Cognitive Networks: Towards Self-Aware Networks

11.2. Cognitive Radio Networks

11.2.1. Cognitive Radio Network Functions

11.2.1.1. Spectrum Sensing

One of the primary requirements of cognitive networks is their ability to scan the spectral band and identify vacant channels available for opportunistic transmission. As the primary user network is physically separate from the secondary user network, the secondary users do not get any direct feedback from primary users regarding their transmission. The secondary users have to depend on their own individual or cooperative sensing ability to detect primary user transmissions. Since the primary users can be spread across a huge geographical area, sensing the entire spectral band accurately is a challenging task ^{[] []}. The secondary users have to rely on weak primary transmission signals to estimate their presence. Most of the research on spectrum-sensing techniques falls into three categories: transmitter detection, cooperative detection and interference-based detection ^[]. The main aim of all these techniques is to avoid interference to primary transmissions. The amount of interference caused by all the secondary users at a point in space is referred to as the interference temperature ^[] at that point. When a primary user transmission is taking place, the interference temperature should be below a specified threshold near the primary receivers. However, this is not easy to achieve as the location of the primary receiver is not known to the secondary users. Additionally, when multiple ...