ibc basic knowledge

8/13/2019 IBC Basic Knowledge

1/13

RTWP (Received Total Wideband Power)

Received Total Wideband Power.

Represents a measure of UMTS technology: the total level of noise within the UMTS frequency band of any cell.

RTWP is related to uplink interference, and its monitoring helps control the call drops - mainly CS. It also has

importance in the capacity management, as it provides information for the Congestion Control regarding Uplink

Interference.

In UMTS, the uplink interference may vary due to several factors, such as the number of users in the cell, the

Service, Connection Types and Conditions of Radio, etc..

As our goal is to always be as simple as possible, we will not delve in terms of formulas or concepts involved. We

will then know the typical values, and know what must be done in case of problems.

Typical Values

Ok, we know that RTWP can help us in checking the uplink interference, then we need to know its typical values.

In a network is not loaded, normal, acceptable RTWP Average value is generally around -104.5 and -105.5 dBm.


2/13

Values around -95 dBm indicate that the cell has some uplink interferers.

If the value is around -85 dBm, the situation is ugly, with strong uplink interferers.

Usually we have High, Low and Medium measures of RTWP. However, the maximum and minimum values are

recommended only as auxiliary or reference, since they may have been caused by a peak of access, or even been

forced to have a momentary value due to some algorithm i.e..

Thus, the value that helps us, and has the most accurate information is the same Mean RTWP!

For cases in which cell has two carriers, the difference between them RTWP should not exceed 6 dB.

Based on these typical values, most vendors have an alarm: RTWP "Very High. "

What to do in case of problems?

We have seen that RTWP can cause performance degradation, mainly CS Call Drops. Note: Actually, it's not RTWPthat causes performance degradation. What happens is that when its value is 'bad', it's actually indicating the

presence of interference - the latter being responsible for degradation.

But what can we do when we find bad values?

If RTWP is not at acceptable levels, some actions should be taken.

The first thing to do is check if there is a configuration issue with the RNC or NodeB. This is the mostcommon case, especially in cases of new activations.

Once verified the parameter settings, the next step is the physical examination, especially jumpers andcables, often partially reversed. It also should be checked if there is faulty transmitters, or any other

problem that could generate intermodulation between the NodeB and the antenna. If the parameter settings and hardware are ok, the chance is very high that we have external interference,

such as a Interferer Repeater.

In cases where there may be external interference, we must begin to act after such a prioritization based on how

much this is affecting the cell KPI's across the network, if it carry high traffic, major subscribers, etc..


3/13

Note: There are many forms of interference in the uplink, both internal and external. Only a few are listed above.

The deepening of all possibilities is beyond the goal of being simple to teach the concepts, but this is a suggestion

for whoever wants to deepen the study, identification and elimination of interference.

In practice

to find - and eliminate - problems of interference is one of the biggest challenges in our area. For being such a

complex problem, we recommend that be collected enough data for each investigation. Insufficient data collected

can lead to erroneous conclusions, further worsening the problem.

The uplink interference may appear only in specific periods. Thus, it is recommended that data be collected from

at least one week (7 days) for every 24 hours. Usually this amount of data is sufficient. In the figure below, we see

different days and times - colorful - a fictional example where the interference occurred.

Data should be collected for the suspicious cell, but also for its adjacent cells, allowing it to make a triangulation

increasing the chances of locating the source of interference.

Another way to locate the source of interference is to do a test in field. An antenna guy must gradually change the

azimuth of the antenna, while another professional do RTWP measurements. That is, through the information

directing the antenna and the respective values of RTWP, you can draw conclusions very good.

It is obvious that changing the online system may not be a good practice, and tests can be made with a Yagi

antenna and a Spectrum Analyzer.

Vendors offer several ways to measure RTWP, using the OSS, performance counters and logs.


4/13

Conclusion

In this brief tutorial, we learn what is RTWP, and that the ideal typical value is about -104.5 dBm and -105.5 dBm.

As the RTWP is directly related to Uplink Interference - and we know that interference is the main cause of

performance degradation - have concluded that improving RTWP, ie making is as close as possible to -105

dBm, improving the Call Drop Rate!

