CN102780502A - Method for applying watermark to radio station - Google Patents

Abstract

The invention relates to a general technique of applying a watermark to a radio station. The principle of the general technique is shown in Figure 1. At a transmitting end, a separate device is inserted into the output end of a local oscillator, the device is used for additionally modulating an oscillation source by using a PN (Pseudo-Noise) sequence for only identifying the station, so as to insert the watermark into carrier waves output by the oscillator, and a signal which needs to be sent by the station is transmitted on the basis of the carrier waves into which the watermark is inserted, i.e. an ID (Identity) which identifies the station is added. At a receiving end, a separate and simple device can be used for identifying and extracting the watermark information which is embedded by the oscillator of the station. On the premise that transmitted contents are not processed, the problem of applying the watermark to the radio station is solved by using the method, and normal transmitting and receiving of the signal are not affected.

Description

A kind of method for applying watermark for radio station

Technical field

The present invention proposes a kind of method for applying watermark for radio station of simple general-purpose, can not change the existing emitting portion in radio station, and watermark information is squeezed into for radio station in the case of also not changing the wireless signal content of transmitting. 

Background technology

As the Intelligent control for electromagnetic wave becomes increasingly to facilitate, some potential safety hazards are left in wireless communications.Reliability in the radio communications such as civil aviaton, military affairs, commercial communication, medicine equipment, satellite communication, remote control remote sensing to sending station has very high requirement, and the identification of radio station increasingly becomes a topic for causing extensive concern.Apply watermark for radio station, recognize sending station by extracting watermark in receiving terminal, this problem can be improved well.But general addition digital watermark is added a watermark in information to be sent, this method changes the information of transmission, it is had a certain degree of distortion, and different watermark adding techniques are needed to use for various forms of information, without generality. 

The present invention relates to the technology that a kind of general radio station applies watermark, the use of PN codes sequence is that oscillator adds watermark information, this technology is transparent to the technical approach in radio station, implement specific communications standard of this technology without known particular radio station, the present invention realizes simple, the watermark that can be widely applied to all kinds of radio station applies, and for example, base station applies watermark, applies watermark etc. for broadcasting station. 

The content of the invention：

Any radio station's transmitting all certainly exists an oscillator, and the carrier frequency of radio frequency is directly to produce either oscillator by oscillator to export the product after frequency synthesis.When some radio station has multiple oscillation sources, necessarily there is a decision radio-frequency carrier.This oscillation source for determining to launch radio frequency is represented with " master oscillator " below.Meanwhile, outside situation unless otherwise indicated, " oscillator " appeared below is interpreted as " master oscillator ".When radio station is worked with multi-carrier mode and the non-same local vibration source of multiple carrier waves is generated, " oscillator " refers to the oscillation source of wherein any one carrier wave. 

The principle of the present invention is as shown in Figure 1.Notice that Fig. 1 is only limitted to the principle of the explanation present invention, do not indicate that limitation of the invention.For example it is not to be construed as：The system that the present invention can be implemented necessarily requires the physical entity that " sender modulation " and " local oscillator " are two separation." sender modulation " in Fig. 1 refers to the existing modulation transmission technology in radio station, and its function is to form radio station's transmission signal, generally comprises (but not limited to) such as lower component：Modulator, encoder, frequency converter, amplifier etc.. 

Physically there is the output end in local oscillator to insert an independent device, an additional modulation is produced to oscillation source, be the carrier wave insertion watermark of oscillator output, that is, with the addition of the ID of a sign radio station identity, as shown in Figure 1. 

If it is c (t) that signal, i.e. outgoing carrier signal, which occur, for local oscillator 101, then 102 are

$c\left(t\right)=e^{j(2\mathrm{\π}{f}_{c}t++\mathrm{\θ}\left(t\right))}---\left(1\right)$

Wherein f_cIt is nominal oscillation frequency, θ (t) is the phase jitter of oscillator.By watermark adder 103, addition watermarking device output 104 is

Wherein

To include watermark information additional phase modulation signal embedded by the present invention. 

C (t) in formula (1) is exactly transformed to c ' (t) by present disclosure by formula (2) so that the c ' (t) used instead based on c (t) emitters worked after processing is worked as carrier frequency. 

Under actual conditions, any oscillator is all undesirable, can all be had in certain phase jitter, i.e. formula (1).The radio station of any normal use in practice all has been provided with overcoming the ability of this phase jitter, for example, pass through carrier synchronization, channel estimation etc. method.From formula (2) as can be seen that the watermark signal that the present invention is applied is essentially equivalent to phase jitter, as long as

Excessive, then for the receiver (specifically its carrier extract part) in original system, θ (t) and

And indistinction.Therefore appreciable influence will not be produced to the work in existing radio station by applying watermark. 

