310 likes | 386 Views
A serve flow management strategy for IEEE 802.16 BWA system in TDD mode. Hsin-Hsien Liu 2005 11 15. Outline. Introduction PHY and MAC layers The QoS management for IEEE 802.16 Proposed service flow management Simulation results Conclusion. Introduction.
E N D
A serve flow management strategy for IEEE 802.16 BWA system in TDD mode Hsin-Hsien Liu 2005 11 15
Outline • Introduction • PHY and MAC layers • The QoS management for IEEE 802.16 • Proposed service flow management • Simulation results • Conclusion
Introduction • IEEE 802.16 defines the air interface and MAC protocol for a WMAN, intended for providing high-bandwidth wireless voice and data for residential and enterprise use • The first version was completed in December 2001 • 10-66 GHZ, 32-134Mbps • 802.16a was completed in January 2003 • 2-11 GHZ, up to 75 Mbps
Introduction • 802.16d upgrade to the 802.16a was approved in June 2004 (now named 802.16-2004) and primarily introduces some performance enhancement features in uplink • 802.16e is underway, which to support mobility up to speeds of 70-80 mi/h • Their main advantage is their fast deployment which can result in cost savings
Introduction • IEEE 802.16 MAC protocols have been proposed to support QoS guarantees for various kinds of applications • IEEE 802.16 left the QoS based packet-scheduling algorithms that determine the uplink and downlink bandwidth allocation, undefined
Introduction • Several approaches for bandwidth allocation for TDD mode, they only consider the scheduling for uplink sub-frame • Since most paper applies strict priority queue for different class of service, which leads starvation of low priority service when higher priority service is heavy
PHY and MAC layers • The basic architecture consists of one Base Station (BS), and one or more Subscriber Stations (SSs) • The BS regulates all the communication in the network
PHY and MAC layers • The communication path between SS and BS has two directions • Downlink channel (from BS to SS) • Uplink channel (from SS to BS) • IEEE 802.16 has been designed to support FDD and TDD
PHY and MAC layers • On the downlink, the data packets are broadcasted to all SSs and an SS only picks up the packets destined to it • On the uplink, the BS determines the number of time slots that each SS will be allowed to transmit in an uplink subframe • Uplink map message (UL-MAP) contains information element (IE), which include the transmission opportunities
PHY and MAC layers • After receiving the UL-MAP message, the stations transmit their data in pre-defined time slots as indicated in the IE • A scheduling module for the UL is necessary to be kept in the BS in order to determine the transmission opportunities using the bandwidth requests sent by the SSs
Service flow • Unsolicited Grant Service (UGS) • Support real-time service flows that generate fixed-size data packets on a periodic basis • It allocates a fixed numbers of time slots in each time frame • Real-Time Polling Service (rtPS) • Support real-time service flows that generate variable size data packets on a periodic basis
Service flow • Non-Real-Time Polling Service (nrtPS) • Support delay-tolerant data streams consisting of variable-sized data packets for which a minimum data rate is required • Best Effort Service (BE) • Support data streams for which no minimum service level is required and therefore may be handled on a space-available basis
The QoS management for IEEE 802.16 • Admission control • It is used to limit the number of flows admitted into the network • Buffer management • It is deployed to control the buffer size and decide which packet will drop • Scheduling • It is adopted to determine which packet will be service first in specific queue to guarantee its QoS requirement
The QoS management for IEEE 802.16 • Since 802.16 MAC protocol is connection oriented, the application must establish the connection with BS as well as the associated service flow • BS will assign the connection with a unique connection ID (CID) to each uplink or downlink transmission • When a new service generates or updates its parameters, it will sent message (DSA/DSC) to the BS
Proposed service flow management for IEEE 802.16 • The hierarchical structure of bandwidth allocation
Proposed service flow management for IEEE 802.16 • Bandwidth requirement can be measured by the maximum sustained traffic rate (rmax) and the minimum reserved traffic rate (rmin) • rmax and rmin are carried in the DSA and DSC message at the beginning period of connection setup • The minimum reserved traffic rate is used for admission control • The maximum sustained traffic rate is used for scheduling
Admission control • One principle is to ensure the exiting connection’s QoS will not be degraded significantly and new connection’s QoS will be satisfied • For those connections whose Minimum Reserved traffic rate is equal to zero, they can always be accepted, but the QoS will not be guaranteed
Scheduling architecture • First layer scheduling: Deficit Fair Priority Queue (DFPQ) • There is an active list maintained in BS • The DFPQ only schedules the bandwidth application services in the active list • If the queue is empty, it will be removed from active list • The service flows in active list are queued by strict priority shown in Table 1
Scheduling architecture • First layer scheduling: DFPQ • The scheduler visits each non-empty queue in the active list and determines the number of request in this queue • The variable Deficit Counter is incremented by the value Quantum each time when it is visited
Scheduling architecture • First layer scheduling: DFPQ • If Deficit Counter is more than zero , the variable Deficit Counter is reduced by number of bits in the packet and the packet is transmitted to the output port • The process will be repeated until either the Deficit Counter is no more than zero or the queue is empty • If the queue is empty, the value of Deficit Counter is set to zero • When this condition occurs, the scheduler move on to serve the next non-empty priority queue
Scheduling architecture • Second layer scheduling • Three different algorithms are assigned to three classes of service to match its requirement • rtPS connection: earliest deadline first (EDF) • nrtPS connection: weight fair queue (WFQ) • BE connection: the remaining bandwidth is allocated to each BE connection by round robin (BB)
Scheduling architecture • Buffer management • Used to control the buffer size and decide which packets to drop • Timing sensitive traffic has its maximum delay requirement • Buffer management will drop those packets that exceed their maximum delay
Simulation results • The assumption of total bandwidth is 10Mbps • The duration for each frame is 10 ms, so the bandwidth for a frame is 100Kbit • All packet arrivals occur at the beginning of each frame and the packet arrival process for each connection follows the Poisson distribution with different traffic rate λ
Conclusion • A 2-layer service flow management architecture for IEEE 802.16 is proposed • Compared with fixed bandwidth allocation, the proposed solution improves the performance of throughput under unbalanced uplink and downlink traffic • Better performance in fairness can be achieved by the proposed DEFQ algorithm than strict PQ scheduling
Reference • IEEE 802.16 Standard-Local and Metropolitan Area Networks-part 16. IEEE 802.16-2004 • Jianfeng Chen; Wenhua Jiao; Hongxi Wang; “A Service flow Management Strategy for IEEE 802.16 Broadband Wireless Access Systems in TDD Mode”, Communications, 2005. ICC 2005. 2005 IEEE International Conference onVolume 5, 16-20 May 2005 Page(s):3422 - 3426 • K. Wongthavarawat, and A. Ganz , “Packet Scheduling for QoS Support in IEEE 802.16 Broadband Wireless Access Systems”, International Journal of Communication Systems, Vol. 16, P81-96, 2003 • http://www.google.com/