ECE540 Mobile Communications
Chapter 3
Universal Mobile Telecommunication
System (UMTS)
Dr. Mehaseb Ahmed
Electronics and Communication Department
Misr International University (MIU)
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ECE446 Ch.3 UMTS
Chapter Contents
3.1 Introduction
3.1.1 (3G) Objectives
3.1.3 (3GPP) UMTS Evolution path
3.1.2 (3G) Frequency Allocation
3.2 Wideband Code Division Multiple Access (WCDMA)
3.2.1 Spread Spectrum Principle
3.2.2 Multi-User DSSS (DS-CDMA)
3.2.3 Orthogonality Condition in DS-CDMA
3.3 WCDMA System Capacity
3.4 Codes in WCDMA
3.4.1 Channelization Codes
3.4.4 Code Reuse
3.4 .2 Scrambling Codes
3.4.3 Parameters of WCDMA
3.5 UMTS System Architecture
3.5.1 UMTS High Level System Architecture
3.5.2 Basic UMTS Architecture
3.5.3 UMTS Interfaces
3.6 WCDMA Radio Interface Channels
3.6.1 logical Channels
3.6.3Physical Channels
3.6.2 Transport channels
3.7Power control in WCDMA
3.8 High-Speed Packet Data Transmission
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3.1 Introduction
3.1.1 (3G) Objectives
•
Work on 3G broadband systems commenced in 1985 and was carried out
under the auspices of the International Telecommunication Union (ITU). It was
decided that the new system, eventually named International Mobile
Telecommunications (IMT-2000), would provide the following specifications:
1. High capacity requirements：some systems such as D-AMPS，GSM and PDC
are approaching saturation.
2. High spectral efficiency.
3. High quality of service with complete security and reliability.
4. Backward compatibly with 2G Systems.
5. High speed packet data with ttransmission rates:
- transfer of up to 2 Mbps inside of buildings and for slowly moving mobile
stations (at the speed of less than 10 km/h);
- 384 kbps for terminals moving with a speed of up to 120 km/h in built-up areas;
- 144 kbps in non-built-up areas and in the case of fast moving terminals.
6. Services in real time and multimedia and localization services.
7. Simultaneous invocation of different services.
8. Global roaming.
9. Smooth transition from the second generation systems to that of 3G.
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3.1 Introduction (Continued)
3.1.3 (3GPP) UMTS Evolution path
3GPP
3GPP2
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Fig. 3.2(a) WCDMA is an evolution of GSM/GPRS.
ECE446 Ch.3 UMTS
3.1 Introduction (Continued)
3.1.3 (3GPP) UMTS Evolution path
3GPP
Third Generation
Partnership
Project
The 3rd Generation Partnership Project is an umbrella term for a number of
standards
organizations
which
develop
telecommunications.
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ECE446 Ch.3 UMTS
protocols
for
mobile
3.1 Introduction
3.1.2 (3G) Frequency Allocation
•
1.
2.
➢
➢
➢
Provision of standards for a system that would meet the above prerequisites
was assigned to regional standardization organizations whose activity was
mainly focused on working out a radio interface for the ground segment of the
system
UMTS Terrestrial Radio Access (UTRA).
Broadband Code Division Multiple Access (CDMA) transmission. CDMA stands
for Code Division Multiple Access. WCDMA is the radio access scheme used
for third generation cellular systems.
There is no restriction on time and frequency in this scheme. All the users can
transmit at all times and at all frequencies because users are isolated by code.
It is a Radio Access Technology (RAT), used in the UMTS Radio Access
Network (RAN), based on direct-sequence CDMA with the chip rate of 3.84
Mega chip per second (Mcps). Within 3GPP, WCDMA is called Universal
Terrestrial Radio Access (UTRA ).
Supports multiple services, multiple quality of service (QoS), and higher data
rates (up to 2 Mbps).
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3.2 WCDMA (Continued)
CDMA
Traffic channels: different users
are assigned unique code and
transmitted over the same
frequency band at the same
time, for example, WCDMA
and CDMA2000
Power
TDMA
Power
FDMA
Power
Traffic channels: different time slots
are allocated to different users, for
example, DAMPS and GSM
Traffic channels: different frequency bands are
allocated to different users, for example, AMPS
and TACS
Fig. 3.3 Multiple Access Technologies.
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3.1 Introduction
3.1.2 (3G) Frequency Allocation
•
Frequency allocation plan for the use of radio frequency bands for the UMTS
includes the following frequencies: 1920–1980 MHz for uplink and 2110–2170
MHz for downlink as shown in Figure.
ECE446 Ch.3 UMTS
3.1 Introduction
3.1.2 (3G) Frequency Allocation
•
•
Frequency allocation plan for the use of radio frequency bands for the UMTS
includes the following frequencies: 1920–1980 MHz for uplink and 2110–2170
MHz for downlink as shown in Fig. 3.1 (a and b).
The system can operate in two modes: FDD and TDD duplex, as shown in
Figure
➢ The FDD mode
• The uplink and downlink transmissions employ two separated frequency
bands for this duplex method. A pair of frequency bands with specified
separation is assigned for a connection.
• provides separate 5 MHz channels, both for the link from the base station to
the mobile subscriber (downlink), and from the subscriber to the base
station (uplink).
➢ In the TDD mode
• In this duplex method, uplink and downlink transmissions are carried over
the same frequency band by using synchronized time intervals. Thus time
slots in a physical channel are divided into transmission and reception part.
• the 5 MHz channel is shared between the uplink and the downlink
directions.
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3.1 Introduction (Continued)
3.1.2 (3G) Frequency Allocation
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Fig. 3.1(c) UMTS Duplex in FDD and TDD mode.
