Method for forming transmission frame for transmission

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates generally to communications, and more specifically to satellite broadcasting systems.

【0002】

[Conventional technology]

One system, proposed as the Satellite Digital Audio Radio System (SDARS), is a number of audio and data program channels for broadcasting music and talk shows such as CDs to mobile and fixed receivers (hereinafter briefly programmed). Channel) is supported. For example, this system provides transmission of 100 program channels.

【0003】

[Problems to be Solved by the Invention]

Therefore, there is a demand for a transmission frame structure for efficiently transporting these channels.

【0004】

[Means for solving problems]

As a solution, a transmission frame structure for a satellite digital audio radio system (SDARS) is provided. According to the present invention, the transmitter of the satellite digital audio radio system (hereinafter referred to as SDARS transmitter) divides N program channels into M clusters, each representing at least k program channels (M). > 1, k> 1, N> M, (k) (M) N).

【0005】

The SDARS transmitter further divides each cluster into at least J cluster segments (J> 1) and interleaves these at least J cluster segments from each cluster for transmission.

【0006】

In one embodiment of the invention, the SDARS transmitter produces broadcast transmission signals that include time division multiplexing (TDM) mode and encoded orthogonal frequency multiplexing (OFDM) mode transmission. The SDARS transmitter has four transport mechanisms or traffic channels: (1) "many audio and data program channels" (program channels), (2) cluster control information channels (CC), and (3) global (global). ) Generate transmission signals that support the control information channel (GC) and (4) cluster synchronization channel (CS).

【0007】

Specifically, the SDARS transmitter divides N = 100 program channels into M = 5 clusters. Each cluster consists of global control information, cluster synchronization information, and a program cluster containing k = 20 program channels and CC information.

【0008】

The SDARS transmitter further divides each cluster into J = 255 cluster segments and interleaves the cluster segments from each cluster for transmission.

【0009】

BEST MODE FOR CARRYING OUT THE INVENTION

The concept of the present invention will be described in the section [Satellite Digital Audio Radio System Transmission Format] below. Further explanation will be given in the [Cluster Frame Sync] section following this section.

【0010】

[Satellite Digital Audio Radio System Transmission Format] The "Satellite Digital Audio Radio System" (SDARS system) is a system for broadcasting music and talk shows such as CDs to mobile and fixed receivers. Figure 1 shows an example of a high-level block diagram of an SDARS system based on the principles of the present invention. The SDARS transmitter 10 receives a plurality of audio programs 9 (eg, music, talk show) and generates a broadcast transmission signal 11 including transmission in time division multiplexing (TDM) mode and coded orthogonal frequency multiplexing (OFDM) mode. (OFDM and TDM modulation are known in the art and are not described herein.

【0011】

The total available bandwidth of 12.5MHz is centered at 2362.25MHz (licensed S-band) and is divided into three subband channels. The two satellite channels use the two outer subbands, each occupying a bandwidth of approximately 4.167MHz. A single frequency network (SFN) ground gap filler, a device that fills the gap that occurs during satellite wave reception time, uses an intermediate subband with a bandwidth of approximately 4.167 MHz. By combining time division multiplexing mode and coded orthogonal frequency multiplexing mode, time, frequency, and spatial diversity can be obtained.

【0012】

The SDARS receiver 20 represents one of several receiving stations for restoring one or more audio programs 21 from a received signal for listening and enjoyment. (For those of interest, a further description of SDARS transmission using multiple modulation schemes is available in the US Patent Application of Zheng, Riazi, and Sayeed, entitled "Signal Combining Scheme For Wireless Transmission Systems Having Multiple Modulation." It is described in Schemes, "No. 09 / 428,732, filed on October 28, 1999).

【0013】

The SDARS system provides four transport mechanisms or traffic channels: (1) "many audio and data program channels" (program channels), (2) cluster control information channels (CC), and (3) global control information channels (3) Supports GC) and (4) Cluster Sync Channel (CS).

【0014】

As further described below, due to the nature of the data in different traffic channels, different levels of channel coding provide global control information channels, cluster control information channels, and program channels so that different levels of error correction can be obtained. Applies to.

【0015】

Before describing the actual transmission frame, note FIGS. 2 to 4 that exemplify the concept of the present invention. As shown in FIG. 2 and based on the present invention, an SDARS transmitter (as shown in FIG. 1) transmits an information frame. This information consists of cluster synchronization information, global control information, and a large number of clusters (eg, M clusters), each cluster consisting of k program channels. That is, this results in transmission of a total of N program channels (N = (k) (M)).

【0016】

(In this description, the concept of the present invention will be described as an example in which each cluster consists of k program channels, but the concept of the present invention is that each cluster consists of at least k program channels, that is, a cluster. Consists of more than k program channels, and is therefore equally applicable when (k) (M) N.

【0017】

Next, focusing on FIG. 3, in FIG. 3, the information frame previously shown in FIG. 2 is represented as five clusters (that is, M = 5), and the global control information and the cluster synchronization information are each. It is transmitted as part of the cluster. (Note that clusters are also referred to as cluster frames.) Each cluster consists of one of the above program channels.

