• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.39B no.10
• /
• pp.654-663
• /
• 2014

Heterogeneous network (HetNet) with the various types of cells, e.g., with the different cell size and transmit power, has been introduced to improve the cell coverage and areal capacity in cellular mobile communication system. In this paper, we consider a practical situation in which all cells share the same wireless resource while some of them have a limited backhaul capacity. More specifically, we formularize a cell association problem that utilizes the minimum wireless resource while satisfying the quality of service (QoS) of all users in terms of their transmission time constraint, and propose a distributed algorithm to find the optimal solution. In the event of bottleneck at the backhaul link in some small cells, the proposed algorithm off-loads some users to the adjacent cell with the less congested backhaul capacity. Finally, we verify that the proposed algorithm supports the more numbers of users to satisfy the specified level of QoS than the conventional user association scheme under the limited access and backhaul capacities.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.41 no.12
• /
• pp.1903-1913
• /
• 2016

In this paper, we propose 2-stage beamformer with linear receiver in wireless backhaul downlink system where macro base station has large antenna array with sub-array structure. Also, to compare the system capacity, we apply 3-stage beamformer with zero-forcing precoder and calculate the achievable sum rate of received small cell base stations. Considering scattering and path-loss property of wireless backhaul channel, we combine precoding technique for spatial multiplexing and beamforming technique to overcome path-loss. Therefore, we design DFT-based fixed beam patterns for the first stage. The simulation results show that considering spatial multiplexing, proposed 2-stage beamformer with linear receiver can increase the achievable sum rate as well as reduce the feedback information.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.40 no.6
• /
• pp.1005-1013
• /
• 2015

In this paper, an uplink pilot signal structure is proposed for millimeter wave(mmWave)-based mobile wireless backhaul. For the transmit diversity of two antenna ports, uplink pilot signals generated from the Zadoff-Chu sequence can be mapped in an interleaved mode or continuous mode on the frequency axis, and channel estimation algorithms are different depending on the pilot signal mapping schemes. Through a simulation under Rayleigh fading channel assuming a subway scenario, the interleaved mapping scheme showed no performance degradation compared to the continuous mapping scheme and the implementation complexity of the uplink channel estimator was reduced due to the interleaved mapping scheme.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.8C
• /
• pp.667-679
• /
• 2010

The use of femtocells in buildings and homes has been widely studied as a means to enlarge the cell coverage and increase the network capacity of mobile communication systems. Femtocells for Mobile WiMAX (M-WiMAX) using time division duplexing (TDD) requires frame synchronization with neighboring base stations to avoid interference between uplink and downlink signals. In this paper, we propose a new frame synchronization method for femtocell using IEEE 802.11 based wireless backhaul, which transfers the time information of mobile network to femtocells via the beacon signal provided by IEEE 802.11. Also, in order to reduce timing error of the proposed method, we modify the collision avoidance scheme in the transmitter of IEEE 802.11 and apply a timing estimation technique designed in the sense of least squares to the receiver of IEEE 802.11. Through computer simulations using the proposed scheme, we evaluate the performance of frame synchronization for femtocells and show that the recovered timing information satisfies the timing specification defined by M-WiMAX standard.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.21 no.12
• /
• pp.2261-2269
• /
• 2017

The current LTE network system provides service by locally allocating eNodeB to the EPC(Evolved Packet Core). However, it is not suitable for inter-node communication based on the distributed network environment. In this paper, we propose an integrated system by configuring E-UTRAN and EPC as All-In-One type to enable service in each distributed node. M2M UE is mounted on a each node for wireless In-band backhaul link. The integrated node provides inter-node communication over the wireless in-band backhaul link. If a normal UE moves and an access node changes in the system all entities of LTE integrated into one, it is necessary to change the P-GW which is IP anchor. In order to support the inter-node mobility even if P-GW is changed, We defined UPFE(User Packet Forwarding Extension) scheme and implemented the handover procedure of EPC. Also, we analyze the cell range of the integrated LTE system with the addition of the node and compare the handover delay with the current system.

