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13
Effective capacity maximization in multiantenna channels with covariance feedback
 In Proceedings of IEEE International Conference on Communications (ICC
, 2009
"... Abstract—The optimal transmit strategies of singleuser multiantenna systems with respect to average capacity maximization are well understood. However, the performance measure does neglect delay aspects which are important for higher layer design. Therefore, we consider the maximization of the effe ..."
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Abstract—The optimal transmit strategies of singleuser multiantenna systems with respect to average capacity maximization are well understood. However, the performance measure does neglect delay aspects which are important for higher layer design. Therefore, we consider the maximization of the effective capacity in a singleuser multiantenna system with covariance knowledge. The optimal transmit strategy is derived and the properties as a function of the decayrate requirement of the buffer occupancy are analyzed. In particular, we show that the larger the decayrate requirement, the smaller the beamforming optimality range, i.e., the more spatial eigenmodes are activated. This behavior is illustrated by numerical simulations and explained by the channel hardening effect.
Optimized Opportunistic Multicast Scheduling (OMS) over Wireless Cellular Networks
, 2010
"... Optimized opportunistic multicast scheduling (OMS) is studied for cellular networks, where the problem of efficiently transmitting a common set of fountainencoded data from a single base station to multiple users over quasistatic fading channels is examined. The proposed OMS scheme better balances ..."
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Optimized opportunistic multicast scheduling (OMS) is studied for cellular networks, where the problem of efficiently transmitting a common set of fountainencoded data from a single base station to multiple users over quasistatic fading channels is examined. The proposed OMS scheme better balances the tradeoff between multiuser diversity and multicast gain by transmitting to a subset of users in each time slot using the maximal data rate that ensures successful decoding by these users. We first analyze the system delay in homogeneous networks by capitalizing on extreme value theory and derive the optimal selection ratio (i.e., the portion of users that are selected in each time slot) that minimizes the delay. Then, we extend results to heterogeneous networks where users are subject to different channel statistics. By partitioning users into multiple approximately homogeneous rings, we turn a heterogeneous network into a composite of smaller homogeneous networks and drive the optimal selection ratio for the heterogeneous network. Computer simulations confirm theoretical results and illustrate that the proposed OMS can achieve significant performance gains in both homogeneous and heterogeneous networks as compared with the conventional unicast and broadcast scheduling.
Data Dissemination in Wireless Broadcast Channels: Network Coding versus Cooperation
, 2008
"... Network coding and cooperative diversity have each extensively been explored in the literature as a means to substantially improve the performance of wireless networks. Yet, little work has been conducted to compare their performance under a common framework. Our goal in this paper is to fill in thi ..."
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Network coding and cooperative diversity have each extensively been explored in the literature as a means to substantially improve the performance of wireless networks. Yet, little work has been conducted to compare their performance under a common framework. Our goal in this paper is to fill in this gap. Specifically, we consider a singlehop wireless network consisting of a base station and N receivers. We perform an asymptotic analysis, as N → ∞, of the expected delay associated with the broadcasting of a file consisting of K packets. We show that if K is fixed, cooperation outperforms network coding, in the sense that the expected delay is proportional to K (and thus within a constant factor of the optimal delay) in the former case while it grows logarithmically with N in the latter case. On the other hand, if K grows with N at a rate at least as fast as (log N) r, for r> 1, then we show that the average delay of network coding is also proportional to K and lower than the average delay of cooperation if the packet error probability is smaller than 0.36. Our analytical findings are validated through extensive numerical simulations.
On the DelayThroughput Tradeoff in Distributed Wireless Networks
, 2009
"... The delaythroughput of a singlehop wireless network with n randomly distributed links is analyzed. We consider a general shadowfading model, described by parameters (α, ̟), where α denotes the probability of shadowing and ̟ represents the average crosslink gains. The analysis relies on the distr ..."
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The delaythroughput of a singlehop wireless network with n randomly distributed links is analyzed. We consider a general shadowfading model, described by parameters (α, ̟), where α denotes the probability of shadowing and ̟ represents the average crosslink gains. The analysis relies on the distributed onoff power allocation strategy (i.e., links with a direct channel gain above a certain threshold transmit at full power and the rest remain silent) for the deterministic and stochastic packet arrival processes. In the first part of the paper, we analyze the effective throughput maximization of the network. It is proved that the effective throughput of the network scales as log n ˆα, with ˆα � α̟, despite the packet arrival process. Then, we present the delay characteristics of the underlying network in terms of a packet dropping probability. We derive the necessary conditions in the asymptotic case of n → ∞ such that the packet dropping probabilities tend to zero, while achieving the maximum effective throughput of the network. Finally, we study the tradeoff between the effective throughput of the network and delaybounds for different packet arrival processes. In particular, we determine how much degradation will be enforced in the throughput by introducing other constraints.
Delaythroughput analysis in distributed wireless networks
, 2009
"... I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. ii A primary challenge in wireless networks is to use ava ..."
