Chapter 2
REVIEW OF RELATED LITERATURE
Digital Signage
Television and radio are old media that have been in stores for decades. Living in
the shadow of home entertainment media, VCRs and CRT TV monitors have been used
to stores to provide commercial and product demonstration closer to the where the
purchasing decision really take place. Presenting products at point of purchase (POP) is
the core idea of digital signage.( Lars-Ingemar Lundström,2008)
Digital signage has completely new ways of combining information from
different sources. Digital signage would never work without someone controlling which
content is shown on which screens. The content management server is not only the heart
of a digital signage system but also the spider in the web when it comes to collecting
information from the internet that is to be distributed to the screens.
The content on the screen or the different picture components can be originate
from several separate data files. Also, some content may be live broadcast in real time
and other information may be stored on its way to the screen. The content may have been
stored for a fraction of a second, a couple of minutes, hours, days, months, or perhaps
even years. In modern digital signage systems, the screen are divided into regions and
layers, and the content on the screens is made up of several files. However, the content
files and data streams are not enough. Information and instructions are needed to control
how, where, and when the content files and streams are displayed on the screens. This
control information is stored in scheduling and play list files.
In television, they are ready made, live-transmitted signals that are processed by
the receiving equipment and then presented to the viewers. The content on a digital
signage screen may originate from several different data files. Each file represents the
content in a specific region of the screen. However, this is not the only difference.
Conventional broadcasting is based on real-time distribution. This is not necessarily the
case in a digital signage system. Digital signage system allows automatic content storage
at several locations en route to the viewer. The stored content may also be updated at any
time. In digital signage system, the Internet Protocol (IP) is used to carry the files and the
streams to their destinations. Through an IP-based distribution system would be able to
carry the multimedia content. The Bitrate of an IP distribution can be easily increased to
fit any future need. Using an IP based distribution it is possible to quickly establish a
wireless local area network (WLAN) for digital signage use.
Digital signage provides the possibility of changing the message all the time. The
dynamics allow the content to be adapted to different hours of the day and other
circumstances. Using suitable means of distribution also allows near-real-time or live
update of the content. It provides very accurate control of what appears on the screens.
Digital signage is a name given to any number of methods used to display
multimedia content in public venues.
Alternatively known as dynamic signage,
electronic signage or narrowcasting, networks of digital signs have been deployed across
numerous retail chains, banks, travel hubs and corporate headquarters to deliver
informative and entertaining content to captive audiences and passersby. In its most
basic implementation, a digital sign consists of a playback device (such as a computer,
VCR or DVD player) connected to a display. Depending on the application, the display
might be a small LCD screen, a plasma display panel, or even a video wall composed of a
number of connected screens. With a number of affordable options available, anybody
with a message to send to their out-of-home audience can benefit from a digital signage
installation (wirespring technologies: intro to digital signage.pdf,).
A visual communication network that delivers powerful and appealing videobased messages and call-to-action. Quite simply, this is an attractive method of
communications that is very hard to ignore. Even better than just displaying the message,
the message can be incorporated with moving images, animated logos and video clips and
interactivity to increase the aggregation of personal attention. No print poster can offer
this magnitude of attraction.
Rich media delivered by digital signage displays has
become a staple in entertainment venues where it interweaves advertising with pictures,
trivia and videos. It is also showing up in many retail chains with the intent to inspire
impulse purchases at the point-of-sale. In restaurants, hotels and conference centers,
digital signage directs guests to events, informs them of event schedules, offers ondemand updated menu options and even provides real-time local news information. On
college and university campuses, digital signage now has a broad range of applications –
including emergency messaging, promotional functions and even academic uses.
Multimedia Signage can be a very effective campus communications system.
Information can be segmented and published to the area of campus where it is most
applicable. Near the student service offices, signage provides scheduled campus
announcements: the last day to add or drop a course without a penalty; the next deadlines
for financial aid and the registration schedule for the next semester. In the areas adjacent
to the gym, it can announce sign-ups for intramural teams and results from recent
tournaments, post instructions on how to sign up for a court and provide special facility
hours and trainer availability times. In the campus cafeteria or food court, digital signage
can be used to post today’s menu, advertise overstocked items and offer nutritional
information. Important announcements such as facility issues, special schedules, or
emergency messaging can be immediately and simultaneously posted to every location.
Digital media content can be adapted quickly and at low cost for a specific target.
