Lte Physical Layer Dynamic Transmission Mode Switching Over Mimo Scattering Channels

LTE (Long Term Evolution) is standardized particularly to satisfy the growing demand on high data rate while providing also a high reliability in transmission. The main keys of this promising technology are particularly OFDMA (orthogonal frequency division multiplexing access) in the downlink transmission and SC-FDMA (Single Carrier-Frequency Division Multiplexing Access) for uplink transmission, combined with MIMO (Multiple Input Multiple Output) antenna systems associated with space-time codes as Orthogonal Space-Time Blocks Code (OSTBC), Spatial Multiplexing and Beamforming techniques. LTE network as well as previous wireless communications GSM and further3G technologies, is an air interface-based propagation of waves transmitted from MIMO antenna systems. Since it is often required for performances estimation, channel modeling plays a vital role in wireless systems analysis. Therefore, wireless MIMO channel must be carefully investigated and modeled accurately as real world dictates. MIMO channels are known to be spatially, temporal and frequency correlated channel and then should be designed to translate those triple characteristics.However, challenges remain in modeling accurately MIMO channels and existent space-time and frequency selective geometrical-based channel models in the literature are usually pointed for their lacks, impracticability and complexities. Moreover, MIMO channel spatial correlations (’relation with’) known to be generated from small antenna spacing and scattering environments, decrease the degree of freedom and diversity. This ’relation with’ may affect the reliability of the link of communication for LTE deployment. In order to approach the uncorrelated channel case, a conventional and known alternative is to increase the antenna spacing, but this cannot be done easily for limited space platforms such as the base station as well as the mobile station. Others methods commonly known as precoding system can be used; however such alternatives cannot improve the performance of space-time codes up to that over uncorrelated channel and increase often complexities in implementation.Another challenge in LTE systems, is the estimation of its MIMO channel required for the functionality of quality factors such as channel quality indicator (CQI), rank indicator (RI) and phase matrix indicator (PMI) feedback from the mobile to the eNodeB (enhanced Node B).For a MIMO rapidly time-varying channels, it is practically impossible for a dynamic instantaneous feedback of channel state information (CSI) to work accurately. At least, a deterministic averaged channel estimation or partial channel station in terms of spatial-temporal correlations should be available at the eNodeB for throughput transmission optimization.In LTE/LTE-Advanced, the physical layer in Release9is mapped into multiple transmission modes(TM) TM1, TM2... TM8. Depending on the spatial-temporal correlations level, each TM can be selected instantaneously at the base station for data transmission. Therefore, LTE network can be performing and reaches its targets if only a mechanism with respect to the variation of MIMO channel, allows an optimal switching between TM. However the3GPP is silent about the implementing of an adaptive MIMO switching between those TM and complexities increase since, besides the usual computation of the Signal to Noise Ratio (SNR), the computation of the velocity of the mobile and the channel correlations are required. In this work, I propose practical methods and alternatives to overcome all the above mentioned impairments and challenges:1. On the basis of the well-known single bounce one-ring scattering environment, I propose a wideband or time dispersive channel model by assuming multiple bounces of waves.The proposed MIMO wideband channel is shown realistic, physically satisfactory and more flexible compared with the well-known exponent decay ing-based frequency selective channel assumption that I show physically unrealistic in scattering domain if a suitable Probability Density Function (PDF) of multi path delays, is not investigated.2. By analyzing the interaction which exists between spatial correlation factors, I have proposed a strategy, a wise trade-off between scattering environments parameters and antenna spacing for minimizing correlation without any need of precoding systems, avoiding then complexities.3. I extend the proposed frequency selective (wideband) channel by formulating a full space-time and frequency channel model taking into account the impact of the mobile motion (time domain) on multiple scattering rings within the cell.The model termed as Multi Ring Scattering Channel (MRSC) is strictly elaborated by considering the motion of the user (mobile station) through multiple scattering ring with different size of beamwidth seen at the base station. Especially, I formulate two models of MRSC by assuming different probability distribution function (PDF) of scattering rings. A uniform probability density function has been considered to formulate what I call as a Cluster model. However, in the cell environment, an infinite number of scattering rings can be assumed; in this case, a Gaussian distribution is suitable to describe the statistic characteristic of parameters. Hence, another model is elaborated by applying a Gaussian PDF. Both MRSC channel models can be used for LTE system performances analysis.4. By studying the interaction between the diversity-multiplexing and spatial correlations in MIMO systems, I further adopt the proposed MRSC channel with Gaussian PDF to propose an implementation of an adaptive MIMO switching for LTE optimal transmission selection in regard with the variation of the spatial-temporal correlations. All proposals have been shown improving by simulation results corroborating my studies.5. A special topic on millimeter wave technologies is also foreseen for future gigabit LTE wireless communications systems in this work. I propose the concept of MIMO small antenna demonstrating the possibility of designing multi element small antenna systems extremely exhibiting a high spatial diversity compared to actual microwave communication systems. The proposed MIMO small antenna is also shown to very suitable for required small place platforms.