JP2004517549A - MIMO wireless communication system - Google Patents

Abstract

Previous MIMO systems have used spatial diversity antenna elements in order not to reduce the number of orthogonal channels realized. The present invention recognizes that this leads to a large antenna size compared to multiple beam antennas using closely spaced antenna elements. In order to provide a small antenna unit, while still allowing a MIMO system to be used, the present invention provides that only polarization diversity can be used in a MIMO system without the need for spatially separated antenna elements. Recognize that it can be used. Closely located antenna elements are used and this allows a small MIMO antenna unit to be provided. In addition, such a MIMO system with polarization diversity but no spatial diversity is used in line-of-sight situations and combined with a multi-beam antenna system to further increase capacity.

Description

[0001]
Field of the invention
The present invention is related to a multiple-input multiple-output (MIMO) wireless communication system. The present invention is particularly, but not exclusively, related to a MIMO wireless communication system that uses polarization diversity.
[0002]
Background of the Invention
A MIMO wireless communication system (see FIG. 1) has multiple antennas 10 at a transmitter 11 and one or more antennas 12 at a receiver 13. The antennas 10 and 12 are used in an environment with many multipaths where each signal undergoes multipath propagation due to the presence of various scattering objects (buildings, automobiles, hills, etc.) in the environment. As such, a cloud shape 14 is shown in FIG. 1 to show the scattered signal between the transmitting and receiving antennas. User data is sent out of the transmit antenna using a space-time coded (STC) transmission method known in the art. The receive antenna 12 captures the transmitted signal and signal processing techniques are applied as known in the art to separate the transmitted signal and recover the user data.
[0003]
MIMO wireless communication systems are advantageous in that higher data rates can be obtained, allowing the capacity of the wireless link between the transmitter and the receiver to be improved as compared to previous systems. A multipath-rich environment allows multiple orthogonal channels to be generated between the transmitter and the receiver. Data for a single user is transmitted over the air in parallel over those channels, simultaneously and using the same bandwidth. Thus, higher spectral efficiency than non-MIMO systems is achieved.
[0004]
One problem that exists with MIMO systems relates to the large size of the transmit and receive antenna arrays. Previously, MIMO transmit and receive antenna arrays used spatially separated antenna arrays. That is, the intervals between the individual antenna elements are arranged sufficiently large so that uncorrelated spatial fading can be obtained. This is necessary to prevent reducing the number of orthogonal channels. That is, when the fading characteristics between the antenna elements are similar (there is a correlation), the number of achievable orthogonal channels is reduced. For example, for rooftop installations or tower antennas, separations of up to 20 wavelengths are required to achieve decorrelating fading due to the low angular spread of the multipath.
[0005]
Another problem that exists with MIMO systems is that they are designed for use in environments where scattering occurs more than for line-of-sight conditions. However, line-of-sight conditions occur in many situations, such as communication between a nearby portable wireless device and a fixed wireless access system, where the directional array is used in a subscriber's home. This means that previously, in such line-of-sight conditions, it was not possible to realize the potential capacity available from a MIMO system.
[0006]
The spatial diversity arrangement of previous MIMO systems also means that such systems are not compatible with multi-beam antenna arrangements, which require closely spaced antenna arrays without spatial diversity. A multi-beam antenna arrangement is one in which a plurality of closely spaced antenna elements 21 (see FIG. 2) are used with a beamformer 20 to form two or more directional antenna beams 23. is there. The data to be transmitted enters input 24 and is transmitted to a plurality of user equipment terminals 22. Antenna element spacing is achieved without spatial diversity and typically at half-wavelength antenna spacing. By using multiple directional antenna beams in this manner, the interference between the beams is reduced and thus the downlink capacity is increased. That is, the number of user equipment terminals that can be supported by a single base station including the antenna array 21 is increased. This differs from a MIMO system, as shown in FIG. 1, where the downlink capacity is increased for a particular user or users by increasing the data rate for those users.
[0007]
It is an object of the present invention to provide a MIMO wireless communication system that solves or alleviates one or more of the problems described above.
[0008]
Further, the benefits and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which set forth and illustrate preferred embodiments of the invention.
[0009]
Summary of the Invention
According to a first aspect of the present invention, a multiple-input multiple-output (MIMO) wireless communication system comprises:
A plurality of transmitting antenna elements;
A plurality of receiving antenna elements,
A multiple-input multiple-output (MIMO) wireless communication system is provided wherein the transmitting antenna elements are arranged to provide polarization diversity and the positions of the transmitting antenna elements are arranged to avoid spatial diversity. .
[0010]
This offers the advantage that the transmit antenna elements can be closely spaced to create a compact antenna arrangement, since spatial diversity is avoided. This is particularly important in situations where the antenna element is incorporated into a portable device, such as a personal digital assistant (PDA), cell phone, or other small device. Small antenna arrangements are also advantageous for base station equipment and other outdoor equipment, since the visual effects created are reduced. In addition, manufacturing, transport and storage costs are also reduced.
