Results 1  10
of
25
Relay Selection and Power Allocation in Cooperative Cellular Networks
, 903
"... We consider a system with a single base station communicating with multiple users over orthogonal channels while being assisted by multiple relays. Several recent works have suggested that, in such a scenario, selection, i.e., a single relay helping the source, is the best relaying option in terms o ..."
Abstract

Cited by 9 (0 self)
 Add to MetaCart
(Show Context)
We consider a system with a single base station communicating with multiple users over orthogonal channels while being assisted by multiple relays. Several recent works have suggested that, in such a scenario, selection, i.e., a single relay helping the source, is the best relaying option in terms of the resulting complexity and overhead. However, in a multiuser setting, optimal relay assignment is a combinatorial problem. In this paper, we formulate a related convex optimization problem that provides an extremely tight upper bound on performance and show that selection is, almost always, inherent in the solution. We also provide a heuristic to find a closetooptimal relay assignment and power allocation across users supported by a single relay. Simulation results using realistic channel models demonstrate the efficacy of the proposed schemes, but also raise the question as to whether the gains from relaying are worth the additional costs. I.
On optimal cooperator selection policies for multihop ad hoc networks
 IEEE Trans. Wireless Commun
, 2011
"... Abstract—In this paper we consider wireless cooperative multihop networks, where nodes that have decoded the message at the previous hop cooperate in the transmission toward the next hop, realizing a distributed spacetime coding scheme. Our objective is finding optimal cooperator selection policie ..."
Abstract

Cited by 5 (1 self)
 Add to MetaCart
(Show Context)
Abstract—In this paper we consider wireless cooperative multihop networks, where nodes that have decoded the message at the previous hop cooperate in the transmission toward the next hop, realizing a distributed spacetime coding scheme. Our objective is finding optimal cooperator selection policies for arbitrary topologies with links affected by path loss and multipath fading. To this end, we model the network behavior through a suitable Markov chain and we formulate the cooperator selection process as a stochastic shortest path problem (SSP). Further, we reduce the complexity of the SSP through a novel pruning technique that, starting from the original problem, obtains a reduced Markov chain which is finally embedded into a solver based on focused real time dynamic programming (FRTDP). Our algorithm can find cooperator selection policies for large state spaces and has a bounded (and small) additional cost with respect to that of optimal solutions. Finally, for selected network topologies, we show results which are relevant to the design of practical network protocols and discuss the impact of the set of nodes that are allowed to cooperate at each hop, the optimization criterion and the maximum number of cooperating nodes. Index Terms—Ad hoc wireless networks, automatic repeat request, cooperative communication, MIMO systems, multihop communication, optimal policies. I.
Power allocation based on SEP minimization in twohop decodeandforward relay networks
 IEEE Trans. Signal Process
, 2011
"... Abstract—The problem of optimal power allocation among the relays in a twohop decodeandforward cooperative relay network with independent Rayleigh fading channels is considered. It is assumed that only the relays that decode the source message correctly contribute in data transmission. Moreover, ..."
Abstract

Cited by 4 (2 self)
 Add to MetaCart
(Show Context)
Abstract—The problem of optimal power allocation among the relays in a twohop decodeandforward cooperative relay network with independent Rayleigh fading channels is considered. It is assumed that only the relays that decode the source message correctly contribute in data transmission. Moreover, only the knowledge of statistical channel state information is available. A new simple closedform expression for the average symbol error probability is derived. Based on this expression, a new power allocation method that minimizes the average symbol error probability and takes into account the constraints on the total average power of all the relay nodes and maximum instant power of each relay node is developed. The corresponding optimization problem is shown to be a convex problem that can be solved using interiorpoint methods. However, an approximate closedform solution is obtained and shown to be practically more appealing due to significant complexity reduction. The accuracy of the approximation is discussed. Moreover, the so obtained closedform solution gives additional insights into the optimal power allocation problem. Simulation results confirm the improved performance of the proposed power allocation scheme as compared to other schemes. Index Terms—Cooperative systems, convex optimization, decodeandforward relay networks, power allocation. I.
Power allocations in minimumenergy SERconstrained cooperative networks
 Annals of Telecommunication
, 2009
"... ..."
(Show Context)
Resource Allocation for the Parallel Relay Channel with Multiple Relays
"... Abstract—A cooperative network where the transmission between two nodes is assisted by many halfduplex relays over parallel Gaussian channels is considered. The parallel channel model is suitable for a broadband system, such as orthogonal frequency division multiplexing or a block fading channel. F ..."
Abstract

Cited by 2 (0 self)
 Add to MetaCart
(Show Context)
Abstract—A cooperative network where the transmission between two nodes is assisted by many halfduplex relays over parallel Gaussian channels is considered. The parallel channel model is suitable for a broadband system, such as orthogonal frequency division multiplexing or a block fading channel. For the decodeandforward protocol, an optimization problem for joint power, time and subchannel allocation under pernode power constraints is formulated to maximize the total transmission rate between the source and the destination. To solve this optimization problem, first the optimal power allocation for a given subchannel allocation is found. Then a greedy algorithm that jointly allocates subchannels and power is described. Finally, the time allocation is optimized by a numerical search procedure. The limiting case where the number of subchannels goes to infinity is also studied. Numerical results reveal that the achieved rate for the infinite number of subchannels is an upper bound for the finite subchannel case and the proposed greedy algorithm results in rates close to those for infinite number of subchannels when the number of subchannels is sufficiently large. Furthermore, most of the cooperative gains can be achieved by the use of a small number of relays. Index Terms—Resource allocation, parallel relay channel, user cooperation. I.
On the energy delay tradeoff of HARQIR in wireless multiuser systems
 IEEE Trans. Commun
, 2013
"... Abstract—Energy delay tradeoff (EDT) is a fundamental tradeoff that plays a crucial role in understanding the energy efficiency of various transmission schemes. In particular, for hybrid automatic repeat request (HARQ) protocols, the EDT can be well defined. In this paper, in order to understand the ..."
Abstract

