Communication using transmission of triply polarized waves

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

(Cross-reference to related literature) This application is a partial continuation of US Patent Application No. 09/379151 filed on August 23, 1999.

【0002】

[Technical field to which the invention belongs]

The present invention relates to wireless communication. In particular, the present invention relates to the use of polarized communication signals.

【0003】

[Conventional technology]

Traditional systems transmit from point A to point B over a free space path that directly connects points A and B, and signals that differ only in their polarization mode can have at most two independent channels. It accepts the long-accepted constraints imposed by Maxwell's equations. The reason for this constraint is the fact that the polarization transmission coefficients between points A and B form a rank 2 matrix T. Therefore, prior art has long considered that a signal can be effectively transmitted from point A to point B with at most two polarizations, thereby realizing at most two independent communication channels. .. This is shown in the conventional system of FIG. In this system, the transmitter 10 has one dipole antenna 11 and another dipole antenna 12, and the receiver 20 has one dipole antenna 21 and another dipole antenna 22. Normally, the dipole antennas 11 and 12 are oriented perpendicular to each other, so that the dipole antennas 21 and 22 are also oriented vertically. The most efficient transfer of information from the transmitter to the receiver is in the plane perpendicular to the line where antennas 11 and 12 connect points A and B, and antennas 21 and 22 are planes of antennas 11 and 12. It occurs when it is in a plane parallel to and the dipole antenna 11 is also in a plane containing the antenna 21. Needless to say, other spatial arrangements of antennas 11, 12, 21 and 22 can also be used to transmit information from the transmitter to the receiver, but in this case the efficiency of the communication is reduced (transmit signal energy). Most of them cannot be recovered), and the processing load on the receiver increases (antennas 21 and 22 detect a part of the signals of antennas 11 and 12).

【0004】

[Problems to be Solved by the Invention]

Paths regardless of whether the transmitter has a single antenna (polarized or unpolarized) or two polarized antennas (as shown in Figure 1) There remains a problem with multi-pathing. In particular, multiple paths can cause destructive interference in the received signal and indoor environment, which is a serious problem. This is because there are many reflective surfaces that cause multiple paths, and these reflective surfaces are in the vicinity (resulting in a multiple path signal with significant amplitude).

【0005】

The present invention has been accomplished on the basis of the above, the purpose of which is to improve the problem of fading in a multi-road environment by using a third polarization direction that efficiently generates a third communication channel. , The existence of the reflective surface is to be an advantage from the drawbacks.

【0006】

[Means for solving problems]

By using a receiver that receives and uses polarized signals to include energy in the three orthogonal directions of free space, the fading problem in a multi-road environment is ameliorated and the presence of reflective surfaces benefits from drawbacks. .. Further improved behavior is obtained when the transmitter uses polarized signals so that transmission signal energies are present in three orthogonal directions in free space to transmit information over three independent communication channels. A third communication channel, which was not used in conventional communication systems, can be used to transmit more information or to transmit information with improved polarization diversity, thereby overall communication efficiency. Is improved. The transmission signal having the third polarization direction is generated, for example, by using a transmitter having a third dipole antenna orthogonal to the first and second dipole antennas of the transmitter. To utilize a signal with a third polarization direction, for example, the receiver also has three dipole antennas that are orthogonal to each other.

【0007】

BEST MODE FOR CARRYING OUT THE INVENTION

The arrangement in FIG. 1 is shown to use dipole antennas that are orthogonal to each other. The arrangements disclosed in the following figures and described herein also show that they use dipole antennas that are orthogonal to each other. However, it should be understood that these arrangements are presented herein for the sake of brevity. Other than the three dipole antennas that are orthogonal to each other, and the use of antenna arrangements other than effectively transmitting from one point is within the scope of the invention. The main attribute of the receiving antenna arrangement is the ability to receive signals that are effectively polarized in all three directions orthogonal to each other. However, the transmit and receive antennas used are expected to be constructed to include a single physical hardware unit (base station, mobile radio terminal, etc.).

【0008】

As mentioned above with reference to the perspective view presented in FIG. 1, the positioning of the antennas 11 and 12 with respect to the antennas 21 and 22 is important only if the maximum energy is transferred from the transmitter 10 to the receiver 20. In such a situation, the plane on which the antennas 11 and 12 reside must be parallel to the plane on which the antennas 21 and 22 reside, and these planes are perpendicular to the line 30 connecting points A and B. Must. The arrow 13 indicates the polarization signal on the plane xz, and the arrow 14 indicates the polarization signal on the plane yz. For example, arrows 13 and 14 indicate the same signal strength.

