+ All Categories
Home > Documents > code division Duplexing

code division Duplexing

Date post: 11-Apr-2015
Category:
Upload: vsunny488
View: 2,608 times
Download: 1 times
Share this document with a friend
39
1 Shajeela Beegom B A Shajeela Beegom B A Roll no:047 Roll no:047 MCA B5 MCA B5
Transcript
Page 1: code division Duplexing

11

Shajeela Beegom B AShajeela Beegom B ARoll no:047Roll no:047

MCA B5MCA B5

Page 2: code division Duplexing

22

INTRODUCTIONINTRODUCTION

Reducing interference in a cellular Reducing interference in a cellular system is the most effective system is the most effective approach to increasing radio capacity approach to increasing radio capacity and transmission data rate in the and transmission data rate in the wireless environment. wireless environment.

Therefore, reducing interference is a Therefore, reducing interference is a difficult and important challenge in difficult and important challenge in wireless communicationswireless communications..

Page 3: code division Duplexing

33

Mobile radio networks are operated with Mobile radio networks are operated with finite, limited resources (the spectrum of finite, limited resources (the spectrum of frequencies available) and these resources frequencies available) and these resources have to be used effectively to ensure that all have to be used effectively to ensure that all users receive service, that is quality of service users receive service, that is quality of service is maintained. is maintained.

To utilize spectrum efficiently, two To utilize spectrum efficiently, two transmission techniques need to be transmission techniques need to be consideredconsidered: :

a multiple access schemea multiple access scheme a duplexing systema duplexing system

Page 4: code division Duplexing

44

The industry has already established the best multiple access The industry has already established the best multiple access scheme, code-division multiple access (CDMA), for 3G systemsscheme, code-division multiple access (CDMA), for 3G systems. .

Page 5: code division Duplexing

55

DUPLEXING SYSTEMDUPLEXING SYSTEM

A A duplex communicationduplex communication system system is is a system composed of two connected a system composed of two connected parties or devices which can parties or devices which can communicate with one another in communicate with one another in both directionsboth directions

Currently there exist only two duplexing Currently there exist only two duplexing technologies in wireless communications,technologies in wireless communications,

Frequency division duplexingFrequency division duplexing(FDD) (FDD) TTime division duplexingime division duplexing (TDD). (TDD).

Page 6: code division Duplexing

66

FDDFDD

FDD has been the primary technology FDD has been the primary technology used in the first three generations of used in the first three generations of mobile wireless because of its ability to mobile wireless because of its ability to isolate interference isolate interference

Uses different frequencies to handle Uses different frequencies to handle incoming and outgoing signals.incoming and outgoing signals.

Using an FDD system can eliminate Using an FDD system can eliminate interference among the base stations of interference among the base stations of adjacent cells to the base station of theadjacent cells to the base station of the home cell.home cell.

Page 7: code division Duplexing

77

Page 8: code division Duplexing

88

But…But…

Two types of interference remain in Two types of interference remain in FDD:FDD:

adjacent base-to-home mobile adjacent base-to-home mobile interferenceinterference

and adjacent mobile-to-home base and adjacent mobile-to-home base interference.interference.

Page 9: code division Duplexing

99

TDDTDD TDD is seemingly a more spectral TDD is seemingly a more spectral

efficient technology but has found efficient technology but has found limited use because of interference limited use because of interference and coverage problems.and coverage problems.

Using a TDD system causes four Using a TDD system causes four kinds of interference:kinds of interference:

Page 10: code division Duplexing

1010

Page 11: code division Duplexing

1111

Adjacent base-to-home mobileAdjacent base-to-home mobile Adjacent mobile-to-home baseAdjacent mobile-to-home base Adjacent base-to-home baseAdjacent base-to-home base Adjacent mobile-to-home mobileAdjacent mobile-to-home mobile

So it can only be used for small confined So it can only be used for small confined area systemsarea systems

Page 12: code division Duplexing

1212

CDDCDD Code-division duplexing (CDD) is an Code-division duplexing (CDD) is an

innovative solution that can eliminate innovative solution that can eliminate all kinds of interference.all kinds of interference.

CDMA is the best multiple access CDMA is the best multiple access scheme when compared to all others scheme when compared to all others for combating interference.for combating interference.

A set of smart codes can make a high-A set of smart codes can make a high-capacity CDMA system very effective capacity CDMA system very effective without adding other technologies. without adding other technologies.

The smart code plus TDD is called CDD. The smart code plus TDD is called CDD.

Page 13: code division Duplexing

1313

Page 14: code division Duplexing

1414

SMART CODESSMART CODES

The Large Area Synchronous (LAS) The Large Area Synchronous (LAS) Codes are a set of smart codes that Codes are a set of smart codes that can reduce interference very can reduce interference very effectively. effectively.

The effectiveness of smart codes The effectiveness of smart codes applied to TDD makes it the right applied to TDD makes it the right choice in cellular systems. choice in cellular systems.

The application of LAS Codes in a The application of LAS Codes in a TDD system (called TD-LAS system) TDD system (called TD-LAS system) creates a CDD system.creates a CDD system.

