In cognitive radio networks, how the primary systems can distinguish between primary and secondary users.
In other words, which are the essential parameters that are taken into account to differentiate between PUs and SUs, from the primary system point of view?
In mostly studied cognitive radio networks algorithms, the primary user(s) is(are) oblivious to the existence of the secondary user(s). Secondary user need to detect the activity if the primary user in order to either take opportunity of spectrum holes for transmission of data on secondary links or ii) Perform some advanced signaling schemes/ Power control to avoid interference impact on primary receivers.
Setting a requirement for primary users to detect secondary users activity is not practical in terms of how cognitive radio networks operate. Remember the "Primary" user is the legal incumbent of the channel and no change in the communications protocol should be required.
Theoretically, primary users if they cannot detect the preamble of incoming signal, they can perform energy detection and kind of monitor interference patterns of other users utilizing the channel. This is the common practice in unlicensed bands but again it is a stretch to call it a cognitive radio network.
Dear Hamza
You are saying about the primary users (PUs') ability to detect the the cognitive user (CU) signal, however which is not the major concern of cognitive radio till now. The cognitive radio networks are defined so that the cognitive users perform all the functions such as spectrum sensing, sharing etc to utilize the underutilized band of the primary users however, no extra function need to perform by the primary systems since primary users are the legacy users.
In addition to this, if you wish to differentiate the PU and CU at the PU, the conventional spectrum sensing techniques can be used such as energy detection, cyclostationary detection, matched filter and waveform bases spectrum detection etc.
Dear Hamza,
Generally, there are three spectrum sharing methods in Cognitive Radio Networks.
1. Underlay: In underlay, SUs can transmit in parallel with the PU only if the interference level from SU to PU is less than some threshold. Here, threshold means, the maximum level of interference that PU can tolerate without hampering its target data rate or target SNR/SNIR. The PU does not care about the existence of SU. He only cares about the interference level.
2. Overlay: In overlay, there is a mutual cooperation between PU and SU. So, PU knows the existence of SU. SU may act as a cooperative relay for the PU. In exchange of cooperation, SU can get the opportunity to access the channel with PU based on superposition coding or non-orthogonal multiple access.
3. Opportunistic: In this method, SU can access the channel only if there is no primary transmission. That means, SU has to monitor the channel to know the existence of PU. Here, the responsibility goes to the SU completely. There are different methods such as energy detection, cyclostationary detection, matched filter and waveform bases spectrum detection etc. to detect the existence of PU.
Moreover, hybrid spectrum sharing consists of the combination of above methods.
In addition to the above methods: In Spectrum leasing protocol, PU leases or sells a portion of its time slots or spectrum to the SU. Its depends on the mutual understanding.
Hope this answer may helpful for you. If you have any further questions, please let me know.
Dear all,
Thank you very much for your reply, it was very helpful and very understandable.
Thank you
In the third spectrum sharing method, secondary user need to vacate the channel when primary user appear, how the secondary user distinguish that the coming transmission is from primary or another secondary user when he used energy detection sensing scheme.
There are three approaches of cognitive radio for free spectrum utilization of primary user i.e. Underlay, Overlay, and Interleaved.
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