JP2001086496A - Device and method for transmitting image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a data transmission quantity per packet corresponding to a transmission rate. SOLUTION: When a high speed transmission mode is instructed by a switch 24, a transmission control circuit 22 reduces video compressibility in a video compressing circuit 14, makes a packet generating circuit 16 generate a packet on a condition of code division multiplex number k=8 and makes a spread spectrum transmitting circuit 18 perform spread spectrum transmission with a great radio transmission gain. In the case of a medium speed transmission mode, the transmission control circuit 22 makes the video compressibility of the video compressing circuit 14 medium, makes the code division multiplex number (k) into 4 and makes the radio transmission gain medium. In the case of a low speed transmission mode, the transmission control circuit 22 enlarges the video compressibility of the video compressing circuit 14 and reduces the radio transmission gain on the condition of k=1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image transmitting apparatus and method, and more particularly, to an image transmitting apparatus and method for transmitting an image by a video camera, a digital still camera, or the like.

[0002]

2. Description of the Related Art An existing video transmission apparatus modulates an analog video signal by an analog modulation method such as frequency modulation and transmits the same. On the other hand, a video signal is digitized and digitally modulated and transmitted. Various proposals have been made. In such a digital video transmission system, video data is compressed in advance in order to reduce the amount of transmission data. This enables practical transmission of moving image information and still image information even with a small transmission capacity.

On the other hand, a spread spectrum transmission method has been proposed as a transmission method suitable for wirelessly transmitting image data. In a spread spectrum transmission system using a direct spread system, a transmitting device usually converts a base band signal of a digital signal to be transmitted into a pseudo noise code (PN code).
, A baseband signal having an extremely wider bandwidth than the original data is generated. Further, PSK (phase shift keying) and F
The signal is modulated by a digital modulation method such as SK (frequency shift keying), converted into an RF (radio frequency) signal, and transmitted to the air. The receiving side performs despreading by correlating with the received signal using the same spreading code as the transmitting side, and converts the received signal into a narrowband signal having a bandwidth corresponding to the original data. Subsequently, the original data is reproduced by normal data demodulation.

[0004] In the spread spectrum transmission system, the transmission bandwidth is extremely wide with respect to the information bandwidth. Therefore, under a condition where the transmission bandwidth is constant, only a very low transmission speed can be realized as compared with the ordinary narrow band modulation system.

To solve this problem, a code division multiplex system has been proposed. In this method, a high-speed information signal is converted into a plurality of low-speed parallel data strings, each data string is spread-modulated by a different spreading code sequence that is orthogonal to each other, and then added. To send to. This makes it possible to realize high-speed data transmission under a constant transmission bandwidth without lowering the spreading factor of the spread modulation.

[0006] By combining the spread spectrum transmission method and the image compression coding technique, it becomes possible to transmit high quality images at a practical speed.

[0007]

However, in the code division multiplexing system, the larger the number of multiplexed code divisions, the larger the amount of transmission data. However, depending on the communication environment, the phase of the direct wave and the reflected wave may be different. Due to different phenomena (multipath fading), the level of the composite wave often decreases, and there is a disadvantage that communication failure and communication interruption are likely to occur. For example, when moving image data is transmitted in a compressed state, there is also a problem that the effect of the lack of a part of the data covers a wide area of the video. In other words, in the case of image transmission, a part of data loss has a bad influence on a long-term transmitted image that follows.

[0008] Further, since the amount of information after compression of image data greatly changes depending on conditions such as the picture pattern of an image, there is a problem that transmission cannot be performed at a constant transmission speed.

[0009] An object of the present invention is to provide an image transmitting apparatus and method for solving such a problem.

[0010]

According to the present invention, there is provided an image transmitting apparatus comprising: an image encoding unit for compressing and encoding image information; and a transmission path for transmitting the compressed image information output from the image encoding unit by a spread spectrum method. Transmitting means, transmitting rate specifying means for specifying a transmission rate, a compression rate of the image coding means, and a spread code of the spread spectrum method according to the transmission rate specified by the transmitting rate specifying means. And control means for controlling the number of streams.

