HK1109524B - Single carrier transmission system and method using the same - Google Patents

Description

Single carrier transmission system and method thereof

The present application is a divisional application of an invention patent application having an application date of 30/9/2003, an application number of 03139297.0, entitled "single carrier transmission system and method therefor".

Technical Field

The present invention relates generally to a single carrier transmission system and a method thereof, and more particularly, to a single carrier transmission system and a method thereof capable of improving reliability of a transmitted signal.

Background

In the era of communication multimedia, computers and broadcasting, countries around the world are constantly digitizing analog type broadcasts. Particularly in developed countries such as the united states, europe, and japan, a digital broadcasting system using satellites has been developed and put into practical use. With the rapid development, different standards for digital broadcasting have been proposed in countries, respectively.

On 24.12.1996, the Federal Communications Commission (FCC) in the united states passed the digital television standard of the advanced television systems committee as the broadcast standard for the next generation of TV. All terrestrial broadcast operators must comply with the ATSC standard in relation to the video/audio compression, packet data transmission architecture, modulation and transmission system specifications. Only the specification of the video format is not announced (stated) but is decided by the industry.

According to the ATSC standard, the video compression scheme employs the ISO/IEC IS13812-2 standard for moving Picture experts group-2 (MPEG-2). This standard has been adopted as a standard for all digital broadcasting types around the world. The audio compression scheme employs the digital audio compression-3 (AC-3) standard proposed by Dolby. The ISO/IEC IS13812 standard for MPEG-2 systems has been adopted as a multiplexing method. This multiplexing method is used in european proposals together with video compression schemes. 8-vestigial sideband (8-VSB) is adopted as a method of modulation and transmission. The VSB method is proposed for digital television broadcasting, using a frequency band of 6MHz to obtain a high-band-efficiency data transmission rate of 19.39Mbps with a simple structure. This is also designed to minimize interference with the broadcast channels of the National Television Standards Committee (NTSC) existing broadcast system. This method uses a pilot signal, a segment sync signal, and a field sync signal in order to stably operate even in a noise environment. Further, to avoid errors, the method uses reed-solomon (RS) codes and Trellis (Trellis) coding.

The ATSC digital television standard is for transmitting high quality video, audio and additional data in a 6MHz band using a single carrier VSB method, and supports a simultaneous terrestrial broadcast mode and a high data rate cable broadcast mode. The main aspect of the method is the 8-VSB modulation method, which is a modified form of the existing analog VSB method, and is capable of performing digital signal modulation.

Fig. 1 is a schematic block diagram illustrating a digital broadcasting system according to the ATSC standard. Referring to fig. 1, the digital broadcasting system includes a scrambler 10, a Forward Error Correction (FEC) unit 20, a Multiplexer (MUX)30, a pilot insertion unit 40, a modulation unit 50, and a Radio Frequency (RF) converter 60. The FEC unit 20 includes a reed-solomon (RS) encoder 21, an interleaver 23, and a trellis encoder 25.

The scrambler 10 is called a data randomizer, and performs a randomization operation on a transmitted data signal, thereby preventing a problem of loss of a synchronization signal due to a repeating word such as 00000000b or 11111111b during the transmission of synchronous data. The scrambler 10 changes the bytes of each data signal in a predetermined pattern and this process is reversed so that the exact values are recovered at the receiving end.

The RS encoder 21 is an FEC structure added to the input data stream. FEC is one of the techniques for correcting bit errors occurring during data transmission. Atmospheric noise, multipath frequencies, signal attenuation, and receiver non-linearities are the causes of bit errors. The RS encoder 21 adds 20 bytes at the end of 187 bytes when the transmitted data is in the MPEG-II transport stream. This added 20 bytes is called the reed-solomon parity bytes. The receiver compares the received 187 bytes with the 20 parity bytes, thereby determining the accuracy of the received data. In case an error is detected, the receiver finds the location of the error and recovers the original signal by correcting the distorted bytes. Errors of up to 10 bytes per stream can be recovered by using this method. However, errors of more than 10 bytes are not recoverable, and thus, the entire stream is discarded.

