7/29/2019 49429286-Cellular

1/52

1

by

Lotis P. Patunob, M.Eng., PECE

7/29/2019 49429286-Cellular

2/52

2

1940s MTSs (Mobile Telephone Systems or

Manual Telephone systems):

all calls were handled by an operator, use FM-use a single carrier frequency in the 35 MHz to

45 MHz range for both the mobile unit and base

station

- half duplex operation,-120 kHz bandwidth per channel

-only one conversation could take place at a time

-could not be accessed directly through the PSTN

with five digit long numbers.

Cellular Telephone Service

7/29/2019 49429286-Cellular

3/52

3

1964 IMTS (Improved Mobile TelephoneSystems):

use several carrier frequencies and could,

therefore, handle several simultaneous mobile

conversations at the same time

- high output power between 13 W and 30 W and

a range of 25 mile radius

-with assigned regular PSTN number so could bereach by dialing the PSTN directly, eliminating

the need for an operator

-transmit power a channel bandwidth of 30 kHZ

increasing the number of channels, .

7/29/2019 49429286-Cellular

4/52

4

1983 AMPS (Advanced Mobile Phone System)

the first U.S. cellular telephone system by

AT&T with 666 30 kHz half-duplex mobile

telephone channels, was based on analog radio

technologies and has been phased out.

Cellular Telephone Service

Disadvantages of early mobile telephone

systems: High cost, limited availability, and

narrow frequency allocation.

7/29/2019 49429286-Cellular

5/52

5

AMPS SpecificationsParameter AMPS

Frequency Band:

Forward Link

Reverse Link

869 894 MHz

824 849 MHz

Channel Spacing 30 kHzSpacing between Transmission and Reception 45 MHz

Number of Channels 832

Coverage Radius 2 20 km

Audio Signal

Type of ModulationFrequency Deviation

FM+/- 12 khz

Control Signal

Type of Modulation

Frequency Deviation

FSK

+/- 8 khz

Data Transmission Rate 10 kbps

7/29/2019 49429286-Cellular

6/52

6

Coverage zone a large geographic market

area.

Cells the small sections of the large geographic

area. It is defined by its physical size, and thesize of its population.

a. Macrocells large cells typically have a

radius 1 mile and 15 miles with base station

transmit power between 1 W and 6 W.b. Microcells the smallest cells typically

have a radius of 1500 feet or less with base

station transmit power between 0.1 W & 1 W

Fundamental Concepts of Cellular Phone

7/29/2019 49429286-Cellular

7/52

7

Honeycomb the pattern formed by thehexagonal- shaped cells.

Picocells very small cells used indoor.

7/29/2019 49429286-Cellular

8/52

8

7/29/2019 49429286-Cellular

9/52

9

Different locations of base station transmitters:

1. Center-excited cell

Fundamental Concepts of Cellular Phone

2. Corner-

excited

cell

3. Edge-excited cell

7/29/2019 49429286-Cellular

10/52

10

1. 800 900 MHz original frequency

assignment; previously occupied by UHF TV

channels 68 through 83

2. 824 and 849 MHz reserved for uplink

3. 869 and 849 MHz are for downlink

Both 2) and 3) are divided into 832 channels with30 kHz bandwidth.

4. 30 kHz, 200 kHz, 1.25 MHz the different

bandwidths used in different ways by different

companies in different locations.5. 700 to 800 Mhz abandoned UHF TV

channels for digital high-definition TV in 2009.

6. 1700 to 1750 Mhz from military

7. 1900 to 2300 Mhz available for 3G.

Frequency Allocation:

7/29/2019 49429286-Cellular

11/52

11

Types:

1. Frequency reuse

2. FDMA - the spectrum is divided into manysmaller channels.

3. TDMAmultiple users use different time slots

4. CDMA with unique coding, up to 64

subscribers can share a 1.25 Mhz channel.5. SDMA it uses highly directional antennas to

pinpoint users and reject others on the same

frequency.

