CN102647204A - Scheme for realizing frequency hopping of multiband OFDM (Orthogonal Frequency Division Multiplexing) ultra-wide band system - Google Patents

Abstract

The invention discloses a scheme for realizing frequency hopping and de-hopping in a baseband digital domain aiming at a multiband OFDM (Orthogonal Frequency Division Multiplexing) ultra-wide band system. A transmitter performs baseband hopping on a single-band after a wave form is formed; a radio frequency part uses a single local oscillator to generate a carrier wave frequency of a second band, to modulate three band frequency spectrums of the baseband to a radio frequency; a receiver generates the carrier wave frequency same as that from a transmitting end by the single local oscillator, and the system moves the three band frequency spectrums of the radio frequency to the baseband by virtue of coherent demodulation; and before the matched filtering of the baseband digital domain, the single-band is recovered by carrying out the frequency hopping and de-hopping. By adopting the baseband frequency hopping and de-hopping system, the system radio frequency part just needs the oscillator with single frequency, thereby avoiding using complicated frequency synthesizers, simplifying the complexity of a hardware circuit, not specially designing guard interval for frequency changeover time so as to improve the useful information throughput rate, and providing convenience in timing and synchronization of the digital domain and the control of the frequency hopping and de-hopping. The frequency hopping scheme can be widely applied to a wireless communication system with multiple sub-bands.

Description

A kind of frequency hopping implementation of many band OFDM radio ultra wide band systems

Technical field

The present invention relates to the carrier frequency tracking method of a kind of multi-band OFDM radio ultra wide band system based on time domain expansion (TDS) technology; To the asynchronous carrier frequency offset that causes of oscillator in system receiver and the transmitter; Behind the receiver carrier frequency acquisition, less residual carrier frequency deviation is further estimated and compensation, can be widely used in having in the multi-band OFDM wireless communication system of time domain spreading diversity technology.

Background technology

Ultra broadband (UWB) system has characteristics such as data throughout height, noise resisting ability is strong, ability of anti-multipath is strong, power spectral density is low, technology such as replacing bluetooth is become the preferred option of following Wireless Personal Network.OFDM is high with its availability of frequency spectrum, anti-symbol is crosstalked advantages such as strong, the anti-frequency selective fading ability of (ISI) ability is strong; Become following core technology in local area network (LAN), metropolitan area network and wide area network field, in the net of individual territory, adopt the OFDM technology to realize that UWB will be trend of the times.The ISO/IEC26907 standard of Europe ECMA-368 standard, International Standards Organization and the meeting of International Power working committee all adopts the physical-layer techniques of multi-band OFDM (MB-OFDM) scheme as UWB.The ECMA-368 standard code a kind of UWB system based on MB-OFDM, its transmission rate can be up to 480Mbps, uses the 3.1GHz-10.6GHz frequency range, and it is divided into 14 sub-frequency bands, general 3 frequency bands are one group and develop use.Single band bandwidth is 528MHz, adopts the OFDM technology to generate signal, and system is totally 128 number of sub-carrier (100 information subcarriers, 12 pilot sub-carriers, 10 protection subcarriers and 6 gap carrier waves), and subcarrier spacing is 4.125MHz.Interpolation 37 point protection interval group are grown into 165 OFDM symbol behind the transmitting terminal IFFT, and on the carrier wave that is modulated to different frequency by time-frequency code control timesharing.

The key that the MB-OFDM system is different from the traditional narrow ofdm system is that it comprises a plurality of sub-bands, and each frequency band generates signal by the OFDM technology.A baseband OFDM signal x (t) can be expressed as

x(t)＝x _I(t)+jx _Q(t)

Wherein, x _I(t) and x _Q(t) be real part and the imaginary part of x (t).Existed system adopts the multiband implementation method of RF hopping (RF-FH) more, and promptly the direct frequency hopping of baseband OFDM signal is to a plurality of carrier waves of radio frequency, and radio frequency part adopts frequency synthesizer to produce 3 carrier frequency w _{C, i}, i=1,2,3, at present preceding 3 basebands that use first group more, so centre frequency is respectively 3432MHz, 3960MHz and 4488MHz.Every at a distance from the time of OFDM symbol 312.5ns, carrier frequency according to the certain pattern saltus step once.Up-conversion adopts orthogonal modulation technique, and the bandpass signal y (t) after the modulation can be expressed as

y(t)＝x _I(t)cosω _c，it-x _Q(t)sinω _c，it

After the process impulse response was the channel of h (t), the signal r (t) that receives did

