CN109547037B

CN109547037B - DMB transmitting system capable of simultaneously transmitting III wave band and L wave band

Info

Publication number: CN109547037B
Application number: CN201811615635.7A
Authority: CN
Inventors: 王国裕; 杜鹏; 张红升; 张炎
Original assignee: Chongqing University of Post and Telecommunications
Current assignee: Chongqing University of Post and Telecommunications
Priority date: 2018-12-27
Filing date: 2018-12-27
Publication date: 2020-09-01
Anticipated expiration: 2038-12-27
Also published as: CN109547037A

Abstract

The invention relates to a DMB (digital multimedia broadcasting) transmitting system capable of simultaneously transmitting a III wave band and an L wave band, belonging to the field of wireless communication. The system comprises: the system comprises a COFDM encoder, an up-converter, a power divider, a III-band filter, an L-band frequency conversion module, a power amplifier and a transmitting antenna; the L-band frequency conversion module comprises a low noise amplifier, a phase-locked loop frequency source part, a direct up-conversion module and an L-band-pass filter; the frequency source part of the phase-locked loop comprises a constant temperature crystal oscillator and a PLL. In the L-band frequency conversion module, a III-band signal is amplified by a low-noise amplifier and then is accessed into a direct up-conversion part, a local oscillator signal is accessed into the direct up-conversion part, and the III-band signal and the local oscillator signal are mixed in the direct up-conversion part; and the mixing signals are accessed into an L-band-pass filter for filtering. The invention solves the signal coverage problem in practical application, improves the user experience of DMB products, reduces the cost and simplifies the structure.

Description

DMB transmitting system capable of simultaneously transmitting III wave band and L wave band

Technical Field

The invention belongs to the field of wireless communication, and relates to a DMB (digital multimedia broadcasting) transmitting system capable of simultaneously transmitting a III wave band and an L wave band.

Background

Digital Multimedia Broadcasting (DMB) is developed from Digital Audio Broadcasting, is a wireless high-speed information transmission technology, and fully utilizes DAB (Digital Audio Broadcasting), which functionally expands single Audio information to be transmitted into multiple carriers such as data, characters, graphics, video and the like.

In the practical application of the digital multimedia broadcasting, the system consists of a transmitting system and a wireless receiver of various multimedia terminals.

The existing DMB transmitting system can transmit only a single band (III-band or L-band), and in practical applications, the DMB system generally uses the III-band (174MHz-250 MHz). However, in some application scenarios with many obstacles, the signal coverage of the III-band signal is not very good, and the problem of signal coverage cannot be solved well by increasing the power of the DMB transmitting system to transmit the signal or adjusting the angle of the antenna, thereby reducing the user experience of the DMB product. The L-band (1452MHz-1492MHz) signal has strong penetration capability, and can well solve the problem of signal coverage in the application scene with more obstacles. Meanwhile, the existing DMB receiver can simultaneously receive the III-band signal and the L-band signal.

The existing L-band frequency conversion module is mainly applied to ground equipment for satellite communication. In satellite communication terrestrial equipment, a 70MHz or 140MHz intermediate frequency interface is often used. The traditional frequency conversion mode is that intermediate frequency signals are up-converted twice to C or Ku wave bands, and then are sent to an antenna for transmission after being amplified by a high power amplifier; c or Ku waveband signals received by the antenna are amplified by a low noise amplifier and then are converted into an intermediate frequency of 70MHz or 140MHz through two times of down-conversion. In the frequency conversion mode, the local vibration source required by the second up-conversion of the transmitting channel and the first down-conversion of the receiving channel has high working frequency and the frequency width reaches 500MHz or more, and the technical index requirements can be met by complicated circuit design.

With the rapid development of communication technology, microwave devices suitable for L and LS wave bands are more and more abundant, the cost performance is high, and the power consumption and the volume are smaller and smaller. Therefore, in the existing ground equipment for satellite communication, an intermediate frequency signal is mostly up-converted to an L wave band, then the L wave band is converted to a C or Ku wave band through one-time up-conversion, and finally the L wave band is amplified by a high power amplifier and then sent to an antenna for transmission; the C or Ku wave band signal received by the antenna is firstly amplified by a low noise amplifier and is down-converted to the L wave band for one time. The frequency conversion unit between the 70MHz or 140MHz intermediate frequency and the L-band is usually called L-band frequency conversion module.

