Throughput-Guaranteed Resource-Allocation Algorithms for Relay-Aided Cellular OFDMA System 1 Megumi Kaneko, 2 Petar Popovski, and 1 Kazunori Hayashi 1 Graduate School of Informatics, Department of Systems Science, Kyoto University ( 京都大學 ), Japan 2 Department of Electronic Systems, Aalborg University ( 奧爾堡大學 ), Denmark

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

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 (T BS ) BS–MS or BS–RS RS-Subframe (T RS ) RS–MS TFTF 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 r k,n –for each user k on subchannel n Path Selection –A user is linked to the RS only if r k RS-MS  2 r k BS-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 (T BS ) BS–MS AND BS–RS RS-Subframe (T RS ) RS–MS Time 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 RS BS MS 1 MS 2 r 1 > r 2 Outage ! r1r1 r2r2

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 (T BS ) BS–MS or BS–RS RS-Subframe (T RS ) RS–MS T F /2

Single-Relay Case: FTD Fixed Time-Division Algorithm RS makes its own initial allocation to minimize the outage. –r k,n : achievable rate on subchannel n for user k –β k (t–1) : previous average rate for user k –R : the minimum data rate requirement for user k BS-Subframe (T BS ) BS–MS or BS–RS RS-Subframe (T RS ) RS–MS T F /2 Average rates are higher than their required rates

Single-Relay Case: FTD Fixed Time-Division Algorithm RS makes its own initial allocation to minimize the outage. –r k,n : achievable rate on subchannel n for user k –β k (t–1) : previous average rate for user k –R : the minimum data rate requirement for user k BS-Subframe (T BS ) BS–MS or BS–RS RS-Subframe (T RS ) RS–MS T F /2 Average rates are lower than their required rates

Single-Relay Case: FTD Fixed 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 U Req –φ max : The maximum value of φ for user in U Req BS-Subframe (T BS ) BS–MS or BS–RS RS-Subframe (T RS ) RS–MS T F /2

Single-Relay Case: FTD Fixed Time-Division Algorithm BS RS MS 1 MS 2 MS 3 MS 4 DL Queue: MS 1, MS 2 φ 1 = 500φ 2 = 600φ 3 = 900φ 4 = 400 DL Queue: MS 3, MS 7 φ max φ min φ3φ3 … U Req

Single-Relay Case: FTD Fixed Time-Division Algorithm BS optimizes the final allocation to improve the overall throughput. –BS calculates the number of sub-channels n BR that are required to send all the packets that are queued at the BS of the users in U Req. –The φ metric of the direct user is compared with φ max, and the sub-channel n is allocated to the link with the highest value. RS-Subframe (T RS ) RS–MS T F /2 BS-Subframe (T BS ) BS–MS or BS–RS φ φ max direct user RS BS (950) (400) U Req (φ max )

Single-Relay Case: FTD Fixed Time-Division Algorithm Channel utilization: Number of allocated time slots for user k Number of allocated packets for user k BM / RM BS-Subframe (T BS ) BS–MS (BM) or BS–RS RS-Subframe (T RS ) RS–MS (RM) TFTF

Single-Relay Case: FTD Fixed Time-Division Algorithm Throughput: Number of allocated time slots for user k 1 or 0

Single-Relay Case: ATD Adaptive Time-Division Algorithm Starting from the allocation by the FTD algorithm for T BS = T RS = T F /2, time division can be adapted to increase the overall throughput. BS-Subframe (T BS ) BS–MS or BS–RS RS-Subframe (T RS ) RS–MS T F /2

Multiple-Relay Case: MRPA Multiple-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 (T BS ) BS–MS or BS–RS RS-Subframe (T RS ) RS–MS T F /2 BS RS MS Direct link Relayed link

Multiple-Relay Case: MRPA Multiple-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: MRPA Multiple-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: MRAA Multiple-RS Adaptive Activation Algorithm Without assuming frequency reuse. RS j with the worst throughput is removed, and the RS j -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 U Req 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 U Req 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.

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