A serve flow management strategy for IEEE BWA system in TDD mode Hsin-Hsien Liu

Outline Introduction PHY and MAC layers The QoS management for IEEE Proposed service flow management Simulation results Conclusion

Introduction IEEE 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  GHZ, Mbps a was completed in January 2003  2-11 GHZ, up to 75 Mbps

Introduction d upgrade to the a was approved in June 2004 (now named ) and primarily introduces some performance enhancement features in uplink e is underway, which to support mobility up to speeds of mi/h Their main advantage is their fast deployment which can result in cost savings

Introduction IEEE MAC protocols have been proposed to support QoS guarantees for various kinds of applications IEEE 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 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 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 Since 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

The QoS management for IEEE

Proposed service flow management for IEEE The hierarchical structure of bandwidth allocation

Proposed service flow management for IEEE Bandwidth requirement can be measured by the maximum sustained traffic rate (r max ) and the minimum reserved traffic rate (r min ) r max and r min 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

Simulation results

Conclusion A 2-layer service flow management architecture for IEEE 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 Standard-Local and Metropolitan Area Networks-part 16. IEEE Jianfeng Chen; Wenhua Jiao; Hongxi Wang; “A Service flow Management Strategy for IEEE Broadband Wireless Access Systems in TDD Mode”, Communications, ICC IEEE International Conference on Volume 5, May 2005 Page(s): K. Wongthavarawat, and A. Ganz, “Packet Scheduling for QoS Support in IEEE Broadband Wireless Access Systems”, International Journal of Communication Systems, Vol. 16, P81-96,