HK1118993A - Efficient frame structure for digital satellite communication - Google Patents
Efficient frame structure for digital satellite communication Download PDFInfo
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- HK1118993A HK1118993A HK08110750.1A HK08110750A HK1118993A HK 1118993 A HK1118993 A HK 1118993A HK 08110750 A HK08110750 A HK 08110750A HK 1118993 A HK1118993 A HK 1118993A
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Description
RELATED APPLICATIONS
The present application is related to the application with serial number # entitled "efficient frame structure for VCM/ACM support in digital satellite Transmission System".
Technical Field
The present invention relates to digital satellite communications, and more particularly, to frame structure design of transmitted signals to increase transmission efficiency and FEC performance and simplify implementation of satellite receivers such as synchronization control and FEC encoding.
Background
In modern digital communication systems, such as digital satellite systems, one goal is to be predefinedMaximum transmission bit error rate or Bit Error Rate (BER) is the transmission of digitized data bits representing user information such as video, audio, and other data types from a source (or transmitter) to a destination (or receiver or even multiple receivers). To control transmission errors, a typical transmitter typically adds redundant bits to the original data bit stream for transmission. The process of adding redundant bits is known as Forward Error Control (FEC) coding. In an encoded bit stream, i.e., where the transmitted bits are corrupted by extraneous signals (e.g., noise and/or interference) and distorted by undesirable channel characteristics, the receiver is also able to recover the original information by running an FEC decoding algorithm with an error rate less than a defined threshold. For some applications, e.g. voice communication, a maximum of 10 -2 The BER of (a) is acceptable. While for other applications, such as file transfer and most internet traffic, a zero BER is required. When a zero BER is required, the data is often retransmitted if the receiver detects any uncorrectable errors. For applications such as video conferencing and broadcasting, it is desirable to be able to operate at less than 10 -9 To provide smooth display of video signals on a video monitor. Such a BER is often referred to as a Quasi-Error-Free (QEF) condition.
Even if the QEF is achieved with LDPC codewords, this encoded signal format is still unacceptable for transmission because the receiver cannot decode the received signal without knowing where each encoded portion (e.g., LDPC codeword) started or terminated. A time reference (or marker) is necessary throughout the transmission to help identify the location of such codewords. Similarly, a typical communication system requires that the time and frequency of the receiver be locked to the reference of the transmitter, which is referred to as synchronization.
Also, specific overhead information is typically transmitted periodically to enable the receiver to correctly demodulate the transmitted signal, decode the signal, and extract user information. For at least these reasons, a typical transmitter periodically inserts a synchronization pattern (pattern) and a header into the encoded message, a process known as frame formatting. Typically, the receiver first attempts to lock onto the synchronization pattern and then decodes the preamble and message signal. Frame formatting design is critical to overall system performance and can directly impact the cost of establishing and operating a communication system. Frame formatting design often depends on many factors such as channel characteristics, modulation type, and FEC scheme. A well-designed frame format may result in a high performance receiver that can achieve fast frame capture, reliable tracking (time and frequency lock), and improved FEC decoding performance (e.g., meet required BER) at low cost and minimal overhead.
Disclosure of Invention
According to various embodiments of the present invention, a unique method of framing a satellite transmission message is presented that enables excellent communication performance with a simple receiver implementation. In satellite communications, messages, typically represented in bits after encoding, are grouped into a plurality of successive signal blocks called frames. Typically, each frame includes a frame header and a synchronization waveform to enable the receiver to synchronize the received signal frame, process the header, and decode the message according to the header information indication. In existing systems, such as DVB-S and DVB-S2, a frame typically carries a fixed number of information bits, which are in turn encoded into a codeword. This is acceptable if the system only employs modulation with a fixed dimension, such as 2-dimensional QPSK where one modulation symbol conveys 2 bits and pi/4 QPSK. However, for modern digital satellite applications, it is possible to employ modulations of different dimensions in a single system to take advantage of the powerful error correction capabilities of LDPC codes and other advanced FEC techniques, and to dynamically adjust the modulation and FEC of the system to accommodate time-varying channels. In these cases, even if the number of bits in a frame is fixed, when the frame length is characterized in terms of the number of symbols, its frame length will be different for different modulation dimensions. This difference in symbol length creates difficulties in tracking synchronization waveforms that do not occur at regular time intervals (longer intervals for smaller modulation dimensions) in terms of implementation. In terms of performance, the synchronization performance is not consistent for all modulation dimensions and degrades more for smaller dimensions.
