12-Specific System WiMax

8/13/2019 12-Specific System WiMax

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Victor S. FrostDan F. Servey Distinguished Professor

Electrical Engineering and Computer ScienceUniversity of Kansas2335 Irving Hill Dr.

Lawrence, Kansas 66045Phone: (785) 864-4833 FAX:(785) 864-7789

e-mail: [email protected]://www.ittc.ku.edu/

Specific Systems

Wi-MaxIEEE 802.16

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All material copyright 2006

Victor S. Frost, All Rights Reserved

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Outline

Motivation for IEEE 802.16 Applications Services and QoS Architecture Initialization Phy Layer MAC

Packet formats Access protocol QoS support

Evolution Focus on fixed wireless no mobility IEEE 802.16e

has mobility


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Motivation for IEEE 802.16

Provide all aspect of a wireless MAN Alternative access technology in competition with,

cable, fiber and DSL Higher carrier frequencies (up to 66 GHz) to

support higher data rates RF bandwidth, e.g., 20 MHz Expectations

Higher UE data rates Cost

Lower installation cost Higher equipment cost

Reduced deployment time Ubiquitous coverage

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Overview of IEEE 802.16

Point-to-Multipoint Metropolitan Area Network Connection-oriented Burst based architecture Supports difficult user environments

High bandwidth, hundreds of users per channel Continuous and burst traffic Efficient use of spectrum

Balances between stability of contentionless andefficiency of contention-based operation

Flexible QoS offerings Supports multiple 802.16 PHYs Protocol-Independent core (ATM, IP, Ethernet, )

From: R. Marks, The 802.16 WirelessMAN WirelessMAN MAC: MAC:Its Done, but What Is It? www.ieee802.org/16/docs/01/80216-01_58r1.pdf


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IEEE 206.16 Protocol Architecture

Protocol-Independent core

Modified from: W. Stallings Wireless Communications and Networks,Prentice Hall, Second Edition

Convergence layer:

-Maps upper layer packetsinto MAC frames

-May fragment to gain efficiency

#12 6From: R. Marks, The 802.16 WirelessMAN WirelessMAN MAC: MAC:

Its Done, but What Is It? www.ieee802.org/16/docs/01/80216-01_58r1.pdf


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WiMAX-OFDM

From: IEEE 802 Wireless Systems, B. Walke, S. Mangold, and L. Berlemann, Wiley, 2006

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Services

Support multiple services, e.g., TDM Voice VoIP Digital TV IP

Bridged LAN Backhaul: Cell tower to switch replacingcostly land lines


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QoS Requirements

From: W. Stallings Wireless Communications and Networks,Prentice Hall, Second Edition

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IEEE 802.16 System Reference Points

Assumptions The subscriber stations (SS) are fixed (later version

may allow mobility, i.e., IEEE 802.16e)

Base stations are fixed

High data rates in BOTH upstream and downstreamdirections

Base station maybe heavily loaded

Needs to be spectral efficient

* From: W. Stallings Wireless Communications and Networks,Prentice Hall, Second Edition

*


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Connections

IEEE 802.16 MAC is connection-oriented. Provides Each service mapped to a connection A mechanism for requesting bandwidth, associating

QoS and traffic parameters, transporting information Routing data to the appropriate convergence sublayer, Other actions associated with the contractual terms

of the service.

Connection ID (CID)16 bit field Like virtual circuits

Each SS has a standard 48 bit MAC

address Equipment ID

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Initialization

Channel Acquisition SS scans its frequency list to find an operating

channel (may be configured with a specific BSID to look for)

The SS synchronizes to the downstreamtransmission by detecting the periodic framepreamble

The downstream periodically transmits itsmodulation and FEC schemes using

Downlink Channel Descriptor (DCD) and Uplink Channel Descriptor (UCD) messages

DCD and UDC are transmitted most robust(least efficient burst profile)


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Initialization Ranging

MAP messages are used to define the usage of channel DL-MAP downlink MAP UL-MAP uplink MAP

SS scans the UL-MAP for opportunities to send a ranging messages SS selects a ranging time slot using a truncated exponential

backoff algorithm (like in DOCSIS) Send ranging message (RNG-REQ message) with minimum power If no response increase power and tx again Success of the ranging message at the BS allows for the BS to

send the SS Time synchronization information Power adjustment information Basic Channel ID (CID) Primary Management CID

SS reports to BS PHY capabilities and BS can accept or deny any

capability The above process is repeated to maintain the radio link(Radio link control-RLC)

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Initialization

SS Authentication and Registration Determine if SS can join the network

If authorized then SS registers withthe network

IP connectivity Uses DHCP to get IP address

And address of TFTP server to to obtainconfiguration files.


