GSM vs. CDMA: Understanding the 10 Key Differences


GSM and CDMA are the two most popular networking standards for mobile connectivity. While CDMA is older and now entering a legacy stage, it remains a staple for specific device variants and geographic regions. GSM is the bedrock of advanced cellular networks, fueling the rise of 4G and 5G. This article explains the difference between CDMA and GSM and their relevance in the IoT era. 

Understanding Global System For Mobile Communication (GSM)

GSM is a digital cellular technology that provides mobile data and voice services across devices. Global System for Mobile Communication (GSM) is one of the second-generation telecommunication standards (2G). GSM simply is a wireless network for transmitting data across mobile devices. It has been misunderstood as a mobile phone in some countries and still is even today. However, GSM is not a mobile phone but a means of communication across digital cellular devices.

GSM is simply for wireless data transmission. It was established in 1982 and replaced the 1st generation of telecommunication NMT (1G). GSM is not only used for voice calls; one can also use it for sending text messages and computing data. For instance, a user can connect his GSM-enabled phone with his laptop to send and receive emails and faxes, browse the internet, check security, etc. 

The benefits of GSM include a secure network, extensive coverage, and compatibility with a broad range of accessories and handsets. On the other hand, one of the most significant disadvantages of the GSM is that many users share the same bandwidth. This may result in bandwidth limitations and interference. 

GSM-world reports that there are two billion GSM mobile phone customers globally. China, Russia, India, and Germany are the most significant GSM users in the world. Since many GSM network customers have roaming agreements with international operators, consumers often use their smartphones while traveling abroad.

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Understanding Code Division Multiple Access (CDMA)

Code Division Multiple Access (CDMA) refers to many protocols used in second-and third-generation (3G and 2G) wireless communication, typically employed for mobile communication. The purpose of CDMA technology is to transmit digital information in the form of ones and zeros over the air. 

Multiple access, as its name indicates, allows multiple signals to utilize one transmission channel, boosting the effective use of the bandwidth available. It enables users to send data at any time through the entire frequency spectrum and does not restrict the frequency range of the user.

Therefore, CDMA enables several users to share a frequency band without excessive interference. Now, unlike GSM, CDMA phones are tied to a carrier and do not utilize SIM cards; instead of a SIM card, a phone number is used to connect a CDMA phone to the network. Verizon, Sprint, and US-cellular utilize CDMA networks in the United States. There is no restriction on the number of individuals that may access the CDMA network.

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Differences Between CDMA and GSM 

The word CDMA might sound entirely foreign to individuals outside the United States and specific Asian countries, but most people have heard of GSM. CDMA is a local wireless technology, unlike GSM, which offers global usage. 

Many phone users are not very conversant with the pros and cons of the bands their phone uses. Usually, mobile phone owners get to know about these phone bands when they try to switch carriers. This is when they realize they can not use a specific phone on a mobile network because they are using different technologies that are incompatible with each other.

CDMA and GSM were the most commonly used phone bands and most popular mobile communication standards between 1990-2010. CDMA and GSM are not new radio technologies; they both belong to the second generation of digital mobile standards otherwise known as 2G, which replaced the first-generation analog 1G. 

Third-generation technology replaced second-generation technology as it could meet the data requirements of new digital applications. However, the basic concepts of GSM/CDMA were used in building new standards. 

In the United States, the five most popular mobile networks are Sprint, Verizon, Virgin mobile, T mobile, and AT&T. The first three use CDMA while the last two use GSM. CDMA & GSM phone technologies have an internetwork barrier. This is why AT&T won’t work on a Verizon network, and Verizon will not work on an AT&T network.

The differences between GSM and CDMA technologies include:

1. Area of usage and availability

The CDMA was created in the United States for usage in the United States and certain Asian nations. Countries like South Korea, Japan, and Canada also used CDMA. However, most other countries use GSM, the standard for voice calls. If you intend to use your phone outside the United States, you would probably need a GSM band. GSM offers more expansive international roaming capabilities than the CDMA, which offers only nationwide roaming. 