Although

As in the absence of but if the signal that emitter of the control using c (t) and the emitter using c ' (t) are launched, they have objective difference for the receiver of original system.The existence of applied watermark signal can be identified by certain signal processing technology.Implement the situation of the present invention for example shown in Fig. 2.201 be an isolated system unrelated with former receiver, and the present invention does not do any restriction to its implementation.When detector provides the radio frequency units such as antenna for oneself, radio station ID identification will contact without any with the receiver of original system, also be not required to be spatially in close proximity.For example shown in Fig. 3. 

Brief description of the drawings

Fig. 1 is the schematic diagram that radio station adds watermark；Fig. 2 is the schematic diagram for recognizing radio station watermark；Fig. 3 is the illustration figure of watermark adding method；Fig. 4 is the schematic diagram that watermark addition is realized with VCO；Fig. 5 is the schematic diagram of watermark detector.

Embodiment

In order to further illustrate the present invention, several embodiments are given below.The present embodiment is only limitted to a kind of implementation of the explanation present invention, and the restriction of the coverage to the present invention is not represented. 

Embodiment 1：Realize that watermark is added by I/Q modulation

The method of watermark addition can have diversified forms, and Fig. 3 shows a kind of method.The PN sequence mappings of generation can be phase-modulation or frequency modulated mode by phase calculation 301.When two outputs of phase calculation are set to 0, that is, close watermark addition. 

Embodiment 2：Realize that watermark is added by VCO

Oscillator for many systems is realized using VCO, and the watermark for this kind of system is added, and Fig. 4 mode can be used to realize.When two outputs of phase calculation are set to 0, that is, close watermark addition. 

Embodiment 3：Watermark detection

This example demonstrates that, the watermark added according to the present invention, no matter its specific addition manner is above-described embodiment 1,2 or other method, can be detected in receiving terminal. 

The present invention does not limit the detection method of watermark, and the present embodiment is merely to indicate that the present invention adds the detectability of watermark. 

Consider such a example, it is assumed that transmission signal have passed through single footpath wireless fading channel and reach receiving terminal, receiving signal can be expressed as

Wherein s_L(t)e^jθ(t)It is radio signals, θ (t) is the phase jitter for sending oscillator,

It is the PN code watermark signals of addition, ρ (t) e^jφ(t)It is channel fading, z (t) is interchannel noise.Watermark detector can work in the way of described in Fig. 5.In figure, 502 produce a local watermark signal, and 501 propose to receive the phase bit position of signal, and then the two carries out related operation in 503, correlated results is compared with a thresholding in Threshold detection 504, then judges that expected watermark is present if above predetermined thresholding. 

The watermark that the present invention is designed is the periodic signal repeated for a long time, therefore watermark detector can improve the reliability of watermark identification by multiple cycles. 

Claims (7)

1. a kind of method for applying watermark to radio station.An additional phase modulation is carried out using a carrier wave produced with the unique corresponding PN sequence pairs transmitting oscillator in radio station, so as to generate a carrier wave through processing.It does not change the existing emitting portion in radio station, does not change the wireless signal content of transmitting yet.Any wireless signal of radio station is based on the carrier wave transmitting through processing.

2. the watermark described in claim 1, its refer to it is any different radio station can be enable to distinguish, or the identification information that particular radio station whether there is can be judged.

3. the radio station described in claim 1, it is characterized in that sending wireless signal transfer information by carrier modulation, this information transmission covers any frequency range, and the content-form of transmission includes but is not limited to audio-frequency information, video information and text information.The equipment avatar of this radio station includes but is not limited to mobile phone, base station, broadcasting station.

4. the wireless signal described in claim 3, it is characterized in that being sent by wireless environment, signal form can think data signal, or analog signal, can use any one feasible modulation coding mode.

5. the PN sequences described in claim 1, it is characterized in that：The sequence of values produced by certain rule, its auto-correlation function is with unique properties.This sequence can be binary sequence or multilevel sequence, can be sequence of real numbers or sequence of complex numbers.The including but not limited to modification of m-sequence, M sequence, Gold sequence, chaos sequence and these sequences.

6. the peculiar property described in claim 5, the property for referring to the auto-correlation function is different from the PN sequences and the cross-correlation function of other any signals.

7. the additional phase modulation described in claim 1 refers to any method that addition PN sequences are carried in carrier phase, include but is not limited to：Linear frequency modulation, Linear Phase Modulation.

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