Advances in Wireless Networks: IEEE 802.16(WiMAX)

1. Advances in Wireless Networks:IEEE 802.16(WiMAX) Vinh Do Comp 529 California State University of Northridge

2. Outline • Background • IEEE 802.15: PAN • IEEE 802.11: Wireless LANs • 802.11 last-mile network • Mesh network • IEEE 802.16 -Standards -Physical layer -MAC layer • IEEE 802.20(proposed)

3. wireless hosts • laptop, PDA, IP phone • run applications • may be stationary (non-mobile) or mobile • wireless does not always mean mobility network infrastructure Elements of a wireless network

4. base station • typically connected to wired network • relay - responsible for sending packets between wired network and wireless host(s) in its “area” • e.g., cell towers 802.11, 802.16 access points network infrastructure Elements of a wireless network

5. network infrastructure Elements of a wireless network wireless link • typically used to connect mobile(s) to base station • also used as backbone link • multiple access protocol coordinates link access • various data rates, transmission distance

6. Outdoor 50 – 200m Mid range outdoor 200m – 4Km Long range outdoor 5Km – 20Km Indoor 10 – 30m Characteristics of selected wireless link standards 54 Mbps 802.11{a,g} 5-11 Mbps .11 p-to-p link 802.11b 1 Mbps 802.15 3G 384 Kbps UMTS/WCDMA, CDMA2000 2G 56 Kbps IS-95 CDMA, GSM

7. infrastructure mode • base station connects mobiles into wired or mesh network • handoff: mobile changes base station providing connection into wired network network infrastructure Elements of a wireless network

8. Elements of a wireless network Ad hoc mode • no base stations • nodes can only transmit to other nodes within link coverage • nodes organize themselves into a network: route among themselves

9. Wireless Link Characteristics Differences from wired link …. • decreased signal strength: radio signal attenuates as it propagates through matter (path loss) • interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as well • multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times …. make communication across (even a point to point) wireless link much more “difficult”

10. B A C C C’s signal strength A’s signal strength B A space Wireless network characteristics Multiple wireless senders and receivers create additional problems (beyond multiple access): Hidden terminal problem • B, A hear each other • B, C hear each other • A, C can not hear each other means A, C unaware of their interference at B Signal fading: • B, A hear each other • B, C hear each other • A, C can not hear each other interferring at B

11. P P P P P M M Master device Slave device Parked device (inactive) S S S S 802.15: personal area network(PAN) • replacement for cables (mouse, keyboard, headphones) • ad hoc: no infrastructure • master/slaves: • slaves request permission to send (to master) • less than 10 m diameter • master grants requests • 802.15: evolved from Bluetooth specification • 2.4-2.5 GHz radio band • up to 721 kbps radius of coverage

12. 802.11b 2.4-5 GHz unlicensed radio spectrum up to 11 Mbps direct sequence spread spectrum (DSSS) in physical layer all hosts use the same chipping code widely deployed, using base stations IEEE 802.11 Wireless LAN • 802.11a • 5-6 GHz range • up to 54 Mbps • Orthogonal frequency division multiplexing(OFDM) • 802.11g • 2.4-5 GHz range • up to 54 Mbps • Orthogonal frequency division multiplexing(OFDM) • All use CSMA/CA for multiple access • All have base-station and ad-hoc network versions

13. Wi-Fi with directional antennas

14. Wi-Fi with directional antennas • Increase range of 802.11 • Fixed access/ Last mile usage-802.11 with high speed antennas • 802.11g is often selected -speed -ability to handle interference(OFDM) -interoperability with 802.11b-based devices • Limitation -efficiency of the network decreases as the number of users on 802.11 increases due to the overhead of managing additional subscriber -CSMA/CA contributed to network traffic

15. 802.11 Mesh network as MANs • Interconnect 802.11x based nodes by wireless 802.11 links • 802.11a standard commonly used in AP to AP links (performance and non-chanel overlapped with 802.11b/g) • Properties • 2.4GHz or 5 GHz unlicensed spectrum • up to 54 Mbps • Portable access • Automatic learn and maintain dynamic path configuration • Small nodes act as a simple router • Connection is shared across nodes • Based on propriety solutions • May provide VoIP and QoS • Coverage range can be over 10km • Performance up to 100Mbps • Better suited to blanket large areas with 802.11 access

16. Mesh network topology

17. 802.11 Mesh network(Cont.) • Advantages over single hop and directional last-mile alternatives • Robustness and resiliency • The shorter transmission range limit interference allowing simultaneously, spatially separated data flows • Benefits • Lower costs to the operator due to product availability • Balanced traffic • Flexibility over wired installations can be achieved • Limitations • A large subscriber base is needed to cover large areas • Using omni-directional antennas produces noise into network • Shared bandwidth: more users translate into less banwidth • Latency: latency increases with every hop • Lack of standardization leads to unavailability of QoS.

