• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.7
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• pp.1250-1256
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• 2001

A resource management scheme for ad hoc wireless local area networks (AWLAN's) is presented. This scheme combines distributed resource management scheme and orthogonal frequency division multiplexing-code division multiple access(OFDM-CDMA) technique to support multimedia services with QoS guarantees. The performance evaluation has done in terms of blocking rates and QoS loss probability.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.5
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• pp.965-972
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• 2005

We propose a new resource management scheme, Distributed Channel Allocation Protocol (DCAP), for multimedia Ad Hoc Wireless LANs (AWLANS). This scheme implements a Qualify-of-Service (QoS) providing distributed resource management on the Orthogonal Frequency Division Multiplexing-Code Division Multiple Access (OFDM-CDMA) channel architecture. According to the performance evaluation results for MPEG traffic sources, DCAP can be a good choice of resource management scheme for AWLANs supporting multimedia services on the Broadband Wireless Access(BWA)-type physical layer.

• Journal of the Optical Society of Korea
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• v.17 no.6
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• pp.467-470
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• 2013

We propose a blind feedforward phase noise mitigation method in the time-domain for a coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. By exploiting the redundancy of the cyclic prefix (CP), the proposed scheme acquires the overall phase noise difference information during an OFDM block and attempts to mitigate the phase noise in the time domain using a linear approximation. The proposed algorithm mitigates common phase error (CPE) and inter-carrier-interference (ICI) due to phase noise simultaneously, improving the system performance, especially when decision-directed equalizers are used. The simulation results demonstrate the effectiveness of the proposed feedforward phase noise mitigation approach in time domain.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.8C
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• pp.627-632
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• 2008

The timing offset is one of the main error sources in estimating the frequency offset in orthogonal frequency division multiplexing (OFDM) systems. Although some works have been done to mitigate the influence of the timing offset on the frequency offset estimation, most of the investigations require the knowledge of the timing offset range, which is not generally available in practical systems. In this paper, we propose a new frequency offset estimation scheme using differential combining between two successive correlation samples, which does not require the knowledge of the timing offset range, and thus, is robust to the timing offset variation. The simulation results show that the proposed scheme is not only robust to the timing offset variation, but also generally performs better than the conventional scheme on the average, in the case of the timing offset range being not known exactly.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6A
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• pp.592-598
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• 2008

In this paper, a novel pilot-aided integer frequency offset estimation scheme is proposed for orthogonal Sequency division multiplexing (OFDM)-based digital video broadcasting (DVB) systems. The conventional pilot-aided integer frequency offset estimation scheme proposed for OFDM-based DVB systems exploits the partial information of combinations provided by pilots. Thus, in this paper, we propose a novel integer frequency offset estimation scheme exploiting all information of pilot combinations. To compare the performance of the proposed scheme with that of the conventional scheme, we conduct a simulation in additive white Gaussian noise (AWGN) and multipath Rayleigh channels, which shows that the proposed scheme outperforms the conventional scheme in terms of the probability of integer frequency offset estimation failure.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.12
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• pp.2731-2736
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• 2009

In this paper, a new implementation method of OFDM (orthogonal frequency division multiplexing) system with an orthogonal basis matrix is developed mathematically. The basis matrix is based on the Haar basis but has an appropriate form for modulation of multiple subchannel signals of OFDM. It is verified that the new basis matrix can be expanded with a simple recursive algorithm. The order of synthesis matrix in the transmitter is increased by the factor of two with every expansion. Demodulation in the receiver is carried out by its inverse matrix, which can be generated recursively with the orthogonal basis matrix. It is shown that perfect reconstruction of original signals is possibly achieved in the proposed OFDMsystem.

• Journal of Communications and Networks
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• v.9 no.2
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• pp.118-127
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• 2007

We propose a link adaptation and selection method for the links constituting an orthogonal frequency division multiplexing (OFDM) based wireless relay network. The proposed link adaptation and selection method selects the forwarding, modulation, and channel coding schemes providing the highest end-to-end throughput and decides whether to use the relay or not. The link adaptation and selection is done for each sub-channel based on instantaneous signal to interference plus noise ratio (SINR) conditions in the source-to-destination, source-to-relay and relay-to-destination links. The considered forwarding schemes are amplify and forward (AF) and simple adaptive decode and forward (DF). Efficient adaptive modulation and coding decision rules are provided for various relaying schemes. The proposed end-to-end link adaptation and selection method ensures that the end-to-end throughput is always larger than or equal to that of transmissions without relay and non-adaptive relayed transmissions. Our evaluations show that over the region where relaying improves the end-to-end throughput, the DF scheme provides significant throughput gain over the AF scheme provided that the error propagation is avoided via error detection techniques. We provide a frame structure to enable the proposed link adaptation and selection method for orthogonal frequency division multiple access (OFDMA)-time division duplex relay networks based on the IEEE 802.16e standard.

• Journal of Communications and Networks
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• v.15 no.1
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• pp.8-14
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• 2013

For alleviating the low spectrum efficiency problem of orthogonal frequency division multiplexing (OFDM), due to the strong inter-cell-interference (ICI) at cell's edge, we introduce comb-spectrum code division multiple access (CS-CDMA) into broadband OFDM system at downlink channel for enabling the use of entire spectrum for seamless coverage. In addition, we develop a new method, called orthogonal cell code (OCC) scheme, to assist CS-CDMA for nullifying the ICI from contiguous cells. In system operation, each of the conventional cells is divided into an outer cell and an inner cell, and a mobile station (MS) should access to the CS-CDMA when it is in the outer cell and access to OFDM when it is in the inner cell. This study investigates the spectrum efficiency of using CS-CDMA and makes a comparison with that of long term evolution (LTE) in the following cases; (1) under an assumption of perfect channel state information and (2) based on channel estimates at a MS station. The results show the great advantage of utilizing the proposed system.

• TTA Journal
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• s.84
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• pp.86-92
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• 2002

• The Journal of the Acoustical Society of Korea
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• v.40 no.3
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• pp.219-227
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• 2021

This paper proposed an Orthogonal Frequency Division Multiplexing (OFDM) based biomimetic communication method using a dolphin whistle which covertly transmits communication signals to allies. The proposed method divides the dolphin whistle into several time slots corresponding to a number of OFDM symbols, and modulates the communication signal by mapping differential phase shift keying (DPSK) symbols into subcarriers that have the frequency bands of the dolphin whistle in each slot. The advantages of the proposed method are as follows: In the conventional Chirp Spread Spectrum (CSS) and Frequency Shift Keying (FSK) based biomimetic communication methods, the discontinuity of the frequency contour is large, but the proposed method can reduce the discontinuity. Even if the modulation order is increased, the degradation of the mimicking performance is small. The computer simulations demonstrate that the Bit Error Rate (BER) and mimicking performance of the proposed method are better performance than those of the conventional CSS and FSK.