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Device-to-Device Communications Underlying Cellular Networks Geoffrey Ye Li School of ECE, Georgia Institute of Technology

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Outline Why D2D Communications? Topic 1: QoS-Aware Resource Allocation Topic 2: EE/SE Mode Switching Future Work

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Why D2D Communications? 5G Perspective: Common View Challenges High connection density High date rate High traffic volume High mobility Low latency Design principles Spectrum efficiency Energy efficiency Cost efficiency Source IMT-2020

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Why D2D Communications? (cont.) Advantages of D2D Communications Proximity gain Hop gain Reuse gain Potential Benefits Higher date rate /capacity Lower latency Higher spectrum-, energy-, and cost-efficiency Better robustness

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Why D2D Communications? (cont.) Main Features of Short Range Techniques Feature Name D2DWi-Fi DirectNFCZigBeeBluetooth4.0UWB Standardizat ion 3GPP LTE- Advanced 802.11ISO 13157802.15.4Bluetooth SIG802.15.3a Frequency band Licensed band for LTE-Advanced 2.4 GHz, 5GHz13.56 MHz 868/915MHz, 2.4GHz 2.4GHz3.1-10.6 GHz Max transmission distance 10-1000m200m0.2m10-100m 10m Max data rate 1Gbps250Mbps424kbps250kbps24Mbps480Mbps Device discovery BS coordination ID broadcast and embed soft access point Radio-frequency identification ID broadcast or coordinator assistant Manual pairing Uniformity of service provision YesNo Application Public safety, Content sharing, Local advertising, Cellular relay Content sharing, Group gaming, Device connection Contactless payment systems, Bluetooth and Wi- Fi connections Home Entertainment and Control, Environmental monitoring OBject EXchange, Peripherals connection Wireless USB, High-definition video, Auto Radar

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Applications Why D2D Communications? (cont.) D.-Q. Feng, L. Lu, Y. Yuan-Wu, G. Y. Li, S.-Q. Li and G. Feng, Device-to-Device communications in cellular networks, IEEE Commun. Mag., Apr. 2014.

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Outline Why D2D Communications? Topic 1: QoS-Aware Resource Allocation Topic 2: EE/SE Mode Switching Future Work

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QoS-Aware Resource Allocation System Model Problem Formulation Proposed Three-Step Solution Network Performance

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System Model System Assumption Fully loaded network Uplink spectrum sharing A minimum SINR for each user Perfect CSI at BS Motivation Access more users Without effecting existing cellular users D.-Q. Feng, L. Lu, Y. Yuan-Wu, G. Y. Li, G. Feng and S.-Q. Li, Device-to-Device communications underlaying cellular networks , IEEE Trans. Commun., vol. 61, no. 8, 2013.

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System Model of QoS-Aware Resource Allocation (cont.) System Model Is this D2D pair admissible? If accessible, which channel will be reused?

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Problem Formulation Optimization Problem Objective: maximize overall throughput Variables: power allocation and channel assignment Constraints: minimum SINR and peak power of users MINLP Problem!

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Proposed Three-Step Solution Step 1: Distance-Based Admission Control Step 2: Optimal Power Control Step 3: Maximum Weighted Matching

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Step1 Distance-Based Admission Admissible Area Admissible area Admissible conditions

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Step1 Distance-Based Admission Control (cont.) Admission Criteria denotes the distance between CU i and the receiver of D2D pair j

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Step 2 : Optimal Power Allocation Power Allocation Optimization Problem NP-hard! Z.-Q. Luo and S. Zhang, Dynamic spectrum management: Complexity and duality, IEEE J. Sel. Topics Signal Process., vol. 2, no. 1, pp. 5773, 2008.

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Step 2 : Optimal Power Allocation (cont.) Method for Finding Optimal Power At least one of the D2D pair and the cellular user transmit at the maximum power Optimal point on this line

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Step 2 : Optimal Power Allocation (cont.) potential operation points Optimal Power

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Step 3:Optimal Reuse Partner Selection D2D Throughput Gain Single D2D pair scenario Multiple D2D pairs scenario Date rate of cellular user with D2D Date rate of D2D Date rate of cellular user without D2D Maximum weight bipartite matching problem!

