Additive
The noise is added to the original signal. It does not alter the signal in any other way except by adding itself to it. The received signal can be represented as:
where y(t) is the received signal, x(t) is the transmitted signal, and n(t) is the noise.
White
The term ‘white’ refers to the noise having a flat power spectral density, meaning its power is uniformly distributed across all frequencies. It is analogous to white light, which contains all visible wavelengths equally. This property makes white noise uncorrelated across different frequencies.
Gaussian
The noise amplitude follows a Gaussian distribution, also known as a normal distribution. This means that the noise values are random but have a bell-shaped probability distribution centered at zero (mean = 0). The probability density function (PDF) of Gaussian noise is given by:
where σ^2 is the variance (measure of the noise power).
AWGN is stationary, whereby the statistical properties of the noise do not change over time; memoryless: the noise at any time instant is independent of the noise at any other time instant; and linear: the noise does not distort the shape of the signal, only the amplitude is affected. AWGN is often used in simulations of digital communication systems (e.g., BPSK, QPSK, OFDM) to model the effect of random noise in the channel. It serves as a good approximation for many practical communication channels, especially when there is minimal interference or fading. In electronic warfare (EW), AWGN is often employed to test both offensive and defensive jamming systems.
Typical cases for AWGN include:
- 5G communications
- Satellite communications
- Signal integrity
- Directed energy weapons
Noise Sources and Noise Generation Instruments
A noise source, such as a NC346-series from Maury Microwave, is a common component used to generate AWGN. A noise source consists of a reverse-biased Zener diode, a series resistor, an operational amplifier, and a capacitor, as shown in Figure 2.
The noise generated by a Zener diode has a wide frequency range, with a significant portion being white noise (constant power spectral density). The noise voltage depends on the breakdown voltage of the Zener diode. Diodes with lower breakdown voltages (e.g., 5.1V) are often used, as they tend to produce more noise due to the dominance of Zener noise (tunneling effect).
Noise sources can be combined with amplifiers, precision attenuators, and filters to become semi-automated and automated instruments for generating AWGN with specific power levels and frequencies.
Maury Microwave customizes noise generation instruments to meet specific use-case requirements.
Noise sources can be combined with amplifiers, precision attenuators, and filters to become semi-automated and automated instruments for generating AWGN with specific power levels and frequencies.
The broadband AWGN generator features a powerful single-board computer with a flexible architecture designed to create complex custom noise signals for advanced testing systems. This adaptable platform enables users to address their most demanding design needs. High-precision components deliver strong output power with excellent flatness, while the versatile computer architecture provides control over multiple attenuators, switches, and filter banks (Figure 3).
Noise generation instruments can be automated to set and maintain a highly accurate ratio between a user-supplied carrier and internally generated AWGN, across a wide range of signal power levels and frequencies (Figure 4). The noise generator provides five operating modes: carrier-to-noise (C/N), carrier-to-noise density (C/No), bit energy-to-noise density (Eb/No), carrier-to-interferer (C/I), and power meter. The instrument can also function as a precision noise generator.
An automated solution includes a step attenuator and power sensor on the signal path and automatically adjusts the attenuation to reach the target signal-to-noise ratio (SNR).
Semi-automated allows a signal to pass through the instrument and combine with noise, but does not adjust the signal level (user must manually adjust).
In both cases, an external signal source is required and supplied by the customer.
Noise generation instruments produce AWGN with a high crest factor to simulate realistic “real-world” random jitter (Figure 5). This type of random jitter, often referred to as Rj in the industry-standard jitter hierarchy model, is crucial to manage for the optimal performance of high-speed communication buses and devices. Today’s high-speed digital circuit designers face the challenge of narrow jitter tolerances while striving to achieve high data rates and low bit error rates (BER).
Building a system that not only meets industry specifications but also remains robust against jitter to maintain a low BER is an ongoing challenge, especially as frequency and data rates increase. This noise generation tool allows designers to inject Rj directly into a data stream to assess device performance using typical measurement tools like oscilloscopes or bit error rate testers (BERTs). By adding precise amounts of white noise, the resulting decrease in SNR can be analyzed to evaluate the receiver’s performance. This approach helps minimize the overall timing budget, including necessary margins, to support higher data rates. The noise generator is capable of outputting this random noise (Rj) effectively for these evaluations.
In single-ended transmission, the signal is referenced to a common ground. The data signal is sent over one conductor, and its voltage is measured relative to a shared ground or reference point. Single-ended systems may have lower noise immunity, potentially leading to higher BER, especially in high-speed or noisy environments.
In differential transmission, the signal is sent over two complementary conductors. The voltage difference between the two lines (positive and negative signals) represents the data. Differential signals have better noise immunity since any external noise affects both conductors equally (common-mode noise). The receiver only detects the difference, effectively canceling out the noise.
Examples of delivered Noise Generation Instruments can be found at:
https://maurymw.com/products/noise-generators/programmable-noise-generators/
Including the:
