[Turn] what is Ec/io (and eb/no)?

Ps:http://www.telecomhall.com/what-is-ecio-and-ebno.aspx

If someone asks "which Signal level for good call quality: -80 dbm or-90 dbm?"

Beware, if you respond quickly, you might end up missing. This was because the correct answer is ... it depends! The Signal strength is a very important and essential measure for any technology (GSM, CDMA, UMTS, LTE, etc). However, it isn't the only One:let's talk a little today about another magnitude, equally important:the Signal Noise Ra Tio.

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

So, let's see a little about it?

Eb and No

To begin, we define the basic concepts of Eb and No. They is basic for all digital communication system, and generally we talk about it when we deal with Bit Error rate and a LSO modulation techniques.

Simply put:

• Eb: Bit energy.
  • It represents the amount of energy per bit.
• No: Noise spectral Density.
  • Unit:watts/hz (or Mwatts/hz)

Which brings us to the classic definition of eb/no:

• eb/no: Bit Energy on the spectral Noise Density.
  • Unit:db

It did not help much, does it?

Do not worry. Indeed, only with the theoretical definition was still very difficult to see how this ratio was used, or how it can be Measu Red.
But okay, let ' s walk a little further.

Okay, so what is eb/no measured?

To understand about this ratio can is measured, let's imagine a simple digital communication system.

The ratio eb/no is measured at the 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 is used as follows:for a certain RF signal, which was the bit errors rate? Is this bit error rate acceptable for my system?

Whereas the gain that digital had, then we can set a minimum criterion of signal to noise ratio, in order to having each Ser Vice (voice/data) operating acceptably.

In other words, we can theoretically determine how the performance would is for the digital link.

Note:it is worth remembering here's a very complex subject. As always, we try to introduce to the most simplified possible through the use of examples and simple concepts. Okay?

For example, a concept this could be explored here-since we is talking about digital communication system-is the Nois E figure. But we don't want to repeat the theory explained in the University. Nor is it to has mentioned the noise figure here, but as we talked about it, just understand as a noise level that every Receiver has, and which it is due to the process of amplification and processing of signal.

Concepts like this, and the other even more complex, can is studied, if you wish. But now, let's continue with our signal to noise ratio.

Eb/no-Ec/io

The concept of eb/no applies to any digital communication system. But today we were talking specifically to Ec/io, which is a measure of evaluation and decisions of CDMA and UMTS.

Note:all The technology uses signal-interference ratio. For example, on GSM, we use c/i.

As we are speaking of codes, it becomes easier to understand the concepts by observing a simplified diagram of Spread Spec Trum modulation.

In red, in transmitter has a narrowband signal with data or voice modulated. This signal is spread and transmitted. And spreads through the middle (air). In the receiver, the signal are despread-using the same sequence that was spread-and thus recovering the base Narrowban D signal.

To proceed, we must know some more definitions. However, this is quite delicate, as we enter a conceptual area where we have differences between authors, difference s in Translations/countries, where differences in technologies is applied, etc.

Let's try to define in a generic-a, and only the main.

• No : Spectral Density of Noise;
  • Noise generated by the RF components of the system, the air, among others.
• Io : Interference is the Broadband; Interfering co-channel, including yourself setor.
• E : Is the signal (average) energy-do isn't confuse it with the sinal (average) power.
• B, C, S ...: Energy is the power points in time, therefore related to the measure or ' length ' of the Time (the average power is independent of time).
  • Hence It comes Eb, Ec and Es, respectively relating to Bit Chip and Symbol in different times.

Note:with These concepts, several formulas can be derived with different numerators and denominators. For example, Es = Eb * k, where k = number of bits per symbol. In QPSK modulation, where k = 2, Es = 2 * Eb. And the derivations of formulas can reach far more complex equations, such as the definitions of capacity of a AWGN Chann El, and further deductions for equivalences (ec/no, eb/nt, etc ...). Again, it's not we purpose here today. We only mention a few concepts, related.

Then come back to the practical level-noting that theoretical approaches can is done more easily later, after the basics is understood.

So let's keep today in ratios most common:eb/no and Ec/io.

As we defined eb/no is the Average energy of a bit signal, on the spectral Density of Noise. It is primarily a parameter related to the manufacturer for different bearers (based on the channel model). But it can also vary with the environment (urban, rural, suburban), speed, diversity, use of power control, application Ty PE, etc..

And now we can begin with define Ec/io, one of the most important systems in CDMA and UMTS.

Note:an important observation is the often when we refer to Ec/io, we be actually referring to ec/(Io + No). What happens are that for practical purposes, we are only having ec/io, because the interference is much stronger and the noise C An IS neglected. Otherwise:for CDMA interference is like a noise and then both can be considered the same thing.

