Elements of Cross-Layer System & Network Design for QoS-Enabled Wi-Max Networks
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Elements of Cross-Layer System & Network Design for QoS-Enabled Wi-Max Networks

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The main theme of this workshop is to elucidate medium access control (MAC) layer operation and cross-layer system and network design techniques for providing Quality-of-Service (QoS) in wireless......

The main theme of this workshop is to elucidate medium access control (MAC) layer operation and cross-layer system and network design techniques for providing Quality-of-Service (QoS) in wireless broadband networks, and to put it in the context of military communications. We will use the IEEE 802.16 standard as an example for the rich feature set it presents, and the flexibility it provides for...

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  • Must have a provisioned & managed service at IP/app layer Requires a service provisioning platform that: Provisions customer SLAs at the OSS level Maps provider-level services into WiMAX traffic classes Determines scheduling classes of traffic Performs control of connection at MAC and PHY layer Reports events/statistics/alarms of MAC/PHY parameters in an appropriate fashion to a central management entity

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  • 1. Metanoia, Inc.Critical Systems Thinking™Elements of Cross-Layer System and Network Design for QoS- Enabled Wi-Max Networks Dr. Abhay Karandikar Dr. Vishal Sharma IIT Bombay Metanoia, Inc. http://www.ee.iitb/ac/in/~abhay http://www.metanoia-inc.com © Copyright 2006-07 All Rights Reserved
  • 2. Metanoia, Inc. Critical Systems Thinking™Workshop Overview  IEEE 802.16 standards – an introduction  PHY and MAC: Key design QoS design aspects  Scheduling services & design implications  System architectures for QoS  Cross-layer based scheduling techniques for QoS  Implementation issues in algorithms and protocols  Future of WiMax and applicability to military communications©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 2
  • 3. Metanoia, Inc.Critical Systems Thinking™ Wi-MAX System Architecture
  • 4. Metanoia, Inc.IEEE 802.16 Wireless MAN Critical Systems Thinking™Standard: Background  Developed by IEEE 802.16. WG  Technologies/protocols for air-interface of BWA systems  Specifies PHY and MAC layer 1999 2000 2001 2002 2003 2004 2005 2006 IEEE Std. 802.16-2001 IEEE Std. 802.16-2004 IEEE Std. 802.16e  Evolutionary standard …  Originally -- stationary, enterprise-class deployments (2001)  Enhanced for residential-class applications (2003)  Extended for mobile + fixed terminals (2002-2005)©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 4
  • 5. Metanoia, Inc. Critical Systems Thinking™802.16 Wireless MAN Standard  PHY layer – primary arbiter of physical environment in which technology can operate  MAC layer – essence of standard – supports …  Differentiated QoS – specifies scheduling behavior, not algos.  Many demanding enterprise-class or consumer-class apps.  “Metropolitan”  target scale, not geography  Size of city, but could be rural or urban  Ensures spectrum efficiency – via techniques we see later©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 5
  • 6. Metanoia, Inc. IEEE 802.16 MAN Critical Systems Thinking™ Market Applications and DeploymentWi-Fi Backhaul Mall/Coffee Shop Hotspot Mobile Station (MS) Industrial EnterpriseDSL/CableAlternative Multi-tenant Base Station Customers (condo) (BS) Mesh Node Residential Customer Enterprise Core Network Customer Company Base Station Wired Fiber Extension for warehouse Backhaul (BS) Core Infrastructure ©Copyright 2006-07 All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 6
  • 7. Metanoia, Inc. A Word on QoS Architecture: Critical Systems Thinking™ Basic Elements Signaling From provisioning system Connection Service Admission Control definitions/Rules (CAC) Management Control Plane Plane MeteringIncoming data Packet Shaping/ Marking Scheduling Classification Policing Data Plane ©Copyright 2006-07 All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 7
  • 8. Metanoia, Inc. Critical Systems Thinking™802.16 High-Level System Operation SS1 SS2 BS SS3 SS4©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 8
  • 9. Metanoia, Inc. Critical Systems Thinking™802.16 High-Level System Operation 1 SS1 1 2 3 4 2 SS2 3 BS SS3 4 SS4©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 9
  • 10. Metanoia, Inc. Critical Systems Thinking™802.16 High-Level System Operation 1 Requests SS1 BS computes non- 2 conflicting schedule SS2 Grants 3 UL Control BS UL Data Part Start DL ULSS3 1 3 2 Frame©Copyright 2006-07 SS4All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 10
