3. Contents
Chapter 1........................................................................................1
WCDMA Technology Basics ......................................................1
Key Technologies on WCDMA Wireless Side ........................1
Power Control .............................................................................1
Handover....................................................................................3
RAKE Receiver.............................................................................9
Code Resource Allocation...........................................................10
Admission Control .....................................................................17
Load Control/Congestion Control ...............................................19
Overview and Features of AMR ....................................... 20
4.
5. Confidential and Proprietary Information of ZTE CORPORATION 1
C h a p t e r 1
WCDMATechnology
Basics
Key Technologies on
WCDMA Wireless Side
Power Control
Quality Of Service (QOS) that Radio cell network provides for
each subscriber mainly depends on signal-to-interference ratio
(SIR) of subscriber receiving signals. For CDMA cell system, all
subscribers in same cell use same band and timeslot, and
subscribers are isolated with each other only by the (quasi-)
orthogonalization of spreading code. Correlation characteristics
between each subscriber signals are not so good and signals of
other subscribers interfere signals of current subscribers, due to
multipath and delay of the radio channels.
Increasing of subscribers or power of other subscribers may
enhance interference on current subscriber. Therefore, CDMA
system is a strong power-restricted system and strength of
interference influences system capacity directly.
Power control is regarded as one of the key technologies of
CDMA system. Power control adjusts transmission power of each
subscriber, compensates channel attenuation, countervails
near-far effect and maintains all subscribers at lowest standard
of normal communication. It reduces interference on other
subscribers at most, increases system capacity and prolongs
holding time of mobile phones.
Power control is an important part in the WCDMA system. If all
the MSs in a cell transmit signals at the same power, the signals
from a near MS to the BTS are stronger, and the signals from a
6. WCDMA Wireless Technology
2 Confidential and Proprietary Information of ZTE CORPORATION
far MS to the BTS are weaker. As a result, the strong signals
override the weak signals. This is called Near/Far Effect in the
mobile communication. WCDMA is a self-interference system and
all users use the same frequency. Therefore, the "near-far
effect" is more serious. In addition, for the WCDMA system, the
downlink of the BTS is power restricted. To achieve acceptable
call quality when the TX power is small, both the BTS and the
MS are required to adjust power needed by the transmitter in
real time according to the communication distance and link
quality. This process is called "power control".
Power control of WCDMA includes inner loop power control and
outer loop power control by effect.
Inner loop power control is used to combat channel fade and
loss, so that the SIR or power of the received signals can reach
the specific target value. Outer loop power control generates the
SIR or power threshold for inner power control according to the
QoS in the specific environment. By link, there is uplink power
control and downlink power control. Since the CDMA system
capacity is mainly restricted by that of the uplink, uplink power
control is particularly important.
By link type, there is open loop power control and closed loop
power control. Open loop power control is based on the
assumption that the uplink and downlink channels are
symmetric. It can counteract path loss and shadow fade. Close
loop power control does not need this assumption, and it can
counteract fast fade.
Open Loop Control
1. Uplink open loop control
In the WCDMA system, every MS is calculating the path loss
from the BTS to the MS all the time. When the signal
received by the MS from a BTS is very strong, it indicates
that either the MS is very close to the BTS or the
transmission path is excellent. In this case, the MS can lower
the TX power, while the BTS can still receive signals
normally. On the other way around, when the signal received
by the MS is very weak, its TX power can be increased to
counteract the attenuation. Open loop power control occurs
only when the MS is powered on and only once.
2. Downlink outer loop control
It is the process of estimating the initial TX power of a new
requested service. The system can estimate the initial TX
power of the downlink channel according to the signal quality
of the primary common pilot channel (P-CPICH) measured by
the UE. At the same time, the following factors have to be
taken into account: QoS, data rate, quality factor Eb/No,
real-time total TX power of the downlink, interferences on
this cell by other cells, and so on.
