Spatial Data Focusing Using Time and IQ Resources for Wireless Geocasting

Abstract

Spatial Data Focusing (SDF) is introduced as a novel technique that allows wireless broadcasting of information towards specific spatial locations only. It is shown that this approach allows one to target geographic areas more accurately than traditional power focusing methods, using limited equipment at the transmitter. This paper describes the SDF system model for linear arrays, based on simple modulation techniques and transmitter architectures, both in pure line-of-sight and multipath environments. In particular, the robustness of the scheme is proven for over-the-ground propagation environments. Theoretic results are illustrated by simulations, confirming the increased spatial selectivity of SDF and showing the influence of various design parameters of the scheme on the resulting beam.

OFDM-based Spatial Data Focusing for High Resolution 2-Dimensional Wireless Geocasting

“…Receiver-side signal processing and channel equalization OFDM-SDF's multi-frequency transmission, allows to exploit an additional degree of freedom in the SDF equalization process, in addition to the propagation delay differences exploited in T-SDF. To this end, instead of defining a single reference channel as in [9], a set of reference subcarriers Q ref is defined to be used for channel estimation and equalization. While the choice of this set is free in general, the creation of a 2-dimensionally isolated target area requires that a pair of two reference channels H ref 1 and H ref 2 , respectively with assigned subcarrier sets Q ref 1 and Q ref 2 , is chosen such that they comply to the following specifications:…”

“…The former demonstrates that OFDM-SDF exhibits no tradeoff in terms of angular selectivity compared to T-SDF, as both techniques display the same beamwidth. As a consequence, angular focusing resolution can be manipulated in similar ways, as described in [9]. A BER pattern obtained when performing beamforming (BF) (i.e.…”

“…In [8] and [9], SDF was first introduced by exploiting the temporal dimension to ensure signal orthogonality. This Time-based Spatial Data Focusing (T-SDF) implementation modulates the different data substreams onto time-shifted waveforms and transmits them sequentially in orthogonal time slots.…”

OFDM-Based Spatial Data Focusing for Wireless Physical Layer Geocasting in Multipath Channels

“…At the receiver, differences in propagation conditions between each data substream are exploited upon equalization to induce a location-dependent symbol distortion that restricts the spatial availability of the transmitted data, regardless of received power and SNR. Time-based spatial data focusing (T-SDF), introduced in [24] and [25], exploits the temporal dimension for signal orthogonality. Despite the considerable increase in spatial selectivity over beamforming in the angular domain, T-SDF fails to achieve range-based focusing.…”

“…Preliminary results on OFDM-SDF have been presented in [27]. However, just like [24] and [25], it is limited by omitting a multipath channel analysis and does not provide any performance guarantee in those scenarios. On the other hand, this paper presents an expanded OFDM-SDF scheme that allows for the dual exploitation of OFDM multi-frequency transmission for high-precision uncoupled range-angle-dependent and multipath robust geocasting.…”