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I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. ii A primary challenge in wireless networks is to use available resources efficiently so that the Quality of Service (QoS) is satisfied while maximizing the throughput of the network. Among different resource allocation strategies, power and spectrum allocations have long been regarded as efficient tools to mitigate interference and improve the throughput of the network. Also, achieving a low transmission delay is an important QoS requirement in bufferlimited networks, particularly for users with realtime services. For these networks, too much delay results in dropping some packets. Therefore, the main challenge in networks with realtime services is to utilize an efficient power allocation scheme so that the delay is minimized while achieving a high throughput. This dissertation deals with these problems in distributed wireless networks.
This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, ACCEPTED FOR PUBLICATION 1 NonOrthogonal Opportunistic Beamform
"... Abstract—Aiming to achieve the sumrate capacity in multiuser multiantenna systems where ..."
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Abstract—Aiming to achieve the sumrate capacity in multiuser multiantenna systems where
1Scheduling for Cellular Multicast: A CrossLayer Perspective
, 2007
"... Recent years have witnessed the importance of crosslayer design in wireless communication systems. The adoption of simplied on/off models for the wireless channel, in an attempt to reduce it to the traditional wireline case, has been shown to be highly suboptimal. In this paper, we consider more r ..."
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Recent years have witnessed the importance of crosslayer design in wireless communication systems. The adoption of simplied on/off models for the wireless channel, in an attempt to reduce it to the traditional wireline case, has been shown to be highly suboptimal. In this paper, we consider more realistic models for the wireless channel and demonstrate the signicant performance gains that can be leveraged from the wireless medium through intelligent scheduling strategies. We consider a cellular multicast channel, where a central base station transmits the same information stream to all the users within the system. We design scheduling algorithms for this scenario from a crosslayer perspective, which aids us in exploiting the characteristics of the wireless medium. We consider three classes of scheduling algorithms with progressively increasing complexity and study their asymptotic throughputdelay performance with the number of users in the system. The rst class strives for minimum complexity by resorting to static scheduling along with memoryless decoding. Our analysis reveals the existence of a scheduling scheme, within this class, that achieves nearoptimal scaling laws of both delay and throughput. The second scheduling policy resorts to a higher complexity incremental redundancy encoding/decoding strategy to achieve a superior throughputdelay tradeoff. The third, and most complex, scheduling strategy benets from the cooperation between the different users and is shown to simultaneously achieve the optimal scaling laws of both delay and throughput. We further study the effect of equipping the base station with multiple transmit antennas on the throughput performance of the proposed lowcomplexity static schedulers. Finally, we present simulation results that validate our theoretical claims. I.
Data Dissemination in Wireless Broadcast Channels: Network Coding or Cooperation?
"... Abstract—Network coding and cooperative diversity have each extensively been explored in the literature as a means to substantially improve the performance of wireless networks. Yet, little work has been conducted to compare their performance under a common framework. Our goal in this paper is to fi ..."
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Abstract—Network coding and cooperative diversity have each extensively been explored in the literature as a means to substantially improve the performance of wireless networks. Yet, little work has been conducted to compare their performance under a common framework. Our goal in this paper is to fill in this gap. Specifically, we consider a singlehop wireless network consisting of a base station and N receivers. We perform an asymptotic analysis, as N →∞, of the expected delay associated with the broadcasting of a file consisting of K packets. We show that if K is fixed, cooperation outperforms network coding, in the sense that the expected delay is proportional to K (and thus within a constant factor of the optimal delay) in the former case while it grows logarithmically with N in the latter case. On the other hand, if K grows with N at a rate at least as fast as (log N) r,for r>1, then we show that the average delay of network coding is within a factor less than two of the optimal delay, no worse than the average delay of cooperation. Our analytical findings are validated through extensive numerical simulations. I.
doi:10.1155/2009/271540 Research Article Throughput versus Fairness: ChannelAware Scheduling in Multiple Antenna Downlink
, 2008
"... Channel aware and opportunistic scheduling algorithms exploit the channel knowledge and fading to increase the average throughput. Alternatively, each user could be served equally in order to maximize fairness. Obviously, there is a tradeoff between average throughput and fairness in the system. In ..."
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Channel aware and opportunistic scheduling algorithms exploit the channel knowledge and fading to increase the average throughput. Alternatively, each user could be served equally in order to maximize fairness. Obviously, there is a tradeoff between average throughput and fairness in the system. In this paper, we study four representative schedulers, namely the maximum throughput scheduler (MTS), the proportional fair scheduler (PFS), the (relative) opportunistic round robin scheduler (ORS), and the round robin scheduler (RRS) for a spacetime coded multiple antenna downlink system. The system applies TDMA based scheduling and exploits the multiple antennas in terms of spatial diversity. We show that the average sum rate performance and the average worstcase delay depend strongly on the user distribution within the cell. MTS gains from asymmetrical distributed users whereas the other three schedulers suffer. On the other hand, the average fairness of MTS and PFS decreases with asymmetrical user distribution. The key contribution of this paper is to put these tradeoffs and observations on a solid theoretical basis. Both the PFS and the ORS provide a reasonable performance in terms of throughput and fairness. However, PFS outperforms ORS for symmetrical user distributions, whereas ORS outperforms PFS for asymmetrical user distribution. Copyright © 2009 Eduard A. Jorswieck et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly