CDMA in a Nutshell

9 Jul

Code-Division Multiple Access (CDMA) is a digital wireless technology used in the U.S. by Sprint, Verizon and Virgin among others. It competes with GSM, used by AT&T and T-Mobile. CDMA supports more than 522 million subscribers worldwide, while GSM supports more than 4.4 billion.

CDMA is a “spread spectrum” technology most commonly associated with 2G and 3G wireless networks. It spreads the information contained in a particular signal over a much greater bandwidth than the original signal. There is no hard limit for the number of users who may share one network/tower. Instead, additional users can connect until the network determines that call quality would suffer beyond a set limit.

GSM, on the other hand, uses Time-Division Multiple Access (TDMA) and assigns a specific frequency for each user. This lowers the number of subscribers who can connect to a network at a given time, thus slowing the connection. CDMA provides for better voice and data communications, though both are improving rapidly. CDMA phones do not use SIM cards (GSM does) and charges more for roaming in and out of the U.S.

CDMA systems have been in commercial operation since 1995 and operate in the 800 and 1900 MHz frequency bands with primary markets in the Americas and Asia. CDMA is a military technology first used during World War II by English allies. The Germans were jamming transmissions, so the allies decided to transmit over several frequencies, making it difficult for the Germans to pick up the complete signal. Qualcomm created the early communications chips for CDMA technology, so it had access to the classified information. Once the information became public, Qualcomm claimed patents and became the first to commercialize it.


2 Responses to “CDMA in a Nutshell”


  1. Week 3 : Workshop | MCDM Smartphone Class - 9 July 2010

    […] Derek – CDMA […]

  2. Weeks 3&4 : Workshop | MCDM Smartphone Class - 10 July 2010

    […] Derek – CDMA […]

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