• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.3A
• /
• pp.287-295
• /
• 2011

Cognitive radio (CR) features opportunistic access to spectrum when licensed users (LU) are not operating. To avoid interference to LU, cognitive users (CU) need to perform spectrum sensing. Because of local shadowing, fading, or limited sensing capability, it is suggested that multiple CUs cooperate to detect LU. In cooperative spectrum sensing, CUs should exchange their sensing data with minimum bandwidth and delay. In this paper, we introduce a novel method to efficiently report sensing data to the central node in an infrastructured OFDM-based CR network. All CUs simultaneously report their sensing data over unique and orthogonal signals on locally available subcarriers. By detecting the signals, the central node can determine subcarrier availability for each CU. Implementation challenges are identified and then their solutions are suggested. The proposed method is evaluated through simulation on a realistic channel model. The results show that the proposed method is feasible and efficient.

• Proceedings of the KAIS Fall Conference
• /
• 2010.05a
• /
• pp.507-510
• /
• 2010

OFDM(Orthogonal Frequency Division Multiplexing)은 하나의 데이터 열(data stream)을 낮은 데이터 전송률을 갖는 작은 데이터로 나누고, 이들을 부반송파(subcarrier)를 통해 동시에 전송한다. OFDM이 차세대 전송방식으로 채택된 이유는 주파수 선택적 페이딩(frequency selective fading)이나 협대역(narrow band)간 간섭에 받는 영향이 적어 고속 통신이 가능하기 때문이다. 본 논문에서는 RS 부호(Reed-Solomon Code)를 사용하여 OFDM에서 대용량 데이터를 전송할 때 발생하기 쉬운 연집 오류(burst error)를 정정하도록 하였다. 또한 채널 사이에 파일롯 심볼(pilot symbol)을 삽입하여 채널 추정을 통한 신호의 타이밍 오류도 고려하였다.

• Proceedings of the KAIS Fall Conference
• /
• 2007.11a
• /
• pp.248-251
• /
• 2007

OFDM(Orthogonal Frequency Division Multiplexing)은 하나의 데이터 열(data stream)을 낮은 데이터 전송률을 갖는 작은 데이터로 나누고, 이들을 부반송파(subcarrier)를 통해 동시에 전송한다. OFDM이 차세대 전송방식으로 채택된 이유는 주파수 선택적 페이딩(frequency selective fading)이나 협대역(narrow band)간 간섭에 받는 영향이 적어 고속 통신이 가능하기 때문이다. 본 논문에서는 RS 부호(Reed-Solomon Code)를 사용하여 OFDM에서 대용량 데이터를 전송할 때 발생하기 쉬운 연집 오류(burst error)를 정정하도록 하였다. 또한 채널 사이에 파일롯 심볼(pilot symbol)을 삽입하여 채널 추정을 통한 신호의 타이밍 오류도 고려하였다.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.53 no.2
• /
• pp.3-9
• /
• 2016

In this paper, we propose a Radio over Fiber system for small cell applications and for mobile fronthaul networks supporting cloud-radio access networks(RAN). We built a system with a downlink employing orthogonal frequency division multiplexing (OFDM) techniques and an uplink using single carrier-frequency multiple access(SC-FDMA). System parameters are evaluated for various subcarrier modulations and the results of link performance measurements are analyzed.

• Journal of the Optical Society of Korea
• /
• v.12 no.4
• /
• pp.359-363
• /
• 2008

A novel WDM-PON system delivering bidirectional 1.25-Gbps data and broadcasting data is proposed. A subcarrier signal modulates optical carriers of a Fabry-Perot-laser-diode based broadband light source to broadcast to all users. Reflective semiconductor optical amplifiers are used as modulators for the baseband data at both the optical line terminal and the remote optical network unit for a channel. Bit error rate and error vector magnitude were measured to demonstrate the proposed scheme.

