Random Access And Data Transmission Mechanism Design And Parameter Optimization For LTE-U Systems

As one of the rapidly growing mobile Internet and Internet of Things(IoT)infrastructures,cellular mobile communication systems should be able to support ubiquitous and diverse user equipment/traffic.This raise new demands for the 5th generation(5G)cellular mobile communication system that supports both Human to Human(H2H)communication and Machine to Machine(M2M)communication.However,the Unlicensed Long Term Evolution(LTE-U)technology,which is considered as one of the candidate 5G technologies,cannot directly adopt traditional Long Term Evolution(LTE)'s standards and technologies due to the discontinuous channel,uncertain channel access time,and limited single channel occupancy duration in unlicensed band.This dissertation focuses on the LTE-U system and studies its random access(RA)technology and data transmission technology supporting both H2H and M2M user equipments(UEs).To enable the LTE-U system to operate in the unlicensed band,the concept of"effective channel" is proposed,and the identification and labeling methods of effective frames and effective slots on effective channel are designed.The effective channel is assembled by all the channel occupancy periods head-to-tail in sequence.That is,a channel which is composed by eliminating the non-channel occupation periods from the actual channel.The frames,subframes,and time slots contained in the effective channel are all "effective" which can be used by the LTE-U system.This makes the design difficulty of protocols and operations in LTE-U system greatly reduced.For H2H traffic,we study the random access protocol that meets the regulatory constraints of unlicensed band and minimally modifies the random access protocol of legacy LTE systems.A user grouping and effective window size based RA protocol is proposed.In this protocol,the UEs are divided into several groups,and at any time only one group is activated and allowed for its UEs to send RA attempt,which avoids the intergroup UEs' collision.The backlogged UEs of the activated group are scattered over multiple RA slots to send RA attempt,which alleviates the intragroup UEs' collision.In addition,to avoid the unnecessary retransmissions of preambles caused by the channel uncertainty,the transmission of RA attempt and the reception of RA response are performed on the effective channel that consists of the channel occupancy periods only.The expressions of RA performance are derived.An optimization problem is formulated to maximize the utilization to obtain the optimal number of carrying RA slots.The above theoretical work can provide guidelines for RA parameter settings in LTE-U system.For downlink data transmission of small packet M2M traffic,a mechanism to balance the channel utilization and the user satisfaction is designed.We first define the channel utilization and the unified user satisfaction.Then,we model a two-dimensional optimization problem(PI),which maximizes the weighted sum of channel utilization and user satisfaction by optimizing channel occupancy duration(COD)in time domain and subcarrier allocation in frequency domain.By introducing a control factor,the tradeoff between channel utilization and user satisfaction is achieved.By using Lyapunov optimization theory we first transfer P1 into a new problem,so that it can be solved by using the instant data arrival and channel state information(CSI)of current frame instead of knowing the statistical knowledge of CSIs and data arrivals of all frames in advance.By using Dinkelback theory,we further transform the objective function from its fractional form into a subtractive form which is easy to solve,and then design a heuristic algorithm to solve the transferred problem.This theoretical work can provide guidances for the design of future new radio of LTE-U systems.For massive small sized M2M traffic's uplink data transmission,we design an efficient random access and data transmission system known as distributed queueing random access-multiple-input multiple-output(DQRA-MIMO)data transmission system.This system has the advantages of both efficient collision resolution of DQRA protocol and the efficient data transmission of MIMO technology.To obtain higher throughput under delay constraint and limited time-frequency resources,we match the ability of collision resolution with the capability of MIMO transmission by optimally configuring system parameters.The closed-form expression of throughput is derived,which is a function of the total UEs' traffic arrival rate,average number of packets of each arrival,number of base station antennas,and number of AR slots.An optimization problem is formulated to maximize the throughput to obtain the optimal number of AR slots given a certain delay constraint for M2M traffic.The above theoretical research and verification results also reveal the feasibility for the LTE-U network to support massive small data packet services.