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Abstract—Orthogonal frequency-division multiple access
(OFDMA) is an attractive technique for exploiting multiuser diversity in the downlink of a cellular system. This paper addresses
three problems in multiuser diversity for OFDMA systems.
First, we propose a way to significantly reduce the amount of
channel state information (CSI) feedback without sacrificing
performance too much, by selective and adaptive feedback.
Second, we propose a way to increase the cell throughput and
fairness by appying an opportunistic beamforming scheme to
orthogonal frequency-division multiplexing. This beamforming
scheme increases the frequency fading rate, which increases the
multiuser diversity effect. Thirdly, we deal with the issue of
fairness and quality-of-service (QoS) in opportunistic systems
by proposing a modified proportional fair (PF) scheduler for
OFDMA. Key features in the scheduler are that it incorporates
QoS classes into the PF scheduler and that it has a tunable fairness level. Extensive simulation results are presented to evaluate
the performance of the proposed schemes. The opportunistic
beamforming scheme performed well in comparison with several
other schemes. The modified PF scheduler was able to give users
different QoS, based on their requirements, while still exploiting
multiuser diversity.
Index Terms—Multiple antennas, multiuser diversity, OFDM,
scheduling, wireless system design.
I. INTRODUCTION
OPPORTUNISTIC systems use adaptive modulation in- stead of power control to achieve the target error rates. By
scheduling users with good instantaneous channel conditions,
exploiting multiuser diversity, high system throughput can be
achieved [1]. In the downlink of an opportunistic system with
frequency-selective channels, orthogonal frequency-division
multiple access (OFDMA) is suitable because users can be
scheduled on orthogonal frequency bands. This enables the
exploitation of multiuser diversity in the frequency domain, i.e.,
users can be scheduled also on their frequency fading peaks [2],
[3]. In this paper, we deal with some of the problems with opportunistic OFDMA. We propose an adaptive reduced-feedback
scheme to cope with the significant amount of channel state
Paper approved by T. F. Wong, the Editor for Wideband and Multiple Access
Wireless Systems of the IEEE Communications Society. Manuscript received
October 18, 2004; revised July 30, 2006. This paper was presented in part at the
Vehicular Technology Conference, Milano, Italy, May 2004, and in part at the
Vehicular Technology Conference, Los Angeles, CA, September 2004.
P. Svedman and B. Ottersten are with the KTH School of Electrical Engineering, SE-100 44 Stockholm, Sweden (e-mail: [email protected]).
S. K. Wilson is with the Department of Electrical Engineering, Santa Clara
University, Santa Clara, CA 95053 USA.
L. J. Cimini Jr. is with the Electrical and Computer Engineering Department,
University of Delaware, Newark, DE 19716 USA.
Digital Object Identifier 10.1109/TCOMM.2007.896082
information (CSI) feedback required in a frequency-division
duplexing (FDD) opportunistic OFDMA system. Furthermore,
we propose an opportunistic beamforming scheme for OFDMA
in order to increase the cell throughput and increase fairness.
Fairness and QoS guarantees are usually weak points in opportunistic systems. We propose a modified proportional fair
(PF) scheduler for orthogonal frequency-division multiplexing
(OFDM) that addresses these weaknesses. The scheduler
exploits multiuser diversity, but also tries to meet individual
user requirements on bit rates and delays. The fairness of the
scheduler is tunable; furthermore, a way to couple the scheduler
and the beamformer to Giúp the weakest users is proposed.
Opportunistic beamforming uses multiple antennas at the
transmitter to increase the temporal fading rate of the individual
users [1]. This can Giúp slowly fading users to be scheduled
more often. In addition, the fading rate of the intercell interference (ICI) is increased, which is called opportunistic
nulling. The basic idea of opportunistic beamforming is that
the basestation forms a random beam that is changed for
each transmission block. Users are then scheduled based on
the reported supportable rates. In [1], the concept of using
opportunistic beamforming for frequency-selective fading
channels using OFDMA is outlined. We extend the idea of [1]
by showing how opportunistic beamforming can be applied to
OFDMA in practice. Also in [4], the extension of opportunistic
beamforming to parallel channels is considered, but without
introducing the same randomness in the frequency domain.