$r\left(t\right)=(x_I\left(t\right)\⊗h\left(t\right))\cos {\mathrm{\ω}}_{c,i}t-(x_Q\left(t\right)\⊗h\left(t\right))\sin {\mathrm{\ω}}_{c,i}t$

$=s_I\left(t\right){\cos \mathrm{\ω}}_{c,i}t-s_Q\left(t\right){\sin \mathrm{\ω}}_{c,i}t$

Wherein The expression convolution algorithm, $s_I\left(t\right)=x_I\left(t\right)\⊗h\left(t\right),$ $s_Q\left(t\right)=x_Q\left(t\right)\⊗h\left(t\right).$

This method medium frequency synthesizer (FS) produces 3 local frequencies and carries out mixing as carrier wave and reception signal, and saltus step between 3 frequencies successively.This mode requires that the conversion speed of FS output frequency is fast, stability is high, and hardware circuit is realized comparatively complicated.Forefathers' research points out that the frequency lock speed of standard closed loop phase-locked loop structures FS is very slow, proposes a kind of single-side band modulation frequency synthesizer, but realizes that circuit is very complicated, and design difficulty is bigger.Other has the people to propose the demodulating system of two stages mixing, can quicken frequency inverted, but still needs complicated FS, and faces the problem that frame synchronization realizes difficulty.In the RF-FH receiver, the timing synchronizing information of baseband digital domain feeds back to radio-frequency head and starts dehop, causes long capture time and bigger hunting zone.In addition, it is the symbol protection interval of FS frequency inverted time design certain-length specially that the RF-FH system needs, and this has reduced the band efficiency of system.Except that the multiband implementation of traditional RF-FH; Can also from the radio frequency to the base band, do 3 tunnel parallel down-conversions; The baseband signal of 3 ADC after the 3 tunnel down-conversions into numeric field of sampling is simultaneously done in local oscillator of each route control mixing, base band, has replaced the dehop process with 3 road down-conversions that walk abreast like this; Avoided using complicated frequency synthesizer; Realize that synchronously relative second method is also more convenient, but the design of 3 tunnel down-conversions and 3 AD increases the hardware circuit complexity greatly, hardware resource consumption is more.

Summary of the invention

The objective of the invention is to the multi-band OFDM super broad band radio communication system; A kind of new multiband implementation is proposed; Solve the difficult problem that the realization of high performance frequency synthesizer is difficult in the conventional radio frequency frequency hopping mechanism, radio frequency structure is complicated; Simultaneously analog circuit is transferred to numeric field and realizes, be convenient to system integration, simplification.

Technical scheme of the present invention:

The present invention proposes the multiband implementation that baseband digital domain is carried out frequency hopping and dehop for many band ofdm systems: transmitter carries out baseband hopping (BF-FH) to single band behind Waveform shaping; Radio frequency part produces the carrier frequency of second frequency band with single local oscillator, and 3 band spectrums of base band are modulated to radio frequency; Receiver produces opposite carrier frequency through single local oscillator, and radio frequency 3 band spectrums are moved to base band; Before the baseband digital domain matched filtering, implement dehop and recover single frequency band.

Beneficial effect of the present invention:

The present invention has designed a kind of frequency hopping implementation of many band OFDM radio ultra wide band systems.Baseband hopping is separated jump mechanism makes system's radio frequency part only need the oscillator of single-frequency, avoids the use of complicated frequency synthesizer, has simplified the hardware circuit complexity; Need not specially for frequency inverted time design protection at interval, improved the useful information transmission rate; For reaching dehop control synchronously, the timing of numeric field provides convenient.This hopping scheme can be widely used in having in the wireless communication system of a plurality of sub-bands.

Description of drawings

Fig. 1 is a transmitter RF-FH circuit structure diagram

Fig. 2 is that the RF-FH-OFDM system receives block diagram

Fig. 3 is a transmitter BB-FH circuit structure diagram

Fig. 4 is that the BB-FH-OFDM system receives block diagram

Fig. 5 is RF-FH-OFDM and BB-FH-OFDM spectrum diagram

Embodiment

Be described further below in conjunction with accompanying drawing with through the embodiment specific embodiments of the invention:

The present invention has designed a kind of frequency hopping implementation of many band OFDM radio ultra wide band systems, and it is characterized in that: this programme may further comprise the steps:

A. transmitter carries out baseband hopping to single band behind Waveform shaping;

B. radio frequency part produces the carrier frequency of second frequency band with single local oscillator, and 3 band spectrums of base band are modulated to radio frequency;

C. receiver produces the carrier frequency identical with transmitting terminal through single local oscillator, and system moves radio frequency 3 band spectrums to base band through coherent demodulation;

D. before the baseband digital domain matched filtering, implement dehop and recover single frequency band.

Behind the said Waveform shaping of step a, data are carried out N times of up-sampling, for follow-up numeric field frequency hopping modulation is prepared.