Their contents can be either program-controlled or compiled manually, requiring a
combination of presentation technology, playout hardware (PC systems) and network
connection, in addition to the software for playout, content management and network
management. Digital Signage, as a completely digital communications supply chain using
the integration of technologies for the creation, management, transport and presentation
of still and motion text and graphics, continuously proves itself as a powerful
communications medium. Studies continued to illustrate that digital signage generates
awareness and action, serving as a highly effective tool to inform, engage and influence.
Now digital signage is a media seeking to contribute most fully to communications
objectives, typically in conjunction with other communications devices such as internet,
static signage, print, mobile, TV, etc.
Here are some of Digital Multimedia Signage Applications:

In hotels, communicate with hotel guest with live, updated, usewful and
promotional information at the reception, in the hallway, outside ballrooms and meeting
rooms.

In Shop and supermarket, it stimulate impulse purchases by dynamic promotional
messages or e-catalogs at point of sales

In Restaurant and bar, install digital menu board and raise revenue by dynamic
promotion of special meal deals. Broadcast sport games or create unique atmosphere

In Corporations and offices, convey brand image and synchronize information
instantly between headquarters and branch offices

In School/university campuses, serves as digital bulletin for announcements. Live
broadcast of graduation ceremonies or on-campus sport games from the auditorium
Wireless VGA Extender
A Video Graphic Array (VGA) Extender is an electronic device that increases the
signal strength from a VGA port, most often from a computer. They are often used in
schools, businesses, and homes when multiple monitors are being run off one VGA port,
or if the cable between the monitor and the computer will be excessively long (often
pictures appear blurry or have minor artifacts if the cable runs too far without a booster).
VGA extenders are sometimes called VGA boosters. Through the VGA Extender, you
can use one PC to display identical image and extension of VGA signal up to 180/300
meter on monitors.
A wireless VGA Video Extender kit includes both VGA transmitter and receiver
units, allowing you to make out-of-the way connections from a VGA video source to a
remote VGA monitor. The transmitter and receiver wall plates can be placed in a wall or
ceiling gang for a cleaner, more professional VGA installation, supporting connection
distances up to a maximum of 300m (950ft). Offering maximum versatility and
convenience, the VGA wall plate kit is easy to install; simply wallmount the transmitter
unit near the intended VGA source, then wallmount the receiver unit near the
monitor/projector. The VGA transmitter and receiver units can then be linked using
standard Cat5e or Cat6 cable, providing a high quality video extension while concealing
the cable for neater installation.
Both VGA transmitter and receiver units uses a 12V DC terminal block connector
behind the unit that offers a more secure and economical installation; using Cat5/Cat6
cable to extend the VGA signal offers a cost-effective solution based on the broad
availability of networking cable which is far more flexible than VGA cable, not to
mention less expensive.
VGA Extender via CAT5 up to 300 Feet:
The XTENDEX® ST-C5V-300 VGA Extender transmits VGA video up to 300
feet away from a computer using CAT5/5e/6 cable. The extender supports local and
remote monitors, and is available with optional stereo audio. It supports resolutions to
1920x1440. Complies with CE and RoHS standards. Two-year warranty.
The figure below illustrates the VGA Extender system overview. Connect the
Receiver to 1 or 2 screens, up to 110m/360ft away from the Transmitter (depending on
resolution). From the figure shown, using a VGA extender connecting the server to the
screen using a CAT5 cable.
Extend VGA with L/R audio up to 100 feet at 1280x1024 resolution wirelessly
The Wireless VGA Extender LR allows a VGA display or projector to be
conveniently
located
up
to
100
feet
away
from
the
source.
The Wireless VGA Extender LR features signal transmission through walls at resolutions
of up to 1280x1024, using industry-proven 2.4GHz 802.11b/g/n Wireless network
technology. The Extender can be operated on any one of 4 channels to minimize
interference.
It is a plug-and-play solution and there is no necessary special configuration. The
Wireless VGA Extender LR system consists of a Sender and a Receiver. The Sender is
connected to the VGA source with a VGA cable. The Receiver is connected to the
display with a VGA cable. 12V external power supplies are connected to the Sender and
the Receiver. It supports A/V input sources and also include Component, S-Video and
Composite Video. A/V sources can be individually selected by pressing the Source
Selector button on the front panel of either the Sender unit or the Receiver unit. The
current wireless channel can be selected in the same way with the Channel Selector
button.
