WO2008141704A1

WO2008141704A1 - Method of transmission by a transmitter comprising a single antenna, of a set of data destined for a receiver comprising antennas

Info

Publication number: WO2008141704A1
Application number: PCT/EP2008/002998
Authority: WO
Inventors: Ali Khaleghi; Ghaïs EL ZEIN
Original assignee: Institut National Des Sciences Appliquees; Centre National De La Recherche Scientifique
Priority date: 2007-04-19
Filing date: 2008-04-15
Publication date: 2008-11-27
Also published as: FR2915333B1; FR2915333A1

Abstract

The invention relates to a method of transmission by a transmitter comprising a single antenna, of a set of data destined for a receiver comprising at least one first and one second antenna. The method comprises the steps of: obtaining, (E401) on the basis of information representative of a first existing channel between the antenna of the transmitter and a first antenna of the receiver, a first time reversal filter, obtaining, (E401) on the basis of information representative of a second existing channel between the antenna of the transmitter and the second antenna of the receiver, a second time reversal filter, dividing (E404) the data set into at least a first and a second data stream, filtering (E404) signals representative of the first data stream by the first time reversal filter, filtering (E404) signals representative of the second data stream by the second time reversal filter, transmitting (E405) the sum of the first and second filter streams.

Description

A method of transmitting by a transmitter having a single antenna, a set of data to a receiver comprising antennas.

The present invention relates to a transmission method by a transmitter comprising a single antenna, a set of data to a receiver comprising at least a first and a second antenna.

In telecommunication systems based on the transfer of electromagnetic waves by a transmitter, the electromagnetic waves received by the receiver are not identical to those transferred by the transmitter.

Because of the multiple paths associated with the different reflections of an electromagnetic wave on obstacles, when a transmitter sends an electromagnetic wave, the receiver receives a plurality of electromagnetic waves shifted in time.

New telecommunication methods take advantage of this plurality of received electromagnetic waves. Among these methods, that of time reversal, or Time Reversal in English terminology, transmitted electromagnetic waves is particularly promising. Classically, in a channel learning phase, the transmitter emits an electromagnetic wave, for example For example, in the form of a pulse, the receiver records the received electromagnetic pulses, transfers information representative of the pulses received to the transmitter which calculates a time reversal filter so as to return the transmitted signal temporally. The representative signals of data to be transmitted are filtered by the time reversal filter and then transmitted to the receiver. The transmitter thus transfers a plurality of electromagnetic pulses so that the receiver receives an electromagnetic pulse.

Time reversal has been studied in Single Input Single Output (SISO) telecommunication systems, in which the transmitter and the receiver each have a single antenna. In this case, the multiple paths are combined in phase, and the equivalent channel approaches an ideal Gaussian additive white noise channel.

(BBAG) or AWGN for Additive White Gaussian Noise. Consequently, the transmission capacity according to the theory of Shannon, expressed in bits per second per Hertz, is of the order of C _TR = _ _SISO IOG ₂ (l + /?) Where p is the signal-to-noise reception.

In order to improve the transmission capacity, MISO (Multiple Input Single Output) telecommunication systems have been proposed in which the transmitter comprises M antennas, with M> 1 and the receiver an antenna. These telecommunication systems make it possible to improve the signal-to-noise ratio with a factor M and offer a transmission capacity expressed in bits per second and per Hertz of the order of C _TR _ _MISO = log ₂ (l + Mp). The realization of such telecommunication systems is expensive, particularly for the realization of the transmitter.

The object of the invention is to solve the disadvantages of the prior art by proposing a method and a device for emitting electromagnetic signals to a receiver comprising at least a first and a second antenna which make it possible to increase the capacitance transmission while being simple and inexpensive to perform.

To this end, according to a first aspect, the invention proposes a transmission method by a transmitter comprising a single antenna, a set of data intended for a receiver comprising at least a first and a second antenna, characterized in that the process comprises the steps of: obtaining, from information representative of a first channel existing between the antenna of the transmitter and the first antenna of the receiver, a first time reversal filter,

obtaining, from information representative of a second channel existing between the antenna of the transmitter and the second antenna of the receiver, a second temporal reversal filter,

dividing the data set into at least a first and a second data stream,

filtering signals representative of the first data stream by the first time reversal filter,

filtering signals representative of the second data stream by the second time reversal filter,