GSM can provide international roaming since its service is available in more than 200 countries, allowing its customers to access network services worldwide. GSM is compatible with telephone networks such as the integrated service digital network (ISDN). CDMA, when compared to the GSM, lacks international roaming capabilities.

2. SIM usage

With GSM, you can swap SIM cards if your phone is unlocked and use it anywhere in the world. GSM phones use SIM cards, which help users make necessary changes to the phone whenever the need arises. This makes GSM suitable for someone who travels a lot or intends to go outside the United States. A SIM card helps users easily switch devices by simply porting over your card.

On the other hand, CDMA phones do not require SIM cards because the phone is linked to a network. They have a unique identification number that they use to identify their users. CDMA makes for easy identification of users because the numbers are arranged serially. CDMA phones’ inability to use SIM cards makes it difficult to switch. 

The user must inform the carrier about the new phone before the old serial number can be assigned to the new phone. When the user does not directly buy the phone, carriers may not assign the user’s existing serial number to the new phone. This means the user has to opt for another phone number which is neither palatable nor always feasible. 

3. Limited variety of phones 

In CDMA, there are limited varieties of phones available. The majority of mobile technology companies make use of GSM. On the other hand, GSM users do not encounter this problem. Several mobile phone industries make their phones GSM compatible and offer users a wide variety to choose from. One can easily insert an old SIM into the new phone, thus retaining contacts, important information, and availability to friends, family, and acquaintances. 

4. Frequency or technology usage

GSM uses TDMA and FDMA (time division multiple access and frequency division multiple access) running on 900MHz, 1800MHz, and 1900MHz. While CDMA uses the same frequency, it operates on Code Division Multiple Access technologies. 

5. Security

In CDMA technology, the phone is controlled by the operator, thereby making the phone and security of the user vulnerable; however, in GSM, the phone and operator have no control over the telephone due to GSM’s ability to use a SIM card. Therefore the security of the user is not vulnerable. Regarding the encryption of messages, CDMA provides built-in encryption, while GSM requires the user to add an external encrypting service to their mobile phone. 

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6. Data speed rate

The data speed rate of GSM is 384 kbps using the EDGE data transmission technology. High-Speed Packet Access (HSPA) has a data transfer speed of up to 42 Mbps. CDMA on the other hand has a data speed rate of 2 Mbps employing EVDO technology. This means that the speed rate of CDMA is higher than GSM’s. With CDMA, more than one transmitter can send information through a communication channel, and different bands of frequencies are shared in the network. Despite this, the network has no communication interference, although the same channel is used. 

7. Simultaneous usage of data and voice call

Most CDMA networks do not support data transmission and voice calls at the same time. Because of this, when using a CDMA-enabled mobile phone, the user will often receive many internet notifications, such as emails, messages, and other social media notifications, as soon as they end a call. 

This happens because CDMA phones automatically pause data when used for a voice call. In the presence of WiFi networks, CDMA works well, simultaneously transmitting data while being used for voice calls. This is because the WiFi enables data transmission over the internet while bypassing the phone’s carrier network. However, GSM makes room for both voice calls and data usage simultaneously. Even in the absence of a Wi-Fi connection. 

8. Switch mode

CDMA operates in a packet switch mode, another significant distinction between it and GSM. In the CDMA transmission process, data is broken down into suitably sized pieces or blocks for fast and efficient transfer via different network devices. GSM, on the other hand, makes use of circuit switching mode, and because of the dedicated path establishment, this type of switching is relatively inflexible. 

9. Synchronization of channel

CDMA does not require any synchronization, but the GSM requires the synchronization of channels. The synchronization channel is a downlink-only channel used in GSM cellular telephone systems. The purpose of this synchronization channel is to allow the mobile station, that is, the handset, to quickly identify a nearby cell (a base transceiver station). The synchronization bits are known by both the base transceiver station and the mobile.

