The Research Of LTE Co-frequency Co-time Full Duplex System Self-interference Cancellation Cascade Algorithm

Spectrum resources in the 21 st century is extremely valuable, with the development of wireless communication technology, the total wireless access exponential growth, spectrum resources become increasingly scarce. Improve the spectrum efficiency can access more users and meet each user a higher connection speed data connection service. The current TD-LTE in different time slots, respectively, for sending and receiving data, and FDD-LTE uplink and downlink use different frequency bands, transmission and reception of data are carried out simultaneously, these two methods in the time slot and frequency, respectivel y wasted half of the resources.A long time in academia, it is widely believed that a node can not simultaneously transmit and receive signals in the same frequency band, because the transmission signal can cause a strong self-interference in the receiving antenna in the same frequency. But recently studies have shown that CCFD(Co-frequency Co-time Full Duplex) is likely to be achieved by use various canceling technology. Therefore, we studied the co-frequency co-time full duplex communication mode in this thesis. It is able to achieve that a node can transmit and receive signals at the same time within the same frequency band. Because bandwidth of the LTE signal is relatively large, the canceling effect of the edge frequency of signal is poor, the positional accuracy of the actual project is bad, the antenna cancelation applied directly in LTE can't meet full duplex communication requirements. Therefore, this paper use antenna cancellation and RF cancellation, they are cascade together, this can effectively reduce the drawbacks of antenna cancellation, combined with the existing digital cancellation technology, this method can meet the requirements of LTE full-duplex communication system.This paper studies the CCFD technical advantages over the prior art and the key problems and difficulties, three antennas to achieve antenna cancellation technology, analysis two-way signal amplitude mismatch and antenna placement errors that affect performance, then discuss the advantages and disadvantages in combination of antenna cancellation and MIMO system. In order to solve the issue of the position error of the antenna is very sensitive, we use the RF cancellation, which uses interpolation sampling theorem, and it is similar to the reverse of sampling theorem, we constructed N signals whose time intervals were equal. We saw N-channel signal as the Nyquist sampling sample values, and regarded the coefficient of each signal as the weight of digital samples. And we simulated this method and got its performance curve. Finally, the above two methods are cascaded together, conducted simulation experiments and analysis the simulation results.