  • 11. Metanoia, Inc. Critical Systems Thinking™802.16 High-Level System Operation  Fixed BS (one), distributed SS’s (many)  Time-slotted operation  Time adjusted such that receptions at BS arrive in sync.  Initial ranging for each SS  Multiple access to share radio medium  Bandwidth requests SSs  BS in UL  BS computes non-conflicting schedule  Based on nature of requests, # of SS’s, channel state  Grants BS  SSs in DL  At appointed time, SS’s transmit to BS©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 11
  • 12. Metanoia, Inc.System and Protocol Architecture: Critical Systems Thinking™Components System Architecture Protocol Architecture  Topologies supported  Layered reference model  Framing + slot structure  Convergence sublayer (CS)  Duplexing  Common Part Sublayer (CPS)  Multiplexing – discussed in detail  Multiple access technique  Security sublayer (SS) – not focus of this talk  B/w request/grant mechanism  ARQ protocol  MAC  Adaptive PHY©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 12
  • 13. Metanoia, Inc. Critical Systems Thinking™ TDD Frame Structure -- Details Frames j-3 j-2 j-1 j j+1 j+2 j+3 j+4Preamble DL-subframe UL-subframe SS transition gap TDM portion Frame Adaptive SS1 DIUC a DIDU b DIDU Initial main Request Control sched data data n data -tainance contention Section dataDL-MAP UL-MAP DCD UCD Collision Collision Initial Data Access Burst Request Gap End of Ranging Grant IEs Bandwidth IEs IE MAP IE IE request Unicast Unicast Multicast Broadcast Poll to Poll to Conten- Contention SSi SSj tion IE IE ©Copyright 2006-07 All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 13
  • 14. Metanoia, Inc.Critical Systems Thinking™ MAC and PHY: Key QoS Design Aspects
  • 15. Metanoia, Inc. Critical Systems Thinking™MAC Key Aspects  Centralized scheduling & multiple access  Access overhead ~ zero  Nearly no wasted bandwidth  Data encapsulation  Small headers -- minimize per-PDU overhead  Packing  Multiple SDU’s/PDU for apps. with small pkts. (VoIP, TCP) - efficiency  Fragmentation  Split large SDU’s across PDU’s for real-time adaptation to channel©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 15
  • 16. Metanoia, Inc. Critical Systems Thinking™802.16 MAC Layer − Basics  Functions  Protocol for accessing medium  Radio resource and radio-link control  Security  MAC instance identified by unique 48-bit address  SS can have multiple MAC addresses (with multiple I/Fs)  Full MAC address used only during  Initial registration  Authentication  Not carried in every 802.16 MPDU©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 16
  • 17. Metanoia, Inc. Critical Systems Thinking™MAC Design Features Supporting QoS  RLC (radio link control) pulled into MAC  Enables tighter control of cross-layer scheduling  Connection-oriented MAC  Gives notion of connection ID  Allows management + housekeeping per connection  MAC headers for efficient transport of  Control/signaling information  Bandwidth requests  Efficient transportation of MAC PDUs  Via packing/fragmentation ops.©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 17
  • 18. Metanoia, Inc. Critical Systems Thinking™ARQ + H-ARQ Key Aspects  Process for handling MPDU errors  Error detection via CRC/FEC or checksum  Retransmission (ReTX) strategy  Selective-Repeat (SR) and Go-Back-N (GBN) variant  ReTX unit – block-based  Block size ranging from 1 to 2040 bytes  Compact bitmap-based feedback – for multiple blocks  Cross-layer protocol: involves both PHY and MAC  Negotiated during SS initialization; for OFDMA PHY only  Stop-and-wait with immediate/synchronous feedback©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 18
  • 19. Metanoia, Inc. Critical Systems Thinking™802.16 Protocol Reference Model CS SAP Service-Specific Service-Specific Convergence Sublayer Convergence Sublayers MAC SAP MAC MAC Common Part MAC Common Part Sublayer Sublayer Network Security Sublayer Mgt. Sys. Security Sublayer PHY SAP PHY Physical Layer PHY Layer (PHY) Data/Control Plane Management Plane©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 19
  • 20. Metanoia, Inc. Critical Systems Thinking™ Convergence Sub-layer (CS) : Architecture 1 4’ Data PDU arrives Deliver payload protocol (payload protocol) PDU to higher layer CS SAP CS SAP CS SAP ATM-CS IP-CS Ethernet CS2Map PDU to Svc. Flow 3’ Restore compressed protocol headers 3 Compress redundant MAC SAP hdrs., add PDU hdr. 2’ Receive MSDU MAC Common Part Sublayer 4 Deliver processed pkt. to MAC SAP MAC Security Sublayer Classification &mapping of IP QoS PHY SAP 1’ to 802.16 Qos 5 Scheduling and Reception and transmission decoding ©Copyright 2006-07 All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 20
