Assume we have a few students gathered in a classroom who would like to talk to each other simultaneously. Nothing would be audible if everyone starts speaking at the same time. Either they must take turns to speak or use different languages to communicate. The second option is quite similar to CDMA — students speaking the same language can understand each other, while other languages are perceived as noise and rejected.
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It is this later specification that is synonymous with cdmaOne. Apart from voice the mobile phone system is also able to carry data at rates up to IS history The idea for using the form of modulation known as direct sequence spread spectrum DSSS for a multiple access system for mobile telecommunications came from a California based company called Qualcomm in the s.
Previously DSSS had been mainly used for military or covert communications systems as the transmissions were hard to detect, jam and eavesdrop. The system involved multiplying the required data with another data stream with a much higher data rate.
Known as a spreading code, this widened the bandwidth required for the transmission, spreading it over a wide frequency band. Only when the original spreading code was used in the reconstruction of the data, would the original information be reconstituted. It was reasoned that by having different spreading codes, a multiple access system could be created for use in a mobile phone system. In order to prove that the new system was viable a consortium was set up and Qualcomm was joined by US network operators Nynex and Ameritech to develop the first experimental code division multiple access CDMA system.
Its purpose is to promote CDMA and evolve the technology and standards, although today most of the standards work is carried out by 3GPP2.
It then took a further three years before Hutchison Telecom became the first organisation to launch a system. With the success of the initial IS95 format, improvements were made and the standard was upgraded to IS95B. The main improvement was that this provided for an increased data rate of kbps as data traffic was starting to be carried. The basic CDMA system was later further improved and evolved into a 3G system carrying much higher data rates and introducing new improvements.
The 3G migration of IS95 was given the brand name cdma, and was available in a variety of flavours including cdma 1x, cdma 1x ev-do evolution data only or data optimised and another version was termed cdma 1x ev-dv evolution data and voice , although this version was never seriously deployed. However it offers a number of advantages and as a result has been widely used in many cellular technologies.
DSSS is a form of radio transmission where the data to be transmitted is multiplied with a high data rate bit sequence and then modulated onto an RF carrier to produce a signal with a much wider bandwidth than data alone.
To reconstitute the data at the receiver the same high data rate bit sequence is used to extract the data from the signal. By havng multiple code sequences many different remotes can access the same base station. The improvement in efficiency is hard to define as it depends on many factors including the size of the cells and the level of interference between cells and several other factors. Unlike the more traditional cellular systems where neighbouring cells use different sets of channels, a CDMA system re-uses the same channels.
Signals from other cells will be appear as interference, but the system is able to extract the required signal by using the correct code in the demodulation and signal extraction process.
Often more than one channel is used in each cell, and this provides additional capacity because there is a limit to the amount of traffic that can be supported on each channel.
Mokasa A CDMA subscriber has an account established with one wireless carrier, which provides the user with wireless voice and data services. Simple IP service does not include any tunneling scheme providing mobility on a network layer described in the beginning of this chapter and supports mobility only within certain geographical boundaries. The network will control the transmitted power of the traffic channel to keep the signal quality just good enough, thereby keeping the noise level seen by all other users to a minimum. The variable-rate nature of traffic channels provide lower-rate frames to be transmitted at lower power causing less noise for other signals still to be correctly received. From Wikipedia, the free encyclopedia. The service profile indicates what radio resources the user is authorized to use, such as a maximum bandwidth or access priority.
CDMAONE ARCHITECTURE PDF
IS offered interoperation including handoff with the analog cellular network. Besides technical improvements, the IS documents are much more mature in terms of layout and content. They also provide backwards-compatibility to IS Protocol details[ edit ] cdmaOne network structure The IS standards describe an air interface, a set of protocols used between mobile units and the network. Physical layer[ edit ] IS defines the transmission of signals in both the forward network-to-mobile and reverse mobile-to-network directions.