Radio Channel Estimator

• US 20100087151A1
• Filed: 09/30/2009
• Published: 04/08/2010
• Est. Priority Date: 09/30/2008
• Status: Active Grant

• Current Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Original Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Inventors: Auer, Gunther
• Granted Patent: US 8,260,208 B2
• Time in Patent Office: Days
• US Class Current: 455/67.110
• CPC Class Codes: H04L 25/0232 by interpolation between sounding signals
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

A radio channel estimator (100) for estimating a first radio channel h₁ to obtain a first radio channel estimate ĥ₁, the first radio channel h₁ being comprised in a multiple input multiple output (MIMO=Multiple Input Multiple Output) radio channel extending between at least a first transmit antenna Tx₁ and a second transmit antenna Tx₂ and a receive antenna Rx, the first radio channel h₁ extending between the first transmit antenna Tx₁ and the receive antenna Rx. The radio channel estimator (100) comprises a means (110) for receiving a reference symbol transmitted by the second transmit antenna Tx₂ and a means (120) for estimating a second radio channel ĥ₂ based on the reference symbol, the second radio channel h₂ extending between the second transmit antenna Tx₂ and the receive antenna Rx. The radio channel estimator further comprises a means (130) for processing the estimate ĥ₂ of the second radio channel based on a spatial property of the MIMO radio channel to obtain the first radio channel estimate ĥ₁.

Claims

1. A radio channel estimator (100) for estimating a first radio channel (ĥ

_t) to obtain a first radio channel estimate (ĥ

₁), the first radio channel (h₁) being comprised in a multiple input multiple output (MIMO=multiple input multiple output) radio channel, the MIMO radio channel extending between at least a first transmit antenna (Tx₁), a second transmit antenna (Tx₂) and a receive antenna (Rx), the first radio channel (h₁) extending between the first transmit antenna (Tx₁) and the receive antenna (Rx), comprising;

a means (110) for receiving a reference symbol transmitted by the second transmit antenna (Tx₂);

a means (120) for estimating a second radio channel (ĥ

₂) based on the reference symbol, the second radio channel (h₂) extending between the second transmit antenna (Tx₂) and the receive antenna (Rx); and

a means (130) for processing the estimate (ĥ

₂) of the second radio channel based on a spatial property of the MIMO radio channel to obtain the first radio channel estimate (ĥ

₁).

2. The radio channel estimator (100) of claim 1, wherein the means (110) for receiving is adapted for receiving a further reference symbol from a third transmit antenna (Tx₃), and wherein the means (120) for estimating is adapted for estimating a third radio channel (ĥ

₃) based on the further reference symbol, the third radio channel (h₃) extending between the third transmit antenna (Tx₃) and the receive antenna (Rx), and wherein the means (130) for processing is adapted for processing the estimate (ĥ

₂) of the second radio channel and the estimate (ĥ

₃) of the third radio channel based on the spatial property of the MIMO radio channel to obtain the first radio channel estimate (ĥ

₁).

3. The radio channel estimator (100) of claim 2, wherein the means (130) for processing is adapted for interpolating between the estimate (ĥ

₂) of the second radio channel and the estimate (ĥ

₃) of the third radio channel to obtain the first radio channel estimate (ĥ

₁), wherein the spatial property comprises a correlation property of the first and second radio channels.

4. The radio channel estimator (100) of one of the preceding claims, wherein the means (110) for receiving is adapted for receiving the reference symbol on a first sub carrier having a first sub carrier frequency, and wherein the means (130) for processing the estimate (ĥ

₂) of the second radio channel is adapted for processing the estimate (ĥ

₂) based on the spatial property of the MIMO radio channel to obtain the first radio channel estimate (ĥ

₁) for a second sub carrier, the second sub carrier having a different frequency than the first sub carrier.

5. The radio channel estimator (100) of one of the preceding claims, wherein the means (110) is adapted for receiving reference symbols on a multiplicity of sub carriers, the sub carriers having different sub carrier frequencies, and wherein the means (120) for estimating is adapted for estimating radio channels on the multiplicity of sub carriers and wherein the means (130) for processing is adapted for processing the estimates of the different sub carriers based on the spatial property of the MIMO radio channel to obtain the first radio channel estimate (ĥ

₁) for a sub carrier on which no reference symbol is provided.

6. The radio channel estimator (100) of one of the preceding claims, wherein the means (110) for receiving is adapted for receiving the reference symbol in a first time slot, and wherein the means (120) is adapted for estimating the second radio channel (ĥ

₂) based on the reference symbol in the first time slot, and wherein the means (130) for processing is adapted for processing the estimate (ĥ

₂) of the second radio channel based on the spatial property of the MIMO radio channel to obtain the first radio channel estimate (ĥ

₁) for a second time slot, the second time slot being different from the first time slot.