【0018】

Specifically, each channel consists of 510,000 bits (bits are binary digits as is known in the art), with a cluster synchronization (CS) field with 255 bits and global control information with 3315 bits. Divided into (GC) fields and one program cluster with 506,430 bits. The cluster synchronization field is used for synchronization (described below) and the global control information field is used for global control information (described below).

【0019】

Speaking of program clusters, each program cluster is further divided into cluster control information (CC) (divided into cluster control 1 field and cluster control 2 field), convolutional coded audio, and zero padding fields. (All of these are described below). Convolutional coded audio represents 20 program channels (ie, k = 20). Therefore, 5 clusters (M = 5) represent 100 information program channels.

【0020】

The SDARS transmitters form clusters (each cluster consists of a program channel, a cluster control information channel, a global control information channel, and a cluster synchronization channel), but in terms of transmission, each cluster has an additional 255 cluster segments. Divided into (J = 255) (shown in Figure 3), each cluster segment has one bit from the cluster synchronization field, 13 bits from the global control information field, and a program cluster segment (each program cluster). 1986 bits from) and consists of.

【0021】

(In other words, the cluster synchronization field, the global control information field, and one program cluster are in the smaller 255 parts: the cluster synchronization segment, the global control information segment, and one program cluster segment. It is divided and each constitutes one cluster segment.

【0022】

To further illustrate this, the transmission of cluster segments is shown in FIG. As mentioned above, each cluster consists of 255 cluster segments. The SDARS transmitter interleaves a cluster segment from one cluster into a cluster segment from another cluster. For example, as shown in FIG. 4, the first segment from each cluster is transmitted, then the second segment from each cluster is transmitted, and so on.

【0023】

As a result, cluster segments from the same cluster are separated by at least 4 cluster segments (or M-1 cluster segments).

【0024】

Next, FIG. 5 shows a transmission frame 50 based on the principle of the present invention. As shown in FIG. 1 and described above, TDM is used for two sub-bands and OFDM is used for the remaining one sub-band for transmission. The transmission frame 50 is transmitted in parallel in each band. For the sake of explanation, FIG. 5 shows a transmission frame in the case of TDM. For OFDM, all you have to do is remove the equalizer training sequence (TS) field (described below).

【0025】

The transmission frame 50 is obtained by multiplexing a number of TDM frames shown as 60-1 to 60-n in FIG. In the example, n is equal to 1275. (Each TDM frame also corresponds to one OFDM symbol.) Each TDM frame is preceded by a 48-bit equalizer training sequence (TS). (Equalizer training sequences are known in this art and are not discussed here.

【0026】

Each TDM frame (eg, TDM frame 60-1) represents one cluster segment, as described above and shown in FIG. Each cluster segment is a cluster synchronization bit and a global control bit (encoded as described below) and a portion or segment of the program cluster (which bits are encoded, scrambled, and interleaved as described below). To be processed).

【0027】

(Note that there is no equalizer training sequence in the OFDM transmission frame. The OFDM transmission frame is an aggregate of OFDM symbols 1 to 1275 shown in FIG.

【0028】

In this way, the transmission frame 50 is obtained by multiplexing the cluster of program channels. The total number of bits transmitted in transmission frame 50 is 2,611,200 for TDM and 2,550,000 for OFDM (without TS bits).

【0029】

In Figure 5, a 48-bit training sequence field is inserted before each TDM frame. The 255 bits of the cluster synchronization field is the maximum length PN (pseudo-random number) sequence. (Generation of pseudo-random number sequences is known in this technical field.) Simulation determined that using the same PN sequence for all five clusters is superior in terms of operating performance and realization. Has been (not described here).

【0030】

A cluster sync bit for each cluster is inserted for every M TDMs. Where M is equal to the number of clusters. For example, in the case of M = 5 clusters, for cluster 1, the cluster synchronization bits are inserted over the entire transmission frame, that is, in TDM frames 1, 6, 11, and so on. For cluster 2, the cluster sync bit is inserted in TDM frames 2, 7, 12, etc.

【0031】

This single cluster sync bit for each cluster segment occurs shortly after the training sequence and is added after scrambling and interleaving. The cluster synchronization bits are made visible to the receiver (under the control of the receiver) for synchronization processing prior to descrambling and deinterleaving.

【0032】

The transmission frame format is shown in more detail in Figure 6 in relation to the program cluster. Concatenated coding is used for audio data. The audio data is RS-encoded with a Reed-Solomon (RS) (128,117,8) code. Explaining (128,117,8) means that the total number of symbols is 128, 117 of which carry information, and there are 8 bits for each symbol. (Note that the use of block coding (eg, RS coding), convolutional coding, and perceptual audio coding (PAC) is well known and will not be discussed herein.

【0033】

As a result, each RS word has (128) (8) = 1024 bits. (Note that the size of the RS code is one or a small number of perceptual audio to enable the concealment technique built into the perceptual audio code (not shown) to work in the event of an error. It should be selected to fit only encoded packets.

【0034】

The RS (128,117,8) code corrects 5 RS symbols or 40 bits. For each program channel in a program cluster, Li integers (1 i 20) of RS codewords are generated. These RS codewords are fed to a rate 2/3 punctured convolutional encoder. Since the PAC (Perceptual Audio Codec) codec outputs variable bit rates, the number of RS codewords Li per channel is a random variable. The average number of RS codewords is 16.3 per channel.

【0035】

A tail insertion (eg, zero insertion) is performed for each channel so that the encoders are flush, which causes the trellis (grid) to always start in the zero state for the next RS block group. .. 366-bit zero padding is required for each program channel to obtain integer OFDM symbols and TDM bursts per cluster. This integer must be equal to the number of cluster sync bits per cluster.

【0036】

(When the encryption process is used for the cluster, the zero padding bit may be replaced with the cluster synchronous encryption synchronous bit.

【0037】

As can be seen from FIGS. 3 and 6, the program cluster also consists of cluster control information fields, namely cluster control 1 and cluster control 2. Figure 7 shows the mapping of cluster control information. The cluster control information is used by the corresponding receiver to decode the program channel from the program cluster (eg, to inform the receiver that channel 1 consists of L1 = 15 RS blocks, etc.).

【0038】

As shown in Figure 7, for 20 channels per program cluster, there are 320 uncoded cluster control information bits (16 control bits for each channel). 230 unencoded cluster control information bits are encoded with RS (105,40,8) codes, resulting in 840 bits, to which the last 8 bits are added (eg, 8). Zero bit).

【0039】

The RS-coded bits and endings (which adds up to 848 bits) are further coded with a rate 1/3 convolutional code, which better protects this important information. The resulting 2544 encoded bits are fed into the cluster control 1 field and the cluster control 2 field of one program cluster. That is, each program cluster has the same header cluster control field and trailer cluster control field.

【0040】

As can be seen from FIG. 3, the global control information field carries global control information and consists of 3315 bits. Figure 8 shows the mapping of global control information. There are 40 (or 320 bits) uncoded global control symbols. Concatenated coding is used for global control data. These 40 unencoded symbols are coded with RS (58,40,8) code, resulting in 464 bits, with the last 4 bits added.

【0041】

The RS-coded bits, the end, and (which totals 468 bits) are further coded with a 1/7 rate convolutional code, resulting in 3276 bits. As mentioned above, the global control bits are 255 cluster segments in a cluster by transmitting 13 bits in each cluster segment immediately after each TDM frame or cluster synchronization bit in the OFDM symbol. Divided in between. As a result, 39 bits of zero padding must be added to 3276 bits (ie, the quotient of 3276 divided by 255 is not an integer).

【0042】

Next, FIG. 9 shows the SDARS transmitter 100. Other than the concept of the present invention, the elements shown in FIG. 9 are well known and will not be described in detail here. As mentioned above, the SDARS transmitter supports four transport mechanisms or traffic channels:

【0043】

That is, (1) "many, eg, N audio and data program channels" (program channels) (encoded by encoder 120 (representing N encoders)), (2) cluster control information channels ( CC) (encoded by CC encoder 130), (3) global control information channel (GC) (encoded by GC encoder 140), and (4) cluster synchronization channel (CS) (CS generation) The traffic channel (given by vessel 150).

【0044】

As already mentioned, due to the nature of the data in different traffic channels, different levels of channel coding are applied to the global control information channel, cluster control information channel, and program channel so that different levels of error correction can be obtained. Applies.

【0045】

Global control information (GC) is encoded by the GC encoder 140. Global control information is needed to interpret the configuration of the transmission frame. This global control information includes various information, and the various information is, for example, one or more of the following exemplary information, but is not limited thereto.

【0046】

These exemplary information include the cluster identifier (ID) for each program channel, the number of active program channels, the number of coded clusters, and the transmission parameters for each cluster (eg, UEP (unequal)). With error protection), cluster frame length), program type (audio or data), active transmission mode (multi-descriptive coding, CPPC (complementary pair puncture convolution) code, or other forms of code binding) and related parameters. is there. (Note that other types of information such as access control management information (not shown) may be included in the global control information.

【0047】

The bit rate of the global control information channel is much lower than that of the program channel, so it is coded with a stronger code. For example, the RS (58,40,8) code is used as the external code, and the convolutional code with a rate of 1/7 and a constraint length of 5 is used as the internal code. The output signal of the GC coder is supplied to the transmission frame assembler (assembler) (described below).

【0048】

The cluster control information (CC) is encoded by the CC encoder 130. As mentioned above, the cluster control information consists of the number of blocks of Reed-Solomon (RS) code length for each program channel and the control data for identifying and identifying the position of the program channel in the multiplexing frame. .. Each transmission frame is formed from a series of interleaved cluster segments (equally interleaved cluster frames).

【0049】

For each cluster, there is 320 bits of unencoded cluster control information (ie, 16 bits per channel). Since the cluster control information is extremely important for correctly decoding each program channel in the cluster, it has a stronger code than the code used for the program channel. Used. For example, the RS (105,40,8) code is used as the external code, and the convolutional code with a rate of 1/3 and a constraint length of 9 is used as the internal code.

【0050】

The cluster control information also controls the operation of the cluster frame multiplexer 110 to form each of the M clusters. Each cluster classifier is coded since the static control information, the output signal from the CC encoder 130 also supplied to the cluster frame multiplexer 110.

