HTC Thunderbolt does Voice + Data on Verizon 3G

Anandtech has finally published its review of the HTC Thunderbolt (wiki). I am interested because I have some family considering this phone. As expected the “4G” (Verizon’s LTE) web browsing battery life is abysmal. Also although the screen HTC uses is huge (4.3”), they use one of the four standard Android resolutions (480×800) which doesn’t look all that great (especially when compared with newer phones including the upcoming HTC Sensation which sport the qHD resolutions). Though it should be noted that some of those new higher-res phones (like the Motorola Atrix 4G) don’t display all applications correctly since some applications hardcode their app to run at a certain resolution.

What is special about the HTC Thunderbolt is that it finally simultaneous voice + data to a Verizon smartphone (specifically an Android phone), something the iPhone 4 on Verizon can’t do. To understand how I need to quickly review the chips inside all these smartphones as well as the difference between Verizon and AT&T’s network technology.

GSM vs. CDMA, and now LTE

AT&T uses GSM (as does T-Mobile), which is somewhat more of a global standard (GSM = Global Standard for Mobile Communications) and Verizon (and Sprint) use CDMA.

GSM operators’ data portion is often referred to as UMTS (or HSPA now, or actually HSPA+), whereas data over CDMA is referred to as EVDO. I will use these same names for the post.

GSM can handle voice (this actually includes text messages) and data over 3G (UMTS, or HSPA, HSPA+) together whereas CDMA cannot. That is, if you’re on a call on a GSM network, you can simultaneously download/upload over the internet on your smartphone. On a CDMA network, data transfer (over EVDO) stops during a voice call. The only workaround for getting simultaneous voice/text and data to work together on a CDMA network is to make be on a call and connected to WiFi network. The reason is WiFi transmission is handled by an entirely different chip than your cellular connection.

Beyond this I actually do not fully understand, at least not well enough to discuss in detail how the two technologies handle calls. From what I could understand in my research CDMA is more forgiving when a network is congested, and willing to compress calls (and decrease quality) whereas GSM tends to lock out new calls or kick currents calls off when a network gets congested. This is probably an oversimplification but it also makes sense given AT&T’s penchant for dropping calls.

I should point out here that GSM networks also use SIM cards and CDMA do not, and I have a separate post regarding this that you should read, especially if you’re on AT&T or T-Mobile.


LTE is Verizon’s answer to the fake 4G (I might explain why it’s “fake” in future post) networks T-Mobile, AT&T and Sprint are touting. 4G and LTE are faster than UMTS and EVDO respectively but they’re not technically 4th Generation (perhaps we’ll save that for a later post).

LTE requires a whole new chip because it’s different from Verizon’s CDMA data. (T-Mobile and AT&T’s 4G also requires newer 3G chips that have HSPA+ capabilities, I’m not sure about Sprint as I haven’t read too much on their 4G network.) So now companies like Qualcomm make a separate LTE chip that you can drop into a phone to access their LTE speeds.

Another important thing for Verizon is if you’re using the LTE network for data, you’re not using CDMA for data. Thus if you’re browsing on Verizon’s LTE network, you can simultaneously call and/or receive texts. However as soon as you drop out of an LTE network and back onto a 3G (CDMA) Verizon network your call will likely continue but your data transmission will stop until you’re either back in an LTE network or on a WiFi network.

Unfortunately it looks like the LTE network did go down a little earlier. It’s still a new network and I imagine with more and more adoption of LTE the network will have a few bugs to work out.

A Computer in your Pocket

A smart phone is basically a computer, and so it needs computer parts like a CPU (central processing unit, the brain), a GPU (for graphics) and RAM (working memory, not storage). It also needs connectivity chips for a WiFi connection (all laptops ship with these now) and a radio chipset for cellular connection so you can actually make phone calls (so not something every computer has).  If you are making a phone, you can find all these parts separately then join them together on a “motherboard” so they can communicate with one another, but I imagine that this would take up a lot of space and make the design pretty complicated. Therefore many companies choose to buy (or make) everything in one chip, called a System on a Chip (SoC). This has an important consequence for CDMA phones.

I will use three phones as an example of how this is handled: Nexus One (T-Mobile & AT&T), HTC Droid Incredible (Verizon) and the new HTC Thunderbolt (Verizon LTE). I am not using the iPhone 4 in the example but you’ll see later why.