[0011]
The receiving antenna elements are also placed close together to avoid spatial diversity, but this is not required.
[0012]
The receiving antenna elements are also preferably arranged to provide polarization diversity and to avoid spatial diversity. This offers the advantage that the receiving antenna elements can be located close together, resulting in a compact receiver arrangement.
[0013]
The antenna elements may be individual elements or an array of elements, such as a column array for sector coverage. Also, the antenna elements may be arranged at intervals or in close proximity. For example, a MIMO system having two transmit or receive antenna elements can be provided such that the two antenna elements are closely spaced and form a dual polarization element.
[0014]
Preferably, said antenna element is polarized in one of two substantially orthogonal polarizations. For example, horizontally and predominantly polarized antenna elements may be used. It is not essential that the transmitting and receiving antenna elements are polarized in the same way. For example, the transmitting antenna element can use horizontal and vertical polarizations, while the receiving antenna element can use right-handed or left-handed circularly polarized waves.
[0015]
Preferably, the MIMO system is arranged to operate at a particular wavelength and the spacing between the transmitting antenna elements is shorter than one of the particular wavelengths. This avoids spatial diversity and provides a small transmit antenna design. The inter-element spacing of the receiving antenna elements may be shorter than that particular wavelength, but this is not required. That is, the receiving antenna may have either space or polarization diversity or both.
[0016]
Preferably, the transmitting antenna elements are further arranged together to provide the plurality of antenna beams being used. This allows MIMO communications to be combined with multi-beam communications to improve capacity. Since spatial diversity is not required, the spacing between elements can be close enough to allow multi-beam communication.
[0017]
In one example, the plurality of antenna beams comprises a set of antenna beams, each set being substantially identical to the first antenna beam of the first polarization, but with the first polarization. A second antenna beam provided with a second polarization different from the wave. This allows a MIMO link to be provided using each set of antenna beams.
[0018]
The MIMO wireless communication system is selected from, for example, 2: 2 and 2: 4 MIMO systems. This has a relatively small number of antenna elements, and this facilitates incorporating them into a portable communication device such as a mobile phone.
[0019]
According to another aspect of the invention,
Transmitting a space-time coded signal from a transmitting antenna arrangement having a plurality of transmitting antenna elements;
Receiving a space-time coded signal in a receiving antenna arrangement having a plurality of receiving antenna elements;
Has,
A multi-input, multi-output wireless communication method is provided, wherein the transmitting antenna element is provided with polarization diversity, and the position of the transmitting antenna element is arranged so as to avoid spatial diversity.
[0020]
This offers the advantage that the MIMO communication link is performed without the need for spatial diversity. For example, this allows MIMO links to be used in line-of-sight situations to improve link capacity in those cases.
[0021]
According to another aspect of the invention, there is provided an antenna arrangement for use in a multiple-input multiple-output (MIMO) wireless communication system, comprising a plurality of transmit antenna elements arranged to provide polarization diversity; An antenna arrangement is provided in which the location of the transmitting antenna elements is such that spatial diversity is avoided.
[0022]
Preferred features may be combined as appropriate, as will be apparent to those skilled in the art, and may be combined with any aspect of the invention.
[0023]
To illustrate how the invention may be implemented, embodiments of the invention are described below by way of example only and with reference to the accompanying drawings.
[0024]
Detailed description of the invention
Embodiments of the present invention will now be described by way of example only. These examples show the best ways of practicing the present invention, now known to the applicant, but they are not the only ways this can be achieved.
[0025]
The term "spatial diversity" herein refers to the use of antenna spacing to obtain a low correlation signal for fast fading. The required antenna spacing for low correlation depends on the angle of arrival and the angular spread of the multipath. The lower the angular spread, the greater the required spacing.
[0026]
The term "polarization diversity" here refers to using different antenna polarizations to provide a signal with low correlation. This is facilitated in a propagation environment by advanced polarization conversion. This has the advantage that two antennas with different polarizations can be shared at a common location.
[0027]
In the following example, orthogonally polarized antenna elements are used. However, it is not essential that these polarizations be exactly orthogonal as long as the polarization can be distinguished by the receiver. The term "dually polarized antenna element" herein refers to a single antenna aperture having effectively two closely spaced antenna elements operating at different polarizations.
[0028]
As described above, previous MIMO systems use spatially separated antenna arrays so as not to reduce the number of orthogonal channels implemented. The present invention recognizes that this results in a large antenna placement size compared to a multiple beam antenna system using closely spaced antenna elements. In order to provide a small antenna unit, while still allowing a MIMO system to be utilized, the present invention provides for a polarization diversity-only MIMO system without the need for spatially separated antenna elements. Recognize that it can be used in Closely located antenna elements are used and this allows a small MIMO antenna unit to be provided.
