What is Ultra Wideband?

Ultra Wide Band (UWB) technology is a new type of wireless communication technology. It directly modulate impulse pulses with very steep rise and fall times to make the signal have a bandwidth on the order of GHz.

UWB technology is a new type of wireless communication technology. It works by

UWB is a maverick wireless communication technology that will bring low-power, high-bandwidth, and relatively simple wireless communication technologies to the interface cards and access technologies of wireless local area network LANs and personal area networks. UWB has the following characteristics:

Anti-interference performance

For UWB signals, weak radio pulse signals are dispersed in a wide frequency band during transmission, and the output power is even lower than the noise generated by ordinary equipment. The signal energy is restored during reception, and a spreading gain is generated during the despreading process. Therefore, compared with IEEE 802.11a, IEEE 802.11b, and Bluetooth, UWB has stronger anti-interference performance at the same code speed.

High transfer rate

The data rate of UWB can reach tens of megabits per second to several hundred megabits per second, which is expected to be 100 times higher than Bluetooth, and also higher than IEEE 802.11a and IEEE 802.11b.

Extremely wide bandwidth

UWB uses a bandwidth of more than 1 GHz, up to a few gigahertz, and can work simultaneously with narrow-band communication systems without interference. This opens up a new type of time domain radio resource when frequency resources become increasingly tight.

Large system capacity

Because there is no need to generate a sinusoidal carrier signal, and the impulse sequence can be transmitted directly, the UWB system has a wide spectrum and a low average power, which is conducive to coexistence with other systems, thereby improving the spectrum utilization rate and bringing a great system capacity.

Low transmit power

In short-distance communication applications, the transmission power of ultra-wideband transmitters can usually be less than 1mW. In theory, the interference caused by ultra-wideband signals is only equivalent to a broadband white noise. This is helpful for the good coexistence between ultra-wideband and the existing narrowband communication, which is of great significance for improving the utilization of the wireless spectrum and better alleviating the increasingly tight wireless spectrum resource problem. In addition, the ultra-wideband signal is more concealed, it is not easy to be found and intercepted, and it has high confidentiality.

Good confidentiality

UWB confidentiality is manifested in two aspects: on the one hand, it adopts time-hopping spread spectrum, and the receiver can only solve the transmission data when the transmitting end spreading code is known; on the other hand, the system's transmission power spectral density is extremely low. It cannot be received with a conventional receiver.

Short communication distance

Signal transmission is affected by distance and high-frequency signal strength will decay rapidly, so the use of ultra-wideband is more suitable for short-distance communication.

Multipath resolution

Because it uses narrow pulses with extremely short duration, its temporal and spatial resolution is very strong, which facilitates the development of ranging, positioning, tracking and other activities, and the narrow pulses have good penetration. The UWB encountered is also widely used in infrared communication.

Portable

This technology uses baseband transmission and does not require radio frequency modulation and demodulation, so its equipment has low power consumption and low cost, and its flexible use characteristics also make it more suitable for portable wireless communications. ^[1]

Single-band system

The single-band system uses only a single shaped pulse for data transmission. The signal bandwidth is large, the multipath resolution is high, and the anti-fading capability is strong. However, due to the serious time dispersion of the signal, the complexity of the receiver is high. In addition, in order to solve the coexistence problem and avoid interference with the narrow-band system in the band, the filter used in this system is also relatively complicated. Its typical representative is single-carrier DS-CDMA. In the single-carrier DS-CDMA scheme, the signal after DS-CDMA spread spectrum is modulated on the carrier, so that it can be transmitted in a suitable frequency band. The traditional carrier-free UWB scheme has a lot of low-frequency components, and cannot meet the transmission power limit specified by the FCC. The single-carrier DS-CDMA solution solves this problem through spectrum shift.

Multiband system

The multi-band system refers to dividing the entire frequency band of the planned UWB into several sub-bands. Use part or all of the subbands for data transmission. Signal shaping and data modulation are completed in the baseband and moved to different subbands through the RF carrier, avoiding the frequency band used by traditional narrowband systems. Multi-band systems are divided into multi-band pulse radio and multi-band orthogonal frequency division multiplexing based on the modulation method. Its multiple access problem is solved by frequency hopping technology. Relative to the symbol rate, it can be divided into fast hops and slow hops. MBOA (MultiBand Orthogonal frequency dlision multiplexing Alliance) proposes to divide the UWB frequency band into at least three frequency bands. The orthogonal frequency division multiplexing (OFDM) method is used to further divide the three frequency bands into a large number of narrow channels.

Technically speaking, MBOA and DS-CDMA cannot compromise each other. For radio frequency management, there are two basic principles: first, new radio technologies must not cause harmful interference to existing radio stations (systems); second, they must not put forward protection requirements when they are interfered, that is, they must be able to tolerate existing radios. Various interference. DS-CDMA uses the entire 3.1 to 10.6 GHz band, including some of the frequencies used in traditional wireless technologies, and MBOA uses multiple frequency subbands to easily avoid these frequencies.

