Coordinated Multi-Cell MIMO Transmission with Feedback Based Precoding Control

Multi-Input Multi-Output (MIMO) transmission technique, in which both transmitter and receiver are equipped with multiple antennas, is attracting attention due to its many advantages such as its throughput improvement. For this reason, various cellular mobile radio systems based on MIMO have been developed such as 3GPP LTE (Long Term Evolution) [1] and Mobile WiMAX [2]. MIMO technique is also a promising technique in next generation cellular mobile radio systems such as 3GPP LTE-Advanced [3]. However, in cellular systems, cell-edge users generally suffer from large propagation loss and large inter-cell interference, and it is difficult for conventional single-cell based MIMO technique to improve throughput performance of cell-edge users. So, there is a strong need to improve cell-edge performance for the next generation systems [4]. Multi-cell MIMO transmission technique, in which multiple Base Stations (BSs) synchronize to each other and coordinate their wireless transmission [5]-[7], is a promising candidate due to the large cell-edge performance improvement for next generation cellular mobile systems [4]. On the other hand, adaptive MIMO, in which adaptively changes among multi-antenna transmission methods pre-defined between transmitter and receiver sides, is an effective technique. For example, 3GPP-LTE specifies two adaptive MIMO transmission modes of open-loop MIMO (OL-MIMO) and closed-loop MIMO (CL-MIMO) with simple feedback control, respectively [8]. Consequently, it is considered to be effective that Multi-cell MIMO applies the concept of simple feedback based adaptive MIMO such as the OL-MIMO and the CLMIMO. The OL-MIMO feeds back only transmit rank information (TX rank) corresponding to the number of substreams in spatial multiplexing, and it adaptively switches two precoding types of Space Frequency Block Code based transmit diversity (SFBC) [9] and Space Division Multiplexing without TXbeamforming (SDM) [10]. On the other hand, The CL-MIMO feeds back TX rank as well as an index of selected TX-beamforming matrix (precoding matrix), and it adaptively switches the number of substreams and TX-beamforming matrix. The authors propose two coordinated multi-cell MIMO tansmission methods, based on the OL-MIMO and the CL-MIMO specified in 3GPP-LTE. In this paper, open-loop MIMO based multi-cell MIMO is called as “multi-cell OL-MIMO” and closed-loop MIMO based multi-cell MIMO is called as “multi-cell CL-MIMO”. This paper also investigates the precoding control schemes of the multi-cell MIMO transmission methods. Moreover, it evaluates the proposed multi-cell MIMO schemes and clarifies the effectiveness of multi-cell CL-MIMO.