26-07-2014, 03:00 PM
ULTRA WIDEBAND TECHNOLOGY
[attachment=66277]
INTRODUCTION
UWB is a wireless technology that transmits binary data—the 0s and 1s that are the digital building blocks of modern information systems. It uses low-energy and extremely short duration (in the order of pico seconds) impulses or bursts of RF (radio frequency) energy over a wide spectrum of frequencies, to transmit data over short to medium distances, say about 15—100 m. It doesn’t use carrier wave to transmit data.
UWB is fundamentally different from existing radio frequency technology. For radios today, picture a guy watering his lawn with a garden hose and moving the hose up and down in a smooth vertical motion. You can see a continuous stream of water in an undulating wave. Nearly all radios, cell phones, wireless LANs and so on are like that: a continuous signal that's overlaid with information by using one of several modulation techniques.
Now picture the same guy watering his lawn with a swiveling sprinkler that shoots many, fast, short pulses of water. That's typically what UWB is like: millions of very short, very fast, precisely timed bursts or pulses of energy, measured in nanoseconds and covering a very wide area. By varying the pulse timing according to a complex code, a pulse can represent either a zero or a one: the basis of digital communications.
Wireless technologies such as 802.11b and short-range Bluetooth radios eventually could be replaced by UWB products that would have a throughput capacity 1,000 times greater than 802.11b (11M bit/sec). Those numbers mean UWB systems have the potential to support many more users, at much higher speeds and lower costs, than current wireless LAN systems. Current UWB devices can transmit data up to 100 Mbps, compared to the 1 Mbps of Bluetooth and the 11 Mbps of 802.11b. Best of all, it costs a fraction of current technologies like Blue-tooth, WLANs and Wi-Fi.
HISTORY OF UWB TECHNOLOGY
Ultra-wideband communications is fundamentally different from all other communication techniques because it employs extremely narrow RF pulses to communicate between transmitters and receivers. Utilizing short-duration pulses as the building blocks for communications directly generates a very wide bandwidth and offers several advantages, such as large throughput, covertness, robustness to jamming, and coexistence with current radio services.
Ultra-wideband communications is not a new technology; in fact, it was first employed by Guglielmo Marconi in 1901 to transmit Morse code sequences across the Atlantic Ocean using spark gap radio transmitters. However, the benefit of a large bandwidth and the capability of implementing multiuser systems provided by electromagnetic pulses were never considered at that time.
Approximately fifty years after Marconi, modern pulse-based transmission gained momentum in military applications in the form of impulse radars. Some of the pioneers of modern UWB communications in the United States from the late 1960s are Henning Harmuth of Catholic University of America and Gerald Ross and K. W. Robins of Sperry Rand Corporation [2]. From the 1960s to the 1990s, this technology was restricted to military and Department of Defense (DoD) applications under classified programs such as highly secure communications. Therefore, it is more appropriate to consider UWB as a new name for a long-existing technology.
As interest in the commercialization of UWB has increased over the past several years, developers of UWB systems began pressuring the FCC to approve UWB for commercial use. Sections 1.9 and 1.10 present a detailed recent history of the standardization and worldwide regulation of UWB technology. Figure 1-1 summarizes the development timeline of UWB.
DEVELOPMENT OF UWB TECHNOLOGY
The development of UWB technology stems from work that was undertaken by the US military into defining the behaviour of microwave networks to impulse or transients. The work which was started in 1962. Traditionally networks had been characterised according to their response in the frequency domain where parameters such as amplitude and phase with respect to frequency are important. However the new approach which was to spawn the first ideas about ultra wide band or UWB technology looked at the impulse response.
At the time measurements were difficult to make as test equipment with a sufficiently high bandwidth was not available. The fact that the research was investigating an area where the supporting technologies such as test equipment were not sufficiently developed placed restraints on the research, but nevertheless investigations into the technology continued.
Having looked at the response of microwave networks to impulses, the next major step forward occurred when the techniques were applied to radiating systems. Once this work commenced in 1968 it soon became obvious that UWB technology could be used for radar and communications applications.
