• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.9
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• pp.93-99
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• 1998

A novel four-channel narrowband wavelength demultiplexer using integrated four vertical directional coupler structures is proposed and theoretically investigated. Four ridge waveguide with different ridge width are vertically coupled to a strip-loaded waveguide which results four different wavelengths filtered out to each ridge waveguide. In order to reduce the side-lobes, the coupling coefficients are varied along the propagation direction. The spectral responses of channels were found to be quite uniform. An average channel spacing of 7 nm with power coupling efficiency of ~90%, 3-dB passband width of 2 nm, and 20 dB side-lobe suppression ratio was achieved.

• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.185-188
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• 2005

This paper proposes a new peak-windowing algorithm with window-length adaptation for peak-to-average power reduction (PAPR) of orthogonal frequency division multiplexing (OFDM) systems. Conventional peak windowing algorithm has advantages, such as moderate system complexity with good spectral shape. However, adjacent peak signals within the length of window functions produce the distortion of signal amplitude since window functions might overap with each other. These undesired characteristics of conventional peak windowing algorithm result in the degradation of BER performance. The proposed algorithm outperforms the conventional one with the aid of window-length adaptation. Simulation results show the efficiency of the proposed algorithm under the environments of WiBro downlink systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.9
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• pp.889-897
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• 2002

In this paper, we propose an improved block coding scheme for PAPR reduction in the OFDM communication system. Unlike the conventional block coding scheme which uses one block encoder of subcarrier N, two block encoders of subcarrier N/2 is used for the proposed block coding scheme. This not only improves the coding gain, but enhances the spectral efficiency by twice due to the increment of code rate. PAPR Reduction performance is the same as the conventional block coding. When BER is $10^{-4}$, the proposed block coding scheme has coding gain of 0.5 dB than the conventional scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3C
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• pp.228-236
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• 2006

A Multicarrier code division multiple access(MC-CDMA) is a scheme that combines multicarrier modulation with CDMA. It offers robustness to frequency selective fading effect and can support higher rate data transmission with higher spectral efficiency. The objective of this article is proposed and analyzed a new asynchronous MC-CDMA system with various kinds of data rates which employs a multiple access interference (MAI) canceller. The proposed multirate MC-CDMA system can be accomplished by changing the number of Parallel branch(P) according to their data rate and hybrid interference canceller(HIC) are used for MAI cancellation. We compare the performance of proposed system in terms of average bit error rate(BER) with that of a single rate MC-CDMA system. The results show the large improvement in performance that can be attained by the cancellation scheme under multipath environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.6
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• pp.520-527
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• 2013

In this paper, a joint cell grouping and user association technique proposed for a semi-dynamic grouped network MIMO in a clustered heterogeneous cellular network (HCN). With the conventional macro BSs, small cells are being overlaid to increase a spectral efficiency per area and these small cells are expected to be concentrated to support exponentially increasing data traffic in hot spot areas. The main culprits of performance degradation in the clustered HCN are interference and load imbalance. The proposed scheme jointly handles them to maximize a proportional-fair metric. It is shown that the proposed technique can largely improve user average rate and proportional fairness among users than any other conventional schemes in the clustered HCN.

• ETRI Journal
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• v.39 no.5
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• pp.707-717
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• 2017

This paper presents a novel generalized quadrature spatial modulation (GQSM) transmission scheme using antenna grouping. The proposed GQSM scheme combines QSM and conventional spatial multiplexing (SMux) techniques in order to improve the spectral efficiency (SE) of the system. Analytical and simulation results show that the proposed transmission scheme has minimal losses in terms of the average bit error probability along with the advantage of an increased SE compared with previous SM and QSM schemes. For the case studies, this advantage represents a reduction of up to 81% in terms of the number of required transmit antennas compared with QSM. In addition, a detection architecture based on the ordered successive interference cancellation scheme and the QR decomposition is presented. The proposed QRD-M adaptive algorithm showed a near-maximum-likelihood performance with a complexity reduction of approximately 90%.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.12A
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• pp.975-983
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• 2011

