04-11-2016, 04:28 PM
[attachment=74582]
Abstract:
The requirement for wireless wideband communications is rapidly increasing due to the need to support more users and to provide more information with higher data rates. Ultra wideband (UWB) technology based on the use of very narrow pulses on the order of nanoseconds, covering a very wide bandwidth in the frequency domain, could be a possible solution to this problem. UWB is a wireless technology developed to transfer data at high rates over very short distances at very low power densities and an area of immense current interest, with numerous potential applications. This paper presents the currently UWB technology and its potential applications. How this technology implemented without causing interference to other existing communication is also discussed. The advantages and disadvantages of this technology are looked into deep as well.
Definition:
UWB is a radio technology pioneered by Robert A. Scholtz and others that can use a very low energy level for short range, high bandwidth communications over a large portion of the radio spectrum.
UWB has traditional applications in non-cooperative radar imaging. Most recent applications are target sensor data collection, precision locating and tracking applications.
Evolution:
Ultra-wideband refers to radio systems for communications or measurement purposes. UWB has been considered a revolutionary technology for transmitting large amounts of digital data over a broad frequency spectrum using short pulse, low powered radio signals. The term UWB was introduced by the US Department of Defense (DoD) around 1989 and commonly refers to a signal or system that either has a bandwidth that exceeds twenty percent of the centre frequency or a large absolute bandwidth of more than 500 MHz. Such radio systems have been authorized by the US Federal Communications Commission (FCC) for unlicensed use in the range 3.1–10.6 GHz. In February 2002, the FCC approved the first Report and Order for the commercial use of UWB technology under strict power emission limits. The huge bandwidth coupled with a very low power level makes UWB signals appear more or less like background noise to other wireless communication systems. This allows them to coexist with other radio communication devices as well and make them immune to detection and interception by other narrowband wireless communication receivers. UWB facilitates the efficient use of relatively scarce radio bandwidth, while enabling high data rate personal area network (PAN) wireless connectivity and longer-range, low data rate applications as well as radar and imaging systems.
UWB-enabled sensors are non-destructive and non-invasive measurement devices, collecting information across a much wider frequency range than non-UWB systems. UWB is often called carrier-less because it does not concentrate signal energy around a dedicated frequency.Furthermore, UWB can be used for localisation purposes, where the large bandwidth facilitates an impressive accuracy which benefits both short range localisation and the realisation of autonomous moving devices.
As early as 1901, Marconi employed very large bandwidths to transmit Morse code sequences across the Atlantic Ocean using spark gap radio transmitters. Nevertheless, the benefit of a large bandwidth and the capacity to implement multi-user systems was never considered at that time.
In the 1950s, pulse based transmission gained momentum in military applications in the form of impulse radars.From the 1960s to the 1990s, UWB technology was restricted to military applications under classified DoD programs in the US, aimed at highly secure communication.
Looking at UWB development from a scientific rather than a political perspective, it took until the 1960s when ground-breaking research in time-domain electromagnetic waves started to pave the way for modern UWB technology.
In 1978, Ross and Bennet applied these techniques in radar and communication applications. Although UWB is no new technology, its application for communication is quite new. Recent advances in microelectronics have made UWB ready for use in commercial applications. Therefore, it is more appropriate to consider UWB to be a new name for a long-existing technology.
Most UWB communication systems are either pulse-based or multicarrier-based.For instance, the transmission of low-powered pulses often eliminates the need for a power amplifier (PA) in UWB transmitters.This simplicity makes the all-CMOS (Complementary Metal Oxide Semiconductor) implementation of UWB transceivers possible and translates into smaller form factors and lower production costs. One obvious advantage of a multiband scheme is to avoid sending signals on frequencies where other radio communication devices are present, with the corresponding dis-advantage that this requires sophisticated signal processing techniques and thus more complex transceivers.
