From IEEE Communications Magazine, June 2002 Presented by Hermes Liu

From IEEE Communications Magazine, June 2002 Presented by Hermes Liu
IEEE Standard : A Technical Overview of the WirelessMAN Air Interface for Broadband Wireless Access From IEEE Communications Magazine, June 2002 Presented by Hermes Liu

Authors Carl Eklund, Nokia Research Center Roger B. Marks,
National Institute of Standards and Technology Kenneth L. Stanwood and Stanley Wang, Ensemble Communications Inc. 2018/11/8

Agenda -Introduction -Technology Design -Physical Layer Details
-Medium Access Control Details -Conclusion 2018/11/8

Introduction IEEE 802.16: Wireless MAN
-Provides network access to buildings through exterior antennas and substitute the cabled access network (fiber optic, cable modem, DSL etc.) -Wireless systems have the capacity to address broad geographic areas without the costly cable links. -User inside the building connect to it with Ethernet( 802.3) or Wireless LANs (802.11). -May eventually allow the Wireless MAN networking protocols directly to the individual user by exchange medium access control (MAC) protocol data with each other. 2018/11/8

2018/11/8

Introduction 802.16: 10~66 GHz -Short wavelengths introduce deployment problems. (line-of-sight) -A set of air interfaces based on a common MAC protocol but with PHY spec. dependent on the spectrum 802.16a: 2~11 GHz (licensed and license-exempt) -Reach more customers less expensively but lower data rates. Working Group: -Development of IEEE -Included WirelessMAN air interface -Associates standards and amendments 2018/11/8

Introduction 2018/11/8

Technology Design Medium Access Control
-Point-to-multipoint broadband wireless access -Very high bit rates both uplink and downlink -Hundreds of terminals per channel -Terminals be shared by multiple end users Services: -Legacy time-division multiplex (TDM) data -Internet Protocol (IP) connectivity -Packetized voice over IP (VoIP) -Accommodate both continuous and bursty traffic -Also provide QoS analogous to asynchronous transfer mode (ATM) as well as guaranteed frame rate (GFR) 2018/11/8

-Support backhaul requirements both ATM and packet-based protocol (like TCP) -”Convergence sublayers” are used to map the transport-layer-specific traffic to a MAC, which make the traffic more efficient and flexible -Transport efficiency are addressed at the interface between MAC and PHY, ex: the Modulation and coding schemes (MCS) adjustment -The “request-grant” mechanism is designed to be scalable, efficient, and self-correcting (self-correcting protocol) 2018/11/8

MAC just provide Bandwidth Allocation and QoS Mechanisms, left the scheduling and reservation management unstandardized so that the vendors can differentiate their equipment -Has sublayer which provides authentication, key exchange and encryption a upgrades the MAC to provide automatic repeat request (ARQ) and support for mesh network architecture ※Note: Transport efficiency, Request-grant, Bandwidth allocate, QoS, Authentication, Key exchange, Encryption, Error correct all in MAC 2018/11/8

Technology Design The Physical Layer (10-66 GHz)
-Line-of-sight propagation (short wavelength) -Single-carrier modulation (Wireless MAN SC) -Multiplexing: time-division multiplexing (TDM) -Access: time-division multiple access (TDMA) Duplexing: both TDD and FDD -TDD: UL & DL share a channel but not transmit simultaneously -FDD: UL & DL on separate channels, sometimes simultaneously -Both TDD & FDD support adaptive burst profiles in which MCS can be assigned burst-by-burst 2018/11/8

Technology Design The Physical Layer (2-11 GHz) in 2002
-Non-line-of-sight, multi-path propagation Three air interface specification in draft: -WirelessMAN-SC2: single-carrier modulation -WirelessMAN-OFDM: Orthogonal Frequency Division Multiplexing with 256-point transform, access by TDMA, only for license-exempt bands -WirelessMAN-OFDMA: 2048-point transform, multiple access is provided by addressing a subset of the multiple carriers to individual receivers ※WirelessMAN-OFDM becomes the standard of a 2018/11/8

Physical Layer Details
-The transmission parameters (modulation and coding schemes MCS) from a Base Station (BS) may be adjusted individually to each Subscriber Station (SS) on a frame-by-frame basis -Forward Error Correction (FEC): Reed-Solomon GF (256) with variable block size and error correction capabilities Modulation Technique: -Quadrature Phase Shift Key (QPSK) -16-state Quadrature Amplitude Modulation (16-QAM) -64-state QAM (64-QAM) 2018/11/8