- Issuing the sum of the first and second filtered streams. Correlatively, the present invention relates to a device for transmitting a set of data to a receiver comprising at least a first and a second antenna, characterized in that the transmission device comprises a single antenna and comprises:

means for obtaining, from information representative of a first channel existing between the antenna of the transmission device and the first antenna of the receiver, a first time reversal filter,

means for obtaining, from information representative of a second channel existing between the antenna of the transmission device and the second antenna of the receiver, a second temporal reversal filter,

means for dividing the data set into at least a first and a second data stream,

signal filtering means representative of the first data stream by the first time reversal filter,

means for filtering signals representative of the second data stream by the second time reversal filter; means for adding and transmitting the first and second filtered streams.

Thus, the transmission capacity is increased without the transmitter being expensive to produce. In addition, this capacity thus obtained is greater than that of a conventional SIMO system (Single Input Multiple Output) without time reversal, with or without knowledge of the channel at the transmitter. According to a particular embodiment of the invention, the transmitter determines an intercorrelation between the first channel and the second channel and decides on a processing to be applied for the transmission of the data streams if the determined cross-correlation is greater than a predetermined threshold. Thus, when interference exists between the channels, they strongly penalize the quality of reception of the data. In deciding on a treatment to be applied for the transmission of the data streams if the determined cross-correlation is greater than a predetermined threshold, the present invention guarantees the good reception of the data by the receiver. According to a particular embodiment of the invention, the processing consists in applying, for the transmission of the streams to be filtered by time reversal, the same time reversal filter to the signals representative of the first and second data streams, the time reversal filter being obtained from information representative of one of the channels existing between the antenna of the transmitter and one of the antennas of the receiver.

Thus, the present invention ensures good reception of data by the receiver and according to the level of interference, all the channels will be used or not.

According to one particular embodiment of the invention, the receiver comprises M antennas, with M> 2 ,. For each channel existing between the antenna of the transmitter and each of the M antennas of the receiver, a time reversal filter is obtained. The cross-correlation is determined by calculating the convolution between at least one channel and each time reversal filter, and the processing to be applied for the transmission of the data streams, if at least one determined cross-correlation is greater than the predetermined threshold, is to divide the data set in N <M data stream and filtering each data stream respectively by a time reversal filter different from the or each time reversal filter for which the cross correlation is greater than the predetermined threshold.

Thus, the present invention ensures good reception of data by the receiver and according to the level of interference, all the channels will be used or not. According to one particular embodiment of the invention, the processing to be applied to the second stream is a circular permutation of the coefficients of the filter filter by time reversal the signals representative of the second data stream, the coefficients being shifted to the right according to the first formula: k

or left by circular permutation according to the second formula:

where k is a positive integer value, N is the number of filter coefficients and _n is the nth coefficient of the filter. According to a particular embodiment of the invention, k is equal to the integer value of x * N where:

0 <x ≤ 0.10; for the first formula,

0 <x ≤ 0.25; for the second formula.

Thus, the present invention ensures good reception of data by the receiver while maintaining a high transmission capacity.

The present invention also relates to a transmission system comprising a transmitter as mentioned above and a receiver whose first and second antennas of the receiver are spaced less than 0.4 times the wavelength corresponding to the minimum frequency of the filtered flux spectrum. . Thus, the mutual coupling between the first and second antennas is important and modifies the antenna radiation pattern.

The characteristics of the invention mentioned above, as well as others, will appear more clearly on reading the following description of an exemplary embodiment, said description being made in connection with the attached drawings, among which: FIG. . 1 represents the architecture of the telecommunication system in which the present invention is implemented; FIG. 2 is a block diagram of the transmitter data transmission module according to a first embodiment of the present invention; FIG. 3 shows a block diagram of the transmitter data transmission module according to a second embodiment of the present invention; FIG. 4 represents an algorithm executed by an emitter according to the present invention.

Fig. 1 represents the architecture of the telecommunication system in which the present invention is implemented.

In the telecommunication system according to the present invention, a transmitter 10 comprising a single antenna Ante transfers data to a receiver 20 having M antennas denoted Antrl at AntrM, where M is at least two. This telecommunication system is called a simple multiple-input-output system known by the acronym SIMO.