The interleaver 23 interleaves the order of the data streams, thereby dispersing the transmitted data on a time axis. By doing so, the transmitted data becomes immune (insensitive) to interference. By dispersing the transmitted data, signals in other frequency bands are preserved when noise occurs at a particular location. The receiver reverses the above-described processing, thereby restoring the dispersed signal to exactly the same as the original signal.

Unlike the RS encoder 21, the trellis encoder 25 has a different type of FEC structure. And, unlike the RS encoder 21 constituting the entire MPEG-II stream, the trellis encoder 25 performs encoding in consideration of the influence of time. This is called a convolutional code. The trellis encoder 25 divides the 8-bit byte into 4 2 bits and so on. The 2-bit word is compared with the previous word and a 3-bit binary code is generated with the purpose of describing the change from the previous word to the current word. The 3-bit code is transmitted to the 8-level symbols of the 8-VSB instead of the original 2-bit word (3-bit-8-level). Accordingly, the 2-bit word input to the trellis encoder 25 is converted and output as a 3-bit signal. Because of this feature, 8-VSB is sometimes referred to as an 2/3 rate encoder. The advantage of trellis coding is that the signal can be tracked in time units, thereby clearing error information.

After trellis encoding by the trellis encoder 25, the multiplexer 30 inserts a segment sync and a frame sync in the transmission signal. The pilot insertion unit 40 inserts an ATSC pilot into the transmission signal into which the segment sync and the frame sync are inserted. Here, immediately after modulation is completed, 1.25v with a slight dc offset is applied to the 8-VSB baseband signal. When this occurs, a slight residual carrier appears at the zero frequency point of the modulation spectrum. This generated residual carrier is referred to as the "ATSC pilot.

The modulation unit 50 modulates the signal received from the pilot insertion unit 40 by using 8-VSB modulation. The radio frequency converter 60 converts the modulated signal and outputs the converted signal through an antenna.

The ATSC data segment is made up of 187 bytes and 20 bytes of the original MPEG-II data stream. After trellis encoding, 207 bytes of a segment are changed into 828(207 × 4) 8-level symbol streams.

The segment sync signal is 4 1-byte pulses that are repeatedly added to the beginning of the data segment and the sync byte used to replace the original MPEG-II transport stream. The receiver is able to distinguish the segment sync signal of the repetitive pattern from the completely random data and is also able to accurately recover the clock even when the noise and interference are at a level that does not allow the data to recover itself. The segments of the transmission signal to which the segment sync signal (i.e., segment sync) is assigned are shown in fig. 2. As shown, the segment of the transmission signal includes a segment synchronization signal of 4 symbols, 3 Pseudo Noise (PN) sequences of 63 symbols, respectively, a transmission pattern of 24 symbols, 96 reserved symbols, and 12 pre-code symbols. The PN sequence is a synchronization information sequence used for synchronization and channel estimation of the receiver. The PN sequence is generated by a PN sequence generating unit (not shown) and inserted into the transmission signal by the multiplexer 30.

Fig. 3 is a view showing a frame structure of ATSC data. Referring to fig. 3, a field of ATSC data includes 313 consecutive data segments, and the ATSC field sync (i.e., field sync) becomes a field data segment. An ATSC data frame is composed of 2 ATSC data fields.

The ATSC data field is repeated at a time interval of 24.2ms, similar to the 16.7ms vertical interval for NTSC. The segment sync has a well-known data symbol pattern and is used in the receiver to remove ghosts. More specifically, ghost removal is achieved by comparing error-containing signals to fields synchronously and using the resulting error vector to adjust the characteristics of a ghost-removing equalizer.

