1. Specific Systems Wi-Max IEEE 802.16 #11 Victor S. Frost
Dan F. Servey Distinguished Professor
Electrical Engineering and Computer Science
University of Kansas
2335 Irving Hill Dr.
Lawrence, Kansas 66045
Phone: (785) FAX:(785)
All material copyright 2006
Victor S. Frost, All Rights Reserved
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Aug. 2005

2. Outline Motivation for IEEE 802.16 Applications Services and QoS
Architecture
Initialization
Phy Layer
MAC
Packet formats
Access protocol
QoS support
Evolution
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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
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4. From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC:
Overview of IEEE
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 PHYs
Protocol-Independent core (ATM, IP, Ethernet, …)
From: R. Marks, “The WirelessMAN WirelessMAN MAC: MAC:
It’s Done, but What Is It?”
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5. IEEE 206.16 Protocol Architecture
Convergence layer:
Maps upper layer packets
into MAC frames
May fragment to gain efficiency
Protocol-Independent core
Modified from: W. Stallings Wireless Communications and Networks,
Prentice Hall, Second Edition
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6. From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC:
It’s Done, but What Is It?”
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7. Services Support multiple services, e.g., TDM Voice VoIP Digital TV IP
Bridged LAN
Backhaul: Cell tower to switch replacing costly land lines
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8. QoS Requirements
From: W. Stallings Wireless Communications and Networks,
Prentice Hall, Second Edition
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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 e)
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
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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
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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)
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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)
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13. Initialization SS Authentication and Registration IP connectivity
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.
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14. Initialization Connection set up Privacy and Security Associations
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
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15. Summary Initialization
From: Govindan Nair, et. al., “IEEE Medium Access
Control and Service Provisioning”, Intel Technology Journal, Volume 08 Issue 03,
August 20, 2004 ISSN X
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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
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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
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18. RLC Adaptation Transition to a more robust burst profile.
Transition to a less robust burst profile.
From: Carl Eklund,, et., al., “IEEE Standard :A Technical Overview of the
WirelessMAN™ Air Interface for Broadband Wireless Access,”
IEEE Communications Magazine • June 2002
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19. Physical Layer Summary
Designation
Applicability
MAC
Duplexing
WirelessMAN-SC
10-66 GHz Licensed
Basic
TDD, FDD, HFDD
2-11 GHz Licensed
Basic, (ARQ), (STC), (AAS)
TDD, FDD
WirelessMAN-OFDM
2-11 GHz License-exempt
Basic, (ARQ), (STC), (DFS), (MSH), (AAS)
TDD
WirelessMAN-OFDMA
AAS= Adpative Antenna System
STC= Space time coding
MSH= Mesh
DFS = Dynamic Frequency Selection
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20. Physical Layer Upstream transmission Downstream Channel Bandwidth
TDD or FDD
Demand Assignment Multiple Access
Downstream
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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21. General Downlink Frame Structure
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 *
Downlink Interval Usage Code (DIUC) indicates burst profile
* From: Carl Eklund,, et., al., “IEEE Standard :A Technical Overview of the
WirelessMAN™ Air Interface for Broadband Wireless Access,”
IEEE Communications Magazine • June 2002
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Aug. 2005

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 WirelessMAN WirelessMAN MAC: MAC:
It’s Done, but What Is It?”
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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
From: R. Marks, “The WirelessMAN WirelessMAN MAC: MAC:
It’s Done, but What Is It?”
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24. General Uplink Frame Structure
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 *
Uplink Interval Usage Code (UIUC) indicates burst profile
* From: Carl Eklund,, et., al., “IEEE Standard :A Technical Overview of the
WirelessMAN™ Air Interface for Broadband Wireless Access,”
IEEE Communications Magazine • June 2002
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Aug. 2005

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
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
From: R. Marks, “The WirelessMAN WirelessMAN MAC: MAC:
It’s Done, but What Is It?”
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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
From: R. Marks, “The WirelessMAN WirelessMAN MAC: MAC:
It’s Done, but What Is It?”
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27. From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC:
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 GHz PHY,
Time expressed as arrival time at BS
From: R. Marks, “The WirelessMAN WirelessMAN MAC: MAC:
It’s Done, but What Is It?”
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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
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29. 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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30. PHY Frame-TDD example
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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
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32. From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC:
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
From: R. Marks, “The WirelessMAN WirelessMAN MAC: MAC:
It’s Done, but What Is It?”
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33. From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC:
MAC PDU Transmission
PDU = Data exchanged between peer entities
SDU = Data exchanged between adjunct layers
From: R. Marks, “The WirelessMAN WirelessMAN MAC: MAC:
It’s Done, but What Is It?”
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34. MAC Frame Format MAC header formats Header format drives functionality*
MAC header formats
Generic downlink
Generic uplink
Bandwidth request
Header format drives functionality
Caution: details of fields have changed
* From: W. Stallings Wireless Communications and Networks,
Prentice Hall, Second Edition
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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
* From: W. Stallings Wireless Communications and Networks,
Prentice Hall, Second Edition
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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)
* From: W. Stallings Wireless Communications and Networks,
Prentice Hall, Second Edition
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37. Bandwidth request header*
15 bits used to request transmissions of a number of bytes
* From: W. Stallings Wireless Communications and Networks,
Prentice Hall, Second Edition
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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 net and the backbone may
Result backlog at SS
To recover use the poll-me and slit indicators
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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.
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40. Services Non-real-time Polling Services (nrtPS) Best Effort
Provides guarantee on throughput,
Suitable for non real time services that have variable data size, e. g., .
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
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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
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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
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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
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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
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45. References
Eklund, C., et al., IEEE standard : a technical overview of the WirelessMAN air interface for broadband wireless access. Communications Magazine, IEEE, (6): p
Ghosh, A., et al., Broadband wireless access with WiMax/802.16: current performance benchmarks and future potential. Communications Magazine, IEEE, (2): p
Nair, G., et al., IEEE Medium Access Control and Service Provisioning. Intel Technology Journal, (03): p
Ramachandran, S., C.W. Bostian, and S.F. Midkiff, Performance evaluation of IEEE for broadband wireless access.
R. Marks, “The WirelessMAN WirelessMAN MAC: MAC: It’s Done, but What Is It?”
W. Stallings Wireless Communications and Networks, Prentice Hall, Second Edition, 2005
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46. References
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