WO2001061885A1 - Procedimiento para la repetición de señales en isofrecuencia y repetidor de señales en isofrecuencia - Google Patents
Procedimiento para la repetición de señales en isofrecuencia y repetidor de señales en isofrecuencia Download PDFInfo
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- WO2001061885A1 WO2001061885A1 PCT/ES2001/000035 ES0100035W WO0161885A1 WO 2001061885 A1 WO2001061885 A1 WO 2001061885A1 ES 0100035 W ES0100035 W ES 0100035W WO 0161885 A1 WO0161885 A1 WO 0161885A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/155—Ground-based stations
- H04B7/15564—Relay station antennae loop interference reduction
- H04B7/15585—Relay station antennae loop interference reduction by interference cancellation
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- the invention relates to a method for repeating isofrequency signals, of the type that is used in an isofrequency signal repeater and comprising the steps of: [a] reception of a first radio frequency signal through a receiving antenna , the first radiofrequency signal having a reception power, [b] optionally, conversion of the first radiofrequency signal to a process signal, [c] signal filtering, [d] signal amplification, [e] control automatic signal gain, [f] conversion, if applicable, of the process signal into a second radio frequency signal, [g] power amplification of the second radio frequency signal, [h] output filtering of the second signal radio frequency, and [i] transmission of the second radio frequency signal through a transmitting antenna, where a coupling between the transmitting antenna and the receiving antenna takes place.
- the invention also relates to an isofrequency signal repeater, of the type comprising: [a] a receiving antenna, capable of receiving a first radio frequency signal, with a receiving power, [b] a basic unit, capable of converting , optionally, the first radio frequency signal in a process signal, filter the signal, amplify the signal, perform an automatic gain control to the signal, and convert, if appropriate, the process signal into a second radio frequency signal, [ c] a power amplification unit, [d] an output filter, and [e] a transmitting antenna, where the transmitting antenna and the receiving antenna are capable of experiencing a coupling.
- the present invention therefore relates to a method of signal processing, and its corresponding device, the repeater, to be incorporated in DVB (Digital Video Broadcasting, digital television signal broadcasting) repeaters, of DAB ( Digital audio Broadcasting, broadcasting of digital radio signals), GSM, etc., which transmit on the same channel they receive, so they operate in isofrequency.
- DVB Digital Video Broadcasting, digital television signal broadcasting
- DAB Digital audio Broadcasting, broadcasting of digital radio signals
- GSM Global System for Mobile communications
- This invention allows these repeaters to have high gains, so that for the same level of received signal their transmitted power is increased and, consequently, their coverage area is increased.
- the ultimate purpose of the system is to cover the same service area with a smaller number of repeaters, thus reducing costs.
- the main limitation of repeaters operating in isofrequency lies in the fact that the frequency of reception and transmission of the repeater is the same, so there is a certain degree of coupling between the transmitting and receiving antennas, that is, the receiving antenna receives an echo of the transmitted signal. This may cause the repeater to oscillate. In addition, said coupling distorts the frequency signal. According to the state of the art, an effective way to avoid it, or to reduce it to non-significant values is obtained by reducing the gain of the repeater. However, this also results in reducing its coverage area.
- the repeaters used to date have attempted to alleviate this problem by, for example, the use of transmitting and receiving antennas whose coupling is reduced.
- this solution is expensive and unsatisfactory, since it is not possible to completely avoid coupling.
- the transmitted signal is reflected in an object close to the repeater (a tree, a car, etc.).
- the echo caused by the reflection in said object will introduce a coupling between antennas not foreseen at the time of designing its radiation diagrams, so it cannot be avoided.
- the invention aims to overcome these drawbacks.
- This purpose is achieved by a procedure for repeating signals in isofrequency of the type indicated at the beginning characterized in that it has a cancellation stage of said coupling between said transmitting antenna and said receiving antenna. That is, conceptually, it is not about avoiding the formation of the coupling or echo, which is a solution that has proven to be expensive and of limited results, but the procedure is able to "know" the link you are experiencing, and cancel it. Since the received signal is really the sum of two components: one component is "true" signal to be transmitted, and the other component is due to coupling, the method according to the invention eliminates the component due to signal coupling. received before transmitting it. This allows a series of additional advantages to be achieved. Thus, for example, the procedure allows to cancel in a simple way non-predictable links "a priori", such as those caused by the environment.
- the first radiofrequency signal is transformed or converted into a process signal, such as an intermediate frequency signal (Fl), a baseband signal, etc., but it is also possible to have the entire procedure carried out. on the first radio frequency signal, without conversion.
