Wireless Technologies

1. Wireless Technologies Asim Loan March 28, 2002

2. Outline • Bluetooth • Wireless Personal Area Network (WPAN) • IEEE 802.11a/b/g • Wireless Local Area Network (WLAN) • Frame Format • Range versus Throughput • Multi-channel Multipoint Distribution System (MMDS) • Local Multipoint Distribution System (LMDS) • Wireless Local Loop (WLL) 2

3. Bluetooth 3

4. US/Europe (except Spain & France) 2.4 to 2.4835 GHz (79 Channels) Japan 2.471 to 2.497 GHz (23 Channels) Requirements Channel bandwidth is limited to 1 MHz Spread Spectrum (SS)/Frequency Hopping (FH) must be employed Multiple uncoordinated networks may exist Interference Microwave ovens operate in this band International 2.4 GHz Industrial Scientific and Medical (ISM) Band 4

5. Introduction • Has been approved as a standard by IEEE 802.15.1 • Operates in the 2.4 GHz ISM-Band • Universally portable/interoperable • Provides short range wireless connectivity for personal and business mobile devices • Devices include mobile phones, PC, PDA, digital cameras, etc. • Ericsson, IBM, Intel, Nokia and Toshiba along with more than 500 companies support the standard • Bluetooth supports point to point and point to multipoint connections • Bluetooth devices form unique small ad-hoc networks called piconets • A piconet can have up to seven devices that can actively communicate with each other. Within a piconet, one Bluetooth device acts as a master and • Supplies its slaves with clock and hopping pattern 5

6. Physical Characteristics • Modulation • Gaussian Frequency Shift Keying (GFSK) BT = 0.5, 0.28 < h < 0.35 • Frame is divided into time slots • Time Division Duplexing is used where time slots are 625 ms long • Even time slots are used for master to slave transmission and odd time slots are used for slave to master transmission • Radios hop every packet, i.e., each packet is transmitted on a different hop frequency • Packets can occupy one, three or five time slots. Multi-slot packets use same hop frequency • Bluetooth supports two types of Links • Circuit switched, synchronous, connection oriented links for voice • Packet switched, asynchronous, connection less links for packet data • Nominal transmit power is one mW • Transmit power of up to 100 mW can be used if power control mechanisms are employed 6

7. Physical Characteristics – (Contd.) • Nominal range is 10 cm ~ 10 meters but can be increased to 100 meters by increasing the transmit power • Forward error correction • 1/3 bit repeat code • 2/3 rate shortened Hamming code (15,10) • Error correction via automatic repeat request • 1-bit fast ACK/NAK • Bluetooth employs a low cost, 64 Kbps Continuously Variable Slope Delta (CVSD) modulation technique to encode voice • More tolerant to errors than ADPCM • Bluetooth provides user protection and encryption in the physical layer 7

8. Wireless LAN 8

9. BSS BSS What is WLAN? System Overview • Wireless Local Area Network – a data communication system based on IEEE 802.11 standard that operates within campus, corporate office, etc. • Provides mobility and flexibility in network deployment • More susceptible to environment perturbation and interference, therefore suffers higher packet error rate • High vulnerability to security threats • Supports two topologies: Infrastructure and Independent (ad-hoc) Basic Service Set (BSS) Infrastructure BSS Independent BSS 9

10. WLAN Standards 10

11. IEEE 802.11a 11

12. IEEE 802.11b 12

13. IEEE 802.11g 13

14. Medium Access Modes in IEEE802.11 • Contention Mode • For each packet transmission, all stations are required to contend for access to channel • Use distributed control function (DCF) for asynchronous data which is basically carrier sense multiple access/collision avoidance. Carrier sensing is performed at two levels • Physical carrier sensing • Detecting any activity in channel via received signal strength indicator (RSSI) • MAC virtual carrier sensing • Updating the network allocation vector (NAV) by decoding MPDU duration information from the frame Header • Contention-free Mode • Stations are polled by access point • Use Point Coordination Function (PCF) to determine which station has the right to transmit • Supports time bounded services (voice/video) 14

15. Priority Access • Priority access is controlled through the use of Inter Frame Space time intervals (IFS) • IFSs are mandatory periods of idle times on transmission medium • Three types of IFS are defined (in order of their priority) • Short IFS (SIFS) • Point coordination function or priority IFS (PIFS) • Distributed control function or distributed IFS (DIFS) 15

16. CFP Repetition period CFP CFP CP CP CFP Repetition period B PCF B PCF B DCF DCF Coexistence of PCF & DCF 16

17. DIFS Data Source ACK SIFS Destination DIFS Other stations NAV Defer Access Period Back-off Period Basic DCF Transmission Procedure 17

18. Contention-Free Period CF end PIFS SIFS SIFS SIFS B D1 + Poll D2 + ACK + Poll U1 + ACK U2+ ACK SIFS SIFS Basic PCF Transmission From AP to Station 18

19. Frame Format 19

20. IEEE 802.11a Frame Format 12 non-zero sub-carriers, known pattern 52 non-zero sub-carriers, known pattern 48 Data sub-carriers + 4 Pilot sub-carriers Scrambled Encoded, Punctured and Interleaved BPSK BPSK, QPSK, 16-QAM or 64-QAM SIGNAL Field 20