Generally, a system information signal indicating a transmission mode of a system is inserted after a PN sequence or in a field synchronization unit by using a spread spectrum. However, since the field sync signal does not pass through the FEC unit, multipath or burst noise displayed in the transmission process may cause distortion of the signal. Such distortion of system information subsequently causes reception problems at the receiving end of the digital broadcast signal.

In U.S. patent application No. 09/962,263 (publication No. US2002041608), there is disclosed a VSB reception system, comprising: a tuner tuning an RF signal transmitted from the VSB transmitter; a VSB demodulator demodulating a signal output from the tuner; a demultiplexer demultiplexing the demodulated signal into ATSC data and additional data; a decoder for decoding the ATSC data; and a derandomizer for derandomizing the decoded data.

Disclosure of Invention

Accordingly, an object of the present invention is to provide a digital broadcasting transmission system capable of reliably transmitting a system information signal by using Walsh codes in a single carrier type digital broadcasting system, and a transmission method thereof.

To achieve the above object, a single carrier transmission system is provided. The single carrier transmission system includes: a scrambling unit for scrambling a TS (transport stream) to be transmitted; an FEC unit, which is used for carrying out forward error correction on the TS after the scrambling code from the scrambling code unit to form a coded TS; a PN sequence generating unit for generating a PN sequence; a Walsh code generating unit for generating a Walsh code corresponding to the identification information; a logic coupling unit for logically coupling the Walsh codes generated by the Walsh code generating unit and the PN sequences generated by the PN sequence generating unit; a Multiplexer (MUX) for performing multiplexing by inserting the signal and the segment sync symbol coupled by the logical coupling unit in the encoded TS: a pilot inserting unit for inserting a pilot into the multiplexed TS; a modulation unit for modulating the TS into which the pilot is inserted; and a radio frequency converter for performing radio frequency conversion on the modulated TS from the modulation unit.

According to another aspect of the present invention, a single carrier transmission method is provided. The single carrier transmission method comprises the following steps: scrambling a TS (transport stream) to be transmitted; forward error correcting the scrambled TS to form a coded TS; generating a PN sequence; generating a Walsh code corresponding to one identification information; performing logical coupling of the Walsh codes generated at the Walsh code generating step and the PN sequences generated at the PN sequence generating step; performing multiplexing by inserting the signal and the segment sync symbol coupled in the logical coupling step in the encoded TS; inserting a pilot into said multiplexed TS; modulating the TS with the pilot frequency inserted; and performing radio frequency conversion on the modulated TS from the modulation unit.

Drawings

The above objects and features of the present invention will become more apparent by describing embodiments of the present invention with reference to the attached drawings, in which:

fig. 1 is a block diagram schematically illustrating a digital broadcasting system according to the ATSC standard;

fig. 2 is a view showing a section of a transmission signal in the system of fig. 1;

fig. 3 is a view showing a frame structure of ATSC data;

fig. 4 is a view schematically showing a digital broadcast transmission system according to the present invention;

fig. 5 is a flowchart illustrating a digital broadcast transmission method of the system in fig. 4:

fig. 6 is a view showing a section of a transmission signal according to the present invention;

fig. 7 is a view illustrating a frame structure of a transmission signal of the digital broadcasting transmission system shown in fig. 5.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 4 is a view schematically showing a digital broadcasting system according to one example of the present invention, and fig. 5 is a flowchart showing a digital broadcasting transmission method of the system in fig. 4. Referring to fig. 4, the digital broadcasting system according to the present invention includes a scrambler 100, a Forward Error Correction (FEC) unit 110, a Pseudo Noise (PN) sequence generating unit 120, a Walsh code generating unit 130, a logic coupling unit 140, a Multiplexer (MUX)150, a pilot inserting unit 160, a modulating unit 170, and a Radio Frequency (RF) converter 180. Further, the FEC unit 110 includes a reed-solomon (RS) encoder 111, an interleaver 113, and a trellis encoder 115.

