• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.14 no.10
• /
• pp.4214-4230
• /
• 2020

This paper introduces a pilot allocation scheme for massive MIMO systems based on deep convolutional neural network (CNN) learning. This work is an extension of a prior work on the basic deep learning framework of the pilot assignment problem, the application of which to a high-user density nature is difficult owing to the factorial increase in both input features and output layers. To solve this problem, by adopting the advantages of CNN in learning image data, we design input features that represent users' locations in all the cells as image data with a two-dimensional fixed-size matrix. Furthermore, using a sorting mechanism for applying proper rule, we construct output layers with a linear space complexity according to the number of users. We also develop a theoretical framework for the network capacity model of the massive MIMO systems and apply it to the training process. Finally, we implement the proposed deep CNN-based pilot assignment scheme using a commercial vanilla CNN, which takes into account shift invariant characteristics. Through extensive simulation, we demonstrate that the proposed work realizes about a 98% theoretical upper-bound performance and an elapsed time of 0.842 ms with low complexity in the case of a high-user-density condition.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.9 no.8
• /
• pp.2797-2820
• /
• 2015

In order to accommodate huge number of antennas in a limited antenna size, a large scale antenna array is expected to have a three dimensional (3D) array structure. By using the Active Antenna Systems (AAS), the weights of the antenna elements arranged vertically could be configured adaptively. Then, a degree of freedom (DOF) in the vertical plane is provided for system design. So the three-dimension MIMO (3D MIMO) could be realized to solve the actual implementation problem of the massive MIMO. However, in 3D massive MIMO systems, the pilot contamination problem studied in 2D massive MIMO systems and the inter-cell interference as well as inter-vertical sector interference in 3D MIMO systems with vertical sectorization exist simultaneously, when the number of antenna is not large enough. This paper investigates the interference management towards the above challenges in 3D massive MIMO systems. Here, vertical sectorization based on vertical beamforming is included in the concerned systems. Firstly, a cooperative joint vertical beams adjustment and pilot assignment scheme is developed to improve the channel estimation precision of the uplink with pilots being reused across the vertical sectors. Secondly, a downlink interference coordination scheme by jointly controlling weight vectors and power of vertical beams is proposed, where the estimated channel state information is used in the optimization modelling, and the performance loss induced by pilot contamination could be compensated in some degree. Simulation results show that the proposed joint optimization algorithm with controllable vertical beams' weight vectors outperforms the method combining downtilts adjustment and power allocation.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.2 no.4
• /
• pp.209-221
• /
• 2008

In this paper, we propose a subcarrier allocation method and a composite linear minimum mean square error (LMMSE) channel estimator to increase spectrum efficiency in orthogonal frequency division multiplexing (OFDM) transmit diversity. The pilot symbols for OFDM transmit (Alamouti) diversity are exclusively allocated in two OFDM symbols in different antennas, which causes serious degradation of spectrum efficiency. To reduce the number of pilot symbols, our subcarrier allocation method uses repetition-coded data symbols, and the proposed channel estimator maintains good bit error rate (BER) performance.

• ETRI Journal
• /
• v.44 no.6
• /
• pp.885-902
• /
• 2022

The mmWave cell-free massive MIMO (CFmMIMO), combining the advantages of wide bandwidth in the mmWave frequency band and the high- and uniform-spectral efficiency of CFmMIMO, has recently emerged as one of the enabling technologies for 6G. In this paper, we propose a novel framework for energy-efficient mmWave CFmMIMO systems that uses low-resolution digital-analog converters (DACs) and phase shifters (PSs) to introduce lowcomplexity hybrid precoding. Additionally, we propose a heuristic pilot allocation scheme that makes the best effort to slash some interference from copilot users. The simulation results show that the proposed hybrid precoding and pilot allocation scheme outperforms the existing schemes. Furthermore, we reveal the relationship between the energy and spectral efficiencies for the proposed mmWave CFmMIMO system by modeling the whole network power consumption and observe that the introduction of low-resolution DACs and PSs is effective in increasing the energy efficiency by compromising the spectral efficiency and the network power consumption.

• Journal of the Ergonomics Society of Korea
• /
• v.23 no.1
• /
• pp.49-63
• /
• 2004

In this study. differences in attention allocation patterns between expert and novIce pilots were investigated by a verbal protocol when pilots were engaged in a task during the instrument flight. Ten pilots including experts and novices were participated to conduct a pre-determined task(a fix-to-fix) on F-5E Cockpit Procedure Trainer Simulator. Experts show better performance as expected with more stable variations in speed. altitude. and attitude. In attention allocation patterns. novices allocated about 83% of attentional resources on the primary instruments (airspeed indicator. altitude indicator. and attitude) relating to the task of the basic flight while experts spent 57%. This difference in the availability of attentional resources allowed expert pilots to accomplish the task better than novices. In other words. training a pilot should consider a program for building up wider instrument scanning patterns to become an expert in a shorter time.

