CN101692615A - Carrier synchronization pulse ultra wide-band radio frequency modulation device - Google Patents

Abstract

The invention discloses a realization scheme of a carrier synchronous ultra-wideband signal. The system includes a time-hopping phase modulation module, a pulse forming module, a carrier modulation module and a filter module. The carrier-synchronous ultra-wideband implementation method proposed by the present invention can perform time-hopping-period synchronous modulation on the information sequence, generate carrier-synchronous ultra-wideband transmission signals, greatly reduce the complexity of the synchronization algorithm at the receiving end, and improve the receiving performance of the UWB system. It has a wide range of applications in the field of wireless communication.

Description

Carrier synchronous pulse ultra-wideband radio frequency modulation device

technical field

Based on the carrier cycle modulation (Carrier Cycle Modulation) technology, the present invention proposes a carrier synchronization ultra-wideband (CS-UWB, Carrier Synchronization Ultra Wide-band) signal radio frequency implementation scheme, which belongs to the field of communication.

Background technique

Ultra-wideband technology is a new type of wireless communication technology that uses spectrum resources in a overlapping manner. Its transmission signal bandwidth can be as high as several gigahertz (GHz), so its time-domain signal has extremely strong multipath resolution. In short-distance wireless personal It has great application potential in communication (WPAN, Wireless Personal Local Network). At present, IEEE has promulgated relevant standards for many UWB application scenarios, including the high-speed wireless personal area network standard IEEE802. WBAN, Wireless Body Area Network). In essence, UWB technology belongs to a special spread spectrum communication, which transmits extremely narrow pulses with extremely low duty cycle (LDC, Low Duty Cycle) in bursts, and then obtains ultra-wideband signals with spectrum broadening. With this kind of spread spectrum gain up to 60dB, UWB has an extremely low intercept detection rate (LPD, Low Probability of Detection), and can use extremely low power for communication; according to the UWB spectrum mask specification issued by the US FCC and 2002, Its absolute bandwidth can reach 7.5Ghz, and ultra-wideband signals also have extremely strong multipath resolution, so that it can distinguish dense multipath components in indoor environments, and make full use of multipath components through advanced Rake receiving technology; in addition, the huge bandwidth makes UWB signals have high-precision positioning and ranging capabilities, and also have a wide range of application scenarios in the military field, such as high-resolution radar and through-wall imaging systems.

With the continuous development of ultra-wideband technology, another ultra-wideband technology based on Orthogonal Frequency Division Multiplexing (OFDM, Orthogonal Frequency Division Multiplexing) has emerged. Therefore, the UWB technology system is divided into two, namely IR-UWB (Impulse Radio) and multi-band Orthogonal Frequency Division Multiplexing UWB (MB-OFDM, Multi-band Orthogonal Frequency Division Multiplexing). Pulse radio refers to the traditional ultra-wideband technology that uses ultra-short impulse pulses as information carriers, and realizes high-speed data transmission by modulating the amplitude or phase of nanosecond-level narrow pulse signals. A typical UWB-IR system mainly includes time hopping phase modulation (TH-PPM, Time Hopping Pulse Phase Modulation) and direct spread spectrum modulation (DS-UWB, Direct Spreading). In TH-PPM, the pseudo-random time-hopping sequence is used to control the phase of the narrow pulse to realize the multiple access of the UWB system; while DS-UWB uses the orthogonal code with a very high chip rate to directly implement the narrow pulse carrying information. Sequential spreading for multiple access. The basic idea of MB-OFDM is to divide the frequency band into many sub-bands that are orthogonal to each other, so its time-domain signals generally do not have the characteristics of narrow pulses; in addition to the characteristics of ultra-wideband high-speed data transmission, MB-OFDM also has the ability to resist multipath The advantages of interference, but its mechanism is different from the UWB-IR high-resolution mechanism, and the multipath effect is mainly eliminated by means of the cyclic prefix (CP) in OFDM.

The key algorithms of UWB system physical layer include channel estimation, synchronization acquisition and optimal reception. Since the number of UWB indoor channel multipaths can reach more than 100 (including about 85% energy), it is difficult for conventional channel estimation algorithms to obtain ideal channel estimation performance, or its implementation complexity is unbearable; using the transmission-reference (TR, TransmittedReference) mechanism can Accurate channel estimation is obtained, and ultra-wideband signal coherent reception can be realized with the help of Rake receiver. At present, the synchronous acquisition algorithm mainly uses the concept of "dirty templates" to obtain the time delay through the correlation between two consecutive symbols. In an indoor dense multipath environment, synchronization performance becomes the main factor affecting system reception performance; while in underwater or jungle UWB sensor networks, precise timing also becomes a constraint on network performance because sensor nodes cannot obtain accurate GPS synchronization information. The key.

