Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/69—Spread spectrum techniques
  • H04B1/707—Spread spectrum techniques using direct sequence modulation
  • H04B1/7073—Synchronisation aspects
  • H04B1/7075—Synchronisation aspects with code phase acquisition
  • H04B1/70756—Jumping within the code, i.e. masking or slewing
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B2201/00—Indexing scheme relating to details of transmission systems not covered by a single group of H04B3/00 - H04B13/00
  • H04B2201/69—Orthogonal indexing scheme relating to spread spectrum techniques in general
  • H04B2201/707—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation
  • H04B2201/70707—Efficiency-related aspects

Definitions

• the present invention relates to the minimization of the synchronization time required for a receiver, content in particular.
• UMTS Universal Mobile Telecommunication System
• any message received by a mobile terminal is scrambled on transmission and must therefore be descrambled by means of the same sequence of sequences as that initially generated by the transmitting base station.
• this descrambling must be carried out in synchronism with the scrambling carried out by the base station.
• WCDMA Wideband Code-Division
• synchronization constraints are all the more present at the level of mobile telecommunications terminals of the UMTS type, and more precisely at the level of the following two essential elements included in such a mobile terminal: - the RAKE receiver, or “Rake receiver” in English, which includes among other things the technical body responsible for controlling the synchronization, and in particular that relating to the CPICH pilot channel (for "Common Pilot Indicator Channel", in English or “Common pilot indicator channel” in French) ; - the cell detector, better known under the name of “cell searcher” in English, which operates according to at least the following three main steps: o step 1: search for the primary channel or “Primary Synchronization Channel” (P-SCH) in English; o step 2: synchronization carried out on the secondary channel, or “Secondary Synchronization Channel” (S-SCH) in English; o step 3: correlation measurement on the common pilot indicator channel or CPICH.
• P-SCH Primary Synchronization Channel
• S-SCH Secondary Synchron
• the “slewing” technique therefore amounts to accelerating or slowing down (see freeze) the generator polynomial to reach the desired state corresponding to an alignment of the data received.
• this terminal cannot descramble the received message, so that it loses information and it spends energy unnecessarily. It is therefore important to shorten as much as possible this synchronization delay which depends on the processing time imposed by the technique of
• Periodic generators of very long period are generally employed to produce pseudo-random bit sequences. Such a generator is generally produced by means of a linear feedback shift register (“Linear Feedback Shift Register”) clocked at the rate of a clock signal. The bits of the generated sequences correspond to the outputs of the flip-flops of the register.
• a typical application of the periodic generator is scrambling.
• a message to be transmitted is modulated on two channels, the phase I channel and the quadrature channel Q.
• Each of the I and Q channels is scrambled by means of a system of two generators (" x "and” y "), except that the state of generator X is offset from the state of Y by an interference value characterizing the base station.
• This scrambling code corresponds to a predetermined number of strokes clock.
• a second known solution of the prior art for reducing this waiting time consists in making a jump of a predetermined number of sequences (generally called “immediate shift") to the periodic generators.
• this solution known as “by memorizing masks”, significantly increases the complexity of the generators and the cost price of such devices, not necessarily justified for a mobile telephone terminal of the UMTS type. 3.
• Disadvantages of the Prior Art A first disadvantage of these techniques of the prior art is that they impose a synchronization delay which is sometimes significant but necessary for the terminal to recover the synchronism, this terminal not being able to directly descramble the received message, resulting in possible loss of information and unnecessary energy expenditure.
• a second major drawback associated with these prior art techniques is that they significantly increase the complexity of the generators to be implemented, which most of the time use hardware solutions (or “hardware” in English), which can oppose the constraints of miniaturization of mobile radiocommunication terminals and of the components that they integrate. 4. Objectives of the invention
• the object of the invention is in particular to overcome these drawbacks of the prior art.
• the present invention aims to overcome these drawbacks of the state of the art. More specifically, a first objective of the invention is to provide a generator making it possible to obtain very quickly, almost instantaneously see the desired synchronization or convergence value at the level of the generator polynomial, while guaranteeing very low consumption, during the slewing process at the Rake UMTS receiver.
• a second objective of the invention is to allow the elimination of the delay, sometimes significant, usually encountered in the processing of step 3 of the UMTS "Cell Searcher" and thus eliminate any risk of loss of a frame.
• Another objective of the invention is to provide such a generator, which is of reduced complexity, in terms of number of logic gates implemented in particular, compared to known techniques, and / or in terms of possibilities of using treatments. algorithmic and / or software.