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Initialization

Connection set up Service flows define unidirectional transport Each service flow is mapped to a CID on a specific MAC

address Service flows usually are set up by the BS during

initialization, like permanent virtual circuits (PVCs) CID can be setup on demand, like a switched virtual

circuit (SVCs) using a signaling protocol. Initially each SS sets up three management connections

in each direction (each on own CID) Basic for short time critical MAC and RLC messages Primary for larger delay insensitive messages, eg., for

authentication

Secondary for management, SNMP, TFTP, and DHCP Privacy and Security Associations

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Summary Initialization

From: Govindan Nair, et. al., IEEE 802.16 Medium AccessControl and Service Provisioning, Intel Technology Journal, Volume 08 Issue 03,

August 20, 2004 ISSN 1535-864X


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RLC Adaptation

As part of the MAC the RLC continues toadapt the uplink and downlink burstprofiles to trade: Robustness Efficiency

BS controls all burst profiles Control of uplink burst profile

BS receives uplink messages BS can measure uplink quality

BS specifies burst profile when granting access

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RLC Adaptation

Control of downlink burst profile SS receives downlink transmissions

SS measures downlink quality

Problem: SS must communicate appropriateburst profile to BS

Note SS is required to receive more robustsegments of the downlink transmission in

addition to the negotiated burst profile Change messages must get through andacknowledged


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RLC Adaptation

Uplink Interval Usage Code (UIUC) Defines the burst profiles used by the each SS on the

uplink BS is in control of changed in UL burst profiles BS specifies the UIUC when granting the SS permission

to send on the uplink

Downlink Interval Usage Code (DIUC) Defines the burst profiles for the downlink Each SS can have a different burst profile in the

downlink In the downlink it is the SS that knows the CSI

The BS is still the entity to execute changes in the DIUC Thus a protocol is needed to exchange the information.

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RLC Adaptation

Transition to a less robust burst profile.Transition to a more robust burst profile.

From: Carl Eklund,, et., al., IEEE Standard 802.16:A Technical Overview of theWirelessMAN Air Interface for Broadband Wireless Access,IEEE Communications Magazine June 2002

DLBC= DL Burst Change


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Physical Layer Summary

TDD, FDDBasic, (ARQ),(STC), (AAS)

2-11 GHz Licensed

TDDBasic, (ARQ),(STC), (DFS),(MSH), (AAS)

2-11 GHz License-exempt

WirelessMAN-OFDMA

TDDBasic, (ARQ),(STC), (DFS),(MSH), (AAS)

2-11 GHz License-exempt


2-11 GHz Licensed

WirelessMAN-OFDM


2-11 GHz LicensedWirelessMAN-SC

TDD, FDD, HFDDBasic10-66 GHz LicensedWirelessMAN-SC

DuplexingMACApplicabilityDesignation

AAS= Adpative Antenna SystemSTC= Space time codingMSH= MeshDFS = Dynamic Frequency Selection

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Physical Layer

Burst based architecture Upstream transmission

TDD UL/DL share same channel; do not simultaneous transmit FDD UL/DL on separate chaanel can transmit simultaneously Demand Assignment Multiple Access

Downstream TDD or FDD Continuous mode Burst mode

Capability to dynamically change modulation and FEC

Channel Bandwidth 20 or 25 MHz (US)

28 MHz (Europe) Frames 0.5, 1 or 2 ms Adaptive burst profile; changing

Modulation FEC


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Burst based architecture

Broadcast phase : The information aboutuplink and downlink structure is announced. DL-MAP(Downlink Map)

DL-MAP defines the access to the downlinkinformation

Modulation

FEC

UL-MAP(Uplink Map) UL-MAP message allocates access to the uplink

channel

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General Downlink Frame Structure

Downlink Interval Usage Code (DIUC)indicates burst profile

* From: Carl Eklund,, et., al., IEEE Standard 802.16:A Technical Overview of theWirelessMAN Air Interface for Broadband Wireless Access,IEEE Communications Magazine June 2002

DL MAP contains thechanges in burst profile, i.e.,modulation and FEC

Downlink data is transmittedto each SS according to anegotiated burst profile

Data is transmitted in theTDM part in order ofdecreasing robustness

There maybe a mixture ofburst profiles that varyframe-to-frame

SS listen to all parts of thedownlink frame they arecapable or receiving

*


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Downlink transmissions

Two kinds of bursts: TDM and TDMA All bursts are identified by a DIUC

Downlink Interval Usage Code

TDMA bursts have resync preamble allows formore flexible scheduling

Each terminal listens to all bursts at itsoperational IUC, or at a more robust one, exceptwhen told to transmit

