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Read the principle of antenna diversity technology in one article
Author:admin    Released in:2018-06-06 09:45:40    Written words:【Big】【In the】【Small
Abstract:Multiple paths are an extension of this concept. When radio communication waves are transmitted, they may be received by the receiver with more than one path. Since the reflection of other objects (such as walls and trees) forms multiple paths, the signals may come from multiple paths. Receiving signals from these sources may have a slight time difference, which means a slight phase shift may occur. When these signals are combined, they may cause "attenuation of this disappearing form. One of the worst cases is that the two signals arrive at the receiver with a phase difference of 180°, and the receiver will not be able to see any data, resulting in 100% signal attenuation.

Initially, many designers may be concerned about the complexity of regional specifications because different regional specifications vary across the world. However, as long as more research is done, it is possible to understand and comply with the regulations of different regions, because in each region, there is usually a government unit responsible for promulgating relevant documents to explain the rules related to the specific purpose of the launch.


A more difficult part of understanding in radio communications is that the quality of the radio link is related to a variety of external factors, and the intertwining of multiple variables creates a complex transmission environment that is often difficult to interpret. However, mastering the basic concepts often helps to understand the quality of the changing radiocommunication links. Once these basic concepts are understood, many of these problems can be solved by a low-cost, easy-to-implement technique called antenna diversity. achieve.


Environmental considerations


The primary environmental factor affecting the continued stability of radio communication links is the phenomenon known as multipath/fading and antenna polarization/diversity. The impact of these phenomena on link quality is either constructive or destructive, depending on the specific environment. There may be too many situations, so it is very difficult when we try to understand the role of specific environmental conditions at a certain point in time on the radio link and what kind of link quality will result.


Antenna polarization/diversity


This phenomenon known as antenna polarization is caused by the directional properties of a given antenna. Although antenna polarization is sometimes interpreted as attenuation in the quality of certain radio communication links, some radio communication designers often make use of it. This feature adjusts the antenna by limiting the transmit and receive signals to within a defined range of directions. This is possible because the antenna is not uniformly radiated in all directions and this feature can be used to shield RF noise from other sources.


Simply put, the antenna is divided into omnidirectional and directional. When the omnidirectional antenna transmits and receives signals, the strength is the same in all directions, and the directional antenna's transmission and reception signals are limited to one direction. To build a highly robust link, you'll start by understanding the app. For example, if the signal on one link is only from a specific direction, then choosing a directional antenna will benefit more. A receiver equipped with a directional antenna receives a signal from a transmitter located within a range of line-of-sight directions determined by the direction properties of the antenna, while other signals from transmitters outside the range of direction are shielded.


A transmitter equipped with a directional antenna emits most of its energy in a predetermined direction, rather than transmitting in all directions, without reducing its coverage.


To simplify the understanding of the antenna profile, the antenna manufacturer provides an antenna radiation pattern. Antenna radiation patterns have different formats, such as E plane plots and polar plots:


 

 Figure 1

Figure 1. In addition to directionality or shape, the E-surface map provides a lot of information, but it is usually not as clear as the lobes. The lobe map is designed to resemble a compass, making the antenna gain in any given direction easier to understand.


  Figure 2

As shown in Figure 2, the engineer can see an advanced three-dimensional view of how the antenna operates on a predetermined plane. However, antennas also tend to change characteristics on other axes, but generally do not provide 3D graphics data, as this can significantly increase the complexity of the chart. The whip antenna is a typical omnidirectional antenna with a simple three-dimensional profile. In the plan view, the whip antennas provide excellent coverage, but in 3D graphics, they perform very poorly directly above or below themselves, which helps us to understand that the antenna is placed in a two-story indoor environment. Case.


Usually, since the RF signal is reflected by walls and other indoor objects, it is difficult to observe the effect of antenna polarization. However, other effects on the RF signal may be observed to be constructive or destructive. This effect is called Diameter / attenuation. This type of attenuation is usually observed when the transmitter or receiver is moving slightly and the link quality is greatly different. This happens when the antenna is receiving and transmitting the peaks of the signal.


Multiple paths are an extension of this concept. When radio communication waves are transmitted, they may be received by the receiver with more than one path. Since the reflection of other objects (such as walls and trees) forms multiple paths, the signals may come from multiple paths. Receiving signals from these sources may have a slight time difference, which means a slight phase shift may occur. When these signals are combined, they may cause "attenuation of this disappearing form. One of the worst cases is that the two signals arrive at the receiver with a phase difference of 180o, and the receiver will not be able to see any data, resulting in 100. % signal attenuation. In most cases, the receiver is unlikely to receive two signals with a phase offset of 180o, but some phase offsets are still possible when multiple path environments occur. In these cases, some signal attenuation occurs.


Antenna diversity


Antenna diversity is a technique used to restore signal integrity. The antenna that implements antenna diversity in the product has a 90o antenna frame with the other antenna, so the effect of polarization/orientation will not degrade the quality of the potential radio communication link. In addition, each antenna in the product that implements antenna diversity maintains the position of the antenna frame at a distance of at least 1/4 wavelength, thus ensuring that at least one antenna is in the peak of the waveform.


Although antenna diversity is beneficial for restoring signal integrity and maintaining link boundaries from the environment, it must be sacrificed in other respects, meaning that the overall cost of the microcontroller (MCU) increases because of micro-control. The device must be on standby for a long time to evaluate the antenna signal from time to time. The increased microcontroller functionality will result in the need for higher specification and more expensive microcontrollers, and the microcontroller must be “on standby, resulting in reduced battery life. In other cases, the solution with two antennas will increase. Additional space requirements, or the need for additional coding expertise, limits the designer's ability to use a single antenna design.


Encoding an antenna diversity system will increase the coding burden on the design. Many antenna diversity systems are optimized to operate in a synchronized manner. The microcontroller on the receiver has a timing function that lets the receiver know when to start receiving data, in which case the microcontroller can immediately begin evaluating the signals from both antennas. To evaluate this signal, the microcontroller switches each antenna and evaluates the Received Signal Strength Indication level (RSSI). In other products where the receiver does not use a timer, radio communication must detect the start of a packet because the preamble may be misjudged as noise (or vice versa), unfortunately, in a particular antenna. Noise can cause the beginning of the package to be missed.


To confirm that the frequency of this antenna switching is sufficient to capture the packing of one of the antennas, whenever the algorithm enters "Measure SQ function, a timer is started.


Minimum switching time


Where: TPL is the maximum time (eg, packed preamble) that can be allowed to select an antenna in a particular signal portion. N is the number of antennas used by the diversity receiver.


During the "Measure SQ function", the signal quality (SQ) is measured. If the SQ is lower than the signal quality threshold or the timer time is over, the antenna will be switched and the "SQ state" will be started again. On the other hand, if the measured SQ is higher than the SQ threshold, the receiver will continue to use the selected antenna for the reception of the remaining packets.


It may be the case that when the antenna is selected due to a valid signal indication, its signal quality may still be worse than the optimal signal because the measurements made on the antenna may be occupied by noise before the packet arrives. When the first valid signal quality indicator is generated, the EZRadioPRO antenna diversity algorithm will detect other antennas first to see if there is a higher signal quality before selecting the antenna with the highest signal quality.

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