KR20050017112A - Improvements in or relating to multiple transmission channel wireless communication systems - Google Patents

Abstract

The present invention provides a multiple transmission channel wireless communication system, such as a MIMO system, the system comprising a transmission station and at least one receiving station, the at least one station being a plurality of spaced apart An antenna system comprising antenna elements 16A, 16B, each antenna element comprising at least two antennas 20A, 20B of sub-arrays separated by less than half of the frequency of interest. . The antenna of each antenna element can be controlled to provide directional propagation or reception.

Description

Multi-channel wireless communication system and antenna system {IMPROVEMENTS IN OR RELATING TO MULTIPLE TRANSMISSION CHANNEL WIRELESS COMMUNICATION SYSTEMS}

FIELD OF THE INVENTION The present invention relates to multiple transmission channel wireless communication systems such as Multiple Input Multiple Output (MIMO) and spatial diversity wireless communication systems and the like, and more particularly, to such communication. It relates to, but is not limited to, the antenna system used in the system.

See, for example, (1) Forschini G. J, Gans M. J, entitled "On limits of wireless communications in a fading environment when using multiple antennas" (Wireless-Personal-Communications (Netherlands), vol. 6, no.3, pp. 311-335, March 1998) and (2) Telatar IE, entitled "Capacity of multi-antenna Gaussian Channels" (Tech.Rep. # BL0112170-950615-07TM AT & T Bell Laboratories , A recent development of information theory in 1995, has shown that by using multiple antennas at both the transmitter and receiver, an unprecedented level of capability can be achieved in a wireless communication system. This increase is due to the fact that multiple antennas exist at both ends, allowing the spatial separation of the antennas to identify different paths of signal energy transmitted and received in a number of different directions. Thus, multiple signals or substreams can be transmitted and decoded simultaneously. One technique using this is known as Bell Labs Layered Space Time (BLAST), the details of which are (3) "Layered space-time architecture for wireless communication in a fading environment when using multi-element antennas" by Foschini GJ. By title (Bell-Labs-Technical-Journal (US), vol. 1, no. 2, pp. 41-59, Fall 1996) and (4) by Wolniansky PW, Forschini GJ, Golden GD and Valenzuela RA A document entitled "V-BLAST: an architecture for realising very high data rates over the rich-scattering wireless channel" (1998 URSI International Symposium on signal, held in Pisa, Italy, from September 29 to October 2, 1998) , systems, and Electronics' conference newsletter). In BLAST, different sub-streams are delivered to several antennas at the transmitter. The sub-stream is decoded at the receiver using the measurement of the MIMO channel, which allows the process to make the sub-null null and eliminate the effect of the already detected sub-stream. This method requires the information of the channel in the receiver.

Another application of this method is disclosed in unpublished PCT application IB 02/00029 (representative reference number PHGB 010012), wherein the sub-stream is transmitted in several directions and more specifically (in more detail, the transmitter and The maximum power determined by the measurement of the multipath arrival angle at the receiver). The receiver can be used with a transmitter that has no information, such as for example a BLAST transmitter, but this method requires the information of the channel in the transmitter (the angle of transmission to the scatterer).

Both of these methods require an array of antennas and have a basic condition for antenna spacing (ie, the spacing between adjacent antennas should be half of the wavelength 112.) For BLAST, this means that the light beam is uniform on average This is because it is assumed that the distance at which one azimuth is reached and the other antenna must be spaced apart is less than [lambda] / 2, or preferably more than .. Similarly, to clearly specify the beam pattern, an interval of [lambda] / 2 However, there is a fundamental limit to the number of antennas that can be packed within a given area for a given wavelength, and therefore it seems difficult to clearly specify the beam pattern. In addition, each antenna recovers a base band signal from the RF signal received by this antenna. It requires each processor to group. The processes signals of a plurality of RF separately takes a relatively difficult and expensive.

1 is a schematic block diagram of a MIMO system.

2 is a diagram illustrating an antenna element including two pairs of orthogonally arranged antennas.

