GSM LTE phone vs CDMA LTE phone radio

Discussion in 'iPhone' started by giper54, Jul 30, 2012.

  1. giper54 macrumors newbie

    Joined:
    Apr 30, 2012
    #1
    I found an interesting article about radios and LTE connections. The Radio Performance Disparity of the Galaxy Nexus on GSM and CDMA - Mobile Central - Binary Outcast

    I have the oppurtunity to either go with ATT or Verizon. The article makes it seems that GSM is a better bet for LTE phones especially in areas with poor reception. I am hoping people can provide insight/comments on LTE phones for GSM and CDMA carriers and the article.

    The Radio Performance Disparity of the Galaxy Nexus on GSM and CDMA

    The Samsung Galaxy Nexus. It's Google's flagship phone that is designed to complement the Android 4.0 “Ice Cream Sandwich” operating system software. With high end specifications (for 2011) and highly optimized software, the Galaxy Nexus is supposed to show off what Android can really do without any interference from carriers and OEMs. However, that wound up not truly being the case in the United States with the CDMA/LTE variant for Verizon Wireless and Sprint.

    By and large, the CDMA/LTE variant sold by Verizon Wireless and Sprint is the same as the original HSPA+ model that is now sold by Google on the Play Store (at least in terms of hardware). It has the same CPU, RAM, NFC chip, screen, cameras, etc. The only hardware difference is the cellular radio structure.

    The original UMTS HSPA+ model uses an Intel XG626 baseband modem that is connected to an antenna structure that supports quad-band GSM and penta-band WCDMA for global usage. For Americans, it means that it works on the HSPA+ networks for both AT&T and T-Mobile USA.

    The CDMA/LTE variant uses a VIA Telecom CBP7.1 CDMA2000 baseband modem, connected to an antenna structure that supports dual-band CDMA2000. The Sprint model adds another CDMA2000 band that is exclusive to Sprint. Both CDMA/LTE variants use a Samsung CMC221 LTE baseband modem, but the Verizon Wireless variant is set up for LTE band class 13 (Upper 700MHz C block), while the Sprint variant is set up for LTE band class 25 (U.S. Extended PCS, also known as PCS+G). The Verizon Galaxy Nexus has a user-accessible SIM card slot while the Sprint one does not.

    While the Intel (formerly Infineon) baseband used to be troublesome on AT&T's network (as many iPhone users that didn't own an iPhone 4S can attest to), the latest generation of basebands work fine on both AT&T and T-Mobile. With 3GPP Release 7 support, it has a maximum downlink throughput of 21Mbps while it has a maximum uplink throughput of 5.76Mbps. In general, the Galaxy Nexus works very well on AT&T and T-Mobile.

    However, it isn't the same for the CDMA variants of the Galaxy Nexus. The VIA Telecom CDMA chip is notorious for weak performance. Other notable devices that use the chip are the Samsung DROID Charge and the Samsung Stratosphere. Searching on the web about these devices turns up a lot of complaints about CDMA service quality with these devices.

    Jason Perlow of ZDNet experienced more than his fair share of issues while trying to live off of the 4G LTE connection his Galaxy Nexus provided. But he was trying to live off of 4G LTE, not CDMA2000. So why was he affected? Well, the truth is, CDMA/LTE devices require both radios to be active and connected. Not to mention, network authentication and feature provisioning actually goes through the CDMA system, not the LTE one.

    The bridge between CDMA2000 and LTE is rather brittle and is prone to failure, because LTE wasn't designed to be bridged with CDMA2000 like that. It was intended to be installed alongside GSM and WCDMA networks, and it handles it a lot better with those networks. So when something goes wrong in the rather terribly buggy CDMA system, the whole phone can and usually does fail. If Verizon Wireless had upgraded the CDMA2000 system to UMTS HSPA+ like most other CDMA2000 carriers across the globe, it would have avoided dealing with this problem.

