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28th May 2006
Implementation and Evaluation of a MAC Scheduling Architecture for IEEE 802.16 WirelessMANs
byAbhishek Maheshwari
under the supervision ofDr. Bhaskaran Raman
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OutlineMotivationIEEE 802.16 MACProblem StatementRelated WorkScheduling ArchitectureNS-2 ImplementationSimulation AnalysisConclusionsFuture Work
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MotivationFeatures
Large spamming area (up 30 miles)Data rate (variable and high up to 75 Mpbs)Large frequency band (2-11 GHz)NLOSMobilityTDD and FDD modesPMP and Mesh networksHalf and Full duplex modesEasy deployment
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Motivation
ApplicationsDisaster recovery placesWiFi backhaulQoS for VoIP and other real-time applicationsWireless access to rural areasA replacement of DSLWeb access at home and commercial places
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IEEE 802.16 ArchitectureBase Station (BS)Subscriber Station (SS)Only BS-SS communicationTDMA MAC styleUplink (SS to BS) and Downlink (BS to SS)
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IEEE 802.16 MAC
Connection formation through management messagesRequest-Grant mechanism for slot allocationSlots are specified in UL-MAPEach SS sends data in specified slotsThree ways – contention, piggyback and use granted slots
Frame
Downlink Uplink Bandwidth
Data uplink
Ranging
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Problem StatementScheduling Architecture for slots allocationEvaluation of scheduling architectureComparative performance analysis with and without bandwidth contention period
Why simulationsDeployed architecture is not availableEasy and fast first level testing through simulations
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IEEE 802.16 MAC QoSFour Flows types
UGS – CBR traffic (VoIP without silence)rtPS – VBR traffic (VoIP with silence, video traffic)nrtPS – non real-timer traffic (FTP)BE – traffic with no QoS (telnet, http)
Slots allocationGPC – per connection bandwidth allocationGPSS – per SS bandwidth allocation
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Related WorkSupriya (05) – Qualnet, GPSS, weighted max-min fair allocation (uplink) and WFQ (downlink) with constant weightChu(02) – GPSS, WRR (uplink) without mentioned weights, No resultsHawa(02) – PWFQ without priority and weight mentionedMoraes(05) – SSs priority, Transmission + TDMA, two versions for uplink slotsGanz(03) – strict priority with overall bandwidth allocation moduleOh(05) – optimal contention period, 2 times the number of users, one b/w request in each frame
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Weighted Fair Queuing (WFQ)
Bit-by-bit round robinF(i,k,t) = max{F(i,k-1,t),R(t)}+P(I,k,t)/w(i)Round number – the index of round in bit-by-bit round robin schedulingPacket served in finish time orderUpdate round number on each packet arrival or departureScheduling is done based on weights and length of flow queue
classify Finish timecalculation
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Scheduling ArchitectureDesign Goals
Delay bound for real-time (UGS and rtPS flows) trafficQoS to all applications (number and type of flows only matters)GPC slots allocation modeEasy to implement
Design DecisionsWFQ as downlink and uplink scheduling algorithmBit-wise-bit fair allocationGuarantee time bound on packet transmissionProtects responsive flows against unresponsive flows also calledflow isolation
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Scheduling Architecture
Ranging
SS
BS
Classifier
Downlink Period
SS Uplink
CID 1
Data Uplink Period
CID 2 CID 3 CID 4 ……...CID N
IP Packets
UL-MAP
BS Downlink
IP Packets Packets to Link Layer
Packets to Link Layer
Packets from SS
Packets from BS
Classifier
BS Allocation ModuleWFQ
WFQ
Connections Queues
RangingDownlink Period CID 1 CID 2 CID N
NBWC
……...Bandwidth BWC
Classify the packets
based on flowID
GPC allocation
mode
BroadcastChannel
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Other DetailsEach SS can have as many flows and maintains the same number of MAC level queuesBS has only one MAC level queueAdmission controlForever loop and polling time
Connections do not have any packetsBS does not allocate slots for connectionsPolling time – Every connection should be able to communicate its queue information to BS within this timeUnicast request slots from ranging periodChoice of polling time depends on number and types of flows and their weights
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NS-2 Implementation DetailsSupported features
Interface between MAC and LLTDD frame structureGPC mode bandwidth allocationRANG-REQ, REG-REQ, BW-REQ, CONN-REQRANG-RSP, REG-RSP, CONN-RSPIEEE 802.16 MAC frame structureAll four uplink scheduling servicesMAC level packet association based on flowID
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Modified NS-2 Node
Protocol Agent
Link Layer
802.11 PHY
Channel
802.16 MAC
ARP
Routing Agent
Propagationand
antenna models
WFQ
Entry addr classifier
port classifier
Old architecture
802.16 MAC
Link Layer
802.16 MAC
802.11 PHY
Channel
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Simulation AnalysisAssumptions
Only IEEE 802.16 MAC CPS layerNo DCD and UCDNo guard timer for synchronizationNo admission controlNo ARQ/ACK mechanismIEEE 802.11 PHY layer
