Leaky transmission line and MIMO communication system based on leaky transmission line

Technical field

The present invention relates to the field of wireless communications , and especially to a leaky transmission line and an MIMO communication system based on the leaky transmission line.

Background art

There are a lot of arguments for wireless communications due to the finite wireless spectrum and complex wireless transmission environment thereof ( which mainly refers to fading and multi -path) . Nowadays, multiple input multiple output (MIMO) may be the most important technology adopted by the wireless communication criteria (e.g. 3G, 3G LTE , IEEE 802.16 as well as IEEE 802.11η) . Generally, channel fading is deemed as an adverse factor in wireless communication systems, while MIMO technology can significantly overcome channel fading by way of employing multi -antenna at the transmitting and receiving ends, thereby improving throughput and reliability .

Recently, WLAN technique is usually selected as the basis of wireless auto train control (ATC) and passenger information system (PIS) of subway systems. IEEE 802.11η based on MIMO-OFDM technology is wireless communication criteria desired by users to provide the PIS system with a higher data rate . However, in order to provide adequate throughput, 802.11η has to operate in a multi -stream MIMO mode, requiring that the transmitting end and receiving end have multiple antennas, and requiring that all transmitting/receiving (TX/RX) antenna pairs haves irrelevant multi -path channels therebetween, specifically, having well -conditioned channel matrices. The elements in the channel matrix are composed of channel transmission coefficients between TX/RX antenna pairs . The channel matrix having a well condition means that the channel matrix has an inverse matrix, and transmitted data canbe reconstructed at the receiving end through the inverse matrix.

For some applications demanding wireless coverage along well-defined paths, a leaky coaxial cable has advantages over the traditional antennas. In Fig. 1 is shown the basic structure of a leaky coaxial cable in the prior art. Differing from common coaxial cables, the leaky coaxial cable is evenly arranged with gaps in its outer layer conductor, so as to radiate signals as evenly as possible. As shown in Fig. 1, the radio frequency (RF) signal fed back to the leaky coaxial cable can not only propagate inside the cable, but can also to some degree propagate/radiate into adjacent areas of the cable through the surface of the cable; likely, the RF signal incident onto the surface of the cable can also to some degree propagate inside the cable. Thus, the leaky coaxial cable can leak in or leak out RF signals through the gaps in the outer layer conductor along the entire cable length, and it accordingly can be deemed as a special type of antenna. Wireless coverage of a typical leaky coaxial cable is limited merely within adjacent area (for example, within a few meters) , thereby being capable of avoiding the interference from other systems. Typical application scenarios of the leaky coaxial cable include tunnels, aerial transport planes and so on.

However, when in the MIMO communication system is employed a single leaky coaxial cable, because it is equivalent to only employing one antenna, it is difficult to improve system throughput, and it is also difficult to reconstruct MIMO data streams at the receiving end. Whereas for several leaky coaxial cables being aligned in parallel and running in a close distance, because the channel transmission coefficients in the channel matrix are quite similar, although the channel matrix has an inverse matrix, each small error (noise) will affect extremely greatly the reconstruction of the MIMO data stream. Therefore, it is difficult for the channel matrix to satisfy the demand of MIMO transmission (poorly conditioned) , or even impossible to reconstruct MIMO data streams at the receiving end .

In order to reconstruct MIMO data streams at the receiving end, a method which can be adopted in the prior art is to space out a plurality of leaky coaxial cables sufficiently far. However, this solution is not practicable in most cases, for example in scenarios with a limited space, it is impossible to space out a plurality of leaky coaxial cables too far. Certainly, the leaky coaxial cable described here can also be replaced by other leaky transmission lines (e.g. leaky waveguides) . Test results of providing a WLAN coverage inside the chamber of an aircraft by using this method have already been disclosed in the following literature:

M. Lieberei, C. Zimmermann, P. Beinschob, U. Zoelzer : "MIMO WIRELESS COMMUNICATION IN AN AIRCRAFT USING OMNIDIRECTIONAL AND LEAKY LINE ANTENNAS" , Workshop on Aviation System Technology 2009.

