Future Personal Area Networks ZigBee and UWB ?

1. Networks: L14 Future Personal Area NetworksZigBee and UWB ? GSM GPRS/2½G UMTS/3G High Power Long Range 802.11g 802.11b 802.11a BlueTooth Low Power Short Range UWB ZigBee Text Graphics Internet Audio Video Multi-channel Video Low Data Rate High Data Rate

2. Networks: L14 ZigBee • Low data rate, low power consumption, low cost wireless networking • Target Applications : • Home Automation • security, remote control of domestic appliances, heating/ventilation/air conditioning (HVAC), lighting, curtains etc. • Consumer Electronics • TV, VCR, DVD, CD, toys, games etc. • PC peripherals • mouse, keyboard, joystick, gamepad etc. • Personal healthcare • monitors, diagnostics, sensors etc. • Industrial & Commercial • monitors, sensors, automation, control etc.

3. Networks: L14 • ZigBee Alliance : • promoted by Philips, Mitsubishi, Motorola, Invensys • many others also developing the technology and products • Physical & MAC protocol layers just now standardised as IEEE 802.15.4 • Alliance members still developing upper protocol layers, profiles etc. • Characteristics : • data rates : • 250kbps in 2.4GHz ISM band • 20kbps in 868MHz band (Europe) • 40kbps in 915MHz band (USA) • low power consumption • battery life of 6months to 2 years on 2 AA batteries – 0.1% duty cycle • low cost : $2 - $3 expected • claimed to be significantly lower than other technologies and standards • range : 10m to 30m nominally, perhaps up to 75m • depending on power output required for a given application

4. Networks: L14 • star topology • one full function master and up to 254 reduced function clients • full function device (FFD) network coordinator capable, talks to any other device • reduced function device (RFD) limited to star topology, only talks to master • virtual peer-to-peer defined • clustered stars • master communicates with other masters, each with their own clients • up to 100 co-located networks

5. Networks: L14 • network coordinator/master • transmits network beacons • sets up a network • manages network nodes • stores network node information • receives constantly • network client • generally battery powered • searches for available networks • transfers data from its application as necessary • determines whether data is pending • requests data from the network coordinator • can sleep for extended periods • 8-bit micro-controller adequate for both master and client • full protocol stack <32Kb, reduced function stack <4Kb • coordinator may require extra RAM for node database, transaction table etc.

6. Networks: L14 • operating frequency bands • 868MHz/915MHz • channel 0 : • channels 1-10 : • Binary Phase Shift Keying (BPSK) modulation • 2.4GHz • channels 11-26 : • Quadrature Phase Shift Keying (O-QPSK) 868.3MHz 2MHz 902MHz 928MHz 5MHz 2.4GHz 2.4835GHz

7. Networks: L14 • CSMA-CA channel access • fully handshaked protocol for transfer reliability - ACK/NAK return packets • optional guaranteed time slots • typical intended traffic types : • periodic data • application definded rate e.g. sensors • intermittent data • application/external stimulus defined rate e.g. light switch • repetitive low latency data • allocated time slots e.g. mouse • devices can hibernate until an external event triggers an interrupt • security • data integrity and authentication using IEEE defined protocols • all devices have unique 64 bit IEEE addresses • addressing modes: • network + device identifier (star) • source/destination identifier (peer-to-peer)

8. Networks: L14 • Protocol architecture : Application Customer Application Interface Network Layer Data Link Layer ZigBee MAC Layer IEEE MAC Layer Physical Layer Silicon ZigBee Stack Application

9. Networks: L14 • Physical frame structure : • MAC frame structure : • data frame • beacon frame • network information • frame structure • notification of pending node messages • acknowledgment frame • command frame • status, network association, device synchronisation, beacon management etc. synch. preamble start of packet delimiter PSDU length Physical Service Data Unit (PSDU) 32 bits 8 bits 8 bits 0-127 octets MAC header MAC Service Data Unit (MSDU) MAC footer

10. Networks: L14 • optional superframe structure : 15ms slot 1 slot 2 slot 23 Network beacon transmitted by network master Space reserved for beacon growth due to pending node messages Contention period : access by any node using CSMA-CA Reserved for nodes requiring guaranteed bandwidth

11. Networks: L14 • Master/Slave network connection : Master Slave Permit connection Connect Beacon Tx Connect ACK Rx Connect confirm ACK New device Connect confirm

12. Networks: L14 • Mediation device operation for peer-to-peer connection: Source node Master Destn. node Query RTS RTS reply ACK Query response CTS Data ACK

13. Networks: L14 • Comparison with Bluetooth • ultra low power consumption • 255 devices per network instead of 7 per piconet • data rate 250kbps instead of 1Mbps • aimed at industrial control applications and home automation, not audio • not expected to be incorporated in cellphones and headsets • probably cheaper than Bluetooth • protocol stack implementation ~32kb instead of 256kb • Bluetooth better for audio, graphics, FTP, ad hoc networks • ZigBee better for static networks, lots of devices, small data packets and infrequent use • typical timing values : • new slave connection : 30ms (ZigBee) versus >3s (Bluetooth) • changing from sleeping to active : 15ms versus 3s • active slave access time : 15ms versus 2ms

