cdma technologies for cellular phone system
DESCRIPTION
CDMA Technologies for Cellular Phone System. July 7th, 2004 Takashi INOUE KDDI R&D Laboratories Inc. Contents. Introduction Spread Spectrum Technology DS-CDMA Spreading Codes Features of CDMA RAKE Receiver Power Control Frequency Allocation Soft Handoff Conclusion. - PowerPoint PPT PresentationTRANSCRIPT
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 1
CDMA Technologies for Cellular Phone System
CDMA Technologies for Cellular Phone System
July 7th, 2004
Takashi INOUE
KDDI R&D Laboratories Inc.
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 2
ContentsContents
• Introduction• Spread Spectrum Technology• DS-CDMA• Spreading Codes• Features of CDMA
– RAKE Receiver– Power Control– Frequency Allocation– Soft Handoff
• Conclusion
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 3
Introduction: Overview of Cellular systems
Introduction: Overview of Cellular systems
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 4
Evolution of Cellular SystemsEvolution of Cellular Systems
1st.Generation(1980s)
Analog
NMT CT0TACS CT1AMPS
3rd. Generation(2000s)
2nd. Generation(1990s)
Digital
GSM DECT DCS1800 CT2PDC PHSIS-54IS-95IS-136UP-PCS
IMT-2000 CDMA2000 W-CDMA
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 5
Major Operators of Cellular Phone Services in Japan
Major Operators of Cellular Phone Services in Japan
Operator2G 3G
FrequencyRemarks for 3G handset
KDDI/au800 MHz(1.5GHz
For Tu-Ka)
800MHz2GHz
backward compatibility with 2G (cdmaOne)
NTT DoCoMo 800 MHz1.5GHz
2GHzW-CDMA singleW-CDMA/PDC Dual
J-Phone(vodaphone) 1.5 GHz 2GHz
W-CDMA singleW-CDMA/GSM Dual
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 6
Japan’s Cellular Market Growth HistoryJapan’s Cellular Market Growth History
0
10,000,000
20,000,000
30,000,000
40,000,000
50,000,000
60,000,000
70,000,000
80,000,000
198819891990199119921993199419951996199719981999200020012002
CDMA2000 1x ,W-CDMA /6,093K
cdmaOne /7,757K
PDC/60,517K(NTT DoCoMo,KDDI, Tu-Ka,J-phone)
Analog / 0(endof Srv.)
end of Mar. 2003Total No. of Subscribers: 74,368K
(end of each fiscal year)
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 7
Growth of 3G Mobile Subscribers in Japan
Growth of 3G Mobile Subscribers in Japan
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
J-phone
FOMA
CDMA2000 1x
The number of subscribers surpassed 7 million in March, 2003
Oct- 01 Nov- 01Dec- 01 J an- 02 Feb- 02 Mar- 02 Apr- 02 May- 02 J un- 02 J ul- 02 Aug- 02 Sep- 02 Oct- 02 Nov- 02Dec- 02 J an- 03 Feb- 03 Mar- 03334 696 1151 1644 2142 2652 3293 3897 4673 5312 5891 6805
11 14 27 43 56 89 106 112 115 127 134 136 142 149 152 154 191 3301 4 9 25
No.
of
Sub
s.
(x1,0
00)
CDMA2000 1x
FOMAJ-phone
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 8
Requirements for 3G mobile systemsRequirements for 3G mobile systems
• High Capacity• Tolerance for interference• Privacy• Tolerance for fading• Ability to various data rate transmission• Flexible QoS
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 9
IMT-2000 systems approved by ITU-RIMT-2000 systems approved by ITU-R
Popular name
Access method
Body of Technical
Spec production
IMT-DS IMT-MC IMT-TC IMT-SC IMT-FT
(Direct Sequence) (Multi Carrier) (Time Code) (Single Carrier) (Frequency Time)
W-CDMA CDMA2000UTRA-TDD
UWC-136 DECT
CDMA-FDD CDMA-TDDCDMA-FDD TDMA-TDDTDMA-FDD
3GPP(FDD)
3GPP2 3GPP(TDD)
CWTS
IS-136 DECT
ESTIESTI TIA
TTAT1
CWTSARIB/TTC ARIB/TTC
CWTS
TTA
ESTI
TTAT1
CWTS
TIA
Approved in 2000 as ITU-R M.1457
TD-CDMATD-SCDMA
Organization Partners
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 10
Duplex & Multiple Access MethodsDuplex & Multiple Access Methods
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 11
Duplex Methods of Radio LinksDuplex Methods of Radio Links
Mobile Station
Base Station
Forward link
Reverse link
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 12
Frequency Division Duplex (FDD)Frequency Division Duplex (FDD)
• Forward link frequency and reverse link frequency is different
• In each link, signals are continuously transmitted in parallel.