• International Journal of Contents
• /
• v.14 no.2
• /
• pp.1-6
• /
• 2018

In a wireless mobile communication system, a pilot signal has been considered to be a necessary signal for estimating a changing channel between a base station and a terminal. All mobile communication systems developed so far have a specification for transmitting pilot signals. However, although the pilot signal transmission is easy to estimate the channel,(Ed: unclear wording: it is easy to use the pilot signal transmission to estimate the channel?) it should be minimized because it uses radio resources for data transmission. In this paper, we propose a pilotless channel estimation scheme (PCE) by introducing the clustering method of unsupervised learning used in our deep learning into channel estimation.(Ed: highlight- unclear) The PCE estimates the channel using only the data symbols without using the pilot signal at all. Also, to apply PCE to a real system, we evaluated the performance of PCE based on the resource block (RB), which is a resource allocation unit used in LTE. According to the results of this study, the PCE always provides a better mean square error (MSE) performance than the least square estimator using pilots, although it does not use the pilot signal at all. The MSE performance of the PCE is affected by the number of data symbols used and the frequency selectivity of the channel. In this paper, we provide simulation results considering various effects(Ed: unclear, clarify).

• Journal of Korean Society of Industrial and Systems Engineering
• /
• v.43 no.4
• /
• pp.150-160
• /
• 2020

In this paper, we introduce a pilot's scheduling model which is able to maintain and balance their capabilities for each relevant skill level in military helicopter squadron. Flight scheduler has to consider many factors related pilot's flight information and spends a lot of times and efforts for flight planning without scientific process depending on his/her own capability and experience. This model reflected overall characteristics that include pilot's progression by basis monthly and cumulative flight hours, operational recent flight data and quickly find out a pinpoint areas of concern with respect to their mission subjects etc. There also include essential several constraints, such as personnel qualifications, and Army helicopter training policy's constraints such as regulations and guidelines. We presented binary Integer Programming (IP) mathematical formulation for optimization and demonstrated its effectiveness by comparisons of real schedule versus model's solution to several cases experimental scenarios and greedy random simulation model. The model made the schedule in less than 30 minutes, including the data preprocessing process, and the results of the allocation were more equal than the actual one. This makes it possible to reduce the workload of the scheduler and effectively manages the pilot's skills. We expect to set up and improve better flight planning and combat readiness in Korea Army aviation.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.3A
• /
• pp.291-303
• /
• 2006

In this paper, we analyze functional requirements of the IEEE 802.22 WRAN, and propose a downlink 프레임 structure satisfying the requirements. The proposed downlink 프레임 structure maximizes e transmission efficiency by adopting the cognative radio to assign the sub-channel by reflecting the channel environment of WRAN. We also calculate the signalling overhead for both downlink and uplink, and analyze the performances of time synchronization, frequency synchronization and cell identification based on the 프리앰블 in downlink and suggest the channel estimation method tough 프리앰블 or pilot. As a final result, e stationary beamforming (SBF) algorithm with dynamic channel allocation(DCA) is proposed. The proposed OFDMA downlink 프레임 structure with channel adaptive sub-channel allocation for cognitive radio applications is verified to meet the requirements of IEEE 802.22 WRAN, by computer simulations.

• Korean Journal of Agricultural Science
• /
• v.22 no.2
• /
• pp.209-222
• /
• 1995

To mitigate the development gap between urban and rural area, the government has implemented project planning as the Rural Integrated Development in each Gun level since 1986. On account of shortage of the development fund, the government had changed the Gun level development into Myeon level development so called the Rural Central Settlement Zone Development. The government had started nine pilot projects throughout Korea from 1990. This study is aimed at identifing problems that found in the course of implementation of the projects and recommending the new direction of the successful implementation of the projects in the future. The problems and directions found in the cource of project implementation were as follows: 1. Project implementation by investment priority considering economic and financial rate of return should be made. 2. Objective project planning should be made. 3. Equal allocation of the limited investment fund by group interest and egoism should be prohibited. 4. Enforcement of special man power should be taken into account. 5. Unification of the diversified existing terms and conditions of loans for house construction and improvement. 6. Road development oriented budget allocation should be improved. 7. Sufficient development fund should be procured considering the present rate of sufficiency of the project cost as 36%. 8. Sufficient supply of the credit loans for improvement of living environment of the farmers should be realized. 9. Rational implementation planning in connection with farm household income source development should be made.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.9C
• /
• pp.661-668
• /
• 2008

In this paper, a channel estimation technique based on pilot tones is proposed for cooperative SFBC-OFDM systems with a STO(Symbol Timing Offset). In a cooperative SFBC-OFDM system, the STO between RS(Relay Station) and MS(Mobile Station) varies depending on the location of MS. Since the STO causes distortion in the form of phase rotation, a channel estimation technique based on linear interpolation with respect to phase and amplitude is proposed for the case of orthogonal pilot allocation. Also, a channel estimation technique is proposed by solving nonlinear equation for the case of pilot structure with orthogonal code. It is shown by computer simulation that the performance of channel estimation can be significantly improved when the proposed techniques are applied to cooperative SFBC-OFDM systems with STO.