Quasi-cyclic (QC) low-density parity-check (LDPC) codes form an important subclass of LDPC codes. These codes have encoding advantage over other types of LDPC codes. This paper addresses the issue of ...efficient encoding of QC-LDPC codes. Two methods are presented to find the generator matrices of QC-LDPC codes in systematic-circulant (SC) form from their parity-check matrices, given in circulant form. Based on the SC form of the generator matrix of a QC-LDPC code, various types of encoding circuits using simple shift registers are devised. It is shown that the encoding complexity of a QC-LDPC code is linearly proportional to the number of parity bits of the code for serial encoding, and to the length of the code for high-speed parallel encoding.
In the development of Sanya Incoherent Scatter Radar (SYISR), which is a major scientific instrument project founded by the National Natural Science Foundation of China (NSFC), we established a ...prototype system of 8 subarrays (named SYISR-8 hereafter), including 256 transceiver modules totally, beginning in July 2018 to verify the functions of the radar. Based on SYISR-8, we configured the system to detect the meteor echo with high range resolution. During a continuous observation interval of 16 h, 55 meteor echo events were found. Among these events, 34 cases were head echoes, 18 cases were specular trail echoes, and 3 cases were head echo and nonspecular trail echo concurrent events. We have observed 2 potential direct meteoroid fragmentation cases of all 55 meteor events. It demonstrates that potential direct observation of meteoroid fragmentation could be observed by a relatively small aperture and power using pulse compression processing. However, the occurrence ratio of meteoroid fragmentation in our experiment is approximately 6%, which is considerably lower than that observed in previous studies, which needs further investigation.
•Meteor echoes observation results by SYISR-8 are demonstrated in a high range resolution mode.•The SYISR-8 was configured to detect meteoroid with 37.5m resolution through pulse compression technique.•Two potential direct meteoroid fragmentation cases were observed for the first time to our knowledge using the SYISR-8.•Typical meteor echoes could be observed by a high range resolution radar with relatively small aperture and power.
This paper presents five methods for constructing nonbinary LDPC codes based on finite geometries. These methods result in five classes of nonbinary LDPC codes, one class of cyclic LDPC codes, three ...classes of quasi-cyclic LDPC codes and one class of structured regular LDPC codes. Experimental results show that constructed codes in these classes decoded with iterative decoding based on belief propagation perform very well over the AWGN channel and they achieve significant coding gains over Reed-Solomon codes of the same lengths and rates with either algebraic hard-decision decoding or Kotter-Vardy algebraic soft-decision decoding at the expense of a larger decoding computational complexity.
The identification and distinction of fluvial from lacustrine deposits and the recognition of catchment changes are crucial for the reconstruction of climate changes in terrestrial environments. The ...investigated drill core succession shows a general evolution from red–brown claystones to white–grey marlstones and microcrystalline limestones, which all have previously been considered as relict deposits of an impact ejecta‐dammed lake, falling within the mid‐Miocene Climate Transition. However, recent mammal biostratigraphic dating suggests a likely pre‐impact age. Indeed, no pebbles from impact ejecta have been detected; only local clasts of Mesozoic formations, in addition to rare Palaeozoic lydites from outside of the study area. Lithofacies analysis demonstrates only the absence of lacustrine criteria, except for one charophyte‐bearing mudstone. Instead, the succession is characterized by less diagnostic floodplain fines with palaeosols, palustrine limestones with root voids and intercalated thin sandstone beds. Carbonate isotope signatures of the mottled marlstones, palustrine limestones and mud‐supported conglomerates substantiate the interpretation of a fluvial setting. Low, invariant δ18Ocarb reflects a short water residence time and highly variable δ13Ccarb indicates a variable degree of pedogenesis. Carbonate 87Sr/86Sr ratios of the entire succession show a unidirectional trend from 0.7103 to 0.7112, indicating a change of the solute provenance from Triassic to Jurassic rocks, identical to the provenance trend from extraclasts. The increase in carbonate along the succession is therefore independent from climate changes but reflects a base‐level rise from the level of the siliciclastic Upper Triassic to the carbonate‐bearing Lower to Middle Jurassic bedrocks. This study demonstrates that, when information on sedimentary architecture is limited, a combination of facies criteria (i.e. presence or absence of specific sedimentary structures and diagnostic organisms), component provenance, and stable and radiogenic isotopes is required to unequivocally distinguish between lacustrine and fluvial sediments, and to disentangle regional geological effects in the catchment and climate influences.