Thus, various embodiments of the present invention eliminate the above-described problems by ensuring that the number of symbols in a frame remains constant. According to various embodiments of the present invention, the frame format is designed to allow multiple LDPC (or other FEC) codewords to be included in a frame for efficient transmission purposes. In these embodiments, each codeword may have a different modulation dimension and/or coding efficiency. According to various embodiments of the invention, a synchronization waveform called a Unique Word (UW) is followed by an Auxiliary Control Code (ACC) and a frame header. The UW, ACC and frame header are appended to the beginning of each frame. According to these embodiments of the invention, the receiver knows where to find the UW, ACC and header, making synchronization control extremely simple.
According to various embodiments of the present invention, the uniformly distributed UWs also guarantee synchronization performance at the same time. The UW is judiciously designed to exhibit adequate synchronization performance under the worst satellite channel conditions, such as transponder distortion, low quality receiver LNA (low noise amplifier), large frequency and/or time offsets. According to various embodiments of the present invention, the ACC may employ a simple orthogonal tone code (orthogonal tone code) to carry information about modulation and/or coding efficiency. The frame header may be designed to carry sufficient information needed to decode multiple codewords while maintaining a minimum overhead.
According to various embodiments of the present invention, the pilot waveform is inserted uniformly during a frame to further enhance synchronization performance. Moreover, the size of each pilot segment can be adjusted based on channel conditions, thereby reducing overhead when conditions such as channel conditions and modulation and coding efficiency allow the use of fewer or zero pilot segments. To avoid uneven spectral distribution, the frame may be scrambled by a random sequence, which may be a member of a Gold sequence set.
According to various embodiments of the invention, a frame format for digital satellite transmission may have: a plurality of frames, each frame having a fixed number of modulated symbols regardless of a modulation type of a system, and each frame starting with a unique word; wherein the spacing in number of symbols between any two consecutive unique words is the same regardless of the modulation type of the system.
According to various embodiments of the present invention, a digital satellite transmission system transmits a periodic unique word, comprising: a transmitter for transmitting a periodic unique word comprising a 64-symbol QPSK modulated waveform having baseband I and Q bits defined as follows:
UW I ＝0x40F0B6EC088E3A21，
UW Q ＝0xEB498CA3B538F49D.
according to various embodiments of the present invention, a digital storage medium may store a unique word, including: a memory for storing a unique word, the unique word comprising baseband I and Q bits defined as:
UW I ＝0x40F0B6EC088E3A21，
UW Q ＝0xEB498CA3B538F49D.
according to various embodiments of the invention, a plurality of evenly distributed pilot segments are inserted into each frame, which pilot segments are identical for all frames with respect to position and waveform, regardless of the type of modulation employed.
According to various embodiments of the invention, the length of the pilot segment is adjustable.
According to various embodiments of the present invention, the number of symbols in each frame, in addition to the unique word, secondary control code and pilot band, may just accommodate a different number of codewords for each different modulation.
According to various embodiments of the present invention, a plurality of codewords in each frame share a frame header.
According to various embodiments of the present invention, network operation information and/or other private information may be sent over multiple network bytes in the header of each frame.
According to various embodiments of the invention, a digital satellite receiver system may process a received signal, comprising: a receiver that receives the signal; and a processor for processing the signal; wherein the signal comprises a frame format containing a fixed number of modulation symbols per frame and a unique word starting at each frame.
According to various embodiments of the present invention, a digital satellite receiver system may include: a receiver for receiving a signal, wherein the receiver achieves synchronization of the signal based on a QPSK modulated unique word having I and Q defined as follows:
UW I ＝0x40F0B6EC088E3A21，
UW Q ＝0xEB498CA3B538F49D.
according to various embodiments of the invention, the receiver is capable of handling an inserted pilot segment of a given length if in a pilot mode of operation.
According to various embodiments of the present invention, the receiver is able to decode multiple FEC codewords in a single frame, independent of the modulation employed.