18. 802.16.1 10-66GHz unlicensed band LOS Up to 134Mbps 802.16.2: minimizing interference between coexisting WMANs 802.16-2004 (replace 802.16a/REVd) 2.5GHz, 3.5GHz licensed bands 5.8GHz licensed exempt band NLOS up to 75 Mbps Fixed end point 3 to 5 miles; Maximum range 30 miles based on tower height, antenna gain and transmit power. IEEE 802.16 standards

19. IEEE 802.16 standards(Cont.) • 802.16e • 2-6 GHz license band • NLOS • up to 15 Mbps • Mobility, regional roaming • Support mobile user traveling at speeds up to 95 miles/hr • 1 to 3 miles • Interoperability • Built in QoS • High performance • Smart antennas • Intelligent APs to monitor traffic

20. Point to Multipoint Wireless MAN • Base Station(BS) connected to public networks • BS serves Subscriber Stations(SSs) • SS typically serves a building(business or residence) • Provide SS with first-mile access to public networks • Multiple services with different QoS • Compare to a wireless LAN • Many more users • Multimedia QoS • Longer distance • Higher data rate

22. WIMAX network topology(fixed endpoints)

23. WIMAX backhaul for a Wi-Fi mesh topology

24. WIMAX as an intra mesh backhaul option

25. WIMAX as a client connection option

26. IEEE 802.16 standards

27. Physical layer characteristics • Line of sight(LOS)- because of 10-66GHz • Broadband chanels • Wide channels(20,25 or 28 MHz) • High capacity(down and up links) • Multiple Access • TDM/TDMA • High rate burst modems • Adaptive burst profile on both uplink and downlink • Multiple duplex schemes • Time division Duplex (TDD) • Frequency division duplex (FDD)-including burst FDD • Support for half duplex terminals • Adaptive modulation • QPSK, QAM16, QAM64

28. Adaptive Modulation • Allow a wireless system to choose the higher modulation depending on the channel conditions • Lower modulation(QPSK) for higher range • Higher modulation(QAM) for lower range(increase throughput)

29. Baud Rate and Channel Size(10-66 GHz) • Flexible plan--allowing manufacturers to choose according to spectrum requirements QPSK Bit Rate (Mbits/s) 32 40 44.8 16-QAM Bit Rate (Mbits/s) 64 80 89.6 64-QAM Bit Rate (Mbits/s) 96 120 134.4 Channel Width (MHz) 20 25 28

30. Adaptive Burst profile • Burst profile • Modulation • Reed Solomon FEC(forward error correction) • to recover error frame lost due to frequency selective fading or burst error • Automatic repeat request (ARQ) is used to correct errors that can not be corrected by FEC • Dynamically assigned according to link conditions • Burst by burst, per subscriber station • Trade-off capacity vs robustness in real time • Roughly double capacity for the same cell area • Burst profile for downlink channel is well known and robust • Up to 12 burst profiles can be defined • The parameters of each are communicated to the SSs via MAC messages during the frame control section of the downlink frame

31. Duplex scheme • The downlink channel is time division multiplex(TDM) • Information for each SS multiplexed onto a single stream of data and received by all SSs within the same sector • The uplink is time division multiple access(TDMA) • Channel is divided into a number of time slots which are assigned various uses(registration, user traffic) • Frequency division duplex(FDD) • DL and UL on the separate RF channel • Support half-duplex SSs (SS does not transmit/receive simultaneously) • Time division duplex(TDD) • DL and UL time-shared the same RF channel • SS does not transmit/receive simultaneously

32. TDD Frame(10-66GHz) Frame duration: .5ms, 1ms, 2ms Physical slot(PS) = 4 QAM symbols(1QAM symbol = 4bits)

33. TDD downlink subframe • DIUC: Downlink interval usage code • Tr/Rx: gap between the downlink burst and subsequent uplink bust • Allows time for the BS to switch from transmit to receive mode and SSs to switch from receive to transmit mode

34. FDD framing Example of FDD bandwidth allocation

35. FDD downlink subframe TDMA portion: transmit data to some half-duplex SSs(the ones scheduled to transmit earlier in the frame than they receive) -Need preamble to re-sync(carrier phase)

36. Uplink subframe

37. Uplink subframe descriptions • Initial maintenance opportunities • Ranging • To determine network delay or to request power or profile change • Collisions may occur in this interval • Request contention opps • SSs request bandwith in response to polling from BS. • Collisions may occur in this interval • Schedule data • SSs transmit data bursts in the intervals granted by the BS • Transition gaps between data intervals for synchronization purposes.

