数字AM技术系列报告之三 法国Thomcast公司Skywave2000多载波系统(第二讲)

QAM调制方式 Thomcast的天波2000系统采用多载波并行传输(COFDM),每一载波采用正交调幅16QAM、64QAM或256QAM。 64QAM每个符号6比特,编码率2/3,每符号净4比特。 16QAM每个符号4比特,编码率3/4,每符号净3比特。 256QAM每个符号8比特,编码率3/4,每符号净6比特。

Investigation of system structure and information processing mechanism for cognitive skywave over-the-horizon radar

Based on the cognitive radar concept and the basic connotation of cognitive skywave over-the-horizon radar（SWOTHR）, the system structure and information processingmechanism about cognitive SWOTHR are researched. Amongthem, the hybrid network system architecture which is thedistributed configuration combining with the centralized cognition and its soft/hardware framework with the sense-detectionintegration are proposed, and the information processing framebased on the lens principle and its information processing flowwith receive-transmit joint adaption are designed, which buildand parse the work law for cognition and its self feedback adjustment with the lens focus model and five stages informationprocessing sequence. After that, the system simulation andthe performance analysis and comparison are provided, whichinitially proves the rationality and advantages of the proposedideas. Finally, four important development ideas of futureSWOTHR toward ＂high frequency intelligence information processing system＂ are discussed, which are scene information fusion, dynamic reconfigurable system, hierarchical and modulardesign, and sustainable development. Then the conclusion thatthe cognitive SWOTHR can cause the performance improvement is gotten.

Use of piecewise polynomial phase modeling to compensate ionospheric phase contamination in skywave radar systems

Recognition and correction of ionospheric phase path contamination is a vital part of the global radar signal processing sequence. A number of model-based correction algorithms have been developed to deal with the radar performance degradation due to the ionospheric distortion and contamination. This paper addresses a novel parametric estimation and compensation method based on High-order Ambiguity Function (HAF) to solve the problem of phase path contamination of HF skywave radar signals. When signal-to-noise ratio and data sequence available satisfy the predefined conditions, the ionospheric phase path contamination may be modeled by a polynomial phase signal (PPS). As a new parametric tool for analyzing the PPS, HAF is introduced to estimate parameters of the polynomial-phase model and reconstruct the correction signal. Using the reconstructed correction signal, compensation can be performed before coherent integration so that the original echo spectrum can be restored. A piecewise scheme is proposed to track rapid variation of the phase contamination based on HAF method, and it can remove the Doppler spread effect caused by the ionosphere nonstationarity. Simulation and experimental results are given to demonstrate the efficiency of the proposed algorithm.

HF Communications: Past, Present, and Future

High frequency(HF) communication, commonly covering frequency range between 3 and 30 MHz, is an important wireless communication paradigm to offer over-thehorizon or even global communications with ranges up to thousands of kilometers via skywave propagation with ionospheric refraction. It has widespread applications in fields such as emergency communications in disaster areas, remote communications with aircrafts or ships and non-light-of-the-sight military operations. This tutorial article overviews the history of HF communication, demystifies the recent advances, and provides a preview of the next few years, which the authors believe will see fruitful outputs towards wideband, intelligent and integrated HF communications. Specifically, we first present brief preliminaries on the unique features of HF communications to facilitate general readers in the communication community. Then, we provide a historical review to show the technical evolution on the three generations of HF communication systems. Further, we highlight the key challenges and research directions. We hope that this article will stimulate more interests in addressing the technical challenges on the research and development of future HF radio communication systems.

太空冲击波——探秘“天浪”Sky Wave

1997年11月,在日本东京举行的第32界国际汽车、摩托车展览会上,铃木公司推出了一款新型的250mL大排量踏板车,起名为Sky Wave,意思是“太空冲击波”或“天浪”(见图1)。虽然本田公司和雅马哈公司在此之前已推出了此种大排量的踏板车,但由于此车外观更加美观豪华,功能日趋实用合理,故仍引起了参观者的普遍关注。1998年2月该车正式销售后,真如冲击波一般在摩托车市场上掀起了层层波浪,大大推动了大排量踏板车家族的繁荣。

爱迪德IRDETO PISYS FOR DTV为天浪卫视提供内容保护

2005年7月27日，爱迪德公司宣布，AsiaSat（亚洲卫星）公司下属子公司Skywave（天浪卫视）选择了爱迪德公司为其直接入户（DTH）卫星电视业务提供保护。Skywave节目涵盖娱乐、新闻、体育、影视、时尚和记录片等内容，通过多达40个地方和国际电视频道，以普通话、粤语、英语及其他亚洲语言提供直接入户的数字品质节目。

坐式车之王——铃木Sky Wave 400

相对于骑式车而言,坐式车以实用见长,而大排量的坐式车则以性能优越、豪华舒适、适合长途行驶赢得了人们的青睐。最早是本田公司在1984年推出的“船王”Fusion,在当时的大排量坐式车市场一枝独秀,很是风光了不少年头。而到了90年代中期。雅马哈公司推出的Majesty车系的大获成功则成为大排量坐式车市场竞争的引爆剂,铃木公司推出的Sky Wave(天浪)车系加上本田公司推出的Fusion的新款车Foresight使市场的竞争趋于白热化。