CN113132039B

CN113132039B - RDS and FM pilot signal carrier and phase synchronization method

Info

Publication number: CN113132039B
Application number: CN202110663278.7A
Authority: CN
Inventors: 李俊
Original assignee: Chengdu Dexin Digital Technology Co ltd
Current assignee: Chengdu Dexin Digital Technology Co ltd
Priority date: 2021-06-16
Filing date: 2021-06-16
Publication date: 2021-09-03
Anticipated expiration: 2041-06-16
Also published as: CN113132039A

Abstract

The invention discloses a method for synchronizing RDS and FM pilot signal carriers and phases, which is specifically S1: demodulating an RDS input signal to obtain first RDS original data; s2: carrying out rate adaptation on the first RDS original data to obtain second RDS original data; s3: and modulating the second RDS original data to obtain an RDS output signal with the same frequency and the same phase as the FM signal. The steps are all carried out under the condition of one reference clock in the FM modulator, the same reference source with the 19kHz pilot signal output by the FM modulator is realized, the relation that the 19kHz pilot signal output by the FM modulator and the 57kHz RDS subcarrier frequency are 3-order harmonic waves and the same phase is further realized, the national standard requirement is met, a better transmitting signal is realized, and the receiving interference is reduced.

Description

RDS and FM pilot signal carrier and phase synchronization method

Technical Field

The invention relates to the field of wireless communication, in particular to an RDS and FM pilot signal carrier and a phase synchronization method.

Background

The RDS technology is to utilize FM multiplex technology, add a subcarrier channel in the spare frequency band of FM broadcast to transmit data, the RDS data signal occupies 57 + -2.4 kHz baseband frequency, it will not interfere stereo broadcast, will not reduce the broadcast quality, at the same time, add a subcarrier channel in the spare frequency band of FM broadcast, will not be interfered by the broadcast program.

In order to transmit fast data messages via the FM band, a series of standard specifications are established by international authorities, and currently, there are mainly european Radio Data System (RDS) specifications and american Radio Broadcast Digital System (RBDS). Through the RDS/RBDS technology, the FM can transmit text information, so that how to accurately and quickly perform related tests for ensuring the reliable operation of an RDS/RBDS system becomes a very critical ring in the FM industrial chain, and is also a problem for a plurality of mobile equipment manufacturers.

The existing FM modulator supporting the RDS function adopts analog RDS modulation waveform and audio signal input, wherein the audio signal is a single-channel or stereo audio signal of 0-15 kHz, the RDS is an RDS encoder output analog waveform, and is a 57kHz analog waveform for RDS encoding and forming.

The 19kHz pilot signal of the prior art modulated signal is generated in the FM modulator, while the 57kHz carrier signal of the RDS signal is generated in the RDS encoder, the two are different devices, and the same reference clock is used, which causes the frequency deviation and the phase deviation of the two, and causes the receiving performance to be reduced. The national standard GB/T15770-1995 broadcast data System (RDS) specification also requires that the subcarrier frequency of the RDS signal be locked to the same phase at the third harmonic of the 19kHz pilot with a tolerance of 10 ° for phase angle. The prior art and implementation schemes cannot meet this requirement, and most devices in practical applications cannot implement the frequency and phase relationship between the 57kHz subcarrier frequency of the RDS signal and the 19kHz pilot signal of the FM signal.

Disclosure of Invention

The invention provides an RDS and FM pilot signal carrier and phase synchronization method, aiming at solving the problem that the receiving performance is reduced due to deviation of the frequency and the phase between the 57kHz subcarrier frequency of an RDS signal and the 19kHz pilot signal of an FM signal.

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

the invention provides a method for synchronizing RDS and FM pilot signal carriers and phases, which comprises the following steps:

s1: demodulating an RDS input signal to obtain first RDS original data;

s2: carrying out rate adaptation on the first RDS original data to obtain second RDS original data;

s3: and modulating the second RDS original data to obtain an RDS output signal with the same frequency and the same phase as the FM signal.

Further, the S1 specifically includes:

and demodulating the RDS signal with the carrier frequency of 57kHz into original bit data before RDS coding or RDS data after RDS coding in an FM modulator to obtain first RDS original data.

