CDMA2000 1xEV-DO Basics

CDMA2000 1xEV-DO cell phone system is a standard that has evolved from the CDMA2000 mobile phone system and it is now firmly established in many areas of the world. The letters EV-DO sometimes referred to as EVDO stand for Evolution Data Only or Data Optimised. From the 1xEV-DO title it can be seen that it is a data only mobile telecommunications standard that can be run on CDMA2000 networks.

The concept of CDMA2000 1xEV-DO is that is a packet data only carrier - voice can be carried either by using Voice over IP, VoIP, or by using a fall-back to a CDMA2000 1X carrier. The fall-back mode is the one that tends to be used more widely as most operators have a CDMA2000 1X system in place.

CDMA2000 1xEV-DO Basics

The CDMA2000 1x EV-DO cell phone system is defined under IS-856 (TIA-856) rather than IS-2000 (TIA-2000) that defines the other CDMA2000 standards.

The EV-DO, IS-856 standard has undergone several revisions since it was first launched:

• EV-DO Release 0 (Rel. 0):   This was the first release of the EV-DO standard.
• EV-DO Revision A (Rev. A):   This revision of the standard introduced a significant increase in data rates.
• EV-DO Revision B (Rev. B):   The EV-DO Rev. B version of the standard introduced a number of updates including multicarrier operation as a software upgrade and higher order modulation with the introduction of new hardware. These two upgrades can be undertaken separately.
• EV-DO Advanced:   This software only upgrade introduced a number of smart features into the EV-DO standard.
• EV-DO Revision C (Rev.C):   This is the Ultra-Mobile Broadband standard. This is not now being pursued as the evolution from EV-DO is now to LTE for 4G services.

It can be seen that the data rates have risen considerable with successive releases and revisions of the EV-DO standard.

Data rates for CDMA2000 1xEV-DO

The CDMA2000 1xEV-DO 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 to enable the standard to be optimised for data applications. If voice is required then a dual mode phone using separate 1X channel for the voice call is needed. In fact the "phones" used for data only applications are referred to as Access Terminals or ATs.

EV-DO tabular summary

The table below gives an overview of the capabilities of the different releases and revisions of the CDMA2000 1x EV-DO standard.

CDMA2000 1XEV-DO RELEASE / REVISION	MAX DOWNLINK DATA RATE (AVERAGE THROUGHPUT)	MAX UPLINK DATA RATE (AVERAGE THROUGHPUT)	COMMENTS
Rel. 0	2.4 Mbps (300-600 kbps)	153.4 kbps (70-90 kbps)	The first release of CDMA2000 1x EV-DO. 1.25 MHz FDD channels.
Rev. A	3.1 Mbps (600-1400kbps)	1.8 Mbps (500-800kbps)	Backwards compatible with EV-DO Rel. 0. 1.25 MHz FDD channels.
Rev. B software	9.3 Mbps	5.4 Mbps	These figures are for operation in a 5 MHz FDD channel and for the EV-DO Rev. B software upgrade. The software upgrade provides the multi-carrier facility. Figures are for the software upgrade only.
DO Rev. B hardware	14.7 Mbps	5.4 Mbps	These figures are for operation in a 5 MHz FDD channel and for the EV-DO Rev. B hardware upgrade as well as the software upgrade. The hardware upgrade allows higher order modulation (up to 64QAM) to be used.
DO Advanced	19.6 Mbps	7.2 Mbps	Figures for 4 x 1.25 MHz FDD channels

While many of the upgrades are implemented by software upgrades at the base station, new handsets, or Access Terminals, ATs are required to be able to utilise the features and data rates available. However ATs are normally replaced relatively frequently and as a result the new features are steadily taken up over time.

CDMA2000 1X / 1XRTT basics tutorial

CDMA2000 is the evolution of the original IS-95 cdmaOne system. CDMA2000 has a number of evolutions of which the first was CDMA2000 1X, sometimes also called CDMA2000 1XRTT.

CDMA2000 1X which is also standardised as IS-2000 supports circuit-switched voice, and has the capability to provide up and sometimes beyond 35 simultaneous call per sector and as such it doubles the capacity of the original IS-95 networks. It also enables the transmission and reception of data at rates up to 153 kbps in both directions. It was recognized by the International Telecommunications Union (ITU) as an IMT-2000 standard in November 1999.

