ES2306557B1 - PROCEDURE FOR THE TRANSMISSION AND RECEPTION OF SIGNS WITH DIFFERENT SAMPLING FREQUENCIES. - Google Patents

Abstract

Procedure of transmission and reception of signals with different sampling frequencies.

It allows to reduce the cost of the receivers by using fast Fourier transforms, of periodically, to convert the signals received from the temporal domain to the frequency domain, with a number of samples such that its realization results in a lower cost. The procedure of the invention introduces a small loss in exchange for its realization, but said loss of benefits is assumed in the transmission of coexistence signals or other signals commonly used in communication systems since allows the use of different sampling frequencies, both in the transmitter as in the receivers, which reduces the cost.

Description

Procedure of transmission and reception of signals with different sampling frequencies.

Object of the invention

The present invention, as expressed in the statement of this specification refers to a procedure of transmission and reception of signals with different sampling frequencies The technical field of the invention is that of data telecommunications in any transmission medium, and its main advantage is that it allows the use of receivers simpler, and therefore of lower cost, when always using Fast Fourier Transforms (FFTs) with a number of samples such that they are easily realizable, regardless of whether sampling frequencies in the transmitter and receivers are different. In this way the number of sampling frequencies that They can be used is unlimited.

In this document FFT refers to the usual abbreviation (of Fast Fourier Transform) of a algorithm that allows to calculate the discrete Fourier transform (DFT) more efficiently.

Background of the invention

In multiple communications systems They use signals to indicate certain events to the receiver. These signals do not carry data, but the only necessary information for the receiver is to detect if they have been transmitted or not.

Usually these signals are simple signals,  generated from several repetitions of a base signal.

For example, these types of signals are used to distinguish communications in coexistence procedures. The Spanish patent ES2221803 stands out in the state of the art of title "Access procedure to the transmission medium of multiple communications nodes on the power grid "where the transmitter periodically sends coexistence signals, such as previously described, to allow access to the channel. He procedure of the invention presented in this patent can be used in combination with the previous one, enabling receivers simpler that are able to detect the signals of Coexistence of the transmitter with a low cost.

Also these signals also tend be used at the beginning of the data frames to indicate the beginning of them. This is the case of another antecedent of the invention, constituted by the 802.11a standard, in which also similar signals are sent at the beginning of the transmitted frames, so it could be used in combination with the procedure claimed to obtain the advantages indicated above.

Description of the invention

To achieve the objectives and avoid drawbacks indicated in previous sections, the invention It consists of a procedure for transmitting and receiving signals with different sampling frequencies in the transmitter and between receivers, where there are multiple communications and are transmitted signals constructed from N consecutive repetitions of a base signal of duration Ts in which the base signal can change from sign in each repetition, and it is characterized because each receiver Performs fast Fourier transforms (FFTs) periodically, with a period Ts seconds, for which it takes a number of samples which allows to perform the FFT easily, although the duration of the FFT is somewhat greater or less than the Ts period.

In addition, the procedure envisages filling in with zeros the input samples to the FFTs generated from the received signal to avoid the introduction of the same sample in two consecutive FFTs.

The Ts period, indicated above, is a integer number of samples of the clocks of the different transmitters and receivers, so that transmitters can generate a signal of duration Ts and the receivers can calculate displacement between FFTs without error.

Finally, the transmission pre-calculates the base signal of duration Ts and is stored in a memory that is read N consecutive times to generate the signal.

Then, to facilitate a better understanding of this descriptive report and being an integral part of the same, some figures are accompanied in which with character illustrative and not limiting the object of the invention.

Brief description of the figures

Figure 1.- Represents an example with a transmitter and several receivers with different frequencies of sampling between which there is communication.

Figure 2.- Shows an example of the signals sent by the transmitter of figure 1 and the samples used following the procedure of the invention in each of the receivers

Description of an embodiment of the invention

Then the description of a exemplary embodiment of the invention, referring to the numbering adopted in the figures.

Figure 1 shows an example in which there is a transmitter (1) and two receivers, (2) and (3), capable of receiving signals emitted by the transmitter. In this specific example of realization, the generated signals are coexistence signals that They are transmitted on multiple carriers. In addition, the transmitter of the coexistence signals uses an 80 MHz clock while the  Receiver clock frequencies are 85 and 75 MHz respectively. In other cases the frequency range may be greater or less than the one presented in this example of realization, no being limiting for the performance of the procedure of the invention.

