1. Performance Analysis of an innovative scheduling algorithm for OFDMA based IEEE 802.16a systems E. Baccarelli, M.Biagi, C.Pelizzoni, N.Cordeschi This work has been partially supported by Italian National project: Wireless8O2.16 Multi-antenna mEsh Networks (WOMEN)under grant number 2005093248.

2. Outline  Introduction to the 802.16 Systems  Description of the IEEE 802.16 standard  The proposed algorithm of Scheduling for IEEE 802.16 systems  Test model and simulation results  Conclusions

3. Innovative Contributions  Definition of a new strategy of scheduling for IEEE 802.16 systems, able to support  multiservice traffic  adaptive modulation  Implementation of the scheduling algorithm by adopting the “OPNET simulator”  Performance analysis of the proposed scheduling algorithm in terms of transfer delay, jitter and throughput

4. Frequency: 2-11 GHz Non line of Sight Centralized Access Control Connection-Oriented MAC QoS implemented with a proper packet queuing and scheduling strategy Adaptive modulation and coding SS3 BS SSn Ethernet LAN IP Backbone CS 1 CS 2 CS 3 CS 1 CS 2 CS 3 Ethernet LAN IEEE 802.16 Systems UL-MAP downlink uplink Requested band Allocated band BS: Base Station SS: Subscriber Station CS : Service Category

5. Stack Protocol Convergence Sublayer (CS) Mapping of MAC SDUs onto the 802.16 service classes MAC Common Part Sublayer (CPS) Radio Access Control Traffic transport in variable length MAC PDUs (fragmentation, packing) PHYsical layer Adaptive modulation and coding

6. Supporting of the QoS  Service classes  Always on Sources  Peridically guaranteed bandwidth  Cell-based traffic E.g.: Voice over IP UGS  On/Off Sources  Fixed bandwidth and garanteed on demand  packet-based Traffic E.g.: Video Conferences  Sorgenti On/Off  Minimum guaranteed bandwidth on demand  packet-based Traffic E.g.:TCP, Telnet  On/Off Source  packet-based Traffic E.g.: E-mail rtPS BE nrtPS Unsolicited Grant Servicereal time Polling Service non real time Polling Service Best Effort

7. Modulation based on the current channel state  Adopted Modulations 1.QPSK 2.16 QAM 3.64 QAM Adaptive Modulation

8. Frame Structure  FCH (Frame Control Header): contains information on DL-MAP  DL–MAP : indicates the bursts position in the downlink frame and the currently adopted modulation and coding scheme  UL-MAP : indicates the bursts position allowed to the SS into the uplink frame and the modulation and coding scheme to be adopted  Frame length: 2 ms  roll-off : 0.25  Channel bandwidth: 10 MHz 14400 simbols per frame DL burst 2 OFDMA symbol uplink DL burst 2 Preambolo FCH DL - MAP UL - MAP sottocanale ranging downlink N° logico sottocanale DL burst 1 DL burst 2 DL burst 3 DL burst 4 UL burst 1 UL burst 5 UL burst 3 UL burst 4 UL burst 2 DL burst 5

9. OFDMA (1/2) Subchannel s  An 802.16a OFDMA symbol contains 60 sub-channels with 2 cluster each  Any cluster is composed by 14 adjacent sub-carriers (2 pilots sub-carriers e 12 data sub- carriers ) Cluster structure for even symbols Cluster structure for odd symbols Subchannel 1 Pilot Carriers Subchannel 2 Subchannel s

10. time Subchannels OFDMA (2/2) Sub-channels allocation to different transmit users Advantages Resource adaptive allocation Mitigation of the intra-cell interference Mitigation of the inter-cell interference Increasing of the uplink power efficiency Counterparts High sensitivity to time and frequency synchronization errors

11. It divides the available band to the different traffic classes by adopting a strictly hierarchic algorithm It updates the available band basing on current modulation scheme Base Station DL Scheduler(1/2) DL Frame Available bandwidth Residual bandwidth

12. Base Station DL Scheduler(2/2) Modified Largest Weighted Delay First (M-LWDF)- It determinates the priority by using the following la relation Allowed band to the current frame Connection equivalent band Packet delay on the top of the sub-queue Modified Proportional Fair (M-PF)- It determinates the priority by adopting the following relation T i = Maximum allowable delay = probability to overcome T i threshold Allowed band to the current frame Connection mean rate Packet delay on the top of the sub-queue

13. Simulation Tool ®

14. Performance analisys for rtPS traffic (1/2) Checking for the IEEE 802.16 QoS constraints  Downlink transmission  QPSK modulation  Maximum system capacity : 14.4 Mb/s  Total traffic 15.5 Mb/s  Guaranteed traffic 14.1 Mb/s  T i =10 ms,  Downlink transmission  QPSK modulation  Maximum system capacity : 14.4 Mb/s  Total traffic 15.5 Mb/s  Guaranteed traffic 14.1 Mb/s  T i =10 ms, Task Operating conditions Performance parameters  Transfer delay  Jitter  Throughput  Transfer delay  Jitter  Throughput

15. Jitter Transfer delay Output data rateInput data rate Performance analysis of rtPS traffic (2/2)

16. Checking for the IEEE 802.16 QoS constraints Task Condizioni di sistema Performance parameters  Transfer delay of 4 service traffic classes  Downlink transmission  QPSK modulation  Maximum system capacity : 14.4 Mb/s  Total Traffic 16.7 Mb/s  Guaranteed traffic 14.2 Mb/s  rtPS (, T i =10 ms)  nrtPS (, T i =10 ms)  Downlink transmission  QPSK modulation  Maximum system capacity : 14.4 Mb/s  Total Traffic 16.7 Mb/s  Guaranteed traffic 14.2 Mb/s  rtPS (, T i =10 ms)  nrtPS (, T i =10 ms) Performance analysis of heterogeneous traffic (1/2)

17. Transfer delay (UGS) Transfer delay (rtPS) Transfer delay ( nrtPS) Transfer delay (BE) Performance analysis of heterogeneous traffic (2/2)

18. Task Operating conditions Performance parameters  Transfer delay of 4 service traffic classes  Downlink transmission  Adaptive modulation (QPSK, 16 QAM, 64 QAM)  Total traffic 16.7 Mb/s  Guaranteed traffic 14.2 Mb/s  rtPS (, T i =10 ms)  nrtPS (, T i =10 ms)  Downlink transmission  Adaptive modulation (QPSK, 16 QAM, 64 QAM)  Total traffic 16.7 Mb/s  Guaranteed traffic 14.2 Mb/s  rtPS (, T i =10 ms)  nrtPS (, T i =10 ms) Performance analisys with heterogeneous traffic and adaptive modulation (1/2) Checking for the IEEE 802.16 QoS constraints when adaptive modulation is supported Checking for the IEEE 802.16 QoS constraints when adaptive modulation is supported

19. Performance analisys with heterogeneous traffic and adaptive modulation (1/2) Transfer delay rtPS Transfer delay (s) Transfer delay nrtPS Transfer delay (s) Transfer delay (BE) Transfer delay (s)

20. Conclusions The adopted strategy of scheduling is able: to fully meet the QoS constrains in terms of transfers delay to efficiently manage the available bandwidth to efficiently manage the heterogeneous traffic to support the adaptive modulation letting the traffic transfer delay jitter be controlled basing it on the channel state conditions The adopted strategy of scheduling is able: to fully meet the QoS constrains in terms of transfers delay to efficiently manage the available bandwidth to efficiently manage the heterogeneous traffic to support the adaptive modulation letting the traffic transfer delay jitter be controlled basing it on the channel state conditions