Development of Wireless Networks

Transcription

1 Development of Wireless Networks

2 Cellular Revolution In 1990 mobile phone users populate 11 million. By 2004 the figure will become 1 billion Phones are most obvious sign of the success of wireless technology. Handsets are getting smaller, lighter, yet more powerful Service prices are dropping Service quality are being improved The applications have expanded from voice application to Internet applications 2

3 Problems with Wireless Networks Operates in a less controlled environment, so is more susceptible to interference, signal loss, noise, and eavesdropping. Generally, wireless facilities have lower data rates than guided facilities. Frequencies can be more easily reused with guided media than with wireless media. 3

4 Mobile Telephony First Generation (AMPS) analog voice communication using frequency modulation. Second Generation (GSM) digital techniques and time-division multiple access (TDMA) or code-division multiple access (CDMA) Third Generation evolving from second-generation wireless systems will integrate services into one set of standards. 4

5 Advanced Mobile Phone Service 5

6 AMPS Components Mobile Units contains a modem that can switch between many frequencies 3 identification numbers: electronic serial number, system ID number, mobile ID number Base Transceiver full-duplex communication with the mobile Mobile Switching Center 6

7 AMPS Spectral allocation in North America Two 25-MHz bands are allocated to AMPS: MHz from the base station to the mobile unit, MHz from the mobile unit to the base station The bandwidth has been split into two 12.5 MHz in each direction for two operators to compete each other. A 12.5 MHz channel allows 416 channels. Spatial allocation frequencies are assigned to each cell Depends on the pattern of cells. Each cell may have N/n frequencies, where N = 395, and n = 7 is the smallest pattern Original cells are km in size. 1.5-km is the practical minimum size. Too small size will have more frequency change. Transferring from one base transceiver to another is called handoff. 7

8 A Seven-Cell Cluster Frequency Reuse Space-division multiplexing (SDM): using the same spectral band in two physically disjoint places 8

9 Global System for Mobile Communication Developed to provide common 2nd-generation technology for Europe 200 million customers worldwide, almost 5 million in the North America GSM transmission is encrypted, using stream cipher A5 for transmissions from subscriber to transceiver. A3 is used for authentication. It uses subscriber identity module (SIM) in the form of smart card. Supports both data and image services based on ISDN model, with rates up to 9.6 kbps Spectral allocation: 25 MHz for base transmission ( MHz), 25 MHz for mobile transmission ( MHz) 9

10 GSM Layout HLR, VLR, AuC, EIR Mobile Service Switching Center (MSSC) HLR: home location register database VLR: visitor location register AuC: authentication center EIR: equipment identity register database 10

11 Multiple Access Four ways to divide the spectrum among active users frequency-division multiplexing (FDM) time-division multiplexing (TDM) code-division multiplexing (CDM) space-division multiplexing (SDM) 11

12 Choice of Access Methods A random access scheme using FDM, TDM, SDM or CDM to dynamically assign sub-channels to users is called random access method, e.g. FDMA, TDMA, CDMA, SDMA. FDM, used in 1st generation systems, wastes spectrum Debate over TDMA vs CDMA for 2nd generation TDMA advocates argue there is more successful experience with TDMA. CDMA proponents argue that CDMA offers additional features as well, such as increased range. TDMA systems have achieved an early lead in actual implementations CDMA seems to be the access method of choice for third-generation systems 12

13 Third Generation Systems IMT-2000 defined the 3rd-generation capacities: voice quality, 144kbps data rate for high speed mobile, 384 kbps data rate for low speed mobile, Mbps office use, packet/circuit switching, Internet interface, more efficiency of spectrum use, more mobile equipment support, flexible for new services and technologies. Intended to provide high speed wireless communications for multimedia, data, and video Personal communications services (PCSs) and personal communication networks (PCNs) are objectives for third-generation wireless. Planned technology is digital using TDMA or CDMA to provide efficient spectrum use and high capacity PCS handsets are designed to be low power, small and light Future public land mobile telecommunications systems (FPLMTS) includes both terrestrial and satellite-based services 13

14 Wireless Application Protocol (WAP) A universal, open standard developed by WAP forum to provide services: wireless phone, pager, personal digital assistants, Internet, web, etc. It is designed to work with all wireless network technologies It is based on Internet standards: IP, XML, HTML and http WAP specification includes: WWW Programming Model Wireless markup language (WML) Specification of a small browser A lightweight communications protocol stack A framework for wireless telephony applications (WTAs) 14

15 Wireless Telephony Applications 15

16 Satellite Orbits 16

17 Types of LEOs Little LEOs: Intended to work at communication frequencies below1 GHz using no more than 5 MHz of bandwidth and supporting data rates up to 10 kbps Big LEOs: Work at frequencies above 1 GHz and supporting data rates up to a few megabits per second 17

18 Iridium: A 3 rd Generation Satellite System 66 small LEOs Services: voice, paging, wireless phone Proposed in 1987 Put in service 1999 Named for the element iridium because 77 electrons match the number of satellites Transmissions between satellites $5 billion to implement Motorola 9505 terminal for Iridium weighs about 13 oz. (370g) 2.4 hour talk time, 24 hours standby time Using L band ( MHz) for ground communications and GHz between satellites 18

19 Cellular Revolution In 1990 mobile phone users populate 11 million. By 2004 the figure will become 1 billion Phones are most obvious sign of the success of wireless technology. Handsets are getting smaller, lighter, yet more powerful Service prices are dropping Service quality are being improved The applications have expanded from voice application to Internet applications 19