IMPORTANT : Seizing the opportunity, see what was stated at the start of this tutorial - dictionary - by describing

RTWP. Remember that this site has been the subject of a very interesting tutorial in the TipsSection. If you have

not visited this section of the portal yet , I strongly recommend, because it has many issues that help in our growth

in telecom and IT area.
http://www.telecomhall.com/tips.aspxhttp://www.telecomhall.com/tips.aspxhttp://www.telecomhall.com/tips.aspxhttp://www.telecomhall.com/tips.aspx


5/13

RF Components - RF Power Divider and RF Power Combiner

To know all the equipments used in your area and work, is a basic necessity of any professional. And understand its

features and functions (applications) often represents the difference when getting a new job, or find solutions to

problems.

In the Telecommunications & IT area we have a wide range of equipment (or components), which vary according

to the specific area of expertise. For each of these equipment you can find a huge documentation available in the

form of catalogs, courses, white papers, presentations, etc.

Many times however the basics - the most important - are not fully understood by all, even by those who use them

in practice.

With the goal of explaining in a simple way the main features of RF components, we initiate today this new series

here at telecomHall.

However we'll no delve into details as calculations and definitions - more extensive or complex. Let's just stick to

the main objective: to meet the basic and essential part of each equipment. With this basis, any deepening in the

studies can be done more easily, if you want.

And to start, let's meet two of these elements: the RF Power Splitter (or 'Splitter') and the RF Power Combiner.

Goal

Present in a simple way RF components: Splitter and Combiner.


6/13

RF Power Divider

Let's start with one of the most simple and intuitive of these components: splitter.

Splitter, as the name implies, divides.

In nature we can see an example of splitter on a river that has an obstacle, and splits into two. In this case, part of

the water continues down a path, and another part by another way.

In the case of RF Dividers, instead of water, it is the RF signal that is divided - in that case the input signal is

'divided': the form remains unchanged, but the 'power' is splitted. For this reason, the RF dividers are known as RF

'Power' Splitters.

In the following figure, we see a simple illustration of a Splitter. The signal (represented by large red circles) goes in

one side and out the other two (B) and (C).

Note that the output signal is the same (has the same form), but each output has 'half' the power of the original

signal (small red circles).

Basically, that's what the divisor does. And the next question then would be: 'Why or where do I use the splitter?'.

Imagine the following situation: a small rural community was contemplated by the RF planning of your company

with the installation of a new BTS. The point for the installation of the Tower has already been acquired: its on asmall hill in the Centre of 3 small regions, with good line of sight to all, as seen in the figure below.


7/13

Unfortunately, for reasons of 'cost reduction', the BTS has only 2 cells.

But there are 3 regions to be served (covered). And then, what to do?

Ok, we know that in the case shown above the ideal solution would be the installation of 3 cells but we don't

have this configuration available! Given this scenario, the alternatives would be leaving one of the small

communities without coverage or ... install a divider (splitter).

We can minimize the problem presented by simply using a divider (splitter) split one cell into 2 cells, attending all

3 regions of interest, and achieving the satisfaction of a larger number of people (all potential new customers).


8/13

An important observation in the case above is that the cell that is 'NOT' divided (yellow in the figure) should cover

the denser region, because that is what will have the greatest traffic. And the cell that will be divided will cover

simultaneously the other 2 smaller regions (in blue in the figure).

In addition, each of the two cells in blue has half the power of the yellow sector (considering the same transmitter

power for each one). This 3 dB difference must be taken into account so there's no loss of quality, mainly in

'indoor' regions. Anyway, this can be fixed through adjustments, if for example it is possible to increase the power

of the transmitter. Will depend of course on how is the quality in the regions met usually in cases like this, we

don't have many losses in practice.

And as already mentioned, this is not the 'final solution', but it sure is the best action to take, considering the

scenario above - cover all small regions. In the future, with the development and progress of each of these regions

(and consequently greater use of telecommunications services) we will have then justifications for expansion of

the third cell in BTS.


9/13

Ok, we've seen how an RF Power Divider works, and also a good example of its implementation.

But the dividers not only divide for 2 outputs. We have for example a splitter with 4 outputs. In this case, each

output will be 1/4 of the original signal strength (remember that dividers always divide 'equally' the input signalbetween all outputs).

