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The rapid growth of wireless industry and continuous emergence of new applications increase the demand for wireless spectrum. However, currently the spectrum assigned to different organisations is not utilised efficiently. Particularly, when an infrastructure of a service provider is overloaded and cannot accommodate more users because of the channel scarcity, the infrastructures of other service providers operating in the same area might be in under-loaded status. However, without a proper spectrum sharing scheme, the overloaded infrastructure cannot use the channels licensed to other service providers. This leads to low spectrum utilisation efficiency and higher call blocking rate of service providers. Significant research has been conducted to study sharing channels between cells within one service provider; however, sharing spectrum across different service providers is still under investigation. This paper proposes deploying a network of fixed cognitive radio (CR) nodes to maintain spectrum sharing across multiple service providers operating in the same geographical area. These CR nodes estimate the spectrum utilisation in a given area, and cooperate to provide the spectrum usage information for the overloaded infrastructures of service providers. This work discusses the implementation of the proposed CR-based spectrum sharing technique, and studies the impact of spectrum sharing on the service provider's performance. It is shown that the proposed technique reduces the call blocking rate and improves the spectrum utilisation efficiency. This technique removes the need of sensing spectrum in each user. Thus, it reduces the cost, complexity and battery power consumption of user devices.