Post on 25-Nov-2015
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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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