How To Interpret Ec/No parameters in 4G modems.


Scope


This article applies for all 2G, 3G and LTE devices. 


Intended Audiance


Public


In This Task


- Summary of issue


- Solution

        

- Related Articles


- Troubleshooting


Prerequisites


dB, dBm, dBi and dBd:

https://help.venntelecom.com/a/solutions/articles/44001930982?lang=en 


Summary


All devices (smartfones, 4G routers, ...) display some parameters to help optimizing 2G/3G/4G connexions.


This article explains how to interpret and optimize one of them : Ec/Io.


The Signal Strength is a very important and essential measure for any technology (GSM, CDMA, UMTS, LTE, etc.). However, it is not the only one. This article talks about another magnitude, equally important: Ec/Io (db), which impacts quality of signal.


Although this ratio is of fundamental importance to any cellular system, it is not well understood by many professionals. On the opposite side, professionals with a good understanding of this ratio are able to correctly assess the RF links, and also to perform more extensive optimizations, obtaining the best possible performance of the system.


There are many different factors that influence signal strength and quality, including but not limited to:

  • Tower load
  • Proximity to the cellular tower
  • Signal going through a cellular repeater
  • Competing signals
  • Physical barriers (mountains, buildings, trains, etc.)
  • Weather


Important note: measurements like Signal Quality Ec/Io do not incorporate all of the relevant factors to describe the quality of the connection. 


The other values to take in account are described in other related articles:


  • SINR - Signal-to-Interference-plus-Noise Ratio  (signal quality) (dB) (LTE only)
  • RSSI - Received Signal Strength Indication (signal power) (dBm) (2G, 3G and LTE)
  • RSCP - Received Signal Code Power (signal power) (dBm) (3G only)
  • RSRP - Reference Signal Received Power  (signal power) (dBm) (LTE only)
  • RSRQ - Reference Signal Received Quality (signal quality) (dB) (LTE only)



Disclaimers

  • Both Signal Strength and Signal Quality must be considered for successful cellular data connection
  • Measured or reported values vary by modem, carrier, and network environment
  • There is no black/white answer to what constitutes a successful connection
  • Although signal strength may appear to be adequate, throughput speeds may vary due to dependencies on cellular tower loads


Note that Power parametrs are expressed in dBm, Quality parameters in dB


Solution


Noise


Let's say you are having a conversation with someone in a kitchen that happens to have a loud refregirator.

Let's say the refregirator makes a noise of 50 dB.


If that someone whispers at 30 dB (signal) you will understand nothing. If that someone speaks at 60 dB you will still not understand everything. But if that someone speaks at 90 dB it may seem mre like a shouting match but at least every word will be clearly heard.


That's the idea behind as signal-to-noise ratio.



Eb/No


To begin, let's define the basic concepts of Eb and No. They are basic for any digital communication system, and generally we talk about it when we deal with Bit Error Rate and also Modulation techniques.


Bit Energy (amount energy per bit) on the Spectral Noise Density. Unit : dB


The ratio Eb/No is measured at the input of receiver, and serves to indicate how strong the signal is.



Depending on the modulation technique used (BPSK, QPSK, etc.) we have different curves for Bit Error Rate x Eb/No.

These curves are used as follows: for a certain RF signal, which is the bit errors rate that I have? Is this bit error rate acceptable for my system?


Whereas the gain that digital has, then we can set a minimum criterion of signal to noise ratio, in order to have each service (Voice/Data) operating acceptably.


 

 

In other words, the performance can theoretically be determined for the digital link.


The concept of Eb/No applies to any digital communication system. But today we will talk specifically about Ec/Io which is derived from it




Ec/Io (signal quality) (dB)


Ec /Io Indicates the downlink carrier-to-interference ratio (signal quality). 

Ec /Io is a negative dB value. 


Values closer to 0 are better signals.


So,this is a ratio of 'good' energy over 'bad' energy, or 'cleaness' of signal.



In following diagram : In red, in transmitter have a narrowband signal with data or voice modulated. This signal is spread and then transmitted through the middle (air). In the receiver, the signal is despread - using the same sequence that was spread - and thus recovering the base narrowband signal. 




A first observation is that often when we refer to Ec/Io, we are actually referring to Ec/(Io + No).

What happens is that for practical purposes the interference is much stronger than the noise which can be neglected.


To remember for further explanations:


Ec = Io + No
Ec = Io  when in a perfect world without noise


Downlink carrier-to-interference ratio =  Ec/(Io + No)
Downlink carrier-to-interference ratio =  Ec/Io when in a perfect world without noise


Ec/Io Positive and Ec/Io Negative ?


In terms of values and talking logarithmicaly:


- If any ratio is less than 1, then the value is negative. 

- If any ratio is greater than 1, then the value ispositive.



Why should we use Ec/Io?


A more natural question would be: why can we not simply use the Signal Strength measured by the mobile ?


The answer is simple: the measured signal level corresponds to the Total RF power - All cells that the mobile sees.

So we need another quick and simple measure that allows us to evaluate the contribution of each sector individually.


Measured Signal Level = Total RF Power (Io + No) - All other Cell Powers


Total RF Power (Io+ No) = Measured Signal Level + All other channels


In UMTS and CDMA systems there is a pilot channel and some other control channels such as paging, and traffic channels.


The pilot channel signal of each sector assesses the quality, if the level of the pilot is good, then the traffic channels will be good to in this sector. Likewise, if the pilot channel is degraded, so will the other channels (including traffic), and it is best to avoid using the traffic channels in this sector.


The Ec/Io varies with several factors, such as the Traffic Load and and RF Scenario.

Of course, the Ec/Io is the final composition of all these factors simultaneously (Composite Ec/Io), but it's easier to understand talking about each one separately.