【0051】

N program channels are supplied to the encoder group 120 consisting of N encoders. The output signal from the encoder group 12 is supplied to the cluster frame multiplexer 110. For the sake of explanation, it is assumed that N = 100 and each program channel is an audio (music and / or audio) signal and / or a data signal.

【0052】

In addition, 50 of the program channels represent, for example, music, each of these program channels has an average transmission rate of 64 kbps, the remaining 50 program channels represent, for example, audio, and each of these program channels is average. Assume a transmission rate of 24 kbps.

【0053】

As shown in FIGS. 6 and 9, the size of the RS block for each encoder is 128 symbols (128 × 8 = 1024 bits). RS (128,117) Provides error correction capability with 5 symbols (40 bits). Convolutional coding is given by K = 9, rate 2/3 (obtained by puncturing the population rate (rate 1/2) with the puncture pattern 1011).

【0054】

Before continuing with the discussion in Figure 9, I would like to note the following: As shown in Figure 6, 20 program channels are assigned to each cluster. This is a fixed or constant capacity channel. Therefore, the same number of RS blocks are used to transmit each program channel in a cluster. (Here, as an example, there are 16.3 RS blocks per program channel.

【0055】

However, as mentioned above, the perceptual audio coding (PAC) scheme itself provides variable bit rate. In other words, for many program channels, the instantaneous bit request is significantly higher than the average bit rate for some short time. This leads to two concerns.

【0056】

One concern is the need to maintain a constant bit rate for the block of encoder 120. This can be solved by using appropriate buffering and rate control techniques (not shown) known in the art. The second concern is that some program channels momentarily require more bits to transmit than others.

【0057】

If a fixed number of RS blocks were used for each of the 20 program channels, then some program channels would be "underrun" (ie, need less than 16.3 RS blocks at a given time, and therefore only. On the other hand, other program channels will "overrun" (ie, require more than 16.3 RS blocks at a given moment), thus adding more. You will experience a condition that will require bandwidth).

【0058】

Although not required in the present invention (because the concept of the present invention deals with the formatting of transmitted signals), it is advantageous to use a noise distribution strategy to perform perceptual audio coding of the program channel. Yes, which calculates bit requirements for each program channel based on a perceptual model (not shown). This is known as "statistical joint bit allocation".

【0059】

In statistically congruent bit allocation, bits (ie, bandwidth) are allocated from a common bit pool to the program channel. Here, the common bit pool is a program cluster consisting of 326 RS blocks. As shown in Figure 6, the program channel consists of Li RS blocks, where Li is a random variable taken from a pool of 326 RS blocks. This allows bandwidth to be passed from less demanding program channels to more demanding program channels on an instantaneous basis.

【0060】

Therefore, according to the statistically congruent bit allocation, the degree of undercoding is reduced to a negligible level, and a constant bit rate is maintained. In statistical congruence bit allocation, the entire transmission frame of perceptual audio-encoded packets is buffered and stored (not shown) for each of the five clusters, along with cluster control information, prior to RS coding.

【0061】

(Conversely, as mentioned above, the same number of RS blocks can be used for each program channel, but this will probably lead to more "overruns" and "underruns".

【0062】

Returning to FIG. 9, 20 encoded program channels for each cluster are then multiplexed in the cluster frame multiplexer 110 with the same headers and trailer cluster control fields. The cluster frame multiplexer 110 is controlled by the cluster control information signal.

【0063】

The cluster frame multiplexer 110 supplies M clusters to the corresponding M scrambler / interleaver group 155. The scrambler / interleaver group scrambles and interleaves each cluster and supplies M scrambled and interleaved output signals to the transmission frame assembly 160.

【0064】

The CS generator 150 forms a cluster synchronization (CS) channel, which is used internally in the system for transmission frame and cluster synchronization, carrier synchronization, and channel state estimation. Other than cluster frame synchronization, synchronization methods and channel state estimation are well known and will not be described further here.

【0065】

US Patent Application of Zheng, Riazi, and Sayeed, entitled "A Cluster Frame Synchronization Scheme For A Satellite Digital Audio Radio System," No.09 / 464,831, filed on December 16 , 1999).

【0066】

To briefly touch on FIG. 10, the figure shows a CS generator 150 consisting of an 8-stage linear feedback shift register. The output signal from the CS generator 150 is supplied to the transmission frame assembly 160.

【0067】

Returning to FIG. 9, the transmission frame assembler 160 multiplexes the encoded global control bits from the GC encoder 140, the cluster synchronization bits from the CS generator 150, and the M clusters. Form a transmission frame as shown in Figure 5 (excluding the training sequence (TS) field). The transmission frame is modulated for transmission via the modulator 190. In this example, the modulator 190 is composed of three types of modulation functions (however, only one type is required for the present invention).

【0068】

Specifically, the output signal from the transmission frame assembly 160 is fed through the 4 second (sec) delay element 170 to the OFDM modulator of the modulator 190. (Note that the 4-second delay is merely an example. In fact, some implementation systems of the present invention do not require the delay itself.

