WCDMA RNP Radio Network Dimension Ing Huawei
Transcript of WCDMA RNP Radio Network Dimension Ing Huawei
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Edited by Document version WCDMA RNP
WCDMA RNP Radio Network
Dimensioning PrinciplesFor internal use only
Prepared by URNP-SANA Date 2003-12-19
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Granted by Date
Huawei Technologies Co., Ltd.
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WCDMA RNP Radio Network Dimensioning Principle For internal use only
Revision record
Date Revision version
Revision Description Author
2003-12-19 1.00 Initial issued Wu Zhong
2004-06-15 1.10 In Chapter 3 “Capacity Dimensioning Principle”, replacing the old algorithm with the new one, that is Kaufman Robert algorithm for CS services, and Nokia algorithm for PS services.
Wu Zhong
2005-08-18 1.20 Change CE number in the Table1 and revise according to review.
Qinyan
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WCDMA RNP Radio Network Dimensioning Principle For internal use only
Table of Contents
1Overview....................................................................................................................................................82Link Budget Principle.................................................................................................................................83Capacity Dimensioning Principle...............................................................................................................93.1Brief Introduction to Cell Capacity Dimensioning................................................................................93.2Dimensioning of Cell Uplink Capacity of Mixed Services..................................................................11
3.2.1 Calculating Single User Load of Each Service in Cell Uplink......................................123.2.2 Calculating Total Number of Users Supported by Cell.................................................133.2.3 Calculating Cell Load of Single PS Service...................................................................133.2.4 Calculating Cell Load for All PS Services......................................................................153.2.5 Calculating CS Service GoS............................................................................................15
3.3Dimensioning of Cell Downlink Capacity of Mixed Services.............................................................163.3.1 Calculating Single User Load of Each Service in Cell Downlink.................................163.3.2 Calculating Total Number of Users Supported by Cell.................................................173.3.3 Calculating the Cell Load of Single PS Service............................................................183.3.4 Calculating the Cell Load of All PS Services.................................................................183.3.5 Calculating GoS of CS Service........................................................................................18
3.4Balance between Cell Coverage and Cell Capacity.............................................................................194NodeB CE Dimensioning Principle..........................................................................................................204.1Brief Introduction to NodeB CE Dimensioning..................................................................................204.2NodeB CE Number Calculation..........................................................................................................21
5Iub Interface Flow Dimensioning Principle..............................................................................................245.1Brief Introduction to Iub Interface.......................................................................................................245.2Basic Ideas for Iub Interface Flow Dimensioning...............................................................................275.3Dimensioning of Iub Interface Transmission Flow.............................................................................27
5.3.1 Dimensioning of Iub User Plane Flow.............................................................................275.3.2 Iub Control Plane Flow Dimensioning.............................................................................375.3.3 Iub Maintenance Bandwidth.............................................................................................425.3.4 Dimensioning of Total Transmission Flow of Iub Interface..........................................425.3.5 Iub E1 Configuration..........................................................................................................43
6Pending Problems.....................................................................................................................................437Appendix..................................................................................................................................................447.1About Soft Blocking Probability.........................................................................................................44
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List of Tables
Table 1 Corresponding relation between bearer rate and CE_Amplitude...................................................21Table 2 Rate of FP control frame..........................................................................................................31Table 3 Rate of FP common channel.....................................................................................................32Table 4 Rate of signaling of Iub interface control plane............................................................................41
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List of Figures
Figure 1 Basic idea of coverage and capacity iteration dimensioning.........................................................20Figure 2 UTRAN structure diagram........................................................................................................24Figure 3 Iub interface protocol structure..................................................................................................26
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WCDMA RNP Radio Network Dimensioning Principle
Key word: WCDMA radio network dimensioning, capacity dimensioning, CE, Iub,
interface
Abstract: This document is a summary collection of the dimensioning principles such as
capacity dimensioning, NodeB CE number dimensioning and Iub interface
transmission flow dimensioning based on the relevant documents of these
dimensioning principles. It emphasizes on the explanation of the detailed
process and theory of the capacity dimensioning for the mixed services.
List of abbreviations:
Abbreviations Full spelling
AAL ATM Adaptation Layer
AMR Adaptive Multi Rate
ATM Asynchronous Transfer Mode
BLER Block Error Ratio
CCH Control Channel
CE Channel Element
CS Circuit Switched
DCH Dedicated CHannel
DL Downlink
EIRP Equivalent Isotropic Radiated Power
FP Frame Protocol
GoS Grade of Service
HT Hilly Terrain
NodeB
PS Packet Switched
RA Rural Area
RNP Radio Network Planning
SHO Soft HandOver
TCH Traffic Channel
TMA Tower Mounted Amplifier
TU Typical Urban
UE User Equipment
UL Uplink
UMTS Universal Mobile
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Abbreviations Full spelling
Telecommunications
System
WCDMA Wideband Code Division Multiple
Access
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1 Overview
WCDMA radio network dimensioning involves cell uplink/downlink link budget, cell
uplink/downlink capacity dimensioning, NodeB CE number dimensioning and NodeB Iub
interface transmission flow dimensioning, and so on. These dimensioning principles are
introduced in dedicated documents separately, but provided no convenience for viewing
and learning the WCDMA radio network dimensioning principles as a whole. For this, the
document summaries these principles, providing clear physical explanations on various
parts of the radio network dimensioning principles, and providing mathematical deduction
process as much as possible.
This document comprises the following chapters:
Chapter 1: Brief introduction to the objective and main contents of this document.
Chapter 2: Introduction to the link budget principle. (To keep the integrity of the radio
network dimensioning principles, this part is presented as a chapter providing the
reference documents only, without the specific link budget principle).
Chapter 3: The capacity dimensioning principles are given, including the uplink
capacity and downlink capacity dimensioning principles.
Chapter 4: The dimensioning principle and dimensioning process of the number of
NodeB CEs are explained.
Chapter 5: The dimensioning principle and dimensioning process of NodeB Iub
interface transmission flow are described in detail.
Chapter 6: The pending problems in the radio network dimensioning are proposed.
Chapter 7: Appendixes.
2 Link Budget Principle
With link budget, we can work out the cell coverage radius in different scenarios and
different services covered. For the link budget principle, refer to WCDMA RNP
Technology Research on Special Topics – High-Level Design Specifications for Link
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budget Tool [1]. It is not further described here.
3 Capacity Dimensioning Principle
3.1 Brief Introduction to Cell Capacity Dimensioning
The WCDMA system can provide the users with diversified services, such as voice
service, CS data service, and PS services at various rates. For these mixed services, the
analysis of the cell capacity is very complicated, and there is no good solution method
yet.
Before the capacity dimensioning for mixed services, you need to determine the
solutions for the following problems:
(1) GoS for CS services and PS services
GoS of CS services: It is the requirement on the blocking probability of the CS
services. For example, the GoS of the AMR12.2k voice
service can be represented by a blocking probability of
2%; and that of the Videophone can be represented by a
blocking probability of 5%.
GoS of PS services: It is the requirement on the probability for the delay which
dues to queuing of the PS services. For example, for a
90% probability, the queuing delay should be less than 2s.
(2) CS Service: Mixed sevice capacity dimensioning method
The Kaufman Robert algorithm is used to meet different GoS requirements of
various CS services. In the uplink capacity dimensioning, the uplink load of CS
service is taken as shared resource at the cell level; while in the donwlink
capacity dimensioning, the downlink transmit power of CS service is taken as
the shared resource at the cell level.
(3) PS service: Mixed service capacity dimensioning method
Before the RRM simulation result comes out1, the PS service dimensioning is
1 The RRM simulation team will provide the simulation result with the GoS requirement of PS
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performed with ErlangC, which can embody the GoS requirement of the PS
services. Dimensioning the PS services respectively. Then, dimensoning uplink
capacity , and sum up the uplink load generated by each PS service as the cell
uplink load requirement of all the PS services; for donwlink capacity
dimensioning, sum up the downlink transmit powers of each PS service as the
downlink transmit power of all donwlink PS services.
(4) Consideration on soft handover proportion
Uplink capacity dimensioning: Wihtout considering the influence of soft
handover on the uplink traffic
The uplink MDC gain is calculated based on
0.3dB.
Downlink capacity dimensioning: Considering the influence of soft handover
on the downlink transmit power
The downlink MDC gain is calculated based
on 1.0dB.