According to the invention, the transmitter 10 emits a test electromagnetic wave such as a pulse via its antenna Ante. The receiver 20 measures the response of the channel h _/ (t), h.2 (t), H _M (O for each of its antennas Antrl, Antr2 to AntrM .The response of each channel h _m (t) with m- M is representative of the multiple paths, propagation delays and attenuations of the transmitted electromagnetic signal.The receiver 20 transfers information representative of the response of each channel h _m (t) to the transmitter 10. The transmitter 10 has a filter calculation module 120 which determines M time reversal filters C _/ (t), C ₂ (t), C _M (O- each time reversal filter C _m (t) is calculated respectively from h _m (t ) with m ^≈ \ Mr.

The transmitter 10 comprises a transmission module 100. The transmission module 100 breaks down the data set to be transmitted to the receiver 20 into at most M data streams xi (t), X2 (t) and X _M (O which are respectively filtered by a respective time reversal filter Ci (O, C2 (t), C _M (O) to finally be summed and transmitted simultaneously to the receiver 20. The transmission module 100 will be described in more detail with reference to FIGS. 3.

Transmitter 10 includes an intercorrelation computation module 130 which determines at least the intercorrelation between at least one channel and another channel.

For example, the intercorrelation between at least one channel and another channel is performed by calculating the convolution between the channel and the filter filter by time reversal the signals representative of a data stream transmitted on the other channel.

The transmitter 10 includes a decision module 110 which determines at least one processing to be performed on at least one data stream according to the at least one computed cross-correlation.

Each channel hj (t), h2 (0,

j ° ^ue I ^e as a filter and the data stream Xi (O _^'χ 2 (0 to X _M (O are respectively received by the antennas Antrl AntrM receiver 20. The receiver 20 has M receive modules RXi , RX ₂ to RX _M - Each receive module RX _m , with m = \ to M, processes the data flow x _m (0 with m = \ to M. The data streams are then grouped into a set of data by a PS series parallel converter. If X (t) is the set of data to be transmitted, xj (t), X ₂ (t) and _M X (O are the M data streams, the electromagnetic signal S (t) transferred by the transmitter 10 is equal

M to: S {i) = Σx _m (t) CC _m (t) where représente represents the convolution product.

Each time reversal filter C _m (t) is calculated according to the following formula: C _m {i) = A _m h _m {-t) where A _m is the emission amplitude of the data stream

A _m is for example equal to where

|| / t _m I is the average power of the channel h _m between the Ante antenna of the transmitter and the Antrm antenna of the receiver. According to the first example, a channel having a low average power on reception has only a small part of the transmission power. According to the second example, each channel has the same transmission power. The signal received by the reception module RX _m is given by: y _m (t) = S (t) h _m (t) + N (t)

M y _m {t) = A _m R _h, (* 0® "( ') + Σ _k R _hkhm A (t) ®x _k (t) + N (t) k = \ k ≠ m wherein N ( ή is the noise at the receiver 20, R _hh (t) = h _m (-t) h _m (() is the autocorrelation of h _m (t) representative of the desired signal.

R _h (t) = h _k {-t) h _m (t) represents the convolution between k! C ^th temporal reversal filter _k (t) and the m ^th channel h _m or in other words the cross-correlation between the / ^th channel of the m h _k and ^ιeme channel hm

The transmission capacity of the SIMO system according to the present invention is of the order of: C _S IMO = ^{M iθ} + U + ± M ⁽ \ -N + IJ) where S is the received power, / the power of the interference signals and N the power of the noise at the receiver 20. The division by M of the The power of the received signal is due to the normalization of the transmitted power. Moreover, this equation also shows a linear increase in capacity as a function of the number of antennas. This result shows an improvement of the capacity compared to a conventional SIMO system not using time reversal whose capacity of

(S transmission is given by: C _slMO _ _classi = log ₂ \ ^{] + M} -

The present invention thus proposes a technique exploiting the knowledge of the channel and making it possible to increase the transmission capacity.

It should be noted here that the interference signals depend on the decorrelation between the channels which is defined by the spreading of the propagation delays of the reflected electromagnetic waves, the angular spread of the reflected electromagnetic waves and the effective distance of decorrelation. between the antennas Antrl to AntrM of the receiver 20. The effective distance is different from the physical distance. When the antennas Antrl to AntrM are spaced less than 0.4 times the wavelength corresponding to the minimum frequency of the spectrum of the transmitted signal, the mutual coupling is important and modifies the radiation pattern of antennas Antrl to AntrM. The effective decorrelation distance is reduced, which further decorrelates the channels.