【0069】

Similarly, the output signal from the transmission frame assembly 160 also passes through the training insertion element 165, where the training sequence field for the TDM signal is inserted (see Figure 5). The output signal from the training insertion element 165 is fed to the two TDM modulators of the modulator 190 (one of the output signals first passes through the 4-second delay element 175).

【0070】

In other words, the entire transmission frame is fed to the satellite 1 (not shown) TDM modulator, and the delayed transmission frame is relayed to the satellite 2 (not shown) TDM modulator and terrestrial relay within a single frequency network (SFN). It is sent to the OFDM modulator of the instrument (not shown) (gap filler). Depending on the delayed communication path (path), the signal blocking state may continue for up to several seconds when the mobile receiver (not shown) passes through the underpass. Even in such a case, this delayed communication path (path) causes the signal blocking state to continue for up to several seconds. Preventing interruption of broadcasting services is ensured.

【0071】

The TDM signal is QPSK modulated (4 phase shift keying). The OFDM signal is formed by IFFT (Inverse Fast Fourier Transform) processing of DQPSK (Difference 4-Phase Shift Keying) modulated data. A guard section is inserted into the signal, which prevents the Rayleigh channel's multipath effect on the OFDM symbol (ie, a training sequence (TS) bit that is not in the OFDM frame).

【0072】

The transmit link for the TDM signal consists of a satellite transponder and a Rician channel in an area away from the city, while the transmit link for an OFDM signal is a single frequency in a terrestrial repeater and a Rayleigh channel in an urban area. Has a channel.

【0073】

Returning to Figure 5, each TDM frame or OFDM symbol has a total of 2000 bits, with 1 bit of cluster control, 13 bits of encoded global control information, and interleaved audio 1986, which is a cluster segment for that cluster. Consists of bits. The total number of bits in the data frame is 2,550,000 bits (not including the 48-bit training sequence field).

【0074】

Next, a more detailed block diagram of another exemplary SDARS transmitter 200 is shown in FIG. Other than the concept of the present invention, the elements shown in FIG. 11 are well known and will not be described in detail here. As can be seen, FIG. 11 is similar to FIG. For illustration purposes, the SDARS transmitter of FIG. 11 illustrates the PAC (Perceptual Audio Coding) Audio Cluster Coder 205. The encoder 200 performs perceptual audio coding (PAC) of the program channel. The encoder 200 is also connected to the congruent bit allocation and buffer element 210 (the congruent bit allocation was described above).

【0075】

As described above, the joint bit allocation and buffer element 210 buffers and stores the entire transmission frame to control the PAC audio cluster encoder 205.

【0076】

In the illustrated transmission frame structure, the number of program channels in the program cluster and the underlying RS coding method can be easily changed to a different number. The program cluster can also be divided into subclusters. For example, a cluster can be divided into two subclusters, one for fixed bitrate channels and the other for variable bitrate channels. In this case, the joint bit distribution coding only needs to be done within the subcluster containing the variable bit rate channel.

【0077】

Moreover, RS coding can be performed over a large number of channels. RS coding across a large number of channels will spread burst errors from uncorrectable RS blocks to a large number of channels, thus reducing the size of burst errors on individual channels and error hiding performance. Is improved.

【0078】

To make the RS coding scheme across subclusters and multiple channels, it is only necessary to modify the cluster control information channel based on the proposed frame structure. This is because the cluster control information bits vary in the subcluster and multi-channel RS coding schemes.

【0079】

As described above, based on the present invention, a transmission frame structure for a satellite digital audio radio system has been illustrated and described. This illustrated frame structure is suitable for both TDM mode transmissions from two satellites and OFDM mode transmissions from ground gap fillers. This transmission frame structure provides a unique format for transmission of multiple audio data channels.

【0080】

[Cluster Frame Synchronization] For satellite signals, TDM frames and timing synchronization are based on the correlation with the detection of the training sequence (TS) described above. Acquisition of TDM consists of acquisition of time, frame, carrier synchronization, and equalizer count. For terrestrial repeater signals, OFDM frames and timing synchronization are based on GIB (guard interval based) carrier tracking and timing restoration algorithms.

【0081】

The acquisition of OFDM consists of acquisition of time, frame, and carrier synchronization. In this description, this is referred to as "timing / frame and carrier synchronization". Algorithms for timing / frame and carrier synchronization are known in the art.

【0082】

(See, for example: John G. Proakis, "Digital Communications," McGraw-Hill, third Edition, 1995; Heinrich Meyr et al, "Digital Communication Receivers," John Wiley & Sons, 1998; and JV Beek, M. Sandell and PO Borjesson, "ML estimation of time and frequency offset in OFDM systems," IEEE Transactions on Signal Processing, Vol. 45, No. 7, July 1997, pp 1800-1805) [0083]

The above frame structure (eg, Figure 5) ensures that one TDM frame fits into one OFDM symbol, so both TDM and OFDM paths are provided as long as timing / frame and carrier synchronization is acquired. The cluster synchronization bit of the cluster synchronization channel for is immediately identified.

