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3GPP NR Sidelink Transmissions Toward 5G V2X
(2020-01-01)
Lien, Shao-Yu
;
Deng, Der-Jiunn
;
Lin, Chun-Cheng
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Tsai, Hua-Lung
;
Chen, Tao
Featuring direct communications between two user equipments (UEs) without signal relay through a base station, 3GPP sidelink transmissions have manifested their crucial roles in the Long-Term Evolution (LTE) Advanced (LTE-A) for public safety and vehicle-to-everything (V2X) services. With this successful development in LTE-A, the evolution of sidelink transmissions continues in 3GPP New Radio (NR), which renders sidelink an inevitable component as well as downlink and uplink. Targeting at offering low latency, high reliability and high throughout V2X services for advanced driving use cases, a number of new sidelink functions not provided in the LTE-A are supported in NR, including the feedback channel, grant-free access, enhanced channel sensing procedure, and new control channel design. To fully comprehend these new functions, this paper therefore provides essential knowledge of 3GPP NR sidelink transmissions, including the physical layer structure, resource allocation mechanisms, resource sensing and selection procedures, synchronization, and quality-of-service (QoS) management. Furthermore, this paper also provides performance evaluation to assess the gains brought from the new control channel design. As NR sidelink transmissions have been regarded as a foundation to provide advanced services other than V2X in future releases (e.g., advanced relay), potential enhancements are also discussed to serve the urgent demand in corresponding normative works.
Performances of M-ACO-OFDM, DCO-OFDM and M-GLIM OFDM in Visible Light Communication Systems
(2019-01-01)
Assaidah
;
Chow, C. W.
;
交大名義發表
;
光電工程學系
;
National Chiao Tung University
Orthogonal frequency division multiplexing (OFDM) is a promising modulation used in bandwith limited system due to its improved spectral efficiency. In this work, we propose a modified asymmetrically clipped optical OFDM (M-ACO-OFDM) and modified generalised light emitting diode index modulation OFDM (M-GLIM-OFDM) in order to gain the same bandwith efficiency with conventional direct-current biased optical OFDM (DCO-OFDM). Their performances are compared for a 500 MHz bandwith limited system. Simulation results show that although there are sacrifice of 3dB receiver sensitivity of the proposed M-ACO-OFDM and M-GLIM-OFDM when compared with the original OFDM signal, there is about 8 dB improvement in peak-to-average power ratio (PAPR) reduction.
Artificial Neural-Network-Based Pre-Distortion for High Loss-Budget 60-km Long-Reach Passive Optical Network
(2020-01-01)
Nguyen, Hong-Minh
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Huang, Szu-Chi
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Wei, Chia-Chien
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Chuang, Chun-Yen
;
Chen, Jason Jyehong
High launch optical power can compensate for severe fading and power loss in long-reach passive optical networks (LR-PONs); however, it also aggravates nonlinear degradation, which necessitates the use of complex DSP-based nonlinear compensation techniques at optical network users (ONUs). DSP-related techniques also necessitate the use of additional hardware/software components by the receiver, which can greatly increase implementation costs and energy consumption, particularly when dealing with large-scale ONU deployment. This is the first study to propose artificial neural network (ANN)-based pre-distortion to eliminate the need for complex DSP at ONUs in a high-launch-power LR-PON, thereby permitting the use of a simplified architecture at the user end. In the first phase of the study, the proposed ANN-based pre-distortion scheme was implemented in a single-channel IMDD OFDM LR-PON, which achieved a data rate of >55 Gbps over 60-km transmission with a loss budget of 30 dB without the need for optical inline- or pre-amplification. In the second phase of experiments, the same scheme was applied to a 4-channel wavelength division multiplexing (WDM) OFDM LR-PON. Here, the proposed scheme achieved data rates of >200 Gbps using launch power of 18 dBm per lane, resulting in a loss budget of roughly 29 dB over 60-km single mode fiber transmission.
