Initially, many designers may be concerned about the complexity of regional norms, because in different regions of the world, norms vary. However, as long as more research is done, it will be able to understand and comply with the regulations of different regions, because, in each region, there is usually one government unit responsible for promulgating the relevant documents to explain "the rules relating to specific-purpose transmitters."

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Antenna diversity technology principle
Written By Calio Huang
Initially, many designers may be concerned about the complexity of regional norms, because in
different regions of the world, norms vary. However, as long as more research is done, it will be
able to understand and comply with the regulations of different regions, because, in each region,
there is usually one government unit responsible for promulgating the relevant documents to
explain "the rules relating to specific-purpose transmitters."
Part of the more difficult aspect of radio communications is that the quality of the radio link is
linked to a variety of external factors. The combination of multiple variables creates a complex
transmission environment that is often difficult to interpret. However, mastering the basic
concepts often helps to understand the changing quality of the radio link, many of which can be
solved by a technique known as antenna diversity that is low-cost and easy to implement once
these basic concepts are understood achieve.
Environmental considerations
The primary environmental factors that affect the consistent stability of a radio communication
link are phenomena known as multipath/fading and antenna polarization/diversity. The impact
these phenomena have on the link quality is either constructive or destructive, depending on the
specific environment. There may be too many things happening, so it is very difficult when we try
to understand the role of certain 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, and although antenna polarization is sometimes interpreted as the degradation in
the quality of certain radio communication links, some radio communication designers often
utilize This feature to adjust the antenna, by limiting the send and receive signals within the limits
of the direction of its reach. This is possible because the antenna radiates unevenly in all
directions and uses this feature to shield RF noise from other (directional) sources.
Simply put, the antenna is divided into two kinds of omnidirectional and directional. The
omnidirectional antenna transmits and receives signals with the same strength in all directions,
while the directional antennas transmit and receive signals are confined within a range of
directions. To build a highly robust link, you must start by understanding this application. For
example: If the signal on one link only comes from a particular direction, then it is far more
beneficial to choose a directional antenna. Receivers equipped with directional antennas receive
signals from transmitters located within the range of line-of-sight determined by antenna
direction attributes, while signals from other transmitters located outside of that range are
masked.
A transmitter with a directional antenna transmits most of its energy in a predetermined
direction rather than in all directions without reducing its coverage.
In order to simplify the understanding of the antenna profile, antenna manufacturers provide
antenna radiation patterns. Antenna patterns have different patterns, such as E plane plot and
polar plot:

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figure 1
Figure 1. In addition to the directionality or shape, the E-Plane provides a wealth of information,
but it is often not as clear as the lobe diagram illustrates. The lobe map is designed to be a
compass-like, making it easier to understand the antenna gain in any given direction.
figure 2
As shown in Figure 2, engineers can see an advanced three-dimensional view of how the antenna
works on the intended plane. Antennas, however, also tend to change characteristics on other
axes, but usually do not provide 3D graphics data as this can significantly increase the complexity
of the graph. The rod antenna is a typical omnidirectional antenna with a simple
three-dimensional profile. Rod aerials provide excellent coverage in plan view, but in 3D they
perform poorly above or below themselves, helping us to better understand the antenna being
placed in a two-story indoor environment Case.
In general, it is not easy to observe the effects of antenna polarization due to the RF signal being

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reflected by walls and other indoor objects. However, other effects that may be constructive or
destructive to RF signals can still be observed. This effect is referred to as multi Path/attenuation.
This attenuation is usually observed when the transmitter or receiver is slightly displaced and has
a large difference in the quality of the link. This happens when the antenna is receiving and
transmitting the signal's crest.
Multiple paths are an extension of this concept. When radio communication waves are
transmitted, there may be more than one path they receive by the receiver, which may come
from multiple paths due to the reflection of other objects, such as walls and trees. Receiving
signals from these sources may arrive slightly shorter, which means a slight phase shift may occur.
When these signals are combined, they may result in "attenuating this disappearing form." One
of the worst cases is that the two signals arrive at the receiver at a phase difference of 180 °and
the receiver will not be able to see any data resulting in 100 % Of the signal attenuation in most
cases, the receiver is unlikely to receive two signals 180o phase offset, but when the multi-path
environment, some of the phase shift is still possible, Under these circumstances, some signal
degradation occurs.
Antenna diversity
Antenna diversity is a technique that is used to restore signal integrity. Antennas that implement
antenna diversity in the product have a 90o antenna mount with the other antenna so that the
effects of polarization /directivity will not reduce the quality of the potential radio
communication link. In addition, each antenna in a product that implements antenna diversity
maintains its antenna shelf at a distance of at least a quarter of a wavelength, which ensures that
at least one antenna is in the crest of the waveform.
While antenna diversity is quite beneficial for restoring signal integrity and for maintaining link
boundaries from the environment, significant sacrifices must be made in other areas, which
means an increase in the overall cost of a microcontroller (MCU) as a result of micro-control The
device must be on standby for a long time to evaluate the antenna signal from time to time. The
addition of microcontroller functionality will result in the need for higher-profile and more
expensive microcontrollers, which must be "on-call," leading to reduced battery life. In other
cases, the solution with two antennas will increase Additional space requirements or the need
for additional coding expertise, all limit the designer to a single antenna design.
Coding an antenna diversity system will increase the design coding burden. 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 begin receiving data. In these
cases, the microcontroller can immediately begin evaluating the signals from both antennas. To
evaluate this signal, the microcontroller switches each antenna and assesses the Received Signal
Strength Indication (RSSI) level. In other products where the receiver does not use a timer, radio
communications must detect the beginning of a packet because the preamble may be misjudged
as noise (or vice versa), and unfortunately, the strength of a particular antenna Noise may cause
the beginning of the package to be missed.
To confirm that the frequency of this antenna switch is sufficient to capture the packing of one of
the antennas, a timer is started whenever the algorithm enters the Measurement SQ function.
At least switching time

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Where TPL is the longest time (eg, packetized preamble) that can be tolerated in a particular
signal portion to select an antenna N is the number of antennas used by the diversity receiver.
During the "Measure SQ" function, the signal quality (SQ) is measured. If SQ is below the signal
quality threshold or the timer expires, the antenna is switched and the "Measure SQ" status is
activated again. On the other hand, if the measured SQ is above the SQ threshold, the receiver
continues to use the selected antenna to receive the remaining packs.
It may be that when the antenna is selected because of a valid signal indication, the signal quality
may still be worse than the best signal, since 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 Radio antenna diversity algorithm first detects the other antenna before selecting
the one with the highest signal quality to see if there is a higher signal quality.