Abstract— In this paper, the system capacity of a multi-cell IEEE 802.16j system operating in transparent mode is investigated. A previous published analytical model is used and incorporates interference from neighbouring cells. The model can be used to determine downlink performance under max-min fairness constraints for both sectored and omnidirectional systems with different amounts of relays. The study provides guidelines on the design of 802.16j systems operating in transparent mode – specifically, how to maximise throughput for such systems. It is shown that inter-cell interference from relays is limited in a suburban environment and that relays can deliver significant gains over single hop systems: gains of 30% and 60% can be achieved without and with spatial reuse in an omnidirectional system while 15% and 25% in a sectorised system. Index Terms—IEEE 802.16j, transparent relay, multicell, interference, spatial reuse, performance I. INTRODUCTION EEE 802.16j Multihop Relay (MR) [1] have the potential to achieve cost savings while realising greater coverage and/or capacity for IEEE 802.16e-2005 [2] systems. The standard defines two modes of operation – transparent mode and non- transparent mode. The former is specifically designed to enhance the system throughput within the base station (BS) cell coverage, while the latter is intended to provide coverage extension and to a lesser extent throughput enhancement. The specifications for both operating modes differ in several aspects, primarily the frame structure, and lead to different issues with the system design. Here, the focus is on transparent mode operation. One important aspect in such systems is the impact of the additional inter-cell interference arising from transparent relays in neighbouring co-channel cells. It is unclear what performance gain can be achieved through the deployment of transparent relays over traditional multi-cell 802.16e systems under different configurations. Indeed, many parameters have a significant impact on the performance of these systems and hence, multiple parameters need to be considered simultaneously to determine a system design which maximises the achievable gain for such systems. The objective of this work is then to investigate the achievable performance gain in a suburban environment from the deployment of transparent relays in an omnidirectional and sectorised system, respectively. The analysis carried out here takes into account the following parameters: the cell range, the tree topology determined through a path selection algorithm, the relay positioning within a cell, the number of relays in each cell and the transmit power at the relay stations (RS). The aggregate system throughput in the omnidirectional case and the sectorised case are determined under max-min fairness in which approximately equal performance is delivered to all subscribers, in scenarios with and without spatial reuse. The study is a development of previous work [3][4] and two contributions are made in this work. First, inter-cell interference is included into the analytical model [3] and the graph based model [4] used to determine the performance of multicell transparent relay mode 802.16j system under different frequency reuses and antenna types at the BS. Secondly, guidelines are provided on the system design in order to maximise the gain that can be achieved through transparent relays. The paper is structured as follows. In section 2, the related work on the system capacity of 802.16j system is presented. The system model is described in section 3, with a description of the system architecture under study and the propagation and interference model used. Next, in section 4, a description on the configuration of several parameters pertinent to the system design is given. Finally, the results of the analysis for both the omnidirectional and sectored cases are presented in section 5 and the paper is concluded in section 6. II. RELATED WORK While the 802.16j standard is expected to be ratified in the first half of 2009, some research work is starting to appear on the gain that can be achieved in 802.16j systems. This work can be broadly divided in studies focusing on single cell systems and multi-cell systems in which the BSs are assumed synchronised. Under some specific assumptions on the system configuration, the work in [4] answers some initial question on the achievable throughput gain with single cell transparent mode 802.16j systems. The paper shows that through the deployment of transparent relays 55% and 125% gain can be achieved in the downlink (DL) over 802.16e systems without and with spatial reuse, respectively. Hence, the deployment of RSs provides significant gain over 802.16e systems in the DL System-Level Performance Evaluation of Multi-cell Transparent Mode Relay 802.16j Systems Vasken Genc, Seán Murphy, John Murphy, Abdelhamid Nafaa UCD School of Computer Science and Informatics University College Dublin, Belfield, Dublin 4, Ireland vasken.genc@ucdconnect.ie, sean.murphy@iname.com, j.murphy@ucd.ie, nafaa@ieee.org I This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE "GLOBECOM" 2009 proceedings. 978-1-4244-4148-8/09/$25.00 ©2009