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WiMAX for Broadband Wireless Access

WiMAX for Broadband Wireless Access. By: Karim M. El Defrawy ICS UCI-2005. Outline. What is WiMAX 802.16 Introduction 802.16 MAC Highlights 802.16 Reference Model MAC Convergence Sub-Layer (CS) MAC Common Part Sub-Layer (CPS) MAC Privacy Sub-Layer (PS) Questions. What is WiMAX?.

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WiMAX for Broadband Wireless Access

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  1. WiMAX for Broadband Wireless Access By: Karim M. El Defrawy ICS UCI-2005

  2. Outline • What is WiMAX • 802.16 Introduction • 802.16 MAC Highlights • 802.16 Reference Model • MAC Convergence Sub-Layer (CS) • MAC Common Part Sub-Layer (CPS) • MAC Privacy Sub-Layer (PS) • Questions

  3. What is WiMAX? • Worldwide Interoperability for Microwave Access (WiMAX) is the common name associated to the IEEE 802.16a/REVd/e standards. • These standards are issued by the IEEE 802.16 subgroup that originally covered the Wireless Local Loop technologies with radio spectrum from 10 to 66 GHz.

  4. IEEE 802.16 -- Introduction • IEEE 802.16 (2001) • Air Interface for Fixed Broadband Wireless Access System MAC and PHY Specifications for 10 – 66 GHZ (LoS) • One PHY: Single Carrier • Connection-oriented, TDM/TDMA MAC, QoS, Privacy • IEEE 802.16a (January 2003) • Amendment to 802.16, MAC Modifications and Additional PHY Specifications for 2 – 11 GHz (NLoS) • Three PHYs: OFDM, OFDMA, Single Carrier • Additional MAC functions: OFDM and OFDMA PHY support, Mesh topology support, ARQ • IEEE 802.16d (July 2004) • Combines both IEEE 802.16 and 802.16a • Some modifications to the MAC and PHY • IEEE 802.16e (2005?) • Amendment to 802.16-2004 • MAC Modifications for limited mobility

  5. IEEE 802.16 -- Introduction Coverage range up to 50km and speeds up to 70Mbps(shared among users).

  6. IEEE 802.16 -- Introduction Source: WiMAX, making ubiquitous high-speed data services a reality, White Paper, Alcatel.

  7. IEEE 802.16 MAC -- Highlights • WirelessMAN: Point-to-Multipoint and optional mesh topology • Connection-oriented • Multiple Access: DL TDM & TDMA, UL TDMA;UL OFDMA & TDMA, DL OFDMA & TDMA (Optional) • PHY considerations that affect the MAC • Duplex: TDD, FDD, FDX FDD BS and SS, HDX FDD SS • Adaptive burst profiles (Modulation and FEC) on both DL and UL • Protocol-independent core (ATM, IP, Ethernet) • Flexible QoS offering (CBR, rt-VBR, nrt-VBR, BE) • Strong security support

  8. Reference Model

  9. Adaptive PHY Source: Understanding WiMAX and 3G for Portable/Mobile Broadband Wireless, Technical White Paper, Intel.

  10. Adaptive Burst Profiles • Burst profile: Modulation and FEC • On DL, multiple SSs can associate the same DL burst • On UL, SS transmits in an given time slot with a specific burst • Dynamically assigned according to link conditions • Burst by burst • Trade-off capacity vs. robustness in real time

  11. Duplex Scheme Support • The duplex scheme is Usually specified by regulatory bodies, e.g., FCC • Time-Division Duplex (TDD) • Downlink & Uplink time share the same RF channel • Dynamic asymmetry • does not transmit & receive simultaneously (low cost) • Frequency-Division Duplex (FDD) • Downlink & Uplink on separate RF channels • Full Duplexing (FDX): can Tx and Rx simultaneously; • Half-duplexing (HDX) SSs supported (low cost)

  12. IEEE 802.16 MAC – OFDM PHY TDDFrame Structure

  13. IEEE 802.16 MAC – OFDM PHY FDDFrame Structure

  14. FDD MAPs Time Relevance DL MAP UL MAP DL MAP UL MAP DOWNLINK UPLINK frame Broadcast Half Duplex T erminal #1 Full Duplex Capable User Half Duplex T erminal #2

  15. IEEE 802.16 MAC addressing and Identifiers • SS has 48-bit IEEE MAC address • BS has 48-bit base station ID • Not a MAC address • 24-bit operator indicator • 16-bit connection ID (CID) • 32-bit service flow ID (SFID) • 16-bit security association ID (SAID)

  16. IEEE 802.16 MAC – Convergence Sub-Layer (CS) • ATM Convergence Sub-Layer: • Support for VP/VC switched connections • Support for end-to-end signaling of dynamically created connections • ATM header suppression • Full QoS support • Packet Convergence Sub-Layer: • Initial support for Ethernet, VLAN, IPv4, and IPv6 • Payload header suppression • Full QoS support

