CDMA vs GSM ( Difference Between CDMA and GSM )

We are living in the era of technology, and the most ubiquitous technology we experience every day is cellular phone technology. These cell phones are wireless, and they can connect us to the furthest reach of the world. The cell phone network’s basic structure consists of many base stations to cover a certain area, and through these base stations, the mobile phones get call, text, and internet services. These base stations are assigned with multiple radio frequency bands to communicate. The frequency bands which can be utilized for such communication purposes are limited in numbers, and they are considered valuable resources.

In order to reuse the frequency bands to allocate many cell phone subscribers utilizing limited resources, multiple access schemes are adopted by the mobile phone network operators. The multiple access techniques are used to distinguish signals from several different transmitters covered by a single base station and squeeze multiple phone calls or Internet connections into one radio channel. CDMA and GSM are two such methods widely adopted by carrier companies. These technologies are critical for end users when buying a new smartphone or switching carriers.

What is GSM?

The Global System for Mobile Communications (GSM) is a network protocol for digital cellular voice telecommunications developed by ETSI (European Telecommunication Standards Institute). GSM has a collection of standard applications and features available to mobile phone subscribers. It is a widely accepted networking protocol for 2G digital communication networks all over the world. Since it’s common among standard among different countries, it’s possible to use the same phones with different companies’ services or even roam into foreign countries.

The GSM standards are implemented in hardware and software by equipment manufacturers and mobile phone operators. This service is designed to locate a moving phone anywhere in the world. This network technology can also accommodate the relatively small battery capacity, limited input/output capabilities, and weak radio transmitters on mobile devices.

The GSM network has evolved from a digital circuit-switched 2G network designed to replace the first generation analog network. “GSM” is a trademark owned by the GSM Association. This network can handle full-duplex communication (meaning natural phone conversation) and internet service via GPRS or EDGE services. Consequently, the 2G network evolved to 3G UMTS standard and then 4G LTE standards.

Several frequency ranges are used to operate GSM networks. The 2G GSM network operates in the 900 MHz or 1800 MHz bands. If these bands are occupied in any region (Canada and USA), the 850 MHz and 1900 MHz bands are utilized. Most of the 3G GSM networks in Europe use 2100 MHZ frequency bands. Whatever the frequency band is, each band is divided into 8 full rate or 16 half rate radio channels allocated to the end-user. These 8 radio channels are grouped into TDMA (Time Division Multiple Access) frames.

TDMA operation - (CDMA vs GSM)
TDMA operation

Operation

When you make a phone call, your voice is converted into digital data. This data is placed inside a single radio channel of those 8 channels of TDMA frame and transmitted to the nearest base station. In the picture above, these channels are separated by different shades of black on the graph. Your data and the other signals are packed together like “call1call2call3”, and the receiver on the other end listens only to the assigned time slot and pieces the call back together.

If you want to connect to a GSM network, you will need a billing type (prepaid or postpaid), a subscriber identity module (SIM card), and a mobile device compatible with GSM network. When the SIM card is activated for the first time,  the billing relationship is established and the phone number which is also known as Mobile Subscriber Integrated Services Digital Network Number (MSISDN) is programmed by the subscriber.

The SIM itself is tied to the network rather than the actual phone. Hence, the removable SIM card allows phones to be instantly activated, interchanged, swapped out, and upgraded, all without carrier intervention. It has its own memory known as HLR (Home Location Register) to store billing information, contact numbers, type of service available, and other information.

What is CDMA?

Code Division Multiple Access (CDMA) is another method of multiple access where several transmitters can send information simultaneously over a single communication channel. This technology was first developed in 1957 in the Soviet Union (USSR). An early version of CDMA was implemented in the Global Positioning System. The other versions of CDMA are Qualcomm standard IS-95 (CDMAONE), Qualcomm standard IS-2000 (CDMA2000), and UMTS 3G mobile phone standard (W-CDMA).

There are two basic CDMA types, and they are synchronous (orthogonal codes) and asynchronous (pseudorandom codes). CDMA technology more effectively utilizes the frequency bandwidth. It is shown in the picture comparing the technologies that, in CDMA technology, it is possible to transmit data from several users using a single channel and time slot. In practice, 61 concurrent users can communicate via 1.2288 MHz channel by processing each voice packet with two PN codes.

Although, in theory, there are 64 codes (Walsh Code) available to distinguish different callers, operational limits and quality of service reduce the number. CDMA technology is used in ultra-high-frequency (UHF) cellular telephone systems, bands ranging between 800-MHz and 1.9-GHz.

Founded in December 1993, CDMA Development Group (CDG) is dedicated to the future development and evolution of advanced wireless telecommunication systems. CDG is associated with service providers, infrastructure manufacturers, device vendors, test equipment vendors, application developers, and content providers.