Note:
(i) RNC: Generally speaking, we perform soft handover processing for all the services with the
bearer rate less than 384k. In the network dimensioning, we may give a high-level item for setting
whether to perform soft handover processing for the services with the bearer rate above 64k.
(ii) Algorithm group: There is no simulation on the corresponding relation between the services with
different bearer rates and the MDC gains. After discussion with the simuation engineers, the MDC gain
varies a little with the services at different bearer rates. In the network dimensioning, we can consider
the MDC gains are identical for all sevices.
(5) Activity factors of various services
AMR voice service: the activity factor is 0.67.
CS data service: the activity factor is 1.0.
PS data service: the activity factor is 0.9 as recommended.
Note:
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Suppose the DCCC switch is turned on, the activity factor of PS services should be close to 1, and
it is recommended to be 0.9.
The following are the cell uplink dimensioning process and cell downlink capacity
dimensioning process:
Note:
The cell capacity discussed here is specially for dedicated channel, instead of common channel.
Generally, some low-rate services (for example, lower than 32kbps) can be borne by common channels.
The capacity of common channel is under research.
3.2 Dimensioning of Cell Uplink Capacity of Mixed Services
Before the cell uplink capacity dimensioning, here brief the calculation of the cell
uplink load first.
The documentation of WCDMA for UMTS [3] provides the uplink load calculation, as
shown below:
ηUL=(1+ f ) .∑j=1
N1
1+W /R j
(Eb /No ) j . ρ j (3-1)
The Radio Network Planning and Optimization for UMTS [4] provides the result, as
shown below:
ηUL=(1+f .N S
ξ ).∑j=1
N1
1+W /R j
(Eb /No ) j
. ρ j
(3-2)
Note:
(i) In the above two formulae, f refers to the neighboring cell interference factor, W is the chip
rate, R j is the bit rate of service j ,
ρ j spcifies the activity factor of the sevice j , and N indicates
N users are connected simultaneously in the same cell.
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(ii) In the formula (3-2), N S specifies the sectorization gain, and ξ refers to the number of sectors
of the BS.
The main difference between the formula (3-1) and the formula (3-2): a) (Eb /N o) j
in the formula (3-1) corresponds to the activity factor ρ j
, while that in the formula (3-2)
corresponds to full rate, so they are consistent in principle; b) In the formula (3-2),
sectorization gain is considered.
In the currernt calculation, we use the formula (3-1). But the existing (Eb /N o) j
is
obtained by means of simulation with full rate (that means the activity factor is 1), we
should use the formula (3-2).
Hence, for the cell uplink capacity calculation presents below, we use the formula (3-
2) for description and explanation.
3.2.1 Calculating Single User Load of Each Service in Cell Uplink
The single user load should be calculated for the users with soft handover and the
users without soft handover respectively. As the service with soft handover has
MDC gain, the corresponding single user load will be smaller. With the formula (3-
2), we can work it out as follows:
(1) Service j
, without soft handover: uplink load of a single user
L j1=1
1+W /R j
(Eb/No ) j . ρ j (1)
(2) Service j
, with soft handover: uplink load of a single user
L j2=1
1+W /R j
(Eb/N o−MDCUL ) j. ρ j (2)
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(3) Service j
, all users: uplink load of a single user
L j=L j 1+L j2×SHO
1+SHO (3)
Note:
(1) W : 3.84MHz.
(2) R j : Bearer rate of service j .
(3) ρ j : Activity factor of service j .
(4) (Eb /N 0) j : Demodulation performance of the receiver of NodeB of service j .
(5) MDCUL : The MDC gain of uplink of service j .
(6) SHO: Ratio of users performing uplink soft handover.
3.2.2 Calculating Total Number of Users Supported by Cell
Calculate the number of covered users by means of link budget as the total number
of users the cell uplink needs to support.
Note: The above is only for the case of single carrier. For the case of multi-carriers,
it is calculated as follows:
TotalNumberOfUsersSupportedByCell= NumberOfCoveredUsersNumberOfCarriers
.
Note:
(1) Calculate the cell coverage radius based on link budget result, and then work out the cell
coverage area.
(2) Calculate the total number of users supported by the cell based on the density of traffic and cell
coverage area.
(3) In terms of capacity, the number of users to be supported is greater than or equal to the number
of covered users, so the number of covered users calculated by means of link budget can be an input
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for capacity dimensioning. It is similar for the downlink.
(4) If the total number of covered users can’t meet the GoS requirement of CS or PS service, the
capacity will be limited; otherwise, the coverage is limited.
3.2.3 Calculating Cell Load of Single PS Service
(1) Calculate the total throughput (Kbps) of PS services:
TotalThroughputRate=TotalUserNumber×ThroughputOfSingleUserInBusyHours /3600
(4)
(2) Calculate the traffic in the case of no neighbouring interference:
λμ=TotalThroughputRate
R× ρ×(1+NeighboringCellInterferenceFactor )
(5)
(3) Calculate the maximum channel number corresponding to the traffic with the
premise of meeting the GoS requirement:
For PS services, the probability that the delay is less than t t arg et
is
Pr [CallDelay<t t arg et ].
According to the ErlangC calculation formula, the relation between maximum
channel number and GoS is shown blow:
Pr [CallDelay>t t arg et ]=1−Pr [CallDelay<tt arg et ]¿ Pr [CallDelay ]⋅Pr [CallDelay>t t arg et ]
¿p0⋅(λμ )
m
m!⋅(1− λμm)
⋅e−(m−λ
μ )H
⋅t targ et
(6)
Note:
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(1) m refers to the maximum channel number.
(2) H=
Ls
( ρ⋅R ) specifies the average call duration.
(3) LS is the average length of session of PS services. It is an input parameter. From the view of
service model, the average length vary with different PS services. For www, the average length of uplink
session is 12000Bytes, and that of downlink is 60000Bytes.
(4)
p0=[∑k=0
m−1 ( λμ )k
k !+
( λμ )m
m!⋅(1−
λμm) ]
−1
.
(4) Calculate the cell load of this PS service:
ηPS j=m×L j
¿m×1
1+W /R j
( Eb /N o−MDCUL ) j . ρ j (7)
3.2.4 Calculating Cell Load for All PS Services
Sum up the cell load of each PS service to get the uplink cell load of all the PS
services.
ηPSUL=∑
j
ηPS j
(8)
3.2.5 Calculating CS Service GoS
(1) Calculate the total cell load allowed for CS services:
CSServiceCellLoad=TotalCellUplinkLoad−PSServiceCellLoad (9)
(2) Calculate the traffic of each CS service in the case of no neighboring cell
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interference:
λμ=TrafficOfSingleUserInBusyHours×TotalNumberOfUsersSupported×(1+NeighboringCellInterferenceFactor)
(10)
(3) Calculate the blocking probability of each CS service:
Bk=∑
c=C−bk+1
C
G(c )
∑c=0
C
G(c ) (11)
Note:
(1) Bk : Blocking probability of service k.
(2) G(c )=∑
n⋅b=c
a1n1
n1 !⋅⋯⋅
aK
nK
nK ! , and this relation is setup: c⋅G(c )=∑
k=1
K
ak⋅bk⋅G(c−bk )
. Where, K refers to the total CS bearer service in the cell, ak indicates the cell traffic corresponding to
the CS service k, bk indicates the single user load corresponding to the CS service k, and
nk refers to
the number of users simultaneously connected of the CS service k.
(3) C refers to the maximum load allowed by the CS service of the cell uplink, c ¿ C .
(4) Please note that both cell load and single user load are less than 100%, we can not calculate
the blocking probability of each service with the formula (11). To use the formula (11) properly, it is
necessary to adjust the cell uplink load of CS service and the single user load of CS service based on a
specific ratio. It is recommended to enlarge the single user load and cell uplink load by 10000 times.
Suppose the cell uplink load of CS service is 30%, and the single user load of the voice service is
0.82%. In the actual calculation, we can set the cell load of the CS service to 3000, and the single user
load of the voice service to 82. Of course, in the actual calculation process, we can find a suitable
multiple for enlarging based on the precision of the calculation result and the calculation rate.
