It is of interest for future mobile communication systems that mobile relay nodes (MRNs), i.e., relays mounted on top of transportation vehicles, are deployed in order to improve the system performance. A multi-MRN aided multiuser system is considered in this paper. The performance of the direct transmission mode and the MRN assisted transmission mode under different vehicle penetration loss (VPL) are compared. The users are separated into two categories in which the direct transmission mode and the MRN assisted transmission mode are selected to employ, respectively. A novel power allocation algorithm is proposed to improve the average system capacity under the constraint of total transmit power. The different power allocation schemes are applied for users in two categories to improve the system performance. It is demonstrated by simulation results that the proposed algorithm outperforms the average power allocation algorithm.

In this paper, coordinated beamforming scheme in distributed antenna systems (DASs) used for energy efficient transmission is developed. The major problem is non-convex of the optimization problem and is difficult to solve directly due to the fractional form. It is transformed into an equivalent subtractive-form optimization problem, by which we tackle this problem through a two-layer optimization algorithm. The out layer problem is solved by one dimension search method. The inner-layer sub-problem is solved with an optimal beamforming algorithm which is developed by exploiting the relationship between the user rate and the mean square error (MSE) of the received signal. The simulations illustrate that the higher energy efficiency can be achieved with the proposed algorithm than the weighted minimum mean square error (WMMSE) algorithm.

With the rapid growth of global mobile data transmission, the conventional multiple-input multiple-output (MIMO) systems are not able to accommodate the increasing data demand. The massive MIMO has been proposed as one of the key technologies for the next generation wireless communication systems. Compared to the conventional MIMO systems, massive MIMO systems are advantaged in energy and spectral efficiency. However, the advantage of massive MIMO systems is realized only when the channel state information (CSI) is acquired by both the base station (BS) and users accurately. In frequency division duplex (FDD) massive MIMO systems, the overhead of channel estimation could overwhelm the precious downlink resource. In this paper, a design method of optimal training sequence is studied based on the sequential channel estimation scheme with Kalman filter. Simulation results show the performance of the proposed optimal training sequence outperforms the exist ones.