According to various embodiments of the present invention, the receiver is able to decode all codewords in a frame based only on the header embedded in the first codeword of the frame, regardless of the number of codewords in the frame.
According to various embodiments of the present invention, the receiver is able to decode the network operation information and/or other specific information located immediately after the header field in each frame for any modulation.
According to various embodiments of the present invention, a digital communication system may have: a transmitter for transmitting a digital signal; and a receiver for receiving the digital signal; wherein the digital signal comprises a plurality of frames, each frame comprising at least one codeword, wherein said system supports at least two different modulations, and wherein each of the plurality of frames has the same number of symbols.
According to various embodiments of the invention, the plurality of frames have the same fixed physical time for a given transmission rate or symbol rate.
According to various embodiments of the present invention, codewords in the same frame may have different modulations for Adaptive Code Modulation (ACM) modes.
According to various embodiments of the invention, each of the plurality of frames further comprises a unique word at a predetermined location.
According to various embodiments of the invention, the predetermined location is at the beginning of a frame.
According to various embodiments of the present invention, the first codeword of each frame includes a header that includes a number of network bytes to send network operator (operator) information and other private information.
According to various embodiments of the invention, the header further comprises a PSTART indicator to identify where the payload data begins.
According to various embodiments of the invention, the header further comprises an LBYTE portion to indicate the frame length.
According to various embodiments of the invention, the header further includes a PBYTE portion to indicate the amount of padding added to the first codeword.
According to various embodiments of the invention, the header further includes a PBYTE portion to indicate the amount of padding added to the frame.
According to various embodiments of the present invention, the number of codewords in a frame is determined by the modulation of the frame.
According to various embodiments of the present invention, a method of transmitting a digital signal may include: transmitting the digital signal; and receiving the digital signal; wherein the digital signal comprises a plurality of frames, each frame comprising at least one codeword, wherein the system supports at least two different modulations, and wherein each of the plurality of frames has the same number of symbols.
According to various embodiments of the invention, the unique word is received at a fixed rate.
According to various embodiments of the invention, the fixed rate is a predetermined rate.
According to various embodiments of the present invention, a digital communication system may have: a receiver for receiving the digital signal; wherein the digital signal comprises a plurality of frames, each frame comprising at least one codeword, wherein said system supports at least two different modulations, and wherein each of the plurality of frames is transmitted in the same amount of time.
According to various embodiments of the present invention, a digital communication system may have: a transmitter for transmitting the digital signal; wherein the digital signal comprises a plurality of frames, each frame comprising at least one codeword, wherein said system supports at least two different modulations, and wherein each of the plurality of frames is transmitted in the same amount of time.
Drawings
FIG. 1 is an exemplary block diagram illustrating a satellite transmitter including a framing process to convert raw user data into modulated frames, in accordance with embodiments of the present invention;
FIG. 2 illustrates an exemplary formed frame structure according to an embodiment of the present invention;
FIG. 3 illustrates an exemplary encoded data block including a plurality of codewords to be formatted into the structure of FIG. 2, according to an embodiment of the present invention;
FIG. 4 illustrates an exemplary scrambling code sequence generator according to an embodiment of the present invention;
FIG. 5 illustrates an exemplary format of a first codeword in a frame according to an embodiment of the invention;
FIG. 6 illustrates a second exemplary format of a first codeword in a frame according to an embodiment of the invention;
FIG. 7 illustrates a third exemplary format of a first codeword in a frame according to an embodiment of the invention;
FIG. 8 illustrates an exemplary diagram of a Next Frame Composition Table (NFCT) applied in a first codeword design for an ACM according to an embodiment of the present invention; and
fig. 9 illustrates an exemplary format of all codewords except a first codeword in an exemplary frame according to an embodiment of the present invention.
Detailed Description
According to various embodiments of the present invention, a method of formatting a satellite transmission signal provides an efficient signaling structure for a satellite receiver to achieve fast acquisition, reliable signal tracking, and message decoding with minimal transmission overhead.
It should be appreciated that various communication systems requiring frame formatting may choose to employ the techniques described herein. For example, a terrestrial digital broadcasting system may employ the present invention.