This patent proposes a synchronous ultra-wideband system based on carrier cycle modulation technology. It is a new type of wireless communication system based on precise carrier synchronization and extremely low transmit power spectral density. Due to the precise synchronization information of the modulation information, there are obvious carrier synchronization signal components in the power spectrum of the transmitted signal, and the side lobe power spectrum of the signal spectrum is extremely wide and the amplitude is very low. It has similar signal characteristics to traditional UWB signals, and also has high-speed communication and high-speed Potential for precision positioning.

Contents of the invention

The present invention proposes a novel carrier synchronization ultra-wideband signal implementation method. This solution can also use the carrier component carried in the received signal to carry out precise synchronization while using the extremely low power spectrum to transmit the signal, which greatly reduces the synchronization acquisition algorithm at the receiving end. The complexity of the implementation can effectively improve the transmission performance of the UWB system, and it is expected to further expand its transmission distance, so that UWB has a wider application space. In addition, the modulated main lobe signal spectrum has an extremely low power spectral density, which can use spectrum resources in a overlapping manner, greatly improving spectrum utilization. Therefore, while ensuring high-speed information transmission, this scheme can greatly reduce the complexity of the synchronization algorithm at the receiving end and improve the timing performance of the receiving end.

The present invention adopts the following technical solutions: first, the sending end produces a periodic impulse sequence ∑ _n δ (t-nT _b ), wherein T _b represents the symbol duration of the information sequence to be sent, and the corresponding information rate is R _b =1/ T _b , the sequence does not carry any transmission information; then, use the pseudo-random sequence generator to generate two multi-ary random sequences, namely the signature sequence {B _n } and the time drift sequence {T _n }, in {B _n } and {T _n }, the periodic impulse sequence generates a random time delay B _n Δ+T _n , where Δ is a unit random displacement corresponding to the user’s characteristic time-hopping sequence {B _n }. The time-modulated baseband sequence can be expressed as ∑ _n δ(t-nT _b -B _n T ₁ -T _n ); after that, after the pulse shaper p(t), the baseband waveform and the unipolar binary information sequence to be sent a=(..., a ₀ , a ₁ ,...a _n , a _n+1 ,...) are multiplied, and a DC bias D is added to obtain a random pulse position baseband encoded signal ∑ _n a _n p(t-nT _b -B _n T ₁ -T _n )+D, where the shaped pulse duration T ₀ should satisfy T ₀ =kT _b , and T ₀ <<T _b ; finally, the carrier phase of the baseband signal Modulation (Phase Modulation, PM), that is, to obtain a carrier-synchronous ultra-wideband modulation signal.

Due to the use of periodic synchronous modulation, the distance between the carrier frequency f _c and the baseband pulse duration satisfies f _c =1/T ₀ , that is, T _c =T ₀ ; the position of the carrier in the power spectrum of the above-mentioned modulated signal contains an obvious synchronous signal component, continuous The width of the main lobe of the spectrum is about 2/T ₀ ; when p(t) adopts a rectangular wave, the continuous spectrum of the signal to be transmitted is attenuated according to sinx/x. It needs to be band-pass filtered first, and the filter bandwidth is selected as 2f _c ; if the pulse shaping directly adopts out-of-band fast-attenuating waveforms (such as Gaussian waveforms, raised cosine waveforms, etc.), the filtering operation at the sending end can be avoided.

According to the realization excitation of carrier-synchronous pulse ultra-wideband in this patent, two other carrier-synchronous ultra-wideband modulation schemes are further proposed: direct sequence spread spectrum carrier-synchronous ultra-wideband modulation and time-hopping carrier-synchronous ultra-wideband modulation.

In the direct sequence spread spectrum carrier synchronous UWB modulation scheme, the bipolar binary digital sequence to be transmitted is recorded as b=(..., b ₀ , b ₁ ,..., b _k , b _k+1 , .. .) at a rate of R _b =1/T _b . Each bit is repeated N _s times through a repetition encoder to generate a repeating bipolar binary sequence:

a=(...,a ₀ ,a ₁ ,...,a _j ,a _j+1 ,...)=(...,b ₀ ,b ₀ ,...b ₀ ,b ₁ , b ₁ ,...b ₁ ,b _k ,b _k ,...b _k ,b _k+1 ,b _k+1 ,...b _k+1 ,...)

