Wireless Personal area networksWPANs By Engr. Sherjeel Farooqui
WAN 2G, 3G 2km/link national areas MAN 802.16 2-6km PAN 802.15.x 10m LAN 802.11 100m Overview of wireless networks
IEEE 802.15 - General • Wireless Personal Area Networks (WPANs) • Short Range • Low Power • Low Cost • Small Networks • Communication within a persons operating space
802.15 division • IEEE 802.15 is the 15th working group of the IEEE 802 • which specializes in Wireless PAN (Personal Area Network) standards. • It includes four main task groups (numbered from 1 to 4).
802.15 Task Groups • Task group 1 (WPAN/Bluetooth) IEEE 802.15.1-2002 has derived a Wireless Personal Area Network standard based on the Bluetooth v1.1 specifications. It includes a medium access control and physical layer specification. An updated version, IEEE 802.15.1-2005, has been published. • Task group 2 (Coexistence) IEEE 802.15.2-2003 addresses the issue of coexistence of wireless personal area networks (WPAN) with other Wireless Devices operating in Unlicensed Frequency Bands such as wireless local area networks (WLAN).
802.15 Task Groups • Task group 3 (High Rate WPAN) IEEE 802.15.3-2003 is a MAC and PHY standard for high-rate (11 to 55 Mb/s) WPANs , for applications which involve imaging and multimedia. • Task group 4 (Low Rate WPAN) IEEE 802.15.4-2003 (Low Rate WPAN) deals with low data rate but very long battery life (months or even years) and very low complexity. The first edition of the 802.15.4 standard was released in May 2003. In March 2004, after forming Task Group 4b, task group 4 put itself in hibernation. The ZigBee set of high level communication protocols is based upon the specification produced by the IEEE 802.15.4 task group
Bluetooth • Bluetooth wireless technology is a short-range communications technology intended to replace the cables connecting portable and/or fixed devices while maintaining high levels of security. • The key features of Bluetooth technology are robustness, low power, and low cost. The Bluetooth specification defines a uniform structure for a wide range of devices to connect and communicate with each other. www.bluethooth.com
Bluetooth’s Objectives • Global usage. • Voice and data handling. • The ability to establish ad-hoc connections. • The ability to withstand interference from other sources in open band. • Very small size, in order to accommodate integration into variety of devices • Negligible power consumption in comparison to other devices for similar use. • An open interface standard. • Competitively low cost of all units, as compared to their non-Bluetooth Correspondents.
APPLICATIONS OF BLUETOOTH • Phones and pagers • Modems • LAN access devices • Headsets • Notebook computers • Desktop and handheld computers • Printers • Fax machines • Keyboards • Joysticks
Bluetooth Application Areas • Data and voice access points • Real-time voice and data transmissions • Cable replacement • Eliminates need for numerous cable attachments for connection • Ad hoc networking • Device with Bluetooth radio can establish connection with another when in range
Features of Bluetooth Technology • Bluetooth is based upon small, high performance integrated radio transceivers, each of which is allocated a unique 48-bit address derived from the IEEE 802 standards. • It operates in the unrestricted 2.4 GHz ISM "free band", which is available globally, although slight variation of location and width of band apply. • Bluetooth uses the unlicensed ISM (Industrial, Scientific and Medical) band, 2400 - 2483.5 MHz, thereby maximizing communication compatibility worldwide • The range is set at 10 meters to optimize for target market of mobile and business user. The range can, however, be increased to 100 meters. • Gross data rate is 1Mbit/s, with second generation providing increase to 2Mbit/s, and further to 3Mbits/s
Landline Cable Replacement Data/Voice Access Points Personal Ad-hoc Networks What does Bluetooth do for you?
Features of Bluetooth Technology • Bluetooth uses a packet switching protocol, based on a frequency hoping scheme with 1600 hops/sec 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. • It has low power consumption, drawing only 0.3 mA in standby mode. This 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 would be lower.