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Open loop power control is simple and direct, without
needing exchange of control information between the MS and
the BTS. In addition, it features a higher control speed and
needs few overheads. However, in the WCDMA system,
different frequencies are used in uplink/downlink
transmission. The frequency difference is far greater than the
coherent bandwidth of channels. Therefore, it cannot be
assumed that the fade characteristic of the downlink channel
is equal to that of the uplink channel. This is the limitation of
the open loop power control.
Inner Loop Control
In this case, the receiver compares the signal-interference ratio
of the received signal with the target value of the control
channel. Then, it returns a transmission power control (TPC)
command to the sender. The sender determines whether to
increase or reduce the TX power based on the closed loop power
control algorithm specified by the upper layer, and makes
adjustments at the specified step according to the received
command.
Outer Loop Control
Outer loop power control is a supplement to closed loop power
control. The working principle of uplink outer loop power control
is: Compare the actual block error (BLER) ratio of the
transmission channel with the target block error (BLER) ratio,
then, slowly adjust the target signal-interference ratio
(SIRTarget) so that the service quality is not affected by the
change of the radio environment, and that a relatively constant
communication quality can be maintained.
Outer loop power control usually adjusts the target SIR based on
BLER, to make the QoS meet the requirements. Since different
services have different QoS, there are different target SIRs.
Downlink outer loop power control is similar to downlink inner
loop power control.
Handover
Concept of handover: UTRAN distributes radio resources for UE
in the new cell because of UE’s moving and system load. Then
UE synchronizes with the new cell and transmits data each
other. Handover is a very important technology in mobile
communication system networking.
Handover falls into:
1. Soft handover
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4 Confidential and Proprietary Information of ZTE CORPORATION
Soft handover of cells under same Node B (softer handover)
Soft handover of cells between different Nodes B
Soft handover of cells in same band between different RNCs
(involving Iur interface)
2. Hard handover
Hard handover between different operators
Hard handover in same operator (forced hard handover)
Hard handover between systems (such as, with GSM)
Hard handover between different modes (such as,
between FDD and TDD)
Handover refers to the redistribution of radio resource in mobile
communication system in cell structure, to keep discontinuous
communication of mobile phones when moving a mobile station
from a district to another.
FI GU R E 1 HAN D OVER TYPES I N WCDM A
Handover
in the mode
Handover
between modes
Handover
between systems
Soft handover (Micro diversity)
Softer handover (Among sectors)
Hard handover (Among frequencies)
Handover of FDD-TDD
UTRA FDD - GSM
R4 UTRA FDD-CDMA2000
Hard handover refers to deleting the old link and then building a
new link. Services break off during the handover.
Soft handover refers to adding a new link (the old and the new
links exist at the same time) and deleting the old one after
stabilization. Services continue in the handover.
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FI GU R E 2 HAR D HAN D OVER
Node B
Node B
Cell 1 Cell 2
FI GU R E 3 SOF T HAN D OVER
Node B
Node B
Cell 1 Cell 2
Softer handover refers to handover between cells with same
frequency and in same base station. Difference of soft handover
and softer handover is that combination of radio links is realized
by RNC for soft handover while is realized in Node B (decided by
RNC) for softer handover.
Inter-frequency hard handover refers to handover between cells
with different carriers in WCDMA.
Inter-system hard handover refers to handover between
WCDMA and other systems (such as, GSM).
1. General flow of handover:
1) Measurement (UE)
2) Reoport on measurement results (report from UE to RNC)
3) RNC decides whether to perform handover accpridng to the
report and algorithm (RNC sends the command of handover
to UE if it is necessary).