  17. IEEE 802.16 MAC -- CS– Packet Convergence Sub-Layer • Functions: • Classification: mapping the higher layer PDUs (Protocol Data Units) into appropriate MAC connections • Payload header suppression (optional) • MAC SDU (Service Data Unit), i.e, CS PDU, formatting

  18. IEEE 802.16 MAC -- CPS– MAC PDU Format

  19. IEEE 802.16 MAC -- CPS-- Three Types of MAC PDUs • Data MAC PDUs • HT = 0 • Payloads are MAC SDUs/segments, i.e., data from upper layer (CS PDUs) • Transmitted on data connections • Management MAC PDUs • HT =0 • Payloads are MAC management messages or IP packets encapsulated in MAC CS PDUs • Transmitted on management connections • BW Req. MAC PDUs • HT =1; and no payload, i.e., just a Header

  20. IEEE 802.16 MAC -- CPS– Data Packet Encapsulations

  21. IEEE 802.16 MAC – CPS-- MAC Management Connections • Each SS has 3 management connections in each direction: • Basic Connection: • short and time-urgent MAC management messages • MAC mgmt messages as MAC PDU payloads • Primary Management connection: • longer and more delay tolerant MAC mgmt messages • MAC mgmt messages as MAC PDU payloads • Secondary Management Connection: • Standard based mgmt messages, e.g., DHCP, SNMP, …etc • IP packets based CS PDU as MAC PDU payload

  22. IEEE 802.16 MAC – CPS – MAC Management Messages • MAC mgmt message format: • MAC mgmt msg can be sent on: Basic connections; Primary mgmt connection; Broadcast connection; and initial ranging connections • 41 MAC mgmt msgs specified in 802.16 • The TLV (type/length/value) encoding scheme is used in MAC mgmt msg, e.g., in UCD msg for UL burst profiles, • (type=1, length=1, value=1)  QPSK modulation • (type=1, length=1, value=2)  16QAM modulation • (type=1, length=1, value=3)  64QAM modulation

  23. IEEE 802.16 MAC – CPS – MAC PDU Transmission • MAC PDUs are transmitted in PHY Bursts • The PHY burst can contain multiple FEC blocks • MAC PDUs may span FEC block boundaries • Concatenation • Packing • Segmentation • Sub-headers

  24. IEEE 802.16 MAC – CPS – MAC PDU Concatenation

  25. IEEE 802.16 MAC – CPS – MAC PDU Fragmentation

  26. IEEE 802.16 MAC – CPS – MAC PDU Packing

  27. IEEE 802.16 MAC – CPS QoS • Three components of 802.16 QoS • Service flow QoS scheduling • Dynamic service establishment • Two-phase activation model (admit first, then activate) • Service Flow • A unidirectional MAC-layer transport service characterized by a set of QoS parameters, e.g., latency, jitter, and throughput assurances • Identified by a 32-bit SFID (Service Flow ID) • Three types of service flows • Provisioned: controlled by network management system • Admitted: the required resources reserved by BS, but not active • Active: the required resources committed by the BS

  28. IEEE 802.16 MAC – CPS – Uplink Service Classes • UGS: Unsolicited Grant Services • rtPS: Real-time Polling Services • nrtPS: Non-real-time Polling Services • BE: Best Effort

  29. IEEE 802.16 MAC – CPS – Uplink Services: UGS • UGS: Unsolicited Grant Services • For CBR or CBR-like services, e.g., T1/E1. • The BS scheduler offers fixed size UL BW grants on a real-time periodic basis. • The SS does not need to send any explicit UL BW req.

  30. IEEE 802.16 MAC – CPS – Uplink Services: rtPS • rtPS: Real-time Polling Services • For rt-VBR-like services, e.g., MPEG video. • The BS scheduler offers real-time, periodic, UL BW request opportunities. • The SS uses the offered UL BW req. opportunity to specify the desired UL BW grant. • The SS cannot use contention-based BW req.

  31. IEEE 802.16 MAC – CPS – Uplink Services: nrtPS • nrtPS: non-real-time polling services • For nrt-VBR-like services, such as, bandwidth-intensive file transfer. • The BS scheduler shall provide timely (on a order of a second or less) UL BW request opportunities. • The SS can use contention-based BW req. opportunities to send BW req.

  32. IEEE 802.16 MAC – CPS – Uplink Services: BE • BE: Best Effort • For best-effort traffic, e.g., HTTP, SMTP. • The SS uses the contention-based BW request opportunities.