[0029]
It is generally accepted that previous MIMO systems used polarization diversity, but this was always in addition to spatial diversity. For example, Lucent Technologies, in their paper, Oct. 13, 2000, R1-00-1219, "Practical Aspects of Multiple Antenna Structures for HSDPA," describes a multiple antenna structure using a code reuse mechanism. Describes the requirements for the antenna spacing. They illustrate that at both the base station transmitter and the terminal receiver, sufficient spacing between antennas is required for decorrelated fading. They describe the use of dual polarization antennas, but this is only in addition to spatial diversity.
[0030]
A further advantage is achieved because the present invention allows closely spaced antenna elements to be used in a MIMO system (by using polarization diversity instead of spatial diversity). This means that an arrangement with closely spaced antenna elements can be formed and arranged to provide both a multiple beam antenna system operating simultaneously with the MIMO communication system. This provides increased capacity and allows to combine the advantages of a multi-beam antenna system with those of a MIMO system.
[0031]
As mentioned above, the present invention recognizes that only polarization diversity can be used in a MIMO system without the need for spatially separated antenna elements. This will be described in more detail below.
[0032]
Contrary to expectations, the use of polarized antennas at the base stations and terminals of the STC system improves the resilience and strength of the communication link, allows the use of smaller antenna structures, and reduces the use of rural or suburban areas. It has been found that even in low-scatter environments, where there is a line-of-sight component of line of sight and fixed radio access applications, it has the added benefit of maintaining multiple orthogonal channels. Prior art STC or MIMO systems have relied on spatially uncorrelated antennas in multipath-rich environments. We have found that the use of polarized antennas in MIMO systems works surprisingly better than expected and offers the additional advantage that STC systems can operate in low scattering environments.
[0033]
This antenna configuration allows MIMO to be employed in environments where there is a line of sight line component, or indeed only a line of sight line component. This is important because it allows MIMO to be applied to fixed radio access mechanisms, where the subscriber antenna is probably mounted outside the eaves-level user's home. This also means that MIMO can be applied to better environments, such as rural areas.
[0034]
For a highly scattering environment, spatial fading usually follows a Rayleigh distribution, and this means that as the multiple antenna configurations of the terminal are moved, the received signal at each element will either fade up or fade down. means. This results in a change in the gain of the orthogonal channels, and a 2: 2 system (ie, two antenna elements at the transmitter and two at the receiver) using spatially separated antennas (ie, spatial diversity). For one antenna element), the channel gain distribution is shown in FIG. 3 (lines A and B). Similar distributions are found for 2: 4, 2: n (where n is any integer greater than 2) and similar MIMO systems. FIG. 3 also shows the Rayleigh distribution for a wireless link having one antenna at each end (see line Z). FIG. 3 assumes that the transmit and receive antennas have decorrelated (dissimilar) fading characteristics.
[0035]
Often, the angular spread at the base station is small and this can lead to correlated fading. Correlated fading has the effect of reducing the gain of the weaker MIMO channel, and within the limits at which the base antenna is fully correlated, the gain of the weaker channel goes to zero. In other words, for a 2: 2, 2: 4, 2: n or similar MIMO system, when the antennas at one end of the link are fully correlated, the number of orthogonal channels is reduced to one. This also applies to 2: 4, 2: n or similar MIMO systems. The distribution for power gain then decreases to that shown in line C of FIG. 3 (ie, line D is absent).
[0036]
If a dual polarization element is used in place of a spatially separated antenna, the second channel will never be lost for 2: 2, 2: 4, 2: n or similar systems. . This is because in a Rayleigh fading environment, fading characteristics for different polarizations are always uncorrelated. Taking the limited case, assume that there is no polarization conversion in the environment, but assume that multipath scattering still occurs in the environment. Due to the two orthogonal polarizations, there are two orthogonal paths in this case. Thus, the same two polarizations are used at both ends of the link. At any one time, the stronger channel is simply the receiving element with the highest received signal level. The power gain distributions for the strongest and weakest channels are shown in lines E and F in FIG. These are shown in comparison to the distributions (lines A and B in FIG. 4) for a polarization-diversity-free configuration in which the antennas at the transmitting and receiving ends have uncorrelated fading. The main point is that two orthogonal channels remain even with no polarization conversion, and that the use of polarization is stronger than using spatial diversity.
[0037]
MIMO systems usually start with the requirement of a highly scattered environment from which multiple orthogonal channels are extracted. This aspect of the invention starts in the opposite direction, even in the absence of any multipath, by starting with an antenna configuration that already has orthogonal paths. Multipath scattering in the environment disturbs the system from this initial state, and some spatiotemporal processing can be applied to recover the orthogonal channels. The difference from existing MIMO systems that relies on spatial diversity is that multiple orthogonal channels disappear because multipath scattering is reduced. With the present invention, multiple orthogonal channels are maintained because multipath scattering is reduced.