  • 21. Metanoia, Inc.Protocol Architecture: Critical Systems Thinking™Common Part Sub-layer (CPS) Supports multiple MAC CSs MAC SDU’s Medium Access, Performs core MAC functions, Connection Management, QoS (scheduling, CAC) independent of CS MAC SAP  Oblivious to internals of MAC MAC Common Part CS PDU Sublayer Transforms MSDUs from CS MAC Security Sublayer into MPDUs  Via various operations, some PHY SAP of which we see later Encapsulation of MAC payload, privacy key mgt. protocol Responsible for media MAC PDU’s access, connection mgt, QoS©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 21
  • 22. Metanoia, Inc. Critical Systems Thinking™PHY Key Aspects  WirelessMAN-SC  Modulation  10-66 GHz operations  BPSK  LOS necessary  QPSK  QAM  WirelessMAN-SCa  2-11 GHz operation  Physical slot-WirelessMAN-SC  Simpler Tx, complex Rx due  4 QAM symbols to multipath  OFDM  2-11 GHz operation  NLOS transmission©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 22
  • 23. Metanoia, Inc.PHY Modulation and Coding Critical Systems Thinking™Schemes for 802.16dRate ID Modulation Coding Information Information Peak data rate rate bits/symbol bits/OFDM symbol in 5MHz (Mb/s) 0 BPSK 1/2 0.5 88 1.89 1 QPSK 1/2 1 184 3.95 2 QPSK 3/4 0.5 280 6.00 3 16QAM 1/2 2 376 8.06 4 16QAM 3/4 3 568 12.18 5 64QAM 2/3 4 760 16.30 6 64QAM 3/4 4.5 856 18.36 Source: [GWA05]©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 23
  • 24. Metanoia, Inc.Critical Systems Thinking™ Scheduling Services and Design Implications
  • 25. Metanoia, Inc. Critical Systems Thinking™Enforcing QoS Requirements -- Options Applications: voice, video, data, multi-media, gaming  Widely varying QoS needs Quality-of-Service Prioritized QoS Parameterized QoS  Network treats traffic based on  Network guarantees a set of QoS relative priority parameters for traffic  E.g. Diffserv approach  E.g. ATM approach©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 25
  • 26. Metanoia, Inc. Critical Systems Thinking™Quality of Service (QoS) Parameters  Bit level  Minimum BER Requires Effective  Packet level Link level Scheduling  Throughput Algorithms  Delay  Jitter  Packet Loss  Call level  Blocking probability  Dropping probability  Application level  End-to-End Throughput / response time  Peak signal-to-noise ratio©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 26
  • 27. Metanoia, Inc. Critical Systems Thinking™QoS in Access Networks  # flows limited  per-flow QoS possible  Adverse channel environment, b/w scarcity ⇒ Wireless access is the bottleneck  Connection-oriented services with guaranteed perf. will help ensure end-to-end QoS©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 27
  • 28. Metanoia, Inc. Critical Systems Thinking™Wireless QoS: What’s Different?  Variable capacity networks  High probability of error  Variable airtime for transmitting data  Depends on AMC, FEC, link quality  Fairness is an issue©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 28
  • 29. Metanoia, Inc. Critical Systems Thinking™Differentiated QoS: What is needed?  Flexible PHY and MAC framing  Centrally-controlled MAC  Sophisticated AMC, FEC, retransmission schemes  Ability to give QoS on DL and UL  Symmetric operation – high throughput in both UL/DL  Efficient scaling with sufficient per-subscriber throughput©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 29
  • 30. Metanoia, Inc. Critical Systems Thinking™Wi-MAX QoS Classes Low M TD 1 /E T1 Unsolicited Grant Service eo id Delay Tolerance V (UGS) g IP in o am , V re V St I PT Real Time Polling Service ng si P (rtPS) w T ro d F B e eb pe W hS Non Real Time Polling Service ig H (nrtPS) ai l m E P FT Best Effort (BE) High©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 30
  • 31. Metanoia, Inc.QoS Classes in 802.16 and Critical Systems Thinking™Characterizing Parameters Type Service Flow Parameters - Max. sustainable traffic rate - Max. latency UGS - Tolerated jitter - Request/transmission policy - Min. reserved traffic rate Unsolicited Grant Service - Max. sustainable traffic rate (UGS) rt-PS - Max. latency - Request/transmission policy Real-Time Polling Service - Min. reserved rate (rtPS) - Max. sustainable rate nrt-PS - Priority - Request/transmission policyNon Real-Time Polling Service - Max. sustainable traffic rate (nrtPS) BE - Priority - Request/transmission policy Best Effort (BE)©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 31
  • 32. Metanoia, Inc. Critical Systems Thinking™ Mapping Applications to 802.16 QoS Enterprise Enterprise Provider IP QoS 802.16 TrafficApplications (100s) Service Classes Service Classes PHBs Types (8-11) (3-5) (5-8) (4) VoIP VoD Voice H.323, SIP Video EF OSPF, RIP, BGP, Real-time SNMP, NFS UGS Signaling AF3, CS6, SAP, Oracle, BEA Control CS3 rt-PS Control SNA Critical AF2, CS2 Critical Data nrt-PS Messaging AF1 Bulk Bulk Data Email BE Best Effort BE BE FTP/HTTP Scavenger Data apps., Intranet Web KaZaa, Quake, recreational video ©Copyright 2006-07 All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 32
  • 33. Metanoia, Inc.Critical Systems Thinking™ System Architectures for QoS
