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Design and Analysis of Multi-Hop D2D Communications

Presented by Chandra R. Murthy Joint work with Sireesha Madabushi, Govind R. Gopal, and Vinnu Bhardwaj Signal Processing for Communications (SPC) Lab Indian Institute of Science (IISc) Bangalore, India

June 23, 2016

Multi-hop D2D SPC Lab, IISc 1 / 10

Introduction

D2D Communications

Direct communication between a pair of devices without going through the base station

Major challenges

◮ Interference avoidance/cancellation ◮ Device discovery ◮ Resource management ◮ Mode selection

Multi-hop D2D SPC Lab, IISc 2 / 10

Goals of this Study

Motivation

◮ Direct path is not always feasible! ◮ But other high rate D2D links may be feasible!! ◮ Is it possible to route data over multiple hops?

Aim

◮ Maximize throughput between a source-destination pair under an

interference constraint imposed by the cellular network

◮ D2D multi-hop paths are allowed

Method

Two part approach:

• 1. Optimal route discovery
• 2. Sequential link activation and its throughput analysis

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System Model

◮ M D2D users and N base

stations (BSs)

◮ Uplink-inband D2D ◮ Locations of D2D users and

BSs are known, locations of cellular users are unknown

◮ Channels undergo path-loss and

Rayleigh fading

◮ Only statistical CSI is

available/used for routing

Base station Cellular user D2D source D2D destination D2D relay Interference Cellular/D2D data

Figure: Uplink-inband D2D with M = 3 D2D users and N = 1 BS

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The Two Schemes

◮ Fixed rate scheme: all feasible D2D links achieve the same rate ◮ Fixed outage scheme: each D2D link provides its own rate at a

given outage probability

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Fixed Rate Scheme: Overview

Given: From cellular network

◮ Interference threshold at the BS, γbs ◮ Interference outage probability, pb: Pr{Pint b

> γbs} ≤ pb From D2D network

◮ SINR threshold at D2D Rx, γth ◮ Data outage probability, pd2d: Pr{SINRtr ≤ γth} ≤ pd2d

• 1. Determine the feasible links according to the constraints above
• 2. Get the rate matrix and apply routing algorithm
• 3. For the throughput-optimal route, apply sequential link activation

(SLA) scheme for data transmission

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Fixed Outage Scheme: Overview

Given: From cellular network,

◮ Interference threshold at the BS, γbs ◮ Interference outage probability, pb: Pr{Pint b

≥ γbs} ≤ pb From D2D network,

◮ Data outage probability, pd2d: Pr{log2(1 + SINRtr) ≤ Rtr} ≤ pd2d

• 1. Calculate the highest possible link rates for the data outage

probability, pd2d

• 2. Apply Dijkstra’s routing algorithm on the rate matrix
• 3. For the throughput-optimal route, apply modified sequential link

activation (M-SLA) scheme for data transmission

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Comparison of the Schemes

Fixed rate Fixed outage All links achieve same rate with different

• utage probabilities

different rates with same outage probability Throughput

(1−pout) Nhops R

(1 − pout)Reff Delay

Nhops (1−pout)R 1 (1−pout)Reff

Off-diag entries

• f rate matrix

can be zeros are all non-zero As γth/pd2d increases more and more links become infeasible more links start supporting higher rates

Table: Different cases for link feasibility analysis during routing and data

• transmission. R = log2(1 + γth), Reff =
• 1

RS1 + . . . + 1 RKD

−1

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Conclusion

◮ Proposed two schemes for D2D communication system design ◮ Found a throughput optimal route with the help of well-known

Dijkstra’s algorithm

◮ Obtained expressions for throughput during data transmission

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D2D Mode Selection: An Information Theoretic Perspective

◮ System Model: Single cell with 2 Tx-Rx pairs, simplex

communication1

◮ Possible modes of operation:

• 1. Conventional cellular mode
• 2. MAC-BC cellular mode
• 3. Dedicated D2D mode
• 4. Mixed cellular-D2D mode

◮ Goals:

• 1. Characterize achievable rates under different modes
• 2. Propose and analyze algorithms for mode selection
• 3. Handoff from D2D mode to cellular mode and vice versa
• 4. Extend to K user pairs, account for inter-cell interference, etc . . .

1Joint work with Ribhu, Kausik Koneripalli, and Vinnu Bhardwaj

Multi-hop D2D SPC Lab, IISc 10 / 10