KR20070076692A - Method for muliplexing cdm channels, method for receiving cdm channels mutiplexed based on the same, and cdm receiver therefor - Google Patents

Abstract

A method for multiplexing a CDM(Code Division Multiplexing) channel, a CDM receiver thereby, and a receiving method are provided to transmit signals at various rates by applying OVSFs(Orthogonal Variable Spreading Factors) to an actual CDM transmission system in multiplexing a CDM channel. A broadcast signal receiving part receives multiplexed channels so that identical broadcast contents can be transmitted through many channels having their respective OVSFs at the same time(S10). A demultiplexing part demultiplexes the received channels for the restoration of the broadcast contents(S20). An error correction part corrects errors for the received channels according to an FEC(Forward Error Correction) scheme. An A/V decoding part receives the error-corrected channels and decodes video/audio signals(S30). The error correction part measures the BER(Bit Error Rate) of each of the demultiplexed channels through a BER measurement part(S40). A demultiplexing control part controls the demultiplexing part according to each measured BER(S50). For example, suppose that the demultiplexing part is demultiplexing the second channel using the second OVSF, the demultiplexing control part keeps restoring the contents from the second channel using the second OVSF if the measured BER is within an appointed range(S70).

Description

Method for muliplexing CDM channels, method for receiving CDM channels mutiplexed based on the same, and CDM receiver therefor}

1 is a schematic service configuration diagram of a satellite DMB system.

2 is a schematic configuration diagram of a satellite DMB system transmission stage.

3 is a detailed view of the CDM block of FIG.

4 is a graph illustrating a diffusion process of a CDM channel.

5 is a configuration diagram of a transmission frame of a pilot channel in satellite DMB.

6 is a diagram illustrating an overall configuration of a payload unit of a pilot channel.

FIG. 7 is a diagram illustrating the configuration of all control information fields of FIG. 6.

FIG. 8 is a diagram illustrating a CDM channel configuration information field of FIG. 6.

9 is a schematic structural diagram of a broadcast receiving terminal according to the present invention.

10 is a schematic flowchart illustrating a CDM channel reception method according to the present invention implemented in the broadcast receiving terminal of FIG.

<Description of the symbols for the main parts of the drawings>

900: broadcast receiving terminal 910: broadcast signal receiving unit

920: demultiplexer 930: error correction

935: reception rate measuring unit 940: A / V decoding unit

950: demultiplexing control unit

The present invention relates to code division multiplexing (CDM), and more particularly, to a method for multiplexing a CDM channel in consideration of a reception environment, and a CDM receiver and a reception method accordingly.

First, a method of multiplexing a CDM channel will be described using satellite DMB currently being promoted in Korea as an example.

1 is a schematic service configuration diagram of a satellite DMB system.

As shown in FIG. 1, the broadcasting center delivers digital broadcasting content data to a satellite through a ground station. The satellite divides this signal into two types: a signal that the terminal can receive directly and a signal for a Gap-Filler. The shadow area repeater is a device for a shadow area where the satellite signal does not reach, and serves to retransmit the signal received from the satellite into a signal that can be received by the terminal.

A transmission terminal of the satellite DMB system among the satellite DMB systems will be described with reference to FIG. 2. 2 is a schematic configuration diagram of a satellite DMB system transmission stage.

As shown in FIG. 2, the transmitting end of the satellite DMB system transmits broadcast data using a CDM method. Unlike frequency division multiplexing (FDM) carrying multiple data streams on different carrier frequencies, and time division multiplexing (TDM) transmitting data streams in different time intervals, CDMs can orchestrate multiple data Transmit with code.

At the transmitting end of the satellite DMB system, the data stream passes through a concatenation encoder in which an RS code (Reed Solomon code) and a convolutional code are serially connected to an interleaver for error correction.

The satellite DMB system uses a Walsh code as an orthogonal code, which will be described with reference to FIG. 3. 3 is a detailed view of the CDM block of FIG.

As shown in FIG. 3, the data stream of each CDM channel is modulated with a Walsh code pre-assigned to each channel and then multiplied by a pseudorandom sequence (described below). Band spreading occurs while the Walsh code is multiplied, see FIG. 4. 4 is a graph illustrating a diffusion process of a CDM channel.