  33. IEEE 802.16 MAC – CPS – Bandwidth Grant • BW grants are per Subscriber Station: • Allows real-time reaction to QoS need, i.e., SS may re-distribute bandwidth among its connections, maintaining QoS and service-level agreements • Lower overhead, i.e., less UL-MAP entries compare to grant per connection • Off- loading base station’s work • Requires intelligent subscriber station to redistribute the allocated BW among connections

  34. IEEE 802.16 MAC – CPS – BW Request/Grant Mechanisms • Implicit requests (UGS): No actual requests • BW request messages, i.e., BW req. header • Sends in either a contention-based BW req. slot or a regular UL allocation for the SS;he special B • Requests up to 32 KB with a single message Request • Incremental or aggregate, as indicated by MAC header– • Piggybacked request (for non-UGS services only) • Presented in Grant Management (GM) sub-header in a data MAC PDU of the same UL connection • is always incremental • Up to 32 KB per request for the CID • Poll-Me bit • Presented in the GM sub-header on a UGS connection • request a bandwidth req. opportunity for non-UGS services

  35. IEEE 802.16 MAC – CPS -- Contention UL Access • Two types of Contention based UL slots • Initial Ranging • Used for new SS to join the system • Requires a long preamble • BW Request • Used for sending BW req • Short preamble • Collision Detection and Resolution • Detection: SS does not get the expected response in a given time • Resolution: a truncated binary exponential backoff window

  36. IEEE 802.16 MAC – CPS UL Sub-Frame Structure Source: http://www.cygnuscom.com/pdf/WP_PN_Article.pdf

  37. IEEE 802.16 MAC – CPS – Ranging • Ranging is a process of acquiring the correct timing offset, and PHY parameters, such as, Tx power level, frequency offset, etc. so that the SS can communicate with the BS correctly. • BS performs measurements and feedback. • SS performs necessary adjustments. • Two types of Ranging: • Initial ranging: for a new SS to join the system • Periodic ranging (also called maintenance ranging): dynamically maintain a good RF link.

  38. IEEE 802.16 MAC – CPS – Automatic Repeat reQuest (ARQ) • A Layer-2 sliding-window based flow control mechanism. • Per connection basis. • Only effective to non-real-time applications. • Uses a 11-bit sequence number field. • Uses CRC-32 checksum of MAC PDU to check data errors. • Maintain the same fragmentation structure for Retransmission. • Optional.

  39. IEEE 802.16 MAC – Privacy Sub-layer (PS) • Two Major Functions: • Secures over-the-air transmissions • Protects from theft of service • Two component protocols: • Data encryption protocol • A client/server model based Key management protocol (Privacy Key Management, or PKM)

  40. IEEE 802.16 MAC – PS -- Security Associations • A set of privacy information, e.g., encryption keys, used encryption algorithm • Three types of Security Associations (SAs) • Primary SA: established during initial registration • Static SA: provisioned within the BS • Dynamic SA: dynamically created on the fly • Identified by a 16-bit SAID • Connections are mapped to SAs

  41. IEEE 802.16 MAC – PS -- Multi-level Keys and Their Usage • Public Key • Contained in X.509 digital certificate • Issued by SS manufacturers • Used to encrypt AK • Authorization Key (AK) • Provided by BS to SS at authorization • Used to derive KEK • Key Encryption Key (KEK) • Derived from AK • Used to encrypt TEK • Traffic Encryption Key (TEK) • Provided by BS to SS at key exchange • Used to encrypt traffic data payload

  42. IEEE 802.16 MAC – PS -- Data Encryption • Use DES (Data Encryption Standard) in CBC (Cipher Block Chaining) mode with IV (Initialization Vector). • CBC IV is calculated from • IV parameter in TEK keying info; and • PHY synchronization field in DL-MAP. • Only MAC PDU payload (including sub-headers) is encrypted. • MAC PDU headers are unencrypted. • Management messages are unencrypted.

  43. IEEE 802.16 MAC – one big item is out of scope Scheduler

  44. Questions ??

  45. References • IEEE802.16-2004 • Alcatel White Paper: WiMAX, making ubiquitous high-speed data services a reality • Intel White Paper: Understanding WiMAX and 3G for Portable/Mobile Broadband Wireless • WiMAX Forum: www.wimaxforum.com • http://en.wikipedia.org/wiki/WiMax

  46. IEEE 802.16 MAC – commonly used terms • BS – Base Station • SS – Subscriber Station, (i.e., CPE) • DL – Downlink, i.e. from BS to SS • UL – Uplink, i.e. from SS to BS • FDD – Frequency Division Duplex • TDD – Time Division Duplex • TDMA – Time Division Multiple Access • TDM – Time Division Multiplexing • OFDM – Orthogonal Frequency Division Multiplexing • OFDMA - Orthogonal Frequency Division Multiple Access • QoS – Quality of Service

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