A/V Input Formats:
1. CVBS : NTSC / PAL / SECAM
2. S-Video : NTSC / PAL / SECAM
3. Y/Pb/Pr : 480i/p , 576i/p , 720p (50/60Hz) , 1080i/p (50/60Hz).
4. VGA : 640x480, 800X600 , 1024X768 , 1280X768 ,1280X960 , 1280X1024
Output Formats & Frequencies:
1. Y/Pb/Pr : 480p (60Hz), 576p (50Hz), 720p (60Hz)
2. VGA : 640x480 (60Hz), 800X600 (60Hz), 1024X768 (60Hz), 1280X768 (60Hz),
1280X1024 (60Hz)
The following shows the transfer frame rates:
800X600(60Hz)(4:3) → 800X600 (60fps)
VGA :
1024X768(60Hz)(4:3) → 1024X768 (30fps)
1280X768(60Hz)(5:3) → 1280X768 (30fps)
1280X960(60Hz)(4:3) → 1024X768 (30fps)
1280X1024(60Hz)(5:4) → 1280X1024 (30fps)
The resolutions having 1024 vertical pixels or 720p resolution and higher will
have half of the usual frame rate.
Specifications:
Wireless Standard ...................................................................... IEEE 802.11b/g/n
Antenna Type .......................................................... External Dipole antenna 2dBi
PCM Encoding ................................................................... 48KHz 16-bit sampling
Power Supply .......................................................................... 2 x 12V @ 1A each
Audio Inputs/Outputs ....................................................... 3.5mm mini-stereo jacks
Video Inputs:
Composite & S-Video ......................................................... NTSC / PAL / SECAM
Y/Pb/Pr ................................ 480i/p , 576i/p , 720p (50/60Hz) , 1080i/p (50/60Hz)
VGA ........................... 800X600 , 1024X768 , 1280X768 ,1280X960, 1280X1024
Video Outputs:
Y/Pb/Pr ................................................... 480p (60Hz), 576p (50Hz), 720p (60Hz)
VGA .............................. 640x480 , 800X600 , 1024X768 ,1280X768 ,1280X1024
Switchable 802.11b/g/n Channels .......................................................... 3, 6, 9, 11
Operating Temperature ............................................. 0-40 C ambient temperature
Operating Humidity ............................................ 90% maximum (non-condensing)
Dimensions ................................................... 7.05 (L) x 4.17 (W) x 0.9 (H) per unit
LCD Technology
Liquid Crystal Display (LCD) is now a key device in multimedia equipment, and
demand for LCDs with improve performance (e.g. lighter, thinner, lower cost, and power
consumption, higher luminance and definition and larger screens are increasing.
Professor Allan Hedge stated that the conventional computer systems have used
cathode ray tube (CRT) technology for the computer display. However, in the past
decade technological advances in thin film transistor (TFT) liquid crystal displays
(LCDs) have made this an increasingly popular technology. Modern LCDs can offer
several advantages over CRTs in terms of visual work performance, space and energy
savings. Recent research studies have compared whether visual work performance is
superior for LCDs compared to CRTs for typical visual work. (2003)
Professor Allan hedge also stated the significant benefits of LCDs have been
shown to be that visual search times for text targets embedded in a screen of text are 22%
faster for LCDs than CRTs, and also faster for low contrast, small characters. Eye
fixation times are 9% shorter and 15% fewer eye fixations are needed to read the same
information from an LCD versus a CRT. Visual search error frequency is 22% less when
reading from an LCD than a CRT. LCDs have been shown to allow for greater postural
variety during computer work. LCDs are free from flicker because they do not rely on a
scanning electron beam. CRTs are more prone to flicker. LCDs are free from geometric
image distortions at the screen edges because they are a flat matrix display where every
pixel is active; CRTs are subject to peripheral distortion of the image as the electron
beam becomes progressively more tangential to the monitor screen phosphors at the
edges, hence CRT screens typically have a black deadspace around them.
These
improvements in the quality of the visual image with LCDs are thought to be responsible
for the improvements in visual performance. (2003)
LCDs have uniform screen brightness and the screen is covered with a flexible
surface that is substantially less prone to specular glare compared to a glass covered CRT
screen. LCDs are flicker free, which should reduce the risks of headaches, and the
reductions in occulomotor effort (number of fixations) and the reductions in specular
glare problems with LCDs should reduce complaints of eyestrain. However, additional
research is required to confirm these predict benefits. An LCD display is much thinner
and lighter than a CRT display of the equivalent viewing area. An LCD occupies
substantially less space than a CRT (an LCD is usually <20% of the footprint of a CRT
for the equivalent viewing area. The front of the LCD screen needs to be at a similar
distance to the eye, so the space saving occurs behind the screen.