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3.1 Introduction
3.1.2 (3G) Frequency Allocation
UMTS Bandwidth or Channel Spacing The nominal channel spacing is 5 MHz.
Channel Raster The channel raster is 200 KHz, which means that the center
frequency must be an integer multiple of 200 KHz.
Channel Number The carrier frequency is designated by the UTRA Absolute
Radio Frequency Channel Number (UARFCN), where:
Fcenter = UARFCN * 200 KHz
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Fig. 3.1(d) Frequency Reuse.
ECE446 Ch.3 UMTS
3.1 Introduction
3.1.2 (3G) Frequency Allocation
Frequency Reuse: In a 3G cellular network neighboring cells can operate on the
same carrier frequency. When configuring a 3G network, frequency planning
is not needed. (Other planning is needed!).
Fig. 3.1(d) Frequency Reuse.
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3.2 WCDMA (Continued)
3.2.1 Spread Spectrum Principle
1. Time - Frequency Duality
• The power spectrum of a succession 0 and 1 coded with the NRZ is composed
of lobes that cut the frequency axis at multiple of the bit rate (1/T). The main
part of the power (> 90%) is located in the first lobe which has a maximum
value of a2T = Eb at f = 0, where Eb is the energy of the bit.
• Therefore, the faster is the bit rate (the smaller is T), the more energy is spread
on the spectrum or frequency domain, as illustrated in Fig, 3.4.
2. Direct Sequence Spread Spectrum (DSSS) - Transmission
• Spreading spectrum consists in increasing artificially the transmission rate (chip
rate) in order to spread the energy of the information signal on a wide
frequency band without modifying the data rate, as shown in Fig, 3.5.
• For UMTS, the number of chips per bits is called the processing gain or
Spreading Factor (SF), or Processing gain, Gp which is given by:
Tbit Nchip Chip Rate
SF =
=
=
= Gp
Tchip Nbit
Bit Rate
Tbit = SFxTchip
Bit Rate x SF = Chip Rate = (3.84 Mcps )
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(3.1)
(3.2)
(3.3)
3.2 WCDMA (Continued)
3.2.1 Spread Spectrum Principle
1. Time - Frequency Duality
Fig. 3.4 Time - frequency duality.
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3.2 WCDMA (Continued)
3.2.1 Spread Spectrum Principle
2. Direct Sequence Spread Spectrum (DSSS) – Transmission (Spreading)
Fig. 3.5(a) DSSS transmission.
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3.2 WCDMA (Continued)
3.2.1 Spread Spectrum Principle
2. Direct Sequence Spread Spectrum (DSSS) – Transmission (Spreading)
Fig. 3.5(b) DSSS transmission (effect of the spreading).
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3.2 WCDMA (Continued)
3.2.1 Spread Spectrum Principle
3. Direct Sequence Spread Spectrum (DSSS) – Reception (Despreading)
• To be able to perform the dispreading operation, the receiver must not only
know the sequence used to spread the data signal, but the sequence of the
received signal and the locally generated spreading sequence must be
synchronized.
Fig. 3.6(a) DSSS reception.
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3.2 WCDMA (Continued)
3.2.1 Spread Spectrum Principle
3. Direct Sequence Spread Spectrum (DSSS) – Reception (Despreading)
Fig. 3.6(b) DSSS reception (effect of the despreading).
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3.2 WCDMA (Continued)
3.2.1 Spread Spectrum Principle
3. Direct Sequence Spread Spectrum (DSSS) – Reception (Despreading)
Transmitter
Receiver
Spreading
Despread
Digital
signal s(t)
Spreading signal
m(t)
Code
c(t)
Power
Frequency
Digital signal
s(t)
Code
c(t)
Power
Power
Frequency
Fig. 3.6(c) DSSS Transmission and reception.
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Frequency
3.2 WCDMA (Continued)
3.2.2 Multi-User DSSS (DS-CDMA)
1. Data Transmission
• The different user data are spread with different orthogonal codes and added
together synchronously, as shown in Fig. 3.7.
Fig. 3.7 Transmitted signal (Downlink case).
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3.2 WCDMA (Continued)
3.2.2 Multi-User DSSS (DS-CDMA)
2. Data Reception for User 1
• User1 receives the composite signal, multiplies it synchronously with its
dedicated code: if for a bit period the mean value found is positive, then the
receiver decided that the transmitter sends a (1), if it is negative, it decided that
the transmitter sends a (-1), as shown in Fig. 3.8.
Fig. 3.8 Data extraction User 1 (reception).
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3.2 WCDMA (Continued)
3.2.2 Multi-User DSSS (DS-CDMA)
3. Data Reception for User 2
• User 2 receives the composite signal, multiplies it synchronously with its
dedicated code: if for a bit period the mean value found is positive, then the
receiver decided that the transmitter sends a (1), if it is negative, it decided that
the transmitter sends a (-1), as shown in Fig. 3.9.
Fig. 3.9 Data extraction User 2 (reception).
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3.2 WCDMA (Continued)
3.2.2 Multi-User DSSS (DS-CDMA)
Fig. 3.10 Multi-User DSSS (DS-CDMA) operation.
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3.2 WCDMA (Continued)
3.2.2 Multi-User DSSS (DS-CDMA)
• Codes discriminate users or multiplexing users data, as shown in Fig. 3.11.
Spreading
Code 1
Code 2
User 1
User 2
Code 3
Code 4
User 3
Code 5
User 4
User 5
Power spectrum
Composite signal
5 MHz
Fig. 3.11 Multiplexing users’ data through codes.
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3.2 WCDMA (Continued)
3.2.2 Multi-User DSSS (DS-CDMA)
• Decode one user form multiple, as shown in Fig. 3.12.