According to various embodiments of the present invention, the frame structure is used for a variety of purposes, such as providing a frame time stamp for a receiver to decode a message, providing a specific signal that allows the receiver to acquire the signal when accessing the network and reduces time and/or frequency errors to be able to reliably demodulate and decode, and providing header information for demodulation and decoding control and user packet stripping. In some cases, the particular signal may also be used for channel estimation and/or other Digital Signal Processing (DSP) purposes.
Shown in fig. 1 is a block diagram of a satellite transmitter that includes a framing process to convert raw user data into modulated frames in accordance with an embodiment of the present invention. The input data bits to be transmitted are first divided into successive groups, shown as group n and group n +1. Each group contains a number of information bits required for a corresponding frame. The header is then prepended to each information group by a header (H) insertion module. The header is further divided by a codeword grouping module into j (integer) subgroups (sg) along with each group, each subgroup carrying an equal number of bits. For purposes of illustration, j represents the number of subgroups in each group. For each sub-group, the FEC encoder calculates fixed length error checking and error correction parity bits (P) based on the data pattern of the sub-group and appends these parity bits to the end of the associated sub-group to form a codeword.
According to various embodiments of the present invention, the symbol mapping module maps the bit stream for each codeword into a modulation symbol according to the corresponding modulation type in the codeword. After symbol mapping, all frames are of equal length, regardless of the modulation used.
According to various embodiments of the present invention, the pilot insertion module may uniformly insert a plurality of pilot waves (p) into the encoded frame as shown in fig. 1. In addition, the UW and ACC insertion modules will add UW and ACC sequentially to the beginning of each frame. The symbol scrambler scrambles the symbols of each frame except UW using a fixed scrambling pattern. Eventually, all symbols may be modulated to a radio frequency for transmission over an antenna.
Different satellite transponders may use different modulations and different FEC codes using a broadcast mode, according to various embodiments of the present invention. However, for each transponder with a specified modulation and FEC, the number of information bits (e.g., in group n and group n + 1) is the same for all frames. According to various embodiments of the present invention, the receiver is designed to be able to handle signals with different modulations and FEC in situations where it is required that the receiver be tuned to different satellite transponders. Variations in signal modulation in such systems cause difficulties in physical layer implementation if the frame format is not properly designed.
Maintaining the same number of symbols in each frame for different modulations brings multiple benefits. Although the use of UW for synchronization is a common approach for many digital communication systems, UW utilizing this particular frame structure will occur at a constant rate, independent of the modulation used, according to various embodiments of the present invention. Therefore, it is very easy for the receiver to acquire and lock the UW waveform, thereby greatly simplifying the implementation of the receiver. Furthermore, also due to the uniformly distributed UW waveform, synchronization performance can be easily achieved and maintained independent of modulation. Furthermore, according to various embodiments of the present invention, this design enables multiple codewords to occur in each frame, thus providing higher transmission efficiency for relatively short but powerful FEC codewords due to less overhead, especially for higher dimension modulation accommodating more codewords in a frame.
Fig. 2 illustrates an exemplary frame structure of a transmission frame according to an embodiment of the present invention. The frame starts with a UW of 64 symbols, followed by 64 symbols ACC, and m +1 segments of encoded data (or payload data) separated by m evenly distributed pilots. UW is designed to produce good detection characteristics to provide fast capture. According to various embodiments of the invention, UW is a 64 symbol QPSK modulated waveform with I and Q defined as follows:
UW I ＝0x40F0B6EC088E3A21，
UW Q ＝0xEB498CA3B538F49D.
according to various embodiments of the present invention, the ACC may employ multi-tone (multi-tone) modulation to transmit a plurality of information bits containing information about the modulation type and FEC coding efficiency for proper demodulation and decoding. An exemplary ACC carrying 8 bits of information is generated by an 8 tone (8-tone) generator matrix defined as follows.
Wherein
Obviously, each row (G) of the matrix G 0 To g 7 ) Are tones orthogonal to the other rows. B for content 0 b 1 b 2 b 3 b 4 b 5 b 6 b 7 The multi-tone modulation results in:
B＝b 0 g 0 +b 1 g 1 +…+b 7 g 7
where the sum (sum) represents an exclusive or (xor) operation. The 128-bit vector B can be alternately distributed to I and Q of the QPSK modulator to produce the final 64-symbol ACC waveform.