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3.3 Dimensioning of Cell Downlink Capacity of Mixed Services
3.3.1 Calculating Single User Load of Each Service in Cell Downlink
(1) Service j
, wihtout soft handover: average transmit power of a single user
p j1=( Eb
N o)Tx , j∗ρ j∗PDCH
WR j
∗(θ+ f +N 0
PDCH /CL j)
(12)
(2)Service j
, with soft handover: average transmit power of a single user
p j2=( Eb
No
−MDCDL)Tx , j∗ρ j∗PDCH
WR j
∗(θ+ f +N0
PDCH /CL j) (13)
(3)Service j
, all users: average transmit power of a single user
p j=p j1+ p j 2×SHO
1+SHO (14)
Note:
(1) W : 3.84MHz
(2) R j : Bearer rate of service j ,
ρ j : Activity factor of service j
(3) SHO: Ratio of users performing downlink soft handover
(4) (Eb /N 0) j : Performance of the transmit end of the NodeB of service j
(5) MDCDL : Downlink MDC gain of service j
(6) PDCH : Total transmit power of the downlink service channel
(7) θ : Average non-orthogonality factor; f : Neighboring cell interference factor
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(8) N0 : the floor noise of the receiving end of the UE, including thermal noise, Noise Figure and
background noise
(9) CL j : Average coupling loss of cell downlink
Note:
CL j=AverageMaximumCouplingLossOfCellDownlinkWorkedOutByMeansOfLinkBudget+10 lg(7/30 )
.
3.3.2 Calculating Total Number of Users Supported by Cell
Calculate the number of covered users based on the link budget result, and take it as the
number of users that the cell downlink needs to support.
Note: The above is only for the case of single carrier. For the case of multi-carriers, it
is calcualted as follows:
TotalNumberOfUsersSupportedByCell= NumberOfCoveredUsersNumberOfCarriers
.
Note:
The total number of users supported by the cell downlink is calculated in the similar method of
uplink capcity dimensioning.
3.3.3 Calculating the Cell Load of Single PS Service
(1) Calculate the traffic of a PS service:
λμ=TotalUserNumber×ThroughputOfSingleUserInBusyHours×(1+SHO)3600×R×ρ
(15)
(2) Calculate the maximum channel number corresponding to the traffic with the
premise of meeting the GoS requirement.
The calculation method is the same as that for uplink.
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Based on the ErlangC calculation formula, the maximum channel number m
with the GoS requirement of the PS service can be worked out:
(3) Calculate the downlink transmit power of this PS service:
PPS j=m×P j
¿m×p j1+ p j 2×SHO
1+SHO (16)
3.3.4 Calculating the Cell Load of All PS Services
Sum up the downlink transmit power of each PS service to get the downlink transmit power
of all the PS services in the cell:
PPSDL=∑
j
PPS j
(17)
3.3.5 Calculating GoS of CS Service
(1) Calculate the traffic of each CS service in the case of soft handover:
λμ=TrafficOfSingleUserInBusyHours×TotalNumberOfUsersSupported×(1+SHO)
(18)
(2) Calculte the transmit power of a signle user of each CS service of the cell
downlink:
It is worked out with the formula (14).
(3) Calculate the blocking probability of each CS service:
Bk=∑
c=C−bk+1
C
G(c )
∑c=0
C
G(c ) (19)
Please note that the downlink resource here refers to the downlink transmit power of CS
service. As the downlink transmit power of PS service has been worked out with the formula (18),
so we can get the maximum CS service transmit power by subtracting the PS service transmit
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power from the total transmit power. Suppose the target load of the cell downlink is 75%, with
25% for common channels and 50% for traffic channel. If the maximum transmit power of the cell
downlink is 20W, the total transmit power of the traffic channels will be 10W. Suppose the
transmit power of PS service is 5W, the maximum transmit power of CS service will be 5W too.
Note:
(1) Bk : Blocking probability of service k
(2) G(c )=∑
n⋅b=c
a1n1
n1 !⋅⋯⋅
aK
nK
nK ! , and a relation is set up:: c⋅G(c )=∑
k=1
K
ak⋅bk⋅G(c−bk ).
Where, K refers to the total number of CS service types in the cell. But being different from the above,
ak specifies the cell traffic corresponding to CS service k, bk specifies the average transmit power of a
single user corresponding to CS service k, and nk specifies the number of users connected with the CS
service simultaneously.
(3) C specifies the maximum transmit power of CS service in the cell, c refers to a certain
transmit power, and c ¿ C ;
(4) Similar to uplink dimensioning, it is necessary to present the transmit power of CS service of cell
downlink and the transmit power of a single user in integers. It is recommended to use mW as the
power unit. In the actual iteration dimensioning, you can select a suitable unit for optimal dimensioning
precision and dimensioning speed, for example, 5mW.
3.4 Balance between Cell Coverage and Cell Capacity
The cell coverage radius corresponding to the cell load can be worked out by means
of link budget, together with the density of traffic, the number of covered users can be
calculated. Then based on the number of users supported by the uplink cell and that
supported by the downlink cell worked out by means of uplink/dowlink capacity
dimensioning, compare the number of the covered users with the cell capacity. If the
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coverage and capacity are not balanced, you can balance them by adjusting the cell load
(uplink load or downlink load), so as to complete the iteration dimensioning to get the cell
radius after coverage and capacity balancing. For a certain coverage area, the minimum
number of NodeBs required for coverage and the maximum number of users supported
by each sector can be worked out.[7].
The following figure shows the basic idea of coverage and capacity iteration
dimensioning.
Figure 1 Basic idea of coverage and capacity iteration dimensioning
4 NodeB CE Dimensioning Principle
4.1 Brief Introduction to NodeB CE Dimensioning
CE, channel element, corresponds to basic base band processing unit one by one.
For the existing NodeB version, the CE resource of NodeB is shared within the site.
Huawei recommends calculating the number of CEs based on Site.
In the calculation of the number of CEs, use the principle similar to that for NodeB
capacity dimensioning, namely, Campbell theorem, and then combine different bearers
into a virtual bearer to get the Erlangs of this virtual bearer, including uplink Erlang and
downlink Erlang. With this method, the number of NodeB CEs worked out will be neither
optimistic nor pessimistic. The documentations [2, 8] provide the comparison result.
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With the ErlangB calculation formula based on a certain blocking probability, you can
work out the trunks required for the corresponding virtual bearer (for uplink and downlink
respectively). Based on the trunks required for virtual bearer together with the
CE_Amplitude under this virtual bearer, you can work out the number of CEs of uplink
and downlink of the NodeB site.
Of course, you can further calculate the number of uplink boards and downlink
boards to be configured in NodeB.
4.2 NodeB CE Number Calculation
1. Corresponding relation between bearer rate and CE_Amplitude
Different bearer rates may consume different numbers of CEs. The corresponding
relations between bearer rates and the equivalent CE numbers are shown in the
following table.
Table 1 Corresponding relation between bearer rate and CE_Amplitude
UL CE_Amplitude DL CE_Amplitude
AMR12.2k 1.00 AMR12.2k 1.00
CS64k 3.00 CS64k 2.00
PS64 3.00 PS64 2.00
PS144 5.00 PS144 4.00
PS384 10.00 PS384 8.00
Note:
The bearer rates and the corresponding CE_Amplitude in the table above, are provided by NodeB.
2. Calculation of NodeB CE number
(a) Calculate the traffic at each bearer rate within NodeB: Erlangi
(The suffix i
represents different bearer rates)
For voice service and CS data, as the traffic of a single user in busy hours is
known, you can calculate the corresponding Erlangvoice
and ErlangCSdata
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based on the number of users supported by NodeB,. For example, Erlangvoice
= Traffic of a single user in busy hours × number of users supported by NodeB.
The traffic of the CS data service can be calculated in the same method.
For PS services, as the throughput of a single user in busy hours is known,
you can calculate the traffic of a single user of the corresponding PS service in
busy hours. Together with the number of users supported by NodeB, you can
calculate Erlang
of the PS service with the method similar to that for Erlang
of CS service.
The following is the calculation fomula of the traffic for a single user of the PS
service in busy hours.
TrafficOfSingleUserOfPSServiceInBusyHours= ThroughputOfSingleUserInBusyHours(kbit)BearerRate(kbps)×3600×ChannelOccupationRatio
.
(b) Calculate the CE_Amplitude of the virtual service: VitualCE Amplitude
With the campbell theory, you can convert the mixed service (at different
bearer rates) to a certain virtual service, so as to calculate the CE_Amplitude of
this virtual service, as shown below:
.
(c) Calculate virtual traffic: VitualCE Amplitude
Obviously, the virtual traffic can be calculated as follows:
( _ )_ _
_ _
i ii
CE Amplitude ErlangVirtual CE Traffic
Virtual CE Amplitude
.
