| 1. |
- Lin, Jiaqian, et al.
(author)
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A study on performance improvement of IMDD-UFMC with modified K-means non-uniform quantization
- 2020
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In: Optics Communications. - : Elsevier BV. - 0030-4018. ; 476
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Journal article (peer-reviewed)abstract
- In this paper, a modified K-means-based low complexity the nonuniform quantization scheme is proposed in the intensity-modulated direct detection universal filter multicarrier (IMDD-UFMC) system to improve system performance. Owing to the good cluster property of our scheme, the optimal quantization levels can be directly figured out, and the complexity induced by the probability density function (PDF) estimation can be reduced. By utilizing this scheme, the low quantization noise and peak-to-average power ratio (PAPR) can be achieved by assigning finer quantization steps for the low-level area signals. And, to manifest this scheme, the IMDD-UFMC-based numerical simulation and experimental platform with 10-Gb/s 16-QAM signal over 20 km fiber are constructed. The corresponding results show that our method always achieves the better performance, measuring in the form with the error-vector-magnitudes and bit error rate, compared to the common uniform quantization scheme even with the low-bit resolution case.
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| 2. |
- Pang, Xiaodan, Dr., et al.
(author)
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200 Gbps & x002F;Lane IM & x002F;DD Technologies for Short Reach Optical Interconnects
- 2020
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In: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 38:2, s. 492-503
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Journal article (peer-reviewed)abstract
- Client-side optics are facing an ever-increasing upgrading pace, driven by upcoming 5G related services and datacenter applications. The demand for a single lane data rate is soon approaching 200 Gbps. To meet such high-speed requirement, all segments of traditional intensity modulation direct detection (IM & x002F;DD) technologies are being challenged. The characteristics of electrical and optoelectronic components and the performance of modulation, coding, and digital signal processing (DSP) techniques are being stretched to their limits. In this context, we witnessed technological breakthroughs in several aspects, including development of broadband devices, novel modulation formats and coding, and high-performance DSP algorithms for the past few years. A great momentum has been accumulated to overcome the aforementioned challenges. In this article, we focus on IM & x002F;DD transmissions, and provide an overview of recent research and development efforts on key enabling technologies for 200 Gbps per lane and beyond. Our recent demonstrations of 200 Gbps short-reach transmissions with 4-level pulse amplitude modulation (PAM) and discrete multitone signals are also presented as examples to show the system requirements in terms of device characteristics and DSP performance. Apart from digital coherent technologies and advanced direct detection systems, such as Stokes-vector and Kramers-Kronig schemes, we expect high-speed IM & x002F;DD systems will remain advantageous in terms of system cost, power consumption, and footprint for short reach applications in the short- to mid- term perspective.
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| 3. |
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| 4. |
- Pang, Xiaodan, Dr., et al.
(author)
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Key technologies to enable terabit-scale digital radio-over-fiber systems
- 2019
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 9781510625327
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Conference paper (peer-reviewed)abstract
- With the approach of the 5G era, stringent requirements are imposed on the data transport solutions, including both of the supported transmission reach and the capacity. Radio-over-fiber technologies are considered to be promising candidates to cope with both aspects, owing to the low-loss and broad-bandwidth nature of the optical fibers. Meanwhile with such optical transport solutions, signals can be collected from the distributed remote radio sites and processed in a centralized manner. In this report, we target on the digital radio-over-fiber systems, and discuss about several key technologies, focusing on the aspects of coding and transmission, which could potentially enable terabit-scale data transport.
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| 5. |
- Xue, Lei, 1992, et al.
