Television – Basic receiver with additional function – Multimode
Reexamination Certificate
2000-12-28
2003-10-07
Lee, Michael H. (Department: 2614)
Television
Basic receiver with additional function
Multimode
C348S388100, C348S716000, C348S718000, C375S240240
Reexamination Certificate
active
06630964
ABSTRACT:
FIELD OF THE INVENTION
The invention is related to the field of receivers for digital transmissions and more specifically to receivers for encoded digital television signals based on multiple standards.
BACKGROUND OF THE INVENTION
Today, there are at least three media over which digital video is delivered to the home—cable, satellite and terrestrial. In each case, a video signal is channel encoded and modulated to convert the video data to a form suitable for transmission over the chosen medium. An inverse operation is performed at the receiver to retrieve the transmitted signal. The device which performs the demodulation and channel decoding is known as a channel decoder.
Since the characteristics of each medium are different, each has its own associated transmission standard. In addition, standards are different in different regions of the world. In the U.S., the standard for terrestrial transmission is trellis coded 8-level Vestigial Side-band (8-VSB) modulation prescribed by the Advanced Television Systems Committee (ATSC) and cable transmission will probably use the same standard. The 8-VSB standard for terrestrial broadcasting allows either QPSK or QAM to be used and cable broadcasting will probably use 256-QAM for HDTV. In Europe, the Digital Video Broadcasting (DVB) group prescribes three different standards DVB-S, DVB-C and DVB-T for satellite, cable and terrestrial broadcasting respectively. The modulation scheme used in Europe for these DVB standards is Coded Orthogonal Frequency Division Multiplexing (COFDM). For terrestrial broadcasting, Japan has adapted Bandwidth Segmented Transmission (BST) Orthogonal Frequency Division Multiplexing (OFDM) which is similar to COFDM. 8-VSB and COFDM are radically different transmission schemes.
8-VSB is essentially an 8-level amplitude modulation scheme with a suppressed lower side band. The synch byte of 188 byte MPEG packets is stripped off and the remaining 187 bytes are pseudo-randomized. A Reed-Solomon encoder encodes the 187 byte blocks into 207 byte blocks with forward error correction. A data interleaver reorders the bytes within a block. The trellis encoder converts each byte to four 8-level channel symbols. A MUX inserts a synch byte after each 824 symbols resulting in a block of 825 symbols. A pilot signal is inserted for use equalization in the receiver. The resulting information stream is used to modulate a carrier which is radio frequency (RF) up-converted to the desired frequency and transmitted.
Herein the term stream simply means an ordered sequence of samples. This definition of a stream deviates from that often used in the video decoding community where a stream is usually defined as an ordered sequence of packets. A packet is a structured data element containing at least several bytes of data, but a sample is at most a complex number.
In COFDM the synch bytes are stripped from MPEG packets which are randomized and provided as a stream of samples. The stream is formed into 204,188 byte blocks of error encoded information by a Reed-Solomon encoder. As an outer code, the information is convolutionally interleaved with a depth of 12. A punctuated convolutional code is used as an inner code at least for DVB-T and DVB-S. A block-based interleaver rearranges the information. The signal is mapped to quadrature phase keyed (QPK) modulation or a level (e.g. 8, 16, 32, 64 or 128 level) of quadrature amplitude modulation depending on the bit rate and ruggedness required for the system. Pilot signals are mixed with the information and the signal is framed. Then an Inverse fast Fourier transformer converts the result into either 1705 carriers (called 2K) or 6817 carriers (called 8K) with 24 bit complex samples. Cyclic prefixes and guard bands are then added. Then the signal is RF up-converted to the desired frequency and transmitted.
A major difference in the architecture of channel decoders for VSB and OFDM transmissions concerns the respective block sizes of information required for processing and the operations that are performed on the blocks. For VSB, there is only one carrier so that demodulation is fairly simple and may be performed on a symbol by symbol basis. The resulting blocks of information are only 207 bytes and after forward error correction the blocks are only 187 bytes. Thus, only relatively small amounts of data need to be moved between processors and stored in the processors for processing. On the other hand, OFDM uses 2K or 8K carriers with 24 bit samples and demodulation requires fast Fourier transforms of the 2K or 8K by 24 bit blocks and is quite complicated. The storage requirements are thus much larger and moving data as a stream between processors for each operation is no longer practical so that the processors need to share a memory.
Both the 8-VSB and the COFDM channel decoders first perform a sample rate conversion. In the 8-VSB channel decoder, an SQRC filter operates on the output of the sample rate converter to provide timing recovery information that is fed back for the sample rate conversion. In the COFDM receiver the guard bands are removed from the output of the sample rate converter and the resulting information is subjected to an FFT. Intermediate synchronization information extracted during the FFT, is fed back to the sample rate conversion and other information added to the output of the sample rate conversion prior to guard band removal. Then the output of the FFT is subjected to channel estimation which is used in channel correction of the output of the FFT.
Two common approaches to designing channel decoders are the so called hardware approach and the software approach. In the hardware approach, special purpose processors (SPPs) are provided to perform the functions required for the channel decoding, for example, Application Specific Integrated Circuits (ASICs) or Field modified Programmable Gate Arrays (FPGAs) may be provided. These special purpose processors are able to operate at very high speeds. They also minimize the amount of hardware required and minimize software programming development time.
In the so called software approach, digital signal processors (DSPs) are programmed to perform each required function. DSPs are similar to general purpose processors with some modifications for more efficient signal processing. Programmed DSPs do not operate as quickly as SPPs and occupy more space than SPPs. DSPs are essentially off-the-shelf designs, so they reduce hardware development costs. Generally, DSPs can be used to provide a more flexible solution that may be upgraded as standards change.
A digital signal processor and shared memory scheme with arbitration is disclosed in U.S. Pat. No. 5,685,005 to Garde. A method of generating special purpose processors for particular problems is disclosed in U.S. Pat. No. 6,075,935 to Ussery. Ussery also discloses respective memories shared between respective pairs of parallel processors. A multiprocessor system for video processing re-configurable for SIMD or MIMD processing and accessing shared memory through a crossbar switch is disclosed in U.S. Pat. No. 5,471,592 to Gove. Gove uses a master processor to control the processing including the connections of the crossbar switch to interconnect the processors and the memory. U.S. Pat. No. 5,046,080 to Lee discloses a videophone system with multiple pipelined DSPs each accessing two buses, a VME bus and a memory bus.
Those skilled in the art are also directed to U.S. patent application Ser. No. 09/639,149 filed Aug. 8, 2000 by Vaidyanathan et. al. which discloses a sample-based communications network.
The above citations are hereby incorporated herein in whole by reference.
SUMMARY OF THE INVENTION
In the invention herein, a channel decoder includes a multitude of channel decoding functional units. A first plurality of the functional units communicate through a sample-based communication unit for channel decoding streams of sample-based channel encoded signals such as an 8-VSB transmission. The first functional units receive a stream of samples from the sample-based communication unit, st
Burns Geoffrey Francis
Vaidyanathan Krishnamurthy
Belk Michael E.
Koninklijke Philips Electronics , N.V.
Lee Michael H.
Yenke Brian
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