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Intelligent selection of threshold in cognitive radio system

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Abstract

To evaluate the performance of cognitive radio (CR) under the energy detection scheme, the proper selection of threshold is an important and a critical task. The threshold is generally selected, either under a target probability of detection \((\overline{P_d})\) called as the constant detection rate (CDR) principle, or under the target probability of false alarm \((\overline{P_{fa}})\), called as the constant false alarm rate (CFAR) principle. To ensure sufficient protection to the licensed users (or primary users), the selection of threshold under the CDR principle is best suited. This paper discusses and analyzes the inefficiency of CR under the blind use of CDR principle, mainly, when primary receiver is located at a sufficient distance d from the secondary transmitter where signal to interference plus noise ratio (SINR) is larger than a cut-off value \(SINR_{th}\) (which is a minimum SINR required to properly decode the intended information of primary user). To overcome this inefficiency, we propose an approach which while considering distance d between the secondary transmitter and primary receiver as an important parameter, makes an interference-aware selection of threshold based on the CDR and CFAR principles. Under the proposed approach, the CR system achieves a significant gain in its throughput even under the low signal to noise ratio conditions.

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Notes

  1. Based on the settings of various parameters assumed (assumptions are given in Sect. 5), the value of critical distance \(d_c\) may vary.

  2. As per the properties of the Q function Q(x), it shows sharp variation for a given range of x, as \(x\epsilon ({-4, 4})\), however, beyond this range, the variations are negligible. So, this results in an un-noticeable variation to the achieved simulation curves (for some range of variable on x-axis), as depicted in Figs. 2 and 3.

  3. During sensing, the distance between the secondary transmitter and primary transmitter (\(d_{ps}\)) may also be computed as follows: The term \(P_{rps}\) in Eq. (21) shows the power of primary transmitter received at the sensing node (i.e. secondary transmitter). Since, the values \(P_{rps}\), \(P_p\), r and the constant c are already known at the CR end, the distance \(d_{ps}\) can be computed as:

    $$\begin{aligned} d_{ps} =exp\left( {\frac{1}{r}.ln\left( {c.\frac{P_p}{P_{rps}}} \right) } \right) \end{aligned}$$

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Authors and Affiliations

  1. Electronics and Communication Engineering, National Institute of Technology Kurukshetra (NITKKR), Kurukshetra, Haryana, India

    Gaurav Verma & O. P. Sahu

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  1. Gaurav Verma
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  2. O. P. Sahu
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Correspondence to Gaurav Verma.

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Verma, G., Sahu, O.P. Intelligent selection of threshold in cognitive radio system. Telecommun Syst 63, 547–556 (2016). https://doi.org/10.1007/s11235-016-0141-y

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