The electrical performance of the feed array is degraded because of the position deviation of the array elements caused by manufacturing and processing, which cannot meet the high performance feeding ...requirements of large feed arrays. In this paper, a radiation field model of the helical antenna array considering the position deviation of array elements is proposed to investigate the influence law of position deviation on the electrical performance of the feed array. With the established model, the rectangular planar array and the circular array of the helical antenna with a radiating cup are discussed and the relationship between electrical performance index and position deviation is established by numerical analysis and curve fitting method. The research results show that the position deviation of the antenna array elements will lead to the rise of the sidelobe level, the deviation of the beam pointing, and the increase of the return loss. The valuable simulation results provided by this work can be used in antenna engineering, guiding antenna designers to set optimal parameters when fabricating antennae.
The plasma lines observed by Sanya incoherent scatter radar (SYISR) are dependent on the enhancement of Langmuir waves due to superthermal photoelectrons generated by solar EUV radiation. The plasma ...line power spectrum can be obtained using long-pulse and alternating-code transmission signals during the period from sunrise to noon almost every day. For the power spectrum of the long pulse, the CLEAN algorithm that has been applied in this field is used to verify the feasibility of this method for SYISR in only a few cases. However, it is difficult to deal with alternating code with such a low SNR using the general deconvolution method. The irreversible-migration filtering (IMF) method has been developed to separate signal noise from the measurements of the alternating code. Some experimental results from the SYISR measurements validate the excellent performance of the IMF method for alternating code. Additionally, an example observation of the electron density with a high time and range resolution is derived. The results show that plasma line detection can be a powerful new observational capability for SYISR as an ionospheric experimental mode for ionospheric calibration, when possible, which can be simultaneously measured with the ion line for constant radar calibration in the standard fitting of the ion line.
This paper is concerned with construction of quasi-cyclic (QC) low-density parity-check (LDPC) codes for three different types of channels: the additive white Gaussian noise, the binary random ...erasure, and the binary burst erasure channels. Two algebraic methods for systematic construction of QC-LDPC codes are presented. Codes constructed perform well over all three types of channels
In the late 1950s and early 1960s, finite fields were successfully used to construct linear block codes, especially cyclic codes, with large minimum distances for hard-decision algebraic decoding, ...such as Bose-Chaudhuri-Hocquenghem (BCH) and Reed-Solomon (RS) codes. This paper shows that finite fields can also be successfully used to construct algebraic low-density parity-check (LDPC) codes for iterative soft-decision decoding. Methods of construction are presented. LDPC codes constructed by these methods are quasi-cyclic (QC) and they perform very well over the additive white Gaussian noise (AWGN), binary random, and burst erasure channels with iterative decoding in terms of bit-error probability, block-error probability, error-floor, and rate of decoding convergence, collectively. Particularly, they have low error floors. Since the codes are QC, they can be encoded using simple shift registers with linear complexity.
As the first advanced modular phase array incoherent scatter radar (ISR) established in the Eastern Hemisphere at low latitudes, Sanya ISR (SYISR) can measure the line-of-sight (LOS) velocity of ion ...drift in multiple directions, potentially yielding the spatial distribution of ionospheric plasma drift. Three beam-scanning modes are designed for plasma drift detection: meridian, zonal and cross-shaped (both meridian and zonal) plane, which will provide the distribution of plasma drift in latitude/longitude as well as altitude. The altitude profile of plasma drift and the first presented distribution of low latitude plasma drift in the meridian plane for March to May 2021 are inversed through LOS velocity using cross-shaped and meridian beam-scanning modes, respectively. A statistical correlation coefficient between the vpn and crest-to-trough ratio (CTR) of equatorial ionization anomaly (EIA) TEC and a case study of magnetic storm response in plasma drift show that the inversed plasma drift can be a good indicator in response to the changes in atmospheric tide and solar wind at different time scales and explain the corresponding ionospheric electron density variations at low and equatorial latitudes. This study proves that the SYISR-measured plasma drift is reliable and will play an important role in the atmosphere-ionosphere-magnetospheric coupling study in the East Asian region.
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