The rate at which work was undertaken was increased in the 1970s and 80s as the supporting technologies became available. During this period it was termed carrier free or impulse technology. The term ultra wide band or UWB was only coined in the later 1980s by the US Department of Defense. However by this time many patentees had been awarded and a considerable degree of development had been invested in the technology.
Development of UWB technology was primarily intended for military applications and it was classified. As a result little development took place in the commercial arena. However in the years following 2000, commercial wireless communications became established. Technologies such as 802.11 (Wi-Fi), Bluetooth and others became established. These paved the way, and showed the flexibility offered by wireless communications for a very wide variety of applications from mobile phone peripheral connectivity to mobility and connectivity for laptops. These technologies and others grew rapidly. Accordingly commercial applications for ultra wideband UWB became very apparent and commercial exploitation started
One of the major limitations to the speed at which UWB could enter the commercial marketplace was legislation. In view of the fact that UWB occupies a wide bandwidth, even though at a low power level, it has to exist alongside traditional transmissions without causing any undue interference. Accordingly the legislative bodies and in particular the FCC in the USA have been proceeding with caution. Any changes in direction required will be far more difficult to address in later years once UWB technology is firmly established. Despite this UWB transmissions are allowed, provided that they remain within a given power density and frequency profile. This ensures that the allowed transmission levels do not cause any noticeable interference to existing transmissions.
Spectrum Definition
Many countries have allocated spectrum for UWB use, with various restrictions and power output limits. The standardized output level for UWB communications is –41.3dBm/MHz. The WiMedia Alliance has defined fourteen 500-MHz bands to divide up the 3.1-10.6 GHz spectrum allocated for Ultra-Wideband communications in the U.S. in 2002.
Many countries had already allocated some spectrum <6 GHz for other uses such as GPS and satellite communications and therefore desired a way to protect those existing devices and applications while allocating additional spectrum for UWB communications, with the idea that UWB devices would avoid the traditional transmitters when they came into geographical proximity or radio range. DAA stands for “Detect and Avoid” and is a similar technique to cognitive radio that was defined for this legacy coexistence. Cognitive radio attempts to detect “primary users” and switch communications to another unused channel. Cognitive Radio is often in the news for trying to make use of the “White Space” between legacy TV broadcast channels. DAA is different in that UWB communications continue on the same band, but actually notch out the transmit spectrum around the legacy channel, so that they don’t interfere but can make use of the channel. The requirement of DAA was placed on the Band Group 1 spectrum by the E.U. and others in 2006 with an implementation deadline of Dec 31, 2010. Due to the U.S. recession and financial difficulties for the UWB developing companies, there was less pressure on the E.U. to exactly define how silicon should implement DAA and companies have not fully implemented DAA. Therefore, devices with global regulatory certification usually use BG3 and BG6 since those bands do not have a DAA requirement. However, China did formally extend their DAA enforcement deadline to Dec 31st, 2013 for Bands 1, 2, and 3 and South Korea formally extended their DAA enforcement deadline to Dec 31st, 2016 for Band
Back to basics
To understand UWB, we’ll first look at radio communication and how data is transmitted traditionally. All of us have dropped pebbles in a water pool at some point in our lives. Remember the ripples traveling outwards from the point where the pebble enters the water up to the boundary?
Normal radio waves are sine waves or smoothly fluctuating waves like these ripples. Traditionally, radio communications stay within the allocated frequency band. We normally use a carrier wave to transmit data. The carrier wave is imprinted with data by modulating any of the following— amplitude, frequency or phase of the carrier wave. Three common ways of modulating a sine wave are AM (Amplitude Modulation), FM (Frequency Modulation) and PM (Pulse Modulation). Refer to the above diagrams to understand how radio waves transmit data).
What happens when you listen to news from an AM radio station, say an All India Radio medium wave station? The sine wave of the announcer’s voice is combined with the transmitter’s sine wave (carrier wave) to vary its amplitude, and then transmitted. In AM, the amplitude of the sine wave or rather its peak-to-peak voltage changes. FM stations and other wireless technologies including cordless phones, cell phones and WLANs use FM, where based on the information signal, the transmitter’s sine wave frequency changes slightly. In PM, the carrier or sine wave is turned on and off to send data. In its simplest form, it can be a kind of Morse code. (See diagrams for a basic idea of how narrow-band communications work). The receiver in each case is specially tuned to decode information in the carrier wave.