The scrambler 100, called a data randomizer, performs a randomization operation on a transmitted data signal in order to prevent a problem of a loss of a synchronization signal due to a repeating word such as 00000000b or 11111111b during a synchronous data transmission. The scrambler 10 changes the bytes of each data signal in a predetermined pattern, and the process is reversed at the receiving end to recover the exact original values.

The FEC unit 110 corrects errors with respect to the input data stream. Since the operations of the RS encoder 111, the interleaver 113, and the trellis encoder 115 are performed according to the ATSC standard, further explanation will be omitted herein.

The PN sequence generating unit 120 generates a PN sequence, i.e., it generates synchronization information for synchronization between the transmitting end and the receiving end, and then transmits the generated PN sequence to the multiplexer 150. The PN sequence generated by the PN sequence generating unit may be implemented into different numbers of symbols, such as 255 symbols, 511 symbols, 1023 symbols, 2047 symbols, and 8191 symbols. Also, the "transmission side" in this specification refers to a reception side equipped with a digital broadcast transmission system for transmitting digital broadcasts according to a single carrier scheme, and the "reception side" refers to a reception side receiving digital broadcasts of transmission according to a single carrier scheme.

The Walsh code generating unit 130 generates additional information about the transmitting end, i.e., it generates a Walsh code. The "additional information" refers to identification information provided by the transmission end for the reception end to quickly and easily decode the received signal. The identification information may include at least one of a mapping method, a code rate, frame structure information on a transmitted TS, and data dispersion information. Further, the Walsh codes are formed from groups of bit streams of the same size, and the bit stream is formed from 2^NForm (N ═ natural number).

The logic coupling unit 140 logically couples the PN sequence generated by the PN sequence generating unit 120 and the Walsh code generated by the Walsh code generating unit 130. Logic coupling element 140 is preferably an exclusive-or gate for exclusive-or coupling the PN sequence and the Walsh code.

After trellis encoding performed by the trellis encoder 115, the multiplexer 150 inserts a segment sync and a frame sync in the transmission signal. Further, the multiplexer 150 inserts the PN sequence and the Walsh code coupled by the logic coupling unit 140 into the transmission signal. The pilot insertion unit 160 inserts a pilot in the transmission signal in which the segment sync and the frame sync are inserted. As described above, the pilot refers to a residual carrier occurring at a zero frequency point of the modulation spectrum.

Modulation section 170 modulates the signal received from pilot insertion section 160.

Digital modulation is a process of converting one of the phase, amplitude, and frequency of a carrier wave into a digital signal. Among them, Phase Shift Keying (PSK) is a process of changing a phase according to a digital value. The most basic PSK is binary phase shift keying with a phase separation of 180 ° between the '0' and '1' carriers of the 1-bit signal. Quadrature Phase Shift Keying (QPSK) is a process of having a phase interval of 90 ° with 4 2 bits corresponding to 1 symbol. A value obtained by multiplying the cosine wave by the BPSK signal and a value obtained by multiplying the sine wave by the BPSK signal are added and transmitted. 8-PSK transmits a single symbol with 8-level signals, the 8-level signals having 3 bits and a phase interval of 45 °, respectively. Since 8-PSK transmits three times BPSK's information over the same bandwidth, 8-PSK has much higher frequency efficiency. However, it is susceptible to noise due to the narrow spacing between phases, and therefore requires very high power to maintain the same transmission error rate.

Amplitude keying (ASK) is a process of changing the amplitude of a carrier wave. ASK is almost similar to Amplitude Modulation (AM) except that the modulation signal is not sequential, but rather follows a predetermined number of amplitude levels. For example, the modulated wave has 8 levels through ASK processing of 3-bit information, and has 16 levels through ASK processing of 4-bit information. The modulated wave signal is a double sideband signal.