• the invention aims to present an alternative of much less complexity to reduce the waiting time, in particular when the generators are late and thus favor the convergence of the pseudo-random generators in a given state d a predetermined position to be reached, which corresponds to the association of predetermined synchronization time intervals and of a synchronization symbol.
• An additional objective of the invention is therefore to propose a technique which can be applied both to a Rake UMTS receiver to give it instant synchronization capacity, and to the optimization of step 3 of operation of the “Cell searcher”, so that there is no longer any loss of time intervals during the correlation processing on the CPICH channel, nor any possible loss of frame. 5.
• Essential characteristics of the invention are achieved using a method of synchronization of a device for receiving scrambled data by means of at least one sequence. periodic interference organized in K time intervals each comprising N bit periods called symbols.
• Such a method comprises a step of calculating a synchronization value of at least one pseudo-random generator of the scrambling sequence, in a synchronization time interval and in a period of predetermined synchronization bits. It allows in particular and advantageously, during the calculation step, to progress in the scrambling sequence by hopping of at least one time interval and at least one bit period, by implementing a matrix calculation of the synchronization value.
• the matrix calculation implements a multiplication of an initialization value of the pseudo-random generator by at least one predetermined passage matrix.
• the method according to the invention makes it possible to progress in the sequence of bits by hopping at least one time interval, by calculating the value of the generator polynomial at the boundaries of the intervals, until the synchronization time interval is determined. . Also advantageously, the value of the pseudo-random generator at the boundaries of the time intervals is determined, from the value initialization, by successive multiplications by a time interval passage matrix.
• the value of the pseudo-random generator at the boundaries of the bit periods is determined, from the value of the generator at the boundaries of the intervals, by successive multiplications by a bit period transition matrix.
• Frame loss is reduced to a maximum of two CPICH symbols.
• the data is scrambled according to at least two scrambling sequences X and Y, and the initialization value for the sequence Y is fixed.
• the initialization value for the sequence X is characteristic of a device for transmitting scrambled data.
• the scrambling sequences X and Y are respectively obtained from the generator polynomials "x" and "y".
• the periodic scrambling sequence being organized in K time intervals each comprising N bit periods
• the symbol passing matrix for the sequence X is the matrix (M ⁇ ) N
• the interval passing matrix of time for said sequence X is the matrix M.
• the periodic jamming sequence being organized in
• the symbol passing matrix for the sequence Y is the matrix My and in that the value of the generator polynomial at the boundaries of the intervals for the sequence Y is determined from a table vectors associated with the polynomial generator of the sequence Y.
• the successive jumps of bit period have a value expressed in the form of a power of two, these bits being able to take only two values: zero or one.
• the Euclidean division of ⁇ by i then becomes very simple to perform.
• the synchronization method implements the UMTS standard ("Universal Mobile Telecommunications System” for "Universal mobile telecommunications system"), the bit periods then being CPICH symbols (for "Common Pilot Indicator Channel", in English or “Common Pilot Indicator Channel” in French).
• the reception device comprises at least one RAKE receiver and cell search means of the Cell Searcher type.
• the Rake receiver comprises the organ of the mobile terminal responsible for the servo relating to synchronization.
• the Rake receiver Upon awakening, it receives in particular a starting or initialization point, from which it performs the servo-control of the schedule for receiving the data received.
• the Rake receiver therefore has a dual function, a first one for synchronization control relative to the CPICH pilot channel, and a second one for synchronizing the data received.
• the cell searcher of a UMTS mobile terminal when switched on, performs the following three steps: step 1: search for the strongest transmitting station; step 2: determination of the primary channel or P-SCH (for “Primary Synchronization Channel” in English); step 3: synchronization on the secondary channel or S-SCH (for “Secondary Synchronization Channel” in English). It is from these last two steps in particular that the Cell Searcher is capable of delivering the coordinates for the start of the frame and slot time interval corresponding to the strongest transmitting station.
• the bit period passing matrix for the sequence X is the matrix:
• time interval passage matrix for the sequence X is the matrix:
• the invention also preferably relates to a device for receiving scrambled data by means of at least one periodic scrambling sequence, and organized in time intervals each comprising at least one bit period called symbol.
• a device according to the invention thus advantageously comprises means for synchronizing the device themselves comprising means for calculating a synchronization value of at least one polynomial generating the scrambling sequence, by progression in the sequence, by jumps of at least one bit period.
• the calculation means preferably implement a matrix calculation of the synchronization value.
• the calculation means comprise a first register comprising flip-flops outputting the bits of the sequence making it possible to obtain the synchronization value.
• each flip-flop is connected to the output of a multiplexer controlled by a selection signal (SEL). Also preferably, when the selection signal selects the input at the bottom of the multiplexer, the passage matrix M x is applied and when the selection signal selects the input at the top of the multiplexer, the passage matrix M is applied.