Cited by 1 (0 self)
 Add to MetaCart
(Show Context)
Abstract—Energy delay tradeoff (EDT) is a fundamental tradeoff that plays a crucial role in understanding the energy efficiency of various transmission schemes. In particular, for hybrid automatic repeat request (HARQ) protocols, the EDT can be well defined. In this paper, in order to understand the EDT for a wireless multiuser system, we consider various downlink transmission schemes where the HARQ with incremental redundancy (HARQIR) protocol is employed for reliable transmissions to users. For a given total power, the impact of different transmission schemes in conjunction with power allocation on EDT is extensively studied. Among the transmission schemes, it is shown that the thresholdbased transmission (TBT) scheme efficiently lowers the minimum energy per bit (EB) in spite of limited prior channel state information (CSI) feedback. The study is further extended to a more plausible scenario where users have different channel statistics. In doing so, we consider a proportional fairness scheduling based on relative channel gain that can be easily accommodated in the proposed TBT scheme, and study its EDT behaviors. Performance evaluations show that the schemes incorporating proportional fairness achieve good EDT performances while guaranteeing the fairness among users. Index Terms—Energy efficiency, hybrid automatic repeat request (HARQ), power allocation. I.
Minimum energy consumption design of a twohop relay network for qos guarantee
 in Wireless Telecommunications Symposium (WTS), 2010. IEEE
"... Minimum energy consumption design of A twohop relay network for QoS guarantee ..."
Abstract

Cited by 1 (0 self)
 Add to MetaCart
(Show Context)
Minimum energy consumption design of A twohop relay network for QoS guarantee
unknown title
"... RESEARCH IN WIRELESS COMMUNICATIONS AND NETWORKING has beenpopularly advocated. It is wellknown that a crucial, and thus intensivelystudied, issue for improving the performance of wireless networks, i.e., increasing network capacity and operation efficiency, is the efficient management of the avai ..."
Abstract
 Add to MetaCart
(Show Context)
RESEARCH IN WIRELESS COMMUNICATIONS AND NETWORKING has beenpopularly advocated. It is wellknown that a crucial, and thus intensivelystudied, issue for improving the performance of wireless networks, i.e., increasing network capacity and operation efficiency, is the efficient management of the available radio resources. This thesis, which consists of three major parts, explores resource allocation problems in wireless data networks using convex optimization. In the first part, a beamforming technique is developed to solve the spectrum sharing problem in wireless networks where secondary users can coexist with primary users without causing excessive interference. The proposed problems can be solved efficiently using semidefinite programming. The second part investigates different power allocation schemes for multiuser relay networks using geometric programming. Since it is typically not possible to guarantee the qualityofservice for all users in powerlimited relay networks, admission control may be necessary. For such cases, an efficient heuristicbased algorithm for solving the joint admission control and power allocation problem is developed. The last part presents a joint crosslayer optimization approach in multihop wireless networks. Given the constraints of the total available
Optimal Distributed Coding Schemes for Energy Efficiency in the Fading Relay Channel
"... Abstract—We propose three energyoptimal distributed schemes for the halfduplex relay channel with block fading to maintain a desired source rate. We consider both network energy consumption and consumption of the relay alone, assuming only local channel knowledge. Then, we combine both into a gen ..."
Abstract
 Add to MetaCart
(Show Context)
Abstract—We propose three energyoptimal distributed schemes for the halfduplex relay channel with block fading to maintain a desired source rate. We consider both network energy consumption and consumption of the relay alone, assuming only local channel knowledge. Then, we combine both into a generalized distributed energyefficient scheme. In these schemes, the source uses message splitting and allocates resources dynamically, such that direct transmission, decodeforward or partial decodeforward is performed at each block, depending on the channel quality. The optimal distributed power allocation is computed from the corresponding centralized scheme by using an estimate of the relay consumption. Compared to decodeforward with no message splitting as often used in distributed designs, the proposed schemes significantly decrease the peak power and provide up to 15 % average energy gain for the network consumption and a minimum of 3.3dB gain for the relay consumption.
Research Article EnergyEfficient Relaying Strategy with Network Coding in TwoWay Parallel Channels
"... which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We consider a twoway communication assisted by parallel regenerative decodeandforward relays operating in orthogonal channels. In a system with limited channel state informa ..."
Abstract
 Add to MetaCart
(Show Context)
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We consider a twoway communication assisted by parallel regenerative decodeandforward relays operating in orthogonal channels. In a system with limited channel state information at each source and relay node, an optimum distributed power allocation strategy is proposed to minimize the total transmit power, providing a target signaltonoise ratio at each destination with a target outage probability. Moreover, combined with opportunistic relaying and network coding, a distributed decision mechanism is proposed for the relay node to decide whether to help the transmission or not. In this proposal, each source works out the transmit power and the decision threshold then broadcasts them. The selected relay compares the decision threshold with the channel gain of its weaker relaytodestination link, then determines whether to forward the networkcoded data or not. Simulation results show the advantage of this strategy in terms of energy efficiency for a twohop twoway communication scenario. The proposed strategy is very flexible as it can trade outage to power consumption and vice versa. 1.