CDMA mobile networks: Difference between IS95 And CDMA2000

While the focus in mobile communications today is mainly on 4G LTE and 5G NR technologies, 2G and 3G cellular technologies are still in operation. The majority of 2G and 3G networks in the world follow the GSM track, but there are many mobile operators that use CDMA-based mobile networks, IS95 (cdmaONE) and IS2000 (CDMA2000) for 2G and 3G cellular services.

IS-95 (Interim Standard 1995) is a second-generation (2G) cellular technology that introduced the first-ever CDMA-based mobile network in 1995; CDMA2000 or IS-2000 is the successor of IS-95 that allows IS-95 networks to migrate to 3G. The commercial name for IS-95 is cdmaOne.

IS95 is 2G like GSM and CDMA2000 is 3G like UMTS

IS95 offers 2G cellular services using the narrowband CDMA technology for its radio access just like GSM offers 2G services using FDMA and TDMA for the radio access; CDMA2000 offers 3G services and is a successor of IS95 just like UMTS is a successor of GSM and offers 3G services using Wideband CDMA.

There have been two key paths for the deployment of 2G (second generation) and 3G (third-generation) mobile networks in mobile communications. The first path uses GSM (Global System for Mobile Communications) and UMTS (Universal Mobile Telecommunication System) technologies, while the other path adopted IS-95 and CDMA2000.

In many parts of the world, especially in European countries, it is more likely to find GSM and UMTS networks for 2G and 3G cellular services. However, CDMA (Code Division Multiple Access) networks are also used by many operators worldwide, including some operators in the US, Asia and South America.

What are the key differences between IS95 and CDMA2000?

Commercial namecdmaOneCDMA2000 and CDMA2000 1xRTT
Standard nameInterim Standard 1995 or IS95 or IS-95Interim Standard 2000 or IS2000 or IS-2000
Carrier bandwidth1.25 MHz1.25 MHz and 3.75 MHz for 3G data rates
Channel separation1.25 MHz1.25 MHz
Frequency bands850 MHz and 1900 MHz850 MHz and 1900 MHz
Duplex schemeFrequency Division Duplex – FDDFrequency Division Duplex – FDD
VariantsIS95A and IS95Bcdma2000- 1 x RTT, cdma2000- 1x EVDO, cdma2000- 1 x EVDV, cdma2000-3xRTT
Peak downlink data ratesIS95A: 14.4 kbps
IS95B: 115.2 kbps
CDMA – 1xRTT: 153 kbps
CDMA EVDO Rev 0: 2.4 MBps
CDMA EVDO Rev A: 3.1
CDMA EVDO Rev B: 14.7 Mbps
—Table showing the key differences between IS95 and CDMA2000 technologies—

IS-95 (cdmaOne) is a 2G technology

IS95 or Interim Standard 1995 is a second-generation (2G) cellular technology that introduced the first-ever CDMA-based mobile network. It uses the spread spectrum technology with a carrier bandwidth of 1.25 MHz to enable voice and data services, offering peak data rates of up to 115.2 kbps.

—What is IS-95 (Interim Standard 1995) or cdmaOne?—

IS95 or Interim Standard 1995 was introduced to deliver 2G cellular services through the Code Division Multiple Access (CDMA) technology. The proprietary name for IS-95 is cdmaOne, and it is a digital technology that employs CDMA for its air interface. IS95 was the first-ever standard in mobile communications that was based on CDMA technology.

Cellular services before that were using FDMA (Frequency Division Multiple Access) for the analogue mobile networks (1G) and a combination of FDMA and TDMA (Time Division Multiple Access) for digital mobile networks (2G). The standard IS-95 has two variants, IS-95A and IS-95 B. IS95 can operate in two frequency bands: 850 MHz and 1900 MHz.

IS-95 employs Frequency Divison Duplex (FDD) and uses separate bands for uplink and downlink. It can use either 824MHz-894MHz or 1850-1990 MHz with separate frequency bands for the uplink and the downlink. The carrier frequencies used in IS-95 have a bandwidth of 1.25 MHz, and the channel separation (difference between the centre frequencies of two channels) is also 1.25 MHz.

IS95A can enable data rates of up to 14.4 kbps, which can be improved to 115 kbps with the technology enhancements in IS95B. IS-95 provides capacity advantages for its ability to accommodate more users per MHz of the bandwidth.

The power consumption in these networks is low, allowing users to make phone calls in decent quality even when the signal strength is not at its best. Low power consumption also extends the cell coverage, which increases the cell’s size. IS95 networks also have soft handovers (SHO) that are more robust than the “hard” handovers in TDMA/FDMA technologies.

CDMA2000 is a 3G technology

CDMA2000, also known as CDMA2000 1xRTT or IS-2000, is a technology standard used for delivering 3G cellular services. CDMA2000 is a successor of IS95 (cdmaOne), and it offers 3G mobile services as specified in IMT2000, enabling peak data rates of up to 153 kbps in the original launch.

Mobile networks worldwide follow two main paths for migrating from 2G to 3G. The first path is for GSM networks that employ the UMTS technology for 3G migration, whereas the other path is CDMA2000 which allows both IS-95 (cdma2000) and D-AMPS (Digital Advanced Mobile Phone System) to migrate to 3G.

