curs 1 3g core network
TRANSCRIPT
3G Core Network Engineeringby René ANDREESCU
Curs 1
3G Core Network Engineering by René ANDREESCU
Why a third generation?
3G Core Network Engineering by René ANDREESCU
• The goal of the UMTS (universal mobile telecommunications system) is to deliver multimedia services to the user in the mobile domain. UMTS and multimedia services have a significant impact not only on the RF (radio frequency) network, but also on the core network architecture. Care must be taken to allow current GSM (global system mobile) operators to protect their infrastructure investments when their networks are upgraded to support UMTS.
3G Core Network Engineering by René ANDREESCU
Network Architecture
3G Core Network Engineering by René ANDREESCU
RAN Interfaces
3G Core Network Engineering by René ANDREESCU
Frequency Allocation
3G Core Network Engineering by René ANDREESCU
Network Architecture
3G Core Network Engineering by René ANDREESCU
Network Architecture
3G Core Network Engineering by René ANDREESCU
The core network handles call control and mobility management functionalities, while the UTRAN (UMTS terrestrial radio access network) manages the
radio packet transmission and resource management.Packet routing and transfer within the core network are supported by definition of new
logical network nodes called GGSN (gateway GPRS [general packet radio system] support node)
and SGSN (serving GPRS support node).
The GGSN is basically a packet router with additional mobility management features, and it connects with various network elements through standardized interfaces.
The GGSN acts as a physical interface to the external packet data networks (e.g., the Internet).
The SGSN handles packet delivery to and from mobile terminals.
Each SGSN is responsible for delivering packets to the terminals within its service area. GGSN and SGSN are capable of supporting terminal data rates up to 2 Mbps.
3G Core Network Engineering by René ANDREESCU
A UTRAN consists of one or more RNSs (radio network subsystems), which in turn consist of base stations (Node Bs) and RNCs (radio network controllers).
The RNS performs all of the radio resource and air interface management functionalities. The UMTS network architecture inherits most of its structure from the GSM model in the UTRAN.
3G Core Network Engineering by René ANDREESCU
Spectrum of Two WCDMA Carriers with 5 MHz Channel Spacing (Unlike GSM and TDMA, the same carriers can be used in all of the cells. Thus, the reuse factor for this
system is N = 1, while the GSM reuse factor is typically N = 4.)
3G Core Network Engineering by René ANDREESCU
WCDMA Carrier
3G Core Network Engineering by René ANDREESCU
• Duplex method: FDD/TDD• Channel spacing: 5 MHz• Carrier chip rate: 3.84 Mcps• Time slot structure: 15 slots/frame• Frame length: 10 ms• Modulation: QPSK• Detection: based on pilot symbols• Intra-frequency Handover: soft• Inter-frequency Handover: hard• Spreading factors:
Up-link: 4..256Down-link: 4..512
FDD
3G Core Network Engineering by René ANDREESCU
Used Modulations
3G Core Network Engineering by René ANDREESCU
In CDMA new channels are created by assigning more spreading codes. As long as the interference is low enough, we can open up a new channel for communication.
3G Core Network Engineering by René ANDREESCU
Spread Spectrum Techniques
3G Core Network Engineering by René ANDREESCU
Direct-Sequence – Spread Spectrum ( DSSS)
3G Core Network Engineering by René ANDREESCU
8 bit code8 bit code
DataData
Data x CodeData x Code
emissionemission
receivereceiveCodeCode
Data x CodeData x Code
Principles
3G Core Network Engineering
by René ANDREESCU
8-bit Code8-bit Code
Received signalReceived signal
Signal x CodeSignal x Code
Valid 1 Valid 0
IntegrationIntegration
Valid receiver
3G Core Network Engineering
by René ANDREESCU
Received signalReceived signal
Other codeOther code
Signal x codeSignal x code
integrationintegration
Invalid receiver
In practice: Gold code 32 bits
3G Core Network Engineering
by René ANDREESCU
3G Core Network Engineering by René ANDREESCU
x=1+X2+X5
Gold code generator basis
3G Core Network Engineering by René ANDREESCU
Direct-Sequence – Spread Spectrum ( DSSS)
3G Core Network Engineering by René ANDREESCU
Direct-Sequence – Spread Spectrum ( DSSS)
If we want to exploit the multi-path channel, the despreading becomes a bit more complicated ...
... but we gain frequency diversity.
3G Core Network Engineering by René ANDREESCU
3G Core Network Engineering by René ANDREESCU
• The jamming gain (J/C) tells us how much stronger a jamming signal can be, compared to the wanted signal:
This expression gives us a simple way of calculating how many users we can have in our system, if we regard the other users as jammers.
QUICK EXAMPLE:Assuming a spreading factor M=512 and an optimal processing gain of Gp=M, and a required (Eb/N0) of 10 dB for proper reception, we get
Hence, we can have 51 other users (with their own spreading codes and equal power) in our system.
3G Core Network Engineering by René ANDREESCU
• The jamming margin gives us a conservative measure on the number of users, since it assumes that we do not use any advanced detection scheme ... only despreading of each user and detection.
• Since a base-station has knowledge about the spreading codes of all users in a cell, it can detect all users jointly and thereby perform interference cancellation. This is called multi-user detection and requires high processing power of the base station.
3G Core Network Engineering by René ANDREESCU
• Since users in a cell are separated by codes, and transmit simultaneously in the same frequency band, we can use the same frequency band in all cells in a cellular system.
