Introduction to 3G

IMPORTANT JARGONS OF 3G Compiled by A.R.Parmar,

SDE QoS, ATD

POLE CAPACITY

The uplink noise increases with the loading exponentially. When the uplink noise approaches infinity then no more users can be added to a cell and the cell loading is close to 100% and has reached its pole capacity.

Uplink Pole Capacity =

_____(W/R)_________ =120.6

(1+f) * AF *10^(EbNo/10)

Where

W is Chip Rate ( For UMTS 3.84Mcps)

R is User Data Rate (assume 12.2 kbps for CS)

f is other-cell to in-cell interference ratio (65%)

EbNo required (5dB)

AF is Activity Factor (50%) 2

POLE CAPACITY

Downlink Pole Capacity =

_____(W/R)_________ =64.06

(1-+f) * AF *10^(EbNo/10)

Where

is Orthogonality factor (55%)

* NB: PS-128 & PS-384 has 128K on Uplink

UL DL

CS 12.2 K 120.6 64.1

PS 64K 34.8 12.8

PS 128K 16.2 8.4

PS 384K 16.2 2.8

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USER CAPACITY

Maximum Number of Users(M) of a cell

M= _________W__________________

(EbNo * (1+i) * R ) *

= _________3840000________ = 32.8

(3dB * (1+0.6) * 12200) * 0.5

Where

W is chip Rate

EbNo assumed as 3 dB

i is other-cell to in-cell interference (60%)

R is user data Rate (For CS 12.2 Kbps)

is loading factor (50%)

Take CS 12.2K for example:

For CS -12.2K bearer needs 1 SF128 Code ( Full Rate voice is on SF=128, meaning a maximum of 128 simultaneous voice calls on a 5Mhz carrier)

Total Available Code for CS 12.2K = 128 2(1 SF64) 2 (4 SF 256) =124

Consider Soft HO factor 1.8 and loading Factor 50% M= (124/1.8) * 0.5 = 34 user per cell

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3G QUALITY

Eb/No Eb is Bit energy

It represent the amount of energy per bit

No is noise spectral density

Unit is Watts/Hz

Eb/No : Bit Energy on Spectral Noise Density Unit is dB

Eb/No is measured at receiver end and indicates how strong the signal is.

Eb/No target on Uplink for CS is 5 to 6dB and for PS is 3 to 4 dB

On Downlink for CS is 6 to 7 dB and for PS is 5 to 6 dB

CS is real time, so needs higher Eb/No to maintian strong RF link

Whereas PS has better error correction capability, so lower Eb/No

Eb/No is applies to Digital communication system but in UMTS we use Ec/Io (In GSM we use C/I)

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3G QUALITY

Ec/Io & Ec/No

E is average signal Energy

b, c, s : Energy are power point in time therefore related to

measure or length of the time (average power is

independent of time)

Io : Interfering co-channel including self

No : Spectral density of Noise (excludes self)

Noise generated by the RF components of the system

We have Ec/Io in air which is spread across the spectrum

then we have Negative value i.e. Energy is lower than

Total Interference. It is measured at input of receiver.

Eb/No is in the total baseband then we have Positive Value

. It is measured at output of receiver

Ec/Io is used to measure quality of pilot channel

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3G POWER

RSCP : Received Signal Code Power

It is energy per chip in CPICH averaged over 512 chips

The RSCP is the measurement by the UE of the power that is assigned to specific coded physical channel that is received

It is measured in dBm and is based on number of measurement average over specific period.

RSSI : Received Signal strength Indicator

It is the total received wideband power over 5MHz including thermal noise.

It is estimating the uplink interference at the Node-B, and by difference with the thermal noise, the rise due to traffic and external interference. 7

3G BASIC

Relation between RSCP & RSSI:

Ec/No of a UE is :

The measure of PCICPH (Code Power) over Total

wideband power of that particular carrier.