Okay, let's stop with the issues and concepts, and talk a little on the values of these indicators and their use in PRA Ctice.

Eb/no Positive and Ec/io negative?

In terms of values, and talking logarithmicly, if any ratio are less than 1, then the value is negative. If greater than 1, positive.

We have ec/io in the air, which are spread across the spectrum:then we have negative value to the ratio of energy on the T Otal Noise (the energy was lower than the total interference). It is measured at the input of receiver (NodeB, UE, etc).

Regarding eb/no, it is in the baseband after despreading and decoded only for one user-then we have a positive amount of Energy over the total noise. It is measured at the output of receiver (NodeB, UE, etc).

Why should we use Ec/io?

A more natural question would be:why we can not simply use the Signal strength measured by the mobile as a guide for Oper Ations such as handover?

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 this allows us to evaluate the contribution of each sector individually.

We used to measure the pilot channel signal of all sector to assess the quality:if the level of the pilot are good, then Also is good levels for the traffic channels for we call in this sector. Likewise, if the pilot channel is degraded, so'll the other channels (including traffic) be, and it's best to avoid usi Ng the traffic channels in this sector.

UMTS and CDMA Systems, we have a pilot channel, some other control channels such as paging, and traffic channels.

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 UN Derstand talking about each one separately.

Change in Ec/io according to the Sector traffic Load

Each sector transmits a certain power. Suppose in our example we have a pilot channel power setting of 2 W, and a power of the other control channels also fixed at 2 W.

To make it easier to understand, we calculate the Ec/io (pilot channel power to total power) of this sector in a situation Where we have no busy traffic channel (0 W).

Thus we have:

Ec = 2 W

Io = 0 + 2 + 2 = 4 W

Ec/io = (2/4) = 0.5 = 3 DB

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

Ec = 2 W

Io = 2 + 2 + 6 = Ten W

Ec/io = (2/10) = 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 AB Out the same initially transmitted.

Ec/io = (2/8) = 0.25 = 6 DB

Whereas a signal coming from this sector in the mobile at level of-90 dBm (Io = -90 dbm), we have Ec = -90 dBm + (-6 db) = -96 dBm.

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 of-90 dBm).

now has Io = -83 dBm (which is the sum of five signals of-90 dBm). And the power of our pilot channel remains the same (Ec = -96 dBm).

Thus: Ec/io = -96-( -83) = -13 DB

conclusion: As many more sectors serves the mobile, the Ec/io worsens.

This situation where we had many overlapping sectors, and with the same level of signal are known as Pilot pollution-the Mobile sees them all at Once-each acting as interferer.

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

Okay, and what is typical values?

We have seen. For CDMA and UMTS systems, the measurement of ec/io which are very important in the analysis, especially In handover decisions.

And now also understand the measure Ec/io as the ratio of ' good ' energy over ' bad ' energy, or ' cleaness ' of signal.

But what is the practical 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 has dropped calls, or can not connect. But what's 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) is shown in the DIA Gram below.

A composite Ec/io ~-Ten db is a reasonable the value to consider as good.

Note:see We is talking about negative values, and considering them ' good '. In other words, we were saying that below the Noise (and still has a good situation).

This was a characteristic of the system itself, and Ec/io ' most negative ' or ' less negative ' are going to allow assessment O f the communication.

In situations where Ec/io are 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 was very low, even if you had a good signal level, you can not connect, O R The call would drop constantly.

I hope you ' ve managed to understand, the Ec/io is important for CDMA and UMTS. Note, however, that's matter is very complex, and supplementary reading-books and Internet-can further help you bec ome an expert on the subject.

Anyway, the content displayed serves as an excellent reference, especially if your ' re not familiar with the concept of sign Al over noise for CDMA and UMTS.

And the Signal to Noise Ratio for other technologies?

The ratio Ec/io is the most commonly used to assess the condition of energy over interference, but applies only in Technol Ogies that use codes (EC).

But the concepts understood here to CDMA and UMTS is very similar-apply-for any technology, eg GSM, where we use the c/i.

Anyway, this was a topic for another tutorial, we saw today Ec/io.

Conclusion

Today we had a brief introduction on the Ec/io ratio, a measurement for decisions in CDMA and UMTS, and used togheter with The measured Signal strength.

We have seen this it represents the ratio of signal energy within the duration of a chip of the pilot channel, on the Spec Tral Density of Noise + interference.

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

Returning to We original QUESTION:A strong signal level does not necessarily indicate a strong ec/io:it depends on the level of interference.

[Turn] what is Ec/io (and eb/no)?