Further, the RDS data after the RDS coding is obtained by RDS coding and packaging the original bit data before the RDS coding;

and the RDS data after the RDS coding is decoded and split to obtain the original bit data before the RDS coding.

Further, the S2 specifically includes:

and carrying out rate adaptation on the first RDS original data under a reference clock adopted by an FM modulator to obtain second RDS original data.

Further, the S3 specifically includes:

s31: a 114kHz clock oscillator in the FM modulator performs frequency division by two to obtain a 57kHz subcarrier;

s32: and modulating the second RDS original data to a 57kHz subcarrier to obtain an RDS output signal with the same frequency and the same phase as the FM signal.

Further, the FM pilot signal is spatially divided into two audio signals, a left channel signal L and a right channel signal R.

Further, the left channel signal L and the right channel signal R are added to form a sum signal L + R;

the left channel signal L and the right channel signal R are subtracted to form a difference signal L-R.

Further:

l1: a 114kHz clock oscillator in the FM modulator divides frequency by three to obtain a subcarrier of 38 kHz;

l2: the difference signal L-R carries out suppressed carrier double sideband modulation on the subcarrier of 38 kHz;

l3: and adding the modulation signal and the sum signal L + R for synthesis to obtain an FM baseband signal.

Further, a 114kHz clock oscillator in the FM modulator is divided by six to obtain a pilot signal of 19 kHz.

Further, the FM baseband signal, the 19kHz pilot signal, and the RDS output signal are synthesized to obtain an FM stereo multiplex signal.

The invention provides a method for synchronizing RDS and FM pilot signal carriers and phases, which has the following beneficial effects: through the technical scheme, the invention can realize the relationship that the 19kHz pilot signal output by FM modulation and the RDS subcarrier frequency of 57kHz are 3 harmonics and the same phase, realize better transmitted signals and reduce receiving interference.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive exercise.

FIG. 1 is a simplified circuit diagram of RDS and FM pilot carrier and phase synchronization methods.

Detailed Description

In order to make the objects, features and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the embodiments described below are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it is to be understood that when an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. When a component is referred to as being "disposed on" another component, it can be directly on the other component or intervening components may also be present.

Furthermore, the terms "long", "short", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of describing the present invention, but do not indicate or imply that the referred devices or elements must have the specific orientations, be configured to operate in the specific orientations, and thus are not to be construed as limitations of the present invention.

The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.

As shown in fig. 1, the technical solution of the present invention does not need to change the RDS input signal, and the specific process is to demodulate the RDS input signal of 57kHz in the FM modulator, wherein different demodulation processes can obtain two different first RDS raw data, the first is the raw information bit data before the RDS input signal is encoded, and the second is the RDS data frame encapsulated according to the RDS specification after the RDS input signal is encoded; the original information bit data before the RDS input signal is coded can obtain the RDS data frame through RDS coding and packaging, and similarly, the RDS data frame is decoded, and the original information bit data before the RDS input signal is coded can also be obtained; in this embodiment, the result of demodulating the RDS input signal is preferably the original information bit data before encoding the RDS input signal, so that it can be checked whether the data of the RDS input has errors.

Due to the rate of the first RDS raw data and the rate of the FM modulated RDS data, both use different reference clocks. For example, the reference clock of the first RDS raw data depends on the RDS input signal generating device, such as an RDS encoder, and the rate of the FM modulated RDS data depends on the reference clock employed by the FM modulator. And different reference clocks can cause the data rates of the two to generate difference, so that rate adaptation is needed, the first RDS original data is subjected to rate adaptation under the reference clock adopted by the FM modulator, the second RDS original data is obtained, and data transmission errors are avoided.