- a process signal such as an intermediate frequency signal (Fl), a baseband signal, etc.
- a further improvement is to perform an adaptive procedure that permanently estimates the coupling between antennas, even while the repeater is operational. This allows cancellation of time-varying couplings, such as those generated by elements of the mobile environment.
- the cancellation stage comprises a negative feedback. Since the received signal is really the sum of two components, as already indicated above, by the negative feedback the signal received is subtracted from a component equal (or very similar) to the component due to the coupling. In this way the signal that is transmitted is free of the component due to the coupling.
- the proposed procedure is more agile and cheaper than the existing ones, because its implementation does not require the alteration of the radiation patterns between antennas but a simple filtering of the transmitted signal that is easily reconfigurable and whose cost is reduced.
- the present invention also proposes an isofrequency signal repeater of the type indicated at the beginning characterized in that it includes a device suitable for canceling said coupling between said transmitting antenna and said receiving antenna.
- FIG. 1 generic block diagram of a signal repeater in conventional isofrequency.
- Fig. 2 simplified model of a signal repeater in conventional isofrequency.
- FIG. 3 block diagram of an example of a conventional isofrequency signal repeater.
- Fig. 4 simplified model of a signal repeater in conventional isofrequency, with the transfer function expressed in complex variable.
- Fig. 5 simplified model of an isofrequency signal repeater according to the invention.
- FIG. 6 block diagram of an isofrequency signal repeater according to the invention.
- Fig. 7 block diagram of an analog delay line.
- Fig. 8 time chart showing the variation of the repeater gain during the acquisition and monitoring phases.
- Fig. 9 a first alternative of signal sampling strategy used in the estimation of the filter response.
- Fig. 10 a second alternative of signal sampling strategy used in the estimation of the filter response.
- Fig. 11 a repeater with the entire intermediate frequency stage implemented digitally.
- Fig. 12 a third alternative of signal sampling strategy used in the estimation of the filter response.
- FIG. 13 diagram of an A / D conversion stage (analog / digital).
- Fig. 14 diagram of a D / A conversion stage (digital / analog).
- Fig. 15 adaptive filter broken down into two blocks.
- Fig. 16 block diagram of the analog implementation of the coefficient calculation according to the LMS algorithm.
- Fig. 17 analog embodiment of the correlation loop to obtain the coefficients.
- Fig. 18 section of two cells equivalent to that of Fig. 17, of the analog embodiment of the adaptive filter.
- Fig. 19 realization of an integrator by means of an operational amplifier.
- Fig. 20 resistive distributor scheme using a star network.
- FIG. 21 block diagram of a repeater according to the invention with a digital embodiment of the adaptive filter.
- Fig. 22 structure of the digital embodiment of the adaptive filter.
- Fig. 23 calculation of adaptive filter coefficients.
- Fig. 24 analog-digital conversions for the adaptive filter.
- Fig. 25 detailed structure of the adaptive filter.
- Fig. 26, Data Framer scheme.
- Fig. 28 structure of each of the coefficients ⁇ tap) of the filter.
- Table 1 content of the Look-up Table (LUT).
- FIG. 1 A generic block diagram of an isofrequency signal repeater is shown in Fig. 1.
- the incoming radio frequency (RF) signal SE (received by the receiving antenna) is converted to an intermediate frequency signal (Fl), and an intermediate frequency band pass filter FFI filters other unwanted received signals.
- Fl intermediate frequency signal
- FFI intermediate frequency band pass filter
- a converter converts the intermediate frequency signal back into a radio frequency signal, on the same channel as the received radio frequency signal.
- the signal is amplified to the required output level by an output AP power amplifier and ST is transmitted.
- An isofrequency signal repeater is substantially a filtered amplifier, and can be modeled as shown in Fig. 2. Within the corresponding signal bandwidth, the repeater acts as an AMP amplifier, followed by a cell. delay, of value ⁇ . This delay is due to the FFI intermediate frequency bandpass filter. The receiving and transmitting antennas are not perfectly isolated between them, so there is a coupling between the two that generates a feedback or feedback of the output signal in the input signal. This coupling effect can be modeled as a gain feedback line B, as shown in Fig. 2. Additionally, this coupling line also has a delay, but this delay is much less than the delay ⁇ , so That can be despised.
- the system transfer function is:
- the response in amplitude is not flat, but presents a curl that depends on the AB product, whose expression is:
- the profit margin which can be defined as the difference between the antenna isolation and the repeater gain:
- Gain margin (dB) -20 log (AB)
- the key point in the operation of an isofrequency signal repeater is the compromise between a minimum gain margin, which allows to obtain a maximum gain and, therefore, the maximum output power, and the maximum authorized amplitude curling.
