Yasunori Futatsugi

Comparative Analysis on Interference Suppressive Transmission Schemes for White Space Radio Access

With opening up of the TV white spaces for opportunistic access, designing a flexible physical layer (PHY) scheme has become an important focus for cognitive radio (CR) systems. Two possible PHY design solutions proposed are: generalized frequency division multiplexing (GFDM) and interference avoidance by partitioned frequency and time domain transmission (IA-PFT). Both of these methods extend the orthogonal frequency division multiplexing (OFDM) scheme to be applicable as a flexible CR PHY solution in a fragmented spectrum. In GFDM, introduction of pulse shaping filters reduces the out-of-band radiation of the opportunistic signals into the frequency band of the incumbent users; while in IA-PFT, simultaneous cancellation carrier insertion and time windowing technique suppress spectral leakage into the incumbent band of operation. In this paper, these two different approaches are compared in terms of interference suppression, transmission performance and processing complexity.

Interference Avoidance Transmission by Partitioned Frequency- and Time-Domain Processing

This paper presents an interference avoidance transmission technique for dynamic spectrum access (DSA). Generally, OFDM transmission induces high out-of-band emission due to the side-lobes of the transmitted sub-carriers. For a DSA based OFDM system, it is thus important to reduce the out-of-band emission. Aiming at providing high suppression effect for an interference avoidance notch, an interference avoidance transmission by partitioned frequency- and time-domain processing (IA-PFT) is proposed. IA-PFT is configured by a partitioned combination of the CC processing in the frequency domain and windowing processing in the time domain. Computer simulations show that IA-PFT reduces the interference power spectrum density under the condition of a highly prioritized wireless microphone in white space. Moreover, it is shown that IA-PFT realizes transmission performance and PAPR performance as much as those attained by conventional interference avoidance methods.

Performance improvement in LEO-to-ground free space optical communication systems with adaptive distributed frame repetition

We proposed and evaluated the effectiveness of a simple rate control technique of Adaptive Distributed Frame Repetition (ADFR), which achieves both high speed link in the stable condition and suppresses the influence of turbulence-induced fading in the unstable condition. In order to estimate its performance in the LEO-to-Ground link with 10-Gb/s modulation speed, we developed a numerical simulator which enables us to calculate the frame error rate and the throughput under the specific turbulence condition emulated by random phase screens. We confirmed that ADFR can increase the link duration and the capacity by increasing the tolerance to the fading especially in the region of lower elevation angle. In addition, we evaluated its effectiveness through the comparison with the general adaptive rate control, in which the receiver sensitivity can be manipulated in accordance with the link conditions. The results show that ADFR provides similar performances with the sufficient received optical power.

A partial spectrum transmission method for dynamic spectrum access

This paper proposes a partial spectrum transmission (PST) method for dynamic spectrum access (DSA). For DSA, it is preferable to select modulation scheme which is appropriate for the low-priority users condition and radio environment by taking into account the required Eb/N0, frequency efficiency and PARR. When received SINR condition is better, QAM is selected for high-speed packet communication. However, QAM may cause link performance degradation due to the shorter Euclidean distance. On the other hand, PSK is capable of preventing such performance degradation. In this paper, we propose a PST method using PSK. It is shown by computer simulations that the required Eb/N0 at a BLER of 10-2 and the PAPR for the proposed PST (1/2) are approximately maximum 1dB better than those of 16QAM respectively.