Measure of PCPICH =RSCP (dBm)

Measure of Total WideBand power = RSSI (dBm)

So, Ec/No = RSCP/RSSI (But we cannot divide dBm values

so we apply logarithmic rules as below)

RSCP (dBm) = RSSI(dBm)+Ec/No(dB)

Or Ec/No(dB) = RSCP - RSSI

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CQI- CHANNEL QUALITY INDEX

In Idle mode and with no resource allocated, a UE will measure

as low as 0 dB Ec/No

In HS mode and with no resource allocated on DCH(all power

is given to HSDPA), a UE will measure as low as -10 dB.

Hence, it means that as interference plays part in live network

with shared users, Ec/No will give false value for an HSDPA

user and will show a very poor value.

So, we establish that

Ec/No measured during HSDPA transmission could not

mask true conditions.

So, we should monitor Ec/No in Idle mode only, which

reflects true condition of interference and coverage

HSDPA sessions adds to overall load of the cell which is

taken into consideration during computing to Ec/No.

So alternative to Ec/No is HS session is CQI

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CQI- CHANNEL QUALITY INDEX

HSDPA utilizes link adaption techniques to substitute power control and variable spreading factors.

Transmit bit rate on HS-DSCH is 2ms TTI

UE periodically sends CQI to serving HS-DSCH cell on high speed dedicated physical control channel (HS-DPCCH)

CQI tells Node-B Scheduler, the data rate the UE expects to be able to receive at a given point.

Note: HSDPA system defines different CQI mapping for different UE categories.

Steps: CQI values are used by link adaption algorithm at Node-B. Every CQI

value reported corresponds to TBS (Transport Block Size) that can be granted on a particular Modulation type and Number of Codes

Simultaneously, there is BLER calculation going on and UL HARQ (Hybrid Auto repeat Request) mechanism is helping in maintaining BLER to below 10%

So Data Rate (bps) = TBS (bits)/ TTI (sec)* (1-BLER)

The CQI value ranges from 0 ~ 30. 30 indicates the best channel quality and 0,1 indicates the poorest channel quality

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PROCESSING GAIN

Processing Gain : It is gain achieved by spreading

narrow band into wideband spectrum.

Channelization Code or Spreading Code It is signal specific.

It transform every data symbol into a number of

chips, thus bandwidth of signal increases.

So, narrowband signal is spread into wideband signal

with chip rate of 3.84 Mcps

Scrambling Code It is equipment Specific.

It provides separation between equipment

Code identification during cell search procedure is

limit to 512 code 11

PROCESSING GAIN

OVSF: Orthogonal Variable Spreading Factor

Channelization codes are OVSF Codes

Length is equal to spreading factor. 4 to 256 codes

Codes are managed by RNC

Orthogonality enables to separate UL & DL

channels.

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HANDOVER IN 3G

Soft Handover : Soft handover refers to the process that allows a Mobile connection to be served simultaneously by several cells, adding and dropping them as needed.

Possible as same frequency is used and cells are separated only by codes.

Advantages :

It increases the reliability of transmission

Reduces transmit power requirement for each link used

UE at the boundary among several cells, uses the minimum transmit power on either link

Disadvantages:

Information is on multiple link, hence resource utilization is more

More transmission means more energy in air, which means more interference in downlink direction. 13

HANDOVER IN 3G

Softer Handover: It is soft Handover within

sectors of same Node-B.

It is internal procedure for Node-B, which save

transmission capacity between Node-B and RNC.

In HSDPA

Only on R-99 (Control Channel) Soft HO is

supported.

Not supported on Dedicated Channels

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HANDOVER IN 3G

Hard Handover:

Break before make

Interfrequency Handover

Inter Technology Handover (IRAT HO)

3G to 2G

3G to 4G

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SOFT HANDOVER OVERHEAD

SHO : Soft Handover OverHead

Soft Handover Overhead is the additional load on Iub compared to Iu caused by duplicated traffic between RNC and Node-B to serve the different legs of UEs active sets that are connected to different Node-Bs.