CDMA2000 evolution

The aim of the CDMA2000 is to provide a migration path from the original cdmaOne / IS-95 system through the CDMA2000 1X format to further high speed formats. These different standards have all been standardised under the IS-format and a diagram of the migration path is given below:

CDMA2000 Evolution

The CDMA2000 1X format is the basic 3G standard, but in what is termed CDMA2000 1xEv, there are further developments. There are basically two routes for the evolution that were initially proposed, only one of which was deployed:

• CDMA2000 1X EV-DO:   The first of these known as CDMA2000 1xEV-DO (EVolution Data Only or as is becoming more widely known Evolution Data Optimised) is something of a sideline from the main evolutionary development of the standard. It is defined under IS-856 rather than IS-2000, and as the name indicates it only carries data, but at speeds up to 3.1Mbps in the forward direction and 1.8 Mbps in the reverse direction, the speed in the reverse link being upgraded as part of Release A of the standard. The first commercial CDMA2000 1xEV-DO network was deployed by SK Telecom (Korea) in January 2002.
• CDMA2000 1X EV-DV:   The second is CDMA2000 1X EV-DV (Evolution Data and Voice). The idea was that this system would carry both data and voice services. It was never deployed as the EV-DO system was deployed in preference and there was no requirement for a data and voice service as voice could be carried on DO as either VoIP or by falling back to the CDMA2000 1X format.

CDMA2000 1XRTT and 3XRTT

The CDMA2000 1XRTT and 3XRTT terms refer to what are termed "Radio Transmission Technologies". The original IS-95 and deployments of CDMA2000 utilised the 1.25 MHz channel spacing. This provided what is effectively the first phase of the 3G development and roll out. However to enhance the performance beyond that possible using the technologies such as 1xEV-DO and 1xEV-DV, the channel bandwidth of 1.25 MHz was deemed insufficient for even higher data rates. Accordingly by increasing the bandwidth, higher data rates were possible. The further evolution of the CDMA2000 system involves utilising channel bandwidths of 3 times the standard 1.25 MHz bandwidth under what was termed 3XRTT. Further bandwidth increases to 5X, 7X and so forth could in theory be contemplated.

For CDMA2000 1XRTT technology, a Spreading Rate 1 (SR1) was used where the signal was spread to occupy a bandwidth of 1.25 MHz. Here the spread rate was the same as that used for IS-95, i.e. 1.2288 Mcps. For 3XRTT technology, Spreading Rate 3 (SR3) was used. Here the spreading rate was 3.6864 Mcps. It was found that if the spreading rate remained the same but the data rate increased, as happens with video downloads and other 3G applications, the processing gain decreased. Accordingly the coverage and signal strength needed to be improved to match the new conditions. By increasing the spreading rate, the performance could be boosted without the need for improvements in coverage.

CDMA2000 1X overview

There are a number of updates and changes that were introduced to improve the performance of CDMA2000 1X, IS2000 over cdmaOne IS-95. However in all cases backward compatibility is maintained, allowing both IS-95 and CDMA2000 mobiles to access the same base stations. This provided a cost effective upgrade path for both users and operators.

For CDMA2000 1X, several new methods of coding and spreading were used and these enabled much higher capacities to be achieved.