In EUWB all commercially attractive system architectures were considered including the IEEE 802.15.4a and ECMA standards. In this White Paper we will also describe the benefits of UWB technology and demonstrate its superiority in many application areas.The majority of the UWB industry players that became suppliers of WiMedia and Wireless USB solutions are fabless semiconductor manufacturers. A need for simple, high speed wireless connectivity and the increasing relevance of transmitting and synchronizing stored data could be translated into direct benefits for the consumer.
Essential features of UWB Technology:
Since by definition a signal or system is called UWB if it has either a bandwidth that exceeds twenty percent of the centre frequency or a large absolute bandwidth of more than 500 MHz, several physical layers are considered as UWB. The two major physical layers (PHY) that have been standardised are the multiband (MB-)OFDM waveform and the impulse radio waveform. However, other equipment exists using less conventional waveforms, namely chirp and frequency hopping (FH) waveforms.
Impulse Radio:
Impulse radio (IR) technology and its opportunities have been known about for decades. The technique uses very short pulses for the transmitted radio signal instead of modulated continuous sine waves. Due to the time/frequency duality, IR naturally falls within the scope of UWB technologies as defined by the regulators. Early implementations were developed by the US army around 1960, in particular for radar applications and electro-magnetic weapons. Similar implementations followed later in the public domain in the imaging, medical and construction fields, and more recently, IR has been considered for communication purposes. Although the communication potential of impulse radio has been apparent for a long time, the technical requirements for implementing an efficient impulse radio transceiver only became achievable over the last ten years. On the other hand, carrier-based radio technologies have continued to improve their performance and still meet market requirements, meaning that there has been little reason for spending time and money on developing IR technology.
During the last ten years, a combination of factors has changed the situation, leading to a renewed interest for impulse radio techniques:
• Wide adoption of location-based services based on GPS stimulated the demand to extend them into indoor environments.
• Silicon technology was not a blocking point anymore.
• Emerging applications based on sensors networks, in particular in the industrial sector, created a need for ultra-low power RF communication skills which have to be robust in harsh environments.
Due to its obvious market impact the high data rate aspect was considered first. In 2003, Freescale demonstrated a working IR, low power and high data rate video streaming application. More recently, Nokia demonstrated an IR-based ultra-low power, high data rate download application for embedded devices, too. Nevertheless, these implementations have remained in the proof-of-concept state up to now and the vast majority of key chip vendors involved in UWB preferred an alternative implementation based a combination of OFDM and frequency hopping. This second approach is discussed in the following section.As mentioned before, one of the earliest applications of impulse radio was radar. The use of very short pulses allowed detailed analysis of the channel impulse response which made the resolution of small size objects possible without suffering fading effects. A simplified application of this capability is the detection of the received RF wave leading edge. Combined with an accurate time base, this allows RF wave time of flight estimation, and consequently distance measurement, between the transmitter and the receiver. Compared to approaches based on signal strength in traditional RF systems like Wi-Fi or ZigBee, this technique proves to be more accurate and easier to deploy.
All these considerations led to the adoption of the IEEE 802.15.4a standard in 2007. This standard proposes use of IR for distance measurement and data transmission. Proprietary solutions were also proposed by “historical” companies in the field of IR.
Implementation considerations:
The use of pulses for carrying transmitted information opens the door to several modulation options. The first one is pulse polarity modulation, as depicted in the below Figure1. Amplitude modulations other than binary ones are generally not used due to the low associated performance/complexity trade-off.
Multiband OFDM:
The high data rate (HDR) MB-OFDM Physical layer has been defined by the WiMedia Alliance and standardised within the ECMA framework. This standard has two versions, mainly differing in the supported aggregate data rates and the techniques used to achieve those rates: modulation and channel coding and the maximal allowed packet size. The following sub-sections describe some of the major Physical layer characteristics.
Transmitted Power:
The UWB transmitted power level is limited under all regulations according to the maximum power density of the signal. Put simply, the limitation level according to the European regulation is –41.3 dBm/MHz.Accordingly, the total transmitted power is approximately –14 dBm for a single sub-band. This regulatory limitation also forces the UWB HDR to strive for a spectrally flat transmission with minimal periodical elements which may create a stronger spectral imprint at some frequencies forcing a decrease of the total power.
