We propose a layered asymmetrically clipped optical fast orthogonal frequency division multiplexing(ACO-FOFDM)scheme for intensitymodulated and directdetected(IM/DD)systems. Layered ACO-FOFDM can compensate the weakne...We propose a layered asymmetrically clipped optical fast orthogonal frequency division multiplexing(ACO-FOFDM)scheme for intensitymodulated and directdetected(IM/DD)systems. Layered ACO-FOFDM can compensate the weaknessof conventional ACO-FOFDM in low spectral efficiency. For FOFDM system, the utilization of discrete cosine transform(DCT) instead of fast Fourier transform(FFT) can reduce thecomputational complexity without any influence on bit errorrate(BER) performance. At transmitter, the superposition ofmultiple layers is performed in frequency domain, and the iterative receiver is used to recover transmitted signals by subtracting the clipping noise of each layer. We compare theBER performance of the proposed layered ACO-FOFDM system and DC-offset FOFDM(DCO-FOFDM) system with optimal DCbias at the same spectral efficiency. Simulation results show that in terms of optical bit energy to noise powerratio, the layered ACO-OFDM system has 1.23 dB, 2.77 dB,3.67 dB and 0.78 dB improvement at the forward error correction(FEC) limit compared with DCO-FOFDM system whenthe spectral efficiencies are 1 bit/s/Hz, 2 bits/s/Hz, 3 bits/s/Hz and 4 bits/s/Hz. The layered ACO-FOFDM system with zero DC-bias is more suitable for adaptive system, so this system also has potential for application in IM/DD systems.展开更多
Commercial agricultural production, which has altered the global distribution of farmland, garden plot, and woodland, cuts links between cities and their neighboring production land, as well as links between productio...Commercial agricultural production, which has altered the global distribution of farmland, garden plot, and woodland, cuts links between cities and their neighboring production land, as well as links between production land and the environment, affecting the quality of food supply and inducing ecological crisis. Closely related to urban-rural public welfare and regional ecological security, sustainable food supply, which is featured by various types, local production, and short-chain transportation, is an effective way to address the negative impact of commercial agriculture. This paper clarifies the important role of agricultural and forest land in urban fringe areas through analyzing the functional connotation and spatial bases of sustainable food supply, and proposes a planning strategy for systematic land protection and efficient spatial management in accordance with the current situation of food supply and compound demands in urban areas. Specifically, it consists of: identifying the land and the support space with potential for diversified food production;establishing an agriculture and forestry support network system and integrating it into regional landscape ecological network;guiding the low impact utilization of production units by following the natural process and resource characteristics;enhancing land protection efficiency based on supporting links.展开更多
Being an important part of a region’s ecological space,the habitat units on the urban fringe continuously provide multiple services for the city and its residents and guarantee the ecological security of the local te...Being an important part of a region’s ecological space,the habitat units on the urban fringe continuously provide multiple services for the city and its residents and guarantee the ecological security of the local territory.Mainly composed of farmlands,secondary woodlands,ditches and ponds,etc.,they are typical semi-natural habitat which is subject to the influences of both the human society and the natural environment.As they involve multiple stakeholders and concern complex ownerships,top-down measures are difficult to be implemented,as presented by the Not-In-MyBackyard(NIMBY)phenomenon against protected areas.Based on the Actor-Network Theory,this paper clarifies the intrinsic relationship between the maintenance of urban fringe habitat units and the relevant social elements.Through the case study on Yilan’s practice of protecting and utilizing agricultural and forestry resources in Taiwan,China,the paper explores the community supported management and control strategies for the purposes of enhancing the protection of habitat units and promoting the effectiveness of regional services,which are implemented through the steps of implementing such translation methods as Obligatory Passage Point setting and benefit granting,recruiting and mobilizing relevant actors to form a network,and realizing the substantial protection of habitat units.展开更多
基金supported in part by National Natural Science Foundation of China under Grant Nos.61427813 and 61331010in part by ZTE Industry-Academia-Research Cooperation Funds
文摘We propose a layered asymmetrically clipped optical fast orthogonal frequency division multiplexing(ACO-FOFDM)scheme for intensitymodulated and directdetected(IM/DD)systems. Layered ACO-FOFDM can compensate the weaknessof conventional ACO-FOFDM in low spectral efficiency. For FOFDM system, the utilization of discrete cosine transform(DCT) instead of fast Fourier transform(FFT) can reduce thecomputational complexity without any influence on bit errorrate(BER) performance. At transmitter, the superposition ofmultiple layers is performed in frequency domain, and the iterative receiver is used to recover transmitted signals by subtracting the clipping noise of each layer. We compare theBER performance of the proposed layered ACO-FOFDM system and DC-offset FOFDM(DCO-FOFDM) system with optimal DCbias at the same spectral efficiency. Simulation results show that in terms of optical bit energy to noise powerratio, the layered ACO-OFDM system has 1.23 dB, 2.77 dB,3.67 dB and 0.78 dB improvement at the forward error correction(FEC) limit compared with DCO-FOFDM system whenthe spectral efficiencies are 1 bit/s/Hz, 2 bits/s/Hz, 3 bits/s/Hz and 4 bits/s/Hz. The layered ACO-FOFDM system with zero DC-bias is more suitable for adaptive system, so this system also has potential for application in IM/DD systems.
基金supported by the National Natural Science Foundation of China (No.51908469)the Natural Science Foundation of Sichuan,China (No.2022NSFSC1069)the Project of the Tuojiang River Basin High-Quality Development Research Center,a key research base of social sciences in Sichuan Province (No.TJGZL2021-12)。
文摘Commercial agricultural production, which has altered the global distribution of farmland, garden plot, and woodland, cuts links between cities and their neighboring production land, as well as links between production land and the environment, affecting the quality of food supply and inducing ecological crisis. Closely related to urban-rural public welfare and regional ecological security, sustainable food supply, which is featured by various types, local production, and short-chain transportation, is an effective way to address the negative impact of commercial agriculture. This paper clarifies the important role of agricultural and forest land in urban fringe areas through analyzing the functional connotation and spatial bases of sustainable food supply, and proposes a planning strategy for systematic land protection and efficient spatial management in accordance with the current situation of food supply and compound demands in urban areas. Specifically, it consists of: identifying the land and the support space with potential for diversified food production;establishing an agriculture and forestry support network system and integrating it into regional landscape ecological network;guiding the low impact utilization of production units by following the natural process and resource characteristics;enhancing land protection efficiency based on supporting links.
基金The National Natural Science Foundation of China(52008062,51908469)The Science and Technology Research Program of Chongqing Municipal Education Commission(KJQN202100735)Tuojiang River Basin High-quality Development Research Center,A Key Research Base of Social Sciences in Sichuan Province(TJGZL2021-12).
基金Supported by National Natural Science Foundation of China(Grant No.51908469,52008062)Tuojiang River Basin High-quality Development Research Center,a key research base of Social Sciences in Sichuan Province(Grant No.TJGZL2021-12)Fundamental Research Funds for the Central Universities(Grant No.2682020CX38)。
文摘Being an important part of a region’s ecological space,the habitat units on the urban fringe continuously provide multiple services for the city and its residents and guarantee the ecological security of the local territory.Mainly composed of farmlands,secondary woodlands,ditches and ponds,etc.,they are typical semi-natural habitat which is subject to the influences of both the human society and the natural environment.As they involve multiple stakeholders and concern complex ownerships,top-down measures are difficult to be implemented,as presented by the Not-In-MyBackyard(NIMBY)phenomenon against protected areas.Based on the Actor-Network Theory,this paper clarifies the intrinsic relationship between the maintenance of urban fringe habitat units and the relevant social elements.Through the case study on Yilan’s practice of protecting and utilizing agricultural and forestry resources in Taiwan,China,the paper explores the community supported management and control strategies for the purposes of enhancing the protection of habitat units and promoting the effectiveness of regional services,which are implemented through the steps of implementing such translation methods as Obligatory Passage Point setting and benefit granting,recruiting and mobilizing relevant actors to form a network,and realizing the substantial protection of habitat units.
