15 August 2013
Our main research focuses on the following three fields: cognitive radio network systems (in particular, spectrum sensing techniques of OFDM signals); distributed estimation and detection in wireless sensor networks; and narrowband wireless communication systems. Cognitive radio techniques are expected to be a key technology used to achieve efficient usage of the available spectrum. In systems, spectrum sensing techniques play an important role because users must seek the radio spectrum correctly around themselves in cognitive radio networks. The aim of our lab is to develop cognitive radio techniques which are applicable to the low cost wireless receiver while keeping good performance.
We particularly enjoy the fact that research interests in which we are currently working may be adopted in the equipment of near-future wireless communication systems. Additionally, I (Shusuke Narieda) particularly enjoy working with a great team of lab members who are all students (20 – 22 years old) as they inspire me with their fresh ideas.
In our Letter, we have proposed a novel spectrum sensing technique based on feature (cyclostationarity) detection of OFDM signals for cognitive radio networks. The proposed techniques can reduce the computational complexity compared to the conventional techniques. In general, feature-detection-based spectrum sensing techniques using signal cyclostationarity is frequently used for signal detection, and the calculation of the cyclic autocorrelation function is required for these techniques. Our proposed spectrum sensing technique shows a simple calculation for a cyclic autocorrelation function. We evaluate the proposed technique by computational experiments and measurement.
Traditionally, there is no research that discusses the simplification of the implementation of feature-detection based OFDM spectrum sensing techniques, to the best of our knowledge. We believe that the development of a cost effective solution must be required for new widespread wireless communication systems. In our proposed spectrum sensing techniques, since no reference tables in the hardware, e.g. FPGA, are required, only a few adders are needed.
The next steps of our research are to compensate for analogue RF impairments in the spectrum sensing techniques of OFDM signals for cognitive radio networks. A wireless receiver is composed of several analogue RF circuits, e.g. low noise amplifier, phase shifter, oscillator, automatic gain control, filter and analogue-to-digital converter. The impairments caused by these circuits come from analogue circuit imperfection, e.g. I/Q imbalance at the phase shifter, sampling jitter and clock frequency offset at the analogue-to-digital converter. These effects of these circuits on wireless communications cannot be ignored. As well as affecting the general wireless receiver for single carrier or OFDM signals, it is known that the effects degrade the results of spectrum sensing in cognitive radio networks. The effects must be compensated to achieve the development of a cost effective solution for cognitive radio networks. As mentioned above, we believe that such compensation techniques needed for a new wireless communication system to become widely used.
Cognitive radio networks have the potential to alleviate the exhaustion of the spectrum for wireless communications. But for practical applications the problems to be solved extend over a wide range in the physical, data link and application layer, and so on. We hope that the current work that is happening in our lab will contribute, even in just a small way, to the progress of the future of wireless communications.
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