• ETRI Journal
• /
• v.40 no.4
• /
• pp.537-545
• /
• 2018

In this paper, we present a comprehensive analytical study of the symbol error rate (SER) of single-carrier frequency-division multiple access (SC-FDMA) with zero-forcing frequency domain equalization (ZF-FDE) over a Rayleigh fading channel. SC-FDMA is considered as a potential waveform candidate for fifth-generation (5G) radio access networks (RANs). First, the $N_C$ fold convolution of the noise distribution of an orthogonal frequency-division multiplexing (OFDM) system is computed for each value of the signal-to-noise ratio (SNR) in order to determine the noise distribution of the SC-FDMA system. $N_C$ is the number of subcarriers assigned to a user or the size of the discrete Fourier transform (DFT) precoding. Here, we present a simple alternative method of calculating the SER by simplifying the $N_C$ fold convolution using time and amplitude scaling properties. The effects of the $N_C$ fold convolution and SNR over the computation of the SER of the SC-FDMA system has been separated out. As a result, the proposed approach only requires the computation of the $N_C$ fold convolution once, and it is used for different values of SNR to calculate the SER of SC-FDMA systems.

• The Journal of the Korea Contents Association
• /
• v.10 no.10
• /
• pp.94-101
• /
• 2010

In this paper, a WLED communication system with SC-FDMA technique is proposed. OFDM is a promising technique to realize high-speed WLED communication system. However, because of the PAPR, the system performance can be significantly compromised by non-linear distortions in the transmission chain. Furthermore, the overload current due to peak signal power lead the WLED equipment over bright which is harmful to equipment life and human‘s eye. The novel WLED communication system proposed in this paper solved these problems by using SC-FDMA technique which has an inherent low PAPR property. The severity of PAPR performances expressed by CCDF curve and the BER performances under different modulation schemes are analyzed in this paper.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.12 no.7
• /
• pp.2998-3017
• /
• 2018

Massive (large-scale) MIMO (multiple-input multiple-output) is one of the key technologies in next-generation wireless communication systems. This paper proposes a high-performance low-complexity turbo receiver for SC-FDMA (single-carrier frequency-division multiple access) based MMIMO (massive MIMO) systems. Because SC-FDMA technology has the desirable characteristics of OFDMA (orthogonal frequency division multiple access) and the low PAPR (peak-to-average power ratio) of SC transmission schemes, the 3GPP LTE (long-term evolution) has adopted it as the uplink transmission to meet the demand high data rate and low error rate performance. The complexity of computing will be increased greatly in base station with massive MIMO (MMIMO) system. In this paper, a low-complexity adaptive turbo equalization receiver based on normalized minimal symbol-error-rate for MMIMO SC-FDMA system is proposed. The proposed receiver is with low complexity than that of the conventional turbo MMSE (minimum mean square error) equalizer and is also with better bit error rate (BER) performance than that of the conventional adaptive turbo MMSE equalizer. Simulation results confirm the effectiveness of the proposed scheme.

• Journal of Institute of Control, Robotics and Systems
• /
• v.12 no.10
• /
• pp.989-995
• /
• 2006

This paper shows that the OFDM(Orthogonal Frequency Division Multiplex) system is robust to multipath than CDMA (Code Division Multiple Access) system and it has a strong possibility to be utilized as a supplementing wireless location system for the forthcoming portable internet network. The OFDM system based on IEEE 802.16e is a wireless TDD (Time Division Duplex) OFDMA (Orthogonal Frequency Division Multiple Access) system providing portable internet services in 2.3 GHz frequency band and is scheduled in service in Korea starting in 2006. In this paper, multipath error is calculated using a two-ray model and compared with that of a CDMA system which is following IS-95. The OFDM system shows a maximum multipath error of 3 m while a CDMA system shows a maximum multipath error of 61 m. For this simulation, an early-late technique is used. This technique is usually used to match synchronization of signal in DLL(Delay Lock Loop).

• Journal of Internet Computing and Services
• /
• v.9 no.4
• /
• pp.1-10
• /
• 2008

In this paper, a packet scheduling algorithm, called the modified PLFS, is proposed for real-time traffic in IEEE 802.22 WRAN systems. The modified PLFS(Packet Loss Fair Scheduling) algorithm utilizes not only the delay of the Head of Line(HOL) packets in buffer of each user but also the amount of expected loss packets in the next-next frame when a service will not be given in the next frame. The performances of the modified PLFS are compared with those of PLFS and M-LWDF in terms of the average packet loss rate and throughput. The simulation results show that the proposed scheduling algorithm performs much better than the PLFS and M-LWDF algorithms.

