February 28, 2010
Posted by: admin : Category:
Mobile Technology
GSM, for its transmission speed and other features, is a standard second generation (2G). Its extension to 3G called UMTS and differs in its higher speed of transmission, using slightly different network architecture and especially the use of different radio protocols (W-CDMA). The GSM Association (GSMA or GSM Association), this standard is the most widespread in the world, with 82% of terminals in use worldwide. A GSM has more than 3,000 million users in 212 different countries, being the predominant standard in Europe, South America, Asia and Oceania, and at great length in North America.
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February 15, 2010
Posted by: admin : Category:
Mobile Technology
Access to the channel used in GPRS is based on a frequency division duplex and TDMA. During the connection, the user is assigned a physical channel, formed by a temporary block on a specific carrier. This channel will be up or down depending on whether the user will receive or send data. This is combined with statistical multiplexing in the time domain, allowing multiple users to share the same physical channel, either upward or downward. The packets have constant length, corresponding to the GSM time slot. The downstream channel uses a queue FIFO for packets waiting, while the upstream channel uses a scheme similar to that of ALOHA with reservation. In short, it uses a system similar to ALOHA slotted during the containment phase, and TDMA with a tail FIFO during the data transmission.
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