RF UWB Ultra-wideband 2.8-10.5G Spot Can Be Shot

Technical characteristics of UWB(1) High transmiion rate and large space capacityAccording to Shannon's channel capacity formula, in the additive Gauian noise (AWGN) channel, the upper limit of the system's error-free transmiion rate is:C=B×log2(1+SNR)Among them, B (unit: Hz) is the channel , and SNR is the signal-to-noise ratio. In the UWB system, the signal B is as high as 500MHz to 7.5GHz. Therefore, even if the signal-to-noise ratio (SNR) is very low, UWB syst can achieve transmiion rates of several hundred megabits to 1Gb/s over short distances. For example, if a 7 GHz is used, the theoretical channel capacity can reach 1 Gb/s even with a signal-to-noise ratio as low as -10 dB. Therefore, it is very suitable to apply UWB technology to short-distance high-speed transmiion ocns (such as high-speed WPAN), which can greatly improve the space capacity. Theoretical research shows that the reachable space capacity of UWB-based WPAN is 1 to 2 orders of magnitude higher than the current Wstandard IEEE 802.11.a.(2) Suitable for short-distance communicationAccording to FCC regulations, the radiated power of UWB syst is very limited, and the total radiated power in the 3.1GHz to 10.6GHz frequency band is only 0.55mW, which is much lower than that of traditional narrowband syst. As the transmiion distance increases, the signal power will continue to decay. Therefore, the received signal-to-noise ratio can be expreed as a function of transmiion distance SNRr (d ). According to Shannon's formula, the channel capacity can be expreed as a function of distanceC(d)=B×log2[1+SNRr(d )] (2)In addition, UWB signals have extremely rich frequency components. It is well known that wirele channels exhibit different fading characteristics in different frequency bands. Since the high frequency signal fades very fast with the increase of the transmiion distance, this causes the distortion of the UWB signal, which seriously affects the system performance. Studies have shown that when the distance between the transceivers is le than 10m, the channel capacity of the UWB system is higher than that of the Wsystem in the 5GHz band. When the distance between the transceivers exceeds 12m, the UWB system's advantage in channel capacity will no longer exist. Therefore, UWB syst are particularly suitable for short-range communications.(3) Good coexistence and confidentialityDue to the extremely low radiation spectral density of the UWB system (le than -41.3dBm/MHz), for the traditional narrowband system, the spectral density of the UWB signal is even lower than the background noise level, and the interference of the UWB signal to the narrowband system can be regarded as a broadband noise. Therefore, the UWB system has good coexistence with the traditional narrowband system, which is very beneficial to improve the utilization rate of the increasingly tight wirele spectrum resources. At the same time, the extremely low radiation spectral density makes UWB signals highly concealed and difficult to be intercepted, which is very beneficial to improving communication confidentiality.(4) Strong multipath resolution and high positioning accuracyBecause the UWB signal adopts the narrow pulse with extremely short duration, its time and space resolution ability is very strong. Therefore, the multipath resolution of UWB signals is extremely high. The extremely high multipath resolution capability endows the UWB signal with high-precision ranging and positioning capabilities. For communication syst, the multipath resolution of UWB signals must be analyzed dialectically. The time selectivity and frequency selectivity of wirele channels are the key factors that restrict the performance of wirele communication syst. In narrowband syst, indistinguishable multipath will cause fading, while UWB signals can separate them and combine them using diversity reception techniques. Therefore, UWB system has strong anti-fading ability. However, the extremely high multipath resolution of UWB signals also leads to severe time dispersion of signal energy (frequency selective fading). This will pose serious challenges to receiver design. In the actual UWB system design, the signal and receiver complexity must be compromised to obtainIdeal price/performance ratio.