• ETRI Journal
• /
• v.44 no.6
• /
• pp.966-976
• /
• 2022

Optical wireless communication, or free space optics, is a promising solution for backhauls in sixth-generation mobile systems. However, the susceptibility of optical links to weather conditions has led to FSO links being furnished with radio frequency (RF) backups. These Hybrid FSO/RF systems provide enhanced link availability but lead to RF resource wastage. Cognitive radio technology, in contrast, is well known for its optimal use of RF resources and may be combined with an FSO link to create a Cognitive Hybrid FSO/RF system. This work uses such a system to analyze a configuration for a mobile backhaul in sixth-generation mobile systems. This configuration can seamlessly coexist with established large scale RF cellular networks. The performance of this configuration is analyzed with respect to outage probability and average bit error by considering the impact of optical channel turbulence, misalignment loss, RF interference, and noise. Mathematical closed-form expressions are verified by simulations.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.12B
• /
• pp.1647-1658
• /
• 2011

This paper suggests the methods to improve the wireless backhaul link of the Relay FDD mode that 3GPP LTE-Advanced supports. New RRC message and Relay startsup procedure are introduced to apply Carrier Aggregation in the Relay wireless backhaul. Also, we design new reference signal that makes Type 1 Relay operated in full-duplexing, expecting to maximize the radio resource utilization. And, we propose the efficient configuration for the periodic uplink control information under the backhaul subframe allocation method in LTE-Advanced Relay. Hereafter, the standard activities in the 3GPP RAN is supposed to focus on the improvement of the LTE-Advanced features. Therefore, the suggestions in this paper are expected to be actively discussed in the LTE-Advanced future releases.

• ETRI Journal
• /
• v.45 no.5
• /
• pp.781-794
• /
• 2023

Uncrewed aerial vehicles (UAVs) have become a vital element in nonterrestrial networks, especially with respect to 5G communication systems and beyond. The use of UAVs in support of 4G/5G base station (uncrewed aerial vehicle base station [UAV-BS]) has proven to be a practical solution for extending cellular network services to areas where conventional infrastructures are unavailable. In this study, we introduce a UAV-BS system that utilizes a high-capacity wireless backhaul operating in millimeter-wave frequency bands. This system can achieve a maximum throughput of 1.3 Gbps while delivering data at a rate of 300 Mbps, even at distances of 10 km. We also present the details of our testbed implementation alongside the performance results obtained from field tests.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.14 no.5
• /
• pp.44-51
• /
• 2015

The deployment of high capacity backhaul is required due to explosive growth in mobile data services. For rapid backhaul deployment, point to point microwave is a much easier and cheaper technology. The space diversity scheme is used in point to point microwave links. The purpose of space diversity is to overcome fading by combining signals from two separate receiver antennas. For signal combining algorithm, maximum power and minimum distortion methods were used and these algorithms were reported not to be good enough for robustness in selective fading. In this paper, a more practically efficient signal combining scheme from the main and diversity branch is proposed and evaluated in selective fading channel. The proposed algorithm has shown significant performance improvement in terms of signal spectrum.

• Electronics and Telecommunications Trends
• /
• v.33 no.5
• /
• pp.64-75
• /
• 2018

People usually check their social media, e-mail, and online news on their smartphones using their carrier network. During this process, much of the data traffic is offloaded to ubiquitous Wi-Fi networks. Such offloading will continue to increase rapidly because of flourishing public Wi-Fi networks located around the world. In this technical report, we first investigate domestic public Wi-Fi projects, and followed by foreign projects. In addition, we investigate the Wi-Fi technology evolution that has been standardized in IEEE 802. More and more people are tending to use Wi-Fi, not only at home or work, but also on public transport such as buses and trains. Hence, it is important to come up with ideas that can realize Wi-Fi onboard. The key technologies needed here are related to a mobile wireless backhaul between trains and trackside radio equipment, or between buses and roadside units. Thus, we also investigate the mobile wireless backhaul technologies and their trends.