In downlink as BS is in center transmitting with high power so cognitive users are placed outside a guard zone, however, in uplink system, the mobile phones transmit at low power so cognitive users can be placed in the same cell but a certain region of interference has to be computed around CU. Is this concept right?
Hi Astha, you will probably find this interesting:
http://ecewp.ece.wpi.edu/wordpress/wireless/textbooks/cr-textbook/
The above link provides a separate slide presentation for each book chapter.
The short answer is that there are alternative protocols for CR. In one case, the primary user is king, and either spectrum sensing and/or a location database will dictate whether any secondary user can have access. This applies, for instance, to the TV bands.
In other cases, secondary users can use the band but must keep monitoring for primary users, and cease transmissions if the primary user comes online.
In still other cases, multiple users can share the band, but must keep their interference levels below a certain threshold level.
What you cite, I think, is a case of frequency division duplexing, in which some other users might want access to the very low power uplink frequency simultaneously used by a base station. The same rules have to apply, though. The signal from the handset back to the base station would be clobbered if some other transmitter came online, on that uplink frequency, and was closer to the BS than the users' handsets might be. These are tricky scenarios. If this new user wants to share the uplink frequency band, by guaranteeing interference only below a certain threshold level, this new user would have to take into account the location of the BS also, not just the location of the other user(s) on this uplink band.
Hello Astha,
The short answer is no, CR users are not placed differently because the medium access protocol has to be able to tackle both cases. However, the manner in which spectrum is shared may have implications on location. More specifically, while spectrum underlay observes the interference level at the PU side and uses TPC to keep the SINR below a certain threshold, spectrum interweave relies on spectrum sensing to detect the activity of the PU. In the former case, terminals locations make a difference on the achievable throughput (due to the TPC) while in the latter case, throughput is affected only by the accuracy of the spectrum sensing process, which in turn depends - albeit indirectly - on location information.
Hope this helps.
By reading some papers on exploiting spatial opportunity, I saw some uses primary exclusive zones (PEZ) concept where CUs are placed outside of PEZ while one paper I saw was based on utilizing the opportunity in antipodal area of cell. So, can I say these are two ways of exploiting spatial opportunity in cellular networks.
1) Cognitive radio in a frequency-planned environment: some basic limits
2) Interference Model for Cognitive Coexistence in Cellular Systems
- Badges
- Science topic
- Similar topics
- Biological Science
- Bioecology
- Systems Ecology
- Landscape Ecology
- Connectivity