Author Topic: Mobile Phone Voice Quality, CDMA/GSM and what's next  (Read 92 times)

Offline AL_as_needed

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Mobile Phone Voice Quality, CDMA/GSM and what's next
« on: November 18, 2017, 08:53:27 PM »
As per the social requirements of generation, I have a cell phone.... and since collecting phones, I have noticed the voice quality is really really bad.  One would thing some 800$ device should sound better than a 302, but nope! When home I use an Xlink to simulate a land line as the cell likes to drop calls when moved around the living area, plus I hate being pestered with text messages and other notifications for meaningless info.
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Offline TelePlay

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Re: Mobile Phone Voice Quality, CDMA/GSM and what's next
« Reply #1 on: November 19, 2017, 10:41:03 AM »
As per the social requirements of generation, I have a cell phone.... and since collecting phones, I have noticed the voice quality is really really bad.  One would thing some 800$ device should sound better than a 302, but nope!

For those who may be interested, PCS transmission is a chopped digital sent via CDMA technology (TDMA and FDMA were abandoned some 15 years ago as problematic and unable to handle high volumes). Given that and all of the variables (distance to tower, moving while talking, weather, structures, other nearby phones on the same channel, other RF sources, sun spots, etc), yes, the quality of sound on a PCS has to be much worse than an analog copper line, all of the time, no exceptions.

Each word spoken is chopped up into many segments in the phone and each segment assigned a library defined "sound" binary code which is sent and when received, that binary code is passed through the receiving phones library which produces the sound. What you hear is a reasonable facsimile of what was spoken (a bunch of pre-set sound segments pasted together to form a word) which is close to what was spoken. No where near the quality of sound produced via DC voltage over a copper wire.

With hundreds of people talking on the same digital channel at any one time chopped and coded (CDMA) for efficient use of the frequency being used, the "word bits" are intermixed with the other calls and affected by interference so when re-creating the word on the receiving end, the phone's processor does its best, which is usually not good, to recreate the spoken word. My biggest complaint is time delay which results from speaking over the other half of the call, both people end up speaking at the same time due to a lag in converting the digital signal back to sound. Quality is never good. This is a simple overview of how they work.

     https://www.mat.ucsb.edu/g.legrady/academic/courses/03w200a/projects/wireless/cell_technology.htm

Keep in mind that a "cell" or cellular phone was analog (like CB) communication. PCS (personal communications service) is digital, chopped and recreated received sound which can lag. A cell phone was connected to a tower all of the time when turned on (fast battery drain) and PCS phones only access the tower a couple of times a minute to let reassure the tower and phone that both are still there so the carrier knows which tower to use to send a ring signal when someone calls your phone (slow battery drain when not being used).

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Code Division Multiple Access (CDMA) is a sort of multiplexing that facilitates various signals to occupy a single transmission channel. It optimizes the use of available bandwidth. The technology is commonly used in ultra-high-frequency (UHF) cellular telephone systems, bands ranging between the 800-MHz and 1.9-GHz.
            John . . .

              

Offline shadow67

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Re: Mobile Phone Voice Quality, CDMA/GSM and what's next
« Reply #2 on: November 19, 2017, 10:05:38 PM »
Historically speaking, AT&T and T-Mobile until recently used what is called GSM, which has been the standard in Europe for many years. This technology requires a SIM card in the phone. Verizon and Sprint have used CDMA, the technology mentioned in the prior post, which if I recall correctly is a proprietary technology created by Qualcomm that they then licensed to different manufacturers.  The two are incompatible, which is why when looking at unlocked wireless phones one may see that in the U.S. a particular phone may only operate on AT&T or T-Mobile. A GSM phone can be used on another GSM carrier by simply swapping out the SIM card (if the phone is not locked to the network). A CDMA phone can not be used on another network generally speaking. With the advent of LTE 4G networks all of the carriers are now going to a technology called VoLTE. This makes new phones more apt to work on other carriers, but only if unlocked and only if the phone works on the frequencies each carrier uses.

Offline AE_Collector

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Re: Mobile Phone Voice Quality, CDMA/GSM and what's next
« Reply #3 on: November 19, 2017, 11:36:40 PM »
Yeah I think CDMA is in its way to the history books soon. For awhile it looked as though GSM and CDMA would both survive but I think the writing is on the wall now. CDMA is gone or very close to gone in Canada after being the standard for both Bell and Telus.

Terry
« Last Edit: November 20, 2017, 12:38:37 AM by AE_Collector »

Offline TelePlay

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Re: Mobile Phone Voice Quality, CDMA/GSM and what's next
« Reply #4 on: November 19, 2017, 11:49:09 PM »
What ever they decide to go with, it's still going to be a chopped, digital signal where each word spoken is broken into small segments, matched to a sound library in the phone and the digital code for that sound transmitted to the receiving tower, the switch, the transmitting tower and to the receiving phone where the digital sound code is sent to the speaker and comes close to the spoken word on the receiving end. There is not way modern phone quality will ever come close to analog copper. Way to many variables to mess up the chopping and recreation of a string of words in a sentence. And if you think about it, digital is so fast that there are probably over a hundred other conversations taking place on the same channel at the same time with each bit of a word separated by a hundred other bits of a word spoken by a hundred other people talking on their phones. TDMA was a mess, using time to determine which bit of a word is heard by which phone. Code made it so only those bits with the right code were heard by one phone. But that had its problems so nice to know they are going to a new system to move chopped up words from on phone to another. Hopefully it will be better than CDMA/GSM but it will never match hard wired analog quality.
            John . . .

              

Offline twocvbloke

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Re: Mobile Phone Voice Quality, CDMA/GSM and what's next
« Reply #5 on: November 20, 2017, 09:42:24 AM »
The irony is, most 3G services are WCDMA, though they're used mostly for data rather than voice (some 3G networks use 2G (GSM) for voice calls, though with 4G LTE services these days, they're just using the data stream to carry the voice as a digital service), but still uses SIM cards to identify the subscriber & phone... :)

As for GSM, it's not far off being phased out in many countries to make way for expanded 4G services and the upcoming 5G services, so older mobile phones that are only 2G enabled (usually the traditional basic "dumb phones" (I don't like that term!!) used for calls and texting) will no longer be of any use, which is a shame as some phones are quite tough and long-lasting (the original Nokia 3310 for example), but that's progress for you, upgrade or be left behind... :-\

Offline AL_as_needed

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Re: Mobile Phone Voice Quality, CDMA/GSM and what's next
« Reply #6 on: December 03, 2017, 10:03:57 AM »
Thanks for the info Teleplay!

This has well drifted into to waters of "things over my head" in terms of technical detail. That being said, it is fascinating! I never knew just how cell-phones worked beyond the digital wireless radio like transmission aspect. Breaking down voice into tones matched to an on board sound library is very interesting. While the quality is lacking, I will have to give credit to the minds who came up with this as a means of transmitting and receiving voice data
TWinbrook7