Cypress CY62167EV18 Instrukcja Użytkownika Pobierz pdf (Strona 20)

US

2012/0147184

A1

transmitter

Which

is

operating

using

diversity

or multiple

transmitters

can

use

betWeen

100

mW

to

1

.5

W

during

the

Tx

period

instead

of

a

feW

hundred

microWatts

in

other

periods.

This

level

of

poWer

consumption

during

the

transmission

of

data

can

be

a distinguishing

feature

of

this

system

compared

to

existing

loW

poWer

remote

sensor

systems.

[0129]

In

the

image

transmission

operation,

various

battery

operated

camera

systems

Which

transmit data

intermittently,

can

have

a

transmitter-off

to

transmitter-on

ratio

of

10

or

less.

As

such,

the

transmitter

in

these

Wireless

camera

systems

is

on

most

of

the

time.

In

contrast,

of

the

transmitter

in

the

present

systems

can

be

designed

to

have

a

high-bandWidth

radio

for

transmission

and

such

a

high-bandWidth-ratio

trans

mitter

is

on

only

for

a

short

period

of

time.

In

this

manner,

the

burst

transmission

of

the

current

Wireless

cameras

systems

can

have

a

transmitter-off

to

transmitter-on

ratio

of

much

greater

than

10

and

thus

provide

signi?cant

saving

in

poWer

consumption.

[0130]

HoWever,

the

system

timing

needs

to

take

into

account

the

“Wasted”

time

necessary

to

setup

and

tear

doWn

the

link

during

Which

the radio

is

active,

Which

is

TW.

In

order

to

approach

the

ideal

e?iciency,

period

TW

needs

to

be

amor

tized

across

a

relatively

long

period

of

active

data

transmis

sion

time

(Tx).

This

means

that

the

time in-betWeen

bursting

the

radio,

as

represented

by

Tc,

can be

extended

as

TW

increases

to

maintain

the

same

ef?ciency

level.

Hence

the

ef?ciency

(E,

in

percentage)

can

be

determined

by

E:

—

-100%

(Tx+Tw)

[013

1]

Given

the

above,

the

average

optimum

time

betWeen

transmission

of

the

burst

of

audio/video

(Tc)

data

for

a

given

ef?ciency

E,

can

be

determined

as

folloWs:

Bm E

[0132]

The

folloWing

example

can

better

illustrate

the

equation

above:

[0133]

TW:3

ms

(highly

optimized

system)

[0134]

Bin:54

M

bits/

sec

(ideal

802.11g

data

rate)

[0135]

Bs:192 k

bits/sec

(5

frames/sec

With

0.5

bits/pixel

at

320x240,

no

audio)

[0136]

E:75%

[0137]

Then

the best

cycle

time

to

set-up

and

burst

trans

mission

is,

Tc:2.53

seconds.

[0138]

System

latency

(or

lag)

can be

greater

than

or

equal

to

Tc.

If

latency

is

too

high

an

unacceptable

lag

can

occur

betWeen

the

capturing

of

audio/video

information

to

its

avail

ability

to

serve

a

surveillance

application.

To

reduce

latency

Without

negatively

impacting

energy consumption,

signi?

cant

optimizations

need

be

made

to

the

MAC

behavior

in

order

to

reduce

TW.

In

order

to

reduce time

period

TW

during

steady

state

conditions

(i.e.

not during

discovery

or

initializa

tion

states)

certain

modi?cations

can

be

made.

For

example,

a

modi?cation

to

the

regular

beacon

behavior

of

802.11

can

be

made.

When

the

high-bandWidth

radio

is

sWitched

on

for

transmission,

it

can

be

assumed

to

be

synchronized

With

the

base

station.

Thus,

the

usual

discovery

period

can

be

avoided

and

the

high-bandWidth

radio

can

advance

immediately

to

the

Jun.

14,

2012

authentication

request

and

reply,

folloWed

by

the

associated

request

and

reply

messages.

Further,

When

the

high-band

Width

radio

is

sWitched

on,

communication

can

be

made

for

data

transfer

only.

