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

Abstract

IEEE Transactions on Vehicular Technology (ISSN: 0018-9545)Citation for the published paper: Nagalapur, K. ; Brännström, F. ; Ström, E. et al. (2016) "An 802.11p Cross-Layered Pilot Scheme for Time-and Frequency-Varying Channels and Its Hardware Implementation".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.

Performance Analysis of Receivers Using Sector Antennas for Broadcast Vehicular Communications

“…For the chosen packet length and the transmission rate, the threshold ψ used in the decoding criterion depends on the channel, desired reliability, and the channel estimation scheme used at the receiver. We use a threshold of ψ = 10 dB for the results discussed in this section (see [26] for the influence of different channels and the channel estimation schemes on the threshold). The MAC parameters AIFSN and W , listed in Table I, used to derive the transmission probability τ N correspond to the AC assigned to CAMs [27, Table 5].…”

“…The received powers in an annular sector are modeled as i.i.d RVs with pdf f P (p) in (26). We use 2J nonoverlapping annular sectors with the receiver at their origin to distribute the vehicles.…”

“…The probability Pr {Γ j ≥ ψ} in (18) requires the joint distribution f P (j) (1) ,P (j) I (u, v). Substituting the power distribution given by (26) in (10) we have…”

Deep Neural Network Augmented Wireless Channel Estimation on System on Chip

“…However, it performs poorly at a low signal-tonoise ratio (SNR) [5]. Other techniques like linear minimum mean square error (LMMSE) offer better performance than LS but need prior knowledge of noise, and second-order channel statistics [6]. Furthermore, it is computationally intensive [6], [7].…”

Preamble-Based Adaptive Channel Estimation for IEEE 802.11p

“…They are typically divided into two categories, i.e., with and without changing the IEEE 802.11p standard. With respect to the schemes that change the standard structure [16,17,18,19,20,21], because they can supplement the lack of pilots of IEEE 802.11p, outstanding performance can be obtained compared to approaches that do not modify IEEE 802.11p. However, these methods cause compatibility and interoperability problems with standard equipment.…”