Ultra wideband communication trends and challenges
radio communication has developed remarkably. Many wireless communication systems have arrived. As a result, convenient frequency for radio systems is draining. Cognitive Radio has drawn attention as a new technology that improves frequency utilization efficiency and mitigates interference to primary radio system . Cognitive Radio is a radio or system that senses, is aware of its operational environment, dynamically and autonomously adjusts its radio operating parameters, and makes a commission with desired quality of one user of communication possible. By applying this technology, much more users can use wireless system without interference from other systems. On the other hand, UWB wireless communication systems have attracted attention as a new system that enables low power consumption, high speed communications, low costs and accurate locations capability. Since the UWB band overlaps the spectrum of existing narrowband and wideband systems, its worldwide acceptance is mainly conditioned by coexistence issues. Regulatory bodies, such as Federal Communication (FCC) in U.S., have imposed restrictions on UWB transmissions, even though they do not automatically guarantee conflicting free coexistence. Therefore, Detect and Avoid (DAA) are studied to mitigate interference to primary radio system. General interference mitigation methods, which are not limited to UWB only, are presented in . Collaborative and non-collaborative coexistence mechanisms are proposed. In the collaborative scenario, different systems are able to share information and negotiation channel access. In the non-collaborative scenario, different systems do not have the ability to coordinate their transmission. There, wireless systems can only use strategies such as carrier sense multiple access or adaptive frequency hopping. The disadvantage of such strategies is that the channel is not used to its maximum efficiency. However, since existing systems are usually not collaborating, we consider the non-collaborative approach as more promising for UWB systems and use it as basis for our considerations.
Almost conventional DAA technologies are mechanisms on time domain or frequency domain. In the DAA technologies on time domain, the UWB system detects any other wireless system with power detect. The UWB system transmits in the time between adjacent bursts of existing wireless systems where the channel is not occupied. In the DAA technologies on frequency domain, the UWB system detects frequencies which any other wireless system uses and transmits by using adaptive frequency hopping or pulse which is framed to avoid frequencies used by any other systems. However, these technologies have some issues. The issues on time domain have a risk of losing communication opportunities of UWB and on frequency domain have pulse shape distortion which influence orthogonality of waveform. In this paper, we propose the access control which can avoid interference by using an array antenna. An array antenna is equipped by WPAN coordinator to use adaptive beamforming. This algorithm for access control can not only avoid interference to wireless local area networks (WLAN) nodes but also make an environment in which WPAN nodes can communicate actively.