Multiple Access refers how the subscribersare allocated to the assigned frequency

spectrum.

7/29/2019 49429286-Cellular

12/52

12

Frequency reuse the

process in which the

same set of

frequencies

(channels) can be

allocated to more

than one cell,provided the cells are

separated by

sufficient distance.

Clustergroups of cells

Frequency Reuse

7/29/2019 49429286-Cellular

13/52

13

The number of channels available in a cluster, F:

F = GN

The total channel capacity in a given area, C:

C = mF

Where:G = # of channels in a cell

N = # of cells in a cluster = 3, 7, or 12

m = # of clusters in a given area

Frequency Reuse

7/29/2019 49429286-Cellular

14/52

14

If the cluster size is reduced and cell size held

constant, more clusters are required to cover a

given area, and the total channel capacity

increases. Therefore the channel capacity isdirectly proportional to the number of times the

cluster is duplicated.

The frequency reuse factor of a cellular

telephone system is inversely proportional to thenumber of cells in a cluster. Therefore, each cell

within a cluster is assigned 1/Nth of the total

available channels in a cluster.

Note:

7/29/2019 49429286-Cellular

15/52

15

Determine the number of channels per cluster

and the total channel capacity for a cellular

telephone area comprised or 10 clusters withseven cells in each cluster and 10 channels in

each cell.

Example:

F = 10(7) channels per cluster

C = 10(7)(10) total channels

7/29/2019 49429286-Cellular

16/52

16

Frequency Reuse Factor, FRF: - the number of

subscribers who can use the same set of

frequencies in nonadjacent cells at the sametime in a small area like city is generally 4.

FRF = N/C

Where: N = total number of full-duplexchannels in an area

C = total number of full-duplex

channels in a cell

Frequency Reuse

7/29/2019 49429286-Cellular

17/52

17

Note: Splitting the cells (each with its own base

station) effectively allows more calls to be

handled by the system, provided the cells do

not become too small. If < 1500 feet indiameter, interference will occur between

adjacent cells.

The relationship between frequency reuseand cluster size determines how cellular

telephone systems can be rescaled when

subscriber density increases.

7/29/2019 49429286-Cellular

18/52

18

Cells use a hexagonal shape, which provides

exactly six equidistant neighboring cell are

separated by multiples of 60. Therefore, a

limited number of cluster sizes and cell

layouts is possible. To connect cells without

gaps in between (tesselate), the geometry of a

hexagon is such that the # of cells per cluster

can have only values that satisfy the equation

Where: i and j = nonnegative integers

Frequency Reuse

7/29/2019 49429286-Cellular

19/52

19

The process of finding the tier with the

nearest co channel cells (first tier):

1. Move i cells throughthe center of successive

cells.

2. Turn 60 in a counter-

clockwise direction.

3. Move j cells forward

through the center of

successive cells

Frequency Reuse

7/29/2019 49429286-Cellular

20/52

20

Determine the number of cells in a cluster and

locate the first tier co-channel cells for the

following values: j = 2 and i = 3.

Example:

There six nearest first-tier 1 co-channel cells

for cell A.

7/29/2019 49429286-Cellular

21/52

21

Two major kinds of interferences produced

within a cellular telephone system:

1. Co-channel interference - the interferencethat occurs between co-channel cells (two cells

using the same set of frequencies).

Note: To reduce co-channel interference, acertain minimum distance must separate co-

channels. It cant be reduce by simply increasing

transmit powers.

Interference

7/29/2019 49429286-Cellular

22/52

22

Note:

Interference

between cells isproportional not

to the distance

between the two

cells but rather tothe ratio of the

distance to the

cells radius.

Interference

7/29/2019 49429286-Cellular

23/52

23

Since a cells radius is proportional to transmitpower, more radio channels can be added to a

system by either:

1. Decreasing the transmit power per cell.

2. Making cells smaller.3. Filling vacated coverage areas with new cells.

Note:

In a cellular system where all cells areapproximately the same size, co-channel

interference is dependent on the radius (R) of

the cells and the distance to the center of the

nearest co-channel cell (D).

