Software-defined Radio
using Xilinx


A software-defined radio (SDR) allows for digital communication systems to easily adopt more sophisticated coding and modulation technologies, which is extremely important in meeting the ever-increasing demands of the wireless communication industry. An SDR has been constructed, using the Simulink tool, and implemented on the Virtex-II Field Programmable Gate Array (FPGA) development kit. In Simulink, the Xilinx system generator block set allows for easy fixed-point simulation, system testing, and implementation on hardware. The modulation scheme used in the system is Quadrature Phase-Shift Keying (QPSK). During transmission, the QPSK signal experiences frequency and phase shifts and the signal constellation rotates after coarse carrier synchronization at the receiver.  A phase-locked loop (PLL) circuit is designed to lock onto the QPSK constellation and allow recovery of data from the received signal. However, the QPSK signal locking is still subject to phase ambiguity. To resolve the phase ambiguity, a differential coding scheme is also implemented.   


Software-defined radios provide a versatile wireless communication solution for a wide range of applications, including cellular telephones, global positioning systems, and military grade communications. The SDR is applicable in nearly any wireless communication system and when implemented on a Field Programmable Gate Array (FPGA), the true advantages of this hybrid system are apparent.
    The SDR is a very cost-effective system in many ways. Since all hardware is physically programmed using software, re-design becomes relatively simple. Rather than discarding old hardware, the SDR is simply reprogrammed, updated and loaded back onto the FPGA, saving both time and money. The SDR also provides a capability for high quality communication without a need for expensive broadcasting equipment.
    In addition to its cost benefits, the SDR is also a very powerful and flexible system. In wireless communication, this means faster data rates and highly configurable modulation technology. For these reasons, the SDR is a rapidly emerging methodology in digital communication system design and implementation.
    Quadrature phase shift keying is a modulation scheme which sends a pair of bits per symbol, increasing data rate by a factor of two. Other modulation schemes such as 8PSK and 16PSK increase data rate even further, sending triplets and quadruplets of bits per symbol. A typical problem in QPSK and in wireless communication is carrier synchronization, or the synchronization of the oscillator at the receiver [1]. In order to do so, a phase-locked loop circuit must be introduced to the receiver [2]. This provides the local oscillator at the receiver with a frequency adjustment. However, once this correction is made, a static phase error called phase ambiguity will still exist. In QPSK systems [3], this phase ambiguity will be any multiple of 90 degrees. In order to properly decode transmitted data, a differential encoding scheme is implemented which corrects any phase ambiguity.

Designed by:

Anton S. Rodriguez & Michael C. Mensinger Jr.


Dr. In Soo Ahn & Dr. Yufeng Lu

Department of Electrical and Computer Engineering
Bradley University, Peoria IL 61625