21. Preamble (144 or 72 bits) Header (48 bits) PSDU 1 Mbps 1 Mbps [long] 2 Mbps [short] 1, 2, 5.5 or 11 Mbps Sync (128 or 56) SFD (16) Signal (8) Service (8) Length (16) CRC (16) All 1’s [long] All 0’s [short] 0xF3A0 [long] 0x05CF [short] 0x0A – 1 Mbps 0x14 – 2 Mbps 0x37 – 5.5 Mbps 0x6E – 11 Mbps Number of ms CCK or PBCC CCK length extension field Rest reserved IEEE 802.11b Frame Format 21

22. Range Versus Throughput - WLAN 22

23. Indoor Path Loss Model Where • d is the distance between the transmitter and receiver in meters • PTX,PWRis the transmit power • PRX,SENis the receiver sensitivity • GANT,Tis the total antenna gain • Free space propagation, with a path loss coefficient of 2, is possible up to free space distance, d0 • l is the wavelength in meters • n is the path loss coefficient and varies between 2 and 5. For open plan buildings, n is 2.2. For semi-open buildings, n is 3.3 and for closed buildings, n is 4.5 • LM is the loss in dB and is due to (a) floor and wall attenuation and (b) lognormal shadowing 23

24. Path Loss Versus Range 24

25. Link Budget Assumptions 25

26. Protocol Assumptions 26

27. Range Versus Throughput – PCF in 0 ns 27

28. Range Versus Throughput – DCF in 0 ns 28

29. Range Versus Throughput – DCF, Ad-hoc in 0 ns 29

30. Multi-channel Multipoint Distribution System 30

31. Overview • No standard is available yet • The intent was to provide an alternative to cable television by using wireless technology to transmit one direction video signals to the user • The signals from a satellite or another source are demodulated and re-converted to MMDS frequencies and then transmitted to the user. The receiver simply converts the signal to VHF/UHF frequency that is directly fed to the television • Spectrum allocation is in the 2.1 to 2.7 GHz band • MMDS requires line of sight between the transmitter and receiver • The range depends upon transmit power and terrain • Transmit power is in the range of one to one hundred Watts • The original concept of providing wireless cable did not take off because of the availability of satellite based low cost video programming • The US government has now allowed MMDS to carry bidirectional traffic and therefore MMDS can now provide high speed internet access, telephone, fax and television without a cable 31

32. Local Multipoint Distribution System 32

33. Overview • No standard is available yet • LMDS is a broadband wireless access networking solution and it provides an alternative to fiber, coax, Asymmetric Digital Subscriber Line (ADSL)/Very high rate Digital Subscriber Line (VDSL) and offers high capacity locally compared with other radio solutions • In US 1.3 GHz bandwidth has been allocated in the 28 GHz band. Europe has allocated the 40 GHz band for LMDS applications • Susceptible to fog and rain • The operators are free to use the spectrum as they wish. Bidirectional communication that provides high speed internet access, interactive TV, e-commerce and telemedicine is planned • The range is around three to five miles therefore the coverage area consists of small cells wherein point to multipoint communication is possible • Two layered cellular architecture is also an option • LMDS applications are short range and therefore find application in the urban areas 33

34. Wireless Local Loop 34

35. Overview • No standard is available yet • WLL system uses radio technology as opposed to traditional copper wire to provide local telephone service • In a WLL system the coverage area is divided into cells and the base stations can be connected to the central office (CO) either directly, if there is adequate capacity on the CO switch, or via a private branch exchange • The WLL system performs better than a cellular system because interference can be reduced by using directional antennas • WLL system can also be used to provide telephone services in rural areas, across bodies of water or can even serve as a backup for existing wire line network • Depending on the subscriber density, traffic conditions and service needs any of the existing cellular technologies (both digital and analog) can be used as a platform for a WLL system 35

36. Back Up Charts 36

37. Modulation / Mapping 37

38. d0 d0 SR d1 d1 4 DBPSK / DQPSK Modulation Assign “00” to 0, “01” to 90, “10” to 180 and “11” to 270 Phase change is equivalent to modulo 4 addition 0 1 1 0 0 0 1 1 n-1 n After QPSK convert, DQPSK encoding is equivalent to modulo 4 addition 38

39. CCK Modulation • Following formula is used to generate the code word [8-complex chips] that will be used for spreading Common to all chips Common to all odd chips Common to all odd pairs of chips Common to all odd quads of chips Indicates the symbol’s phase Cover code optimizes the sequence correlation properties and minimizes dc offsets in the codes Phase is DQPSK encoded. It rotates the symbol relative to the preceding symbol 39

40. 0 1 1 0 0 0 1 1 CCK Modulation – (Contd.) DQPSK Encoding p QPSK Encoding for 11 Mbps For 5.5 Mbps, j2 = p d2 + p/2, j3 = 0 and j4 = p d3 i.e., re-use 11 Mbps modulator by setting d2 = d2, d3 = 1, d4 = 0, d5 = 0, d6 = d3, d7 = 0 40