Power spectrum
a2Tbit = Ebit
Eb/Io required
Maximum Interference level
gain
Unwanted power from
other sources
Echip
Fig. 3.12 Demultiplexing user data through codes.
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Available power
to share between
users
3.2 WCDMA (Continued)
3.2.3 Orthogonality Condition in DS-CDMA
• In DS-CDMA, all users codes must be orthogonal. Orthogonality means there is
no correlation between codes, so, Ck presence does not affect Cj energy. If the
synchronization at To is not respected, then there is no orthogonality anymore
→ Cj and Ck interfere, as shown in Fig. 3.13.
Fig. 3.13(a) Orthogonality Condition in DS-CDMA.
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3.2 WCDMA (Continued)
3.2.3 Orthogonality Condition in DS-CDMA
Code Division Multiple Access
Fig. 3.13(b) Orthogonality Condition in DS-CDMA.
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3.2 WCDMA (Continued)
3.2.3 Orthogonality Condition in DS-CDMA
• Orthogonal Variable Spreading Factor (OVSF) Walsh code tree generator is
shown in Fig. 3.14.
Fig. 3.14(a) OVSF code tree generator .
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3.2 WCDMA (Continued)
3.2.3 Orthogonality Condition in DS-CDMA
Fig. 3.14(b) OVSF Walsh code tree generator .
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3.2 WCDMA (Continued)
3.2.3 Orthogonality Condition in DS-CDMA
• The Walsh codes generated within the same layer constitute a set of
orthogonal codes. Furthermore, any two codes of different layers are
orthogonal except when one of the two codes is a father code of the other. For
example C4,1 is not orthogonal with C1,0 and C2,0, but is orthogonal with C2,1 as
shown in Fig, 3.14.
Channelization
Codes - OVSF
Fig. 3.14(c) Orthogonal and nonorthogonal codes.
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3.3 WCDMA System Capacity
•
The capacity in CDMA system is interference limited. The interference per bit is
described as energy per bit divided by total interference in the transmission
bandwidth. In CDMA the interference in communication bandwidth is generated
by all other users. We assume that the interference is characterized as a zeromean AWGN process.
Uplink Single-cell System Model
• Coarse estimate of the reverse
link (uplink) capacity of system
shown in Fig. 3.15.
Assumptions
• Single Cell
• Total active users Ku
• The interference caused by other
users in the cell can be modeled
as AWGN.
• Perfect power control is used, i.e.
the received power of each user
at the base station is the same.
• Random sequences
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Fig. 3.15 Single cell capacity.
ECE446 Ch.3 UMTS
3.3 WCDMA System Capacity (Continued)
•
If the received signal power of each user is Ps watts, and the background noise
can be ignored (ex: micro-cells), then the total interference power (MAI) at the
output of the desired user’s detector is given by:
(3.4)
I  K −1 P
(
•
•
)
s
where Ku is the total number of equal energy users in the cell. Suppose each
user can operate against Gaussian noise at a bit-energy-to-noise density level
of Eb/Io as illustrated in Fig. 3.16.
Let W be the entire spread bandwidth, then the total interference spectral
density can be expressed as:
I
I0 =
W
•
u
Watts / Hz (one − sided )
(3.5)
Also, the transmitted or received energy signal per bit, Eb is given by:
P
(3.6)
Eb = s = Ps xTb
Rb
where Rb is the transmitted data rate and Tb is the bit duration. So the
total number of users in the cell, Ku is calculated from (3.4) to (3.6) as:
I
I o xW W / Rb
(Ku − 1) = =
=
(3.7)
Ps Eb xRb Eb / I o
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3.3 WCDMA System Capacity (Continued)
•
For identical power for each customer; the ratio W/ Rb is called the coding gain
or Processing gain, Gp which is calculated from (3.7) as:
Gp
W / Rb
(Ku − 1) =
=
Eb / I o Eb / I o
•
 Eb / I o =
Gp
(Ku − 1)
=
SF
(Ku − 1)
(3.8)
Eq. (3.8) contains only the interference from the host cell. The interference from
the other cells is f times the interference from the host cell. That means the
total interference is increased by the factor (1+ f ), where f is called the other
cell relative interference factor, f .
Gp
W / Rb
SF
(Ku − 1) =
=
=
(Eb / I o )(1 + f ) (Eb / I o )(1 + f ) (Eb / I o )(1 + f )
(3.9)
Soft Capacity
• The ability to maintain the orthogonality between a big number of codes
depend on the noise and interference.
• So, Soft Capacity is Interference limited. If there is no noise and interference
capacity can go to infinity but this never happens.
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3.3 WCDMA System Capacity (Continued)
Power spectrum
a2Tbit = Ebit
Eb/Io required
Maximum Interference level
gain
Unwanted power from
other sources
Echip
Fig. 3.16 (a) Single cell capacity.
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Available power
to share between
users
3.3 WCDMA System Capacity (Continued)
Fig. 3.16(b) Single cell capacity
(load In neighboring cell).
Example 3.1
A DS-CDMA system has spreading code rate or chipping rate, W = 3.84 Mchip/s
and user transmission data rate, Rb = 15 kb/s. How many users, Ku that can one
cell can serve when the required performance requires signal to interference ratio,
SIR = (Eb/I0)= 9 dB.
Solution Eb/ Io = 9 dB → 7.94
Rb = 15 kb/s and W = 3.84 Mchip/s
Processing gain, Gp which is calculated from (3.8) as:
W 3.84 x106
Gp =
=
= 256
Rb 15 x1013
The number of users, Ku that can one cell can serve is given by (3.8) as:
Ku =
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Gp
Eb / I o
+1 =
256
+ 1 = 33 user
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ECE446 Ch.3 UMTS
3.3 WCDMA System Capacity (Continued)
Example 3.2
In 3G-WCDMA cellular system has the information bit rate, Rb = 4.8 kb/s and the
chip rate, W = 3.84 Mchip/s. If the input signal power at the receiver, Ps = 25 mW
and noise power, N = 2 W, do the following:
a) Determine and calculate the processing gain Gp.
b) Calculate the signal to noise ratio at the input and at the output of the receiver.
