Throughput-Guaranteed Resource-Allocation

Algorithms for Relay-Aided Cellular OFDMA System

1Megumi Kaneko, 2Petar Popovski, and 1Kazunori Hayashi

1 Graduate School of Informatics, Department of Systems Science, Kyoto University (京都大學 ), Japan2 Department of Electronic Systems, Aalborg University (奧爾堡大學 ), Denmark

< IEEE Transactions on Vehicular Technology, vol. 58, no. 4, MAY 2009 >

Outline

• Introduction

• System model

• Goal

• Proposed Resource-Allocation Algorithms– Single-Relay Case: FTD and ATD

– Multiple-Relay Case: MRPA and MRAA

• Performance

• Conclusion

Introduction

• Installing relay stations in strategic positions in a cell– higher data rates can be provided in remote or shadowed areas

of the cell

– low-cost devices that can easily be deployed

BS

RS

MS

Direct link

Relayed link

Relayed link

Introduction

• This paper investigates the problem of resource allocation for a relay-aided cellular system based on OFDMA.

• This paper focuses on the downlink (DL) transmission from a BS to mobile stations (MSs) or RS in a single cell.

BS-Subframe (TBS)

BS–MSor

BS–RS

RS-Subframe (TRS)

RS–MS

TF

Time

Freq.

System model

• Relay station– stores the received packets

– decodes the received packets

– re-modulates the received packets

• Assume that packets sent to the RS in a frame cannot immediately be forwarded due to hardware limitations– The data for relayed users takes two frames to be delivered.

– The data for direct users takes one frame.

System model

• MSs feed back to the BS their CSI on every subchannel.– CSI = Channel-State Information

• Assumption that BS knows the achievable rate rk,n

– for each user k on subchannel n

• Path Selection– A user is linked to the RS only if rk

RS-MS 2 rkBS-MS ;

– Otherwise, it is linked to the BS.

Goal

• The BS-subframe is shared between the – direct users and BS-RS links

– If the BS forwarded all the packets for the relayed users as they arrive in the BS queue, there will be less resource that is available for the direct users.

BS-Subframe (TBS)

BS–MSAND

BS–RS

RS-Subframe (TRS)

RS–MSTime

Freq. relayed users

direct users

Goal

• The target of this work is to design an algorithms with good throughput and outage performance.– Single-Relay Case

– Multiple-Relay Case

RSBS

MS1

MS2

r1 > r2Outage !

r1

r2

Proposed Resource-Allocation Algorithms

• RS makes its own initial allocation to minimize the outage.

• BS optimizes the final allocation to improve the overall throughput.

– Single-Relay Case: FTD and ATD

– Multiple-Relay Case: MRPA and MRAA

BS-Subframe (TBS)

BS–MSor

BS–RS

RS-Subframe (TRS)

RS–MS

TF/2 TF/2

Single-Relay Case: FTDFixed Time-Division Algorithm

• RS makes its own initial allocation to minimize the outage.– rk,n : achievable rate on subchannel n for user k

– βk (t–1) : previous average rate for user k

– R : the minimum data rate requirement for user k

BS-Subframe (TBS)

BS–MSor

BS–RS

RS-Subframe (TRS)

RS–MS

TF/2 TF/2

3181.1

350350

300330)1(

,,

Rt

nknk

k

r

Average rates are higher than their required rates

42283.0

350350

300250)1(

,,

Rt

nknk

k

r

Single-Relay Case: FTDFixed Time-Division Algorithm

• RS makes its own initial allocation to minimize the outage.– rk,n : achievable rate on subchannel n for user k

– βk (t–1) : previous average rate for user k

– R : the minimum data rate requirement for user k

BS-Subframe (TBS)

BS–MSor

BS–RS

RS-Subframe (TRS)

RS–MS

TF/2 TF/2

Average rates are lower than their required rates

Single-Relay Case: FTDFixed Time-Division Algorithm

• If user k has the higher φ and its packets are queued at the RS, the user k is serviced first by RS.

