AS (Azimuth spread)

Introduction:

In wireless communication systems, the propagation of electromagnetic waves in the atmosphere is influenced by various factors, including path loss, fading, and multipath propagation. Multipath propagation is a phenomenon that occurs when multiple copies of the transmitted signal reach the receiver through different paths. Each copy of the signal may have different propagation characteristics due to differences in the physical environment, such as reflection, diffraction, and scattering. The combined effect of these copies can result in constructive or destructive interference, leading to signal variations at the receiver.

One of the important parameters that describe the characteristics of multipath propagation is the Azimuth Spread (AS). In this article, we will explain what azimuth spread is, how it is measured, and its importance in wireless communication.

What is Azimuth Spread (AS)?

Azimuth Spread is a measure of the angular spread of the multipath components arriving at the receiver. It describes the range of angles over which the signal power is distributed due to multipath propagation. The angular spread is typically defined in the horizontal plane, i.e., the plane perpendicular to the direction of the transmitter-receiver path. The AS is a function of the physical environment, including the terrain, buildings, and other obstructions that can cause signal reflections, diffraction, and scattering.

How is Azimuth Spread measured?

Azimuth Spread can be measured in several ways, depending on the measurement equipment and the measurement environment. One common method is to use a directional antenna at the receiver to measure the power of the received signal as a function of the antenna's direction. By rotating the antenna and measuring the signal power at different angles, the angular spread of the signal can be estimated. Another method is to use a channel sounder, which is a specialized measurement device that can measure the characteristics of the wireless channel, including the power and delay of the multipath components. The channel sounder can be used to estimate the AS by analyzing the distribution of the arrival angles of the multipath components.

Why is Azimuth Spread important in wireless communication?

Azimuth Spread is an important parameter in wireless communication because it affects the quality of the received signal. When the AS is small, i.e., the angular spread of the signal is narrow, the signal components arriving at the receiver are more coherent, resulting in less signal variations due to multipath propagation. In contrast, when the AS is large, i.e., the angular spread of the signal is wide, the signal components arriving at the receiver may be more spread out in time and frequency, resulting in more severe fading and signal variations. Therefore, knowledge of the AS is crucial for designing wireless communication systems that can mitigate the effects of multipath propagation.

One application where AS is particularly important is in the design of wireless networks that use beamforming techniques to improve the signal quality. Beamforming is a signal processing technique that involves adjusting the phase and amplitude of the signals transmitted by an array of antennas to form a directional beam towards the receiver. By directing the transmitted signal towards the receiver, beamforming can improve the signal-to-noise ratio (SNR) and reduce interference from other sources. However, the effectiveness of beamforming depends on the accuracy of the beam direction, which is influenced by the AS. If the AS is large, the beam direction may be less accurate, leading to degraded signal quality.

Another application where AS is important is in the design of wireless systems that use diversity techniques to mitigate the effects of fading. Diversity techniques involve using multiple antennas at the transmitter and/or receiver to improve the signal quality by exploiting the variations in the received signal caused by multipath propagation. The effectiveness of diversity techniques depends on the statistical properties of the fading channel, including the AS. If the AS is small, diversity techniques may be less effective since the signal variations due to multipath propagation may be small. In contrast, if the AS is large, diversity techniques may be more effective since the signal variations due to multipath propagation may be more significant.

Moreover, the AS is also used in the design and optimization of wireless communication systems that use frequency-selective channels, such as OFDM (Orthogonal Frequency Division Multiplexing). In OFDM systems, the available bandwidth is divided into subcarriers, each of which is modulated with a different symbol. The subcarriers are spaced such that they are orthogonal to each other, which reduces interference between adjacent subcarriers. However, the effectiveness of OFDM depends on the channel characteristics, including the AS. If the AS is large, the subcarriers may experience different fading characteristics, which can result in inter-carrier interference (ICI) and degrade the system performance. Therefore, the AS is an important parameter that needs to be considered in the design and optimization of OFDM systems.

Conclusion:

In summary, Azimuth Spread is an important parameter that describes the angular spread of the multipath components arriving at the receiver in wireless communication systems. The AS is influenced by the physical environment, including the terrain, buildings, and other obstructions that can cause signal reflections, diffraction, and scattering. The AS is crucial for designing wireless communication systems that can mitigate the effects of multipath propagation, such as beamforming and diversity techniques. Moreover, the AS is also important in the design and optimization of wireless systems that use frequency-selective channels, such as OFDM. Therefore, the AS is a fundamental parameter that needs to be considered in the design, optimization, and evaluation of wireless communication systems.