IEEE 802.20 – Mobile Broadband Wireless Access

University of Kansas | School of Engineering

Department of Electrical Engineering and Computer Science

Ramya Naidu M April 29, 2008 1

IEEE 802.20 – Mobile Broadband Wireless Access




Abstract

Mobile Broadband Wireless Access (802.20) is a IEEE standard formed to develop a cellular standard that focuses on vehicular mobility in a metropolitan area environment. It falls under the WWAN category. It is a packet switched technology, designed to operate in frequencies below 3.5 GHz and optimized to carry IP traffic for mobile users traveling with speeds up to 250 km/h.

Standard includes Physical and MAC layer specifications and is compatible to 802 Architecture and Functional requirements




IEEE 802.20 – Outline• Motivation for new Standard

• Services and Applications

• Physical Layer

• MAC Layer

• Handoff procedures

• Comparison between 802.20 and 802.16e

• Conclusion




Motivation for new Standard – IEEE 802.20• Wi-Max was designed to provide broadband wireless access and aims at maximizing throughput rather than mobility

• 802.20 is the first standard that takes into consideration mobility classes, with speeds up to 250 km/h

• Extends broadband wireless access to mobile users

• Approved Dec 11th 2002, Nicknamed as Mobile-Fi

• Optimized for high speed IP based wireless data service

• The standard forms the basis of seamless integration of – work, home and mobile




IEEE 802.20 : Services

Vision of a seamless integration of three user domains: work, home and mobile.

WorkDomain

HomeDomain

SeamlessSeamlessUbiquitousUbiquitousExperienceExperience

MobileDomain

Portable Remote Access Services

Field Service Apps

Hotel/Motel

Portable ServicesMobile Commerce

Services

Mobile Office (Voice and Data Apps)

High BW Connectivity

Video Streaming -Conferencing Apps

PortableOffice

Reservations-Listings Directions Services Video Streaming -

Conferencing Apps

Video Streaming -Conferencing Apps

Mobile BroadbandWireless Access

From “IEEE 802.20 System Requirement V1.0”, P802.20-PD-06r1, [1]




IEEE 802.20 – Mission and Scope of Project • The goal is to enable worldwide deployment of affordable, always-on, ubiquitous mobile broadband wireless access networks. To ensure co-existence and compatibility.Scope :• To develop specification of Physical and MAC layers of the air interface

• Operating in licensed bands below 3.5 GHz

• Optimized for IP-data transport

• Offers Peak data rates per user in excess of 1Mbps

• Support vehicular mobility of 250 Km/h in a MAN environment

From ”Mission and Scope”, http://ieee802.org/20/index.html




IEEE 802.20 : Services• Supports video, full graphic web browsing, e-mail, file transfer, streaming video and audio. • IP Multicast• Location-Based-Servers.• VPN connections• VoIP• On-line multiplayer gaming• Broadcast and Multicast support

• Needs a PC card interface with devices.





Example - Railway Application• 802.20 based Broadband Railroad Digital Network – BRDN

• Meet the ever-increasing demand for M-commerce and Wi-Fi enabled trains• 802.20 was selected since it supports high speeds

From “IEEE 802.20 Based Broadband Railroad Digital Network - The Infrastructure for M-Commerce on the Train ”, [10]




802.20 FeaturesCharacteristic Target Value

Mobility Vehicular mobility classes up to 250 km/hr (as defined in ITU-R M.1034-1)

Sustained spectral efficiency > 1 b/s/Hz/cell

Peak user data rate (Downlink (DL)) > 1 Mbps*

Peak user data rate (Uplink (UL)) > 300 kbps*

Peak aggregate data rate per cell (DL) > 4 Mbps*

Peak aggregate data rate per cell (UL) > 800 kbps*

Airlink MAC frame RTT < 10 ms

Bandwidth e.g., 1.25 MHz, 5 MHz

Spectrum (Maximum operating frequency) < 3.5 GHz

Spectrum (Frequency Arrangements) Supports FDD (Frequency Division Duplexing) and TDD (Time Division Duplexing) frequency arrangements

Spectrum Allocations Licensed spectrum allocated to the mobile service





IEEE 802.20: Network Architecture

• Access Network: Collection of Access Nodes or Access Points.

AT can be in communication with more that one Access Node

Each AN-AT pairing has its own protocol stack - ROUTE

• Serving Access Node: Access Point housing serving sector.

• Contains sector that provides air-interface attachment for the AT

Routes can be tunneled between ANs without the serving AN needing to read the or manage the packet exchanged

Changes based on radio conditions

• Anchor Access Node: Access Point that provides internet connectivity.