-The frame (0.5, 1, or 2 ms) is divided into physical slots for bandwidth allocation and identification of PHY transitions -TDD: UL subframe follows DL subframe on the same carrier frequency -FDD: UL & DL subframes are in time but on separate frequency. 2018/11/8

the downlink subframe starts with a frame control sectoin that contains the DL-MAP and UL-MAP DL-MAP: for the current downlink frame UL-MAP: for a specified time in the future DL-MAP specifies when physical layer transitions occur within the downlink subframe The recipient SS is indicated in the MAC headers rather than in the DL-MAP So SSs listen to all portions of the downlink subframe they can receive. frame control section Figure 1. The downlink subframe structure DIUC: Downlink Interval Usage Code 2018/11/8

Figure 2. The uplink subframe structure UIUC: specified burst profile 2018/11/8

Figure 3. TC PDU format. Transmission Convergence (TC) Sublayer: -performs the transformation of variable length MAC protocol data unit (PDUs) into fixed length FEC blocks (padding) -Allows resynchronization in case the previous FEC block had irrecoverable errors 把不同長度的PDC 放在固定長度的FEC block裡 2018/11/8

Medium Access Control Details
Service-Specific Convergence Sublayers Interface to higher layers Common Part Sublayer: Carries out the key MAC functions Privacy Sublayer: Privacy protocol and security 2018/11/8

Service-Specific Convergence Sublayers: -Classify service data units (SDUs) to the proper MAC connection ex. Legacy TDM, IP, VoIP, ATM with GFR -Preserve or enable QoS -Enable bandwidth allocation -Payload header suppression and reconstruction -ATM Con. Sublayer: for ATM services -Packet Con. Sublayer: packet services (IPv4, IPv6, Ethernet, VLAN) 2018/11/8

Common Part Sublayer: General Architecture 802.16: point to multipoint -DL: TDM -UL:TDMA -Connection-oriented: all services are mapped to a connection -Requesting bandwidth -QOS -Traffic parameters -Transporting & routing data -Connections are referenced with 16-bit Connection identifiers (CID) 2018/11/8

Common Part Sublayer: Three QoS levels to SS -Basic connection: short, time critical MAC and radio link control (RLC) message -Primary management connection: longer, delay-tolerant message (ex. authentication, connection setup) -Secondary message connection: standards-based management message (ex. DHCP, TFTP, SNMP) Transport connection (for contracted services) -Unidirectional, UL and DL QoS and traffic parameters, assigned to services in pairs. Reserved connections -Connection-based initial access, broadcast, multicast 2018/11/8

MAC PDU Formats -Data unit exchanged between the MAC layers of the BS and its SS. Two format: -Generic Header, -Bandwidth Request Header (no payload) -Fixed length MAC header -Variable length payload -Cyclic redundancy check (CRC) , optional 2018/11/8

(Generic header) 2018/11/8

MAC PDU Formats Three types of MAC subheader -Grant management subheader: SS use it to request bandwidth to BS -Fragmentation subheader Fragmentation is a MAC SDU is divided into one or more MAC SDU segment Indicates the presence and orientation in the payload of any fragments of SDUs -Packing subheader Packing is multiple MAC SDUs are packed into a single MAC PDU payload Indicate the packing of multiple SDUs into a single SDU 2018/11/8

PHY support -The MAC builds the DL subframe starting with a frame control section containing the DL-MAP (PHY transitions) and UP-MAP (bandwidth allocations and burst profiles) messages. 2018/11/8

Radio Link Control (RLC) -Burst profiles for the DL are tagged with Downlink Interval Usage Code (DIUC), for the UL are tagged with UIUC. -Ranging request (RNG-REQ): power leveling and ranging -Ranging response (RNG-RSP): power and ranging adjustment -RLC monitor and control the burst profiles. RLC can adapt the SS’s current UL and DL burst profiles to a balance between robustness and efficiency (ex. rain fades or good weather) RNG-REQ SS BS 2018/11/8 RNG-RSP

