What is meant by Code Division Duplexing?

CDD or the Code Division Duplexing is a duplexing system that is perhaps the most spectrum – efficient one. In this article we discuss about this system. 

But first let us look at the scenario of the spectrum efficiency. 

- Elimination of interference is very complicated as well as an important issue when it comes to the implementation of the wireless communications. 

- With the increasing spectrum efficiency, interference becomes compulsory to be eliminated.

- Reducing the interference is very much important in order to increase the transmission data rate and the radio capacity of the wireless communications. 

- By duplexing, we mean that using two separate channels for the transmission of information in a two way communication in two different directions. 

- Currently we have only two working technologies in this regard namely:

1. Frequency division duplexing or FDD and
2. Time – division technology or TDD

- The former is the primary technology used in wireless because of its characteristic ability of interference isolation.

- The latter is kind of a spectral efficient technology.

- At present, frequency–division duplexing or FDD is mostly used by all the cellular systems for eliminating the interference that occurs in the adjacent cells. 

- A number of technologies are used today that have been successful in limiting the effects of the interference. 

- But they have not been successful in eliminating two particular types of interference namely:

1. Adjacent base – to – home mobile interference and
2. Adjacent mobile – to – home base interference

- Time Division Duplexing or TDD has not been put to use for the cellular systems since this one is much susceptible to different types of interference  

- TDD is not just subjected to the above mentioned two forms of interference rather it faces additional adjacent mobile to home and base to home interference.

- This limits the use of time division duplexing to the systems confined to a small area. 

- In Code–Division Duplexing, all these types of interference are eliminated making it the most spectrum efficient one. 

- However, proper CDD systems are not a perfect reality yet.

- CDD represents an innovative solution.

- Another best multiple access scheme is the CDMA (code – division multiple access) since it is more effective in eliminating the interference when compared to the other technologies. 

- Code – division duplexing is a combination of TDD and smart codes. 

- The CDD can be turned in to reality only with these smart codes. 

- CDMA based on these smart codes is termed as LAS – CDMA where LAS represents the smart codes set. 

- This technology holds the promise for increasing the spectral efficiency as well as capacity of the mobile networks. 

- For the efficient utilization of the spectrum, two technologies are required:

1. A multiple access scheme and
2. A duplexing system

- The industry has already established CDMA as the best out of three available (the other two are FDMA and TDMA). 

- Next, a duplexing system remains to be selected. 

- FDD has been the most common choice till now. 

- It makes use of different frequencies for handling the outgoing and incoming signals. 

- On the other hand, TDD operates on a single frequency but uses different time slots. 

- Using a TDD system provides a benefit of alternating sending and receiving in a single frequency. 

- Smart codes ensure that the code–division duplexing system is not like TDD but much better than that. 

- An interference limited environment was generated by the cellular systems using multiple frequencies in multiple cells. 

- Later, cells started using same frequency but still the environment was interference limited. 

- But the CDD system promises to change this environment in to one that is noise limited.