14. Networks: L14 Ultra Wide Band (UWB) • Recent headlines : • “UWB Communications may be in your future” • “Ultrawideband renews high-speed wireless hopes” • “Ultrawideband radio set to redefine wireless signalling” • “Ultrawideband wants to rule wireless networking” • “A Technology to Consider : Ultrawideband” • “Ultra Wideband Technology – The Wave of the Future?” • “Ultra-Wideband : Multimedia Unplugged” • “Ultrawideband : an electronic free lunch?” • but also sadly : • “UWB in Limbo” • “MBOA Falls Short Again” • Multiband OFDM Alliance – set up to define UWB standards

15. Networks: L14 • What is UWB? • transmissions consist of very narrow individual square wave pulses • widths typically range from 100psec to 1.5nsec • emitted at precisely timed nanosecond intervals • Fourier Analysis applied against time duration of the pulse width • shows that the bandwidth occupied is proportional to narrowness of pulse • a 200psec pulse occupies more than 5GHz around a 2GHz centre frequency • transmitted energy is divided across the wide range of frequencies • at any individual frequency, energy measured is at extremely low levels • hence pulses are within the noise floor of the electromagnetic environment • to extract a UWB transmission, the receiver must correlate the RF signal with an expected waveform • i.e. it must know exactly when the pulse may be expected • each individual bit spread over several pulses • received signal at expected pulse times then integrated to raise the signal above the noise level

16. Networks: L14 • a variety of methods possible to modulate information onto the pulse stream • e.g. relative to a fixed repetition rate, an early pulse = 0, a late pulse = 1 • varying amplitude or pulse width also • arguments still in progress as to best method • Properties • original Marconi spark gap transmitters were ultra-wideband • so-called Baseband radio since there is no carrier frequency to be modulated • though the pulse repetition rate is the equivalent • reinvented in the military in the 1960s for Radar and secure transmissions • becoming prominent again now because of technology developments • only the latest CMOS processes are fast enough to handle the narrow pulses and controlled high repetition rates required • at 0.25 micron and smaller feature sizes • only CMOS promises the low fabrication costs required for mass market applications • should always be cheaper than carrier-based technologies • no such circuitry required

17. Networks: L14 • just four essential components: • the UWB transmit/receive chip • the antenna • a digital baseband processor to handle packetising, error correction etc, • embedded firmware and protocols that drive the processor • signal below the noise level • should not interfere with other transmissions above the noise floor • in theory! • inherently longer range than carrier-modulated systems • only pulse detection required • maintaining integrity of modulation not involved • almost impossible to intercept • need to know the exact timing of the transmitted pulses • this would be made private for security • e.g. a pseudo-random sequence with secure key

18. Networks: L14 • multi-path fading can almost be eliminated • caused by reflections from adjacent surfaces e.g. nearby buildings • UWB pulses so narrow that any reflected pulse will be out of the expected receive-time window and therefore ignored • not line-of-sight • signals propagate through walls and other obstacles • UWB has been used for ground-penetrating radar • also used for through-the-wall imaging • pulses received at a time indicating that they have been reflected from a nearby wall can be ignored • pulses reflections received later will be from objects beyond the wall • the inverse of removing multi-path signals • UWB chipsets have already reached 40Mbps at ranges of 60m • using 50 to 70 milliwatts of power • (802.11 sends at 11/54Mbps using 100 milliwatts over 30m) • PulseLink Inc. have demonstrated 400Mbps

19. Networks: L14 • Applications: • wireless audio, video and data over LANs for home and office • cable replacement - the Bluetooth and ZigBee market? • 802.11 also? • geo-position location to centimetre accuracy • a by-product of sending and receiving data between multiple UWB devices • and precise timing of pulse arrivals • car and home security radars • also possible to use UWB over cable • to coexist with cable frequency bands • up to 1.2Gigabit downstream and 120MBps upstream transmission rates demonstrated by Pulse-Link • HDTV, interactive services etc.

20. Networks: L14 • Regulation and Licensing issues • UWB sidesteps the need for allocation of dedicated frequency bands • may avoid any upcoming crunch in allocations • should be able to co-exist with other radio transmissions • other users still concerned however • e.g. hospital equipment might be affected • GPS transmissions may be affected • too many co-existing UWB transmissions will eventually raise the noise floor • and degrade effectiveness of 802.11, Bluetooth etc. • Federal Communications Commission (FCC) in USA allowed experimental UWB transmissions to start in 2000 • according to FCC, UWB is any signal occupying at least 500MHz, and in the frequency band from 3.1GHz to 10.6GHz • strict limits on radiated power • formal rule changes permit UWB from Feb. 2002

21. Networks: L14 • IEEE standardisation effort • rival groups competing for a 802.15.3a standard to be established • MBOA : Intel, Philips, Mitsubishi, Texas Instruments, General Atomics et al. • versus Motorola, XtremeSpectrum Inc., Partus-Cerva et al. • consensus is that a multi-band system of some sort would be best • i.e. several separate GHz-wide bands • neither quite a simple as the baseband system first envisaged • going back to carrier-based systems and using OFDM and frequency-hopping • suggested that transmission bands should be above 3.1GHz • to avoid GPS interference • as of September 2003, no agreement has been reached • the 75% majority needed not achieved • European regulators still holding fire