• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10A
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• pp.839-846
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• 2011

Link Adaptation should select the best modulation and coding scheme (MCS) which gives the highest throughput as channel conditions vary. Several link adaptation algorithms for wireless local area network (WLAN) have been proposed but for the future WLAN systems such as 802.11n system, these algorithms do not guarantee the best performance. In this paper, we propose a new link adaptation algorithm in which an MCS level is chosen by the received SNR plus the offset value obtained from the transmission results. The performance of proposed algorithm is simulated by an IEEE 802.11n system. From the analysis, we conclude the proposed algorithm performs better than the well-known link adaptation algorithms such as auto rate fallback and general SNR-based techniques. Particularly, the proposed algorithm improves throughput when the packet error ratio (PER) is constrained for fast fading channels.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5B
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• pp.469-479
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• 2009

The GEM frame is used a mean to deliver the variable length user data and consists of the header and the payload in the G-PON system. The HEC field of header protects contents of the header and is used to maintain GEM frame synchronization at the same time. When an LCDG (Loss of GEM Channel Delineation) occurs while receiving frames, the receiver have to discard corrupted frames until acquiring the synchronization again. Accordingly, high-speed synchronization method is required to minimize the frame loss. In this paper, we suggest not only a main state machine but a sub-state machine to reduce the frame loss when undetectable errors occurred in the GEM header. Also, we provide a more efficient and fast parallel structure to detect the starting point of the header. Finally, the proposed method is implemented with the FPGA and verified by the logic analyzer.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.12
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• pp.2744-2754
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• 1997

Recently, the Multi-Layer Restoration(MLR) algorithm was proposed by British Telecom(BT) to restore the network failures in Digital Cross-connect System(DCS) mesh survival network[1, 2]. This algorithm has multi restoration stage which is composed of the pre-planned and dynamic restoration. This algorithm is effective its ability in link or node failures. This reason is that it does not restore in the pre-planned rstoration stage but in dynamic restoration stage. In this paper, we propose the MLR with pre-planned Multi-Chooser(PMC) and successive restoration ratio algorithm. This proposed algorithm has a excellent performance for restortion time and ratio, spare channel availability and fast restoration from multiple link failure or node failure. This paper proposed the modeling and restoration algorithm, and analyzed the performance of the algorithm by simulation using OPNET(OPtimized Network Engineering Tools).

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.7
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• pp.1321-1327
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• 2009

In this paper, as the mobile communication service is widely used and the demand for wireless repeaters is rapidly increasing because of the easiness of extending service areas. But a wireless repeater has a problem the oscillation due to feedback signal. We proposed a new hybrid interference canceller using the adaptive filter with CMA(Constant Modulus Algorithm)-Grouped LMS(Least Mean Square) algorithm in the adaptive interference canceller. The proposed interference canceller has better channel adaptive performance and a lower MSE(Mean Square Error) than conventional structure because it uses the cancellation method of Grouped LMS algorithm. The proposed detector uses the LMS algorithms with two different step size to reduce mean square error and to obtain fast convergence. This structure reduces the number of iterations for the same MSE performance and hardware complexity compared to conventional nonlinear interference canceller.

• Journal of Korea Society of Industrial Information Systems
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• v.27 no.5
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• pp.25-36
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• 2022

This paper proposes a random sign reversal technique in space frequency block code for single carrier modulation. The traditional space time and frequency block coding technique may be confronted with radio environments openly, severe radio hijacking problems are to be overcome. In order to avoid such an open radio issue, random coded data protection technique for space-time block code was proposed, but this algorithm can change channel combination per an Orthogonal Frequency Division Multiplexing block. This kind of slow switching increases the probability that nearby receivers will detect the transmitted data. This paper proposes a fast switching algorithm per data symbols' basis which is a random sign reversal technique in space frequency block code for Single Carrier Modulation. It is shown in simulation that the proposed one has a superior performance in comparison with the performance of the receiver which do not know the random timing sequence of sign reversal.

• The KIPS Transactions:PartC
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• v.14C no.4
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• pp.349-358
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• 2007