    Also, the CDMA/LTE Galaxy Nexus lies to you (at least, it does now). Originally, the “bars” that indicate signal strength would actually indicate the signal strength of LTE if it was connected to an LTE network. When everyone started complaining about how weak the signal was compared to the Motorola DROID RAZR and Motorola DROID Bionic, Anandtech investigated. It turned out that the signal strength was actually accurate, and that LTE signals are incredibly weak. Previous devices used the CDMA signal strength to determine how many “bars” of signal you have. The Galaxy Nexus did not. It used the LTE signal strength when it was connected to LTE, and the CDMA signal strength when it wasn't. Verizon Wireless issued an update shortly afterward that changed the behavior to match older LTE devices. Newer LTE devices do the same as well.

    Combining the fact that the Galaxy Nexus has to work incredibly hard to maintain an LTE signal with the fact that the CDMA2000 radio is horrible and has a difficult time holding onto the connection will lead anyone to the conclusion that it is a recipe for disaster. Is it any wonder why Jason Perlow and many others have so many problems with the CDMA/LTE version of the Galaxy Nexus? Not really.

    Of course, this is excluding all the issues with timely updates that Verizon Wireless has caused for Galaxy Nexus owners. Including this issue just makes the problem worse. There are ways to work around some of the issues, though some workarounds will result in permanent degradation of performance. However, it doesn't mean anything if it takes forever for anyone to get any updates that implement them.

    In the end, I really can't solidly recommend the CDMA/LTE version of the Galaxy Nexus to anyone. Nor can I recommend any CDMA2000 device that uses a VIA Telecom CDMA baseband modem. The pitfalls just make it a bad experience for everyone.[
     
  2. Diseal3 macrumors 65816

    Joined:
    Jun 29, 2008
    #2
    What does galaxy nexus radio have to do with the CDMA or GSM iPhone?
     
  3. Agent-P macrumors 68030

    Agent-P

    Joined:
    Dec 5, 2009
    Location:
    The Tri-State Area
    #3
    I believe (and I may be wrong about this) that those chips are made by Qualcomm. It is assumed that if the next iPhone does have LTE, it will be using either the same or a similar Qualcomm chip. So that would influence how it would be different for the Verizon and AT&T iPhones. (Again, I may be wrong about this, so someone correct me if I am).
     
  4. Diseal3 macrumors 65816

    Joined:
    Jun 29, 2008
    #4
    Yea but then he mentioned the Intel radio chips. I'm sure apple has something lined up with Qualcomm to get early access to newer gen chips.
     
  5. kdarling macrumors demi-god

    kdarling

    Joined:
    Jun 9, 2007
    Location:
    First university coding class = 46 years ago
    #5
    Nonsense.

    LTE is not bound to either GSM or UMTS-3G. (For that matter, UMTS-3G didn't require GSM either.)

    LTE works fine alone or with CDMA or UMTS networks.
     
  6. giper54 thread starter macrumors newbie

    Joined:
    Apr 30, 2012
    #6
  7. giper54 thread starter macrumors newbie

    Joined:
    Apr 30, 2012
  8. profets macrumors 68040

    Joined:
    Mar 18, 2009
    #8
    I can't remember off the top of my head, but I think there was a newer chipset that Qualcomm may have ready for this iPhone that would encompass gsm/edge/hspa, cdma/evdo and multiple LTE bands as used by at&t and verizon. Essentially preventing multiple models like the current iPad has.
     
  9. ElZeus macrumors regular

    Joined:
    May 26, 2008
    #9
  10. Menel macrumors 603

    Menel

    Joined:
    Aug 4, 2011
    Location:
    ATL
    #10
    I was under the impression the current iPad, iPad 3rd gen, has only one hardware model (edit: for cellular/LTE)

    It's only sold separately if/when you are setting up a carrier account.
     
  11. profets macrumors 68040

    Joined:
    Mar 18, 2009
    #11
    Definitely two cellular iPad models (3rd gen). Only in the US anyway (gsm/edge/hspa/lte and CDMA/evdo/lte)
     
  12. Menel macrumors 603

    Menel

    Joined:
    Aug 4, 2011
    Location:
    ATL
    #12
    iLounge claims the CDMA version will also do GSM.
    http://www.ilounge.com/index.php/re...eration-with-wi-fi-wi-fi-4g-16gb-32gb-64gb/P4

    The only reason the ATT/GSM version can't do Verizon CDMA roaming is likely agency agreements, and registration of the IMEI number or whatever Verizon it is SIM-less Verizon requires.
     
