Performance Analysis for Partial Feedback Downlink MIMO with Unitary Codebook Beamforming for LTE

Abstract

Until recently, mobile communication tasks have been grouped into different layers in a hierarchical layer approach. In this conventional approach, layer-specific protocols are developed and optimised independently. As new wireless applications emerge, requiring high data rates and flexibility for supporting applications with significantly varying QoS requirements, it has become imperative that a higher level of communication between adjacent layers needs to be established. A unitary codebook based beamforming approach has been proposed for LTE that incorporates an improved cross-layer interface in order to improve service to users according to specified QoS criteria. This paper examines this beamforming approach under partial feedback conditions for different MIMO configurations. It is shown that non-obvious precoding matrix selection strategies and scheduling policies for the DLC, can achieve superior performance for LTE system, whilst meeting the QoS requirements of urgent users. I.INDRODUCTIONEmerging wireless communications systems that include a variety of different applications (e.g. real time video, voice, data) have changed the scope and design principles of wireless technologies. The need to provide high data rates for users within a congested channel environment has resulted in the emergence of Multiple Input Multiple Output (MIMO) antenna technologies and Orthogonal Frequency Division Multiplexing (OFDM). OFDM splits a high data rate stream into several lower rate orthogonal parallel streams. This approach is an attractive solution towards designing systems that are expected to operate in Non Line-of-Sight (NLOS) channels due to high tolerance to delay spread effects achieved by the a longer symbol duration and the use of a Cyclic Prefix (CP). The additional degree of freedom enabled by the use of multiple antennas at the transmitter and the receiver enables multiple users to be simultaneously scheduled on the same subchannel, or the assignment of multiple streams to the same user.The advent of new wireless applications, has highlighted the need for a better cross-layer cooperation that can support traffic with flexible Quality of Service (QoS) requirements, such as maximum packet delay, constraints of successful packet transmission. Recently, a Multiuser, Multiple Input Multiple Output (MIMO) scheduling and precoding method has been proposed for the Long Term Evolution (LTE) of 3G systems [1], that incorporates an improved interface between the Physical (PHY) and the Data Link Control (DLC) layers in order to provide increased support for on demand QoS [2]. In [3], a precoding method for a MIMO-OFDMA scheme has been proposed in accordance to the LTE standard [1]. This precoding method relies on the use of a known codebook of unitary matrices, which is determined offline, generated according to a Fourier basis that provides uniform coverage across a sector.The benefits from the symbiotic effect of a cross-layer design have been studied in [2]. This paper considers different codebook sizes o...

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