An LCD can save the most space when it is mounted on an articulating arm, so
that the user can easily move this out of the way to access the work surface for other
activities. An LCD can also save space because it can be placed on a narrower work
surface at the same screen to eye distance. The lighter weight and thinner profile of an
LCD makes it easier to reposition. Functional workstation areas are reduced by 10-20%.
LCDs use considerably less energy than CRTs, both when running and also when in
standby mode.
Overall, LCDs can reduce display energy use by some 60%.
For
example, a 15” LCD uses around 25 watts when operational and around 3 watts when in
standby mode, compared with an equivalent viewing area 17” CRT that uses 80 watts
when operational and 5 watts in standby mode. LCD screens recover from standby faster
than CRTs and consume less power when they do they this. LCDs do not emit the same
heat load as does a CRT, and this saves energy on air conditioning in a building. The
uniform brightness of an LCD screen means that the screen can better tolerate variations
in light levels and reductions in lighting also saves energy. A recent Japanese study
estimates that if Japan continues on its path towards replacing old CRTs with new LCDs
so that some 76% of displays will be LCDs by the end of 2003, this will save 3 billion
kWh of power consumption (the equivalent of the total power consumption of 1,000,000
households or the power production of about 3 nuclear power plants).
With an LCD the whole screen area is active and viewable so there is no image
loss at the boundaries, whereas the viewable screen area of a CRT is smaller than the
monitor face. Consequently a 15” LCD can give the equivalent area of a 17” CRT, and a
17” LCD the equivalent of a 19” CRT. Unlike CRTs, LCDs are free from VLF/ELF
electromagnetic radiation emissions associated with the scanning electron beam required
for a CRT. For most office tasks the color and video quality of both LCDs and CRTs
will be equivalent.
For high end color graphics, CRTs can offer some advantages
because LCDs can only display the colors available in the pixels, and so they can have
less of a color depth than CRTs. Some LCDs (low cost, low resolution) have pixels that
respond too slowly for accurate video rendering, and some tearing of the video image can
occur, which usually is not an issue for CRTs.
© Professor Alan Hedge, Cornell University, May, 2003.
LCD are the most cost-efficient flat panel displays. It is based on large fluorescent
white light source in front of which there is a filter that provides polarized light. LCD
screens are popular because they are very insensitive to burn-in effects, which can be
caused by the sometimes static content used for digital signage. In comparison to the
competing technology of plasma flat-panel display, it is easier to make tiny pixels and
achieve high resolution on an LCD.
WLAN (Wireless Local Area Network)
A WLAN is a type of Local Area Network (LAN) that uses high frequency radio
waves rather than wires to communicate and transmit data.
It is a flexible data
communication system implemented as an extension to or as an alternative for, a wired
LAN.
The benefits of using a WLAN instead of a wired network connection:

Increased Productivity - WLAN provides "untethered" network and
Internet access.

Fast and Simple Network Set-up - There are no cables to install at a users
desk or work area.

Installation Flexibility - WLANs can be installed in places where wires
can't, and they facilitate temporary set-up and relocation.

Reduced Cost-of-Ownership - Wireless LANS reduce installation costs
because there is no cabling; as a result, savings are greatest in frequently
changing environments.

Scalability - Network expansion and reconfiguration may be less
complicated than expanding a wired network
WLAN is also known as WiFi which is a short range wireless technology that
connects a wireless device such as iPaQ to an access point that is connected to a wired
network. WLAN operates at a speed of 11 Mbps, which is very fast in the word of
wireless data and has a range of 100 feet.(Derek Ball and Dayton Foster, 2008)
Intel WLAN products are compatible with products from different vendors
employing the same technology (i.e., IEEE 802.11a, 802.11b, or 802.11g); Choosing
products that are Wi-Fi* certified will help insure compatibility.
Wi-Fi is the
trademarked name that the Wi-Fi Alliance uses to signify WLAN product
interoperability. The name stands for "wireless fidelity." Wi-Fi Alliance performs
elaborate tests on WLAN products and those that pass the tests are awarded the Wi-Fi
logo. IEEE 802.11b, 802.11g, and 802.11a are industry standard specifications issued by
the Institute of Electrical and Electronic Engineers (IEEE). These specifications define
the proper operation of Wireless Local Area Networks (WLANs). Radio Frequency (RF)
range, especially in indoor environments, is a function of transmitted power, antenna
design, receiver design, and interference. Interactions with typical building objects,
including walls, metal objects, windows, and even people, can affect how signals
propagate, and thus what range and coverage a particular system achieves. The range of
coverage for typical WLAN systems varies depending on the number and types of
obstacles encountered. Coverage can be provided for a greater area through the use of
multiple access points, wireless repeaters or wireless bridges.