【0009】

Needless to say, regardless of the orientation of antennas 11 and 12 (relative to antennas 21 and 22), all transmitted signals can be represented by signals that are polarized along the x-axis, y-axis and z-axis of FIG. .. Figure 2 shows the arrangement of the receiver's antenna in some arbitrary orientation with respect to the transmitter's antenna. In this arrangement, the arrangement of antennas 11-12 is rotated and the plane on which the antennas 11 and 12 are present is perpendicular to line 31. The drawing is two-dimensional and it can be difficult to perceive the direction of line 31. Therefore, point 15 is at a distance R from antennas 11 and 12 along line 30, and if you rotate line 30 around point A to coincide with line 31, point 15 will move to point 16. Suppose. To move from point 15 to point 16, it must move along the x, y, and z axes. This means that signals polarized orthogonal to line 31 are considered to have signal components along the x, y and z axes, and these signals do not show three independent signals. It is shown visually.

【0010】

Mathematically, it can be expressed as follows.

[Number 1]

<img file="JP2001237757A_D0001.tif" />Or r = Hs Where s₁And s₂Is the signal transmitted by the antennas 11 and 12, and the matrix H, as its element, is the transmission coefficient of the propagation channel between points A and B for the signal polarized in the three orthogonal directions. Including, r₁, R₂, And r₃Is a signal present at point B of the receiver in the three orthogonal directions. The rank of the matrix is the largest square array in the matrix where the determinants do not disappear. Therefore, the rank of the matrix H is 2.

[Outside 1]

<img file="JP2001237757A_D0002.tif" />【0011】

Needless to say, since the arrangement shown in FIG. 2 has only two receiver antennas, the equation (1) is modified as follows.

[Number 2]

<img file="JP2001237757A_D0003.tif" />【0012】

For receiver and transmitter antennas, if one of the rows in H contains all zero coefficients and the row containing all zero coefficients is the first or second row, then one of the receiver antennas is nothing. It can be arranged so that it will not be received. It is also possible that one of the coefficients in a non-zero row is zero, so that one receiving antenna receives only one of the transmitting signals. This is, this is not related to those of the signal itself r₁= h₁₁s₁+ h₁₂s₂Receive a signal such as s₂From s₁Not bad enough to separate.

【0013】

However, considering the arrangement of FIG. 3, in this arrangement, the antenna of the transmitter 10 is arranged as shown in FIG. 2, but the receiver 20 is a third dipole antenna orthogonal to the dipole antennas 21 and 22. Has 23. The relationship between the transmitted signal and the received signal is as shown in Eq. (1). In this case, there are three detection signals. Therefore, even if one of the lines in equation (1) is transformed to zero, there are still two executable signals. In addition, s₁And s₂Since the signals are transmitted in different polarization directions, the coefficients of the T column cannot all be zero. Therefore, the transmission signal s₁And s₂Is always possible. From the above, it can be understood that by using the third receiver antenna, it is not necessary to arrange the transmitter antenna and the receiver antenna.

【0014】

Alternatively, the antenna of transmitter 10 is arranged so that it is maximally received by receiver 20 (as shown in FIG. 1), but there is a second reflection path between the transmitter and the receiver. Think. It has an inclined surface 40 and is shown in FIG. Here, the transmitter has two antennas 11 and 12, and the receiver has two antennas 21 and 22. It can be easily observed that there are paths 41-42 starting at transmitter 10 and reflecting off slope 40 to reach receiver 20. The direction of the signal arriving via paths 41-42 is not along path 30 (ie, it enters B at an angle other than 90 degrees with respect to the plane containing antennas 21 and 22). The signal that reaches point B is represented as follows.

[Number 3]

<img file="JP2001237757A_D0004.tif" />Or [Number 4]

<img file="JP2001237757A_D0005.tif" />Or [Number 5]

<img file="JP2001237757A_D0006.tif" />【0015】

Furthermore, in the arrangement where there are only two receiver antennas at point B, Eq. (4) becomes as follows.

[Number 6]

<img file="JP2001237757A_D0007.tif" />【0016】

Here, the likelihood of a row where all terms are zero is very small. Fading can be reduced even when this possibility is small in the arrangement of FIG. In this arrangement, the receiver is the signal r of equation (6).₁, R₂And r₃Has antennas 21, 22 and 23 formed to receive.

