#11 1 Victor S. Frost Dan F. Servey Distinguished Professor Electrical Engineering and Computer Science University of Kansas 2335 Irving Hill Dr. Lawrence,

#11 1

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]

http://www.ittc.ku.edu/

Specific Systems

Wi-MaxIEEE 802.16

#11

All material copyright 2006Victor S. Frost, All Rights Reserved

http://www.ittc.ku.edu/

#11 2

Outline

• Motivation for IEEE 802.16 Applications

• Services and QoS• Architecture• Initialization• Phy Layer• MAC

– Packet formats– Access protocol– QoS support

• Evolution

#11 3

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 (10 to 66

GHz) to support higher data rates• Expectations

– Cost• Lower installation cost• Higher equipment cost

– Reduced deployment time– Ubiquitous coverage

#11 4

Overview of IEEE 802.16• Point-to-Multipoint• Metropolitan Area Network • Connection-oriented• Supports difficult user environments

– High bandwidth, hundreds of users per channel– Continuous and burst traffic

• – Very efficient use of spectrum• Balances between stability of contentionless

and efficiency 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:

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

#11 5

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 packets into MAC frames

-May fragment to gain efficiency

#11 6From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC:

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

#11 7

Services

• Support multiple services, e.g.,– TDM– Voice– VoIP– Digital TV– IP– Bridged LAN– Backhaul: Cell tower to switch

replacing costly land lines

#11 8

QoS Requirements

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

#11 9

IEEE 802.16 System Reference Points

• Assumptions– The subscriber stations (SS) are fixed– Base stations are fixed (later version may allow

mobility, i.e., IEEE 802.16e)– High data rates in BOTH upstream and

downstream directions– Base station maybe heavily loaded– Needs to be spectral efficient

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

*

#11 10

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 • 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

#11 11

Initialization

• Channel Acquisition– SS scans its frequency list to find an

operating channel (may be configured with a specific BS ID to look for)

– The SS synchronizes to the downstream transmission by detecting the periodic frame preamble

– The downstream periodically transmits its modulation 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)

#11 12

Initialization• Ranging

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

• SS scans the UP-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)

#11 13

Initialization

• SS Authentication and Registration– Determine if SS can join the network– If authorized then SS registers with

the network

• IP connectivity– Uses DHCP to get IP address– And address of TFTP server to to

obtain configuration files.

#11 14

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 directsion• 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

#11 15

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

#11 16

RLC Adaptation

• As Part of the MAC the RLC continues to adapt the uplink and downlink burst profiles 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

#11 17

RLC Adaptation

• Control of downlink burst profile• SS receives downlink transmissions• SS measures downlink quality• Problem: SS must communicate

appropriate burst profile to BS• Note SS is required to receive more

robust segments of the downlink transmission in addition to the negotiated burst profile

• Change messages must get through and acknowledged

#11 18

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

#11 19

Physical Layer SummaryDesignation Applicability MAC Duplexing

WirelessMAN-SC 10-66 GHz Licensed

Basic TDD, FDD, HFDD

WirelessMAN-SC 2-11 GHz Licensed Basic, (ARQ), (STC), (AAS)

TDD, FDD

WirelessMAN-OFDM

2-11 GHz Licensed Basic, (ARQ), (STC), (AAS)

TDD, FDD

2-11 GHz License-exempt

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

TDD

WirelessMAN-OFDMA

2-11 GHz Licensed Basic, (ARQ), (STC), (AAS)

TDD, FDD

2-11 GHz License-exempt

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

TDD

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

#11 20

Physical Layer

• Upstream transmission– TDD or FDD– 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

#11 21

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 the changes in burst profile, i.e., modulation and FEC

• Downlink data is transmitted to each SS according to a negotiated burst profile

• Data is transmitted in the TDM part in order of decreasing robustness

• There maybe a mixture of burst profiles that vary frame to frame

• SS listen to all parts of the downlink frame they are capable or receiving

*

#11 22

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 for more flexible scheduling

• Each terminal listens to all bursts at its operational IUC, or at a more robust one, except when 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

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

#11 23

Downlink Channel Descriptor

• Used for advertising downlink burst profiles

• Burst profile of DL broadcast channel is well 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


#11 24

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 to specific SS

• SS transmit bursts as defined in the UIUC

• SS tx their assigned allocations in the UIUC

• Uplink subframe uses DOCSIS like contention for transmission in contention slots

• Burst profiles can be changed dynamically

• SS transition gap are guard times

*

#11 25

Uplink Transmissions Uplink

• 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 concatenated

into a single PHY burst a single PHY burst


#11 26

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


#11 27

Uplink MAP Message

• UL-MAP message defines usage of the uplink

• 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 expressed as arrival time at BS


#11 28

Uplink scheduling

• Uplink direction uses a schedule to allocate uplink capacity

• Uses a request-grant mechanism• Specification of sechduling service

is established at connection set up time.

• Scheduling services are based on DOCSIS

#11 29

Class of uplink services

• Unsolicited Grant Service• Real time Polling Service• Non real time Polling Service• Best Effort• Like DOCSIS

• More later….

#11 30

PHY Frame-TDD example

#11 31

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 a contention basis

• Collisions on request messages are resolved using truncated binary exponential backoff algorithm

• BS collects requests and sends schedules on the downlink via an allocation map

#11 32

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 FEC blocks


#11 33

MAC PDU Transmission


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

#11 34

MAC Frame Format


• MAC header formats– Generic downlink– Generic uplink– Bandwidth request

• Header format drives functionality• Caution: details of fields have changed

*

#11 35

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 at start of frame use for ARQ process

• FC-Fragment control• FSN- Fragment seq #• HCS-Header check

sequence. Only covers header

*


#11 36

Generic uplink header• Added 8 bit grant

management field- three types– USG

• SI-Slip indicator, reports to BS that SS’s queue is backlogged so BS 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 is activity

• Suited for VoIP with speech detection

– 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 rtPS flow

– Piggyback request (because not use separate bw request message)


#11 37

Bandwidth request header

• 15 bits used to request transmissions of a number of bytes

*


#11 38

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 slit indicators

#11 39

Services

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

dedicated request opportunities to meet real-time requirements.

– 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.

#11 40

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 explicit

processes

#11 41

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

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

#11 42

Classes of SS

• Grant per SS (GPSS)• Grants given to all connections on

an SS as an aggregate• GPSS SS needs to manage all the

traffic thus the QoS for different applications

• Can react more quickly to changes

#11 43

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

#11 44

Protocols for grants• How to deal with lost grants or unsatisfied

grants?– ARQ like protocol not used because takes too much

time– A self correcting protocol is used.

• Note requests are usually incremental that is a change 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 incremental request is lost

• Solution: Occasionally send aggregate bandwidth requirement of SS, resets perception of current allocated BW to SS

#11 45

References • Eklund, C., et al., IEEE standard 802.16: a technical

overview of the WirelessMAN air interface for broadband wireless access. Communications Magazine, IEEE, 2002. 40(6): p. 98-107.

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

• Nair, G., et al., IEEE 802.16 Medium Access Control and Service 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: It’s 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

http://www.ieee802.org/16/docs/01/80216-01_58r1.pdf

#11 46

References

Documents

#11 1 Victor S. Frost Dan F. Servey Distinguished Professor Electrical Engineering and Computer Science University of Kansas 2335 Irving Hill Dr. Lawrence,