Pilot Design For Compressive Sensing Based Channel Estimation In MTC

The new generation of machine type communications(MTC)is an important part of the Internet of Things and has good application prospects.Compared with traditional communications,it has low mobility,low cost of devices,small size data and other features.In MTC,a number of devices are present in a cell,but only a few of them attempt to access by sending preambles or pilots during the random access procedure,while many other devices are idactive,which leads to network overload and waste of resources.The related research on how to design pilots has important theoretical and practical value for solving problems such as network congestion.Therefore,this paper proposes two methods for designing pilots.The specific results and innovations are as follows:(1)Using the known Sidel'nikov sequences to design new pilots.This paper analyzes the characteristics of the equipments in MTC and finds that they are sparse when performing random access.Combining the above characteristics with compressive sensing theory,this paper concludes that there is a theoretical relationship between the coherence of the CS measurement matrix and the pilots for CS-based detection and channel estimation.And the uniqueness of CS recovery can be guaranteed by using a lower coherence with characteristics.According to this premise,adding a certain multiplication and shift to the known Sidel'nikov sequences can be used to design more qualified pilots,and using the multiplicative and additive characters to prove that the designed pilots can guarantee the uniqueness of the CS recovery.Simulation results show that the pilots designed with Sidel'nikov sequences have good performance.(2)The proposed method uses m sequences that are pseudo-random sequences with good correlation.According to the coherence of the CS measurement matrix and the inverse discrete fourier transform of an element-wise product of a pair of distinct pilots are equal,that is,the low coherence can guarantee the uniqueness of the CS recovery.The uniqueness of CS recovery can be guaranteed by the value of the inverse discrete fourier transform of an element-wise product of a pair of distinct pilots as low as possible.Therefore,the existing deterministic m sequences are extended to design more well-performing pilots.and using multiplicative additive characters to prove the value of the inverse discrete fourier transform of an element-wise product of a pair of distinct pilots is relatively low.The simulation results show that the pilots designed with m sequences have better performance.