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Low complexity resource allocation with opportunistic feedback over downlink OFDMA networks
 IEEE JSAC
"... Abstract—Optimal tone allocation in downlink OFDMA networks is a nonconvex NPhard problem that requires extensive feedback for channel information. In this paper, two constantcomplexity limitedfeedback algorithms are proposed to achieve nearoptimal performance. First, using opportunistic feedbac ..."
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Cited by 23 (1 self)
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Abstract—Optimal tone allocation in downlink OFDMA networks is a nonconvex NPhard problem that requires extensive feedback for channel information. In this paper, two constantcomplexity limitedfeedback algorithms are proposed to achieve nearoptimal performance. First, using opportunistic feedback, the proposed schemes are shown to reduce feedback overhead by requiring only users likely to be allocated resources to feed back. There are differences between the two proposed schemes for implementation of the feedback protocol. One scheme requires less feedback but is contentionbased, while the other scheme is sequential and thus avoids possible collisions leading to slightly higher performance, but needs more feedback. Second, complexity is reduced for resource allocation by solving the optimization problem in a distributed manner, rather than centrally at the base station. As shown both analytically and through numerical results, these distributed algorithms reduce the required feedback overhead significantly, and achieve constant computational complexity with little performance loss compared to the optimal solution. Index Terms—OFDMA dowlink system, Resource allocation, Limited CSIT, Opportunistic feedback, Low transmit complexity.
Multiuser diversity vs. accurate channel feedback for mimo broadcast channel”, submitted to
 IEEE ICC
, 2008
"... Abstract — A multiple transmit antenna, single receive antenna (per receiver) downlink channel with limited channel feedback is considered. Given a constraint on the total systemwide channel feedback, the following question is considered: is it preferable to get lowrate feedback from a large numbe ..."
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Cited by 19 (2 self)
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Abstract — A multiple transmit antenna, single receive antenna (per receiver) downlink channel with limited channel feedback is considered. Given a constraint on the total systemwide channel feedback, the following question is considered: is it preferable to get lowrate feedback from a large number of receivers or to receive highrate/highquality feedback from a smaller number of (randomly selected) receivers? Acquiring feedback from many users allows multiuser diversity to be exploited, while highrate feedback allows for very precise selection of beamforming directions. It is shown that systems in which a limited number of users feedback highrate channel information significantly outperform lowrate/many user systems. While capacity increases only double logarithmically with the number of users, the marginal benefit of channel feedback is very significant up to the point where the CSI is essentially perfect. I.
1 MultiUser Diversity vs. Accurate Channel State Information in MIMO Downlink Channels
"... In a multiple transmit antenna, single antenna per receiver downlink channel with limited channel state feedback, we consider the following question: given a constraint on the total systemwide feedback load, is it preferable to get lowrate/coarse channel feedback from a large number of receivers o ..."
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Cited by 11 (0 self)
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In a multiple transmit antenna, single antenna per receiver downlink channel with limited channel state feedback, we consider the following question: given a constraint on the total systemwide feedback load, is it preferable to get lowrate/coarse channel feedback from a large number of receivers or highrate/highquality feedback from a smaller number of receivers? Acquiring feedback from many receivers allows multiuser diversity to be exploited, while highrate feedback allows for very precise selection of beamforming directions. We show that there is a strong preference for obtaining highquality feedback, and that obtaining nearperfect channel information from as many receivers as possible provides a significantly larger sum rate than collecting a few feedback bits from a large number of users. I.
A limitedfeedback scheduling and beamforming scheme for multiuser multiantenna systems
 in Proc. Global Telecommun. Conf. (GLOBECOM
, 2011
"... Abstract—This paper proposes an efficient twostage limitedfeedback beamforming and scheduling scheme for multipleantenna cellular communication systems. The system model includes a basestation with M antennas and a large pool of users with a total feedback rate of B bits per fading block. The feed ..."