3 is a view showing a direction application range of a beam irradiated in two directions compared to an omnidirectional beam.

4 is a schematic block diagram of an antenna diversity apparatus.

5 illustrates a high density MIMO system with directional antenna elements.

6 is a diagram illustrating a high density MIMO system in which any device may be switched in one of two directions.

FIG. 7 is a diagram illustrating an embodiment of an antenna device supplied with a sub-array consisting of two antenna elements using a directional coupler.

8 through 10 are diagrams illustrating an antenna device for a switched MIMO system.

It is an object of the present invention to increase the number of antennas that can be packed in a given area without adversely affecting the operation of the system.

According to a first aspect of the present invention, there is provided a multiple transmission channel wireless communication system, the multiple transmission channel wireless communication system comprising a transmission station and at least one receiving station, wherein the at least one station comprises a plurality of spaced antennas An antenna system comprising elements, each antenna element comprising a sub-array of at least two antennas spaced apart by λ / 2 of the frequency of interest.

According to a second aspect of the invention, there is provided an antenna system for use in a multiple transmission channel wireless communication system, the antenna system comprising a plurality of spaced apart antenna elements, each antenna element being less than λ / 2 of the frequency of interest It comprises a sub-array consisting of at least two antennas apart.

The present invention provides that each antenna element of a large antenna array can be replaced by a sub-array consisting of antennas arranged at narrow intervals, and by preprocessing the RF signal received by the antenna of the sub-array using an RF network. It is based on the recognition that it is possible to reduce the number of base band processors required compared to having one processor for each antenna. In other words, a MIMO system (or spatial diversity system) consisting of an array of N elements (each element containing n antennas) may generally form at least nN directional beams. In one extreme case for a MIMO system, if all n beams of N elements are used, an nN × nN MIMO system can be created in the space normally occupied by the N × N system. Each branch may be decoratedrelated by a combination of pattern (amplitude and phase) and spatial diversity. Since spatial diversity depends on the spatial separation of the elements, two identical beam patterns spaced apart are somewhat uncorrelated. As another best case, n beams may be selected for each of the N devices to provide an N × N system.

The use of spatial diversity is known as the use of two antenna elements in a communication system such as digitally enhanced cordless telecommunications (DECT). Each antenna element is omnidirectional and is designed to be independent of other antenna elements. In order to avoid separating the antenna elements by a large distance and optionally to prevent detuning unused antenna elements, patent application WO 01171843 (Attorney Docket No. PHGB 000033) provides a plurality of An antenna diversity arrangement having an antenna is disclosed. If a signal with the appropriate amplitude and phase allows generation of a plurality of antenna beams, the correlation coefficient between any pair of beams will be substantially zero. The resulting antenna diversity device can optionally include a pair of antennas that are in close proximity to each other and have a near zero correlation between any pair of antenna beams, thereby providing a dense and effective device. There is no disclosure of such a device in a MIMO system such as BLAST and the like.

Hereinafter, the present invention will be described by way of example with reference to the accompanying drawings.

In the drawings, like reference numerals have been used to denote like features.

Referring to FIG. 1, the MIMO system includes a radio transmitter (Tx) 10 and two radio receivers (Rx) 12A, 12B. As mentioned in the introduction paragraph, typically the Tx 10 and Rx 12A, 12B have multiple antenna elements because the signal energy associated with multiple signals or sub-streams is transmitted and received from several different directions. do. Optionally, information about the angles at the time of transmission and reception can be used to select the beam direction in which the signal with the maximum power is achieved. For simplicity of explanation, Tx 10 and Rx 12A, 12B each have the same antenna system 14. Antenna system 14 comprises at least two antenna elements 16A, 16B, which are spaced apart by substantially half (λ / 2) of the wavelength of the desired or center frequency. Each antenna element 16A, 16B includes RF networks 18A, 18B, and two antennas 20A, 20B are connected to each. The antennas 20A, 20B of each antenna element 16A, 16B are spaced apart by less than [lambda] / 2 (typically less than [lambda] / 4) or have a difference of 90 [deg.] For the beam irradiated in the opposite direction. The electrical spacing for the uncorrelated beam can optionally be 125 °, for example.