之后，脉冲成形器产生一个速率为R_p＝N_s/T_b＝1/T_s(脉冲/s)的单位脉冲序列，该脉冲序列相隔T_S。成形脉冲的时域波形p(t)可是矩形波，也可以是其它任意合适波形。p(t)持续时间一般远小于T_s。成形后脉冲波形与双极性二进制序列d相乘，并加入直流偏置D，即可获得基带调制信号并在此基础上进行载波相位调制。由于采用单周期载波调制，因此载波周期T_c与成形脉冲持续时间T₀之间需满足T_c＝T₀；为了加速已调信号谱中旁瓣分量的衰减速度，进而减少对于相邻信道的干扰，在发送至无线信道之前需对已调信号带通滤波。该方案对应实现结构如2所示。Next, the pseudo-random code generator generates a bipolar binary PN sequence c=(..., c ₀ , c ₁ ,..., c _j , c _j+1 ...) with period _Np . c is multiplied by the source bipolar binary sequence a to get

The pulse shaper then generates a train of unit pulses at a rate R _p =N _s /T _b =1/T _s (pulse/s), separated by T _s . The time-domain waveform p(t) of the shaped pulse can be a rectangular wave, or any other suitable waveform. The duration of p(t) is generally much smaller than T _s . After shaping, the pulse waveform is multiplied by the bipolar binary sequence d, and the DC bias D is added to obtain the baseband modulation signal, and the carrier phase modulation is performed on this basis. Since the single-cycle carrier modulation is used, T _c = T ₀ must be satisfied between the carrier cycle T _c and the shaped pulse duration T ₀ ; in order to accelerate the attenuation speed of the side lobe component in the modulated signal spectrum, and then reduce the adjacent channel interference, the modulated signal needs to be band-pass filtered before being sent to the wireless channel. The corresponding implementation structure of this scheme is shown in 2.

In the time-hopping carrier synchronous ultra-wideband modulation scheme, compared with the realization structure shown in Figure 1, this scheme uses information sequences to control random displacement. First, the sender generates a periodic impulse sequence ∑ _n δ(t-nT _b ), and then uses a pseudo-random sequence generator to generate two multi-ary random sequences, namely, the signature sequence {B _n } and the time drift sequence {T _n }; Under the joint action of {B _n }, {T _n } and information sequence {a _n }, the periodic impulse sequence will generate a random delay a _n +B _n T ₁ +T _n , where T ₁ A period of random displacement controlled by the user characteristic time-hopping sequence {B _n }, the baseband sequence after time-hopping modulation can be expressed as ∑ _n δ(t-nT _b -B _n T ₁ -T _n -a _n ); after that , after passing through the pulse shaper p(t), add a DC bias D to obtain a baseband encoded signal with random pulse position ∑ _n p(t-nT _b -B _n T ₁ -T _n -a _n )+D, where the shaping The pulse duration T ₀ should satisfy T ₀ << T _b ; finally, carrier phase modulation (Phase Modulation, PM) is performed on the baseband signal to obtain a carrier synchronous ultra-wideband modulation signal; single-cycle modulation is adopted, and the carrier frequency f f _c =1/T ₀ is satisfied between _c and the baseband pulse duration. The corresponding implementation structure of this scheme is shown in Figure 3 .

The advantages of the present invention are:

1) The technical solution of the present invention can generate carrier-synchronous ultra-wideband signals, overcome the influence of indoor dense multipath environment, reduce the difficulty of realizing the synchronization acquisition algorithm at the receiving end, improve the synchronization timing accuracy, and improve the overall transmission performance of the UWB system.

2) The technical solution of the present invention can obtain extremely low power spectral density. With the help of the huge spread spectrum gain implied in the modulated signal, reliable information transmission can be realized in the case of extremely low power spectrum, and it has many advantages of traditional ultra-wideband. Such as low interference and excellent privacy.

3) The technical solution of the present invention is flexible to implement, and the carrier frequency and side lobe bandwidth can be flexibly selected according to the spectrum usage, so that an ultra-wideband signal with any spectrum can be flexibly generated.

4) The technical solution of the present invention is simple to implement and can be applied to various application scenarios on a large scale.

