y = wlanScramble(bits,scramInit) scrambles or descrambles the binary input bits for the specified initial scramble state, using a 127-length frame-synchronous scrambler. The frame-synchronous scrambler uses the generator polynomial defined in sections 188.8.131.52 and 20.3.9 of . The transmitter and receiver use the same scrambler to scramble bits at the transmitter and descramble bits at the receiver, respectively.
Section 184.108.40.206 of  specifies the scrambling and descrambling process applied to the transmitted data. The header and data fields that follow the scrambler initialization field (including data padding bits) are scrambled by XORing each bit with a length-127 periodic sequence generated by the polynomial S(x) = x7+x4+1. The octets of the PSDU are placed into a bit stream, and, within each octet, bit 0 (LSB) is first and bit 7 (MSB) is last. This figure demonstrates the sequence generation and XOR operation.
Scrambler often referred as randomizer basically removes long stream of o's and 1's from thedata. It is used in wireless transmitter and receiver chain. It is part of layer-1 or physical layer.Circuit on the left is the one most often used as scrambler circuit and is specified in IEEE wireless standardsviz. wimax,wlan etc. we will see how we can develop matlab code for this circuit on this page.
scrambler = comm.Scrambler(base,poly,cond) creates the scrambler object with the CalculationBase property set to base, the Polynomial property set to poly, and the InitialConditions property set to cond.
Connections for linear feedback shift registers in the scrambler, specified as a character vector, integer vector, or binary vector. The Polynomial property defines if each switch in the scrambler is on or off. Specify the polynomial as:
Create scrambler and descrambler objects, specifying the calculation base, polynomial, and initial conditions using input arguments. The scrambler and descrambler polynomials are specified with different but equivalent data formats.
Create scrambler and descrambler System objects having a calculation base of 4. Set the InitialConditionsSource property to 'Input port' so you can set the initial conditions as an argument to the object.
Comparing the shift register specified in 802.11 with the shift register implementated using a comm.PNSequence System object, note that the two shift register schematics are mirror images of each other. Therefore, when configuring the comm.PNSequence System object to implement an additive scrambler, you must reverse values for the generator polynomial, the initial states, and the mask output. To take the output of the register from the leading end, specify a shift value of 7.
Define variables for the generator polynomial, shift value for the output, an initial shift register state, a frame of input data, and a variable containing the 127-bit scrambler sequence specified in section 220.127.116.11 of the IEEE 802.11 standard. Create a PN sequence object that initializes the registers by using an input argument.
I tried to write the descrambling part as describe in this matlab link, as far as i know to convert it to descrambler i need to invert the xor bit when i assign it to the output as follows output[i] = state = !xor ^ input[i] and also need to reset the state back to 0's before calling a descramble function but I do not get the correct output similar to the input of the scrambler. Should i change something else as well?
In telecommunications, a scrambler is a device that transposes or inverts signals or otherwise encodes a message at the sender's side to make the message unintelligible at a receiver not equipped with an appropriately set descrambling device. Whereas encryption usually refers to operations carried out in the digital domain, scrambling usually refers to operations carried out in the analog domain. Scrambling is accomplished by the addition of components to the original signal or the changing of some important component of the original signal in order to make extraction of the original signal difficult. Examples of the latter might include removing or changing vertical or horizontal sync pulses in television signals; televisions will not be able to display a picture from such a signal. Some modern scramblers are actually encryption devices, the name remaining due to the similarities in use, as opposed to internal operation.
In telecommunications and recording, a scrambler (also referred to as a randomizer) is a device that manipulates a data stream before transmitting. The manipulations are reversed by a descrambler at the receiving side. Scrambling is widely used in satellite, radio relay communications and PSTN modems. A scrambler can be placed just before a FEC coder, or it can be placed after the FEC, just before the modulation or line code. A scrambler in this context has nothing to do with encrypting, as the intent is not to render the message unintelligible, but to give the transmitted data useful engineering properties.
A scrambler replaces sequences (referred to as whitening sequences) with other sequences without removing undesirable sequences, and as a result it changes the probability of occurrence of vexatious sequences. Clearly it is not foolproof as there are input sequences that yield all-zeros, all-ones, or other undesirable periodic output sequences. A scrambler is therefore not a good substitute for a line code, which, through a coding step, removes unwanted sequences.