In this paper, we investigate how the IEEE 802.16 based wireless system can adopt the network coding. To avoid the problem of overhearing, we focus on the bidirectional traffic, where each end node exchanges network coded data over a relay node. The bidirectional traffic is usually observed in Internet, where TCP makes congestion control and error recovery based on the acknowledgement from the opposite direction. Thus, enhancing the spectral efficiency of wireless Internet through the network coding is expected. Our simulation with realistic radio characteristics and TCP-like traffic shows that the network coding improves the throughput by an average of 36 percent compared to the simple relay case.

• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.389-393
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• 2008

OFDM (Orthogonal Frequency Division Multiplexing) modulation using the orthogonal subcarriers reduces the delay spread by increasing robustness to multipath fading and can use overlapped bandwidth due to orthogonality on frequency domain. Thus data rate and spectral efficiency are increased. Because of these reason, OFDM is used for high speed data transmission for multimedia transmission as HSDPA, WiBro, WLAN. However OFDM also has drawbacks that have the high PAPR (Peak to Average Power Ratio). This high PAPR takes place because of parallel processing a number of data at once using a FFT processor. By high PAPR, amplifier doesn't act in dynamic range, so that BER performance is worse. In this paper, we reduce the PAPR using SLM(Selective Mapping). SLM doesn't effect on BER performance, but should transmit the side information for demodulation [2]. Also PAPR is higher as the number of FFT processor is larger. Thus SLM has high complexity. In this paper, we analyze the performance of SLM using scaling for no side information.

• ETRI Journal
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• v.44 no.3
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• pp.361-378
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• 2022

In 5G, the required target for interruption time during a handover (HO) is 0 ms. However, when a handover failure (HOF) occurs, the interruption time increases significantly to more than hundreds of milliseconds. Therefore, to fulfill the requirement in as many scenarios as possible, we need to minimize HOF rate as close to zero as possible. 3GPP has recently introduced conditional HO (CHO) to improve mobility robustness. In this study, we propose "ZEro handover failure with Unforced and automatic time-to-execute Scaling" (ZEUS) algorithm to optimize HO parameters easily in the CHO. Analysis and simulation results demonstrate that ZEUS can achieve a zero HOF rate without increasing the ping-pong rate. These two metrics are typically used to assess an HO algorithm because there is a tradeoff between them. With the introduction of the CHO, which solves the tradeoff, only these two metrics are insufficient anymore. Therefore, to evaluate the optimality of an HO algorithm, we define a new integrated HO performance metric, mobility-aware average effective spectral efficiency (MASE). The simulation results show that ZEUS provides higher MASE than LTE and other CHO variants.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.1
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• pp.185-201
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• 2023

Grant-free random access (GFRA) can reduce the access delay and signaling cost, and satisfy the short transmission packet and strict delay constraints requirement in internet of things (IoT). IoT is a major trend in the future, which is characterized by the variety of applications and devices. However, most existing studies on GFRA only consider a single type of device and omit the effect of access delay. In this paper, we study GFRA in multicell massive multipleinput multiple-output (MIMO) systems where different types of devices with various configurations and requirements co-exist. By introducing the backoff mechanism, each device is randomly activated according to the backoff parameter, and active devices randomly select an orthogonal pilot sequence from a predefined pilot pool. An analytical approximation of the average spectral efficiency for each type of device is derived. Based on it, we obtain the optimal backoff parameter for each type of devices under their delay constraints. It is found that the optimal backoff parameters are closely related to the device number and delay constraint. In general, devices that have larger quantity should have more backoff time before they are allowed to access. However, as the delay constraint become stricter, the required backoff time reduces gradually, and the device with larger quantity may have less backoff time than that with smaller quantity when its delay constraint is extremely strict. When the pilot length is short, the effect of delay constraints mentioned above works more obviously.