Which Phone to choose - CDMA or GSM

In this article the advantages and features of both CDMA and GSM technology is described, followed by comparison between the two.

CDMA (Code Division Multiple Access) is a channel access method which allows several transmitters to send information simultaneously over a single communication channel and hence multiplexing many users over the same physical channel. This technology is used by cell phone companies to allow many users to share the bandwidth of frequencies.

CDMA is a digital cellular technology that uses “spread spectrum” techniques. Unlike GSM technology that uses TDMA (Time Division Multiple Access), CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence.

CDMA consistently provides better capacity for voice and data communications than GSM, allowing more subscribers to connect at any given time. CDMA technology separates signals from both data and voice and then transmits using wide frequency range. Because of this more space is available for transferring data. This is one of the primary reasons to select CDMA for 3G (3rd generation) as preferred technology.

CDMA is widely used in Asia and in particular South Korea. It has 17% of world cell phone market share.

GSM (Global System for Mobil communication) is the most popular standard for cell phones in the world. According to GSM association, it’s estimated 82% of the global cell phone market uses GSM standard. More than 3 billion people from 212 countries use GSM phones.

GSM is a cellular network. The cell phone users connect to it by searching for cells in the immediate vicinity.

GSM networks commonly operate in four different frequency ranges, 850MHz, 900MHz, 1800MHZ and 1900MHz. In US and Canada 850MHz and 1900MHz are used.
GSM-900 uses 890–915 MHz to send information from the cell phone to base station (uplink) and 935–960 MHz for sending information from base station to cell phone (downlink), providing 124 RF channels (channel numbers 1 to 124) spaced at 200 kHz.

GSM is considered as 2G (2nd generation) cell phone technology for providing digital signaling and speech.

Some of main features of GSM phones are as follows:
• Provides international roaming very common between cell phone users.
• Provides capability to prevent fraud when cell phone is stolen or lost.
• Provides low-cost SMS (short message service), also known as “text messaging” service, as an alternative to voice calls.
• Provides one international Emergency phone number, “112”, which can be used by international travelers to connect to emergency services without knowing the local emergency number.

One of the key features of GSM is the SIM (Subscriber Identity Module), commonly known as a SIM card. The SIM card contains the user's subscription information and phone book. The cell phone user can retain his or her information after switching the phone by removing the SIM card from the old phone and putting it in the new one. Alternatively, the user can also change service provider while keeping the same phone by changing the SIM card. Some service providers block this action by allowing the phone to accept only a single SIM issued by them.

Which cell phone technology to choose, CDMA or GSM

There are many opinions on the advantages and features of CDMA and GSM technologies and which one is a better choice.

The GSM phone vendors claim that GSM is a feature rich system. It has more services and allows more data transfer. On the other hand the CDMA phone vendors claim that CDMA technology is maturing and is capable of providing the same features found on GSM. Some analyst, such as Dell’Oro Group even go further and has declared CDMA already "dead.” They believe because the large service providers like Sprint Nextel and Verizon Wireless, are not spending that much on CDMA and putting all their effort on GSM growth, means that CDMA market is dead.

Nowadays, it is not possible to say that GSM services are better than CDMA. Most of the features, such as, Multimedia messages, video, high-speed Internet access, digital camera and even PDA function can be found on both technologies. The new CDMA 1XRTT technology is more advanced than EDGE (Enhanced Data Rates for Global Evolution) technology from the beginning of 3G generation, allowing higher transfer rates.

The GSM SIM advantage is being challenged by CDMA service providers by allowing users to store their phone book on operator’s database and recovering it when cell phone is lost or stolen. This brings advantage over GSM, in which when cell phone is lost or stolen, phone book recovery is not possible because the SIM card along with the phone gets lost too.

Recently GSM operators are offering SIM backup to counter CDMA database feature.

How cell phone communication works

Communication between base stations and cell phone is established by a negotiation upon call origination. Once communication is established between base and mobile, movement of the cell phone is detected and the service is handed over from one base station to another. One cell at a time services each mobile in the narrowband services.

Cell Phone Network

The cell phone network is large and complicated. This network enables the service providers to provide services such as voice and text messaging. In summary the cell phone network consists of the three main sections:
1. The base Station Subsystem, including the base stations and their controller
2. Network and Switching Subsystems or core network
3. GPRS (General Packet Radio Services) Core network, which allows packet based Internet connections

History

CDMA is a military technology first used during World War II by English allies to block German attempts at jamming transmissions. The allies decided to transmit over several frequencies, instead of one, making it difficult for the Germans to pick up the complete signal. Qualcomm created the first communications chips for CDMA technology and first to commercialize it..

Future Alternatives

Mobile VoIP (Voice over IP) will become an important service in the coming years as device manufacturers exploit more powerful processors and less costly memory to meet user never ending needs.

Glossary

• TDMA (Time Division Multiple Access): works by dividing the spectrum into frequency channels and each user uses each channel for a specific time, to avoid interference.
• CDMA 1XRTT: 2.5G technology which allows data transfers up to 144 Kbps.
• EDGE (Enhanced Data Rates for Global Evolution): Technology promoted by GSM operators. Before migrating to WCDMA, EDGE will allow third generation data and voice access with 384 kbps transfer rate.
• EV-DO: Third generation from CDMA 1xEV-DO technology. "EV" comes from Evolution and "DO" from data-only. It uses a second channel, of 1.25 MHz, exclusively for data transmission. Some countries are already running this standard. In the USA, Verizon and Sprint started this technology in 2004. This technology allows hi-speed Internet access (2.4 Mbps) using the cell phone or using a wireless connection from a laptop or PDA.
• EV-DV: Evolution of EV-DO, but still under development. "DV" comes from data-and-voice. It uses the same channel for transmitting data and voice. The transfer rate can reach 5.2 Mbps.
• WCDMA: Wideband CDMA. Third generation technology that will be adopted by GSM operators. Its European version is known as UMTS (Universal Mobile telecommunication System). It can reach transfer rates up to 2 Mbps.
• 2G technologies can be divided into TDMA-based and CDMA-based standards depending on the type of multiplexing used. The main 2G standards are: GSM (TDMA-based) – used in all countries; IS-95 (CDMA-based), also know as CDMA – used in America and part of Aisa; PDC (TDMA-based) – used in Japan only; iDEN (TDMA-based), proprietary network used by Nextel in US and Telus Mobility in Canada; IS-136 (TDMA-based), also know as TDMA in US.
• 2.5G services enable high-speed data transfer over upgraded existing 2G networks.
• 3G technologies enable network operators to offer users a wider range of more advanced services including wide-area wireless voice telephony, video calls, and broadband wireless data, all in a mobile environment. Additional features also include HSPA data transmission capabilities able to deliver speeds up to 14.4Mbit/s on the downlink and 5.8Mbit/s on the uplink.
• 4G system will be able to provide a comprehensive IP solution where voice, data and streamed multimedia can be given to users on an "Anytime, Anywhere" basis, and at higher data rates than previous generations. Currently there is no commercial 4G but that is being standardized globally, with expected commercial 4G launches starting around 2012-2015.

About me:

bruce atlasi is a professional computer engineer, skilled in telecomm and datacomm technologies and architecture. He has diverse working experience with many telecomm start-ups and fortune 100 companies, including Cisco Systems, IBM, and Siemens. He regularly blogs on About Hi-Tech site.