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设计供战术军事环境使用的综合通信、导航和识别系统时,其中的一个关键是决定信号结构。系统在可能的敌方环境中,为了减小敌方干扰及我方互扰,也为了允许所有用户共用相同频谱,建议系统采用扩展频谱信号结构。而特别引人注目的是,采用跳频技术,其载频可在大量伪随机地选择的频率内进行快速而且相关地跳动。快跳频(FFH)的优点是接收机可在毫秒内实现同步,同时共用同频带的用户数目异常大,甚至当其他用户的干扰信号功率远大于个别用户接收机的输入功率时也是这样。Northrop 公司设计了一种综合战术 CNI(天体导航与识别)系统,以适应快速移动的军队用户要求,该系统采用快跳频信号结构,其基本方块为 FFH 射频线路。该射频线路允许两个用户具有同步时钟以决定彼此间的距离和速度。此外,在两个方向上都可用同一线路来传输话音或数据。给每个用户分配一个独特的跳频码,使得每个用户可保密而独立地完成通信、导航和识别功能,而不使同地区的用户互相干扰。系统结构复杂,涉及到单个地面站和多个地面站及中继站。其中单个地面站作为参考点并控制视距内的全部用户,中继站可提高导航精度和把系统的测距范围扩展到视距之外。为了促进 FFHCNI 技术尽可能广泛使用,Northrop 公司很强调在设备设计中应用全数字信号处理技术和大规模集成电路,以获得小而轻及廉价的硬设备,由这些方法所获得的经济效果使 FFHCNI 设备可用于 RPV’S(遥控飞机)系统和直升飞机中,这些系统对航空电子设备的尺寸和重量要求很严格。
One of the keys to designing an integrated communications, navigation and identification system for use in a tactical military environment is determining the signal structure. In a possible hostile environment, in order to reduce hostile interference and our mutual interference, and in order to allow all users to share the same spectrum, it is proposed that the system adopt a spread spectrum signal structure. Of particular interest is the use of frequency-hopping techniques whose carrier frequency can be quickly and perturbed over a large number of pseudo-randomly chosen frequencies. The advantage of fast frequency hopping (FFH) is that the receiver can synchronize in milliseconds while the number of users sharing the same frequency band is unusually large, even when the interference signal power of other users is much greater than the input power of individual user receivers. Northrop designed a comprehensive tactical CNI (celestial navigation and recognition) system to accommodate fast-moving military users. The system employs a fast frequency hopping (FHF) signal structure and its basic block is an FFH RF line. The RF line allows two users to have synchronized clocks to determine the distance and speed between each other. In addition, the same line can be used to transmit voice or data in both directions. Each user is assigned a unique hopping code so that each user can perform the communication, navigation and identification functions in a confidential and independent manner without interfering with users in the same area. System structure is complex, involving a single ground station and multiple ground stations and relay stations. In which a single ground station serves as a reference point and controls all users within the line of sight, the relay station can improve navigation accuracy and extend the range of the system beyond the line-of-sight. To promote the widest possible use of FFHCNI technology, Northrop emphasizes the use of all-digital signal processing (LSI) and LSIs in device design to achieve small, light and inexpensive hard-ware, and the economic benefits of these approaches have made FFHCNI The equipment can be used in RPV’s (remotely piloted aircraft) systems and helicopters, which have strict requirements on the size and weight of avionics.