What type of modulation is used in cell phones - a.m or f.m. ?

Answer 1

Neither, they've got their own range of airwaves that varies from company to company. Most carriers are using the GSM3 range at the moment; except for sprint, who uses CDMA.

Answer 2

2

Answer 3

Based on the technologies used, I'd say a form of FM.

GSM is a combination of Time- and Frequency-Division Multiple Access (TDMA/FDMA). The FDMA part involves the division by frequency of the (maximum) 25 MHz bandwidth into 124 carrier frequencies spaced 200 kHz apart. One or more carrier frequencies are assigned to each base station. Each of these carrier frequencies is then divided in time, using a TDMA scheme. The fundamental unit of time in this TDMA scheme is called a burst period and it lasts 15/26 ms (or approx. 0.577 ms). Eight burst periods are grouped into a TDMA frame (120/26 ms, or approx. 4.615 ms), which forms the basic unit for the definition of logical channels. One physical channel is one burst period per TDMA frame.

CDMA stands for Code Division Multiple Access and refers to a technology for the radio link which utilizes spread spectrum communication with very tightly controlled power levels by all participants. There is currently (2/2000) only one commercial system which uses CDMA, covered by the specifications IS-95 and J-STD-008, and thus the term CDMA is often used to refer to that system. In future, other systems will adopt a CDMA air interface. CDMA was designed by Qualcomm in the US.

TDMA (Time Division Multiple Access) refers to a digital RF link where multiple phones share a single carrier frequency by taking turns. Each phone gets the channel exclusively for a certain time slice, then gives it up while all the other phones take their turn. TDMA is also used sometimes to refer specifically to the standard covered by IS-136, which is a source of confusion because GSM also uses a TDMA air interface, as does IDEN, and neither of those systems are compatible with IS-136.

Answer 4

Definitely not AM, and not a typical FM. It is an incredibly complex method of digital RF comms. I think "spread spectrum" is commonly used, which spreads the frequencies out over a range. The details of this and the digital codes is how Qualcomm makes its billions.

There are two basic types: GSM used in Europe & many US carriers; and CDMA used by Sprint. GMS is based on TDMA "Time Division Multiple Access" and CDMA (Qualcomm's) is "Code Division Multiple Access."

I think CDMA is generally superior, but GSM seems to be winning the market, partly because Qualcomm charges too much in royalties.

Answer 5

Neither. It's a digital signal. The data is split into bytes- 1s and 0s then split again into bits - this is then reversed on the other end. So the modulation you describe is non existant.

Answer 6

To be honest, I don't think so

Answer 7

thank you for the replies, greatly appreciated