cdma 1xevdo

7/31/2019 cdma 1xevdo

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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 TelecommunicationsUnion (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


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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 ismaintained, 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.


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Reverse link upgrades: Similarly there were significant changes on the reverse link whereseveral 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 achievethis, 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.


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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 eitherby 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 increasein 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 ofthe EV-DO standard.


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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.


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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.

The channel structure within CDMA2000 1xEV-DO has been optimised to allow high speed data

transmission. Accordingly the EVDO channel structure is different to that of other CDMA2000 systems.

Forward link EVDO channelsA number of EVDO channels are transmitted in the forward direction to enable signalling, data and

other capabilities to be handled. These channels include the Traffic channel, MAC channel, Control

channel and Pilot. These are time division multiplexed.

Traffic Channel: This channels uses Quadrature Phase Shift Keying (QPSK) modulation for

data rates up to 1.2288 Mbps. For higher data rates, higher order modulation techniques are

used in the form of 8PSK with 3 bits per symbol or 16QAM with 4 bits per symbol. The levels


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of the I and Q symbols are chosen so that the average power becomes 1.

The Incoming data to be used as the modulation comes from the from the turbo coder and is

scrambled by mixing it with a Pseudo Random Number (PN) sequence. The initial state of the

PN is derived from known parameters, and is unique for each user. Every packet starts at the

same initial value of the PN sequence.

At the beginning of the transmission to each user, there is a preamble that contains the user

ID for the data. Its repeat rate is determined by the data rate because lower data rates

require higher repeat values. However even at its largest, the preamble will fill no more than

half the first slot.

Control Channel: This channel carries the signalling and overhead messages.

Pilot: The differentiator between the cell and the sector is still the PN offset of the pilot

channel and the pilot signal is only gated on for 192 chips per slot.

Medium Access Control (MAC) Channel: This channel carries a number of controls

including the Reverse Power Control (RPC), the Data Rate Control (DRC) Lock, and the reverse

activity (RA) channels.

EV-DO reverse Link

The EVDO channels for the reverse link have a structure similar to that for CDMA2000. The following

channels are transmitted in addition to those used with 1X:

Reverse Rate Indicator (RRI) Channel: This indicates the data rate of the Reverse Data

Channel.

Acknowledgement (Ack) Channel: This channel is transmitted after the AT detects a

frame with the preamble detailing it to be the recipient of the data.Data Rate Control (DRC) Channel: This channel contains a four bit word in each slot to

allow the choice of 12 different transmission rates.


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CDMA2000 1xEV-DO Rev. B is an enhanced for of the CDMA2000 1xEV-DO standard that provides

much high data download rates than the previous forms of EV-DO, as well as enhancing efficiency of

the system for operators.

The EV-DO Rev B enhancements have been launched on a number of networks, although users need

the Rev B handsets or dongles to be able to take advantage of the improvements.

Although there are a number of changes that are included in the EV-DO Rev B updates, speeds up to14.7 Mbps can be achieved in the downlink

EV-DO Rev B basics

The EV-DO Rev B upgrade to the standard CDMA2000 EV-DO scheme incorporates a number of

changes over the Rev A system. These enable the system to provide a much higher level of

performance, allowing more effective operation for video streaming, gaming and other high data

applications.

The main updates to the system to achieve the required EV-DO Rev B performance are:

Carrier aggregation / carrier bundling: the specification for EV-DO Rev B enablescarriers to be aggregated to enable higher data rates to be carried. Typically it is envisaged

that two or three carriers will be aggregated in view of the spectrum limitations, but more can

be added if required. Carrier aggregation improves the peak data rates for individual users to

be increased along with the average throughput rates. This is because of the statistical nature

of the data capacity usage and the creation of a larger data pipe.

Higher order modulation: The EV-DO Rev B standard allows the use of higher order

modulation - up to 64QAM - this enables higher data rates to be achieved.. This can be used

where the link quality is sufficiently good to allow the use of this modulation, otherwise lower

order modulation schemes are used.

Reduced latency: Using a technique called Statistical Multiplexing across the aggregated

carriers the level of latency is reduced. The technique uses the multiple carriers and resulting

additional capacity to reduce packet wait times. This improves the level of latency for sensitive

services such as gaming, video telephony, remote console sessions and web browsing.

