Study On The Resource Allocation For B3G/4G Systems

The lack of radio resource in mobile communication system leads to the importance of resource allocation in the aspect of system performance. With the rapid development of mobile communication technologies and the commercialization of various mobile communication systems in recent years, the user requirements for traffic and mobile high data rate have been increasingly rich with more and more types of traffics. High data rate transmission has become the main goal of future mobile communication systems. Meanwhile, the development of advanced communication technologies and the rapid evolution of mobile communication system standards, also with the diversification of mobile communication network architectures have made the radio resource allocation as one of the core issues for the research on mobile communication systems. Therefore, it is very important for B3G/4G communication systems to make sure how to utilize the precious radio resource in order to satisfy the requirements of various traffics better.This thesis focuses on the cross-layer resource allocation for OFDM-based B3G/4G mobile systems in mixed traffic scenario. A unified utility function for mixed traffic scenario is first studied by analyzing requirements of different kinds of traffic models. Afterwards, the optimization resource allocation model for mixed traffic based on the unified utility function is built. The optimal resource allocation strategy can be derivated from the solution of the optimization model. Based on the theoretical derivation, algorithms for the resource allocation strategy are designed. In this way, the framework for the cross-layer resource allocation based on the unified utility function in mixed traffic scenario can be established. Accordingly, the resource allocation strategies for various advanced communication technologies and the performance in B3G/4G systems are also studied. Finally, a unified system-level simulation methodology and the simulation framework as well as the design of the general system-level simulation platform are proposed. It can be used to evaluate the performances of different communication systems or technical solutions. The main ideas, results, and contributions of this thesis are generalized as follows:(1) A unified utility function for the mixed traffic in mobile communication systems is proposed. In regard to the fact that the key point of utility-based cross-layer resource allocation lies in the design of the utility function, its form directly determines the realization and the performance of resource allocation strategy. Besides, in future mobile communication systems, various traffic models in mixed traffic have different requirements of performances and priorities. Therefore, this thesis proposed a unified utility function for the mixed traffic scenario in mobile communication systems. This utility function has the identical form for different traffic models and uses different parameters to distinguish them. The unified utilify function can simplify the study of resource allocation strategies and the design of algorithms in mixed traffic model. It also can automatically satisfy the practical requirements from different types of traffic and guarantee the priorities of various traffic models. The analysis of utility function is the basis of the study on resource allocation strategies.(2) The resource allocation strategy and its related algorithms are studied based on the unified utility function for the mixed traffic scenario in B3G/4G systems. Based on the study of the unified utility functaion, the cross-layer resource allocation framework has been built based on the unified utility function in OFDM systems. Firstly, the optimization model for resource allocation is built. In order to satisfy requirements of performance priorities from different types of traffics, the maximization of the aggregated utility of all users in the system is modeled as the optimization objective, and the restraints of total resources as well as the QoS requirements for different types of traffics are modeled as the constraints. After that, the unified derivation of the resource allocation strategy can be obtained through the theoretical analysis on the model. The requirements from different types of traffic can be satisfied in the proposed strategy through different parameter values. Meanwhile, the resource allocation strategy based on the unified utility function can automatically guarantee the priority of different traffic models. In order to apply the proposed strategy in practical systems, heuristic algorithms are designed for different traffic scenarios. After that, the complexity and the reliability of the algorithms are analyzed. Finally, the performances of the proposed resource allocation strategy and the algorithms are evaluated through simulation. From the simulation results, it can be found that the resource allocation strategy based on the unified utility function can automatically satisfy the resource requirements from QoS traffic, and guarantee the fairness among the BE traffic users in the mixed traffic scenario.(3) An inter-cell coordinated resource allocation is studied under the coordinated multi-point transmission (CoMP) technology. In LTE-A system with CoMP, the resources in different cells can be allocated coordinatedly, to improve the performance of cell-edge users. In this thesis, the inter-cell coordinated resource allocation strategy in OFDM systems is analyzed. The utility-based method is also adopted and the optimization model is built based on the utility function. The model here considers users in multiple coordinated cells and the relevant resources. In the coordinated resource allocation strategy, the resources of coordinated cells are jointly allocated to control the inter-cell interference (ICI). The disadvantage of the propsed strategy is the extremely high complexity. Thus, in this thesis, the complexity of the proposed strategy is analyzed to find out the factors that influence the complexity. The complexity is lowered to apply the proposed strategy in practical systems. Through the analysis and simulations, it can be found that the inter-cell coordinated resource allocation strategy can effectively improve the cell-edge performance so as to achieve better fairness. Meanwhile, coordinated BSs need to share some signaling, including the channel state information of MSs, the scheduling information, etc. through the backhaul network. Therefore, the inter-cell coordinated resource allocation strategy can improve the performance of cell-edge users and control the ICI at the cost of some system signaling overhead and the algorithm complexity. (4) The scheduling strategy in LTE-A system with carrier aggregation (CA) technology is analyzed. In CA, the available bandwidth in the system consists of several continuous or non-continuous sub-bands, and the system serves users by designing the proper resource allocation strategy. Based on that whether the transmitted data queues of users can use all the available sub-bands, the scheduler models can be divided into the following two categories:the joint queue scheduler (JQS) and the non-joint queue scheduler (NJQS). In the JQS, each user’s data stream has only one queue for all the sub-bands, and the JQS maps different users’data streams onto the resource blocks of all the sub-bands. In the NJQS, each user’s data streams will be allocated to different sub-bands first, and the NJQS maps the data in each queue onto the resource blocks of the corresponding sub-band. Besides, the scheduler for the independent carrier (IC) is also proposed here for the comparison. In IC, each user is restricted to use the resource on only one sub-band up to the end of user stream. In this thesis, the queue theory is used to compare the QoS performances of different schedulers under scenarios with delay-sensitive traffics. Moreover, comparions on aspects of hardware, compatibility, data rate are also developed. These schedulers have their unique advantages and appropriate scenarios. Especially in the delay-sensitive traffics, the JQS outperforms the NJQS. Finally, the advantages of CA and the performance comparisons of different schedulers can be obtained by LTE-A system-level simulation under scenarios with different traffic models.(5) A unified system-level simulation methodology and a simulation process are proposed, and a general model of the system-level simulation platform as well as the framework is built. To evaluate the performances of different mobile communication systems reasonably and compare them fairly, a unified simulation methodology and a simulation process are proposed, as well as the design of the general simulation platform. This unified methodology with generality can be applied in the performance evaluation of different mobile communication systems. First, the unified models for the modules in the system-level simulation are built, and the simulation parameters and configurations can be unified in different systems. Thus, the unified system-level simulation methodology can be built to compare the performances of different systems fairly. Based on the unified simulation methodology, a unified system-level simulation platform is designed and built, which can be used to evaluate the total system performances of different communication systems and the relevant technical solutions that are studied in this thesis.