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FI GU R E 4 HAN D OVER FL OW
(A) RNC send measurement
control message to UE
(B) UE measures according to
RNC's requirement and send
measurement report message
to RNC
(C) RNC stores its measured
results of each cell in different
carriers, for different UE
(D) Estimate signal quality of
each carrier on the report
(between bands and systems)
(E) Quality
judgment
Quality of current
carrier is good
Quality of other
systems is good
Quality of other
carriers is good
(F) Maintain
avtivated set and
monitoring set
(inclduing current
and different carrier)
(G) Corresponds to
allocation resources
of virtue activated
set cell, prepared for
handover
(H) In corresponding
cell, allocate
resources and
prepared for
handover
(I) Determine the target cell and send the handover command if handover is
required
In 3GPP, events correlative to handover are:
Event correlative to soft handover in the band: 1A ~ 1F
Measured value is usually Ec/N0 of pilot channel, reflecting the
quality of a certain cell. 3GPP defines a series of measurement
events in the band. UE reports corresponding events when
meeting definitions.
Event Description
1A
Quality of target cell improves, entering a report
range of relatively activating set quality
Event 1B
Quality of target cell decreases, depart from a report
range of relatively activating set quality
Event 1C
The quality of a non-activated set cell is better than
that of a certain activated set cell
Event 1D Best cell generates change
Event 1E
Quality of target cell improves, better than an
absolute threshold
Event 1F
Quality of target cell decreases, worse than an
absolute threshold
Event correlative to hard handover between bands: 2A ~ 2F
Ec/N0 is measured value, reflecting quality of operators by
measuring cells at different bands. UE reports corresponding
events when meeting definitions.
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Event Description
Event 2A Best band generates change
Event 2B
Quality of currently-used band is worse than an
absolute threshold and that of non-used band is better
than an absolute threshold
Event 2C
Quality of non-used band is better than an absolute
threshold
Event 2D
Quality of currently-used band is worse than an
absolute threshold
Event 2E
Quality of non-used band is worse than an absolute
threshold
Event 2F
Quality of currently-used band is better than an
absolute threshold
Event correlative to handover between systems: 3A ~ 3D
RSSI is measured value for GSM. UE reports corresponding
events when meeting definitions.
Event Description
Event 3A
Quality of currently-used UTRAN operator is worse
than an absolute threshold and quality of other radio
systems is better than an absolute threshold
Event 3B
Quality of other radio systems is worse than an
absolute threshold
Event 3C
Quality of other radio systems is better than an
absolute threshold
Event 3D Best cell in other systems generates change
For example: Adding a radio link in soft handover.
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8 Confidential and Proprietary Information of ZTE CORPORATION
FI GU R E 5 SOF T HAN D OVER (AD D I N G A LI N K ) SI GN AL I N G FL OW
UE Target Node B Source Node B RNC
RRC: Measurement Report(Event 1a) (From Source Node B to RNC)
NBAP: Radio Link Setup Request
NBAP: Radio Link Setup Response
Executing handover
judgement and
adding a radio link
in Target Node B
Start to receive
Distributing transmission resources on Iub interface
Start to send
RRC: Active Set Update(E1a) (From Source Node B to UE)
RRC: Active Set Update Complete (From Source & Target Node B to RNC
simutaneously)
UE connects to Source Node B and Target Node B simutaneously
2. Compression mode
UE has only one RF reception unit and can only decode
signals of one frequency at one time. Therefore, compression
mode is necessary if measuring two cells of different bands
or I different cells.
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FI GU R E 6 COMPR ESSI ON M OD E PR I N C I PL E
Dat a Compressi on1 Frame/ 10 ms
1 f rame
Compressed
I dl e t i me f or
het ero-f requency
measurement
1 f rame
uncompressed
In compression mode, Node B compresses data when sending
some downlink channel frames. UE takes advantage of
remaining time for measurement of different bands.
Compression mode can be realized by drilling and halving
spreading factors, and so on. When measuring between
frequencies, the system negotiates with UE whther to support
and select compression mode.
RAKE Receiver
Since multipath signals contain useful information, CDMA
receivers improve the S/N of the received signals by combining
multipath signals. What a RAKE receiver does is to receive the
various channels of signals from multipath signals through
multiple related detectors, and then combine them. The RAKE
receiver is a classical diversity receiver specially designed for the
CDMA system. Its theoretical basis is that when the propagation
delay exceeds one chip code cycle, multipath signals are actually
seen to be mutually irrelevant.
