Lecture#5 21 4-2013
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WCDMA Principles
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Transcript of Lecture#5 21 4-2013
WCDMA Principles
Multiple Access Technology
User FrequencyTime
Power
Traffic channels: different users are assigned unique code and transmitted over the same frequency band at the same time, for example, WCDMA and CDMA2000
Traffic channels: different frequency bands are allocated to different users,for example, AMPS and TACS
Traffic channels: different time slots are allocated to different users, for
example, DAMPS and GSM
FrequencyTime
Power
FrequencyTime
Power
FDMA
TDMA
CDMA
User
User User
User User
Duplex Spacing: 190 MHz
FDD
Time
Frequency
Power
5 MHz 5 MHz
Code Multiplex
UL DLUMTS USER 1
UMTS USER 2
Time
Frequency
Power
TDD
5 MHz
Code Multiplex&
Time Division
666.67 s
DLUL
DLDL
UL
UMTS USER 2
UMTS USER 1
Multiple Access Technology• WCDMA: FDD or TDD
Uplink: 1920 MHz - 1980 MHzDownlink: 2110 MHz - 2170 MHz
Each carrier is 5 MHz width.
Binary data to transmit 0 1 0 0 1 0
The faster is the bit rate, the more the energy is spread on the spectrum
+ a
- a
a2T0
s(t)
T0
1/T0 2/T0 Frequency
Time
0 1 0 0 1 0+ a
- a
a2T1
s(t)
T1
1/T1 2/T1Frequency
NRZ coding
Time
0 1 0 0 1 0
Power spectrum
Spread Spectrum Principle• 1 - Time - Frequency Duality
Tbit
Tchip
Data sequence
spreading sequence
transmitted sequence
a2Tbit = Ebit
1/Tbit
Tchip = Echip
1/Tchip
Frequency
a2Tchip
1/Tchip
+a
-a
-1
+1
-a
+a
x
=
Data sequence
Transmitted signal
Spreading sequence generator
Modulation
x(t)Power spectrum
Spread Spectrum Principle• 2 – Transmission (Spreading)
Tbit
Tchip
Data sequence
spreading sequence
received sequence
a2Tbit = Ebit
Power spectrum
1/Tbit
Tchip = Echip
1/Tchip
Frequencya2Tchip+a
-a
-1
+1
-a
+a
x
=
1/Tchip
Received signal
Data sequence
Spreading sequence generator
Demodulation
x(t)
Spread Spectrum Principle• 3 – Reception (Dispreading)
Multi-user
-11User 1
User 2
Code 1: Cch (SF= )
Code 2: Cch (SF= )
TransmittedSignal
(fixed Chip Rate)
1-11 1-11
=
+*
*=
=2
-2
0
1
1 -1 -1 1 1 1 -1-1
1 -1-11
1
-1
1
-1
Multi-user - Data Transmission
-11User 1
User 2
Code 1: Cch (SF= )
Code 2: Cch (SF= )
TransmittedSignal
(fixed Chip Rate)
1-11 1-11
=
+*
*=
=2
-2
0
1
1 -1 -1 1 1 1 -1-1
1 -1-11
1
-1
1
-1
Multi-user - Data Extraction (Reception)
« »« »« 1 »
ReceivedSignal
User 2 ?
Code 2
Soft Bits2 2
+= 4
0 0
=+
=+
=+
==
« » « »« »
*
2
0
-2
2
0
-2
=
1
-1
Rake Receiver
TXD(t)
Delay 0
Delay 1
C(t-0)
(+) D(t)
C(t-1)
Delay (1)
RX
C(t-n)
Delay (0)
Delay (n)RX
RX
C(t)
0
1
n
D(t)
D(t)
Take advantage of multipath diversity
BTS
UE
Adaptive channel Delay
WCDMA Principles• Multiplexing users data
Power spectrum
User 1User 2
User 3
User 4User 5
Spreading
Code 1Code 2Code 3Code 4Code 5
Composite signal
5 MHzCodes discriminate users
Unwanted Powerfrom other sources
Using the “right” mathematical sequences any Code Channel can be extractedfrom the received composite signal
WCDMA Principles• 5 - Extraction
Maximum noise level
Eb/No required
WCDMA Principles
Power spectrum
Available power to share between users
a2Tbit = Ebit
gain
Unwanted power from other sources
Eb / No
Echip
Eb / No = (C / I) x processing gain
a2Tbit = Ebit
Power spectrum
Maximum noise level
Eb/No required
Unwanted power from other sources
Eb/No
Power control
Power , Interference , Capacity .