  • 34. Metanoia, Inc.System-Level View of QoS in 802.16 Critical Systems Thinking™Networks: Building Blocks @ Subscriber Station (SS) @ Base Station (BS)  SS UL scheduler  BS UL grant scheduler  Request generator  UL/DL MAP generators  Contention resolution module  DL/UL data schedulers  UL traffic classifier  UL channel monitor  DL channel monitor  BS periodic grant generator  Contention ratio calculator (CRC)  Contention slot allocator (CSA)  Frame partitioner  Frame generator©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 34
  • 35. Metanoia, Inc.Representative Subscriber Station Critical Systems Thinking™(SS) QoS Architecture Bandwidth Queue Requests Information UL B/w Request Generator Request Retry Size Signal Class 1 CRM Grant Size UL Traffic Class 2 Classifier Uplink Data SS UL Data (to BS) UL Class 3 Scheduler Traffic Grant Class n Size Uplink Multi-class Downlink Data Queues Downlink Data (to clients)©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 35
  • 36. Metanoia, Inc.Representative Base Station (BS) Critical Systems Thinking™QoS Architecture To network DSA_REQ UL Data UL data Uplink Traffic Shaper Admission Control B/w requests Channel sense DSA_RSP Channel BS Periodic B/w Monitor Grant Generator Queue info. Request BS Upstream Grants status Scheduler UL B/w Request CRC Queue Status UL Subframe UL MAP Contention start Generator ratio Frame Partitioner CSA DL Subframe Slots allocated DL Data queue start Downlink status Frame Generator Outgoing Class 1 frame to SSs Classifier Class 2 Shaper Traffic Traffic Generator DL MAP BS DL Data Class 3 Scheduler Class n DL Scheduler DL data from Periodic Poll network DL Data Queues Generator©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 36
  • 37. Metanoia, Inc.Critical Systems Thinking™ Cross-Layer Based Scheduling Techniques for QoS © Copyright 2006 All Rights Reserved
  • 38. Metanoia, Inc.Critical Systems Thinking™ At the start … © Copyright 2006 All Rights Reserved
  • 39. Metanoia, Inc. Critical Systems Thinking™A Layered View of Networks Application Transport View the physical layer as a “reliable bit pipe” Network MAC PHY  Network engineer’s viewpoint  Allocate the resources of the reliable bit-pipe efficiently  Communication engineers viewpoint  Build better pipes  Higher reliability, better spectral efficiency©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 39
  • 40. Scheduling in Wireline Networks Metanoia, Inc. Critical Systems Thinking™(Network Layer)  Frame-based scheduling  Time split into frames  Max. amount of traffic that session may transmit during the frame is reserved  e.g., Round Robin, Deficit Round Robin S©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 40
  • 41. Scheduling in Wireline Networks Metanoia, Inc. Critical Systems Thinking™(Network Layer)  Sorted-priority scheduling  Global parameter p associated with each user  Updated on packet arrival and departure  Packet time-stamped with a value = f(p)  Packets sorted based on their timestamps 4 3 7 5 S 1 2 3 4 5 6 7 6 2 1©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 41
  • 42. Metanoia, Inc. Critical Systems Thinking™Cross-Layer Design  Wireless channel characterized by …  Signal strength variation (fading) over time, frequency, space  Interference  Limited battery life at hosts  Physical layer no longer viewable as fixed-rate bit pipe  Resource allocation must account for channel quality  Adaptive MAC  Adaptive PHY – modulation and coding Significant performance gains in wireless networks by Cross-Layer Design©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 42
  • 43. Metanoia, Inc. Critical Systems Thinking™Scheduling in Wi-Max  Determines  Transmission opportunities Sub Channel  Appropriate burst profile  Transmission Opportunities o n si Time slot  TDMA is m ne  Timeslots ns o T ra Z  OFDM PHY Scheduling Axes  DL – (Time slots)  UL – (Time slots within individual sub-channels)  OFDMA  DL/UL opportunities -- time slots within sub-channels  MIMO  Normal zone  Transmit diversity zone  AAS zone©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 43
  • 44. Metanoia, Inc. Critical Systems Thinking™Wireless Channel Fading  Large-scale  Signal-strength variation due to path loss  Medium-scale  Caused by shadowing due to obstructions  Buildings, hills, rain, and foliage  Small-scale  Due to multipath between transmitter and receiver  Constructive/destructive interference by signals from multiple paths©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 44
  • 45. Metanoia, Inc. Critical Systems Thinking™Small-Scale Fading Signal Strength TimeVariation over frequency Variation over time Frequency selective  Fast  Amp. gains, phase shifts vary with freq.  Coherence time Tc < Symbol period T Flat fading  Slow  Multipath delay < Symbol period T  Coherence time Tc >> Symbol period T  Delay spread Td << Symbol period T  Coherence b/w Wc >> Signal b/w W©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 45