RAKE reception separates and combines multipath signals.
Different from the IS-95 A, WCDMA has three times of multipath
resolving power. In addition, in a WCDMA system, the pilot
information sent by the user can be used for coherent
combination on the reverse link. The theoretical analysis of
WCDMA shows that if the reverse link uses 8-path RAKE
reception, over 75% signal energies are used. The suppression
of the RAKE reception for multiple access interference depends
on the correlation between the different user characteristic
codes.
14. WCDMA Wireless Technology
10 Confidential and Proprietary Information of ZTE CORPORATION
Code Resource Allocation
In WCDMA, code resources fall into channelization codes,
scrambling codes and synchronization codes.
InＷＣＤＭＡ mobile communication system, primary scrambling
codes are to differentiate cells, channelization codes are to differ
physical channels on the downlink, and scrambling codes are to
differentiate users on the uplink. Orthogonal Variable Spreading
Factor (OVSF) is precious ans scarce resource, so one cell
corresponds to one code table. To access more users and to
increase system capacity, make use of code resources
reasonably. It is very important to plan and manage downlink
channelization code resources.
Although there are many scrambling codes on the uplink, it is
necessary to plan scrambling of RNC, to avoid different users in
different RNC use same scrambling codes.
Channelization Code
1. Brief introduction
Channelization codes are based on OVSF technology, which
can change the spreading factor and ensure orthogonality
between different spreading codes of different length. On the
downlink, channelization codes are to differentiate
transmission from the same source, that is, downlinks within
a sector, while on the uplink, to differentiate dedicated
physical channels of all uplinks from a UE (including
dedicated physical data channel and dedicated physical
control channel).
2. Generation principle
Cch，n，m indicates channelization codes with spreading factor
(SF) of n and code of m.
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FI GU R E 7 CH AN N EL I Z ATI ON COD E GEN ER ATI ON PR I N C I PL E
CC
CC
CC
CC
CC
CC
C
C
C
C
C
C
11
11
CC
CC
C
C
1C
1-ch,2n,2n1-ch,2n,2n
1-ch,2n,2n1-ch,2n,2n
ch,2n,1ch,2n,1
ch,2n,1ch,2n,1
ch,2n,0ch,2n,0
ch,2n,0ch,2n,0
1-1)1),2(nnch,2
2-1)1),2(nch,2(n
1),3ch,2(n
1),2ch,2(n
,11nch,2
01)ch,2(n
ch,1,0ch,1,0
ch,1,001ch
12ch
2,0ch
ch,1,0
－
－
－
＝
－
＝
－
＝
＝
＋＋（
＋
）＋（
，
，，
，，
，
3. Selection rule
Codes are selected from the code tree.
FI GU R E 8 CH AN N EL I Z ATI ON COD E TR EE
SF = 1 SF = 2 SF = 4
Cch,1,0 = (1)
Cch,2,0 = (1,1)
Cch,2,1 =
(1,-1)
Cch,4,0 =(1,1,1,1)
Cch,4,1 =
(1,1,-1,-1)
C ch,4,2 =
(1,-1,1,-1)
Cch,4,3 =
(1,-1,-1,1)
There are some restrictions to channelization codes used by
same information source. For physical channelization, all codes
in a lower branch of the code tree are not in use, that is, all
high-order spreading factors after the code cannot be used.
Likewise, the low-order spreading factors from the branch to the
root cannot be used. red codes are those that have been
allocated and blue codes are those that cannot be allocated.
16. WCDMA Wireless Technology
12 Confidential and Proprietary Information of ZTE CORPORATION
FI GU R E 9 EXAMPL E F OR COD E AL L OC ATI ON
SF=8
SF=32
SF=16
4. Specific allocation
1) Allocation of downlink common channelization code
Channelization codes used on primary common pilot channel
(P_CPICH) and primary common control physical channel
(P_CCPCH) are fixed, which are Cch,256,0 and Cch,256,1
respectively.