Mobile Station
Base Station
Forward link (F1)
Reverse link (F2)
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 13
Time Division Duplex (TDD)Time Division Duplex (TDD)
• Forward link frequency and reverse link frequency is the same.
• In each link, signals are incontinuously transmitted by turns just like a ping-pong.
Mobile Station
Base Station
Forward link (F1)
Reverse link (F1)
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 14
Example of FDD systemsExample of FDD systems
Transmitter
Receiver
BPF: Band Pass Filter
BPF
BPF
Transmitter
Receiver
BPF
BPF
F1
F2 F1
F2
Mobile Station Base Station
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 15
Example of TDD SystemsExample of TDD Systems
Transmitter
Receiver
BPF: Band Pass Filter
BPF
Transmitter
Receiver
BPF
F1 F1
Mobile Station Base Station
Synchronous Switches
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 16
Multiple Access MethodsMultiple Access Methods
Mobile Station
Base Station
Mobile StationMobile Station
Mobile Station
Forward link
Reverse link
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 17
FDMA OverviewFDMA Overview
A A
B B
C C
Freq
uenc
y
Time
f2
f1
f0
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 18
TDMA OverviewTDMA Overview
C B A C B A C B A C B A
C
A
B
Time
f0
Freq
uenc
y
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 19
What is CDMA ?What is CDMA ?
Sender Receiver
Code A
A
Code B
B
AB
AB
CBC
A
Code A
AB
C
Time
Freq
uenc
y
BC
B
A
Base-band Spectrum Radio Spectrum
spread spectrum
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 20
Summary of Multiple AccessSummary of Multiple Access
FDMA
TDMA
CDMA
time
time
time
pow
er
pow
er
pow
er
frequency
frequency
frequency
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 21
Spread Spectrum TechnologySpread Spectrum Technology
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 22
How to spread spectrum...How to spread spectrum...
Direct Sequence (DS)
Modulation(primary modulation)
Modulation(primary modulation)
user data
Sp
rea
din
g(s
ec
on
da
ry m
od
ula
tio
n)
Sp
rea
din
g(s
ec
on
da
ry m
od
ula
tio
n)
Tx
Base-bandFrequency
Po
we
rD
en
sity
RadioFrequency
Po
we
rD
en
sity
TIME
data rate
10110100
spreading sequence(spreading code)
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 23
Demodulating DS Signals (1/2)Demodulating DS Signals (1/2)
If you know the correct spreading sequence (code) ,
RadioFrequency
Po
we
rD
en
sity
received signal
spreading sequence(spreading code)
you can find the spreading timing which gives the maximum detected power, and
Accumulate for one bit duration
Accumulate for one bit duration
Demodulated data
Base-bandFrequency
gathering energy !
10110100
1011010010110100 10110100
TIME
0100101110110100 10110100
0 01
1111111100000000 00000000
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 24
Demodulating DS Signals (2/2)Demodulating DS Signals (2/2)
If you don’t know the correct spreading sequence (code) •••
Base-bandFrequency
received signal
spreading sequence(spreading code)
you cannot find the spreading timing without correct spreading code, and
Accumulate for one bit duration
Accumulate for one bit duration
Demodulated data
RadioFrequency
Po
we
rD
en
sity
01010101 01010101 01010101
10101010 10101010 10101010
TIME
0100101110110100 10110100
No data can be detected
- --
1011010010110100 10110100
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 25
Feature of SSFeature of SS
Privacy, Security
RadioFrequency
Po
we
rD
en
sity
Power density of SS-signals could be lower than the noise density.
transmitted SS-signal
••••
••
Noise
Po
we
rD
en
sity
RadioFrequency
Noise
••••
••received signal de-
modulator
de-modulator
Base-bandFrequency
Po
we
rD
en
sityWith incorrect code
(or carrier frequency),SS-signal itself cannot be detected.
They cannot perceive the existence of communication, because of signal behind the noise.
