550 likes | 561 Vues
Explore QoS strategies, simulation results, and proposed algorithms for Scheduling in IEEE 802.16 systems. Learn about MAC layer services and QoS architecture in wireless networks.
E N D
Quality of Service Schedulingfor 802.16Broadband Wireless Access Systems Sih-Han Chen Department of Computer Science and Information Engineering National Taipei University of Technology 2006.11.21
Outline • Overview IEEE 802.16 • IEEE 802.16 MAC and QoS • Proposed QoS strategy • Simulation result • Summary and Reference
Wireless Technologies Bandwidth IEEE 802.15 IEEE 802.11 IEEE 802.16 3GPP 1 Gbps 802.15.3 High Speed Wireless PAN 100 Mbps Wi-Fi 802.11a/g Wi-Fi 802.11b Wi-MAX 802.16 (802.16-2004 & 802.16e) 10 Mbps 4G 3G 2.5G 1 Mbps 802.15.1 Bluetooth <1m 10m 100m Up to 50Km Up to 80Km PAN LAN MAN WAN PAN: Personal area networks MAN: Metropolitan area networks LAN: Local area networks Wide area networks
Downlink Subframe Broadcast
Outline • Overview IEEE 802.16 • IEEE 802.16 MAC and QoS • Proposed QoS strategy • Simulation result • Summary and Reference
MAC Convergence Sublayer • Functions: • Classification processing of higher-layer PDUs • Delivery to proper MAC SAP • Receives CS PDUs from peer • Two sublayers specified: • ATM convergence sublayer • Packet convergence sublayer Service Specific Convergence Sublayer (CS)
ATM Convergence Sublayer • ATM cells mapped to MAC frames • Differentiates Virtual Path switched / Virtual Channel switched ATM connections • Assigns channel ID (CID) • Can perform Payload Header Suppression (PHS)
Packet Convergence Sublayer • Used for all packet-based protocols, such as IPv4, IPv6, Ethernet, and VLAN • Similar functions as ATM convergence sublayer, including PHS
Defines multiple-access mechanism Functions : connection establishment connection maintenance Call admission control bandwidth request bandwidth allocation MAC Common Part Sublayer MAC Common Part Sublayer (MPC)
Security Sublayer • Two component protocols • Encapsulation protocol for data encryption • Privacy key management (PKM) • describes how the BS distributes keys to client SS Security Sublayer
Media Acces Control (MAC) • Connection orienteded • Service Flow(SF) • Connection ID (CID) • Channel access: • UL-MAP • Defines uplink channel access • Defines uplink data burst profiles • DL-MAP • Defines downlink data burst profiles • UL-MAP and DL-MAP are both transmitted in the beginning of each downlink subframe (FDD and TDD).
Bandwidth Request • SSs may request bandwidth in 3 ways: • Use the ”contention request opportunities” interval upon being polled by the BS (unicast, multicast or broadcast poll) • Send a standalone MAC message called ”BW request” in an already granted slot • Piggyback a BW request message on a data packet
BS grants/allocates bandwidth in one of two modes Grant Per Subscriber Station (GPSS) Grant Per Connection (GPC) Decision based on requestedBW, QoS parameters and available resources Grants are realized through the UL-MAP Bandwidth Allocation
Service Classes • Unsolicited Grant Services (UGS): • Constant Bit Rate (CBR) services, • T1/E1 emulation, and Voice Over IP (VoIP) • Real-Time Polling Services (rtPS): • real-time services variable size data packets • MPEG video or VoIP with silence suppression. • Non-Real-Time Polling Services (nrtPS): • Used for delay tolerant traffic requiring some minimum data rate • FTP • Best Effort Services (BE) : • Used for streams with no rate guarantees. • WEB , HTTP
QoS mechanisms • Classification • Mapping from MAC SDU fields (e.g destination IP address or TOS field to CID and SFID • Call admission Control • Scheduling • Downlink scheduling module • Uplink scheduling module • No algorithms defined in standard