For S_CPICH, PICH, AICH, AP-AICH, CSICH and CD/CA_ICH
common channels, channelization codes with the spreading
factor of 256 are used. Generally, several such channels
have been planned when a cell is set up and the
channelization codes for them have been allocated in
advance (therefore, dynamic application is unnecessary).
For S_CCPCH, since the data rate borne on it is not fixed, its
spreading factor can be selected between 4 and 256.
Generally, a corresponding spreading factor is determined for
it according to the permitted transmittable data rate during
common channel setup and then a channelization code is
allocated for it.
2) Allocation of downlink dedicated channelization code
As the parameters vary, the principle of optimized and
dynamic code allocation is followed for dedicated physical
channels.
3) Allocation of uplink common channelization code
PRACH: Its preamble signature s (0< = s< = 15) refers to
the 16 nodes on the code tree, which corresponds to length
16 of the channelization code. The sub-tree of the specified
node is used to spread the message part. Spreading code of
the control part: Cc = Cch,256,m, m = 16 × s + 15 spreading
factor of the data part: Ranging between 32 and 256. More
exactly, spreading code Cd = Cch,SF,m, m = SF × s/16.
4) Allocation of uplink dedicated channelization code
PCPCH: Control channel Cc = Cch,256,0, data channel Cd =
Cch,SF,k, SF = {256, 128, …, 4}, k = SF/4, and power control
forward channelization code Cch,256,0.
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Scrambling Code
1. Brief introduction
Scrambling codes are used after spreading, which will not
change signal bandwidth. They are only used to differentiate
UEs or Nodes B.
2. Generation
1) Long scrambling code sequence
Long scrambling code sequences Clong,1,n and Clong,2,n are
generated from 38400 chip packet mode 2 of two 25-order
polynomial m sequences.
Suppose that x and y stands for two M sequences. x
sequence is generated by using multinomial X25+X3+1 and
y sequence is generated by using multinomial
X25+X3+X2+X+1. They form a Gold sequence. Clong,2,n is
the 16777232 code chip shifted from sequence Clong,1,n.
The construction of xn and y of M sequence is:
Initial conditions:
xn(0) = n0, xn(1) = n1, …,xn(22) = n22, xn(23) =
n23,xn(24) = 1.
y(0) = y(1) = … = y(23) = y(24) = 1.
Recursive expression:
xn(i+25) = xn(i+3)+ xn(i)modulo 2, i = 0, …, 225-27.
y(i+25) = y(i+3)+y(i+2)+y(i+1)+y(i) modulo 2, i = 0, …,
225-27.
Definition:
zn(i) = xn(i)+ y(i)modulo 2, i = 0, 1, 2, …, 225-2.
。22，，1，0
1)(1
0)(1
)( 25
ifor
izif
izif
iZ
n
n
n
clong, 1, n(i) = Zn(i), i = 0, 1, 2, …, 225 – 2
clong, 2, n(i) = Zn((i + 16777232) modulo (225 – 1)), i = 0,
1, 2, …, 225 – 2.
Finally, the definition of long scrambling code sequence is as
follows:
2/211)()( ,2,,1,, icjiciC nlong
i
nlongnlong
i = 0, 1, ..., 225 - 2; indicates round-off.
