Studies On Key Techniques Of Energy Efficient Wireless Access To 6G Internet Of Things Networks

The new generation of internet of things(Io T)systems is facing a series of technical challenges due to the dramatic growth on the number of user terminals accessing the Io T networks,the requirements of much smaller delay and largely enhanced security over the whole networks,and the remarkable energy consumption.This dissertation focuses on the future techniques and service requirements of the six generation(6G)mobile wireless communications and studies five aspects of 6G Io T networks including the guaranteed security of the wireless access from terminal stations over Io T networks,simultaneous wireless energy and information transfer in Io T networks,interference suppression over heterogeneous Io T networks,adaptive offloading over mobile edge computation with guaranteed very short delay,and intelligent reflective surface aided novel Io T networks.For each of the five aspects,both theoretical performance analysis and optimal algorithmic design are carried out.The goal of the thesis is to develop optimal resource management and scheduling approaches for the 6G Io T networks,in order to achieve high performances of the wireless access to Io T networks from the security,delay,and energy efficiency perspectives.The main contents of the whole dissertation are listed below,(1)Considering the difficulty of charging for massive terminals in Io T networks,we propose an efficient approach for both wireless power transfer in downlink broadcast channel(BC)and wireless information transmission in uplink multiple access channel(MAC).We derive an analytical expression for the defined energy efficiency function in terms of the statistics of the wireless channel possibility distribution.An optimization problem is formulated by maximizing the corresponding energy efficiency function,under the constraint of Qo S requirement in terms of the minimum total throughput across all the multiple uplink channels,where the unknown parameter is the transmit power from the access point(AP).The lambert function properties are utilized to derive the final solution in a closed form.Also,the best number of transmit antennas is mathematically derived,resulting in optimum energy efficiency.Computer simulation results show that the energy efficiency does not always improve with increasing the number of antennas at AP,and it becomes worse once the number of antennas exceeds the threshold since more antennas consume much more power while yielding only a much smaller throughput gain.(2)To deal with the strong interference to both single hop and dual hop wireless access terminals over the heterogeneous Io T networks,we propose a method for jointly designing one receive beamforming vector and two transmit beamforming vectors for the forwarding terminal with multiple antennas.The optimization problem is established based on maximizing the energy efficiency.The receive beamforming vector is proved to be able to match the wireless channel from AP to the forwarding terminal,and the transmit vectors are derived using the generalized eigen value decomposition.Finally,a three-step iterative algorithm is developed to update the three beamforming vectors.Both theoretical derivations and numerical simulations demonstrate the remarkable improvement in suppressing the co-channel interference within the heterogeneous Io T networks.(3)Concerning the requirement on the delay of the Io T networks for certain applications,the mobile edge computation(MEC)aided Io T is addressed by focusing on the adaptive offloading from the terminal to the MEC.The offloading factor is optimized for the terminal according to the cost function of minimizing the energy consumption with the constraint of maximum threshold over the delay.Here,the delay consists of the processing time at the terminal of low computation capability,and the transmission duration of the wireless uplink offloading from terminal to the MEC.Note that the computation duration at the MCE is neglected since MCE typically has very strong computation capability.The established complicated problem is tackled case by case to obtain the final solution.The theoretical performance evaluation is also carried out by deriving the lower bound function of the energy efficiency based on the inequality relaxation method.It is discovered that the derived lower bound function consists of the offloading factor,the total computation time,and the statistics of the wireless offloading channel in terms of the channel mean and covariance.(4)Considering the delay is severely affected by the infinite length of the channel coding that is widely assumed in literature for the study of the well-known Shannon Capacity,we propose to employ the limited length of channel coding in the Io T networks with strict delay requirement.This scenario consists of one eavesdropper terminal,multiple legitimate terminals,and one AP.The secured energy efficiency is maximized under the constraint of the Qo S over the minimum of the secured throughput,where the new capacity formula is utilized that involves the length of the channel coding.Both the upper and the lower bound functions are derived for the received signal to noise ratio(SNR)at each legitimate terminal.The convex optimization method is used to solve this problem.Moreover,the limiting offloading factor is derived with the transmit power in the high regime.This expression reveals the relationship between the transmit power and the channel coding length,where the channel coding length directly determines the delay.Hence,the derived results measure well the relationship among the secured energy efficiency,the transmit power,and the length of short channel coding within the studied secured Io T networks with limited length of channel coding.(5)It is known that current techniques for Io T networks cannot change the wireless channel such as adjusting the direction of the multi-path.By exploiting the adjustment of the scatters and thus to adaptively changing each multi-path to coherently arrive at the terminal,we propose the reflective intelligent surface(RIS)aided Io T secured access techniques.The theoretical trade-off is conducted for the energy efficiency and the spectral efficiency of the new Io T networks.The energy efficiency is derived to the upper bound in the high transmit power regime.This expression involves the number of reflective surface elements,and the statistics of the wireless channel,which avoids the instantaneous channel fading coefficients.Finally,the energy efficiency in this scenario is expressed in terms of the spectral efficiency,which shows the key performances of the RIS aided new Io T networks.Also,the overhead of signalling among many distributed RISs is addressed by designing an algorithm of selecting RISs,where the path loss and the slow varying instantaneous signalling are exploited.Simulation results show a remarkable reduction of overhead yet with good performance improvement.