Demonstrating the Practical Challenges of Wireless Communications
Most electronics education worldwide teaches wireless communications with a typical focus on communications theory. At the University of Southampton, educators have taken a different outlook in teaching students the practical aspects of communication technology to better prepare them for their careers in industry. Students focus on the rapid prototyping of a wireless communications system with live radio frequency (RF) signal streaming for a practical approach to communications education. With this approach, students gain a valuable experience in manipulating live signals for a greater understanding of wireless communication and the associated practical challenges.
A Real Communications System to Demonstrate Practical Concepts
The University of Southampton have accomplished this demonstration of the practical concepts of wireless communication as part of their masters course in wireless communications. The focus was on creating a wireless communications system to demonstrate the concept of differential-quadrature phase-shift keying(DQPSK) and how it is used within wireless communications. The students were given a USRP™ (Universal Software Radio Peripheral) and tasked with building a DPSK transceiver in a practical session. Before this they attended a one-hour lecture on the USRP and how to use it to achieve their learning outcomes. Additionally were given a pre-session assignment to do, which familiarised them with LabVIEW and its environment.
Practical Challenges of Wireless Communication
Southampton students were tasked with building one half of a wireless communications system. The setup consisted of an incomplete DQPSK demodulator, which needed to be completed so that a modulated signal sent by a separate USRP device could be decoded. To complete this task, a number of steps covering different concepts are required so that the end result is a fully working communications system.
Figure 1. Block Diagram of the System
The students first applied a filter to the received and down-converted signal and compared this to the input of the filter in the transmitter of the system. They then down sampled the data to detect, synchronize, and extract the DPSK symbols from the waveform and compare them to those in the transmitter. Finally, students demodulated and decoded these DPSK symbols to recover the message bits, which are again compared with those in the transmitter.
After these three features were implemented into the demodulator, students rigorously tested their system by comparing their constellation graph and signal eye diagram to those of the transmitter, which is shown below.
Figure 2: Constellation graph and eye diagram.
The constellation diagram gives a visual overview of how the different phases in the phase-shift keying modulation scheme matched up to symbols and how they are represented within the signal envelope. They are important because they give a visual overview of how much interference or distortion is in a signal or channel and are a quick way of seeing if everything is functioning normally. The eye diagram gives a similar visual reference in that it helps show all of the different types of symbols within a channel superimposed over each other to see the characteristics of the system. From this students could infer characteristics such as if the symbols were too long, short, or noisy or poorly synchronized. If the eye is “open”, as it is in the above diagram, then it infers minimal distortion in the signal. If the signal was distorted, then the eye pattern begins to close, decreasing the spaces in the pattern.
Four Out of Five Students Would Like to Make More Use of USRPs
After the conclusion of the module on communications system, students completed questionnaires about their satisfaction and provided feedback on the practical session.
More than four out of five students, 82 percent, said that in the future they would like to make use of the USRP in the taught aspects of their course. In addition, 75 percent of students said that they would like to make use of the USRP in their MSc research projects—showing its great potential in all aspects of wireless communications education and research.
One student said that “The USRP gives an avenue for exploration. It is a good tool to bridge the gap between practical and theory.” Whilst another said that “The USRP vividly helps me understand the theory that I learned in class.” This shows that Southampton has created a strong benchmark in practical communications education.