[0038]
MIMO systems have been developed with spatial diversity in mind due to the need to use many antennas at each end of the wireless link. However, for a practical system, the number of antennas to be used at each end of the link is likely to be limited between two and four. One embodiment of the present invention starts with the case where two antenna elements are used at each end of the link. We use two spatially separated antennas at each end of the link and if there is no fading, the antennas at each end are fully correlated. In this case, the best we can do is to achieve 3 dB of power gain from the two element arrays at each end of the link, for a total signal-to-noise ratio increase of 6 dB. This means that the achieved capacity compared to a link with a single antenna at each end is shown in FIG. 5 (for different values of signal to noise ratio, SNR).
[0039]
In contrast, if a dual polarization element is used at each end of the link, two orthogonal paths already exist. Thus, data can be transmitted in parallel over these two paths. For example, if a vertically polarized element and a horizontally polarized element are used at each end, the two orthogonal paths are a vertical-to-vertical link and a horizontal-to-horizontal link. In this case, the capacity of a 2: 2 polarization diversity MIMO system compared to a link with a single (co-polarized) antenna at each end of the link is shown in FIG. It can be seen that higher capacity gains are achieved at certain locations with high signal-to-noise ratio (> 6 dB). This effect is also seen for 2: 4, 2: n or similar MIMO systems. Strictly, it should be compared with the result of having two identical polarization elements at each end used for beamforming. This result for this case actually corresponds exactly to the result of 2: 2 spatial diversity shown in FIG. 5 with a 3 dB array gain at each end of the link. Then, by comparing the results of FIGS. 5 and 6, it can be seen that the capacity for the polarization diversity configuration is lower than the spatial diversity configuration for the SNR of 0 dB. The highest gain comes from MIMO with high SNR.
[0040]
Another advantage to note here is that the dual polarization elements can be placed close together, and thus if two spatially separated antennas can be provided, It is possible to simply have two spatially separated dual polarization elements. In a fading-free environment, spatial separation cannot provide MIMO with any additional orthogonal channels, but the additional gain (6 dB; 3 dB from each end) is required to provide additional capacity gain. It can be used to improve SNR. To take this further, MIMO employs fixed radios using outdoor directional eave height subscriber antennas by employing dual polarized antenna elements at both the base and subscriber antennas. It can be applied to access systems. Outdoor antennas are typically required to avoid the high transmission losses associated with RF (radio frequency) transmission into buildings. Eave height mounting often means that there is a line of sight to the base station. Therefore, directional antennas are used to maximize the signal-to-noise ratio and to minimize interference to the rest of the network. However, in these low fading environments, link capacity is greatly increased by combining 2: 2, 2: n or similar polarization diversity MIMO with high gain subscriber and base station antennas. .
[0041]
Consider a suburban or rural environment and a mobile terminal, i.e., a type of mobile device. In a given environment, the angular spread, especially at the base station, is very low, such as for a spatial diversity MIOM configuration, so that the correlation between the antennas is very high. In the case of polarization diversity, the correlation between antennas is low, and the polarization conversion is also low. Thus, there is a distribution of values for the capacity of the two orthogonal paths, and these are shown in FIGS. For the case of spatial diversity, there is a very small angular spread at the base station and the base station antenna elements are assumed to be fully correlated. For the case of polarization diversity, the antenna elements at both ends are completely uncorrelated, but it is assumed that there is no polarization conversion in the environment. Clearly, the capacity achieved with a polarization diversity arrangement is at a maximum. Note that the distribution of the power gain for these cases is shown in FIGS.
[0042]
Finally, if we look in a multipath-rich environment where the spatial diversity is uncorrelated at both ends, and again if Rayleigh fading is assumed for all paths, the resulting capacity distribution is shown in FIG. It is shown.
[0043]
In this environment, the polarization conversion is likely to be very high. We assume that the cross-polarization ratio is 0 dB, and the capacity curve for the 2: 2 polarization diversity MIMO configuration is exactly reduced to that shown in FIG. Are equivalent. This also occurs for 2: 4, 2: n or similar polarization diversity MIMO configurations.
[0044]
Measurements for a 2: 2 MIMO system clearly show that polarization diversity performs better than a spatial diversity antenna configuration. This finding can be extended to 2: n MIMO systems and other suitable MIMO configurations. Measurements were made using outdoor base stations and indoor subscriber terminals in a suburban environment. This result for the power gain of two orthogonal MIMO paths is shown in FIG. This path gain for the polarization diversity antenna configuration is higher than that obtained for the spatial diversity antenna configuration. Note that a 10 wavelength separation was used for the antenna at the base station and a 0.5 wavelength separation was used for the antenna at the subscriber for the spatial diversity configuration. Thus, the measurements clearly show that polarization diversity is even stronger than spatial diversity.