DBPC: DL burst profile change 2018/11/8

2018/11/8

Uplink scheduling services -Each connection in the uplink direction is mapped to a scheduling service. Unsolicited Polling Service (UGS): -Need constant bandwidth allocation Real-time polling service: -suited for VoIP, streaming video or audio Non-real-time polling service: -tolerate longer delays and are rather insensitive to delay jitter. Suited for Internet access with minimum guaranteed rate and for ATM GFR connections Best effort service: -Neither throughput nor delay guarantees are provided 2018/11/8

Bandwidth Request and Grants Grant per connection (GPC): -bandwidth is granted explicitly to a connection, and SS uses the grant only for that connection. RLC and other management protocols use bandwidth allocated to the management connections. Grant per SS (GPSS): -SSs are granted bandwidth aggregated into a single grant to the SS itself. Is the only class of SS allowed with the GHz PHY. Request by DBPC-REQ -The two class of SS allow a trade-off between simplicity (GPC) and efficiency (GPSS) 2018/11/8

Bandwidth Request and Grants Reasons for failure bandwidth request- -The BS/ SS did not see the request due to irrecoverable PHY errors or collision of a contention-based reservation -The BS did not have sufficient bandwidth available -The GPSS SS used the bandwidth for another purpose -In self-correcting protocol, these are treated the same. After a timeout appropriate for the QoS of the connection, the SS simply requests again. -Less bandwidth, less delay than acknowledge protocol 2018/11/8

Bandwidth Request and Grants Ways to request bandwidth- -Use “Poll-me bit” in grant management subheader when have unsolicited grant service (UGS) -”Piggyback” a request for additional bandwidth in grant management subheader within a MAC PDU for the same connection (GPC) -Use Bandwidth Request Header in MAC PDU with no payload (GPSS) -In addition to polling individual SSs, the BS may issue a broadcast poll by allocating a request interval to the broadcast CID 2018/11/8

Channel Acquisition -The MAC protocol includes initialization procedure, need no manual configuration. An SS begins scanning frequency to find an operating channel. -After decide which channel, the SS tries to synchronize to the downlink transmission by detecting the periodic frame preambles. -After the PHY is synchronized, the SS can learn the modulation and FEC (Forward Error Correction) schemes (MCS) used on the carrier. 2018/11/8

Initial Ranging and Negotiation of SS Capabilities -The SS uses a “truncated exponential backoff algorithm” to determine which initial ranging slot it will use to send a ranging request message. -The SS will send the burst using the minimum power setting and will try again with higher power if it does not receive a ranging response. -The BS commands a timing advance and a power adjustment to the SS in the ranging response. -The response also provides the SS with the” basic” and “primary management” CIDs 2018/11/8

SS Authentication and Registration -manufacturer-issued factory-installed X.509 digital certificate -Certificate of the manufacturer These two establish a link between the 48-bit MAC address of the SS and its public RSA key, are sent to the BS in the Authorization Request and Authentication Information message The BS will respond to its request with an Authorization Reply containing an Authorization Key (AK) encrypted with the SS’s public key After that, the SS will register with the network, and establish the “secondary management connection”, determine capabilities, and which version of IP will be used. 2018/11/8

IP Connectivity Get an IP address via DHCP Connection Setup Use service flows with two-phase activation, setup by the BS, and can be dynamically established by SS. Privacy Sublayer The privacy protocol is based on the Privacy Key Management (PKM) protocol and provide stronger cryptographic methods such as Advanced Encryption Standard (AES) 2018/11/8

Security Associations -SA is a set of cryptographic methods and the associated keying material, contains the information about which algorithms to apply, which key to use. Every SS establishes at least one SA during initialization. Each connection is mapped to an SA. Cryptographic Methods Authentication & Authorization for SS Traffic encryption Exchange of transmission encryption keys PKM protocol uses X.509 with RSA public key Data encryption Standard (DES) in the cipher block chaining (CBC) with 56-bit keys 3DES 2018/11/8

Conclusion -IEEE provides a platform for the development and deployment of metropolitan area networks broadband wireless access. -Allow for multiple vendors to produce interoperable equipment, meanwhile differentiation as well. -The efficiency of a transition will be optimized by adaptive burst profile feature and scheduling algorithm, and schemes…etc. -Power consumption concern, may apply optimization of ranging mechanism -The IEEE wirelessMAN becomes a major alternative for broadband access. 2018/11/8

The End Thanks for your patience!!

From IEEE Communications Magazine, June 2002 Presented by Hermes Liu

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From IEEE Communications Magazine, June 2002 Presented by Hermes Liu

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