Fig. 2 shows a block diagram of the data transmission module of an emitter according to a first embodiment of the present invention.

The transmission module 100 comprises a parallel serial converter SP1, M time reversal filters Cj (t), C2 (t), CM (O) ^{and an} add summing circuit The parallel serial converter SP1 divides the data set to be transmitted. at most M data flow xi (t), X ₂ (t) and X _M (O- According to the value calculated by the intercorrelation calculation module 130 of the cross correlation between each channel / z * with k = 1 at M, and each channel h _m with m ≠ k, the decision module 110 controls the parallel serial converter SP1 not to form a stream xrft) from the data set X (t) if the correlation between the channel h _k and the channel h _m , at the time of the decision on the k ^th channel, is greater than a predetermined threshold which depends on the level of interference supported by the system. Each intercorrelation is obtained by determining the convolution between each time reversal filter C _k (t) with A = 1 to M, and each channel h _m , with m ≠ k.

The maximum M data streams xι (t), X ₂ (t) and X _M (O are respectively filtered by a time reversal filter Ci (O, Cj (O-, C _M (OP ^or finally summed by the summing circuit add and transmitted simultaneously to the receiver 20.

Each data stream is thus simultaneously transmitted to the receiver 20.

Fig. 3 shows a block diagram of the data transmission module of a transmitter according to a second embodiment of the present invention.

The transmission module 100 comprises a parallel serial converter SP2, M time reversal filters Ci (t), C ₂ (t), C _M (O-M permutation Permcirl PermcirM permutation means and a summation circuit add.

The parallel serial converter SP2 divides the data set to be transmitted into M data streams xj (t), X2 (0 and XM (O-

Each Permcirk circular permutation means is capable of performing a circular permutation of the coefficients of the time reversal filter C _m (0-

OR

Each time reversal filter C _m (0 is equal to: C _1n (t) = Σa>"δ (t - τ _n ) n = 0 where a _n represents the ^nth coefficient of the rn ^th filter, δ (0 is the function of Dirac, τ _n is the value of the time shift of the coefficient.

The filter coefficients are shifted to the right by circular permutation according to the first formula:

(** - * ₊ »0 <« <To: a "ï a V .. *. N ≥ k or left by circular permutation according to the second formula:

where k is a positive integer value. According to a particular embodiment of the invention, by using the circular permutation, the value of the peak power in reception can undergo a reduction which depends on the value of the offset operated. Moreover, these losses are not identical for a right or left circular permutation.

For example, for losses set to a decibel, the offset must be limited to the integer value of x * N where:

0 <x ≤ 0.10; for the first formula, 0 <x ≤ 0.25; for the second formula. According to the value calculated by the intercorrelation calculation module 130 of the convolution between each time reversal filter Ck (O ^and each channel h _m , with m ≠ k, the decision module 110 controls whether or not the Permcirk circular permutation means for it to switch the coefficients of the time reversal filter C _k (t) if the convolution between the time reversal filter C _k (t) and the channel h _m is greater than a predetermined threshold which depends on the interference level tolerated by the system.

The M data streams xi (t), X ₂ (t) and x _M (t) are respectively filtered by a time reversal filter Ci (t), C ₂ (t), C _M (O to finally be summed by the summation circuit add and transmitted simultaneously to the receiver 20.

Fig. 4 represents an algorithm executed by the transmitter according to the present invention.

In step E400, the transmitter 10 receives, from the receiver 20, information representative of the response of each channel Ji] (O, Ji2 (0, H _M (O for each of the antennas Antrl, Antr2 to AntrM of the receiver 20 .

In the next step E401, the data transmission device 10 determines

M time reversal filters C] (O, C ₂ (t), C _M (O- Each time reversal filter C _m (t) is calculated according to the following formula: C _1n (t) - A _m h _m (- t).

In the next step E402, the data transmission device 10 calculates for k varying from 1 to M and m varying from 1 to M and m ≠ k, the convolution * M. (<) = ** (-0 ® Λw (O •

In the next step E403, the transmitter 10 determines whether each convolution value, calculated at the decision time, is greater than a predetermined threshold. If a cross-correlation value is greater than the predetermined threshold, the data transmission device 10 decides on a processing to be performed on the data stream corresponding to the cross-correlation value greater than the predetermined threshold.

