Araştırma Çıktıları / Scopus
https://hdl.handle.net/20.500.12469/1248
20211022T02:40:01Z

Flexible LED Index Modulation for MIMO Optical Wireless Communications
https://hdl.handle.net/20.500.12469/4091
Flexible LED Index Modulation for MIMO Optical Wireless Communications
Yeşilkaya, Anıl; Purwita, Ardimas Andi; Panayırcı, Erdal; Poor, H. Vincent; Haas, Harald
The limited bandwidth of optical wireless communication (OWC) frontend devices motivates the use of multipleinput multipleoutput (MIMO) techniques to enhance data rates. It is known that very high multiplexing gains can be achieved by spatial multiplexing (SMX) at the cost of prohibitive detection complexity. Alternatively, in spatial modulation (SM), a single light emitting diode (LED) is activated per time instance where information is carried by both the signal and the LED index. Since only one LED is active, both the transmitter (TX) and receiver (RX) complexity reduce significantly while retaining the information transmission in the spatial domain. However, this simplified TX utilization approach leads SM to suffer from significant spectral efficiency losses compared to SMX. In this paper, we propose a technique that benefits from the advantages of both systems. Accordingly, the proposed flexible LED index modulation (FLIM) technique harnesses the inactive state of the LEDs as a transmit symbol. Therefore, the number of active LEDs changes in each transmission, unlike conventional techniques. Moreover, the system complexity is reduced by employing a linear minimum mean squared error (MMSE) equalizer and an angle perturbed receiver. Numerical results show that FLIM outperforms the reference systems by at least 6 dB in the low and medium/high spectral efficiency regions.
20200101T00:00:00Z

Scheduling and Relay Selection for FullDuplex Wireless Powered Cooperative Communication Networks
https://hdl.handle.net/20.500.12469/4090
Scheduling and Relay Selection for FullDuplex Wireless Powered Cooperative Communication Networks
Iqbal, Muhammad Shahid; Syed, Kazmi Abbas Adil; Coleri, Sinem; Sadi, Yalçın
In this manuscript, we consider a fullduplex wireless powered cooperative communication system where the users communicate with a hybrid access point through relays. We formulate an optimization problem with the objective to minimize the total transmission time through user scheduling and relay selection while considering the traffic demand, energy causality and initial battery levels of the users. The formulated optimization problem is a mixed integer nonlinear programming problem, hence difficult to solve for the global optimal solution. As a solution strategy, we decompose the problem into sub problems: time allocation, scheduling and relay selection. In the time allocation problem; the schedule and relays are assumed to be preknown, we derive the optimal solution by using the optimality analysis. For the scheduling problem; we assume that users know their relays, we determine the optimal schedule. For the relay selection problem; users transmit their information in a predetermined order, we determine the optimal relays for each user. For the overall scheduling and relay selection problem, we propose a heuristic algorithm which iteratively determines the scheduling and relay selection in polynomial time by using the optimal solutions of the individual relay selection and scheduling problems. Through simulations, we demonstrate that the scheduling length can be significantly reduced through proper scheduling and relay selection. The proposed algorithm performs very close to the optimal solution for different maximum user transmit power, network densities, initial battery levels and hybrid access point power levels. © 2020 IEEE.
20200101T00:00:00Z

EnergyEfficient Resources Allocation with MillimeterWave Massive MIMO in Ultra Dense HetNets by SWIPT and CoMP
https://hdl.handle.net/20.500.12469/4072
EnergyEfficient Resources Allocation with MillimeterWave Massive MIMO in Ultra Dense HetNets by SWIPT and CoMP
Yonghong Dai, Bin Li,; Dong, Zhicheng; Panayirci, Erdal; Jiang, Huilin; Jiang, Hao
Ultradense HetNets (UDN)based MillimeterWave (mmWave) massive MIMO is considered a promising technology for 5th generation (5G) wireless communications systems since it can offer massively available bandwidth and improve energy efficiency (EE) substantially. However, in UDN, the power consumption of the system increases sharply with the increase of network density. In this paper, we investigate the optimization of the EE in the mmWave massive MIMO systems with UDN. To develop the functions of massive MIMO, we first propose a system model where the massive MIMO harvests electromagnetic energy from the environment employing simultaneous wireless information and power transfer (SWIPT) technology, implemented at the base station (BS). Then, the EE optimization problem is formulated for 5G mmWave massive MIMO systems within the UDN. Considering the nonconcave feature of the objective function, an iterative EE algorithm is developed, based on Dinkelbach method. To utilize the role of coordinated multipoint transmission and reception (CoMP) for improving the EE, a coordinated user(UE)BS association algorithmbased CoMP with maximum energy efficiency (MaxEE) is proposed. The simulation results demonstrate that the proposed algorithm has a substantially faster convergence rate and is very effective, compared with existing methods.
20210101T00:00:00Z

On list kcoloring convex bipartite graphs
https://hdl.handle.net/20.500.12469/4071
On list kcoloring convex bipartite graphs
Diaz, Josep; Diner, Öznur Yaşar; Serna, Maria; Oriol, Serra
List kColoring (LikCol) is the decision problem asking if a given graph admits a proper coloring compatible with a given list assignment to its vertices with colors in {1, 2, …, k}. The problem is known to be NPhard even for k = 3 within the class of 3regular planar bipartite graphs and for k = 4 within the class of chordal bipartite graphs. In 2015 Huang, Johnson and Paulusma asked for the complexity of Li 3Col in the class of chordal bipartite graphs. In this paper, we give a partial answer to this question by showing that LikCol is polynomial in the class of convex bipartite graphs. We show first that biconvex bipartite graphs admit a multichain ordering, extending the classes of graphs where a polynomial algorithm of Enright et al. (SIAM J Discrete Math 28(4):1675–1685, 2014) can be applied to the problem. We provide a dynamic programming algorithm to solve the LikCol in the class of convex bipartite graphs. Finally, we show how our algorithm can be modified to solve the more general LiHCol problem on convex bipartite graphs.
20210101T00:00:00Z