My GSM to CDMA findings

#1

I recently signed up for Republic Wireless and received a GSM sim. Then I switched to a CDMA sim due to coverage issues.

My findings.

  1. The coverage is much better with the CDMA sim where I am.

  2. The CDMA sim appears to use less mobile data according to the Republic Wireless app. (I went from using 30 megabytes a day to 15 megabytes or less. Might be a placebo effect. Seems like the GSM sim was using data while idle and the CDMA sim doesn’t.)

  3. The CDMA LTE likes to turn itself off while on WiFi and takes about 30 seconds to reconnect when WiFi is lost… The GSM would transfer almost instantly. (I fixed this by going to developer options and enabling “mobile networks always on”)

  4. It appears that Republic Wireless doesn’t use the 1x CDMA network. (On sprint phones that 1x network is always connected even with LTE connected. Republic doesn’t appear to do this, however they may use it as a fallback if there is no LTE. Not sure about that as I haven’t been able to test that yet as I get great coverage.)

  5. CDMA LTE is about the same speed at GSM LTE! (I was not expecting that. I thought that CDMA would be much slower. I actually get better CDMA speeds with Republic Wireless on CDMA than I do with Sprint. Go figure.)

  6. Battery life seems to be better. (probably due to having better signal strength.)

Just my 2 cents. Has anyone else noticed any of this?

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#2

Highly variable by location. The CDMA carrier used to have better coverage here. That changed about a year ago with the GSM carrier now superior. (DC Metro Area)

Placebo. There is no mechanism for the SIM to use more or less data. Data is used by the apps and the OS and they don’t care the type of network they are connected to.

Makes sense, with the GSM partner LTE is likely already connected because of VoLTE. On the other hand Sprint has very little VoLTE deployed and therefore with wifi on the phone is likely on the 1x network for calling and must reconnect for LTE data.

They do indeed or you would have no calling off WiFi.

Again highly area dependent. Absolutely not true where I am (where the GSM partner is 4-5x faster).

You’ve probably got the right answer there.

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#3

Since we’re comparing notes, the LTE speeds of both Republic’s GSM and CDMA network partners are roughly equivalent where I am in South Florida. Generally, 3G GSM fallback technology is far superior in speed to CDMA 3G fallback technology and that is definitively true in my area. In fact, I delayed becoming a Republic member until late 2014 because of the ahem “quality” of Republic’s CDMA network partner when that network was limited to 3G. It wasn’t until they lit up LTE that their network could reasonably compete with that of Republic’s GSM network partner. Overall, Republic’s GSM partner remains the superior network in my area.

This might be more than a placebo. GSM networks allow for simultaneous use of voice and data where CDMA networks (unless LTE is involved) do not. For example, absent LTE, one cannot use Google Maps and talk on the phone simultaneously on a CDMA network. This is easily done on a GSM network. Therefore, apps using background data might use more data on a GSM network while talking on one’s phone as opposed to a CDMA network.

As @louisdi observes, absent VoLTE cellular calls on Republic’s CDMA partner’s network are most definitely using 1xRTT. Otherwise, cellular calls would fail.

For the sake of clarity LTE is LTE. From a technical standpoint, there is no such thing as CDMA LTE. Republic uses the terms GSM and CDMA to differentiate between its network partners (largely because it’s contractually obligated not to name its GSM partner). LTE is an evolution of GSM (not CDMA) technology. For purposes of 4G (and beyond) even so-called CDMA carriers are effectively using GSM technology.

Perhaps, however, another difference between GSM and CDMA as technologies is GSM does not boost radio power in the same way CDMA does in the presence of weak signal. A phone attached to a GSM network where cellular signal is weak will tend not to drain its battery to the extent the same phone attached to a CDMA network with weak signal would.

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#4

This is a great discussion to have, thank you for sharing your observations @l33tlinuxh4x0r.

Since many of the pros and cons of each network’s coverage will be relative to your location, it would be great if anyone chiming in would also give a general idea of the area where you use our service.

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#10

This is really great information. It would be great if this thread could somehow be pinned so that it doesn’t expire.

I’m sure that the forum can get big and unwieldy with lots of older data but expiring threads is one thing that I dislike about the new system format. I used to be able to comb through threads looking for answers to my questions, obviating the need to post a question that others had previously posted. –Just my feedback.

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#11

RW sent me a G4 provisioned with a CDMA SIM as a replacement for a Ascend GSM only phone after the coverage check by zip was introduced. At that time CDMA was the only network was recommending for my zip, 31324

I had also head CDMA data might be worse. Speeds were awful with the 3.0 CDMA at less than 1Mbps download and I didn’t use much if any of my 1MB per month. Once my 6 months of free service ended, I reactivated my G3 on the 2.0 refund plan and seldom used data assuming the CDMA data would be lousy as with the G4. I eventually found my G3 was unable to get LTE due to a SIM or reactivation problem. Support sent me a new SIM and my G3 CDMA speeds are now comparable to my good RW GSM data speeds on my other phones.

Without obtaining a new 3.0 CDMA card how would I know if 3.0 CDMA works at my location or I have a defective G4 phone that won’t receive Sprint’s LTE frequencies? GSM LTE works fine in the G4 but the CDMA LTE was lousy. Is it possible something went wrong during the activation?

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