On The Capacity Degradation in W-CDMA Uplink/Downlink Due to Indoor Traffic J. Pérez-Romero, O. Sallent, R. Agustí Departament de Teoria del Senyal i Comunicacions Universitat Politècnica de Catalunya C/ Jordi Girona, 1 - 08034 Barcelona - Spain E-mail : [jorperez, sallent, ramon] @ tsc.upc.es Abstract Indoor traffic is expected to be key in 3G networks. Nevertheless, the implications of indoor traffic in a 3G WCDMA- based network may be significantly different from those already well know in 2G TDMA-based networks. This papers reveals, by means of a simple analytical model that uplink is much more sensitive than downlink in WCDMA in terms of capacity degradation due to increased indoor traffic levels. Additionally, by means of system level simulation the capacity degradation in different conditions is assessed in both links. Keywords: W-CDMA, indoor, capacity, uplink, downlink I. INTRODUCTION Indoor traffic is very important in nowadays 2G networks, as remarkable traffic load is originated in buildings. Typically, in GSM in building coverage can be provided in a first step by tuning transmitted power levels. In a second step and to respond also to capacity demands, indoor coverage can also be provided by deploying hierarchical cell structures with micro and picocells. W-CDMA access networks provide an inherent flexibility to handle the provision of future 3G mobile multimedia services [1]. Although 3G traffic demand profiles are expected to be different from the 2G ones because of the different services nature, clearly indoor traffic will be even more key in 3G since the envisaged high bit rate services will have the tendency for a static user behaviour, in many cases indoor. Furthermore, data traffic will exhibit in many cases an asymmetric behaviour with more traffic generated in the downlink than in the uplink. Nevertheless, the implications of indoor traffic in 3G W- CDMA based systems may significantly differ from 2G TDMA-based solutions because transmitted power levels are the key radio resources in W-CDMA. The higher power levels needed for indoor service will lower cell capacity. Consequently, it can be important for a network operator to quantify the impact that indoor traffic may have on the overall system efficiency in order to devise suitable deployment guidelines (i.e. how fast the transition from outdoor macrocell sites to indoor micro and picocells distributions should be carried out). Besides, taking into account different radio bearer services (e.g. 64 kb/s uplink with 64 kb/s downlink; 64 kb/s uplink with 384 kb/s downlink, etc.) different levels of capacity degradation as well as different link direction constraints may appear. In this framework, this paper is intended to devise the impact on system capacity deriving from different percentages of indoor traffic in the scenario. Firstly, by means of a simple analytical model it will be shown that uplink direction reveals to be much more sensitive to indoor traffic than downlink, so that higher degradations are expected in the uplink. Secondly, different radio bearers with different asymmetry levels are studied by means of system level simulations in both uplink and downlink directions. The complete set of obtained results may help to provide the indications on how and when new infrastructure and/or new cell hierarchies need to be deployed in a given scenario as user density and demanded services evolve. We note that, once the above decision is taken, different works that have been published in the open literature, analysing the problem of indoor coverage in W-CDMA [2-4] can provide the guidelines to succeed in engineering hierarchical cell structures deployment. The rest of the paper is organized as follows. In Section 2, a simple analytical model to derive the transmitted power increase by an uplink mobile indoor compared to an outdoor mobile is achieved. Similarly, the required downlink Node B transmitted power increase to a downlink indoor user compared to an outdoor one is devised. Then, Section 3 describes the system level simulation set to attain performance figures in Section 4 to conform that indoor traffic is affecting more the uplink than the downlink. II. INDOOR TRAFFIC IN UPLINK/DOWNLINK Let consider the two different situations shown in Figure 1: case (a) stands for a given mobile in an outdoor location and case (b) stands for the mobile at the same distance from the cell site but considering it indoor.