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An Image Fingerprinting System Based on Color Histogram of Affine Covariant Region
Jinho Choi,Dalwon Jang,Chang D. Yoo 대한전자공학회 2010 ICEIC:International Conference on Electronics, Inf Vol.1 No.1
In this paper, we propose a content-based image fingerprinting system which uses color histograms of affine covariant regions as a local fingerprint of an image. We focus on the robustness for various distortions and computational efficiency. Given a query, the system first extracts local fingerprints from affine covariant regions. The local fingerprints are based on the color histogram, and the affine covariant regions are detected using the maximally stable extremal region (MSER) detector. After extracting local fingerprints, the system searches local fingerprints in fingerprint database for the nearest neighbor of the query local fingerprints. Then, the query image is identified. Experimental results show that that our system is robust against cropping, resizing, rotation, and small color changes with efficient computational cost.
Compressive Channel Division Multiple Access for MTC Under Frequency-Selective Fading
Jinho Choi,Nam Yul Yu Institute of Electrical and Electronics Engineers 2017 IEEE Transactions on Communications Vol. No.
<P>In this paper, we study random access for machine-type communications based on a multiple access scheme that exploits different channel state information (CSI) from active devices under frequency-selective fading, which is called channel division multiple access (ChDMA). In ChDMA, in order to use a low-complexity compressive sensing (CS) algorithm for multiuser detection (MUD) with a high transmission rate, we propose to use index modulation. Since the CSI is used as a signature for MUD, the CSI estimation becomes crucial. For the CSI estimation, pilot transmission can be considered where each active device randomly chooses a pilot from a set of pre-determined pilots. Since the CSI estimation suffers from pilot collision in this case, we propose multiple pilot transmissions and show that a low probability of collision can be achieved. A CS-based approach is derived not only to estimate the CSI, but also to detect randomly selected multiple pilot signals by exploiting the sparsity of active devices over frequency-selective fading channels.</P>
Jinho Choi,Jihong Park,Shiva Pokhrel 한국통신학회 2021 Journal of communications and networks Vol.23 No.1
Improving the data rate of machine-type communication(MTC) is essential in supporting emerging Internet of things (IoT)applications ranging from real-time surveillance to edge machinelearning. To this end, in this paper we propose a resource allocationapproach for uplink transmissions within a random access procedurein MTC by exploiting multichannel selection diversity, coinedexplore-before-talk (EBT). Each user in EBT first sends pilot signalsthrough multiple channels that are initially allocated by a basestation (BS) for exploration, and then the BS informs a subset ofinitially allocated channels that are associated with high signal-tonoiseratios (SNRs) for data packet transmission by the user whilereleasing the rest of the channels for other users. Consequently,EBT exploits a multichannel selection diversity gain during datapacket transmission, at the cost of exploration during pilot transmission. We optimize this exploration-exploitation trade-off, by derivingclosed-form mean data rate and resource outage probabilityexpressions. Numerical results corroborate that EBT achieves ahigher mean data rate while satisfying the same outage constraint,compared to a conventional MTC protocol without exploration.
On Improving Throughput of Multichannel ALOHA using Preamble-based Exploration
Jinho Choi 한국통신학회 2020 Journal of communications and networks Vol.22 No.5
Machine-type communication (MTC) has been extensively studied to provide connectivity for devices and sensors in theInternet-of-thing (IoT). Thanks to the sparse activity, random access, e.g., ALOHA, is employed for MTC to lower signaling overhead. In this paper, we propose to adopt exploration for multichannel ALOHA by transmitting preambles before transmitting datapackets in MTC, and show that the maximum throughput can beimproved by a factor of 2 − e−1 ≈ 1.632, In the proposed approach, a base station (BS) needs to send the feedback informationto active users to inform the numbers of transmitted preambles inmultiple channels, which can be reliably estimated as in compressive random access. A steady-state analysis is also performed withfast retrial, which shows that the probability of packet collision becomes lower and, as a result, the delay outage probability is greatlyreduced for a lightly loaded system. Simulation results also confirmthe results from analysis.