According to various embodiments of the invention, the number of payload segments (m + 1) between two consecutive pilot segments in each frame is determined by the frame length in symbols and the distance between the two pilot segments, which is designed to provide reliable synchronization with minimum overhead. According to various embodiments of the present invention, it is highly desirable to keep the pilot pattern and position constant for different modulations and FEC decoding. According to various embodiments of the present invention, the desired information length between two consecutive pilots is 1280 symbols, regardless of the modulation used. The size of each pilot wave may also be adjustable. The frame of the extreme case may contain no pilots in order to achieve a minimum overhead. In this case, the modulation dimension is typically low and the channel is typically good (fair).
As shown in fig. 3, according to an embodiment of the present invention, the number of LDPC codewords in each frame as payload data is set to an integer. This has the advantage that a simple decoder control logic is obtained, wherein the decoder does not need to decode the payload across frame boundaries.
Furthermore, according to the exemplary embodiment of fig. 3, the codeword itself is designed to have a constant bit length to simplify the decoding implementation. The number of codewords in a frame thus depends on the modulation dimension. Higher modulation dimensions result in more codewords in a frame. The following description demonstrates the relationship of the modulation dimension to the number of codewords. If N is the number of bits per codeword (constant for all codewords) and D is the modulation dimension per codeword, the number of symbols M in each codeword is:
M＝N/D.
thus, as shown in this example, to ensure that each codeword has an integer number of symbols, N must be divisible by all possible modulation dimensions D. In particular, in the embodiment of the invention shown in fig. 3, the design is N =15360. The number of symbols in the codewords corresponding to modulation dimensions 2,3, 4 and 5 are 7680, 5120, 3840 and 3072, respectively. The number of payload symbols per frame is designated 30720 according to various embodiments of the present invention. Thus, each frame carries 4, 6, 8 and 10 codewords corresponding to modulation dimensions 2,3, 4 and 5. Even for non-constant modulation (e.g., ACM mode), other combinations of 10 codeword modulations can be provided, which is sufficient for ACM applications. Table 1 lists possible combinations of codeword modulations. There are 14 possible codeword assignments. For example, a combination of 5 indicates that a frame may employ 3 codewords of modulation dimension 2 and 2 codewords of dimension 4. The order in which these codewords are arranged is arbitrary and flexible enough for the network operator.
In addition, table 1 provides a very efficient method of utilizing frame resources. In examples where the user data may not be contiguous, it may not be necessary to follow the format defined in the table. For this reason, there may be some unused symbols near the end of the frame. These symbols may be defined as dummy symbols (dummy symbols) and may be modulated by a bit pattern of all 0 s (zeros). Continuing with the example above, the number of dummy symbols is given by
N dummy ＝30720-7680N 1 -5120N 2 -5120N 3 -3840N 3 -3072N 4
Wherein, N 1 ，N 2 ，N 3 And N 4 Respectively the number of codewords of modulation dimensions 2,3, 4 and 5 in the frame. Please note that if N is 1 ，N 2 ，N 3 And N 4 Is one of the modes listed in Table 1, then N dummy =0 (to 100% efficiency).
TABLE 1 codeword assignment for various modulation dimensions
| Combined index | |||||||||||||||
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | ||
| Regulating device System for making Vitamin C Number of | 2 | 4 | 6 | 8 | 10 | 3 | 2 | 2 | 2 | 1 | 1 | 1 | |||
| 3 | 3 | 3 | 3 | 3 | |||||||||||
| 4 | 2 | 4 | 6 | 2 | 2 | 4 | 4 | ||||||||
| 5 | 5 | 5 | 5 | 5 | |||||||||||
Fig. 4 is an example of a frame scrambler capable of supporting frame lengths of up to 30,000 symbols, in accordance with various embodiments of the present invention. In this example, two 15-bit shift registers are used to generate two maximal length pseudorandom sequences, which are the preferred pair of Gold sequence sets. One Gold sequence is the sum of two m-sequences. If the Gold sequence is combined with the upper sequence, the final scrambling sequence with the value of {0,1,2,3} element can be obtained. This sequence is then used to rotate the input (I, Q) symbols according to the table 2 definitions. The same scrambling pattern may be used for each new frame.