Supported frequencies:
The HDR PHY is modulated by OFDM symbols spanning 528 MHz of contiguous bandwidth. Each allocation of 528 MHz is called a band. Every two or three bands are grouped into a band group, in which devices may access in the same transmission, according to the TFC in use. The WiMedia frequency plan is constructed of five orthogonal band groups (BG) and one additional overlapping band group. Most band groups are composed of three separate bands except for BG#5 which has only two bands. Below Figure gives an explicit description of the WiMedia frequency plan including bandwidth and centre frequencies.
Data Rates:
Coding and Modulation:
The first version of the standard for the HDR UWB PHY supported rates up to 480Mbit/sec achieved by using convolutional (Viterbi) channel coding. Recently, a new standard version has been released which supports additional data rates up to 1024 Mbit/sec as well as an additional operational mode to some of the pre-existing data rates. All existing MB-OFDM UWB chips (including the EUWB “open platform”) support only rates up to480 Mbit/sec conforming to the first version of the standard. The below table lists the data rates supported by both standards, their associated modulation, coding type and data rate.
Ranging and Location Awareness:
The WiMedia PHY specifications define an optional measurement for ranging and location awareness based on propagation delay measurements that are intended to achieve an accuracy of ±60 cm in line-of-sight (LOS) conditions. The timing reference point is defined as the beginning of the first channel estimation symbol in the PHY convergence protocol (PLCP) preamble.
Support for range measurement in the PHY is based on counting the arrival time and storing it in a register. Such a counter may be clocked by a frequency source of 528 MHz to achieve a 56.8 cm ranging uncertainty. To provide increased precision, optional implementations may clock bit 2 at 1056 MHz (28.4 cm), bit 1 at 2112 MHz (14.2 cm), or clock bit 0 at 4224 MHz (7.1 cm).
Abstract:
The requirement for wireless wideband communications is rapidly increasing due to the need to support more users and to provide more information with higher data rates. Ultra wideband (UWB) technology based on the use of very narrow pulses on the order of nanoseconds, covering a very wide bandwidth in the frequency domain, could be a possible solution to this problem. UWB is a wireless technology developed to transfer data at high rates over very short distances at very low power densities and an area of immense current interest, with numerous potential applications. This paper presents the currently UWB technology and its potential applications. How this technology implemented without causing interference to other existing communication is also discussed. The advantages and disadvantages of this technology are looked into deep as well.
Definition:
UWB is a radio technology pioneered by Robert A. Scholtz and others that can use a very low energy level for short range, high bandwidth communications over a large portion of the radio spectrum.
UWB has traditional applications in non-cooperative radar imaging. Most recent applications are target sensor data collection, precision locating and tracking applications.
Evolution:
Ultra-wideband refers to radio systems for communications or measurement purposes. UWB has been considered a revolutionary technology for transmitting large amounts of digital data over a broad frequency spectrum using short pulse, low powered radio signals. The term UWB was introduced by the US Department of Defense (DoD) around 1989 and commonly refers to a signal or system that either has a bandwidth that exceeds twenty percent of the centre frequency or a large absolute bandwidth of more than 500 MHz. Such radio systems have been authorized by the US Federal Communications Commission (FCC) for unlicensed use in the range 3.1–10.6 GHz. In February 2002, the FCC approved the first Report and Order for the commercial use of UWB technology under strict power emission limits. The huge bandwidth coupled with a very low power level makes UWB signals appear more or less like background noise to other wireless communication systems. This allows them to coexist with other radio communication devices as well and make them immune to detection and interception by other narrowband wireless communication receivers. UWB facilitates the efficient use of relatively scarce radio bandwidth, while enabling high data rate personal area network (PAN) wireless connectivity and longer-range, low data rate applications as well as radar and imaging systems.