【0084】

The cluster synchronization channel allows the receiver to acquire cluster synchronization, which compensates for differential channel propagation delay, identifies individual cluster frames from the received data stream, identifies the global control channel, and clusters. The interleaver releaser can be synchronized. As mentioned earlier, the cluster synchronization (CS) field (see, eg, Figure 3) is a 255-bit maximum length PN (pseudo-random number) sequence. For operational performance and realization reasons, all clusters use the same PN sequence as the synchronous term.

【0085】

An exemplary receiver 300 based on the principles of the present invention is shown in FIG. Other than the concept of the present invention, the elements of the receiver 300 are well known and will not be described in detail here. The receiver 300 is composed of an RF (radio frequency) front end 310, and the RF front end 310 has AGC (automatic gain control) and IF (intermediate frequency) AGC functions. Transmission signals (eg, TDM and OFDM signals) are received at the RF front end 310 and sampled at intermediate frequencies using a single ADC (analog-to-digital converter) (not shown).

【0086】

The RF front end 310 is connected to a digital downconverter 320, which transforms the signal down into a baseband signal stream, as is known in the art (the digital downconverter 320 It is also assumed to have a timing error and frequency offset compensation function).

【0087】

Three baseband signal streams (TDM, TDM delayed version, and OFDM) are fed to the corresponding TDM demodulator and OFDM demodulator of demodulator element 330. The TDM demodulator has a matching filter, a frame synchronizer, a carrier wave synchronizer, a DFE equalizer, and a noise dispersion estimator, as is known in the art.

【0088】

OFDM demodulators have the functions of frequency offset compensation, GIB carrier and timing synchronization, OFDM demodulation, and DQPSK demodulation, as is known in the art. Demodulated signals (demodulated signals) (330-1, 330-2, and 330-3) are fed to the demultiplexer 340 (described below), where the demultiplexer 340 provides information on M clusters and global control information. Restore channels (these are encoded versions).

【0089】

Other elements of the receiver, such as a connected channel decoding chain that complements the coding performed on the SDARS transmitter (as shown in FIGS. 9 and 11) for program channels and global control information, are not shown.

【0090】

(For those of interest, a further description of SDARS receivers that receive multiple modulation schemes and use techniques such as MRC (Maximum Rate Combination) is described in the US Patent Application of Zheng, Riazi above. , and Sayeed, entitled "Signal Combining Scheme For Wireless Transmission Systems Having Multiple Modulation Schemes.") Also, for example, instead of combining the received signals via the MRC method, the receiver simply has the strongest received signal. Can also be used (eg, using the Signal Noise Ratio (SNR) as a reference).

【0091】

Next, a block diagram of a portion of the restored data stream after the demodulator element 330 is illustrated in Figure 13 (which is the output from the demodulator, demodulated signals 330-1, 330-2, and 330-. It is a typical example of each of 3). (FIG. 13 is similar to FIG. 4 above.) These demodulated signals are fed to the demultiplexer 340. The demultiplexer 340 is shown in more detail in FIG.

【0092】

The demultiplexer 340 consists of three identical elements 340-1, 340-2, and 340-3, each processing the corresponding one of the output signals of the demodulator element 330. Since each element is the same, only element 340-1 will be described. Output signal 330-1 is fed to the frame demultiplexer 405 (DEMUX), which is a cluster of cluster synchronization channels (CS) and global control information channels (GC) and program channels for the TDM transmit path (cluster data). ) And are separated.

【0093】

A cluster synchronization channel is supplied to the CS demultiplexer 410, and the CS demultiplexer 410 separates the cluster synchronization bits for each of the M (here, M = 5 as an example) clusters. (As shown in Figure 4, one of the 255-bit cluster synchronization terms for each cluster is inserted within each of the five TDM frames or OFDM symbols throughout the transmission frame. For different clusters TDM frames or OFDM The symbols alternate in cluster 1 through cluster 5 within the transmission frame.

【0094】

As already shown, the cluster sync field is a 255-bit maximum length PN sequence with very good autocorrelation characteristics. The automatic correlation function of the periodic PN sequence is the PN sequence {S_n} Is defined by the following equation. R_m= ΣS_nS_{n + m}0 m L-1 (1) Where L is the length of the sequence (here equal to 255).

【0095】

Sequence {S_nSince} is periodic with period L, the autocorrelation sequence is also periodic with period L. PN sequences usually have a correlation characteristic similar to white noise. Therefore, the start position of the cluster or the cluster frame can be known from the peak of the correlation result.

【0096】

To identify 5 different clusters, it is necessary to use 5 different cluster synchronization terms (PN sequences). However, due to incomplete orthogonality, cross-correlation between the five PN sequences results in poor operating performance. Therefore, the same cluster sync word is used for all five clusters.

【0097】

For this reason, five parallel correlators that correlate to each of the five receive cluster synchronous bitstreams are needed to identify the individual clusters. Therefore, each of the restored cluster sync words from the CS demultiplexer 410 is fed to the corresponding correlator element 415.

【0098】

Input signal Y of each correlator_nCan be modeled as Y_n= A_nS_n+ N_n (2) Here, A_n, S_nAnd N_nRepresents the receive cluster sync signal amplitude, bit value, and noise, respectively.

【0099】

Output signal C of each correlator_mIs given by the following equation. C_m= Σ_{n = 1}^LY_mnS_n(3) (As can be seen in Figure 14, the output signal of each correlator is also filtered by a high frequency filter to improve performance. Each high frequency filter removes low frequency components due to fading of the radio channel. To do.