Change in Ec/Io according to the Sector Traffic Load

 

 

Thus we have (no noise so No = 0):


Ec = 2 W

Total RF Power (Io) = Measured Signal Level + All other channels


Io = 0 + 2 + 2 = 4 W


Ec/Io = (2/4) = 0.5 W


As per definition of dB:


Io/Ec = 10 Log (0,5) = -3 dB


Now assume that several traffic channels are busy (eg use 6 W for traffic channels). This is a situation of traffic load, we'll see how is Ec/Io.


 

Thus we have (no noise so No = 0):


Ec = 2 W


Total RF Power (Io) = Measured Signal Level + All other channels

Io = 6 + 2 + 2 = 10 W


Ec/Io = (2/10) = 0.2

As per definition of dB:


Io/Ec = 10 Log (0,2) = -7 dB

 

Conclusion: as the traffic load in the sector increases, the Ec/Io worsens.



Change in Ec/Io according to the scenario RF


According to the RF scenario - a single server sector, some or many servers sectors - we can also take various measures to Ec/Io.


Considering first a situation without external interference, with only one server sector (dominant), the ratio Ec/Io is about the same initially transmitted.


 


Ec = 2W


Total RF Power (Io) = Measured Signal Level + All other channels

Io = 4 + 2 + 2 = 8 W


Ec/Io = (2/8) = 0.25 W


As per definition of dB:


Io/Ec = 10 Log (0,2) = -6 dB


Let us now consider another situation. Instead of one, we have five sectors signal arriving at the mobile (for simplicity, all with the same level).



 

Now have:


Ec = 2W

Total RF Power (Io) = Measured Signal Level + All other channels

Io = 4 + 2 + 2 + 2 +  2 + 4 +2 +2 + 4 + 2 + 2 + 4 + 2 + 2 + 4 = 40 W


Ec/Io = 0.05


As per definition of dB:


Io/Ec = 10 Log (0,05) = -13 dB



Conclusion: as many more sectors serves the mobile, the Ec/Io worsens.

 

This situation where we have many overlapping sectors, and with the same level of signal is known as Pilot Pollution - the mobile sees them all at once - each acting as interferer to each other.


The solution in such cases is to eliminate unwanted signals, by setting power parameters or physical adjustments (tilt, azimuth), leaving just dominant signals which should exist at this problematic place.


What are typical values?


The value of Ec/Io fluctuates (varies), as well as any wireless signal. If the value starts to get too low, you start to have dropped calls, or can not connect. But what then is a good range of Ec/Io for a sign?


In practical terms, values of Ec/Io for a good evaluation of the network (in terms of this indicator) are shown in the diagram below.

 


A composite Ec/Io ~ - 10 db is a reasonable value to consider as good.


Note: See we are talking about negative values, and considering them 'good'. In other words, we are saying that energy is below the Noise (and still have a good situation).

This is a characteristic of the system itself, and Ec/Io 'most negative' or 'less negative' is going to allow assessment of the communication.

In situations where Ec/Io is very low (high negative number), and the signal level too (also high negative number), first we need to worry in enhancing the weak signal.


Another typical situation: if the measured Ec/Io is very low, even if you have a good signal level, you can not connect, or the call will drop constantly.


Conclusion


This is a very important measure, which somehow ignores the overall strength of the signal, and focuses on how best to evaluate the pilot channel signal is desired, in relation to noise that interferes with it.


The EC/IO is a measure of the quality/cleanliness of the signal from the tower to the modem and indicates the signal-tonoise ratio (the ratio of the received/good energy to the interference/bad energy). 

It is measured in decibels (dB). 


In a perfect world, where there is no true interference, the interference level is equal to the noise level resulting in an 

Ec/Io = 0 dB. Once the Ec/Io is above ~ -7.0 dB, your connection is going to suffer.


There are several factors that can contribute to a higher Ec/Io value, including florescent lighting, electric motors, equipment, power supplies, bad/poor cabling, trees, hills, buildings, walls, shorted connectors, inaccurate antenna alignment, wrong antenna polarization, congestion at the tower, etc.



 

Some articles give the levels in a slightly different way.



There are several factors that can contribute to a higher EC/IO value, including florescent lighting, electric motors, equipment, power supplies, bad/poor cabling, trees, hills, buildings, walls, shorted connectors, inaccurate antenna alignment, wrong antenna polarization, congestion at the tower, etc. 


Ec/Io and other measures



As mentionned in the summary, remember that measurements like Signal Quality (Ec/Io) do not incorporate all of the relevant factors to describe the quality of the connection.


The other values to take in account are described in related articles:


  • SINR - Signal-to-Interference-plus-Noise Ratio (signal quality) (dB) (LTE only)
  • RSSI - Received Signal Strength Indication (signal power) (dBm) (2G, 3G and LTE)
  • RSCP - Received Signal Code Power (signal power) (dBm) (3G only)
  • RSRP - Reference Signal Received Power  (signal power) (dBm) (LTE only)
  • RSRQ - Reference Signal Received Quality (signal quality) (dB) (LTE only)



For formula lovers, relationships between Ec/Io and other measurements: 



Used forFor 3G only:



Related Articles


https://help.venntelecom.com/a/solutions/articles/44001930982/edit?lang=en

https://help.venntelecom.com/a/solutions/articles/44001930601?lang=en 

https://help.venntelecom.com/a/solutions/articles/44001931194?lang=en

https://help.venntelecom.com/a/solutions/articles/44001930999?lang=en

https://help.venntelecom.com/a/solutions/articles/44001931273?lang=en



Troubleshooting


For troubleshooting please contact Venn on +32 318 48 25.