Description of drawings

Figure 1 is a block diagram of the radio frequency structure of the carrier-synchronous pulse ultra-wideband system.

Fig. 2 is a block diagram of a carrier synchronous ultra-wideband radio frequency structure based on direct spread spectrum modulation.

Fig. 3 is a block diagram of a carrier-synchronous ultra-wideband radio frequency structure based on time-hopping modulation.

Fig. 4 is the time-domain waveform of the carrier synchronous ultra-wideband system.

Fig. 5 is a carrier synchronous ultra-wideband power spectrum diagram.

Fig. 6 is a carrier synchronous ultra-wideband power spectrum diagram after transmission filtering.

Detailed ways

The invention mainly proposes a carrier synchronization ultra-wideband signal modulation scheme. Compared with the classic ultra-wideband modulation mechanism based on narrow pulses, the present invention further introduces carrier cycle modulation on the basis of time-hopping modulation, so that the information carried in the ultra-wideband transmission signal and the modulation information are accurately synchronized with the carrier signal. The receiving end uses a phase-locked loop (Phase Lock Loop, PLL) to accurately extract the synchronization information to provide precise timing signals for ultra-wideband correlation decoding, greatly reducing the algorithm complexity and hardware implementation difficulty of ultra-wideband synchronization capture, and effectively improving system reception. performance.

The specific steps of the carrier synchronous UWB modulation method are summarized as follows:

1) The sending end generates a periodic impulse sequence ∑ _n δ(t-nT _b ), where T _b represents the symbol duration of the information sequence to be sent.

2) Use a pseudo-random sequence generator to generate multi-ary random codes {B _n } and {T _n }, whose period is expressed as N _p . Under the precise control of {B _n } and {T _n }, the periodic sequence will generate a certain random time delay ∑ _n δ(t-nT _b -B _n T ₁ -T _n ), as shown in Figure 4, the random The time delay τ=B _n T ₁ +T _n is strictly relative to the initial time of the information symbol, and satisfies τ<T _b . Generally speaking, the larger the value range of {B _n }, the more ideal the obtained UWB signal spectrum.

3) After the time-hopping modulated baseband impulse sequence passes through the pulse shaping filter, ∑ _n p(t-nT _b -B _n T ₁ -T _n ) is obtained, where p(t) represents the selected baseband pulse waveform. Common shaped pulses include rectangular pulses, Gaussian pulses, etc. The rectangular pulses are expressed as:

$\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="T"\; filenames="H2009100932895E0000021.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& {\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="T"\; filenames="H2009100932895E0000021.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}\end{array}\right.$

A Gaussian pulse can be written as:

$\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>$

In the formula, t ₀ is the center of the baseband waveform, which is taken as T ₀ /2; and σ determines the continuous width of p(t), which can be taken as T ₀ /6.

4) The unipolar binary information sequence to be sent is denoted as a=(...,a ₀ ,a ₁ ,...a _n ,a _n+1 ,...), where a _n ∈{-1, 0}. Using the information sequence to control the amplitude of the baseband time-hopping pulse sequence, the baseband encoded signal Σ _n a _n p(t-nT _b -B _n T ₁ -T _n )+D can be obtained.

5) Adding a DC bias D to the time-hopping sequence carrying information, and performing carrier phase modulation on the obtained signal, you can obtain a synchronous UWB signal based on a period-modulated carrier:

s(t)＝{∑ _n a _n (t-nT _b -B _n T ₁ -T _n )+D}sin(2πf _c t)

In the formula, T ₀ =kT _c is satisfied between the carrier period T _c and the pulse duration T ₀ , and k is a positive integer. The carrier component in the modulated signal is related to the DC offset D, the shaped pulse duration T ₀ and the information symbol duration T _b . Generally, D takes a positive value and the larger the absolute value is, the stronger the carrier component is; T _b /T _o takes an integer value M, and the larger M is, the stronger the carrier component is. At the same time, the value of D will also affect the time-domain shape of the modulated signal: when D=-0.5, the modulated signal has BPSK characteristics; when D≠-0.5, the modulated signal belongs to the joint modulation of amplitude and phase.

6) Perform band-pass filtering on s(t) before sending, the center frequency of the filter is f _c , and the bandwidth is 2f _c . If p(t) has better sidelobe attenuation characteristics in the frequency domain, this step can be omitted.

7) Under the Gaussian channel, the receiver first uses band-pass filtering to filter out-of-band channel noise components to improve the detection signal-to-noise ratio. The filter has a center frequency of f _c and a bandwidth of 2f _c .