Operation

As mentioned before, CDMA is a multiple-access technique to allows several users to utilize the network simultaneously. The voice data from a phone is converted to digital signal, and this signal is again mixed with code (also known as Walsh code or spread spectrum code) and then transmitted to the base station. A picture is given below to help you to visualize the process.

Here, voice or internet data from different users are denoted as d1, d2, d3, and d4. The data is then mixed or modulated with codes named c1, c2, c3, and c4 respectively. These codes are generated in your device and then the data is modulated with the help of a special digital circuit (XOR gate). The encoding process of the CDMA technology provides good separation between the signal of the desired user and other users’ signals. After encoding data from multiple users, the signal is sent through a radio channel altogether.

Conceptual representation of CDMA operation - (CDMA vs GSM)
Conceptual representation of CDMA operation

The sender’s signal is then processed by the base station, which is an essential element of the CDMA network. This data rate is either 13kbps or 8kbps, and this data is again converted to 64 kbps data rate for the mobile switching center (MSC). MSC is the entity that manages the establishment, connection, maintenance, and disposal of calls within the network and also with the outside world. MSC also maintains a database called HLR/AC ( Home Location Register/Authentication Center). This database stores the information of billing, device type, network identities like SID, NID, ESN, and authentication.

Once the signal is processed in the base station and MSC, it is routed to the destination, and the receiver gets the signal. The base station can distinguish calls for different users from the signal as they have different orthogonal spreading codes. The receiver will extract only the designated part of the signal using digital code, and because of the spreading coding, the interference between signals is minimal. Normally, the phone’s hardware performs all these tasks, and it doesn’t require any SIM-like devices.

Will GSM Phones Work on CDMA Networks and Vice Versa?

Generally, no. As explained earlier, GSM and CDMA phones have some fundamental differences, and you won’t be able to get service if you want to use GSM phones with CDMA carriers and vice versa. Sometimes, GSM carrier companies provide carrier-locked phones which are not compatible with other GSM service providers. These phones can be unlocked sometimes.

However, there are some recently developed devices like iPhone 8b or 8 Plus, Google Nexus, Galaxy S20 etc. which are compatible with GSM, CDMA, and LTE technology.

GSM vs CDMA: Main Differences

GSM Vs CDMA; To explain the main difference, let’s consider a simple analogy. Think of a room full of people who want to talk to each other. But if everyone starts to talk at the same time, no one will be able to hear anything. To avoid confusion, there are several techniques, such as people could take turns speaking (time division or GSM), speak at different pitches (frequency division), or speak in different languages (code division or CDMA).

Comparison between TDMA (GSM) and CDMA
Comparison between TDMA (GSM) and CDMA

Some other aspects of both the GSM and CDMA have to be considered by the customer and they are:

Connectivity

in 2G and 3G networks, GSM phones require SIM cards to connect to the network. For this purpose, GSM phones have built-in SIM card slots. If you want to upgrade or change your device, all you have to do is to insert your SIM card inside your new device (which obviously is not locked to a specific service provider company). The phone number, billing, and identifying information are stored in the SIM card, and hence you can make the transition without any issue in the GSM system.

On the other hand, common CDMA devices have no SIM card and CDMA is a hardware-based service. A particular handset is assigned with a phone number and network identifying information. So, in order to change your handset, you have to contact the service provider and deactivate the current service first. After that, you have to purchase the company-approved set.

Network coverage

as discussed earlier, GSM standard is widely accepted all over the world and operates in over 193 countries and territories by achieving over 90% market share. So, international roaming is possible with GSM devices. The CDMA network is very popular in America, Canada, and Japan. But international roaming is not always possible with every service provider.

Quality of the calls

Although, the quality of the call is highly dependent on the network coverage and the plan of the service. However, CDMA technology offers reduced chance of cross-talk and better security. Also, CDMA has better efficiency using the frequency bandwidth. But it is hard to notice as GSM carrier service is more common, and hence it has superior coverage than CDMA service.

Which One is Better GSM Or CDMA?

With the advancement of network technologies, the difference between GSM and CDMA is disappearing. The 3G GSM is actually CDMA technology with SIM card, and the actual name of this technology is Wideband Code Division Multiple Access (WCDMA). The service providers who are utilizing WCDMA have their older version of GSM network activated. This question about which one of GSM and CDMA actually is not a technical question, it is more about marketing.

However, earlier versions of GSM and CDMA have their own highs and lows. For starters, CDMA has lower chance of cross-talk and better security against eavesdropping than GSM. CDMA technology can accommodate more callers at a time with the same amount of bandwidth as GSM. In case your phone gets lost or stolen, CDMA operators store your phone book on the operator’s database.

GSM phones have lower power consumption and hence higher battery life than CDMA phones. Also, GSM networks are available worldwide, and international roaming is possible with these operators. Besides, it’s quite easy to change your phone or service providers with GSM technology; all you have to do is change your phone and insert the SIM or change the SIM card when you are changing the carrier. Recently, the GSM service providers offer SIM backup options to preserve your personal information and contacts.

