Software Defined
Radio Testbed
Team may11-18
Members: Alex Dolan, Mohammad Khan, Ahmet Unsal
Adviser: Dr. Aditya Ramamoorthy
Presentation Overview
 Background Information
 Requirements
 Deliverables
 System Design
 Implementation
 Testing & Analysis/ Error Calculations
 Image File Transfer
 Conclusion
Background Information
Problem
• MATLAB Simulink is a
relatively new platform for
Software Defined Radio.
• Very little work has been
done to build a
communication system of
SDR using this platform.
Solution
• Build a Digital Communication
System using MATLAB
Simulink and USRP2.
• Implement the Physical Layer
in MATLAB Simulink
environment.
• Utilize the Universal Software
Radio Peripheral-2 (USRP2) to
send and receive the physical
packet over the air.
• Test the communication
System using data packets.
Functional Requirements
 Use of Universal Software Radio Peripheral 2 (USRP2) & MATLAB
Simulink
 Non Coherent schemes like FSK, DBPSK modulation schemes must
be implemented
 Build point to point digital communication system
 Maximum bandwidth utilization
 Transmission rate of 100-125 kbits/sec
 Test limitations of MATLAB & Simulink as a platform for SDR
 System must be reusable for academic purposes and further
research
Resource Requirements
• USRP2
 Daughter boards (RFX2400, RFX400 etc.) (80 MHz-2.9 GHz)
 Connection Cables (Ethernet cable)
 Data transmission and reception
 A/D and D/A conversion
 Up Conversion and Down Conversion
• Computers
 MATLAB/ Simulink
 Data generation, digital modulation, demodulation, filtering, error
control, synchronization etc. to make data usable.
 Very High speed computers needed to process data (e.g. Intel i7)
 Windows Operating System
Deliverables
• Functional Digital Communication System
 Using USRP2 and MATLAB / Simulink
 Simulink will be used to generate and process signals on
transmitter side.
 USRP2s on both sides will transmit and receive signals
 Simulink on the receiver side will process received signals
 Data packets should be transferrable using the system
• Complete documentation
 Reports (Weekly + Final)
 Commented Models & Code
 Build instructions
 Repository Access
Schedule
System Design Process
Build & test models in Simulink
environment
Simulate with/without white
Gaussian noise
Use simulation results to create
models for over the air
transmission
Test models and document
results
System Decomposition
• CPU1 generates data from MATLAB & passes to USRP2
• USRP2 on the transmitter side transmits the data over the air
• USRP2 on the receiver side receives the data & passes to MATLAB on CPU2
• MATLAB receives the data from USRP2 & analyzes it to make it usable
CPU1 / MATLAB
USRP2 / Data TX
USRP2 / Data RX
CPU2 / MATLAB
System Decomposition
PHY
RF Daughterboard
(USRP2)
Rx / Tx
Testing & Logging
• Physical layer:
• MATLAB Simulink
• FSK, DBPSK modulation / demodulation, signal processing
• Synchronization and packetization
• USRP-2
• Ethernet interface with 100 MSamples/s, A/D & D/A conversion
• Testing and Logging:
• Tools used to test the system
• Tracks progress and success
Implementation
Built models of physical layers inside MATLAB environment
Focused on two schemes:
DBPSK (Differential Binary Phase Shift Keying)
FSK (Frequency Shift Keying)
Tested models with/without noise induced environment
Next phase: Built over the air models using USRP2s
MATLAB Simulation
MATLAB models of DBPSK & FSK
Simulated with and without noise
Fig: A preliminary binary FSK model for MATLAB
Over the Air Physical Layer
Design FSK & DBPSK models, fit for over the air transmission
Sampling time, center frequency becomes important
Sampling time has to be consistent throughout the whole
system
Over the Air Physical Layer
More signal processing needed to be added
Timing recovery, filters, etc.
There was no synchronization between USRP2s, so
recovery of data had to be designed
Testing & Analysis
• Tested primarily in three phases.
 Single bit Transmission Reception
 Known Binary Sequence Transmission Reception
 Image File Transfer
• Single Bit Transmission


Continuously transmitting one bit over the air
Looking at the scope on the receiver end to verify
Testing & Analysis
• Known Binary sequence transmission



Encoded data to add headers and footers, creating a frame
ready for transmission
Receiver side, sent the data to MATLAB workspace for analysis
Created a script file to analyze the workspace data using
autocorrelation techniques
Fig: FSK transmitter with known binary sequence
Error Rate Calculation
• Transmitted 128-bit sequence
(including header, data,
footer) & calculated bit errors
• Exported data from Simulink
model to Workspace and
processed the data from
there
• The xcorr function was used
to determine the location of
frames, headers and footers
• Plotted this function to
observe trends
Fig: Plot of xcorr function on received data
Testing & Analysis
• Tested both systems for continuous single bit & known
sequence
• FSK showed better performance
• DBPSK had errors not suitable for data transmission
• Proceeded to image file transfer for FSK
Image File Transfer
Transmitter Side
• Image files needed to be encoded to packets for use on the
system
• Encoded the image files to become a binary matrix, utilizing a
colormap that is known on both sides
• A typical frame would include:
 Header
 CRC (Cycling Redundancy Check) bits
 Position indicating bits
 Payload data
 Footer
• Once encoded, the image file is ready for transmission
Image File Transfer
Receiver Architecture
• Received data is sent to workspace
• Each frame is defined, and analyzed
• CRC bits are used to check for accuracy
 If CRC check passes, the payload data of the frame is placed
where the position indicating bits indicate
 If CRC check fails, the program moves on to the next frame
• When all the frames pass CRC checks, and are assembled, image
transfer is complete
Image File Transfer
• Started with small binary images
• Finally worked with .gif format
• Each pixel is composed of 8 bits, then converted to an integrer.
• Successfully transferred small image
Conclusion
Lessons Learned
 How to manage our time
requirements
 How to manage focus in
a research based
project.
 Gained experience
working on an
application of our area of
study.
Results Achieved
 Discovered capabilities
and shortcomings of a
point to point data
communication system
in Simulink.
 Application
 Image file transfer
successful
 Potential for more
applications
Thank you for your patience.
Questions?