In FIG. 4, let m (t) be the data stream to be transmitted through any CDM channel and c (t) the Walsh code corresponding to the CDM channel. In addition, suppose that the length of the Walsh code is 2 and thus the Spreading Factor (SF) is 2.

Then, as shown in Figure 4, the bandwidth of the signal multiplied by m (t) and c (t) is increased by the bandwidth of the Walsh code. The bandwidth of the Walsh code is about 1 / T _C. That is, 1 / T _C is called the chip rate as the inverse of the period of one bit of Walsh code. In the real satellite DMB system, the data symbol rate before spreading is 256ksymbol / sec and SF uses a Walsh code of 64, which increases the bandwidth by 64 times to about 16.384MHz.

Referring back to FIG. 3, when a spread spectrum signal passes through a wireless channel due to its wide bandwidth, multipath fading occurs, resulting in multiple identical signals having different time delays. If only one signal is to be received, signals with different time delays act as interference. To overcome this drawback, a pseudo random sequence is used as shown in FIG. 3. Pseudorandom sequence is excellent in autocorrelation and can be used to remove interference due to multipath fading during despreading at the receiver. Finally, the spread signal is carried on a QPSK (Quadrapture Phase Shift Keying) modulation and then carried on a carrier.

2, one of the CDM channels uses a pilot channel and uses a 0 th Walsh code. As can be seen in Figure 2, the pilot channel has no bit interleaver unlike other CDM channels. This is to prevent the time delay caused by the interleaver because the data transmitted on the pilot channel contains important information for the receiver to operate. Instead, the pilot channel is transmitted at a power as high as 3dB to prevent an increase in bit error rate due to the absence of a bit interleaver.

Recently, Orthogonal Variable Spreading Factor (OVSF) has been introduced as orthogonal code of CDM. Orthogonal variable spreading codes, like Walsh codes, can be coded differently while maintaining orthogonality between codes. Therefore, when the orthogonal variable spreading code is applied to the CDM transmission scheme, the CDM channels can transmit the data stream at a variable data rate without being damaged by mutual orthogonality. For example, suppose you send a data stream with a data rate of 256 Kbps to a CDM channel using a Walsh code of length 64. If we use a 32-bit orthogonal variable code, we can increase the data rate to 512 Kbps with the same bandwidth. However, in this case, since the length of the orthogonal code is shortened, the bit error rate is increased.

However, the variable orthogonal spreading code itself has been introduced as described above, but a specific method of how the variable orthogonal spreading code is actually used in a CDM-based system has not been introduced yet. In other words, when the CDM transmitter uses a variable orthogonal spreading code of a different length for each CDM channel, a method of informing the receiver of which length of the variable orthogonal spreading code is used for each CDM channel is not yet introduced. It is not.

Accordingly, the present invention has been proposed to solve the above-mentioned problems, and provides a CDM channel multiplexing method and a CDM receiver and reception method for enabling a variable orthogonal spreading code to be used in an actual CDM based system. The purpose.

In order to achieve the above object, the present invention provides a method of multiplexing a plurality of channels using a CDM (Code Division Multiplexing) method, wherein the channels are divided into a plurality of channel groups, and each channel group has a variable length orthogonal variable. Provided is a CDM channel multiplexing method characterized in that the multiplexing of the channels by applying a spreading code.

In order to achieve the above object, the present invention provides a signal receiver for receiving a code division multiplexing (CDM) multiplexed channel such that the same signal is transmitted simultaneously through multiple channels to which different orthogonal variable spread codes are applied. Demultiplexing unit for demultiplexing the channel by applying an orthogonal variable spreading code, a receiving rate measuring unit for measuring the reception rate of the demultiplexed channel, and the demultiplexing unit in accordance with the receiving rate of the receiving rate measuring unit To provide a CDM channel receiver including a control unit for controlling the orthogonal variable spreading code to be used.

In addition, in order to achieve the above object, the present invention, the step of receiving the CDM (Code Division Multiplexing) multiplexed channel so that the same signal is transmitted at the same time through multiple channels to which different orthogonal variable spread code is applied, for the restoration of the signal Demultiplexing the channel by applying an orthogonal variable spreading code, measuring a reception rate of a demultiplexed channel, and changing an orthogonal variable spreading code applied in the demultiplexing step based on the reception rate Provides a method for receiving a CDM channel.