7. The radio channel estimator (100) of one of the preceding claims, wherein the means (110) is adapted for receiving reference symbols in a multiplicity of time slots, and wherein the means (120) is adapted for estimating radio channels based on the multiplicity of reference symbols received in the multiplicity of time slots, and wherein the means (130) for processing is adapted for processing the estimates of the multiplicity of radio channels based on the spatial property of the MIMO radio channel to obtain the first radio channel estimate (ĥ

₁) for a time slot for which no reference symbol was provided.

8. The radio channel estimator (100) of one of the preceding claims, wherein the means (130) for processing is adapted for processing the estimate (ĥ

₂) of the second radio channel based on a three-dimensional Wiener filter based on a three-dimensional cross-correlation in time, frequency and space dimensions.

9. The radio channel estimator (100) of one of the preceding claims, wherein the means (130) for processing is adapted for processing the estimate (ĥ

₂) of the second radio channel based on a spatial property of the MIMO radio channel according to three one-dimensional Wiener filters, one Wiener filter being based on a correlation property in the time domain, one Wiener filter being based on a correlation property in the frequency domain and one Wiener filter being based on a correlation property in the spatial domain as the spatial property of the MIMO radio channel.

10. The radio channel estimator (100) of one of the preceding claims, wherein the means (110) is adapted for receiving reference symbols in equidistant time slots, equidistant sub carriers and/or for equidistant transmit antennas.

11. The radio channel estimator (100) of one of the preceding claims, wherein the means (110) for receiving is adapted for receiving reference symbols with irregular time spacing, irregular frequency spacing and/or irregular spatial separation.

16. A system comprising a radio channel estimator according to one of the claims 1 to 11 and the transmitter according to claim 13.

12. Method for estimating a first radio channel (h₁) to obtain a first radio channel estimate (ĥ

₁), the first radio channel (ĥ

₁) being comprised in a MIMO radio channel (MIMO=Multiple Input Multiple Output) extending between at least a first transmit antenna (Tx₁), a second transmit antenna (Tx₂) and a receive antenna (Rx), the first radio channel (h₁) extending between the first transmit antenna (Tx₁) and the receive antenna (Rx), comprising the steps of;

receiving a reference symbol transmitted by the second transmit antenna (Tx₂);

estimating a second radio channel (ĥ

₂) based on the reference symbol, the second radio channel (h₂) extending between the second transmit antenna (Tx₂) and the receive antenna (Rx); and

processing the estimate (ĥ

₂) of the second radio channel based on a spatial property of the MIMO radio channel to obtain the first radio channel estimate (ĥ

₁).

15. Computer program having a program code for performing the method of one of the claim 12 or 14 when the program code runs on a computer or processor.

13. A transmitter for enabling radio channel estimation of a MIMO (MIMO=Multiple Input Multiple Output) radio channel, the MIMO radio channel extending between at least a first transmit antenna (Tx₁), a second transmit antenna (Tx₂) and a receive antenna (Rx), the MIMO radio channel having a coherence time, a coherence bandwidth and a coherence length, the spacing between the first transmit antenna (Tx₁) and the second transmit antenna being less than the coherence length, comprising:

a means for transmitting a first reference symbol on the first transmit antenna (Tx₁) at a first time instant on a carrier frequency; and

a means for transmitting a second reference symbol on the second transmit antenna (Tx₂) at a second time instant on the carrier frequency,

wherein the first and the second time instants are separated by more than the coherence time and transmission of reference symbols on the first transmit antenna (Tx₁) and on the second transmit antenna (Tx₂) is suspended between the first and the second time instants and within the coherence bandwidth from the carrier frequency.

14. A method for enabling radio channel estimation of a MIMO (MIMO=Multiple Input Multiple Output) radio channel, the MIMO radio channel extending between at least a first transmit antenna (Tx₁), a second transmit antenna (Tx₂) and a receive antenna (Rx), the MIMO radio channel having a coherence time, a coherence bandwidth and a coherence length, the spacing between the first transmit antenna (Tx₁) and the second transmit antenna being less than the coherence length, comprising the steps of

transmitting a first reference symbol on the first transmit antenna (Tx₁) at a first time instant on a carrier frequency;

and

transmitting a second reference symbol on the second transmit antenna (Tx₂) at a second time instant on the carrier frequency,

wherein the first and the second time instants are separated by more than the coherence time and transmission of reference symbols on the first transmit antenna (Tx₁) and on the second transmit antenna (Tx₂) is suspended between the first and the second time instants and within the coherence bandwidth from the carrier frequency.