Falling for you was never on my plan
And surely it was not just for fun
Wish you would see what I really feel
That I’m falling for you and it is for real
You’ve got all that I was looking for
You’re beautiful outside and all through your core
Talented and smart that’s what you are
And more precious than a thousand gold bar
Though you never believe any single word I say
And sometimes you would push me away
Still I will do my best just be with you and to stay
Coz believe it or not you’re one of the reasons why I pray
You’re one of the reasons why I was able to smile
The reason why my heart beats even after it die
That is the reason why I conceder my self lucky to met you
Coz you're the girl that turn my dark sky into blue
Huwebes, Hunyo 7, 2012
Biyernes, Marso 9, 2012
LOW EARTH ORBIT SATELLITE
LOW EARTH ORBIT SATELLITE
Low Earth Orbit satellite must travel very quickly to resist the pull of gravity approximately 17,000 mile per hour. Because of this, Low Earth Orbit satellite can orbit the planet in as little as 90 minutes.
Traditionally, communications satellites have operated in geo-stationary orbit (GSO), 35,000 km above the equator, and low Earth orbit (LEO) satellites have been used for weather monitoring, resource mapping, and Earth sensing. By the start of the new millennium, in five years, revolution will have occurred in the communication satellite industry with LEO satellite networks becoming key pathways of the information superhighway.
Low Earth Orbit (LEO) satellites are satellites that operate in orbits of around 100 km to 1,000 km above the Earth’s surface – much lower than traditional communications satellites – which bring them into frequent radio contact with ground stations. LEOs are used for a variety of civil, scientific and military roles including Earth observation, radar, optical, telecoms and demonstrator.
LEO satellite constellations now form a vital link in the expanding communications and observation networks that are essential for global economic development, especially in remote areas. Reliability is therefore a key issue for satellite manufacturers and operators.
Kinds of LEO
Little LEO
Little LEO are required to offer non-voice services for example vehicle tracking, environmental monitoring and two-way data communication. A little LEO is a constellation of small, low-earth orbiting satellites, use for short, and narrowband communication. Little LEO are small, Low cost, class of satellites.
Big LEO
Big LEO are used for technology devices such as high speed, high bandwidth data communications, and video conferencing. They can carry voice and high speed data services. They are aimed at data communications and real time voice into hand held devices. Big LEO can also offer global services, which are also subject to regulatory requirements. Advantage of LEO
- A LEO satellite’s proximity to earth compared to a GEO satellite gives it a better signal strength and less of a time delay, which makes it better for point to point communication.
- A LEO satellite’s smaller area of coverage is less of a waste of bandwidth.
Disadvantage of LEO
- A network of LEO satellites is needed, which can be costly.
- LEO satellites have to compensate for Doppler shifts cause by their relative movement.
- Atmospheric drag affects LEO satellites, causing gradual orbital deterioration.
Linggo, Marso 4, 2012
3G
3G
3G or 3rd generation mobile telecommunications is a generation of standards for mobile phones and mobile telecommunication services fulfilling the International Mobile Telecommunications-2000 (IMT-2000) specifications by the International Telecommunication Union.
Time line in using 3G
GPRS
GPRS operates at much higher speeds than cur rent networks, providing advantages from a software perspective. Wireless middleware currently is required to enable slow speed mobile clients to work with fast networks for applications such as e−mail, databases, groupware, or Internet access. With GPRS, wireless middleware will probably be unnecessary, making it easier to deploy wireless solutions.
EDGE
Beyond GPRS, EDGE takes the cellular community one step closer to UMTS. It provides higher data rates than GPRS and introduces a new modulation scheme called 8−Phase Shift Keying (PSK). The TDMA community also adopted EDGE for their migration to UMTS. The data rates allocated for EDGE are started at 384 Kbps and above as a second stage to GPRS. EDGE uses the same modulation techniques as many of our existing TDMA infrastructures using Gaussian Minimum Shift Keying (GMSK) 8−PSK. Moreover EDGE uses a combination of FDMA and TDMA as the multiple access control methods.
WHY EDGE?
