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When consumers think about mobile network providers, their primary concern is with regards to coverage, quality, support, pricing, and other factors but when you pick a network carrier, you also make the choice between a GSM network or a CDMA network, at least in the US.

You have probably come across these terms in the past, when picking a mobile phone, or when first joining, or switching, network carriers, but what do they mean, and what is the difference between the two? We find out, as we take a closer look at GSM vs CDMA, and what it signifies for us as a consumer.

What is GSM?

GSM stands for Global System for Mobile Communication, and is now considered the standard for communication globally, particularly in Asia and Europe, with its availability in over 210 countries worldwide. It functions on four distinct frequency bands, 900 MHz and 1800 MHz is Europe and Asia, and 850 MHz and 1900 MHz in North and South America. The GSM Association is an international organization founded in 1987, that is intended to develop and oversee the expansion of the GSM wireless standard.

GSM uses a variant of TDMA (time division multiple access) that divides the frequency bands into multiple channels. With GSM, our voice is transformed into digital data, which is given a channel and a time slot. On the other end, the receiver listens only to the assigned time slot, with the call pieced together. Obviously, this happens in a negligible amount of time, and the receiver doesn’t notice the “break,” or time division, that occurs.

What is CDMA?

CDMA, or code division multiple access, was a standard designed and patented by Qualcomm, but subsequently used as the basis for the CDMA2000 and WCDMA standards for 3G. However, because of its proprietary nature, CDMA hasn’t seen the global adoption that GSM has, with less than 18% of the networks around the world using CDMA, and is primarily found in the US, with Verizon Wireless and Sprint both using CDMA networks, as well as in South Korea and Russia. You can find the full list of CDMA networks here.

CDMA networks layer digitalized calls over one another, assigning unique codes to differentiate between them. Every call data is encoded with a different key, and the calls are then transmitted at the same time. The receivers each have the unique key as well, to split the combined signal into its individual calls.

Differences

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Both are multiple access standards, which means that multiple calls can go through a single tower, but as you can see, the major difference between the two has to do with the way your data is converted into the radio waves that your phone broadcasts and receives. There are of course, more practical considerations that matter more for us as a consumer, which you can find listed below –

  • SIM cards: Before the advent of 4G LTE, the obvious difference between GSM and CDMA devices were with regards to the SIM card. GSM handsets came with a SIM card slot, while CDMA phones did not. In other words, CDMA is a handset based standard, with a phone number linked to a particular device. If you wanted to upgrade to another phone, you would have to get in touch with the network carrier, de-activate the old device and activate the new one. On the other hand, with GSM devices, the phone number is linked to the SIM card, so when switching devices, all you have to do is pop the SIM card into a new phone and you are good to go. (This is obviously without taking into consideration GSM devices being locked to network carriers, as seen in the US).
  • Network coverage: Network coverage doesn’t depend on whether it is  GSM or CDMA network, but rather on the infrastructure the carrier has in place. GSM networks are far more popular globally, but in the US, Verizon Wireless, a CDMA network, boasts the highest number of subscribers in the country.
  • International roaming: In your home market, it doesn’t matter what kind of network it is, with the focus instead on the available coverage. However, when it comes to international roaming, GSM has the upper hand, with their being a lot more GSM networks around the world, along with roaming deals between these providers. With a GSM phone, you also have the advantage of picking up a local SIM card wherever you are, assuming that you have an unlocked device. You may not get full access to data connectivity, depending on the device and network compatibility though.

The future

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With the advent of 4G and the adoption of LTE and LTE-Advanced as the standard by the majority of network carriers worldwide, the debate of GSM vs CDMA matters less everyday. You may have noticed the latest smartphones intended for CDMA networks also come with SIM card slots, to take advantage of the network’s 4G LTE capabilities.

While GSM and CDMA devices cannot be interchanged even now, and will never be cross-compatible, that won’t make a difference as we continue to make a push towards 4G LTE. Unless international roaming is a factor, as far as your voice call and 3G data needs are concerned, both GSM and CDMA networks are equally good, with factors like availability, coverage, customer service, and price, more at play here.

It’s also worth noting that many CDMA phones – like those offered from Verizon – also have support for GSM technology when roaming, so international travelers don’t really even have to worry much about this anymore.

Ankit Banerjee
My primary profession lies in the Network Design Engineering field. I have always been passionate about the latest trends in mobile communication advances around the world.