Collaborative Relay Beamforming Based on Minimum Power for M2M Devices in Multicell Systems

Recently, machine-to-machine (M2M) communication has been studied in the single cell system. However, in the multicell system multiple M2M type devices at the edge of a cell may suffer from the strong interference that consists of the intercell interference from other cells and the intracell interference from other M2M devices in the local cell. In this paper, we study the relay beamforming strategy to guarantee the quality of service (QoS) requirements of the multiple destination devices in multicell systems. We minimize the transmit power of the base stations (BSs) and relays to save the power of M2M devices, while guaranteeing the receive signal-to-interference-and-noise ratio (SINR) of the destination devices. The main contribution of this paper is that we propose an iterative algorithm to jointly optimize the BS and relay beamforming weights with minimizing the BS and relay power under the receive SINR constraints in the perfect channel state information (CSI). Using the semidefinite relaxation (SDR) technology, the optimization problems for the BS and relay beamforming weights can be effectively solved. In addition, we also discuss the issue of imperfect CSI in practice. Simulation results validate our theoretical analysis and demonstrate that our proposed iterative scheme can achieve near-optimal performance within a few iterations. 1. Introduction Recently, machine-to-machine (M2M) communication has been studied by many standards as the European Telecommunications Standards Institute (ETSI) [1] and 3rd Generation Partnership Project (3GPP) [2, 3]. Machine-type communication devices, such as smart meters, automotive applications, and smart phones, can communicate in M2M systems, which do not necessarily need human intervention [4]. According to the 3GPP standards, the base station (BS) can be used to manage the M2M devices and many BSs can divide the M2M devices into multiple cells [5]. The M2M devices communicate with each other through the BS in the cell system [6]. To offer the high data-rate for the M2M systems, multiple-input multiple-output (MIMO) antenna systems can increase the channel capacity for given transmit power and bandwith in previous studies [7]. However, the performance of MIMO systems may degrade due to correlated signals among antennas and cannot offer high coverage in large areas for M2M devices. Recently, many literatures research on the relay devices to guarantee the quality of service (QoS) requirements of the destination devices [8]. The BS transmit signals to the destination devices with the help of one or more relay