# Multi-Attributes, Utility-Based, Channel Quality Ranking Mechanism for Cognitive Radio Networks
## 4 Discussion  
The proposed model was evaluated experimentally using two parameters: the information capacity and the occupancy of the free channel, which was determined by using spectrum sensing. These two parameters involve several other parameters. For instance, the capacity in its calculation involves two main parameters, which are the bandwidth of the channel and the level of noise represented by the signal-to-noise ratio. The data rate is also considered, which involves a modulation and coding techniques. One of the advantages of the proposed model is its modularity as one can easily include as many parameters as needed to evaluate the quality of the channel. For instance, one crucial parameter that can be included in the channel quality ranking is the bit error rate. In the case of the communication systems, the reliability is commonly expressed using the bit error rate (BER). The BER can be defined as the ratio between the number of corrupted bits and the total number of transmitted bits during a period of time. The knowledge of the BER associated with each channel at any time can help to evaluate the quality of the channel, and thus, can improve the quality of service by enabling the selection of a channel with a minimum BER for transmission. Clearly, the smaller the BER, the more reliable the communication system is. To measure the BER, several techniques have been proposed [33]. For instance, the authors of [34] have proposed a technique that measures the BER in the Additive White Gaussian Noise (AWGN) channel using as few as 32 pilot samples to estimate the BER with an error of 0.00066. The signal-to-interference-plus-noise-ratio (SINR) is another crucial parameter in channel quality ranking, especially in cognitive radio networks [35], since interference is one of the critical factors that affects the performance of communication in these networks. The SINR is the relative ratio between the power of the transmitted signal and the interference power added to the noise power. This parameter is affected by several parameters such as shadowing and path loss. Another aspect that has to be considered in channel quality ranking is the security risk associated with each specific channel. The cognitive radio network is subject to several attacks that can create a denial of service [36; 37; 38]. For instance, if a channel is jammed, the communication is interrupted. To avoid jamming attacks, it is possible to calculate, for instance, the probability that a channel will be jammed. A secondary user can choose the channel with a lower attack probability. Another advantage of the proposed model is that it involves several parameters in the process of the selection of the best communication channel, which contrasts to other models that consider only one parameter, such as the occupancy of the channel. The selection of the best channel based on the occupancy can lead to the selection of a channel with a high remaining idle time, but this channel can have a low bandwidth or can experience a high level of noise, which does not allow secondary users to achieve a high data rate. This clearly show the outperformance of the proposed model compared with other techniques. Once the selection of the best channel is done, secondary users can choose the optimal parameters of transmission such as the modulation technique, the coding rate, and the power of transmission that allow them to achieve the maximum data rate. Several algorithms can be applied in this stage, such as genetic algorithms discussed in the introduction section. Table 4 gives a comparison between ranking mechanisms. This table shows that our algorithm ranks the channels based on the capacity that involves in its calculation the bandwidth, level of noise within a channel, and the occupancy. A machine-learning model is used to predict the utility value of each frequency channel. The model involves several parameters jointly in the process of the channel ranking.