7/29/2019 49429286-Cellular

24/52

24

Co-channel reuse ratio,Q = D/R increasing the

D/R ratio increases the

spatial separation

between co-channel cellsrelative to the coverage

distance.

Note: The smaller the value of Q, the larger thechannel capacity since the cluster size is also

smaller. However, a large value of Q improves the

co-channel interference and, thus, the overall

transmission quality.

7/29/2019 49429286-Cellular

25/52

25

2. Adjacent-channel interference occurswhen transmissions from adjacent channels

(channels next to one another in the frequencydomain) interfere with each other.

- results from imperfect filters in receivers that

allow nearby frequencies to enter the receiver.

Near-far effect: Adjacent-channel interference is

most prevalent when an adjacent channel is

transmitting very close to a mobile units

receiver at the same time the mobile unit istrying to receive transmission from the base

station on an adjacent frequency.

- most prevalent when a mobile unit is receiving

a weak signal from the base station.

7/29/2019 49429286-Cellular

26/52

26

7/29/2019 49429286-Cellular

27/52

27

Two methods of increasing the capacity of acellular system: 1. Cell Splitting

2. Sectoring

1. Cell Splitting when the area of a cell, or

independent component coverage areas of a

cellular system, is further divided, thus creating

more cell areas.

- occurs when traffic levels in a cell reach the

point where channel availability is jeopardized.

- the process of subdividing highly congested

cells into smaller cells each with their own base

station and set of channel frequencies.

7/29/2019 49429286-Cellular

28/52

28

With cell splitting, a large number of low-power

transmitters take over an area previously served

by a single, higher-powered transmitter.

Note: Splitting cell areas

creates new cells,

providing an increase inthe degree of frequency

reuse, thus increasing

the channel capacity of

a cellular network.

If the radius of a cell is divided in half, four

times as many smaller cells could be created to

provide service to the same coverage area.

7/29/2019 49429286-Cellular

29/52

29

Maximum traffic load the point when a cell

reaches maximum capacity occurs when the

number of subscribers wishing to place a call atany given time equals the number of channels in

the cell.

Blocking - if a new call is initiated in an area

where all the channels are in use.

More Base station transfers the major

drawback of cell splitting, more handoffs per call

and a higher processing load per subscriber. Ithas been proven that a reduction of a cell radius

by a factor of 4 produces a 10-fold increase in the

handoff rate per subscriber.

7/29/2019 49429286-Cellular

30/52

30

Example:

Determine

a. The channel capacityfor a cellular telephone

area comprised of

seven macrocells with

10 channels per cell.

b. Channel capacity if

each macrocell is split

into four minicells.

c. Channel capacity if

each minicell is further

split into four

microcells.

Solution:

7/29/2019 49429286-Cellular

31/52

31

2. Sectoring another means of increasing the

channel capacity of a cellular telephone system is

to decrease the D/R ratio while maintaining the

same cell radius.

- capacity improvement can be achieved by

reducing the number of cells in a cluster, thus

increasing the frequency reuse. To accomplish

this, the relative interference must be reduced

without decreasing transmit power.

- co-channel interference can be decreased byreplacing a single omnidirectional antenna with

several directional antennas, each radiating

within a smaller area.

7/29/2019 49429286-Cellular

32/52

32

Sectors the smaller areas.

Sectoring - decreasing co-channel interference

while increasing capacity by using directional

antennas.

Space diversity - placing two receive antennas

one above the other. It improves reception byeffectively providing a larger target for signals

radiated from mobile units.

Terms:

7/29/2019 49429286-Cellular

33/52

33

Note: The separation between the two receive

antennas depends on the height of the antennas

above the ground.

30 m above ground: require 8separation

50 m above ground: require 11separation

7/29/2019 49429286-Cellular

34/52

34

Techniques incorporated when additional cells

are required within the reuse distance:

1. Segmentation divides a group of channels

into smaller groupings or segments of mutually

exclusive frequencies; cell sites, which are within

the reuse distance are assigned their own segment

of the channel group.