• SEL selection signal
• the reception device applies to fields belonging to the group comprising: the optimization of step 3 of the UMTS cell searcher; speeding up the slewing process of a UMTS rake receiver; optimizing the operation of a UMTS equalizer; - the pre-calculation of the initial value (or “seed” in English) of a linear feedback shift register (or “LFSR: Linear Feedback Shift Register” in English).
• LFSR Linear Feedback Shift Register
• Such a terminal thus preferably comprises means for synchronizing said reception means comprising means for calculating a synchronization value of at least one polynomial generating the scrambling sequence, by progression in the sequence by hopping at least minus one bit period, the calculation means implementing a matrix calculation of the synchronization value.
• the invention is based on a completely new and inventive approach for almost direct determination of the synchronization value ("scrambling" code) - given by a predetermined synchronization time interval and a synchronization symbol - of at least minus a polynomial generating a scrambling sequence, synchronization value, and with a minimum of processing.
• FIG. 2 illustrates the general implementation mechanism of “Turbo scrambling” (in English) or “scrambling turbo” in French, according to the invention
• - Figure 3 shows a linear feedback shift register (or "LFSR: Linear Feedback Shift Register” in English) simple to 7 states
• FIG. 4 illustrates the modifications made to the LFSR of FIG. 3 to accelerate the traversal in the sequence of its possible successive states
• FIG. 5 gives an example of an optimized sequence allowing a faster browsing of the states of the sequence of the LFSR of FIG. 3, following the modifications made in FIG. 4;
• FIG. 1 shows a linear feedback shift register
• FIG. 6 presents an example of modification made on an LFSR-X downlink descrambler making it possible to perform jumps of four states;
• - Figure 7 gives an example of hardware modification made on an LFSR-Y descrambler to be able to make jumps of four states;
• FIG. 8 gives an illustration of an LFSR-X defined in the 3G TS25.213 standard with eighteen flip-flops D all clocked by the same clock;
• FIG. 9 illustrates the results of the application of the mechanism according to the invention for the “accelerated slewing”.
• this sequence of the code (consisting of N “chips”) is unique for a given user and that it constitutes the coding key of the received signal; it is kept if the data symbol was 1, inverted otherwise.
• L is the length of the code and each symbol has a duration denoted Tb
• the new modulated signal has a bit rate N times greater than the signal initially sent by l user and will therefore use a frequency band N times wider.
• the receiver must perform the same operation, that is to say generate the same spreading sequence and multiply it with the received signal; the data encoded by this sequence are then restored.
• Each of the data sequences (11) Data 0 ... Data N can be divided into the form of regular time intervals (12) themselves composed of N bit periods (13) (or symbols) S 0 to S m .
• each sequence (11) of the scrambling code is made up of 38400 time intervals (12) to which the polynomial generating the scrambling code is applied to obtain the values of the scrambling code (14) X 0 ... X N , which then make it possible to recover the good values of the scrambled data transmitted R 0 ... R ⁇ (15), by application of the following formula: R ; ⁇ Datai XOR S t XOR X,.
• Such a method is based on a matrix calculation making it possible to jump the generator polynomial, directly from a first known position, to a second position also known and characteristic of the synchronization value.
• This approach is illustrated in FIG. 2 which makes it possible to better visualize the principle according to the invention consisting on the one hand in a succession of jumps over the time intervals until positioning on the desired time interval, then performing as many symbol jumps as necessary in this time interval, until positioning itself on the correct symbol value, the time interval and the symbol thus obtained being representative of the synchronization value desired to initiate descrambling of the sequence of data received.
• the synchronization value given by the association of a time interval reference and a symbol reference requires in the context of the treatments applied to the “Cell Searcher” and to the UMTS “Rake” receiver, to determine with accuracy the references of the CPICH time intervals and symbols corresponding to this value.
• This determination is carried out according to the following technique in the context of the Cell Searcher: 1) the generator polynomial is awakened; 2) the cell searcher having its own time counter (or "timer" in English), you never know where it is, especially since the time reference it uses is not the same as shared on the network. Therefore, during this second step, the cell searcher is left to determine the information concerning the synchronization value from its steps 1 (search for the strongest transmitting station and determination of the PCH channel).
• step 3 of the cell searcher is launched so as to obtain the measurements on the CPICH channel.
• the Cell searcher is the first block activated when the mobile terminal is switched on. It therefore retrieves the strongest transmitting station before carrying out its own synchronization.