3 mid-band frequencies selecting for use in the said baseband hopping process of step a are respectively-F, and 0, F, wherein F is the modulation bandwidth of single band ofdm system.

The said baseband hopping of step a carries out based on system time frequency sign indicating number pattern.

Baseband hopping among the step a is after the analog signal of digital-to-analogue conversion output connects the low pass filter that cut-off frequency is 3F/2.

Dehop starts the timing Synchronization Control of the moment by baseband digital domain in the steps d.

Embodiment

Apply the present invention in the MB-OFDM-UWB system of 200Mbps pattern of ECMA-368 standard code, system adopts first group of 3 frequency band, and its centre frequency is respectively 3432MHz, 3960MHz and 4488MHz, and the time-frequency code pattern is 1,2,3,1,2,3.

System transmitter generates the single band baseband signal that bandwidth is 528MHz after carrying out the IFFT quadrature modulation.This signal is carried out 6 times of up-samplings; And the signal behind the up-sampling carried out the raised cosine waveform moulding; Thus, centre frequency is on frequency spectrum, the be separated by space of 5 single band bandwidth of signal that 0 signal and centre frequency are 6 times of 528MHz, and this lays the first stone for baseband hopping.According to 1,2,3,1,2,3 time-frequency code pattern with the timesharing of single band frequency spectrum be modulated on the centre frequency of 3 frequency bands, wherein 3 mid-band frequencies are respectively-528MHz, 0,528MHz.Numeric field signal after the frequency hopping is converted into analog signal output by digital to analog converter, and the baseband low pass filters cut-off frequency is taken as 3 * 528MHz/2=792MHz.In the up-converter circuit of radio frequency part; Adopting local oscillator to produce frequency is the single carrier wave of 3960MHz; This carrier wave is modulated to radio frequency with 3 band spectrums of base band, thereby realizes that equally centre frequency is 3 modulation bands of 3432MHz, 3960MHz and 4488MHz.Receiver employing local oscillator generation frequency is that the single carrier wave of 3960MHz is moved base band through coherent demodulation with radio frequency 3 band spectrums.Analog to digital converter is with the base-band analog signal into numeric field of sampling; The carrier frequency of base band dehop is initiated on first mid-band frequency; Carry out the timing Synchronous Processing to receiving data; Find the correct original position of a frame, start dehop according to timing position and recover the single band frequency spectrum, wherein dehop 3 carrier frequencies are opposite with transmitter.

Claims (6)

1. be with the frequency hopping implementation of OFDM radio ultra wide band system one kind, it is characterized in that: this programme may further comprise the steps more:

A. transmitter carries out baseband hopping to single band behind Waveform shaping;

B. radio frequency part produces the carrier frequency of second frequency band with single local oscillator, and three band spectrums of base band are modulated to radio frequency;

C. receiver produces the carrier frequency identical with transmitting terminal through single local oscillator, and system moves radio frequency three band spectrums to base band through coherent demodulation;

D. before the baseband digital domain matched filtering, implement dehop and recover single frequency band.

2. the frequency hopping implementation of a kind of many band OFDM radio ultra wide band systems according to claim 1 is characterized in that: behind the said Waveform shaping of step a, data are carried out N times of up-sampling, for follow-up numeric field frequency hopping modulation is prepared.

3. the frequency hopping implementation of a kind of many band OFDM radio ultra wide band systems according to claim 1; It is characterized in that: three mid-band frequencies selecting for use in the said baseband hopping process of step a are respectively-F; 0, F, wherein F is the modulation bandwidth of single band ofdm system.

4. the frequency hopping implementation of a kind of many band OFDM radio ultra wide band systems according to claim 1, it is characterized in that: the said baseband hopping of step a carries out based on system time frequency sign indicating number pattern.

5. the frequency hopping implementation of a kind of many band OFDM radio ultra wide band systems according to claim 1 is characterized in that: baseband hopping among the step a is after the analog signal of digital-to-analogue conversion output connects the low pass filter that cut-off frequency is 3F/2.

6. the frequency hopping implementation of a kind of many band OFDM radio ultra wide band systems according to claim 1 is characterized in that: dehop starts the timing Synchronization Control of the moment by baseband digital domain in the steps d.

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