(author)
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Optics-simplified DSP for 50 Gb/s PON downstream transmission using 10 Gb/s optical devices
- 2020
-
In: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 38:3, s. 583-589
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Journal article (peer-reviewed)abstract
- Directly-modulated laser (DML) is widely employed in intensity modulation and direct detection (IMDD) system due to its low cost and high output power. However, the corresponding frequency chirp is regarded as one of the main disadvantages for its application in passive optical networks (PONs). In this paper, we theoretically analyze the frequency response evolution of DML based system under different chirp and dispersion conditions, proving that the system bandwidth can be improved by interactions between negative dispersion and DML chirp. Based on this concept, we experimentally demonstrated downstream 50 Gb/s PAM4 signal transmission over 20 km single-mode fiber (SMF) access based on the 10 Gb/s DML operating at 1310 nm and avalanche photodiode (APD). A dispersion-shifted fiber (DSF) providing -150 ps/nm dispersion at 1310 nm in the optical line terminal (OLT) is used to pre-equalize the frequency response of bandwidth-limited directly modulated signals in the optical domain. Thanks to our proposed dispersion-supported equalization (DSE) technique, the system bandwidth can be improved by 5 GHz. Feed-forward equalization (FFE), decision feedback equalization (DFE) and Volterra filter are employed to evaluate the signal performance improvement, respectively. By evaluating the receiver sensitivity, the DSE combined with FFE scheme shows 2 dB improvement than the complex Volterra algorithm, indicating its potential to reduce the complexity of digital signal processing (DSP) and therefore a lower cost and power consumption in PON.
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| 6. |
- Zhang, Lu, et al.
(author)
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Digital mobile fronthaul employing differential pulse code modulation with suppressed quantization noise
- 2017
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In: Optics Express. - : Optical Society of America. - 1094-4087. ; 25:25, s. 31921-31936
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Journal article (peer-reviewed)abstract
- A differential pulse code modulation (DPCM) based digital mobile fronthaul architecture is proposed and experimentally demonstrated. By using a linear predictor in the DPCM encoding process, the quantization noise can be effectively suppressed and a prediction gain of 7~8 dB can be obtained. Experimental validation is carried out with a 20 km 15-Gbaud/λ 4-level pulse amplitude modulation (PAM4) intensity modulation and direct detection system. The results verify the feasibility of supporting 163, 122, 98, 81 20-MHz 4, 16, 64, 256 QAM based antenna-carrier (AxC) containers with only 3, 4, 5, 6 quantization bits at a sampling rate of 30.72MSa/s in LTE-A environment. Further increasing the number of quantization bits to 8 and 9, 1024 quadrature amplitude modulation (1024 QAM) and 4096 QAM transmission can be realized with error vector magnitude (EVM) lower than 1% and 0.5%, respectively. The supported number of AxCs in the proposed DPCM-based fronthaul is increased and the EVM is greatly reduced compared to the common public radio interface (CPRI) based fronthaul that uses pulse code modulation. Besides, the DPCM-based fronthaul is also experimentally demonstrated to support universal filtered multicarrier signal that is one candidate waveform for the 5th generation mobile systems.
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| 7. |
- Zhang, Lu, et al.
(author)
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Digital Radio-Over-Multicore-Fiber System with Self-Homodyne Coherent Detection and Entropy Coding for Mobile Fronthaul
- 2018
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In: European Conference on Optical Communication, ECOC. - : Institute of Electrical and Electronics Engineers (IEEE).
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Conference paper (peer-reviewed)abstract
- We experimentally demonstrate a 28-Gbaud 16-QAM self-homodyne digital radio-over-33.6km-7-core-fiber system with entropy coding for mobile fronthaul, achieving error-free carrier aggregation of 330 100-MHz 4096-QAM 5G-new-radio channels and 921 100-MHz QPSK 5G-new-radio channels with CPRI-equivalent data rate up to 3.73-Tbit/s.
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| 8. |
- Zhang, Lu, et al.
(author)
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Fixed and Mobile Convergence with Stacked Modulation
- 2018
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In: 22ND INTERNATIONAL CONFERENCE ON OPTICAL NETWORK DESIGN AND MODELING (ONDM 2018). - : IEEE. ; , s. 36-40
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Conference paper (peer-reviewed)abstract
- We propose a stacked modulation mechanism to realize the transmission convergence of fixed broadband and wireless access networks. As an integrated solution, the direct current biased analog signal for wireless data is multiplied by the digital optical signal carrying fixed broadband service, where the low-speed analog signal becomes an envelope of the high-speed digital signal. At the receiver, the analog signal is firstly recovered with the image edge detection algorithm, after which the digital signal is recovered with the least-square algorithm. This scheme can realize fixed and mobile convergence with a single wavelength, which reduces the access network cost in terms of number of transceivers. Besides, the link capacity and spectrum efficiency are also improved. Moreover, this method is compatible with the existing access networks since the transceivers can be adopted to the scenario by turning off the unused modules. Simulation results show that in case of intensity modulation direct detection system sensitivity, penalty of only 1 similar to 2 dB can be obtained for the 10Gbps/lambda passive optical network when broadband access services are favored. Meanwhile, the wireless service needs more power than the broadband service to achieve the QoT requirements, and it has a higher penalty (similar to 5 dB) compared with broadband access services.