- FIG. 3 A block diagram of an example of a signal repeater in conventional isofrequency is shown in Fig. 3. It comprises a basic UB unit, an AP power amplification unit and an FS output filter unit.
- the basic unit UB performs the following functions:
- the AP power amplification unit performs power amplification
- the output filter FS performs a final filtering of the signal to eliminate unwanted signals out of band.
- the basic unit UB consists of the following components:
- a first CONV1 converter which, in turn, comprises a radio frequency channel converter received at an intermediate frequency, an intermediate frequency filter FFI, and automatic gain control CAG.
- PRLIN linearity precorrector which is a circuit that compensates for the intrinsically nonlinear behavior of the amplification unit 4 - a second CONV2 converter, which includes an intermediate frequency converter to the output radio frequency channel and the output level control circuit.
- Figs. 4-5 illustrate the basic differences between existing isofrequency repeaters and the proposed invention, where the notation (s) refers to the representation of linear systems through their transfer function in terms of the complex variable s.
- Fig. 4 shows the basic block diagram of a conventional isofrequency signal repeater, where the main chain of the repeater receives an input signal SE and transmits an output signal ST. The main chain has been modeled with an H (s) response, and a G gain. The coupling between antennas, linearly modeled by an A (s) response, has also been indicated in dashed lines. In this way it is observed that the signal SE entering the REP repeater through the receiving antenna is the sum of the desired received signal S1 plus a coupling signal.
- Fig. 5 shows the block diagram of a repeater incorporating an embodiment of the proposed invention. It consists of a negative feedback of the transmitted signal ST, which is processed by the adaptive filter FAD, expressed in a complex variable such as F (s), and subsequently cancels the echoes, that is, the collection, at the input of the repeater.
- the proposed procedure is similar to the echo cancellation systems used in communications over long-distance telephone lines.
- the objectives are different.
- the objective of the proposed invention is to allow a repeater to be implemented with a large gain while remaining stable and, for example in the case of a DVB signal, the temporal dispersion of the transmitted signal ST is significantly shorter than the duration of the cyclic prefix.
- the desired objective is to eliminate the transmitted signal component introduced by the hybrid in step 2 from the received signal. 4-wire threads.
- A) architecture for the insertion of adaptive treatment in the isofrequency signal repeater B) filter implementation architecture for signal processing, C) algorithm for the estimation of the filter coefficients.
- analog configuration one of the possible configurations of the proposed invention, fully implemented with analog technology, is described in detail. This is hereinafter referred to as analog configuration. Subsequently, some digital alternatives for its implementation are described briefly, called digital configurations, which are distinguished from the analog in that they implement the adaptive filter digitally, but whose principles are common to it, so they should be considered parts of the same invention.
- FIG. 6 describes in more detail an embodiment of a repeater according to the invention, summarizing all the repeater stages that are relevant in the invention.
- the coupling has been modeled linearly and the repeater has an adaptive FAD filter that estimates the value of the coupling in the frequency band occupied by the signal and cancels its contribution to the transmitted signal ST, so that the repeater behaves as if it did not exist.
- the proposed repeater works at intermediate frequency (Fl).
- Fl intermediate frequency
- other alternatives can also be used operating in baseband or other frequencies, as discussed in the section on digital configurations.
- the repeater of Fig. 6 additionally has an RFF radio frequency filter, and an ARF radio frequency amplifier at the input of the equipment.
- the adaptive FAD filter takes the signal from the main chain after the CAG (Automatic Gain Control). This detail is important in order to establish the performance of the system, since in this case the temporal variations of the filter coefficients are only due to the variation of the couplings between antennas, but not to variations in the repeater gain. However, it is also possible to make the adaptive filter FAD take the signal before the CAG.
- CAG Automatic Gain Control
- the adaptive filter FAD is preferably implemented by means of an analog delay line and multipliers that weigh and add the signal to the output of each of the delay cells T (Fig. 7).
- the number of cells and multipliers depends on the compromise established between the complexity of the system and the level of cancellation of the links that you want to achieve.
- the delay introduced by each T cell must be chosen according to the intermediate frequency value and the signal bandwidth.
- the implemented filter has a periodic frequency response, so it is necessary to introduce certain restrictions in the delay in order to ensure that freedom is available to cancel the coupling between antennas in the entire frequency band occupied by the signal .
