Improvement and Expansion of Operational Range for STPA-BAA Spectrum Superposing Scheme Using Subcarrier Adaptive Modulation

Due to the demand for high-speed and large-capacity, wider transmission bandwidth is essential in wireless communication systems. It causes frequency resource shortage especially in microwave band. Therefore, efficient use of frequency resources even in different wireless communication systems is an important issue. As a technique to realize this, a frequency sharing scheme using subcarrier transmission power assignment (STPA) and blind adaptive array (BAA) has been proposed. Even when multiple systems use the same frequency band, it enables the secondary receiver to suppress interference with almost the same level of the desired signal by STPA-BAA. It is also effective in reducing interference to the primary receiver that has no interference suppression function. However, the STPA-BAA has a problem that the operational range is limited due to lowering the power of most of subcarriers. This paper attempts to resolve this issue by introducing subcarrier adaptive modulation. It can effectively expand the operational range of our proposed approach even in the low signal-to-noise-power-ratio (SNR) region.