Code Division Duplexing
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Computer Science Clay
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01-03-2009, 10:21 AM


Code Division Duplexing

Reducing interference in a cellular system is the most effective approach to increasing radio capacity and transmission data rate in the wireless environment. Therefore, reducing interference is a difficult and important challenge in wireless communications.

In every two-way communication system it is necessary to use separate channels to transmit information in each direction. This is called duplexing. Currently there exist only two duplexing technologies in wireless communications, Frequency division duplexing (FDD) and time division duplexing (TDD). FDD has been the primary technology used in the first three generations of mobile wireless because of its ability to isolate interference. TDD is seemingly a more spectral efficient technology but has found limited use because of interference and coverage problems.

Code-division duplexing (CDD) is an innovative solution that can eliminate all kinds of interference. 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. The smart code plus TDD is called CDD.

This paper will elaborate on a set of smart codes that will make an efficient CDD system a reality. The CDMA system based on this is known as the LAS-CDMA, where LAS is a set of smart codes. LAS-CDMA is a new coding technology that will increase the capacity and spectral efficiency of mobile networks. The advanced technology uses a set of smart codes to restrict interference, a property that adversely affects the efficiency of CDMA networks.

To utilize spectrum efficiently, two transmission techniques need to be considered: one is a multiple access scheme and the other a duplexing system. There are three multiple access schemes namely TDMA, FDMA and CDMA.

The industry has already established the best multiple access scheme, code-division multiple access (CDMA), for 3G systems. The next step is to select the best duplexing system. Duplexing systems are used for two-way communications. Presently, there are only two duplexing systems used: frequency-division duplexing (FDD), and time-division duplexing (TDD). The former uses different frequencies to handle incoming and outgoing signals.

The latter uses a single frequency but different time slots to handle incoming and outgoing signals.

In the current cellular duplexing systems, FDD has been the appropriate choice, not TDD. Currently, all cellular systems use frequency-division duplexing in an attempt to eliminate interference from adjacent cells. The use of many technologies has limited the effects of interference but still certain types of interference remain. Time-division duplexing has not been used for mobile cellular systems because it is even more susceptible to different forms of interference.

TDD can only be used for small confined area systems. Code-division duplexing is an innovative solution that can eliminate all kinds of interference. Eliminating all types of interference makes CDD the most spectrum efficient duplexing system.

CDMA overview

Interference and Capacity One of the key criteria in evaluating a communication system is its spectral efficiency, or the system capacity, for a given system bandwidth, or sometimes, the total data rate supported by the system. For a given bandwidth, the system capacity for narrow band radio systems is dimension limited, while the system capacity of a traditional CDMA system is interference limited.

Traditional CDMA systems are all self-interference system. Three types of interference are usually considered. By ISI we mean Inter Symbol Interference, which is created by the multi-path replica of the useful signal itself; MAI, or Mutual Access Interference, which is the interference created by the signals and their multi-path replica from the other users onto the useful signal; and ACI, or Adjacent Cell Interference, which is all the interfering signals from the adjacent cellsss onto the useful signal.
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ninemartin
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30-05-2010, 04:14 PM

more about this topic
send me some latest seminar and presentation topics.
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Sidewinder
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30-05-2010, 10:53 PM

A most spectrum-efficient duplexing system: CDD
For increasing spectrum efficiency in telecommunication , we have to eliminate interference. At present, all cellular systems use FDD (Frequency Division Duplexing) in an attempt to eliminate the interference from the adjacent cells. But the adjacent base-tohome mobile interference still remains unsolved. the adjacent base-to-home mobile interference, the additional adjacent base-to-home base interference, and adjacent mobile-to-home mobile interference restricts the use of TDD (Time Division Duplexing). CDD (Code Division Duplexing) can eliminate all three kinds of interference; the adjacent base-to-home mobile, the adjacent baseto-home base, and the adjacent mobile- to- home in cellular systems. Thus it becomes the most spectrum efficient duplexing system.

sciencestaged/4229472/the-most-spectrum-efficient-duplexing-system:-cdd.html

Methods and apparatus for wireless communication using code division duplex time-slotted CDMA
In a first technique in accordance with the invention, referred to as code division duplex (CDD) time-slotted CDMA, uplink and downlink portions of the system are separated using code division duplexing as well as the the users within a given cell are also separated using codes. Both the CDD and TDD techniques may make use of an electronically-steered beam . This is being designed to provide simultaneous coverage within a given cell for two or more users separated by codes.in accordance with the invention, referred to as orthogonal frequency division multiplexing (OFDM), uplink and downlink portions of the system are separated in frequency.
patentstorm.us/patents/6813254/fulltext.html
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project report helper
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#4
29-10-2010, 03:23 PM


.pptx   rk.pptx (Size: 599.43 KB / Downloads: 75)
CODE DIVISION DUPLEXING

INTRODUCTION

Reducing interference in a cellular system is the most effective approach to increasing radio capacity and transmission data rate in the wireless environment.
To utilize spectrum efficiently, two transmission techniques need to be considered:
one is a multiple access scheme and the other a duplexing system.
There are three multiple access schemes namely
TDMA
FDMA and
CDMA
There are three duplexing system namely
FDD
TDD and
CDD
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Uma Bali
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#5
01-03-2011, 09:04 PM

plz mail me on this topic..
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enam
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15-08-2011, 07:53 PM

give a report under this.
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16-08-2011, 09:56 AM


To get more information about the topic "Code Division Duplexing " please refer the link below

topicideashow-to-code-division-duplexing--1922

topicideashow-to-code-division-duplexing--783

topicideashow-to-code-division-duplexing--4042
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