| With the rapid development of multimedia technologies,people's requirements of data rate have undergone an exponential increase.This trend makes the information link of terahertz bit per second become reality in the next five to ten years.In light of the fact that there exists a serious contradiction between the demand and reality of the communication capacity in millimeter(MM)-wave communication system,the existed strategies cannot meet people's requirements in the future.Therefore,it's necessary to expand the capacity of communication channel as well as to seek new resources at higher spectrum area.Evidently,the high data rate communications,like terahertz and optical communications,will become the future trend of wireless communications.Due to the rapidly increasing carrier frequency and bandwidth,high data rate communications operating at higher spectrum may meet new challenges in terms of the key signal processing techniques at the receiver,including: 1)Larger frequency deviation of broadband signal synchronization technology: the bandwidth of the received signal in terahertz spectrum is beyond the sampling bandwidth limitation of Analog to Digital(AD),making the synchronization in terahertz band be forced to process in analog domain,whose performance would be lower than that obtained in digital domain.2)Low resource consumption in large frequency offset time-varying channel estimate technology: when multi-users' signals transfer through the wireless channel,the quality of signal demodulation will be impacted substantially by the joint influence of large frequency offset caused by asynchronous clock in transceiver system and time-varying multipath fading channel,thus leading to a severely degaraded demodulation performance.3)Anti-phase noise based high order modulation and demodulation technology: When carrier is generated by mixer in terahertz communication,too much phase noise may also be generated.Even if synchronization and channel estimation are completed,the residual phase noise will still seriously degrade the demodulation performance of high order modulated signal.4)The compressed receiving technology of broadband signal: the bandwidth of signal is far beyond the limit of AD in high data rate wireless communications systems operating at high spectrum.That means the signal processing cannot be implemented in digital domain,where is more flexibility and have many algorithms to enhance the performance of data transmission.In this thesis,we aim to improve the reliability of wireless signal reception in high carrier spectra.The critical functionality of this work is to suppress the carrier interference.The technology bottlenecks in terms of signal synchronization,channel estimation,phase noise resistance demodulation and compressed receiver are broken though in thisthesis.and the main innovations of this thesis are reflected as follows:1)To address the problem of carrier synchronization in digital domain,a narrow band pilot code assisted synchronization algorithm is proposed,which is capable of breaking though the sampling band limitation of AD.Compared with the normal pilot aided carrier synchronization technology in analog domain,the proposed one can prevent mutual interference between the pilot and signal.Meanwhile,this technology can reduce the transmission power as well as improve the transmission efficiency.2)On the premise of realizing carrier synchronization,a low resource consumption joint estimation algorithm for high carrier frequency system is proposed for estimating the large frequency deviation,multi-path delay,amplitude and phase in the time-varying channel.The proposed algorithm is capable of breaking though the bottlenecks of channel estimation with large frequency offsets.Furthermore,the estimation results are close to the Cramer-Rao Lower Bound(CRLB)at high Signal-to Noise Ratio(SNR).Compared with Repeated Weighed Boosting Search(RWBS)estimation algorithms,the proposed technique obtained a better performance in terms of frequency estimation accuracy when there are many users.Meanwhile,the computational complexity of proposed one is obviously less than RWBS.3)A new constellation called “spiral quadrature amplitude modulation(SQAM)” as well as a new phase noise optimized demodulation algorithm is proposed.These proposed algorithms can supress the residual phase noise in the high carrier frequency high order modulated receiving systems,which may seriously impact the demodulation performance.When the variation of phase noise is assumed to be 0.1,it was shown that the 64 SQAM constellations can be demodulated with negligible errors at high SNR.However,the 64 QAM constellations failed to demodulate.Hopefully,all the researches in this thesis can provide technical foundation for improving the communication reliability of the future wireless communications systems.Among these researches,carrier synchronization technology can pass through the sampling limitation of AD,effectively reduce the transmission power,and improve the synchronization accuracy.This carrier synchronization technology paves the way for facilitating the reliability of long distance and high data rate communications.Furthermore,the proposed channel estimation algorithm can improve the estimation precision with large frequency offsets,which is the technical support of multi-users detection.In addition,the proposed SQAM is regarded as an effectively phase noise suppressing technique,which can help us to enhance the quality of communication.Finally,the proposed compressed receiver design illustrates a realizable implementation scheme,which enables us to directly use the compressed signal to implement the phase capture and tracking.The proposed design will become a kind of feasible scheme for the future compressive receiver. |
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