Downlink Transmission of Distributed Antenna Systems in High Building Environments Hassan Osman, Huiling Zhu, Temitope Alade and Jiangzhou Wang University of Kent, Canterbury, CT2 7NT, United Kingdom, {ho33, h.zhu, ta320, j.z.wang}@kent.ac.uk ABSTRACT Over the last few years high data rate wireless transmission has gained considerable attention in hot spot areas, including high buildings. It has been demonstrated that distributed antenna systems (DASs) improve the performance of the indoor environment by covering dead spots. In this paper, a DAS architecture for high buildings is investigated, proposed and analyzed. The goal is to provide high data rate for indoor mobile users by exploiting spatial diversity and reducing the distance of radio transmission. In this system, the frequency is reused among floors. The radio signals in high buildings can propagate vertically and reach the neighbouring floors. Therefore, the performance of the system is limited by co- channel interference. Direct propagation inside the building and reflection from nearby buildings have been considered in the channel model. Based on the theoretical analysis, the impact of the position of the user on the performance is discussed in terms of the bit error rate (BER). It is also demonstrated how the attenuation caused by the floor separation in high buildings should be taken into consideration during the planning of the frequency reuse factor. Index Terms – Indoor wireless communication, DAS, co- channel interference, frequency reuse factor. I. Introduction Future wireless communication systems are expected to provide high data rate transmission in indoor environments such as office buildings, warehouses and factories. Recently, the transmission of wireless data has been growing fast and the mobile communications industry expect that wireless high data rate services will form the foundation for future services. Although voice and low data rate services were the first applications for mobile users, the focus in recent years has shifted. Advancement in technologies and the need for wireless communications services offered by the service providers have led to an increased level of high data transmission in mobile applications. Delivering a high speed wireless transmission for indoor environments is becoming a challenge in recent years. The indoor channel suffers from severe multipath fading, which seriously degrades the performance of the communication systems [1]. The modern high buildings can represent a harsh propagation environment because, the metallic structure of the building, metallic window shield and furniture can prove to be real reflectors and blockers of the signals. The penetration and propagation loss among floors is also present. However, for existing wireless communication it is a challenge to deliver high data rates transmission for indoor users because the distance between the outdoor base station and the user is too far. Therefore to cope with the future wireless transmission demand, the distance between the base station and indoor user should be shortened. An effective and feasible solution for this problem is the indoor distributed antenna systems (DASs) [2]. Indoor DASs have gained considerable attention, due to its capability to improve the coverage in indoor communications, and it also helps to increase the data rate transmission and the spectral efficiency. The diversity offered by the DAS can combat shadowing and fast fading. The DAS not only reduces transmit power, cover dead spots and provide macrodiversity of the large scale fading, but also have the capability to enhance signal quality, increase system capacity and reduce transmission distance [3, 4]. The DAS comprises a number of antennas that are spaced apart from one another. These antennas, called remote antenna units (RAUs) are separated and connected to a central unit (CU) via optical fibres or coaxial cables. In the proposed DAS in a high building environment, a number of neighboring floors are grouped together and are controlled by one CU. In this system, downlink transmission is considered where a CU transmits information to the user in the reference floor, the RAUs in the floor first receive the signal from the CU via optical fibres, and then forward it to the user via radio channels. Thus, multiple RAUs on the floor provide spatial diversity by sending the same data to the user. Due to limited available spectrum, the same spectrum can be vertically reused among floors controlled by different CUs. However, co-channel interference will exist among the floors using the same spectrum. In high buildings, it has been demonstrated that the radio signal propagates among the floors and can reach the other floors. According to measurements results [5, 6], the radio signal reaching the other floors can be strong in some circumstances. Indoor DAS has not been investigated yet in high buildings, although some propagation measurements have been presented for the indoor environments. A vertical spectrum reuse among floors in a building was presented in [7] by evaluating the outage probability. However, only one BS with one antenna unit was considered for each floor and the bit error rate (BER) performance was not evaluated. In the work presented in [8], the spectrum efficiency in high buildings based on the position of the base station has been presented. However, the vertical frequency reuse of DAS in a high building has not yet been studied. In this paper, mathematical channel model based on measurements results has been proposed for high building environments, the indoor DAS has been investigated in terms of BER performance. The influence of the position of the user in the reference floor 978-1-61284-231-8/11/$26.00 ©2011 IEEE This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE ICC 2011 proceedings