Page 15: code division Duplexing

1515

cont…cont…

The CDMA system based on this is known The CDMA system based on this is known as the LAS-CDMA.as the LAS-CDMA.

LAS-CDMA is a new coding technology LAS-CDMA is a new coding technology that will increase the capacity and spectral that will increase the capacity and spectral efficiency of mobile networks. efficiency of mobile networks.

The advanced technology uses a set of The advanced technology uses a set of smart codes to restrict interference, a smart codes to restrict interference, a property that adversely affects the property that adversely affects the efficiency of CDMA networks.efficiency of CDMA networks.

Page 16: code division Duplexing

1616

Cont..Cont.. The code used in today’s CDMA scheme is The code used in today’s CDMA scheme is

the Walsh code, which is not too smart. the Walsh code, which is not too smart. Walsh codes have the orthogonality Walsh codes have the orthogonality

property among codes while the time shift property among codes while the time shift TT= 0 (i.e., no time shift = 0 (i.e., no time shift t )t )

However, in the mobile radio However, in the mobile radio environment the signal arrival can have a environment the signal arrival can have a long time shift. long time shift.

The property of Walsh codes cannot The property of Walsh codes cannot properly be applied to this environmentproperly be applied to this environment

Page 17: code division Duplexing

1717

Cont…Cont… Now there is a set of smart codes Now there is a set of smart codes

that have orthogonality among the that have orthogonality among the codes for time shift codes for time shift TT≠0.≠0.

The codes arrive at the terminals at The codes arrive at the terminals at different time shifts; because of the different time shifts; because of the orthogonal nature, all undesired orthogonal nature, all undesired codes are blocked.codes are blocked.

Thus, smart codes are the proper Thus, smart codes are the proper codes to handle this situation. codes to handle this situation.

Page 18: code division Duplexing

1818

Page 19: code division Duplexing

1919

The properties of smart codes have to The properties of smart codes have to meet the following requirements:meet the following requirements:

Auto-correlationAuto-correlation Rxx(Rxx(T T )= 0 for )= 0 for T T =0=0 =d =d for for TT!=0,within window !=0,within window T0T0 Cross-correlation Cross-correlation Rxy Rxy ((TT) = ) = dd for all for all T T, within window , within window

TT0,Where 0,Where T0T0 is a correlation window, d is a correlation window, d can be zero or low correlation value.can be zero or low correlation value.

Page 20: code division Duplexing

2020

Outside the correlation window is Outside the correlation window is beyond the time delay spread range beyond the time delay spread range of the received signal. of the received signal.

Although the correlation value Although the correlation value outside the range is high, there is no outside the range is high, there is no impact on our desired signalimpact on our desired signal

Page 21: code division Duplexing

2121

With this property, we can illustrate theWith this property, we can illustrate themerit of using this smart code.merit of using this smart code.

Page 22: code division Duplexing

2222

Assume that eight smart codes are Assume that eight smart codes are transmitted transmitted

They arrive at the receiver of Code C1 at They arrive at the receiver of Code C1 at different times due to the multipaths different times due to the multipaths caused by different reflectors. caused by different reflectors.

Because of the cross-correlation property, Because of the cross-correlation property, the desired code to be received is C1the desired code to be received is C1

However, many C1 codes can be received However, many C1 codes can be received due to the effects of the multipaths.due to the effects of the multipaths.

This does not occur though; due to the This does not occur though; due to the auto-correlation property, only Code C1 at auto-correlation property, only Code C1 at time t1 is receivedtime t1 is received

Page 23: code division Duplexing

2323

We do not need the strength of more We do not need the strength of more than one path signal to be added for than one path signal to be added for increasing carrier-to-interference increasing carrier-to-interference ratio (C/I) since we are only receiving ratio (C/I) since we are only receiving carrier-to-noise ratio (C/N), not C/I. carrier-to-noise ratio (C/N), not C/I.

The rest of the signals from different The rest of the signals from different paths do not cause any interference, paths do not cause any interference, and there is no need to use any and there is no need to use any means to collect them for the means to collect them for the purpose of reducing interferencepurpose of reducing interference

Page 24: code division Duplexing

2424

USING SMART CODE SEQUENCES TOUSING SMART CODE SEQUENCES TOREDUCE INTERFERENCEREDUCE INTERFERENCE

Smart code sequences have two Smart code sequences have two properties:properties:

Auto-correlation equals zero, which Auto-correlation equals zero, which causes no multipath interference.causes no multipath interference.

Cross-correlation equals zero, which Cross-correlation equals zero, which causes no multi-user interferencecauses no multi-user interference

Smart code sequences will effectively Smart code sequences will effectively work in TDD scenarios and become a work in TDD scenarios and become a CDD systemCDD system

Page 25: code division Duplexing

2525

Page 26: code division Duplexing

2626

Adv: of smart codesAdv: of smart codes The two different smart codes can isolate

interference at the same frequency and in the same time frame.