Figure 2 shows the arrival of signals at the time of the scheme shown in figure 1 and the samples which are used in the FFTs in both receivers.

Coexistence signals consist of repetition of a base signal of duration Ts = 6.4 \ mus (4), which corresponds to a whole number of samples in the three clocks (specifically 512 samples at 80 MHz, 480 samples at 75 MHz and 544 samples at 85 MHz). In the upper part of figure 1 you can observe the signal of coexistence in transmission (1), which It consists of 5 repetitions of the base signal.

Each receiver will perform FFTs (9) consecutively with separation of Ts = 6.4. Displacement initial (offset) with respect to the transmitted signal is random for each receiver, (5) in the receiver (2) and (6) in the receiver (3), but such displacement does not affect the process, since important is that consecutive FFTs (9) are carried out on the same signal. If the signs alternate with each repetition, the FFTs (9) are performed on the same signal but with the sign changed. Then the phase in each carrier is calculated, and the difference in phase with the same carrier in the previous symbol. Finally I know add differences in carrier groups to have a reliable detection.

In the state of the art the FFTs of the receivers would be performed on the samples found in the period Ts (4) of the received signal, this is 544 samples for the first receiver (2) 85 MHz and 480 for the second receiver (3) 75 MHz. East number of samples, not being a power of 2, is very inefficient to carry out, which entails extra costs in the concrete realization of the receivers.

With the process of the invention, the receiver does not have to perform FFTs over a time Ts (4), but that the duration may be somewhat greater or less as long as the displacement between consecutive FFTs is the period Ts. This so recipients can take as many samples as they wish to perform the FFTs so that they are easily realizable (this It is normally that the number of samples is a power of 2). In this specific example of embodiment both the first and the second receiver takes 512 samples, so the period of time in which the samples received are entered into the FFT for first receiver (2) will be approximately 6.02 \ mus (7) (something less than Ts and corresponding to 512 samples at 85 MHz) and for second receiver (3) will be approximately 6.83 \ mus (8) (something greater than Ts and corresponding to 512 samples at 75 MHz).

In the second receiver (3) there will be overlap between  the FFTs to be carried out in two consecutive Ts (4) periods. For avoid it, you can fill with zeros the last samples of the FFT in order not to enter the same sample in two Consecutive FFTs.

Also in the transmitter it is necessary to perform an IFFT (fast reverse Fourier transform) of duration Ts to generate the base signal and that can have any number of samples (that is, not necessarily a multiple of 2). This does not It is no problem since the base signal only has to be calculate once you can always be the same, and therefore you can precalculate and store in memory to be used later.

The process of the invention produces a small loss of benefits since the carriers of the receiver are not in the same position as in the transmitter, and by therefore, the receiver is calculating the phases in frequencies that correspond to the lobes of the transmitter sync (which are due to the frequency representation of a signal of limited duration, that is, limited by a rectangular function in time), with what that the signal amplitude is somewhat smaller and 1 noise affects something plus. In practice this loss is small and perfectly Assumable in multiple applications, such as coexistence of multiple communications systems.

Claims (4)

1. Procedure for transmitting and receiving signals with different sampling frequencies, where there are multiple communications and signals constructed from N consecutive repetitions of a base signal of duration Ts in which the base signal can change sign at each repetition are transmitted, characterized in that each receiver performs fast Fourier transforms (FFTs) periodically, with a period of Ts seconds, for which it takes a number of samples that allows the FFT to be easily performed, even if the duration of the FFT is somewhat greater or less than the Ts period. 2. Procedure for transmitting and receiving signals with different sampling frequencies, according to claim 1, characterized in that the input samples to the FFTs generated from the received signal are filled with zeros to avoid the introduction of the same sample in two FFTs consecutive. 3. Procedure for transmitting and receiving signals with different sampling frequencies, according to claim 1, characterized in that the period Ts is an integer number of samples of the clocks of the different transmitters and receivers, so that the transmitters generate a signal of duration Ts and the receivers calculate the displacement between FFTs without error. 4. Procedure for transmitting and receiving signals with different sampling frequencies, according to claim 1, characterized in that in transmission the base signal of duration Ts is pre-calculated and stored in a memory that is read N consecutive times to generate the signal.