The existing L-band frequency conversion module usually employs a secondary frequency conversion scheme (wanglong, L-band direct modem converter and L-band converter [ J ] communication and broadcast television, 2007(4):17-20) to up-convert the signal to the L-band. The first frequency conversion is divided into a low intermediate frequency (lower than the lowest frequency) scheme and a high intermediate frequency (higher than the highest frequency) scheme, and the local vibration source is a point frequency source. The high-intermediate frequency scheme is more beneficial to the suppression of stray signals and local oscillator leakage signals. And the second frequency conversion local vibration source is a frequency source. In the secondary frequency conversion scheme, two mixers, two filters, two frequency synthesizers and two crystal oscillators are needed, and the used devices are relatively more, so that the problems of large size, high power consumption and inconvenience for integration exist. The intermediate frequency interface adopted by the existing L-band frequency conversion module is 70MHz or 140 MHz. And the common output frequency range is 950MHz-1450MHz, the output frequency bandwidth is 500MHz, obviously the existing L-band frequency conversion module applied to the satellite communication ground equipment is not applicable to the DMB transmitting system.

Therefore, in order to solve the signal coverage problem in the application environment with more obstacles and improve the user experience of DMB products, the III-band signal and the L-band signal can be transmitted simultaneously in the same DMB system. In a DMB system applying the III-band signal, a set of DMB transmitting system for transmitting the L-band signal is added, which obviously has too high cost and is difficult to implement. The invention designs a DMB transmitting system which can simultaneously transmit III wave band signals and L wave band signals from the aspects of low cost, simple structure and easy realization.

Disclosure of Invention

In view of the above, an object of the present invention is to provide a DMB transmitting system capable of transmitting III-band and L-band signals simultaneously, wherein an L-band frequency conversion module for direct frequency up-conversion is applied to the DMB transmitting system capable of transmitting III-band signals, so that the system can transmit III-band signals and L-band signals simultaneously, thereby solving the signal coverage problem in practical application, improving user experience of DMB products, reducing cost, simplifying structure, and facilitating implementation.

In order to achieve the purpose, the invention provides the following technical scheme:

a DMB transmitting system capable of simultaneously transmitting a III-band and an L-band, comprising: the system comprises a COFDM encoder, an up-converter, a power divider, a III-band filter, an L-band frequency conversion module, a power amplifier and a transmitting antenna; the L-band frequency conversion module comprises a low noise amplifier, a phase-locked loop frequency source part, a direct up-conversion module and an L-band-pass filter; the Phase-Locked Loop frequency source part comprises a constant temperature crystal oscillator and a Phase-Locked Loop (PLL);

in the L-band frequency conversion module, a III-band signal from the power divider is amplified by a low noise amplifier and then is accessed to a direct up-conversion part (based on ADL5350), meanwhile, a local oscillator signal with stable high frequency obtained by a phase-locked loop frequency source part (based on ADF4351) controlled by a program is accessed to the direct up-conversion part, and the III-band signal and the local oscillator signal are mixed in the direct up-conversion part; the mixing includes both up-conversion and down-conversion, and there are also frequency conversions of many interference signals, so that the mixing signal output by the direct up-conversion module needs to be accessed to an L-band-pass filter with good performance for filtering, and the interference signal is filtered.

Further, the COFDM encoder includes a convolutional coding module, a time interleaving module, a frequency interleaving module, a DQPSK modulation module, and an OFDM modulation module, which are connected in sequence, and codes data to be transmitted through a Field-programmable gate Array (Field-programmable gate Array FPGA).

Further, the signal modulated by the OFDM modulation module sequentially passes through an up-converter, a filter and a power divider to obtain two paths of III-band signals, and one path of III-band signal is amplified by a power amplifier and then is sent out by a transmitting antenna; and the other path of III wave band signal is firstly converted into an L wave band through an L wave band frequency conversion module, and then is transmitted out through a transmitting antenna after being amplified by a power amplifier.

Further, the up-converter, the III-band filter, the power divider and the L-band frequency conversion module are integrated on one board.

Further, the up-converter adopts an AD9957 chip.

Further, the direct up-conversion part adopts an ADL5350 chip to realize frequency mixing of the amplified III-band signal and the local oscillator signal and up-convert the III-band signal to an L-band.

Furthermore, the PLL adopts an ADF4351 chip, and is controlled by a program, so that the output frequency of the L-band frequency conversion module is adjustable.

Further, the L-band-pass filter is a microstrip hairpin filter or a cavity filter.

The invention has the beneficial effects that:

the existing DMB transmitting system can only transmit signals of a single frequency band, and has a great limitation in practical application. The existing L-band frequency conversion module applied to satellite communication adopts an intermediate frequency interface (70MHz or 140MHz), utilizes a secondary frequency conversion mode to up-convert an intermediate frequency signal to an L band, has a complex structure, and is not beneficial to realizing the requirements of miniaturization, low power consumption and high integration level. The DMB transmitting system provided by the invention applies the direct up-conversion L-waveband frequency conversion module to the DMB transmitting system which transmits the III-waveband signal, so that the DMB transmitting system can transmit the III-waveband signal and the L-waveband signal simultaneously, thereby solving the signal coverage problem under the condition of more obstacles, improving the user experience of DMB products, and meeting the requirements of low cost, simple structure and easy realization.

