• Journal of the Korea Institute of Military Science and Technology
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• v.12 no.2
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• pp.182-190
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• 2009

GPS receivers can be disrupted by intentional or unintentional jamming, then it is unable to receive GPS signals and it is impossible to get the correct navigation results. Anti-jamming schemes using array antennas are being studied well due to high performance of those, and the efforts to apply them to GPS receiver are also being done. A GPS receiver structure for a multiple beam-forming scheme among those schemes has been proposed in this paper, and the performance is also compared with that using a general GPS receiver structure. For a general GPS receiver structure, each satellite signal which is formed by a beam-forming scheme is summed to be processed in a part of digital signal processing. For a proposed GPS receiver structure, however, each satellite signal is respectively processed by a designated channel in a part of digital signal processing. Finally, it is confirmed that the proposed GPS receiver structure is superior to a general GPS receiver structure in a point of the carrier to noise power ratio and the navigation accuracy using a software platform.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10A
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• pp.974-983
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• 2007

In this paper, a low complexity subcarrier allocation scheme is proposed for multiuser MIMO-OFDM systems with zero-forcing beamformer (ZFBF) so that the total transmit power can be minimized satisfying given target data rate. Since the optimal method requires very high computational complexity, we propose a low complextiy suboptimal method. Using the fact that the effective channel gain is proportional to the orthogonallity of channels of multiplexed users, a user set with the highest orthogonality of channel among users is assigned to each subcarrier in order to minimize required transmit power. The numerical results show that the proposed suboptimal method can reduce computational complexity with little performance loss.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.9
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• pp.1090-1097
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• 2007

The multibeam surveillance radar is a state-of art of 3D radar technology. It applies the stacked beam-on-received realized by a digital beamformer. In this paper, a design concept of beamformer and a method of target altitude extraction for multibeam surveillance radar in the normal environmental condition considering no multipath situations are proposed and investigated. The extraction algorithm based on antenna sine space coordinated system in a FFT digital beamformer is described. The proposed algorithm is simulated by 1 look-up table data and confirmed to have consistent results in accordance with a variety of target altitudes and a full radar frequency range.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.5
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• pp.2124-2141
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• 2018

Recent studies have revealed the efficacy of incorporating delayed channel state information at transmit side (CSIT) in transmission scheme design. This paper focuses on transmit precoder design to maximize the ergodic sum-rate in a two-user Multiple-Input Single-Output (MISO) system with delayed and statistical CSIT. A new transmit strategy which precodes signals in all transmit slots is proposed in this paper, denoted as all time-slots precoding Alternative MAT (AAMAT). There is a common procedure in conventional delayed-CSIT based schemes, which is retransmitting the overheard interferences. Since the retransmitting signal is intended to both users, all previous schemes tend to use only one antenna. We however figure out an improvement in spectral efficiency could be realized if all antennas can be utilized. In this paper, we detail the design of the procoder which enabling all antennas and also we compute a lower bound of the ergodic sum-rate in an ideal condition. In addition, simulation results demonstrate the superiority of our proposed scheme.

• The Journal of the Acoustical Society of Korea
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• v.22 no.1
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• pp.1-6
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• 2003

This paper analyses the performance of either the minimum variance distortionless response (MVDR) or the recursive least square (RLS) beamformer structured on the systolic array. Provided that the snapshot vector including the desired user's signal and the interferences with the noise is received at the array antenna. In order to improve the quality of received signal, MVDR or RLS algorithm can be utilized to update the beamformer weights recursively. Furthermore to increase the channel capacity, by the usage of the above schemes, the effect of the spatial filtering can be obtained which constructively combining multipath components corresponding to the desired user whereas the multiple access interferences (MAI) is nulled out on spatial domain. This paper introduces the MVDR and RLS beamformer structured on systolic array conducting the spatial filtering, and its performance under the multipath fading channel in the presence of multiple access interferences will be analyzed. To show the superior spatial filtering performances of the proposed scheme employing the systolic way structured beamformer, the computer simulations are carried out. And the validity of practical deployment of the proposed scheme will be confirmed throughout showing the BER behaviors and the beampatterns.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.12
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• pp.1076-1084
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• 2012