[0045]
As mentioned above, one advantage of a MIMO system that uses only polarization diversity instead of spatial diversity is that the line-of-sight situation is adapted. Four examples of situations where a MIMO system with only polarization diversity can be used are described with reference to FIGS. 11-14 and many of these include line-of-sight situations. In each of these examples, the antenna configuration is combined with a suitable space-time coding scheme to provide a MIMO system.
[0046]
FIG. 11 shows two wireless portable devices 111, 112, such as personal digital assistants (PDAs) or laptop computers, adapted to communicate with each other using a MIMO system using only polarization diversity. Any suitable portable device may be used and the communication may be between different such portable devices. A plurality of polarized antenna elements are integrated in each of the portable wireless devices 111 and 112. Any preferred type of polarization may be used, horizontal / vertical polarization, left and right hand circular polarization, ± 45 ° polarization, or other types. Each portable device 111, 112 is dual-polarized, ie, operates with two different polarizations, and has an antenna element or has a set of antenna elements, and each component of such a set is substantially It is either polarized orthogonally with respect to the other components of the set. The antenna may be, for example, a printed dual polarization patch antenna, a crossed dipole / monopole type element, a crossed slot or a right and left handed circularly polarized antenna.
[0047]
A preferred number of antenna elements are used in each portable device, and there may be more antenna elements in one device than in other devices. However, in a preferred embodiment, two dual-polarized antenna elements are used in each device, or two in one device and four in the other.
[0048]
In the example shown in FIG. 11, horizontal (H) and vertical (V) polarization antenna elements are used in each portable device. The resulting MIMO system provides two orthogonal channels, indicated by arrows VV and HH in FIG. Scattering in the environment causes some polarization conversion and this is indicated by the dashed arrows VH and HV in FIG. In this situation, the portable devices are typically close to each other (eg, <10 m apart), so that there is a high probability that there is a line of sight. However, since MIMO with polarization diversity is used, as opposed to spatial diversity, such line-of-sight MIMO communication is effective.
[0049]
FIG. 12 shows a fixed radio access system having a base station antenna 120 having a plurality of antenna elements 121 and a directional subscriber antenna 122 having a plurality of antenna elements 123. In each case, the antenna element may be double polarized or polarized as described with reference to FIG. Also, with respect to FIG. 11, any preferred number of antenna elements may be used, however, 2: 2 or 2: 4 MIMO systems are provided with horizontal (H) and vertical (V) polarization. Is preferred. The directivity of the subscriber array 122 increases the signal-to-noise ratio, and a 2: 2 MIMO system constitutes two parallel orthogonal channels (HH, VV in FIG. 12). The use of MIMO with polarization diversity over spatial diversity, even when line-of-sight line conditions are involved, allows effective communication to be established.
[0050]
FIG. 14 shows an indoor wireless local area network (WLAN) base station 140 that is mounted on the ceiling but can be located in any suitable location. This base station 140 communicates with a PC 141 having a plurality of polarization antenna elements. In this example, another wireless modem 142 connected to PC 141 is used. Wireless modem 142 has an integrated dual polarization antenna element. This is an example, but the antenna element may be of any type and is connected or integrated with a suitable type of terminal. Base station 140 also has multiple polarization antennas and communicates with user terminal 140 via a MIMO link. There is a possibility of line-of-sight situations, especially in large open plan offices, as well as large amounts of multipath scatter. The use of two polarized antenna elements ensures that there are at least two orthogonal paths at every location with respect to the base station. This is true even if the base station is outdoors and the user is near the base station.
[0051]
FIG. 13 shows a base station antenna array 130 having a plurality of polarization antenna elements. MIMO communication at a mobile or mobile user terminal 131 occurs with a user terminal that also has multiple polarization antenna elements as described above. In such a situation, the polarization conversion is usually low, the line-of-sight path is often present, and the angular spread is often low at both ends of the link. By using MIMO with only polarization diversity (i.e., without spatial diversity), the link capacity can be increased as compared to using MIMO with only spatial diversity. In addition, the antenna elements can be arranged in close proximity, which allows them to be more easily integrated into portable terminals or other user terminals with limited space.
[0052]
In another example, the base station of FIG. 13 is modified to provide multiple antenna beams in addition to MIMO communication. This allows the capacity to be further increased compared to using MIMO communication alone. This will be described in further detail with reference to FIGS. 15A and 15B, which show an example of how a MIMO system with polarization diversity but without space diversity can be combined with a multi-beam antenna.
[0053]
As described above with reference to FIG. 2, a multi-beam antenna system requires closely spaced antenna elements, for example, with half-wave spacing. FIG. 15A shows an example of a base station antenna array 150 having such closely positioned antenna elements 151. In this case, each antenna element is a row of six polarized antenna elements. Six such rows are used at half-wavelength intervals in the azimuthal range. As shown in FIG. 15B, two beamformers are used with this array to form three antenna beams at each of the two polarizations. One beamformer forms three antenna beams A1, A2, A3 at one polarization, ie, + 45 °, while another beamformer forms another antenna beam, ie, −45 °. Form three antenna beams B1, B2, B3. Any preferred type of beamformer may be used, such as the modified Butler matrix beamformer shown in FIG.