• If user k has the higher φ than the allocated one but its packets are not queued at the RS, RS sends a Request Message to the BS.– User k set UReq

– φmax : The maximum value of φ for user in UReq

BS-Subframe (TBS)

BS–MSor

BS–RS

RS-Subframe (TRS)

RS–MS

TF/2 TF/2

Single-Relay Case: FTDFixed Time-Division Algorithm

BS

RS

MS1 MS2 MS3 MS4

DL Queue: MS1, MS2

φ1= 500 φ2= 600 φ3= 900 φ4= 400

DL Queue: MS3, MS7

φmax

φmin

φ3…

UReq

Single-Relay Case: FTDFixed Time-Division Algorithm

• BS optimizes the final allocation to improve the overall throughput.– BS calculates the number of sub-channels nBR that are required t

o send all the packets that are queued at the BS of the users in UReq.

– The φ metric of the direct user is compared with φmax, and the sub-channel n is allocated to the link with the highest value.

RS-Subframe (TRS)

RS–MS

TF/2 TF/2

BS-Subframe (TBS)

BS–MSor

BS–RS

φ

φmax

direct user

RS

BS

(950)

(400)

UReq (φmax)

Single-Relay Case: FTDFixed Time-Division Algorithm

• Channel utilization:

Number of allocated time slots for user k

Number of allocated packets for user kBM / RM

BS-Subframe (TBS)

BS–MS (BM)or

BS–RS

RS-Subframe (TRS)

RS–MS (RM)

TF

Single-Relay Case: FTDFixed Time-Division Algorithm

• Throughput:

Number of allocated time slots for user k

1 or 0

Single-Relay Case: ATDAdaptive Time-Division Algorithm

• Starting from the allocation by the FTD algorithm for TBS = TRS = TF /2, time division can be adapted to increase the overall throughput.

BS-Subframe (TBS)

BS–MSor

BS–RS

RS-Subframe (TRS)

RS–MS

TF/2 TF/2

Multiple-Relay Case: MRPAMultiple-RS Parallel with Activation Algorithm

• Path Selection (user k is on direct or relayed link)– User id linked to the RS only if ;

otherwise, it is linked to the BS. Due to• The data for relayed users takes at least two frames to be delivered.

• The data for direct users takes only one frame.

Direct link

Relayed link

BS-Subframe (TBS)

BS–MSor

BS–RS

RS-Subframe (TRS)

RS–MS

TF/2 TF/2

BS

RS

MS

Direct link

Relayed link

Multiple-Relay Case: MRPAMultiple-RS Parallel with Activation Algorithm

• If the number I of relays is an even number, there are I/2 relay pairs by regrouping the diametrically opposed relays.– Frequency reuse because of minimized interference.

• FTD-based resource allocation.

BS

RS1

RS6

RS5

RS4

RS3

RS2

Direct link

Relayed link

Multiple-Relay Case: MRPAMultiple-RS Parallel with Activation Algorithm

• If the number I of relays is an even number, there are I/2 relay pairs by regrouping the diametrically opposed relays.– Frequency reuse because of minimized interference.

• FTD-based resource allocation.

BS

RS1

RS6

RS5

RS4

RS3

RS2

Direct link

Relayed link

Multiple-Relay Case: MRAAMultiple-RS Adaptive Activation Algorithm

• Without assuming frequency reuse.

• RSj with the worst throughput is removed, and the RSj-subframe is reallocated to the BS-subframe.

– For higher throughput performance

– ATD-like resource allocation

BS

RS6

RS4

RS3

RS2

Performance– 實驗參數

• BS Cell : 1000m radius

• Relay placed in 800m away from BS

• BS/RS Power: 20/5 W

• Subchannels : 12

• Frame duration : 12 ms

• Packet arrive at BS : Poisson process

Performance – Single-Relay Case

Upper Bound

All Fwd: Relays selected in random w/o UReq

PFS: Proportional Fair Scheduling w/o considering R and w/o Relays

Upper / Lower Bound

Packets from BS through RS to MS is in the same frame

Performance – Single-Relay Case

Lower Bound

All Fwd: Relays selected in random w/o UReq

PFS: Proportional Fair Scheduling w/o considering R and w/o Relays

Upper Bound (throughput)

Performance – Multiple-Relay Case

Upper Bound

PFS: Proportional Fair Scheduling w/o considering R and w/o Relays

Performance – Multiple-Relay Case

Lower Bound

PFS: Proportional Fair Scheduling w/o considering R and w/o Relays

Conclusion

• This paper investigated the problem of resource allocation for a relay-aided cellular system based on OFDMA.

• Design FTD, ATD, MRPA and MRAA algorithms for good throughput and outage performance.

The End

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