- a means of avoiding co-channel interference,although it lowers the capacity of a cell by

enabling reuse inside the reuse distance, which is

normally prohibited.

7/29/2019 49429286-Cellular

35/52

35

Techniques incorporated when additional cellsare required within the reuse distance:

2. Dualization a means of avoiding full-cell

splitting where the entire area would otherwise

need to be segmented into smaller cells.

- its major drawback is that it requires an extra

base station in the middle of a cell. There are now

two base stations in a cell; one a high-powerstation that covers the entire secondary cell and

one a low-power station that covers the smaller

primary cell.

7/29/2019 49429286-Cellular

36/52

36

Terms:

Radio network is defined by a set of radio-

frequency transceivers located within each cells

Base stations the locations of radio-frequency

transceivers, consists of a low-power radiotransceiver, power amplifiers, a control unit

(computer), and other hardware, depending on the

system configuration. It can improve transmission

quality, but they cannot increase the channelcapacity within the fixed bandwidth of the

network. It serves as central control for all users

within that cell.

- are distributed over the area of system coverage.

7/29/2019 49429286-Cellular

37/52

37

Terms:

Cell-site controller handles all cell-site control

and switching functions.

Mobile Telephone Switching Office (MTSO)

controls channel assignment, call processing, calsetup, and call termination which includes

signaling, switching, supervision, and allocating

radio-frequency channels.

provides a centralized administration andmaintenance point for the entire network and

interfaces with the PTN over wireline voice

trunks to honor services from conventional

wireline telephone subscribers.

7/29/2019 49429286-Cellular

38/52

38

7/29/2019 49429286-Cellular

39/52

39

Roaming and HandoffsRoaming - is when a mobile unit moves from one

cell to another possibly from one companys

service area into another companys service area

(requiring roaming agreements).Handoff / Handover the transfer of a mobile

unit from one base stations control to another

base stations control.

4 stages of handoff:

1. Initiation either the mobile unit of the

network determines the need for a handoff and

initiates the necessary network procedures.

7/29/2019 49429286-Cellular

40/52

40

4 Stages of handoff:

2. Resource reservation appropriate network

procedures reserve the resources needed to

support the handoff (i.e. a voice and a controlchannel).

3. Execution the actual transfer of control from

one base station to another base station takes

place.4. Completion unnecessary network resources

are relinquished and made available to another

mobile units.

7/29/2019 49429286-Cellular

41/52

41

Types of Handoff:1. Hard Handoff a connection that is

momentarily broken during the cell-to-cell

transfer. It is a break-before-make process.

- generally occur when a mobile unit is passed

between disjointed systems with different

frequency assignments, air interface

characteristics, or technologies.2. Soft Handoff a flawless handoff, normally

takes approximately 200ms, which is imperceptible

to voice telephone users, although the delay may be

disruptive when transmitting data

7/29/2019 49429286-Cellular

42/52

42

7/29/2019 49429286-Cellular

43/52

43

6 Essential Components:

1. Electronic Switching Center the heart of a

cellular telephone system. It controls switching

between the public wireline telephone network and

the cell-site base stations for wireline-to-mobile...

2.Cell-site Controller manage each of the radio

channels at each site, supervise calls, tx/rx on off.3. Radio transceivers - transmitter/receiver

4. System interconnections used four-wire leased

lines to connect switching centers to cell sites and

to PTN.5. Mobile telephone units

6. Common Communications Protocol - governs

the way telephone calls are established and

disconnected.

7/29/2019 49429286-Cellular

44/52

44

Cellular Telephone Call Processing

1. User channel the actual voice channel where

mobile users communicate directly with othermobile and wireline subscribers through a base

station.

2. Control channel used for transferring control

and diagnostic information between mobile users

and a central cellular telephone switch through a

base station.