[0054]
FIG. 22 is a schematic diagram of a modified Butler matrix beamformer. This shows a 6 by 6 Butler matrix 222, implemented in a planar structure with concentric layout hybrid couplers, easily implemented in a triplate. Three antenna beams (A, B, C) are generated by combining adjacent beam ports as shown. This is described in detail in US patent application Ser. No. 09 / 394,835, assigned to our Nortel Network, and is incorporated herein by reference. A particular advantage of using such a beamformer is that insertion loss is minimized.
[0055]
Beams A1, B1 are used to form a first MIMO communication link with subscriber station 152, while beams A2, B2 are used by subscriber station 153 (or other suitable subscriptions served by beams A2, B2). And the third MIMO link is used to establish a second MIMO link with any subscriber station (eg, 154) served by beams A3 and B3. As used to configure, the base station is also adapted to use space-time coding across a set of antenna beams.
[0056]
Since only polarization diversity is used for a MIMO system, it is possible to combine MIMO and a multi-beam arrangement in this way. In the first order, this has the advantage of increased capacity, since the capacity gains of multi-beam and MIMO systems are independent. The resulting hybrid system shares the benefits of both approaches.
[0057]
A specific embodiment of a combined MIMO and multi-beam arrangement adapted for either mobile or fixed wireless applications is described. FIG. 16 shows a case where a fixed wireless application is included. Base station 160 provides a communication link to a customer premises equipment (CPE) 161 that includes four polarized antenna elements having four receiver chains and two transmitter chains. The base station is preferably 3-sectored, and within each sector, two polarizations with a 2-branch MIMO transmission on the downlink, as described with reference to FIGS. 15A and 15B. There are provided three beam outputs.
[0058]
FIG. 17 shows a base station (BTS) structure. Six rows of cross-polarized antenna arrays 170 are provided for each facet of the base station, and are common to both downlink and uplink designs. Each antenna facet serves as a single sector of the cell of the base station and uses two radio frequency (RF) beamformers to provide three beam outputs of both two polarizations. It is also possible to provide different numbers of beam outputs. For example, 4 beams per sector provides a large capacity, but requires additional RF feeder cables and additional upconverter and downconverter modules. Any suitable beamformer can be used, and in a preferred example, an orthogonal 6-way modified Butler matrix beamformer (see, for example, FIG. 22) is used, which is a low-loss solution ( The quadrature beamformer itself is nominally lossless) and provides a suitable beam width, crossover between adjacent beams and sidelobe levels. FIG. 18 shows the resulting beam pattern plotted with a conventional 65 ° beamwidth full sector pattern (see line 180) consistent with a tri-cellular deployment for comparison purposes. This beam pattern was obtained for a dipole element array at a 45 ° angle and shows three main beams 181, 182, 183. An advantage of the resulting beam pattern is that the degree of overlap of adjacent beams is reduced, especially in close range, to minimize the interference experienced within large portions of the sector. Thus, low crossover or cusp levels along with suppressed sidelobes are dominant. The beams are relatively narrow (beam width of about 25 ° or less) and are about every 40 ° apart.
[0059]
The beamformer is preferably integrated with the antenna facet, as this eliminates the need for active phase calibration through the RF chain. However, this is not required. Beamformers that are not so integrated can be used.
[0060]
In addition to multi-beam sectorization, a two-branch MIMO transmission on the downlink is provided. MIMO transmission is achieved by using a polarized antenna array 170. The same set of beams is formed on the two orthogonal polarizations, and the transmission is coded over the corresponding set of beams using a suitable space-time coding scheme. Such an approach offers the benefits of both multi-beam and STC from a single small antenna aperture.
[0061]
For the uplink, the same multi-beam configuration as for the downlink is preferably used with polarization diversity. Beam directivity provides significant interference reduction. Subscribers located at the cusp of the beam tend to suffer from degraded link performance compared to subscribers located at the peak of the beam. However, degradation is minimized by coherently combining adjacent beam outputs (at both polarizations) to achieve improved gain and increased diversity benefits.
[0062]
The invention is particularly suitable for the downlink (moving from the base station) or other user terminals, where the capacity load is likely to be greatest, for example the provision of services to end users such as web pages and Internet applications. Related.
[0063]
As mentioned above, any suitable type of space-time coding method can be used. For example, space-time block coding (STBC) shown in the top layer of FIG. 19; layered space-time (BLAST) further applicable to fixed or floating applications and shown in the middle layer of FIG. 19; and There is a space-time trellis coding (STTC) suitable for both mobile and fixed applications and shown at the bottom of FIG.
[0064]
Another preferred method is feedback space-time coding with separated sub-channels, as in FIG. This type of feedback or eigenmode STC simplifies the reception process by separating the parallel streams of the transmitter. It requires feedback of MIMO channel weights from receive to transmit and is most suitable for low Doppler fixed or idle applications.
