One of major issues in the efficient use of radio resource for multiuser multiple-input/multiple-output (MU-MIMO) systems is the selection of users to achieve the maximum system throughput. The optimal user selection algorithm, which requires exhaustive search, is prohibitive due to its high computational complexity where Block diagonalization (BD) method is applied and known as a suboptimal precoding technique for downlink MU-MIMO systems, which intents to perfectly eliminate inter-user interference. In this paper, we propose efficient, iterative user selection algorithms with low complexity, where the product of eigenvalues of effective channels is utilized as a selection metric by applying the concept of principal angles between subspaces. And, we further examined the applicability of the proposed algorithms to limited feedback systems and proportional fair (PF) scheduling. Through computational complexity analysis, we show that the proposed algorithm has low complexity with a little loss in throughput. Simulation results validate that the proposed algorithm achieves almost the same system throughput by a capacity-based algorithm under high SNR regime with considerable reduction in complexity.

In downlink multi-user multiple-input/multiple- output (MU-MIMO) systems with BD where there are a lot of users, selecting a user set supported by a base station (BS) is very critical to maximize the total throughput. The optimal user selection algorithm, which requires exhaustive search, is computationally prohibitive in real systems. In this paper, we propose a user selection algorithm with low complexity, where the product of eigenvalues of effective channels is utilized as a selection metric. We adopt the concept of principal angles between subspaces to obtain the product of eigenvalues of effective channel matrix at each iteration. Contrary to conventional low complex user selection algorithms, the proposed algorithm is straightforward to apply to PF scheduling because the proposed selection metric indicates data rate in high SNR regime. Computational complexity analysis and simulation results show that the proposed algorithm achieves almost the same the system throughput of capacity-based algorithm in high SNR regime with considerable reduction in complexity.

Existing positioning systems such as global positioning system (GPS) or WiFi positioning system (WPS) are limited mainly to outdoor applications or are of poor accuracy without associated maps. Indoor work environment where one spend most of the time and wide adoption of smartphones with numerous embedded sensors provide new opportunities for researches on indoor user positioning. In this paper, we present an indoor positioning scheme using recently introduced smartphones equipped with sensors such as accelerometer, magnetometer, and gyroscope. We propose a practical indoor positioning method to handle complicated human movements and noisy inertial sensors in smartphones. We focus on providing indoor locations with accuracy by applying improved heading estimation solution. The key concept is to reduce errors caused by directional change since the critical component of positioning system is a heading orientation. We have simply used iPhone 4S for experiments and validated its practical usage in indoor environments. The extensive experimental results show that our system is needily applicable as a fundamental system for various mobile services on smartphones providing 2.42 times accuracy over than traditional methods on the average.

In this paper, we address the issue of resource management for coordinated multi-point transmission/reception (CoMP) systems. We propose a dynamic transmission mode selection scheme combined with proportional fair (PF) scheduling, where each cell performs scheduling in a consecutive order. Based on the prior user selection information, each cell decides transmission mode, and makes user scheduling according to the selected transmission mode. Furthermore, we extend precoding matrix indicator (PMI) coordination in order to mitigate intra-cluster interference. The proposed scheme provides adequate resource allocation in JT-CoMP systems without central scheduling unit. Simulation results show that the proposed algorithm provides significant edge user throughput gain without any loss in average throughput.