Code Division Duplexing
#1

Introduction
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 cells onto the useful signal
Reply
#2
i wanted ppt /slides
Reply
#3
hi
you can refer this page to get the details on code-division-duplexing

http://studentbank.in/report-code-divisi...xing--1922
Reply
#4
Code division duplexing


Abstract

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.

Introduction

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.

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 InterSymbol 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 cells onto the useful signal.

Why Reduce Interference In A Cellular System
Reducing interference in a cellular system is the most effective approach to increasing radio capacity and/or transmission data rate in the wireless environment. Therefore, reducing interference is a difficult and important challenge in wireless communications. The interference in an FDD system using a CDMA scheme is shown in Fig. 2. Looking at Fig. 3, we realize that a TDD system is very undesirable to use in a large-area cellular system.

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. 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.






Attached Files
.doc   Code division.doc (Size: 309 KB / Downloads: 2)
Reply

Important Note..!

If you are not satisfied with above reply ,..Please

ASK HERE

So that we will collect data for you and will made reply to the request....OR try below "QUICK REPLY" box to add a reply to this page
Popular Searches: colegio seminario las, what is the difference between duplexing and multiplexing, duplexing and speed, ncaa division 2 college football, code division duplexing in mobile computing, duplexing copier, seminar code division duplexing,

[-]
Quick Reply
Message
Type your reply to this message here.

Image Verification
Please enter the text contained within the image into the text box below it. This process is used to prevent automated spam bots.
Image Verification
(case insensitive)

Possibly Related Threads...
Thread Author Replies Views Last Post
  Code Division Multiple Access (CDMA) computer science crazy 2 4,123 07-02-2012, 04:05 PM
Last Post: seminar addict
  Wavelength Division Multiplexing (WDM) computer science crazy 1 2,093 24-08-2011, 10:54 AM
Last Post: smart paper boy
  Optical Networking and Dense Wavelength Division Multiplexing computer science crazy 1 3,091 20-04-2011, 11:34 AM
Last Post: seminar class
  Time Division Multiple Access (TDMA) mechanical engineering crazy 3 2,585 29-01-2010, 03:31 AM
Last Post: Shammakh
  Dense Wavelength Division Multiplexing electrical engineering 0 1,091 29-12-2009, 02:25 PM
Last Post: electrical engineering
Thumbs Up Frequency Division Multiple Access (FDMA) computer science crazy 0 1,343 15-02-2009, 12:45 PM
Last Post: computer science crazy
Thumbs Up Wavelength Division Multiplexing (WDM) computer science crazy 0 1,107 15-02-2009, 12:44 PM
Last Post: computer science crazy
  Frequency Division Multiple Access (FDMA) computer science crazy 0 3,230 21-09-2008, 11:23 AM
Last Post: computer science crazy
  Time Division Multiple Access (TDMA) computer science crazy 0 2,028 21-09-2008, 11:07 AM
Last Post: computer science crazy
  Orthogonal Frequency Division Multiplplexing computer science crazy 0 1,104 21-09-2008, 10:53 AM
Last Post: computer science crazy

Forum Jump: