Downlink capacity enhancement scheme based on cognitive radio for cellular relay networks

Abstract

Relay transmission strategy in cellular wireless communications systems were originally proposed to cover dead spots, e.g., subways, tunnels or in-building areas, where a base station (BS) cannot appropriately support mobile users. Recent studies have shown that a cellular system adopting relay transmission strategy has other potential advantages such as increased system capacity and performance improvement if relay stations (RSs) cooperate for transmission. Without cooperation between RSs, however, these advantages are limited due to intra-cell and inter-cell interference. Dedicated allocation of frequency band to RSs can circumvent the interference problem, but it sacrifices spectral efficiency. In most radio systems, users rarely utilize all the assigned frequency bands at a certain time and a location. Such a frequency band not occupied by a primary user (PU) is called a $\It{spectrum hole}$. The spectral inefficiency caused by the spectrum holes motivated $\It{cognitive radio}$ (CR) technology that present unlicensed secondary users (SUs) an opportunity for using spectrum holes. CR makes an SU to and use the spectrum hole without interrupting the operation of PU. The fact that CR technique brings more efficient spectrum utilization motivates its adoption to cellular relay networks. The advantage is interference reduction between RSs and BS by allocating orthogonal frequency bands to RSs from BSs for downlink. Even though the same advantage can be achieved by using a dedicated channel which is orthogonal to cellular band, it is much more efficient to use orthogonal bands by opportunistic spectrum access in terms of spectral efficiency. In this thesis, we propose two operating scenarios of employing cognitive radio to downlink of relay networks. The first scenario uses ISM band while the second scenario exploits opportunity of channel use at UHF spectrum. The capacity gain over conventional relay is investigated in terms of system capacity, which is un...