【0100】

The synchronization position for a particular cluster is determined from the peak of the correlation result. I would like to reiterate the following here. That is, the same cluster synchronization term is used for all five clusters, the cluster synchronization bits for each cluster are inserted within each of the five TDM frames or OFDM symbols throughout the transmission frame, and the TDM frames or OFDM symbols are inserted. Cluster 1 to cluster 5 appear alternately in the transmission frame. Therefore, it is possible to individually determine the synchronization position for each of the individual clusters from each phase of the five correlation peaks.

【0101】

From this, the five output signals from the correlator element 415 are supplied to the peak detector 420. The peak detector 420 detects the first five consecutive correlated peaks and compares the phases of these first five consecutive correlated peaks with each other. This is shown in FIG.

【0102】

As shown in FIG. 15, the five output signals from the correlator element 415 are represented as 416-1, 416-2, 416-3, 416-4, and 416-5. As can be seen in Figure 15, the relative phases of the first five consecutive correlated peaks indicate the location of the cluster.

【0103】

In this example, output signal 416-1 corresponds to synchronization for cluster 2 (ie, occurs second) and output signal 4162 corresponds to synchronization for cluster 3 (ie, occurs third). , Output signal 416-3 corresponds to synchronization for cluster 4 (ie, occurs fourth), output signal 416-4 corresponds to synchronization for cluster 5 (ie, occurs fifth), output signal 416 -5 corresponds to synchronization for cluster 1 (ie, occurs first).

【0104】

Moreover, in order to improve the cluster synchronization detection probability and reduce the probability of false alarm, the five cluster correlation results can be temporally aligned to the peak and combined. This is done by the combinator 425. Combination 425 receives the first five consecutive correlation peaks from peak detector 420 and produces combination signal 426-1 as shown in FIG. The combination of the five correlation results yields a peak-to-noise ratio of about 5 times, thus significantly improving performance.

【0105】

(From Figure 15, it can be seen that signal 426-1 is simply a combination of the last detected input signal (represented here by signal 416-4) and the other remaining inputs. Each signal is temporally shifted and combined by the combiner 425.

【0106】

In this example, the combined signal 426-1 represents the detection of a peak for TDM transmission. Similarly, the remaining elements of the demultiplexer 340, namely elements 340-2 and 340-3, produce the combined signals 426-2 and 426-3. These are estimates of sync positions associated with TDM (delayed version) transmissions and OFDM transmissions, respectively.

【0107】

As shown in FIG. 16, the synchronous position signals 340-1, 345-2, and 340-3 can be used for time alignment (time alignment) to align the temporal positions of the data streams of the three transmission paths. This is because if the maximum rate combination is disclosed in the US Patent Application of Riazi, Sayeed, and Zheng, entitled "Maximum Ratio Combining Scheme for Satellite Digital Audio Broadcast System with Terrestrial Gap Fillers." Useful when used.

【0108】

In this case, the demultiplexer 340 additionally includes elements 430-1, 430-2, and 430-3. These elements 430-1, 430-2, and 430-3 operate on the respective estimates of the synchronous position signals 340-1, 34-2, and 340-3, and the peak position for each transmission path. To detect. (These elements can also be provided externally to the demultiplexer 340.

【0109】

Output signals from elements 430-1, 430-2, and 430-3 are supplied to the time alignment element 440. (Note that the output signal from element 430-1 is first supplied to element 435 with a 4-second delay.

【0110】

FIG. 17 is an explanatory diagram of time alignment of the three transmission paths performed by the time alignment element 440. The time alignment process first finds three peaks within half the length of the transmission frame window and then uses relative differential delay to adjust the time alignment for the three transmission paths.

【0111】

For the sake of detail, FIG. 18 and FIG. 19 show an example of applying cluster synchronization with a few additions. As with the previous description, the elements of FIGS. 18 and 19 are assumed to be part of the demultiplexer 340 for simplicity. In FIG. 18, cluster synchronization is used to time-align the cluster portion of the three types of transmission frames.

【0112】

Each cluster synchronization signal is fed to its own cluster timing control element (eg, 455-1, 455-2, and 455-3), and the cluster timing control element is associated with the associated cluster buffer (eg, 460-1, 460-). 2,460-3) Adjust the buffer size. Each cluster data stream from a particular transmission is fed into its own cluster buffer (eg, 460-1, 460-2, 460-3).

【0113】

Output signals (466-1, 466-2, and 466-3) from each cluster buffer are supplied to the time alignment buffer 470, and the time alignment buffer 70 is the signals 466-1, 466-2, and 466-3. Perform time alignment. (Note that the output signal from the cluster buffer 460-1 is further supplied to the delay element 465-1 for 4 seconds before being supplied to the time alignment buffer 470.

【0114】

The time-aligned buffer 470 feeds the three time-aligned signals to the MRC (maximum rate combination) element 475, which weights, for example, the signal-to-noise (SN) ratio for each stream. Combine these three signals using a weighted) factor and a signal-to-noise ratio combination. (For example, if the signal-to-noise ratio of the TDM (delayed version) transmission path is low, the time-aligned signal corresponding to the TDM (delayed version) transmission path is less weighted when combining the three transmission paths.

