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TiVo Hacking Book to be Released
weaknees writes "Wired News
reports that O'Reilly press has book in the works loaded with TiVo Hacks. The
author, an MIT guy, is collecting
100 hacks for TiVo, but is shying away from the most controversial hacks.... The
brief article points out that the most avid TiVo hackers seem intent on respecting
TiVo's interest in having hackers stay away from things like subscription theft
and video extraction."
fp
first post lolz
Trellis Description of a Convolutional Encoder
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A trellis description of a convolutional encoder shows how each possible input to the encoder influences both the output and the state transitions of the encoder. This section describes trellises, describes how to represent trellises in MATLAB, and gives an example of a MATLAB trellis.
The figure below depicts a trellis for the convolutional encoder from the previous section. The encoder has four states (numbered in binary from 00 to 11), a one-bit input, and a two-bit output. (The ratio of input bits to output bits makes this encoder a rate-1/2 encoder.) Each solid arrow shows how the encoder changes its state if the current input is zero, and each dashed arrow shows how the encoder changes its state if the current input is one. The octal numbers above each arrow indicate the current output of the encoder.
Figure 2-2: A Trellis for a 4-State Rate-1/2 Convolutional Encoder
As an example of interpreting this trellis diagram, if the encoder is in the 10 state and receives an input of zero, then it outputs the code symbol 3 and changes to the 01 state. If it is in the 10 state and receives an input of one, then it outputs the code symbol 0 and changes to the 11 state.
Note that any polynomial description of a convolutional encoder is equivalent to some trellis description, although some trellises have no corresponding polynomial descriptions.
Specifying a Trellis in MATLAB
To specify a trellis in MATLAB, use a specific form of a MATLAB structure called a trellis structure. A trellis structure must have five fields, as in the table below.
Table 2-4: Fields of a Trellis Structure for a Rate k/n Code Field in Trellis Structure
Dimensions
Meaning
numInputSymbols
Scalar
Number of input symbols to the encoder: 2k
numOutputsymbols
Scalar
Number of output symbols from the encoder: 2n
numStates
Scalar
Number of states in the encoder
nextStates
numStates-by-2k matrix
Next states for all combinations of current state and current input
outputs
numStates-by-2k matrix
Outputs (in decimal) for all combinations of current state and current input
Note While your trellis structure can have any name, its fields must have the exact names as in the table. Field names are case-sensitive.
In the nextStates matrix, each entry is an integer between 0 and numStates-1. The element in the ith row and jth column denotes the next state when the starting state is i-1 and the input bits have decimal representation j-1. To convert the input bits to a decimal value, use the first input bit as the most significant bit (MSB). For example, the second column of the nextStates matrix stores the next states when the current set of input values is {0,...,0,1}. To learn how to assign numbers to states, see the reference page for istrellis.
In the outputs matrix, the element in the ith row and jth column denotes the encoder's output when the starting state is i-1 and the input bits have decimal representation j-1. To convert to decimal value, use the first output bit as the MSB.
How to Create a MATLAB Trellis Structure
Once you know what information you want to put into each field, you can create a trellis structure in any of these ways:
* Define each of the five fields individually, using structurename.fieldname notation. For example, set the first field of a structure called s using the command below. Use additional commands to define the other fields.
s.numInputSymbols = 2;
The reference page for the istrellis function illustrates this approach.
* Collect all field names and their values in a single struct command. For example:
s = struct('numInputSymbols',2,'numOutputSymbols',2,..
'numStates',2,'nextStates',[0 1;0 1],'outputs',[0 0;1 1]);
* Start with a polyn
MTV gave an award to Gollum?
Once upon a time whilst walking in a park I asked a geek "Do you have a girlfriend?". He responded with a very puzzled look. "A girlfriend?," he mused, "Who is the developer?". I chuckled and told him this was not an open source project. He then became slightly angry and inquired, "Are you trying to insult me? Only the best geeks use open source only! What planet are you living on?!". I reassured him I was well aware of his integrity as a geek (white skin, clumsy, pants that are too short, lack of daily shower, pocket protector etc), and explained, "A girlfriend is a female who to a male (most oftenly a male) has an intimate friendship." He gave me a very confused look. "I have never heard of such a thing.. this.. g-g-irlfriend?" He asked me, sounding very baffled. "I have heard of friends before, those pets other people have. But what is this thing you say.. Grill?". "Girl," I corrected. Then I asked him to sit down on a bench nearby so I could explain it too him, the poor, helpless thing. I told him that for human beings to reproduce, sexual intercourse must occur between a male and a female. "Perhaps you hear the trolls mention a thing called "pussy" on slashdot?". The geek burst into laughter, "Haha, you have been browsing at -1 lately, haven't you? You know that is just troll talk. Those silly trolls never have anything intelligent to say."
My face turned serious. "My dear geek, are you not aware of the female population amongst you? Do you not stare in the street and want to hump a post when you pass by a hot, slim, gorgeous looking chick with a firm bust and well sculpted ass?". The geek immediately began to appear as if he was having a nervous breakdown. His glasses began to fog up and he took them off to wipe them with this linux embroidered shirt, "I think I know what you are talking about. Those things are icky. They have cooties. Get away from me!" I felt offended. "Nonsense, I pleaded! Pussy is a beautiful thing. A sacred thing that you should strive to give pleasure to." The geek would not listen and he began to cry. "STOP IT!! You are EVIL!!" He then, quite geekishly, skipped off down the path.
I walked back to my house feeling rather disheartened. 'Why don't they listen to me' I asked myself? When I got home my girlfriend opened the door. She was wearing short-shorts and a sports bra. She had been doing the thigh master for the past 30 minutes and was sweating. I could see her dark nipples underneath her slightly damp bra. Oh god I could fuck her to the moon and back. I could smell her horniness the second I took my shoes off. I chased her, both of us laughing, to our bedroom [THE FOLLOWING has been censored for the well-being of geeks].... Six hours later, finally satisfied a little, I sat up and noticed that same geek hiding in the trees. He had been watching us the entire time. I swear his penis had to have been the size of a fucking horse cock (not bad for a geek, i might add), and he appeared as if he had gone into a state of shock. I could see cum stains forming near the bulge of his pant zipper. I thought to myself. There is one geek, finally brought into the real world.