TABLE 2 code element scrambling logic
| S(k) | I scrambled (k) | Q scrambled (k) |
| 0 | I(k) | Q(k) |
| 1 | -Q(k) | I(k) |
| 2 | -I(k) | -Q(k) |
| 3 | Q(k) | -I(k) |
According to various embodiments of the present invention, the header is embedded only in the first codeword of each frame as shown in fig. 1. The codeword length is usually much larger than the header. According to various embodiments of the present invention, sharing the header embedded in the first codeword by all codewords in a frame allows for a more efficient and simplified decoder implementation. Fig. 5-7 show three exemplary formats of the first codeword, where the use of each format is application dependent. For example, the format in fig. 7 is used in ACM applications. In these figures, the length of each functional field in the code word is expressed using bytes (= 8 bits) for convenience.
All three exemplary formats share the following common fields:
NBYTES: these multiple 16 bytes can be used to convey important information of the network operator and other proprietary information. One benefit of transmitting the dedicated information in the physical layer is that the user can decode the information quickly without waiting for the higher layer message to be decoded. Another advantage is that the dedicated data information does not need to interrupt a continuous data stream, such as a transport stream, at a higher layer. The receiver on the physical layer can directly output the data stream to the higher layer. Therefore, the total transmission and reception of both the dedicated data and the continuous data is very simple.
FBYTES: these 8 bits of FBYTE can be used to carry information such as the mode of operation, stream type, user ID, etc.
PSTART: this byte may define the starting position of the first complete user packet in the first codeword with respect to the beginning of the user data. PSTART is used because the codeword and user packet are generally not aligned.
In addition to the common fields described above, LBYTE can be used to define the user packet length as shown in fig. 6 and 7. This format may be used in applications where the receiver does not know the user packet length in advance. If the user data does not completely fill the frame, the number of bytes filled with zero may be defined using the stuff bytes (PBYTES) in FIG. 6 and FIG. 7. An exemplary exception to PBYTES may be when used in ACM mode, where PBYTES may only represent the number of zeros padded into the first codeword.
In ACM applications where each codeword in a frame may be independent of each other in terms of modulation type and/or FEC coding efficiency, the Next Frame Construction Table (NFCT) may be designed for use, in accordance with various embodiments of the present invention. The NFCT may be used to define the composition of the next frame of the current frame. NFCT after PBYTES takes the syntax shown in table 3. The corresponding bit and byte positions are shown in fig. 7.
TABLE 3NFCT definitions
| Syntax of a sentence | Number of bits | |
| Retention | Information | |
| Next_Frame_Composition_Table(){ | ||
| Codeword_count_in_next_frame | 4 | |
| 4 | ||
| For(i＝0；i＜＝codeword_count_in_next_frame；i++){ | ||
| Status | 1 | |
| Modulation | 2 | |
| Code_rate | 4 | |
| Padding_in_bytes | 16 | |
| 1 | ||
| } | ||
| } | ||
The terms in fig. 8 may be defined as follows in various exemplary embodiments of the present invention:
code _ count _ in _ next _ frame: this may be a 4-bit field indicating the number of LDPC codewords in the next frame minus one. The Codeword index i may start from 0 to end with code _ count _ in _ next _ frame ≧ 0. Thus, in the exemplary embodiment, at least one codeword is always transmitted in a frame, i.e., the first codeword of each frame is guaranteed to be transmitted.
Status:1 bit, indicating the codeword state. 1= payload, 0= no payload data or null codeword (zero padding). When the status bit is 0, there may be no need to demodulate and/or decode the codeword.
Modulation:2 bits, representing the modulation scheme.
Code _ rate:4 bits, representing the coding efficiency.
Padding _ in _ bytes: zero padded in a particular codeword, expressed in number of bytes, where the number of bytes to be padded with zeros is given by:
wherein b is 15 To b 11 Is reserved, and b 0 Representing the LSB of the 16 bits.
It should be understood that some fields may have different bit widths in different applications.
Fig. 9 shows an exemplary codeword format for codewords other than the first one.
According to various embodiments of the present invention, the codeword may be completed by appending FEC check bytes including a CRC error check field and an LDPC error correction field.
