ECE 8863: Cognitive Radio Networks

Lab 3: Dynamic Spectrum Access

Cognitive radio technology promises to overcome the problem of spectrum scarcity resulting from the current approach of fixed spectrum allocation. Each cognitive radio should be able to learn/understand the radio environment and to dynamically adapt its operating parameters to make best use of the available spectrum. This is achieved by equipping radio devices with enabling capabilities such as spectrum sensing, adaptive transmission, and software reconfigurability.

In this lab, we aim to design a simple cognitive radio network that features dynamic spectrum access capabilities. After finishing this lab, you will know how to

  • Understand the fundamentals of Dynamic Spectrum Access.
  • Explore the importance of common control channels.
  • Exercise engineering design skills to realize dynamic spectrum access features in wireless networks.

 

Scenario Description

Assume a primary user that is sharing the spectrum with two cognitive radio nodes A, B as shown in Figure 1. The shared spectrum is comprised of four channels. The bandwidth of each channel is 5 MHz. On one hand, we assume one of these channels to be available for cognitive radio nodes all the time (i.e. CH4), however, it is not allowed to be used for regular communications. On the other hand, we assume that the primary user is occupying two channels out of the three communication channels (CH 1-3) by frequently hopping between them.

Lab3 Setup

Figure 1. Lab 3 Setup

In this scenario, you are required to design a cognitive radio transceiver that is capable of:

  1. Finding a white space and establishing communication

This is considered a network initiation stage. The primary user will be already occupying two channels and one channel out of CH 1-3 will be available for cognitive radio communication.

  1. Detecting interference and recovering communication

During the cognitive radio communication, the primary user can change its frequency hopping sequence to a new frequency pair causing interference to the cognitive radio. Hence, the cognitive radio has to detect that interference and be able to allocate a new white space and recover/resume its communication on the newly discovered white space.

 

Files

  1. lab3_pu.py: This is a Primary User (PU) that will transmit and receive packets to itself with USRP1 while hopping frequencies. You do not need to edit this file.
  2. lab3_cr1.py: This is Secondary User 1 (SU1). It's job is to sense the channels and send commands to Secondary User 2 (SU2) on the control channel. It includes an energy detector already.
  3. lab3_cr2.py: This is SU2. It's job is to receive commands from SU1 on the control channel and send data packets to SU1 on a data channel not used by the PU.

 

Steps

  1. Turn on USRPs 1-3 and the spectrum analyzer. Set the spectrum analyzer to view 900-950 MHz.
  2. Analyze how the PU operates by reading through lab3_pu.py. Run it and see how it behaves on the spectrum analyzer. You may change some variables at the top to see how they affect the packet error rate.
  3. Establish control channel communication by editing lab3_cr1.py and lab3_cr2.py. By default, SU1 sends the command "1234" on the control channel to SU2, but it likely will not work with the default settings. Show your working control channel to your TA before moving on.
  4. Change the transmission frequency of SU2 based on a command received from SU1 on the control channel. This will be your dynamic spectrum access protocol.
  5. Establish data communication between SU1 and SU2 in the whitespace determined by SU1. Show your successful cognitive radio network to your TA!
  6. When done, please turn in your SU code and answer the following questions:

Hw1 Q6:

  1. Describe the settings you had to configure in order to make your control channel work.
  2. Describe the protocol that you used to establish successful data communication in words or a diagram.
  3. How might you increase the data rate of your cognitive radio network?

 

Resources


Questions? E-mail: infocom@ece.gatech.edu

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