Solution a) the processing gain Gp is given by (3.8) as:
W 3.84 x106
Gp =
=
= 800
Rb 4.8 x103
 G p = 10 log 800 = 29.03 dB
b) The signal to noise ratio at the input of the receiver:
−3
Ps 25x10
S
=
=
= 12.5x10−3
 
2
 N inp N
(
)
S
   = 10log 12.5x10−3 = −19.03 dB
 N inp
The signal to noise ratio at the output of the receiver:
S
S
S
−3
=
xG
=
12
.
5
x
10
x
800
=
10

 
 
  = 10 log (10 ) = 10 dB
p
 N out  N inp
 N out
S
S
(
dB
)
=
 
  (dB ) + G p (dB ) = −19.03 + 29.03 = 10 dB
 N out
 N inp
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3.3 WCDMA System Capacity (Continued)
Example 3.3
In 3G-WCDMA cellular system has the information bit rate, Rb = 9.6 kb/s and the
processing gain Gp = 26.02 dB. If the input signal power at the receiver, Ps = 15
mW and noise power, N = 1.5 W, do the following:
a) The chip rate, W.
b) Calculate the signal to noise ratio at the input and at the output of the receiver.
Solution a) the processing gain Gp is given by (3.8) as:
Gp (dB) = 10logGp = 26.02 dB  Gp = 102.602 = 400
Gp = W / Rb  W = Gp xRb = 400x9.6 = 3.84 MHz = 3.84 Chip / sec
b) The signal to noise ratio at the input of the receiver:
Ps 15x10−3
S
S
−2
=
=
=
0
.
01

 
  = 10log 1x10 = −20 dB
1.5
 N inp N
 N inp
(
The signal to noise ratio at the output of the receiver:
)
S
S
S
−2
=
xG
=
1
x
10
x
400
=
4

 
 
  = 10 log (4 ) = 6 dB
p
 N out  N inp
 N out
S
S
(
dB
)
=
 
  (dB ) + G p (dB ) = −20.02 + 26.02 = 6 dB
 N out
 N inp
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3.3 WCDMA System Capacity (Continued)
Example 3.4
In an Omni-directional 3G-WCDMA cellular system the required performance
requires Signal to Interference Ratio, SIR = (Eb/I0) = 10 dB is required for each
user. If the baseband data rate for each user Rb = 10 kb/s, and the cell capacity,
Ku = 101 subscribers. Do the following:
a) Determine the system chipping rate. Ignore voice activity considerations.
b) Repeat when the voice activity is considered to be  = 40 % and Tri-Sectors
are used.
Solution
Eb/ Io = 10 dB → 10, Rb = 10 kb/s and Ku = number of customers = 101 user.
a) The number of users, Ku that can one cell can serve is given by (3.8) as:
Gp
W / Rb
(Ku − 1) =
=
 W = Rb x( Ku − 1)( Eb / I o )
Eb / I o Eb / I o
W = Rb x( Ku − 1)( Eb / I o ) = 10 x103 x100 x10 = 10 Mchip / s
b) α (Voice activity) = 40 % ; Hence Eb/ Io = (W / Rb) / ((Ku – 1) * α)
W = Chipping rate = α *Rb * (Ku /3 - 1)*{ Eb/ No} = 1.306.67 Mchip/s
Comment: By introducing both of the voice activity factor (less than 100%) as well
as the system sectorization, the system chipping rate is decreased. So, the
required RF bandwidth is reduced and the same data rate is serviced.
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3.3 WCDMA System Capacity (Continued)
Example 3.5
An Omni-directional 3G-WCDMA cellular system has the following specifications:
spread symbol rate, W = 3.84 Mchip/s, user data rate, Rb = 7.5 kb/s and the Walsh
spreading codes are generated at a rate, Rcode = 30 kb/s . Each user should have a
unique Walsh code, so calculate the number of users, ku can be admitted into the
system in the following cases:
a) The target SIR = 10 dB and the other cell relative interference factor, f = 0.6.
b) The target SIR = 5 dB and the other cell relative interference factor, f = 0.6.
c) The target SIR = 5 dB and the other cell relative interference factor, f = 0.2.
Solution
• The system is limited either by amount of available OVSF (Walsh) codes or
interference. If the capacity limited by interference is more than amount of the
available codes, the system is limited by the amount of Walsh codes, NWalsh:
NWalsh
W
3.84x106
=
=
=
= 128 codes
3
Walsh Rate Rcode 30x10
Chip Rate
That is we have available 128 different Walsh codes.