Therefore, the problem to be solved in the present invention is, for those systems using leaky transmission lines in the scenario of a limited space, how to obtain wireless channels supporting high data rate MIMO communication, wherein in the scenario of a limited space, the spaces between the leaky transmission lines are very close .

Contents of the invention

In view of this, a primary object of the present invention is to provide a leaky transmission line and an MIMO communication system based on the leaky transmission line.

To achieve the above-mentioned object, the technical solution of the present invention is particularly implemented as follows: a leaky transmission line, comprising leaky sections and non- leaky sections, wherein the leaky sections and the non- leaky sections are alternate . An embodiment of the present invention is that, said leaky section and non- leaky section are of the same order of magnitude in length.

An embodiment of the present invention is that , said non- leaky section is obtained according to the following manners: omitting the gap in anouter conductor of a line section, corresponding to said non-leaky section, of the existing leaky transmission line, or arranging an electricity conducting sleeve on a line section, corresponding to said non- leaky section, of the existing leaky transmission line, or covering the gap in anouter conductor of a line section, corresponding to said non-leaky section, of the existing leaky transmission line with a metal strip.

An embodiment of the present invention is that, when said leaky transmission line is applied together with other leaky transmission lines, the leaky transmission line is aligned in parallel to other transmission lines, and the leaky sections of the leaky transmission line locate spatially at the same positions as the non-leaky sections of any one of the other leaky transmission lines, and the non- leaky sections of the leaky transmission line locate spatially at the same positions as the leaky sections of any one of the other leaky transmission lines.

An embodiment of the present invention is that, said leaky transmission line is a leaky coaxial cable or a leaky waveguide.

An MIMO communication system based on a leaky transmission line, comprising an access point and a client terminal, wherein the access point is connected with no less than two leaky transmission lines, characterized in that each leaky transmission line comprises leaky sections and non- leaky sections, and the leaky sections and the non- leaky sections are alternate.

An embodiment of the present invention is that, during the alignment of said no less than two leaky transmission lines, the leaky sections of one leaky transmission line locate spatially at the same positions as the non- leaky sections of any one of the other leaky transmission lines, the leaky sections of the leaky transmission line locate spatially at the same positions as the non- leaky sections of any one of the other leaky transmission lines, the non- leaky sections of the leaky transmission line locate spatially at the same positions as the leaky sections of any one of the other leaky transmission lines .

An embodiment of the present invention is that, the lengths of the leaky sections of said no less than two leaky transmission lines are equal or unequal, and the lengths of the non- leaky sections of said no less than two leaky transmission lines are equal or unequal .

An embodiment of the present invention is that, there are overlaps between the leaky sections of said no less than two leaky transmission lines, or there are overlaps between the non- leaky sections of said no less than two leaky transmission lines, or there are overlaps between both the leaky sections and the non- leaky sections of said no less than two leaky transmission lines, or there are overlaps between neither the leaky sections nor the non- leaky sections of said no less than two leaky transmission lines.

An embodiment of the present invention is that, said client terminal is connected with no less than two antennas, the distances between said leaky transmission lines and said antennas, the spaces between said antennas, and the lengths of the leaky sections and non- leaky sections of said leaky transmission lines are of the same order of magnitude . An embodiment of the present invention is that, said leaky transmission line is a leaky coaxial cable or a leaky waveguide.

It can be seen from the above-mentioned technical solution that, the leaky transmission line proposed in the present invention is able to change the radiation features of the traditional leaky transmission lines , and therefore even if the space between the leaky transmission lines is small, the transmitted data can be reconstructed at the receiving end, thereby achieving MIMO communication of a high data rate.