IEEE 802.11
IEEE 802.11 is a set of standards carrying out wireless local area network
(WLAN) computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are
implemented by the IEEE LAN/MAN Standards Committee (IEEE 802). 802.11b and
802.11g use the 2.4 GHz ISM band, operating in the United States under Part 15 of the
US Federal Communications Commission Rules and Regulations. Because of this choice
of frequency band, 802.11b and g equipment may occasionally suffer interference from
microwave ovens, cordless telephones and Bluetooth devices. Both 802.11 and Bluetooth
control their interference and susceptibility to interference by using spread spectrum
modulation. Bluetooth uses a frequency hopping spread spectrum signaling method
(FHSS), while 802.11b and 802.11g use the direct sequence spread spectrum signaling
(DSSS) and orthogonal frequency division multiplexing (OFDM) methods, respectively.
802.11a uses the 5 GHz U-NII band, which, for much of the world, offers at least 19 nonoverlapping channels rather than the 3 offered in the 2.4 GHz ISM frequency band.[2]
Better or worse performance with higher or lower frequencies (channels) may be
realized, depending on the environment.
802.11a
Release
date
October
1999
Op.
Throughput
Frequency
(typ.)
5 GHz
27 Mbps
Net Bit
Rate
(max.)
54 Mbps
Gross Bit Max Indoor Max Outdoor
Rate (max.)
Range
Range
72 Mbps
~50 ft/15
meters
~100 ft/30
meters
The 802.11a standard uses the same data link layer protocol and frame format as
the original standard, but an OFDM based air interface (physical layer). It operates in the
5 GHz band with a maximum net data rate of 54 Mbps, plus error correction code, which
yields realistic net. achievable throughput in the mid-20 Mbps. Since the 2.4 GHz band is
heavily used to the point of being crowded, using the relatively un-used 5 GHz band
gives 802.11a a significant advantage. However, this high carrier frequency also brings a
disadvantage: The effective overall range of 802.11a is less than that of 802.11b/g. In
theory, 802.11a signals are absorbed more readily by walls and other solid objects in their
path due to their smaller wavelength and, as a result, cannot penetrate as far as those of
802.11b. In practice, 802.11b typically has a higher range at low speeds where will
reduce speed to 5 Mbps or even 1 Mbps at low signal strengths. However, at higher
speeds, 802.11a often has the same or greater range due to less interference.
802.11b
Release
Op.
Throughput
date Frequency
(typ.)
Net Bit Gross
Max
Max
Rate Bit Rate Indoor Outdoor
(max.) (max.) Range Range
October
2.4 GHz
1999
11
Mbps
~5 Mbps
--
~150
~300
feet/45 feet/90
meters meters
802.11b has a maximum raw data rate of 11 Mbps and uses the same media
access method defined in the original standard. 802.11b products appeared on the market
in early 2000, since 802.11b is a direct extension of the modulation technique defined in
the original standard. The dramatic increase in throughput of 802.11b along with
simultaneous substantial price reductions led to the rapid acceptance of 802.11b as the
definitive wireless LAN technology. 802.11b devices suffer interference from other
products operating in the 2.4 GHz band. Devices operating in the 2.4 GHz range include:
microwave ovens, Bluetooth devices, baby monitors and cordless telephones.
802.11b WLANs operate at speeds up to 11 Mbps. 802.11a and 802.11g WLANs
operate at speeds up to 54Mbps. The number of users is virtually unlimited. The number
of users can be expanded by installing multiple access points. By installing multiple
access points in the same location, set at different frequencies (channels), the wireless
network can expand to accommodate additional simultaneous users in the same area.
Similarly, a WLAN can support more users by installing additional access points in
various locations in the building. This increases the total number of users and allows
roaming throughout the building or across the campus.
802.11g
Release
Op.
Throughput
date Frequency
(typ.)
June
2003
2.4 GHz
~22 Mbps
Net Bit Gross Bit
Rate
Rate
(max.)
(max.)
