>REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT)< 1 Abstract— This paper deals with the study and implementation of a complete OFDM Time Reversal Prototype in a multiple input, single output (MISO) context. After describing the principles and architecture in details, several pre-coding techniques are presented. Measurements results are discussed and performances are evaluated. Index Terms— MISO, Time Reversal, Test-bed, Pre-coding I. INTRODUCTION Nowadays, wireless communication systems demand a constant increase of data rates and performances. In this context, a lot of multiple-input multiple-output (MIMO) schemes such as classic beamforming techniques, spatial multiplexing techniques, orthogonal space-time codes [1], etc. have been studied and have shown significant improvements in terms of diversity and throughput. Regarding MIMO schemes, a lot of systems are based on the availability of channel state information (CSI) at the transmitter side. One of the most famous techniques is based on singular value decomposition (SVD) that makes it possible to exploit spatial diversity [2]. In the proposed study, we decided to focus on wireless systems that are composed of several small cells, or access points, dispatched in a close indoor environment. Regarding the nature of the transmission channel, we decided to investigate the MISO Time Reversal (TR) technique since it provides very interesting performances in such a context [3]. It has also been demonstrated that such a technique exhibits a level of performance that is comparable with SVD as the number of transmitting antennas grows [4], [5].Another important property of TR is that it allows building much simpler and thus cheaper receivers while adding some complexity at the transmitter side. In this paper, we concentrate on the time compression and spatial focusing performances of TR in an indoor environment. The rest of this paper is organized as follows: in section II, the time reversal concepts are introduced and detailed. In section III, a first MISO hardware/software platform is described. Section IV describes several configurations that have been implemented and tested on the testbed. In section V, experimental results and measurements are provided. II. TIME REVERSAL STRATEGY TR principles are presented in details for acoustic and electromagnetic waves in [6] and [7] respectively. This well-known strategy consists in pre-filtering the transmitted signal by applying the time reversed and conjugated image of the channel impulse response. This technique relies on the idea that the propagation channel is reciprocal between the transmitter and the receiver. TR relies on the knowledge of the channel at the transmitter side For OFDM systems, it has been shown that TR can be applied in either time and frequency domain and exhibit the same level of performance. In the frequency domain and in a MISO OFDM scheme, the received symbol can be expressed as:                  where   is the number of transmit antennas,   is the complex channel coefficient on the m-th subcarrier of the ODFM symbol for the k-th transmit antenna.   is the data symbol and   is the noise term associated to the m- th subcarrier of the n-th OFDM symbol. III. PROPOSED PLATFORM DESCRIPTION The prototype consists of one transmitter (Tx) and one receiver (Rx) implemented on separate WARP FPGA-based motherboards [8]. Fig. 1 depicts the overall architecture of the prototype including the interfaces and cables between the boards. The transmitter is composed of 3 RF modules connected to 3 transmitting antennas. On the receiver side, 1 target antenna is connected to RF board. Fig. 1. System Description IV. STUDIED CONFIGURATIONS Since the proposed software-defined platform is very flexible, it makes it possible to test several configurations in order to evaluate and compare multiple approaches. In this work, three techniques have been implemented. A. Classic OFDM The first configuration is a simple OFDM chain without data pre-coding at the transmitter side. Implementation of a Time-Reversal MISO OFDM Test-Bed J.-C Prévotet, Y. Kokar, M. Hélard, M. Crussière