Talk:Code-division multiple access

Commercial Aspects of GSM vs CDMA?

I came to Wikipedia wanting a brief, introductory overview of why my Sprint CDMA phone can't be used in many places overseas (unless it has a GSM "on the side" built in, like in the Blackberry 9630 or the iPhone 4S phones). I want to know why some countries chose GSM and others chose CDMA or mixed. Why does the US have so much more CDMA than the rest of world? I want to know why some carriers use CDMA and others use GSM. (I'm curious what it means to 'unlock' a GSM phone, and if the same thing can be done with dual-system phones like the iPhone 4s or Blackberry 9630 Tour.) In short, I really don't care at all about the underlying physics or electrical engineering. I'm interested in the business, commercial, user, and political (standard-setting) side of things. Perhaps there are articles on this, but they are not clearly linked, if so. Or perhaps they don't exist? 68.50.169.175 (talk) 11:53, 20 October 2011 (UTC)

If you don't care about the underlying physics or electrical engineering of Code Division Multiple Access, you could do as the item at the top of the page says, and, "For the mobile phone technology referred to as CDMA, see IS-95 and CDMA2000." Unfortunately, the initialism "CDMA", while originally used to refer to Code Division Multiple Access, has also come to be used to refer to "Qualcomm's CDMA-based mobile phone standards". Your Sprint phone is a "CDMA phone" in both senses; a 3G "GSM" phone is a "CDMA" phone only in the former sense. (Yes, a 3G "GSM" phone, using UMTS, is using, on a 3G network, a Code Division Multiple Access-based technology, W-CDMA. That doesn't mean it'll work on a "CDMA", i.e. IS-95 or CDMA2000, network, unless it's a dual-system phone.)

Unfortunately, those pages are also a bit technical, and don't give much in the way of the commercial history of those technlogies. The pages where discussing the commercial aspects and history of the two main streams of mobile phone standards would be most appropriate, such as history of mobile phones, don't seem to give the full details on that.

"Carrier locking" of GSM phones is described in SIM lock.

Perhaps CDMA should be made a disambiguation page, with links both to the IS-95 and CDMA2000 pages and the Code division multiple access page, and with the two pages about Qualcomm's standards pointing to whatever pages, if any, end up giving a historical discussion of various mobile phone standards and technologies. Guy Harris (talk) 19:37, 20 October 2011 (UTC)

The commercial viewpoint is fairly simple, in the same way that the US chose NTSC television standard when the rest of the world chose PAL, the US sticks with imperial measures when the rest of the world uses Metric. It separates and protects the US market for local players. In reality any technical disadvantage is too small to create an uproar. — Preceding unsigned comment added by CEN888 (talk • contribs) 09:43, 6 March 2012 (UTC)

Why is bandwidth proportional to 1 / T

From the article:

The data signal with pulse duration of Tb is XOR’ed with the code signal with pulse duration of Tc. (Note: bandwidth is proportional to 1 / T where T = bit time) Therefore, the bandwidth of the data signal is 1 / Tb and the bandwidth of the spread spectrum signal is 1 / Tc.

Why is the bandwidth proportional to 1 / T? Is that dependent on modulation? Could someone either explain why this is so, or put a link in that sentence to an article that explains why this is so.

77.67.176.125 (talk) 20:58, 7 March 2012 (UTC)

This is explained here. Note the reference to Hartley's Law. Maybe a link to Hartley's Law will do? 93.189.156.99 (talk) 07:57, 23 September 2013 (UTC)

Is the diagram of 4 orthogonal signals actually orthogonal?

Seems like their dot product is 4. — Preceding unsigned comment added by 50.76.46.94 (talk) 15:32, 23 March 2012 (UTC)

If you take any two of these signals, their 'dot product' should (and I think does) come out to be zero. Actually, what's going on is that a transmitter transmits one code, and the receiver multiplies each of the samples it gets by its code, then sums the result. If the Tx and the Rx are using the same code, this will be positive or negative; if they're using a different code it will be zero.--IanHarvey (talk) 11:40, 22 October 2012 (UTC)

Dubious

The text claims that a Soviet mobile phone was 3 cubic metres in size. This can't possibly be correct. That's equivalent to about 106 cubic feet^[1], or the entire interior capacity of a 2007 Ford Crown Victoria^[2]. Pburka (talk) 04:13, 10 February 2013 (UTC)

Wouldn't be one of these monsters? 93.189.156.99 (talk) 08:17, 23 September 2013 (UTC)

It is an obvious mistake. They meant 0.3 cubic meters. But this is not the main thing. Isn't it funny that the entire history of CDMA consists of only the Soviet history and in the times when USSR didn't have near the technology to make it. And nothing is mentioned about USA usage of it in 70s, 80s and 90s for military and cellular services. This is obviously an example of Russian attempt to claim that everything was invented there. I was born in USSR in 1950s and lived there till 90s and I know what I am saying. Their pride is hurting because Russia is decades behind the West and they found a way to spread propaganda about their successes. Really funny. — Preceding unsigned comment added by 12.216.208.194 (talk • contribs) 20:29, 8 May 2014‎ (UTC

I have added the reference to the Kupriyanovich 1957 patent to the article. Can somebody check whether it really describes a mobile phone system using what we call CDMA? I find it rather incredible. While it can be possible that the first work about code-division multiple access principle was published in 1935 by Dmitry Ageev, and that Leonid Kupriyanovich in 1957 made a working prototype of a wireless device allowing to make phone calls, and perhaps that spread-spectrum technology was used in USSR since 1970s, it is hardly true that the 1957 Leonid Kupriyanovich's device used CDMA. There was not electronic component base in 1950s to produce a device with weight of 3 kg with CDMA technology in the eastern block, and there is no reason why even the first prototype should use CDMA. I've spent some time with the text, so I can supply the corrected text of the patent in Russian language. The patent describes the device build from vacuum tubes. Kolarp (talk) 21:27, 9 July 2020 (UTC)

Please explain the coding step in the example:

In the example box, where does the encoding step come from?

encode0 = 2(1, 0, 1, 1) – (1, 1, 1, 1) = (1, –1, 1, 1)

I see that we multiply the signal by 2 and then subtract a vector of all ones. Where does this come from? It is not clear in the explanation so 2D-V where D is the data vector and V is (1,1,1,1).

Please explain.

Thanks! — Preceding unsigned comment added by 70.163.0.234 (talk) 13:13, 12 August 2016 (UTC)

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It's not clear why the archived version is necessary; why is the status of the site from 2011-02-08 of more interest than the status of the site from any other day, including today? Guy Harris (talk) 07:30, 10 August 2017 (UTC)

Barker Codes

In this article we have, "Due to their very advantageous auto- and crosscorrelation characteristics, these spreading sequences have also been used for radar applications for many decades, where they are called Barker codes (with a very short sequence length of typically 8 to 32)."

The text "length of typically 8 to 32" is misleading. Listed in the Barker code article, "Only nine Barker sequences are known, all of length N at most 13." — Preceding unsigned comment added by Rwg1975 (talk • contribs) 13:56, 30 January 2022 (UTC)

Spread-spectrum multiple access

Is spread-spectrum multiple access a synonym for code-division multiple access? (see Talk:Channel_access_method#Code_division_multiple_access_(CDMA)/Spread_spectrum_multiple_access_(SSMA)) ~Kvng (talk) 17:53, 5 June 2022 (UTC)