Call Admission Control in IEEE 802.16 • Admission control • To ensure required QoS is guaranteed while admit a new connection • Assessment of admission connection • Usually use traffic descriptor and effective bandwidth • But… • Traffic descriptors may not reflect the real traffic • Traffic descriptors is very simple (peak rate, avg. rate, etc…) • Users may overestimate their requirements • QoS is uneasy to guarantee
Outline • Overview IEEE 802.16 • IEEE 802.16 MAC and QoS • Proposed QoS strategy • Simulation result • Summary and Reference
Scheduling Algorithm at BS • Define two types of queue • Type (I) queue • Type (I I) queue • Admission Control • Scheduling Algorithm
At BS Scheduling for Type I queue • Type I queue Use for • UGS • Dedicated request opportunities for rtps and nrtps • Guarantee grants to be scheduled without interrupt • First-in First-out (FIFO),is employed
At BS Scheduling for Type II queue • Type II queue Use for • rtPS,nrtPS,and BE • To Guarantee • Minimum bandwidth for each service flow • Fairness to distributing excess bandwidth • To propose a fair queuing algorithm
Type II QueueBandwidth Allocation • Grant Per Connection (GPC) • BiMIN:the minimum reserved bandwidth for connection i • BRi:bandwidth currently demanded by the connection
Call Admission Control (CAC) • The sum of minimum reserved bandwidth for all the connection should not exceed the available bandwidth B
A Extended Issue • It also can be wasted when : • Certain of connections don’t need so much bandwidth • Solution: • It allows the empty connection queue to contribute its unused portion to the next round of excess bandwidth allocation
Scheduling Algorithm at SS • WHY ? • Due to the large Round Trip Delay (RTD) • Possible collision occurred in the uplink channel • So…BS has only limited or even outdated information about each uplink connection
At SS UGS Queue Scheduling • Properties • Critical delay • Critical delay jitter • Firstly guarantee the bandwidth
At SS rpPS Queue Scheduling • Properties • Should meet tight delay bound • Each packet of rtPS should be mark a deline • t:arrival time • tolerated delay:Maximum Latency for each service flow • Schedule base on the deadline stamp
At SS nrtPS Queue Scheduling • Properties • Target at maintaining throughput • Each packed with a virtual time stamp • When a new packer arrives in,the virtual time must be calculated at first
At SS BE Queue Scheduling • Properties • There is no QoS guarantee required • A simple FIFO mechanisms is applied
Outline • Overview IEEE 802.16 • IEEE 802.16 MAC and QoS • Proposed QoS strategy • Simulation result • Summary and Reference
Simulation Environment • Used NS2 • PMP MAC operation • TDD-OFDM • One BS and 20 SSs
Outline • Overview IEEE 802.16 • IEEE 802.16 MAC and QoS • Proposed QoS strategy • Simulation result • Summary and Reference
Summary • Introduced a hierarchicaldistributed QoS • At BS • Guarantee the minimum bandwidth • Fairness distributing excess bandwidth • At SS • Flexible QoS support four service flow • Reduce the delay of real-time application • Guarantee the throughput of non-real-time application
References [1] Sun, J.; Yanling Yao; Hongfei Zhu,“Quality of Service Scheduling for 802.16 Broadband Wireless Access Systems” Vehicular Technology Conference, 2006. VTC 2006-Spring. IEEE 63rd Volume 3, 2006 Page(s):1221 - 1225 [2] Jayaparvathy, R.; Sureshkumar, G.; Kanakasabapathy, P., “Performance evaluation of scheduling schemes for fixed broadband wireless access systems”,2005 13th IEEE International Conference on Volume 2, 16-18 Nov. 2005 Page(s):6 pp. [3] IEEE 802.16 Standard (2004), "IEEE Standard For Local and Metropolitan Area Networks - Part 16:Air Interface for Fixed Broadband Wireless Access Systems".