The construction of a Golay complementary sequence (GCS) set with small number of constituent sequences and flexible length has long been an open problem. Compared with the 2-phase GCS pairs, more possible lengths were founded in literatures by extending the phase and the number of con-stituent sequences. For both mathematical theory and engineering applications, it is desirable to keep the number of constituent sequences as small as possible. In this work, we construct a 4-phase GCS set of 23+ [log2$r$sequences of arbitrary length$n$, where the 1013-base expansion of$n$has$r$nonzero digits. Specifically, the 4-phase GCS octets (sets of eight sequences) cover all the lengths no greater than 1013.

Sequences with low aperiodic autocorrelation side-lobes have been extensively researched in literatures. With sufficiently low integrated sidelobe level (ISL), their power spectrums are asymptotically flat over the whole frequency domain. However, for the beam sweeping in the massive multi-input multi-output (MIMO) broadcast channels, the flat spectrum should be constrained in a passband with tunable bandwidth to achieve the flexible tradeoffs between the beamforming gain and the beam sweeping time. Motivated by this application, we construct a family of sequences termed the generalized step-chirp (GSC) sequence with a closed-form expression, where some parameters can be tuned to adjust the bandwidth flexibly. In addition to the application in beam sweeping, some GSC sequences are closely connected with Mow's unified construction of sequences with perfect periodic autocorrelations, and may have a coarser phase resolution than the Mow sequence while their ISLs are comparable.

Motivated by the recent application of two-dimensional Golay complementary arrays (2-D GCA) in uniform rectangular array (URA) -based omnidirectional precoding for the next generation of cellular communications, we propose in this paper new constructions of GCA pairs and GCA quads, which allow for more possible sizes. These constructions are facilitated by four identities over a commutative ring, of which two are established results of quaternions and octonions and the others are novel. We prove that the size of a 4-phase GCA pair is possible if the product of the array sizes in all dimensions is a 4-phase Golay number with an additional constraint on the factorization of the product. For 2-phase 2-D GCA quads, all sizes no greater than$78\times 78$can be covered. For 4-phase GCA quads, all the positive integers within 1000 can be covered for the size in one dimension. Besides producing GCAs that can accommodate to antenna arrays of various sizes, this study also yields new Hadamard matrices of sizes previously unavailable.

The wireless in-band full-duplex (IBFD) technology can in theory double the system capacity over the conventional frequency division duplex (FDD) or time-division duplex (TDD) alternatives. But the strong self-interference of the IBFD can cause excessive quantization noise at the output of the analog-to-digital converters (ADCs), which hampers its real implementation. Fortunately, the reconfigurable intelligent surface (RIS) can reconfigure the wireless channels by dynamically adjusting the reflection coefficients, which makes it a promising solution to self-interference mitigation (SIM) for the IBFD system. This paper considers a RIS-assisted IBFD (RAIBFD) system where a full-duplex base station (BS), assisted by a co-located RIS, receives and transmits signals on the same frequency band simultaneously. We propose to jointly design the DL precoding matrix and the RIS coefficients to mitigate the strong self-interference before the ADCs of finite bit resolutions. To gauge the performance of the proposed RAIBFD system, we also consider an idealistic RIS-assisted IBFD (I-RAIBFD) system with ADCs of infinite bit resolutions and RIS-assisted FDD (RAFDD) system, and take them as performance benchmarks. The effectiveness of the proposed RAIBFD system is verified by simulation studies, even if the phases of the RIS have only finite resolutions.

This paper describes work currently underway aiming to develop a distributed collaborative infrastructure to support the national science, especially the biosafety research in China. The irresistible trend of e-Science indicates that in the future more and more scientific researches will be carried out through close cooperation among collaborators. Following this trend, we need an infrastructure to satisfy the needs among institutes located across China. In this paper, we analyze the requirements for creating and maintaining a coherent Grid-enabled application management framework in a distributed environment from domain experts' and administrators' perspectives. Under such framework, we further develop computational and instrumental tools with Grid technology. As Grid is evolving over recent years towards the use of service-oriented architecture, we propose a solution with designing and implementing featured services based on the real demand of the biosafety research. This scalable architecture allows it grow into a bigger and comprehensive system with large amount of resources to better support scientific research and education.

In hybrid moving-picture coding schemes, motion estimation is conducted in two stages, one at integer pixel accuracy and the other at subpixel accuracy. In very low bit-rate coding, some fast motion-search algorithms are able to decrease their search points to about ten pixels at the integer pixel search stage. There remains, however, a need to study fast computing for the subpixel motion estimation. A novel, fast-search algorithm using parabolic prediction is proposed in this paper particularly for the half-pixel motion vector estimation. It needs to check only three half-pixels rather than the eight pixels, which are used in the full half-pixel motion search scheme (FHPS). Experimental results show that this algorithm preserves the image quality and has little influence on the bit-rate when compared to that of the referenced FHPS strategy.