• An advantage of CDMA is that the establishment of new “channels” can be done as long as the interference is kept below a certain level. This gives a flexibility which we do not have in FDMA and CDMA.
• Another advantage of CDMA is that we can establish channels with
different spreading factors, allowing different data rates.
3G Core Network Engineering by René ANDREESCU
• The available radio resource is shared among users in a multiple access scheme.
• When we apply a cellular structure, we can reuse the same channel again after a certain distance.
• In cellular systems the limiting factor is interference.
• For FDMA and TDMA the tolerance against interference determines the possible cluster size and thereby the amount of resources available in each cell.
• For CDMA systems, we use cluster size one, and the number of users depends on code properties and the capacity to perform interference cancellation (multi-user detection).
3G Core Network Engineering by René ANDREESCU
Codes and their use
3G Core Network Engineering by René ANDREESCU
CDMA Equation
Important terms when talking about spread spectrum are the so-called spreading factor SF and the spreading gain SG.
SF describes the ratio of the information data rate (represented by the bit duration Tbit ) to the rate of the spreading code (represented by the chip duration Tchip )
3G Core Network Engineering by René ANDREESCU
Let us denote the signal level before despreading thechip energy to interference ratio Ec/I [dB]
and the signal level after despreading the bit energy to interference ratio
Eb/I [dB].
Than Ec/I [dB], Eb/I [dB] and SG are related by:
CDMA Equation
3G Core Network Engineering by René ANDREESCU
The factor OF [dB] describes the degree of orthogonalitybetween wanted user signal and interference signal.
The orthogonality factor (OF) for e.g. Gaussian noise equals 0 dB. Therefore, in a Gaussian noise environment the wanted user signal level is increased by an amount of SG dB.
CDMA Orthogonality
3G Core Network Engineering by René ANDREESCU
The reference sensitivity is the minimum receiver input power measured at the antenna port at which the bit error rate (BER) does not exceed a value of 10-3 .
This testcase determines the tolerable noise figure of the receiver front end.
The cumulative value of the incoming signal power is -106,7 dBm.
The wanted user signal level before despreading Ec/I is -117dBm
The reference channel is a 30 ksps channel which yields an SF of 128.
Reference Sensitivity Level Testcase
3G Core Network Engineering by René ANDREESCU
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From the calculated link budget, the cell range R can be easily calculated for a known propagation model, for example the Okumura-Hata or the Walfish-Ikegami model.
In this case the Okumura-Hata model is used, because it offers better results for urban areas. The propagation model describes the average signal propagation in that environment, and it converts the maximum allowed propagation loss in dB to the maximum cell range in kilometers.
As an example we can take the Okumura-Hata propataion model for an urban macro cell with base station antenna height of 30m, mobile antenna height of 1.5m and carrier frequncy of 1950 MHz:
Propagation Model
3G Core Network Engineering by René ANDREESCU
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Simulating the MORANS scenario (Mobile Radio Access Network reference Scenarios ) a second model can be used. The MORANS scenario offers path-loss information in a 25m grid to every base station. The model which was used to calculate the path loss matrices is a modified COST-Hata model:
MORANS Propagation Model
d Distance between receiver and transmitter in kmHeff Effective height of transmitter in mDiff Diffraction value according to DeygoutClutter Clutter dependent correction factor
3G Core Network Engineering by René ANDREESCU
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The RLB as described previously does not offer the possibility to calculate the allowed path-loss for users with different services (speech, data, ...). That can be done using the load factor, which is calculated for uplink and downlink in different ways.
The term service mix means that several service profiles (so called ”bearers”) are defined, and the service mix is defined as the percentage of the subscribers who use these separate bearers. Table shows examples for these bearers.
Integration of Service Mix
3G Core Network Engineering by René ANDREESCU
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The uplink load factor can be written as
As in Eqution can be seen, the service mix is not included. It can beintegrated by making a linear combination of the separate parameters,weighted by that leads to Equation.
Uplink Load Factor
3G Core Network Engineering by René ANDREESCU
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Parameters used in uplink load factor calculation
3G Core Network Engineering by René ANDREESCU
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The downlink load factor can be written as
As in Eqution can be seen, the service mix is not included. Therefor the individual services are integrated by linear combination, where is the percentage of subscribers, which ones are using carrier k. This relationship is shown in Equation.
Downlink Load Factor
3G Core Network Engineering by René ANDREESCU
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Parameters used in downlink load factor calculation
3G Core Network Engineering by René ANDREESCU
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The next Table shows an example for the extended RLB. In this example two groups, which use different carriers are presented. The parameters for the individual bearers can be found in Table of slide nr. 20
RLB and Service Mix
Integrating the load factor in the RLB can be done in the same way for up- and downlink using the following equation:
3G Core Network Engineering by René ANDREESCU
Cell Search
3G Core Network Engineering by René ANDREESCU
Open loop Power Control ( PC )
3G Core Network Engineering by René ANDREESCU
3G Core Network Engineering by René ANDREESCU
WCDMA Power Control
3G Core Network Engineering by René ANDREESCU
Gain of fast Power Control in WCDMA
3G Core Network Engineering by René ANDREESCU
Rx and Tx power versus interference levels
3G Core Network Engineering by René ANDREESCU
WCDMA Power Control in Soft Handover
3G Core Network Engineering by René ANDREESCU
Softer Handover
3G Core Network Engineering by René ANDREESCU
Soft Handover
3G Core Network Engineering by René ANDREESCU
Soft Handover with Iur connection