WCDMA Principles
• Eb / No & Power Control
Scrambling code
Channelization code 1
Channelization code 2
Channelization code 3
User 1 signal
User 2 signal
User 3 signal
BTS
Code Multiplexing• 1 - Downlink Transmission on a Cell Level
BTS
Scrambling code 3
User 3 signal
Channelization code
Scrambling code 2
User 2 signal
Channelization code
Scrambling code 1
User 1 signal
Channelization code
Code Multiplexing• 2 - Uplink Transmission on a Cell Level
Functions and Features of the Scrambling and Channelization Codes
Channelization (Orthogonal) code Scrambling (Pseudorandom) code
Purpose
Uplinks: Distinguish physical data (DPDCH) and control channels (DPCCH).Down links: Distinguish the down links of different users in the same cell.
Uplinks: Distinguish terminalsDown links: Distinguish cells
Length 4~256 chips (1.0-66.7 us)The down links contain 512 chips
Uplinks: 10 ms = 38400 chips or =66.7 us = 256 chipsDown links: 10 ms = 38400 chips
Code cluster OVSF (Orthogonal Variable Spreading Factor) Long 10 ms code: Gold code
Spreading spectrum Yes, transport bandwidth is added. No, transport bandwidth is not
affected.
Functions and Features of the Scrambling and Channelization Codes
Cch,1,0 = 1
Cch,2,0 = 1 1
Cch,4,0 = 1 1 1 1
Cch,4,1 = 1 1 -1 -1
Cch,2,1 = 1 -1
Cch,4,2 = 1 -1 1 -1
Cch,4,3 = 1 -1 -1 1
SF = 1 SF = 2 SF = 4 SF = 8 SF = 16, 32, 64, 128, 256, 512.
Cch,2,0 = 1 1
Cch,2,1 = 1 -1
Cch,4,0 = 1 1 1 1
Cch,4,1 = 1 1 -1 -1
Cch,4,2 = 1 -1 1 -1
Cch,4,3 = 1 -1 -1 1
Channelization Codes - OVSF• 1 - Orthogonal Variable Spreading Factor (OVSF): code tree generator
+
-1 -1 -1
-1 -1 -1 -1
1 1 1 1
1 1 1 1
-1
*
1 1 1 1-1 -1 -1 -1
Cj
Ck
T0 synchronization
= 0+
-1 -1 -1
-1 -1 -1 -1
1 1 1 1
1 1 1 1
-1
*
1 1 1 11 -1 1 -1
Cj
Ck
no T0 synchronization
= 4
Orthogonal Non orthogonalNo correlation Small correlation
Channelization Codes - OVSF• 2 - Orthogonality
Interference level
Example: 2 UEs at the same distance from the BTS using 2 data rates
Eb/No required
SF =
128
Service provided: Speech
Interference level
Eb/No required SF
= 8
Service provided: Data 144
User 2 needs more power for the UL & DL for the same quality as
user 1
UE2UE1
Speech 8 kbps Data 144 kbpsThe higher the SF, the less power requiredBTS
Received powerReceived power
Coverage Limits (1)
SF = 128
Speech 8 kbps Data 64 kbps Data 384 kbpsBTS
SF = 32
SF = 4
Coverage Limits (2)
Receiver sensitivity (x kbps)
BS Receiver
Maximum Noise Floor
Lowest Despread Signal
BTS
UE1x kbps x kbps
UE2 UE3x kbps
Eb/No
ProcessingGain
Uplink Limits (1)
BS Power Amplifier50 W
0 W
BTS
BTS
UE1 UE2 UE3 UE4
Capacity Limits (1)
UE2 UE3UE1
BS Power Amplifier50 W
0 W
UE4
BTS
BTS
Capacity Limits (2)
Power Control in UMTS
Power Control in UMTS
Power Control in UMTS