- the filter coefficients are preferably estimated adaptively and constantly while the repeater is in operation. This is because the coupling between antennas is unknown a priori, since it depends on the configuration of the main chain (antennas, filters and amplifiers used) and the environment where the repeater is located (nearby obstacles, reflectivity and their distance , -l ⁇
- An embodiment of the proposed invention estimates the filter coefficients based on the optimization of a quadratic cost function: the minimization of the signal power at point A of Fig. 6.
- This criterion is based on the property Statistical of incorrectness between the desired received signal and that induced in the antenna by the couplings, thanks to which it is demonstrated that the power at point A is minimal when it has been possible to cancel said couplings.
- it In order to ensure the proper functioning of the criterion, it must be ensured that the main chain introduces a delay equal to or greater than the minimum for which the desired incorrectness is met. Optionally you can enter this error delay in the conversion stage.
- the minimization of power at point A is equivalent to a criterion of minimum mean square error, which can be optimized with many different adaptive algorithms.
- LMS Least Mean Squares
- NLMS normalized LMS
- the algorithm used is not the object of this invention, and any algorithm of which its convergence and good performance in monitoring can be used can be used (see other alternative algorithms in the digital configurations section).
- the FAD adaptive filter encounters two basic restrictions.
- the first restriction is the need to guarantee a minimum delay in the main chain, as discussed above. This delay can be introduced in said conversion stage.
- the second restriction lies in the fact that the coupling can cause a signal of a level much lower than the desired signal on the receiving antenna (otherwise the repeater would oscillate), so that the signal to Noise (SNR) for the purpose of coupling identification is very low. This forces to force a very slow evolution of the adaptive system coefficients in order to compensate for the loss of SNR with a temporary averaging of the signal.
- Fig. 5 shows the closed loop structure of the REP isofrequency repeater, the coupling between antennas and the FAD adaptive filter.
- This structure causes cancellation errors to be fed back to the system and to the transmitted signal, which may cause the system to oscillate - remember that stability depends on the loop gain G ⁇ (s) - (A (s) -F (s )) -. To avoid this, it is advisable to provide mechanisms that ensure that the system remains stable at all times.
- This drawback which does not appear in the echo cancellation systems used in communications over long-distance telephone lines, makes it advisable to establish two phases in the operation of the proposed invention: the FADQ acquisition phase and the FSEG monitoring phase (Fig. 8 ).
- the FADQ acquisition phase is performed only once, during the initialization or start-up of the repeater.
- the repeater gain is kept reduced (G ⁇ n ⁇ ), so that it is stable regardless of the cancellation level achieved by the adaptive system.
- the adaptive algorithm estimates the value of the optimal coefficients of the adaptive filter and reduces the coupling to levels below the desired one.
- the gain is kept low for a sufficient time to allow the convergence of the algorithm and, subsequently, increases slowly until reaching its usual value ( Gfin ).
- the repeater operates normally, having reached the desired gain and cancellation levels.
- the adaptive filter adaptation algorithm remains in operation to detect and follow possible variations in the frequency response of the coupling between antennas without having to restart the repeater.
- the analog configuration of the invention has two basic limitations. First, the limitations on complexity that it imposes on by itself the fact that it is analog, either in the number of coefficients of the adaptive filter, in the type of adaptive filter or even in the adaptive algorithm used. Secondly, the technological problems linked to the implementation of the adaptive algorithm such as the offset of the integrators used in the LMS, although alternatives can be found that alleviate the seriousness of this problem (see [2]). However, a preferred solution to both problems is to use, at least partially, digital technology, so the alternatives offered by the digital configuration of the proposed invention are described below.
- Figs. 9, 10 and 12 correspond to different sampling strategies of the signal used in estimating the response of the FAD adaptive filter
- Fig. 11 corresponds to the case in which it is decided to digitally implement the entire Fl stage (frequency intermediate) of the repeater.
- the signal can be regenerated (demodulation and modulation), greatly improving the performance of the repeater
- the sampling of the signals can be performed in baseband (called l / Q sampling), so that the analytical signal is recovered, or in the pass-band signal (called Fl sampling), either in the signal in Fl or transferred to another lower frequency that is more convenient from a sampling point of view.
- sampling alternatives discussed below generation of the analytical signal, heterodination
- a / D converters results in four possible configurations that differ from each other by the fact of working with real or complex coefficients and / or error signals.
- the four combinations lead to similar solutions and cancellation levels, all of them require a different design of the sampling frequency and the number of adaptive filter coefficients, although this design is always based on the principles already set forth for the analog configuration.
- adaptive algorithms have a faster convergence in those configurations that work with complex coefficients, but this improvement is compensated by a greater technological complexity of the implementation of the A / D and D / A conversion.