Each burst may contain data for several terminals SS must recognize the PDUs with known CIDs

DL-MAP message signals downlink usage


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Downlink Channel Descriptor

Used for advertising downlink burstprofiles

Burst profile of DL broadcast channel iswell known

All others are acquired Burst profiles can be changed on the fly

without interrupting the service Not intended as 'super-adaptive'

modulation Establishes association between DIUC and

actual PHY parameters



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General Uplink Frame Structure

Uplink Interval Usage Code(UIUC) indicates burst profile

* From: Carl Eklund,, et., al., IEEE Standard 802.16:A Technical Overview of theWirelessMAN Air Interface for Broadband Wireless Access,IEEE Communications Magazine June 2002

UL-MAP grants BW tospecific SS

SS transmit bursts asdefined in the UIUC

SS tx their assignedallocations in the UIUC

Uplink subframe usesDOCSIS like contention fortransmission in contentionslots

Burst profiles can be changeddynamically, frame-to-frame

SS transition gap are guardtimes

*

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Uplink Transmissions Invited transmissions Transmissions in contention slots

Bandwidth requests Contention resolved using truncated exponential backoff

Transmissions in initial ranging slots RNG-REQ Contention resolved using truncated exponential backoff

Bursts defined by UIUCs Transmissions allocated by the UL-MAP message

All transmissions have synchronization preamble Ideally, all data from a single SS is concatenatedinto a single PHY burst



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Uplink Channel Descriptor

Defines uplink burst profiles Sent regularly All Uplink Burst profiles are acquired Burst profiles can be changed on the

fly Establishes association between

UIUC and actual PHY parameters


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Uplink MAP Message

UL-MAP message defines usage of theuplink

Contains the "grants"

Grants addressed to the SS

Time given in mini-slots unit of uplink bandwidth allocation

2m

physical slots in 10-66 GHz PHY, Time is referenced to arrival time at BS



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Uplink scheduling

Uplink direction uses a schedule toallocate uplink capacity

Uses a request-grant mechanism

Specification of scheduling service isestablished at connection set up time.

Scheduling services are based onDOCSIS

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Class of uplink services

Unsolicited Grant Service

Real time Polling Service

Non real time Polling Service

Best Effort

Like DOCSIS

More later.


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PHY Frame-TDD example

DLFP=Downlink Frame PrefixFCH=Frame Control Header

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MAC overview

Uses Demand Assigned Multiple Access (DAMA)TDMA

BS controls allocations of uplink bandwidth Unit of allocation is a mini-slot SS requests transmission opportunities on the

uplink for a specific number of minislots on acontention basis

Collisions on request messages are resolved usingtruncated binary exponential backoff algorithm

BS collects requests and sends schedules on thedownlink via an allocation map


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MAC PDU Transmission

MAC PDUs are transmitted in PHY bursts A single PHY burst can contain multiple

Concatenated Concatenated MAC MAC The PHY burst can contain multiple FEC

blocks MAC PDUs may span FEC block boundaries The convergence layer between the MAC

and the PHY allows for capturing the start of the

next MAC PDU in case of erroneous FECblocks


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MAC PDU Transmission


PDU = Data exchanged between peer entitiesSDU = Data exchanged between adjunct layers


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MAC Frame Format


Three MAC header formats Generic downlink

Generic uplink

Bandwidth request

Header format drives functionality

Caution: details of fields may havechanged

*

3 types

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Generic downlink header

EC-Encryption control EKS-Encryption control

sequence, vector of key HT-Header type generic or

bw req ARQ-indictor for link ARQ.

IF ARQ the 2 bytes atstart of frame use forARQ process

FC-Fragment control

FSN- Fragment seq # HCS-Header check

sequence. Only coversheader

*



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Generic uplink header Added 8 bit grant management

field- three types USG (Unsolicited Grant Service) SI-Slip indicator, reports to BS

that SSs queue is backlogged soBS can take action to resolve

PM-Poll me Grants per interval # grants

required by connection Piggy-pack request number of

bytes requested USG with activity detection

Can switch to USG when there isactivity

Suited for VoIP with speechdetection

UGS-AD starts as rtPS flow Detects VoIP do BW req to go

to UGS Upon end of VoIP use BW req

with 0 Bytes to go back to rtPSflow

Piggyback request (because notuse separate bw requestmessage)