EDGE is a new modulation scheme that is more bandwidth efficient than the GMSK modulation scheme used in the GSM standard. It provides a promising migration strategy for HSCSD and GPRS. The technology defines a new physical layer: 8−PSK modulation, instead of GMSK. 8−PSK enables each pulse to carry 3 bits of information versus the GMSK 1−bit−per−pulse rate. Therefore, EDGE has the potential to increase the data rate of existing GSM systems by a factor of three.
EDGE retains other existing GSM parameters, including a frame length, eight time slots per frame, and a 270.833 kHz symbol rate. The GSM 200 kHz channel spacing is also maintained in EDGE, enabling the use of existing spectrum bands. This fact is likely to encourage deployment of EDGE technology on a global scale.
UMTS
UMTS is a modular concept that takes full advantage of the trend of converging existing and future information networks, devices, and services, and the potential synergies that can be derived from such convergence. UMTS will move mobile communications forward from where we are today into the 3G services and will deliver speech, data, pictures, graphics, video communication, and other wideband information direct to people on the move. UMTS is one of the major new 3G mobile communications systems being developed within the framework, which has been defined by the ITU and is known as IMT−2000.
WCDMA
WCDMA is an ITU standard derived from CDMA and is officially known as IMT−2000 direct spread. WCDMA is a 3G mobile wireless technology offering much higher data speeds to mobile and portable wireless devices than commonly offered in today's market.
WCDMA can support mobile/portable voice, images, data, and video communications at up to 2 Mbps (local area access) or 384 Kbps (wide area access). The input signals are digitized and transmitted in coded, spread−spectrum mode over a broad range of frequencies. A 5 MHz wide carrier is used compared with a 200 kHz wide carrier for narrowband CDMA.
Applications of 3G
Online e−mail
Access to the World Wide Web
Enhanced short message services
Wireless imaging with instant photos or graphics
Video services
Document/information sharing
Surveillance
Voice messaging via Internet
Broadcasting
GPRS
GPRS
GPRS is a key milestone f o r GSM data. It offers end users new data services a n d enables operators to offer radically new pricing options. Using the existing GSM radio infrastructure, up−front investments for operators are relatively low.
What is GPRS
As stated previously, GPRS stands for General (or generic) Packet Radio Service. GPRS extends the packet data capabilities of the GSM networks from Packet Data on Signaling−channel Service (PDSS) to higher data rates and longer messages.
GPRS is a packet oriented mobile data service on the 2G and 3G cellular communication system's global system for mobile communications (GSM). GPRS was originally standardized by European Telecommunication Standard Institute (ETSI) in response to the earlier CDPD and i-mode packet-switched cellular technologies. It is now maintained by the 3rd Generation Partnership Project.
GPRS Network View
Why does GPRS was develop
GPRS was developed to enable GSM operators to meet the growing demands for wireless packet data service that is a result of the explosive growth of the Internet and corporate intranets. Applications using these networks require relatively high throughput and are characterized by bursty traffic patterns and asymmetrical throughput needs. Applications, such as web browsing, typically result in bursts of network traffic while information is being transmitted or received, followed by long idle periods while the data is being viewed.
GPRS Radio Technology
Packet switching means that the GPRS radio resources are used only when users are actually sending or receiving data. Rather than dedicating a radio channel to one mobile user for a fixed period of time, the available radio resources can be concurrently shared by several users. This efficient use of the scarce radio resources means that a larger number of GPRS users can share the same bandwidth and be served from a single cell. The actual number of users supported depends on the application being used and how much data each user has to send or receive.
Sample Application of GPRS
Many applications fit into the mode of GPRS and IPs. These applications are merely a means to an end. In other scenarios, the features and applications can be met with other technologies. The issue at hand is that the use of GPRS facilitates these applications and drives the acceptance ratio.
Chat
Chat can be distinguished from general information services because the source of the information is a person with the chat protocol, whereas it tends to be from an Internet site for information services.
Textual and Visual Information
A wide range of content can be delivered to mobile phone users, ranging from share prices, sports scores, weather, flight information, news headlines, prayer reminders, lottery results, jokes, horoscopes, traffic, location−sensitive services, and so on. This information does not necessarily need to be textual — it may be maps or graphs or other types of visual information.
