Analysis of Queue Behavior in Multi User Cognitive Radio Networks

Abstract

The wireless Radio Frequency (RF) spectrum is getting highly congested due to the continuous increase in the demand for high data rate services. The concept of Cognitive Radio (CR) allows secondary/unlicensed users to use a part/slice of a licensed spectrum (which is referred to as a channel), as long as the primary/licensed user is not transmitting in that channel during that time. In order to find the primary free channels in the RF spectrum, CR must perform spectrum sensing before it can transmit its signal. The problem gets compounded when there are multiple secondary users trying to sense, find and access the available free channels. newlineIn many situations, the data packets of CRs arrive in bursts and are stored in a buffer/queue, before getting transmitted. The stability of queues is critical to recognize the quality of communication experienced by the secondary users. Also, due to hardware limitations, CRs may need to do spectrum sensing in each channel separately. CR will have an order in which it generally proceeds to sequentially sense the various channels available, which is referred to as the channel sensing order. Each CR needs to find not just a free channel but also a good quality channel i.e., if a channel it senses to be free has a very poor signal-to-noise ratio (SNR), it can skip the channel and continue sensing according to its sensing order with the hope of finding a better-quality channel in the future that will result in a higher effective throughput. Under these conditions, optimal sensing order to maximize the overall throughput of the CRN can be obtained. In this present study, the stability behavior of queues in multi-user CRN with optimal and sub-optimal/intuitive sensing orders has been analyzed. newlineFirst, the case when there is a centralized coordinator who controls the channel sensing and scheduling process is considered.