Abstract
Unmanned aerial vehicles (UAVs) have gained a significant popularity in the recent past owing to their easy deployability and wide range of applications. In most of the short- and medium-range applications, Wi-Fi is used as the access technology for establishing communication between the ground stations and the UAVs. Although Wi-Fi is known to perform well in most of the scenarios, it is important to note that Wi-Fi has been mainly designed for indoor communication in rich scattering environments, whereas the air-to-ground (A2G) channel is characterized by sparse scattering. Considering this important difference in the channel characteristics, we revisit some of the Wi-Fi features and propose efficient design alternatives. First, we provide a statistical model for the sparse A2G channel and design an optimal time-domain quantizer (TDQ) for its feedback. In contrast to the frequency-domain quantizer (FDQ) of the IEEE 802.11n/ac Standard, the proposed TDQ exploits the time-domain sparsity in the channel and requires about 15 times lesser quantization bits than FDQ. Second, we propose a beamforming (BF) scheme with the aid of full-diversity rotation (FDR) matrices and analytically evaluate its symbol error probability in order to quantify the attainable diversity order. Our numerical simulations demonstrate that the proposed FDR-BF scheme outperforms the relevant benchmark schemes in both coded as well as uncoded scenarios. Specifically, the proposed FDR-BF scheme was observed to attain a signal-to-noise ratio gain as high as 6dB compared with the popular geometric mean decomposition-based BF scheme, when operating at an elevation angle of 7.5°.
Highlights
The future wireless infrastructure is envisaged to grow beyond the terrestrial realm owing to the rapid proliferation of deployable unmanned aerial vehicles (UAV), such as drones, tethered helikites, mini aircrafts etc. [1]-[4]
We show that the proposed time-domain quantizer (TDQ) would significantly reduce the feedback overhead involved in the beamforming, while attaining the same performance as that of frequency-domain quantizer (FDQ). 3) In contrast to the existing beamforming schemes [19][26] discussed earlier, we propose a full-diversity rotation (FDR) [39]-[41] aided beamformer (FDR-BF) that attains the maximum achievable transmit diversity gain without compromising the multiplexing gain
Proposed TDQ for A2G channel In multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM) systems employing beamforming, CSI is required at the transmitter, which is attained by quantizing the channel at the receiver and sending the same to the transmitter
Summary
The future wireless infrastructure is envisaged to grow beyond the terrestrial realm owing to the rapid proliferation of deployable unmanned aerial vehicles (UAV), such as drones, tethered helikites, mini aircrafts etc. [1]-[4]. Adaptive modulation and coding was designed in [8] Among these diverse wireless access technologies, WiFi has gained a significant popularity among drones [9]-[14] owing to its ubiquity and versatile infrastructure based and ad-hoc modes of operation, which are sufficient to cater for a wide range of applications. We first propose a simple statistical channel model and provide the specific model parameters that fit the A2G channel measurement data given in [27] for the elevation angles of Ψ ∈ {7.5o, 15o, 22.5o, 30o} We use this channel model for designing the timedomain channel quantizer as well as for the performance evaluation of the proposed scheme. C and R represent the field of complex and real numbers, respectively
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