【0017】

FIG. 6 shows an arrangement in which both the transmitter 10 and the receiver 20 use three mutually orthogonal antennas in an environment having multiple paths. In this case, the transfer function is represented by r = H's, where, [Number 7]

<img file="JP2001237757A_D0008.tif" />【0018】

Therefore, it can be shown that the rank 3 matrix H'is capable of maintaining three independent information channels. Therefore, the transmitter 10 of FIG. 6 is capable of advantageously transmitting three independent signals, whereby the arrangement of FIG. 6 is a high data rate transmission in a cellular environment where multiple paths exist, such as indoors. It is a very suitable arrangement for. A third independent channel can be used to transmit additional information, to transmit information with additional redundancy, or for a combination of the two.

【0019】

FIG. 7 shows a block diagram of the structure of a transmitter / receiver unit using three dipole antennas orthogonal to each other. Antennas 21, 22 and 23 are respectively connected to a port, which receives a signal from that antenna and sends the signal to that antenna. For example, in FIG. 7, the antenna 21 sends a signal to the receiver 30, and the transmitter 31 sends the signal to the antenna 21. The receiver 30 gives the output signal to the detector 32, and the detector 32 receives the signal r.₁Is detected and sent to processor 100. Similarly, the receiver 40 receives the signal of the antenna 22 and gives the output signal to the detector 42, which the detector 42 signals r.₂Is detected and sent to processor 100. Similarly, the receiver 50 receives the signal of the antenna 23 and gives the output signal to the detector 52, which is the signal r.₂Is detected and sent to processor 100. In conventional means (ie, means involving the reception of known pilot signals), the element of H'is known to processor 100, which is s = (H').^-1Signal s by evaluating r₁, S₂And s₃To calculate. s = (H')^-1r. For transmission, signals X1, X2 and X3 are given to encoders 33, 43 and 53, respectively, where these signals are encoded and given to transmitters 31, 41 and 51, respectively. Transmitters 31, 41 and 51 send their signals to antennas 21, 22 and 23.

【0020】

The above discloses the principles of the invention by exemplifying embodiments. It should be understood that other embodiments can also be used and that the features of the illustrated embodiments do not necessarily constitute a feasible design requirement. As an example, it is desirable to have three dipole antennas that are orthogonal to each other in space, but it should be understood that the arrangement may not necessarily have this orientation. Thus, within the scope of the present disclosure, the term "orthogonal" includes, if necessary, "substantially orthogonal".

【0021】

Broad definition of tripole antenna In the above discussion, an exemplary transmit or receive antenna arrangement according to the invention with three dipole elements oriented in directions orthogonal to each other has been described. In fact, the antenna arrangement corresponding to the present invention, referred to herein as a "tripole antenna", can be characterized by more general terms. The broad definition of a tripole antenna is well explained with reference to Figure 8. FIG. 8 shows an antenna 110 having three signal connections 121-123. Antenna 110 may consist of a single element or may include multiple antenna elements. Antenna 110 can be used to transmit or receive high frequency signals. The excitation of the antenna 110 by the incident electromagnetic wave induces an output current at some or all of the signal connections 121-123.

【0022】

Each output current has an amplitude whose magnitude is real. Each output current also has a relative phase shift. In conventional practice, the combination of magnitude and relative phase shift can be represented as a complex number, which is referred to herein as compound current amplitude. Output i corresponding to each of signal connection parts 121 to 123₁, I₂And i₃(Represented as compound current amplitude) is nicely integrated into the output vector below.

[Number 8]

<img file="JP2001237757A_D0009.tif" />【0023】

According to the broad definition herein, the antennas 110 have polarized waves that are orthogonal to each other and have their respective induction output vectors i.⁽¹⁾, I⁽²⁾And i⁽³⁾Is a tripole antenna when three incident plane waves can be found together in a composite three-dimensional vector space. The "polarized waves orthogonal to each other" may include not only linearly polarized waves but also circularly polarized waves and elliptically polarized waves.

【0024】

The above definition can be shown more accurately by the following matrix.

[Number 9]

<img file="JP2001237757A_D0010.tif" />In these terms, the derived output vectors, when J is the maximum rank matrix, are collectively spread over a composite 3D vector space. Within the scope of the present invention, J is considered to be the maximum rank if the maximum ratio of the singular value to the minimum is 50 or less. Therefore, in mathematical terms, three incident plane waves have been found that induce an output current such that the antenna 110 has polarizations orthogonal to each other and the matrix J has a maximum singular value less than 50 times the minimum singular value. If you get it, it's a tripole antenna.

【0025】

In certain embodiments, including exemplary embodiments with three orthogonal dipole elements, the maximum singular value is no more than 10 times the minimum singular value in order to properly select the plane of polarization as described above. It becomes.

