Ultra-wideband communication technology and its application

Abstract: UWB (Ultra-Wide Bandwidth) Impulse Radio technology is very different from other communication technologies. It has the advantages of low signal power spectral density, difficult detection, and low system complexity, especially for indoor applications. High-speed wireless access and military communications in dense multipath locations. The signal representation of UWB system is introduced, its characteristics are analyzed, and the current research and application of ultra-wideband communication are introduced.

UWB technology is a new type of wireless communication technology. It directly modulates the impulse with very steep rise and fall times, giving the signal a bandwidth of the order of GHz. Ultra-wideband technology solves the major communication problems that have plagued traditional wireless technologies for many years. It has insensitivity to channel fading, low power spectral density of transmitted signals, low interception capability, low system complexity, and can provide several centimeters of positioning accuracy. advantage.

1 Ultra-wideband signals and their characteristics

The US Federal Communications Commission (FCC) provides:

Partial bandwidth The number is called the UWB signal. Among them, part of the bandwidth is the value measured by the signal power spectral density at -10dB. Figure 1 shows the comparison of the power spectral density of the UWB signal with the narrow and wide signal; the UWB signal format is shown in Figure 2.

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 the sum of a large number of single-cycle pulses with different time shifts. w(t) denotes a single-cycle pulse waveform transmitted, which may be a single-cycle Gaussian pulse or its first-order, second-order differential pulses, starting from the zero time (t(k)=0) of the transmitter clock. The start time of the jth pulse is . Carefully analyze each time-shift component:

(1) Pulse sequence of the same time shift: The form of the pulse represents a single-cycle pulse with a time step of Tf, the duty cycle is extremely low, and the frame length or pulse repetition time Tf (Frame TIme) is typically one hundred to one thousand times the single-cycle pulse width. Similar to the ALOHA system, such a pulse sequence is highly susceptible to random collisions.

(2) Pseudo-random hopping: To reduce the conflict when multiple access is received, each user is assigned a specific pseudo-random sequence. It is called a time hopping code and its period is Np. Each symbol of the time-hopping code is an integer and satisfies . Thus, the time-hopping code adds a time shift to each pulse, and the additional time shift of the j-th single-cycle pulse is second.

Since the output of the single-cycle pulse correlator takes a certain amount of time, the NhTc/Tf should be strictly less than one. However, if NhTc is too small, the probability of collisions when multiple users access is still large. Conversely, if the NhTc is large enough and the time-hopping code design is reasonable, the multi-user interference can be approximated as an additive white Gaussian noise AWGN (AddiTIveWhite Gauss Noise) signal.

Since the time hopping code is a periodic sequence of periods Np, then Also a sequence of Np cycles with a period of Tp = NpTf. Another function of the time-hopping code is to make the power spectral density of the UWB signal flatter.

(3) Data modulation: The data sequence {di(k)} transmitted by the kth user is a binary data stream. Ns single-cycle pulses are transmitted per symbol, which increases the processing gain of the signal.

In this modulation mode, the duration of one 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 signals has the following characteristics: the signal duration is extremely short, and it is a nanosecond, sub-nanosecond pulse, and the signal duty ratio is extremely low (1% to 0.1%), so there is a very Good multipath immunity; spectrum is quite wide, up to GHz, and power spectral density is low, so UWB signal has low interference to other systems and strong anti-interception ability; UWB system has high processing gain, and its total processing gain PC is:

For example, when a binary UWB communication system Tf=1μs, Tc=1 ns, Ns=100, and bit rate Rs=10 kbps, the processing gain of the system UWB signal is 50 dB. The processing gain is very high compared to other communication systems.

In addition, the UWB signal is a sequence of extremely narrow pulses, so it has a very strong penetrating ability, and can identify hidden objects or objects moving behind the wall. It can realize the combination of three functions of radar, positioning and communication, suitable for military use. Tactical communication.

image 3

2 Ultra-wideband signal transmitter, receiver basic structure

2.1 Transmitter and related receiver models

The structure of the UWB transceiver is relatively simple compared to the conventional wireless transceiver architecture. As shown in Figure 3, at the transmitting end, the data is directly modulated by the RF pulse, and then further delayed by the programmable delay device, and finally transmitted through the UWB antenna. At the receiving end, the signal is multiplied by the local template waveform by the correlator, integrated and sent to the baseband signal processing circuit through the sample and hold circuit, and the programmable delay is controlled by the capture tracking part, the clock oscillator and the (time hopping) code generator. The local template waveform is generated according to the corresponding delay and multiplied by the received signal. The entire transceiver is composed almost entirely of digital circuits, which is convenient for cost reduction and miniaturization.