UWB-enabled sensors are non-destructive and non-invasive measurement devices, collecting information across a much wider frequency range than non-UWB systems. UWB is often called carrier-less because it does not concentrate signal energy around a dedicated frequency.Furthermore, UWB can be used for localisation purposes, where the large bandwidth facilitates an impressive accuracy which benefits both short range localisation and the realisation of autonomous moving devices.
As early as 1901, Marconi employed very large bandwidths to transmit Morse code sequences across the Atlantic Ocean using spark gap radio transmitters. Nevertheless, the benefit of a large bandwidth and the capacity to implement multi-user systems was never considered at that time.
In the 1950s, pulse based transmission gained momentum in military applications in the form of impulse radars.From the 1960s to the 1990s, UWB technology was restricted to military applications under classified DoD programs in the US, aimed at highly secure communication.
Looking at UWB development from a scientific rather than a political perspective, it took until the 1960s when ground-breaking research in time-domain electromagnetic waves started to pave the way for modern UWB technology.
In 1978, Ross and Bennet applied these techniques in radar and communication applications. Although UWB is no new technology, its application for communication is quite new. Recent advances in microelectronics have made UWB ready for use in commercial applications. Therefore, it is more appropriate to consider UWB to be a new name for a long-existing technology.
Most UWB communication systems are either pulse-based or multicarrier-based.For instance, the transmission of low-powered pulses often eliminates the need for a power amplifier (PA) in UWB transmitters.This simplicity makes the all-CMOS (Complementary Metal Oxide Semiconductor) implementation of UWB transceivers possible and translates into smaller form factors and lower production costs. One obvious advantage of a multiband scheme is to avoid sending signals on frequencies where other radio communication devices are present, with the corresponding dis-advantage that this requires sophisticated signal processing techniques and thus more complex transceivers.
In EUWB all commercially attractive system architectures were considered including the IEEE 802.15.4a and ECMA standards. In this White Paper we will also describe the benefits of UWB technology and demonstrate its superiority in many application areas.The majority of the UWB industry players that became suppliers of WiMedia and Wireless USB solutions are fabless semiconductor manufacturers. A need for simple, high speed wireless connectivity and the increasing relevance of transmitting and synchronizing stored data could be translated into direct benefits for the consumer.
Essential features of UWB Technology:
Since by definition a signal or system is called UWB if it has either a bandwidth that exceeds twenty percent of the centre frequency or a large absolute bandwidth of more than 500 MHz, several physical layers are considered as UWB. The two major physical layers (PHY) that have been standardised are the multiband (MB-)OFDM waveform and the impulse radio waveform. However, other equipment exists using less conventional waveforms, namely chirp and frequency hopping (FH) waveforms.
Impulse Radio:
Impulse radio (IR) technology and its opportunities have been known about for decades. The technique uses very short pulses for the transmitted radio signal instead of modulated continuous sine waves. Due to the time/frequency duality, IR naturally falls within the scope of UWB technologies as defined by the regulators. Early implementations were developed by the US army around 1960, in particular for radar applications and electro-magnetic weapons. Similar implementations followed later in the public domain in the imaging, medical and construction fields, and more recently, IR has been considered for communication purposes. Although the communication potential of impulse radio has been apparent for a long time, the technical requirements for implementing an efficient impulse radio transceiver only became achievable over the last ten years. On the other hand, carrier-based radio technologies have continued to improve their performance and still meet market requirements, meaning that there has been little reason for spending time and money on developing IR technology.
During the last ten years, a combination of factors has changed the situation, leading to a renewed interest for impulse radio techniques:
• Wide adoption of location-based services based on GPS stimulated the demand to extend them into indoor environments.
• Silicon technology was not a blocking point anymore.
• Emerging applications based on sensors networks, in particular in the industrial sector, created a need for ultra-low power RF communication skills which have to be robust in harsh environments.