Under multipath transmission conditions, the interference caused when the center frequency is three times the pilot signal frequency (19 kHz) and is in phase lock with the pilot signal frequency is minimal; however, due to the different phase between the RDS input signal and the FM modulated pilot signal, a deviation of the signal received at the receiving end may occur. In order to realize the standard 3-harmonic frequency and the completely same phase of the 57kHz carrier signal and the 19kHz pilot signal used for FM modulation, the same reference source is adopted, namely a 114kHz clock oscillator is subjected to frequency division by two in an FM modulator to obtain a 57kHz subcarrier, and the second RDS original data is subjected to double-sideband modulation for inhibiting the subcarrier of the 57kHz subcarrier, so that the standard 3-harmonic frequency and the completely same phase can be realized.

The audio signal input to the FM modulator is divided into two paths, one for the left channel signal L and one for the right channel signal R. And the frequencies of the left channel signal L and the right channel signal R are both 15 Hz-50 Hz. The left channel signal L and the right channel signal R are added to form a sum signal L + R, and the left channel signal L and the right channel signal R are subtracted to form a difference signal L-R. As shown in fig. 1, the 114kHz clock oscillator is divided by three to obtain a 38kHz subcarrier, the difference signal L-R performs suppressed carrier double sideband modulation on the 38kHz subcarrier, and then is added to the sum signal L + R to be synthesized as a baseband signal of the FM modulation signal. In practical application, the frequency is 0 kHz-15 kHz for transmitting a sum signal L + R, and 23 kHz-53 kHz for transmitting a difference signal L-R, wherein the carrier frequency of the difference signal L-R is 38 kHz.

At a receiving end, the sum signal L + R and the difference signal L-R are added to restore a left channel signal L, and the sum signal L + R and the difference signal L-R are subtracted to restore a right channel signal R. In order for the receiving end to extract the coherent carrier, a single frequency signal needs to be transmitted at 19kHz, so that a 114kHz clock oscillator needs to be divided by six inside the FM modulator to obtain a 19kHz pilot signal, which is chosen because it is easier to separate from the frequency division multiplexed signal at the receiving end.

Through the description of the specific embodiment, it can be known that the invention can realize the relationship that the 19kHz pilot signal of FM modulation output and the RDS subcarrier frequency of 57kHz are 3 harmonics and the same phase, realize better transmitting signals and reduce receiving interference.

The foregoing description of the embodiments has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same elements or features may also vary in many respects. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Example embodiments are provided so that this disclosure will be thorough and will fully convey the scope to those skilled in the art. Numerous details are set forth, such as examples of specific parts, devices, and methods, in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In certain example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises" and "comprising" are intended to be inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed and illustrated, unless explicitly indicated as an order of performance. It should also be understood that additional or alternative steps may be employed.

Claims

1. An RDS and FM pilot carrier and phase synchronization method, the method comprising:

s1: demodulating an RDS input signal to obtain first RDS original data;

s2: carrying out rate adaptation on the first RDS original data under a reference clock adopted by an FM modulator to obtain second RDS original data;

s3: and modulating the second RDS original data, specifically, performing frequency division by two on a 114kHz clock oscillator in the FM modulator to obtain a 57kHz subcarrier, and modulating the 57kHz subcarrier by the second RDS original data to obtain an RDS output signal with the same frequency and the same phase as the FM signal.

2. The method of claim 1, wherein the step S1 comprises:

3. An RDS and FM pilot carrier and phase synchronization method as claimed in claim 2,

the original bit data before the RDS coding is encoded and packaged by the RDS to obtain RDS data after the RDS coding;

4. An RDS and FM pilot carrier and phase synchronization method as claimed in claim 1, wherein the FM pilot is spatially divided into two audio signals, a left channel signal L and a right channel signal R.

5. An RDS and FM pilot carrier and phase synchronization method as claimed in claim 4,

the left channel signal L and the right channel signal R are added to form a sum signal L + R;

6. An RDS and FM pilot carrier and phase synchronization method as claimed in claim 5,

7. An RDS and FM pilot carrier and phase synchronization method as claimed in claim 6, wherein the FM modulator has a 114kHz clock oscillator divided by six to obtain a 19kHz pilot signal.

8. An RDS and FM pilot carrier and phase synchronization method as claimed in claim 7, wherein said FM baseband signal, said 19kHz pilot signal and said RDS output signal are combined to obtain an FM stereo multiplex signal.