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(d) Calculate the virtual trunks required: VitualCETrunk
In the view of soft handover ratio and GoS, you can use the ErlangB formula to
calculate the virtual trunks corresponding to the virtual traffic, as shown
below:
VirtualCETrunk=ErlangB−1 [VirtualCETraffic
×(1+SHO ) GoS ].
Where, SHO
represents the ratio of soft handover.
(e) Calculate the number of CEs required for NodeB: CENum
The virtual trunks and the corresponding CE_Amplitude are worked out with
the above formula. Then you can calculate the number of CEs to be configured
for the NodeB. However, for virtual service, adding one trunk requires adding
VitualCE Amplitude
CEs, as the following formula:
CENum=⌊VirtualCEAmplitude×(VirtualCETrunk
+1 )⌋.
(f) Calculate the number of uplink boards and downlink boards to be configured:
NumberofUplinkBoards= ⌈ NumberOfUplinkCEsOfNodeBNumberOfCEsPr ovidedByUplinkBoard
⌉,
NumberofDownlinkBoards=⌈ NumberOfDownlinkCEsOfNodeBNumberOfCEs Pr ovidedByDownlinkBoard
⌉
.
Note:
(i) Currently, the uplink board can provide 128 CEs, and the downlink board can provide 384 CEs at
the maximum.
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(ii) The NodeB CE number dimensioning is to calculate the number of uplink CEs and downlink CEs
respectively, or in one process. What’s difference is the Erlang corresponding to different bearer rates in
NodeB of the uplink and downlink may be different.
5 Iub Interface Flow Dimensioning Principle
5.1 Brief Introduction to Iub Interface
The UMTS system is composed of three parts: CN, UTRAN and UE. The interface
between CN and UTRAN is defined as Iu interface, and that between UTRAN and UE is
defined as Uu interface. UTRAN can comprise multiple radio network subsystems (RNS).
Each RNS can contain one RNC and one or more NodeBs.
The interface between RNC and NodeB is Iub interface. The following is the
structure diagram of UTRAN:
Figure 2 UTRAN structure diagram
In the 3GPP protocol, all the interfaces in UTRAN and the interface between UTRAN
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and CN apply the Asynchronous Transfer Mode (ATM) as the transmission mechanism.
The Iub interface is open. The basic functions implemented by the Iub interface are
as follows:
(1) Iub transmission resource management
(2) NodeB operation and maintenance, including: Iub link management, cell
configuration management, radio network performance measurement,
common transmission channel management, radio resource management,
radio network configuration queue, and so on.
(3) System information management
(4) Common channel traffic management, including access control, power
management, data transmission, and so on.
(5) Dedicated channel traffic management, including radio link management, radio
link monitoring, channel allocation/cancellation, power management,
measurement report, dedicated transmission channel management, data
transmission, and so on.
(6) Common channel traffic management, including channel allocation/cancellation,
power management, transmission channel management, data transmission,
and so on.
(7) Timing and synchronization management, including: transmission channel
synchronization (frame synchronization), NodeB-RNC node synchronization,
NodeB-NodeB node synchronization.
The protocol structure of Iub interface is as follows[9]:
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Figure 3 Iub interface protocol structure
From the view of horizontal plane of the above figure, the protocol structure
comprises radio network layer and transmission network layer; from the view of vertical
plane, the protocol structure comprises control plane and user plane.
An Iub interface is connected with one RNC and one NodeB. The transmission
information in the Iub interface can be divided into three types:
(1) Radio application relevant signaling: The Iub interface allows the negotiation
between RNC and NodeB for the relevant radio resource. The information for
broadcast channel control and the information transmitted on the broadcast
channel are this type of signaling. In addition, the operation maintenance
signaling between NodeB and RNC belong to this type of signaling.
(2) Iub dedicated channel data stream
(3) Iub common channel data stream
The dimensioning of the transmission flow of the Iub interface involves not only the
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service data transmission flow of the expected users on the Iub interface, but also the
factors like signaling flow. Based on the related documentations[10] and Huawei’s relevant
document[11], the transmission bandwidth required for the Iub interface and the relevant
transmission configurations as well can be calculated.
5.2 Basic Ideas for Iub Interface Flow Dimensioning
The main purpose of the Iub interface transmission flow is to provide reference for
interface configuration in the engineering procedure, as well as the interface
configuration in other occasions.
The following factors need to be considered for the dimensioning of data
transmission flow of the Iub Interface:
(1) FP data frame utilization
(2) AAL2 utilization ratio
(3) NBAP flow
(4) AAL5 utilization ratio
(5) ATM cell utilization ratio
(6) E1 utilization ratio
(7) ALCAP flow
(8) FP payload flow
(9) FP control frame flow
(10) Operation maintenance signaling flow
We can view from the protocol structure of Iub interface from Figure 3 that the
transmission flow of the Iub interface is the sum of three parts of flows, that is, Iub user
plane flow + Iub control plane flow + Iub maintenance bandwidth. Therefore, the following
are the dimensioning procedures for Iub user plane flow and Iub control plane flow
respectively.
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5.3 Dimensioning of Iub Interface Transmission Flow
5.3.1 Dimensioning of Iub User Plane Flow
1. Flow features with considering FP/AAL2 encapsulation overhead
For the frame format, refer to TS25.427. As the overhead of the uplink FP frame is
greater than that of the downlink FP, the flow should be calculated based on the uplink
FP overhead.
The data encapsulated by FP is then encapsulated by AAL2. During AAL2
encapsulation, 3 bytes of overhead (CID/LI/UUI/HEC) is added to the header of each
micro cell. The payload of each micro cell is 44 bytes, and the excessive ones will be
segmented for encapsulation.
The calculation formula for the data rate after FP/AAL2 encapsulation is as follows:
(Header CRC/FT+CFN+TFI+TB+QE+CRCI+spare+CRC+AAL2 HEAD)×8/TTI .
Note:
According to the protocol, the spare of data frame is 0 to 2 bytes, the spare of control frame is 0 to
32 types. The RNC supports filling in, but not during transmitting (that means it is not for downlink).
In the following flow calculation, it is specified that the uplink data frame uses a 2-byte spare, and
the control frame uses a 0-byte spare, for calculating the maximum flow in theory, and the one in the
actual application can be analogized according to NodeB.
The following are the data rates of the AMR full rate service after FP/AAL2
encapsulation (The ARM takes the coding unit of 20ms, that is, 50 frames/s, and full rate
means the channel activity factor is 1)
12.2kbps: (1+1+3+11+13+8+1+1+2+2+3)×8/0.02=18.4kbps
10.2kbps: (1+1+3+9+13+5+1+1+2+2+3)×8/0.02=16.4kbps
7.95kbps: (1+1+3+10+11+1+1+2+2+3)×8/0.02=14kbps
7.4kbps: (1+1+2+8+11+1+1+2+2+3)×8/0.02 =12.8kbps
6.7kbps: (1+1+2+8+10+1+1+2+2+3)×8/0.02=12.4kbps
5.9kbps: (1+1+2+7+8+1+1+2+2+3)×8/0.02=11.2kbps
5.15kbps: (1+1+2+7+7+1+1+2+2+3)×8/0.02=10.8kbps
4.75kbps: (1+1+2+6+7+1+1+2+2+3)×8/0.02=10.4kbps
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The data rate of CS data service after FP/AAL2 encapsulation (full rate):
32kbps: (1+1+1+1×80+1+1+2+2+3×3)×8/0.02=39.2kbps (TTI=20ms)
64kbps: (1+1+1+2×80+1+1+2+2+3×4)×8/0.02=72.4kbps (TTI=20ms)
14.4kbps: (1+1+1+1×72+1+1+2+2+3×2)×8/0.04=17.4kbps (TTI= 40ms)
28.8kbps: (1+1+1+2×72+1+1+2+2+3×4)×8/0.04=33kbps (TTI= 40ms)
57.6kbps: (1+1+1+4×72+1+1+2+2+3×7)×8/0.04=63.6kbps (TTI= 40ms)
The data rate of PS data service after FP/AAL2 encapsulation (full rate):
8kbps: 1+1+1+1×42+1+1+2+2+3×2)×8/0.04=11.4kbps (TTI=40ms)
16kbps: (1+1+1+1×42+1+1+2+2+3×2)×8/0.02=22.8kbps (TTI=20ms)
32kbps: (1+1+1+2×42+1+1+2+2+3×3)×8/0.02=40.8kbps (TTI=20ms)
64kbps: (1+1+1+4×42+1+1+2+2+3×5)×8/0.02=76.8kbps (TTI=20ms)
128kbps: (1+1+1+8×42+1+1+2+2+3×8)×8/0.02=147.6kbps (TTI=20ms)
144kbps: (1+1+1+9×42+1+1+2+2+3×9)×8/0.02=165.6kbps (TTI=20ms)
256kbps: (1+1+1+8×42+1+1+2+2+3×8)×8/0.01=295.2kbps (TTI=10ms)
384kbps: (1+1+1+12×42+1+1+2+2+3×12)×8/0.01=439.2kbps (TTI=10ms)
3.4kbps channel associated signaling overhead (full rate):
(1+1+1+1×19+1+1+2+2+3)×8/0.04=6.2kbps (TTI=40ms)
2. FP control frame overhead
(a) TIMING ADJUSTMENT: 5byte, Spare Extension: 0--32byte
When a time window appears, NodeB sends the time adjusting frame,
supposed once per 100TTI (TTI=20ms) for each DCH bearer, the flow will be
16 bps.