10. Affordability of GSM and CDMA

When it comes to price and costs, the average cost of a phone call made on CDMA mobile is cheaper than that of GSM. One would assume that with the relatively affordable rates, users will far more commonly use CDMA technology in poor and developing countries. However, the problem is that CDMA companies have not done much to expand their horizons. CDMA is mainly restricted to major countries, giving GSM more opportunities to penetrate and build cell sites in various countries.

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Other differences

There are other unique things to note about the two technologies. For example;

  • The CDMA phone has no absolute limit on the number of users, and it makes for the easy addition of more users, given that the processing power is sufficient. In contrast, the number of GSM users is restricted by the technology used. 
  • CDMA does not make room for the availability of a variety of handsets in CDMA, as in the case of GSM users. The code is allocated to each user in CDMA, and the intervention is reduced.
  • CDMA has a very high spectral capacity that can accommodate more users per MHz of bandwidth. It is built on spread spectrum technology, which bolsters the use of available bandwidth and allows users to broadcast simultaneously throughout the frequency spectrum.
  • GSM utilizes the wedge spectrum, which may also be called a carrier. There are several time slots, and every user is allotted a unique time slot. Until a current call concludes, no new call may contact the carrier. GSM provides high-fidelity voice calls and practical spectrum usage, but its major disadvantage is that many users share the same bandwidth. This can cause interference, and due to this, limitations occur, causing disruption in service and angst for GSM users. 
  • Another challenging factor for the GSM is the fact that electronic interference can occur. This is the reason for sensitive equipment advice, requesting that one should turn phones off because it can create interference with such equipment. Examples of such sensitive locations are hospitals and airplanes. 
  • CDMA requires network provisioning; however, GSM does not need any network provisioning. The good thing about CDMA is that it requires low power yet gives high voice quality and high signal quality. It operates on a very low power level which the GSM cannot work on.

With all this being said, one can ask what network is better than the other. In reality, neither GSM nor CDMA can be rightly said to be better than the other. 

They both have advantages and disadvantages, and one should make decisions depending on the use case. Moreover, as the demand for data continues growing due to the advancement of IoT, the need for GSM and CDMA declined and the need for LTE, 4G, and 5G has risen. However, if your phone supports 2G or 3G, upgrading to 4G or 5G is advisable because most companies will be decommissioning 2G and 3G by the end of 2022.

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Application Of GSM In IoT

Internet of things, known as IoT, refers to the network of physical objects “things” with sensors, software, processors, and other technologies enabling these “things” to connect and exchange data over the internet. The interesting thing about IoT systems is that they do all these without necessarily requiring a human-to-machine interaction. 

Having said this, how is GSM applicable to IoT? 

GSM has been widely used worldwide, making it easier for IoT devices to access networks while roaming. GSM for IoT is a Low Power Wide Area Network (LPWAN) technology designed to provide long-range and less complicated cellular communication for the devices in a way that conserves energy. Most IoT devices that rely on GSM networks are battery-powered cellular IoT devices.

Most IoT devices are built on the GSM network because of their global coverage and long-range connectivity. This global coverage enables these IoT devices to exchange data across a wide geographical area.

As earlier mentioned, GSM operates on LPWAN. It has a low bandwidth requirement, resulting in less energy consumption. In other words, using GSM allows for less power consumption and frequent replacement or recharging of batteries used to power IoT devices. These IoT devices can last longer and be more affordable.

The flexibility of GSM networks and their compatibility with a wider variety of devices allows these IoT devices to exchange data between devices. Using a GSM network in IoT devices makes it possible for a higher number of subscribers to a machine, thus increasing the GSM network’s capacity. GSM has a high transmission quality; using SAIC and DAIC techniques provides high data transmission between IoT devices. 

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