The concept of the present invention can be applied to all communication schemes based on the CDM scheme. However, for simplicity of description in the following description, the concept of the present invention will be described taking satellite DMB currently being promoted in Korea as an example.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention that can specifically achieve the above object will be described. In the following embodiment, the above-described object of the present invention is implemented by using pilot data of a pilot channel among CDM channels of satellite DMB.

First, a description will be given of the transmission frame configuration of the pilot channel in satellite DMB with reference to FIG. 5 is a configuration diagram of a transmission frame of a pilot channel in satellite DMB.

The pilot data transmitted through the pilot channel is intended to provide the receiver with various information necessary for receiving the CDM signal, and the structure thereof is illustrated in FIG. 5.

The transmission frame of pilot data consists of a super frame consisting of six frames. In each frame, the PS (Pilot Symbol) is a null symbol, so that the channel information, ie, channel gain and phase, required for the rake receiver to operate can be known. At the head of each frame, D ₁ (unique word), i.e., a unique word, having a specific bit pattern of 4 bytes is arranged to synchronize the frame. D ₂ is a frame counter that is incremented from 0 to 5 per frame and is used to synchronize the super frame. The remaining parts D ₃ to D ₅₁ are payload parts in which pilot data is recorded.

6 to 8 will be described in more detail with respect to the payload unit. 6 is a diagram showing the overall configuration of the payload unit of the pilot channel, FIG. 7 is a diagram showing the configuration of the entire control information field of FIG. 6, and FIG. 8 is a diagram showing the CDM channel configuration information field of FIG.

The payload section can be divided into six frames as described above, and each frame includes two sets of total control information fields, a CDM channel configuration information field, a receiver additional information field, and a CRC field. In the present specification, all these fields are not described, but only the entire control information field and the CDM channel configuration information field applied in the embodiment of the present invention will be described.

The total control information field consists of an identification information field (7 bits) and a receiver start signal (1 bit) (see Fig. 7). In the currently-promoting satellite DMB system, the identification information field is fixed to '0100000' to indicate that the payload part is composed of CDM channel configuration information and additional information at receiver startup. A value other than '0100000' in the identification information field is currently reserved. Accordingly, in the present invention, the identification information field has information regarding the length of the variable orthogonal spreading code of a group of CDM channels belonging to the CDM channel configuration information field corresponding to the entire control information field by using the reserved value. Suggest. This will be described later.

The CDM channel configuration information field has information on the nth to n + 9th (n = 1, 11, 21, 31, 41, 51), or the 61st to 63rd CDM channels (see FIG. 8). . In the CDM channel configuration information field, the size of the interleaver is recorded in the interleave mode field, and the code rate of convolutional code is recorded in the CC mode field. The number of transport streams (TS) to be transmitted by the CDM channel is recorded in the TS_ID field, and the minimum and maximum values of TS packets to be transmitted by the CDM channel are recorded in the PID (Packet ID) minimum and maximum fields. The version information field records a value that is incremented by one whenever the setting is changed. In particular, the PID maximum value and the PID minimum value field are information necessary for the broadcast receiving terminal to select a CDM channel to receive.

The broadcast receiving terminal can know the PID of the broadcast to be received through the PMT (Program Map Table), and can know which CDM channel is transmitted through the CDM channel configuration information transmitted through the pilot channel. do.

Again referring to FIG. 7 for information about transmission of a variable orthogonal spreading code length of a CDM channel.

As shown in Fig. 7, the identification information field of the total control information is composed of seven bits. According to the embodiment of the present invention, if the 'b7' bit is set to 1 of the 7 bits, the CDM channel belonging to the CDM channel configuration information corresponding to the entire control information is a 64-bit orthogonal code used in the satellite DMB system. It is proposed to indicate that an orthogonal variable spreading code of other bits is used.

And bits 'b6' to 'b0' indicate the length of the orthogonal variable spreading code used for the CDM channel belonging to the CDM channel configuration information. Since the length of the orthogonal variable spreading code can be represented by an n power of 2 (2 ^ n), it is preferable to express only n values as the 'b6' bits to 'b0' bits. For example, when the length of the orthogonal variable spreading code is 128, 'b6b5b4b3b2b1b0' becomes '0000111'.