Reducing the Impact of Nonlinear Distortion in DML-Based OFDM Transmission by Frequency Gap
(2018-12-01)
Hong-Minh Nguyen
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Wei, Chia-Chien
;
Chuang, Chun-Yen
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Chen, Jyehong
;
Taga, Hidenori
This paper demonstrates a novel approach to reducing in-band nonlinear distortion in DML-based OFDM transmission by introducing a frequency gap between the optical carrier and signal band. This scheme greatly increases tolerance to nonlinear distortion caused by the interaction between laser chirp and chromatic dispersion. Tuning the frequency gap between 2 to 5 GHz (in accordance with the transmission distance) makes it possible to mitigate a considerable proportion of dispersion-induced nonlinear distortion. Experiment results revealed that the proposed scheme can increase the achievable data rate by up to 136%, compared to conventional OFDM over 300 km of dispersion-uncompensated standard single mode fiber. Following transmission over more than 200 km, the proposed modulation scheme also outperforms conventional OFDM incorporating with a Volterra equalizer by up to 24%. We also conducted optimization of DML bias current and driving voltage. Our results show that operating at high bias and driving voltage can greatly improve data rates following the mitigation of distortion via gapped OFDM.
58.74-Gb/s 2 x 2 MIMO 60-GHz Optical/Wireless System With Simple Power-Detector Down-Conversion
(2019-06-01)
Chen, Wen-Huang
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Chen, Chao-Wei
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Lin, Chun-Ting
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Wei, Chia-Chien
;
Chi, Sien
We demonstrate a 58.74-Gb/s V-band orthogonal frequency-division multiplexing (OFDM) radio-over-fiber (RoF) system employing the 2 x 2 multiple-input-multiple-output (MIMO) technology and power detector for down-conversion for the first time. Additional radio frequency (RF) tone is generated and transmitted from central station to replace the local oscillator at wireless receiver for power detector down-conversion. To enhance spectrum efficiency, the gap between OFDM signal and RF tone is not needed. However, the down-converted signal will suffer signal-to-signal beating interference (SSBI). In this letter, we propose and successfully employ the 2 x 2 MIMO SSBI mitigation schemes to mitigate SSBI, resulting in 45% capacity improvement.
Reliable OFDM Receiver With Ultra-Low Resolution ADC
(2019-05-01)
Wang, Hanging
;
Shih, Wan-Ting
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Wen, Chao-Kai
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Jin, Shi
;
電控工程研究所
The use of low-resolution analog-to-digital converters can significantly reduce power consumption and hardware cost. However, their resulting severe nonlinear distortion makes achieving reliable data transmission challenging. For orthogonal frequency division multiplexing (OFDM) transmission, the orthogonality among subcarriers is destroyed. This invalidates conventional OFDM receivers relying heavily on this orthogonality. In this paper, we move on to quantized OFDM (Q-OFDM) prototyping implementation based on our previous achievement in optimal Q-OFDM detection. First, we propose a novel Q-OFDM channel estimator by extending the generalized Turbo (GTurbo) framework formerly applied for optimal detection. Specifically, we integrate a type of robust linear OFDM channel estimator into the original GTurbo framework, and derive its corresponding extrinsic information to guarantee its convergence. We also propose feasible schemes for automatic gain control, noise power estimation, and synchronization. Combined with the proposed inference algorithms, we develop an efficient Q-OFDM receiver architecture. Furthermore, we construct a proof-of-concept prototyping system and conduct over-the-air (OTA) experiments to examine its feasibility and reliability. This is the first work that focuses on both algorithm design and system implementation in the field of low-resolution quantization communication. The results of the numerical simulation and OTA experiment demonstrate that reliable data transmission can be achieved.
APD-based Delay-Division-Multiplexing OFDM-PONs
(2018-01-01)
Hsu, Jhih-Hao
;
Yu, Min
;
Chia-Chien
;
Lin, Chi-Hsiang
;
Lin, Chun-Ting
Based on pre-allocated relative sampling delays among optical network users (ONUs) in an orthogonal frequency division multiplexing (OFDM) passive optical network (PON), the delay-division-multiplexing (DDM) technique employs signal pre-processing to enable demand data to be received by sub-Nyquist analog-to-digital sampling. This work employed an avalanche photodiode (APD) in a DDM-OFDM-PON to achieve higher loss budget, compared to a p-i-n photodiode (PIN). To successfully enable the pre-processing, however, the knowledge of channel response is required; thus, it is critical to estimate complete channel response in DDM-OFDM systems under the constraint of sub-Nyquist sampling. To avoid spectral overlapping in channel estimation, the subcarriers of training symbols in different frequency zones are allocated to different time slots. Unfortunately, this scheme may sustain inaccurate channel estimation due to different degrees of APD saturation for training subcarriers at different frequency zones, leading to significant penalty in performance. Thus, careful control of electrical driving power and optical received power for the training symbols will be important to reduce the impact of saturation on channel estimation, thereby improving transmission performance. We experimentally examined the impact of the accuracy of channel estimation in a 25-Gbps APD-based OFDM-PON. Compared to a PIN, we successfully demonstrated the DDM scheme based on an APD and 1/32 of Nyquist rate with 5-dB improvement in sensitivity after 25-km fiber transmission.
