New time domain equalizer for multitone vehicle to vehicle communications

Pre-FFT time domain equalization plays an important role in OFDM systems experiencing delay spread that is larger than the OFDM cyclic-prefix duration. In such systems the time domain equalizer shortens the channel, so that ordinary OFDM proceeding may follow. The equalizers usually require a long training period, which grows with the delay spread, and are to be updated to accommodate channel variations. Due to these reasons they have mostly been implemented in wireline links such as ADSL, in which long training is allowed and the channel is quasi-static. The IEEE 802.11p is an emerging OFDM based standard for vehicle to vehicle communications, which borrows much of its physical layer from the indoor centric IEEE 802.11g (WiFi). Thus, it is no surprise that the IEEE 802.11p suffers from insufficient cyclic-prefix duration and pilot density, in high mobility outdoor environments. In this paper we propose new time domain equalizers, which are tailored for the IEEE 802.11p requirements, in terms of fast convergence on the preamble and the accommodation of high mobility. We show that in benchmark scenarios, the proposed equalizers are a key to reliable vehicle to vehicle communications.