• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.1
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• pp.36-41
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• 2009

In general, accurate attitude information is essential to perform the mission. Two algorithms are well-known to determine the attitude through two or more vector observations. One is deterministic method such as TRIAD algorithm, the other is optimal method such as QUEST algorithm. This Paper suggests the idea to improve performance of the TRIAD algorithm and to determine the attitude by combination of different sensors. First, we change the attitude matrix to Euler angle instead of using orthogonalization method and also use covariance in place of variance, then apply an unbiased minimum variance formula for more accurate solutions. We also suggest the methodology to determine the attitude when more than two measurements are given. The performance of the Averaging TRIAD algorithm upon the combination of different sensors is analyzed by numerical simulation in terms of standard deviation and probability.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.11A
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• pp.1013-1020
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• 2008

Cognitive radio(CR) techniques have been considered as a strong solution of frequency scarcity due to the limitation of frequency resource, In this paper, an orthogonal beamforming method is proposed that enables cognitive radio systems to coexist with a primary users' system in the same spectrum and region without causing interference to primary systems. The orthogonal multiple beams for multi-users of CR systems are obtained through the generation of orthogonal subspaces from primary users' channel state information. To increase the sum-rate of the CR systems, the proposed scheme adopts opportunistic radio resource allocation techniques. Simulation results provides that the proposed scheme achieves 2.72bps/Hz, the sum-rate capacity at 20 cognitive users in an area with two antennas at the cognitive radio basestation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.8A
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• pp.827-835
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• 2007

In this paper, the extension method of data transmission range as adapting AAS(Adaptive Antenna Systems) in ECMA(European Computer Manufacturers Association) standard MB-OFDM(MultiBand-Orthogonal Frequency Division Multiplexing) UWB systems is proposed, and the complementary beamforming method which can solve hidden beam problem when we adapt AAS in CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance) systems is proposed. To design the complementary beamforming, Gram-Schmidt orthogonalization is utilized, whose beam pattern exhibits perfect nulling at the main beam angles and provides uniform power for detection of channel utilization out of main beam. The proposed method can be utilized with any arbitrary beamforming when we make main beamforming. Through computer simulation, it can be shown that proposed AAS and complementary beamforming increase data transmission range from 2m to 3.95m in 480Mbps data transmission system and increase throughput about 20% as compared with general UWB AAS systems.