CELLULAR TELEPHONE CONCEPTS

Opiz, Claris Mae M.BS ECE 5-1

Outline

• Introduction• Mobile Telephone Service• Evolution of Cellular Telephone• Cellular Telephone• Frequency Reuse• Interference• Cell Splitting, Sectoring, Segmentation, and

Dualization• Cellular System Topology• Cellular Telephone Network Components• Cellular Telephone Call Processing

Began in 1940s and called MTS (mobile telephone systems or sometimes manual telephone systems).

The MTS system was comparable to a party line, as all subscriber with their mobile telephones turned on could hear any conversation.

Use a push- to- talk (PPT) switch to activate the transceiver.

MTS numbers were generally five digits long and could not be accessed directly through the public switched telephone network (PSTN).

Mobile Telephone Service

Was introduced in 1964, used several carrier frequencies and could handle several simultaneous mobile conversations at the same time.

Like MTS, its base station transmitters outputted powers in the 100- W to 200- W range and mobile units transmitted between 5W and 25W.

Improved Mobile Telephone Service

High costLimited availability Narrow frequency allocation

Why early MTS were not widely used?

Mobile- any radio transmitter, receiver, or transceiver that could be moved while in operation.

Portable- a relatively small radio unit that was handheld, battery powered and easily carried by a person moving at walking speed.

Mobile Telephone- is a one- to- one system that permits two- way simultaneous transmission and, for privacy, each telephone is assigned a unique telephone number.

Terminology

Similar to two- way mobile radio in that most communications occurs between base stations and mobile units.

Communicate directly with base station that are fixed- position transceivers with relatively high- power transmitters and receivers.

Cellular Telephone

June 17, 1946, AT&T and Southwestern Bell introduced the first American commercial mobile radio- telephone service to private customers.

In 1947, AT&T introduced a radio- telephone service they called highway service between New York and Boston.

Evolution of Cellular Telephone

Date Event

June 17, 1946

AT&T and Southwestern Bell introduced the first American commercial mobile radio- telephone service to private customers

1947 AT&T introduced a radio- telephone service they called highway service between New York and Boston

1940’s The first half duplex, PPT FM mobile telephone was introduced

1950’s FCC doubled the number of mobile telephone channels

1960 AT&T introduced direct- dialing, full-duplex mobile telephone service

1968 AT&T proposed the concept of cellular mobile system

1966 Unveiled the mobile shoe phone

1974 FCC allocated additional 40MHz bandwidth for cellular telephone

Evolution of Cellular Telephone

Date Event

1975 FCC granted AT&T the first license to operate a developmental cellular telephone service in Chicago

1976 Bell Mobile Phone service for New York City offered only 12 channels that serve 543 subscribers

1991 First digital cellular services were introduced in several major U.S. cities

Nov. 17, 1998 Subsidiary of Motorola Corporation implemented a satellite- based wireless personal communication satellite system called Iridium

By subdividing a relatively large geographic market area, called coverage zone, into small sections, called cells, the concept of frequency reuse could be employed to dramatically increase the capacity of mobile telephone channel.

This system allow a large number of users to share the limited number of common- usage radio channels available in the region

Cellular Telephone

With the cellular concept, each area is further divided into hexagonal- shaped cells that fit together to form a honeycomb pattern.

Physical size of a cell, varies, depending on the user density and patterns.

Fundamental Concepts of Cellular Telephone

The hexagon shape was chosen because it provides the most effective transmission by approximating a circular path while eliminating the gaps inherently present between adjacent circles.

Why Hexagon?

Microcells are used most often in high- density areas such as found in large cities and inside buildings.

Fundamental Concepts of Cellular Telephone

The smallest cells typically have a radius of 1500 feet or less with base station transmit powers between 0.1W and 1W.

Microcells

In well- shielded area or areas with high levels of interference picocells are used because cellular radio signals are too weak to provide reliable communications indoors.

Fundamental Concepts of Cellular Telephone

A picocell is a small cellular basestation typically covering a small area, such as in-building (offices, shopping malls, train stations, etc.), or more recently in-aircraft.

Picocell

It is the process in which the same set of frequencies can be allocated to more than one cell are separated by sufficient distance

Cluster- has seven cells in it, and all cells are assigned to the same number of full- duplex cellular telephone channels.

Frequency Reuse

F = GN

F= number of full- duplex cellular channels available in a cluster

G= number of channels in a cellN= number of cells in a cluster

Total number of cellular channels in a cluster

C = mGN= mF

where:C= total channel capacity in a given aream= number of cluster in a given areaG= number of channels in a cellN= number of cells in a cluster

note: when N( cluster size) is reduced and the cell is held constant, more clusters are required to cover given area and the total channel capacity increases

Total number of cellular channels when cluster is duplicated m times

The number of simultaneous users is generally four, but in densely populated area, that number may be significantly higher.

Frequency Reuse Factor (FRF)

FRF = N/C

Where: FRF= frequency reuse factor (unitless)N= total number of full- duplex channels in an

areaC= total number of full- duplex channels in a cell

Is a form of external noise and, as the name implies, means “to disturb or detract from”.