The time adjusting frame seldom occurs in the actual environment.
(b) DL SYNCHRONIZATION: 3byte. Spare Extension: 0--32byte
Transport channel synchronization is used for the synchronization of the initial
setup stage, and for the troubleshooting for the bottom layer AAL2 as well.
The flow of synchronization for the initial stage can be omitted (as service data
transmission has not started yet), and that of the synchronization for
troubleshooting is related to the detection cycle.
For example, if the detection is performed once per 5s, the flow will be 9.6
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bps.
(c) UL SYNCHRONIZATION: 5byte, Spare Extension: 0--32byte
The transport channel synchronization is used for the synchronization of the
initial setup stage, and for the troubleshooting for the bottom layer AAL2 as
well. The flow of synchronization for the initial stage can be omitted (as service
data transmission has not started yet), and that of the synchronization for
troubleshooting is related to the detection cycle.
For example, if the detection is performed once per 5s, the flow will be 64 bps.
(d) OUTER LOOP POWER CONTROL: 3byte, Spare Extension: 0--32byte
The SIR used for updating outer loop power control. Suppose it is once per
400ms, the load flow will be 120 bps.
(e) DL NODE SYNCHRONIZATION: 5byte, Spare Extension: 0--32byte
Node synchronization is used for Iub delay estimation. It does not attach to call
service, thus can be omitted.
(f) UL NODE SYNCHRONIZATION: 11byte, Spare Extension: 0--32byte
Node synchronization is used for Iub delay estimation. It does not attach to call
service, thus can be omitted.
(g) DSCH TFCI SIGNALLING [FDD]: 5byte, Spare Extension: 0--32byte, once
per10ms
At present, the system does not support DSCH, so the flow of DSCH TFCI
SIGNALLING is not considered for the moment.
(h) RADIO INTERFACE PARAMETER UPDATE [FDD]: 6byte, Spare Extension: 0--
32byte
Radio parameter update will be initiated after the handover is completed and
RLS is added. It can be omitted.
Note:
The typical structure of control frame is: (Frame CRC+FT)+Control Frame Type+Control
Information+Spare Extension. Where Frame CRC+FT is 1byte, and Control Frame Type is 1byte.
In the above calculation, the uplink control frame uses a 32-byte spare, for calcualting the maximum
flow in theory. It can be analogized according to the realization of the NodeB in the actual application.
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Spare filling is not performed for the downlink RNC.
The following table lists the data rates corresponding to various FP control frames.
Table 2 Rate of FP control frame
Message name Rate (bps)
TIMING ADJUSTMENT 160
DL SYNCHRONIZATION 9.6
UL SYNCHRONIZATION 64
OUTER LOOP POWER CONTROL 120
DL NODE SYNCHRONIZATION It is used for Iub delay estimation, and it does not attach to call service, thus can be omitted.
UL NODE SYNCHRONIZATION It is used for Iub delay estimation, and it does not attach to call service, thus can be omitted.
DSCH TFCI SIGNALLING[FDD] The system does not support DSCH, so it is not considered for the moment.
RADIO INTERFACE PARAMETERUPDATE[FDD]
Radio parameter update will be initiated after the handover is completed and RLS is added, so it can be omitted.
From the above analysis, the flow of control frame is much lower than that of service
data frame, so it can be omitted.
3. Common channel
Common channel is set up in the cell setup stage with the default channel
configurations for general cases.
The default configurations of various channels are as follows:
(a) RACH
TBSize=168 or 360bit, TTI=10ms, the maximum traffic is calculated based on
360 bits.
Header CRC/TF+CFN+TFI+PropagationDelay+TB+CRCI+spare+CRC+AAL2
header
The flow after FP/AAL2 encapsulation is:
(1+1+1+1+360 / 8+1+2+2+3×2)×8 / 0.01 = 48kbps.
Each cell can be configured with one to two RACH channels.
(b) FACH
(i) FACH signaling
TBSize=168, TBNum=2, TTI=10ms
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Header CRC/TF+CFN+TFI+TransmitPowerLevel+TB+spare+CRC+AAL2
header
The flow after FP/AAL2 encapsulation is:
(1+1+1+1+168×2 / 8+2+3×2)×8 / 0.01 = 43.2kbps.
(ii) FACH data
TBSize=360, TBNum=1, TTI=10ms
Header CRC/TF+CFN+TFI+Transmit power level+TB+spare+CRC+AAL2
header
The flow after FP/AAL2 encapsulation is:
(1+1+1+1+360 / 8+2+3×2)×8 / 0.01 = 45.6kbps.
Each cell can be configured with one to four FACH channels. In case there is
only one FACH channel, the signaling and data are multiplexed, in the
configuration mode for signaling FACH.
(c) PCH
TBSize=240, TBNum=1, TTI=10ms
Header CRC/TF+CFN/PI+TFI+PI-bitmap+TB+spare+CRC+AAL2 header
The length of PI-bitmap is related to the configuration of common channel.
Corresponding to the configurations of 18, 36, 72 and 144 segments of the PI,
it is 3, 5, 9 and 18 bytes in length.
The current common channel uses configuration of the PI with 18 segments.
The traffic after FP/AAL2 encapsulation is:
(1+2+1+3+30+2+3)×8 / 0.01 = 33.6kbps.
Each cell supports one PCH channel.
The following table lists the rates of various FP common channels:
Table 3 Rate of FP common channel
Common
channel name
Rate (kbps) Ramark
RACH 48 Each cell can be configured with one to two RACHs channels.In Huawei’s product, each cell is configured with one RACH channels.
FACH Signaling rate: 43.2 Each cell can be configured with one to four FACHs
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Data rate: 45.6 channels.In case of there is only one FACH, the signaling and data will be multiplexed, in the configuration mode of signaling FACH.In Huawei’s product, each cell is configured with two FACHs, one of which for signaling transmission and the other for data transmission.
PCH 33.6 Each cell supports one PCH.
4. AAL2 sub-multiplexing
The AAL2 multiplexing can improve the ATM transmission efficiency, but the
additional overhead caused by sub-multiplexing must be considered. When configuring
the flow of Iub interface, it is recommended to add 10% of AAL2 multiplexing overhead to
it.
In the case of AAL2 multiplexing, each ATM cell has 1 byte of overhead (STF
domain). In addition, the header of each ATM cell has 5 bytes of overhead.
Note:
At present, the TIMER_CU of the AAL2 micro code is set to 500us, that is, a single cell may be in
the 500us additional delay brought by sub-multiplexing, namely the maximum PAD filling rate of AAL2.
The data of a single application are transmitted equably (for example, AMR TTI=20ms), but the
transmission between multiple upper-layer applications are not dispersed equally. That is to say, the
flow peak value may occur in a period of time due to the concurrent transmission of multiple
applications; and may be idle for a period of time. This is the case of uneven peak/off-peak. As the
buffer of the AAL2 micro cell is restricted, if the buffer is full when the transmission failure due to burst
flow, the QoS will be surely lowered, thus affecting the performance of the equipment. Therefore, the
ATM flow must be able to adapt to this application requirement.
