With the rapid development of mobile Internet and urban constructions, high-volume and dynamic indoor communications bring challenges to cellular systems. High penetration loss and deep shadowing channels of indoor users may substantially degrade the transmission efficiency and system throughput. To address this issue, this paper proposes a solution using Floating Relay (FR) given the mature technologies of unmanned aerial vehicle (UAV). We target the undesirable channel conditions of indoor users, introduce the FR into the cellular system to improve transmission efficiency and maximize system throughput. Considering the capacity limit of the FR's back-haul link and the maximum transmission power of each user, an optimization problem is formulated to maximize the system throughput. The optimal power allocation strategy is then obtained for each user, and two effective online 3-D placement algorithms are proposed for the FR to approach the optimal location in the unpredictable and predictable scenarios, respectively. Extensive simulations are conducted. The achieved maximum system throughput, convergence rate, and accumulated throughput are used to evaluate the proposed algorithms. According to the comparisons between the two proposed algorithms and with off-line schemes, they show superiorities in their targeted scenarios, respectively.

Due to the massive growth in the number of wireless devices and their traffic, the problem of sharing channel access has become much severe in wireless networks. Group Synchronized Distributed Coordination Function (GS-DCF) was introduced in the IEEE 802.11ah standard to group users and give each group a Restricted Access Window (RAW) to compete in. However, how to group users remains an open issue which has a great impact on the network performance. In this paper, an RSS- based grouping strategy is proposed to solve the hidden terminal problem in wireless networks. The analytical and simulation results are then provided to demonstrate the advantages of this scheme over conventional grouping strategies. According to the results, the proposed RSS-based grouping scheme will make the probability of hidden terminal negligible and thus substantially improve the network performance.

The rapid development of the Internet of Things (IoT) has brought big challenges to the traditional cellular networks such as super dense devices and deep fading channels. These new challenges will lead to a significant transmission efficiency degradation and increase the device's power consumption, especially in the uplink. A huge pressure will be also imposed to the enhanced Node B's (eNB) scheduler due to the large number of users. In this paper, a semi- centralized controlled cooperative method is proposed for the uplink cellular transmission, where the User Equipment (UE) relay will be randomly selected according to a certain density decided by the eNB. Two specific cooperative schemes based on the Device-to- Device (D2D) are proposed, which are the random UE relay scheme and the one further combined with the Network Coding (NC). The theoretical analyses for both of them are given and corresponding closed-form results are derived. The D2D interference is considered and modelled based on the stochastic geometry. The performance gains are identified by numerical evaluations in various scenarios and the comparisons between two cooperative schemes are made as well. Also, these results can provide an important guideline for the eNB to determine the optimal density of the UE relays.

With the rapid development of the Internet of Things (IoT), the new challenges brought by the MTC traffic imposed a great pressure to the traditional cellular networks. The new MTC features like small-data transmission, large number of devices and deep fading channels will lead to a significant spectrum efficiency degradation and thus affect the regular Human-to-Human (H2H) communications. In this paper, we proposed a semi-centralized controlled cooperative method to improve the MTC transmission efficiency in the cellular uplink, which is backward- compatible with current LTE/LTE-A protocol and easy for implementation. Two cooperative transmission schemes based on the Device-to-Device (D2D) communications were applied, which are the Random User-Equipment (UE) Relay scheme (RUR) and the Network Coding scheme (NC). The D2D interference was analyzed based on the stochastic geometry, and 2 layers of scheduling were also considered. Intensive simulations were conducted. From the simulation results, a significant gain was achieved by the proposed method especially for the small data traffic. Also, a comparison was made between the RUR and NC schemes, and the suitable scenarios for each scheme can be identified.