Talk:Code-division multiple access

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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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]