One of the main problems with FDD opportunistic OFDMA
systems is the large amount of feedback required from the users.
Because users can be scheduled on different frequency subbands, users must feed back measurement information about
each subband. We propose to reduce the feedback by grouping
adjacent subcarriers into clusters [5] and only feeding back information about the strongest clusters. Additionally, we observe
that the suitable feedback rate per user depends on the number of
users, and we design the adaptive feedback scheme accordingly.
Alternatively, the feedback load can be reduced by feeding back
information only from users with channel quality above a certain predefined threshold [6]. Clustered OFDMA and multiuser
diversity were also studied in [2] and [3], where the authors
showed an increase in spectral efficiency as the number of users
grew. We propose the use of identical beamforming weights on
all subcarriers within each cluster and independent weights between the clusters. This keeps the correlation high between the
subcarriers within the clusters so that feedback of only one value
is sufficient, e.g., the supportable rate of the weakest subcarrier within the cluster. Furthermore, by having different beam-
[22] D. Bertsekas and R. Gallager, Data Networks, 2nd ed. Englewood
Cliffs, NJ: Prentice-Hall, 1991.
[23] S. Shenker, “Fundamental design issues for the future internet,” IEEE
J. Sel. Areas Commun., vol. 13, no. 6, pp. 1176–1188, Sep. 1995.
[24] J. M. Cioffi, G. P. Dudevoir, M. V. Eyuboglu, and G. D. Forney,
“MMSE decision-feedback equalizers and coding—Part II: Coding
results,” IEEE Trans. Commun., vol. 43, no. 10, pp. 2595–2604, Oct.
1995.
[25] Spatial channel model for multiple input multiple output simulations
(V6.1.0), TR 25.996 3GPP, 2003 [Online]. Available:
3gpp.org/ftp/Specs/html-info/25996.htm
[26] P. Dent, G. E. Bottomley, and T. Croft, “Jakes fading model revisited,”
Electron. Lett., vol. 29, pp. 1162–1163, Jun. 1993.
[27] P. Svedman, S. K. Wilson, and B. Ottersten, “A QOS-aware proportional fair scheduler for opportunistic OFDM,” in Proc. IEEE Veh.
Technol. Conf., Sep. 2004, vol. 1, pp. 558–562.
Patrick Svedman (S’03) received the M.Sc. degree
in electrical engineering in 1999 from the Royal
Institute of Technology (KTH), Stockholm, Sweden,
where he is currently working toward the Ph.D.
degree.
In 1999–2001, he worked at Nokia Networks with
digital ASIC design for 3G. His research interests
include wireless multiuser communications with an
emphasis on OFDMA and multiple-antenna systems.
Sarah Kate Wilson (M’87–SM’99) received the
AB degree in mathematics from Bryn Mawr College, Bryn Mawr, PA, in 1979, and the M.S. and
Ph.D. degrees in electrical engineering from Stanford University, Stanford, CA, in 1987 and 1994,
respectively.
She has worked in industry as a programmer/analyst, research engineer, and project manager. She
was an Assistant Professor at Purdue University and
the Lulea University of Technology (LTU) and was
a guest professor/researcher at the Royal Institute
of Technology in Sweden. Currently, she is an Assistant Professor and a
David Packard Fellow in the Electrical Engineering Department, Santa Clara
University, Santa Clara, CA.
Dr. Wilson has served as an Associate Editor for the IEEE TRANSACTIONS ON
WIRELESS COMMUNICATIONS and is currently an Associate Editor for the IEEE
TRANSACTIONS ON COMMUNICATIONS and IEEE COMMUNICATIONS LETTERS.
Leonard J. Cimini, Jr. (S’77–M’82–SM’89–F’00)
received the Ph.D. degree in electrical engineering
from the University of Pennsylvania, Philadelphia, in
1982.
He was with AT&T, first in Bell Labs and
then AT&T Labs, for 20 years. His research has
concentrated on lightwave and wireless communications, and his main emphasis has been on devising
techniques for overcoming the bit-rate limitations
imposed by the radio environment. In this context, he
pioneered the application of OFDM to the emerging
field of wireless communications. He has been a Professor in the Electrical and
Computer Engineering Department, University of Delaware, Newark, since
2002.
