Utilizing OFDM guard interval for spectrum sensing.

摘要

Spectrum is a precious resource in wireless communications. Currently spectrum is statically allocated to applications. This results in inefficient usage of spectrum. This is motivating opportunistic spectrum usage systems and dynamic spectrum access systems.; Spectrum sensing is a crucial functionality for dynamic spectrum management. Many digital communication signals show second order periodicity, i.e., their autocorrelation is periodic. Cyclic spectral analysis techniques exploit this characteristics of digital communication signals. This sensing technique is very attractive because it does not require coherency and synchronization. Also it can distinguish various signal properties and works in low SNR environments. Hence, a cyclostationary feature detection approach has been chosen for spectrum sensing.; Spectrum sensing interval is a very important medium access control design parameter in determining sensing accuracy and probability of missed detection. Instead of allocating explicit sensing interval in the opportunistic spectrum usage MAC we have embodied the sensing interval in the OFDM guard interval. This provides very high rate spectrum measurement and identification of idle spectral spaces.; OFDM achieves very high spectral efficiency by orthogonal placement of carriers. The orthogonality is attributed to cyclic prefix which achieves cyclic convolution, thus, avoiding inter-carrier interference. For incorporating spectrum sensing interval into OFDM guard interval, cyclic prefix is not sent. This potentially affects orthogonality of OFDM sub-carriers. To remedy this situation, cyclic convolution is secured at the receiver side. It is shown that there is no effect on BER under this scheme.; We have used IEEE 802.22 framework for demonstrating the scheme. IEEE 802.22 is an upcoming standard based on cognitive radio technology. The purpose of this standard is to promote dynamic spectrum management approaches. The High UHF channel space is owned by digital TV(DTV) transmitters. Under the FEC NPRM proposal this spectral range can be used by secondary users without affecting spectrum rights of incumbents. We have shown that using the proposed scheme the presence of primary users(DTV) could be detected reliably. Also there is no need to explicitly allocate sensing interval. Thus this approach provides bandwidth savings and high sensing reliability to manage and mitigate interference to the incumbents.