Take the 12.2kbps AMR voice for example, the length of each micro cell is 46 bytes. If the
TIMER_CU of only one micro cell expires, the PAD of one byte is added. If the single TIMER_CUs of
two micro cells expire, the PAD of two bytes is added behind the second one. If the TIMER_CUs of
three micro cells expire, the former two cells are transmitted, and the third one will be transmitted in the
next time of expiration. Similarly, one AAL2 PACH can bear 248 CIDs, which is updated once per 20ms.
The maximum PAD added is 248 bytes (it is an extreme), and the minimum PAD added is 13 bytes (it is
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transmitted at each TIMER_CU). The corresponding maximum sub-multiplexing overhead is 99.2kpbs,
with 2% of multiplexing overhead increased. Take the 10.2kbps AMR voice for example, the extreme
multiplexing overhead is 7.8%.
By means of analysis on other service types, you can get the application with the lower rate, whose
extreme multiplexing overhead is the larger.
5. Activity rate of 3.4K channel associated signaling channel
The RRC signaling exchanged for each call and the length are shown as follows:
Where, the red ones are for uplink and the blue ones are for downlink.[3].
RB Release 96
RB Release Complete 80
RB Setup 208
RB Setup Complete 83
RRC Connection Release 8
RRC Connection Release Complete 6
RRC Connection Request 91
RRC Connection Setup 159
RRC Connection Setup Complete 45
Initial Direct Transfer 40
Uplink Direct Transfer 60
Downlink direct Transfer 60
UE Capability Enquiry 46 RNC ==> UE
UE Capability Information 80 UE ==> RNC
UE Capability Information confirm 46 RNC ==> UE
Measurement Control 50
Measurement Report 68 (Event triggering
measurement report)
Active Set Update 54 (Soft handover signaling)
Active Set Update Complete 78 (Soft handover signaling)
The algorithm of switch setting can be used for the measurement on Uu interface.
The measurement modules involved include AMRC, DCCC, HO and LCS. Different
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report modes are used for different measurement items. Event report, periodical report
and the period of periodical report are configurable at the background. There are six
periodical measurement reports and 6 event reports at the maximum. As LCS is used for
location only, it is not considered.
Each UE uses one type of service only, and use only two HO periodical
measurement items (mutually exclusive) and one AMRC or DCCC measurement item,
use only four HO event measurement items and one AMRC or DCCC event
measurement item. Suppose the period of periodical report is 1s, the event report is
transmitted once per 30s, the soft handover overhead is 30%, and there are 3 branches
(it is necessary to transmit the activity set update message for twice), the call duration is
60s, and the connecting time is 10s, you can get that the time from conversation to data
transmission is 50s.
The calculation formula is: (Total byte number×8bit / 60s)/ 3400bit/s).
Downlink: ((96+208+8+60+46+46+50×8+54×30%×2)×8/60)/3400 =3.5%;
Uplink: ((80+83+6+45+40+60+80+68×50×3+68×5×2+78×30%×2)×8/60)/ 3400 =
44%.
Because most RRC flows use the RCL confirmation mode, the activity rate of
3.4kbps channel associated signaling is 50%.
6. User plane flow of Iub interface
User plane flow=Common channel flow + Voice service flow + Data service flow +
Channel associated signaling flow
User plane flow (downlink)
=(FACH (Signaling) × The number of FACHs (Signaling)+ FACH (data)× The
number of FACHs (data) + PCH× the number of PCHs+ 12.2AMR rate × The
number of voice users × Voice activity factor + PS rate × The number of data
users × Data activity factor + Channel associated signaling flow× The number
of users × Signaling activity factor) × AAL2 sub-multiplexing × ATM
multiplexing
= (43.2×NFACH signaling + 45.6×NFACH data + 33.6×NPCH +18.4×Nvoice×VADV +
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Vdata×Ndata×VADD+ 6.2×VADS×(Nvoice+Ndata))×1.1×53 / 47
User plane flow (uplink)
=(RACH × The number of RACH + 12.2AMR rate ×The number of voice users
× Voice activity factor + PS rate ×The number of data users × Data activity
factor +Channel associated signaling flow × The number of users ×
Signaling activity factor) × AAL2 sub-multiplexing × ATM multiplexing
= ( 48×NRACH + 18.4 × Nvoice× VADV + Vdata×Ndata × VADD + 6.2 × VADS ×
(Nvoice+Ndata)) × 1.1 × 53 / 47
Minimum number of AAL2 Paths = ⌈(Nvoice+Ndata)×2240
⌉.
Note:
(i) The flow unit above is kbps.
(ii) NRACH, NFACH signaling, NFACH data and NPCH are the numbers of various types of common channels
supported by the whole NodeB.
(iii) Nvoice and Ndata are the number of voice users and the number of data users of the whole NodeB.
(iv) Vdata is the rate after FP/AAL2 encapsulation, which is contained when the data service is used.
(v) The common channel needs to bear the UE common procedures and the low-rate PS service,
so it has a high multiplexing efficiency, with the channel activity factor being 1. Generally, for voice
service, data service and channel associated signaling, it is used discontinuously, so it is necessary to
consider the activity factor. The activity factor of voice VADV ranges from 0.5 to 1. As the usage
character of the data service is unknown, it is recommended to set its acticity factor VADD to 1 for
guaranteeing its QoS, and set the activity factor VADS of signaling to 0.5.
(vi) If the common procedures of UE (such as attach, detach and short message) are implemented
with dedicated channel, it is necessary to add the requirement on the flow of these procedures. The
additioal flow = The number of Iub service users (considering the convergence ratio) × The number of
sevices in busy hour/3600 × Common procedure duration × 6.2 × VADS × 1.1 × 53/47.
(vii) If the tranamission equipment has plentiful resources, in terms of engineering, 25 percent of
headroom will be added for supporting burst service.
(viii) For the user plane of Iub interface, CBR and RT-VBR are used for PVC in most cases. In the
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configuration, if CBR is used, it is required that its PCR be greater than or equal to the flow calculated
above; if RT-VBR is used, it is required that its SCR be greater than or equal to the above value. In
addition, the PCR is 120% of the SCR.
5.3.2 Iub Control Plane Flow Dimensioning
1. Control Plane composition
The Iub control plane is composed of one NCP link, one to n CCP links and one
ALCAP link. The NCP link is for transmitting the message related to the common
procedures, such as audit, cell setup/deletion/re-configuration, common channel
setup/deletion/re-configuration, common measurement and radio link setup. The
CCP links bears the messages related to dedicated procedures, such as RL
addition/deletion/re-configuration, RL recovery failure and dedicated
measurement. The ALCAP link is for transmitting the AAL2 connection message
at the Iub interface. The NCP/CCP/ALCAP link is over SAAL directly. Four bytes
of protocol head overhead are added for the SAAL (SSCOP). In addition, for the
SSCOP, one to three bytes should be filled in so as to align the PDU 4 bytes.
2. Overhead of AAL5
The control plane adopts AAL5 encapsulation, and the relation between SDU and
PDU of AAL5 is as follows:
If (SDU mod 48) > 40, then PDU = (SDU – SDU mod 48))+96.
Or, PDU = (SDU – (SDU mod 48)) + 48.
3. The signaling exchanged for one call of a single service.
The red ones are for uplink and the blue ones are for downlink. The column in the
middle specifies the actual length, and the last column specifies the length of the
message after AAL5 encapsulation.
RL_SET_REQ 122 => 144 <NCP>
RL_SET_RESPONSE 74 => 96 <NCP>
RL_RESTORE_INDICATION 27 => 48 <CCP>
RL_RECONFIG_PREP 299 => 336 <CCP>
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RL_RECONFIG_READY 62 => 96 <CCP>
RL_RECONFIG_COMMIT 21 => 48 <CCP>
DEDI_MEASUREMENT_INIT 53 => 96 <CCP>
DEDI_MEASUREMENT_RESPONSE 19 => 48 <CCP>
DEDI_MEASUREMENT_REPORT 36 => 48 (TCP, AMRC/DCCC/DPB)
DEDI_MEASUREMENT_REPORT 36 => 48 (SIR, OLPC)
DEDI_MEASUREMENT_TERMINATE 16 => 48 <CCP>
RL_DELETE 34 => 48 <CCP>
RL_DELETE _RESPONSE 17 => 48 <CCP>
Four ALCAP signaling:
ERQ 76 => 96 <ALCAP>
ECF 13 => 48 <ALCAP>
RLSD 12 => 48 <ALCAP>
RLC 6 => 48 <ALCAP>
Common measurement:
COMM_MEASUREMENT_INIT45 => 96 (RTWP)<NCP>
COMM_MEASUREMENT_INIT45 => 96 (TCP) <NCP>
COMM_MEASUREMENT_RESPONSE 19 => 48 <NCP>
COMM_MEASUREMENT_REPORT 29 => 48 (RTWP) <NCP>
COMM_MEASUREMENT_REPORT 28 => 48 (TCP) <NCP>
Calculating with the consideration of IMSI attach, IMSI detach, location update, SMS
overhead: four times/user/h, based on the convergence ratio of 40, with the ratio of
processing frequency to call frequency is (40×4/3600): (1/60), that is 2.67. (Refer to the
MOT traffic model).
