Browsing by Author "Shen, Li-Hsiang"

Now showing 1 - 7 of 7

A Multi-Objective Model Checking for Transmission Policy Optimization in Hybrid Powered Small Cell Networks
(2020-01-01)
Yu, Chih-Min
;
Tala't, Mohammad
;
Shen, Li-Hsiang
;
Kai-Ten Feng
;
電機工程學系
In the fifth generation (5G) communication system, maximizing energy utilization is one of the key challenges especially with limited green energy sources. In particular, it is important to determine the optimal transmission policy for the hybrid model with grid and green energy in small cell networks. The optimal transmission policy should minimize both grid power consumption and wastage of green harvested energy at the same time; while satisfying the quality of service (QoS) requirements such as minimum packet drop probability. In contrast to existing policies with a single objective for the hybrid powered small cell networks, the proposed transmission policy adopts a multi-objective model checking for Markov decision process (MOMC-MDP) with a linear temporal logic (LTL) scheme. The MOMC-MDP firstly determines all feasible decisions for packet transmissions in every time slot, and then chooses one of the best feasible decisions to obtain the optimal transmission policy. Three dimension Markov decision process (3D-MDP) that includes packet buffer, battery capacity, and channel state, are used with the age of information (AoI) of the packet arrivals to improve the overall performance of the proposed MOMC-MDP scheme. Numerical results validate that the proposed MOMC-MDP with AoI can provide higher green energy utilization compared to the conventional MDP-based schemes.
Design and Analysis of Multi-User Association and Beam Training Schemes for Millimeter Wave Based WLANs
(2020-07-01)
Shen, Li-Hsiang
;
Chen, Yi-Ching
;
Feng, Kai-Ten
;
電機工程學系
;
Department of Electrical and Computer Engineering
Millimeter wave (mmWave) in the unlicensed 60 GHz band provides extremely large spectrum utilization, which is a promising technique due to the rapid growth of wireless communication services. With wireless devices explosively increasing, the limited number of association and beamforming training (A-BFT) opportunities in conventional protocol leads to high packet collisions. In this paper, we design a novel non-slotted A-BFT frame structure for multi-users in order to alleviate packet collisions providing flexible training slots. To further reduce collision occurrence, we propose two association mechanisms including the time-based distributed coordination function (TDCF) and time-based beam collision avoidance (TBCA) schemes. The theoretical closed-forms of both TDCF and TBCA methods are also derived, and proved to outperform the random association. Furthermore, the adaptive beam search (ABS) and dynamic A-BFT adjustment (DAA) schemes are proposed to consider historical beam training information by adjusting the number of training beams and A-BFT length, respectively. Simulations are conducted to show that our proposed ABS, DAA, and TDCF/TBCA mechanisms outperform existing methods; whereas higher spectrum efficiency can be achieved by proposed non-slotted frame structure compared to conventional slotted structure.
Enhanced Multi-User Beamforming Protocol for Millimeter Wave Wireless Local Area Networks
(2018-01-01)
Chen, Yi-Ching
;
Shen, Li-Hsiang
;
Feng, Kai-Ten
;
電機工程學系
;
Department of Electrical and Computer Engineering
MmWave in the unlicensed 60GHz band is highly discussed due to the rapid growth of wireless communication services. The utilization of microwave spectrum below 10 GHz is almost reaching its limit. Beamforming (BF) has become an essential technique to compensate the high path loss phenomenon of mmWave. IEEE 802.11ad and 802.11ay standardization task group institute directional multi-gigabit (DMG) wireless local area networks (WLANs) supporting mmWave techniques. With wireless devices explosively increasing, the limited number of BF slots in conventional DMG protocols leads to high packet collision probability, which potentially degrades the system performance. Most of the existing research does not take the multi-user BF contention problem into consideration. In this paper, we design a non-slotted association beamforming training (A-BET) frame structure for multi-users without separating A-BFT slots in order to alleviate packet collisions due to the shortage of contention and training frames. This new proposed structure allows collisions with useful information left in remaining non-collided slots or frames in order to leverage the insufficiency of BF training for multiple devices. Furthermore, in order to further reduce BF collision probability, we propose two multiuser beamforming training mechanisms, including the time-based distributed coordination function (TDCF) and time-based beam-collision avoidance (TBCA) schemes. Simulation results demonstrate that our new proposed frame structure along with proposed TDCF and TBCA mechanisms outperforms 802.11ad protocol.