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Step 3:Optimal Reuse Partner Selection (cont.) Multiple D2D Pairs and Reuse Candidate Matching Maximum weight bipartite matching: Classic Kuhn-Munkres algorithm

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Summary of Proposed Three-Step Solution Step 1: Distance-Based Admission Control Find all the admissible D2D pair Find all the reuse candidates for each admissible D2D pair Step 2: Optimal Power Control Optimal power allocation for each D2D pair and its reuse partner Step 3: Maximum weighted matching Find the optimal D2D pairs and reuse partners matching

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Network Performance Simulation Parameters Cell radius500 m Uplink bandwidth5 MHz Pathloss exponent4 Pathloss constant0.01 Noise power-174 dBm/Hz Maximum D2D Tx power21, 24 dBm Maximum RCU Tx power24 dBm Minimum SINR of RCU[0, 25] dB Minimum SINR of D2D,[0, 25] dB Multiple-path fadingExponential distribution with unit mean ShadowingLog-normal distribution with standard deviation of 8dB

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Effect of D2D Cluster Radius Network Performance (cont.) Performance decrease with the radius of D2D cluster

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Effect of The Number of Active Cellular Users and D2D Pairs Network Performance (cont.) Existing a saturation point for the D2D pairs

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Outline Why D2D Communications? Topic 1: QoS-Aware Resource Allocation Topic 2: EE/SE Mode Switching Future Work

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EE/SE Mode Switching Motivation System Model Problem Formulation EE/SE Optimization Network Performance

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Motivation New Freedom For Potential D2D Users Three transmission modes Dedicated mode : Dedicated resource with direct link Reusing mode : Reusing resource with direct link Cellular mode : Conventional BS-relaying link Dedicated modeReusing modeCellular mode

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System Model Basic User Scenario: Single D2D pair and single cellular user Prioritized Traffic: Weighted user throughput Uplink Spectrum Sharing Guaranteed QoS Perfect CSI at BS D.-Q. Feng, G.-D. Yu, Y. Yuan-Wu, G. Y. Li, S.-Q. Li and G. Feng, Mode switching for device-to- device communications in cellular networks, invited paper), IEEE GlobalSIP'14, Atlanta, 2014.

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Problem Formulation Objective: Maximize overall EE(SE) EE(SE) Metric: Sum of weighted throughput/total power consumption (bandwidth) Mode Selection: denote the max EE(SE) in dedicated mode, reusing mode and cellular mode, respectively.

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EE Optimization at Dedicated Mode EE Optimization Problem Variables: spectrum and power

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EE Optimization at Dedicated Mode (cont.) Parametric Transformation For Nonlinear Fractional Programing (NFP) Dinkelbach Algorithm for NFP The critical step : Subproblem W. Dinkelbach, On nonlinear fractional programming, Management Science, 1967, 13(7): 492-498.

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EE Optimization at Dedicated Mode (cont.) EE Subproblem at Dedicated Mode Standard convex optimization problem Interior point method Logarithmic barrier function to remove inequality constraints Quasi-Newton method to obtain search direction Backtracking line search for step size S. P. Boyd and L. Vandenberghe, Convex optimization. Cambridge university press, 2004.

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EE Optimization at Reusing Mode EE optimization problem Variables power

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EE Optimization at Reusing Mode (cont.) Parametric Transformation for NFP EE Subproblem at Reusing Mode NP hard, however, objective function with difference of convex (D. C.) structure, G. R. Lanckriet and B. K. Sriperumbudur, On the convergence of the concave-convex procedure, in Proc. Advances in Neural Inform. Process. Syst., 2009, pp. 17591767.

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EE Optimization at Reusing Mode (cont.) Concave-Convex Procedure (CCCP) for D.C. Optimization Objective function differentiable Sequential convex approximation Properties For a fixed point is a stationary point that satisfies the KKT conditions of the D.C. problem CCCP Algorithm

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EE Optimization at Cellular Mode EE optimization problem Variables: spectrum, power Assuming, then, the same form as in the dedicated mode

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Network Performance Simulation Parameters Cell radius500 m Uplink bandwidth1.25 MHz Pathloss exponent4 Pathloss constant0.01 Noise power-174 dBm/Hz Maximum D2D Tx power125/250 mW Maximum RCU Tx power250 mW QoS of RCU[0, 1] Mbit QoS of RCU of D2D[0, 1] Mbit Multiple-path fadingExponential distribution with unit mean ShadowingLog-normal distribution with standard deviation of 8dB

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Switching vs Single Mode Transmission Network Performance (cont.) Mode switching Single mode

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EE SE Tradeoff Network Performance (cont.) EE gap SE gap Higher EE but lower SE Higher SE but lower EE

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Network Performance (cont.) Optimal Modes Reusing Mode for EE Dedicated Mode for SE

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Future Work Full-Duplex D2D Communications Unlicensed- Band D2D Communications D2D-Aissitend Small Cell Deployment Cooperative D2D Caching

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Thank you!