An image transmitting method according to the present invention comprises: an image encoding step of compressing and encoding image information; a transmitting step of transmitting compressed image information obtained by the image encoding step to a transmission path by a spread spectrum method. A transmission rate designating step of designating a transmission rate, and a control step of controlling a compression rate of the image encoding step and a number of spread code sequences of the spread spectrum system according to the transmission rate designated in the transmission rate designating step. And characterized in that:

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic block diagram showing an embodiment of the present invention. Reference numeral 10 denotes a portable video transmitter (for example, a digital video camera), which allows the video camera 12 to photograph a desired subject. The video compression circuit 14 converts the digital video signal output from the camera 12 into, for example, a DV
Compression encoding at a plurality of compression rates according to the MPEG system or the MPEG system. The packet generation circuit 16 adds a header information from the transmission control circuit (microcomputer) 22 to the compressed video data output from the video compression circuit 14 to generate a packet of a predetermined size. Supply. The header information supplied from the transmission control circuit 22 to the packet generation circuit 16 includes information designating the number k of code division multiplexes in the spread spectrum transmission circuit 18. The spread spectrum transmission circuit 18 performs spread spectrum modulation on the packet output from the packet generation circuit 16 with the multiplex number k according to the code division multiplex number k included in the header, converts the packet into a radio signal, and outputs the radio signal to the antenna 20. .

The switch 24 provides a user with a plurality of transmission modes prepared in advance. The transmission mode includes a high-speed transmission mode, a medium-speed transmission mode, and a low-speed transmission mode. The switch 24 is a transfer mode instruction unit for inputting the transmission mode selected by the user to the transmission control circuit 22.

As described above, (the antenna 20 of) the transmitter 10
Transmitted to the air from the antenna 40 of the receiver 40
2 and input to the spread spectrum receiving circuit 44. The spread spectrum receiving circuit 44 includes the antenna 4
After converting the RF signal from 2 into a predetermined band, the received packet is despread modulated according to the code division multiplexing number k included in the header of the received packet to restore the packet before transmission. The packet decomposer 46 extracts only the compressed video data from the output of the spread spectrum reception circuit 44 and supplies it to the video decompression circuit 48. The video expansion circuit 48 expands the compressed video data to restore the original video data. NTSC
The encoder 50 converts the video data restored by the video decompression circuit 48 into an analog NTSC video signal and applies it to the monitor 52. Thereby, the camera 1 of the transmitter 10
2 is displayed on the screen of the monitor 52.

FIG. 2 shows the basic structure of a packet transmitted in this embodiment. One packet includes a header 60 and a data body 62. The data body 62 contains compressed video data or message data to be transmitted. The data body 62 of one packet contains a part or all of the compressed image data for one screen. Header 60
Includes a number k of code division multiplexes for controlling the transmission rate of the data body 62, a flag indicating whether or not the data is approved, a frame type, a data length, a transmission destination ID, and a checksum. The number k of code division multiplexes determines the transmission rate of the data body 62 to be spread spectrum modulated. The frame type indicates whether the data contained in the data body 62 is compressed video data or message data indicating a command or status. The data length indicates the length of the data body 62. The destination ID is
This is an ID code for specifying a receiver at the transmission destination when a plurality of receivers are provided. The checksum is a code for confirming on the receiving side whether or not the data of the header 60 has been transmitted correctly.

FIG. 3 is a schematic block diagram of the spread spectrum transmitting circuit 18. The input terminal 80 receives the packet data output from the packet generation circuit 16. The code division multiplex number register 82 extracts the code division multiplex number k from the header 60 of the packet from the packet generation circuit 14 and holds it until the next packet. The header determination circuit 84 determines whether the data currently input from the packet generation circuit 14 is the header 60 of the packet,
The switch 86 is controlled based on the result of the determination. The switch 86 selects k = 1 for the header 60 according to the determination result of the header determination circuit 84, and also sets the code division multiplex number register 82 for the data other than the header, that is, for the data body 62.
Of the parallel number control circuit 8
Set to 8.