Note: one of the most important points when it comes to RF Dividers is the insertion loss, i.e. the loss that we've

added to the system when we inserted such elements. The bigger the loss entered in the system, the lower part of

the signal will arrive at your destination, which is bad.

So when we talk about that in a 4 outputs splitter will have 1/4 of the original signal strength on each output we're

'disregarding' the loss by inserting the component itself, and considering only the loss resulting from the division of

signal (whose order of magnitude is much larger).

So in practice what are the losses that I have using the RF Splitter (splitter)?

Assuming NULL the loss by inserting the element (i.e. kept the characteristic impedance of the system), and taking

into account only the loss by dividing the signal into more outputs, we have the following correspondence table of

'Number of Output Ports' x 'Power Level Reduction' in a Divider (splitter).


10/13

For example, if at the input of a 4 output divider we have a signal of -84 dBm, there will be a signal of -90 dBm in

each one of its outputs.

Another important information regarding RF Power Dividers (splitters) is about isolation, i.e. a signal should not

interfere with the other. For this, it is important to know the characteristics of construction.

Its construction can be through the use of resistors or transformers, being these last used in examples like the

above. But beyond our scope today, and later we'll explain in a simple manner its construction and operation,

explaining in more detail how this isolation works.

For now, just know that all RF Splitter are passive elements, i.e. you don't need power.

Yet we are also NOT analysing other aspects such as different frequencies or technologies. Let's first understand

the most important aspects (main) in its simplest form. In the next series of tutorials let's gradually assimilating the

countless possibilities of combination and use of such equipment.

At this point then we already know the RF Power Divider, we understand its basic operation and for what it serves,and we also saw a practical example of use.

Let's continue and learn a 'new' RF component.

What do you think would happen if we reversed the use of equipment that we showed at the beginning of this

tutorial?


11/13

RF Power Combiner

If we reverse the use of equipment shown at the beginning of the tutorial, inputting 2 different signals on ports (B)

and (C), we have the sum, or 'combination' of these signs on the output (A).

You've probably noticed that, actually, the combiner is nothing more than a divider, but used in the reverse way,

right?

And that's exactly what it is: a RF Power Combiner simply combines (sum) different signals in a single output. In the

above case, the signals are transmitted over port B and C go out through that output (A).

In the same way as the divider, the name is suggestive: the combiner combines! At first you can find very simple ...

and it really is, but it is extremely important for all systems where we need group (and ungroup) signals with same

or similar characteristics.

The RF Power Combiner then are used in applications where it is necessary to transmit/send multiple signals over a

single medium.

We will use the same example above, to see how this is done. A user (in yellow in the figure) transmits his

conversation, which arrives via antenna (1) to the BTS (2). Another user (red) also broadcasts their conversation,

only via antenna (3) until the same BTS. On BTS then these signals are present (summed or combined), and the BTS

can then continue the processing of each one of the calls.


12/13

See that the different signals of each one of the users (yellow and red) were then summed (or combined) in a

combiner, and both signal followed by a single cable from antennas to the BTS.


13/13

The combiner doesn't make any kind of transformation or change in the signal. Simply combines them into a single

output.

And also it is easy to understand that all the features as Loss and Isolation of RF Power Combiner are the same

we've previously seen for the divider. As the divider, the combiner is also a passive element.

Ok, you now know what is a RF Power Combiner!

What we've seen so far applies to signals that have the same characteristics, no matter the frequency: the splitter

and combiner 'don't care' about the frequency.

But what about when we need to convey different and specific frequencies via a single broadband antenna, what

do we do?

In this case, we need to 'adjust' the RF filters to ensure that interconnection in a single transmission medium.

But this is already subject to the next tutorial in this series.

Conclusion

We completed the first tutorial in the series of RF components, understanding in a simple way what are and what

are they for: RF Power Combiners and Splitters. Now we are prepared to meet and understand other elements

(the next tutorials).

It is very important that these basic concepts (in a simple way) are well understood, because it is very common

that questions arise in the definitions between these elements and other elements that we'll see in sequence.

In fact, there may be doubt even among combiner and splitter, because we have seen that a combiner can be used

as splitter and vice versa. That is, often the difference is only in use.

ibc basic knowledge

Documents