A Channel Estimation Scheme for Analog Network Coding based on OFDM in a Multipath Fading Environment

The capacity of future wireless networks must be increased to accommodate more demanding wireless devices and applications. Network coding at the physical layer, although originally applied in wired networks, can be used to exploit the broadcasting capability of the wireless channel to increase network capacity. A wireless channel is characterized by multipath fading which produces interference and distorts the transmitted signal. Recently, broadband analog network coding (ANC) was proposed to cope with multipath fading assuming full knowledge of the channel state information (CSI). However, broadband ANC requires accurate channel estimation (CE) for self-information removal and signal recovery. In this thesis, we propose a two-stage pilot-assisted CE scheme for broadband ANC based on orthogonal frequency division multiplexing (OFDM) radio access. The proposed CE scheme is divided into two stages. During the first stage the users transmit their pilot signals to the relay which estimates the both CSIs from the interfered signal, and during the second stage the relay broadcast its pilot signal to the users which estimates the corresponding CSI. The CE at the relay during the first stage is possible because the pilot signals transmitted by the users are designed to avoid pilot interference and consequently, allow the relay to estimate the CSIs from both users. It was shown by computer simulation that, even with imperfect CSI, the bit-error-rate performance of broadband ANC gives a satisfactory performance for a low and moderate mobile terminal speed in a multipath fading channel.