Usage of a carrier wave within a narrow band effectively means limiting amount of data that can be imprinted on to it. Hence the importance of UWB.
INTRODUCTION
“Ultra-wideband” has its roots in the original “spark-gap” transmitters that pioneered radio technology. This history is well known and has been well documented in both professional histories and in popular treatments. The development of UWB antennas has not been subjected to similar scrutiny. As a consequence, designs have been forgotten and then re-discovered by later investigators. This section aims to fill this void by offering a brief history of UWB antennas.
2. SPARK GAP DAYS
Ironically, the very patent which inaugurated the concept of narrowband frequency domain radio also disclosed some of the first ultra-wideband antennas. In 1898, Oliver Lodge introduced the concept of “syntony,” the idea that a transmitter and a receiver should be tuned to the same frequency so as to maximize the received signal . In this same patent, Lodge discussed a variety of “capacity areas,” or antennas, that will be quite familiar to modern eyes:
THE DIFFERENCE IN THE TRANSMISSION METHODS OF UWB HAS SEVERAL IMPLICATIONS
• For one thing, because UWB pulses don't actually use a traditional radio signal, called a carrier, UWB transmissions don't take up any of the radio spectrum. Spectrum is limited, and demand for it is growing fast. That's one reason for the FCC interest: UWB would allow a whole new class, and volume, of voice and data communications that, in effect, wouldn't take up any more "space" in the crowded radio spectrum.
• Second, and partly as a result of the fact that UWB doesn't use a traditional radio signal, UWB transmitters and receivers will be much simpler to build, run and maintain than those in use today. For UWB, you don't need complex radio frequency converters and modulators. We only need a digital method to construct the pulses and modulate them. This can all go on a single chip. One vendor already does this on a chip the size of a penny.
• Third, because UWB operates in the electronic "noise" area of the spectrum, it requires little power. These systems can use 50 to 70 milliwatts of power.That is one ten-thousandth the power of a cell phone. The low power limits the range, but there are features of pulse transmission and some tuning techniques that can, in effect, extend or maintain the range.
• In addition, low power and the characteristic wide spread of the pulses means the pulses don't use up already crowded chunks of the radio spectrum, today occupied by 802.11b wireless LANs and Bluetooth devices.
• Despite the low power, UWB also has greater capacity - higher bandwidth for more users - compared with these other technologies. Time Domain began testing its just-fabricated, second-generation UWB chipset using silicon germanium technology created by IBM. The new chipset can reach 40M bit/sec, compared with just 2.5M bit/sec for the first chipset two years ago. Another start-up, Fantasma Networks, which Pulse-Link acquired , claims to have reached 60M bit/sec.
• Finally, UWB promises to be highly secure. It's very difficult to filter a pulse signal out of the flood of background electronic noise, and vendors such as Time Domain are encrypting the zeros and ones being transmitted by the pulses.
CONCLUSION
UWB is undoubtedly a niche technology which holds promise in a wide area. But, its success depends on scoring against a handful of rival technologies in which companies have invested billions. Those who’ve invested their money will not hasten to consider an upstart rival, even if it offers better services. It seems that UWB will most probably succeed in WPANs as a means of delivering data-intensive applications like video. Imagine downloading the latest blockbuster on your portable player while tanking up at the petrol pump! But, this dream will take at least a year to materialize at the current pace of things.
The U.S. Navy, plans to put a UWB location marker on almost everything it ships overseas, just to keep track of all the stuff and keep it from being stolen.
UWB products will probably begin to hit the market in the next 18 to 24 months. In addition to radios, these products will include radar and electronic positioning devices.
The bottom line is that the FCC's move to make more unlicensed spectrum available is proving to be a huge success for the wireless industry and for consumers. The latest entrant, UWB, is entering an industry and market dramatically matured through the experience of its predecessors Bluetooth and WiFi. If UWB proponents can quickly knock out the issues of standards and interoperability it will allow the powerful forces of Moore's law and economies of scale to start their work early bringing consumers cost effective products within a few short years from today. If the industry has learned from its past mistakes and it looks like it has, UWB is poised for dramatic growth and success in a way not witnessed before for any wireless technology.