• ETRI Journal
• /
• v.37 no.3
• /
• pp.471-479
• /
• 2015

Traditional designs of cognitive radio (CR) focus on maximizing system throughput. In this paper, we study the joint overlay and underlay power allocation problem for orthogonal frequency-division multiple access-based CR. Instead of maximizing system throughput, we aim to maximize system energy efficiency (EE), measured by a "bit per Joule" metric, while maintaining the minimal rate requirement of a given CR system, under the total power constraint of a secondary user and interference constraints of primary users. The formulated energy-efficient power allocation (EEPA) problem is nonconvex; to make it solvable, we first transform the original problem into a convex optimization problem via fractional programming, and then the Lagrange dual decomposition method is used to solve the equivalent convex optimization problem. Finally, an optimal EEPA allocation scheme is proposed. Numerical results show that the proposed method can achieve better EE performance.

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

• Information and Communications Magazine
• /
• v.24 no.3
• /
• pp.97-111
• /
• 2007

전 세계적으로 2세대 및 3세대 무선이동통신 서비스의 성공적인 상용화에 힘입어 현재 3.5세대 이동통신시스템의 상용화 단계까지 이르렀다. 한걸음 더 나아가 3GPP/3GPP2에서는 MT-2000 고도화시스템에 대한 표준화 작업이 활발히 진행되고 있다. 각 표준화 기구에서 제시한 향후 표준화 일정 및 현재의 기술개발 추세로 미루어 볼 때 수년 내에 무선통신시스템의 새로운 장이 펼쳐질 것으로 기대된다. 특히 3GPP에서는 기존 3G-WCDMA 무선접속기술 대신에 하향 OFDMA 및 상향 SC-FDMA 무선접속기술을 이용하는 E-UTRA/UTRAN 시스템의 표준화 작업을 진행하고 있다. 특히 이 표준화 작업에 전 세계 운영회사, 제조사, 표준화 기구 및 관련종사자들의 관심이 어느 때보다 높기 때문에 표준 기술의 논의 및 검증이 더 활발히 진행되고 있으며 이는 표준기술 완성도를 높여 향후 발간될 LTE 시스템의 경쟁력 제고에 크게 이바지 할 것으로 예상된다. 현재 LTE 표준화 작업은 3단계로 나누어 진행되어 왔으며 2006년 3월 현재 마지막 세 번째 단계를 막 시작하는 시기에 있다. 이에 즈음하여 본기고문에서는 LTE 표준기술의 이해를 돕고 및 향후 표준화에 대한 향방을 가늠하는데 일부 도움을 제공하기 위해 현재까지 진행된 물리계층 표준기술 및 향후 해결해야할 문제들에 대해서 개념위주로 기술하였다. 기고문은 LTE 시스템 요구사항 및 향후 일정을 서론부에 제시하고 이어 E-UTRAN 프로토콜 구조, 상 하향 무선접속 기술, 물리계층 기술표준 현황, 그리고 마지막으로 맺음말의 순으로 구성되어 있다.

• KIPS Transactions on Computer and Communication Systems
• /
• v.5 no.5
• /
• pp.103-108
• /
• 2016

In this paper, we propose a resource allocation scheme that guarantees transmission rate for each mobile stations by mitigating interference between a base station-to-mobile station link and a relay station-to-mobile station link. Specifically, we dynamically adjust the boundary between access zone and relay zone using signal to interference plus noise ratio. Moreover, we cluster the mobile stations under sever interference and manage the channel quality of these mobile stations by allocating additional radio resource. Our simulation results show that the proposed scheme can improve the efficiency of radio resources and ensure fairness among mobile stations.

• Journal of Internet Computing and Services
• /
• v.22 no.5
• /
• pp.1-8
• /
• 2021

Small-cells in heterogeneous networks are one of the important technologies to increase the coverage and capacity in 5G cellular networks. However, due to the randomly arranged small-cells, co-tier and cross-tier interference increase, deteriorating the system performance of the network. In order to manage the interference, some channel management methods use fractional frequency reuse(FFR) that divides the cell coverage into the inner region(IR) and outer region(OR) based on the distance from the macro base station(MBS). However, since it is impossible to properly measure the distance in the method with FFR, we propose a new interference aware FFR(IA-FFR) method to enhance the system performance. That is, the proposed IA-FFR method divides the MUEs and SBSs into the IR and OR groups based on the signal to interference plus noise ratio(SINR) of macro user equipments(MUEs) and received signals strength of small-cell base stations(SBSs) from the MBS, respectively, and then dynamically assigns subchannels to MUEs and small-cell user equipments. As a result, the proposed IA-FFR method outperforms other methods in terms of the system capacity and outage probability.