• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.5
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• pp.443-450
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• 2013

We consider user pairing and resource allocation for the uplink of cellular systems employing virtual multiple input multiple output (MIMO). As a multiple access scheme, discrete Fourier transform spread orthogonal frequency division multiple access (DFTS-OFDMA) is adopted for more flexible resource allocation than single carrier (SC)-OFDMA adopted in the Long Term Evolution (LTE) system. We formulate the optimization problems of user pairing and resource allocation to maximize the throughput of the DFTS-OFDMA system under different constraints. The DFTS-OFDMA allowing non-contiguous subcarrier allocation and redundant user assignment provides a better throughput than the SC-FDMA at lower complexity in finding the optimal solution but at the cost of the increased control information indicating the allocated resources.

• ETRI Journal
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• v.40 no.4
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• pp.537-545
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• 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
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• v.10 no.10
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• pp.94-101
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• 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.

• Proceedings of the Korean Society of Computer Information Conference
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• 2011.06a
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• pp.63-66
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• 2011

본 논문에서는 현재 3GPP에서 진행되고 있는 차세대 이동통신 기술 표준, 즉 LTE 시스템의 하향링크 전송방식의 수신성능을 향상시키기 위해 기지국(BS)과 단말(MS) 사이에 릴레이(RS) 설치를 제안하고, BS의 위치와 설치된 RS의 거리를 각각 500m, 1000m로 하고 RS의 전송방식을 OFDMA와 SC-FDMA를 선택함으로써 수신성능을 높이기 위한 연구를 수행하였다. 연구결과 RS의 위치가 BS와 가까울수록 RS에서는 SC-FDMA를 사용하는 것이 좋게 나왔고, 반대로 BS와 RS의 거리가 멀어질수록 RS에서는 OFDMA를 사용하는 것의 성능이 좋은 것으로 나왔다. 또한 BS와 MS 거리의 중심지역에서는 그 상황에 맞는 전송방식을 사용함으로써 시스템의 수신성능을 향상시킬 수 있었다.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.6
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• pp.23-28
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• 2009

In this paper, we proposed and analyzed the performance of the adaptive switching equalization for SC-FDMA system. It is well known that SC-FDMA system have a fairly similar structure to OFDMA system. Furthermore, SC-FDMA system has great advantage of low PAPR compare to OFDM system. However, this system often suffers from wireless channel characteristics such as multipath fading and increased channel impulse response and so on. To reduce this channel influence, it strongly requires efficient adaptive equalization. Therefore, the proposed system operated upon two modes namely, ZF mode for slow speed and MMSE mode for high speed. From the simulation results, we can confirm that the proposed scheme has more efficient performance from the system complexity point of view. So we can expect that the proposed system will be applied design of 3GPP LTE uplink.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.5
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• pp.258-270
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• 2014

In this paper, we investigate channel capacity of two kinds of uplink OFDMA (Orthogonal Frequency Division Multiple Access) schemes, i.e. ZCZ (Zero Correlation Zone) code time-spread OFDMA and sparse SC-FDMA (Single Carrier Frequency Division Mmultiple Access) robust to access timing offset (TO) among multiple users. In order to reflect the practical condition, we consider not only access TO among multiple users but also peak to average power ratio (PAPR) which is one of hot issues of uplink OFDMA. In the case with access TO among multiple users, the amplified signal of users by power control might affect a severe interference to signals of other users. Meanwhile, amplified signal by considering distance between user and base station might be distorted due to the limit of amplifier and thus the performance might degrade. In order to achieve the maximum channel capacity, we investigate the combinations of transmit power so called ASF (adaptive scaling factor) by numerical simulations. We check that the channel capacity of the case with ASF increases compared to the case with considering only distance i.e. ASF=1. From the simulation results, In the case of high signal to noise ratio (SNR), ZCZ code time-spread OFDMA achieves higher channel capacity compared to sparse block SC-FDMA. On the other hand, in the case of low SNR, the sparse block SC-FDMA achieves better performance compared to ZCZ time-spread OFDMA.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.7
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• pp.2998-3017
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• 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 the Institute of Electronics Engineers of Korea TC
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• v.49 no.6
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• pp.71-76
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• 2012

Recently, the huge growth of mobile data traffic has driven the earlier commercialization of LTE network and the evolution of LTE-Adv has been accelerated because of this trend of mobile traffic surges. Thus it has enabled the global connectivity and roaming capability due to continual standardization activities. The 3rd generation mobile communication system has been improved through incorporating technologies of HSDPA, MBMS and HSUPA etc continuously. Also, OFDMA/SC-FDMA-based LTE standardization has been under way. In this paper, the architectures of LTE network and protocol have been introduced and their inherent operation mechanisms have also been explored in order to give some insights about the LTE/LTE-Adv networks while their architectures are considered as most prominent candidate for worldwide standard by ITU-R and mobile operators for international communication networks.

• Proceedings of the Korea Information Processing Society Conference
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• 2010.11a
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• pp.988-991
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• 2010

본 논문에서는 현재 3GPP에서 진행되고 있는 차세대 이동통신 기술 표준, 즉 LTE 시스템의 하향링크 전송방식의 수신성능을 향상시키기 위해 기지국(BS)과 단말(MS) 사이에 릴레이(RS) 설치를 제안하고, BS의 위치와 설치된 RS의 거리를 각각 500m, 1000m로 하고 RS의 전송방식을 OFDMA와 SC-FDMA를 선택함으로써 수신성능을 높이기 위한 연구를 수행 하였다. 연구결과 RS의 위치가 BS와 가까울수록 RS에서는 SC-FDMA를 사용하는 것이 좋게 나왔고, 반대로 BS와 RS의 거리가 멀어질수록 RS에서는 OFDMA를 사용하는 것의 성능이 좋은 것으로 나왔다. 또한 BS와 MS 거리의 중심지역에서는 그 상황에 맞는 전송방식을 사용함으로써 시스템의 수신성능을 향상시킬 수 있었다. 본 논문에서 시뮬레이션 한 결과를 토대로 실제 LTE 시스템에 적용하였을 때, 셀 커버지지를 확장 시켜 시스템 전체의 수신성능을 향상 시킬 수 있을 것으로 보였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.5A
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• pp.417-425
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• 2007

While the cyclic prefix lengths of downlink OFDMA(Orthogonal Frequency Division Multiple Access) systems are determined based on the maximum delay spreads encountered in cellular environments, the guard interval of uplink OFDMA systems should consider the timing offsets of uplink signals as well as the delay spread lengths. Especially in the cases of initial accesses, handovers, and considerable time elapsed without data transmissions between base and mobile stations in a large cell, uplink timing offsets can be large and a very long guard interval length may be required. In order to keep the small size of the cyclic prefix in uplink OFDMA systems, the systems require a method of extending the guard intervals for users with large timing offsets without affecting the cyclic prefix length of the system. This paper proposes a method extending the guard intervals of individual users in uplink OFDMA systems.