Quality of Service in WiMAX and LTE Networks

1. Quality of Service in WiMAX and LTE Networks Mehdi Alasti and Behnam Neekzad, Clearwire Jie Hui and Rath Vannithamby, Intel Labs IEEE Communications Magazine • May 2010 報告者：李宗穎

2. Outline • Introduction • QoS in IEEE 802.16e • QoS in IEEE 802.16m • QoS in Long Term Evolution (LTE) • Comparison and Conclusions

3. Introduction • 4G broadband wireless technologies such as IEEE 802.16e, IEEE 802.16m, and 3GPP LTE have been designed with different QoS frameworks • Guarantee different traffic patterns and distinct QoS requirements

4. QoS in IEEE 802.16e The QoS framework in IEEE 802.16e is based on service flows Service Flow

5. 802.16e MS 802.16e BS DSA_REQ DSX_RVD DSD DSC NULL DSA_RSP DSA DSA_ACK OPERATIONAL 802.16e Service Flow Management • Dynamic Service Change (DSC) • Dynamic Service Delete (DSD) • Dynamic Service Activate (DSA)

6. 802.16e Service Flow ID (SFID)

7. Service Flow Types in IEEE 802.16 • Unsolicited grant service (UGS) • Supports real-time traffic with fixed-size data packets on a periodic basis • Real-time polling service (rtPS) • Supports real-time traffic with variable-size data packets on a periodic basis • Non-real-time polling service (nrtPS) • Supports delay-tolerant traffic that requires a minimum reserved rate • Best effort (BE) service • Supports regular data services

8. IEEE 802.16 BandwidthRequest (BR) and Grant Mechanism • Contention-based (nrtPS、BE) • BS allocates bandwidth for the BR message • MS uses a code-division multiple access (CDMA)-based mechanism • Contention free-based (rtPS、nrtPS) • piggybacked bandwidth request • BS polls MS periodically • set poll me (PM) bit in the header of a UGS

9. Request/Grant for ertPS (802.16e) • using by VoIP with silence suppression • during a talk spurt • BS provides unicast grants in an unsolicited manner as in UGS • An MS uses its periodic allocation for both data transfer and bandwidth request adjustments • during a silence period • the allocation is taken from the ertPS SF • the MS sends a BR message to the BS with a silence-to-talk-spurt transition

10. IEEE 802.16m QoS Framework • IEEE 802.16m advanced air interface (AAI), provides a more flexible and efficient QoS framework • adaptive granting and polling (aGP) service • quick access • delayed BR • and priority controlled access

11. adaptive granting and polling (aGP) service • UGS, ertPS, and rtPS are not efficient for applications such as online games, VoIP with adaptive multi-rate (AMR), and delay-sensitive TCP based services • more flexible QoS scheduling service to support the adaptation of both the allocation size and inter-arrival

12. the new QoS parameters in the aGP service • primary grant polling interval (GPI) and primary grant size; and optional ones: secondary GPI, secondary grant size, and adaptation method • Advanced BS (ABS) grant advanced MS (AMS) UL allocation GPI with grant size • ABS poll AMS for BR periodically every GPI

13. aGP mechanism • During a service, the traffic characteristics and QoS requirements may change • adaptation of scheduling state includes switching between using primary and secondary SF QoS parameters or changing the GPI and/or grant size

14. mix of IEEE 802.16m and legacy IEEE 802.16e • AMS handover from an IEEE 802.16m network to an IEEE 802.16e network • If primary grant size value is equal to the BR header size, it means this aGP SF is primarily polling-based SF, and hence should be mapped to an rtPS SF • Otherwise, this aGP SF is primarily a granting based service, and thus should be mapped to an ertPS SF

15. Quick Access • the BR message is communicated from MS to BS only after random access is successful • Random access delay is a significant part of UL access delay • Quick access in IEEE 802.16m helps reduce the random access delay • Quick Access Message • 12-bit station ID and 4-bit predefined BR index

16. Contention-based Random Access BW-REQ 3-step contention-based BW-REQ 5-step contention-based BW-REQ

17. Delayed BR for BE • The service-specific BR header specifies a minimum grant delayto indicate the minimum delay of the requested grant for BE scheduling service • When an AMS is cleaning out its buffers, in one UL transmission it can send a delayed BR asking for future packet(s) with minimum expected grant delay if AMS can predict the future packet(s) arrival time

18. Priority Controlled Access • An operator can assign AMS with different access classes and block random access from certain AMSs by assigning a minimum access class of the network higher than the access class of those AMSs • The BR timer and random backoff parameters can also use different values to support differentiated random access in IEEE 802.16m

19. LTE QoS Framework • The traffic running between a particularclient application and a service can bedifferentiated into separate service data flows(SDFs) • SDFs mapped to the same bearerreceive a common QoS treatment

20. LTE bearer • A bearer is assigned a scalar value referred to as a QoS class identifier (QCI) • Guaranteed bit rate (GBR) • Non-guaranteed bit rate (non-GBR) • A non-GBR bearer is referred to as the default bearer, which is also used to establish IP connectivity, similar to the initial SF in WiMAX

21. QoS attributes associated with the LTE bearer • QoS class identifier (QCI) • A scalar representing a set of packet forwarding treatments • Allocation and retention priority (ARP) • A parameter used by call admission control and overload control • Maximum bit rate (MBR) • Guaranteed bit rate (GBE) • Aggregate MBR (AMBR) • The total amount of bit rate of a group of non-GBR bearers

22. LTE standardized QCI characteristics

23. LTE Air Interface Scheduler • the LTE air interface scheduler uses the following information as input • Radio conditions at the UE identified • The QoS attributes of bearers • The interference situation in the neighboring cells

24. Buffer Status Reporting • The buffer status reporting mechanism informs the UL packet scheduler about the amount of buffered data at the UE • A periodic BSR trigger does not cause a service request (SR) transmission from the UE • Otherwise, the SR is transmitted via a random access procedure • Short format can be used to report on one radio bearer group • Long format one can be used for four groups

25. 802.16 and LTE comparison (1/3) • QoS transport unit • IEEE 802.16  service flow between MS and BS • LTE  bearer between UE and the PDNGW • QoS scheduling types • IEEE 802.16  UGS, ertPS, rtPS, nrtPS, BE, and aGP service • LTE  GBR mechanism is like rtPS; non-GBR mechanism is like BE

26. 802.16 and LTE comparison (2/3) • QoS parameters per transport unit • LTE MBR and GBR are similar to IEEE 802.16 maximum sustained traffic rate and minimum reserved traffic rate • LTE AMBR allows the operator to rate cap the total non-GBR bearers of a subscriber

27. 802.16 and LTE comparison (3/3) • QoS handling in the control plane • The SF QoS parameters are signaled in IEEE 802.16 via DSx/AAI-DSx messages • In LTE the QCI and associated nine standardized characteristics are not signaled on any interface

28. Conclusion • Fourth-generation wireless technologies such as IEEE 802.16e, IEEE 802.16m, and LTE are designed to support current and future QoS needs • This article explains the QoS framework of IEEE 802.16e, IEEE 802.16m, and LTE, and compares their QoS features against each other