  • 46. Metanoia, Inc. Critical Systems Thinking™Effects of Channel Fading  BER: additive white Gaussian noise (AWGN) without fading − K 2 ( SNR )  Pe ≈ K1e  Constants K1 and K2 depend on the modulation scheme  BER: AWGN wireless channel with fading −1  Pe = K ( SNR )  Non-fading channel  BER decays exponentially with SNR  Fading channel  BER decays inversely with SNR©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 46
  • 47. Metanoia, Inc. Critical Systems Thinking™Fading Countermeasures Diversity Type WiMAX CDMA Multi Carrier Modulation Frequency Rake Receiver (OFDM) Adaptive Modulation and Time Coding Coding (AMC) Base Station Spatial MIMO (Soft Handoff) MIMO©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 47
  • 48. Metanoia, Inc.Critical Systems Thinking™ Multiuser Diversity: A New Paradigm for Scheduling © Copyright 2006 All Rights Reserved
  • 49. Metanoia, Inc. Critical Systems Thinking™SNR Fluctuations in a Multiuser System User 1 User 2SNR User 3 Time©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 49
  • 50. Multi-User Diversity and Metanoia, Inc. Critical Systems Thinking™Opportunistic Scheduling h1 BS h2 SS1 S Scheduler hk SS2 Channel fades independently for each user so … different users experience different channel gains SSk High prob. that some user will have strong channel BS schedules the user with strongest (best) channel Hence … “Opportunistic Scheduling”©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 50
  • 51. Metanoia, Inc. Critical Systems Thinking™Opportunistic Scheduling in WiMAX  Channel-quality measurements  Each user performs RSSI and CINR measurements  Reports to BS via REP-RSP messages  BS changes data rate adaptively as a function of channel gain  Adaptive modulation and coding  Transmit at a high rate when the channel is good  Higher constellation 64-QAM and ¾ rate convolutional coding  Transmit at a lower rate when the channel is bad  Lower constellation QPSK and ½ rate convolutional coding©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 51
  • 52. Metanoia, Inc. DRR: A Practical Scheduling Critical Systems Thinking™ Algorithm Round Robin Round Robin Pointer Pointer 1 2 Deficit Deficit Packet sent Counter Counter1 400 500 300 600 1 400 500 300 Balance2 300 400 300 200 0 2 300 400 300 200 6003 550 400 250 0 3 550 400 250 04 350 200 650 0 4 350 200 650 0 600 600 Quantum Quantum Size Size  FairnessDRR = 3*(FairnessWFQ)  Time complexity O(1) Adapted from: [ShV96] ©Copyright 2006-07 All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 52
  • 53. Metanoia, Inc.Opportunistic DRR (O-DRR): Critical Systems Thinking™Fairness and Throughput: Fair among users  Max. difference in allocated bandwidth < 10 % of average Fair among traffic classes  Both class1 and class2 traffic get almost equal number of slots As k increases, fairness decreases (intuitively expected) Source [RBS06a,b]©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 53
  • 54. Metanoia, Inc. Critical Systems Thinking™ O-DRR: Delay Performance Meets delay guarantees of different classes of traffic Packets dropped only if delay is violated  Packet drop < 8.5% for both classes of traffic  For larger k, the dropping percentage is higher  For worst case k=100, 91.5% of traffic meets its delay ©Copyright 2006-07 Source [RBS06b] All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 54
  • 55. Metanoia, Inc.Critical Systems Thinking™ Cross-Layer Scheduling in OFDMA © Copyright 2006 All Rights Reserved
  • 56. Metanoia, Inc. Critical Systems Thinking™OFDM Basics  If coherence bandwidth Wc << signal bandwidth W  Signal experiences frequency-selective fading  Split transmission b/w into large number of sub-carriers W  Create N sub-carriers with bandwidth = WN N 1 1  Symbol time TN ≈ >> ≈ Tm (delay spread) WN Wc  No inter-symbol interference (ISI)  Overlapping bands possible, if sub-carriers are orthogonal©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 56
  • 57. Metanoia, Inc. Critical Systems Thinking™OFDM Symbol in the Frequency Domain N Sub-carriers fs ... Frequency Ideal sampling positions (in frequency domain)©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 57
  • 58. Metanoia, Inc. Critical Systems Thinking™OFDMA Explained  OFDM: PHY layer technique  OFDMA: multiple-access scheme User 1 1  User occupies subset of sub- 1 carriers (traffic channels) User 2 2 2  Sub-carriers assigned to a 2 User 3 3 particular user may change y c 3 over time u en 3 r eq 3 F Time©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 58
  • 59. Metanoia, Inc. Critical Systems Thinking™OFDMA Explained  OFDM: PHY layer technique  OFDMA: multiple-access scheme  User occupies subset of sub- 3 3 2 2 2 2 carriers (traffic channels) y nc 1 1 3 3 q ue 3 3 1 1 F re 3 3 2 2  Sub-carriers assigned to a Time particular user may change over time©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 59
