Quantified Dynamic Spectrum Access Paradigm
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A significant portion of the radio frequency spectrum remains underutilized with exclusive and static allocation of spectrum. Provisioning secondary access to the underutilized spectrum could be beneficial to the incumbents if they could gain significant value out of the fallow spectrum while ensuring protection of their primary services. From incumbent perspective, the spectrum sharing approach needs to be non-harmful as well as efficient. We encountered difficulties when we attempted to quantify the performance of spectrum recovery and exploitation. The existing methodologies to define use of the spectrum and quantify its efficiency are based on the static spectrum assignment paradigm and not suitable for the dynamic spectrum sharing paradigm. Considering spectrum is consumed by transmitters as well as receivers, we argue that there is a need to separately quantify the spectrum consumed by the individual transmitters and receivers when multiple heterogeneous wireless networks are sharing the spectrum in time, space, and frequency dimensions. By discretizing the spectrum dimensions, we developed a methodology for quantifying the spectrum consumption spaces. This is an attempt to adopt the discretized signal processing principle and apply it to spectrum management functions that would bring in simplicity, flexibility, and precision among other advantages. It enables measuring performance of spectrum management functions, defining new metrics, and devising more efficient spectrum management functions. Furthermore, it transforms the spectrum into a resource or a commodity that could be easily understood, and effectively shared or traded in simple and efficient manner. Spectrum-space discretization and the spectrum consumption quantification methodology help to address several challenges in the recovery and exploitation of the underutilized spectrum. First, it facilitates quantifying the spectrum recovered by a spectrum recovery mechanism. This helps to understand the weaknesses of a given spectrum recovery mechanism. It allows comparing performance of multiple spectrum recovery mechanisms. Similarly, it enables quantifying, analyzing, and comparing the performance of the spectrum exploitation mechanisms. We analyze the performance of spectrum recovery and exploitation in case of OSA policy. We observed that a significant amount of the available spectrum cannot be recovered due to the minimum sensitivity and the maximum transmit-power constraints on the secondary user radios. Also, the conservative assumptions regarding the propagation conditions in order to handle the worst-case conditions lead to poor spectrum recovery. We argue that maximizing the recovery and exploitation of spectrum requires knowledge or estimation of the propagation medium parameters and transceiver parameters. The quantification of spectrum consumption spaces brings in a quantified dynamic spectrum access (QDSA) paradigm. The QDSA paradigm adopts a quantified approach while designing spectrum-access policy. This approach seeks to control the spectrum consumption at the lowest granularity of consumption. By precisely controlling the recovered and exploited spectrum, the QDSA paradigm helps to maximize the spectrum sharing potential. It enables articulating, defining and enforcing quantified spectrum-access rights and thus facilitates real-time, fine grained, and dynamic spectrum sharing. The spectrum-access conditions and the propagation conditions are diverse, uncertain, and dynamic. In this regard, we estimate the available spectrum with the aid of an external sensor network. We propose effective fusion of the estimated RF information to lower the uncertainty in estimated spectrum consumption. In order to avoid making conservative assumptions and maximize availability of the spectrum, we also attempt to learn the fine granular propagation environment. In order to maximize exploitation of the recovered spectrum, we investigate the impact of the various design choices for a spectrum access mechanism (SAM). The problem of joint scheduling and spectrum-access footprint allocation is at the heart of maximizing the exploitation of spectrum. This problem is NP-hard and we present a suboptimal approach based on the minimal spectrum consumption cost of a spectrum-access request. We establish the significance of the active role by the incumbents, fine granular spatial reuse opportunities, and the need for transceiver standards for accomplishing efficient usage of the spectrum. We demonstrate that close to 100 spatially overlapping heterogeneous spectrum-access requests can be scheduled in a small 4.3 km x 3.7 km geographical region using the proposed suboptimal approach. By playing an active role in secondary spectrum access, the incumbents can extract a significant value out of the underutilized spectrum while protecting their primary service networks.
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