2.2 Rake receiver model

Since UWB signals need to be analyzed by time domain method, they are mostly used in indoor dense multipath (up to 30 multipaths), and the signal energy of each path is very small, making it difficult to estimate each channel. So it is possible to make Rake reception of UWB signals. The Rake receiver improves the performance of the system by increasing the signal-to-noise ratio of the multipath signals with low energy. Suppose a UWB communication system has Nu users, and its transmission signals are respectively The signal received by a receiver is r(t). If you want to get the data sent by the first user, the block diagram of the Rake receiver is shown in Figure 4.

Figure 4

3 UWB and several other wireless personal area network technologies

Due to the advantages of UWB technology, it has become one of the main technologies of Wireless Personal Area Network (WPAN). The goal of WPAN is to replace the traditional wired cable with radio or infrared, and realize the intelligent interconnection of personal information Terminals within 10m with low price and low power consumption, and build a personalized information network. Its most common application is to connect computers, printers, cordless phones, PDAs, and information appliances. At present, the main technologies for implementing WPAN are: IEEE802.11b (Win), Home RF, IrDA, Bluetooth, and ultra-wideband.

It can be seen from Figure 5 that the advantages of UWB technology are obvious. The main disadvantage is that the transmission power is too small to limit its transmission distance (as shown in Figure 6). That is to say, within 10m, UWB can achieve transmission performance of up to several hundred Mbps, and the performance of IEEE802.11b or Home RF wireless PAN for long-distance applications will be stronger than UWB. UWB and the popular IEEE802.11b and Home RF will not compete directly because UWB is more suitable for indoors with a distance of about 10m. In fact, UWB may be more suitable as a replacement for Bluetooth technology, because the latter transmission rate is far less than the former, and the Bluetooth technology protocol is more complicated.

4 Research and development at home and abroad

4.1 Status of foreign research

Military aspects: As early as 1965, the United States established the technical foundation of UWB. In the next two decades, UWB technology was mainly used for military applications in the United States, and its research institutions were limited to military-related enterprises and research institutions and groups. Currently, the US Department of Defense is developing dozens of UWB systems, including battlefield anti-eavesdropping networks.

Civilian aspects: Due to the advantages of UWB technology, it has great potential in wireless communication. In recent years, foreign research on UWB signal applications 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 vehicle and aircraft collision/failure avoidance, 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, Daimler-Chrysler have been involved in the development of UWB technology, connecting various consumer electronic devices with high data transmission rates to meet consumers' short-range wireless Communication miniaturization, low cost, low power, high speed data transmission and other requirements.

The international academic community is also getting more and more research on ultra-wideband wireless communication. On May 20-23, 2002, the IEEE held a conference to discuss UWB technology and its applications. On February 14, 2002, the US Federal Communications Commission (FCC) officially adopted the UWB technology for civilian use, defining three UWB systems: imaging systems, communication and measurement systems, vehicle radar systems, and three systems. The EIRP (omnidirectional effective radiated power) is specified separately. However, the protocols and standards for UWB technology have not yet been determined. Currently, only the United States allows the use of civilian UWB devices; while Europe is discussing further use of UWB and watching the US UWB standard.

4.2 Status of domestic research

In the "10th Five-Year Plan" 863 Program Communication Technology Theme Research Project released in early September 2001, the key technologies of ultra-wideband wireless communication and its coexistence and compatibility technologies are used as research contents of wireless communication common technologies and innovative technologies, and domestic scholars are encouraged to strengthen this aspect. R&D work. However, the current in-depth research on UWB technology in China is limited to radar. The research on UWB communication system has not yet formed a scale.

others

Terminals&Connectors, Terminals,Terminal Blocks,Wire To Wire Connector

Metal Push Button,Rocker Switch Co., Ltd. , http://www.nbconnectors.com