SDR-proved adaptive OFDM guard interval scheme for rapidly varying time-dispersive vehicular broadcast channels

Driven by the results of existing field measurements for the characterization of vehicular radio channels, particularly vehicle-to-vehicle (V2V) channels, which showed that the effective range of possible maximum delay spreads is extremely wide (ranging from a few ns up to several μs), the strategic choice of Orthogonal Frequency Division Multiplexing (OFDM) with fixed guard interval (GI) duration shall be reconsidered at that point. Here, the major claims, both to optimize the data throughput at good channel conditions and to enable a reliable transmission of safety critical information at harsh environmental conditions, must be taken into account. Thus, in this paper, an adaptive guard interval (AGI) length scheme in context of vehicular ad hoc broadcast communication networks with rapidly time-varying channel conditions is proposed. The approach enables an OFDM symbol-based GI estimation without the prior knowledge of the GI length used in the transmitted symbol. By this means different GI lengths can be detected even within a frame. The suggested approach could be used to improve actual and upcoming physical layer (PHY) specifications, e.g. of Std. IEEE 802.11p. For a physically realistic evaluation of the proposed scheme, a fully IEEE 802.11p standard-compliant and reconfigurable software-defined radio (SDR) transmitter with symbol-based adaptable GI processing but fixed symbol duration is presented.