Dr. Cimini has been very active within the IEEE, and he was the founding Editor-in-Chief of the IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS:
WIRELESS COMMUNICATIONS SERIES. Currently, among other activities, he is
the Chair of the Emerging Technologies Committee of ComSoc and a Member
At-Large of the Board of Governors. He was elected a Fellow of the IEEE in
2000 for contributions to the theory and practice of high-speed wireless communications.
Björn Ottersten (S’87–M’89–SM’99–F’04) was
born in Stockholm, Sweden, in 1961. He received
the M.S. degree in electrical engineering and applied
physics from Linköping University, Linköping,
Sweden, in 1986. In 1989, he received the Ph.D.
degree in electrical engineering from Stanford
University, Stanford, CA.
He has held research positions at the Department of
Electrical Engineering, Linköping University, the Information Systems Laboratory, Stanford University,
and the Katholieke Universiteit Leuven, Leuven, Belgium. During 1996–1997, he was Director of Research at ArrayComm Inc, San
Jose, CA. In 1991 he was appointed Professor of Signal Processing at the Royal
Institute of Technology (KTH), Stockholm, Sweden, and he is currently Dean of
the School of Electrical Engineering at KTH. From 1992 to 2004, he was Head
of the Department for Signals, Sensors, and Systems at KTH. He is also a visiting professor at the University of Luxembourg. His research interests include
wireless communications, stochastic signal processing, sensor array processing,
and time series analysis.
Dr. Ottersten has served as Associate Editor for the IEEE TRANSACTIONS
ON SIGNAL PROCESSING and a member of the editorial board of the EURASIP
Journal of Applied Signal Processing. He is currently editor-in-chief of the
EURASIP Signal Processing Journal and a member of the editorial board of
IEEE Signal Processing Magazine. He received the Signal Processing Society
Paper Award in 1993 and 2001.
Do Drive thay đổi chính sách, nên một số link cũ yêu cầu duyệt download. các bạn chỉ cần làm theo hướng dẫn.
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Abstract—Orthogonal frequency-division multiple access
(OFDMA) is an attractive technique for exploiting multiuser diversity in the downlink of a cellular system. This paper addresses
three problems in multiuser diversity for OFDMA systems.
First, we propose a way to significantly reduce the amount of
channel state information (CSI) feedback without sacrificing
performance too much, by selective and adaptive feedback.
Second, we propose a way to increase the cell throughput and
fairness by appying an opportunistic beamforming scheme to
orthogonal frequency-division multiplexing. This beamforming
scheme increases the frequency fading rate, which increases the
multiuser diversity effect. Thirdly, we deal with the issue of
fairness and quality-of-service (QoS) in opportunistic systems
by proposing a modified proportional fair (PF) scheduler for
OFDMA. Key features in the scheduler are that it incorporates
QoS classes into the PF scheduler and that it has a tunable fairness level. Extensive simulation results are presented to evaluate
the performance of the proposed schemes. The opportunistic
beamforming scheme performed well in comparison with several
other schemes. The modified PF scheduler was able to give users
different QoS, based on their requirements, while still exploiting
multiuser diversity.
Index Terms—Multiple antennas, multiuser diversity, OFDM,
scheduling, wireless system design.
I. INTRODUCTION
OPPORTUNISTIC systems use adaptive modulation in- stead of power control to achieve the target error rates. By
scheduling users with good instantaneous channel conditions,
exploiting multiuser diversity, high system throughput can be
achieved [1]. In the downlink of an opportunistic system with
frequency-selective channels, orthogonal frequency-division
multiple access (OFDMA) is suitable because users can be
scheduled on orthogonal frequency bands. This enables the
exploitation of multiuser diversity in the frequency domain, i.e.,
users can be scheduled also on their frequency fading peaks [2],
[3]. In this paper, we deal with some of the problems with opportunistic OFDMA. We propose an adaptive reduced-feedback
scheme to cope with the significant amount of channel state
Paper approved by T. F. Wong, the Editor for Wideband and Multiple Access
Wireless Systems of the IEEE Communications Society. Manuscript received
October 18, 2004; revised July 30, 2006. This paper was presented in part at the
Vehicular Technology Conference, Milano, Italy, May 2004, and in part at the
Vehicular Technology Conference, Los Angeles, CA, September 2004.
