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Wireless Technologies

TDMA. TDMA = time division multiple accessDigital technologyAllows multiple users to access a single frequency channel without interference by allocating unique time slots to each user within each channel. How TDMA works. TDMA multiplexes three signals over a single channel (three users sharing a

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Wireless Technologies

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    1. Wireless Technologies TDMA, CDMA, & GSM

    2. TDMA TDMA = time division multiple access Digital technology Allows multiple users to access a single frequency channel without interference by allocating unique time slots to each user within each channel

    3. How TDMA works TDMA multiplexes three signals over a single channel (three users sharing a 30–kHz carrier frequency) One channel is divided into six time slots, with each signal using two slots Each caller is assigned a specific time slot for transmission. 3:1 gain over AMPS (advanced mobile phone service)

    4. A single channel can carry all four conversations if each conversation is divided into relatively short fragments, is assigned a time slot, and is transmitted in synchronized timed bursts. After the conversation in time-slot four is transmitted, the process is repeated.

    5. TDMA advantages and disadvantages extended battery life and talk time since the mobile is only transmitting a portion of the time (from 1/3 to 1/10) of the time during conversations. most cost-effective technology for upgrading a current analog system to digital Dual-mode compatibility each user has a predefined time slot, so when moving from one cell to another, if all of the time slots are occupied the call would likely be disconnected. TMDA is subject to multipath distortion. A signal coming from a tower to a handset might come from any one of several directions. It might have bounced off several different buildings before arriving, which can cause interference.

    6. CDMA CDMA = code division multiple access CDMA is a spread-spectrum technology that allows multiple frequencies to be used simultaneously by coding every digital packet it sends with a unique key. A CDMA receiver responds only to that key and can pick out and demodulate the associated signal.

    7. CDMA cont. Operates in the 800MHz band and 1.9GHz PCS (Personal Communications Services) band Uses a 1.25 MHz bandwidth CDMA is widely used in N. America and is expected to be the 3G technology for GSM CDMA phones are noted for their excellent call quality and long battery life.

    8. W-CDMA W-CDMA = Wideband Code Division Multiple Access Provides a higher capacity for voice and data at higher data rates than CDMA Uses a 5 MHz carrier (4 times that of CDMA) Higher data rate than both GSM and GPRS (up to 2 Mbps) W-CDMA is considered a 3G technology

    9. GSM GSM = global system for mobile communication Digital TDMA system now (2G), 3G expected to be W-CDMA Phones use SIM (System Identity Module) cards containing user account information provides a short messaging service (SMS) that enables text messages up to 160 characters in length

    10. GSM specs frequency band—The frequency range specified for GSM is 1,850 to 1,990 MHz (mobile station to base station). duplex distance—The duplex distance is 80 MHz. Duplex distance is the distance between the uplink and downlink frequencies. A channel has two frequencies, 80 MHz apart. channel separation—The separation between adjacent carrier frequencies. In GSM, this is 200 kHz. modulation—Modulation is the process of sending a signal by changing the characteristics of a carrier frequency. This is done in GSM via Gaussian minimum shift keying (GMSK). transmission rate—GSM is a digital system with an over-the-air bit rate of 270 kbps. access method—GSM utilizes the time division multiple access (TDMA) concept. TDMA is a technique in which several different calls may share the same carrier. Each call is assigned a particular time slot.

    11. GPRS GPRS = General Packet Radio Service enhancement to the GSM mobile communications system that supports data packets Allows for continuous flows of data packets for web browsing and file transfer

    12. Wireless Generations 1G: Analog (1970s-1980s) AMPS, TACS, NMT Voice 2G: Digital (1990s) GSM, TDMA, CDMA Mostly for voice, although GSM uses SMS text messaging 2G+: Digital (ongoing) GPRS, EDGE, IS-95B, HDR Packet data enhancements, improved data rates 3G: now UMTS, CDMA2000 High-speed multimedia data and voice Goals of global roaming and high-quality audio and video

    13. Acknowledgements http://www.iec.org/online/tutorials/gsm/ http://www.iec.org/online/tutorials/tdma/ http://www.techweb.com http://www.gsmworld.com http://www.ericsson.com/technology/tech_articles/WCDMA.shtml

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