Cognitive radio (CR) is introduced to efficiently and opportunistically use the limited spectrum to minimize the spectrum scarcity issues. Usually, service providers purchase the spectrum license from the policy-makers and spectrum regulator authority. The non-licensed users cannot utilize the licensed bands even though primary user is not transmitting. It sometimes results in under-utilization of frequency bands, which in turn decreases the spectral efficiency. The CR can opportunistically use the freely available licensed spectrum. To solve the spectrum scarcity problem, we implemented CR using software defined radio on frequency modulated radio band (88–108MHz), because of ease in access and availability. The proposed solution is equally valid for other frequency bands as well, because the printed circuit board adopted here supports frequency from 50MHz to 2.2GHz. The proposed solution uses energy-detection based spectrum-sensing technique for primary user (PU) detection, and afterwards secondary user starts the data transmission over the vacant frequency band. We presented real-time experimental results for the detection probabilities by testing under various false alarm probabilities to verify the efficiency of the designed system. Experimental results show that we can achieve high detection probability even at low receiver sensitivity. When PU becomes active, then the proposed system quickly shift the public-safety user to other available white spaces to avoid halting the licensed user transmission. This solution is beneficial for security and defense organization such as army, traffic wardens, city wardens, and police.

引入认知无线电（CR）可以有效和机会性地使用有限的频谱，以最大程度地减少频谱稀缺问题。通常，服务提供商从政策制定者和频谱监管机构那里购买频谱许可证。即使主要用户未发送，非授权用户也无法使用授权频段。有时会导致频带利用不足，进而降低频谱效率。CR可以机会使用免费提供的许可频谱。为了解决频谱短缺问题，由于易于访问和可用性，我们在调频无线电频段（88-108MHz）上使用软件定义的无线电实现了CR。提出的解决方案同样适用于其他频段，因为此处采用的印刷电路板支持50MHz至2.2GHz的频率。提出的解决方案使用基于能量检测的频谱传感技术进行主要用户（PU）检测，然后次要用户开始在空闲频段上进行数据传输。通过在各种虚警概率下进行测试以验证设计系统的效率，我们提出了检测概率的实时实验结果。实验结果表明，即使在低接收灵敏度的情况下，我们也可以实现较高的检测概率。当PU变为活动状态时，建议的系统会迅速将公共安全用户转移到其他可用空白处，以避免中止许可用户的传输。此解决方案对于诸如军队，交通管理员，城市管理员，