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CR-NOMA (Cognitive radio inspired NOMA)

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Introduction:

Cognitive radio (CR) and non-orthogonal multiple access (NOMA) are two of the most promising technologies in wireless communication. CR allows secondary users to access the spectrum that is not currently used by primary users while NOMA allows multiple users to share the same time and frequency resources by using superposition coding and successive interference cancellation (SIC) techniques. By combining CR and NOMA, cognitive radio-inspired NOMA (CR-NOMA) can significantly enhance the spectral efficiency and energy efficiency of wireless networks. In this article, we will explain CR-NOMA in 2000 words.

Background:

CR technology allows secondary users to access the spectrum that is not currently used by primary users. This enables the efficient utilization of spectrum and provides flexibility in wireless communication. NOMA technology allows multiple users to share the same time and frequency resources by using superposition coding and SIC techniques. NOMA can provide better spectral efficiency and energy efficiency than orthogonal multiple access (OMA) schemes such as time-division multiple access (TDMA) and frequency-division multiple access (FDMA).

Motivation:

The combination of CR and NOMA can provide several benefits such as higher spectral efficiency, better energy efficiency, and increased capacity. The motivation behind CR-NOMA is to improve the utilization of spectrum and provide better QoS for users. CR-NOMA can also provide better reliability and security by using spectrum sensing and interference management techniques.

CR-NOMA:

CR-NOMA can be divided into two categories: CR-NOMA with fixed power allocation and CR-NOMA with dynamic power allocation.

CR-NOMA with fixed power allocation:

In CR-NOMA with fixed power allocation, the power is allocated to users based on their channel gains. The users with weaker channel gains are assigned higher power levels than the users with stronger channel gains. The users with stronger channel gains can decode the messages of weaker users by using SIC techniques.

The steps involved in CR-NOMA with fixed power allocation are as follows:

  1. Spectrum sensing: The cognitive radio senses the spectrum to detect the primary user's presence.
  2. Channel estimation: The cognitive radio estimates the channel gains of the users.
  3. Power allocation: The cognitive radio allocates the power to the users based on their channel gains.
  4. Superposition coding: The cognitive radio encodes the messages of the users using superposition coding.
  5. Transmission: The cognitive radio transmits the signals to the base station.
  6. Reception: The base station receives the signals and uses SIC techniques to decode the messages of the users.

CR-NOMA with dynamic power allocation:

In CR-NOMA with dynamic power allocation, the power is allocated to users dynamically based on the instantaneous channel gains. The users with weaker instantaneous channel gains are assigned higher power levels than the users with stronger instantaneous channel gains. The users with stronger instantaneous channel gains can decode the messages of weaker users by using SIC techniques.

The steps involved in CR-NOMA with dynamic power allocation are as follows:

  1. Spectrum sensing: The cognitive radio senses the spectrum to detect the primary user's presence.
  2. Channel estimation: The cognitive radio estimates the instantaneous channel gains of the users.
  3. Power allocation: The cognitive radio allocates the power to the users dynamically based on their instantaneous channel gains.
  4. Superposition coding: The cognitive radio encodes the messages of the users using superposition coding.
  5. Transmission: The cognitive radio transmits the signals to the base station.
  6. Reception: The base station receives the signals and uses SIC techniques to decode the messages of the users.

Advantages of CR-NOMA:

  1. Higher spectral efficiency: CR-NOMA can provide higher spectral efficiency than OMA schemes such as TDMA and FDMA. By using superposition coding and SIC techniques, multiple users can share the same time and frequency resources, which leads to higher spectral efficiency.
  2. Better energy efficiency: CR-NOMA can provide better energy efficiency than OMA schemes such as TDMA and FDMA. By allocating power based on the channel gains of the users, CR-NOMA can reduce the total transmit power, which leads to better energy efficiency.
  3. Increased capacity: CR-NOMA can increase the capacity of wireless networks by allowing multiple users to share the same time and frequency resources. This can lead to better QoS for users and increase the overall capacity of the network.
  4. Reliability and security: CR-NOMA can provide better reliability and security by using spectrum sensing and interference management techniques. By sensing the spectrum and avoiding the channels used by primary users, CR-NOMA can reduce the interference and improve the reliability of wireless networks.

Applications of CR-NOMA:

  1. 5G and beyond: CR-NOMA can be used in 5G and beyond wireless networks to provide higher spectral efficiency and better energy efficiency. By combining CR and NOMA, CR-NOMA can address the challenges of 5G and beyond wireless networks such as higher data rates, increased capacity, and better QoS.
  2. Internet of Things (IoT): CR-NOMA can be used in IoT applications to improve the utilization of spectrum and provide better QoS for IoT devices. By allowing multiple IoT devices to share the same time and frequency resources, CR-NOMA can increase the capacity of IoT networks and improve the reliability of IoT applications.
  3. Smart cities: CR-NOMA can be used in smart city applications such as smart transportation, smart grid, and smart healthcare. By providing higher spectral efficiency and better energy efficiency, CR-NOMA can improve the performance of smart city applications and provide better QoS for users.

Conclusion:

CR-NOMA is a promising technology that combines the benefits of CR and NOMA. By providing higher spectral efficiency, better energy efficiency, and increased capacity, CR-NOMA can address the challenges of wireless communication and enable the development of new applications such as 5G and beyond, IoT, and smart cities. CR-NOMA can also provide better reliability and security by using spectrum sensing and interference management techniques. Therefore, CR-NOMA is a technology that should be further explored and developed in the future.