P. Svedman and B. Ottersten are with the KTH School of Electrical Engineering, SE-100 44 Stockholm, Sweden (e-mail: [email protected]).
S. K. Wilson is with the Department of Electrical Engineering, Santa Clara
University, Santa Clara, CA 95053 USA.
L. J. Cimini Jr. is with the Electrical and Computer Engineering Department,
University of Delaware, Newark, DE 19716 USA.
Digital Object Identifier 10.1109/TCOMM.2007.896082
information (CSI) feedback required in a frequency-division
duplexing (FDD) opportunistic OFDMA system. Furthermore,
we propose an opportunistic beamforming scheme for OFDMA
in order to increase the cell throughput and increase fairness.
Fairness and QoS guarantees are usually weak points in opportunistic systems. We propose a modified proportional fair
(PF) scheduler for orthogonal frequency-division multiplexing
(OFDM) that addresses these weaknesses. The scheduler
exploits multiuser diversity, but also tries to meet individual
user requirements on bit rates and delays. The fairness of the
scheduler is tunable; furthermore, a way to couple the scheduler
and the beamformer to Giúp the weakest users is proposed.
Opportunistic beamforming uses multiple antennas at the
transmitter to increase the temporal fading rate of the individual
users [1]. This can Giúp slowly fading users to be scheduled
more often. In addition, the fading rate of the intercell interference (ICI) is increased, which is called opportunistic
nulling. The basic idea of opportunistic beamforming is that
the basestation forms a random beam that is changed for
each transmission block. Users are then scheduled based on
the reported supportable rates. In [1], the concept of using
opportunistic beamforming for frequency-selective fading
channels using OFDMA is outlined. We extend the idea of [1]
by showing how opportunistic beamforming can be applied to
OFDMA in practice. Also in [4], the extension of opportunistic
beamforming to parallel channels is considered, but without
introducing the same randomness in the frequency domain.
One of the main problems with FDD opportunistic OFDMA
systems is the large amount of feedback required from the users.
Because users can be scheduled on different frequency subbands, users must feed back measurement information about
each subband. We propose to reduce the feedback by grouping
adjacent subcarriers into clusters [5] and only feeding back information about the strongest clusters. Additionally, we observe
that the suitable feedback rate per user depends on the number of
users, and we design the adaptive feedback scheme accordingly.
Alternatively, the feedback load can be reduced by feeding back
information only from users with channel quality above a certain predefined threshold [6]. Clustered OFDMA and multiuser
diversity were also studied in [2] and [3], where the authors
showed an increase in spectral efficiency as the number of users
grew. We propose the use of identical beamforming weights on
all subcarriers within each cluster and independent weights between the clusters. This keeps the correlation high between the
subcarriers within the clusters so that feedback of only one value
is sufficient, e.g., the supportable rate of the weakest subcarrier within the cluster. Furthermore, by having different beam-
[22] D. Bertsekas and R. Gallager, Data Networks, 2nd ed. Englewood
Cliffs, NJ: Prentice-Hall, 1991.
[23] S. Shenker, “Fundamental design issues for the future internet,” IEEE
J. Sel. Areas Commun., vol. 13, no. 6, pp. 1176–1188, Sep. 1995.
[24] J. M. Cioffi, G. P. Dudevoir, M. V. Eyuboglu, and G. D. Forney,
“MMSE decision-feedback equalizers and coding—Part II: Coding
results,” IEEE Trans. Commun., vol. 43, no. 10, pp. 2595–2604, Oct.
1995.
[25] Spatial channel model for multiple input multiple output simulations
(V6.1.0), TR 25.996 3GPP, 2003 [Online]. Available:
You must be registered for see links
.3gpp.org/ftp/Specs/html-info/25996.htm
[26] P. Dent, G. E. Bottomley, and T. Croft, “Jakes fading model revisited,”
Electron. Lett., vol. 29, pp. 1162–1163, Jun. 1993.