  • 60. Metanoia, Inc. Critical Systems Thinking™802.16 OFDMA Frame Structure OFDM Symbol Number 0 1 3 5 7 9 ... ... N-1 0 ... ... ... M-1 1 FCH UL UL Burst DL Burst MAP #2 #1 (cont.) Sub-channel Logical Number UL Burst S-1 #2 DL Burst S #4 UL Burst Preamble S+1 DL DL Burst #3 MAP #1 ACK UL Burst CH #4 DL Burst DL Burst #3 #5 UL Burst DL Burst #5 UL #6 Ranging MAP DL Burst #7 Fast Feedback (CQICH) Ns Downlink Subframe Guard Uplink Subframe©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 60
  • 61. Metanoia, Inc. Critical Systems Thinking™Opportunistic OFDMA  Total sum capacity is maximized … … if throughput in each sub-carrier is maximized  Schedule each sub-carrier to user with best channel gain  Optimum power allocation  Water-filling  Proportional fairness can be extended to OFDMA  Select users with largest ratio of instantaneous data rate to average data rate©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 61
  • 62. Metanoia, Inc. Critical Systems Thinking™OFDMA Scheduling in IEEE 802.16  Users allocated groups of sub-carriers (sub-channels)  Smallest allocation unit – a slot  Single sub-channel, spanning over 1 to 3 OFDM symbols  Subscriber stations (SSs)  Perform channel-quality measurements  Send feedback to Base Station (BS)  Fast feedback channel (CQICH) allocated  MAC sub-header  DL MAP©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 62
  • 63. Metanoia, Inc.Critical Systems Thinking™ Implementation Issues in Protocols and Algorithms
  • 64. Metanoia, Inc. Critical Systems Thinking™System Design Issues  End-to-end QoS is a must for growing multimedia applications  Access network is the usual bottleneck – more so, if wireless!  Provisioned & perceived QoS may differ markedly for wireless  Must address fading and interference  Wireless QoS thus requires:  Connection-oriented service  Implies a centralized coordinated MAC  Cross-layer based resource allocation  Adaptive MAC  Adaptive PHY©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 64
  • 65. Metanoia, Inc. Critical Systems Thinking™Wi-Max Protocol Implementation Model IP QoS Mapping Layer CS SAP Service-Specific Service-Specific Convergence Convergence Sublayers Sublayer MAC SAP Mapping Layer MAC MAC Common Part Sublayer MAC Common Part Sublayer Tuning Network Layer Mgt. Sys. Security Sublayer Security Sublayer PHY SAP Mapping Layer PHY Physical Layer (PHY) PHY Layer Data/Control Plane Management Plane Realizes cross- layer functions©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 65
  • 66. Metanoia, Inc. Critical Systems Thinking™Implications …  WiMAX has many options and features  Requires a mapping and tuning layer for translating provider managed services finally to bit/packet-level QoS  Mapping and tuning layer must integrate with service provisioning platform  Requires a unified implementation framework©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 66
  • 67. Metanoia, Inc. Critical Systems Thinking™802.16 Challenges in Practice  Fluctuating channel  Adaptive modulation based on link quality  Link quality fluctuation between very high to very low SNR lead to wide variation in data rates  May affect pkt level performance  TCP and BS scheduler  Inappropriate scheduling may lead to time-outs  BW grants need to take into account congestion window  TCP over OFDM  Interactions of TCP over OFDM and fading channel not yet fully understood  OFDMA  Performance degrades due to Doppler spread©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 67
  • 68. Metanoia, Inc.Critical Systems Thinking™ Future of WiMax and Applicability to Military Communications
  • 69. Metanoia, Inc.IEEE 802.16j Mobile Multi-hop Critical Systems Thinking™Relay for Military Mesh Network  Network Elements  MMR BS  Relay Station (RS)  Fixed RS (FRS)  Nomadic Relay Station (NRS)  Typical military environment …  RS pre-planned  Antenna heights less than in a commercial env.  Redundant routes between RS and MMR-BS  Support for NRS©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 69
  • 70. Metanoia, Inc. Critical Systems Thinking™Features of 802.16e  PHY Layers  OFDMA 2048, 1024, 512 FFT modes  STC, MIMO  Extensions for H-ARQ  MAC  Handover support  Power management  Multi-zone frame structure  Frame partitioned into multiple zones  Different sub-channelization schemes supportable in each zone©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 70
  • 71. Metanoia, Inc. Critical Systems Thinking™Mobile Broadband Standardization  Various standards (all based on OFDMA + MIMO)  802.16e  802.16m  3GPP Long Term Evolution (LTE)  3GPP UMB  802.20  IMT-Advanced  May harmonize various projects  Global low-cost 4G standard may emerge based on OFDMA©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 71
  • 72. Metanoia, Inc.Critical Systems Thinking™ Thank You! Questions?