8) Use the phase-locked loop rate to extract accurate synchronization information to provide timing for subsequent signal processing. The correlation receiver uses the receiving template to perform correlation calculations with the input signal, and uses the decision threshold to judge the correlation output, so as to recover the transmitted information.

For the other two synchronous UWB modulation schemes, the RF structures at the transmitting end and the receiving end will be slightly different, so the corresponding time domain waveforms will also be different. Nevertheless, the signal transmission spectrum structures of the three synchronous UWB modulation technologies proposed in this patent are basically the same. We focus on the carrier synchronous ultra-wideband modulation scheme described in the specific implementation mode, and illustrate its power spectrum characteristics in combination with specific simulation examples.

The source generates the binary sequence {a _n } to be transmitted, and its bit duration T _b = 9.6×10 ^-5 s, where T _b is selected to realize the carrier-synchronous UWB transmission signal from the perspective of relative bandwidth, ensuring that its relative bandwidth is greater than 20%; the value of user time-hopping code B _n follows a discrete uniform distribution on [0, 11], and T _n follows a continuous uniform distribution on [0, 7.5×10 ^-6 ]. The baseband waveform p(t) is a square wave, the pulse duration T ₀ =6×10 ^-6 s, the center frequency of the carrier wave f _c =166.67kHZ, and the value of the DC bias D is 1.

The power spectral density of the carrier synchronous UWB signal obtained by simulation is shown in Figure 5: First, the center frequency of the synchronous carrier UWB signal spectrum is half of the main lobe width of the signal, so the relative bandwidth is about 50%, which meets the definition requirements of UWB relative bandwidth ; Secondly, there is a very strong synchronous carrier component at the center frequency of the main lobe, and the receiving end can obtain precise synchronous timing by using a simple phase-locked loop, and the width of the main lobe is widened and the amplitude is extremely low; finally, the bandwidth is 2f _c to send the filter After side lobe filtering is performed on the modulated signal, the carrier synchronous ultra-wideband transmission signal can be obtained. The power spectrum of the signal transmitted in the wireless channel is shown in Figure 6.

Claims (6)

1. A carrier synchronous ultra-wideband radio frequency implementation scheme, which can realize UWB modulation signals carrying synchronous carrier components. It is characterized in that: a new synchronous UWB signal modulation method, its power spectrum contains obvious synchronous signal components, and the receiving end can obtain accurate timing and synchronous information by using a simple phase-locked loop, reducing the difficulty of synchronous acquisition and improving the receiving performance. 2. The realization method of carrier synchronous ultra-wideband signal according to claim 1, it is characterized in that: utilize the impulse sequence phase delay of pseudo-random sequence control, send information sequence then control impulse signal amplitude, this modulation sequence is passed through pulse After shaping the filter, superimpose the DC bias, and carry out carrier phase modulation on this basis, as shown in Figure 1. 3. the realization method of carrier synchronous ultra-wideband signal according to claim 2, it is characterized in that: a kind of novel synchronous ultra-wideband modulation technique superimposes DC bias on the basis of spread spectrum modulation waveform, and adopts carrier period modulation technique, There is an obvious synchronous carrier signal component in the power spectrum of the modulated signal, as shown in FIG. 2 . 4. The method for realizing the carrier-synchronous ultra-wideband signal according to claim 2, characterized in that: a novel synchronous ultra-wideband modulation technique utilizes the bits of information to be transmitted and the random sequence to jointly control the pulse occurrence position, and superimposes on this basis DC bias, and the use of carrier period modulation technology, so that there is an obvious synchronous carrier signal component in the power spectrum of the modulated signal, as shown in Figure 3. 5. the realization method of carrier synchronous ultra-wideband signal according to claim 1, it is characterized in that: adopt single-cycle modulation, information symbol cycle and carrier cycle keep integral multiple relation; And carrier phase or amplitude change are strictly aligned with information code ; The baseband pulse duration and the information symbol also maintain an integer multiple relationship, as shown in Figure 4. 6. the realization method of carrier synchronous ultra-wideband signal according to claim 1, it is characterized in that: there is obvious carrier synchronous component in UWB modulation signal spectrum, and its sidelobe power spectrum is extremely wide and amplitude is extremely low, can contrast with Spectrum resources are used in an overlapping manner to improve spectrum utilization, as shown in Figures 5 and 6.

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