Still Images
Still images such as photographs, pictures, postcards, greeting cards, presentations, and static web pages can be sent and received over the mobile network as they are across fixed telephone networks. It will be possible with GPRS to post images from a digital camera connected to a GPRS radio device directly to an Internet site, enabling near real−time desktop publishing.
Moving Images
Over time, the nature and form of mobile communication is getting less textual and more visual. The wireless industry is moving from text messages to icons, picture messages to photographs, blueprints to video messages, movie previews being downloaded, and on to full−blown movie watching via data streaming on a mobile device.
Web Browsing
Biyernes, Pebrero 17, 2012
MMDS and LMDS
Multichannel Multipoint Distribution Service (MMDS):
Multichannel Multipoint Distribution Service (MMDS), also known wireless cable, is another wireless broadband technology for Internet access. MMDS has been around since the 1970s and is a well−tested wireless technology, which has been used for TV signal transmission for more than 30 years.
MMDS channels come in 6 MHz chunks and run on licensed and unlicensed channels. Each channel can reach transfer rates as high as 27 Mbps (over unlicensed channels: 99 MHz, 2.4 GHz, and 5.7 to 5.8 GHz) or 1 Gbps (over licensed channels). Typically, a block of 200 MHz is allocated to a licensed carrier in an area.
MMDS is a broadcasting and communications service that operates in the ultra−high−frequency
(UHF) portion of the radio spectrum between 2.1 and 2.7 GHz. MMDS is also known as wireless cable. It was conceived as a substitute for conventional cable television (TV). However, it also has applications in telephone/fax and data communications. MMDS frequencies provide precise, clear, and wide−ranging signal coverage.
The MMDS wireless spectrum originally consisted of 33 analog video channels, which were 6 MHz wide. The evolution of video technology into digital capacities enables the carriers to convert these 33 analog MMDS channels into 99 digital, 10 Mbps data streams, enabling full Ethernet connectivity. Therefore, a carrier with a normal operation can have as much as 1 Gbps of capacity at a single transmitter providing adequate capacities for most applications. This capacity is also readily expandable by using a sector cell concept (see the analog cellular chapter to get a handle on sectors), which reuses the same frequency many times. The combination of super cells and sectors enable the carrier to reuse the same frequency many times by building multiple cell sites. When enough customers sign on and as their bandwidth demands grow, the growth in traffic can be handled expeditiously through a new cell or a new sector.
Limited Frequency Spectrum:
System Configuration:
Signals for MMDS broadcast at the transmitter site originate from a variety of sources, just like at cable head−ends. Satellite, terrestrial, and cable delivered programs, in addition to local baseband services, comprise the material to be delivered over MMDS. All satellite−delivered baseband formats are remodulated and subsequently up−converted to microwave frequencies. Terrestrially delivered signals are usually passed through a heterodyne processor prior to up−conversion to the desired MMDS frequencies. Repeater stations can be used to direct MMDS signals to blocked areas. The typical range of a transmitting antenna can reach up to 35 miles, depending on the broadcast power. Transmitters usually operate in the 1 to 100 watt range. MMDS is a line−of−sight service, so it does not work well around mountains, but it will work in rural areas, where copper lines are not available.
How a wireless cable system works:
- The cable studio, along with the head−end, receives programming from a variety of sources (see the following sect ion) . Each source is assigned a channel number, processed to improve quality, encoded, and then sent to a transmitter. The signal is broadcast in the super−high−frequency (SHF) range. Using an omni−directional transmit pattern, the signal reaches subscribers located up to 50 KM from the antenna, depending on the terrain and transmit power.
- Wireless cable signals are received by the subscriber's small rooftop antenna, decoded (pay TV), and down−converted to standard TV channels on the subscriber's TV set.
- One of the two systems are normally used for multiple−dwellings (condo, apartment, and so on) to receive and distribute wireless TV.
- The building management pays for all units to receive the programming from a single communal antenna. This agreed fee is usually based on the number of potential viewers.
- I n other buildings, a single community antenna is installed with each tenant subscribing separately and billed separately by the cable company
- In all cases, deposits are paid by subscribers that cover receiver system costs, much like cable subscriber
Advantages of Using MMDS:
- It has chunks of under−utilized spectrum that will become increasingly valuable and flexible.