The serial-to-parallel converter 90 includes a packet generation circuit 1
6 is converted into a data string of the parallel number k (maximum n) set by the parallel number control circuit 88. The spreading code generator 92 generates a spreading code PN0 dedicated to synchronization and n spreading codes PN1 to PNn for data.
1-94-n output n spread codes PN from the spread code generator 92 to n parallel data outputs of the serial / parallel converter 90.
1 to PNn to generate a plurality of code channels. The switch 96 switches the multipliers 94-2 to 94-n according to the selection signal output from the selection signal generation circuit 98.
The valid code channel is selected from among. The selection signal generation circuit 98 controls the switch 96 so as to select the number of code channels corresponding to the parallel number k set in the parallel number control circuit 88. Here, when k = 1, the switch 9
No. 6 does not select the output of any of the multipliers 94-2 to 94-n.

The adder 100 has a spreading code PN0 for synchronization output from the spreading code generator 92, an output of the multiplier 94-1 and a multiplier 94-2 selected by the switch 96.
９４94-n are added. The RF circuit 102 converts the output of the adder 100 into a transmission frequency signal and supplies the signal to the antenna 20. The gain control circuit 104 controls the RF circuit 10 according to the code division multiplex number k from the parallel number control circuit 88.
2 is controlled.

FIG. 4 is a schematic block diagram of the spread spectrum receiving circuit 44. As shown in FIG. The RF circuit 110 converts an RF signal from the antenna 42 into a predetermined frequency band. The synchronization circuit 112 generates a code synchronization signal and a clock signal synchronized with the spread code and the clock on the transmission side according to the output of the RF circuit 110. The code generation circuit 114 uses the same spread code PN0 as the spread code generator 92 on the transmission side in accordance with the code synchronization signal and the clock output from the synchronization circuit 112.
~ PNn. The carrier reproducing circuit 116 is provided with a carrier reproducing spread code PN0 generated by the code generator 114.
, The carrier signal is reproduced from the output of the RF circuit 110. The baseband demodulation circuit 118 includes a code synchronization signal and a clock from the synchronization circuit 112, spread codes PN1 to PNn from the code generator 114, and the carrier reproduction circuit 11
6 according to the carrier signal reproduced by the RF circuit 110.
, And demodulates baseband data in each code channel.

The code division multiplex number register 120 extracts the code division multiplex number k included in the header 60 from the data of the first code channel output from the baseband demodulation circuit 118 and temporarily stores the data until the next packet. . The header determination circuit 122 is a circuit similar to the header determination circuit 84 on the transmission side, and determines whether the data of the first code channel output from the baseband demodulation circuit 118 is the header 60 or the data body 62, Switch 124 depending on the result
Switch. The switch 124 is connected to the header determination circuit 12
2, k = 1 is selected for the header 60, and the value k held in the code division multiplex register 120 is selected for other than the header, that is, for the data body 62, and the selected k value is controlled in parallel number. The circuit 126 is supplied. The parallel-to-serial converter 128 synthesizes a data string of the number of parallels k (maximum n) specified by the parallel number control circuit 126 from the n outputs of the baseband demodulation circuit 118 and converts the data into serial data. The output of the parallel / serial converter 128 is supplied to the packet decomposer 46.

FIG. 5 is a flowchart showing the operation of the transmission control circuit 22. The characteristic operation of the present embodiment will be described with reference to FIG. First, the transmission control circuit 22
To determine which of the high-speed transmission mode, the medium-speed transmission mode, and the low-speed transmission mode is instructed (S1,
S4).

In the high-speed transmission mode (S1), the transmission control circuit 22 increases the transmission data amount by reducing the video compression ratio in the video compression circuit 14 (S2), and sets the number of code division multiplexes to k = 8. The packet generation circuit 16 generates a packet (S3). Since the number k of code division multiplexes is large, the gain control circuit 104 increases the radio transmission gain. As a result, high-quality video data is transmitted at a high transmission rate so as to have a substantially constant frame rate.

