MIMO wireless communication system

• US 6,870,515 B2
• Filed: 10/11/2001
• Issued: 03/22/2005
• Est. Priority Date: 12/28/2000
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Ward, Chris, Kitchener, Dean, Smith, Martin
• Primary Examiner(s): Wimer, Michael C.
• Application Number:
  US09/975,653
• Publication Number:
  US 20020085643A1
• Time in Patent Office: 1,258 Days
• Field of Search: 343/795, 343/797, 343/754, 343/815, 343/853, 342/361, 455/562.1
• US Class Current: 343/853
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0469 taking special antenna structures, e.g. cross polarized antennas into account
• CPC Class Codes: H04B 7/0626 Channel coefficients, e.g. channel state information [CSI]
• CPC Class Codes: H04B 7/0673 using feedback from receiving side
• CPC Class Codes: H04B 7/0891 Space-time diversity rake receivers H04B1/7115; space-time decoding H04L1/0631
• CPC Class Codes: H04B 7/10 Polarisation diversity; Directional diversity
• CPC Class Codes: H04L 1/0625 Transmitter arrangements

Abstract

Previous MIMO systems have used spatially diverse antenna elements in order not to reduce the number of orthogonal channels that can be realized. The present invention recognizes that this leads to large antenna sizes, as compared to multiple beam antenna systems which use closely spaced antenna elements. In order to provide a compact antenna unit, while still allowing a MIMO system to be exploited, the present invention recognizes that polarization diversity only can be used in a MIMO system without the need for spatially diverse antenna elements. Closely spaced antenna elements are used and this enables a compact MIMO antenna unit to be provided. In addition, such MIMO systems with polarization diversity but no spatial diversity can advantageously be used in line of sight situations and also combined with multi-beam antenna systems to further increase capacity.

Claims

1. A multiple-input multiple-output (MIMO) wireless communications system comprising:

(i) a plurality polaised antenna array located at a transmitter, the array comprising a plurality of transmit antenna elements;

(ii) a beamformer for coherently combining elements of a same polarisation to form a first directional beam having a first polarisation and a second directional beam having a second polarisation; and

(iii) a plurality of receive antenna elements located at a receiver;

wherein the first and second beams provide two independent MIMO channels between the transmitter and the receiver.

2. A MIMO wireless communications system as claimed in claim 1 wherein each of said transmit antenna elements is polarised at one of two first substantially orthogonal polarisations.

3. A MIMO wireless communications system as claimed in claim 2 wherein each of said receive antenna elements is polarised at one of two second substantially orthogonal polarisations.

4. A MIMO wireless communications system as claimed in claim 3 wherein said two first substantially orthogonal polarisations are different from said two second substantially orthogonal polarisations.

5. A MIMO wireless communications system as claimed in claim 1 wherein said plurality of transmit antenna elements comprises one or more dual-polar-elements each such dual-polar-element being two co-located antenna elements operable from a single antenna aperture.

6. A MIMO wireless communications system as claimed in claim 1 which is arranged to operate at a particular wavelength and and wherein the inter-element spacing of the transmit antenna elements is less than one of the particular wavelength.

7. A MIMO wireless communications system as claimed in claim 1 which is arranged to provide both non-MIMO communications and MIMO communications substantially simultaneously.

8. A MIMO wireless communications system as claimed in claim 1, comprising one or more beamformers integral with the transmit antenna elements.

9. A MIMO wireless communications system as claimed in claim 1 wherein said beamformer forms a plurality of pairs of antenna beams, each pair comprising a first antenna beam of a first polarisation and a second antenna beam, substantially identical to the first but provided at a second polarisation different from the first polarisation.

10. A MIMO wireless communications system as claimed in claim 9 wherein each of said pairs of antenna beams is arranged to provide a two-branch MIMO input.

11. A MIMO wireless communications system as claimed in claim 1 which is selected from a 2:

2 and a 2;

4 MIMO system.

12. A MIMO wireless communications system as claimed in claim 1 which is selected from a fixed wireless access system, a personal area network, a wireless local area network, and a mobile communications network.

13. A MIMO wireless communications system as claimed in claim 1 wherein each of said transmit antenna elements comprises a column of antenna elements.

14. A multiple-input multiple-output wireless communications method comprising the steps of:

(i) forming a first directional beam having a first polarisation and a second directional beam having a second polarisation from a transmit dual polarised antenna array comprising a plurality of antenna elements by coherently combining elements of a same polarisation;

(ii) transmitting a space-time coded signal from a transmit antenna array; and

(iii) receiving the space-time coded signal at a receive antenna arrangement comprising a plurality of receive antenna elements;

wherein said first and second beams provide two independent MIMO channels between the transmit antenna array and the receive antenna arrangement.

15. A method as claimed in claim 14 which further comprises:

(i) positioning the transmit antenna array and the receive antenna arrangement such that a line of sight path is present between those two arrangements; and

(ii) using said transmit antenna array to transmit the space-time coded signal to the receive antenna arrangement at least partly along said line of sight path.

16. A method as claimed in claim 14 which further comprises transmitting a non-space-time coded signal from the transmit antenna array simultaneously with the space-time coded signal.

17. An antenna arrangement for use in a multiple-input multiple-output (MIMO) wireless communications system, said antenna arrangement comprising

a dual polarised antenna array comprising a plurality of transmit antenna elements and

a beamformer for coherently combining elements of a same polarisation to form a first directional beam having a first polarisation and a second directional beam having a second polarisation, wherein the first and second beams provide two independent MIMO channels between said antenna arrangement and a receive antenna arrangement.

18. An antenna arrangement as claimed in claim 17 which is arranged to operate at a particular wavelength and wherein the transmit antenna elements have an inter-element spacing which is less than one of the particular wavelength.

19. An antenna arrangement as claimed in claim 17 which is also suitable for use in a non-MIMO communications system simultaneously with use in the MIMO communications system.

20. A method of operating an antenna arrangement as claimed in claim 17 which comprises transmitting space-time coded signals from said antenna arrangement.

21. A method of operating an antenna arrangement as claimed in claim 17 which further comprises a plurality of receive antenna elements and wherein said method comprises receiving space-time coded signals at said antenna arrangement, said signals being polarisation diverse and having a substantially insignificant amount of spatial diversity.