The number of users, Ku that can one cell can serve is given by (3.9) as:
Gp
W / Rb
SF
(Ku − 1) =
=
=
(Eb / I o )(1 + f ) (Eb / I o )(1 + f ) (Eb / I o )(1 + f )
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3.3 WCDMA System Capacity (Continued)
Example 3.5Solution
The processing gain Gp is given by (3.8) as:
6
W 3.84 x10
Gp =
=
= 512
3
Rb 7.5 x10
a) For SIR = 10 dB → SIR = 10, and f = 0.6, the number of users, ku calculated as:
Ku =
Gp
(Eb / I o )(1 + f )
+1 =
512
+ 1 = 32 user
(10)(1.6)
Note: ku = 32 < NWalsh
b) For SIR = 5 dB → SIR = 3.16, and f = 0.6, the number of users, ku calculated as:
Ku =
Gp
(Eb / I o )(1 + f )
+1=
512
+ 1 = 89 user Note: ku = 89 < NWalsh
(3.16 )(1.6)
c) For SIR = 5 dB → SIR = 3.16, and f = 0.2, the number of users, ku calculated as:
Ku =
Gp
(Eb / I o )(1 + f )
+1 =
512
+ 1 = 136 user
(3.16 )(1.2)
In this case, interference allows more users, ku to admit the cell more than the
available Walsh codes, NWalsh =128. So the maximum allowable number is:
Nusers = MinKu , NWalsh = 128 user
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3.4 Codes in WCDMA

Spreading consists of 2 steps：
•
Channelization operation，which transforms data symbols into chips. Thus
increasing the bandwidth of the signal, The number of chips per data
symbol is called the Spreading Factor (SF). The operation is done by
multiplying with OVSF code.
Scrambling operation is applied to the spreaded signal. The operation is
done by multiplying with Pseudo Noise (PN) code as shown in Fig. 3.16(a).
•
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Fig. 3.16(a) Codes in WCDMA.
ECE446 Ch.3 UMTS
3.4 Codes in WCDMA (Continued)
3.4.1 Channelization Codes
•
Channelization codes are used for retaining orthogonality of signals coming
from different physical channels.
•
Orthogonal
Variable
Spreading
Factor
(OVSF)
Codes
are
used
as
channelization codes. The OVSF codes can be defined using a code tree.
•
In the code tree the channelization codes are uniquely described as Cch,SF,k,
where SF is the Spreading Factor of the code and k the code number, 0 ≤ k ≤
SF-1. The length of an OVSF code is an even number of chips and the number
of codes is equal to the number of chips.
•
As the chip rate is constant, the different lengths of code enable different user
data rates to be coded. It makes spreading for the spectrum.
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ECE446 Ch.3 UMTS
3.4 Codes in WCDMA (Continued)
3.4. 2 Scrambling Code
•
Scrambling codes are used to separate different sources. In the scrambling
process the code sequence is multiplied with a pseudorandom scrambling code
and it doesn’t spread the spectrum.
•
The code used for scrambling of the uplink may be of either long or short type.
There are 224 long scrambling codes for uplink and 218 short for downlink.
•
Scrambling code: Pseudo-random Codes (GOLD sequence).
Generation of Gold Code using
LFSR
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ECE446 Ch.3 UMTS
3.4 Codes in WCDMA (Continued)
•
•
•
A mobile station or UE is surrounded by BSs, all of which are transmitting on
the same WCDMA frequency.
It must be able to discriminate between the different cells of different base
stations and listen to only one set of code channels.
Therefore two types of codes are used: Channelization Codes and
Scrambling Codes as shown in Fig. 3.16(b).
Scrambling code
BTS
Channelization code 1
User 1 signal
Channelization code 2
User 2 signal
Channelization code 3
User 3 signal
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Fig. 3.16(b) WCDMA downlink transmission on a cell level.
ECE446 Ch.3 UMTS
3.4 Codes in WCDMA (Continued)
Scrambling code 1
Channelization code
User 1 signal
Scrambling code 2
Channelization code
BTS
User 2 signal
Scrambling code 3
Channelization code
User 3 signal
Fig. 3.16(c) WCDMA uplink transmission on a cell level.
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ECE446 Ch.3 UMTS
3.4 Codes in WCDMA (Continued)
3.4.1 Channelization Codes
•
•
•
Channelization codes are used for retaining orthogonality of signals coming
from different physical channels. In UL they distinguish data channels and
controlling channels coming from the same user. In DL they distinguish calls
carried out within the same cell (by different users) as shown in Fig. 3.17.
Channelization codes are used in for downlink (DL) to separate connections to
different users in one cell as shown in Fig. 3.17(a) and channelization code
period is up to 512 chips for downlink.
Channelization codes are used to separate channels from the same terminal.
Channelization codes are used in UL for the separation of different services
(applications/channels) as shown in Fig. 3.17(b). Channelization code period
1.0 - 66.7 s → (4-256 chips) for uplink.
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ECE446 Ch.3 UMTS
3.4 Codes in WCDMA (Continued)
3.4.1 Channelization Codes
(a)
(b)
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Fig. 3.17 Channelization codes.
ECE446 Ch.3 UMTS
3.4 Codes in WCDMA (Continued)
3.4. 2 Scrambling Code
•
•
•
•
•
•
•
•
•
Scrambling codes are used to separate different sources. In the scrambling
process the code sequence is multiplied with a pseudorandom scrambling code
and it doesn’t spread the spectrum.
The code used for scrambling of the uplink may be of either long or short type.
There are 224 long scrambling codes for uplink and 218 short for downlink.
Scrambling code: Pseudo-random Codes (GOLD sequence).
Downlink: scrambling codes are used to reduce the inter-base station
interference. Typically, each Cell has only one scrambling code for UEs to
separate cells. (512 SCs).
Scrambling codes are used in DL for the separation of different cells and for the
identification of particular cells.
For downlink, a total of 218-1 = 262,143 scrambling codes can be generated.
Scrambling codes k = 0, 1, …, 8191 are used.
Uplink: scrambling codes are used to separate the terminals. For UL, a total of
224-1 = 16.8 millions SCs are used.
Scrambling codes are used in UL for the separation of different users and for
the identification of mobile stations.
Scrambling code period is 10 ms, or 38400 chips for uplink and downlink or
Scrambling code period is 66.7 s = 256 chips for uplink.