[attachment=66277]
INTRODUCTION
UWB is a wireless technology that transmits binary data—the 0s and 1s that are the digital building blocks of modern information systems. It uses low-energy and extremely short duration (in the order of pico seconds) impulses or bursts of RF (radio frequency) energy over a wide spectrum of frequencies, to transmit data over short to medium distances, say about 15—100 m. It doesn’t use carrier wave to transmit data.
UWB is fundamentally different from existing radio frequency technology. For radios today, picture a guy watering his lawn with a garden hose and moving the hose up and down in a smooth vertical motion. You can see a continuous stream of water in an undulating wave. Nearly all radios, cell phones, wireless LANs and so on are like that: a continuous signal that's overlaid with information by using one of several modulation techniques.
Now picture the same guy watering his lawn with a swiveling sprinkler that shoots many, fast, short pulses of water. That's typically what UWB is like: millions of very short, very fast, precisely timed bursts or pulses of energy, measured in nanoseconds and covering a very wide area. By varying the pulse timing according to a complex code, a pulse can represent either a zero or a one: the basis of digital communications.
Wireless technologies such as 802.11b and short-range Bluetooth radios eventually could be replaced by UWB products that would have a throughput capacity 1,000 times greater than 802.11b (11M bit/sec). Those numbers mean UWB systems have the potential to support many more users, at much higher speeds and lower costs, than current wireless LAN systems. Current UWB devices can transmit data up to 100 Mbps, compared to the 1 Mbps of Bluetooth and the 11 Mbps of 802.11b. Best of all, it costs a fraction of current technologies like Blue-tooth, WLANs and Wi-Fi.
HISTORY OF UWB TECHNOLOGY
Ultra-wideband communications is fundamentally different from all other communication techniques because it employs extremely narrow RF pulses to communicate between transmitters and receivers. Utilizing short-duration pulses as the building blocks for communications directly generates a very wide bandwidth and offers several advantages, such as large throughput, covertness, robustness to jamming, and coexistence with current radio services.
Ultra-wideband communications is not a new technology; in fact, it was first employed by Guglielmo Marconi in 1901 to transmit Morse code sequences across the Atlantic Ocean using spark gap radio transmitters. However, the benefit of a large bandwidth and the capability of implementing multiuser systems provided by electromagnetic pulses were never considered at that time.
Approximately fifty years after Marconi, modern pulse-based transmission gained momentum in military applications in the form of impulse radars. Some of the pioneers of modern UWB communications in the United States from the late 1960s are Henning Harmuth of Catholic University of America and Gerald Ross and K. W. Robins of Sperry Rand Corporation [2]. From the 1960s to the 1990s, this technology was restricted to military and Department of Defense (DoD) applications under classified programs such as highly secure communications. Therefore, it is more appropriate to consider UWB as a new name for a long-existing technology.
As interest in the commercialization of UWB has increased over the past several years, developers of UWB systems began pressuring the FCC to approve UWB for commercial use. Sections 1.9 and 1.10 present a detailed recent history of the standardization and worldwide regulation of UWB technology. Figure 1-1 summarizes the development timeline of UWB.
DEVELOPMENT OF UWB TECHNOLOGY
The development of UWB technology stems from work that was undertaken by the US military into defining the behaviour of microwave networks to impulse or transients. The work which was started in 1962. Traditionally networks had been characterised according to their response in the frequency domain where parameters such as amplitude and phase with respect to frequency are important. However the new approach which was to spawn the first ideas about ultra wide band or UWB technology looked at the impulse response.
At the time measurements were difficult to make as test equipment with a sufficiently high bandwidth was not available. The fact that the research was investigating an area where the supporting technologies such as test equipment were not sufficiently developed placed restraints on the research, but nevertheless investigations into the technology continued.
Having looked at the response of microwave networks to impulses, the next major step forward occurred when the techniques were applied to radiating systems. Once this work commenced in 1968 it soon became obvious that UWB technology could be used for radar and communications applications.
The rate at which work was undertaken was increased in the 1970s and 80s as the supporting technologies became available. During this period it was termed carrier free or impulse technology. The term ultra wide band or UWB was only coined in the later 1980s by the US Department of Defense. However by this time many patentees had been awarded and a considerable degree of development had been invested in the technology.
