Research On Random Access And Resource Location For Standalone LTE-U System In Unlicensed Band

Standalone Long-Term Evaluation in Unlicensed band(SA LTE-U)system is one of the main solutions to alleviate the conflict between the scarcity in available licensed radio spectrum and the growing mobile data traffic.However,to coexist with the incumbent unlicensed band systems such as Wireless Local Area Networks(WLAN)in a friendly and fairly manner,the moment when SA LTE-U system occupies the channel is uncertain and each channel occupancy time is limited,causing invalid resources location,frequent interaction interruption in random access procedure,collision caused by the user accumulation,imbalance between the collision resolution ability in random access and uplink data transmission capability.This thesis investigates resource location and random access for SA LTE-U system.Resource location technology is studied.The concepts of the effective channel and effective frame number(EFN)are proposed so as to address the performance degradation caused by the discontinuous and time-uncertain practical channel.The method of generating and updating EFN is designed,the way of carrying and decoding EFN is given.The temporal positions of several types of subframe are expressed mathematically as functions of EFN,so that the obtained temporal positions fall into the channel occupancy duration and the subframe categories keep correct.Finally,the effectiveness of the proposed resource location scheme is verified by simulation.Random access and collision control are investigated to solve the problem that the collision becomes severer and the existing random access protocols are inapplicable under the discontinuous and time-uncertain practical channel condition.A new random access protocol based on the effective channel and effective window is designed to avoid the unaccomplished interaction and the long stay in random access procedure.Thus,the system performance and channel utilization can be improved.In order to cope with the severe collision among the users accumulated in the channel non-occupancy duration and starting random access procedure simultaneously when the channel is available for SA LTE-U system,a collision control method based on the exponentially attenuated probability is proposed.Then,the access ratio,reselection ratio and access delay are defined as performance metrics.Performance analysis is done so as to obtain the expressions of the aforesaid metrics.Finally,the effectiveness of the proposed protocol and collision control method is verified by numerical calculations and simulations.The resource allocation is studied to balance the collision resolution ability in random access and the uplink data transmission capability of SA LTE-U system.We formulate an optimization problem that maximize the number of the uplink shared channels for data transmission,under the condition of discontinuous and time-uncertain channel in unlicensed band,and with the constraints of average random access delay and user collision probability.Then,the method of joint arrival rate and maximum likelihood estimation is proposed to predict the number of users that may initiate random access simultaneously.An algorithm is developed to solve the optimal number of random access channels from the aforementioned optimization problem,so that the system performance and user experience can be improved.