[27] P. Svedman, S. K. Wilson, and B. Ottersten, “A QOS-aware proportional fair scheduler for opportunistic OFDM,” in Proc. IEEE Veh.
Technol. Conf., Sep. 2004, vol. 1, pp. 558–562.
Patrick Svedman (S’03) received the M.Sc. degree
in electrical engineering in 1999 from the Royal
Institute of Technology (KTH), Stockholm, Sweden,
where he is currently working toward the Ph.D.
degree.
In 1999–2001, he worked at Nokia Networks with
digital ASIC design for 3G. His research interests
include wireless multiuser communications with an
emphasis on OFDMA and multiple-antenna systems.
Sarah Kate Wilson (M’87–SM’99) received the
AB degree in mathematics from Bryn Mawr College, Bryn Mawr, PA, in 1979, and the M.S. and
Ph.D. degrees in electrical engineering from Stanford University, Stanford, CA, in 1987 and 1994,
respectively.
She has worked in industry as a programmer/analyst, research engineer, and project manager. She
was an Assistant Professor at Purdue University and
the Lulea University of Technology (LTU) and was
a guest professor/researcher at the Royal Institute
of Technology in Sweden. Currently, she is an Assistant Professor and a
David Packard Fellow in the Electrical Engineering Department, Santa Clara
University, Santa Clara, CA.
Dr. Wilson has served as an Associate Editor for the IEEE TRANSACTIONS ON
WIRELESS COMMUNICATIONS and is currently an Associate Editor for the IEEE
TRANSACTIONS ON COMMUNICATIONS and IEEE COMMUNICATIONS LETTERS.
Leonard J. Cimini, Jr. (S’77–M’82–SM’89–F’00)
received the Ph.D. degree in electrical engineering
from the University of Pennsylvania, Philadelphia, in
1982.
He was with AT&T, first in Bell Labs and
then AT&T Labs, for 20 years. His research has
concentrated on lightwave and wireless communications, and his main emphasis has been on devising
techniques for overcoming the bit-rate limitations
imposed by the radio environment. In this context, he
pioneered the application of OFDM to the emerging
field of wireless communications. He has been a Professor in the Electrical and
Computer Engineering Department, University of Delaware, Newark, since
2002.
Dr. Cimini has been very active within the IEEE, and he was the founding Editor-in-Chief of the IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS:
WIRELESS COMMUNICATIONS SERIES. Currently, among other activities, he is
the Chair of the Emerging Technologies Committee of ComSoc and a Member
At-Large of the Board of Governors. He was elected a Fellow of the IEEE in
2000 for contributions to the theory and practice of high-speed wireless communications.
Björn Ottersten (S’87–M’89–SM’99–F’04) was
born in Stockholm, Sweden, in 1961. He received
the M.S. degree in electrical engineering and applied
physics from Linköping University, Linköping,
Sweden, in 1986. In 1989, he received the Ph.D.
degree in electrical engineering from Stanford
University, Stanford, CA.
He has held research positions at the Department of
Electrical Engineering, Linköping University, the Information Systems Laboratory, Stanford University,
and the Katholieke Universiteit Leuven, Leuven, Belgium. During 1996–1997, he was Director of Research at ArrayComm Inc, San
Jose, CA. In 1991 he was appointed Professor of Signal Processing at the Royal
Institute of Technology (KTH), Stockholm, Sweden, and he is currently Dean of
the School of Electrical Engineering at KTH. From 1992 to 2004, he was Head
of the Department for Signals, Sensors, and Systems at KTH. He is also a visiting professor at the University of Luxembourg. His research interests include
wireless communications, stochastic signal processing, sensor array processing,
and time series analysis.
Dr. Ottersten has served as Associate Editor for the IEEE TRANSACTIONS
ON SIGNAL PROCESSING and a member of the editorial board of the EURASIP
Journal of Applied Signal Processing. He is currently editor-in-chief of the
EURASIP Signal Processing Journal and a member of the editorial board of
IEEE Signal Processing Magazine. He received the Signal Processing Society
Paper Award in 1993 and 2001.
Do Drive thay đổi chính sách, nên một số link cũ yêu cầu duyệt download. các bạn chỉ cần làm theo hướng dẫn.
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You must be registered for see links