[0139]

The

above

scheme

can

be

implemented

to

provide

a

signi?cant

improvement

because

the

Wireless

camera

com

munication

can

operate

on

a

time

frame

determined

by

the

need

to

transmit data

of

interest,

and

not

on

a

time

frame

determined

by

the

client

surveillance

softWare

application.

Also,

When

multiple

cameras

are

connected

to

the

netWork

using

this

method,

the

transmission

burst

cycle

for

each

cam

era

can

be

set

so as

not

to

interfere

Which

each

other.

For

example,

this

can

be

done

at

initialization

time

by

the

burst

reception

store/

control

processing

module

of

the

base

station.

[0140]

In

one

implementation,

a

timestamp

can be

inserted

in

the

captured

images

based

on

the

time

that

the

images

Were

captured

by

the

Wireless

video

camera.

In

this

manner,

any

latency

betWeen

the

time

of

data

capture

and

the

time

of

vieWing

or

manipulating

the

images

at

the

client

device

can

be

accommodated.

For

example,

suppose

that

a

series

of

images

Were

captured

at

12:00

a.m.,

hoWever,

due

to

a

temporary

failure

or

delay

in

the

transmission

the

client

device

does

not

receive

the

images

until

12:10

am.

The

inserted

timestamps

in

the

captured

images

can

be

used

as

the

reference

point

for

image

processing

or

manipulation.

The

insertion

of

the

times

tamps

can

occur

at

the

camera

or

at

the

base

station.

[0141]

The

base

station’s

high-bandWidth

radio

MAC

?rm

Ware

can

take

advantage

of

“knowing”

for

long

extended

periods

of time

What

speci?c

Wireless

camera

radios

are

asso

ciated

With

it.

This

can

alloW

set-up

and

tear

doWn

of

connec

tions

Without

discovery

sequences,

by

only

requiring

connec

tion

via

authentication

request

and

reply

folloWed

by

the

associated

request

and

reply

messages.

The

base

station

can

be

implemented

in

various

con?gurations.

In

one

implemen

tation,

a

base

station

implementing

standard

802.1

1

protocols

can

be

used

by

the

system.

[0142]

Non

Clear

Channel

Environments

[0143]

In

a

non-clear

channel

environment

(e.g.,

during

interference

from

other

transmitters

Which

may

be

using

the

channel)

the

high-bandWidth

radio

transmission

period

can

be

“skipped”

and

the

data

that

Was

to

be

transmitted

can

be

temporarily

stored

and

transmitted

on

the

next

available

cycle.

In

these

conditions,

the

period

and

timing

of

transmis

sion

bursts

can

vary

based

on

channel

conditions.

[0144]

For

example,

in

one

implementation,

the

camera

can

include

a separate

loW

poWer

circuitry

to

determine

if

a

high

bandWidth

radio

transmission

channel

is

open

or

not

prior

to

a

transmission

cycle.

This information

can

be

used

to

deter

mine

if

the

high-bandWidth

radio

in

the

camera

is

activated

from

a

poWer

doWn

mode

or

that

transmission period

is

“skipped”

by

the

camera.

Using

standard

802.11

MAC

pro

tocol,

if

the

channel

is

open

the

camera

can

initiate

the

trans

mission

process

by

sending

a

Request

to

Send

(RTS)

frame.

The

base

station

can

then

reply

With

a

Clear

To

Send

(CTS)

frame.

As

speci?ed

by

the

standard,

any

other

node

receiving

the

CTS

frame

should

refrain

from

sending

data

for

a

given

time.

[0145]

FIG.

5A

shoWs

a

How

chart

of

a

MAC

algorithm

500

that

can

be

used

by

the

Wireless

camera.

At

505,

the

Wireless

camera

is

initialized,

e.g.,

by

going

through

a

discovery

mode.

At

510,

the

Wireless

camera

scans

for

the

base

station.

At

515,

the

system

con?gures

the

Wireless

camera

to

synchro

nize

With

the

base

station.

Once

the

Wireless

camera

has

been

initialized

and

synchronized

With

a

base

station,

the

camera

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