The capabilities of smart codes eliminate The capabilities of smart codes eliminate the known near-far effect in mobile the known near-far effect in mobile communication systems. communication systems.

The inherent properties of smart codes The inherent properties of smart codes eliminate the need for the following eliminate the need for the following technologies: take receiver, power control, technologies: take receiver, power control, joint detection etc..joint detection etc..

Page 27: code division Duplexing

2727

Adv: of using CDDAdv: of using CDD

Any single (unpaired) spectrum band with a bandwidth equal to 1.6 MHz can be used for the CDD application.

The system is simple. The handset is also simple. Since no duplexer is needed, the handset

cost can be lower and the size of the handset smaller.

Power consumption is lower due to only one single spectrum band being operable.

Page 28: code division Duplexing

2828

CDD is like TDD, the ideal system for CDD is like TDD, the ideal system for asymmetrical traffic.asymmetrical traffic.

CDD has the highest spectrum CDD has the highest spectrum efficiency and can be used in the new efficiency and can be used in the new third-generation (3G) systems.third-generation (3G) systems.

The CDD system changes the The CDD system changes the environment from an interference-environment from an interference-limited one to a noise-limited onelimited one to a noise-limited one

Page 29: code division Duplexing

2929

Diff: btw TDD & CDDDiff: btw TDD & CDD

Page 30: code division Duplexing

3030

In other TDD systems the codes are not In other TDD systems the codes are not smart, so the receiver not only receives smart, so the receiver not only receives its desired code, but also receives its desired code, but also receives interference (I) from other cells.interference (I) from other cells.

Sometimes, the interference is so high Sometimes, the interference is so high it can mask the desired signal.it can mask the desired signal.

In the LAS CDD system, because of the In the LAS CDD system, because of the smart codes, the receiver only receives smart codes, the receiver only receives the desired code, no interference.the desired code, no interference.

Page 31: code division Duplexing

3131

THE TRIAL OF THE CDD SYSTEM

A working trial of the CDD system has been in Shanghai, China, since the beginning of September 2001.

Voice and video was transmitted at 384 kb/s through a 1.6 MHz unpaired band while the mobile was traveling at speeds in excess of 30 mph.

The trial successfully proved the technology and concept of a CDD system

Page 32: code division Duplexing

3232

A WIRELESS IP NETWORK SOLUTION

A CDD system is ideal for Internet communications, which makes a total wireless IP network solution highly desirable.

On December 15, 1999, four companies — Vodafone Airtouch, Cisco Systems, Hyundai, and Telos Technology— made a demo for a switch less IP core network in Reno, Nevada [6].

The iBTS connects to the IP core network, as shown in Fig.

Page 33: code division Duplexing

3333

Page 34: code division Duplexing

3434

The function of the switch is broken down into two:

mobility management and call processing. The handoff function is carried by the

selective distribution unit (SDU). The separated functions are placed on the

gateways to the core network. The demo of carrying voice over IP from

mobile to mobile and mobile to landline was successful.

The CDD system’s future IP core network will follow this approach.

The cost will be lower, and add-on features can be very flexible and easy.

Page 35: code division Duplexing

3535

CDD TECHNOLOGY IS ANEW MILESTONE

The LAS smart codes are the next breakthrough The LAS smart codes are the next breakthrough technology.technology.

Applying LAS technology to a TDD system Applying LAS technology to a TDD system becomes a CDD system.becomes a CDD system.

The benefit of using a TDD system for The benefit of using a TDD system for communications is that the sending and receiving communications is that the sending and receiving are alternating in time at a single frequency. are alternating in time at a single frequency.

Without the sending and receiving occurring at Without the sending and receiving occurring at the same time we can use the same smart code the same time we can use the same smart code for both sending and receiving;for both sending and receiving;

thus, thus, LAS + TDD = CDDLAS + TDD = CDD.. CDD is no more like TDD and is a better system CDD is no more like TDD and is a better system

for cellular.for cellular.

Page 36: code division Duplexing

3636

REDUCE INTERFERENCE-LIMITED ENVIRONMENT

TO NOISE-LIMITED ENVIRONMENT

Before 1989, cellular systems were using multiple cells with multiple frequencies assigned in each

cell. These systems generate an interference-

limited environment. After 1989, multiple cells used the same

frequency. Although the capacity increased using CDMA, the system is still in an interference-limited environment.

After 2000, the CDD system is developed. This system changes the environment from an

interference- limited one to a noise-limited one.

Page 37: code division Duplexing

3737

CONCLUSION

We are convinced that CDMA is the best multiple access scheme when compared to all others for combating interference.

However, the codes in CDMA can be more than one type of code.

A set of smart codes can make a high-capacity CDMA system very effective without adding other technologies.

Page 38: code division Duplexing

3838

The smart code plus TDD is called CDD, which is a new 3G technology.

A CDD system is simpler in design and lower cost.

CDD is an ideal system for a total IP network solution: new 3G technology + IP core network.

Hopefully, a CDD system will be the system of choice for future 3G networks.

Page 39: code division Duplexing

3939


Recommended