Software Defined Radio Testbed

Team may11-18Members: 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 receptionA/D and D/A conversionUp Conversion and Down Conversion

• ComputersMATLAB/ 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 / SimulinkSimulink will be used to generate and process signals on

transmitter side.USRP2s on both sides will transmit and receive signalsSimulink on the receiver side will process received signalsData packets should be transferrable using the system

• Complete documentationReports (Weekly + Final)Commented Models & CodeBuild instructionsRepository 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 usableCPU1 / MATLAB

USRP2 / Data TX

USRP2 / Data RX

CPU2 / MATLAB

System Decomposition• 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 successTesting & Logging

PHY

RF Daughterboard (USRP2)

Rx / Tx

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 SimulationMATLAB models of DBPSK & FSKSimulated with and without noise

Fig: A preliminary binary FSK model for MATLAB

Over the Air Physical LayerDesign FSK & DBPSK models, fit for over the air transmissionSampling time, center frequency becomes importantSampling 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 ReceptionKnown 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) bitsPosition indicating bits Payload dataFooter

• 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?