Ethernet Passive Optical Network(EPON), which is one of PON technologies for realizing FTTx(Fiber-To-The-Curb/Home/Office), can cost-effectively construct optical access networks. In addition, EPON can provide high transmission rate up to 10Gbps and it is compatible with existing customer devices equipped with Ethernet card. To effectively control frame transmission from ONUs to OLT EPON can use Multi-Point Control Protocol(MPCP) with additional control functions in addition to Media Access Control(MAC) protocol function. For EPON, many researches on intra- and inter-ONU scheduling algorithms have been performed. Among the inter-ONU scheduling algorithms, IPS(Interleaved Polling with Stop) based on polling scheme is efficient because OLT assigns available time portion to each ONU given the request information from all ONUs. Since the IPS needs an idle time period on uplink between two consecutive frame transmission periods, it wastes time without frame transmissions. In this paper, we propose a dynamic bandwidth allocation algorithm to increase the channel utilization on uplink and evaluate its performance using simulations. The simulation results show that the proposed Two-phase Cycle Danamic Bandwidth Allocation(TCDBA) algorithm improves the throughput about 15%, compared with the IPS and Fast Gate Dynamic Bandwidth Allocation(FGDBA). Also, the average transmission time of the proposed algorithm is lower than those of other schemes.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.3
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• pp.63-69
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• 2013

This paper related with the performance of SE-MMA (Signed-Error MMA) that is the reduction of computational operation number in algorithm than MMA blind eualization algorithm which are possible to elimination of intersymbol interferance in the band limited and time dispersive nonlinear communication channel. In MMA algorithm which are possible to reduction of amplitude and phase rotation by intersymbol interference that is occurred in channel without using the training sequence, it uses the error signal that is the difference of the equalizer output and constant modulus, the statisticlly characteristic of transmitted signal. But in SE-MMA, it uses the polarity of the error signal, then it is possible to reduce the updating the tap coefficient and to simplify the H/W implementation. The computer simulation were performed in order to compare the performance of SE-MMA and conventional MMA algorithm. For this, the recovered signal constellation that is the output of the equalizer, the convergence performance by MSE, MD (maximum distortion) and residual isi characteristic learning curve, SER were used. As a result of simulation, the SE-MMA has more fast convergence speed than the MMA. But in the other index after reaching the seady state, it gives more worst performance values in the used index.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11B
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• pp.1583-1594
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• 2001

In this paper, the transmission structure and procedure of a random access channel for the IMT-2000 satellite radio specification are presented. The proposed random access method has much commonality with that of the 3GPP FD specification which is a terrestrial radio interface of IMT-2000. The proposed method was designed by considering characteristics of satellite link as we71 as the commonality with the terrestrial component. A preamble consists of sub-preamble repetition and a message is transmitted along with the preamble successively. The propose method has fast indication of preamble acquisition by physical layer. The proposed method has been included in the SAT-CDMA which is a radio transmission technology Proposed by TTA, KOREA and approved as a satellite radio interface at ITU-R. Additionally, in this Paper the signaling delay for the proposed random access channel will be analyzed and it will be compared to that of the random access methods using a conventional ALOHA procedure and the 3GPP procedure in aspect of the signaling delay. When the SAT-CDMA satellite constellation at the height of about 1600 km is considered, the delay of the proposed method was estimated to 100 ms less than that of the conventional ALOHA. This delay difference increases with 7he number of retransmissions. The delay is reduced by 30 ms, compared with the 3GPP method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4C
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• pp.331-340
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• 2006

In this Paper, we propose to extend the TSS-LS(Two-Step Search scheme with Linear search based Second step) scheme which was already proposed by the authors for coherent UWB(Ultra Wide Band) systems, to rapid and reliable acquisition of noncoherent UWB systems in multipath channels. The proposed noncoherent TSS-LS employing simple energy window banks utilizes two different thresholds and search windows to achieve fast acquisition. Furthermore, the linear search is adopted for the second step in the proposed scheme to correctly find the starting point in the range of effective delay spread of the multipath channels, and to obtain reliable BER(Bit Error Rate) performance of the noncoherent UWB systems. Simulation results with multipath channel models by IEEE 802.15.3a show that the proposed two-step search scheme can achieve significant reduction of the required mean acquisition time as compared to general search schemes. ]n addition, the proposed scheme achieves quite good BER performance for large signal-to-noise ratios, which is favorably comparable to the case of ideal perfect timing.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.05a
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• pp.609-611
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• 2010

IPTV(Internet Protocol Television)is the point in commercial and broadcast content from the numerous channels that are growing exponentially, Many people with mobile devices anywhere, anytime you want to use IPTV, demand will increase. Numerous channels for collecting information about EPG (Electronic Program Guide) service, IP (Internet Protoco) communications using a fast search of content for broadcast EPG is time to take advantage of the service. Using the current wired network, the Android-based IPTV services to take advantage of the EPG in the mobile environment to provide an environment being studied, and Country of the European digital broadcast standard DVB-MHP standard is followed by subsequent research and development of the EPG service is required. In this study, using the existing wired network, IPTV EPG service information of the channel in a mobile environment user-friendly as possible by providing channels for EPG service information to users quickly and easily search for content to provide an environment and Android-based mobile IPTV environment to take advantage of the EPG service channels of broadcast channels with in the EPG service for users to gather information retrieval system is proposed.