Hybrid frequency re-use: EV-DO Rev B utilises a system known as hybrid frequency re-

use. This provides a reduction in levels of interference from the adjacent sectors especially to

users at the edge of the cell. It has the effect of increasing the data rates that can be

provided.

Improved support for asymmetric data flow: One of the major issues with any system

using paired frequency spectrum is the asymmetric data flow - more data flows in the

downlink than in the uplink. The EV-DO Rev B has additional support to enable more efficient

utilisation of the resources.

EV-DO Rev B performance

CDMA2000 EV-DO Rev B provides some significant increases in performance over the previous

versions of EV-DO.


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EV-DO RELEASE /

REVISION

DOWNLINK DATA

RATE (PEAK)

UPLINK DATA

RATE (PEAK)

CHANNEL

CONFIGURATION

Rel. 0 2.4 Mbps 153 kbps 1.25 MHz FDD

Rev. A 3.1 Mbps 1.8 Mbps 1.25 MHz FDD

Rev. B (Multi-

Carrier only)

9.3 Mbps 5.4 Mbps 5 MHz FDD

Rev. B (MC + H/W

upgrade)

14.7 Mbps 5.4 Mbps 5 MHz FDD

EV-DO Rev B migration

The migration from Rev A to EV-DO Rev. B can be undertaken in two stages. This approach was

adopted to provide operators with the most effective upgrade path for their individual requirements.

These two stages or phases are outlined below:

Rev. B software upgrade: The main upgrade in this section is the multi-carrier facility.

Rev. B hardware upgrade: The main upgrade in this section is the move to 64QAM to

provide higher data rates on each channel when link conditions are suitable.


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DO Advanced is the next state in the evolution of CDMA2000 1xEV-DO beyond the Rev. B. DO

Advanced brings a number of new features that not only improve the performance as seen by the

user, but also improve the efficiency of the network for the operator, and allow improvements that

bring in additional revenue.

The upgrade required for DO Advanced is simply a software upgrade, making the change exceptionally

easy for the operator. While new devices will be able to take full advantage of the improvementsbrought about by the introduction of DO Advanced, existing devices will also see an improvement.

Overcoming network loading problems with DO Advanced

One of the key issues with any cellular network is that of load balancing - the loading is inherently

uneven and it changes according to the time of day. It is often found that a fully loaded sector is

surrounded by lightly loaded ones.

CDMA2000 EV-DO Advanced incorporates a number of measures to ensure that the load is evened out

across the network. This will not only improve the situation for the operator, but also for the user.

To allow the improvement of the network performance DO Advanced incorporates three main

techniques, referred to as Smart Network techniques:

Network Load Balancing: This feature of DO Advanced off-loads users on the edge of

heavily loaded sectors to any lightly loaded neighbouring sectors. This will only be achieved if

the performance can either be maintained or improved. Off-loading not only alleviates

congestion over the radio access network, but also within the backhaul elements of the

network. In this way it improves the overall network capacity.

Demand Matched Configuration : This DO Advanced feature controls the power levels of

the different sectors and also the different carriers. The power level is based upon the amount

of load they carry. In scenarios where the loading is uneven, the transmit power of the second

and third carriers of lightly loaded sectors is reduced to minimize interference, and this in turn

increases the capacity of highly loaded neighbouring sectors as a result of the lower

interference levels.

Distributed Network Scheduler: This DO Advanced feature increases data rates for users,

especially at the edge of the cell in "hot-spot" deployment situations, by assigning the most

suitable carriers to them, without sacrificing the gains achieved through Multicarrier. In such

scenarios, the secondary carriers will most likely be the appropriate carriers to assign as they

will have larger coverage area because of lower interference.

DO Advanced - Enhanced Connection Management

Enhanced Connection Management, ECM, is another key feature within ED-DO Advanced. ECMmanages bursty applications such as push/pull mobile email, as well as device enhancements to

improve performance without impacting infrastructure or standards.

ECM optimizes the process of allocation and de-allocation of resources to such applications and

improves the usage of access and paging channels, resulting in support for a large number of

simultaneous connected devices.


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DO Advanced summary

The transition to EV-DO Advanced is a very simple implementation for the operator. It simply consists

of a software upgrade. As many software upgrades can be implemented remotely, the DO Advanced

upgrade can be a very cost effective way of improving the performance of the network without major

investment in new hardware.

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