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| 9. |
- Zhang, Lu, et al.
(author)
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Nonlinearity-aware 200 Gbit/s DMT transmission for C-band short-reach optical interconnects with a single packaged electro-absorption modulated laser
- 2018
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In: Optics Letters. - : OPTICAL SOC AMER. - 0146-9592 .- 1539-4794. ; 43:2, s. 182-185
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Journal article (peer-reviewed)abstract
- We experimentally demonstrate the transmission of a 200 Gbit/s discrete multitone (DMT) at the soft forward error correction limit in an intensity-modulation direct-detection system with a single C-band packaged distributed feedback laser and traveling-wave electro absorption modulator (DFB-TWEAM), digital-to-analog converter and photodiode. The bit-power loaded DMT signal is transmitted over 1.6 km standard single-mode fiber with a net rate of 166.7 Gbit/s, achieving an effective electrical spectrum efficiency of 4.93 bit/s/Hz. Meanwhile, net rates of 174.2 Gbit/s and 179.5 Gbit/s are also demonstrated over 0.8 km SSMF and in an optical back-to-back case, respectively. The feature of the packaged DFB-TWEAM is presented. The nonlinearity-aware digital signal processing algorithm for channel equalization is mathematically described, which improves the signal-to-noise ratio up to 3.5 dB.
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| 10. |
- Zhang, Lu, et al.
(author)
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Spectrally efficient digitized radio-over-fiber system with k-means clustering-based multidimensional quantization
- 2018
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In: Optics Letters. - : Optical Society of America. - 0146-9592 .- 1539-4794. ; 43:7, s. 1546-1549
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Journal article (peer-reviewed)abstract
- We propose a spectrally efficient digitized radio-over-fiber (D-RoF) system by grouping highly correlated neighboring samples of the analog signals into multidimensional vectors, where the k-means clustering algorithm is adopted for adaptive quantization. A 30 Gbit/s D-RoF system is experimentally demonstrated to validate the proposed scheme, reporting a carrier aggregation of up to 40 100 MHz orthogonal frequency division multiplexing (OFDM) channels with quadrate amplitude modulation (QAM) order of 4 and an aggregation of 10 100 MHz OFDM channels with a QAM order of 16384. The equivalent common public radio interface rates from 37 to 150 Gbit/s are supported. Besides, the error vector magnitude (EVM) of 8% is achieved with the number of quantization bits of 4, and the EVM can be further reduced to 1% by increasing the number of quantization bits to 7. Compared with conventional pulse coding modulation-based D-RoF systems, the proposed D-RoF system improves the signal-to-noise-ratio up to similar to 9 dB and greatly reduces the EVM, given the same number of quantization bits. (c) 2018 Optical Society of America
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| 11. |
- Zhang, Lu, et al.
(author)
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Toward terabit digital radio over fiber systems : Architecture and key technologies
- 2019
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In: IEEE Communications Magazine. - : Institute of Electrical and Electronics Engineers Inc.. - 0163-6804 .- 1558-1896. ; 57:4, s. 131-137
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Journal article (peer-reviewed)abstract
- To support massive deployment of broadband radio applications, such as 5G and high-definition videos for terrestrial televisions, large system capacity and high spectrum efficiency are highly demanded in radio over fiber (RoF) systems. In this article, we propose a terabit digital RoF system capable of providing high-speed transmission, where multicore fiber (MCF) is introduced for the access segment between the central unit and remote unit. Two key technologies that greatly enhance system capacity and spectrum efficiency, namely MCF enabled self-homodyne detection and compressed quantization, are demonstrated.
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