Network Coding Testbed

Jeremy Bergan, Ben Green, Alex Lee

Presentation Overview

• Background Information • Project Overview

 • Framework Design

 • Plan & Schedule

• Prototyping

• Implementation

• Testing

Solution

• Network Coding is a scheme that has potentially larger throughput than current wired or wireless networks.

     

Problem

• 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 testing and logging layer to track testbed

performance.

     

Network Coding Overview

• Network Codingo Intelligently combining packets at intermediate nodes

to increase network throughput 

    

ANC: Decoding Interfered Signals

1. Node1 and Node2 simultaneously transmito Signals interfere at intermediate node

2. Intermediate node amplifies and forwards combined signal3. Node1 can decode Node2's message based on knowledge

of the message it sent previously 

Sachin Katti, Shyamnath Gollakota, Dina Kattabi, Embracing wireless interference: Analog Network Coding, in ACM SIGCOMM Computer Communication Review v.37, n.4, pp 397 – 408, October 2007

Requirements • Implement a testing framework for wireless networks

• Implement a Network coding scheme with equal or better throughput than traditional networks

   • Implement ANC MAC

   • Practical application to arbitrary network topologies

• Use of Universal Software Radio Peripheral (USRP)  • Use of GNU Radio signal processing libraries

 • Modular design

Deliverables• Network Coding Testbed

• Implement different wireless topologies & protocols

• Complete Documentation• Commented Code• Build Instructions• Repository Access

Resource Requirements• 3 USRPs

• RFX2400 Transceiver Daughterboard

• 3 Computers• Linux Operating System• GNU Radio Installed

Schedule

Design Process• Functional

Decomposition

• Prototype in Matlab

• Test in Matlab

System DesignHost:Generates and interprets data

Network:Packetizes and determines data route

MAC:Arbitrates channel access. Coordinatestransmission among nodes

Physical:Modulation/Demodulation Testing and Logging:Tools used in testing of system

Analog Network Coding Implementation• Physical Layer

o MSK modulationo ANC algorithm for decoding interfered signals

• MAC Layero Modified CSMA/CAo Allows for simultaneous interfering transmissions if they

will be able to be correctly decoded • Network Layer

o Predetermined routingo Similar packet format as 802.11

• Host Layero Random datao Predetermined patterns of data

Testing Procedure

• Implement ANC system in Matlabo Simulation in a controlled environment

 • Tested Matlab simulation

 • Split Matlab simulation to be implemented in GNU Radio

• Write & compile GNU Radio blocks

• Use Python to test each block

• Test entire framework over air

Matlab ANC Simulation

     

• Simulate a transmission and reception of interfered signal

• Decode unknown signal using ANC algorithm

• Advantages:• Debugging system

• Data Visualization

• System organization

Matlab ANC: Transmission

   

   

• Generate two signals with random data bits

• Generate a pilot sequence

• MSK Modulation

• Random overlap between two signals

Matlab ANC: Sampling

   

   

• Use pilot sequence to find start of individual signals

• Sample at optimal time for demodulation

Matlab ANC: Channel Measurements

   

   

• Variance over a sliding window• Indicator of interference

• Amplitude of individual signals• Measured at un-interfered sections

Matlab ANC: Decoding

   

   

• Use amplitude of signals to calculate possible phase pairs

• Use known phase difference to determine unknown phase difference

GNU Radio Implementation

     

• Determine how to port code from Matlab to C++

• Split code into blocks that deal with streams of data

 

GNU Radio Blocks

• Energy Detector• Uses magnitude of signal to determine beginning and

ending of signal.

• Sync Block• Uses pilot sequence to find start of individual signals• Packetizes each signal along with offset information

• Decoding Block• Runs ANC algorithm

GNU Radio Block Testing

• Non – Trivial• Must have entire block before testing• Involves two languages Python and C++

• SWIG makes C++ usable in Python• Lacking documentation

•  Once compiled use Python to test C++ code• Link C++ blocks together using Python• Generate data for blocks using Python

• Use Python modules to generate packets and other inputs

Future Additions to Testbed

• Complete initial design• Add Modulation Schemes to Physical Layer

o MQAMo MPSK

• Network Layer o Implement TCP/IP

• Testing Layero Inter-node Coordinationo Single Computer Simulationo Component Benchmarking

• Other Network Coding Schemes

Lessons Learned

Conclusion

• Plan time requirements better• Gained experience outside of normal area of study• Start prototyping early in first semester

• Designed network testbed that implements ANC• Simulated ANC system in Matlab• Implementation in GNU Radio

• Wrote GNU Radio blocks• Compiled and started testing

Questions?