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14 Confidential and Proprietary Information of ZTE CORPORATION
FI GU R E 10 LON G SC R AMB L I N G COD E SEQU EN C E GEN ER ATOR
clong,1,n
clong,2,n
MSB LSB
2) Short scrambling code sequence
zn(i) = a(i)+2b(i)+2d(i) modulo 4, i = 0, 1, …, 254;
Here, "a (i)" is generated from polynomial expression.
a(0) = 2n0 + 1 modulo 4;
a(i) = 2ni modulo 4, i = 1, 2, …, 7;
a(i) = 3a(i-3)+ a(i-5)+3a(i-6)+2a(i-7)+3a(i-8)modulo 4,
i = 8, 9, …, 254;
Here, "b (i)" is recursive from polynomial expression.
b(i) = n8+i modulo 2, i = 0, 1, …, 7,
b(i) = b(i-1)+ b(i-3)+ b(i-7)+ b(i-8) modulo 2, i = 8, 9, …,
254,
where, g2(x) = x8+x7+x5+x4+1 as;
where, d(i) = n16+i modulo 2, i = 0, 1, …, 7;
d(i) = d(i-1)+ d(i-3)+ d(i-4)+ d(i-8)modulo 2, i = 8, 9, …,
254,
where, zn(255) = zn(0).
Finally, the definition of a short scrambling code sequence is
as follows:
2/256mod211)256mod()( ,2,,1,, icjiciC nshort
i
nshortnshort
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FI GU R E 11 SH OR T SC R AMB L I N G COD E SEQU EN C E GEN ER ATOR
07 4
+ mod n addition
d(i)
12356
2
mod 2
07 4
b(i)
12356
2
mod 2
+
mod 4multiplication
Zn(i)
07 4 12356
+
mod 4
Mapper
C short,1,n(i)
a(i)
+ + +
+ ++
+ ++
3 3
3
2
C short,2,n(i)
3. Usage
1) Downlink
There are altogether 24,576 downlink scrambling codes
numbered as n = 0,..., 24575. They fall into following three
parts:
k = 0, 1, 2,...8191, correspond to 8,192 ordinary scrambling
codes used in normal mode.
k+8192, k = 0, 1, 2, ...8191, are alternative scrambling
codes used in compression mode when "n" is less than SF/2.
They are called left scrambling codes and there are
altogether 8,192.
k+16384, k = 0, 1, 2, ...8191, are alternative scrambling
codes used in compression mode when "n" is more than or
equal to SF/2. They are called right scrambling codes and
there are altogether 8,192.
Here: n is allocated channelization code No.
Rules for ordinary scrambling code allocation
Former 8,192 scrambling codes fall into 512 sets and each
comprises of a primary scrambling code and 15 secondary
scrambling codes following the primary one. Every cell
corresponds to a set of downlink scrambling codes.
Primary scrambling code sequence number: n = 16*I, I = 0,
…, 511,
Scrambling code No. corresponding to the secondary
scrambling code sets: n = 16 * I + K K = 1, …15.
Rule for scrambling code selection during scrambling for
downlink physical channel
For PCIPCH, PCCPCH, S_CPICH, PICH, AICH, AP-AICH,
CSICH and CD/CA_ICH channels, primary scrambling codes
are adopted for scrambling.
20. WCDMA Wireless Technology
16 Confidential and Proprietary Information of ZTE CORPORATION
For their downlink physical channels, either primary
scrambling codes or secondary scrambling codes can be
adopted for scrambling.
2) Uplink
PRACH scrambling code
Construction of preamble code:
4095...,30,1,2kekCkSkC
k
24
j
ssig,nr_pre,sn,pre, ，，＝，＝
＋
Here, message part scrambling code:
Sr_msg，n（i）=Clong，n（I+4096），i=0，1，…，38399
Scrambling code of the message part begins with 4096th
code chip of scrambling code sequence. The first 4096 code
chips serve as preamble scrambling codes of PRACH. That is
to say, same scrambling code sequence No. is used for
preamble scrambling code and message scrambling code of
PRACH. In addition, there are also altogether 8,192
scrambling codes in the message part.
Here, preamble scrambling code is:
Sr_pre，n（i）=Clong，n（i），i=0，1，…，4095; n=0，1，2
，…，8191
There are 8,192 PRACH preamble scrambling codes in total.
They fall into 512 sets and each comprises of 16 scrambling
codes. There are 16 preamble scrambling codes in each cell
in total. The relation between scrambling code sequence
number and corresponding primary scrambling code
sequence of the corresponding cell is: n = 16*m+k m =
0, 1, …, 511; k = 0, 1, …, 15.
