Network Coding Testbed Using Software-Defined RadioAbstractIn current generation networks, network nodes operate by replicating and forwarding the packets they receive. In network coding, nodes operate by combining received packets. This allows for a more efficient and robust network. This project aims to build on previous research as well as develop software that can be used for future research in network coding at Iowa State.

Problem Statement• Current network protocols are not the most efficient.• Network Coding is a scheme that has potentially larger throughput than

current wired or wireless networks.

Solution• Built a network coding testbed to implement network coding protocols and

topologies.• Implement Analog Network Coding (ANC).• Utilize the Universal Software Radio Peripheral (USRP) to send and receive

the physical packet.• Implement a test and logging layer to track testbed performance.

Design Requirement• Integrate our ANC implementation

with a simple traditional wireless network.

• System shows equal or better throughput than a traditional wireless network.

• Each functional block of the system shall be simulated in Matlab before being implemented in GNU Radio.

System DesignThe Testbed is based on a traditional wireless network. Each component is built with a standardized interface so it can be easily modified or swapped out for a new component.• Host Layer: Provides functions for

generating and interpreting data.• Network Layer: Packetization of data

and routing. Contains higher level functions of networking.

• MAC Layer: Coordinates channel access between nodes.

• Physical Layer: Does most signal processing work. Defines modulation, demodulation, carrier sensing, signal filtering. Interfaces with USRP to transmit/receive data.

Technical Details• MSK Modulation: A form of phase shift Keying that creates the signals based

on binary data consisting of sharp transitions. MSK also has very good bit-error properties and a simple demodulation algorithm.

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Project Work Breadown

Research

Implementation

Testing

Documentation

Matlab Simulation SummaryThis project builds on previous research in network coding, particularly Analog Network Coding. Network coding has the potential for much higher throughput than current networks. Our testbed will help develop the research of Analog Network Coding.

Testing• Matlab: Used to test entire system before code was written for GNU Radio.

Tested • GNU Radio Block: After each block was written in C++ we used Python to

connect the blocks and test their functionality. • Over the Air: The final test was to send packets using the USRPs. Our

ultimate goal was to send two packets, have them interfere at a router, and be decoded at the original computer.

Client/Faculty Advisor: Aditya Ramamoorthy May 10-08 http://seniord.ece.iastate.edu/may1008Assitant Advisor: Shizheng Li Ben Green (CprE), Jeremy Bergan (CprE), Alex Lee (EE)

Analog Network Coding• 100% throughput improvement – Normally would take 4 time slots for

transmission, but only takes 2 with ANC.• Interfered message amplified and forwarded – Routing node only amplifies

interfered signal and sends it to the nodes.• Message Decoded at Node - Because each node has knowledge of their sent

packets they can decode the received interfered message.

Variance DetectorThe variance of the received signal

is a good measure of where the interfered section starts and ends

SynchronizationSynchronization of the two signals

by cross-correlation using a known pilot sequence

Phase EstimationDetermining possible phases of

both signals using their known amplitudes and the received sample

Energy DetectorThe beginning and end of the signal

are detected by measuring the energy of the incoming signal

DecodingEstimated phase differences are

compared to known phase differences from sent packet