As the increase of the demands of wireless access, the improvement of capacity is highly required, especially in some long and narrow areas, such as train stations, shopping malls, or airports and so on, which is also called as linear-cell environment. Leaky coaxial (LCX) cable is widely used in wireless transmission communication systems as antenna for linear-cell environment. Usually, other researches just assumed that one LCX is treated as one antenna. Our recent research have proposed that one single LCX cable can be used as two antennas and the method to utilize one composite cable, which consists of a pair of LCXs with different radiation characteristics, to configure a multiple-input and multiple-output (MIMO) system. Compared with the system using Omni-directional antennas, the proposed LCX-MIMO can achieve higher capacity with less interference and less handover process. In addition, our proposal can utilize one LCX cable as two antennas and further configure a 4-by-4 MIMO channel using two LCX cables, which can reduce the required space of equipment and materiel cost.
In this thesis, we will compare the capacity of the LCX-MIMO system with three methods of power allocation as equal power (EP) allocation, Spatial-domain water-filling (SWF) power allocation and Spatial-Frequency domain Water-filling power allocation or Double domains water-filling (DWF) allocation to find the capacity difference with different power allocation strategies. We also investigate the capacity difference between power allocation methods over different frequency band and with different spacing between the LCX cables.
The results of our research show that the proposed system can reduce the space requirement for MIMO deployment for wireless application over linear-cell environments over 2.4GHz band. It also shows that the proposed LCX-MIMO channel has larger capacity than that of using monopole antennas at both sides. Over 5GHz band, the proposed LCX-MIMO channel using water-filling (WF) allocation scheme can have the capacity near to that of $i.i.d.$ channel. On the other hand, the capacity has only minor decrease using the simple equal power allocation scheme if the system utilize LCX cables to configure MIMO systems for both 2.4GHz and 5GHz bands which reduces the computational complexity. The results in 5GHz bands show that it has good channel capacity even if the spacing between the pair of LCXs is as small as 2cm. In addition, it also shows that Double domain WF algorithm improves the capacity compared with other methods at the non line-of-sight.