Lists of CDMA and GSM Carriers (USA)

In the USA, there are many network operators doing business. These carrier companies either have their own network infrastructure, or they lease the network of other companies. The companies who lease the network of other companies are known as mobile virtual network operators (MVNO). The major mobile operators have their own networks. The MVNO operators have more flexibility than the original service provides as they usually lease networks from more than one companies and you will be able to use different networks and services with them. A list of the network operators using GSM or CDMA technologies is given below:

CDMA operators:

  • Verizon Wireless (major carrier)
  • U.S. Cellular (major carrier)
  • Sprint  (major carrier)
  • Alaska Communications
  • Appalachian Wireless
  • Blue Wireless
  • Bluegrass Cellular
  • Bravado Wireless
  • C Spire Wireless
  • Carolina West Wireless
  • Cellcom
  • Chariton Valley Wireless
  • Chat Mobility
  • Choice Wireless
  • Clear Talk
  • Copper Valley Telecom
  • Custer Telephone Cooperative
  • ETC (Enhanced Telecommunication Corporation)
  • GCI Wireless (maintains a CDMA and GSM network; contact provider for more information)
  • Illinois Valley Cellular
  • Inland Cellular
  • Mid-Rivers Communications
  • Mobi PCS
  • MTA Solutions
  • Nemont
  • Nex-Tech Wireless
  • NorthwestCell
  • nTelos
  • Pioneer Cellular
  • Silver Star Communications
  • Sprint
  • Sprocket Wireless
  • STRATA Networks
  • Thumb Cellular
  • United Wireless
  • U.S. Cellular
  • Verizon Wireless
  • Virgin Mobile USA
  • Bell MTS (Canadian)
  • SogetelMobilité (Canadian)

GSM operators:

  • AT&T (major carrier)
  • T-Mobile (major carrier)
  • ASTAC
  • AT&T
  • Big Sky Mobile
  • Cellular One Nation
  • Cordova Wireless
  • Cricket Wireless
  • DTC Wireless
  • GCI Wireless (maintains a GSM and CDMA network; contact provider for more information)
  • Indigo Wireless
  • Pine Cellular
  • Plateau Wireless
  • Union Wireless
  • West Central Wireless
  • Rogers (Canada)
  • Videotron Mobile (Canada)
  • Ice Wireless (Canada)

How to Check CDMA or GSM

Now, if you are wondering about a phone, whether it’s GSM or CDMA compatible, then here are some few tips to help you out.

  • SIM card slots: the obvious sign of a conventional GSM phone would be the dedicated SIM slot to insert the SIM card. This slot is generally placed on either side or in the back of the battery of the device. Modern 4G LTE smartphones are CDMA compatible and have SIM slots. But if your phone doesn’t have a SIM slot, then it’s definitely a CDMA phone.
SIM card slot on the back of the battery
SIM card slot on the back of the battery
SIM card slot on the side
SIM card slot on the side
  • Carrier companies: if your phone is purchased directly from the service provider then it will help you to find out the network technology of your phone.  Although Verizon uses CDMA technology in its networks, this company normally sells phones that are equipped with both technologies. AT&T and T-Mobile are GSM network operators, and they offer GSM devices. Sprint is a CDMA carrier company. These are the major mobile companies in the USA. Usually, phones from manufacturing companies or factory unlocked phones are compatible with both GSM and CDMA technologies.
  • Phone settings: unfortunately, phones don’t have labels to tell you about the network technology used in the device. You have to check the device settings to learn about that. For iPhone, select Settings app and click on General. After that, select About and search for an MEID, ESN, or IMEI number near the bottom of the menu. Phones having MEID or ESN numbers are CDMA devices and IMEI numbers indicate that they are GSM phones. As for Android sets, click Settings and go to System. Then select About phone where you will find Status icon. Click it and look for an MEID, ESN, or IMEI number.
  • Google search with model number: another option to discover the network type of your device is to search the internet. Almost every major manufacturer and service provider has its own website, which contains information about their devices. There are also third-party websites showcasing customer reviews and technical details as well. They can be valuable resources.

GSM vs CDMA: The Future

Networking technologies are constantly evolving as the requirements of high-quality voice call, video call, high-speed internet connections, and multimedia messaging are skyrocketing day by day. Engineers and technologists are always trying to provide better services and eliminate the existing problems. So, the networking standards and other services are always changing.

As mobile networks are entering the 4G era, the difference between GSM and CDMA are getting blurred. The LTE technologies are trying to combine the facilities of both GSM and CDMA together. In the future, new technologies like 5G network will be implemented where the choice between GSM and CDMA becomes even less relevant.

But for 2G and 3G networks, GSM and CDMA handsets will never be interchangeable. For local use, both GSM and CDMA work just fine for voice call and 3G data services. So, for now, you have to check for the device compatibility with GSM or CDMA which won’t be necessary for the future anymore.