Additive scramblers (they are also referred to as synchronous) transform the input data stream by applying a pseudo-random binary sequence (PRBS) (by modulo-two addition). Sometimes a pre-calculated PRBS stored in the read-only memory is used, but more often it is generated by a linear-feedback shift register (LFSR).
The first voice scramblers were invented at Bell Labs in the period just before World War II. These sets consisted of electronics that could mix two signals or alternatively "subtract" one signal back out again. The two signals were provided by a telephone and a record player. A matching pair of records was produced, each containing the same recording of noise. The recording was played into the telephone, and the mixed signal was sent over the wire. The noise was then subtracted out at the far end using the matching record, leaving the original voice signal intact. Eavesdroppers would hear only the noisy signal, unable to understand the voice.
The noise was provided on large shellac phonograph records made in pairs, shipped as needed, and destroyed after use. This worked, but was enormously awkward. Just achieving synchronization of the two records proved difficult. Post-war electronics made such systems much easier to work with by creating pseudo-random noise based on a short input tone. In use, the caller would play a tone into the phone, and both scrambler units would then listen to the signal and synchronize to it. This provided limited security, however, as any listener with a basic knowledge of the electronic circuitry could often produce a machine of similar-enough settings to break into the communications.
The latest scramblers are not scramblers in the truest sense of the word, but rather digitizers combined with encryption machines. In these systems the original signal is first converted into digital form, and then the digital data is encrypted and sent. Using modern public-key systems, these "scramblers" are much more secure than their earlier analog counterparts. Only these types of systems are considered secure enough for sensitive data.
The "scramblers" used in cable television are designed to prevent casual signal theft, not to provide any real security. Early versions of these devices simply "inverted" one important component of the TV signal, re-inverting it at the client end for display. Later devices were only slightly more complex, filtering out that component entirely and then adding it by examining other portions of the signal. In both cases the circuitry could be easily built by any reasonably knowledgeable hobbyist. (See Television encryption.)
Descramble in cable television context is the act of taking a scrambled or encrypted video signal that has been provided by a cable television company for premium television services, processed by a scrambler and then supplied over a coaxial cable and delivered to the household where a set-top box reprocesses the signal, thus descrambling it and making it available for viewing on the television set. A descrambler is a device that restores the picture and sound of a scrambled channel. A descrambler must be used with a cable converter box to be able to unencrypt all of the premium & pay-per-view channels of a Cable Television System.
I am currently working on writing a scrambler and DeScrambler code for Orthogonal Frequency Division Multiplexing(OFDM). I am planning to write an algorithm for BPSK, QPSK and QAM scrambler-Descrambler before modulation and transmission.
Now for Hardware design it is different: you perform 'hardware design' but you do 'processor programming', all these MATLAB, Simulink, C, C++ to HDL is just a way to allow much more people (software programmers) to design hardware because HDL requires so much different thinking.
Hi,i am pursuing M.tech and i require LFSR programs code to generate the PN sequence used in wireless communication of different bit (8 bit , 16 bit , 32 bit & 64 bit).i will be very thankful to u.Jitender
hi,i want to generate sscrambler verilog code.so thanks for this but now what about descrambler.can any one help me to generate the descrambler code.i want to verify the scrambler and descrambler process.i will be thankful to u.rakhi
The present paper investigates and describes the German mechanical ciphermachine called Enigma, and presents a possible way to its decryption. DuringWorld War II, the Germans used a typewriter-like machine named Enigma toencrypt military messages. We make an attempt at a historical introduction,and non-technical background information is provided. This paper includesa C program that simulates Enigma, and a method to break its code. The latteris achieved by a simulation of a simplified Bombe, a mechanical device thatwas actually used during WWII at Bletcheley Park, a site in England wherea major deal of the work on breaking Enigma's code was done. Much of thecredit for breaking the code must be given to a group of accomplished Polishmathematicians, and the famous, and in the computer community well knownmathematician Alan Turing. 2b1af7f3a8