  • 73. Metanoia, Inc.Critical Systems Thinking™ Glossary and References
  • 74. Metanoia, Inc. Critical Systems Thinking™ GlossaryAAS Adaptive Antenna Systems CID Connection IdentifierABR Available Bit Rate CINR Carrier to Interference plus Noise RatioACK Acknowledgement CLP Cell Loss PriorityADSL Assymetrical Digital Subscriber Line CLR Cel Loss RatioAMC Adaptive Modulation and Coding CoS Class-of-ServiceARQ Automatic Repeat Request CPS Common Part SublayerATM Asynchronous Transfer Mode CQICH Channel Quality Indicator ChannelAWGN Additive White Gaussian Noise CRA Contention Ratio AlgorithmBE Best Effort CRC Cyclic Redundancy CheckBER Bit Error Rate CRC Contention Ratio CalculatorBoD Bandwidth-on-Demand CS Convergence Sublayerbps bits per second CSA Contention Slot AllocatorBPSK Binary Phase Shift Keying CSMA/CA Carrier Sense Multiple Access/Collision AvoidanceBS Base Station DA-FDRR Demand-Aware Fair Deficit Round RobinBSN Block Sequence Number DC Direct CurrentBWA Broadband Wireless Access DCD Downlink Channel DescriptorCAC Connection Admission Control Diffserv Differentiated ServicesCBR Constant Bit Rate DIUC Downlink Interval Usage CodeCDMA Code Division Multiple Access DL DownlinkCH Channel DOCSIS Data Over Cable Service Interface SpecificationCI CRC Indicator©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 74
  • 75. Metanoia, Inc. Critical Systems Thinking™ GlossaryDRR Deficit Round Robin H-FDD Half Frequency Division DuplexDSL Digital Subscriber Line HT Header TypeEC Encryption Control HTTP Hyper-Text Transfer ProtocolEKS Encryption Key Sequence IFFT Inverse Fast Fourier TransformEV-DO EVolution Data Optimized IFS Inter-Frame SpacingFDD Frequency Division Duples Intserv Integrated ServicesFDMA Frequency Division Multiple Access IP Internet ProtocolFEC Forward Error Correction ISI Inter-Symbol InterferenceFFSH Fast-Feedback Allocation Sub-Header KHz KilohertzFFT Fast Fourier Transform LAN Local Area NetworkFIFO First-In First-Out LEN LengthFSH Fragmentation Sub-Header LOS Line-of-SightFSN Fragment Sequence Number MAC Media Access ControlFTP File Transfer Protocol MAN Metopolitan Area NetworkFUSC Full Usage of Sub-Channels MHz MegahertzGBN Go-Back-N MIMO Multi-Input Multi-OutputGFR Generic Frame Rate MPDU MAC Protocol Data UnitGMSH Grant Management Sub-Header MPLS Multi-Protocol Label SwitchingGSM Global System for Mobile Communications MSDU MAC Service Data UnitHARQ Hybrid ARQ NACK Negative AcknowledgementHCS Header Check Sequence©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 75
  • 76. Metanoia, Inc. Critical Systems Thinking™ GlossaryNFS Network File System QoS Quality-of-ServiceNLOS Non Line-of-Sight QPSK Quadrature Phase Shift Keyingnrt-PS Non Real-Time Polling Service Rcv ReceiveO-DRR Opportunistic Deficit Round Robin Rcvr ReceiverOFDM Orthogonal Frequency Division Multiplexing REQ RequestOFDMA Orthogonal Frequency Divison Multiple Access RNG RangingO-FUSC Optional-Full Usage of Sub-Channels RSP ResponseO-PUSC Optional-Partial Usage of Sub-Channels RSSI Received Signal Strength IndicatorPAR Project Authorization Request Rsv ReservedPCR Peak Cell Rate rt-PS Real-Time Polling ServicePDU Protocol Data Unit Rv ReservedPER Packet Error Rate Rx ReceiverPHSI Payload Header Suppression Index SAP Service Access PointPHSI Payload Header Suppression SC Single CarrierPHY Physical Layer SCR Sustainable Cell RatePM Poll Me SDU Service Data UnitPSH Packing Sub-Header SFID Service Flow IDPTI Payload Type Indicator SI Slip IndicatorPUSC Partial Usage of Sub-Channels SINR Signal to Interference plus Noise RatioQAM Quadrature Amplitude Modulation SNMP Simple Network Management Protocol©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 76