It is calculated in two ways as : Average Active Set Size Total Traffic/Primary Traffic

Secondary Traffic / Primary Traffic

Typical values are like 1.7 (Avg Active Set Size) or 35% (Secondary/Primary Traffic)

SHO is not a problem but a goal to reach.

It is an unavoidable side effect of the RF overlap between different Node-Bs and need for UE to connect and decode the signal from every sectors that is above a certain RSCP level.

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ROLE OF RNC

Role of RNC : It controls the radio resource in its domain as well as UE connections. It is Service Access Point to CN

Node-B also does radio resource management.

Serving RNC : The RNC which provides the Iu connection between a UE and CN There is one serving RNC for a UE connected to CN.

It is in charge of the radio connection between a UE and the UTRAN

Drift RNC : It also provides radio resource to a UE. One UE can may have more than 1 Drift RNC. A Drift RNC offers its radio resource to a serving RNC for a

given user.

Serving and Drift RNCs manage inter-RNC handovers through Iur.

It is possible to change link to CN, so that Drift RNC becomes Serving RNC (SRNC). So, Drift RN subsystem (DRNS) is changed to SRNS. This is called SRNS relocation

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RADIO ACCESS BEARER

Radio Bearer : It is service provided by protocol entity for transfer of data between UE and UTRAN

RB are mapped successively on logical channels, transport channels and physical channels

An RAB must be flexible enough to support different traffic types, activity levels, throughput rates, transfer delays and bit error rates.

QoS parameters may change during an active connection.

RAB Assignment : The RAB provides confidential transport of signaling and user data between UE and CN with appropriate QoS.

Different RABs: CS : AMR 12.2/12.2

CS Streaming: 14.4/14.4

PS : R2: 64/128, 64/384, 64/144, 128/384, 32/32, 64/64,128/128, 144/144

Note that RAB are provided only on user plane 18

RADIO RESOURCE CONNECTION

RRC Connection:

When UE needs to exchange information, it must

first need to establish a signaling link with UTRAN.

It is made through a procedure with RRC protocol

and it is called RRC connection establishment

During this UE sends initial access request on

CCCH(Common Control Channel) to establish a

signalling link which will be carried out on

DCCH(Dedicated Channel)

UE can have zero or one RRC connection

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SET OF PSC

Active Set: Set of cells with which

communication of UE is active.

Typically between 3 to 6

Monitoring Set: It is build by UE by RNC

neighbouring list. RNC selects best cells in this

list for monitoring cells

Maximum number is 32

Detected Set : It is applicable to inter-frequency

measurement made by UEs in CELL_DCH state.

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HSDPA : HIGH SPEED DOWNLINK

PACKET ACCESS

It allows higher downlink peak data rates

HSDPA provides lower latency with reduced Round

Trip Delays enabling great interactive applications.

The Transmission Time Interval (TTI) is shortened to

2ms.

It introduces new common high speed downlink

channel (HS-DSCH) shared by several users.

HS-DSCH : High speed Downlink shared channel

It is transmitted over the entire cell or only part of cell

Does not support Soft Handover

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HSUPA: HIGH SPEED UPLINK PACKET

ACCESS

HSUPA is designed to increase the uplink data

throughput over the air interface theoretical peak

user bit rate (2 Mbps).

E-DCH and enhanced dedicated Channel

Fast retransmission of data

Uplink resource management in nodeB

Received power

Processing resources

Iub bandwidth

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CELL BREATHING

It is a mechanism which allows overloaded cells to offload subscriber traffic to neighbouring cells by changing the geographic size of their service area.

Heavily loaded cells decrease in size while neighbouring cells increase their service area to compensate.

Thus, some traffic is handed off from the overloaded cell to neighbouring cells, resulting in load balancing

In the uplink, as more and more UE are served by a cell, each UE needs to transmit higher power to compensate for the uplink noise rise. As a consequence, the UE with weaker link (UE at greater distance) may not have enough power to reach the NodeB therefore a coverage shrinkage.

In the downlink, the NodeB also needs to transmit higher power as more UE are being served. As a consequence UE with weaker link (greater distance) may not be reachable by the NodeB.

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