Description of the accompanying drawings

Fig. 1 shows the basic structure of a leaky coaxial cable in the prior art;

Fig. 2 shows the basic configuration of a 2 x 2 MIMO communication system in the prior art, which carries out MIMO communication using antennas ;

Fig. 3 shows the basic configuration of a 2 x 2 MIMO communication system in the prior art, which carries out MIMO communication using a traditional leaky coaxial cable;

Fig. 4 shows the basic configuration of a 2 x 2 MIMO communication system carrying out MIMO communication using an improved leaky coaxial cable according to an embodiment of the present invention; and

Fig. 5 shows the alignment manner of a plurality of improved leaky coaxial cables according to an embodiment of the present invention.

Particular embodiments

In order to make the object, technical solution and advantages of the present invention more apparent and clear, the present invention will be further described in detail below with reference to the accompanying drawings and by way of embodiments.

In Fig .2 is shown the basic configuration of a 2 x 2 MIMO communication system in the prior art, which carries out MIMO communication using antennas. The MIMO communication system comprises an access point (AP) and a client terminal (STA) . "2 x 2" means that the AP and STA are respectively provided with two antennas. At any moment, the two antennas of AP can serve as transmitting antennas, while the two antennas of STA serve as receiving antennas; or the two antennas of STA can serve as transmitting antennas, while the two antennas of AP serve as receiving antennas. For the purpose of easy understanding, the embodiments and accompanying drawings hereinafter are all explained by way of a 2 x 2 MIMO communication system example. It can be understood by those skilled in the art that, the present invention is also applicable to the MIMO communication systems having other antenna arrays (for example, 2 x 3 , 3 x 3, 4 x 4 ) .

In the MIMO communication system shown in Fig .2 , the distance between the two antennas of the AP is d _A p , the distance between the two antennas of the STA is d _S TA, and L is the distance between the antenna of the AP and the antenna of the STA. For the sake of easy description, the two antennas of the AP are respectively denoted as ii and i ₂ , and the two antennas of the STA are respectively denoted as ji and j ₂ . The channel transmission coefficient between the antenna ii and ji is hi,i, the channel transmission coefficient between the antenna ii and j ₂ is h _li2 , the channel transmission coefficient between the antenna i ₂ and ji is h _2l± , and the channel transmission coefficient between the antenna i ₂ and j ₂ is h _2;2 . Hence, the channel matrix between the AP and the STA is:

In brief, the channel matrix H is generally used to describe the effect of signal propagation and the amplitude and phase of the signal transmission between two antennas , thus the separation of respective raw data transmitted through different antennas depends on the feature of the channel matrix H. If the channel matrix H is well conditioned, through the inverse matrix of the channel matrix the transmitted raw data can be reconstructed from the received data. In the cases of pure line-of -sight (i.e., no multi -path propagation of significance exists) , if the distance L between the antenna of the AP and the antenna of the STA is very long in comparison with the space between the antennas of the STA and the space between the antennas of the AP, then the channel transmission system between the antennas of the AP and the antennas of the STA will be very similar, that is, the elements in the channel matrix H have very similar amplitudes and phases, and in this case it is impossible for the channel matrix H to have an inverse matrix available for reconstructing raw data. If a transmitting or receiving antenna is moved by a very short distance, the amplitudes and phases of the elements of a corresponding row or column in the channel matrix H will be varied. For example, if the antenna ii of the AP is moved by a very short distance, then the channel transmission coefficients hi , i and h _li2 will be varied, while moving the antenna j i of the STA, the channel transmission coefficients hi , i and h _2l ± will be varied, that is, the amplitudes and phases of these elements will be varied. However, because the spaces between the antennas are very small in comparison with the distance L between the antennas of the AP and the antennas of the STA, even if a certain antenna is moved by a very short distance, the impacts on the amplitudes and the phases of the elements in the channel matrix H will be very weak, and accordingly it will be very difficult for such a channel matrix to satisfy the demands (poorly conditioned) , that is, in this case, it is difficult to reconstruct the raw data at the receiving end, and the MIMO communication of a high data rate is unrealizable. Nevertheless, if the distance L between the antennas of the AP and the antennas of the STA is of a similar order of magnitude to the spaces between the antennas, then moving an antenna has different impacts on the elements (especially on the phases of these elements) of a corresponding row or column in the channel matrix H, and according to geometry, a well -conditioned channel matrix can certainly be obtained at this moment, thereby achieving MIMO communication of a high data rate .