Frequency hopping • The total bandwidth is divided into 79 physical channels. (almost in every country) • Each channel has the bandwidth of 1 MHz. • FH occurs by jumping from one channel to another in pseudorandom sequence. • The hop rate is 1600 hops/sec • Each physical channel is occupied for 0.625ms which is referred as a slot. • Bluetooth uses FH-TDD-TDMA. • Link data rate - a maximum link baseband data rate of 723.2 kb/s is supported, with options for 1/3 bit repetition and 2/3 Hamming FEC (Forward Error Correction). • Speech coding - CVSD - 64kb/s Continuously Variable Slope Delta Modulation. • CVSD supports acceptable speech quality even with 1-3% bit error rate, BER.
Hopping Sequence • We can only predict the hopping sequence if we know two pieces of information. • The first is a portion (the 28 lowest bits) of the piconet master device's numeric address (the "MAC address" or more properly "BD_ADDR"), and the second is the master's clock, a 28 bit integer value that increments 3200 times per second. • If we know both the address and the clock at a particular time, then we can correctly predict the hopping sequence forever. We just have to use the hopping algorithm dictated by the Bluetooth specification.
Hopping Sequence • In total, six types of hopping sequence are defined − five for the basic hop system and one for an adapted set of hop locations used by adaptive frequency hopping (AFH). These sequences are: • An inquiry hopping sequence with 32 wake-up frequencies distributed equally over the 79 MHz, with a period length of 32; • An inquiry response hopping sequence covering 32 response frequencies that are in a one-to-one correspondence to the current inquiry hopping sequence. • A page hopping sequence with 32 wake-up frequencies distributed equally over the 79 MHz, with a period length of 32;
Hopping Sequence • A page response hopping sequence covering 32 response frequencies that are in a one-to-one correspondence to the current page hopping sequence. The master and slave use different rules to obtain the same sequence; • A basic channel hopping sequence which has a very long period length, which does not show repetitive patterns over a short time interval, and which distributes the hop frequencies equally over the 79 MHz during a short time interval. • An adapted channel hopping sequence derived from the basic channel hopping sequence which uses the same channel mechanism and may use fewer than 79 frequencies. The adapted channel hopping sequence is only used in place of the basic channel hopping sequence. All other hopping sequences are not affected by hop sequence adaptation.
Technical Features • 2.4 GHz ISM Open Band • Globally free available frequency • 79 MHz of spectrum = 79 channels • Frequency Hopping & Time Division Duplex (1600 hops/second) • 10-100 Meter Range • Class I – 100 meter (300 feet may be 100mW) • Class II – 20 meter (60 feet with min of 0.25mW(-6dBm) to 2.4mW(4dBm)) • Class III – 10 meter (30 feet 1mW) • 1 Mbps Gross Rate • Simultaneous Voice/Data Capable
Bluetooth Topologies There are 3 types of connections in Bluetooth: • Single-slave • Multi-slave (up to 7 ”slaves” on one master) • Scatternet
Piconet • A piconet is 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 a mobile phone. • The limit is set at 7 units in a piconet (that’s why the required address-space is limited to 3 bits). • All Bluetooth devices are peer units and have identical implementations. • However, when establishing a piconet, one unit will act as a master for synchronization purposes, and the other unit/units will be slave/slaves for the duration of the piconet connection.
Scatternet • A scatternet is a combination of two or more independent non-synchronized piconets that communicate with each other. • A slave as well as a master unit in one piconet can establish this connection by becoming a slave in the other piconet. • It will then relay communications between the piconets, if the need arises.
Addressing • Bluetooth device address (BD_ADDR) • 48 bit IEEE MAC address • Active Member address (AM_ADDR) • 3 bits active slave address • all zero broadcast address • Parked Member address (PM_ADDR) • 8 bit parked slave address
Forming A Piconet • Initially, devices Known only about themselves • No Synchronization • Every one Monitors in standby mode • All devices have the capability of serving as master or slave
Forming a Piconet • Unit establishing the Piconet automatically becomes the master. • It sends an inquiry to discover what other devices are out there. • Addressing • Active devices are assigned a 3-bit active member address(AMA) • Parked devices are assigned an 8-bit parked member address. (PMA) • Standby devices do not need an address.