Hardware system

Compared with the traditional structure, the structure of the UWB receiver is relatively simple. Figure 1 shows the system block diagram of the UWB transmitter and receiver. In UWB transceivers, information can be modulated by different technologies. At the receiving end, the signal energy collected by the antenna is amplified and passed through the relevant post-processing, and then the original information is obtained after threshold detection. Compared with the super-heterodyne receiver, the implementation is relatively simple, without local oscillator, power amplifier, PLL (phase-locked loop), VCO (voltage-controlled oscillator), mixer, etc., the cost is low, and the UWB receiver can be fully Digital implementation, using software radio technology, can dynamically adjust the data rate, power consumption, etc. ^[2]

Because UWB communication uses a fairly wide bandwidth, as if using the entire spectrum, and it can coexist with other applications, UWB can be applied in many fields, such as personal area networks, intelligent transportation systems, wireless sensor networks, radio frequency Identification, imaging applications.

Application in a personal area network

UWB can transmit information in a limited range (such as 4m) at a high data rate (such as 480Mbit / s) and very low power (200W), which is much better than Bluetooth. The data rate of Bluetooth is 1 Mbit / s and the power is 1mW. UWB provides fast access to wireless peripherals to transfer photos, files, and videos. Therefore UWB is particularly suitable for personal area networks. With UWB, you can easily and wirelessly download content from a video camera to a PC for editing at home and in the office, and then send it to a TV for viewing. You can easily implement personal digital assistants (PDAs) and mobile phones wirelessly. Synchronize with PC data, load game and audio / video files to PDA, transfer audio files between MP3 player and multimedia PC, etc.

Intelligent transportation applications

UWB's positioning and search capabilities can be used to make radars that prevent collisions and obstacles. Cars equipped with this radar will be very easy to drive. The radar will alert the driver when there are obstacles in front of, behind, or beside the car. When parking, this UWB-based radar is a powerful assistant for drivers. UWB can also be used to build an intelligent traffic management system. This system should be composed of several station devices and some vehicle-mounted devices to form a wireless communication network. The two devices communicate through UWB to complete various functions. For example, it can realize automatic toll collection without stopping, the vehicle side's positioning measurement at any time, the road information and driving suggestions at any time, the platform side's positioning search and speed measurement of mobile cars, and so on.

Sensor networking

UWB can be used in wireless sensor networks by taking advantage of its low cost and low power consumption. In most applications, sensors are used in specific local areas. It would be particularly convenient for sensors to transmit data wirelessly rather than wiredly. As a wireless sensor network communication technology, it must be low-cost; at the same time, it should be low-power to avoid frequent battery replacement. UWB is the most suitable candidate for wireless sensor network communication technology.

Imaging applications

Because UWB has a good ability to penetrate walls and floors, UWB can be applied to imaging systems. UWB technology can be used to manufacture through-wall radar and ground-penetrating radar. Through-the-wall radar can be used on battlefields and police riot operations to locate enemies behind walls and corners; ground-penetrating radar can be used to detect minerals and search for survivors after an earthquake or other disaster. UWB-based imaging systems can also be used in medical systems that avoid the use of X-rays.

Because UWB has many advantages, it can also be used for intelligent identification, wireless extension of wired networks, and military systems to achieve ultra-secure communication systems. ^[3]

Federal Communications Commission (FCC) regulations: Part of the bandwidth number is called UWB signal. Among them, part of the bandwidth is the value measured at the signal power spectral density at -10dB. A typical pulse position modulation (PPM) UWB signal form [1], [2] is: Str (k) (t) represents the transmitted signal of the kth user, which is a large number of single signals with different time shifts. Sum of periodic pulses. w (t) represents a single-cycle pulse waveform that can be transmitted. It can be a single-cycle Gaussian pulse or its first- and second-order differential pulses, starting from the zero time of the transmitter clock (t (k) = 0). The start time of the j-th pulse is.

Carefully analyze each time-shifted component:

(1) Pulse sequence with the same time shift: The form of the pulse represents a single-cycle pulse with a time step of Tf, its duty cycle is extremely low, and the typical value of the frame length or pulse repetition time Tf (Frame Time) is a single-cycle pulse width A hundred to a thousand times. Similar to the ALOHA system, such pulse sequences are extremely likely to cause random collisions.

(2) Pseudo-random time hopping: In order to reduce conflicts during multiple access, a specific pseudo-random sequence is assigned to each user, which is called a time hopping code, and its period is Np. Each symbol of the time hopping code is an integer and satisfies. In this way, the time jump code adds a time shift to each pulse, and the additional time shift of the j-th single-cycle pulse is seconds. Because it takes a certain time to read the output of the single-cycle pulse correlator, NhTc / Tf should be strictly less than 1. However, if NhTc is too small, the probability of collisions between multiple users will still be high. Conversely, if NhTc is large enough and the time hopping code is designed properly, multi-user interference can be approximated as an Additive White Gauss Noise (AWGN) signal. Since the time hopping code is a periodic sequence with a period of Np, that is also an Np periodic sequence, and its period is Tp = NpTf. Another function of the time hopping code is to make the power spectral density of the UWB signal more flat.