[0065]
Spatial multiplexed space-time coding can also be used as shown in FIG. In this method, independent encoded data streams are sent to different transmit antennas. The receiver is required to perform spatial processing to separate the different transmissions. This requires a clear spatial signature at the receiver and the performance is HH ^* , Where H is the channel matrix. When the eigenvalues are imbalanced, the performance is worse than the eigenmode STC, but the feedback requirements are greatly reduced.
[0066]
In the above embodiment where MIMO and multi-beam systems are combined, a space-time coded MIMO communication method is used for each antenna beam link. For example, consider the case of three antenna beams, each with two polarizations. One of those antenna beams, and the corresponding beam at the other polarization, serve one or more subscribers or users located within the geographical area provided by those beams. . MIMO, space-time coded communication between the base stations and their users occurs via a set of antenna beams. By using MIMO, it is possible to increase the communication rate for those users. The same occurs for users in a geographical area served by the other two sets of antenna beams. In this way, the capacity is increased compared to using three sets of antenna beams without MIMO communication.
[0067]
However, it is also possible to simultaneously provide both MIMO space-time coded communication and non-MIMO, non-space-time coded communication from one or more antenna beams. This has the advantage that non-MIMO compliant traditional user equipment can operate, while at the same time MIMO compliant user equipment can be used. The user or subscriber unit is adapted to be able to distinguish between MIMO and non-MIMO communication packets using a suitable method, such as by having different carrier frequencies for the two types of signals. You. The base station is adapted to multiplex MIMO and non-MIMO packets such that both of these types of communications are transmitted from the base station simultaneously.
[0068]
The ranges and device values given here can be extended or changed without losing the effect sought, as will be apparent to those skilled in the art with an understanding of the teachings herein.
[0069]
The scope of the application is within the scope of the present invention. These include the situations required to provide a MIMO wireless communication system that operates without spatial diversity but instead with polarization diversity. For example, in line-of-sight situations or when MIMO and multi-beam systems are combined.
[Brief description of the drawings]
FIG.
1 is a schematic diagram of a prior art MIMO wireless communication system.
FIG. 2
1 is a schematic diagram of a conventional multi-beam wireless communication system.
FIG. 3
Fig. 4 is a graph of the theoretical distribution of channel power gain for a 2: 2 MIMO system with a spatial diversity antenna for the case where the base station antennas are fully correlated and for the case where they are uncorrelated; 4 is a graph showing a Rayleigh distribution for a 1: 1 system.
FIG. 4
5 is a graph illustrating the theoretical distribution of channel power gain for a 2: 2 MIMO system when a dual polarization element is used instead of a spatially separated antenna with or without polarization conversion. is there.
FIG. 5
FIG. 4 is a graph illustrating the theoretical capacity of a 2: 2 spatial diversity MIMO system compared to a 1: 1 link in a non-fading environment for different values of the signal-to-noise ratio.
FIG. 6
FIG. 6 is a graph showing the theoretical capacity of a 2: 2 polarization diversity MIMO system (without spatial diversity) compared to a 1: 1 link in an environment similar to FIG. 5, but without fading. .
FIG. 7
5 is a graph illustrating theoretical capacity distribution for a 2: 2 spatial diversity MIMO system with fully correlated base station antennas (transmitters) and completely uncorrelated terminals for different values of the signal-to-noise ratio. is there.
FIG. 8
FIG. 8 is a graph for a 2: 2 polarization diversity MIMO system similar to FIG. 7, but without polarization conversion in the environment and (without spatial diversity).
FIG. 9
FIG. 9 is a graph similar to FIGS. 7 and 8 for a 2: 2 spatial diversity MIMO system with completely uncorrelated antenna elements.
FIG. 10
Figure 4 is a graph of empirical results; showing measured distributions of power gain for orthogonal MIMO paths for 2: 2 spatial and polarization diversity configurations.
FIG. 11
FIG. 2 is a schematic diagram of a MIMO communication link between two portable wireless communication terminals of a personal area network.
FIG.
FIG. 2 is a schematic diagram of a MIMO communication link in a fixed wireless access situation.
FIG. 13
FIG. 2 is a schematic diagram of a MIMO communication link between a base station and a mobile or mobile user terminal.
FIG. 14
1 is a schematic diagram of a MIMO communication link in a wireless local area network.
FIG. 15A
1 is a schematic diagram of an antenna array used at a base station in a mobile or fixed wireless access MIMO communication network.
FIG. 15B
FIG. 15B is a schematic diagram of an antenna beam configuration generated using the antenna array of FIG. 15A.
FIG.
FIG. 2 is a schematic diagram of a fixed radio access MIMO arrangement.
FIG.
FIG. 2 is a schematic diagram of a radio frequency configuration of a base station that provides both MIMO and multi-beam communication.
FIG.