3G mobile networks can offer much higher data speeds as compared to the earlier 2G networks. Due to the higher data speeds, 3G networks can support multimedia services, including video streaming.

CDMA2000 networks can operate in both 850 MHz and 1900 MHz frequency bands, just like the earlier IS95 networks with separate frequency bands for uplink and downlink. The uplink in CDMA is called the reverse link, and the downlink is called the forward link. I have written a dedicated post on IS95 frequencies that explains the forward and reverse link channels.

CDMA2000 is backwards compatible with its predecessor, IS95, making the upgrade from IS95 to CDMA2000 easy and seamless. CDMA2000 has seen several enhancements including CDMA2000 1xEVDO (EVolution Data Optimised), CDMA2000 1xEVDV (EVolution Data and Voice) and CDMA2000 3 x RTT (Radio Transmission Technology). It uses the carrier bandwidth of 1.25 MHZ like IS95 and is both circuit-switched and packet-switched.

However, while the standard frequency carrier bandwidth is 1.25 MHz, with 3xRTT, CDMA2000 can aggregate up to three 1.25 MHz channels to get a total bandwidth of 3.75 MHz. For comparison, the UMTS networks have a standard carrier bandwidth of 5 MHz. CDMA2000 1xRTT can support peak data rates of up to 153 kbps in the downlink and the uplink.

With the EVDO Rev B enhancement, CDMA2000 can support maximum data rates of up to 14.7 Mbps. I have written a dedicated post on EVDO that can provide more details on how it improves the data rates for CDMA2000 networks.

How are CDMA-based mobile networks different from GSM?

GSM networks use TDMA/FDMA and require the frequency channels to be planned carefully to avoid co-channel and adjacent channel interference; CDMA networks use spread spectrum technology that employs unique codes for each user and enables the network to use the same frequency carrier in all cells.

CDMA stands for Code Division Multiple Access, and it is a technology that can enable wireless connectivity through the use of specialised codes. The key parameters needed for a CDMA-based mobile network are frequency carrier (channel) and code (e.g. Walsh code). GSM networks use a combination of FDMA (Frequency Division Multiple Access) and TDMA (Time Division Multiple Access) for wireless connectivity.

In GSM networks, the frequency channel allocation needs to be planned very carefully and requires RF engineers to have specialised skills in frequency planning to avoid co-channel and adjacent channel interference. That is because the carrier to interference ratio (C/I) needs to be at an acceptable level in TDMA/FDMA based systems like GSM.

It means that the frequency channel your mobile phone is connected to needs to be stronger than other channels using the same frequency (co-channel) by a good margin. That margin is called the acceptable C/I ratio, expressed in dB. Have a look at the diagram below that shows how four frequency channels are reused to avoid the same frequencies being right next to each other.

Example of frequency reuse in a GSM network where four frequency carriers are used to provide coverage in a geographical area

On the other hand, CDMA networks do not have the frequency reuse limitation and use the same frequency carrier (channel) in all cells. Have a look at the diagram below that shows the concept of universal frequency reuse. CDMA networks use the spread spectrum technology, which is designed to operate at a very low signal-to-noise ratio (SNR) while using a very large bandwidth.

In CDMA networks, the transmitted signal from each mobile user is spread across the available bandwidth and is assigned a unique code (spreading code). A unique de-spreading code is applied to retrieve the original signal at the receiver end. Even though all users use the same frequency carrier, the chances of any co-channel interference are minimised since the spreading and de-spreading codes are unique for each user. Both IS95 and CDMA2000 are built upon the Direct Sequence Spread Spectrum (DSSS) technique.

—Frequency reuse in CDMA networks – same frequency reused by all cells—

Unlike TDMA/FDMA based networks like GSM, where a handover requires a mobile phone to first disconnect from one cell before connecting to a new cell, CDMA networks use a concept called soft handover (handoff). Since CDMA networks use the same frequency across all cells, a mobile phone can communicate with multiple cells simultaneously. As a result, the mobile phone can gradually disconnect from the cells that are no longer in range whilst staying connected to other required cells. Soft handover makes the handoff process more robust, making it less likely to drop the calls.

Here are some helpful downloads

Thank you for reading this post. I hope it helped you in developing a better understanding of cellular networks. Sometimes, we need extra support, especially when preparing for a new job, studying a new topic, or buying a new phone. Whatever you are trying to do, here are some downloads that can help you:

Students & fresh graduates: If you are just starting, the complexity of the cellular industry can be a bit overwhelming. But don’t worry, I have created this FREE ebook so you can familiarise yourself with the basics like 3G, 4G etc. As a next step, check out the latest edition of the same ebook with more details on 4G & 5G networks with diagrams. You can then read Mobile Networks Made Easy, which explains the network nodes, e.g., BTS, MSC, GGSN etc.

Professionals: If you are an experienced professional but new to mobile communications, it may seem hard to compete with someone who has a decade of experience in the cellular industry. But not everyone who works in this industry is always up to date on the bigger picture and the challenges considering how quickly the industry evolves. The bigger picture comes from experience, which is why I’ve carefully put together a few slides to get you started in no time. So if you work in sales, marketing, product, project or any other area of business where you need a high-level view, Introduction to Mobile Communications can give you a quick start. Also, here are some templates to help you prepare your own slides on the product overview and product roadmap.

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