For example, if at the time of decision on the channel between the antennas Ante and Antrl, only R _{Λ Λ} (t) = h ₂ (-t) A A, (t) is greater than the predetermined threshold, remitter 10 decides to perform a process on the data stream X2 (0- In the next step E404, the transmitter 10 applies the process.

According to the first embodiment, and according to the above-mentioned example, the data set is divided into MI data streams x _m (0 with m = \, 3 to M According to the second embodiment, and according to the above-mentioned example, the data set is divided into M data stream and the Permcir2 circular permutation means is activated.

If all intercorrelation values are below the predetermined threshold, the data set is divided into M data flow x _m (t) with m = 1 to M.

In the next step E405, the data streams are summed and transmitted.

Of course, the present invention is not limited to the embodiments described herein, but encompasses, on the contrary, any variant within the scope of those skilled in the art and particularly the combination of different embodiments of the present invention.

Claims

1) Method of transmission by a transmitter comprising a single antenna, a set of data to a receiver comprising at least a first and a second antenna, characterized in that the method comprises the steps of:

obtaining, from information representative of a first channel existing between the antenna of the transmitter and the first antenna of the receiver, a first time reversal filter,

obtaining, from information representative of a second channel existing between the antenna of the transmitter and the second antenna of the receiver, a second time reversal filter, dividing the data set into at least one a first and a second data stream,

- Issuing the sum of the first and second filtered streams.

2) Method according to claim 1, characterized in that the method further comprises the steps of:

determination of an intercorrelation between the first channel and the second channel; decision of a processing to be applied for the transmission of the data streams if the determined cross-correlation is greater than a predetermined threshold.

3) Process according to claim 2, characterized in that the processing to be applied for the transmission of the streams comprises filtering, by the same time reversal filter, the signals representative of the first and second data streams, the time reversal filter. being obtained from information representative of one of the channels existing between the antenna of the transmitter and one of the antennas of the receiver.

4) Method according to claim 2, characterized in that the receiver comprises M antennas, with M> 2, for each channel existing between the antenna of the transmitter and each of the M antennas of the receiver, a time reversal filter being obtained , the intercorrelation being determined by calculating the convolution between at least one channel and each time reversal filter, and in that the treatment to be applied to the transmission of the data streams, if at least one determined cross-correlation is greater than the predetermined threshold, consists in dividing the data set into N <M data stream and filtering each data stream respectively by a time reversal filter different from the or each time reversal filter for which the cross correlation is greater than the predetermined threshold.

5) Method according to claim 2, characterized in that the treatment to be applied to the second stream is a circular permutation of the filter coefficients filtering by time reversal signals representative of the second data stream, the coefficients being shifted to the right according to the first formula "= K ^* K ^*" ° ^≤ n ≥ ^"<k ^k or left by circular permutation according to the second formula: {a _{n + k} 0 ≤ n <N - k

Q ^ι -nn - NKlΔ .k1r + n ≥ N - k where k is a positive integer, N is the number of filter coefficients and _n is the nth filter coefficient. 6) Method according to claim 5, characterized in that k is equal to the integer value of x * N where:

0 <x ≤ 0.10; for the first formula, 0 <x ≤ 0.25; for the second formula.

7) Device for transmitting a set of data to a receiver comprising at least a first and a second antenna, characterized in that the transmission device comprises a single antenna and comprises:

means for obtaining, from information representative of a first channel existing between the antenna of the transmission device and the first antenna of the receiver, a first time reversal filter, means for obtaining from information representative of a second channel existing between the antenna of the transmitting device and the second antenna of the receiver, of a second time reversal filter,

means for dividing the data set into at least a first and a second data stream; means for filtering signals representative of the first data stream by the first time reversal filter;

signal filtering means representative of the second data stream by the second time reversal filter, means for adding and transmitting the first and second filtered streams.

8) System for transmitting a set of data from a transmitter to a receiver comprising at least a first and a second antenna, characterized in that the transmitter comprises a single antenna and comprises: obtaining, from information representative of a first channel existing between the antenna of the transmitting device and the first antenna of the receiver, a first time reversal filter,

means for dividing the data set into at least a first and a second data stream,

means for filtering signals representative of the first data stream by the first time reversal filter; means for filtering signals representative of the second data stream by the second time reversal filter;

means for adding and transmitting the first and second filtered streams and in that the first and second antennas of the receiver are spaced by less than 0.4 times the wavelength corresponding to the minimum frequency of the flux spectrum filtered.