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ECE446 Ch.3 UMTS
3.4 Codes in WCDMA (Continued)
3.4. 2 Scrambling Code
•
The rate of the scrambling sequences in the UMTS system is equal to the chip
rate of spreading sequences (3.84 Mchip/s). As the result of the scrambling
process the rate of the coded stream does not increase the bandwidth.
• Each scrambling sequence consists of two binary code sequences of the same
length that are subsequently treated as the real and imaginary parts of the
complex scrambling sequence.
• The standard defines two types of scrambling codes:
- short sequences S(2) consisting of 256 symbols (repeated with the frequency
of 15 KHz).
- long sequences (Gold codes) consisting of 38400 symbols (repeated every 10
ms).
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ECE446 Ch.3 UMTS
3.4 Codes in WCDMA (Continued)
3.4. 2 Scrambling Code
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Fig. 3.18 Scrambling codes.
ECE446 Ch.3 UMTS
3.4 Codes in WCDMA (Continued)
Parameters of WCDMA
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ECE446 Ch.3 UMTS
3.4 Codes in WCDMA (Continued)
3.4.4 Code Reuse
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Fig. 3.1(a) Code Reuse.
ECE446 Ch.3 UMTS
3.5 UMTS System Architecture
3.5.1 UMTS High Level System Architecture
•
The UMTS network consist of three interacting domains: User Equipment (UE)
UMTS Terrestrial Radio Access Network (UTRAN) and Core Network (CN) as
shown in Fig. 3.20.
UMTS Terrestrial Radio Access Network (UTRAN)
• The UTRAN provides the air interface access method for User Equipment.
• A bigger step in radio access evolution from GSM networks.
• Base Station is referred as Node-B and control equipment for Node-B's is called
Radio Network Controller (RNC)
UMTS Core Network
• The main function of the core network is to provide switching, routing and transit
for user traffic.
• Core network also contains the databases and network management functions.
• The basic Core Network architecture for UMTS is based on GSM network with
GPRS. All equipment has to be modified for UMTS operation and services.
53 of 90
Fig. 3.20 UMTS high level system architecture.
ECE446 Ch.3 UMTS
3.5 UMTS System Architecture (Continued)
3.5.2 Basic UMTS Architecture
• The Basic UMTS Architecture is shown in Fig. 3.21.
• As in GSM General Packet Radio Service (GPRS) system, we have.
- (SGSN) is the Serving GPRS Support Node.
- (GGSN) is the Gateway GPRS Support Node.
Fig. 3.21 UMTS network elements in a PLMN.
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ECE446 Ch.3 UMTS
3.5 UMTS System Architecture (Continued)
3.5.2 Basic UMTS Architecture
1. UE consists of two parts:
- Mobile Equipment (ME) which is the radio terminal used for radio
communication over Uu interface.
- UMTS Subscriber Identity Module (USIM)
• A smart card that holds the subscriber identity
• Performs authentication algorithms
• Stores authentication and encryption keys
• Some subscription information that is needed at the terminal
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ECE446 Ch.3 UMTS
3.5 UMTS System Architecture (Continued)
3.5.2 Basic UMTS Architecture
2. UMTS Terrestrial Radio Access Network (UTRAN)
• Wide band CDMA (WCDMA) technology was selected for UTRAN air interface.
WCDMA has two basic modes of operation: Frequency Division Duplex (FDD)
and Time Division Duplex (TDD). The UTRAN consists of two elements:
Node B
• Air interface Transmission / Reception
• Modulation / Demodulation
• CDMA Physical Channel coding
• Error Handing
• Open loop power control
Radio Network Controller (RNC)
• Admission Control
• Channel/code Allocation
• Power Control Settings
• Handover Control
• Ciphering
• Broadcast Signaling
• Segmentation/Reassembly
• Closed Loop Power Control
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ECE446 Ch.3 UMTS
3.5 UMTS System Architecture (Continued)
3.5.2 Basic UMTS Architecture
3. UMTS Core Network (CN)
•
The Core Network is divided in circuit switched and
packet switched domains. Some of the circuit
switched elements are Mobile services Switching
Centre (MSC), Visitor location register (VLR) and
Gateway MSC. Packet switched elements are
Serving
GPRS
Support
Node
(SGSN)
and
Gateway GPRS Support Node (GGSN). Some
network elements, like EIR, HLR, VLR and AUC
are shared by both domains.
•
Bearer Service or data service is a service that
allows transmission of information signals between
network interfaces.
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ECE446 Ch.3 UMTS
3.6 UMTS Air Interface Protocol Architecture
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ECE446 Ch.3 UMTS
3.6 UMTS Air Interface Protocol Architecture
Fig. 3.23 UMTS Air Interface Protocol Layers.
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ECE446 Ch.3 UMTS
3.6 WCDMA Radio Interface Channels
• Three types of channels have been defined in the UMTS system as in Fig.3.23.
1. Logical channels—allocation to a particular logical channel depends on the kind
of information to be carried by the channel.
2. Transport channels—determine how and with what characteristics information
included in logical channels is to be transmitted.
3. Physical channels—real transmission media in which transmitted information is
mapped in the form of bits and physical symbols. For the UMTS system, the
physical channel defines appropriate frequencies and a set of codes.
Fig. 3.23 UMTS channels.
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ECE446 Ch.3 UMTS
3.7 Power control in WCDMA
•
CDMA system have the embedded characteristics of self-interference, so one
user’s transmission power is interference to other users, the more connected
users, the higher interference.
•
Fast power control can guarantee the service quality and minimize the required
transmission power, and solve the problem of near-far effect, and overcome
fast fading because of the fast power control frequency of 1500Hz.
•
In WCDMA system, power control includes open loop power control and
closed loop power control, open loop power control is used to calculate the
initial transmission power, and the closed loop power control adjusts the
transmission power dynamically and continuously during connection.