Amplitude phase keying is a way of transmitting information on both the carrier and the amplitude of the carrier. Quadrature amplitude modulation changes the quadrature relationship of the carriers, combines the carriers, and transmits the carriers. For example, the 16-QAM may transmit BPSK 4 times information over the same bandwidth. However, since the codes are at narrow intervals, high power is required to maintain the same transmission error rate.

The spectrum of the ASK signal is a double sideband signal, and therefore, it cannot be said that the channel is satisfactorily utilized. Band limiting these signals to vestigial sidebands will produce VSB signals. For example, 3 bits of digital information are represented by 8 levels. The 8-VSB signal is then generated by the band limiting operation of ASK processing and VSB filtering. The conclusion is that: the 8-VSB signal is very similar to the analog VSB except that it may have 8 signals.

The rf converter 180 performs rf conversion on the modulated signals and transmits the modulated signals through an antenna.

Fig. 5 is a flowchart illustrating a digital broadcast transmission method of the system in fig. 4.

Referring to fig. 5, the scrambling unit 100 scrambles a TS (transport stream) to be transmitted at step S510.

In step S520, the FEC unit 110 performs forward error correction on the scrambled TS from the scrambling unit 100 to form an encoded TS.

Meanwhile, the PN sequence generating unit 120 generates a PN sequence at step S530, and the Walsh code generating unit 130 generates a Walsh code corresponding to the identification information at step S540.

Subsequently, at step S550, the logic coupling unit 140 logically couples the PN sequence generated by the PN sequence generating unit 120 and the Walsh code generated by the Walsh code generating unit 130. When the logic coupling unit 140 employs an exclusive or gate circuit, an exclusive or coupling operation is performed on the Walsh code and the PN sequence.

The Multiplexer (MUX)150 performs multiplexing by inserting the signal coupled by the logical coupling unit and the segment sync signal in the encoded TS at step S560.

Subsequently, in step S570, the pilot insertion unit inserts one pilot in the multiplexed TS output from the MUX 150.

Subsequently, the modulation unit 170 receives and modulates the pilot-inserted TS at step S580, and the rf converter 180 converts the modulated TS from the modulation unit 170 and transmits them through the antenna at step S590.

Fig. 6 is a view illustrating a transmission signal segment according to the present invention when a VSB/OQAM modulation mode is used, and fig. 7 is a view illustrating a frame structure of the digital broadcasting transmission signal illustrated in fig. 5. Referring to fig. 6 and 7, a transmission signal segment includes a segment sync signal of 8 symbols, two PN sequences (511 symbols and 253 symbols, respectively) and a system information signal of 32 symbols. Further, the field of the present invention is composed of 13-symbol or 26-symbol or 52-symbol sequential data segments. The field becomes a field data field.

As shown, the segment, field and frame structures according to the present invention are not much different from those of the ATSC standard. Further, the present invention is very useful because the inventive field sync signal does not pass through the FEC unit.

As described above, the synchronization signal does not need to pass through the FEC unit, and can be inserted into the signal according to the additional information using the Walsh code. As a result, the reliability of the transmission signal is enhanced.

Although the preferred embodiments of the present invention have been described, it will be understood by those skilled in the art that the present invention is not limited to the preferred embodiments but various changes and modifications may be made within the spirit and scope of the present invention as defined in the appended claims.

Claims (12)

1. A receiving system, comprising:

an A/D converter converting a received analog signal having system information into a digital signal;

a demodulator for demodulating the digital signal;

a demultiplexer which decomposes the demodulated signal into coded data, a logically coupled PN sequence, and a Walsh code including system information;

an FEC unit performing error correction on the encoded data by using the system information; and

a descrambling unit that descrambles the error-corrected data output from the FEC unit to obtain a transport stream,

wherein the system information includes at least one of a mapping method, a code rate, frame structure information on transmitted data, and data dispersion information.

