Research of Mobile Terminal State Management in Next Generation Mobile Telecommunication Networks
|School||Shanghai Jiaotong University|
|Course||Communication and Information System|
|Keywords||next generation mobile telecommunication system 3G-LTE state management sleep mode operation radio resource control (RRC) mobility management|
With the development of mobile telecommunication network toward packet based broadband all-IP network as well as popularization of smart mobile terminals (WAP mobile phone, portable computer, etc.), varieties of packet based IP multimedia services will dominate the traffic flows of next generation mobile telecommunication system. Unlike the traditional vocal services which are based on circuit switch, the packet based Internet service flows exhibit a prominent discontinuous characteristic, and the arrival patterns of user packets vary with class of service, user custom and degree of network blockage. Therefore, the working states of user terminals in the next generation mobile telecommunication network should not be simply distinguished by“communicating”and“idle”. There will emerge another kind of states, in which the mobile terminal occupies network resources (wireless channels or signalling connections) or power resources (i.e., battery power) but data communication is not in progress. This has put forth a new research task on how to effectively control the state transitions of mobile terminals so that the utilities of network and power resources could be maximized on the basis of guaranteeing a certain level of QoS (quality of service). Such a research is being widely carried on, and achievements have been acquired at each layer of the wireless packet network protocol stack. However, due to the diversity of packet based wireless services and advent of brand-new mobile network infrastructures, the issue of mobile terminal state management is still under further consideration.This thesis has studied the mobile terminals’adaptive state management schemes within the infrastructure of 3G-LTE (3rd Generation Long-term Evolution). The study focuses on the issue of sleep mode operation at MAC (Media Access Control) layer aiming at power saving, as well as control of RRC (radio resource control) connection release at RRC layer aiming at improvement of RRC signalling efficiency and RRC connection occupation efficiency. Considering the high mobility of user terminals, the thesis has also studied the issue of optimizing the state transition behaviours in the mobile scenario.Sleep mode is the basic technique for decreasing user terminals’power consumptions at MAC layers of various wireless networks. Sleep period is the key parameter of sleep mode operation. By recurring to M/G/1 queueing model, Chapter 2 analysed the relationship between sleep mode timer threshold and such performance measures as QoS and user terminal power saving by assuming that the arrival of downlink user data is a Poisson process. Based on this analysis, a threshold constrained dynamic sleep mode operation scheme (TC scheme for short) is put forward. This scheme, which is applied to delay insensitive services, selects the mean packet queue length at the time point of entering communicating sub-state as the constraining threshold. In the implementation of the algorithm, a unique sleep period autonmous adjustment strategy is employed, which is more efficient than the“doubling sleep window”method used in IEEE 802.16e. Simulation results have shown that, the scheme is capable of combining the two targets, i.e., packet queue length restriction and power consumption minimization, in a wide range of user packet arrival rates. As an improvement, another sleep mode operation scheme (TC/RC scheme for short), which is constrained by both the queue length threshold and a reward function, is put forward. This scheme has markedly upgraded QoS under small packet arrival rates while providing nearly the same power saving performance as in the TC scheme. The TC/RC scheme has also proved its optimality under a 2-state Markov modulated Poisson process (MMPP) arrival style.In 3G and 3G-LTE, RRC connection is an important bearer which implements radio resource management, control signalling transfer and mobility management. The existence of a RRC connection is a prerequisite of user packet transfer. A frequent release and reestablishment of RRC connection will not only incur a mass of control signalling, but also result in quite a few occurrences of RRC establishment delay within a session, which degrades QoS. On the other hand, if a RRC connection is maintained for a long time while the terminal has no demand for communication, the utility of RRC resources is decreased, which will also adversely affect QoS. By assuming that the duration of a packet call is Pareto distributed and the inter-arrival time of adjacent packet calls is exponentially distributed, a scheme of dynamicly deciding the RRC release moments within the packet call intervals is put forward in Chapter 3. The optimization target of this scheme is to maximize RRC utility while keeping the probability of RRC reestablishment interval exceeding a certain threshold to below a predefined level. Simulation results have shown that, this scheme has effectively avoided frequent RRC connection release/reestablishment under short session durations, and has guranteed a good RRC connection utilization under long session durations.Since the granularity of a mobile terminal’s mobility management (e.g., cell or location area) is closely related to its RRC state, the amount of mobility management cost varies with the state in which the terminal resides. Therefore, by extending the research issue of Chapter 3, Chapter 4 has taken into account the factor of user mobility in the optimization scheme of user terminal state transition control. Based on the random walk mobility model which assumes an exponential distribution of cell residence time, the improved scheme is capable of deciding whether to release RRC connection according to the user’s current mobility pattern and service style. Moreover, the scheme will automatically adjust the preference of optimization in response to the variation of call inter-arrival time, i.e., when the expected call inter-arrival time is short, the optimization scheme will mainly aim at decreasing amount of control signalling; and when the expected call inter-arrival time is long, the scheme will mainly aim at reducing transfer frequency of signalling message bulks and increase utility of RRC connection. Based on the above“individual”optimization scheme, a global state transition control scheme, which considers both overall QoS of the cell and signalling cost, is put forward. In virtue of inter-cell information exchange, this scheme will predict the approximate amount of RRC resources requested by handover users within a segment of future time, and adjust RRC release behaviours of current users in the cell according to the prediction, so that the drop rate and block rate can both be effectively restricted while prominent increase of total signalling cost can be avoided. Maximum likelihood estimation method and Trimmed tail estimation method are selectively used while estimating key parameter of distribution of packet call duration. Moreover, Liapunov method is utilized to decide the target value of vacant RRC connections. The involvement of above mathematic methods has improved effect of optimization without notably increasing algorithm complexity. The effectiveness of the whole optimization scheme is validated against relevant simulations.