(3) Data modulation: The data sequence {di (k)} sent by the kth user is a binary data stream. Each symbol transmits Ns single-cycle pulses, which increases the signal processing gain. In this modulation mode, the duration of a symbol (or symbol) is Ts = NsTf. For a fixed pulse repetition time Tf, the binary symbol rate Rs is: Obviously, the ultra-wideband pulse communication system using the above signal has the following characteristics: the signal duration is extremely short, which is a nanosecond or subnanosecond pulse, and the signal is occupied. The ratio is extremely low (1% 0.1%), so it has good multipath immunity; the spectrum is quite wide, reaching the order of GHz, and the power spectral density is low, so the UWB signal has little interference with other systems and has the ability to resist interception Strong; UWB system processing gain is very high, and its total processing gain PC is: For example, when a binary UWB communication system Tf = 1s, Tc = 1ns, Ns = 100, bit rate Rs = 10kbps, the system UWB signal processing gain 50dB. Compared with other communication systems, its processing gain is very high. In addition, the UWB signal is a sequence of extremely narrow pulses, so it has a very strong penetrating ability. It can identify hidden objects or moving objects behind the wall. It can realize the combination of three functions of radar, positioning, and communication, suitable for military use. Tactical communication.

1. Transmitter and related receiver model Compared with the traditional wireless transceiver structure, the structure of the UWB transceiver is relatively simple. As shown in FIG. 3, at the transmitting end, the data directly modulates the RF pulse, and then the pulse is further delayed controlled by a programmable delay device, and finally transmitted through an ultra-wideband antenna. At the receiving end, the signal is multiplied by the local template waveform through the correlator, and then integrated into the baseband signal processing circuit through the sample and hold circuit. The programmable delay is controlled by the capture and tracking section, the clock oscillator, and the (time-hopping) code generator. The generator generates a local template waveform according to the corresponding delay, and multiplies the received signal with the received signal. The entire transceiver is composed almost entirely of digital circuits, which facilitates cost reduction and miniaturization.

2. Rake receiver model Because UWB signals need to be analyzed in the time domain method, they are mostly used in the indoor dense multipath (multipath can reach 30), and the signal energy of each path is very small. Each channel makes estimates, so Rake reception of UWB signals is possible. The Rake receiver improves the signal-to-noise ratio of the original multipath signal with very small energy after energy combining to improve system performance. ^[4]

Due to various advantages of UWB technology, it has become one of the main technologies of Wireless Personal Area Network (WPAN).

1. Foreign research status

For military use: As early as 1965, the United States established the technical basis of UWB. In the following two decades, UWB technology was mainly used in military applications in the United States, and its research institutions were limited to military-related enterprises and research institutions and groups. The US Department of Defense is developing dozens of UWB systems, including anti-eavesdropping networks on the battlefield. For civilian use: Due to the advantages of ultra-wideband technology, it has great potential in wireless communication. In recent years, research on UWB signal applications abroad has been popular, mainly for communication (such as home and personal networks, highway information service systems, and Wireless audio, data and video distribution, etc.), radar (such as collision avoidance of vehicles and aircraft, intrusion detection and ground penetrating radar, etc.) and precise positioning (such as asset tracking, personnel positioning, etc.). High-tech companies such as Sony, Time Domain, Motorola, Intel, and Daimler-Chrysler have all been involved in the development of UWB technology, connecting various consumer electronics devices with high data transmission rates to meet consumers' short-range wireless requirements. Communication miniaturization, low cost, low power, high speed data transmission requirements. The research on UWB wireless communication in the international academic circles is also getting deeper and deeper. From May 20th to 23rd, 2002, IEEE held a conference to discuss UWB technology and its application. On February 14, 2002, the U.S. Federal Communications Commission (FCC) officially passed a motion on the application of UWB technology to civilians, defining three UWB systems: imaging systems, communication and measurement systems, vehicle radar systems, and three systems. EIRP (omnidirectional effective radiated power) is specified separately. However, the UWB technology agreement and standards have not yet been determined. Only the United States allows the use of UWB devices for civilian use. Europe is discussing the further use of UWB and is waiting for the UWB standard in the United States.

2. Current status of domestic research

In the "Tenth Five-Year Plan" 863 plan communication technology research project released in early September 2001, the key technologies of ultra-broadband wireless communication and its coexistence and compatibility technology were taken as the research content of common and innovative technologies in wireless communication, and domestic scholars were encouraged to strengthen this R & D work. However, domestic in-depth research on UWB technology is limited to radar, and research on UWB communication systems has not yet taken shape.