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Project Proposal

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Implementing Software Defined Radio – a 16 QAM System using the USRP2 Board Project Proposal Patrick Ellis & Scott Jaris Dr. In Soo Ahn & Dr. Yufeng Lu December 14, 2010Project Summary Software Defined Radio takes what used to be physically ingrained within the radio and provides a variety of hardware and software alternatives that add to it more flexibility and functionality. This project looks to implement a 16QAM communication system using a baseband receiver and transmitter and two USPR2 boards. It will show the benefits of Software Defined Radio (SDR) and will demonstrate the power, flexibility, and advantages that it gives the designer through the ease of modification that it provides. This project does, however, require a great amount of new, unfamiliar software which may prove to be one of its biggest challenges. Complete Description Background Software Defined Radio, as defined by the SDR Forum is a “Radio in which some or all of the physical layer functions are software defined.” Together, the above components will allow the realization of a SDR 16QAM communication system. Each component will be discussed in detail and then the overall system will be explained in the process. Goals The progressive goals of the project are listed as follows. 1. Design16QAM transmitter and receiver modules using GNU Radio companion (no USRP2 board or noise used at this point). 2. Add simulated noise resources to the communication channel within the prior system to introduce fading and multipath effect. 3. Design Decision Feedback Equalizer system to fully recover the transmitted data at the receiver end. 4. Explore the capabilities of GNU radio and boards by small side projects such as an FM receiver in order to more fully encompass the capabilities and span of SDR.Equiptment List The entirety of this project will consist of the following software and equipment: 1. Two USRP2 Boards – Offers a Xilinx Spartan 3 2000 FPGA,14-bit AD and 16-bit DA converters, digital up/down converters, gigabit Ethernet interface, external memory, and SD card. 2. BasicTX and Basic RX Daughterboards – Gives access to all of the signals on daughterboard interface and provide AD/DC outputs with no mixers, filters, or amplifiers. 3. GNU Radio Companion – an open-source software development similar to Simulink in nature whose applications are written in Python and the signal processing paths implemented in C++. 4. Python Interpreter – software to write and debug code written in Python. 5. Ubuntu – Version 8.04 or greater will provide the operating system required for GNU Radio and the USRP2 to function properly. USRP2 The USRP2 is a high speed Ethernet-based board that is specifically built by Ettus Research for software radio. Drivers are open source and there is a variety of free software to integrate such software toolkits as GNU Radio. The USRP2 is built with SDR in mind as it is made to be highly flexible with designer’s specific needs regarding frequency bands, connectors, and different daughterboards. Features: - Xilinx Spartan 3-2000 FPGA - Gigabit Ethernet interface - Two 100MS/s, 14 bit, AD converters o LTC2284 o 72.4dB SNR and 85dB SFDR for signals at Nyquist Frequency - Two 400MS/s, 16 bit, DA converters o AD9777 o 160 MSPS w/o interpolation o Up to 400 MSPS with 8x interpolation- SD card reader - MicroBlaze Processor Core - aeMB software implementation of MicroBlaze BasicTX and BasicRX Daughterboards The BasicRX board has 4 subdevices. Subdevice A is a real signal on antenna RXA, subdevice B is a real signal on antenna RXB, subdevice AB is a quadrature subdevice using both antennas (IQ), and subdevice BA is a quadrature subdevice using both antennas (QI). The Basic TX board is the exact same but with “TX” instead of “RX.” The boards do not allow any tuning of elements or gains, but the ability to up-convert signals greater than the Nyquist rate of the DAC can be done with aliasing. External RF Hardware must be used with these boards and the TVRX antennas. Features: - Serve as RF front end - Modulates output signal to higher frequency - Takes away input signal carrier frequency - BasicRX is a 1-250MHz Receiver - BasicTX is a 1-250MHz Transmitter GNU Radio, Python, and Ubuntu GNU radio is a free software toolset for building and implementing SDR. It is a signal processing package which provides a variety of signal processing blocks as well as the ability to develop ones own blocks. The signal processing blocks are written in C++ and are accessed, called, and implemented by Python; much in the manner an m-file would control a Simulink file. GNU radio, when implemented with the USRP2 must be on a Linux-based system. High Level Block Diagram Figure 1 shows the high level over-all system block diagram that shall be implemented within the final objective. As can be seen, the entire communication system is software-based and only the ADC/DAC and RF are hardware-based. The 16QAM system, orother systems, can be quickly changed through programming the Spartan3-2000 FPGA device on a USRP2 board. Figure 1 clearly points out the relationships between the USRP2, Daughterboards, and GNU Radio. GNU radio initiates the interfacing between the USRP2, daughterboards, and the signal processing that it performs. The daughterboards perform converting (up or down as needed) and the antenna transmits or receives the desired information. Figure 1 – High Level Block Diagram 16 QAM Communication System Figure 2 shows the general flowchart of a 16QAM system which shall be implemented on the USRP2 board via GNU Radio Companion. The 16QAM transmitting and receiving systems are shown on the top and bottom of Figure 2 respectively. The RRC blocks represent root raised cosine filters and the DFE is a decision feedback equalizer. The transmitting side works as follows: The 16QAM mapper takes in the data and selects 4 bits. Two sets of 2 bits are selected and are mapped to one of four values: -3, -1, 1, or 3. One symbol contains the I component and the other the Q component, the values of which are determined from the gray coding scheme. Each symbol stream is sent through the RRC block to decrease bandwidth. They are then used to modulate their respective carrier waveforms and added to form the transmitted signal. At the receiving end, the transmitted signal is split once again into its I and Q components and the modulating signals are brought back to baseband and


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