(5) Small size and low power consumptionThe traditional UWB technology does not need a sine carrier, the data is modulated and transmitted on the nanosecond or sub-nanosecond baseband narrow pulse, and the receiver uses the correlator to directly complete the signal detection. The transceiver does not require complex carrier frequency modulation/demodulation circuits and filters. Therefore, the system complexity can be greatly reduced, and the volume and power consumption of the transceiver can be reduced. The FCC's new definition of UWB increases the difficulty of implementing carrier-free pulse shaping to a certain extent, but with the development of semiconductor technology and the continuous emergence of new pulse generation technologies, UWB syst still inherit the traditional UWB's small size and low power consumption. Features.3 UWB pulse shaping technologyIn any digital communication system, information must be carried by signals that are well matched to the channels. For linear modulation syst, the modulated signal can be uniformly expreed as:s(t)=∑Ing(t -T ) (3)Among them, In is the discrete data symbol sequence carrying information; T is the data symbol duration;g(t) is the time-domain shaped waveform. Many factors such as the working frequency band, signal , radiation spectral density, out-of-band radiation, transmiion performance, and implementation complexity of the communication system all depend on the design of g(t).For the UWB communication system, the of the shaped signa(t) must be greater than 500MHz, and the signal energy should be concentrated in the frequency band of 3.1 GHz to 10.6 GHz. Early UWB syst used nanosecond/sub-nanosecond carrier-free Gauian single-cycle pulses, and the signal spectrum was concentrated below 2 GHz. The FCC's redefinition of UWB and the allocation of spectrum resources have put forward new requirements for signal shaping, and the signal shaping scheme must be adjusted. In recent years, many effective methods have appeared, such as the shaping technology based on carrier modulation, Hermit quadrature pulse shaping, elliptical spherical wave (PSWF) quadrature pulse shaping and so on.3.1 Gauian Single Cycle PulseThe Gauian single-cycle pulse is the derivative of the Gauian pulse, and it is the most representative non-carrier pulse. The pulse waveform of each order can be obtained by succeive derivation of the first derivative of Gauian.With the increase of the order of the pulse signal, the number of zero-croing points gradually increases, and the center frequency of the signal moves to high frequency, but the of the signal does not change significantly, and the relative gradually decreases. Early UWB syst used first-order and second-order pulses, and the signal frequency components continued from DC to 2GHz. According to the new definition of UWB by the FCC, sub-nanosecond pulses of order 4 or more must be used to meet the radiation spectrum requirements. Figure 3 shows a typical 2ns Gauian single-cycle pulse.3.2 Shaping Technology of Carrier ModulationIn principle, as long as the signal -10dB is greater than 500MHz, the UWB requirements can be met. Therefore, the traditional signal shaping scheme for carrier communication system can be transplanted into UWB system. At this time, the ultra-wideband signal design is transformed into a low-pa pulse design, and the signal spectrum can be flexibly moved on the frequency axis through carrier modulation.The shaped pulse with carrier can be expreed as:w(t)=p(t)cos(2πfct)(0≤t ≤Tp) (4)Among them, p(t) is the baseband pulse whose duration is Tp; fc is the carrier frequency, that is, the center frequency of the signal. If the spectrum of the baseband pulse p(t) is P(f ), the spectrum of the final shaped pulse is:It can be seen that the spectrum of the shaped pulse depends on the baseband pulse p(t), as long as the -10dB of p(t) is greater than 250 MHz, the UWB design requirements can be met. By adjusting the carrier frequency fc, the signal spectrum can be made in the range of 3.1 GHz to 10.6 GHz.Flexible movement within the enclosure. If combined with frequency hopping (FH) technology, a frequency hopping multiple acce (FHMA) system can be easily constructed. This pulse shaping technique is used in many IEEE 802.15.3a standard proposals. Figure 4 shows a typical carrier-modified cosine pulse with a center frequency of 3.35 GHz and a -10 dB of 525 MHz.3.3Hermite Quadrature PulseHermite pulse is one of the earliest orthogonal pulse shaping methods proposed for high-speed UWB communication syst. Combined with multi-ary pulse modulation can effectively improve the system transmiion rate. Such pulse waveforms are derived from Hermite polynomials. The characteristic of this pulse shaping method is that the energy is concentrated in the low frequency, and the waveform spectrum of each order differs greatly, and the FCC requirements can be met only by moving the spectrum with the help of the carrier.3.4PSWF quadrature pulsePSWF pulse is a kind of approximate "time-band-limit" signal, which has a very ideal effect in the analysis of band-limited signals.Compared with Hermite pulses, PSWF pulses can be directly designed according