• ETRI Journal
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• 제28권2호
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• pp.227-230
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• 2006

There has been a growing need for increased capacity in cellular systems. This has resulted in the adoption of the code division multiple access (CDMA) system as a multiple channel access method. Thus, it is important to obtain the phase offsets of binary codes in the CDMA system because distinct phase offsets of the same code are used to distinguish signals received at the mobile station from different base stations. This letter proposes an efficient algorithm to compute the phase offset of a binary code in the CDMA system through the use of the basic facts of number theory and a new notion of the subcodes of a given code. We also formulate the algorithm in a compact form.

• 대한임베디드공학회논문지
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• 제11권2호
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• pp.97-105
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• 2016

Microcontrollers (MCUs) for endpoint smart sensor devices of internet-of-thing (IoT) are being implemented as system-on-chip (SoC) with on-chip instruction flash memory, in which user firmware is embedded. MCUs directly fetch binary code-based instructions through bit-line sense amplifier (S/A) integrated with on-chip flash memory. The S/A compares bit cell current with reference current to identify which data are programmed. The S/A in reading '0' (erased) cell data consumes a large sink current, which is greater than off-current for '1' (programmed) cell data. The main motivation of our approach is to reduce the number of accesses of erased cells by binary code level transformation. This paper proposes a built-in write/read path architecture using binary code inversion method based on hot-spot region detection of instruction code access to reduce sensing current in S/A. From the profiling result of instruction access patterns, hot-spot region of an original compiled binary code is conditionally inverted with the proposed bit-inversion techniques. The de-inversion hardware only consumes small logic current instead of analog sink current in S/A and it is integrated with the conventional S/A to restore original binary instructions. The proposed techniques are applied to the fully-custom designed MCU with ARM Cortex-M0$^{TM}$ using 0.18um Magnachip Flash-embedded CMOS process and the benefits in terms of power consumption reduction are evaluated for Dhrystone$^{TM}$ benchmark. The profiling environment of instruction code executions is implemented by extending commercial ARM KEIL$^{TM}$ MDK (MCU Development Kit) with our custom-designed access analyzer.

• 한국멀티미디어학회논문지
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• 제25권10호
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• pp.1416-1432
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• 2022

The access control system is a system that allows users to selectively enter the building by granting an access key to the user for security. Access keys with weak security are easily exposed to attackers and cannot properly perform the role that authenticates users. Access code keys should be protected from forgery or spoofing. For this reason, access key verification service models is important in security. However, most models manage all access keys on one central server. This method not only interrupts all services due to server errors, but also risks forgery and spoofing in the process of transmitting access keys. Therefore, blockchain algorithms are used to reduce this risk. This paper proposes a blockchain-based access key verification service model that used distributed stored blockchain gateways on storing access keys and authenticates the user's identity based on them. To evaluate the performance of this model, an experiment was conducted to confirm the performance of the access key forgery recovery rate and the blockchain network performance. As a result, the proposed method is 100% forgery recovery rate, and the registration and verification process is evaluated at 387.58 TPS and 136.66 TPS.

• 한국ITS학회 논문지
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• 제8권1호
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• pp.110-118
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• 2009

PB/MC-CDMA(Partial Block Multi Carrier Code Division Multilple Access) 시스템은 사용자간의 코드 간 간섭을 줄임으로써 성능을 향상 시키는 시스템이다. 또한, 이 시스템은 심볼 간 간섭을 피하면서 주파수 다이버시티 이득을 얻을 수 있어 MC-CDMA(Multi Carrier Code Division Multiple Access) 시스템보다 향상된 성능을 보여준다. 그러나, 다중캐리어를 사용함으로써 PAPR 문제가 발생하여 시스템의 성능을 저하 시킨다. 이 논문에서는, PB/MC-CDMA 시스템에서 추가적인 정보 없이 여분의 확산 코드를 이용하여 최적화된 확산코드를 선택함으로써, 피크전력을 줄이는 방법을 제안한다. PB/MC-CDMA 시스템은 각 블록 단위로 확산 코드를 재사용함으로써, 여분의 코드가 남게 된다. 이러한 여분의 코드를 여러 개의 그룹으로 나누어 PAPR(Peak to Average Power Ratio)을 계산하고, 피크전력이 최소가 되는 코드를 선택하여 전송함으로써 PAPR 문제를 해결할 수 있는 방법이다.

