3G Basics Definitions

Special Subject: 3G Basic Definitions

Content Definition of Eb/No & Ec/Io What is RTWP?

What is Antenna Electrical and Mechanical Tilt ?

What is RRC and RAB?

© ZTE Corporation. All rights reserved

> Internal Only

Title:Type: Arial

Size ： 30-32ptColor ： The theme blue

Text (1-5 Level):Type ： Arial

Size ： 28~12ptColor ： Black

© ZTE Corporation. All rights reserved.

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

Definition of : Eb and No


> Internal Only

Title:Type: Arial





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.

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 type, etc.

Definition of : Eb and No


> Internal Only

Title:Type: Arial





The concept of Eb/No applies to any digital communication system. But today we are talking specifically to Ec/Io, which is a measure of evaluation and decisions of UMTS.

Note: all the technology uses signal-interference ratio. For example, in GSM, we use C/I.

It becomes easier to understand the concepts by observing a simplified diagram of Spread Spectrum Modulation.

From : Eb/No -> Ec/Io


> Internal Only

Title:Type: Arial





■ 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 not confuse it with the

signal (average) power.■ b, c, s. ..: Energy are 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.

Definition E & N


> Internal Only

Title:Type: Arial





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

■ We have Ec/Io in the air, which is spread across the spectrum: then we have negative value to the ratio of energy on the total noise (the energy is 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).

Eb/No Positive and Ec/Io Negative?


> Internal Only

Title:Type: Arial





■ Why we can not simply use the Signal Strength measured by the mobile as a guide for operations 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 that allows us to evaluate the contribution of each sector individually.

■ We used to measure the pilot channel signal of each sector to assess the quality: if the level of the pilot is good, then also are good levels for the traffic channels for our call in this sector. Likewise, if the pilot channel is degraded, so will the other channels (including traffic) be, 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 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.

Why should we use Ec/Io?


> Internal Only

Title:Type: Arial





Each sector transmits a certain power. Suppose in our example we have a pilot channel power setting of 2 W, and a power of 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

Change in Ec/Io according to the Sector Traffic Load


> Internal Only

Title:Type: Arial





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.

Ec = 2 W Io = 2 + 2 + 6 = 10 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 Sector Traffic Load


> Internal Only

Title:Type: Arial





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/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.

Change in Ec/Io according to the scenario RF


> Internal Only

Title:Type: Arial





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 have 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.



> Internal Only

Title:Type: Arial





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



> Internal Only

Title:Type: Arial





■ In UMTS systems, the measurement of Ec/Io which is very important in the analysis, especially in handover decisions.

■ 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?

■ 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

what are typical values

Content Definition of Eb/No & Ec/Io

What is RTWP? What is Antenna Electrical and Mechanical Tilt ?



What is RTWP?

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..


Typical Values of RTWP

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

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

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.


Typical Values of 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?

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 most common case, especially in cases of new activations.

Once verified the parameter settings, the next step is the physical examination, especially jumpers and cables, 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.


What is RTWP?

What is Antenna Electrical and Mechanical

Tilt ? What is RRC and RAB?


What is Antenna Electrical and Mechanical Tilt ? For a standard antenna, without Tilt, the diagram is formed as

we see in the following figure.


What is Antenna Electrical and Mechanical Tilt ? The mechanical tilt is very easy to be understood: tilting the

antenna, through specific accessories on its bracket, without changing the phase of the input signal, the diagram (and consequently the signal propagation directions) is modified.


What is Antenna Electrical and Mechanical Tilt ? And for the electrical tilt, the modification of the diagram is

obtained by changing the characteristics of signal phase of each element of the antenna


Changes in Radiation diagrams: depends on the Tilt Type See how is the Horizontal Irradiation Diagram for an antenna

with horizontal beamwidth of 90 degrees.


Changes in Radiation diagrams: depends on the Tilt Type With the mechanical tilt, the coverage area is reduced in

central direction, but the coverage area in side directions are increased.

With the electrical tilt, the coverage area suffers a uniform reduction in the direction of the antenna azimuth, that is, the gain is reduced uniformly.


Changes in Radiation diagrams: depends on the Tilt Type


What is RTWP?

What is Antenna Electrical and Mechanical Tilt ?




RAB and RRC are two of the most important concepts because they are responsible for all the negotiation involved in those calls.

we can divide a call into two parts: the signaling (or control) and data (or information)

we can understand the RRC as responsible for the control, and the RAB as responsible for the information part.


What is RRC and RAB? the UTRAN, responsible for creating and maintaining the

communication between the UE and CN so that the QoS requirements of each are met.

UTRAN: UMTS Terrestrial Radio Access Network

NodeB RNC

UE: User Equipment CN: Core Network

MSC: for switched voice services SGSN: for packet-switched services



Sending requests and receipts is part of signaling, or the RRC. The shipment of purchases is the data part, or the RAB. In our scenario, the RRC are the Rails, and RAB is the full service of sending data between the UE and the CN.

RRC: Radio Resource Control RAB: Radio Access Bearer The RRC is in Layer 3 - control plane, while the RAB occurs

between the UE and CN, in the user plane. RAB is the combination of RB and Iu bearer



As examples of RAB for some services and different rates we have:

The Conversational RAB and the Interactive RAB can be used together, and in this case we have a case of MultiRAB.

The RB is a layer 2 connection between the UE and the RNC, and can be used for Signalling and control User Data. When it is used for Signalling or Control Messages is called SRB. And when it is used for user data is called TRB.

SRB: Signalling Radio Bearer (Control Plane) TRB: Traffic Radio Bearer (User Plane)


RRC Connection and RAB example

Whenever the UE needs the UTRAN resources, he asks. So that these resources are allocated, it establishes a RRC connection with some SRBs.

In this case, a RAB connection is created to enable the transfer of user data. We remind you that the RAB consists of RB + Iu bearer. The RAB is created by CN, with a specific QoS request.

For a single UE, there may be multiple RAB for NAS service (CS or PS).

But let's just stick to the initial procedure, that is, how is performed the 'RRC Setup' procedure, from the UE's request.



The RRC has always 3 steps: The UE requests a new connection in the Uplink (‘RRC CONNECTION

REQUEST’); With sufficient resources available, the 'RRC Downlink CONNECTION SETUP'

message is sent, including the reason, along with the SRB configuration; (Note: otherwise, if the RRC connection cannot be established, the message sent is

'RRC CONNECTION SETUP REJECT'). If all goes well, the UE sends the message in the Uplink: ‘RRC CONNECTION SETUP COMPLETE’



After the RRC connection is established, the UTRAN makes the checks between the CN and the UE, for example the authentication and security operations.

And so, the CN informs the RAB to UTRAN in accordance with requirements of the service requested by the UE. As we have seen, RAB occurs after the RRC, and without a RRC connection no RAB may be established

Documents

3G Basics Definitions