Max
Indoor
Range
~150
54 Mbps 128 Mbps feet/45
meters
Max
Outdoor
Range
~300
feet/90
meters
802.11g works in the 2.4 GHz band like 802.11b, but uses the same OFDM based
transmission scheme as 802.11a. It operates at a maximum physical layer bit rate of 54
Mbit/s exclusive of forward error correction codes, or about 22 Mbps average throughput
802.11g hardware is fully backwards compatible with 802.11b hardware and therefore is
encumbered with legacy issues that reduce throughput when compared to 802.11a by
~21%. Most dual-band 802.11a/b products became dual-band/tri-mode, supporting a and
b/g in a single mobile adapter card or access point. Details of making b and g work well
together occupied much of the lingering technical process; in an 802.11g network,
however, activity of an 802.11b participant will reduce the data rate of the overall
802.11g network.
802.11n
802.11n is a recent amendment which improves upon the previous 802.11
standards by adding multiple-input multiple-output (MIMO) and many other newer
features. The IEEE has approved the amendment with an expected publication in mid
October 2009.Enterprises, however, have already begun migrating to 802.11n networks
based on the Wi-Fi Alliance's certification of products conforming to a 2007 draft of the
802.11n proposal.
Release
date
Op.
Throughput
Frequency
(typ.)
5 GHz
September
and/or
11, 2009
2.4 GHz
144 Mbps
Net bit
rate
(max.)
Gross
Max
Max
Bit
Indoor Outdoor
Rate
Range Range
(max.)
600 Mbps ----
~300 ~600
feet/91 feet/182
meters meters
Using a WEP key is the basic security mechanism which is available with all
802.11a, 802.11b and 802.11g devices.
Newer security mechanisms such as Wi-Fi
Protected Access (WPA) and 802.1x are also available with some products. WEP (Wired
Equivalent Privacy) is an optional IEEE 802.11 feature used to provide data security that
is equivalent to that of a typical wired LAN. WEP uses data encryption to provide a
basic level of security for WLAN users. WEP allows the administrator to define an
"encryption key" which is used to encrypt data before it is transmitted through the
airwaves. When WEP is enabled, all stations (clients and Access Points) are required to
have the same WEP key. Network access is denied to anyone who does not have the
correct key. The unlicensed nature of radio-based wireless LANs means that other
products (ex. 2.4 GHz cordless phones, microwave ovens, garage door openers,
Bluetooth™ devices) that transmit energy in the same frequency spectrum can potentially
interfere with a WLAN system. Older microwave ovens are a concern, but most WLAN
manufacturers design their products to account for microwave interference.
RF
interference can also occur if two WLANs are located in close proximity to each other.
This situation is usually dealt with by placing each WLAN on a different RF channel
within allowed frequency range.
RSS feed
RSS is known as "Really Simple Syndication" but sometimes "Rich Site
Summary". RSS is a family of web feed formats used to publish frequently updated work
such as blog entries, news headlines, audio, and video in a standardized format. An RSS
document which is called a "feed", "web feed", or "channel" includes full or summarized
text, plus metadata such as publishing dates and authorship. Web feeds benefit publishers
by letting them syndicate content automatically. They benefit readers who want to
subscribe to timely updates from favored websites or to aggregate feeds from many sites
into one place. RSS feeds can be read using software called an "RSS reader", "feed
reader", or "aggregator", which can be web-based, desktop-based, or mobile-devicebased. A standardized XML file format allows the information to be published once and
viewed by many different programs. The user subscribes to a feed by entering into the
reader the feed's URI or by clicking an RSS icon in a browser that initiates the
subscription process. The RSS reader checks the user's subscribed feeds regularly for new
work, downloads any updates that it finds, and provides a user interface to monitor and
read the feeds. RSS formats are specified using XML, a generic specification for the
creation of data formats. ()
Digital Audio Broadcasting (DAB)
DAB is a digital radio technology for broadcasting radio stations, used in several
countries, particularly in Europe. As of 2006, approximately 1,000 stations worldwide
broadcast in the DAB format. Proponents claim the standard offers several benefits over
existing analogue FM radio, such as more stations in the same broadcast spectrum, and
increased resistance to noise, multipath, fading, and co-channel interference. However,
listening tests carried out by experts in the field of audio have shown that the audio
quality on DAB is lower than on FM in the UK on stationary receivers with strong FMsignal, due to 98% of stereo stations using a bit rate of 128 kbit/s with the MP2 audio
codec, which requires double that amount to achieve perceived CD quality. DAB+ is the
upgraded version of DAB wherein is not forward compatible with DAB+, which means
that DAB-only receivers will not be able to receive DAB+ broadcasts.DAB+ is
approximately twice as efficient as DAB due to the adoption of the AAC+ audio codec,
and DAB+ can provide high quality audio with as low as 64kbit/s. Reception quality will
also be more robust on DAB+ than on DAB due to the addition of Reed-Solomon error
correction coding.DABgives substantially higher spectral efficiency, measured in
programmes per MHz and per transmitter site, than analogue communication. This has
led to an increase in the number of stations available to listeners, especially outside of the
major urban conurbations. The original objectives of converting to digital transmission
were to enable higher fidelity, more stations and more resistance to noise, co-channel
interference and multipath than in analogue FM radio.
