On Channel Estimation for 802.11p in Highly Time-Varying Vehicular Channels

Vehicular wireless channels are highly time-varying and the pilot pattern in the 802.11p orthogonal frequency-division multiplexing frame has been shown to be ill suited for long data packets. The high frame error rate in off-the-shelf chipsets with noniterative receiver configurations is mostly due to the use of outdated channel estimates for equalization. This paper deals with improving the channel estimation in 802.11p systems using a cross layered approach, where known data bits are inserted in the higher layers and a modified receiver makes use of these bits as training data for improved channel estimation. We also describe a noniterative receiver configuration for utilizing the additional training bits and show through simulations that frame error rates close to the case with perfect channel knowledge can be achieved.Comment: 6 pages, 11 figures, conferenc

Chalmers Publication Library An 802.11p Cross-Layered Pilot Scheme for Time-and Frequency-Varying Channels and Its Hardware Implementation An 802.11p Cross-Layered Pilot Scheme for Time-and Frequency-Varying Channels and Its Hardware Implementation

IEEE Transactions on Vehicular Technology (ISSN: 0018-9545) Citation for the published paper: Nagalapur, K. ; Brännström, F. ; Ström, E. et al. (2016) Abstract-Robust channel estimation in IEEE 802.11p systems in highly time-and frequency-varying vehicular channels in combination with long data packets is a challenging task due to the ill-suited pilot pattern. Solutions of increased receiver complexity that use decision feedback and iterative decoding have been proposed to overcome the difficulty in robust channel estimation. In this work, a cross-layered method to introduce complementary training symbols into an 802.11p frame is proposed. In the proposed approach, known bits are multiplexed with the data in higher layers and a modified receiver can utilize these bits as training data for improved channel estimation. A standard receiver treats these bits as data and passes them to the higher layers where they can be removed, making the method compatible with the standard 802.11p transceivers. A software/firmware update of the higher layers is needed in a standard receiver to remove the multiplexed bits. A modified receiver with low complexity channel estimation schemes that utilizes the complementary training symbols is implemented in a field programmable gate array platform. Frame error rate measurements have been performed by interfacing the hardware implementation with a channel emulator. The measurement results follow the computer simulation results validating the hardware implementation. Moreover, measurement results show that the modified receiver follows the performance of an ideal receiver that has full knowledge of the channel (with only an offset in signal-to-noise ratio) and significantly outperforms the commercial 802.11p transceiver we tested