• the scrambling sequence is cut first by time intervals or frames, then by symbol. For the Cell Searcher of the example of FIG. 2 for example, each time interval (20) or frame is divided into ten periods of 256 bits (21).
• the correct desired time interval value is then obtained by performing an iterative calculation from the starting interval (22) denoted “slot0,0”, by multiplication of each time interval by the time interval passage matrix M x : ⁇ YS / ort, 0 - - i M v ⁇ X 2560 * ⁇ YS / o.0,0 '" • ' ⁇ YSto / (i + l), 0 -" J M M X 2560 * ⁇ YSlot ⁇ ifiY
• the correct symbol value desired to recover the synchronization of the transmitted sequence is calculated from the starting symbol of the correct time interval obtained, by iterative multiplication with the passage matrix of symbols M x , as follows: Y _- M 256 * YY - M 256 * y
• FIG. 3 shows a very simple linear feedback shift register or LFSR, producing the 7 successive states following given by the flip-flops Q 0 , Q ⁇ and Q 2 , which output the bits of said sequence making it possible to obtain said desired synchronization value.
• the LFSR is modified to 7 states in FIG. 3 by adding three multiplexers (40, 41, 42) having a common SEL signal which can choose to connect the respective inputs of flip-flops Q 0 , Q ⁇ and Q 2 , or at the top input, or at the bottom input of said multiplexers, as illustrated in FIG. 4.
• the inputs (43, 44, 45) of each flip-flop Q 0 , Q x and Q 2 are therefore connected respectively to the output of one of the multiplexers (40, 41, 42) and controlled by a selection signal (SEL).
• SEL selection signal
• the advantage of the method according to the invention is multiple when it is applied to the LFSR: it allows first of all to precalculate in hardware or “hardware” in English, an initial SEED value, that is to say a starting value of the calculations corresponding to a scrambling code given by a base station), without having to provide multiplexers for preloading the 18 D-FFs.
• the 18 multiplexers implemented in the new architecture of FIG. 6, according to the invention make it possible to replace the eighteen preloading multiplexers usually implemented specially for preloading the LFSR. it also makes it possible, during a process of sequencing by group or “slewing” in English, to reach a predetermined state starting from a starting point (value of SEED for example), much more quickly and at frequency d identical clock.
• This matrix A corresponds to the LFSR-X defined in the 3G TS.25.213 standard, section 5.2.2. It is implemented materially by means of the architecture of FIG. 8 which integrates eighteen flip-flops (810) to (827), all clocked by the same clock.
• the i th component of the vector x k namely: x (i) k represents the state value of the i th th flip-flop (FIG. 8), obtained following the execution of a number k of clock ticks . Each coordinate of this vector therefore has the value of either "0" or "1".
• the vector x 0 is defined as:
• n 16 * i by therefore executing 16 * i clock ticks usually on the LFSR-X, starting from the known and predetermined initial state.
• FIG. 9 illustrates the advantage of the invention for implementing an accelerated slewing process.
• the line 91 represents the evolution of the states of the LFSR used at the level of the transmitting base station. Its evolution takes place in time Te (“Chips” time).
• Each transmitted data frame "traverses" the line 91 from a state S 0 referenced 92 to a state S n referenced 93 in FIG. 9, then returns to S 0 after S n .
• the straight line 91 therefore represents the evolution of the phase of the signal received at each instant.
• we want to start descrambling the received signal which is not normally possible since it would be necessary in this case to take the phase of the two LFSR X and Y of the modem, instantly in their states respective S t .
• the slewing mechanism usually known and used by the solutions of the prior art thus attempts to catch the straight line 91 of FIG. 9 via the straight line 95, but this by accelerating the timing of the two LFSR X and Y, for example by multiplying by eight the time “chip” Te.
• this approach then makes it possible to reach the straight line 91 at time t 3 (96) and to be in phase at this time with the received signal. Thanks to the LFSR X and Y according to the invention, which can switch to perform jumps of N states by clock strokes, it is now possible to catch the phase of the signal received at time t (97) situated well in advance.
• the LFSR-X is first of all initialize with the value of SEED corresponding to the scrambling code (“scrambling code” in English) of the transmitting base station of which one wishes demodulate the signal using the SEED pre-calculation method described for example in paragraph ⁇ .7.5.1;
• n 0 be the value of the time interval counter to be traveled (which performs modulo counts 38399 in the context of UMTS) corresponding to time t 0 (94). It then suffices to choose “j” such that j * N is greater than (n 0 + j) and that (jl) * N is less than (n 0 + j). By developing and solving these two inequalities, we determine the choice of the value of "j” such that: - - ⁇ j ⁇ -.

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• Synchronisation In Digital Transmission Systems (AREA)

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