- the choice of the sampling frequency will depend on the same parameters as in the analog configuration already mentioned (intermediate frequency value adopted in the repeater and signal bandwidth) as well as the selectivity of the filters in the main chain.
- the A / D and D / A conversion stage have a different implementation depending on whether one chooses sampling in l / Q or Fl.
- Fig. 13 shows an outline of the A / D conversion stage.
- the FAL anti-aliasing filter and the local oscillator (f,) are or are not necessary depending on the sampling chosen and how selective the main chain filters are.
- Fig. 14 shows a diagram of the D / A conversion stage.
- the FRE reconstructor filter compensates for the part of the distortion introduced by the D / A converter that has not been digitally corrected.
- the application or not of Local oscillator depends on the type and frequency of sampling used, while the FPB pass-band filter is only necessary if heterodination with the local oscillator is applied and the rear filters of the main chain are not selective enough.
- the adaptive filter can theoretically compensate for such distortions, in practice, especially in multi-carrier systems such as the DVB, it cannot be adapted quickly enough to follow these carrier disturbances.
- the filter can be implemented through an online delay architecture or through a lattice network.
- an impulse response filter of finite (FIR) or infinite (MR) duration can be used.
- IIR filters achieve better performance for the same number of coefficients, but present limitations in their combination with adaptive algorithms. If the environment where the repeater is located causes the very late transmitted signal to appear in the echo receiver antenna (with a delay much longer than the sampling period of the filter), it is advisable to decompose the adaptive filter into two blocks FAD I and FAD II (see fig 15), one of them, the FAD I, operating with the transmitted signal and the other, the FAD II, with the same signal delayed a time interval similar to the time of appearance of the late echoes.
- the filtering process can be implemented in the temporal or frequency domain.
- the use of the FFT or other filter banks with multi-rate (multirate) structures allows reducing the computational cost and improving the convergence of the adaptive algorithm ([10], [5]).
- the frequency implementation of adaptive filters operating in coupling environments between antennas subject to temporary variations limits the tracking capacity of said changes and, in addition, always causes the introduction of a delay in the adaptive filter that can limit its ability to cancel the couplings.
- the adaptive filter coefficients can be estimated with any algorithm that guarantees convergence to the correct solution, that is, the one in which the adaptive filter correctly estimates the coupling between antennas, and which, in addition, is able to follow its temporal variations.
- algorithm that guarantees convergence to the correct solution, that is, the one in which the adaptive filter correctly estimates the coupling between antennas, and which, in addition, is able to follow its temporal variations.
- minimization of the statistical mean power of the error minimum mean squared error
- II minimization of the temporary average power of the error (least squares). Both criteria can be used in both delay line architecture and lattice architecture.
- the stochastic gradient algorithms calculate the gradient with a few iterative applications of the differential calculation chain rule
- said algorithm is a non-linear extension of the LMS called backpropagation algorithm ([1])
- the gradient d The error as a function of the filter coefficients must be derived by the chain rule. If Fig. 6 is observed, the error signal at the output of the adaptive filter is the one that, duly amplified, is transmitted by the repeater.
- the LMS algorithm is an approximation of the gradient that allows reducing the calculation with respect to the chain rule, which would really have to be applied only if the intermediate frequency filter FFI, shown in Fig 6, introduces an appropriate delay, the transmitted signal will be incorrect with the error signal and the LMS will make an increasingly valid gradient approximation
- the most feasible and effective algorithm is the Kalman filter or vacancies of the same RLS or Recursive Least Squares and the fast Kalman filter
- the implementation via lattice netting is preferable to the delay line, since it allows to easily monitor the stability of the adaptive filter during the convergence phase.
- the estimation of the filter coefficients can be made by descending gradient algorithms, algorithms based on the Steiglitz-McBride methodology or on hyperstable algorithms ([12], [7]).
- the first group is based on the minimization of a quadratic error criterion, either based on the output error or the equation error.
- the minimization of the output error (eg using the RPE or Recursive Prediction Error algorithm [9]) is preferable, since the cost function based on the latter does not guarantee convergence to the optimal solution in relation conditions Low noise signal, as is the case with the proposed invention.
- the third group algorithms is the widely known SHARF or Simplified Hyperstable Adaptive Recursive Filter, which has the desired qualities in an adaptive algorithm.
- An example of an analogue embodiment of a repeater for DVB signal is described, which is based on an adaptive impulse response filter of finite duration FIR structure as shown in the
- Fig. 7 composed of a delay line. As illustrated in Fig. 7, the input signal E of the adaptive filter is injected into the delay line. Subsequently, the signals present at the output of each delay are multiplied by their respective coefficients, and finally the results of such multiplications are added to obtain the output signal S of the adaptive filter.
