Comparison of mobile phone standards

Comparison of mobile phone standards

Global System for Mobile Communications (GSM, around 80–85% market share) and IS-95 (around 10–15% market share) were the two most prevalent 2G mobile communication technologies in 2007.[1] In 3G, the most prevalent technology was UMTS with CDMA-2000 in close contention.cdma fixed wireless phone

All radio access technologies have to solve the same problems: to divide the finite RF spectrum among multiple users as efficiently as possible. GSM uses TDMA and FDMA for user and cell separation. UMTS, IS-95 and CDMA-2000 use CDMA. WiMAX and LTE use OFDM.
Time-division multiple access (TDMA) provides multiuser access by chopping up the channel into sequential time slices. Each user of the channel takes turns to transmit and receive signals. In reality, only one person is actually using the channel at a specific moment. This is analogous to time-sharing on a large computer server.
Frequency-division multiple access (FDMA) provides multiuser access by separating the used frequencies. This is used in GSM to separate cells, which then use TDMA to separate users within the cell.
Code-division multiple access (CDMA) This uses a digital modulation called spread spectrum which spreads the voice data over a very wide channel in pseudorandom fashion using a user or cell specific pseudorandom code. The receiver undoes the randomization to collect the bits together and produce the original data. As the codes are pseudorandom and selected in such a way as to cause minimal interference to one another, multiple users can talk at the same time and multiple cells can share the same frequency. This causes an added signal noise forcing all users to use more power, which in exchange decreases cell range and battery life.

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