Investigation Of Preamble Management, Flow Control And Packet Capture In Wireless Random Access

Among various cellular mobile communication systems, uplink random access procedure is essential, including user registration, resource application and data transmission. Based on the chronological order of random access procedure, the existing research can be divided into three classes, i.e. communication resource allocation before random access, flow control protocols during random access, and collision processing after random access if a collision occurs. This thesis covers three aspects of random access techniques, including random access preamble allocation, flow control protocol design and packet capture scheme.Firstly, the random access preamble allocation method for Machine-to-Machine (M2M) traffics and Human-to-Human (H2H) traffics in LTE-Advanced system is studied. The number of M2M traffics is rapidly increasing in next generation mobile communication systems. In order to maximize system capacity, the communication resources should be allocated appropriately to M2M traffics and common H2H traffics. In this thesis, a preamble allocation method for M2M services in 3 GPP LTE-Advanced system is presented. The proposed method splits the set of available random access preambles into three subsets: the first one is for H2H services only, the second is for both H2H and M2M services, and the third is for M2M services only. We model and analyze the throughput performance of the proposed methods, and compare with the two major candidate preamble allocation methods under consideration for possible adoption in LTE-Advanced system. It is shown that the proposed method performs much better in most practical situations.Secondly, the flow control random access protocol for common H2H traffics and event-driven M2M traffics is investigated, respectively.For the flow control protocol for common H2H traffics, the principle and performance of multi-channel slotted ALOHA protocol based on power capture and backoff are analyzed firstly. Since there is a need in theoretical analysis, some important performance measures including access success ratio, throughput and delay performance are analyzed in details, which are shown to corroborate with our computer simulation results. Besides, through extensive simulation results, the influence of parameters such as power capture ratio, the number of channels and the number of user terminals, on the protocol performance is discussed.Based on the performance analysis of multi-channel slotted ALOHA protocol, a flow control random access protocol based on the adaptive dynamic persistence level transition scheme is proposed, which can be applied in UMTS and LTE systems. In our design, different access service classes are considered, and adaptive dynamic persistence level transition scheme is proposed, with persistence probability as the flow control factor. The transition scheme works based on the transmission delay, where the transition points are defined as the intersections of the throughput curves of each persistence level. Dynamic persistence level will change as the average delay is equal to or larger than the delay of current transition point. This thesis analyzes in details the protocol principle as well as the theoretical transition points. Our analytical and simulation results show that, by adopting the random access protocol, the quality of service (QoS) of high priority multimedia traffic is guaranteed when the system load is heavy, and the QoS can reach the system performance adopting the protocol based on the UMTS transition scheme which is controlled by base station. Moreover, the system broadcast resource consumption can also be reduced compared with the protocol based on the traditional transition scheme controlled by base station.Based on the fact that the traffic load of event-driven M2M traffics is heavy and bursty, a flow control random access protocol for LTE system is proposed. The beta distribution is adopted to model the event-driven M2M traffics. This protocol uses the random access preamble free ratio in a fixed number of slots to estimate the channel load and calculate the flow control factor to control the flow. We model and analyze the throughput performance of the proposed protocol, and compare with the random access protocol in LTE-Advanced system. It is shown that the proposed protocol performs much better because it can estimate the system load accurately in most situations and reduce collision by flow control factor.Finally, the capture scheme for spread spectrum slotted ALOHA is studied. A joint delay-power multiple packet capture scheme, that can collect multiple packets simultaneously from different terminals with both delay and power captures, is presented. The corresponding joint delay-power capture probabilities for a spread-spectrum slotted ALOHA packet radio networks where all terminals use a common spreading code under Rayleigh fading with power control are derived. Throughput and delay performance of the spread-spectrum slotted ALOHA packet radio networks with the joint delay-power multiple packet capture effect are shown by our simulation results to be significantly improved compared with the existing schemes.