- System implementation, which is little more than putting an installed transmitter on a high tower and a small receiving antenna on the customer's balcony or roof, is quick and inexpensive.
- Because MMDS services have been around for 30 years, there is a wealth of experience regarding the use and distribution of the services.
Key Elements:
- The Head−End - The key elements in optimizing transmitted signal levels are the selection of the head−end site and the transmitting antenna, transmission feeders, channel combiners, channel diplexers, and transmitters. The head−end's task is to distribute the signal to as many subscribers as possible.
- The Transmit Antenna - The bandwidth allocated to MMDS operators can vary from 200 to over 300 MHz, depending on the number of channels and their spacing.
- The Transmission Line - This is another critical component that can have a substantial effect on system losses. Major Head−end sites typically use 50 or 100 watt transmitters, yet often only 50 percent of this power reaches the antenna after passing through channel combiners and transmission feeders.
- Channel Combiners - MMDS sites normally transmit a number of channels. Special filters (channel combiners) are used to combine the outputs of the transmitters to the transmission feeder and antenna.
Local Multipoint Distribution Service (LMDS):
- Voice dial−up services
- Data
- Internet access
- Video
LMDS operates in the higher frequencies, the radio signals are limited to approximately five miles of point−to−point service.
Architectural concept for the LMDS operation
Modulation and Access Techniques:
The modulation and access method falls into two primary categories, FDMA and TDMA. Each of these techniques differs but also creates other sub modulation capabilities. For the broadband LMDS services, the system is usually separated into both phase and amplitude modulation of the RF. Phase−shift keying (PSK) and amplitude modulation combinations have been successfully used to achieve high rates of multiplexing and carrying capacities.
Two−Way Service:
The TDMA and FDMA modulation techniques on the LMDS network allow for the bidirectional flow between the carrier and the end user. In many cases, a different upstream is required than the downstream.
Microwave and Radio Based System
Microwave:
Table that show’s comparison of frequency bands and distances
Microwave radio relay is a technology for transmitting digital and analog signals, such as long-distance telephone calls, television programs, and computer data, between two locations on a line-of-sight radio path. In microwave radio relay, radio waves are transmitted between the two locations with directional antenna, forming a fixed radio connection between the two points. Long daisy-chained series of such links form transcontinental telephone and/or television communication systems.
Microwave are radio wave with wavelength ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz.
Microwaves are widely used for point-to-point communications because their small wavelength allows conveniently-sized antennas to direct them in narrow beams, which can be pointed directly at the receiving antenna. This allows nearby microwave equipment to use the same frequencies without interfering with each other, as lower frequency radio waves do. Another advantage is that the high frequency of microwaves gives the microwave band a very large information-carrying capacity; the microwave band has a bandwidth 30 times that of all the rest of the radio spectrum below it. A disadvantage is that microwaves are limited to line of sight propagation; they cannot pass around hills or mountains as lower frequency radio waves can.
Properties of a Microwave:
- Suitable over line-of-sight transmission links without obstacles
- Provides large useful bandwidth when compared to lower frequencies (HF, VHF, UHF)
- Affected by the refractive index (temperature, pressure and humidity) of the atmosphere, rain, snow and hail, sand storms, clouds, mist and fog, strongly depending on the frequency.
Comparison of frequency bands and distances:
There are even differences between one type of microwave and another. The differences are due primarily to their respective operating frequencies. Some frequencies are good for distances of 30 or 40 miles and others can barely get you across an office park. Some can only support a couple of T1s or a single video channel and others go to 10 to 45 Mb.
Table that show’s comparison of frequency bands and distances
Other Application of Microwave:
Similarly, microwave transmission is used in LANs, on corporate or college campuses, in airports, and elsewhere. Whether it is collecting data, relaying conversations, or beaming messages from space, microwave makes the wireless revolution possible.
Laptop computers can now send and receive microwave radio transmissions.
Microwave Radio Relay:
Huwebes, Pebrero 9, 2012
xDigital Subscriber line (xDSL)
xDSL belongs to DSL family, the lower case x in xDSL stands for the many variation including the fallowing.