FIG. 18 is a diagram illustrating an antenna beam pattern for the antenna array of FIG. 17.
FIG.
FIG. 3 is a schematic diagram of three space-time coding methods: space-time block coding, layered space-time, and space-time trellis coding.
FIG.
FIG. 4 is a schematic diagram of a feedback space-time coding method using separated sub-channels.
FIG. 21
FIG. 2 is a schematic diagram of a spatial multiplexing space-time encoding method, also known as BLAST.
FIG.
FIG. 2 is a schematic diagram of a beamformer used in one embodiment of the present invention.

Claims (23)

(I) a plurality of transmitting antenna elements;
(Ii) a plurality of receiving antenna elements,
A multiple-input multiple-output (MIMO) wireless communication system, wherein the transmitting antenna elements are arranged to provide polarization diversity, and the positions of the transmitting antenna elements are arranged to avoid spatial diversity. The MIMO wireless communication system according to claim 1, wherein each of the transmit antenna elements is polarized at one of two first substantially orthogonal polarizations. The MIMO wireless communication system according to claim 2, wherein each of the receiving antenna elements is polarized at one of two second substantially orthogonal polarizations. 4. The MIMO wireless communication system according to claim 3, wherein the two first substantially orthogonal polarizations are different from the two second substantially orthogonal polarizations. The plurality of transmit antenna elements have one or more dual polarization elements, each such dual polarization element being two closely spaced elements operable from a single antenna aperture. The MIMO wireless communication system according to claim 1, wherein the MIMO wireless communication system is an antenna element. The MIMO wireless communication system according to any one of claims 1 to 5, wherein the plurality of transmitting antenna elements are provided by an antenna array. The MIMO wireless communication system according to any one of claims 1 to 6, wherein the MIMO wireless communication system is arranged to operate at a specific wavelength, and an inter-element spacing of the transmission antenna elements is shorter than one of the specific wavelengths. The MIMO wireless communication system according to any one of claims 1 to 7, arranged to provide non-MIMO communication in addition to MIMO communication. The MIMO wireless communication system according to any one of claims 1 to 8, wherein the transmitting antenna elements are co-located to provide a plurality of antenna beams being used. 10. The MIMO wireless communication system of claim 9, wherein the plurality of antenna beams are provided using one or more beamformers integrated with a transmitting antenna element. The plurality of antenna beams has a set of antenna beams, each set being substantially the same as the first antenna beam of the first polarization, but different from the first polarization. The MIMO wireless communication system according to claim 9 or 10, comprising a second antenna beam provided at a second polarization. The MIMO wireless communication system according to claim 11, wherein each of the sets of antenna beams is arranged to provide a two-branch MIMO input. The MIMO wireless communication system according to any one of claims 1 to 12, wherein the MIMO wireless communication system is selected from 2: 2 and 2: 4 MIMO systems. The MIMO wireless communication system according to any one of claims 1 to 13, wherein the MIMO wireless communication system is selected from a fixed wireless access system, a personal area network, a wireless local area network, and a mobile communication network. 15. The MIMO wireless communication system according to any one of claims 1 to 14, wherein each of the transmitting antenna elements has a row of antenna elements. (I) transmitting a space-time coded signal from a transmitting antenna arrangement having a plurality of transmitting antenna elements arranged such that polarization diversity is provided and spatial diversity is avoided;
(Ii) receiving a space-time coded signal in a receiving antenna arrangement having a plurality of receiving antenna elements;
A multiple input multiple output wireless communication method comprising: Furthermore,
(I) determining the positions of the transmitting antenna arrangement and the receiving antenna arrangement such that there is a line of sight line between the two arrangements;
17. (ii) using the transmit antenna configuration to transmit a space-time coded signal to a receive antenna configuration at least partially along the line of sight line. The described method. 18. The method according to claim 16 or claim 17, further comprising transmitting a non-space-time coded signal from the transmit antenna arrangement simultaneously with the space-time coded signal. An antenna arrangement for use in a multiple-input multiple-output (MIMO) wireless communication system, comprising a plurality of transmit antenna elements arranged to provide polarization diversity, and wherein the position of the transmit antenna elements is spatial diversity. The antenna arrangement has been made to avoid. 20. The antenna arrangement of claim 19, wherein the antenna arrangement is arranged to operate at a particular wavelength, and wherein the spacing between the transmitting antenna elements is shorter than one of the particular wavelengths. 21. The antenna arrangement according to claim 19 or 20, suitable for use in a non-MIMO communication system as well as in a MIMO communication system. The method of operating an antenna arrangement according to claim 19, comprising transmitting a space-time coded signal from the antenna arrangement. Further, having a plurality of receive antenna elements, the method includes receiving a space-time coded signal at the antenna arrangement, wherein the signal is polarized differently and has a substantially negligible amount. 20. A method for operating an antenna arrangement according to claim 19, having a spatial diversity of:

Images