Development of UWB technology was primarily intended for military applications and it was classified. As a result little development took place in the commercial arena. However in the years following 2000, commercial wireless communications became established. Technologies such as 802.11 (Wi-Fi), Bluetooth and others became established. These paved the way, and showed the flexibility offered by wireless communications for a very wide variety of applications from mobile phone peripheral connectivity to mobility and connectivity for laptops. These technologies and others grew rapidly. Accordingly commercial applications for ultra wideband UWB became very apparent and commercial exploitation started
One of the major limitations to the speed at which UWB could enter the commercial marketplace was legislation. In view of the fact that UWB occupies a wide bandwidth, even though at a low power level, it has to exist alongside traditional transmissions without causing any undue interference. Accordingly the legislative bodies and in particular the FCC in the USA have been proceeding with caution. Any changes in direction required will be far more difficult to address in later years once UWB technology is firmly established. Despite this UWB transmissions are allowed, provided that they remain within a given power density and frequency profile. This ensures that the allowed transmission levels do not cause any noticeable interference to existing transmissions.
Spectrum Definition
Many countries have allocated spectrum for UWB use, with various restrictions and power output limits. The standardized output level for UWB communications is –41.3dBm/MHz. The WiMedia Alliance has defined fourteen 500-MHz bands to divide up the 3.1-10.6 GHz spectrum allocated for Ultra-Wideband communications in the U.S. in 2002.
Many countries had already allocated some spectrum <6 GHz for other uses such as GPS and satellite communications and therefore desired a way to protect those existing devices and applications while allocating additional spectrum for UWB communications, with the idea that UWB devices would avoid the traditional transmitters when they came into geographical proximity or radio range. DAA stands for “Detect and Avoid” and is a similar technique to cognitive radio that was defined for this legacy coexistence. Cognitive radio attempts to detect “primary users” and switch communications to another unused channel. Cognitive Radio is often in the news for trying to make use of the “White Space” between legacy TV broadcast channels. DAA is different in that UWB communications continue on the same band, but actually notch out the transmit spectrum around the legacy channel, so that they don’t interfere but can make use of the channel. The requirement of DAA was placed on the Band Group 1 spectrum by the E.U. and others in 2006 with an implementation deadline of Dec 31, 2010. Due to the U.S. recession and financial difficulties for the UWB developing companies, there was less pressure on the E.U. to exactly define how silicon should implement DAA and companies have not fully implemented DAA. Therefore, devices with global regulatory certification usually use BG3 and BG6 since those bands do not have a DAA requirement. However, China did formally extend their DAA enforcement deadline to Dec 31st, 2013 for Bands 1, 2, and 3 and South Korea formally extended their DAA enforcement deadline to Dec 31st, 2016 for Band
Back to basics
To understand UWB, we’ll first look at radio communication and how data is transmitted traditionally. All of us have dropped pebbles in a water pool at some point in our lives. Remember the ripples traveling outwards from the point where the pebble enters the water up to the boundary?
Normal radio waves are sine waves or smoothly fluctuating waves like these ripples. Traditionally, radio communications stay within the allocated frequency band. We normally use a carrier wave to transmit data. The carrier wave is imprinted with data by modulating any of the following— amplitude, frequency or phase of the carrier wave. Three common ways of modulating a sine wave are AM (Amplitude Modulation), FM (Frequency Modulation) and PM (Pulse Modulation). Refer to the above diagrams to understand how radio waves transmit data).
What happens when you listen to news from an AM radio station, say an All India Radio medium wave station? The sine wave of the announcer’s voice is combined with the transmitter’s sine wave (carrier wave) to vary its amplitude, and then transmitted. In AM, the amplitude of the sine wave or rather its peak-to-peak voltage changes. FM stations and other wireless technologies including cordless phones, cell phones and WLANs use FM, where based on the information signal, the transmitter’s sine wave frequency changes slightly. In PM, the carrier or sine wave is turned on and off to send data. In its simplest form, it can be a kind of Morse code. (See diagrams for a basic idea of how narrow-band communications work). The receiver in each case is specially tuned to decode information in the carrier wave.
