Talk:Chip (CDMA)

What does this have to do with the subject of the article?

In the digital communications field, Sony has already released a number of functional ICs such as PLLs, modulators, and mixers. Now, we are enhancing our CDMA IC lineup, employing a combination of bipolar and GaAs technologies.

That's not the only nonsense. I just took a bunch out. It was obviously copied from some place, so I worry about even the bits that are left. Dicklyon 00:47, 4 July 2007 (UTC)[reply]

I think that one bit is represented by several chips,not like it is stated in article. And then, rate in chips is always higher than rate in bits.I have read it in the book "WCDMA UMTS deployment handbook optimisation and planning aspects" written by people of Qualqomm. Best reagrds,Bartek —Preceding unsigned comment added by 77.253.187.99 (talk) 20:16, 11 June 2008 (UTC)[reply]

Symbol=chip or not?

Hi Oli. I don't understand your last revision to the article. I agree that in the baseband signal, one chip=one pulse. However, the passband RF signal - the physical signal - is always (?) a BPSK modulated signal. So to my understanding, a chip is a BPSK symbol.

Do you have M-ary DS-CDMA modulation with M>2 in mind? I don't know how it works, and I suppose it is not very common.

Chip and chip rate can not be applied to FH-CDMA, but only DS-CDMA.

According to Pseudorandom noise to concept chip rate can be applied to any PN sequence, which is news to me. Mange01 (talk) 02:28, 31 July 2008 (UTC)[reply]

As for M>2, yes! W-CDMA (3G UMTS) uses QPSK in the downlink, and HSDPA uses QAM-16. I believe that HSPA+ will use QAM-64. Note also that in both downlink and uplink for 3G, the pseudorandom code ("scrambling code") is also complex. IS-95 uses QPSK and OQPSK for downlink and uplink, respectively.

I'm reluctant to equate a chip to a symbol, because from an information-theory point of view, "symbol" is usually synonymous with "member of the modulation alphabet", i.e. one unit of data. A chip on its own carries no data, and from a mathematical point of view, the chip sequence can be considered as merely the pulse shape. Oli Filth^{(talk|contribs)} 07:55, 31 July 2008 (UTC)[reply]

So the spreading factor is not number of chips per information bit if M>2? Maybe that should be explaned, and a symbol be defined in this context. M-ary CDMA should be discussed somewhere, for example in the CDMA article. Mange01 (talk) 11:08, 31 July 2008 (UTC)[reply]

Indeed, the spreading factor is the chips/symbols ratio (at the very least, that's how its defined for 3G). You're right, perhaps a brief mention of what a symbol is would be beneficial.

As for the CDMA article, the problem is really that it describes the spreading in terms of XOR-ing, rather than multiplication, which is more general. I'm not sure I have the patience to fix that article at the moment! Oli Filth^{(talk|contribs)} 11:38, 31 July 2008 (UTC)[reply]

Strange merge

The Orthogonal variable spreading factor (OVSF) article, also known as Orthogonal variable spreading function, was merged into this article without prior discussion or template. It don't think it belongs here. The idea was probably that spreading factor is redirected to this article, but the main topic of this article is the chip concept, wich is very different from OVSF. Why not keep OVSF as a separate article?

OVSF is used in WCDMA/UMTS, and is an implementation of direct-sequence spread spectrum/CDMA (direct-sequence spread spectrum/DS-CDMA). It might perhaps fit into one of those articles, if it necessarily has to be merged. Mange01 (talk) 15:29, 22 June 2010 (UTC)[reply]

The reference book (Bousquet) gives a "spreading ratio" which is chips per bit. Furthermore, the degree of spread depends upon the pseudonoise code formed by the chips representing each symbol; i.e. the chips could alternate as a simple pulse train, or they could form a pn sequence. Is this spreading factor, SF, just a proportionality which is achieved when a good code, e.g. Barker code, is used? The ambiguity here might be the result of cobbling together this page, without properly placing the material in context from the original source. Ryan Westafer (talk) 14:36, 20 January 2011 (UTC)[reply]