Cognitive radio (CR) technology offers an innovative solution to improve spectrum efficiency, thus satisfying the greater demand to be placed on the electromagnetic spectrum by future wireless networks and communications. In this sense, the ulti- mate purpose of the spectrum sensing feature in cognitive radio is to determine the absence or presence of licensed users' signals in a frequency band of interest. More- over, due to the wide variety of scenarios in which cognitive radios may operate and the random nature of wireless channels, spectrum sensing algorithms are expected to perform well at a very low signal-to-noise-ratio (SNR), thus playing not only an important but also a very challenging role in CR. In this thesis, locally optimum (LO) detection, (known to be optimum at low SNR), is adopted in the design of blind and semi-blind detection algorithms by fo- cusing on linear modulation in the presence of an unknown phase shift and additive white Gaussian noise. The proposed LO detectors are shown to significantly out- perform the energy detector in the case of BPSK signals and to be less sensitive to noise power mismatch whilst their complexity is only slightly higher than that of the energy detector. Furthermore, the spectrum sensing performance is improved by taking advantage of the spatial diversity gained through cooperation. In addition, next generation wireless networks will need higher data rates to meet the requirements of the expected customers and services. The spectrum sen- sing duration and the secondary user's achievable throughput trade-off problem is addressed here by allowing the constraint on the probability of detection to be in outage with a specified percentage, taking into account the detrimental effect of unknown channel gains over different fading conditions in centralised cooperative networks, which is a more realistic scenario. The spectrum sensing time/secondary user's achievable throughput trade-off is then formulated and optimised accordingly.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:582744 |
| Date | January 2012 |
| Creators | Cardenas Juarez, Marco Aurelio |
| Publisher | University of Leeds |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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