Usage of a carrier wave within a narrow band effectively means limiting amount of data that can be imprinted on to it. Hence the importance of UWB.
INTRODUCTION
“Ultra-wideband” has its roots in the original “spark-gap” transmitters that pioneered radio technology. This history is well known and has been well documented in both professional histories and in popular treatments. The development of UWB antennas has not been subjected to similar scrutiny. As a consequence, designs have been forgotten and then re-discovered by later investigators. This section aims to fill this void by offering a brief history of UWB antennas.
2. SPARK GAP DAYS
Ironically, the very patent which inaugurated the concept of narrowband frequency domain radio also disclosed some of the first ultra-wideband antennas. In 1898, Oliver Lodge introduced the concept of “syntony,” the idea that a transmitter and a receiver should be tuned to the same frequency so as to maximize the received signal . In this same patent, Lodge discussed a variety of “capacity areas,” or antennas, that will be quite familiar to modern eyes:
THE DIFFERENCE IN THE TRANSMISSION METHODS OF UWB HAS SEVERAL IMPLICATIONS
• For one thing, because UWB pulses don't actually use a traditional radio signal, called a carrier, UWB transmissions don't take up any of the radio spectrum. Spectrum is limited, and demand for it is growing fast. That's one reason for the FCC interest: UWB would allow a whole new class, and volume, of voice and data communications that, in effect, wouldn't take up any more "space" in the crowded radio spectrum.
• Second, and partly as a result of the fact that UWB doesn't use a traditional radio signal, UWB transmitters and receivers will be much simpler to build, run and maintain than those in use today. For UWB, you don't need complex radio frequency converters and modulators. We only need a digital method to construct the pulses and modulate them. This can all go on a single chip. One vendor already does this on a chip the size of a penny.
• Third, because UWB operates in the electronic "noise" area of the spectrum, it requires little power. These systems can use 50 to 70 milliwatts of power.That is one ten-thousandth the power of a cell phone. The low power limits the range, but there are features of pulse transmission and some tuning techniques that can, in effect, extend or maintain the range.
• In addition, low power and the characteristic wide spread of the pulses means the pulses don't use up already crowded chunks of the radio spectrum, today occupied by 802.11b wireless LANs and Bluetooth devices.
• Despite the low power, UWB also has greater capacity - higher bandwidth for more users - compared with these other technologies. Time Domain began testing its just-fabricated, second-generation UWB chipset using silicon germanium technology created by IBM. The new chipset can reach 40M bit/sec, compared with just 2.5M bit/sec for the first chipset two years ago. Another start-up, Fantasma Networks, which Pulse-Link acquired , claims to have reached 60M bit/sec.
• Finally, UWB promises to be highly secure. It's very difficult to filter a pulse signal out of the flood of background electronic noise, and vendors such as Time Domain are encrypting the zeros and ones being transmitted by the pulses.
CONCLUSION
UWB is undoubtedly a niche technology which holds promise in a wide area. But, its success depends on scoring against a handful of rival technologies in which companies have invested billions. Those who’ve invested their money will not hasten to consider an upstart rival, even if it offers better services. It seems that UWB will most probably succeed in WPANs as a means of delivering data-intensive applications like video. Imagine downloading the latest blockbuster on your portable player while tanking up at the petrol pump! But, this dream will take at least a year to materialize at the current pace of things.
The U.S. Navy, plans to put a UWB location marker on almost everything it ships overseas, just to keep track of all the stuff and keep it from being stolen.
UWB products will probably begin to hit the market in the next 18 to 24 months. In addition to radios, these products will include radar and electronic positioning devices.
The bottom line is that the FCC's move to make more unlicensed spectrum available is proving to be a huge success for the wireless industry and for consumers. The latest entrant, UWB, is entering an industry and market dramatically matured through the experience of its predecessors Bluetooth and WiFi. If UWB proponents can quickly knock out the issues of standards and interoperability it will allow the powerful forces of Moore's law and economies of scale to start their work early bringing consumers cost effective products within a few short years from today. If the industry has learned from its past mistakes and it looks like it has, UWB is poised for dramatic growth and success in a way not witnessed before for any wireless technology.