The above-explained principles are also suitable for MIMO communication systems in which traditional leaky transmission lines (for example leaky coaxial cables or leaky waveguides) rather than antennas are adopted at the AP end. Here a leaky coaxial cable is taken as an example to give description. In Fig. 3 is shown the basic configuration of a 2 x 2 MIMO communication system in the prior art, which carries out MIMO communication using a traditional leaky coaxial cable. As shown in Fig. 3, the AP is provided with two traditional leaky coaxial cables ii and i ₂ , the STA is provided with two antennas ji and j ₂ , the distance between the leaky coaxial cables ii and i ₂ of the AP is d _ca bie, the distance between the two antennas of the STA is d _S TA, and the distance between the leaky coaxial cables and the antennas of the STA is L. According to the MIMO communication system shown in Fig. 3, the channel matrix between the AP and the STA is:

If the distance L between the leaky coaxial cables of the AP and the antennas of the STA is very large in comparison with the space between the leaky coaxial cables d _ca bie _/ then the channel transmission systems between the leaky coaxial cables of the AP and the antennas of the STA will be very similar, that is, the elements in the channel matrix H have very similar amplitudes and phases, and the channel matrix H cannot have an inverse matrix available for the reconstruction of raw data at this moment . If one of the leaky coaxial cables of the AP or one of the antennas of the STA is moved by a very short distance, then the amplitudes and the phases of a corresponding row or column in the channel matrix H will be varied. However, because both the space between the leaky coaxial cables of the AP and the space between the antennas of the STA are very small in comparison with the distance L between the leaky coaxial cables of the AP and the antennas of the STA, even if a certain leaky coaxial cable or antenna is moved by a very short distance , the impacts on the amplitudes and the phases of the elements in the channel matrix H will be very weak, and accordingly it will be very difficult for such a channel matrix to satisfy the demands (poorly conditioned) , generally not suitable for MIMO communication of a high data rate, especially when the wireless propagation in the leaky coaxial cable is generally controlled by line of sight instead of multi-path.

For the purpose of obtaining a channel matrix suitable for the MIMO communication of a high data rate, in the embodiments of the present invention is provided an improved leaky transmission line, and by way of modifying the radiation feature of the leaky transmission line and modifying the amplitudes and phases of the elements in the channel matrix, a well -conditioned matrix is thereby obtained . Using such an improved leaky transmission line in MIMO communication system, even if the space between the leaky transmission lines is very small, transmitted data can still be reconstructed at the receiving end, thereby achieving the MIMO communication of a high data rate. For the sake of easy understanding, the improved leaky transmission line is described in the embodiments of the present invention by way of the example of an improved leaky coaxial cable.

