Teknillinen tiedekunta, 2013
Professor Mohammed Salem Elmusrati
Master's Degree Programme in Telecommunication Engineering
The licensed spectrum is becoming more congested due to increase in number of mobile users and wireless applications. This increase in spectrum usage necessitates the need to efficiently use the underutilized spectrum. While spectrum allocated to wireless communication is becoming congested, other licensed and unlicensed spectrum are underutilized. In response to this underutilization, cognitive radio has been proposed to support efficient use of the spectrum. With cognitive radio, radio devices can dynamically sense and use idle spectrum (white spaces) using their autonomous detection capability based on different spectrum sharing techniques. These spectrum sharing techniques promote coexistence and cooperation among dissimilar wireless technologies. As with other radio technologies, signal propagation in cognitive radio experiences multipath effects and causes interference with other users. Hence, this thesis extensively investigated the system capacity of cognitive radios when the channel encounters Nakagami-m fading and the maximal ratio combining (MRC) antennas diversity is implemented at the secondary user. The effective and ergodic capacity are mathematically and numerically analyzed and simulated. Therefore, this thesis covers the mathematical frameworks for analyzing the ergodic capacity and effective capacity of spectrum sharing cognitive radios with MRC antennas diversity under Nakagami fading. The maximum achievable information transmission rates at the physical layer (PHY) and the data link layer are obtained using the ergodic capacity and the effective capacity mathematical models respectively. The system capacity in each model scales as a logarithmic function of the channel power gains, subject to the average interference power and the delay quality of service (QoS) constraint in the case of effective capacity. The results obtained depict the maximum achievable information transmission rate when the secondary user (SU) is implemented with multiple antennas based on MRC diversity method, the channel fading statistically follows Nakagami-m distribution and the transmit power of the SU is subject to average interference power constraint to avoid harmful interference with the primary user (PU).
Cognitive radio, spectrum hole, fading, ergodic capacity, effective capacity,Rayleigh, Nakagami-m, white space, multipath, maximal ratio combining, underlay