Quality of Service in WiMAX and LTE Networks

Mehdi Alasti and Behnam Neekzad, ClearwireJie Hui and Rath Vannithamby, Intel Labs

IEEE Communications Magazine • May 2010

報告者：李宗穎

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Outline

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

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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

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QoS in IEEE 802.16eThe QoS framework in IEEE

802.16e is based on service flows

Service Flow

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802.16e Service Flow Management

Dynamic Service Change (DSC) Dynamic Service Delete (DSD) Dynamic Service Activate (DSA)

NULL

OPERATIONAL

DSD

DSA

DSC

802.16eMS

802.16eBS

DSA_REQ

DSA_RSP

DSX_RVD

DSA_ACK

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802.16e Service Flow ID (SFID)

Name SIZE

I Uplink/Downlink 1

S Maximum sustained traffic rate 6

T Traffic indication preference (Sleeping mode) 1

B Maximum traffic burst 6

R Minimum reserved traffic rate 6

L Maximum latency 6

S Fixed-length VS variable length SDU indicator 1

P Paging preference (Idle mode) 1

R Reserved 4

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Service Flow Types in IEEE 802.16

Unsolicited grant service (UGS) Supports real-time traffic with fixed-size data packets o

n 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

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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 (CDM

A)-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

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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 silenc

e-to-talk-spurt transition

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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

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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 suppor

t the adaptation of both the allocation size and inter-arrival

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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 (AM

S) UL allocation GPI with grant size ABS poll AMS for BR periodically every GPI

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aGP mechanism

During a service, the traffic characteristics and QoS requirements may change adaptation of scheduling state includes switchin

g between using primary and secondary SF QoS parameters or changing the GPI and/or grant size

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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 he

ader 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

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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

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Contention-based Random Access BW-REQ

5-step contention-based BW-REQ 3-step contention-based BW-REQ

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Delayed BR for BE

The service-specific BR header specifies a minimum grant delay to 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

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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

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LTE QoS Framework The traffic running between a particular client application

and a service can be differentiated into separate service data flows (SDFs)

SDFs mapped to the same bearer receive a common QoS treatment

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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

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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

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LTE standardized QCI characteristics

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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 ce

lls

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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 pr

ocedure Short format can be used to report on one radio bearer group Long format one can be used for four groups

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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

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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

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802.16 and LTE comparison (3/3)

QoS handling in the control plane The SF QoS parameters are signaled in IEEE 8

02.16 via DSx/AAI-DSx messages In LTE the QCI and associated nine standardize

d characteristics are not signaled on any interface

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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