• Walsh Codes:   The first major change in CDMA2000 1X was that the Walsh Codes used were increased from 64 bits for IS-95 to 128 bits for CDMA2000 1X. In addition to this, CDMA2000 1X used more error coding functions as well and used turbo codes rather than the convolutional codes used for IS-95. This enabled higher speed data to be sent. In addition to this interleaving and symbol repetition were used to provide the various data rates.
• Turbo codes:   Turbo codes were introduced into CDMA2000 1X. They were a new class of error correction codes that enabled transfer rates over a noisy channel to approach the "Shannon" limit. The turbo coding principle was first proposed in 1993 by Professors Claude Berrou and Alain Glaxieux. Originally their claims that the codes could double throughput for a given power were treated with scepticism, but their findings were eventually proved to be true. Turbo coders use powerful interleavers that reduce the susceptibility of a data stream to random and impulsive noise. By working on "soft" bits from a radio receiver, the Turbo codes enable the decoder to extract the maximum level of data from the noisy signals. Turbo codes require two encoders and two decoders per link. These blocks operate in parallel and work synergistically. They also used an iterative process to reduce the amount of processing required, but despite this they still require more processing power than previous coding systems such as convolutional codes.
• Spectrum efficiency:   Apart from the improvements in the spreading and channel generation, there were also changes in the air interface itself. The IS-95 forward link used a form of QPSK where the data on both the I and Q channels are the same. However for CDMA2000 1X the I and Q channels were different, and this gave the advantage that half the bandwidth could be used for the same number of chips, or twice the number of chips can be sent in the same bandwidth. While this did make the reception more sensitive to phase errors, other improvements included an improved system of forward power control and forward transmit diversity.
• Reverse link upgrades:   Similarly there were significant changes on the reverse link where several new channels were added. These included a pilot channel as well as supplemental data channels and a control channel for signalling. Additionally, similar to the forward link the reverse link used Walsh Codes to differentiate between the different channels. A further change was that the format of the carrier modulation was changed. With the reverse link now transmitting multiple channels the use of OQPSK would not prevent zero crossings. To achieve this, the modulation format was changed to a scheme known as Orthogonal Complex Quadrature Phase Shift Keying (OCQPSK). This form of modulation required a number of stages. First the channels to be transmitted were split so that some take the I path and others take the Q path. Next they were scrambled along with the Walsh code spreading. In the scrambling process the probability of zero crossings was identified and using a scheme known as Orthogonal Variable Spreading Function (OVSF) the probability of zero crossings was reduced. Accordingly the channels were spread with a Walsh Code sequence and summed with the correct gain to produce the I and Q sequences. These were then further spread by a long PN code with its mobile specific long mask to identify the mobile and these I and Q sequences were modulated onto the carrier. Although particularly complicated, this form of modulation did have fewer zero crossings and the power amplifier in the mobile did not have to be run in a linear mode, thereby saving battery power.

Summary

The CDMA2000 1X system gave many significant advantages over the original IS-95 scheme. Enabling higher data rates it also allowed improvements in performance as well as improvements in spectrum efficiency that enabled operators to gain a higher return on the spectrum. Also users saw improvements in performance.

IS-95, cdmaOne

IS-95 was the first CDMA mobile phone system to gain widespread use and it is found widely in North America. Its brand name is cdmaOne and the initial specification for the system was IS95A, but its performance was later upgraded under IS-95B. 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 14.4 kbps for IS-95A and 115 kbps for IS-95B.

IS95 / cdmaOne was the fist cellular telecommunications system to use the CDMA - code division multiple access system. Previous systems had used FDMA - frequency division multiple access or TDMA - time division multiple access. With IS-95 being a second generation - 2G system and all the later 3G systems using CDMA as their access system, this meant that IS95 / cdmaOne was a pioneering system.

IS-95 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 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. The IS95 system was widely deployed in North America, and the Asia Pacific region, but there were also networks in South America, Africa, and the Middle East as well as some in Eastern Europe.

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 115 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 cdma2000, and was available in a variety of flavours including cdma2000 1x, cdma2000 1x ev-do (evolution data only or data optimised) and another version was termed cdma2000 1x ev-dv (evolution data and voice), although this version was never seriously deployed.

CDMA within IS-95

The CDMA or code division multiple access system used for IS-95 is very different to other multiple access schemes used in previous cellular systems. However it offers a number of advantages and as a result has been widely used in many cellular technologies.

Note on CDMA:

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.

Click on the link for a CDMA tutorial

The advantage of using CDMA over FDMA and TDMA is that it enables a greater number of users to be supported. 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.

IS95 specification summary

PARAMETER	DETAILS
Multiple Access Scheme	CDMA
Channel bandwidth	1.25 MHz
Data rate	14.4 kbps - IS-95A 115 kbps - IS-95B

IS-95 summary

IS-95, cdmaOne was a revolutionary system for cellular telecommunications. It paved the way for the other CDMA based 3G systems that were to follow around the globe. It enabled greater levels of spectrum efficiency to be gained while also allowing many other improvements to be introduced. IS-95 itself evolved into the variety of cdma2000 schemes including 1x, 1x ev-do, and the plans were ultimately to migrate onto a 4G system known as UMB - Ultra-Mobile Broadband. However IS-95 proved to be a winner in many areas of the globe, particularly in the Americas and the Far East.