专利汇可以提供METHOD AND APPARATUS FOR INTERLEAVING LOW DENSITY PARITY CHECK (LDPC) CODES OVER MOBILE SATELLITE CHANNELS专利检索,专利查询,专利分析的服务。并且Systems, methods and apparatus are described to interleave LDPC coded data for reception over a mobile communications channel, such as, for example, a satellite channel. In exemplary embodiments of the present invention, a method for channel interleaving includes segmenting a large LDPC code block into smaller codewords, randomly shuffling the code segments of each codeword and then convolutionally interleaving the randomly shuffled code words. In exemplary embodiments of the present invention, such random shuffling can guarantee that no two consecutive input code segments will be closer than a defined minimum number of code segments at the output of the shuffler. In exemplary embodiments of the present invention, by keeping data in, for example, manageable sub-sections, accurate SNR estimations, which are needed for the best possible LDPC decoding performance, can be facilitated based on, for example, iterative bit decisions.,下面是METHOD AND APPARATUS FOR INTERLEAVING LOW DENSITY PARITY CHECK (LDPC) CODES OVER MOBILE SATELLITE CHANNELS专利的具体信息内容。
This application claims the benefit of and hereby incorporates by reference U.S. Provisional Patent Application No. 60/963,043, entitled METHOD AND APPARATUS FOR INTERLEAVING LOW DENSITY PARITY CHECK (LDPC) CODES OVER MOBILE SATELLITE CHANNELS, and filed on Aug. 1, 2007.
The present invention relates to satellite broadcast communications, and more particularly to systems and methods for interleaving LDPC coded data over mobile satellite channels.
Mobile receivers of satellite broadcast communications are often faced with signal fades of long duration in particular locations and at particular times. This can be more or less egregious depending upon a given channel's fading characteristics. It is well known that time interleaving a communication signal can be a very effective method to transform a time fading channel into a memory-less channel.
What is thus needed in the art are systems and methods to interleave LDPC coded data for better reception over a mobile satellite channel.
Systems, methods and apparatus are described to interleave LDPC coded data for reception over a mobile communications channel, such as, for example, a satellite channel. In exemplary embodiments of the present invention, a method for channel interleaving includes segmenting a large LDPC code block into smaller codewords, randomly shuffling the code segments of each codeword and then convolutionally interleaving the randomly shuffled code words. In exemplary embodiments of the present invention, such random shuffling can guarantee that no two consecutive input code segments will be closer than a defined minimum number of code segments at the output of the shuffler. In exemplary embodiments of the present invention, by keeping data in, for example, manageable sub-sections, accurate SNR estimations, which are needed for the best possible LDPC decoding performance, can be facilitated based on, for example, iterative bit decisions.
It is noted that the patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawings will be provided by the U.S. Patent Office upon request and payment of the necessary fees.
It is well known that time interleaving a communication signal can be a very effective method for transforming a time fading channel into a memory-less channel. The amount of interleaving that needs to be performed is typically a function of the channel's fading characteristics and system delay tolerance. In a broadcast channel, delay is generally not of major concern. In exemplary embodiments of the present invention this allows for the dedication of large amounts of hardware memory to interleave over as much time as possible.
In exemplary embodiments of the present invention a LDPC code can originate as a large block code (e.g., thousands of bits) using low coding rates. Again with reference to
As shown in
The readout order from the S-random shuffler can, for example, be controlled by a lookup table 320 (labeled “Permutation Table” in
Such S-random shuffling operation can, for example, ensure that random portions of each LDPC code are applied to the convolutional interleaver. This can, for example, minimize the possibility of consecutive data or parity bits being erased due to long fading. It is understood, of course, that this functionality depends upon the length of the fade condition. Thus, if a fade is longer than the convolutional interleaver's time duration, then consecutive data and/or parity bits can be erased by the channel. The output 340 of the S-random shuffler is thus the code block 310 with its various code segments CS now in a very different, randomly permuted order. (It is noted that in
In exemplary embodiments of the present invention each branch of a CI can, for example, be passed an entire code segment of data (100 bits), with each arm of the CI being of varying length. The effect of such a CI operation is to time disperse each of the code segments of data (as noted, in the depicted example of
Similarly,
In exemplary embodiments of the present invention, a LDPC decoder requires knowledge of the received noise variance in order to properly form log likelihood ratios. Log likelihood ratios are, as known, a measure of how likely a soft decision for a given received symbol is. It can be understood as an indication as to how far away a given received symbol is from the x-y axis in an I,Q plot. In general, a slicer can make a hard decision or can give a log likelihood ratio as to the quadrant a particular received symbol is in.
As a received signal is de-interleaved, each segment of that signal will generally have a different noise variance. Thus, in exemplary embodiments of the present invention, a noise variance for each segment can, for example, first be estimated based on traditional noise variance cluster estimates. If the LDPC code contains N segments, then N independent noise variances can, for example, be estimated (one representing the average for each subsection of data samples). It is this metric that allows an LDPC decoder to essentially soft weight the merit of each segment for an iterative decoding process. To simplify the noise estimate, each segment can, for example, be aligned with a physical frame transmission, with one noise variance estimate for each physical frame. The initial noise estimate can, for example, be based on raw sliced decisions, averaging the squared distance of the received signal to the targeted hard decision symbol.
Unfortunately, under low SNR conditions, initial decisions can have large numbers of errors, leading to inaccurate noise estimates. This can be especially true in COFDM reception where the subsection of a signal that is decoded is based on an entire physical frame. This approach does not take into account the fact that some symbols within a COFDM physical frame are in deep nulls or the fact that the COFDM sliced errors are weighted by the channel state information. To improve on the noise variance estimate (which improves the LDPC decoding ability via correct soft weighting of the LDPC codes subsections), in exemplary embodiments of the present invention, the noise variance of each segment can be, for example, re-calculated on every iteration of the LDPC decoder. The idea behind re-calculating at each iteration is that the LDPC decoder comes closer and closer to estimating the correct bit decisions, hence providing a new target hard bit decision for the noise power estimate. After each iteration, the noise estimate improves and the weighting for each segment can correspondingly be subsequently improved. This function allows for improvement in the decoder, particularly under COFDM reception where the initial noise estimates can be highly incorrect, as noted.
In exemplary embodiments of the present invention, if data is interleaved in a manageable fashion, then adaptive estimation of the noise variance can be implemented. Thus, for example, the performance of an exemplary adaptive noise estimator for an exemplary COFDM received signal is shown in
The top curve shown in
The inventive method of interleaving described above has been seen to be every effective in combating severe satellite fading channels. Additionally, such method provides a manageable procedure to accurately obtain noise variance estimates under fading conditions, from either a satellite channel, for example, or from a terrestrial channel.
While the present invention has been described with reference to certain exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is understood that the invention not be limited to any particular embodiment, but that the invention will include all embodiments falling within the scope of the appended claims.
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