Generally, these procedures are implemented on common channels, without
considering this part of overhead. Huawei’s product is set with a switch. That is, the
transmission for the engineering can be performed on both dedicated channels and
common channels. Therefore, the following provides the analysis for both cases
respectively.
(i) NCP
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The radio link setup message and common measure message are major
messages. The procedures for cell management are initial procedures, which can
be omitted during flow calculation. In common measurement, two 200-ms
periodical measurements are started for each cell. Suppose the whole NodeB
support N users concurrently, and each user makes each call in 60s.
The following dedicated channels are used for the IMSI attach and other
procedures:
Downlink:
144×N/60×53/48×8×3.67
=(78×N)bps
Uplink:
((48+48)×M×1000/200+96×N/60×3.67)×53/48×8
=(4240×M+52×N)bps.
The following common channels are used for the IMSI attach and other
procedures:
Downlink:
144×N/60×53/48×8
=(22×N)bps
Uplink:
(96×M×1000/200+96×N/60)×53/48×8
=(4240×M +15×N)bps
Where, M is the number of cells supported by NodeB, and N=Nvoice+Ndata.
(ii) CCP
When the algorithm switch is turned on, the AMRC starts a periodical
measurement with the period of 4.8s, for every RL; the DCCC also starts a
periodical measurement with the period of 640ms, and starts a periodical
measurement with the period of 700ms for each RL in the case of soft
handover. Suppose the soft handover ratio is 30%, and two measurements are
started for each voice and data user and one is started for the attach type
service, the flow is calculated as follows:
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The following dedicated channels are used for the IMSI attach and other
procedures:
Downlink:
((336+48+(96+48)×2+48)+(96+48+48)×2.67)×N/60×53/48×8
=(182×N)bps
Uplink:
((48+96+48×2+48+(48+48+48))×2.67)×Nvoice/60+48×N
voice×(1/4.8+1/0.7×30%)
+(48+96+48×2+48+(48+48+48)×2.67)×Ndata/60+48×Ndata
×(1/0.64+1/0.7×30%))×53/48×8
=(370×Nvoice+968×Ndata)bps
The following common channels are used for the IMSI attach and other
procedures:
Downlink:
(336+48+(96+48)×2+48)×N/60×53/48×8
=(106×N)bps
Uplink:
((48+96+48×2+48)×Nvoice/60+48×N voice×(1/4.8+1/0.7×30%)
+(48+96+48×2+48)×Ndata/60+48×Ndata×(1/0.64+1/0.7×30%))×53/48×8
=(314×Nvoice+891×Ndata)bps
Where, N=Nvoice+Ndata. It is mainly required for measurement.
(iii) ALCAP
Suppose NodeB supports N users simultaneously, and each user makes
each call in 60s.
The following dedicated channels are used for the IMSI attach and other
procedures:
Downlink:
((96+48)×2+(96+48)×2.67)×N/60×53/48×8
=(99×N)bps
Uplink:
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((48+48)×2+(48+48)×2.67)×N/60×53/48×8
=(66×N)bps
The following common channels are used for the IMSI attach and other
procedures:
Downlink:
((96+48)×2)×N / 60×53 / 48×8
=(43×N)bps
Uplink:
((48+48)×2)×N / 60×53 / 48×8
=(29×N)bps
The following table lists the rates of various types of signaling of the Iub interface:
Table 4 Rate of signaling of Iub interface control plane
Name Uplink rate (bps) Downlink rate (bps) Remarks
NCP 4240×M+52×N 78×N Dedicated channels used for the IMSI attach and other procedures
4240×M +15×N 22×N Common channels used for the IMSI attach and other procedures
CCP 370×Nvoice+968×Ndata 182×N Dedicated channels used for the IMSI attach and other procedures
314×Nvoice+891×Ndata 106×N Common channels used for the IMSI attach and other procedures
ALCAP 66×N 99×N Dedicated channels used for the IMSI attach and other procedures
29×N 43×N Common channels used for the IMSI attach and other procedures
Note:
(i) N=Nvoice+Ndata,, and M is the number of cells supported by NodeB.
(ii) To consider the SAAL overhead and link utilization, it is necessary to add 10% of flow headroom
based on the flow mentioned above.
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(iii) As the product supports the two modes of using dedicated channels and common channels for
IMSI attach and other procedures, the larger value of flow in the dimensioning will be used for the
signaling dimensioning. That is to calculate the signaling flow of the Iub interface in the mode of using
dedicated channels for IMSI attach and other procedures.
(iv) The AAL5 overhead has been considered in the signaling rate mentioned above.
5.3.3 Iub Maintenance Bandwidth
The operation and maintenance bandwidth of NodeB is set according to the
configuration.
The typical value of the operation and maintenance bandwidth of NodeB is 640kbps.
5.3.4 Dimensioning of Total Transmission Flow of Iub Interface
Based on the analysis and calculation of the user plane flow and control plane flow of
the Iub interface, together with the Iub interface maintenance bandwidth, the total
transmission flow of the Iub interface can be worked out as follows, considering the
soft handover headroom:
The total transmission flow of the Iub interface = (Iub user plane flow + Iub control
plane flow) × (1+ Soft handover headroom) + NodeB
operation and maintenance bandwidth.
Note:
(i) Sub-multiplexing headroom and burst redundancy are considered in the Iub user plane and
control plane.
(ii) Soft handover headroom should be added to the user plane flow and control plane flow.
5.3.5 Iub E1 Configuration
The utilization of the E1 link can be calculated in two modes, both of which are
supported by Huawei.
(1) UNI mode, the E1 utilization rate is: 1920kbps /2048kbps=93.75%.
(2) IMA mode, in the case of frame length being 32, the E1 utilization rate is:
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1859kbps /2048kbps=90.77%;
in the case of frame length being 64, the E1 utilization rate is:
1889kbps /2048kbps=92.24%;
in the case of frame length being 128, the E1 utilization rate is:
1904kbps /2048kbps=92.97%;
in the case of frame length being 256, the E1 utilization rate is:
1911.5kbps /2048kbps=93.33%.
Therefore, based on the Iub transmission flow considering the E1 utilization, the
number of E1s to be configured can be worked out as follows:
The number of E1s to be configured is
⌈IubInterfaceTotalTransmissionTraffic (Mbps)
2Mbps×E1Utilization⌉.
6 Pending Problems
The above chapters present the WCDMA radio network dimensioning principles. But
our research on the radio network dimensioning is not so deep in many aspects so far,
and some pending problems are to be solved. At present, the purpose of capacity
dimensioning is to calculate the number of users that the cell uplink and downlink can
support under a certain cell load, and then compare the capacity dimensioning result with
the link budget. Is this dimensioning mode the only one for judging whether the coverage
and capacity are balanced? Can the dimensioning and comparison be performed
according to the throughput allowed by the PS service (such dimensioning is reasonable
and in accord with the ErlangC)? For example, based on the number of users covered by
the cell worked out by means of link budget, together with the traffic of a single user in
busy hours of CS service and that of PS service, we can calculate the throughput of the
PS services under a certain cell load with the premise of allowing concurrent CS user
connection. Similarly, by means of capacity dimensioning, we can work out the
throughput of the PS services allowed to access when the coverage requirement is met,
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and then compare the PS service throughput calculated in these two cases, so as to
judge whether the coverage and capacity can be balanced.
