Gia Khanh Tran

Millimeter-Wave Evolution for 5G Cellular Networks

Triggered by the explosion of mobile traffic, 5G (5th Generation) cellular network requires evolution to increase the system rate 1000 times higher than the current systems in 10 years. Motivated by this common problem, there are several studies to integrate mm-wave access into current cellular networks as multi-band heterogeneous networks to exploit the ultra-wideband aspect of the mm-wave band. The authors of this paper have proposed comprehensive architecture of cellular networks with mm-wave access, where mm-wave small cell basestations and a conventional macro basestation are connected to Centralized-RAN (C-RAN) to effectively operate the system by enabling power efficient seamless handover as well as centralized resource control including dynamic cell structuring to match the limited coverage of mm-wave access with high traffic user locations via user-plane/control-plane splitting. In this paper, to prove the effectiveness of the proposed 5G cellular networks with mm-wave access, system level simulation is conducted by introducing an expected future traffic model, a measurement based mm-wave propagation model, and a centralized cell association algorithm by exploiting the C-RAN architecture. The numerical results show the effectiveness of the proposed network to realize 1000 times higher system rate than the current network in 10 years which is not achieved by the small cells using commonly considered 3.5 GHz band. Furthermore, the paper also gives latest status of mm-wave devices and regulations to show the feasibility of using mm-wave in the 5G systems.

Cloud cooperated heterogeneous cellular networks

This paper introduces a concept of cloud cooperated heterogeneous cellular network (C-HetNet) where small power pico base stations (BSs) overlaid on a macrocell are connected to cloud radio access network (C-RAN) to operate cooperatively with the macro BS. Since the macro BS assists operation of the pico BSs, it is easy to deploy multi-band HetNet where e.g. macro BS is operated at 2GHz band and pico BSs at 3GHz or 60GHz band to expand operation bandwidth. Moreover, cell structure of pico BSs are controlled dynamically to track hotspot users via beam steering and cooperative transmission among pico BSs. In this paper, several numerical simulations show effectiveness of the proposed architecture, where 1,000 times system rate than that of current single band cellular network is achieved by using the proposed architecture.

Wireless Grid: Enabling Ubiquitous Sensor Networks with Wireless Energy Supply

Sensor node life-time limitation in wireless sensor networks has long become an issue, preventing it to become a reliable ubiquitous network. In this paper, a new concept called wireless grid, which includes a fusion of wireless sensor network and wireless power transmission is introduced. By doing this, battery life-time problem can be avoided, hence, providing high network reliability. Wireless power transmission scheme adjusted to the sensor network operating environment is proposed to satisfy power requirement at the sensor nodes. Simulation results show that by using the proposed schemes, two power transmission nodes can supply the energy required for sensor nodes operating in a square room of 25m2 with 99% reliability.

Dynamic cell activation and user association for green 5G heterogeneous cellular networks

The mobile traffic explosion predicted to be increased by 1000 times in the next 10 years has become a remarkable issue due to the proliferation of smart devices such as smart phones or tablets. Energy consumption of information processing is also becoming an economic issue for operators. It is a critical task to design the next generation cellular networks (5G) to be both spectral/energy efficient. This paper considers a future C-RAN based cloud cooperated HetNet which enables global resource optimization among smallcells. The architecture allows optimal user association for data offloading as well as dynamic ON/OFF of smallcell BSs in adaptation to daily data traffic. A joint optimization on both user association and dynamic ON/OFF scheme of BSs to maximizing the system rate over consumed energy of the network investigated in the paper reveals that without sacrificing the systems power resource, our proposed approach can effectively deactivate unnecessary BSs and attain the target 1000× system rate gain in the case of mm-wave smallcells.

Shared Remote Radio Head architecture to realize semi-dynamic clustering in CoMP cellular networks

In conventional cellular systems, transmission rate degrades at cell-edge because of inter-cell interference and pathloss. This problem is called “cell-edge problem”. To solve this problem, Coordinated Multi-Point (CoMP) technique has been proposed recently. CoMP can convert inter-cell interference signals from neighbor base stations (BSs) to desired signals. However, CoMP requires accurate synchronization among cooperative BSs as well as Channel State Information (CSI) between target user and all cooperative BSs. For practical realization of CoMP, new BS architecture in which a BS unit is connected to multiple Remote Radio Heads (RRHs) located apart through optical fiber has been proposed. Even using this architecture, however, CoMP can only be realized within the predefined connected RRHs (CoMP cluster). Therefore, cluster-edge users cannot experience throughput improvement by means of CoMP. This paper proposes a novel BS architecture called shared RRH network, in which each RRH is additionally connected to multiple BS units. As flexible clustering is made possible by this architecture, semi-dynamic clustering using geometrically overlapped cluster patterns allocated with orthogonal resources can be achieved which alleviates the cluster-edge problem. Simulation with parameters based on the 3GPP is setup for performance evaluation of the proposed system. Numerical results show that semi-dynamic CoMP using shared RRHs can significantly improve the system performance both at cell-inner and cell-edge compared with the conventional RRH systems, which confirms the effectiveness of the proposed network.