Types of Access Codes • Channel access code (CAC) identifies a piconet • Device access code (DAC) used for paging and subsequent responses • Inquiry access code (IAC) used for inquiry purposes
Inquiry Procedure • Potential master identifies devices in range that wish to participate • Transmits ID packet with inquiry access code (IAC) • Occurs in Inquiry state • Device receives inquiry • Enter Inquiry Response state • Returns FHS packet with address and timing information • Moves to page scan state
Page Procedure • Master uses devices address to calculate a page frequency-hopping sequence • Master pages with ID packet and device access code (DAC) of specific slave • Slave responds with DAC ID packet • Master responds with its FHS packet • Slave confirms receipt with DAC ID • Slaves moves to Connection state
Connecting To Pico Net • Device in standby listens periodically • If device wants to establish a Piconet, it sends an inquiry, broadcast over all wake-up carriers. • It will become master of the Piconet. • If inquiry was successful, devices enter in the page mode. • Devices in standby may respond to the inquiry with its device address. • It will become slave to that master
Page and Connect States • After receiving a response from each device, the master can connect to each device individually • An AMA is assigned • Slave synchronize to the hopping sequence established by the master. • In Active states, master and slave listen, transmit and receive.
Low Power State • Sniff state • Slaves listen to Piconet at a reduce rate. • Master designates certain slot to transmit to slaves in sniff state. • Hold state • Slave stops ACL Transmission, but exchange SCO Packets only. • Park State • Slave releases AMA address and receive PM address. • Still FH synchronized and wakes up periodically to listen to becon.
Scatternet • Piconet with overlapping coverage use different hopping sequences • Collisions may occurs wile multiple Piconet uses same carrier frequency at the same time. • Devices can participate in multiple Piconet simultaneously, creating a scatternet • A devices can only be the master of one Piconet at a time. • A device ma serve as Master in One Piconet and Slave in other Piconet. • A device may serve as slave in multiple piconets.
Piconet channel FH/TDD f5 f1 f4 f3 f2 f6 m s1 s2 625 sec 1600 hops/sec
Multi slot packets (ACL) f1 f5 f4 f6 m s1 s2 625 sec Data rate depends on type of packet Packet can be 1,3,5 slots long. For complete transmission same frequency is used, after transmission the frequency in hope sequence is selected
Multi slot packets (ACL) f1 f6 m s1 s2 625 sec Data rate depends on type of packet Packet can be 1,3,5 slots long. For complete transmission same frequency is used, after transmission the frequency in hope sequence is selected
Physical Link Types • Synchronous Connection Oriented (SCO) Link • Allocate fixed bandwidth between a point to point connection involving master and a single slave. • Master maintains the two consecutive slot for SCO link one for each side. • No ARQ, No CRC • Master can support upto three SCO link and slave can support up to two SCO link. • FEC (optional) • 64 Kbps
Physical Link Types • Asynchronous Connection-less (ACL) Link • Only single ACL link can exsist. • It is the slot which is not used by the SCO Link • Polling access method • ARQ, CRC • FEC (optional) • Symmetric data rate 108 - 433 Kbps • Asymmetric data rate up to 723 Kbps
ACL ACL ACL ACL ACL ACL Mixed Link Example SCO SCO SCO m s1 s2
72 bits 54 bits 0 - 2745 bits Packet Format Access code Header Payload Error correction 1/3 rate FEC 2/3 rate FEC ARQ scheme for the data Synchronization identification Filtering Address Packet Type Flow control ARQ SEQN HEC Smaller than an ATM cell !
Bluetooth Packet Fields • Access code – used for timing synchronization, offset compensation, paging, and inquiry • Header – used to identify packet type and carry protocol control information • Payload – contains user voice or data and payload header, if present
Preamble Sync Word Trailer 64 bits 4 bits 4 bits • It consist of pattern 0101 if the least significant bit (Left most bit) of the SYNC word is 0. • It consist of pattern 1010 if the least significant bit (Left most bit) of the SYNC word is 1. • It consist of pattern 0101 if the most significant bit (Right most bit) of the SYNC word is 1. • It consist of pattern 1010 if the most significant bit (Right most bit) of the SYNC word is 0. Composition Of Access Code