With correct code (and carrier frequency), data can be detected.
Base-bandFrequency
Po
we
rD
en
sity
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 26
DS-CDMADS-CDMA
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 27
Freq.Freq.
BPFDespreader
Code B
Freq.Freq.
BPFDespreader
Code A
DS-CDMA System Overview (Forward link)
DS-CDMA System Overview (Forward link)
CDMA is a multiple spread spectrum.
Difference between each communication path is only the spreading code
Data B
Code B
BPF
Freq.Freq.
•••
Data A
Code A
BPF
Freq.Freq.
MS-A
•••
MS-B
BS
Data A
Data B
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 28
Freq.Freq.
BPFDespreader
Code B
Freq.Freq.
BPFDespreader
Code A
DS-CDMA System Overview (Reverse Link)
DS-CDMA System Overview (Reverse Link)
CDMA is a multiple spread spectrum.
Difference between each communication path is only the spreading code
Data B
Code B
BPF
Freq.Freq.
•••
Data A
Code A
BPF
Freq.Freq.
•••MS-B
MS-A
BS
Data A
Data B
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 29
Spreading CodeSpreading Code
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 30
Cross-CorrelationCross-Correlation
Cross-Correlationbetween Code A and Code B = 6/16
Self-Correlationfor each code is 1.
one data bit duration
Spreading Code A
1 0 10 1 1 0 0 10 1 0 1 0 0 1
one data bit duration
Spreading Code A
1 0 01 1 1 0 0 10 1 0 1 0 0 1
Spreading Code A
1 0 01 1 1 0 0 10 1 0 1 0 0 1
0 0 00 0 0 0 0 00 0 0 0 0 0 0
Spreading Code B
1 0 01 1 0 0 1 11 0 0 1 0 1 1
0 0 00 0 1 0 1 01 1 0 0 0 1 0
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 31
Preferable CodesPreferable Codes
In order to minimize mutual interference in DS-CDMA , the spreading codes
with less cross-correlation should be chosen.
Synchronous DS-CDMA :Orthogonal Codes are appropriate. (Walsh code etc.)
Asynchronous DS-CDMA :• Pseudo-random Noise (PN) codes / Maximum sequence
• Gold codes
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 32
Multiplexing using Walsh CodeMultiplexing using Walsh Code
Code for 00
Code for 01
Code for 10
Code for 11
Data
Modulator
Code for 01
Code for 10
Code for 11
0dtT
Select maximum
value
Code for 00
0dtT
0dtT
0dtT
Demodulator
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 33
Synchronous DS-CDMASynchronous DS-CDMA
Forward Link(Down Link)
Synchronous Chip Timing
A
BA
A
Signal for B Station(after re-spreading)
Less Interference for A station
Synchronous CDMA Systems realized in Point to Multi-point System.e.g., Forward Link (Base Station to Mobile Station) in Mobile Phone.
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 34
Asynchronous DS-CDMAAsynchronous DS-CDMA
In asynchronous CDMA system, orthogonal codes have bad cross-correlation.
Reverse Link(Up Link)
BA
Signal for B Station(after re-spreading)
Big Interference from A station
Asynchronous Chip Timing
Signals from A and B are interfering each other.
A
B
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 35
Features of CDMAFeatures of CDMA
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 36
Mobile Propagation Environment ・・・ Multi-path Fading
Mobile Propagation Environment ・・・ Multi-path Fading
The peaks and bottoms of received power appear, in proportion to Doppler frequency.
Base Station (BS)Mobile Station (MS)
multi-path propagation
Path Delay
Po
we
r
path-2
path-2path-3
path-3
path-1
path-1
TimeP
ow
er
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 37
Fading in non-CDMA SystemFading in non-CDMA System
Path Delay
Po
we
r path-1
path-2
path-3
With low time-resolution,different signal paths cannot be discriminated.
•••These signals sometimes strengthen,
and sometimes cancel out each other, depending on their phase relation.••• This is “fading”.
•••In this case, signal quality is damaged
when signals cancel out each other.In other words, signal quality is dominated
by the probability for detected power to be weaker than minimum required level.
This probability exists with less than two paths.
Time
Po
we
r
Detected Power
In non-CDMA system, “fading” damages signal quality.
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 38
Fading in CDMA System ...Fading in CDMA System ...
