A Study of Improving the Spatial Multiplexing Gain of the Wireless Communication MIMO System with a Low Rank Channel

To meet high communication quality required by all kinds of multimedia wireless communication services, next generation wireless communication systems must be able to achieve high efficiency of data transmission under the provided extremely limited wireless channel resources. Therefore, it is inevitable to effectively allocate the scarce system resources (e.g. bandwidth, power, channel’s degree of freedom) Based on our current research results, in this research project, we will focus on the problem of providing the mobile subscribers in a wireless network with bad channel quality a high throughput data transmission service. The bad channel quality herein means that the MIMO channel matrix seen at a mobile subscriber is a matrix of low rank. Consequently, it greatly reduces the system’s spatial multiplexing gain. In order to boost the spatial multiplexing gain for those subscribers suffering from bad channels, we propose a novel Multiple-point-to-Multiple-point-Multiple-input-Multiple- output-Orthogonal-Frequency-Division-Multiple-Access (M4-OFDMA) wireless commun- ication network frame. The basic idea of the M4-OFDMA system is to employ multiple access points (APs) simultaneously providing communication service in the same time slot and the same frequency band to the subscribers of bad channels. It intends to compensate the spatial multiplexing gain of a low rank channel by using the AP diversity. Taking advantage of multiple uncooperative access points (AP) sending data to multiple stations (STA) simultaneously, the STA of the M4-OFDMA system, when receiving data, have to overcome the problem of high mutual interference from different APs. In order to have mass data streams being reliably transmitted in the network, interference avoidance techniques thus become particularly important to the M4-OFDMA system. Fortunately, incorporating the MIMO and the OFDM technologies, the equalizers of STA in the M4-OFDMA system can use both of the spatial degrees of freedom and the spectral degrees of freedom to effectively mitigate the inter-cell interference and the intra-cell interference. In addition, by using a feedback channel, each STA can send the reduced channel status information (CSI) back to its corresponding APs. Based on the returned CSI, the AP in the M4-OFDMA system can then design the dirty paper codes applicable to its downlink channel for reducing the co-channel interference among the in-cell STAs. This research project will take three years to solve all the encountered problems of the M4-OFDMA system. In the first year, we will develop a subspace-based transmit/receive beamforming algorithm. In the second year, we are going to investigate the channel estimation problem of the M4-OFDMA system. To reduce the computational complexity, we will develop a tree-structured low complexity channel parameter estimation algorithm. In the last year, by using the normal graph approach, we will be devoted to solve the problems of dynamic channel assignment and power allocation for the M4-OFDMA system.

Project ID:PB9709-2023
External Project ID:NSC97-2221-E182-063