Due to its obvious market impact the high data rate aspect was considered first. In 2003, Freescale demonstrated a working IR, low power and high data rate video streaming application. More recently, Nokia demonstrated an IR-based ultra-low power, high data rate download application for embedded devices, too. Nevertheless, these implementations have remained in the proof-of-concept state up to now and the vast majority of key chip vendors involved in UWB preferred an alternative implementation based a combination of OFDM and frequency hopping. This second approach is discussed in the following section.As mentioned before, one of the earliest applications of impulse radio was radar. The use of very short pulses allowed detailed analysis of the channel impulse response which made the resolution of small size objects possible without suffering fading effects. A simplified application of this capability is the detection of the received RF wave leading edge. Combined with an accurate time base, this allows RF wave time of flight estimation, and consequently distance measurement, between the transmitter and the receiver. Compared to approaches based on signal strength in traditional RF systems like Wi-Fi or ZigBee, this technique proves to be more accurate and easier to deploy.
All these considerations led to the adoption of the IEEE 802.15.4a standard in 2007. This standard proposes use of IR for distance measurement and data transmission. Proprietary solutions were also proposed by “historical” companies in the field of IR.
Implementation considerations:
The use of pulses for carrying transmitted information opens the door to several modulation options. The first one is pulse polarity modulation, as depicted in the below Figure1. Amplitude modulations other than binary ones are generally not used due to the low associated performance/complexity trade-off.
Multiband OFDM:
The high data rate (HDR) MB-OFDM Physical layer has been defined by the WiMedia Alliance and standardised within the ECMA framework. This standard has two versions, mainly differing in the supported aggregate data rates and the techniques used to achieve those rates: modulation and channel coding and the maximal allowed packet size. The following sub-sections describe some of the major Physical layer characteristics.
Transmitted Power:
The UWB transmitted power level is limited under all regulations according to the maximum power density of the signal. Put simply, the limitation level according to the European regulation is –41.3 dBm/MHz.Accordingly, the total transmitted power is approximately –14 dBm for a single sub-band. This regulatory limitation also forces the UWB HDR to strive for a spectrally flat transmission with minimal periodical elements which may create a stronger spectral imprint at some frequencies forcing a decrease of the total power.
Supported frequencies:
The HDR PHY is modulated by OFDM symbols spanning 528 MHz of contiguous bandwidth. Each allocation of 528 MHz is called a band. Every two or three bands are grouped into a band group, in which devices may access in the same transmission, according to the TFC in use. The WiMedia frequency plan is constructed of five orthogonal band groups (BG) and one additional overlapping band group. Most band groups are composed of three separate bands except for BG#5 which has only two bands. Below Figure gives an explicit description of the WiMedia frequency plan including bandwidth and centre frequencies.
Data Rates:
Coding and Modulation:
The first version of the standard for the HDR UWB PHY supported rates up to 480Mbit/sec achieved by using convolutional (Viterbi) channel coding. Recently, a new standard version has been released which supports additional data rates up to 1024 Mbit/sec as well as an additional operational mode to some of the pre-existing data rates. All existing MB-OFDM UWB chips (including the EUWB “open platform”) support only rates up to480 Mbit/sec conforming to the first version of the standard. The below table lists the data rates supported by both standards, their associated modulation, coding type and data rate.
Ranging and Location Awareness:
The WiMedia PHY specifications define an optional measurement for ranging and location awareness based on propagation delay measurements that are intended to achieve an accuracy of ±60 cm in line-of-sight (LOS) conditions. The timing reference point is defined as the beginning of the first channel estimation symbol in the PHY convergence protocol (PLCP) preamble.
Support for range measurement in the PHY is based on counting the arrival time and storing it in a register. Such a counter may be clocked by a frequency source of 528 MHz to achieve a 56.8 cm ranging uncertainty. To provide increased precision, optional implementations may clock bit 2 at 1056 MHz (28.4 cm), bit 1 at 2112 MHz (14.2 cm), or clock bit 0 at 4224 MHz (7.1 cm).