The foregoing descriptions of various embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. Accordingly, the scope of the invention is not to be limited by this detailed description, but rather by the claims appended hereto.
Claims (23)
1. A frame format for digital satellite transmission, comprising:
a plurality of frames, independent of the modulation type of the system, each frame having a fixed number of modulated symbols and each frame starting with a unique word;
the spacing in number of symbols between any two consecutive unique words is the same regardless of the modulation type of the system.
2. A digital satellite transmission system for transmitting a periodic unique word, comprising:
a transmitter for transmitting a periodic unique word comprising a 64-symbol QPSK modulated waveform having baseband I and Q bits as defined below:
UW I ＝0x40F0B6EC088E3A21，
UW Q ＝0xEB498CA3B538F49D。
3. a digital storage medium storing a unique word, comprising:
a memory for storing a unique word comprising baseband I and Q bits defined as:
UW I ＝0x40F0B6EC088E3A21，
UW Q ＝0xEB498CA3B538F49D。
4. a digital satellite transmission system according to claim 1, wherein a plurality of evenly distributed pilot segments are inserted into each frame, which pilot segments are identical for all frames with respect to position and waveform, irrespective of the type of modulation employed.
5. A digital satellite transmission system as claimed in claim 4, wherein the length of the pilot band is adjustable.
6. The digital satellite transmission system according to claim 1, wherein the number of symbols per frame, with the exception of the unique word, secondary control code and pilot band, can accommodate exactly the next different number of codewords for each different modulation.
7. The digital satellite transmission system of claim 1, wherein the plurality of codewords in each frame share a frame header.
8. A digital satellite transmission system as claimed in claim 1, wherein network operation information and/or other specific information may be transmitted over a plurality of network bytes in the header of each frame.
9. A digital satellite receiver system for processing a received signal, comprising:
a receiver for receiving a signal; and
a processor for processing the signal; wherein
The signal comprises a frame format containing a fixed number of modulation symbols per frame and a unique word at the beginning of each frame.
10. A digital satellite receiver system, comprising:
a receiver for receiving a signal, wherein the receiver achieves synchronization of the signal based on a QPSK modulated unique word having I and Q defined as follows:
UW I ＝0x40F0B6EC088E3A21，
UW Q ＝0xEB498CA3B538F49D。
11. the method of claim 9, wherein the receiver is capable of handling an inserted pilot segment of a given length if in a pilot mode of operation.
12. The method of claim 9, wherein the receiver is capable of decoding multiple FEC codewords in a single frame independent of the modulation employed.
13. The method of claim 9, wherein the receiver is able to decode all codewords in a frame based only on a header embedded in a first codeword of the frame, regardless of a number of codewords in the frame.
14. The method of claim 9, wherein the receiver is capable of decoding network operation information and/or other specific information located immediately after a header field in each frame for any modulation.
15. A digital communication system, comprising:
a transmitter which transmits a digital signal; and
wherein the digital signal comprises a plurality of frames, each frame comprising at least one codeword, wherein the system supports at least two different modulations, an
Wherein each frame of the plurality of frames has the same number of symbols.
16. The digital communication system of claim 15, wherein the plurality of frames have the same fixed physical time for a given transmission rate or symbol rate.
17. The digital communication system of claim 15, wherein each of the plurality of frames further comprises a unique word at a predetermined location.
18. The digital communication system of claim 17, wherein the predetermined location is at the beginning of a frame.
19. The digital communication system as claimed in claim 15, wherein the first codeword in each frame comprises a header comprising a plurality of network bytes to transmit network operator information.
20. A method of transmitting a digital signal, comprising:
transmitting the digital signal; and
receiving the digital signal;
wherein the digital signal comprises a plurality of frames, each frame comprising at least one codeword, wherein the transmitter and the receiver are capable of handling at least two different modulations, an
Wherein each of the plurality of frames has the same number of symbols.
21. The method of claim 20, wherein the plurality of frames have the same fixed physical time.
22. The method of claim 20, wherein each of the plurality of frames further comprises a unique word at a predetermined location.
23. The method of claim 20, wherein the predetermined location is at the beginning of a frame.
Publications (1)
| Publication Number | Publication Date |
|---|---|
| HK1118993A true HK1118993A (en) | 2009-02-20 |
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