• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.4
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• pp.632-650
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• 2013

The paper considers a spectrum sharing cognitive radio (CR) network coexisting with a primary network under the average interference power constraint. In particular, the secondary user (SU) is assumed to carry delay-sensitive services and thus shall satisfy a given delay quality-of-service (QoS) constraint. The secondary receiver is also assumed to be equipped with multiple antennas to perform maximal ratio combining (MRC) to enhance SU performance. We investigate the effective capacity of the SU with MRC diversity under aforementioned constraints in Nakagami fading environments. Particularly, we derive the optimal power allocation to achieve the maximum effective capacity of the SU, and further derive the effective capacity in closed-form. In addition, we further obtain the closed-form expressions for the effective capacities under three widely used power and rate adaptive transmission schemes, namely, optimal simultaneous power and rate adaptation (opra), truncated channel inversion with fixed rate (tifr) and channel inversion with fixed rate without truncation (cifr). Numerical results supported by simulations are presented to consolidate our studies. The impacts on the effective capacity of various system parameters such as the number of antennas, the average interference power constraint and the delay QoS constraint are investigated in detail. It is shown that MRC diversity can significantly improve the effective capacity of the SU especially for cifr transmission scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4A
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• pp.402-411
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• 2006

In OFDMA system, multiple users transmit signal through the subcarriers assigned to the user. Capabilities of high data-rate transmission in OFDMA system come from the ability to compensate the ICI (Inter Carrier Interference) using a single-tap equalizer and to implement transmitter and receiver by employing high speed FFT circuitry. Issues of time and frequency synchronization in OFDM system is quite essential to preserve the orthogonality among subcarriers not to produce ICI. In this paper, we Int analyze the preamble used in 802.16 d/e and WiBro system. Then we propose an effective timing synchronization algorithm, which is more accurate than the conventional one in the sense of timing position, and integral frequency offset estimation scheme for the simultaneouse estimation of the fractional and integral frequency offset. Through the simulation utilizing the proposed synchronization algorithm and structure, we show that the performance degradation due to the adjacent channel interference can be mitigated for the than conventional ones.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4C
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• pp.485-493
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• 2004

The system performance of 2-Dimensional wavelength hopping/time spreading optical CDMA systems is found to be limited by the occurrence of the beat noise between the components of the signal and the multiple user interference. This paper shows that the performance is analyzed under the beat noise and no beat noise to blow impact of the beat noise. To overcome this problem, the OHL(Optical Hard-Limiter) is used in the receiver. The performance is calculated for a optical CDMA system employing asymmetric and symmetric prime-hop 2-Dimensional codes, respectively The analysis results show that the performance improved 3.5 times of simultaneous users of before and after inserting OHL in the case of no beat noise. In the case of beat noise the performance improved 1.5 times of simultaneous users of before and after inserting OHL. The performance marked use of symmetric prime-hop code.

• Journal of Digital Contents Society
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• v.5 no.1
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• pp.87-94
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• 2004

In this paper, the digital watermarking algorithm is proposed using CDMA technique for protection of the mobile contents in the mobile environment. The digital watermarking was designed to robust the errors in the mobile environment where pathloss, multipath fading, interference, and noise exist. In case of the multimedia content service in the mobile environment, the construction method of the watermark, the algorithm of insertion and detection are also proposed. The watermark consists of the information of the mobile user. Invisibility and robustness required in watermarking are etimated. It is observed that PSNR of the mobile content inserted the watermark is 90.31 dB, and the signal processing and noise attack are also robust. Especially, because random noise occurs in wireless transmission can overcome, the proposed watermarking algorithm is adequate for protection of the multimedia contents in the mobile environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1A
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• pp.24-33
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• 2007