- Asymmetrical digital subscriber line (ADSL)
ADSL is the new modem technology to converge the existing twisted pair telephone lines into the high−speed communications access capability for various services.
ADSL is a modem technology used to transmit speeds of between 1.5 Mbps and 6 Mbps under current technology.
Data rates for ADSL, based on installed wiring at varying gauges.
NOTE: The speeds and distances shown here are the theoretical limits based on good copper.
- Digital subscriber line (IDSL)
DSL refers to a pair of modems that are installed on the local loop to facilitate higher speeds for data transmission.
The IDSL technique is an all digital operating at two channels of 64 Kbps for voice or non voice operation and a 16 Kbps data channel for signaling, control, and data packets. A DSL is used to deliver I SDN services. As the deployment of IDSL was speeding up on the local loop, the providers developed a new twist, called "always on, ISDN" mimicking a leased set of channels that are always connected.
The IDSL line connection enables 128 Kbps in total simultaneously.
- High bit−rate Digital Subscriber Line (HDSL)
HDSL was the first DSL to use higher frequency spectrum of copper, twisted pair cable. HDSL was developed in the US, as a better technology for high-speed, synchronous circuits typically used to interconnect local exchange carrier system, and also to carry high-speed corporate data links and voice channels, using T1 lines.
- Consumer Digital Subscriber Line (CDSL)
CDSL is a model of DSL developed for the consumer that does not who is not looking for symmetrical high−speed communication. With other forms of DSL (such as ADSL and RADSL), splitters are used on the line to separate the voice and the data communications. CDSL does not use, nor need, a splitter on the line. Speeds of up to 1 Mbps in the download direction and 160 Kbps in the upward direction are provided. It is expected that the speeds and DSL will meet the needs of the average consumer for some time to come.
- Single High Speed DSL (SHDSL)
SHDSL is a data communications technology that enables faster data transmission over copper telephone line than a conventional voice modem can provide. Compare to ADSL, SHDSL employs TC-PAM modulation and frequencies that include those used by analog plain old telephone service to provide equal transmit and receive data rates. SHDSL features symmetrical data rates in both the upstream and downstream directions, From 192 kbit/s to 2,312 kbit/s of payload in 8 kbit/s increments for one pair and 384 kbit/s to 4,624 kbit/s in 16 kbit/s increments for two pairs of wires.
- Rate−adaptive digital subscriber line (RADSL)
RADSL is a variation of asymmetric digital subscriber line technology. In RADSL the DSL modem adjust the upstream bandwidth to create a wider frequency band for the downstream traffic. Using this technique the line is more tolerant of errors caused by noise and signal loss.
- Very high−bit rate digital subscriber line (VDSL)
DSL speeds and operations using current methods
xDSL Coding Techniques
- Discreet Multitone - DMT uses multiple narrowband carriers, all transmitting simultaneously in a parallel transmission mode. Each of these carriers carries a portion of the information being transmitted. These multiple discrete bands, or, in the world of frequency division multiplexing, sub-channels, are modulated independently of each other using a carrier frequency located in the center of the frequency being used. These carriers are then processed in parallel form.
- Carrier-less Amplitude Phase Modulation CAP - CAP is closely aligned to QAM. QAM as a technique is widely understood in the industry and well deployed in our older modems. Both CAP and QAM are a single−carrier signal technique. The data rate is divided into two and modulated onto two different orthogonal carriers before being combined and transmitted. The main difference between CAP and QAM is in the way they are implemented. QAM generates two signals with a sine/cosine mixer and combines them onto the analog domain. CAP, on the other hand, generates its two orthogonal signals and executes them digitally. Using two digital transversal bandpass filters with equal amplitude characteristics and a p/2 difference in phase response, the signals are combined and fed into a digital−to−analog converter. Then the data is transmitted. The advantage of CAP over QAM is that CAP is done in silicon, which is more efficient and less expensive.
A design of an ADSL model and its model components
The intent of the model is to show the infrastructure of the network from the customer premises to the network provider.
Source:
Broadband Telecommunication Handbook 2nd edition by: Regis J. "BUD" Bates
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