Analysis of mm-wave Propagation and Interference for Broadband Mobile Networking Maxime Flament and Arne Svensson Communication Systems group, Dept. of Signals and Systems Chalmers University of Technology, SE-412 96 Gothenburg, Sweden Maxime.Flament@s2.chalmers.se, Arne.Svensson@s2.chalmers.se ABSTRACT In the framework of the 4 th Generation Wireless (4GW) Infrastructure project [1], the study of new air interfaces is needed to provide a broadband wireless infrastructure to mobile users. The 60 GHz frequency band presents a very large bandwidth that has been allocated to mobile communication. In this paper, propagation and interference issues in different environments are presented and analyzed to identify the air interface limitations for the deployment of 60 GHz networks. Simulations using a ray-tracing tool show the dynamics of the interference in chosen situations. The very short time variation scales underline the need of ad-hoc solutions, directional antennas, fast and intelligent IP handovers, and efficient network design. 1. INTRODUCTION The millimeter waves are very attractive for broadband mobile telecommunication. Indeed, the 59-64 GHz frequency band has been internationally designated for unlicensed devices [2]. The study of a mobile system at this frequency should provide judicious design methods yielding flexible and reliable mobility. For many reasons, such as limited emitted power, high temperature noise, and high oxygen absorption, the range of a millimeter-wave mobile system is relatively low. Moreover, layers of concrete or wood reflect the electromagnetic waves. Hence, channels in indoor and large area environments show strong multipath behavior. So, the millimeter wave propagation at these frequencies is usually confined within the areas where the antennas are located. The frequency band is therefore even more attractive for broadband mobile telecommunication since it allows better reuse of resources. However, in these environments, unacceptably strong interference situations occur frequently. Typically, in a single frequency network [3], users walking in a hallway will experience bursty interference yielding bad link quality and frequent need for handover. In dynamic situations, interference from other antennas can severely compromise the received signal, for example, while passing in front of an open door in a hallway. In this paper, we show that the Signal-to-Interference ratio (SIR) can drop from 15 dB to 0 dB within a few centimeters. In order to identify the interference issue, we assume that frequency reuse factors higher than one are not an acceptable solution to solve this problem. We assume OFDM modulation with a cyclic prefix long enough to provide a modulation scheme that is able to reduce the effect of the strong multipath situation. However it does not mitigate the strong interference situation, nor reduce the number of handovers. The organization of the paper is as follows. The PCC-4GW working assumptions and link to other research are presented in next section. Two infrastructure scenarios are also described. We then introduce the channel behavior and the way we simulated it along user paths using ray simulation tools. Analysis of received and interference signals and examples of interference situations are discussed in the simulations section. The next section discusses the ways to mitigate the interference issues. Finally, conclusions and future work are presented. 2. 4GW INFRASTRUCTURE The design of an infrastructure for mobile broadband communication at 60 GHz is a real challenge. To start on a good basis, the PCC-4GW group has set up a series of working assumptions (WA) [4]. Below, the relevant WAs for this paper are recalled. The mobile system is supposed to provide up to 100 Mbit/s using unlicensed spectrum and ad-hoc techniques. The 60 GHz frequency band has been identified as one of the potential high-bit-rate bands. Even if the 4GW infrastructure is not only based on the millimeter wave band, particular effort should be provided to identify the limiting factors of such high carrier frequency. One of the important requirements in the design of the air interface is its flexibility. User deployed access points and self-planning capabilities are the underlying factors that will make the 4GW infrastructure economically viable. Indeed, public and private networks are expected to coexist, both offering high bit rate communication and broad range of commercial or non- commercial services. The 4GW infrastructure is meant to use technologies and backbone access that will be available around the year 2010. Therefore, we assume that the fixed infrastructure will be able to provide the required bandwidth to the users connected to the same access point. Assuming small cells and transmission up to 100 Mbit/s, a minimum requirement is for instance the 155 Mbit/s ATM technology. New emerging techniques, such as radio-over-fiber (RoF) or Hybrid Fiber Radio (HFR), are good candidates to reach better system performance. In [5], properties of typical large office and shopping mall environments are described. The first one