7 Appendix
7.1 About Soft Blocking Probability
(1) Features of WCDMA data service
For WCDMA data service, the data rate is high, and the number of users
communicating simultaneously that can be borne is small. That is, the number of
channels is small. However, the channels of WCDMA are different from those of GSM,
which are hard channels. If the number of users is greater than the number of channels,
the excessive users will surely encounter blocking. The blocking probability can be
calculated with the Erlang formula. While the channels of WCDMA is soft channels, and
the number of channels varies with the interference. If the blocking probability of hard
channels is still used, with a threshold being set, and the Erlang value of the data service
being calculated with the Erlang formula, it will make big error. For example:
Create a WCDMA single service data model, with the activity factor being 0.1 and
the maximum channel capacity being 3.9, and then calculate the Erlang traffic when the
blocking probability is 0.02. If the hard threshold is adopted, the maximum channel
number is 3, the traffic will be 10Erlang_B(3, 0.02), that is 6; if the maximum channel
number is 4, the traffic will be 10Erlang_B(4, 0.02), that is 11. That is, when the channel
capacity is changed to 4 from 3.9, the traffic changes a lot, which is not practical at all.
This is because the channel capacity is small for high-rate data service. When the
channel capacity is changed to 4 from 3, it is a large change. But the channel capacity is
large for voice service. For example, when the capacity is changed to 51 from 50, it is a
small change. So the hard channel blocking probability is not suitable for the calculation
of the WCDMA data flow.
(2) New traffic calculation method
We still use the above example.
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When the number of users communicating simultaneously is 3, and the channel
capacity is 3.9, so 0.9 more users can access the system. If the method for hard channel
is used, no more new users can access. However, with the features of CDMA, we can
adopt the probability statistics method for analysis. If the system load is light, it can
accept more new users; if it is heavy, it will accept less new users. Therefore, when the
channel has headroom of 0.9, the new user accepting rate will be taken as 0.9, and the
rejection rate will be 0.1. By far, we can create a new queuing model to get the blocking
probability. In this case, the blocking probability can not be represented by the Erlang
formula, but should be calculated by means of mathematical derivation. The following
shows the derivation process:
Suppose the system is a Lost Call Cleared (LCC) system, which does not provide
queuing function for the call requests. When a user requests for service, the user can
access the system within the preset minimum call setup time if a channel is available. If
all the channels are occupied, the call will be blocked, and the user can not access the
system. The blocked user returns to an infinite user group at once, and can attempt to
access the system any time thereafter.
Suppose P i specifies the probability of i users in the system, specifies the arrival
rate of the users, u refers to the user drop-out rate. Then suppose the system capacity is
c, which is not an integer. Round up c to get the maximum channel numberN c.
According to the detailed derivation process mentioned in Appendix A.1.1 of Reference
[12], we can get:
PN N/N! P0 (7-1)
When the number of users in the system isN, which is the maximum number of
users supported by the system, the blocking probability can be calculated with the Erlang
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formula,
PB PrPrblocked /uN/N!
k0
N
( /uk/k!). As the maximum capacity of the system c
doesn’t reached when the number of users in the system isN, set a c N (where a is
a decimal fraction, and0 a 1), a more users can access the system. In terms of
ratio, the probability of new user permission is a. Therefore, when the number of users
reachesN, new users with the probability of a can access the system and new users with
the probability 1 a will be rejected. This is shown as the following state transition
formula:
PN1 PN a N1u (7-2)
The above formula indicates the new user permission probability is a when the
number of users in the system is N, so that the number of users in the system is N 1.
Based on the probability sum of 1, we can get that P0 ,P1PN1 . k0
N1
Pk 1. Then
substitute the formulae (7-1) and (7-2) into it as follows:
P0 1
k0
N
u k/k!a
N1/N1! ,
PN N/N!
k0
N
u k/k!a
N1/N1! and
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PN1 a
N1/N1!
k0
N
u k/k!a
N1/N1!.
When the system has N users inside, the new user rejection probability is 1 a.
When the system has N 1 users inside, which is the maximum capacity of the system,
no more users can access the system, so the system blocking probability can be worked
out as follows:
PB PN1 1 a PN a. u N1/N1!1 a
u N/N!
k0
N
/uk/k!a u N1/N1!
.
The activity factor is not considered in the formula above. Suppose the activity factor
is v, the blocking probability of the system is.
PB a. vu N1/N1!1 a v
u N/N!
m0
N
v/um/m!a vu N1/N1!
(7-3)
If the traffic and the activity v are specified, PB can be worked out based on the
formula above.
If PB is specified, and the outgoing traffic is vu , you can not get the result with the
above formula, but with the following conversion formula:
PB
(1 aPBa1 au v N1
v
N1/N1!
k0
N1
vu k/k!
(7-4)
The right of the formula (7-4) is the Erlang formula for calculation convenient. The
following is an example of calculating the traffic with the formula (7-4).
(3) Application example
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Suppose the capacity of a system is c 3.1. Round it up to get N 3, and then
a c N 0.1. The Activity factor v 0.1, and specify that PB=0.02, and then
calculate the traffic, as shown below:
First calculate the approximate range v/u:
v/u Erlang_B0.02, 3 0.6022
The left of the formula (7-4) is 0.02
0.9 0.020.10.9 4 1/0.6022 0.0033.
Then the actual traffic is:
/u 1/v Erlang_B0.0033, 46.192.
This is close to the actual situation, because when the capacity is 3, the traffic will be
6.022; when the capacity is 3.1, the traffic will be 6.192. The increase is small, which is in
accord with the actual situation.
Then suppose the channel capacity is 3.9, the left of the formula (7-4) is
0.020.10.020.90.141/0.6022 0.013, then the actual traffic is
/u 1/v Erlang_B0.013, 4 9.5.
When the channel capacity is 4, the traffic is 11. So the traffic when the channel
capacity is 3.9 is very close to the traffic when the channel capacity is 4. It is in accord
with the actual situation.
Suppose the channel capacity is 3.5, the left of the formula is
0.020.5 0.020.50.5 4 1/0.6022 0.005, then the actual traffic is
/u 1/v Erlang_B0.005, 4 7. The traffic is between 6 and 11, which is in
accord with the actual situation.
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Based on these, we can get the following conclusion:
Using the new traffic calculation method solves the problem of traffic mutation
caused by round-up. With the original method, for example, when the channel capacity is
3.99, the traffic can be calculated with the number of channels of 3. When the channel
capacity is 4, the traffic is calculated with the number of channels of 4. The channel
capacity is changed to 4 from 3.99, the traffic mutation occurs. With the new traffic
calculation method, the traffic varies continuously with the channel capacity, without
mutation.
The new traffic calculation method adopts the probability statistics method. The
lighter the load, the higher the user access probability, and vice versa. For example, if the
channel capacity is 3.9, and three channels are in use, a big headroom is available, so
the access probability of the system is big, which is 0.9; if the channel capacity is 3.1,
and three channels are in use, the headroom is small, so the access probability of the
system is small, which is 0.1. This is in accord with the actual situation.
To calculate the blocking probability based on traffic, you can use the formula (7-3).
To calculate the traffic based on blocking probability, you can use the formula (7-4). In
the formula (7-4), you can estimate the traffic first to get the value on the left of the
formula, and then calculate the actual traffic according to the Erlang formula.
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List of references:
[1] Wang Mingmin, WCDMA RNP Technology Research on Special Topics -- High-Level
Design Specifications for Link budget Tool, internal document, 2002-08
[2] AirCom International Limited 2001, UMTS Applied Planning for Experienced
Engineers
[3] Harri Holma and Antti Toskala,WCDMA for UMTS, JOHN WILEY & Sons, LTD., 2000
[4] Jaana Laiho, Achim Wacker, Tomas Novosad, Radio Network Planning and
Optimization for UMTS, JOHN WILEY & Sons, LTD., 2002
[5] Wang Mingmin, WCDMA RNP Technology Research on Special Topics – Calculation
of Downlink Interference Headroom in Link Budget, internal document, 2002-05.
[6] Miao Jiashu, WCDMA RNP Radio Network Dimensioning Guide, internal document,
2002-09
[7] Wu Zhong, WCDMA RNP Low-level Design Specifications for Radio Network
Dimensioning, internal document, 2003-11
[8] Wu Zhong, WCDMA RNP CE Dimensioning Guide, internal document, 2003-07
[9] 3GPP TS 25.427 V3.10.0 (2002-12)
[10] Clint Smith, Daniel Collins, 3G WIRELESS NETWORKS, McGraw-Hill
[11] Win Shengyi, WCDMA RNC Transport Network Layer Traffic Configuration Scheme,
2003-12
[12]Theodore S. Rappaport Radio Communication Principles and Applications, Electronic
Industry Publishing Company, 1999.
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