In this configuration, the data size of the pilot payload unit of FIG. 8 may also be variable. In this case, in order for the broadcast receiving terminal to know the end of the payload data, 'b6' of the total control information of the frame corresponding to the last frame counter is set to '1'.

It should be noted that providing information about the length of the variable orthogonal spreading code of the CDM channel through the bit configuration of the above-described frame is just one example and the scope of the present invention is not limited thereto.

In the above, a specific method for configuring a CDM channel using an orthogonal variable spreading code has been described using satellite DMB as an example. When the orthogonal variable spreading code is applied to the CDM transmission system, it may be considered that the CDM transmission terminal transmits the same signal through two or more channels using different orthogonal transform code. In this case, the CDM receiver can receive the signal at a high transmission rate through a CDM channel transmitted with a short orthogonal variable spreading code in a good transmission environment, and a long orthogonal variable spread in a poor transmission environment. The signal can be received with a low BER through the CDM channel transmitted in the code.

For this purpose, the CDM receiving terminal according to the present invention and the CDM channel receiving method implemented according to the present invention will be described with reference to FIGS. 9 and 10 by taking a broadcast receiving terminal for satellite DMB as an example. 9 is a schematic configuration diagram of a broadcast receiving terminal according to the present invention, and FIG. 10 is a schematic flowchart showing a CDM channel receiving method according to the present invention implemented in the broadcast receiving terminal of FIG.

As shown in FIG. 9, the broadcast receiver terminal includes a broadcast signal receiver 910, a demultiplexer 920, an error correction unit 930, an A / V decoding unit 940, and a demultiplexer controller 950. It is configured to include).

The broadcast signal receiving unit 910 receives the multiplexed channels such that the same broadcast content is transmitted over the same channel through different channels to which different orthogonal variable spread codes are applied according to the aforementioned CDM channel multiplexing scheme [S10]. Hereinafter, for ease of explanation, the broadcast content may include a first orthogonal variable spreading code, a second orthogonal variable spreading code, and a third orthogonal variable spreading code (length of the first orthogonal variable spreading code <second orthogonal variable spreading code). It is assumed that the length of < the length of the third orthogonal transform code) is simultaneously transmitted through each of the first channel, the second channel, and the third channel to which each is applied.

The demultiplexer 920 demultiplexes the channel by applying an orthogonal variable spreading code to restore the broadcast content [S20].

The error correction unit 930 corrects an error of the received channel. Preferably, the error correction unit 930 corrects an error using a forward error correction (FEC) method [S30]. The A / V decoding unit 940 receives the error corrected channel and decodes a video and / or audio signal [S30].

Meanwhile, the error correction unit 930 includes the reception rate measuring unit 935, and the reception rate measuring unit 935 measures the reception rate of the demultiplexed channel [S40]. Although the reception rate measuring unit 935 may measure the reception rate in various ways, it is preferable that the reception rate measuring unit 935 is a BER measuring unit measuring a bit error rate (BER) of the demultiplexed channel. The reception rate measuring unit 935 may be configured as a separate block from the error correction unit 930.

The demultiplexer 950 controls the demultiplexer 920 as follows according to the reception rate of the reception rate measurement unit 935.

For example, suppose that the demultiplexer 920 demultiplexes a second channel using a second orthogonal variable spreading code. At this time, when the reception rate is within a predetermined appropriate reception rate range, the demultiplexing control unit 950 continues to restore the content from the second channel using the second orthogonal variable spreading code. [S50, S70]

However, when the reception rate is less than the appropriate reception rate range, the demultiplexing control unit 950 stops restoring the content from the second channel using the second orthogonal variable spreading code and increases the third orthogonal variable spreading code to increase the reception rate. To restore the content from the third channel. On the contrary, when the reception rate is greater than or equal to the appropriate reception rate range, the demultiplexing control unit 950 restores the content from the first channel using the first orthogonal variable spreading code to increase the reception speed. [S50, S60]

Accordingly, the broadcast receiving terminal may receive the same content by selecting one of several channels according to a reception environment.

It is apparent to those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit and essential features of the present invention. Accordingly, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention.

Referring to the CDM channel multiplexing method according to the present invention described above, and the effects of the CDM receiver and the reception method according to the present invention as follows.

