Survey of RF Communications and Sensing Convergence Research <s> G. CARRIER EXPLOITATION METHODS <s> A new method is described that allows for the non-interfering spectrum coexistence of radar and a wireless communication system employing multiuser subscriber waveforms. To simultaneously achieve compatibility and requisite radar performance, the radar “subscribes” to the network and utilizes K independent subscriptions. In the case of a cellular network, this would correspond to K independent cell subscriptions operating simultaneously. To achieve requisite radar performance, the onboard radar controller performs an adaptive linear combiner optimization of the K simultaneous waveforms to obtain a transmitted composite waveform with far superior useful radar properties (greater power, Doppler tolerance, etc.) than would be achieved by simply using the indigenous unaltered communications network waveforms. The linearity of the superposition ensures that the composite radar waveform behaves as K ordinary users, and thus does not require any special handling by the communications network nor will result in any undue interference. While utilizing communication waveforms for radar is not new, using a plurality of simultaneous waveforms to form a new composite waveform with better radar properties yet preserving network compatibility is entirely new. <s> BIB001 </s> Survey of RF Communications and Sensing Convergence Research <s> G. CARRIER EXPLOITATION METHODS <s> Spectrum sharing is a promising solution for the problem of spectrum congestion. We consider a spectrum sharing scenario between a multiple-input multiple-output (MIMO) radar and Long Term Evolution (LTE) Advanced cellular system. In this paper, we consider resource allocation optimization problem with carrier aggregation. The LTE Advanced system has N BS base stations (BS) which it operates in the radar band on a sharing basis. Our objective is to allocate resources from the LTE Advanced carrier and the MIMO radar carrier to each user equipment (UE) in an LTE Advanced cell based on the running application of UE. Each user application is assigned a utility function based on the type of application. We propose a carrier aggregation resource allocation algorithm to allocate the LTE Advanced and the radar carriers' resources optimally among users based on the type of user application. The algorithm gives priority to users running inelastic traffic when allocating resources. Finally we present simulation results on the performance of the proposed carrier aggregation resource allocation algorithm. <s> BIB002 </s> Survey of RF Communications and Sensing Convergence Research <s> G. CARRIER EXPLOITATION METHODS <s> Radar signal design in a spectrally crowded environment is a very challenging and topical problem due to the increasing demand for both military surveillance/remote-sensing capabilities and civilian wireless services. This paper deals with the synthesis of optimized radar waveforms ensuring spectral compatibility with the overlayed licensed electromagnetic radiators. A priori information, for instance, provided by a radio environmental map (REM), is exploited to force a spectral constraint on the radar waveform, which is thus the result of a constrained optimization process aimed at improving some radar performances (such as detection, sidelobes, resolution, tracking). The feasibility of the waveform optimization problem is extensively studied, and a solution technique leading to an optimal waveform is proposed. The procedure requires the relaxation of the original problem into a convex optimization problem and involves a polynomial computational complexity. At the analysis stage, the waveform performance is studied in terms of trade-off among the achievable signal to interference plus noise ratio (SINR), spectral shape, and the resulting autocorrelation function (ACF). <s> BIB003
Rather than cooperate with cellular systems, some have proposed employing the existing cellular framework as a solution to augment dwindling radar spectrum. For example, when radar functionality is required, systems can subscribe as cellular users and allocate bandwidth within the existing cellular framework BIB001 . We demonstrate an example of the concept outlined in Reference BIB001 , known as radar as a subscriber technology (or RAST), in Figure 15 . In this plot, the radar allocates 8 subscribers and selects 8 codes from the 32-bit Hadamard matrix to best approximate the ideal radar waveform for this system, a linear FM chirp. The approximation improves with the number of subscribers BIB001 . This is further enabled by recent additions to the cellular LTE standard that enable carrier aggregation, or user request of multiple carriers to access larger instantaneous bandwidth BIB002 . While bandwidth is still allocated to isolated users, it is done within a dynamic framework that supports needs-based resource distribution while enabling normal use of high performance cellular infrastructure. Other approaches accepting that cellular infrastructures will dominate aim to design optimal radar waveforms that are robust to in-band, nearby cellular users and also minimize their interference to those users using non-convex optimization techniques BIB003 . 