CPC-based backward-compatible network access for LTE cognitive radio cellular networks

Network access plays an important role in LTE cognitive radio (LTE-CR) cellular networks in determining users´ experiences. An overview is first carried out on network access schemes in existing cognitive cellular networks such as IEEE 802.22 and IEEE 1900.4, based on which it can be seen that cognitive pilot channel (CPC)-based network access is a promising scheme for LTECR, which may provide fast network access and put no stringent requirements on terminals. Next, considering the implementation issues of CPC in practical systems, a CPC-based backward- compatible network access scheme should be designed for LTE-CR to facilitate the application of CR in LTE networks, which could exploit existing LTE structures and technologies to carry CPC information. To achieve this, a new system information block (SIB) should be designed to carry CPC on a current physical downlink shared channel with little standards effort. Moreover, load awareness is introduced so that LTE-CR is activated only when the system load is high. The complete process of this SIB-CPC-based backward-compatible and loadaware network access is described, and its performance is evaluated via simulations. It is shown that the blocking ratio of LTE-CR can be reduced notably compared to that of conventional LTE without CR. Moreover, by selecting an appropriate load threshold to activate LTE-CR, the average user throughput of LTE can be improved with near-zero blocking ratio by offloading users to complementary cognitive spectra.