• Journal of Positioning, Navigation, and Timing
• /
• v.10 no.4
• /
• pp.335-340
• /
• 2021

A constant envelope multiplexing via constellation tailoring scheme is proposed for flexible power allocation of Global Navigation Satellite System (GNSS) signals. The proposed scheme is compared with the coherent adaptive subcarrier modulation (CASM) adopted in the L1 band signals of the Global Positioning System (GPS) in terms of power difference and power loss. Analysis of the constellation optimization results on the power difference and power loss show that the proposed scheme outperforms the CASM of the GPS signals in the allowable power difference of less than 0.1 dB.

• ETRI Journal
• /
• v.41 no.2
• /
• pp.184-196
• /
• 2019

Wavelet packet modulation (WPM) is a multicarrier modulation (MCM) technique that has emerged as a potential alternative to the widely used orthogonal frequency-division multiplexing (OFDM) method. Because WPM has overlapped symbols, equalization cannot rely on the use of the cyclic prefix (CP), which is used in OFDM. This study applies linear minimum mean-square error (MMSE) equalization in the time domain instead of in the frequency domain to achieve low computational complexity. With a modest equalizer filter length, the imperfection of MMSE equalization results in subcarrier attenuation and noise amplification, which are considered in the development of a bit-loading algorithm. Analytical expressions for the bit error rate (BER) performance are derived and validated using simulation results. A performance evaluation is carried out in different test scenarios as per Recommendation ITU-R M.1225. Numerical results show that WPM with equalization-aware bit loading outperforms OFDM with bit loading. Because previous comparisons between WPM and OFDM did not include bit loading, the results obtained provide additional evidence of the benefits of WPM over OFDM.

• ETRI Journal
• /
• v.40 no.6
• /
• pp.726-735
• /
• 2018

Femtocells are good examples of the ultimate networking technology, offering enhanced indoor coverage and higher data rate. However, the dense deployment of femto base stations (FBSs) and the exploitation of subcarrier reuse between macrocell base stations and FBSs result in significant co-tier and cross-tier interference, thus degrading system performance. Therefore, appropriate resource allocations are required to mitigate the interference. This paper proposes a discrete bacterial foraging optimization (DBFO) algorithm to find the optimal resource allocation in two-tier networks. The simulation results showed that DBFO outperforms the random-resource allocation and discrete particle swarm optimization (DPSO) considering the small number of steps taken by particles and bacteria.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2019.05a
• /
• pp.597-599
• /
• 2019

When frequency domain high amplitude impulse is inserted before IFFT in OFDM transmitter, the PAPR of OFDM signal in tme domain can be effectively reduced. In this paper, the degree of PAPR improvement of OFDM communication system with CQAM subcarrier modulation is analysed by adopting impulse insertion technique before IFFT of transmitter. Furthermore, it is verified that additional PAPR performance improvement can be obtained by finding optimum position of impulse insertion for maximizing PAPR reduction.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.12 no.1
• /
• pp.258-269
• /
• 2020

This paper proposes Snapping Shrimp Noise (SSN) detection and corrupted Orthogonal Frequency Division Multiplexing (OFDM) reconstruction methods to increase Bit Error Rate (BER) performance when OFDM transmitted signal is corrupted by impulsive SSNs in underwater acoustic communications. The proposed detection method utilizes multilayer wavelet packet decomposition for detecting impulsive and irregularly concentrated and SSN energy in specific frequency bands of SSN, and the proposed reconstruction scheme uses iterative decision directed-subcarrier reconstruction to recover corrupted OFDM signals using multiple carrier characteristics. Computer simulations were executed to show receiver operating characteristics curve for the detection performance and BER for the reconstruction. The practical ocean experiment of SAVEX 15 demonstrated that the proposed method exhibits a better detection performance compared with conventional detection method and improves BER by 250% and 1230% for uncoded and coded data, respectively, compared with the conventional reconstruction scheme.