【0115】

See also the US Patent Application of Riazi, Sayeed, and Zheng, entitled "Maximum Ratio Combining Scheme for Satellite Digital Audio Broadcast System with Terrestrial Gap Fillers."

【0116】

The output signal from MRC element 475 is fed to the cluster demultiplexer 480, which demultiplexes the cluster data stream into five clusters (demultiplexing). FIG. 19 is an explanatory diagram showing a case where cluster synchronization is used for the global control information (GC) channel, and the same processing as in FIG. 18 is performed here as well, and the description is the same, and thus the description is omitted.

【0117】

The above description relates to an embodiment of the present invention, and a person skilled in the art may consider various modifications of the present invention, all of which are included in the technical scope of the present invention. To. For example, the concept of the present invention has been described for the case of a satellite digital audio radio system (SDARS), but the present invention applies to any system for transmission systems where efficient transport of a significant number of channels is desired. Is possible. It should be noted that the reference numbers described in the claims are for the sake of easy understanding of the invention and should not be construed to limit the technical scope thereof.

【0118】

[Effect of the invention]

As described above, according to the present invention, in a transmission system (for example, SDARS) that supports a large number of audio data program channels, a transmission frame structure that efficiently conveys these channels can be obtained.

[Simple explanation of drawings]

[Figure 1]

This is an example of a high-level block diagram of a satellite digital audio radio system (SDARS).

[Figure 2]

It is explanatory drawing which shows the concept of this invention together with FIG. 3 and FIG.

[Fig. 3]

It is explanatory drawing which shows the concept of this invention together with FIG. 2 and FIG.

[Fig. 4]

It is explanatory drawing which shows the concept of this invention together with FIG. 2 and FIG.

[Fig. 5]

It is explanatory drawing which shows an example of the transmission frame format based on the principle of this invention.

[Fig. 6]

It is explanatory drawing which shows an example of the frame format about the program cluster based on the principle of this invention.

[Fig. 7]

It is explanatory drawing which shows an example of mapping about cluster control information based on the principle of this invention.

[Fig. 8]

It is explanatory drawing which shows an example of the mapping about the global control information based on the principle of this invention.

[Fig. 9]

This is an example of a high-level block diagram of a satellite digital audio radio system transmitter based on the principle of the present invention.

[Fig. 10]

This is an example of a block diagram of the cluster synchronization generator used in the transmitter of FIG.

[Fig. 11]

This is another example of a block diagram of a satellite digital audio radio system transmitter based on the principle of the present invention.

[Fig. 12]

This is an example of a block diagram of a satellite digital audio radio system receiver based on the principle of the present invention.

[Fig. 13]

It is explanatory drawing which shows an example of the restored transmission frame.

[Fig. 14]

This is an example of a block diagram of a demultiplexer based on the principle of the present invention.

[Fig. 15]

It is explanatory drawing which illustrates the cluster synchronization correlation.

[Fig. 16]

It is explanatory drawing which shows other various application examples about cluster synchronization together with FIGS. 17 to 19.

[Fig. 17]

FIG. 5 is an explanatory diagram showing various other application examples for cluster synchronization together with FIGS. 16, 18 and 19.

[Fig. 18]

FIG. 5 is an explanatory diagram showing various other application examples for cluster synchronization together with FIGS. 16, 17, and 19.

[Fig. 19]

It is explanatory drawing which shows other various application examples about cluster synchronization together with FIGS. 16-18.

[Explanation of symbols]

10 Satellite Digital Audio Radio System (SDARS) Transmitter 11 Broadcast transmission signal 20 SDARS receiver 21 Audio program 50 transmission frame 100 SDARS transmitter 110 cluster frame multiplexer 120 coders 130 CC encoder 140 GC encoder 150 CS generator 155 Scrambler / interleaver group 160 Transmission frame assembly 165 Training insertion element 170, 175 4 seconds (sec) delay factor 190 modulator 200 SDARS transmitter 205 PAC Audio Cluster Coder 210 Joint bit allocation and buffer elements 300 receiver 310 RF (radio frequency) front end 320 digital down converter 330 Demodulator element 330-1, 330-2, 330-3 Demodulated signal 340 demultiplexer 340-1, 340-2, 340-3 elements (demultiplexer) 405 frame demultiplexer 410 CS demultiplexer 415 Correlator element 416-1, 416-2, 416-3, 416-4, 416-5 Output signal (from correlator element 415) 420 peak detector 425 Combination device 426-1, 426-2, 426-3 Combination signal 430-1, 430-2, 430-3 elements (peak position detection) 435 4 second delay factor 440 time alignment element 455-1, 455-2, 455-3 Cluster timing control elements 460-1, 460-2, 460-3 cluster buffer 465-1 4 second delay factor 466-1, 466-2, 466-3 Output signal 470 time alignment buffer 475 MRC (maximum rate combination) element 480 cluster demultiplexer 505-1, 505-2, 505-3 GC timing control element 510-1, 510-2, 510-3 GC buffer 515-1 4 second delay factor