  13. AustinIllini macrumors demi-god

    AustinIllini

    Joined:
    Oct 20, 2011
    Location:
    Austin, TX
    #13
  14. profets macrumors 68040

    Joined:
    Mar 18, 2009
    #14
    Sorry, that is true. Both have gsm/edge/hspa, the differences are the Verizon model includes cdma/evdo & LTE (band 700 i think) while AT&T/global model includes LTE (AWS/1700 band). The LTE bands weren't compatible.
     
  15. scaredpoet, Aug 3, 2012
    Last edited: Aug 3, 2012

    scaredpoet macrumors 604

    scaredpoet

    Joined:
    Apr 6, 2007
    #15
    Nope, not nonsense.

    The problem isn't the air interfaces being used. It is correct that LTE doesn't (and shouldn't) care whether GSM, UMTS, HSPA+, FOMA, DECT or whatever is running alongside it. However, LTE is intended to operate using a backend infrastructure and signaling platform known as GSM Map core. Specifically, it's detailed under standard 3GPP TS 29.002 and defines everything from call handling and routing, to data transport and messaging.

    CDMA/2000, or at least the flavor implemented by the likes of Verizon and Sprint, uses variants of a different call handling standard, TIA-41, formerly called IS-41 or ANSI-41 (or just "ANSI" for short). This is absolutely a vestige of the AMPS days, and the desire (at the time) to have a 3G-capable network that was fully compatible with a legacy analog network. AMPS is dead, but its legacy endures.

    The difference to and end user can be seen even on non-LTE phones, most keenly when they compare what an iPhone on AT&T or GSM networks can do (placing a call on hold, 5-way conference calling, selective dropping of callers on a conference, End+Answer on call waiting, UI-based feature controls for call waiting/forwarding/callerID, etc.) compared to what an iPhone on Verizon or other CDMA networks can do (none of the things listed in my previous parens).

    http://support.apple.com/kb/HT4515


    There are procedures and best practices for interoperability between the two systems, but I wouldn't dare call it perfect or seamless. To say that LTE could be suboptimal on a carrier like Verizon is totally likely, for as long as they continue to operate their CDMA2000 network with IS-41, and expect it to play nice with an LTE network intended to run under MAP.

    Will subscribers notice? It depends on how many resources Verizon and Sprint are prepared to throw at the problem. And it won't be a one-time expense. The effort is significant, and will be constant until the day the last CDMA capable mobile phone (or CDMA Onstar-equipped vehicle) is operating on their network.

    It can run fine alongside CDMA, if the "right" choices had been made. But hindsight is 20/20, and most CDMA carriers in North America were more concerned with backward compatibility than forward compability when those choices had to be made. At the time it was most certainly the right choice. But now it will cost them, and so on Verizon's end, it does and will take a lot of work for LTE to work anything approaching smoothly.
     
  16. giper54 thread starter macrumors newbie

    Joined:
    Apr 30, 2012
    #16
    Thank you for the response. Maybe this is why Verizon's network goes down time to time.
     
  17. scaredpoet macrumors 604

    scaredpoet

    Joined:
    Apr 6, 2007
  18. dontwalkhand macrumors 601

    dontwalkhand

    Joined:
    Jul 5, 2007
    Location:
    Phoenix, AZ
    #18
    LTE was the next step up past HSPA+ on GSM. UMB was supposed to be the CDMA variant, but that project got shuttered.

    Therefore, "GSM-Based" vs. "CDMA-based" LTE theoretically aren't any different. The difference would be what it falls back to if the LTE network isn't available, whether if its HSPA+ or 1x/EV-DO.

    The cool part about CDMA-based LTE is that it still authenticates with a SIM-Card for CDMA (called a C-SIM, or used to be called an R-UIM card for CDMA), so it behaves exactly like a GSM phone (though you can't use GSM phones on CDMA networks still)--The only exception would be Sprint, whom admits to embedding the SIM card, even on "global phones."

    Yes, this means you can switch phones without calling VZW, or bothering with PRL updates/*228 :)
     

Share This Page