Note: Base stations transmit on the forwardcontrol channel and forward voice channel &

receive on the reverse control & reverse voice

channel.

7/29/2019 49429286-Cellular

45/52

45

3 Types of Calls:

1. Cellular-to-PSTN

2. Cellular-to-Cellular

3. PSTN-to-Cellular

Digital Cell Phone Systems- developed primarily to expand the capacity of

the cell phone systems already in place.

Advantages:- more reliable in a noisy environment

- digital circuits can be made smaller and more

power-efficient, and therefore handsets can be

more compact and can operate for longer times.

7/29/2019 49429286-Cellular

46/52

46

Advantages:- digital cell phones greatly facilitate the

transmission of data as well as voice so that data

services such as e-mail and Internet access are

possible.2G Cell Phone Systems- most modern digital cell phones

1. GSM Global System for Mobile

Communications uses TDMA, uses a

compression scheme that allows eight telephone

calls to be transmitted concurrently in a single

200 kHz wide channel; GMSK modulation.

7/29/2019 49429286-Cellular

47/52

47

- basic data rate is 270 kbps in the 200 khz

channel.

- considerable error detection and correction

coding is used to improve the reliability in the

presence of noise, multipath fading, &

interference.

- also uses a frequency-hopping scheme tominimize inter-channel interference.

2. IS 136 - the Telecommunications Industry

Association standard that fully describes TDMA.

- 7.4 kbps data rate; permits three subscribers toconcurrently use a single 30 khz channel.

- uses separate channels for simultaneous

transmit and receive; QPSK modulation.

3. Spread Spectrum

7/29/2019 49429286-Cellular

48/52

48

2.5G Cell Phone Systems- refers to a generation of cell phones betweenthe original 2G digital phones and the newer 3G

phones.

- bring data transmission capability to 2Gphones in addition to normal voice service.

- permits subscribers to exchange e-mails and

access the Internet by cell phone.

- because of the small screen size and a small orvery restricted keyboard, data transmission

capability is limited but available to those who

need it.

7/29/2019 49429286-Cellular

49/52

49

1. General Packet Radio Service, GPRS uses

one or more of the eight TDMA time slots in a

GSM phone system to transmit data rather than

digitized voice.

- data rate is from 20 kbps up to 160 kbps

- typical rate is about 40 kbps, which is more

than enough for e-mail and short messageservice but poor for Internet access.

- involves an automatic rate adjustment

algorithm that adjusts the class and data rate to

the robustness of the wireless channel.2. Enhanced Data Rate for GSM Evolution,

EDGE - based upon GPRS system but uses 8-

PSK modulation to achieve even higher data

rates up to 384 kbps, thereby tripling the rate.

7/29/2019 49429286-Cellular

50/52

50

- uses the GPRS class concept whereby the data

rate is a function of the encoding and the

number of time slots used.

- theoretical max. data rate is 473.6 kbps with all

eight slots used; typical everyday rates are

usually over 100 kbps but less than 200 kbps.

- if implemented, EDGE needs linear poweramplifiers at the base station and in the handset.

3. CDMA2000 uses 1.25 MHz wide channels

- packet-based; permits a data rate of 144 kbps

- uses three 1.25 MHZ channels = 3.75 MHz- Evolution-Data Optimized, a recent version has

higher rate approaching 3.1 Mbps downlink and

an uplink rate up to 1.8 Mbps. These speeds

qualify for 3G.

7/29/2019 49429286-Cellular

51/52

51

3G Cell Phone Systems- are true packet data phones

- feature enhanced digital voice and high-speeddata transmission capability.

- described by the term International Mobile

Telecommunications 2000; CDMA 2000.

- frequency range: 1800 to 2200 MHz.- can achieve a data rate up to 2.048 Mbps in a

fixed position; 384 kbps in a slow-moving

pedestrian environment, and 144 kbps in a fast

mobile environment.

- include fast e-mail and Internet access

- permits the transmission of video

- subscribers can watch a movie

7/29/2019 49429286-Cellular

52/52