted. The master unit can put slave units into HOLD mode, where only an internal timer is running. Slave units can also demand to be put into HOLD mode. Data transfer restarts instantly when units transition out of HOLD mode. The HOLD is used when connecting several piconets or managing a low power device such as a temperature sensor.
2-MODES OF OPERATION
1>STANDBY MODE, an unconnected unit periodically "listens" for messages every 1.28 seconds. Each time a device wakes up, it listens on a set of 32 hop frequencies defined for that unit.
2> SNIFF mode, a slave device listens to the piconet at reduced rate, thus reducing its duty cycle. The SNIFF interval is programmable and depends on the application.
3> PARK mode, a device is still synchronized to the piconet but does not participate in the traffic. Parked devices have given up their MAC address and only occasionally listen to the traffic of the master to re-synchronize and check on broadcast messages. It can thus receive broadcasts, but not addressed messages while parked.
THE FEEDBACK FROM RECEIVERING END
The SCO link is symmetric and typically supports time-bounded voice traffic. SCO packets are transmitted over reserved intervals. Once the connection is established, both master and slave units may send SCO packets without being polled. One SCO packet type allows both voice and data transmission - with only the data portion being retransmitted when corrupted. The ACL link is packet oriented and supports both symmetric and asymmetric traffic. The master unit controls the link bandwidth and decides how much piconet bandwidth is given to each slave, and the symmetry of the traffic. Slaves must be polled before they can transmit data. The ACL link also supports broadcast messages from the master to all slaves in the piconet.
Networking requires a complete integration of:
RF processing, including:
antenna subsystem
modulation, up-conversion and power amplification, RF power control
RX signal amplification, down-conversion, filtering, and demodulation
Baseband processing
coding (encryption, scrambling, FEC/channel coding)
decoding (decryption, scrambling, FEC decoding/correction)
Resource (bandwidth) allocation mechanisms
Channel assignment
Quality-of-service (QoS) management, in other words, traffic prioritization
Interference management (suppression/avoidance)
Authentication.(Security management)
Block diagram contents
Services provided:
Sending and receiving of data (of course!)
Name request. The Link Manager has an efficient means to inquire and report a name or device identity up to 16 characters in length.
Link address inquiries.
Connection set-up.
Authentication.
Link mode negotiation and set-up, e.g. data or data/voice. This may be altered during the connection.
The Link Manager decides the actual frame type on a packet-by-packet basis.
CONDITONS REQUIRED FOR GOOD RESPONSE
Based upon a small, high performance integrated radio transceiver, each of which is allocated a unique 48-bit address derived from the IEEE 802 standard.
Operate in the unrestricted 2.45GHz ISM "free band", which is available globally although slight variation of location and width of band apply.
Range set at 10m to optimize for target of mobile and LAPTOP user.
Gross data rate 1 Mbit/s
One-to-one connections allow maximum data transfer rate of 721 kbits/s (3 voice channels).
Uses packet switching protocol based on frequency hop scheme with 1600 hops/s to enable high performance in noisy radio environments. The entire available frequency spectrum is used with 79 hops of 1 Mhz bandwidth, analogous to the IEEE 802.11 standard.
Low power consumption drawing only 0.3 mA in standby mode enables maximum performance longevity for battery powered devices. During data transfer the maximum current drain is 30 mA. However, during pauses or at lower data rates the drain will be lower.
If the above conditions are satisfied we can say that the response of the system is CRITICAL. In some cases the system may me OVERDAMPED.
STABILITY OF THE SYSTEM
The main factors which will affect the stability of the network are:
AUTHENTICATION
Connections may require a one-way, two-way, or no authentication. Authentication is based on a challenge-response algorithm. Authentication is a key component of any Bluetooth system, allowing the user to develop a domain of trust between a personal Bluetooth device, such as allowing only the owner's notebook computer to communicate through the owner's cellular telephone. Encryption is used to protect the privacy of the connection. Bluetooth uses a stream cipher well suited for a silicon implementation with secret key lengths of 0, 40, or 64 bits. Key management is left to higher layer software.
BLUETOOTH BANDWIDTH
Bluetooth is not primarily meant for transferring great amounts of data.(WLAN, which also uses the IEEE 802.11 standard, is better in that respect). The Bluetooth is about 720 kbit/sec. between the master and any one slave unit, after discounting the overhead. As, this is sufficient for telephony, but not quite enough for video conferences and public radio. Such services, along with video and TV, would have to be provided by other means.
Performing frequent pages does not result in a positive user experience.
One of the main reasons an application would want to perform device paging is to simulate a device-proximity detector: When the desired device comes into range, it responds to the application’s page and triggers some specific task in the application. The paging process is a lengthy one, however, and like the inquiry process, results in degraded Bluetooth communication for its duration. In the worst case (when the desired device is not present), the timeout for the page could be as much as 15 seconds
For a device to be visible to an inquiry, it must be in discoverable mode.
The vast majority of devices are not in discoverable mode by default. The user must actively choose to make a device discoverable. In addition, a device that is always in discoverable mode is using more power. Since most Bluetooth-enabled devices are wireless, this means a greater drain on the battery. Finally, a perpetually discoverable device is more vulnerable to unwanted connections.
EXTRA INFORMATION
Wi-Fi requires that users be within the proximity of a transmitter, it offers faster speeds and easy adaptation for programs because it so closely resembles traditional networking. In contrast, Bluetooth would allow devices to communicate directly with one another instead of going through a transmitter.
The Bluetooth baseband protocol is a combination of circuit and packet switching. Time slots can be reserved for synchronous packets. A frequency hop is done for each packet that is transmitted. A packet nominally covers a single time slot, but can be extended to cover up to five slots. Bluetooth can support an asynchronous data channel, up to three simultaneous synchronous voice channels, or a channel which simultaneously supports asynchronous data and synchronous
. The number of hop frequencies varies in different geographic regions; 32 is the number for most countries.
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