In an embodiment of the present invention, an improved coaxial cable comprises radiating sections and non-radiating sections, and the radiating sections and the non-radiating sections are alternate, wherein the radiating section is also referred to as a leaky section, the non-radiating section is also referred to as a non-leaky section. Because the existing leaky coaxial cable radiates signals along the entire cable length, whereas the leaky sections and non- leaky sections of the improved leaky coaxial cable provided in the embodiments of the present invention are alternate , in order to obtain a non- leaky section, the gap in the outer conductor of the cable section, corresponding to the non-leaky section, of existing leaky coaxial cable can be omitted. Because the gap for leaking signals is omitted, the cable section is turned into a non-leaky section and no longer leaks signals. This method for obtaining non-leaky sections is relatively easy to implement during the production of cables. If the gap in the outer conductor of the cable section, corresponding to the non- leaky section, of the existing leaky coaxial cable was not omitted during production, then optionally, the non-leaky section can also be obtained through the following ways: arranging an electricity conducting sleeve ( for example a metal pipe , a metal mesh, a metal thin sheet pipe and the like) on the cable section, corresponding to the non-leaky section, of the existing leaky coaxial cable, or covering the gap in the cable section, corresponding to the non- leaky section, of the existing leaky coaxial cable with a metal strip. For example, attaching a strip of copper tape externally onto the cable section, corresponding to the non-leaky section, of the existing leaky coaxial cable with a metal strip, thus the gap in the cable section can be fully covered. The non- leaky sections obtained through the above-mentioned method can all avoid the gap in the section from leaking signal. The lengths of the leaky sections and the non- leaky sections of the leaky coaxial cable provided in the embodiments of the present invention can be equal , or unequal , as long as they are of the same order of magnitude .

It can be understood by those skilled in the art that , the improvement on the existing leaky coaxial cable in the embodiments of the present invention is likely applicable to other leaky transmission lines, for example leaky waveguides and so on.

In Fig .4 is shown the basic configuration of a 2 x 2 MIMO communication system carrying out MIMO communication using an improved leaky coaxial cable according to an embodiment of the present invention. As shown in Fig. 4, the MIMO communication system comprises an AP and a STA, wherein the AP has two wireless radio frequency (RF) ports , the RF ports are respectively connected with two improved leaky coaxial cables ii and i ₂ , the STA is provided with two antennas ji and j ₂ , the distance between the leaky coaxial cables ii and i ₂ of the AP is dcabie, the distance between the antennas of the STA is d _S TA, and the distance between the leaky coaxial cables and the antennas of the STA is L. In this embodiment, the distance d _ca bie between the leaky coaxial cables is very small in comparison with the distance L between the leaky coaxial cables and the antennas of the STA. In Fig .4 , the leaky sections of the leaky coaxial cable are represented by white line sections, and the non- leaky sections are represented by black line sections.

The number of the improved leaky coaxial cables used in the MIMO communication system is dependent on the number of RF ports of the AP, in this embodiment, the description is by way of example of 2 leaky coaxial cables, it can be understood by those skilled in the art that, in MIMO communication systems more than 2 leaky coaxial cables can be employed to perform MIMO communication according to the number of the RF ports.

In this embodiment, in order to obtain a well -conditioned channel matrix, two leaky coaxial cables of the AP are aligned as followed: two leaky coaxial cables are aligned in parallel, and the leaky sections of various leaky coaxial cables are offset or interleaved, that is, the leaky sections of one leaky coaxial cable locate spatially at the same positions as (i.e. coincide with) the non- leaky sections of anyone of the other leakycoaxial cables , and the non- leaky sections of the leaky coaxial cable locate spatially at the same positions as the leaky sections of any one of the other leaky coaxial cables. The lengths of the leaky sections and non- leaky sections of each leaky coaxial cable shown in Fig. 4 are equal, the lengths of the leaky sections of various leaky coaxial cables are equal, and the lengths of non-leaky sections are also equal. Those skilled in the art canunderstand that , optionally, the lengths of the leaky sections and the non- leaky sections can also be different, and the lengths of the leaky sections and/or non- leaky sections of various leaky coaxial cables can also be different . Due to being limited by various conditions in particular applications, during the alignment of various leaky coaxial cables, the leaky sections and/or non- leaky sections thereof are also allowed for overlapping, as long as it can be ensured that the leaky sections/non- leaky sections of various leaky coaxial cables locate spatially at different positions. This will be described in detail hereinafter.