Benefits of DAB
Improved end-user features
DAB radios automatically tune to all the available stations, offering a list of all
stations. DAB can carry "radiotext" (in DAB terminology, Dynamic Label Segment, or
DLS) from the station giving real-time information such as song titles, music type and
news or traffic updates.
Lower cost
DAB broadcast many channels over one transmitter (multiplex) which lowers
maintenance and transmission costs radically when compared to FM.
Reception quality
The DAB standard integrates features to reduce the negative consequences of
multipath fading and signal noise, which afflict existing analogue systems. Also, as DAB
transmits digital audio, there is no hiss with a weak signal, which can happen on FM.
Less pirate interference
The specialized nature and cost of DAB broadcasting equipment provide barriers
to pirate radio stations broadcasting on DAB.
Variable bandwidth
Mono talk radio, news and weather channels and other non-music programs need
significantly less bandwidth than a typical music radio station, which allows DAB to
carry these programmes at lower bit rates, leaving more bandwidth to be used for other
programs.
FM broadcasting
FM broadcasting is a broadcast technology that uses frequency modulation (FM)
to provide high-fidelity sound over broadcast radio. It is important that stereo broadcasts
should be compatible with mono receivers. For this reason, the left (L) and right (R)
channels are algebraically encoded into sum (L+R) and difference (L−R) signals. A mono
receiver will use just the L+R signal so the listener will hear both channels in the single
loudspeaker. A stereo receiver will add the L+R and L−R signals to recover the Left
channel, and subtract the L+R and L−R signals to recover the Right channel. For
example, if in a certain moment in time, a station wishes to broadcast the following
signals, L=5 and R=3, then L+R=8 whereas L-R=2. The station will broadcast these two
signals, 8 and 2. The receiver will now recreate the original signals like this:
L=(8+2)/2=5, R=(8-2)/2=3. The (L+R) Main channel signal is transmitted as baseband
audio in the range of 30 Hz to 15 kHz. The (L−R) Sub-channel signal is modulated onto a
38 kHz double-sideband suppressed carrier (DSBSC) signal occupying the baseband
range of 23 to 53 kHz. The final multiplex signal from the stereo generator contains the
Main Channel (L+R), the pilot tone, and the sub-channel (L−R). This composite signal,
along with any other sub-carriers (SCA), modulates the FM transmitter. Converting the
multiplex signal back into left and right audio signals is performed by a stereo decoder,
which is built into stereo receivers.
In order to preserve stereo separation and signal-to-noise parameters, it is normal
practice to apply pre-emphasis to the left and right channels before encoding, and to
apply de-emphasis at the receiver after decoding. Stereo FM signals are more susceptible
to noise and multipath distortion than are mono FM signals. This is due to imbalance of
FM sideband ratios of the additional modulating signals created by the pilot tone and the
sub-carrier channel. In addition, for a given RF level at the receiver, the signal-to-noise
ratio for the stereo signal will be worse than for the mono receiver. The point at which the
receiver input RF level reaches maximum monaural signal-to-noise ratio will be 23 dB
lower than the receiver input RF level for maximum stereo signal-to-noise ratio. For this
reason many FM stereo receivers include a stereo/mono switch to allow listening in mono
when reception conditions are less than ideal, and most car radios are arranged to reduce
the separation as the signal-to-noise ratio worsens, eventually going to mono while still
indicating a stereo signal is being received.
Stream FLV files from Flash Media Server
The requirements for streaming FLV files from Flash Media Server are different
depending on whether native bandwidth detection is available from your Flash Video
Streaming Service provider.
Native bandwidth detection means that the bandwidth
detection is built-in to the streaming server and it provides better performance.