In this paper, two different dynamic cell coordination strategies for frequency flat and selective fading are proposed for efficient subcarrier allocation in the joint consideration of adaptive modulation and variable frequency reuse in the channel-aware OFDMA downlink multicellular environment. Compared to a conventional OFDMA system without cell coordination, where system throughput may become degraded due to the persistent interference from other cells, the proposed system dynamically allows RNC to apply different reuse factors on each subchannel and scheduling in consideration of channel and interference conditions of individual users so as to increase the system throughput and guarantee QoS of each user. In a frequency flat fading, the dynamic scheme with the proposed scheduling achieves on average three times larger throughput than the conventional dynamic scheme [8]. In a selective fading channel, the proposed schemes showed 2.6 times as large throughput as that of a single reuse factor of one for all subchannels.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.197-199
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• 2016

In this paper, we investigate a market equilibrium in multi-channel sharing cognitive radio networks (CRNs): it is assumed that every subchannel is orthogonally licensed to a single primary user (PU), and can be shared with multiple secondary users (SUs). We model this sharing as a spectrum market where PUs offer SUs their subchannels with limiting the interference from SUs; the SUs purchase the right to transmit over the subchannels while observing the interference limits set by the PUs and their budget constraints. The utility function of SU is defined as least achievable transmission rate, and that of PU is given by the net profit. We define a market equilibrium in the context of extended Fisher model, and show that the equilibrium is yielded by solving an optimization problem, Eisenberg-Gale convex program.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.10
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• pp.904-910
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• 2016

The choice of nulling antenna type to be used for a given specification of user locations usually centers on whether to use a phased array antenna(PAA) or a multiple-beam antenna(MBA) for a satellite payload. This paper considers a MBA to analysis the nulling effect in the Korean peninsula jamming circumstance. First, the nulling performance and characteristics on the region of the earth coverage are confirmed with respect to the case of 7 beams. Then, optimum results are derived and compared to what can be accomplished with a fixed set of beams(the case of 10 and 19 beams are considered) for null steering to reject interference is investigated for a MBA.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.5
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• pp.881-888
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• 2020

In this paper, in order to improve the degraded BER performance of the stronger channel user in non-orthogonal multiple access(: NOMA) with interactive mobile users, we propose the negative correlation bit-to-symbol(: B2S) mapping. First, the closed-form expression for the BER of the negative correlation B2S mapping receiver is derived, and then it is shown that the BER of the negative correlation B2S mapping receiver is improved, compared with those of the ideal perfect successive interference cancellation(: SIC) receiver and positive correlation receiver. Additionally, based on the analytical expression, signal-to-noise(: SNR) gain is calculated, and the superiority of the negative correlation B2S mapping receiver is validated.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.2 s.332
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• pp.17-22
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• 2005

This paper presents our investigation for the effect of symbol timing errors in orthogonal frequency division multiple access (OFDMA) uplink systems. We express the symbol timing errors between users as the symbol timing misalignments with respect to the desired user. Then, we derive an explicit expression of the average effective signal-to-interference-plus-noise ratio. (SINR) as a function of the maximum value of the symbol timing misalignments. Based on the resulting SINR degradation, we evaluate the SINR gain with guard subcarriers in order to mitigate the effect of the symbol timing misalignments.

• ETRI Journal
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• v.39 no.6
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• pp.794-802
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• 2017

In this paper, a wireless powered communication network (WPCN) consisting of a hybrid access point (H-AP) and multiple user equipment (UE), all of which operate in full-duplex (FD), is described. We first propose a transceiver structure that enables FD operation of each UE to simultaneously receive energy in the downlink (DL) and transmit information in the uplink (UL). We then provide an energy usage model in the proposed UE transceiver that accounts for the energy leakage from the transmit chain to the receive chain. It is shown that the throughput of an FD WPCN using the proposed FD UE (FD-WPCN-FD) can be maximized by optimal allocation of the UL transmission time to the UE by solving a convex optimization problem. Simulation results reveal that the use of the proposed FD UE efficiently improves the throughput of a WPCN with a practical self-interference cancellation capability at the H-AP. Compared to the WPCN with FD H-AP and half-duplex (HD) UE, FD-WPCN-FD achieved an 18% throughput gain. In addition, the throughput of FD-WPCN-FD was shown to be 25% greater than that of WPCN in which an H-AP and UE operated in HD.