Joint Sensing Duration Adaptation, User Matching, and Power Allocation for Cognitive OFDM-NOMA Systems
(2018-02-01)
Xu, Wenjun
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Li, Xue
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Lee, Chia-Han
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Pan, Miao
;
Feng, Zhiyong
In this paper, the non-orthogonal multiple access (NOMA) technology is integrated into cognitive orthogonal frequency-division multiplexing (OFDM) systems, called cognitive OFDM-NOMA, to boost the system capacity. First, a capacity maximization problem is considered in half-duplex cognitive OFDM-NOMA systems with two accessible users on each subcarrier. Due to the intractability of the considered problem, we decompose it into three subproblems, i.e., the optimization of, respectively, sensing duration, user scheduling, and power allocation. By investigating and exploiting the characteristics of each subproblem, the optimal sensing duration adaptation, a matching-theory-based user scheduling, and the optimal power allocation are proposed correspondingly. An alternate iteration framework is further proposed to jointly optimize these three subproblems, with its convergence proved. Moreover, based on the non-cooperative game theory, a generalized power allocation algorithm is proposed and then used in the framework to accommodate half-duplex cognitive OFDM-NOMA systems with multiple users on each subcarrier. Finally, the proposed framework is extended to solve the capacity maximization problem in full-duplex cognitive OFDM-NOMA systems. Simulation results validate the superior performance of the proposed algorithms. For example, for the case of two accessible users, the proposed framework approaches the optimal solution with less than 1% capacity loss and 120 times lower complexity compared with exhaustive search.
A MMSE Joint Feedback Feed-forward Equalizer for FBMC-OQAM Baseband Receiver in the 60 GHz Band
(2017-12-01)
Liu, Chun-Yi
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Leong, Edmund Wen Jen
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Wu, Chang-Ting
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Sie, Meng-Siou
;
Lopez, Henry
In this paper, a minimum mean square error (MMSE) joint feedback feed-forward equalizer (MJFFE) is proposed to deterministically suppress the inter-symbol interference and inter-carrier interference that arose from the filter bank multi-carrier in a long multipath channel of the 60-GHz indoor wireless transmission. The decision device is discarded in the decision feedback loop to reduce error propagation while at the same time applying the MMSE criterion to prevent over compensation influenced by additive white Gaussian noise. As a result, in an non-line-of-sight (NLOS) channel with 7.65-ns rms delay spread, a 3-tap MJFFE provides 3-dB improvement at the bit error rate (BER) 10(-2) crossing and improve error floor effect at the BER 10(-3) crossing, as compared with the 1-tap zero-forcing equalizer. Furthermore, the proposed equalizer coefficients calculation based on linear convolution for the MJFFE is also presented. The hardware complexity achieves 50% reduction by using several methods including multiplexing, memory sharing, and computation element sharing.
Joint AoA and Channel Estimation for SIMO- OFDM Systems: A Compressive-Sensing Approach
(2016-05)
Chen, Chih-Yu
;
Wu, Wen-Rong
;
Gau, Chi-Shiang
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資訊工程學系
;
電機學院
Millimeter-wave (mmWave) transmission has been considered in future fifth generation (5G) communication systems. Since the pathloss in mmWave is severe, beamforming with antenna arrays, an enabling technology in the 5G era, will become a must. To conduct receive beamforming, however, we need to know the information about the angle-of-arrival (AoA). In this paper, we consider joint AoA and channel estimation for single-input-multiple-output (SIMO) OFDM systems. As known, wireless channels are sparse, and this is particularly true for mmWave environments. Conventional compressive-sensing (CS) based channel estimation methods only consider single-input-single-output systems. We propose new matching-pursuit-based CS methods for channel estimation in SIMO-OFDM systems, using frequency-domain pilots. With the estimated channels, AoA\'s are then estimated by the maximum-likelihood method. Since a hidden parameter is involved in the problem, an expectation-maximization (EM) algorithm is then employed. The Cramer-Rao lower bound (CRLB) is also derived for the AoA estimation. Simulation results show that the proposed channel estimation can significantly outperform existing methods while the proposed AoA estimation attains the CRLB.

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