Research On Wireless Resource Management And Feedback Reliability In LTE / LTE - A System

With the rapid growth of wireless communication for data services, the traditional network can not guarantee the experience of users.3GPP Long Ter-m Evolution(LTE), which is designed to further improve the data rates over air interface, can be regarded as a standard for wireless communication of high-speed data for mobile phones and data terminals. The combination of multiple-input multiple-output (MIMO) and orthogonal frequency division multiplex-ing (OFDM) is a key technology to facilitate the spatial multiplexing for nex-t generation wireless communications. Compared with the third generation communication networks, LTE employs a flat architecture and achieves signif-icant throughput performance improvement. Furthermore, with the increase of mobile internet applications,3GPP focuses on LTE-Advance(LTE-A) and its subsequent versions. High-performance low-cost LTE hotspot/indoor(LTE-Hi) deployment and3-dimension (3D) MIMO technology had been introduced.MIMO-OFDM technology has been developed with the evolution of LTE systems to facilitate the spatial multiplexing on the sufficient time-frequency resource blocks (RBs) and increase diversity and degrees of freedom in wire-less communications, resulting in more challenges of radio resource manage-ment. Since the adjacent cells reuse the frequency spectrum in MIMO-OFDM systems, co-channel interference caused by transmission in neighboring cells remains a major impairment that limits throughput. Therefore, resource man-agement has been studied and investigated to guarantee user experience. On the other hand, the closed-loop concept is introduced in LTE system, which requires the calculation of channel state information (CSI) at the transmitter. With the presence of CSI, closed-loop systems provide the dynamical transmis-sion modes control and resource management scheme to perform channel adap-tion. If such CSI is inaccurately calculated, the system performance would be decreased significantly. Based on the above-mentioned problems in LTE/LTE-A systems, this dissertation researches in the following two parts:1)In a variety of LTE/LTE-A scenarios, we propose resource management schemes to miti-gate the co-channel interference and achieve the performance improvement.2)We attempt to solve the unreliable feedback problem, leading to a certain performance improvement. Main researches and contributions of this disserta-tion are summarized in the following:Firstly, the resource management scheme in LTE homogeneous is studied. Considering the severe penalty of the overall cell throughput, the cell-center users’performance requirement is designed as the system constraints. Note that the ratio of transmit powers for cell-center users to cell-edge users can be adjusted in soft frequency reuse(SFR) scheme, we propose resource allocation schemes to optimize both of cell-edge and cell-center users’throughput.Secondly, the resource management schemes in LTE-Hi scenarios are s-tudied. We firstly solve the resource management problem in urban indoor s-cenarios, and propose an Relative Narrow-band Transmit Power (RNTP) based resource allocation algorithm with interacting signalling through X2interface. Using a LTE system level simulator, our proposed RNTP-based resource al-location algorithm is evaluated and proved to be an effective resource man-agement scheme without developing new protocols. We secondly focus on resource allocation in two-tier femtocell networks. Here, we define the sys-tem constrains consist of the outage constraints of two-tier users and macrocell spectral efficiency requirement. This dissertation aims to optimize the system throughput taking into account system constraints and presents a novel resource management strategy, to adaptively choose fractional frequency reuse (FFR) schemes for macro and femto networks.Thirdly, this dissertation investigates resource management for antenna ar-ray systems in3D MIMO-OFDM systems. Cell-center user and cell-edge user specific downtilts are accordingly partitioned through dynamic vertical beam-forming in the3D MIMO-OFDM communication systems. Taking these user specific downtilts into consideration, the objective of our proposed resource allocation scheme is to maximize both the cell-edge users’ and cell-center users’throughput, where RB assignment, power allocation and downtilts ad-justment are jointly optimized. Here, partial joint process (JP) coordinated multiple point (COMP) transmission mode and FFR scheme are introduced in this dissertation. Simulation results show that all of our proposed algorithms outperform the resource allocation scheme with fixed downtilts.Fourthly, this dissertation investigates the unreliable feedback in LTE/LTE-A systems, and focuses on unreliable RI management. In the view point of theoretical analysis, we introduce channel condition number to quan-tify the channel correlation degree in MIMO-OFDM systems, and propose a condition number based RI selection algorithm at the user side as well as at the base station side. After that, we predict the condition number at the base station side to solve the feedback period and delay problem, and choose the optimal number of transmitted data streams for unreliable RI management. In the view point of LTE/LTE-A systems, the differences of channel capacity for transmitted data streams are utilized to quantify the channel correlation degree. Taking the block error rate (BLER) into consideration, we propose an accu-rate throughput calculation algorithm at UE side as well as at eNB side. On the basis of ATC algorithm, we propose an accurate RI selection algorithm to periodically choose the preferred number of transmission spatial layers at the user side. Furthermore, based on the proposed accurate capacity calcula-tion algorithm, CQI adjustment scheme is proposed for spatial layer selection. Simulation results show that the proposed unreliable RI management strategies ensure that eNB can choose the reasonable transmitted data streams, and yield up significant throughput improvement in LTE system.Finally, conclusions and future works are summarized.