Because CDMA has high time-resolution,different path delay of CDMA signals
can be discriminated.•••Therefore, energy from all paths can be summed
by adjusting their phases and path delays.••• This is a principle of RAKE receiver.
Path Delay
Po
we
r path-1
path-2
path-3
CDMAReceiver
CDMAReceiver
•••
Synchron
ization
Add
er
Path Delay
Po
we
r
CODE Awith timing of path-1
path-1
Po
we
r
path-1
path-2
path-3
Path Delay
Po
we
r
CODE Awith timing of path-2
path-2
interference from path-2 and path-3
•••
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 39
Fading in CDMA System (continued)Fading in CDMA System (continued)
In CDMA system, multi-path propagation improves the signal quality by use of RAKE receiver.
Time
Po
we
r Detected Power
RAKEreceiver
Less fluctuation of detected power, because of adding all
energy .
Po
we
r
path-1
path-2
path-3
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 40
Near-Far ProblemNear-Far Problem
CODE B
CDMATransmitter
DATA B
CODE A
CDMAReceiverCODE A
CDMATransmitter
DATA A
P
• Desired Signal Power = P/Lp-a• Interfered Signal Power =
P/Lp-b/(processing gain )
Demodulated DATA
P
Lp-a
Lp-b
When user B is close to the receiver and user A is far from the receiver,
Lp-a could be much bigger than Lp-b.In this case, desired signal power is
smaller than the interfered power.
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 41
Power Control...Power Control...
AB
Time
De
tect
ed
Po
we
r
from A
from B
When all mobile stations transmit the signals at the same power (MS),
the received levels at the base station are different from each other,
which depend on the distances between BS and MSs.
Moreover, the received level fluctuates quickly due to fading.
In order to maintain the received level at BS, power control technique must be
employed in CDMA systems.
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 42
Power Control (continued)Power Control (continued)
(((
②
①
Open Loop Power Control Closed Loop Power Control
estimating path loss
calculating transmission
power
transmitmeasuring received power
transmit receive
decide transmission
power
transmit measuring received power
power control command
about 1000 times per second
①
②
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 43
Effect of Power ControlEffect of Power Control
AB
Time
De
tect
ed
Po
we
r
from MS B from MS A
closed loop power
control for MS B.
for MS A
.
Effect of Power Control• Power control is capable of compensating the fading fluctuation.
• Received power from all MS are controlled to be equal.
... Near-Far problem is mitigated by the power control.
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 44
Frequency Allocation (1/2)Frequency Allocation (1/2)
In FDMA or TDMA,
radio resource is allocated not to interfere among neighbor cells.
f1f2
f3f4
f5f6
f7
cell :a “cell” means covered area by one base station.
• Neighbor cells cannot use the same (identical) frequency band (or time slot).
• The left figure shows the simple cell allocation with seven bands of frequency.
• In actual situation, because of complicated radio propagation and irregular cell allocation, it is not easy to allocate frequency (or time slot) appropriately.
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 45
Frequency Allocation (2/2)Frequency Allocation (2/2)
In CDMA,
identical radio resource can be used among all cells,
because CDMA channels use same frequency simultaneously.
• Frequency allocation in CDMA
is not necessary.
• In this sense, CDMA cellular
system is easy to be designed.
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 46
Soft Handoff (1/2)Soft Handoff (1/2)
Handoff :• Cellular system tracks mobile stations in order to maintain their communication links.
• When mobile station goes to neighbor cell, communication link switches from current cell to the neighbor cell.
Hard Handoff :• In FDMA or TDMA cellular system, new communication establishes after breaking current communication at the moment doing handoff. Communication between MS and BS breaks at the moment switching frequency or time slot.
Hard handoff : connect (new cell B) after break (old cell A)
switching
Cell B Cell A
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 47
Soft Handoff (2/2)Soft Handoff (2/2)
Σ
Cell B Cell A
Soft handoff : break (old cell A) after connect (new cell B)
transmitting same signal from both BS A and BS B simultaneously to the MS
Soft Handoff :• In CDMA cellular system, communication does not break even at the moment doing handoff, because switching frequency or time slot is not required.
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 48
ConclusionConclusion
• CDMA is based on the spread spectrum technique which has been used at military field.
• CDMA cellular system is deemed superior to the FDMA and TDMA cellular systems for the time being.
• Therefore, CDMA technique becomes more important in radio communication systems.