Drawings

In order to make the object, technical scheme and beneficial effect of the invention more clear, the invention provides the following drawings for explanation:

fig. 1 is a block diagram of a DMB transmitting system according to the present invention;

FIG. 2 is an L-band frequency conversion module;

FIG. 3 is an internal functional block diagram of an AD9957 up-converter;

fig. 4 is a block diagram of a DMB receiving end;

FIG. 5 is a schematic diagram of an L-band hairpin-pass filter;

FIG. 6 is a L-band hairpin-band filter layout;

fig. 7 is a diagram of the filtering effect of the L-band hairpin-type band-pass filter.

Detailed Description

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in fig. 1, a DMB transmitting system capable of simultaneously transmitting a III-band and an L-band according to the present invention includes: the system comprises a COFDM encoder, an up-converter, a power divider, a III-band filter, an L-band frequency conversion module, a power amplifier and a transmitting antenna; the up-converter, the III-band filter, the power divider and the L-band frequency conversion module are integrated on one board. The COFDM encoder comprises a convolutional coding module, a time interleaving module, a frequency interleaving module, a DQPSK modulation module and an OFDM modulation module which are sequentially connected, and the data to be transmitted is encoded through a Field-Programmable Gate Array (FPGA). As shown in fig. 2, the L-band frequency conversion module includes a low noise amplifier, a phase-locked loop frequency source portion, a direct up-conversion module, and an L-band bandpass filter; the phase-locked loop frequency source part comprises a constant temperature crystal oscillator and a PLL.

The signal modulated by the OFDM modulation module sequentially passes through an up-converter, a filter and a power divider to obtain two paths of III-band signals, and one path of III-band signal is amplified by a power amplifier and then is sent out by a transmitting antenna; and the other path of III wave band signal is firstly converted into an L wave band through an L wave band frequency conversion module, and then is transmitted out through a transmitting antenna after being amplified by a power amplifier.

And the direct up-conversion part adopts an ADL5350 chip to realize the frequency mixing of the amplified III-band signal and the local oscillator signal and up-convert the III-band signal to an L-band. The PLL adopts an ADF4351 chip, and is controlled by a program, so that the output frequency of the L-band frequency conversion module is adjustable. The L-band-pass filter adopts a microstrip line hairpin filter or a cavity filter, and the principle effect is shown in figures 5-7.

In this embodiment, the up-converter adopts an AD9957 device, and as shown in fig. 3, its interior mainly consists of a digital processing unit and a logic control unit. The data processing unit mainly comprises: a data composite processing unit, an inverted CCI (interpolated cascaded integrator filter), a fixed interpolation filter, a CCI programmable interpolation filter, a quadrature modulator, a direct digital synthesizer DDS, an inverted SINC filter, an output amplitude multiplier, a digital-to-analog converter 14, a PLL, and a clock control. The logic control unit includes: control registers, level translation control, mode selection logic, mode control, etc. The functions of the various modules are as follows:

(1) a data composite processing unit: in the mode of a quadrature adjuster, the baseband signal input to the AD9957 is an alternating I, Q component, and the data complex processing unit needs to identify and separate the input I/Q data, convert the data into I, Q two parallel data streams, and send the data streams to the next stage of circuit.

(2) Fixing an interpolation filter: the parallel I/Q two paths of data streams output by the data compound processing unit need to be processed by a filter to realize oversampling. The fixed interpolation filter is composed of a 2-stage half-band filter HBF, mainly performs fixed interpolation on input data, i.e., the interpolation factor is fixed (4 times), and it has a low-pass characteristic. Each stage of half-band filter can increase the sampling rate by one time. Meanwhile, in order to make the signal band in the flat portion of the filter, it is generally necessary to increase the cutoff frequency of the half band filter.

(3) Cascaded integrator comb (CCI) filter: is a programmable over-sampling filter. The CCI filter is formed by cascading an integrator and a comb filter, and an interpolation factor R of the CCI filter can be controlled in a programming mode, namely the CCI filter can control the interpolation multiple of data, and the variation range of the CCI filter is 2-63 times. The fixed interpolation filter and the CCI filter are matched for use, so that 8-252 interpolation multiples can be provided, which is the key point for realizing any baseband symbol rate by an AD9957 device.

