Which telecommunication service is better for you?
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Presentation on theme: "Which telecommunication service is better for you?"— Presentation transcript:
1 Which telecommunication service is better for you? CDMA/FDMA/TDMAWhich telecommunication service is better for you?
2 International Cocktail Party FDMA – Large room divided up into small rooms. Each pair of people takes turns speaking.TDMA – Large room divided up into small rooms. Three pairs of people per room, however, each pair gets 20 seconds to speak.CDMA – No small rooms. Everyone is speaking in different languages. If voice volume is minimized, the number of people is maximized.
3 Definitions TDMA – Time Division Multiple Access FDMA – Frequency Division Multiple AccessCDMA – Code Division Multiple Access
4 General Specification of TDMA Rx: MHz Tx: MHz832 Channels spaced 30kHz apart (3 users/channel)DQPSK modulation scheme48.6kbps bit rateInterim Standard (IS) – 54Digital AMPS (Advanced Mobile Phone System)Uses Time Division Duplexing (TDD) usually
6 Advantages of TDMA Flexible bit rate No frequency guard band required No need for precise narrowband filtersEasy for mobile or base stations to initiate and execute hands offExtended battery lifeTDMA installations offer savings in base station equipment, space and maintenanceThe most cost-effective technology for upgrading a current analog system to digital
7 Disadvantages to using TDMA Requires network-wide timing synchronizationRequires signal processing fro matched filtering and correlation detectionDemands high peak power on uplink in transient modeMultipath distortion
8 General Specification of FDMA Rx: MHz Tx: MHz832 Channels spaced 30kHz apart (3 users/channel)DQPSK modulation scheme48.6kbps bit rateUsed in analog cellular phone systems (i.e. AMPS)Uses Frequency Division Duplexing (FDD)ISI (Intersymbol Interference) is low
9 FDMA Operation Number of FDMA Channels In the U.S. each cellular carrier is allocated 416 channels where:
10 Advantages of FDMA If channel is not in use, it sits idle Channel bandwidth is relatively narrow (30kHz)Simple algorithmically, and from a hardware standpointFairly efficient when the number of stations is small and the traffic is uniformly constantCapacity increase can be obtained by reducing the information bit rate and using efficient digital codeNo need for network timingNo restriction regarding the type of baseband or type of modulation
11 Disadvantages to using FDMA The presence of guard bandsRequires right RF filtering to minimize adjacent channel interferenceMaximum bit rate per channel is fixedSmall inhibiting flexibility in bit rate capabilityDoes not differ significantly from analog system
12 General Specification of CDMA Rx: MHz Tx: MHz20 Channels spaced 1250kHz apart (798 users/channel)QPSK/(Offset) OQPSK modulation scheme1.2288Mbps bit rateIS-95 standardOperates at both 800 and 1900 MHz frequency bands
14 Advantages of CDMAMany users of CDMA use the same frequency, TDD or FDD may be usedMultipath fading may be substantially reduced because of large signal bandwidthNo absolute limit on the number of usersEasy addition of more usersImpossible for hackers to decipher the code sentBetter signal qualityNo sense of handoff when changing cells
15 Disadvantages to using CDMA As the number of users increases, the overall quality of service decreasesSelf-jammingNear- Far- problem arises