In the case of the medium-speed transmission mode (S4), the transmission control circuit 22 sets the video compression ratio in the video compression circuit 14 to a medium value so that the transmission data amount is also a medium value (S5). The number of division multiplexes is set to k = 4, and the packet generation circuit 16 generates a packet (S6). Since the number k of code division multiplexes is medium, the wireless transmission gain is also medium. As a result, video data of medium image quality is transmitted at a substantially constant frame rate at a medium transmission rate.

In the case of a low-speed transmission mode that is neither high-speed nor medium-speed (S4), the transmission control circuit 22
Is increased to reduce the amount of transmission data (S7), and the packet generation circuit 16 is caused to generate a packet by setting the number of code division multiplexing k = 1 (S8). Since the number k of code division multiplexes is small, the radio transmission gain is also small. Thus, low-quality video data is transmitted at a low transmission rate so as to have a substantially constant frame rate.

By repeating the above, the data transmission amount per packet is dynamically changed according to the designated transmission mode.

[0027]

As can be easily understood from the above description, according to the present invention, the image compression ratio and the number k of code division multiplexes for spread spectrum transmission are adjusted in accordance with the transmission rate. The image data can be transmitted in a state where it is in a closed state.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a packet.

FIG. 3 is a schematic configuration block diagram of a spread spectrum transmission circuit 18.

FIG. 4 is a schematic configuration block diagram of a spread spectrum receiving circuit 44;

5 is an operation flowchart of a transmission control circuit 22. FIG.

[Explanation of symbols]

 10: Video transmitter 12: Video camera 14: Video compression circuit 16: Packet generation circuit 18: Spread spectrum transmission circuit 20: Antenna 22: Transmission control circuit (microcomputer) 24: Switch 40: Receiver 42: Antenna 44: Spectrum Spread receiving circuit 46: Packet decomposer 48: Video expansion circuit 50: NTSC encoder 52: Monitor 60: Header 62: Data body 80: Input terminal 82: Code division multiplex number register 84: Header judgment circuit 86: Switch 88: Parallel number Control circuit 90: Serial-parallel converter 92: Spread code generator 94-1 to 94-n: Multiplier 96: Switch 98: Selection signal generation circuit 100: Adder 102: RF circuit 110: RF circuit 112: Synchronization circuit 114 : Code generation circuit 116: carrier reproduction circuit 118: base Baseband demodulation circuit 120: code division multiplex number register 122: header determining circuit 124: switch 126: parallel number control circuit 128: parallel to serial converter

Claims (7)

[Claims] An image encoding means for compressing and encoding image information, a transmitting means for transmitting compressed image information output from the image encoding means to a transmission line by a spread spectrum method, and a transmission for designating a transmission rate Rate specifying means, and control means for controlling the compression rate of the image coding means and the number of spread code sequences of the spread spectrum system according to the transmission rate specified by the transmission rate specifying means. Characteristic image transmission device. 2. The image transmitting apparatus according to claim 1, further comprising an imaging unit that supplies the image signal to the video encoding unit. 3. The transmitting means comprises a spread spectrum transmitting means for spreading, modulating, and multiplexing the compressed video information with n spread code sequences, and transmitting the multiplexed data. The image transmitting device according to claim 1, wherein the image transmission device can be changed. 4. The control unit according to claim 3, wherein the higher the transmission rate specified by the transmission rate designating unit, the lower the compression rate of the image encoding unit and the larger the number of spread code sequences. Video transmission device. 5. An image encoding step of compressing and encoding image information, a transmitting step of transmitting compressed image information obtained by the image encoding step to a transmission path by a spread spectrum method, and a transmission rate designating a transmission rate. And a control step of controlling the compression rate of the image encoding step and the number of spreading code sequences of the spread spectrum system according to the transmission rate specified in the transmission rate specifying step. Image transmission method. 6. The transmission step includes a spread spectrum transmission step of spreading and modulating the compressed video information with n spread code sequences, and then multiplexing and transmitting the compressed video information. 6. The image transmission method according to claim 5, wherein the variable is variable. 7. The control step according to claim 5, wherein the higher the transmission rate specified in the transmission rate specifying step, the lower the compression rate of the image encoding step and the larger the number of spreading code sequences. Video transmission method.