The CCI filter also has a low-pass frequency response characteristic, and may generate a certain attenuation to the interpolated signal passing through the CCI filter, and different insertion factors may introduce different losses and attenuations. The frequency of the transmitted data also affects the attenuation slope of the signal.

(4) An anti-CCI filter: the AD9957 device is to eliminate the attenuation slope of I/Q data stream caused by CCI filter, and it is pre-processed by an inverse CCI filter before inputting CCI filter to implement the pre-compensation function of the attenuation.

(5) A quadrature modulator: the digital baseband signal is modulated onto a carrier wave of a desired frequency.

(6) DDS: for generating exactly orthogonal sine and cosine digital carrier signals. DDS is essentially a frequency divider that divides a system clock (fsysclk) by a programmed frequency control word (FTW) to produce a sine-cosine carrier of the desired frequency. The output carrier frequency fout is related to the frequency control word (FTW) and the system clock (fsysclk) as follows:

Fout＝(FTW*fsysclk)/2³²

(7) an inverse SINC filter: the modulated digital signal is converted to an analog signal by a 14-bit DAC.

(8) An output amplitude multiplier: the output signal amplitude is controlled with an 8-bit digital multiplier.

(9) A PLL phase-locked loop module: the frequency conversion or division of the reference clock is realized by setting a corresponding register control word.

(10) A clock control unit: the control clock unit controls and generates the operation clocks required by the respective modules, and coordinates the operations between the respective modules.

The wireless receiver of various multimedia terminals is matched with the transmitting system. In practical application, a low-power-consumption and high-integration digital broadcast baseband decoding chip is taken as a core, a low-power-consumption and high-sensitivity wireless receiving module is designed, and the module is taken as the core to drive various terminals such as a loudspeaker, a Light Emitting Diode (LED) screen, a Liquid Crystal Display (LCD) screen and the like through different control circuits. The DMB receiving end structure employed in the present embodiment is as shown in fig. 4.

The transmitting system is successfully applied to a DMB (digital multimedia broadcasting) transmitting system of Chongqing post and telecommunications university, realizes that the same DMB (digital multimedia broadcasting) transmitting system transmits signals of two wave bands, improves the signal coverage problem of places with more barriers, such as a bottom building of a teaching building, improves the user experience degree, and reduces the accident rate in large-scale examinations, such as level four and level six examinations.

Finally, it is noted that the above-mentioned preferred embodiments illustrate rather than limit the invention, and that, although the invention has been described in detail with reference to the above-mentioned preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

1. A DMB transmitting system capable of simultaneously transmitting a III-band and an L-band, the transmitting system comprising: the system comprises a COFDM encoder, an up-converter, a power divider, a III-band filter, an L-band frequency conversion module, a power amplifier and a transmitting antenna; the L-band frequency conversion module comprises a low noise amplifier, a phase-locked loop frequency source part, a direct up-conversion module and an L-band-pass filter; the Phase-Locked Loop frequency source part comprises a constant temperature crystal oscillator and a Phase-Locked Loop (PLL); the COFDM encoder comprises an OFDM modulation module;

in the L-band frequency conversion module, a III-band signal from the power divider is amplified by a low-noise amplifier and then is accessed to a direct up-conversion module, a local oscillator signal obtained by a frequency source part of a phase-locked loop controlled by a program is accessed to the direct up-conversion module, and the III-band signal and the local oscillator signal are mixed by the direct up-conversion module; the mixing signal output by the direct up-conversion module is accessed to an L-band-pass filter for filtering, and an interference signal is filtered;

2. The DMB transmitting system as recited in claim 1, wherein the COFDM encoder includes a convolutional coding module, a time interleaving module, a frequency interleaving module, a DQPSK modulation module and an OFDM modulation module, which are connected in sequence, and the coding of data to be transmitted is implemented by a Field-Programmable Gate Array (FPGA).

3. The DMB transmitting system as recited in claim 1, wherein the up-converter, the III-band filter, the power divider and the L-band frequency converting module are integrated on a board.

4. The DMB transmitting system as recited in claim 1, wherein the up-converter employs an AD9957 chip.

5. The DMB transmitting system as recited in claim 1, wherein the direct up-conversion module employs an ADL5350 chip to implement frequency mixing of the amplified III-band signal and the local oscillator signal, and up-convert the III-band signal to the L-band.

6. The DMB transmitting system as recited in claim 1, wherein the PLL employs an ADF4351 chip, and the PLL is programmed to make the output frequency of the L-band frequency conversion module adjustable.

7. The DMB transmitting system of claim 1, wherein the L-band-pass filter employs a microstrip line hairpin filter or a cavity filter.