Simultaneous Communication and Localization for 60 GHz UWB OFDM systems Ahmadreza Jafari, Julien Sarrazin, David lautru, Aziz Benlarbi-Delaï UPMC Univ Paris 06, UR2 L2E F-75005, Paris, France ahmadreza.jafari@etu.upmc.fr Luca Petrillo, Philippe De Doncker OPERA Department Ecole polytechnique de Bruxelles Bruxelles 1050, Belgium Abstract—A new method for indoor localization at 60 GHz is proposed. This method is based on the extraction of the TDOA (Time Difference of Arrival), using a MISO system. With this method, unlike conventional TDOA measurements, it is possible to perform communication and localization at the same time by transmitting two identical UWB OFDM signals using two antennas at the TX and extracting TDOA from the interference spectrum of these two signals at the RX. The improvement of the localization precision is also studied via a multi-band approach to use the whole spectrum assigned to 60 GHz communications. This whole study is made within the framework of the WiGig alliance specifications. The simulations performed with commercial software, confirm the theoretical results while experimental measurements are implemented at lower frequencies to prove this approach. I. INTRODUCTION In the coming years, home wireless systems are expected to provide multi gigabit data rates, thus replacing cables for indoor communications. Wideband communications using complex modulations such as OFDM (Orthogonal Frequency Division Multiplexing) are more and more used in the short- range applications such as video streaming, wireless USB ... However, the current commercial wireless systems do not still reach the necessary data rate for heavy applications like HD video. So, an effort exists to develop a wireless UWB (Ultra Wide Band) technology at 60 GHz, where 5 GHz bandwidth is available internationally. In this context, IEEE 802.15.3c standard was already proposed, whereas other specifications, for example WiGig, are being elaborated [1,2]. Furthermore, energy consumption in wireless networks is an essential factor with respect to its impact upon the environment as well as autonomy of the system. For 60 GHz communications, this is even more problematic than in conventional wireless networks because of the strong millimeter wave attenuation. Focalization of energy can lead to decrease the consumption and to improve the distance range of the wireless communications. This is why under development 60 GHz standards consider beamforming. However, to be able to focalize, the communicating devices should determine their locations. In this article, a new technique of localization for wideband wireless networks at 60 GHz adapted to indoor applications is presented. This method is based on conventional TDOA (Time Difference Of Arrival) measurements. However, it uses interferences in OFDM signal spectrum at RX in order to extract the TDOA. With this approach, we are capable of performing localization and the data transmission simultaneously. The paper is organized as follows. In section 2, theory, concepts and formulations are presented. In section 3, a simulation example is given. Finally, the section 4 will conclude the paper. II. CONCEPT AND FORMULATIONS The method of localization proposed in this article is based on extracting TDOA from interferences between the OFDM signals transmitted by two antennas at 60 GHz. To implement this technique, a MISO (Multi Input, Single Output) structure is considered. To do so, a reference device (RD) with two antennas   and   and a mobile device (MD) are placed in an indoor environment. The distance between MD and   is   and between MD and   is   . In the case of LOS (Line Of Sight) between RD and MD, the delays of propagation are   =   /c and   =   /c, with c the speed of light and   and   the channel gains respectively between   and MD and between   and MD.   and   transmit the same OFDM 60 GHz signals with a sample rate frequency   , N carriers and M data carriers. Furthermore, the delay   is considered, as it has been suggested in [3], to vary the delay of the signal in a predetermined way. Considering x(t) the modulated baseband signal transmitted by both antennas, the following equation is obtained:                                         (1)          (2) Where A is a real constant,   are complex coefficients, with k the carrier index and   the RF frequency. The MD receives:                  (3) In the case   =A  , the received signal can be written as:          (4) Where τ =   +   -   . The signal received in the frequency domain can be presented as follows:                                  (5) Each pair of carriers  is canceled for values of τ given by: