Chirp waveform plays a significant role in radar and communication systems for its ability of pulse compression and spread spectrum. This paper presents a principle of orthogonally multiplexing a bank of linear chirp waveforms within the same bandwidth. The amplitude and phase of the chirps are modulated for information communication. As Fourier transform is the basis for orthogonal frequency division multiplexing (OFDM), Fresnel transform underlies the proposed orthogonal chirp division multiplexing (OCDM). Digital implementation of the OCDM system using discrete Fresnel transform is proposed. Based on the convolution theorem of the Fresnel transform, the transmission of the OCDM signal is analyzed under the linear time-invariant or quasi-static channel with additive noise, which can generalize typical linear transmission channels. Based on the eigen-decomposition of Fresnel transform, efficient digital signal processing algorithm is proposed for compensating channel dispersion by linear single-tap equalizers. The implementation details of the OCDM system is discussed with emphasis on its compatibility to the OFDM system. Finally, simulation are provided to validate the feasibility of the proposed OCDM under wireless channels. It is shown that the OCDM system is able to utilize the multipath diversity and outperforms the OFDM system under the multipath fading channels.

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Plant phenology was assessed as one of the most key Essential Biodiversity Variables on species functional traits, which underpins a variety of aspects of ecosystem function and is a vital determinant of species distribution. Flowering phenology is one of the most sensitive indicators of the effects of recent climatic change. Understanding of intraspecific variation in phenological responses to climate change can contribute to the accurate prediction of phenology and the assessment of potential impacts of climate change on organisms. However, this intraspecific variation in phenological sensitivity in natural systems is still unclear, especially at large spatial scales. Using the widespread perennial herb Spiranthes sinensis, we quantified intraspecific variation in phenological responses to warming among groups located along climatic gradients. Phenological data were derived from 1,681 collections of herbarium specimens and photographs across eastern Asia and southeastern Australia over the period 1902–2017 and spans eight humid and eight non‐humid regions. We found that peak flowering dates of Spiranthe sinensis (FLss) showed substantial intraspecific variation in temperature sensitivity, ranging from −5.16 ± 1.13 to 4.16 ± 0.90 days/°C. Across all 16 regions, FLss exhibited the strongest delayed response to warming in southeastern Australia. Temperature sensitivity of the FLss was significantly correlated with annual precipitation and aridity index of a region, suggesting a possible role of declined water availability in reducing temperature sensitivity. Notably, contrasting phenological responses to warming were found between collections with different humidity regimes: humid regions generally flowered earlier (M: −3.57 days/°C) and non‐humid regions exhibited slightly delayed flowering (M: 1.25 days/°C). These findings provide empirical evidence of substantial intraspecific variation in phenological sensitivity across large spatial scales, and highlights that soil water availability may play a key role in a warming planet, especially in non‐humid regions.

Acid rain is a serious environmental problem worldwide. In this study, a pot experiment using forest soils planted with the seedlings of four woody species was performed with weekly treatments of pH 4.40, 4.00, 3.52, and 3.05 simulated acid rain (SAR) for 42 months compared to a control of pH 5.00 lake water. The cumulative amounts of C and N mineralization in the five treated soils were determined after incubation at 25 • C for 65 d to examine the effects of SAR treatments. For all five treatments, cumulative CO 2 -C production ranged from 20.24 to 27.81 mg kg −1 dry soil, net production of available N from 17.37 to 48.95 mg kg −1 dry soil, and net production of NO − 3 -N from 9.09 to 46.23 mg kg −1 dry soil. SAR treatments generally enhanced the emission of CO 2 -C from the soils; however, SAR with pH 3.05 inhibited the emission. SAR treatments decreased the net production of available N and NO 3 -N. The cumulative CH 4 and N 2 O productions from the soils increased with increasing amount of simulated acid rain. The cumulative CO 2 -C production and the net production of available N of the soil under Acmena acuminatissima were significantly higher (P ≤ 0.05) than those under Schima superba and Cryptocarya concinna. The mineralization of soil organic C was related to the contents of soil organic C and N, but was not related to soil pH. However, the overall effect of acid rain on the storage of soil organic matter and the cycling of important nutrients depended on the amount of acid deposition and the types of forests.