Competitive Exams CDMA 2000 System

One of the major cell/mobile phone or cellular telecommunications technologies today is the CDMA-1/CDMA-2000 system. One of its strengths is that it has focussed on being an evolutionary technology moving from standards such as IS-95 (IS-95A and IS-95B) for CDMA-1 through to standards including IS-2000 and IS-856 for CDMA2000 1X, 1xEv, 1xEV-DO and 1xEV-DV. Currently the standard uses one standard channel under a system known as 1X RTT, although for the future three channels (3X RTT) may be used.

In view of the fact that the CDMA2000 system has been designed to be an evolutionary standard, it is relatively easy to introduce upgrades to the system. This has made it particularly popular with operators because the cost of upgrading to the new standards is much less, and they can have users with a variety of types of phone on the same network. Thus users may operate CDMA-1 phones on the same network as CDMA2000 1X or CDMA2000 1xEV-DV phones.

The first CDMA networks in the form of IS-95/CDMA-1 were the first deployments of CDMA technology, the technology that is being used for all 3G cell phone systems. This formed the basis for a unique evolutionary system as CDMA2000. CDMA2000 is a well established 3G technology, and it is particularly successful in the USA, and Asia Pacific regions as well as having a significant presence in many other parts of the world. It was able to offer 3G services well before W-CDMA became established, and it is now continuing to build on this success.

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 1980s. 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. Later the team was expanded as Motorola and AT&T (now Lucent) joined to bring their resources to speed development. As a result the new standard was published as IS-95A in 1995 under the auspices of the Cellular Telecommunications Industry Association (CTIA) and the Telecommunications Industry Association (TIA). As part of the development of CDMA an organisation called the CDMA Development Group (CDG) was formed from the founding network and manufacturers. 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. It is now widely deployed in North America, and the Asia Pacific region, but there are also networks in South America, Africa, and the Middle East as well as some in Eastern Europe.

System Basics

The CDMA system was totally unlike any system used before. In the UK the original TACS system had used a channel spacing of 25 kHz and AMPS in the US had used 30 kHz. The new GSM system used 200 kHz channels whilst the US-TDMA standard kept compatibility with AMPS and was based around 30 kHz channels. CDMA, IS-95A, used a 1.25 MHz bandwidth and this was much wider than anything that had been used before. CDMA operates well with a wide bandwidth, but it was limited to 1.25MHz to remain compatible with the spectrum allocations that were available.

CDMA, Code Division Multiple Access, is a multiple access scheme used by many 3G cellular technologies, and other forms of wireless technology. It uses a process called Direct Sequence Spread Spectrum where spreading codes are used to spread a signal out over a given bandwidth and then reconstituting the data in the receiver by using the same spreading code. By supplying different spreading codes to different users, several users are able to utilises the same frequency without mutual interference.

There were other differences as well. CDMA mobiles did not have SIM cards, although recently this has changed. Instead the subscriber data has simply been stored in memory of the mobile with a method of over-the-air programming of this data being available.

CDMA-1 Standard

The first offerings of CDMA under the guise of IS-95 catered for voice as well as data up to a speed of 14.4 kbps. However with the market moving towards data applications, the IS-95 specification was upgraded to IS-95B to cater for the needs of operators. This new specification allowed packet switched data transmission up to a speed of 64 kbps. IS-95B was first deployed in September 1999 in Korea and has since been adopted by operators in Japan and Peru.

Often IS-95 A and B versions are marketed under the brand name CDMA-1. This is a registered trademark of the CDMA Development Group.

CDMA2000 1X Standard

CDMA-1 had been very successful and was introduced into many countries, but with operators seeing revenue from voice services levelling off, the pressure to migrate to 3G technologies where data speeds were higher and revenue growth could be maintained. As a result of this the IS-2000 standard was developed to enable the higher 3G data rates to be provided.

Within IS-2000 a number of further developments were included. It was envisaged that with many more areas moving towards 3G standards and the old AMPS systems being made obsolete it would be possible to have systems operating on a wider bandwidth. As a result of this the new standards allowed for systems that would use the single channel bandwidth (1X or 1X RTT) and also ones that would use three times the bandwidth (3X). Currently all work is focussed on the 1X systems, with the idea for the 3X (or 3X RTT) systems to be used some time in the future.

CDMA2000 1X can double the voice capacity of CDMA-1 networks and delivers peak packet data speeds of 307 kbps in mobile environments although today's commercial CDMA2000 1X networks (phase 1) support a peak data rate of 153.6 kbps. CDMA2000 1X has been designated a 3G standard and it is now widely deployed.

Evolution

CDMA2000 1X is the basic 3G standard, in fact some people only consider it a 2.75G system, and it is being developed beyond this. In what is termed CDMA2000 1xEv, there are further developments to bring it in line with the UMTS or Wideband CDMA system that is being deployed in Western Europe and many other areas.

The first of these known as CDMA2000 1xEV-DO (EVolution Data Only) is something of a sideline from the main evolutionary development of the standard. It is defined under IS-856 rather than IS-2000, and is as the name indicates is only carries data, but at speeds up to 2.4Mbps in the forward direction and the same as 1X in the reverse direction.

The forward channel forms a dedicated variable-rate, packet data channel with signalling and control time multiplexed into it. The channel is itself time-divided and allocated to each user on a demand and opportunity driven basis. A data only format was adopted so that the system could be optimised for data applications, and if voice is required then a dual mode phone using separate 1X channel for the voice call is required. In fact the “phones” used for data only applications are referred to as Access Terminals or ATs.

The first commercial CDMA2000 1xEV-DO network was deployed by SK Telecom (Korea) in January 2002. Now operators in Brazil Ecuador, Indonesia, Jamaica, Puerto Rico, Taiwan and the USA to mention but a few have all launched networks and more are to follow.

Data and voice

The next logical evolution of the system is to incorporate both data and voice into the standard. This is exactly what CDMA2000 1xEV-DV achieves. This is catered for under Release C of the IS-2000 standard. And is effectively 1X with additional high speed data channels. In this way it is able to provide complete backward compatibility with both CDMA2000 1X and CDMA-1. In addition to this the migration requires comparatively few upgrades to a 1X system and as such it is a very attractive option for network operators. Further developments are available under Release D of the IS-2000 standard. This provides for 3.1 Mbps data in both directions as well as many other upgrades.