• 융합신호처리학회논문지
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• 제6권4호
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• pp.206-211
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• 2005

본 논문에서는 블루투스 기저대역에 적용하기 위한 상관기와 액세스 코드 생성모듈의 설계에 대해 다룬다. 상관기와 액세스 코드 생성 모듈은 블루투스 유닛 사이의 연결설정과 패킷판별, 클록 동기화를 수행한다. 상관기 모듈은 1Mb/s 전송속도를 가지는 입력신호에 대해 슬라이딩 윈도우 상관을 취하여 유용한 패킷판별과 클록 동기화를 행하며, 그 구성은 Wallace tree 구조의 CSA(Carry Save Adder)와 임계 값 판별기로 구성된다. 액세스 코드 생성모듈은 블루투스 표준안에서 제시한 4단계의 생성과정에 따라 설계하였으며 BCH(Bose-Chadhuri-Hocquenghem)순회 부호기(cyclic code)와 제어장치로 구성된다. 의사 랜덤 시퀀스는 동기화 문제를 해결하기 위해 임의의 저장장치에 저장된 형태로 사용하였다. 본 논문에서 제시한 상관기와 액세스 코드 생성모듈은 하드웨어 묘사언어인 VHDL로 설계되었으며 시뮬레이션 및 테스트를 위해 Xilinx FPGA를 사용하여 검증하였다. 설계된 회로의 합성결과는 치대 4.689ns의 임계지연과 최대 7-bit까지의 상관허용 오차를 보여준다.

• 기술혁신학회지
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• 제3권1호
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• pp.127-138
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• 2000

This pape applies the multi-attribute utility theory for estimating the non-economci value of technology. The technology of the code division multiple access in mobile communications is used as a case study. The technology of the code division multiple access in mobile communications is used as a case study. The result shows that the multi-attribute utility theory is a useful method for es-tinmating the non-economic value of technology and gaining an insight into the importance of tech-nology innovation.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -1
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• pp.536-539
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• 2002

The use of concatenated codes in noncoherent synchronous optical fiber CDMA networks is proposed. The concatenated code sequences are generated using balanced Walsh code sequences and Walsh code sequences. The selection of balanced Walsh code sequences is presented and the design of fully programmable transmitter and receiver is reported. The analysis of the system BER performance shows that multiple-access interference is completely eliminated and the BER performance of the proposed system is better than that of the non-coherent synchronous optical fiber CDMA system using optical orthogonal codes with double hard-limiters.

• 전자공학회논문지
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• 제50권5호
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• pp.121-127
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• 2013

작은 입력신호의 spectral-amplitude-code(SAC) optical code-division multiple-access (OCDMA) 시스템에는 nonideal symmetric balance incomplete block design(BIBD) code의 사용이 효율적이나 충분한 사용자를 수용하지 못하는 단점이 있다. 이를 극복하기 위하여 본 논문에서는 ideal BIBD code를 공간 코드로 사용하고 nonideal code를 파장 코드로 사용하는 two-dimensional(2-D) BIBD code를 제안한다. 사용자 수에 따른 bit error-rate(BER) 분석을 통하여 제안하는 2-D BIBD code가 1-D BIBD code에 비하여 최대사용자 수를 현저하게 증가시킬 수 있음을 알 수 있다.

• 한국전자파학회지:전자파기술
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• 제3권2호
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• pp.22-29
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• 1992

최근 CDMA(code dicision multiple-access)를 이용한 다원 접속방식이 각광을 받고 있다. 한편, 동일한 섬유 대역폭을 유지하면서도 높은 데이타 전송율과 에러성능이 요구되므로 높은 코드율을 가지는 콘볼루션 코드와 이에 상응하는 디코딩 기법이 필요한 실정이다. Punctured 콘볼루션 코드는 높은 코드율에 비해 디코더가 복잡하지 않다는 장점 때문에 최근 여러가지 시스템에서 선호되고 있다. 본 논문에서는 punctured 콘보루션 코딩 방식과 경판정 Viteri 디코딩을 이용한 CDMA 패킷 무선 동선 시스템의 패컷 에러 확률(packet error probability)을 구하였으며 일반식인 콘볼루션 코드를 사용했을 때와 비교하였다.

• ETRI Journal
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• 제23권2호
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• pp.52-60
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• 2001

In this paper, a medium access control protocol is proposed for integrated voice and data services in wireless local networks. Uplink channels for the proposed protocol are composed of time slots with multiple spreading codes per slot based on slotted code division multiple access (CDMA) systems. The proposed protocol uses spreading code sensing and reservation schemes. This protocol gives higher access priority to delay-sensitive voice traffic than to data traffic. The voice terminal reserves an available spreading code to transmit multiple voice packets during a talkspurt. On the other hand, the data terminal transmits a packet without making a reservation over one of the available spreading codes that are not used by voice terminals. In this protocol, voice packets do not come into collision with data packets. The numerical results show that this protocol can increase the system capacity for voice service by applying the reservation scheme. The performance for data traffic will decrease in the case of high voice traffic load because of its low access priority. But it shows that the data traffic performance can be increased in proportion to the number of spreading codes.