【0026】

As mentioned above, the broad definition of tripole antennas above is applicable to both receive and transmit antennas. Other definitions that are particularly useful in the range of transmitting antennas are explained in the far-field radiation image of the antenna. According to this definition, the antenna 110 corresponds to any cross-polarization of the radiated electric field at each point in the far-field radiation image of the antenna with the appropriate combination of inputs at connections 121-123 (corresponding to each composite baseband signal). If it can be produced by), it is a tripole antenna. In use, the average power given to the three connections is usually equal. For example, the average power given to any one connection is typically at least 1% of the total average power given to all three connections.

【0027】

The above definition is when it is understood that "each point in the far-field radiation image" refers to a point where there is a substantial electric field amplitude (eg, at least 5% of the peak amplitude at a given distance from the antenna). Is provided for directional antennas.

【0028】

The various antenna arrangements satisfy at least one of the broad definitions of tripole antennas herein. One such arrangement already mentioned above includes three mutually orthogonal dipole elements. A pair of dipole elements should be considered substantially orthogonal if their orthogonality is within 15 °. In fact, the dipole elements do not necessarily have to be orthogonal in order to qualify as a tripole antenna. For example, if the angle between each element pair and between each element and the surface defined by the other two elements is about 15 ° or less, then the arrangement of the three dipole elements is , Acts as a tripole antenna. As a result, it may be advantageous to use a tripole antenna containing dipole elements arranged at a reciprocal angle of less than 90 °, such as 45 °, 30 ° or 15 °.

【0029】

Directivity of tripole antenna Some tripole antenna designs, such as those consisting of three orthogonal dipole elements, have a radiation or sensitivity pattern that extends in virtually all directions. However, other tripole antenna designs have substantial directivity. Directivity is useful, for example, to avoid interference in a specified direction. Directivity can be achieved, for example, by arranging a large number of tripole antennas in a phase array according to known techniques. According to known techniques, directivity can also be achieved by placing a conductive shield or reflective element adjacent to one or more elements of the tripole antenna. For example, by using a metal shield, the tripole antenna can be substantially radiated into a right cone sector with a 100 ° full apex angle or received from a right cone sector with a 100 ° full apex angle. Is easily formed.

【0030】

Polarization diversity in a small antenna arrangement It is well known in the art that the effects of unwanted fading can be reduced by using an array of spatially separated antenna elements for transmission or reception instead of a single antenna. By spatially separating the antenna elements, it is possible to provide two or more independent propagation paths. The independent routes improve the likelihood of acceptable reception, even if the propagation conditions (which are unlikely to affect all routes equally) are poor. In addition, known detection methods can be used to improve signal quality by averaging well-independent noise components of two or more receiving channels. Such a communication method using spatially separated antenna arrays is often referred to as a "spatial diversity" method.

【0031】

By using the tripole antenna, the same advantages as those obtained by the spatial diversity method can be obtained. Tripole antennas have the other advantage that independent polarization channels can be provided without the need for significant spatial separation between antenna elements. In fact, transmissions along each axis of polarization can effectively radiate from only one point. As a result, the benefits of diversity (in this case, polarized diversities rather than spatial diversities) can also be enjoyed in small communication terminals such as mobile phones that do not have enough space to install spatially extended arrays.

【0032】

Specifically, it is often feasible and advantageous to use a tripole antenna or antenna arrangement 110 whose maximum dimension D is less than or equal to one wavelength at the transmit or receive carrier frequency. That is, the entire antenna arrangement (not including cables 131-133) is fitted within the sphere of dimension D. Similarly, in the case of an antenna arrangement having a large number of elements, it is advantageous that the maximum distance from any element to any other element is one wavelength or less.

【0033】

Receive and transmit diversity Needless to say to those skilled in the art, antenna arrangements according to the invention are readily used with a wide range of analog and digital modulation schemes. Also, it goes without saying that the two methods, which use a large number of polarized channels, (a) increase the redundancy in the transmitted signal corresponding to a single communication channel and improve the quality in the received signal, and (b). ) Increasing the capacity of radio channels by transmitting independent signals corresponding to separate communication channels. The first of these effects is sometimes referred to as "reception diversity" and the second effect is sometimes referred to as "transmission diversity".

【0034】

Several simultaneous patent applications transferred to the same assignee as the present application describe techniques for achieving diversity using spatially extended antenna arrays. These include Application No. 08/673981 by GJ Foschini, filed on July 1, 1996, Application No. 09/060657 by GJ Foschini et al., Submitted on April 15, 1998, June 1999. Includes provisional application No. 60/141504 by GJ Foschini et al., Submitted on 28th May, and 09/438900 by B. Hassibi, filed on 12th November 1999.