According to Janine C. Warner, to stream multimedia means to play a file while it
is downloading from the server. Here’s how streaming works, when you click a linked
into a video file, your computer begins to download it from the server, the video or audio
files begins to play as soon as enough of the file downloads successfully to ensure an
uninterrupted experience. If you don’t use streaming, the entire file must download
before playing. Although it can take the same time to download the entire file, streaming
can greatly reduce the time your visitors need to wait before the time they start viewing a
video online. (2008)
Managing bandwidth
You can control the amount of data the server sends to each client by providing an
approximate bandwidth capacity.
You can do so in several ways. One way is to
configure the capacity for the Flash Media Server in the configuration file (Config.xml).
Another way is to use NetStream receive Video to specify the frame rate per second of
the incoming video. A third way to match the data flow with capacity is to use Camera
set Quality on the client side and Client set Bandwidth Limit on the server side to inform
the server of the client's capacity.
Another option for managing bandwidth is, in Flash Player, the NetStream class
provides properties for playing Flash Video (FLV) files from Flash Media Server. An
event handler on Status is invoked when a status is changed or an error is posted in the
NetStream.
A status message,NetStream.Play.InsufficientBW, shows that data playing
through the NetStream is slower than the normal speed. Data can be slower than normal
speed for many reasons. For example, the client can have insufficient bandwidth or the
server can be busy and not send data at the expected rate.
Digital Signage Related Studies
Enhancing Digital Advertising using Dynamically Configurable Multimedia
From the article of John V Harrison and Anna Andrusiewicz stated that
information describing the demographics of people expected to view signage can be used
to dynamically configure multimedia advertisements to better target customer segments.
The advertiser can create an ad that can be instantiated with different audio, video,
images and text based on demographics. The instantiation of ad components can occur
prior to transmission, or alternatively, can be performed by the display controller in real
time. Current multimedia standards provide support for dynamic configuration. They also
state that a marketing team can create a dynamically configurable digital advertisement
that includes multiple instances of each multimedia component of the advertisement.
They have concluded that accurate demographic information can be obtained by staff at
the sign’s venue. However, an alternate effective approach is to have the display
controller sample the people viewing the sign using a digital camera that automatically
takes still photos at regular intervals. These images can be manually reviewed to obtain
infer some demographic information, e.g., age, ethnicity. A microphone can obtain audio
samples to identify languages spoken near the sign.
References:
Wikipedia. "Throughput", Wikimedia Foundation
Inc, http://en.wikipedia.org/wiki/Throughput, Brandon Hodgson , 2006.
Ziefle, M. (2001) Aging, Visual Performance and Eyestrain in Different Screen
Technologies, Proceedings of the Human Factors and Ergonomics Society 45th Annual
Meeting, Volume 1, Minneapolis/St Paul, Minnesota, October 8-12, 2001. The Human
Factors and Ergonomics Society, Santa Monica, California, Pages: 262-266.
Naesaenen, R.; Karlsson, J.; and Ojanpaeae, H. (2001) Display quality and the speed of
visual letter search, Displays; 22(4): 107-113.
Menozzi, M., Lang, F., Naepflin, U., Zeller, C. and Krueger, H. (2001) CRT versus LCD:
Effects of refresh rate, display technology and background luminance in visual
performance. Displays, 22(3): 79-85.
Nylen, P. (2002) Comparison of Stationary LCD and CRT Screens - Some Visual and
Musculoskeletal Aspects WWDU 2002 - World Wide Work. Proceedings of the 6th
International Scientific Conference on Work with Display Units, Edited by H. Luczak,
A.E. Cakir and G. Cakir. ERGONOMIC Institut fur Arbeits- und Sozialforschung,
Forschungsgesellschaft mbH, Berlin. Pages: 682-684.
KSBA (1998) Flat panel monitors: “Expensive” technology that saves money, Scope,
LCD vs CRT: Reasons to choose a flat panel monitor, http://www.empower.gb.com
Energy savings of LCDs, http://home.jeita.or.jp/device/lirec/english/enviro/contribut.html
BOOKS:
Lars-Ingemar Lundström(2008), Digital Signage Broadcasting: Content Management and
Distribution Techniques, Elvisier Inc, 30 corporate drive, suite 400 Burlington ,
MA01803,USA
Derek Ball and Dayton Foster(2008), How to do everything with your iPAQ pocket PC,
3rd edition, Mc Graw Hill
Janine C. Warner(2008), Dreamweaver CS4 for Dummies, Wiley Publishing, Inc.
Indianapolis, Indiana
Internet:
http://en.wikipedia.org/wiki/RSS