To support the development of low altitude economy, the air-ground integrated sensing and communication (ISAC) networks need to be constructed to provide reliable and robust communication and sensing services. In this paper, the sensing capabilities in the cooperative air-ground ISAC networks are evaluated in terms of area radar detection coverage probability under a constant false alarm rate, where the distribution of aggregated sensing interferences is analyzed as a key intermediate result. Compared with the analysis based on the strongest interferer approximation, taking the aggregated sensing interference into consideration is better suited for pico-cell scenarios with high base station density. Simulations are conducted to validate the analysis.

With the access to tens of gigahertz of bandwidth, terahertz (THz) wideband communication emerges as a promising technology for the upcoming next generation mobile networks. To deal with the severe path loss and blockage of THz signals, massive multiple-input multiple-output and intelligent reflecting surface (IRS) can be jointly employed. Due to the extremely large signal bandwidth, the beams generated by the transmit hybrid beamforming may point to different directions around the target direction at different frequencies, which results in the beam splitting effect (BSE). In this paper, a new system design namelyTHzCondenseris introduced to mitigate the BSE, where the signals generated by each transmit radio frequency (RF) chain are reflected by one of the distributed IRSs in a one-to-one manner via the joint transmit and IRS beamforming design, thus creating adjustable multi-path components to achieve both high spatial multiplexing gain and array gain. Moreover, for practical scenarios when the number of transmit RF chains is more than that of IRSs, each IRS may need to reflect the signals generated by multiple RF chains in a one-to-many manner. For the above two cases, the joint beamforming design problems are efficiently solved to maximize the achievable rate. Simulations are conducted to verify the effectiveness of the proposed algorithms for mitigating the BSE and improving the achievable rate in IRS-aided THz wideband communications.

To support the development of air-ground integrated sensing and communication (ISAC), network-level performance analysis is needed for providing an essential guide on the network design. Following the widely adopted orthogonal frequency-division multiplexing (OFDM) technology in existing wireless systems, a cooperative air-ground wireless network based on OFDM-ISAC is introduced in this paper, where the ISAC-enabled base stations (BSs) following the two-dimensional homogeneous Poisson point process (HPPP) distribution serve the terrestrial communication users while sensing the aerial targets. In particular, cooperative beamforming schemes are designed for mitigating the interference among ISAC BSs. First, we analyze the communication as well as sensing performances in terms of different metrics including area communication coverage probability, area communication spectral efficiency, area radar detection coverage probability, and average Cramér-Rao Bound. Simulation results are then presented to validate the theoretical analysis and illustrate the effects of key system parameters on the network performance. It is observed that both the communication and sensing (C&S) performances depend on the BS density and height, while the sensing performance also depends on the height of sensing target together with the numbers of OFDM subcarriers and symbols. Moreover, there exists a tradeoff between the C&S performances with respect to the BS density and height. The results of this paper provide useful guidance to the design and implementation of air-ground wireless network for harnessing the dual benefits of ISAC.

Recently, channel state information (CSI) extracted from Wi-Fi signals has enabled a variety of Wi-Fi sensing applications beyond communications. However, the extraction of CSI relies on specific Wi-Fi devices, which severely limits the CSI-based sensing applications. In this paper, we exploit the beamforming matrix, a compressed version of CSI that is fed back from the beamformee to the beamformer without encryption, for Wi-Fi sensing. In order to recover more channel information from the beamforming matrix for sensing, a QR decomposition (QRD)-based beamforming feedback scheme is proposed in this paper. We analyze the effectiveness of the proposed QRD-based scheme in terms of sensing and communication performance. Simulation results show that the Doppler frequency shift, time of flight, angle of departure, as well as the amplitude information can be recovered using the proposed scheme and at the same time, the spectral efficiency of the proposed QRD-based scheme is comparable to that of the existing SVD-based scheme. We implement the proposed scheme on IEEE 802.11ac/ax based Wi-Fi devices. The experimental results on human respiration and finger tracking demonstrate that the proposed scheme works well for practical Wi-Fi sensing.