What we want to evaluateEffect of one type of flow on other type of flowComparative performance analysis of BWC and NBWC modesChoice of bandwidth contention period for BWC mode
MAC common part sublayer
Privacy Sublayer
Service Specific Convergence Sublayer
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Flow Specifications and WeightsUGS – CBR traffic with 28 Bytes packet and 22.4 Kbps rate (G.729 codec)rtPS – Video traces with 64 Kbps (H.263 codec)nrtPS – FTP traffic from ns-2BE – Telnet traffic from ns-2Weights are in the ratio of minimum reserved bandwidth of flows
UGS 22.4rtPS 64.0
nrtPS 100.0
BE 10.0
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Parameter Choices (uplink flows)Data rate 11 MbpsBasic rate 1 MbpsSlot time 8 micro sec
Frame length 10 msec
Uplink frame 8 msec
Downlink frame 2 msec
Ranging period 100 slots (=0.8 msec)
Bandwidth contention 100 slots (=0.8 msec)
Data uplink slots (BWC) 800 slots (=6.4 msec)
Data uplink slots (NBWC) 900 slots (=7.2 msec)
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Delay Analysis of UGS flowsUGS delay increases after a fix number of rtPS flowsUGS flows are not able to send queue information to BS in contention manner
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Delay Analysis of UGS flowsIncrement in delay is linear for nrtPS flowsUGS queues relatively non-active than nrtPS queues
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Delay Analysis of UGS flowsUGS delay is constant with BE flowsPackets are very rare in BE flows thus fewer BE connection take part in contention
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Delay Analysis of UGS flowsUGS delay is more affected by nrtPSflows
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Delay Analysis of rtPS flowsrtPS delay is irregular but lies in a certain rangertPS flows needs more slots to convey queue information to BS
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Delay Analysis of rtPS flows
rtPS delay increases in NBWC mode also with nrtPS flowsrtPS delay increases linearly after a certain number of nrtPS flows in BWC mode
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Throughput Analysis of rtPS flowsWith UGS flows sudden decrement in throughput then stableUGS flows occupy the slots which were previously allocated to nrtPS flows
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Total Throughput in BWC and NBWC modes
For rtPS and BE flows total throughput is sameFor nrtPS flows NBWC mode throughput is higher
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Total Throughput in BWC and NBWC modes
Total throughput achieved for nrtPS flows is more in NBWC mode
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Total Throughput in BWC and NBWC modes
Similar to throughput of nrtPS flows graphThroughput of NBWC mode is higher than BWC mode
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Optimum value of Bandwidth Contention
For 30 UGS flows delay is minimum at 100 slotsrtPS delay is not very regular
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Comparison between BWC and NBWC modes
Average UGS delayAlmost constant but higher in BWC mode with BE flowsLinear increase with nrtPS flows but with higher slop in BWC modeAlmost constant up to a certain number of rtPS flows than linear increment in BWC mode while constant in NBWC mode
Average rtPS delayIrregular delay behavior of rtPS flows in BWC modeDelay is more in BWC mode in all cases
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Comparison between BWC and NBWC modes
nrtPS throughout Decreases linearly with rtpS and BE flows in both modesSudden decrement then stable with UGS flows in both modes
Total throughout Similar to nrtPS throughputAlmost constant with BE flows in both modesLies in certain range with rtPS flows in both modesSudden decrement then stable with UGS flows in both modes
NBWC mode perform better or equivalent with BWC mode
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Parameter Choices (downlink flows)Data rate 11 MbpsBasic rate 1 MbpsSlot time 8 micro sec
Frame length 10 msec
Uplink frame 2 msec
Downlink frame 8 msec
Ranging period 25 slots (=0.2 msec)
Bandwidth contention 25 slots (=0.2 msec)
Data uplink slots (BWC) 200 slots (=1.6 msec)
Downlink slots 1000 slots (=8.0 msec)
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Delay Analysis
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Throughput AnalysisExpected outputLinear decrement with BE and rtPSflowsSudden decrement then stable with UGS flows
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ConclusionsSimple approach
Only minimal required modulesWFQ well known for 20 decades nowOne module with two copy
NBWC mode completely remove the bandwidth contention periodRemove the possibility of collision at BSOverhead is less compared to BWC mode
PerformanceDelay is less in all case in NBWC modeThroughput is higher because of removal of bandwidth contention period
DrawbackForerver loopPolling time concept
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Future Work
ARQ/ACK mechanism implementationFragmentationHTTP traffic as BE flowClassification of packetsOrder of bandwidth contention periodPolling time calculationDynamic variation in framesize
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Acknowledgements
Ayush Ghai and Nihit PurwarAlexander SayenkoDr. Sridhar Iyer
Thank You ☺
Questions ?