Nexus One

  • Uses the Qualcomm QSD8250 SoC, this chip has a 1 GHz single core CPU, Adreno 200 GPU, and has embedded cellular chips that handle GSM calls as well as 3G data (UMTS) and a GPS chip.
  • Since it is a GSM chip it can transmit information (in this case, a phone voice conversation or a text message) while 3G UMTS data is transmitting.
  • Wi-Fi is handled by a separate Broadcom BCM4329 chip, which also provides Bluetooth and FM radio (though FM radio is not utilized, which I’m upset about)


HTC Droid Incredible, a “cousin” of the Nexus One built for Verizon

  • Uses the Qualcomm QSD8650 SoC, this chip is virtually the same as the one in the Nexus One. It has a 1 GHz single core CPU, Adreno 200 GPU, embedded cellular chip that can handle GSM calls as well as UMTS data, but can also do CDMA voice and EVDO, and of course the GPS chip.
  • Although the SoC has GSM capabilities, the phone itself does not have a SIM slot and thus could not be used on a standard GSM network.
  • CDMA voice/data is handled by one chip, and since CDMA does not allow one receiver/transmitter to transmit voice/text and data simultaneously, on the HTC Droid Incredible if you’re on a phone call you cannot browse the internet over the 3G connection.
  • Uses the same Broadcom BCM4329 chip as the Nexus One for Wi-Fi, again also giving capabilities of Bluetooth and FM radio.
  • Since Wi-Fi connection is handled by a different chip (i.e., not the QSD8650 SoC’s CDMA chip), you CAN be on a phone call and browse the internet or use apps that need the internet over Wi-Fi simultaneously


HTC Thunderbolt with LTE (the point of this post)

  • has a Qualcomm chip (MSM8655) which has the a 1 GHz CPU, Adreno 205 GPU, an embedded cellular chip that handles CDMA call and data.
  • Since this is an LTE-capable phone, HTC had to buy a separate chip for LTE, the Qualcomm MDM9600, something apparently only HTC can use (for now) due to their relationship with Qualcomm
  • WiFi is handled by a separate chip, which provides Bluetooth as well.

I can’t find a spec page but the fact that HTC went with the MDM9600 is significant. This chip handles LTE, but it also has the capability for EVDO communication. That means the HTC Thunderbolt has two chips in it that can handle EVDO data (thanks to that Anandtech review), the MSM8655 and the MDM9600. What this means is even when you’re not using LTE (either you’re not in an LTE area, or you’ve simply turned LTE off to save battery) you can use the HTC Thunderbolt on Verizon’s network to use voice/text (on a phone call) and still transmit data over 3G (EVDO). The phone will simply use the LTE chip’s EVDO cellular connection to transmit the data, bypassing the chip that’s being used to make phone calls.

The LG Revolution (long rumored to have Netflix streaming capabilities) also has an MSM8655 but it’s LTE chip is LTE-only, no additional EVDO, therefore voice and data together is NOT possible over regular 3G (EVDO). The Revolution obviously can handle voice and data together IF you’re on an LTE network or on a WiFi network. Same thing with Droid Bionic.


iPhone 4

  • both the AT&T and Verizon models (as well as the first iPad and the 4th gen iPod Touch) are powered by the Apple A4, which is a system-on-a-chip (SoC) that houses the CPU and GPU together. However this SoC combination does not provide any cellular connection, for that Apple relies on a separate chipset
  • AT&T – Infineon and Skyworks Solutions made a quad-band 3G UMTS antenna
  • Verizon – Qualcomm’s MDM6600 chipset which handles both CDMA/EVDO (voice and data respectively) and actually simultaneously can handle GSM and 14.4Mbps HPSA+. So like the one used in the HTC Droid Incredible this chipset can handle both EVDO and UMTS.

Because of space constraints in the Verizon iPhone Apple chose not to include the rest of the required GSM setup (SIM card, among other things), but if they had that one phone would have worked on both Verizon and AT&T.

Anyway since there is only one chip that handles EVDO on a Verizon iPhone 4, the phone cannot transmit voice/text and data together over Verizon’s 3G (EVDO). Again, if you’re downloading something or using an app that requires internet, the data transfer will stop if the phone is sent a text or you’re being called. If you’re on a call you cannot browse the internet over 3G. If you’re on a WiFi network, you can talk and transmit data simultaneously.

Voice + Data simultaneously, is it important?

Hopefully Verizon’s LTE, once all their phones transition over, will allow all phones to have simultaneous voice and data (in Verizon’s network, that’s SVLTE). It’s rare that a phone on Verizon can do data and EVDO together. For now the HTC Thunderbolt is that phone, and it’s an Android phone. If you think you need voice and data together when you’re out and about, this is the phone to check out.

As an example of when I use the data and voice together on AT&T’s 3G: every Android phone has built-in Google turn-by-turn voice navigation. Every so often while on the route the phone updates traffic and directions, or maybe I make a detour and a new route needs to be calculated, the phone relies on the 3G connection to do that. If I were on a phone call on Verizon’s EVDO network while using Navigation directions cannot update. There are many other examples of course, I just thought I would present one simple one that would actually have an impact on my experience as a somewhat heavy Android user.

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