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Abstract—This paper proposes an efficient twostage limitedfeedback beamforming and scheduling scheme for multipleantenna cellular communication systems. The system model includes a basestation with M antennas and a large pool of users with a total feedback rate of B bits per fading block. The feedback process is divided into two stages. In the first stage, the users measure their channel gains from each antenna and feedback the index of the antenna with the highest channel gain along with the gain itself. Based on this information, the basestation schedules M users with the highest channel gains from its M antennas and polls those users for explicit quantization of their vector channels in the second stage. Based on these quantized channels, the basestation then forms zeroforcing beamforming vectors for downlink transmission. This paper presents an approximate analysis for the proposed scheme which is used to optimize the bit allocation between the two feedback stages. It is shown that for a total number of feedback bits B, the number of feedback bits assigned to the second stage, B2, should scale as M(M−1)log(SNR × B). In particular, the fraction B2/B behaves as logB/B in the asymptotic regime where B → ∞. Further, the approximate downlink sum rate is shown to scale as M log SNR + M loglogB, suggesting that both multiuser multiplexing and multiuser diversity gains are realized. As the numerical results verify, the proposed feedback scheme, in spite of its low complexity, performs very close to the more complicated beamforming and scheduling schemes in the literature and in fact outperforms such schemes in the highSNR regime. I.
Opportunistic Feedback in OFDMA Downlink
"... Abstract—This paper presents an opportunistic feedback (OF) protocol that reduces the amount of channelstateinformation (CSI) feedback for the OFDMA downlink system. The OF protocol associates a channel value instead of a user to each feedback slot. The users access the slots opportunistically bas ..."
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Abstract—This paper presents an opportunistic feedback (OF) protocol that reduces the amount of channelstateinformation (CSI) feedback for the OFDMA downlink system. The OF protocol associates a channel value instead of a user to each feedback slot. The users access the slots opportunistically based on their channel state measurement for each tone. This allows the base station (BS) to deduce the channel state from the slot index without explicit channelstate feedback, and also solve the resource allocation problem on the fly. The OF protocol is designed to support heterogeneous traffic, where users with deadlinesensitive (DS) applications are prioritized over besteffort (BE) users. The proposed OF protocol (a) requires finite number of feedback slots upper bounded by a small number, (b) is fully distributed, and (c) provides QoS to the DS applications. I.
Opportunistic Feedback Protocol for Achieving SumCapacity of the MIMO Broadcast Channel
"... Abstract—This paper presents an opportunistic feedback (OF) protocol that achieves the asymptotic sumcapacity of the fading broadcast channel (BC) with a limited amount of feedback. The OF protocol associates a channel value instead of a user to each feedback slot. The users access the slots opport ..."
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Abstract—This paper presents an opportunistic feedback (OF) protocol that achieves the asymptotic sumcapacity of the fading broadcast channel (BC) with a limited amount of feedback. The OF protocol associates a channel value instead of a user to each feedback slot. The users access the slots opportunistically based on their channel state measurement. This allows the basestation to deduce the channel state from the slot index without explicit channelstate feedback. This protocol is then extended to the MIMO BC by using zeroforcing beamforming and random beamforming. The OF protocol is analytically shown to (a) require finite number of feedback slots upper bounded by a small number, (b) be fully distributed, (c) need minimal transmission energy during feedback and (d) asymptotically achieve the sumcapacity of the MIMO BC. Comparison with other opportunistic feedback schemes shows that the proposed scheme has substantially larger sumrate with a lower feedback overhead. I.
Achieving SumCapacity of the MIMO BC with Large Transmit Array using OneShot Scalable Feedback Protocol
"... Abstract — We consider a MIMO broadcast channel (BC) with large M and K, where M is the number of transmit antennas and K is the number of singleantenna users; and propose a scalable feedback protocol that achieves the sumcapacity with limited feedback of channel state information (CSI). In our ea ..."
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Abstract — We consider a MIMO broadcast channel (BC) with large M and K, where M is the number of transmit antennas and K is the number of singleantenna users; and propose a scalable feedback protocol that achieves the sumcapacity with limited feedback of channel state information (CSI). In our earlier work, we showed that if feedback time slots correspond to channel gains and not to users, the sumcapacity M log log K can be achieved with feedback resources growing only as M log K, unlike linearly as MK for conventional schemes. In this work, we show that feedback requirement can further be reduced by half or more, while still achieving the sumcapacity. A scalable feedback (SF) protocol using Random Beamforming (RBF) is proposed, which a) requires finite number of feedback slots upper bounded by a constant, b) is fully distributed, c) needs finite transmission energy during feedback and d) achieves the sumcapacity. Numerical results show that feedback load is substantially reduced as compared to conventional schemes, as well as our own previously proposed SF scheme. I.