- obtaining the value of the coefficients is based on the LMS or Least Mean Squares algorithm.
- Fig. 16 shows the implementation by means of a correlation loop of the coefficient calculation according to the LMS algorithm. Said algorithm calculates each of the coefficients according to the following expression:
- the signal x (t) is that of the delay output
- the signal r (t) is the one that is present in the receiving antenna
- e a (t) is the error signal after cancellation, since (t) is the set of coefficients.
- ⁇ 3 is the adaptation constant, which sets the convergence speed of the algorithm, as well as the magnitude of the oscillation of the coefficients with respect to the final solution.
- the elements M1 and M2 are multipliers, the INT element is the integrator and the SUM element is the sum of the signals multiplied by the respective coefficients.
- Single frequency or isofrequency repeaters usually have intermediate frequency processing, which allows the use of high selectivity filters.
- the realization of the adaptive filter can be carried out at the same intermediate frequency of the repeater, or at a second lower intermediate frequency, in case the possible advantages of operating at a lower frequency compensate for the increase in complexity by having to add a converter first to second intermediate frequency before the adaptive filter, and another second to first intermediate frequency converter, at the output of said filter.
- the block diagram of the implementation example at hand is the one shown in Fig. 6. Blocks used
- Fig. 17 shows the block diagram of one of these cells, where it is seen that an x (t-iT) signal enters, a DIS distributor distributes it, on the one hand, to a delay T to obtain an x output ( t- (i + 1) T), on the other hand, to a multiplier M2, and, on the other hand, to a multiplier M1.
- the error signal e (t) also arrives at the multiplier M1.
- Fig. 18 shows a two cell section, CEL1 and CEL2, of the analog embodiment of the adaptive filter.
- Delay blocks can be made using the following techniques:
- SAW Surface acoustic wave delay
- Resonator circuits for example LC, ceramic or dielectric.
- Transmission lines for example coaxial, microstrip or stripline lines.
- multipliers can be made using the following techniques:
- Integrators Integrators can be performed using the following techniques:
- Fig. 19 shows an embodiment of the integrator by means of an operational amplifier, where E indicates the input and S the output of the integrator.
- FIG. 20 An exemplary embodiment of a resistive distributor by means of a star resistor network is shown in Fig. 20, where E also indicates the input and S the outputs of the distributor.
- Signal amplifiers can be performed using the following techniques:
- the adder adds the signals obtained at the output of each of the M2 multipliers of the cells.
- Fig. 21 the block diagram of the transmitter is also shown for DVB signal, in which the adaptive filter is implemented digitally. Similar to the analog case, the RF input signal SE is converted to intermediate frequency (Fl), where a Fl FFI filter rejects possible out-of-band signals, and finally converts it back to RF. In the digital embodiment, the corresponding A / D and D / A conversions are necessary, as shown in Fig. 21.
- the operation of the transmitter is as follows: the signal r [n] received by the antenna (which is actually composed of the desired signal plus the echoes caused by the transmitting antenna) an estimate s [n] of the signals is subtracted unwanted obtained by the adaptive filter FAD, obtaining an error signal e [n] that will pass through the FFI filter of Fl and will be converted back to RF.
- the structure of the adaptive filter made digitally is shown in Fig. 22. Essentially it is a FIR filter of variable coefficients, where these are periodically updated by the LMS algorithm. For instant n, the LMS algorithm calculates the new coefficients as follows:
- This operation is performed for each of the filter coefficients.
- the constant ⁇ has the function of adjusting the adaptation step. The higher its value the faster the algorithm will converge; in return, the coefficients will have a greater oscillation around the optimal solution. There is, therefore, a compromise between speed of convergence and stability of the coefficients around the optimal solution.
- FIG. 25 A more detailed structure of the adaptive filter is that shown in Fig. 25.
- Data-Framer DF Its function is to fragment the input data x [n] (12 bits) into four parts, resulting in 3 bits to which a control bit is added. Because four cycles will be required to process each sample, the system clock frequency must be four times the sampling frequency.
- Table Generator TG It is responsible for calculating the partial products of each coefficient and loading them into the LUT (ook-Up Table) of the corresponding tap.
- Each Tap has its own coefficient assigned, and is responsible for multiplying it by the input data.
- Adder tree This is a registered adder tree that obtains the sum of all partial results delivered by the coefficients.
- the 12-bit data enters a REG12 register at the FMUE sampling frequency, and exits, through a REGC control register fragmented into 4 parts of 4 bits each (each of these parts is known as octet), at a frequency 4xFMUE 4 times higher than the FMUE sampling frequency.
