Analog-to-Digital Converter Loading Analysis Considerations for Satellite Communications Systems

D. Taggart, Rajendra Kumar, Y. Krikorian, G. Goo, Joseph Chen, Robert Martinez, Tom Tam, Edward Serhal
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引用次数: 8

Abstract

In contemporary communication satellite systems, uplink radio frequency (RF) signals are amplified, downconverted to intermediate frequency (IF) and/or baseband, and after appropriate filtering, are input to an analog-to-digital converter (ADC). The ADC digital output is signal processed for a variety of purposes, such as signal channelization and switching. In these systems, a foremost realization problem is the ADC, which must operate to satisfy the sampling theorem, which necessitates a sampling rate at least twice the received signal bandwidth. When the signal consists of numerous multiplexed signals, a critical matter in ADC performance is the degree of signal clipping, which arises when the instantaneous ADC input signal magnitude surpasses the maximum range of the ADC. Since at least some clipping is often present, the total ADC noise output consists of clipping plus quantization noise. A figure of merit for the ADC is the signal-to-noise ratio (SNR) of the ADC, which is defined as the ratio of input signal average power to the ADC output average noise power. The SNR is determined by, among other things, the ADC load factor, which is the ratio of the ADC input signal average power, and the ADC maximum peak power output. This paper describes analysis and simulation results on SNR versus the ADC load factor when the input signal is composed of many digitally modulated carriers. A nine-signal 8-ary phase shift key (8-PSK) modulated carrier case is considered with each signal band limited. It is important to note that for this particular ADC input, it is shown that the probability density function (PDF) is Gaussian-like. This is significant since this means that the SNR versus ADC load factor curve for the nine 8-PSK signal case will have nearly identical characteristics to that when the ADC input is white Gaussian noise. Additionally, this paper discusses what occurs when the ADC is strongly driven into the clipping region. This discussion is enhanced by comparing the ADC to a limiter in this highly distorted region. Analysis and simulation results are provided to describe ADC performance characteristics in this highly distorted region.
卫星通信系统模数转换器负载分析的考虑
在当代通信卫星系统中,上行射频(RF)信号被放大,下变频到中频(IF)和/或基带,并经过适当滤波后输入到模数转换器(ADC)。ADC数字输出是用于各种目的的信号处理,例如信号信道化和开关。在这些系统中,最重要的实现问题是ADC,它必须满足采样定理,这需要采样率至少是接收信号带宽的两倍。当信号由多个复用信号组成时,ADC性能中的一个关键问题是信号削波程度,当ADC的瞬时输入信号幅度超过ADC的最大范围时,就会出现信号削波程度。由于通常至少存在一些削波,因此总的ADC噪声输出由削波加量化噪声组成。ADC的优劣指标是ADC的信噪比(SNR),定义为输入信号平均功率与ADC输出平均噪声功率之比。信噪比是由ADC负载因子决定的,它是ADC输入信号平均功率与ADC最大峰值输出功率之比。本文描述了当输入信号由多个数字调制载波组成时,信噪比与ADC负载因子的关系的分析和仿真结果。在每个信号频带有限的情况下,考虑了9个信号8位相移键(8-PSK)调制载波情况。值得注意的是,对于这个特定的ADC输入,表明概率密度函数(PDF)是类高斯的。这一点很重要,因为这意味着9个8-PSK信号情况下的信噪比与ADC负载因子曲线将具有与ADC输入为高斯白噪声时几乎相同的特性。此外,本文还讨论了当ADC被强驱动到裁剪区域时发生的情况。通过将ADC与这个高度失真区域的限幅器进行比较,进一步加强了这一讨论。分析和仿真结果描述了ADC在这一高度失真区域的性能特征。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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