Cell association method for multiband heterogeneous networks

In traditional heterogeneous cellular networks (Het-Net), base stations (BS) basically associate users based on received signal power. However, in the case of multiband HetNet, in which macro BSs and smallcell BSs use different frequency bands, this conventional cell association method is not effective because there is no interference between macro BSs and smallcell BSs. Additionally, there are huge differences in coverage and available bandwidth. These differences cause inefficient association which causes the imbalance between achievable rate and traffic demand. In order to overcome this problem, we propose a novel cell association method based on the combinatorial optimization. The proposed method considers achievable rates, traffic demands and the number of users belonging to each BSs simultaneously. Numerical simulation results show that the proposed association method achieves system rate gain twice as high as the conventional one.

Optimization of picocell locations and its parameters in heterogeneous networks with hotspots

This work analyzes the optimal pico base station (BS) deployment in heterogeneous cellular networks (HetNet) with hotspots. Most of conventional works for HetNet focused on interference coordination and effective cell association methods, however, the problem of pico BS deployment (cell planning) for HetNet with hotspots has not been analyzed so much. In this paper, we extend the previously proposed optimization problem in terms of network parameters (spectrum splitting ratio and SINR bias value) to the optimal pico BS locations to maximize the system rate. Furthermore, the average user and outage user rates are evaluated numerically to show the effectiveness of the proposed optimization method. Numerical results show that the optimized pico BS locations can improve both the average and outage user rates in HetNet with hotspots.

Performance Analysis of MIMO-OFDM Systems using Indoor Wideband MIMO Channel Measurement Data

In this paper, throughput performance of MIMO-OFDM system in real residential home environment was evaluated by using wideband MIMO channel measurement data. Computer simulations were carried out to compare the performance of MIMO-OFDM systems with various detection methods, i.e. MMSE, VBLAST, QRM-MLD and SVD-MIMO, in addition to that of the SISO-OFDM system. The results showed that the SVD-MIMO transmission can provide the highest average and outage throughput under the assumption of perfect CSI feedback. On the other hand, QRM-MLD yielded the best performance among the systems without CSI available at the transmitter. It was also found that the outage throughput performance of MMSE and VBLAST degrades severely due to the existence of spatial correlation in the real home environment

Localization of illegal radios utilizing cross-correlation of channel impulse response with interpolation in urban scenarios

Fingerprint-based localization is expected to be superior compared to other conventional range-based localization techniques especially in dense urban scenarios which are generally non line-of-sight (NLOS). However, when we consider localizing illegal radios whose parameters such as bandwidth and center frequency are unknown, there is a high possibility that the initial parameters used to create the fingerprint database in the training phase do not match the illegal radios parameters. In this paper, a novel fingerprint-based localization technique which utilizes interpolated channel impulse response (CIR) cross-correlations as fingerprints is proposed, which does not require a priori information of the illegal radio. Results show that the proposed technique is very promising in localizing illegal radios in urban NLOS environments.

Experiment on battery-less sensor activation via multi-point wireless energy transmission

This paper presents an indoor experiment to verify the battery-less sensor activation via multi-point wireless energy transmission with carrier shift diversity which realizes seamless coverage extension of the sensor activation. The multi-point scheme is employed to overcome path-loss attenuation. The carrier shift diversity has been developed to achieve uniform coverage of power transmission by combating standing-wave problem caused by multi-point transmitters as well as multipath waves, while its effectiveness on activation of battery-less sensors has never been studied in real environments. In this paper, we develop prototype hardware of battery-less sensor and conduct an indoor experiment with the developed sensor node. The experimental results show that the coverage of single-point and simple multi-point wireless energy transmission are limited at 44% and 70% respectively, while that of the proposed multi-point wireless energy transmission with carrier shift diversity achieves 100% to activate the developed sensor node which consumes -4 dBm for a transmission period of 1s.