In the case of Tx 10, data is encoded by encoder 22, and the encoded signal is modulated by modulator 24 on a carrier. The modulated signal is supplied to a power amplifier 26, which has an output terminal connected by lines 21A and 21B to respective RF networks 18A and 18B. Feed arrangements 18A, 18B may control the pair of antennas 20A, 20B respectively to propagate a signal in a predetermined direction (s).

At each receiver (Rx) 12A, 12B, each RF network 18A, 18B is connected to an RF stage 28 and its output terminal is connected to a demodulator 30. The decoder 32 is connected to the output terminal of the demodulator 30.

The RF network 18A, 18B processes RF signals from both antennas 20A, 20B, thereby reducing the number of receivers and baseband processors compared to having one receiver and baseband processors per antenna. do. In addition, this RF network solves the RF interaction problem that can be issued between very close antennas in an advantageous manner. As a further refinement, receiver RF networks 18A and 18B may control their respective antennas so that signals can be detected from the direction in which the maximum power is received.

FIG. 2 shows a modification of the antenna elements 16A and 16B shown in FIG. In this variant, each antenna of the antenna elements 16A, 16B comprises orthogonal polarization, respectively, including a pair of orthogonally arranged antennas 20A, 20A 'and 20B, 20B'.

To help understand how to control the transmission direction and / or the reception direction using the RF network, reference was made to FIG. 3 which shows an example of a direction coverage for two element antenna arrays as shown in FIG. 4. . The transmitter 34 with the diversity device may transmit and receive using the omni-directional beam 36, the first directional beam 38 shown in broken lines and the second directional beam 40 shown in broken lines. .

Referring to FIG. 4, it is assumed that antenna elements 20A and 20B are located on a single axis. In the first transmission mode, the antenna element 20A is considered as a reference, and the amplitude and phase of the supply signal to the antenna element 20B are adjusted by the stage 42 to form a directional beam in a specific direction. In the second transmission mode, the relative amplitude and phase are inverted, thus forming a directional beam in the opposite direction. The stage 42 may adjust the phase of the signal by ± 180 °. Considering the nature of the antenna system, the same description above can also be applied to achieving antenna directionality at reception.

FIG. 5 shows a pair of antenna elements arranged close enough to significantly increase mutual couplings and have the effect of causing re-radiation from adjacent antennas. This, in contrast to omnidirectional, where there is no mutual coupling, causes the radiation pattern for each antenna to be directional when other antennas are present. Increased directionality generally means that each antenna is sampled with different multipaths or with differently weighted combinations of the same multipath, so that correlations tend to be reduced.

According to the invention, the antenna element comprises an array formed of two or more antennas arranged at narrow intervals, which are combined to form a larger antenna system. The MIMO system (or spatial diversity system) consists of an array of N antenna elements, so to speak, each of which typically contains n antennas capable of forming n directional beams. In one extreme case for a MIMO system, if all n beams of N elements are used, an nN × nN MIMO system can be created in the space normally occupied by the N × N system. Each branch may be uncorrelated by a combination of pattern (amplitude and phase) and spatial diversity. Since spatial diversity depends on the spatial separation of the antennas, each containing an antenna element, two identical beam patterns spaced apart are somewhat uncorrelated. As another best case, n beams may be selected for each of the N devices to provide an N × N system.

A possible drawback to having a high density MIMO system of the type shown in FIG. 5, which can be a receiver for a 4x4 MIMO system (also a 1x4 diversity receiver), is that the instantaneous reception angle will have a narrow angle distribution. As is possible, this creates the problem that very uneven power is received across the beam, and may provide the effect that some beams cannot receive certain power from any sub-stream. This can be fatal in terms of MIMO, since the number of received samples of a sub-stream (antenna or different beam pattern) is less than the number of sub-streams (ie, the number of independent expressions is uncertain). Less than the number), making it impossible to reliably decode the sub-stream.