There are two major kinds of interferences produced within a cellular telephone system:- Co- channel Interference- Adjacent- channel Interference

Interference

Interference between two cells using the same set of frequencies.

It cannot be reduced by simply increasing transmit powers.

To reduce co- channel interference, a certain minimum distance must separate co- channels.

Co- channel Interference

It occurs when transmissions from the adjacent channels interfere with each other.

It is most prevalent when an adjacent channel is transmitting very close to a mobile unit’s receiver at the same time the mobile unit is trying to receive transmissions from the base station on an adjacent frequency.

Also called near- far effect.

Adjacent- Channel Interference

Cell Splitting, Sectoring, Segmentation, and Dualization

It is when the area of a cell, or independent component coverage areas of a cellular system, is further, divided, thus creating more cell areas.

Cell splitting is the resizing or redistribution of cell areas.

Its purpose is to increase the channel capacity and improve he availability and reliability of a cellular telephone network.

Cell Splitting

It is the decreasing the co- channel interference while increasing the capacity by using directional antennas.

By sectoring you gain better control of interference issues. That is, you're transmitting in one direction instead of broadcasting all around, like with an omnidirectional antenna, so you can tighten up your frequency re-use

Sectoring

- These are techniques

incorporated when additional cells

are required within the reuse

distance.

Segmentation and Dualization

Segmentation is a means of avoiding co-channel interference, although lowers the capacity of a cell by enabling he reuse inside the reuse distance.

Dualization is a means of avoiding full- cell splitting where the entire area would otherwise need to be segmented into smaller cells.

Segmentation and Dualization

Cellular System Topology

Roaming is when a mobile unit moves from one cell to another.

It is a general term referring to the extension of connectivity service in a location that is different from the home location where the service was registered.

Roaming is divided into "SIM-based roaming" and "Username/password-based roaming", whereby the technical term "roaming" also encompasses roaming between networks of different network standards.

Roaming

SIM-based (roaming): GSM subscriber roams onto a Public WLAN operated by:◦ their GSM Operator, or◦ another Operator who has a roaming agreement

with their GSM Operator. Username/password based roaming:

GSM subscriber roams onto a Public WLAN operated by:◦ their GSM Operator, or◦ another Operator who has a roaming agreement

with their GSM Operator.

Roaming

It is the transfer of a mobile unit from one base station’s control to another base station’s control.

It should be performed as infrequently as possible and be completely transparent to the subscriber.

It is consists of four stages: (1) initiation (2) resource reservation (3)execution and (4) completion.

Handoffs

1. Initiation. Either the mobile unit or the network determines the need for a handoff and initiates the necessary network procedures.

2. Resource reservation. Appropriate network procedures reserve the resources needed to support the handoff.

3. Execution. The actual transfer of control of one base station from another base station takes place.

4. Completion. Unnecessary network resources are relinquished and made available to other mobile units.

Four Stages of Handoff

A hard handover is one in which the channel in the source cell is released and only then the channel in the target cell is engaged.

A soft handover is one in which the channel in the source cell is retained and used for a while in parallel with the channel in the target cell. In this case the connection to the target is established before the connection to the source is broken, hence this handovers is called make-before-break. The interval, during which the two connections are used in parallel, may be brief or substantial.

Types of Handover/ Handoffs

This standard allow mobile units to roam

and to perform handoffs of calls already

in progress when a mobile unit moves

from one cellular system into another

without subscriber intervention.

IS- 41 Standard

Cellular Telephone Network

Components

It is a digital telephone exchange located in the MTSO that is the heart of cellular telephone system.

Performs two functions:◦ Controls switching between the public wireline

telephone network and the cell- site base stations for wireline-to-mobile, mobile-to-wireline, and mobile-to-mobile.

◦ Process data received from the cell- site controllers.

Electronic Switching Centers

This manage each of the radio transmitter

and receiver on and off, injects data onto

the control and voice channels, and

performs diagnostic test on cell- site

equipments

Cell- Site Controllers

It is used with cellular telephone system voice channels, can be either narrow band FM for analog systems or either PSK or QAM for digital systems with an effective audio-frequency band comparable to a standard telephone circuit.

It modulates a signal being transmitted and demodulates a signal being received.

Radio Tranceivers

System uses four- wire leased lines to connect switching centers to cell site and to public telephone network.

One dedicated four- wire trunk circuit for each of the cell’s voice channels.

System Interconnects

Portable units have a lower output power, have a less efficient antenna and operate exclusively on batteries.

Mobile phone consists of a control unit, multiple- frequency radio transceiver, a logic unit and mobile antenna.

Mobile and Portable Telephone Units

This protocols are made to govern the way telephone calls are established and disconnected.

A communications protocol is a formal description of digital message formats and the rules for exchanging those messages in or between computing systems and in telecommunications. Protocols may include signaling, authentication and error detection and correction capabilities.

Communications Protocol

Call Procedures