RF Technologies and - PowerPoint Presentation

Slide1

RF Technologies and Sectorization

EECS 4215

1Slide2

Duplex

Duplex: a point-to-point system composed of 2 connected parties/devices that can communication with one another in both directions.

Full duplex: both parties can communicate with each other simultaneously.

Examples: telephone

Half duplex: each party can communicate with the other but not simultaneously.

Example: walkie-talkie two-way radio

Simplex: one device transmits and the others can only "listen”

Example: broadcast radio and TV, surveillance cameras, baby monitorsSlide3

Full Duplex Emulation

Emulates full duplex communication over a half duplex communication link.Time-division duplexing (TDD)

Frequency-division duplexing (FDD)Slide4

Time-Division Duplexing

Applying time division multiplexing to separate uplink and downlink signals.

Suitable for cases where there is asymmetry of the uplink and downlink data rates.

More time slots are allocated as data rate increases.

Examples:

UMTS 3G air interface TD-CDMA for indoor communications

Chinese TD-SCDMA 3G air interface and TD-LTE 4GSlide5

Frequency-Division Duplexing

The transmitter and receiver operate at different frequencies.Can be efficient in the case of symmetric traffic.

TDD: waste bandwidth during switch-overs; higher latency; more complex circuitry.

Examples:

m

ost cellular systems (cdma2000, UMTS/W-CDMA)

IEEE 802.16

WiMaxSlide6

Cellular Frequency Bands (4.3)

The 850-MHz Band

The

1900-MHz

Band

The 700-MHz

Band

The 2100-MHz “AWS”

Band

6Slide7

The 850-MHz Band

.

The 850-MHz spectrum (in use since

1983) had

been unused for years and even TV industry did not use the spectrum

.

7Slide8

Benefits of 850-MHz Frequency

Has a

very

short signal wavelength

(i.e., 12

in

).

Tends

to be line of sight, similar to light

itself.

Easily

reflected off buildings, cars, and trucks

.

Easily

absorbed by foliage (i.e., trees and the forest

).

Good: efficient frequency re-use

Bad: signal attenuation

8Slide9

The 1900-MHz Band

Allocated by the FCC to the “PCS” carriers in 1991. PCS Service launched in

1996.

Also called “PCS band”.

Signal strength of 850-MHz

spectrum

is

better than

1900-MHz

spectrum in

hard-to-reach

places.

New

700-MHz spectrum will be even better than the 850-MHz spectrum in this

regard

9Slide10

Illustrating 1900-MHz Band

The 1900-MHz (“PCS”) frequency band. Note the physical separation between the multiple blocks.

A

D

B

E

F

C

License-

exempt PCS

A′

D′

B′

E′

F′

C′

 15 MHz5 MHz15 MHz5 MHz5 MHz15 MHz15 MHz5 MHz15 MHz5 MHz5 MHz15 MHz1850     19101930   1990

10Slide11

The 700-MHz Band

Until 2009, a key section of the 700-MHz spectrum band was owned by broadcasters and used for analog

television.

In

2009 it was turned over to the federal

government

Able

to penetrate

walls.

D

esirable

for

broadband

communications in general and public-safety uses in particular

.

Carriers

who purchased 700-MHz licenses intend to use them for 4G/LTE

deployments.

11Slide12

Categories and Cost

Lower 700-MHz

: The

lower band is 48

MHz.

Upper 700-MHz

: The upper

band is 60

MHz.

Cost

of building a nationwide wireless

network

Over

the 700-MHz spectrum is around $2

billion

Over the 1900-MHz

PCS

band is around $4 billionCosts are lower in rural areas, due to less interference and wide-open

spaces.

Because

each tower broadcasting at 700 MHz covers twice as many square miles

12Slide13

Auction of 700-MHz UHF Spectrum

The

2008 auction divided the 700-MHz UHF spectrum into five

blocks:

Block A: 12-MHz

bandwidth

Block B: 12-MHz bandwidth

Block C: 22-MHz

bandwidth

Block D: 10-MHz bandwidth

Block E: 6-MHz

bandwidth

Total of $19.592

billion raised in the

auction.

Verizon

Wireless and AT&T Mobility together accounted for $16.3 billion of the total revenue

13Slide14

Illustrating 700-MHz

Spectrum

The 700-MHz frequency band. Most carriers who have purchased this spectrum intend to use it for 4G / LTE deployments.

14Slide15

The 2100-MHz AWS Band

AWS: Advanced Wireless Service

Used

for mobile voice and data services, video, and

messaging.

Used

in the United States and

Canada.

Frequency range:

From

1710 to 1755 MHz for the

uplink

From

2110 to 2155 MHz for the

downlink

AWS frequency bands were auctioned in the United States in the summer of

2006.

