CDMA vs. GSM Examined: Which 3G Network is Superior?

By Wesley Fenlon

4G may be all the rage, but we still use our 3G networks every day. And not all 3G networks are created equal.

So the Verizon iPhone is finally here. It’s a CDMA phone, otherwise identical to the GSM handset that’s been available on AT&T since last summer. With Verizon plunging full-speed ahead with its 4G LTE network and Sprint and T-Mobile continuing to add devices for their WiMAX and HSPA+ networks, it seems like the iPhone 4 is falling behind the times. 4G will see tremendous growth in the next two years, but for now additional fees and relatively spotty coverage will keep plenty of consumers on trusty 3G networks.



UMTS) standard with High-Speed Downlink Packet Access (HSDP). HSDPA is part of the High Speed Packet Access family and supports download speeds of up to 14 megabits/s. For reference, T-Mobile’s so-called 4G network runs on a faster standard, HSPA+, and should in theory be able to reach speeds up to 42 megabits/s.

Whew, that’s a lot of acronyms. Confused yet? Let’s break HSPA down into something more manageable.

Network Design
It’s easy for all these technologies to blur together. For instance, AT&T uses a radio channel called WCDMA, or Wideband CDMA, to allocate resources between data and voice calls and support its mobile broadband connections. WCDMA’s “wideband” name comes from the fact that the technology transmits on 5MHz-wide radio channels. Despite the similar names, WCDMA is engineered differently than the CDMA networks we’ll get to in a bit.

Today’s phones support multiple bands, meaning they can transmit and receive over different portions of the spectrum. As AT&T explains about GSM: “GSM operates in the primary spectrum range of 890-915 MHz (uplink) and 935-960 MHz (downlink), with subsequent adaptations to operate in 1800 MHz (Digital Cellular System or GSM 1800) and 1900 MHz (Personal Communications Services or GSM 1900).”

Naturally, different networks require different antennas, which is why the Verizon iPhone has a slightly different antenna design than the GSM iPhone for AT&T. For instance, a five-band cellular antenna may cover GSM/GPRS/UMTS/HSDPA protocols.

Network Speed
GSM’s network page. Here we can seek out specific networks in the United States and see currently live and planned future networks. AT&T and T-Mobile are the big GSM networks in the US. Using HSDPA and HSUPA (high-speed uplink packet access) their 3G networks reach theoretical max speeds of 7.2Mb/s down and 1.4Mb/s up.

That may be the capability of the HSPA network, but you aren’t likely to reach those kinds of speeds. Here’s what AT&T has to say about its own network: “AT&T has engineered its network so that most users' experience typical downlink throughput rates of 700 kilobits per second (Kbps) to 1.7 Mbps, with bursts over 1 Mbps. Typical uplink rates are 500 Kbps to 1.2 Mbps.”

Bottom line: AT&T’s 3G in the US maxes out at 7.2Mbps, but the average speed is more like 2.11Mbps. 


EV-DO, or Evolution-Data Optimized.

Network Design
Before its EV-DO revisions, CDMA2000 rolled out as a 3G network back in 2000: “CDMA2000 1X (IS-2000) is an IMT-2000 (3G) technology, designed to deliver high-quality voice and high-speed data. It is an efficient wireless technology for circuit-switched voice communications and it supports packet data speeds of up to 153.6 kbps in a single 1.25 MHz radio channel.”

The second revision of EV-DO, EV-DO Rev. A, launched in 2006, bringing with it a wide range of changes to support higher data bandwidth and throughput. Despite the improvements of EV-DO REv. A, CDMA technology still faces one major problem: it doesn’t support simultaneous voice and data transmissions. The radio in CDMA phones is used to for EV-DO data transmission and to access the circuit-switched network for voice calls. If you’re making a call, access to the 3G network has to be cut off.

Compared to GSM, CDMA2000 is a narrow-band transmission that uses only 1.25 MHz channels (compared to the wideband 5 MHz we mentioned earlier). This makes it more flexible at greater capacities. LIke GSM, CDMA2000 operates in many portions of the wireless spectrum.

Rev. B, makes concurrent voice and data usage possible. But no cellular carrier in the US has rolled out EV-DO, and the focus on 4G networks means simultaneous voice and data with 3G isn’t a huge priority.

On the bright side, if you plan to access 4G services, 4G devices like the HTC EVO on Sprint can use multiple radios to provide data and voice services simultaneously. You won’t have access to 3G while making a call, but you can utilize the 4G or Wi-Fi radios for data access.

Network Speed
supports speeds up to 3.1 Mbps down and 1.8 Mbps up. As we mentioned earlier, speeds on AT&T’s 3G GSM network don’t hit the maximum advertised capabilities, and the same holds true for CDMA. PC Mag’s national 3G tests from summer 2010 reflected average speeds of 1.01 Mbps down, .35 Mbps up for Verizon and .99 Mbps down, .30 Mbps up from Sprint. Both carriers have put 3G services on the back-burner, focusing instead on rolling out the LTE and WiMAX networks that will become standard within the next few years. 

Bottom Line: EV-DO Rev. B has the potential for high download speeds, but current 3G networks on EV-DO Rev. A only average about 1 Mbps down.   


CDMA 3G networks are held back by their inability to use voice and data services simultaneously. They also offer overall slower speeds, but AT&T’s heavily-populated GSM network has issues with consistent performance. CDMA phones can potentially draw more power than GSM handsets, shortening their battery life.

AT&T is currently upgrading its HSPA network to HSPA+, much like T-Mobile’s, and plans to launch a 4G LTE network later in 2011. While AT&T is late to the game, its 3G network will be in better shape than Sprint’s or Verizon’s when it moves on to a next-gen LTE network.
Image via Flickr user mohdrais