• May change to minimize the number of hops a packet has to traverse to reach the AT

From “UMBFDD Draft Technology Overview”, IEEE C802.20-07/09, [2]




Protocol Layering – 802.20

From “FDD Technology overview presentation”, IEEE C802.20-05-59r1, [5]

• Application Sublayer

• Radio Link Sublayer

• Lower MAC Layer

• Physical Layer




Physical Layer• System is deployable in 1.25 - 20 MHz flexible bandwidths

•Targets cell radius of 15km

• Bandwidths supports Frequency and Time Division Duplexing

• Reverse links support both CDMA and OFDMA• CDMA is used for low rate data transmissions• Also supports the option of fast frequency hopping spread spectrum technology – Flash-OFDM

• Forward links support OFDMA

• The system uses Adaptive Coding and Modulation • Supports QPSK, 16 QAM, 8-PSK and 64 QAM

• Support Hybrid ARQ

• Frequency reuse - Fractional Frequency Reuse FFR

From “Draft Standard for Local and Metropolitan Area Networks – Standard Air Interface for Mobile Broadband Wireless Access Systems Supporting Vehicular Mobility – Physical and Media Access Control Layer Specification”, IEEE 802.20/D3.0m, [4]




Fractional Frequency reuse FFR

Figure. Fractional Frequency ReuseF1, F2, and F3 are different sets of sub-channels, allocated to users at cell edges.F = F1+F2+F3. The whole sub-channels (F) are allocated to users at cell centers

From “Fraction Frequency Re-use”, www.conniq.com/WiMAX/images/fractional-frequency-reuse [3]




Physical Layer (Contd)

• Error Detection• CRC – 24 bits for Data Channels and 9 bits for dedicated control channels

• Forward Error Correction• turbo codes, convolutional codes and LDPC codes

• Standard defines Physical channels - Forward and Reverse Channels• Separate channels for Control and Traffic• Channels have unique modulation, encodings and purpose• CDMA and OFDM control channels are used• CDMA Control Channels are preferred for Fast Access and Fast request• CDMA control channels provides efficient handoff control• OFDMA Control Channels are used for highly periodic control transmissions – CQI





Physical Layer (contd)

• Forward Channels :


Forward Link Channels





• Reverse Link Channels






• Transmission in the FL and RL is divided into units of superframes • In FDD, each superframe consists of 25 PHY frames• In 1:1 TDD, 4 FL frames , 4 RL Frames are transmitted


FDD Super frame Structure

TDD Super frame Structure





• Power control• Fast closed loop power control

• Standard has mechanism for inactive mode and active mode

• Supports Multi-antenna capability in both Access Nodes and Mobile Terminals




Addressing • AT Addressing

• UATI: Universal Access Terminal Identifier 128 bits – temporary identity given by the system Not hardware derived, therefore not unique. Not used to resolve identity of AT Shortened – 32 bits used for paging.

• MACID11 bits longAT assigned one MACID per sector.Unique within the sectorUsed to exchange unicast packets with AT

• Does not require IP address assigned to the AT to operate• Does not use EUI-48 bits or 64 bits given to AT for during it manufacture.





MAC Layer• Some Protocols used

• Basic packet consolidation protocol Provides packet consolidation on the transmit side and de-multiplexing on receive

side Protocol maintains 2 token buckets for each stream

– They could be used for traffic policing and shaping– Or to hint the scheduler for transmission

Consolidated packet : consists of route packets from upper layers– Given the transmission rate, the length of packet should not increase the maximum payload

size. Along with packets received from upper layers, priority and transmission deadlines

could also be included


rnaidu




MAC Layer (contd)

• Basic Access Channel MAC protocol • Describes procedures for AT and AN to transmit and receive Access Probe• Access Probe used for initial access or handoff• AN responds to Access Probe with a Access Grant• Protocol defines Ns and Np.


Access Sequence




MAC Layer (contd)

• Basic Reverse Traffic Channel MAC Protocol• Assignments are specified by set of hop-ports and PHY frames • Hop-ports assigned for a given set of PHY frames for particular AT.• Sets of hop-ports are assigned in assignment blocks using channel tree• Transmission is multiplexed in time and frequency domain

•Basic Forward Traffic Channel MAC Protocol• Defines procedures required for an AN to transmit and AT to receive• Transmission is multiplexed in time and frequency domain• Uses MACID assigned to AT ( unique in sector )





Radio Link Protocol• Provides segmentation and reassembly• Ensures in order delivery of upper layer packets even during handoff• Increases link layer reliability through NACK transmission• QoS support – defines multiple flows


QoS Implementation




QoS (contd)

• RL and FL subband scheduling• Multi-user diversity gains through frequency sensitive scheduling

enables multi-user diversity gains for latency sensitive users• Design supports two hopping modes

diversity mode - global hopping across the band subband mode-localized hopping


Subband Scheduling




Handoff• Important feature of cellular mobility• Types of Handoffs

• Inter-sector • Inter-Access Node• Inter-carrier

• Desired Characteristics• Minimize MAC/Network layer signaling overhead• Minimize latency for handoff decisions

In Layer 1 and layer 2 handoff In Layer 3 handoff

• 802.20 proposes to use:• Mobile Controlled Handoff (MIP4) and Network Controlled Handoff• Layer 2 triggers (Low Latency MIPv4)• Make before break technique ( MIP4 MBB)

