Electrical and Electronic Engineering - Research Publications
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ItemMaximizing Sum-Rate via Relay Selection and Power Control in Dual-Hop Networks(IEEE, 2022-01-01)In this paper, we focus on the sum-rate optimization problem in a general dual-hop relay network by considering the joint relay selection and power control in the presence of interference. First, we propose a new relay selection algorithm which has better sum-rate performance than the existing relay selection techniques. Then we combine relay selection and power control to propose a novel iterative algorithm based on the tight lower bound approximation which maximizes the achievable sum-rate. We also prove that for the special case of two-user networks, binary power allocation is optimum for at least two transmitting nodes. Extensive numerical examples are used to compare the performance of the proposed algorithm and to illustrate the accuracy of the analysis.
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ItemOptimal Routing for Multi-User Multi-Hop Relay Networks Via Dynamic Programming(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2022-05-23)In this letter, we study the relay selection problem in multi-user, multi-hop relay networks with the objective of minimizing the network outage probability. When only one user is present, it is well known that the optimal relay selection problem can be solved efficiently via dynamic programming. This solution breaks down in the multi-user scenario due to dependence between users. We resolve this challenge using a novel relay aggregation approach. On the expanded trellis, dynamic programming can be used to solve the optimal relay selection problem with computational complexity linear in the number of hops. Numerical examples illustrate the efficient use of this algorithm for relay networks.
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ItemSum-Rate Optimization in Flexible Half-Duplex Networks With Transmitter/Receiver Scheduling(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2022-07-01)In this paper, we focus on the problem of transmitter and receiver scheduling to maximize the achievable sum-rate of a flexible half-duplex network where nodes have the flexibility to either transmit, receive or be silent in a given time slot. We consider a network with multiple transmitters and receivers where each transmitter has specific information it needs to send to a set of receiving nodes. First, we conduct some structural analysis and show that the achievable sum-rate is maximized when each transmitter only transmits to a single receiver at a given time. Next, we consider one instance of the flexible network and by reducing the symmetric multiple receiver network to a single receiver network, we also show that the achievable sum-rate is maximized when either one transmitter or all the transmitters transmit. In fact, there exists a unique received signal-to-noise ratio at which the optimality changes from all-to-one. Finally, we design a novel low-cost algorithm that gives a sub-optimal solution to the achievable sum-rate maximization problem in a flexible half-duplex network. We also provide a comprehensive comparison of the proposed algorithm with respect to existing resource allocation techniques, and observe that our proposed algorithm provides significant sum-rate gains.
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ItemReliability Characterization for SIMO Communication Systems With Low-Resolution Phase Quantization Under Rayleigh Fading(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2021-01-01)
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ItemNo Preview AvailableDecentralized Relay Selection in Multi-User Multihop Decode-and-Forward Relay Networks(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2018-05-01)
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ItemLow-Resolution Quantization in Phase Modulated Systems: Optimum Detectors and Error Rate Analysis(Institute of Electrical and Electronics Engineers (IEEE), 2020-07-20)This paper studies optimum detectors and error rate analysis for wireless systems with low-resolution quantizers in the presence of fading and noise. A universal lower bound on the average symbol error probability ( SEP ), correct for all M -ary modulation schemes, is obtained when the number of quantization bits is not enough to resolve M signal points. In the special case of M -ary phase shift keying ( M -PSK), the maximum likelihood detector is derived. Utilizing the structure of the derived detector, a general average SEP expression for M -PSK modulation with n -bit quantization is obtained when the wireless channel is subject to fading with a circularly-symmetric distribution. For the Nakagami- m fading, it is shown that a transceiver architecture with n -bit quantization is asymptotically optimum in terms of communication reliability if n≥log2M+1 . That is, the decay exponent for the average SEP is the same and equal to m with infinite-bit and n -bit quantizers for n≥log2M+1 . On the other hand, it is only equal to 12 and 0 for n=log2M and n
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ItemChemical Reactions-based Detection Mechanism for Molecular Communications(IEEE, 2020-05)In molecular communications, the direct detection of signaling molecules may be challenging due to the lack of suitable sensors and interference from co-existing substances in the environment. Motivated by examples in nature, we investigate an indirect detection mechanism using chemical reactions between the signaling molecules and a molecular probe to produce an easy-to-measure product at the receiver. The underlying reaction-diffusion equations that describe the concentrations of the reactant and product molecules in the system are non-linear and coupled, and cannot be solved in closed-form. To analyze these molecule concentrations, we develop an efficient iterative algorithm by discretizing the time variable and solving for the space variables in each time step. We also derive insightful closed-form solutions for a special case. The accuracy of the proposed algorithm is verified by particle-based simulations. Our results show that the concentration of the product molecules has a similar characteristic over time as the concentration of the signaling molecules. We analyze the bit error rate (BER) for a threshold detector and highlight that significant improvements in the BER can be achieved by carefully choosing the molecular probe and optimizing the detection threshold.
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ItemCentralized Scheduling with Sum-Rate optimization in Flexible Half-Duplex Networks(IEEE, 2020-05)In this paper, we focus on maximization of the instantaneous sum-rate in flexible half-duplex networks, where nodes have the flexibility to choose to either transmit, receive or be silent in a given time slot. Since the corresponding optimization problem is NP-hard, we design low-cost algorithms that give sub-optimal solutions with good performance. We first consider two existing approximation techniques to simplify the sum-rate optimization problem: arithmetic-geometric means inequality and another utilising the tight lower bound approximation. We then propose a novel pattern search algorithm that performs close to exhaustive search but with significantly lower complexity. Comparing the performance of the proposed algorithm with respect to existing resource allocation techniques, we observe that our proposed algorithm provides significant sum-rate gains.
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ItemBinary Power Optimality for Two Link Full-Duplex Network(IEEE, 2020-05)In this paper, we analyse the optimality of binary power allocation in a network that includes full-duplex communication links. Considering a network with four communicating nodes, two of them operating in half-duplex mode and the other two in full-duplex mode, we prove that binary power allocation is optimum for the full-duplex nodes when maximizing the sum rate. We also prove that, for half-duplex nodes binary power allocation is not optimum in general. However, for the two special cases, 1) the low signal-to-noise-plus-interference (SINR) regime and, 2) the approximation by the arithmetic mean-geometric mean inequality, binary power allocation is optimum for the approximated sum rate even for the half-duplex nodes. We further analyse a third special case using a symmetric network for which the optimum power allocation is binary, under a sufficient condition. Numerical examples are included to illustrate the accuracy of the results.
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ItemTwo-Way Communications via Reconfigurable Intelligent Surface(IEEE, 2020-06-19)The novel reconfigurable intelligent surface (RIS) is an emerging technology which facilitates high spectrum and energy efficiencies in Beyond 5G and 6G wireless communication applications. Against this backdrop, this paper investigates two-way communications via reconfigurable intelligent surfaces (RISs) where two users communicate through a common RIS. We assume that uplink and downlink communication channels between two users and the RIS can be reciprocal. We first obtain the optimal phase adjustment at the RIS. We then derive the exact outage probability and the average throughput in closed-forms for single-element RIS. To evaluate multiple-element RIS, we first introduce a gamma approximation to model a product of Rayleigh random variables, and then derive approximations for the outage probability and the average throughput. For large average signal-to-interference-plus-noise ratio (SINR) \rho, asymptotic analXsis also shows that the outage decreases at the rate (\log(\rho)/\rho) where L is the number of elements, whereas the throughput increases with the rate \log(\rho).