- the three bits of the lowest weight of each octet correspond to three bits of the input data; the bit of greater weight is of control, and only one is worth when the fourth and last octet of the data is being processed.
- bits 5, 4 and 3 are selected (the next three bits of less weight) and the control signal is still zero. Then, when the counter is worth 2, bits 8, 7 and 6 are selected, with the control signal still equal to zero. Finally the counter is worth 3, the bits are selected
- TG Generator This is responsible for calculating the partial products of each coefficient according to Table 1.
- Mux5 The function of Mux5 is to send to the output register either a zero or the output of the adder.
- the Mux5 control signal is the OR of the 3 bits of the lowest counter weight. This allows us to select a zero for memory positions 0 and 8 (as shown in Table 1).
- the adder is fed back through its own output, getting the results for addresses 1 to 7 and 9 to 11. Addresses 12 to 15 require negative results, so through Mux4 we select the complement to 2 of the coefficient. Finally, through Mux6 we select a zero for addresses 12 to 15, since from this moment the results become negative.
- Fig. 28 shows the structure for each of the tap that make up the filter. It consists of three distinct parts:
- Time Skew Buffer TSB This is a 4x4 bit shift register, in this way the TSB is able to host a sample integer (divided into 4 parts of 4 bits each). Each clock cycle delivers an octet to the Partial Product Multiplier PPM and also to the next tap.
- the First_oct signal is also output from the TSB, which is activated only when the octet of the lowest weight of the four that make up the sample is leaving.
- the Time Skew Buffer TSB receives the deadly information from the REGC control register.
- Partial Product Multiplier PPM It consists of two RAM memories (called LUT: Look-Up-Table) that store the partial products of the coefficient according to table 1. At the same time you access one of the LUTs to read the partial result of the multiplication, the Table Generator TG is writing in the other LUT, using the data and addr buses, the partial products corresponding to the new coefficient that the LMS algorithm will have calculated.
- the multiplexers Mux ⁇ and Mux9 are controlled by the bank_sel signal and are complementary, that is, when one selects its input 0 the other selects its input 1 and vice versa. This allows the addr and data signals to be routed to the corresponding LUT.
- the Mux10 multiplexer also controlled by the bank_sel signal, selects the data that comes out of the LUT that contains the partial products of the current coefficient (it should be remembered that in the meantime the other LUT is being updated with the partial products of the new coefficients).
- the two write_en signals that enable writing to the corresponding LUT are generated by the two AND doors and the bank_sel and tap_sel signals.
- Scaling Accumulator SCA Its mission is to properly accumulate the partial results of each octet to get the complete multiplication solution (24 bits in total). It is observed that it is an adder fed back by its own output, conveniently scaled (the 13 bits of the most weight are fed back and the bit of the highest weight is replicated three times). Mux11, which is controlled by the first_oct signal, allows the first octet to pass directly to the output; the other three octets that make up the sample pass through the adder. Obviously all the steps and elements described above are schematic, to facilitate the understanding of the invention.
- the order indicated in the stages of the procedure is purely a descriptive order and does not have to coincide with the actual order of the procedure. It is only intended to say that the process comprises said steps, that is, that it includes them, but it is not being indicated that the sequence of carrying out the stages is the one indicated.
- the stages of filtering, amplification and automatic gain control of the process signal that, as we have already indicated above, are usually carried out in several steps, they do not always follow the order indicated in the text, it is even frequent that the different steps of one stage are intertwined with the steps of the other stages. Therefore, it is convenient to insist on the fact that the stages mentioned in the text and the claims only indicate the existence of said stages, without restricting the number of steps in which they are carried out or the order in which they take place.
