WLL(Wireless Local Loop)• It is a system that connects subscribers to local telephone

station wirelessly.

• Multipoint service is commonly used for WLL(wireless local loop), which serve a predetermined set of stationary subscribers (home / office),located within a certain radius, whose subscriber units (i.e. voice phone, modem) are equipped with a small receiving antenna oriented towards the transmitter.

• Classic WLL systems use 2.4 GHz band & have coverage radius of 8-10 kms .

Wireless with Limited Mobility(WLL-M)

• Similar to classic WLL.

• Supports placement of subscribers unit anywhere within the coverage radius , without the need for readjustment of service parameters affecting the radio link (RL) between the transmitting antenna & subscriber unit.

Fully Mobile Wireless Phones

• Supports wireless telephones which are fully mobile i.e. they can maintain their radio link with the transmitter while moving (exposed or inside a vehicle ).

• Enables a “mobile” to move from coverage area of one transmitter to an adjacent one , without “dropping a call in progress”.

• If “Roaming & Registration” are provided ,the phone may be used in different cities & countries , on wireless networks operated by different service providers.

Generations of Mobile Phone Technologies

First Generation (Analog voice)• The Advanced Mobile Phone System (AMPS) was first

developed in 1982 (Motorola).• Divides geographic region into areas ( later called “cells”).• Each area is typically 10 – 20 km across.• Each cell uses some set of frequencies, not used by any of

its immediate neighbor cells, in order to reduce / prevent interference.

• Each cell supports approximately 45 simultaneous voice calls.

• At the center of each cell is a base – station (BS) consisting of transmitter and receiver, with which all mobiles in the cell are connected via radio link .

• For each mobile , the RL consist of 2 simplex channels (transmitter + Receiver).

One for forward Communication(BS to MS) One for Reverse Communication(MS to BS)• In AMPS , each simplex channel is 30 KHz wide.• AMPS supports total of 832 transmit channels in 824 – 849 MHz

range(Reverse Communication). 869 - 894 MHz for Forward Communication• AMPS classifies channels into 4 types ,based on the purpose of each

channel & direction of communication:

a) Control (base to phone) – used to manage the system. b) Paging (base to phone) – used to alert mobiles about incoming

calls. c) Access (bidirectional) – for setting up calls & assigning data

channels. d) Data (bidirectional) – for voice transmission.

(Freq DivisionDuplex)

AMPS (Advance Mobile Phone System):

Frequency Reuse Factor: A frequency reuse pattern is a configuration of N cells, N being the reuse factor, in which each cell uses a unique set of frequencies. When the pattern is repeated , the frequencies can be reused.

B

A

ED

C

F

G

B

A

ED

C

F

G

B

A

ED

C

F

G Frequency Reuse: Frequencies are not reused in a group of 7 adjacent cells

FDMA (Frequency Div Multiple Access): one frequencyper user channel

Advanced Mobile Phone System

(a) Frequencies are not reused in adjacent cells.(b) To add more users, smaller cells can be used.

Second Generation (Digital voice ,Basic data services)

Second Generation

IS-136 GSM IS-95 D-AMPS CDMA

• IS-136 - Interim Standard 136• GSM – Global System for Mobile Communication• CDMA – Code Division Multiple Access

D-AMPS

• The Product of the evolution of the analog AMPS into digital system is digital AMPS(D-AMPS) which uses additional 30 KHz channels , but these are located in the 1850 – 1990 MHz range & employ digital transmission.

• D-AMPS uses the same bands and channels as AMPS.

• D-AMPS mobiles digitize and compress human voice using a vocoder ( voice coder) that can transmit voice at 8 kbps .

• As a result ,D-AMPS supports up to 7 users per 30 KHz channel pair by using TDM (in addition to FDM),thereby supporting more simultaneous calls per cell.

• D-AMPS has a frequency reuse factor of 7.• Voice quality is superior since digital transmission is

used.• D-AMPS is still widely used in US & Japan.

GSM• A European standard that was developed to provide a

common 2g technology for all Europe.• Bands: GSM uses two bands for duplex communication.• Each band is 25MHz in width, shifted towards 900MHz.• Each band is divided into 124 channels of 200 KHz

separated by Guard Bands. • Reverse Band : 890 MHz – 915 MHz• Forward band : 935 MHz – 960 MHz• GSM allows a reuse factor as low as 3.

IS-95• Dominant 2G standard in North America.• Based on CDMA and DSSS (Direct Sequence Spread

Spectrum).• Bands and Channels: Two bands for duplex communication.• Bands can be traditional ISM 800 MHz or ISM 1900 MHz• Each band is divided into 20 channels of 1.228 MHz separated

by guard bands.• Each IS-95 channel is equivalent to 41 AMPS channels(41 * 30

KHz = 1.23 MHz).• The frequency reuse factor is normally one because the

interferences from neighboring cells cannot affect CDMA or DSSS transmission.

• CDMA allows reuse of same spectrum over all cells.

Third Generation• The 3G concept started in 1992,when ITU issued a blueprint called

the Internet Mobile Communication 2000 (IMT-2000). The blueprint defines some criteria for the 3G technology as outlined below:

1) Voice quality comparable to that of the existing public telephone network.

2) Date rate of 144 kbps in a moving vehicle (car), 384 kbps for pedestrians , 2 Mbps for stationary user.

3) Support for packet –switched & circuit switched data services.4) A band of 2 GHz.5) Bandwidths of 2 MHz .6) Interface to the internet. The main goal of 3G cellular telephony is to provide universal

personal communication.

• At present there are two main competing technologies being deployed to provide 3G services i.e. W-CDMA(aka UMTS) proposed by Ericsson and CDMA-2000(evolved from CdmaOne) proposed by Qualcomm

• CDMA-2000 evolved from IS-95, while W-CDMA evolved from GSM .

• Networks based on interim (2.5 G) technologies have been also deployed.E,g EDGE,GPRS,etc.

• UMTS – Universal Mobile Telecommunications System• GPRS – General Packet Radio Service• EDGE – Enhanced Data Rates for GSM Evolution.

• LTE Phones(Long Term Evolution ) use OFDM(Orthogonal Frequency Division Multiplexing ) – 4G service.