Since each sub-array can select one of several possible directions, this situation is less likely to occur in the apparatus shown in FIG. 6, which can select the beam direction to receive a certain amount of power. In the case of the example shown in FIG. 6, both beams were chosen to face the direction in which most multipaths arrive. In this example, it is in the same direction. The degree of decorrelation may be as good or less as good as the spatial diversity of the omni-directional antenna, but its spatial separation is a mechanism to de-correlate two branches for the same device spacing. However, there is approximately an additional 3 dB of gain in the two branches' end-fire direction, which can offset any capacity reduction due to additional correlation.

The example shown in FIG. 6 is an extreme example since it is assumed that no power comes from the opposite direction, so it would be better for the two beams to have the same direction. If this assumption is not made, it may be better to choose a switching algorithm that chooses the strongest direction since the correlation between branches can be the most important factor. Thus, although the power from the opposite direction may be smaller, the overall correlation may be smaller by selecting that direction. This needs to be compromised for the fact that the power difference across the entire power and branch is smaller.

Comparing the apparatus shown in Figs. 5 and 6, the high density method (Fig. 5) and N, which use all possible modes of providing an nN × nN MIMO system in the space of the N × N system, have problems of reliability, and N There is a tradeoff between a switched architecture (FIG. 6) which provides an xN system but which is likely to increase reliability and capacity.

Referring to FIG. 7, a high density MIMO system includes arrays of antenna elements 16A and 16B respectively formed by antennas 20A and 20B, the phases of which are either digital or using RF phase shifters. It is formed using phase shifts in the digital domain. 7 shows a 4x4 MIMO transmitter using hybrid couplers 42A and 42B to form a phase of a pair of antennas 20A and 20B arranged at narrow intervals. Hybrid couplers 42A and 42B are supplied with pairs of signal voltages s ₁ , s ₂ and s ₃ , s _4, respectively. When the signal voltages s ₁ , s ₃ are higher than the signal voltages s ₂ , s ₃ , the antenna element is directional in the directions d ₁ , d ₃ . In the opposite situation, the antenna elements 16A, 16B are directional in the directions d ₂ , d ₄ .

At the receiver, the four ports of hybrid coupler 42A or 42B may be four branches of the MIMO receiver. This principle can be extended for all N when n = 2. Problems that can occur in this device are related to finding a suitable match between the source, hybrid coupler and antenna because the impedance between different ports of the coupler varies for different phase shifts. Another method of applying phase shift is to use digital beam forming techniques, where the problem of impedance matching of the array is virtually eliminated. It should be noted that in this case of MIMO it is necessary to have an RF transmitter and receiver as long as the sub-stream is present.

FIG. 8 illustrates one embodiment of a portion of a switched MIMO system that includes either 16A or 16B of two antenna elements, where each antenna element includes antennas 20A and 20B. . In this embodiment, each antenna element 16A or 16B is controlled to select one of two possible beams, so that only two sub-streams are transmitted or only two samples of the sub-streams are received. Switched parasitics antennas can be used to switch the antennas 20A and 20B of each antenna element. As shown in FIG. 8, the directional beams are formed using complex voltages V ₁ and V ₂ supplied to the antennas 20A and 20B, respectively. The complex impedance of the resulting antenna is Z ₁ and Z _2, respectively. In addition, the same beam pattern may be generated by replacing the source V ₂ with a pure reactance (-jX ₂ ) that is an imaginary part of the impedance of the antenna 20B. Using such reactance means, this interaction can produce a voltage very close to the correct supply voltage when the source V ₂ is replaced with a pure reactance (-jX ₂ ). This technique works best when each part of the impedance is small. This is shown in FIG.