to the target frequency band and requirements, and do not require complex carrier modulation for spectral shifts. Therefore, the PSWF pulse belongs to the carrierle shaping technology, which is beneficial to simplify the complexity of the transceiver.4 UWB modulation and multiple acce technologyThe modulation mode refers to how the signal carries information. It not only determines the effectivene and reliability of the communication system, but also affects the spectrum structure of the signal and the complexity of the receiver. For the multiple acce technology to solve the problem of multiple users sharing the channel, a reasonable multiple acce scheme can greatly improve the multi-user capacity while reducing the interference between users. The modulation methods used in UWB syst can be divided into two categories: modulation based on ultra-wideband pulses and orthogonal multi-carrier modulation based on OFDM. Multiple acce technologies include: time hopping multiple acce, frequency hopping multiple acce, direct spread code division multiple acce, wavelength division multiple acce, etc. In the system design, the modulation mode and the multiple acce mode can be reasonably combined.4.1 UWB modulation technology(1) Pulse position modulationPulse Position Modulation (PPM) is a modulation method that uses the pulse position to carry data information. According to the number of discrete data symbol states used, it can be divided into binary PPM (2PPM) and multi-ary PPM (MPPM). In this modulation method, there are 2 or M positions where a pulse may appear in a pulse repetition period, and the pulse positions correspond to the symbol states one-to-one. According to the relationship between the distance between adjacent pulse positions and the pulse width, it can be divided into partially overlapping PPM and orthogonal PPM (OPPM). In the partially overlapping PPM, in order to ensure the reliability of the system transmiion, the adjacent pulse positions are usually selected as the negative peak points of the pulse autocorrelation function, so as to maximize the Euclidean distance of adjacent symbols. In OPPM, the pulse position is usually determined at intervals of the pulse width. The receiver uses the correlator to perform coherent detection at the corresponding location. In view of the complexity and power limitation of the UWB system, in practical applications, the commonly used modulation method is 2PPM or 2OPPM.The advantage of PPM is that it only needs to control the pulse position according to the data symbol, and does not need to control the pulse amplitude and polarity, which facilitates modulation and demodulation with low complexity. Therefore, PPM is a modulation method widely used in early UWB syst. However, since the PPM signal is unipolar, there are on discrete spectral lines with higher amplitudes in its radiation spectrum. If these lines are not suppreed, it will be difficult to meet the FCC radiation spectrum requirements.(2) Pulse Amplitude ModulationPulse Amplitude Modulation (PAM) is a digitalIt is one of the most commonly used modulation methods in digital communication syst. In UWB system, considering the realization complexity and power efficiency, it is not suitable to adopt multi-ary PAM (MPAM). There are two types of PAM commonly used in UWB syst: On-Off Keying (OOK) and Binary Phase Shift Keying (BPSK). The former can use incoherent detection to reduce receiver complexity, while the latter can better ensure transmiion reliability by using coherent detection.Compared with 2PPM, under the premise of the same radiation power, BPSK can obtain higher transmiion reliability, and there are no discrete spectral lines in the radiation spectrum.(3) Waveform modulationWaveform modulation (PWSK) is a modulation method proposed by combining multiple quadrature waveforms such as Hermite pulses. In this modulation mode, M mutually orthogonal equal-energy pulse waveforms are used to carry data information, and each pulse waveform corresponds to an M-ary data symbol. At the receiving end, M parallel correlators are used for signal reception, and maximum likelihood detection is used to complete data recovery. Since the various pulse energies are equal, the transmiion efficiency can be improved without increasing the radiated power. With the same pulse width, a higher symbol transmiion rate than MPPM can be achieved. With the same symbol rate, its power efficiency and reliability are higher than MPAM. Since this modulation method requires more shaping filters and correlators, its implementation complexity is high. Therefore, it is le used in practical syst and is currently limited to theoretical research.About shipping
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