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Bandwidth request header

15 bits used torequesttransmissions of anumber of bytes

*



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Services

Unsolicited grant service (UGS) Transport fixed data periodically No explicit BW requests Limit on jitter = one frame time Provides guarantees on

throughput, latency, jitter

Not allowed to use random access opportunities Targeted for

T1/E1 over ATM ATM CBR

Buffer build up Not expected for CBR, but Grants may be lost Clock skew between the 802.16 net and the backbone may

Result backlog at SS To recover use the poll-me and slip indicators

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Services

Real-time polling service-rtPS Target services that are bursty but offers periodic

dedicated request opportunities to meet real-timerequirements.

Does not use contention process to request bandwidth,used explicit MAC message

Variable packet size Requests imply increased latency and overhead Suitable for

VoIP with silence detection MPEG Video

This is like rt-VBR ATM Provides guarantee on throughput Little less focus on latency.


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Services

Non-real-time Polling Services (nrtPS) Provides guarantee on throughput, Suitable for non real time services that have variable

data size, e. g., e-mail. Like rt-polling except but polls are less frequently Allowed to use contention requests May use Grant Management sub-header to request BW New request can be piggybacked with each new request

can be piggybacked with each transmitted PDU

Best Effort Provides no guarantees

Can request bandwidth using contention or explicitprocesses

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Classes of SS

An SS can have one for more connections

Grant per connection (GPC) class Bandwidth is granted explicitly for each

connection

SS needs to track each connection thus morecomplex

Less flexible

Less scaleable, more state to track Less efficient, because not as much sharing


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Classes of SS

Grant per SS (GPSS)

Grants given to all connections on anSS as an aggregate

GPSS SS needs to manage all thetraffic thus the QoS for differentapplications

Can react more quickly to changes

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Protocols for grants

Grants can be lost because: Errors cause the BS not to receive request

Errors cause the grant involved in collision

Errors cause the SS not to receive grant

Bandwidth not provided because: Not enough available downstream bandwidth

GPSS stole the bandwidth for other purpose


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Protocols for grants

How to deal with lost grants or unsatisfied grants? ARQ like protocol not used because takes too muchtime

A self correcting protocol is used.

Note requests are usually incremental that is achange from current allocation.

Set timer suitable for QoS If timer fires, SS requests again But the perception of current allocated BW at the

BS may not track right because an incrementalrequest is lost

Solution: Occasionally send aggregate bandwidthrequirement of SS, resets perception of currentallocated BW to SS

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802.16 Standards History

802.16a(Jan 2003)

Extension for 2-11 GHz: Targeted for non-line-of-sight, Point-to-Multi-Point applications likelast mile broadband access

802.16(Dec 2001)

Original fixed wireless broadband air Interfacefor 10 66 GHz: Line-of-sight only, Point-to-Multi-Point applications

802.16c(2002)

802.16 AmendmentWiMAX System Profiles

10 - 66 GHz

802.16REVd(802.16-2004)

(Oct 2004)

Adds WiMAX System Profiles and Errata for 2-

11 GHz

802.16e(802.16-2005)

(Dec 2005)

MAC/PHY Enhancements to support subscribersmoving at vehicular speeds

First standard based on proprietary implementations of DOCSIS/HFCarchitecture in wireless domain


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IEEE 802.16-Summary

Commonalities with DOCSIS

DOCSIS Not adaptive

Focus on support of IP

Adaptive burst transmissionarchitecture

Targeted for muliprotocol & services

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References

Eklund, C., et al., IEEE standard 802.16: a technical overviewof the WirelessMAN air interface for broadband wirelessaccess. Communications Magazine, IEEE, 2002. 40(6): p. 98-107.

Ghosh, A., et al., Broadband wireless access withWiMax/802.16: current performance benchmarks and futurepotential. Communications Magazine, IEEE, 2005. 43(2): p.129-136.

Nair, G., et al., IEEE 802.16 Medium Access Control andService Provisioning. Intel Technology Journal, 2004.08(03): p. 213-228.

Ramachandran, S., C.W. Bostian, and S.F. Midkiff,Performance evaluation of IEEE 802.16 for broadband

wireless access. R. Marks, The 802.16 WirelessMAN WirelessMAN MAC:MAC: Its Done, but What Is It?www.ieee802.org/16/docs/01/80216-01_58r1.pdf

W. Stallings Wireless Communications and Networks,Prentice Hall, Second Edition, 2005

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12-Specific System WiMax