  • 77. Metanoia, Inc. Critical Systems Thinking™ GlossarySNR Signal to Noise Ratio VoIP Voice-over-IP VPI Virtual Path IdentifierS-OFDMA Scalable Orthogonal Frequency Division Multiple Access WDRR Wireless Deficit Round RobinSR Selective Repeat WG Working GroupSS Subscriber Station Wi-Fi Wireless Hi-FidelityTC Traffic Category WLAN Wireless LANTCP Transmission Control ProtocolTDD Time Division DuplexTDMA Time Division Multiple AccessTFTP Trival File Transfer ProtocolTLV Type-Length-ValueTx Transmitter or TransmitUBR Unspecified Bit RateUCD Uplink Channel DescriptorUF-DRR Uniformly Fair Deficit Round RobinUGS Unsolicited Grant ServiceUIUC Uplink Interval Usage CodeUL UplinkVBR Variable Bit RateVCI Virtual Circuit IdentifierVOD Video-on-Demand©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 77
  • 78. Metanoia, Inc. Critical Systems Thinking™References and Readings (1)  [FaL02] H. Fattah and C. Leung, “A Efficient Scheduling Algorithm for Packet Cellular Networks,” in Proc. VTC, vol. 4, pp. 2419-2423, September 2002.  [GWA05] A. Ghosh, G. R. Walter, J. G. Andrews, and R. Chen, “Broadband Wireless Access withWiMax/8O2.16: Current Performance Benchmarks and Future Potential,” IEEE Commun. Magazine, vol. 45, pp. 129-136, February 2005.  [IEEE04] LAN/MAN Standards Committee, “IEEE Standards for Local and Metropolitan Area Network: Part 16: Air Interface for Fixed Broadband Wireless Access Systems,” IEEE Computer Society and IEEE Microwave Theory and Techniques Society, May 2004.  [IEEE05] LAN/MAN Standards Committee, “IEEE Standards for Local and Metropolitan Area Network: Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems (Amendments for Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands),” IEEE Computer Society and IEEE Microwave Theory and Techniques Society, September 2005.  [RBS06a] H. Rath, A. Bhorkar, and V. Sharma, “An Opportunistic Deficit Round Robin (O-DRR) Uplink Scheduling Scheme for Wi-Max Networks,” Proc. IETE Int’l Conf. on Next-Generation Networks (ICNGN’06), Mumbai, 9-11 February, 2006.©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 78
  • 79. Metanoia, Inc. Critical Systems Thinking™References and Readings (2)  [RBS06b] H. Rath, A. Bhorkar, and V. Sharma, “An Opportunistic Uplink Scheduling Scheme to Achieve Bandwidth Fairness and Delay for Multiclass Traffic in Wi-Max (IEEE 802.16) Broadband Wireless Networks,” to appear IEEE Globecom’06, San Francisco, CA, 27 Nov. – 1 Dec. 2006.  [ShV96] M. Shreedhar and G. Varghese, “Efficient Fair Queueing Using Deficit Round Robin,” IEEE/ACM Trans. on Networking, vol. 4, no. 3, pp. 375-385, June 1996.  [SRK03] S. Shakkottai, T. S. Rappaport, and P. C. Karlsson, “Cross Layer Design for Wireless Networks,” IEEE Commun. Magazine, vol. 41, no. 10, pp. 74-80, October 2003.  [Vam06] N. Vamaney, “Scheduling in IEEE 802.16 Metropolitan Area Networks,” M. Tech. Dissertation, Dept. of Electrical Engineering, IIT Bombay, September 2006.©Copyright 2006-07All Rights Reserved Milcom’07, 29-31 October 2007, Orlando, FL 79