•
Open loop power control is used in two cases, the first one is on PRACH to
decide the initial transmission power of PRACH preamble, the second case is
on DPCCH (Dedicated Physical Control Channel) to decide the initial
transmission power of DPCCH power control preamble. closed loop power
control is applied on DPCCH and DPDCH (Dedicated Physical Data Channel).
For other common channels, power control is not applied.
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ECE446 Ch.3 UMTS
3.7 Power control in WCDMA (Continued)
3.7.1 Purpose of uplink power control
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ECE446 Ch.3 UMTS
3.7 Power control in WCDMA (Continued)
3.7.2 Purpose of downlink power control
•
The downlink has different characteristics from the uplink, because the
downlink interference is related to multi-path, and the downlink’s transmission
power is shared by all downlink channels, so usually the downlink capacity is
considered to be limited by transmission power.
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ECE446 Ch.3 UMTS
3.7 Power control in WCDMA (Continued)
3.7.3 Open Loop Power Control
•
•
UE estimates the power loss of signals on the propagation path by measuring
the received level of the downlink pilot channel from the BTS, then calculates
the transmission power of the uplink channel.
If no response is received, the UE waits a defined time and retransmits with a
higher power level. The UE continues to do this until it receives a response.
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ECE446 Ch.3 UMTS
3.7 Power control in WCDMA (Continued)
3.7.4 Closed Loop Power Control
•
•
▪
▪
▪
▪
When the communication is established, power is controlled by the Closed
Loop.
The following procedure is called Uplink Power Control:
The RNC sets the target BLER (BLock Error Rate) level for the service. It
derives from it a SIR (Signal to Interference Ratio) target, and sends it to the
BTS.
The BTS estimates an UL SIR, compares it to the target SIR, and decides to
increase or decrease the power of the UE. This is done 1500 times/second
(Inner Loop) to achieve the minimum output power.
The RNC calculates the SIR target once every 10 ms (or more, depending on
service) and adjusts the SIR target. (Outer Loop).
In order to indicate to the UE to increase or decrease its power, the BTS
sends TPC (Transmit Power Control) bits.
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ECE446 Ch.3 UMTS
UMTS Evolution path
UMTS Evolution path
WCDMA is an evolution of GSM/GPRS.
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
•
•
High-Speed Downlink Packet Access (HSDPA) transmission in the downlink has
been included in the system specification by 3GPP in release 5. Its introduction is
aimed at increasing transmission speed in the downlink and at shortening delays
in the network.
HSDPA is a packet-based data service that operates with data transmission up to
14.4 Mbps over a 5MHz bandwidth in WCDMA downlink. HSDPA implementations
as defined by 3GPP include Adaptive Modulation and Coding (AMC), MultipleInput Multiple-Output (MIMO), Hybrid Automatic Repeat reQuest (HARQ), Radio
channel dependent scheduling, and fast cell search.
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
•
The following list includes the technologies integrated in the HSDPA concept that
make HSDPA one of the important steps in the evolution of WCDMA:
1. Adaptive Modulation and Coding (AMC).
2. Link Adaptation.
3. Fast and Fair Scheduling at Node-B.
4. Hybrid Automatic Repeat Request (H-ARQ) with soft combining.
5. Short Transmission Time Interval (TTI).
6. New MAC-hs in NodeB and UE
7. New HSDPA Physical and Transport Channels.
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
3.8.1 Adaptive Modulation and Coding (AMC)
•
•
•
AMC is a key feature of HSDPA allowing adjustment of modulation between
QPSK and 16-QAM according to radio conditions and retransmission ratio. In
addition a variable code rate is used to flexibly adapt the data rate to the physical
channel capacity depending on the UE’s downlink C/I.
In HSDPA the transmission power is kept constant over the TTI (length of the
frame is referred to as Transmit Time Interval) and uses Adaptive Modulation and
Coding (AMC) as an alternative method to power control in order to improve the
spectral efficiency.
The Node-B receives the Channel Quality indicator (CQI) report and power
measurements on the associated channels.
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
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Rate
Control
Power
Control
3.8.1 Adaptive Modulation and Coding (AMC)
• Based on these information it determines the transmission data rate. In HSDPA,
users close to the Node-B are generally assigned higher modulation with higher
code rates (i.e. 16QAM and 3/4 code rate), and both decreases as the distance
between UE and Node-B increases.
ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
3.8.2 Link Adaptation
• The link adaptation functionality must select the Modulation and Coding Scheme
(MCS) and the number of multi-codes from a set of reference ones that the UE is
capable of supporting. The selection criterion can be based on various sources:
▪ Channel Quality Indicator (CQI): the UE sends in the uplink a report that provides
implicit information about the instantaneous signal quality received by the user.
The Channel Quality Indicator (CQI) species the Transport Block Size (TBS),
number of codes and modulation.
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
3.8.2 Link Adaptation
▪ The process of link adaptation is a dynamic one and the signal and protocol
parameters change as the radio link conditions change, in High-Speed Downlink
Packet Access (HSDPA) in Universal Mobile Telecommunications System
(UMTS) this can take place every 2 ms. The NodeB collect parameters related to
wireless link and UE for link adaptation and packet scheduling. These parameters
are:
➢ Channel Quality Indicator (CQI): the UE sends in the uplink a report that provides
implicit information about the instantaneous signal quality received by the user.
The Channel Quality Indicator (CQI) species the Transport Block Size (TBS),
number of codes and modulation.
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
3.8.2 Link Adaptation
➢ Power Measurements on the Associated DPCH: every user to be mapped on to
HS-DSCH (High Speed Downlink Shared Channel) runs a parallel DPCH
(Downlink dedicated physical channel) for signaling purposes, whose transmission
power can be used to gain knowledge about the instantaneous status of the user's
channel quality.