It can be seen from the MIMO communication system shown in Fig. 4 that, because the distances from various leaky sections of the leaky coaxial cable ii of the AP to the antenna ji of the STA are different, the signal transmitted from the leaky coaxial cable ii to the antenna ji is the superposition of the signals transmitted from various leaky sections of ii. Likewise, the signal transmitted from the leaky coaxial cable i ₂ to the antenna ji is also the superposition of the signals transmitted from various leaky sections of i ₂ . Because the leaky sections and non- leaky sections of the leaky coaxial cable ii are alternate, the leaky sections and non- leaky sections of the leaky coaxial cable i ₂ are also alternate, and the leaky sections of the leaky coaxial cable ii locate at the same positions as the non- leaky sections of the leaky coaxial cable i ₂ , the channel generated between the leaky coaxial cable ii and the antenna ji is completely different from the channel generated between the leaky coaxial cable i ₂ and the antenna ji. As long as the distance L between the leaky coaxial cables of the AP and the antennas of the STA, the space d _S TA between the antennas of the STA, and the lengths of the leaky sections and the non- leaky sections of the leaky coaxial cables are of the same order of magnitude, the channel transmission coefficients in the channel matrix between the AP and the STA will be completely different from the coefficients in the channel matrices shown in Fig. 2 and Fig. 3, that is, the amplitudes and phases of the elements in the channel matrix differ completely from the amplitudes and phases of the elements in the matrices shown in Fig. 2 and Fig. 3. In other words, the signal transmitted from the leaky coaxial cable ii differs completely from the signal transmitted from the leaky coaxial cable i ₂ in amplitude and phase (especially in phase) ; and contrarily, the signals transmitted from the antennas to the leaky coaxial cables are also of the same case. Accordingly, the channel matrix between the AP and the STA has an inverse matrix, by way of which inverse matrix the transmitted signal can be reconstructed at the receiving end.

It can be seen from this embodiment that , if two existing leaky coaxial cables are placed relatively close, it is equivalent to placing two antennas relatively close, whereas for using the improved leaky coaxial cable, because the leaky sections and the non- leaky sections are alternate, it is equivalent to increasing the distances between leaky sections, thus being able to achieve the effect achieved by placing the existing leaky coaxial cables relatively distant. Therefore, in the embodiments of the present invention, even if the distance d _ca bie between the leaky coaxial cables is very small, as long as the distance L between the leaky coaxial cables of the AP and the antennas of the STA, the space d _ST A between the antennas of the STA, and the lengths of the leaky sections and the non- leaky sections of the leakycoaxial cables are of the same order of magnitude , the transmitted signal can be reconstructed at the receiving end.

However, if the L is much greater than d _ST A _/ then the channel matrix between the AP and the STA will be adverse for MIMO communication of a high data rate. Whereas in most practical applications, it is not a difficult condition to space an appropriate distance between the antennas of the STA and to space an appropriate distance between the leaky coaxial cables of the AP and the antennas of the STA, so as to enable the L, d _ST A, and the lengths of the leaky sections and non- leaky sections of the leaky coaxial cable to be of the same order of magnitude.

Fig. 5 shows an alignment manner of a plurality of improved leaky coaxial cables according to an embodiment of the present invention. For the sake of easy understanding, in Fig. 5 is merely illustrated the alignment of 2 or 3 leaky coaxial cables, those skilled in the art can understand that the alignment of more than 3 leaky coaxial cables is identical to the alignment shown in Fig. 5 in principle.

As shown in example (1) in Fig.5, two leaky coaxial cables are aligned in parallel, the leaky sections of one leaky coaxial cable locate at the same positions as the non- leaky sections of any one of other leaky coaxial cables, and there are overlaps between the leaky sections of two leaky coaxial cables. In example (1) , the lengths of the leaky sections of each leaky coaxial cable are identical, so are the lengths of the non- leaky sections, but the lengths of the leaky section and the non- leaky section are different (in example

(1) , the length of the leaky section is greater than that of the non- leaky section) ; furthermore, the length of the leaky section of one leaky coaxial cable is the same as the length of the leaky section of the other leaky coaxial cable, and the length of the non- leaky section of one leaky coaxial cable is also the same as the length of the non- leaky section of the other leaky coaxial cable . Thus, there will be overlaps between the leaky sections of these two leaky coaxial cables. As shown in example (1) , the lengths of the overlapping parts of the leaky sections are equal.