In the CS/CB(Coordinated Scheduling/Beamforming) scheme, the cell edge user throughput is increased by selecting MIMO (Multiple Input Multiple Output) precoders which can minimize the interferences from adjacent base stations (BSs). However, in current LTE(Long Term Evolution) systems, the serving cell is selected in the initialization stage by using the synchronization signals and cell specific reference signals transmitted by adjacent BSs with a single antenna. The selected BS in the initialization stage may not be the best one since the MIMO precoding gain has not been considered in the cell selection stage. In this paper, a new cell selection technique is proposed for LTE systems with MIMO precoder by taking into account the effect of the precoder in the initialization stage. The proposed technique enables a user equipment (UE) in the cell boundary to select the serving BS by using the information (channel rank, effective channel capacity, and effective SINR(Signal to Interference plus Noise Ratio)) acquired from cell specific reference signals of candidate BSs. It is verified by computer simulation that the proposed technique can increase the channel capacity significantly in the multi-cell environments, compared with the conventional CS/CB scheme.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.2
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• pp.187-195
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• 2012

In this paper, we propose the optimization of subarray configurations for linear array to minimize the side lobe level (SLL) in sum beam pattern based on the genetic algorithm. The operations of genetic algorithm are modified to be applied to subarray configurations. Using the proposed method, we construct subarray structure with 16 irregular subarray elements from 40 linear array elements to minimize the SLL in sum beam pattern in case of applying the adaptive beamforming(ABF) to suppress the jamming power, whose the SLL is 10 dB lower than that of regular subarray configuration.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.3
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• pp.280-285
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• 2015

We consider a linear transceiver design method for multi-user multiple-input multiple-output (MIMO) downlink channels where a base station (BS) equipped with a finitely large number of antennas. Although a matched-filter precoder is a capacity-achieving method in massive MIMO downlink systems, it cannot guarantee to achieve the multi-user MIMO capacity in a finitely large number of antennas due to inter-user interferences. In this paper, we propose a two-stage precoder design method that maximizes the sum-rate of cell-edge users when the BS equipped with a finitely large number of antennas. At the first stage, a matched-filter precoder is adopted to exploit both beamforming gain and the reduction of the dimension of effective channels. Then, we derive the second stage precoder that maximizes the sum-rate by minimizing the weighted mean square error (WMSE). From simulation and analysis, we verify the effectiveness of the proposed method.

• Journal of Broadcast Engineering
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• v.11 no.4 s.33
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• pp.521-532
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• 2006

Recently, many research initiatives have been underway to improve reception performance of ATSC based DTV signal in mobile channel by adopting multiple antennas. In this paper, we propose a new mobile channel model which can be applicable to any array geometry. And then we propose new channel estimation algorithm which uses PN5l1 sequence in field synch. The proposed algorithm is to estimate channel by correlating the input signal in If frequency band and finding maximum peak, which does not need complicated synchronization circuit. Finally, we propose new receiver structures which can be implemented at the front-end of the existing receiver with no modification. With computer simulation, we verify the performance of the proposed model and verify the performance of the receiver structure with computer simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.1A
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• pp.64-72
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• 2012

We consider multiuser multiple antenna two-way relaying systems in which all users exchange their data with their counterparts with the help of a relay. The systems complete all data exchanges in two time phases called multiple access phase and broadcasting phase for spectral efficiency and therby require an effective scheme reducing self-interference (SI) and multiuser interference (MUI). Different from the conventional scheme suppressing both SI and MUI at the relay, the proposed scheme adopts SI cancelation (SIC) at the users and renders the relay to suppress the MUI mainly considering the SIC output. We analyze the symbol error rate (SER) and the achievable diversity order of the proposed scheme when the multiple access phase is dominant in the performance and obtain simulation results on the SER and the sum rate under various conditions. The results show that the proposed scheme improves the symbol error rate and the sum rate remarkably at the cost of complexity increase.