15Slide16

Illustrating 2100-MHz “AWS” Band

The AWS/2100-MHz spectrum band.

16Slide17

In-Building Coverage (4.4)

Some large office buildings have a metallic

coating, usually green or gold, added to their window glass to reduce the degree to which heat from direct sunlight will warm the

buildings.

The coating makes it difficult for RF to penetrate these buildings.

Solution: use a microcell in the building.

17Slide18

Radio Frequency Channelization and Spectrum Allocation (4.6)

Today, all channelization occurs using

“

automatic frequency planning” tools.

These

sophisticated software programs automate most, if not all, of the frequency and channel assignments throughout a wireless network

.

18Slide19

Paired Channels

All wireless transmissions require a paired channel to function.Two

radio channels are required for every wireless transmission—one for transmit, one for receive

.

Mobile transmit frequency is the same as base station receive frequency and base station transmit frequencies are the same as mobile receive frequencies.

19Slide20

Forward Channel

The channel transmitted from the base station to the subscriber’s mobile phone is known as the downlink, or the forward

channel.

A paired channel is the combination of the forward

channel.

When the channels use different frequencies, this is known as frequency-division duplexing

.

When

the channels use the same frequency, it is known as time-division duplexing.

20Slide21

Illustrating Paired Channels

Paired channels in a wireless system. One channel is required for the uplink, and one channel for the downlink.

21Slide22

Channel Spacing

When analog AMPS was the only technology used, channel spacing referred to the amount of radio spectrum that was allocated to every cellular transmission

.

Today, the majority of wireless transmissions use CDMA or W-CDMA

technology.

Automatic Frequency Planning (AFP)

tools:

Today, all frequency and “channel” planning and assignments are done via these software tools

22Slide23

Control Channels

Data signaling channel that handles the administrative

overheads.

Also

called “

pilot”

channel

Each cell base station in a wireless system has at least one control channel assigned to it

.

In sectorized base stations, each sector will have its own control

channel

On pressing the

send button when placing a call, the phone again rescans for the strongest control channel signal in its assigned frequency band.

23Slide24

Administration Tasks of Control Channels

Setup of wireless calls, both mobile-originated and mobile-terminated, and locating (paging) mobile

phones.

Collecting

call

information.

Collecting traffic data from base

stations.

Autonomous mobile

registration.

Initiating or assisting in mobile

call-handoffs.

24Slide25

Example of Control Channels

25Slide26

Frequencies in Control Channels

Control channel frequencies will be different for each wireless carrier in every market.

Like

all carrier-assigned frequencies,

control channel frequencies are also programmed

into the cell phones during the manufacturing process.

26Slide27

Sectorization (5.7)

It’s necessary to develop a means to increase systems’ capacity without having constantly split cells

(costly

undertakings).

We sectorize the base stations in

order to obtain more capacity from each base station deployment.Slide28

Migration from Omnidirectional Antenna

Replacement of Omnidirectional

antenna at base stations

is of the ways to increase the

capacity of a cellular

network:

With

three (or six) directional (i.e., sector) antennas of 120 (or 60) degrees beamwidths

.

Each

sector is viewed as a new cell, with its own (set of) frequencies/channels.

This

migration from an

omni

cell to a sectorized cell occurs at the same physical base station location.Slide29

Illustrating Conversion from Omni to Sectorized Cells

Conversion from omnidirectional cell site configuration to sectorized cell site

configuration.Slide30

Benefits of Sectorization

Substantially reduces the interference among co-channel cells.Allows

for

more

dense degree of frequency

reuse.

Range of each sector is bit larger than

omni

cell.

The directional antennas supporting each sector are collocated at the same base station.

All

base station/radio equipment for each “subcell,” or sector, is housed in the same base station shelter as well.Slide31

Objective of Sectorization

To support 360-degree coverage from a single location:

With a three-sectored site, 120-degree beamwidth sector antennas would be used

.

With

a four-sectored site, 90-degree or narrower beamwidth sector antennas would be used

.

With a six-sectored site,

60-degree beamwidth antennas would be

used.Slide32

Sectorization vs Wireless engineering and

Operations

Sectorization facilitates wireless engineering and operations in the following ways

:

Minimizes

or eliminates co-channel interference

.

Optimizes

the frequency-reuse

plan.

Increases

the capacity of any given coverage area when compared to the capacity that would be offered using

omni

antennas.

Each sector has its own assignment of frequencies, radio channels and control channel.Slide33

Illustrating Sectorization of Cell Sites

Sectorization of cell sites using 120-degree beamwidth antennas, resulting in three

sectors (

alpha, beta and gamma

)

per cell. Note the coverage overlap between cell sites and

sectors.