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Radio Relay Systems (AREA)
- Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
- Variable-Direction Aerials And Aerial Arrays (AREA)
- Amplifiers (AREA)
- Control Of Amplification And Gain Control (AREA)
- Reduction Or Emphasis Of Bandwidth Of Signals (AREA)
Abstract
Description
Claims
Priority Applications (9)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
ES01903794T ES2218379T3 (es) | 2000-02-18 | 2001-02-08 | Procedimiento para la repeticion de señales en isofrecuencia y repetidor de señales en isofrecuencia. |
US10/203,940 US7043203B2 (en) | 2000-02-18 | 2001-02-08 | Process for re-transmitting single frequency signals and a single frequency signal repeater |
EP01903794A EP1261148B1 (en) | 2000-02-18 | 2001-02-08 | Method for repeating isofrequency signals and isofrequency signal repeater |
AU2001231766A AU2001231766B2 (en) | 2000-02-18 | 2001-02-08 | Method for repeating isofrequency signals and isofrequency signal repeater |
AT01903794T ATE263459T1 (de) | 2000-02-18 | 2001-02-08 | Verfahren zur zwischenverstärkung von isofrequenzsignalen und isofrequenzsignal- zwischenverstärker |
BRPI0108495-0A BRPI0108495B1 (pt) | 2000-02-18 | 2001-02-08 | Processo para retransmitir sinais de freqüencia individuais e um repetidor de sinal de freqüência individual |
DE60102570T DE60102570T2 (de) | 2000-02-18 | 2001-02-08 | Verfahren zur zwischenverstärkung von isofrequenzsignalen und isofrequenzsignal-zwischenverstärker |
JP2001560562A JP2003523690A (ja) | 2000-02-18 | 2001-02-08 | 単一周波信号の再送信方法と単一周波信号中継器 |
AU3176601A AU3176601A (en) | 2000-02-18 | 2001-02-08 | Method for repeating isofrequency signals and isofrequency signal repeater |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
ES200000379A ES2160087B1 (es) | 2000-02-18 | 2000-02-18 | Procedimiento para la repeticion de señales en insofrecuencia y repetidor de señales en isofrecuencia. |
ESP200000379 | 2000-02-18 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2001061885A1 true WO2001061885A1 (es) | 2001-08-23 |
Family
ID=8492361
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/ES2001/000035 WO2001061885A1 (es) | 2000-02-18 | 2001-02-08 | Procedimiento para la repetición de señales en isofrecuencia y repetidor de señales en isofrecuencia |
Country Status (10)
Country | Link |
---|---|
US (1) | US7043203B2 (es) |
EP (1) | EP1261148B1 (es) |
JP (1) | JP2003523690A (es) |
CN (1) | CN100393000C (es) |
AT (1) | ATE263459T1 (es) |
AU (2) | AU3176601A (es) |
BR (1) | BRPI0108495B1 (es) |
DE (1) | DE60102570T2 (es) |
ES (2) | ES2160087B1 (es) |
WO (1) | WO2001061885A1 (es) |
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- 2001-02-08 BR BRPI0108495-0A patent/BRPI0108495B1/pt not_active IP Right Cessation
- 2001-02-08 JP JP2001560562A patent/JP2003523690A/ja active Pending
- 2001-02-08 EP EP01903794A patent/EP1261148B1/en not_active Expired - Lifetime
- 2001-02-08 WO PCT/ES2001/000035 patent/WO2001061885A1/es active IP Right Grant
- 2001-02-08 CN CNB018052134A patent/CN100393000C/zh not_active Expired - Fee Related
- 2001-02-08 AU AU3176601A patent/AU3176601A/xx active Pending
- 2001-02-08 US US10/203,940 patent/US7043203B2/en not_active Expired - Fee Related
- 2001-02-08 DE DE60102570T patent/DE60102570T2/de not_active Expired - Lifetime
- 2001-02-08 AU AU2001231766A patent/AU2001231766B2/en not_active Ceased
- 2001-02-08 AT AT01903794T patent/ATE263459T1/de not_active IP Right Cessation
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Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7826801B2 (en) | 2006-03-07 | 2010-11-02 | Airpoint | Adaptive forward error corrector and method thereof, and TDD radio repeating apparatus using the same |
IL269198A (en) * | 2019-09-09 | 2021-03-25 | Goodtechcom Ltd | System and method for installing and buffering a cellular radiation source |
Also Published As
Publication number | Publication date |
---|---|
AU2001231766B2 (en) | 2004-12-09 |
DE60102570D1 (de) | 2004-05-06 |
US20030022626A1 (en) | 2003-01-30 |
CN1404666A (zh) | 2003-03-19 |
AU3176601A (en) | 2001-08-27 |
ES2160087R (es) | 2001-11-01 |
JP2003523690A (ja) | 2003-08-05 |
CN100393000C (zh) | 2008-06-04 |
EP1261148B1 (en) | 2004-03-31 |
BRPI0108495B1 (pt) | 2015-05-19 |
ATE263459T1 (de) | 2004-04-15 |
ES2160087B1 (es) | 2003-03-01 |
ES2218379T3 (es) | 2004-11-16 |
US7043203B2 (en) | 2006-05-09 |
ES2160087A2 (es) | 2001-10-16 |
EP1261148A1 (en) | 2002-11-27 |
BR0108495A (pt) | 2002-12-17 |
DE60102570T2 (de) | 2005-01-05 |
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