Published on March 5, 2014
By:- Mustahid Ali
Presentational Outline Definition of WLL Two important issue Capacity and Efficiency The Future Technologies Wireless Standards Disadvantages of WLL Scope of WLL
What is WLL ? “In telephone network, a Wireless Local Loop is a generic term for an access system that uses a wireless link to connect subscriber to their local exchange in place of conventional copper cable. Using a wireless link shortens the construction period and also reduces installation and operating cost.”
Difference between WLL and mobile system . Mobile system - connect people on the move - universal coverage - moderate voice quality - Traffic per subscriber is supposed to be not very high.
Difference between WLL and mobile System Wireless in Local Loop - Serve subscribers at homes or offices. -Voice quality must be high. -Long conversation facility -High Traffic support.
Efficiency Consideration Depends on use and reuse of spectrum which is governed by the following : channel pay load signaling overhead modulation efficiency cell-radius choice of multiple access interference reduction techniques
Channel Pay Load Higher bit rate pay load large frequency resources Voice Communication required lower bit rate voice codec
Signaling Overhead Used in setting up, monitoring and tearing down of a call Carried out between subscriber and base stations More sophisticated system more signaling requirement It is an overhead
Modulation Efficiency Direct bearing on efficient use of spectrum QAM, QPSK, MSK techniques are used Efficient techniques are expensive
Cell Radius Subscriber Density is N – Channels Available e – Traffic / Subscriber in Erlang r – Radius of a cell
FTDMA - Frequency signal is divided into frequency channels - Channels are assigned to users on demand - Used for both analog and digital signals TDMA - Careers used for transmission of multiple time multiplexed channels - provided batter reuse factor for digital signal
CDMA - Each bit is uniquely coded - Receiver use decoder to separate data - Interference is very small MC-TDMA - Use dynamic channel selection - Frame is divide into time slots
Sectorization Voice Activity Detection Frequency Hopping
Capacity of WLL System Capacity = C = Number of Subscriber/ sq. km. is
S – Total spectrum available M – Multi Access Efficiency + Modulation Efficiency + Effect of Overhead R – Reuse Efficiency x – Payload in bps Required / Subscriber Te – Trunking Efficiency e– Erlang Traffic / Subscriber ns – Number of Non Overlapping Sector used per Cell r – radius in KM. for each Cell
Space-Time processing - Smart Antenna Technology - Transmit Diversity Schemes Turbo Codes Multi User Detection
Wireless Standards First Generation Standards -Promised Wide – Scale Mobile communication -AMPS(USA), NTT (Japan), NMT (Europe) Second Generation Standards -Marked as late eighties and early nineties -Technology used TDMA,GSM -Wireless Standards Used AMPS,IS-95,DECT Third Generation Standards -DECT Evaluation towards third Generation
Disadvantages Relatively new technology Network capacity needs improvement Has yet to be fully implemented to maximize utilization and economy
Developed vs. Developing Developed: Wire line service Firmly established, cellular penetration is relatively high Incumbent operator would use it to install 2nd, 3rd lines, coverage to rural areas 2nd or 3rd competitive operator deploy it for fast & cost effective deployment Quick way to establish market presence cellular complement to their offerings
Developed vs. Developing Developing Quick & easy to deploy in countries with little copper line service, so as to accommodate people on enormous waiting lists for basic service Low maintenance costs Allows more competition in provider market
Potential Without the need to have a physical link in the last mile, WLL offers us a variety of applications that will further enhance our capability to communicate and transfer information
Potential Suitable for the deployment of communication facilities in provinces where tele-density is low and geographical terrain is unsuitable for the setting-up of infrastructure
Abbreviation Used FDMA - Frequency Division Multiple Access TDMA – Time Division Multiple Access CDMA – Code Division Multiple Access MC-TDMA – Multi Career TDMA QAM – Quadrature Amplitude Modulation QPSK - Quadrature Phase Shift Keying MSK – Minimum Shift Keying AMPS – Advance Mobile Phone Service GSM – Global Service Mobile communication DECT – Digital European Cordless Telephone
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