From “Mobile-Controlled Handoff for MBWA”, IEEE C802.20-03/17, [6]




Handoff (contd)

• Mobile controlled Handoff• Consider : Inter-Sector or Inter AN : Layer 2 Handoff• Uses 2 control channels - R-CQICH and R-REQCH • For FL handoff: AT monitors R-CQICH of all sectors in active set• For RL handoff: AT uses R-REQCH to indicate the desired RL sector• Handoff completes when AT receives assignment from new sector


Forward Link Handoff Reverse Link Handoff




Handoff (contd)• Layer 2 Triggers to Network Layer

• During Layer 3 Handoffs ( different IP subnet)• A significant percentage of handoffs between 802.20 Access Nodes is likely to cause a cause

layer 3 handoff due to high speed mobility in MA environment• IEEE 802.20, proposes to use layer 2 triggers along with Mobile IP to reduce the latency in Mobile

IP ( RFC 4881)

From “Support for Layer 2 Triggers for Faster Handoffs”, IEEE P802.20-03/95 [7]




Handoff (contd)

• Make-Before-Break • Mobile maintains PHY and MAC connectivity with more than one Access Node (BS)• Resources in new Access Node are allocated before releasing resources in the old

Access Node• This helps in reducing handoff latency • Improves performance – reducing packet loss

Inter-Base Tunnel

From “Handoff procedure for MBWA”, IEEE C802.20-03/85, [6]

Layer 3 Handoff




Difference Between 802.20 and 802.16e

From “MBWA and 802.16e: Two Markets –Two Projects”, [14] and “MBWA 802.20: A Comparison with Mobile WiMax“, http://ieee802.org/20/Contributions.html

Features 802.20 802.16e

Operating Spectrum 3.5 GHz 2 – 6 GHz

Typical Channel Bandwidth Between 1.25 MHz to 5 MHz Greater than 5Mhz

Speed Supports Vehicular mobility 250km/h Supports > 60 km/h

FL capacity 3 times more users than 802.16e

VoIP capacity Greater by 3 times than 802.16e

RL Spectral efficiencies Much better than 802.16e

Latency 802.20 has significantly lower than




Future

• 802.20 currently in final stages of standardization

• Kyocera announces - 802.20 will begin to appear in their iBurst base stations and terminals by the 4th quarter of 2009

“Kyocera enhances iBurst with Mobile Broadband Technology”, http://global.kyocera.com/prdct/telecom/office/iburst/news/080410.html




Conclusion

IEEE 802.20 specifies unique solution to PHY and MAC layer of the air interface operating in the licensed spectrum below 3.4 GHz. The standard provides support to vehicular mobility in metropolitan environment and covers wide area of up to 15 km. The standard uses combination of OFDMA, CDMA, Fast Frequency Hopping spread spectrum technologies, better cell architectures, advanced digital signal processing techniques like Adaptive Antennas and better handoff techniques to achieve its goal.




References[1] IEEE 802.20-PD-06r1, “IEEE 802.20 System Requirement Document (V 1.0)”[2] IEEE C802.20-07/09, “UMBFDD Draft Technology Overview” [3] “Fraction Frequency Re-use”, www.conniq.com/WiMAX/images/fractional-frequency-reuse,

retrieved April 26,2008[4] IEEE 802.20/D3.0m, “Draft Standard for Local and Metropolitan Area Networks – Standard Air

Interface for Mobile Broadband Wireless Access Systems Supporting Vehicular Mobility – Physical and Media Access Control Layer Specification”, November 2007

[5] IEEE C802.20-05-59r1, “FDD Technology overview presentation”[6] IEEE C802.20-03/84, “Handoff procedure for MBWA”[7] IEEE P802.20-03/95, “Support for Layer 2 Triggers for Faster Handoffs”[8] Lawton, George. "What Lies Ahead for Cellular Technology." IEEE Computer Journal 38(6)

(2005): 14-17[9] Kuran, Mehmet S, Tuna Tugcu, and "A Survey on Emerging Broadband Wireless Access

technologies." Science Direct Computer Networks 51(2007): 3013-3046[10] Zou, Fumin, Xinhua Jiang. "IEEE 802.20 Based Broadband Railroad Digital Network - The

Infrastructure for M-Commerce on the Train." The 4th International Conference on Electronic Commerce (ICEB) 2004: 771-776.

[11] EEE 802.20 Working Group, System requirements for 802.20 Mobile Broadband Wireless Access Systems http://www.ieee802.org/20/Contribs/C802.20-06-04.pdf.




Refernces (contd)

[12] http://www.wimax.com/[13] “Kyocera enhances iBurst with Mobile Broadband Technology”,

http://global.kyocera.com/prdct/telecom/office/iburst/news/080410.html, Retrieved April 26, 2008[14] “MBWA and 802.16e: Two Markets –Two Projects”, 802.16sgm-02/16 or 802m_ecsg-02/15

IEEE 802.20 – Mobile Broadband Wireless Access

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