As described above, in the CDM channel multiplexing, an orthogonal variable spread code having various lengths is applied to an actual CDM transmission system to enable signal transmission at various data rates. Therefore, it is possible to increase the transmission speed by using a short orthogonal code in a good transmission environment and to increase the reception rate by using a long orthogonal code in a poor transmission environment. Therefore, according to the present invention, the CDM receiving terminal capable of receiving the CDM multiplexed channel can reduce the reception signal dropout caused by the deterioration of the channel environment, and can receive a high speed signal when the channel environment is improved.

Claims (16)

In the method for multiplexing a plurality of channels using a Code Division Multiplexing (CDM) method, And dividing the channels into a plurality of channel groups, and applying the orthogonal variable spreading codes of different lengths to each channel group to multiplex the channels. The method of claim 1, At least one of the channels is a pilot channel for transmitting pilot data for providing information necessary for reception of the channels. The method of claim 2, And the pilot data includes length information of an orthogonal variable spread code applied to the channel group. The method of claim 3, wherein The pilot data is a CDM channel multiplexing method, characterized in that consisting of a superframe consisting of a plurality of frames. The method of claim 4, wherein And the frame comprises a total control information field and a CDM channel configuration information field corresponding to the total control information field. The method of claim 5, And a length of an orthogonal variable spreading code applied to the one channel group is recorded in the total control information field. The method of claim 1, CDM channel multiplexing method comprising transmitting the same signal through two or more channels belonging to different channel groups. The method of claim 7, wherein And a channel variable to which each of the at least two channels belongs is applied an orthogonal variable spread code having a different length. A signal receiver for receiving a CDM (Code Division Multiplexing) multiplexed channel such that the same signal is simultaneously transmitted through several channels to which different orthogonal variable spread codes are applied; A demultiplexer for demultiplexing the channel by applying an orthogonal variable spreading code to restore the signal; A reception rate measuring unit for measuring a reception ratio of the demultiplexed channel; And And a control unit for controlling an orthogonal variable spreading code to be used for demultiplexing in the demultiplexing unit according to a receiving rate of the receiving rate measuring unit. The method of claim 9, The signal receiver transmits the same signal simultaneously through a first channel and a second channel to which a first orthogonal variable spreading code and a second orthogonal variable spreading code having a length longer than the first orthogonal variable spreading code are simultaneously transmitted. Multiplexing) receive multiplexed channels, The demultiplexer restores the signal from the first channel by applying a first orthogonal variable spreading code when the reception ratio is greater than or equal to a predetermined value under the control of the controller, and when the reception ratio is less than the predetermined value, the second orthogonal variable is controlled. And a spreading code to recover the signal from the second channel. The method of claim 9, The reception rate measuring unit is a CDM channel receiver, characterized in that for measuring the BER (Bit Error Rate) of the demultiplexed signal. The method of claim 11, The demultiplexer restores the signal from the first channel by applying a first orthogonal variable spreading code when the BER is less than a predetermined value, and applies a second orthogonal variable spreading code when the BER is greater than or equal to the predetermined value. CDM channel receiver to recover the signal from two channels. a) receiving a Code Division Multiplexing (CDM) multiplexed channel such that the same signal is transmitted simultaneously over several channels to which different orthogonal variable spread codes are applied; b) demultiplexing the channel by applying an orthogonal variable spreading code to restore the signal; c) measuring the reception rate of the demultiplexed channel; And and d) changing the orthogonal variable spreading code applied in the step b) based on the reception rate. The method of claim 13, In step a), the same signal is transmitted simultaneously through a first channel and a second channel to which a first orthogonal variable spreading code and a second orthogonal variable spreading code longer than the first orthogonal variable spreading code are applied. Code Division Multiplexing) is a step of receiving a multiplexed channel, In step d), when the reception ratio is less than a predetermined value, the first orthogonal variable spreading code is applied to restore the signal from the first channel, and when the reception rate is greater than or equal to the predetermined value, the second orthogonal variable spreading code is applied. Restoring the signal from the second channel by receiving the CDM channel. The method of claim 13, wherein step c) And measuring a bit error rate (BER) of the demultiplexed channel. The method of claim 15, wherein d) If the BER is less than a predetermined value, the first orthogonal variable spreading code is applied to restore the signal from the first channel. If the BER is greater than or equal to the predetermined value, the second orthogonal variable spreading code is applied to the signal from the second channel. CDM channel receiving method comprising the step of recovering the signal.

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