Joint Beam and Subband Resource Allocation with QoS Requirement for Millimeter Wave MIMO Systems
(2017-01-01)
Shen, Li-Hsiang
;
Feng, Kai-Ten
;
電機工程學系
;
Department of Electrical and Computer Engineering
To satisfy future explosive demands of mobile traffic, millimeter wave (mmWave) technology has been widely considered in the next generation wireless networks thanks to its large spectrum and spatial resources. MmWave Hybrid beamforming (HBF) with multi-input multi-output (MIMO) system is a critical technique to support multi-beam operation and reduce the cost and complexity. In this paper, we define inter-user interference in the mainlobe and the sidelobe. With the consideration of quality of service (QoS) requirements, we design a mainlobe interference avoidance (MIA) scheduling algorithm to maximize data throughput under the existence of inter-user interferences. Our proposed scheme allocates system resources by jointly considering not only the subband resources but also the antenna beamwidth and beam direction. Simulation results demonstrate that the proposed scheme outperforms existing heuristic algorithms both in the uniform and hotspot scenarios.
Learning-based Beam Training Algorithms for IEEE 802.11ad/ay Networks
(2019-01-01)
Chang, Ting-Wei
;
Shen, Li-Hsiang
;
Feng, Kai-Ten
;
電機工程學系
;
Department of Electrical and Computer Engineering
Recently, many researches are focusing on millimeter wave (mmWave) due to its large bandwidth resources. In the next 5G generation, wireless multi-gigabit (WiGig) is developed based on IEEE 802.11ad/ay standards at unlicensed mmWave bands for providing extremely high throughput. However, mmWave has high propagation loss due to high frequency transmission properties. Beamforming (BF) technique is adopted to solve this problem, and therefore, we have to perform beam training before data transmission. In the standard, the conventional method for beam training is exhaustive beam search (EBS) which takes too much time so that the data transmission time will decrease. On the other hand, blocked environments may severely degrade WiGig beam training performance, and most of existing algorithms do not consider this issue. Recently, machine and deep learning have been widely used in the wireless communication field. We propose a learning-based beam training (LBT) to simultaneously learn about wireless environments and beam training candidates. We select simplified neural network (NN) model to achieve lower computation overhead. To further refine learning information, we propose two enhanced algorithm, expanded LBT (LBT-E) and history-aided expanded LBT(LBT-HE). LBT-E aims to tackle unexpected slight deviation and LBT-HE make use of historical information to improve beam matching accuracy with acceptable latency. In our simulation, our proposed learning-based schemes achieve much higher throughput compared to EBS and algorithms in existing literatures.
Mobility-Aware Fast Beam Training Scheme for IEEE 802.11ad/ay Wireless Systems
(2018-01-01)
Shen, Li-Hsiang
;
Chen, Yi-Ching
;
Feng, Kai-Ten
;
電機工程學系
;
Department of Electrical and Computer Engineering
Millimeter wave (mmWave) technology provides multi-Gbps services thanks to huge spectrum usage. IEEE 802.11ad/ay standardizes the next generation wireless local area networks (WLANs) for high data rate transmissions at 60 GHz band. Directional beamforming (BF) transmissions overcome the difficulty of high signal attenuation. In addition, a beam sector based scheme for BF training is taken by 802.11ad/ay to tackle sophisticated indoor environments. However, conventional exhaustive beam search (EBS) takes much time and some literatures try to design to reduce training latency. Also, most of papers do not consider about the mobility effect of moving devices, which deteriorates the beam matching outcomes. With the consideration of beam matching accuracy and mobility effects corresponding to historically observed transmitted beams, we propose the mobility-aware fast beam training (MFBT) algorithm. Simulation results show how mobility affects the system in terms of latency and throughput. There are trade-offs when operating with different beamwidth and matching accuracy requirements. Moreover, our proposed algorithm achieves lower latency and higher throughput than other existing beam training schemes.
Optimal Transmission Policy for Maximizing Green Energy Utilization in Small Cell Networks
(2019-01-01)
Tala't, Mohammad
;
Shen, Li-Hsiang
;
Yu, Chih-Min
;
Feng, Kai-Ten
;
電機工程學系
Transmission policy of the hybrid energy model allows maximizing energy utilization of small cells in the wireless system. One of the key challenges in maximization of energy utilization is to minimize the grid power and energy wastage of green harvested energy (GHE) sources simultaneously. In this paper, unlike existing transmission policy solution which focuses only on one highlighted objective, we proposed multi-objective model checking for Markov decision process (MOMC-MDP) with linear temporal logic (LTL) to find the best feasible solution for packet transmissions in each time slot. Based on the MOMC-MDP for different battery status, the optimal transmission policy of small cells is obtained in order to deliver the highest harvest energy sources and guarantee the quality of service (QoS) demands. Numerical results show that the MOMC-MDP scheme can ensure to efficiently use the limited energy of battery while maximizing green energy utilization in real-time transmission.