2. The receiving system of claim 1, wherein the segment of the received signal includes a segment synchronization signal of 8 symbols, two PN sequences of 511 symbols and 253 symbols, respectively, and a system information signal of 32 symbols, and the field is composed of sequential data segments of 13 symbols or 26 symbols or 52 symbols.

3. A receiving method comprising the steps of:

receiving a modulated signal having system information;

converting the received signal into a digital signal;

demodulating the digital signal;

decomposing the demodulated signal into coded data, logically coupled PN sequences, and Walsh codes that include system information;

performing error correction on the encoded data by using the system information; and

descrambling the error corrected data to obtain a transport stream,

wherein the system information includes at least one of a mapping method, a code rate, frame structure information on transmitted data, and data dispersion information.

4. The receiving method as claimed in claim 3, wherein the segment of the received signal includes a segment sync signal of 8 symbols, two PN sequences of 511 symbols and 253 symbols, respectively, and a system information signal of 32 symbols, and the field is composed of sequential data segments of 13 symbols or 26 symbols or 52 symbols.

5. A receiving system, comprising:

a demodulator demodulating the received signal;

an FEC unit performing error correction on the demodulated data by using the system information; and

a descrambling unit for descrambling the error-corrected data,

wherein the receiving system receives a signal having a logically coupled PN sequence and a Walsh code, the Walsh code including system information,

wherein the system information includes at least one of a mapping method, a code rate, frame structure information on transmitted data, and data dispersion information.

6. The receiving system of claim 5, wherein the segment of the received signal includes a segment synchronization signal of 8 symbols, two PN sequences of 511 symbols and 253 symbols, respectively, and a system information signal of 32 symbols, and the field is composed of sequential data segments of 13 symbols or 26 symbols or 52 symbols.

7. A receiving method, comprising:

demodulating the received signal;

performing error correction on the demodulated data; and

descrambling the error corrected data to obtain a transport stream,

wherein the received signal has a logically coupled PN sequence and Walsh code signal, the Walsh code including system information,

wherein the system information includes at least one of a mapping method, a code rate, frame structure information on transmitted data, and data dispersion information.

8. The receiving method as claimed in claim 7, wherein the segment of the received signal includes a segment sync signal of 8 symbols, two PN sequences of 511 symbols and 253 symbols, respectively, and a system information signal of 32 symbols, and the field is composed of sequential data segments of 13 symbols or 26 symbols or 52 symbols.

9. A receiving system that receives a signal including system information, comprising:

a demodulator demodulating the received signal;

an FEC unit performing error correction on the demodulated data; and

a descrambling unit for descrambling the error-corrected data,

wherein the receiving system receives a signal having a logically coupled PN sequence and a Walsh code, the Walsh code including system information,

wherein the FEC unit corrects the demodulated data with errors using the system information,

wherein the system information includes at least one of a mapping method, a code rate, frame structure information on transmitted data, and data dispersion information.

10. The receiving system of claim 9, wherein the segment of the received signal includes a segment synchronization signal of 8 symbols, two PN sequences of 511 symbols and 253 symbols, respectively, and a system information signal of 32 symbols, and the field is composed of sequential data segments of 13 symbols or 26 symbols or 52 symbols.

11. A receiving method of processing a signal including system information, comprising:

demodulating the received signal;

performing error correction on the demodulated data; and

descrambling the error corrected data to obtain a transport stream,

wherein the received signal has a logically coupled PN sequence and Walsh code signal, the Walsh code including system information,

wherein the error correcting step corrects the demodulated data with errors using the system information,

wherein the system information includes at least one of a mapping method, a code rate, frame structure information on transmitted data, and data dispersion information.

12. The receiving method as claimed in claim 11, wherein the segment of the received signal includes a segment sync signal of 8 symbols, two PN sequences of 511 symbols and 253 symbols, respectively, and a system information signal of 32 symbols, and the field is composed of sequential data segments of 13 symbols or 26 symbols or 52 symbols.