➢ Buffer Size: the amount of data in the buffer could also be applied in combination
with previous information to select the transmission parameters.
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
3.8.3 Fast and Fair Scheduling at Node-B
• Typically in WCDMA networks the packet scheduling is done at the RNC, but in
HSDPA the packet scheduler is shifted to the Node-B. This makes the packet
scheduling decisions almost instantaneous. In addition to this, the Transmit Time
Interval (TTI) length is shortened to 2 ms.
• Fast link dependent scheduling methods
• Round Robin (RR)
• Cyclically assign the channel to users without taking channel conditions into
account
• All the users get the same average allocation time
• Simple but poor performance
• Proportional Fair (PF)
• Assign the channel to the user with the best relative channel quality
• High throughput, fair
• Max C/I Ratio
• Assign the channel to the user with the best channel quality
• High system throughput but not fair
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
3.8.3 Fast and Fair Scheduling at Node-B
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
3.8.4 Hybrid Automatic Repeat Request (H-ARQ) with Soft Combining
• HARQ functionality combines retransmission with the original transmissions. In
HSDPA a physical layer retransmission functionality is added that improves the
HSDPA performance and gives robustness against link adaptation errors.
• There a two different ways for HARQ to operate. Either identical retransmission of
the data block are sent or retransmission are not identical and differ in data and
parity bits compared to the original transmission. The first method is known as
chase combining and, the latter as incremental redundancy . The retransmission
protocol selected in HSDPA is the Stop And Wait (SAW) due to the simplicity of
this form of ARQ
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
3.8.5 Short Transmission Time Interval (TTI)
• The length of the frame is referred to as Transmission Time Interval (TTI). The
HS-DSCH which is added in the HSDPA standard uses a TTI length of 2 ms
compared to 10 ms TTI length in Release'99. This is done to reduce the round trip
time, increases the granularity in the scheduling process and for a better tracking
of the time varying radio channel.
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
3.8.6 New MAC-hs in NodeB and UE
The implementation of Medium
Access Control (MAC-hs) in
NodeB and UE is a pre-requisite
for allowing the NodeB to
schedule
transmissions
and
retransmission, to maintain the
HSDPA specific channels and to
operate with AMC and Hybrid
ARQ.
MAC-hs responsible for
• Scheduling
• link adaptation
• HARQ protocol (selects
redundancy versions, controls
L1 soft combining)
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
3.8.7 New HSDPA Physical and Transport Channels
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
3.8.7 New HSDPA Physical and Transport Channels
• High-Speed Downlink Shared Channel (HS-DSCH)
–
Transport channel that carries the user data.
– One transport block of dynamic size per 2 ms TTI.
– Supports link adaptation and hybrid ARQ.
– Mapped to one or several HS-PDSCH (SF=16).
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
3.8.7 New HSDPA Physical and Transport Channels
• High-Speed Downlink Shared Channel (HS-DSCH)
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
3.8.7 New HSDPA Physical and Transport Channels
• High-Speed Downlink Shared Channel (HS-DSCH)
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ECE446 Ch.3 UMTS
3.8 High-Speed Downlink Packet Access (R5→ 3.5G)
3.8.7 New HSDPA Physical and Transport Channels
• High-Speed Downlink Shared Channel (HS-DSCH)
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ECE446 Ch.3 UMTS
UMTS Evolution path
UMTS Evolution path
WCDMA is an evolution of GSM/GPRS.
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ECE446 Ch.3 UMTS
3.9 High-Speed Uplink Packet Access (R6→ 3.75G)
•
High Speed Uplink Packet Access (HSUPA) is also known as Enhanced Uplink or
Enhanced Dedicated channel (E-DCH).
•
It is a complement to HSDPA → HSDPA+HSUPA=HSPA
•
The technique of adaptive modulation and coding used in HSDPA will not be
useful in HSUPA. One of the reasons is that the power resource capabilities of
each individual user are limited.
•
Another reason that doesn’t allow AMC to be used in the uplink is that the
received signal at the NodeB of UEs that transmit at the same time is not orthogon
al and even if just one UE is scheduled at a time other cell interference will not
allow a good quality estimation of the channel.
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ECE446 Ch.3 UMTS
3.9 High-Speed Uplink Packet Access (R6→ 3.75G)
3.9.1 Key technologies with HSUPA
•
Fast Hybrid ARQ (HARQ) i.e. fast retransmissions.
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ECE446 Ch.3 UMTS
3.9 High-Speed Uplink Packet Access (R6→ 3.75G)
3.9.1 Key technologies with HSUPA
•
Fast Hybrid ARQ (HARQ) i.e. fast retransmissions.
In the release 1999 of WCDM the retransmissions are made in the Radio Link
Control level so the retransmission procedures for a packet is located in the RNC.
In the uplink, a packet must arrive to the RNC and a negative acknowledgment
has to come back in order to perform a retransmission. With fast HARQ a
retransmission can be controlled directly by the NodeB reducing the delay so the
retransmissions are performed faster.
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ECE446 Ch.3 UMTS
3.9 High-Speed Uplink Packet Access (R6→ 3.75G)
3.9.1 Key technologies with HSUPA
•
Shorter frame size, 10ms mandatory for all HSUPA capable devices and 2
ms as optional feature.
Data Channel
Control Channel
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E-DCH - Enhanced Dedicated Channel : The Enhanced
Dedicated Channel
(E-DCH)
is an uplink transport channel.
ECE446
Ch.3 UMTS
3.9 High-Speed Uplink Packet Access (R6→ 3.75G)
3.9.1 Key technologies with HSUPA
the theoretical uplink data rate
can be up to 5.76 Mbps
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ECE446 Ch.3 UMTS