【0035】

When a CDMA modulation scheme is used, reception diversity is advantageously achieved by continuously feeding the same signal to the connections 121 through 123 of the transmitting antenna. Thus, each copy of the transmitted signal has a corresponding time delay, which can be considered zero if one of the three copies is the reference signal. The RAKE receiver at the receiving position interprets each of these time delays as corresponding to an individual ghost signal. The RAKE receiver applies known techniques to edit various received ghost signals (actual and simulated signals) into reproduced signals with optimal or near-optimal noise characteristics.

【0036】

RAKE receivers are described in JG Proakis, Digital Communications, 3rd Edition, WCB Division of McGraw-Hill, 1995, pp. 795-806.

【0037】

There are other ways to benefit further from applicable receive diversity even when CDMA is not used. In this regard, it should be noted that maximum diversity is achieved between statistically independent signals. Therefore, when parallel channels contain substantially the same communication data, it is advantageous to process the respective baseband signals so as to effectively randomize (ie, discorrelate) each other. As in the CDMA scheme above, the timing jitter provides one type of randomization. Other types of randomization are provided in the form of random code. For example, if three parallel signals are transmitted, two of these signals will be multiplexed in baseband by each sequence of random numbers, such as a random binary sequence. Random sequences are known by the receiver and are used to reproduce the original signal. In general, the same sequence can be reused repeatedly. Therefore, it is not necessary to continuously generate new random code.

【0038】

In this regard, it is important to note that the tripole receiving antenna generally provides a useful benefit of receiving diversity, even if the transmission is from only a single transmitting antenna element.

【0039】

Signal processing technology As mentioned above, there are known techniques such as using a pilot signal to measure the coefficients of the channel matrix (or "propagation matrix") H. Once appropriate estimates of these coefficients are obtained, the propagation channel is said to be a "known" channel. If the channel is known, at least in some cases, it is advantageous to transmit the converted version Ωs of the transmission signal vector s mentioned above. The conversion Ω is easily selected by a known technique, and the signal reproduction process at the reception position is simplified.

【0040】

As described in the above equation (1), the received signal vector r is associated with the transmitted signal vector s by the channel matrix r = Hs.

[Outside 2]

<img file="JP2001237757A_D0011.tif" />The main advantage of this conversion is that the amount of processing required in the receiver is reduced.

【0041】

[Outside 3]

<img file="JP2001237757A_D0012.tif" />Such factorization is called singular value decomposition. Here, the converted signal vector s'is given by s'= Vs. The main advantage of this transformation is that it provides three uncoupled or nearly uncoupled channels.

【0042】

If desired, the individual components of the vector s can be power compensated before the transformation V is applied, for example, as "water filling" using techniques known in the art. In short, the total channel capacitance is increased by increasing the relative amount of power transmitted on channels with higher signal-to-noise ratios. For this purpose, the singular values of the channel matrix, which are also the diagonal elements of the matrix S, indicate their respective signal-to-noise ratios.

【0043】

As mentioned above, when the conversion Ω is used, the excitation signals given to the respective signal connections 121, 122 and 123 of the transmitting antenna are three original signals with compound weighting factors (parallel signals by a single communication channel). Note that it shows a linear combination (regardless of whether it is an independent signal indicating an individual communication channel).

【0044】

[Effect of the invention]

As described above, according to the present invention, by using a third polarization direction that efficiently generates a third communication channel, the problem of fading in a multi-path environment is improved and the presence of a reflective surface is a drawback. Can be an advantage.

[Simple explanation of drawings]

[Figure 1]

The figure which shows the conventional arrangement.

[Figure 2]

The figure which shows the state which the transmitter antenna is not arranged optimally.

[Fig. 3]

The figure which shows the arrangement which a receiver has three dipole antennas.

[Fig. 4]

The figure which shows the state which the reflection surface contributes to a received signal.

[Fig. 5]

The figure which shows the state which the receiver has three dipole antennas, and the reflection surface contributes to the received signal.

[Fig. 6]

The figure which shows the arrangement which both the transmitter and the receiver have three dipole antennas.

[Fig. 7]

A block diagram of a transmitter / receiver according to the principles disclosed herein.

[Fig. 8]

Block diagram of a tripole antenna with three input or output connections according to the principles disclosed herein.

[Explanation of symbols]

10 transmitter 11 dipole antenna 12 dipole antenna Polarization signal on 13 planes xz 14-plane yz polarization signal 20 receiver 21 dipole antenna 22 dipole antenna 23 dipole antenna 30 lines