As shown in example (2) in Fig.5, two leaky coaxial cables are aligned in parallel, the leaky sections of one leaky coaxial cable locate at the same positions as the non- leaky sections of any one of other leaky coaxial cables, and there are overlaps between the non- leaky sections of these two leakycoaxial cables . Inexample (2) , the lengths of the leaky sections of each leaky coaxial cable are identical, so are the lengths of the non- leaky sections, but the lengths of the leaky section and the non- leaky section are different (in example

(2) , the length of the non-leaky section is greater than that of the leaky section) ; furthermore, the length of the leaky section of one leaky coaxial cable is the same as the length of the leaky section of the other leaky coaxial cable, and the length of the non- leaky section of one leaky coaxial cable is also the same as the length of the non- leaky section of the other leaky coaxial cable . Thus, there will be overlaps between the non- leaky sections of these two leaky coaxial cables. As shown in example (2) , the lengths of the overlapping parts of the non- leaky sections are unequal.

As shown in example (3) in Fig. 5, three leaky coaxial cables are aligned in parallel, the leaky sections of one leaky coaxial cable locate at the same positions as the non- leaky sections of any one of the other leaky coaxial cables, and there are overlaps between both the leaky sections and the non- leaky sections of these three leaky coaxial cables . Inexample (3) , the lengths of the leaky sections of each leaky coaxial cable are identical, so are the lengths of the non- leaky sections, but the lengths of the leaky section and the non-leaky section are different (in example (3) , the length of the leaky section is greater than that of the non- leaky section, it can be understood by those skilled in the art that , in the example , it can also be that the length of the non-leaky section is greater than the length of the leaky section) ; furthermore, the length of the leaky section of one leaky coaxial cable is the same as the length of the leaky section of the other leaky coaxial cables , and the length of the non- leaky section of one leaky coaxial cable is also the same as the length of the non- leaky section of the other leaky coaxial cables .

As shown in example (4) in Fig.5, two leaky coaxial cables are aligned in parallel, the leaky sections of one leaky coaxial cable locate at the same positions as the non- leaky sections of any one of other leaky coaxial cables, and there are overlaps between both the leaky sections and the non- leaky sections of these two leaky coaxial cables . In example (4 ) , the lengths of the leaky sections of each leaky coaxial cable are different, so are the lengths of the non- leaky sections, furthermore, the length of the leaky section of one leaky coaxial cable is different from the length of the leaky section of the other leaky coaxial cable, and the length of the non- leaky section of one leaky coaxial cable is also different from the length of the non- leaky section of the other leaky coaxial cables.

According to the above-described embodiments, in another embodiment of the present invention, the lengths of the leaky section and the non- leaky section of a leaky coaxial cable can also be a constant, that is, the lengths of the leaky section and the non- leaky section are identical, and the lengths of the leaky sections of all leaky coaxial cables are identical , so are the lengths of non- leaky sections , furthermore, there is no overlapping between the leaky sections or non- leaky sections of these leaky coaxial cables , and this embodiment is a special case in the embodiments of the present invention.

It can be understood by those skilled in the art that, the MIMO communication system described in this embodiment can also adopt other improved leaky transmission lines, for example improved leaky waveguides and so on.

The improved leaky transmission line provided in the embodiments of the present invention can operate coordinately with the existing WLAN devices, and can be manufactured with a relatively low cost.

It can be seen from the embodiments of the present invention that, using improved leaky transmission lines in an MIMO communication system, even if these leaky transmission lines are placed relatively close, MIMO communication of a high data rate can still be achieved, therefore being especially suitable for scenarios of a limited space .

What are mentioned above are merely the preferred embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. All modifications, equivalent replacements and improvements within the spirit and principle of the present invention should be covered in the protection scope of the present invention.