DPCH scrambling code
There are numerous scrambling codes available for DPCH. In
addition, scrambling codes generated from a long scrambling
code generator or from a short scrambling code generator
can be used.
Use of long scrambling code:
38399...0,1,iiCiS nlong,nDPCH, ＝，＝
Use of short scrambling code:
38399,...,1,0i,,, ＝iCiS nshortnDPCH
Available scrambling codes on WCDMA uplink is 224 and
codes of 0 to 4095 are allocated to PRACH, 4095 to 40959
are allocated to PCPCH, and the remaining 224 to 40960 are
all for DPCH. During the allocation, ensure that different
uplink scrambling codes are allocated to different UE.
Since scrambling codes are allocated in RNC, uplink
scrambling code resources are same for different RNC, which
21. Chapter 1 WCDMA Technology Basics
Confidential and Proprietary Information of ZTE CORPORATION 17
are 224 to 40960. During the network planning, for those
cells at the edge between different RNCs, keep their
downlink primary scrambling codes different to ensure their
scrambling code sequence different.
Synchronization Code
Synchronization codes fall into primary synchronization codes
and secondary synchronization codes, which are the detection
objects of cell search by a UE. All cells have same primary
synchronization code.
1. Composition of a primary synchronization code
aa,a,-a,a,-a,a,a,a,-a,-a,a,-a,-a,a,a,j1Cpsc＝
11,-1,-1,1,-1,1,-1,1,-1,-1,1,1,1,1,1,x,,x,x,xa 16321 ＝＝
A primary synchronization code is composed of 256 bits in
total, which correspond one by one to 256 chips transmitted
from each time slot of a synchronization channel.
2. Composition of a secondary synchronization code
255z255...2z2),1()1(0z0j1C kscc mmmm hhzhh ，，，＝，
Here,
1k16m －＝
z sequence is a fixed code sequence:
1615,1413121110987654321 x-x-,x-,x-,x-,x-,x-,x-,x,x,x,x,x,x,x,xb ＝
b-b,-b,-b,-b,-b,b,-b,b,-b,-b,b,b,-b,b,b,z ＝
Here, the values of x1, x2, ... x15, x16 are the same as X
values that constitute a primary synchronization code. h
sequence is constituted according to the following rule when
k is 8:
1k
HH
HH
H
1H
1k1k
1k1k
k
0
，
－
＝
＝
－－
－－
Admissi
on Control
Call admission control decides to accept or refuse a new
subscriber, new Radio Access Bearer (RAB) and new Radio Link
(RL)according to current resource (such as, handover). Call
admission control is applicable to original UE access, RAB
designation, reconfiguration and handover. It may lead to
different results because of PRI and actual situations.
22. WCDMA Wireless Technology
18 Confidential and Proprietary Information of ZTE CORPORATION
Call admission control meets QOS of new calls as much as
possible premising the stability of the system, based on
interference measurement, to avoid overloading.
Call admission control falls into:
Uplink call admission control
Downlink call admission control
WCDMA is a self-interference system and there exists power
climbing. The core is power. Uplink capacity depends on whether
total receiving interference power is beyond linear dynamic
range of LNA or not. Downlink capacity depends on whether the
distribution of transmission power completes or not. Process of
call admission control: Measure current load of system cell when
making calls (new access calls and handover calls), forecast and
estimate calls and judge whether to access calls. Take QOS
requirements of calls. That is, communication rate,
communication quality (signal-to-noise ratio and error code
ratio) and delay into consideration when forecasting calls.
Refuse the call when it approaches some threshold.