38. MAC Layer • Designed for Point-to-multipoint broadband wireless access apps • Support difficult user environments • High bandwidth, hundreds of user per channel • Continuous and burst traffic • Very efficient use of spectrum • Protocol independent core • ATM, IP, Ethernet,… • Flexible QoS offerings • Best Effort(BF), rt-VBR,nrt-VBR, ATM CBR • Security • Support PHY alternatives • Adaptive mod, TDD/FDD, single-carrier, OFDM/OFDMA

39. Service-specific convergence sublayers • ATM convergent sublayer defined for ATM services • Packet convergent sublayer • Defined for mapping services such as IPv4, IPv6, Ethernet • Preserve or enable QoS • Enable bandwidth allocation • Classify service data units(SDUs) to the proper MAC connection

40. MAC addressing • SS has 48bits IEEE MAC address • Use mainly as equipment id • 16-bit Connection ID(CID) • Used in MAC PDUs

41. MAC PDU format • The Generic MAC header has fixed format • One or more MAC sub-headers may be part of the payload • The presence of sub-headers is indicated by a Type field in the Generic MAC header

42. Generic MAC header LEN: PDU length in bytes(2048 max) HT: header Type Type: subheader, … CID: Connection ID EC: Encryption Control HCS: Header Check EKS: Encryption Key Sequence CI: CRC indicator Sequence

43. MAC PDU Transmission • MAC PDUs are transmitted in PHY burst • A single burst can contain multiple Concatenated MAC PDUs • The PHY burst can contain multiple FEC blocks • MAC PDUs may span FEC block boundaries • The TC(Transmission convergence) layer between the MAC and PHY allows for capturing the start of the next MAC PDU in case of erroneous FEC blocks

44. Downlink Transmissions • Two kinds of bursts: TDM and TDMA • TDMA bursts have resync preamble • Each terminal listens to all bursts at its operational IUC or a more robust one • Each burst may contain data for several terminals • SS must recognize the PDUs with known CIDs • DL-MAP message signals downlink usage

45. Burst profiles • Each burst profile has mandatory exit threshold and minimum entry threshold • SS allowed to request a less robust DIUC once above the minimum entry level • SS must request fall back to more robust DIUC once at mandatory exit threshold • Requests to change DIUC done with Downlink burst profile change REQ(DBPC-REQ) or RNG-REG messages

46. Transition to more robust burst profile

47. Transition to less robust burst profile

48. Uplink Transmissions • Transmissions in contention slots • Bandwidth requests • Contention resolved using truncated exponential backoff • Transmissions in initial ranging slots • Ranging requests(RNG-REQ) • Contention resolved using truncated exponential backoff • Bursts defined by UIUCs • Transmissions allocated by the UL-MAP message • All transmissions have synchronization preamble

49. Uplink Services • Unsolicited Grant Services (UGS) • Used for constant-bit-rate (CBR) service flows (SFs) • Best Effort (BE) • For best-effort traffic • Real time Polling Services (rtPS) • For rt-VBR SFs such as MEPEG video • None Real time Polling Services (nrtPS) • For nrt SFs with better than BE service such as bandwidth-intensive file transfer

50. Request/Grant scheme • Bandwidth Requests are always per Connection • Self Correcting • No acknowledgement • Grants are either per Connection (GPC) or per SS (GPSS) • Grants (given as durations) are carried in the UL-MAP messages • SS needs to convert the time(durations) to amount of data using information about the UIUC • Bandwidth Grant per Subscriber Station (GPSS) • BS grants bandwidth to the SS • SS may re-distribute bandwidth among its connections • Suitable for many connections per terminal • Low overhead but requires intelligent SS • Bandwidth Grant per Connection (GPC) • BS grants bandwidth to a connection • Mostly suitable for few users per SS • High overhead, but allows simpler SS