In order to generate the beam in the opposite direction, the voltage must be swapped, so that the impedance of the antenna will also be swapped. The antenna 20A may be limited to the impedance (-jX ₂ ), and the antenna 20B may be supplied with the voltage V ₁ .

10 illustrates a combination of these possibilities using a switching architecture with a single antenna element 16A including antennas 20A and 20B. Two sources S1, S2 and two impedances 44, 46, shown at the same pure reactance (-jX ₂ ), are provided, and the first exchange switch 48 is either of the source S1 or impedance 44. Either one is connected to the antenna 20A, and the second exchange switch 50 connects either the impedance 46 or the source S2 to the antenna 20B. If the switches 48 and 50 are in the shown position, the directional lobe is shown in solid lines, and if the switches are in opposite positions as shown by the broken lines, the directional lobe is shown in broken lines.

Advanced antenna systems can be used with transmitters and receivers that operate in accordance with several standards such as UMTS, HiperLan / 2, IEEE 802.11A & B, and the like. This can be used to improve the capacity of mobile and wireless LANs to provide higher data rates, lower power consumption or lower bandwidth wireless communication devices.

Elements expressed in the singular in the specification and claims do not exclude the presence of a plurality of such elements. In addition, the word "comprises" does not exclude the presence of elements or steps other than the listed elements or steps.

By reading this disclosure, other modifications will be apparent to those skilled in the art. Such modifications may include other features and portions thereof already known in the design, manufacture, and use of multiple transport channel wireless communication systems, and may be used in place of or in addition to those previously mentioned herein. In the present invention, the claims are made of a combination of specific features, but the scope disclosed in the present invention also relates to the invention as claimed in any claim and whether to mitigate some or all of the same technical problems as in the present invention. Regardless, it should be understood to include new features, any new combination of features explicitly or implicitly disclosed herein, or generalized features thereof. Applicants of the present invention have mentioned that new claims may be made from such features and / or combinations of such features during the execution of the present application or any additional application derived therefrom.

Claims (14)

Multiple transmission channel wireless communication system, A transmitting station 10 and at least one receiving station 12, At least one said station has an antenna system 14 comprising a plurality of spaced apart antenna elements 16A, 16B, Each said antenna element comprises a sub-array consisting of at least two antennas 20A, 20B which are separated by less than λ / 2 of the frequency of interest. Multiple transmission channel wireless communication system. The method of claim 1, And said antennas (20A, 20B) of said sub-array are connected to an RF network (18A, 18B) to process signals received by said antennas. The method according to claim 1 or 2, And the antennas (20A, 20B) of each of the sub-arrays are spaced apart by less than [lambda] / 4. The method of claim 1, A hybrid coupler (42A, 42B) couples the antennas of each of the sub-arrays together. The method according to claim 1 or 2, And the antennas (20A, 20B) of the sub-array can be switched to achieve directional propagation or reception. The method of claim 1, The antenna system (14) forms a multiple orthogonal antenna beam pattern. The method according to claim 1 or 2, The sub-array includes an antenna (20) configured to provide orthogonal polarization. An antenna system used in a multiple transmission channel wireless communication system, The antenna system comprises a plurality of spaced apart antenna elements 16A, 16B, Each said antenna element comprises a sub-array consisting of at least two antennas 20A, 20B which are separated by less than λ / 2 of the frequency of interest. Antenna system. The method of claim 8, The antenna (20A, 20B) of the sub-array is connected to an RF network (18A, 18B) to process signals received by the antenna. The method according to claim 8 or 9, The antennas (20A, 20B) of each said sub-array are spaced apart by less than [lambda] / 4. The method of claim 8, A hybrid coupler (42A, 42B) coupling the antennas of each of the sub-arrays together. The method according to claim 8 or 9, The antenna (20A, 20B) of the sub-array can be switched to achieve directional propagation or reception. The method according to claim 8 or 9, The antenna system (14) forms a multiple orthogonal antenna beam pattern. The method according to claim 8 or 9, The sub-array includes an antenna (20) configured to provide orthogonal polarization.