Service calls fall into new calls and handover calls. Reserve some
resources for handover calls to ensure high ratio of successful
handovers. PRI of handover calls is distinguished by admission
control threshold. Admission control threshold of new calls is
lower than that of handover calls. New calls are refused when
current load of the cell is higher than admission threshold of new
calls. However, handover calls are accepted. Handover ratio is
better to be at about 35% in soft handover. Handover calls are
also refused when the load of the cell is higher than handover
admission control threshold. Load control threshold is commonly
higher than admission control threshold of handover, to prevent
overloading when radio circumstances change and to ensure the
stable running of the system.
Measurement Related to Admission Control
1. Node B Common Measurement
1) DCH measurement
Major factors to influence WCDMA system capacity (DCH) are
uplink interference and downlink operator emission power.
DCH admission control performs admission decision on these
two parameters. Node reports RTWP and TCP of Node B
common measurement to RNC periodically, so that RNC can
decide whether to access the new call according to latest
load.
2) HS-DSCH measurement
HS-DSCH admission control needs Node B common
measurement information related to HSDPA, including
HS-DSCH required Power, Transmitted operator power of all
codes not used for HS-PDSCH or HS-SCCH transmission.
23. Chapter 1 WCDMA Technology Basics
Confidential and Proprietary Information of ZTE CORPORATION 19
Therefore, open these common measurements
simultaneously in cells supporting HSDPA.
3) RACH measurement
According to policies of ZTE, to estimate the load, RACH
starts up Acknowledged PRACH preambles common
measurement during the admission control, to get actual
utilization ratio of PRACH channel.
2. UE measurement
When predicting downlink power, RNC needs real-time route
loss of UE. RNC can get route loss of UE by different means
according to admission requests type, such as, reporting
through some events of UE.
Load Control/Congestion Control
1. Process of load control
The system measures the load of the system cell at real time
continually. The system load is high and the load enters
unstable running district of the system when load average
value exceeds some threshold value in a set time. Load
control is necessary at the moment.
2． Load control threshold
The core of load control is to access as many services as
possible premising that the system is running stably, to
realize high efficient running. Leave some redundancy,
excluding base line for system breakdown, as threshold value
of load control. Threshold value of load control is larger than
that of admission control.
3． Load control mode
Load control works when system load approaches or exceeds
load threshold value. Main modes:
1） Reduce the load in a rapid mode, which is mainly realizes by
base station (Node B).
Downlink rapid load control: Refusing the command to
increase the power from the mobile station.
Uplink rapid load control: Reducing SIR destination value for
uplink rapid power control.
2） Reduce the load in medium or slow mode, which is mainly
realized by base station controller (RNC).
Commonly, RNC makes judgment and changes max allowed
transmission power, destination SIR value and TFCS by
reconfiguring the RL. In this mode can the system load be
reduced for a long time.
24. WCDMA Wireless Technology
20 Confidential and Proprietary Information of ZTE CORPORATION
Make negotiations if hoping to reduce the system load for a
long time, that is, RNC negotiates with CN to reduce
resource occupation of services during the communications.
Or, share loads with adjacent cells in RNS to reduce the load
of those overloading cells. The taking-in and sending-out of
adjacent cells (covering radius of one cell increases and that
of another adjacent cell decreases) is called cell breathing.
Conclusions:
Reducing the throughput of grouping (reducing the
transmission rate)
Handing over to other WCDMA carrier frequency
Handing over to GSM system
Reducing the rate of real-time services
Executing the call drops
Overview and Features of
AMR
Adaptive Multi Rate (AMR) code is a voice-coding plan. It is
called broadband AMR (AMR-WB or AMR Wideband) in WCDMA.
Current GSM speech coding (FR, HR, EFR and AMR) is applicable
to narrowband speech and audio bandwidth is limited to 3.4 kHz.
Audio bandwidth of AMR-RB extends to 7 kHz, which makes the
voice much clearer and natural, especially in hands-free
situations.
AMR provides eight coding rates of 4.7 k, 5,15 k, 5,9 k, 6,7 k,
7,4 k, 7,95 k, 10.2 k and 12.2 k. Select codes with low rate on
condition that it does not influence communication quality, to
save network resource.
