System and method for distributed input-distributed output wireless communications

• US 20080118004A1
• Filed: 08/20/2007
• Published: 05/22/2008
• Est. Priority Date: 07/30/2004
• Status: Active Grant

• Current Assignee: Rearden, LLC
• Original Assignee: Rearden, LLC
• Inventors: Van Der Laan, Roger, Forenza, Antonio, Speck, John, Heath, Robert, Perlman, Stephen
• Granted Patent: US 7,633,994 B2
• Time in Patent Office: Days
• US Class Current: 375/299
• CPC Class Codes: H04B 7/0684 using different training sequences per antenna
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 2025/0377 during the reception of training signals
• CPC Class Codes: H04L 2025/03802 Signalling on the reverse channel
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0224 using sounding signals
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end

Abstract

A system for compensating for in-phase and quadrature (I/Q) imbalances for multiple antenna systems (MAS) with multi-user (MU) transmissions (defined with the acronym MU-MAS), such as distributed-input distributed-output (DIDO) communication systems, comprising multicarrier modulation, such as orthogonal frequency division multiplexing (OFDM). For example, one embodiment of the system comprises one or more coding modulation units to encode and modulate information bits for each of a plurality of wireless client devices to produce encoded and modulated information bits; one or more mapping units to map the encoded and modulated information bits to complex symbols; and a MU-MAS or DIDO IQ-aware precoding unit to exploit channel state information obtained through feedback from the wireless client devices to compute MU-MAS or DIDO IQ-aware precoding weights, the MU-MAS or DIDO IQ-aware preceding unit precoding the complex symbols obtained from the mapping units using the weights to pre-cancel interference due to I/Q gain and phase imbalances and/or inter-user interference.

Claims

1. A method for compensating for in-phase and quadrature (I/Q) imbalances in a multiple antenna system (MAS) with multi-user (MU) transmissions (“

MU-MAS”

) comprising;

transmitting a training signal from each antenna of a base station to each of a plurality of wireless client devices, each of the client devices analyzing each training signal to generate channel characterization data, and receiving the channel characterization data at the base station;

computing a plurality of MU-MAS precoder weights based on the channel characterization data, the MU-MAS precoder weights calculated to pre-cancel interference due to I/Q gain and phase imbalances and/or inter-user interference;

precoding data using the MU-MAS precoder weights to generate precoded data signals for each antenna of the base station; and

transmitting the precoded data signals through each antenna of the base station to each respective client device.

3. The method as in claim 1 further comprising:

demodulating the data streams at each user device using zero-forcing (ZF), minimum mean-square error (MMSE) or maximum likelihood (ML) receiver to suppress residual interference.

4. The method as in claim 1 wherein precoding is performed using block diagonalization (BD) techniques.

5. The method of claim 1 wherein the MU-MAS system is a distributed-input distributed-output (DIDO) communication system and wherein the MU-MAS precoder weights are DIDO precoder weights.

6. The method as in claim 5 wherein the precoder weights are calculated to cancel inter-user interference but not ICI and wherein the client wireless client devices include receivers with filters for cancelling the ICI.

2. Wherein the base station is an access point coupling the wireless client devices to a wide area network.

7. A system for compensating for in-phase and quadrature (I/Q) imbalances for MU-MAS communication comprising:

one or more coding modulation units to encode and modulate information bits for each of a plurality of wireless client devices to produce encoded and modulated information bits;

one or more mapping units to map the encoded and modulated information bits to complex symbols; and

a MU-MAS IQ-aware precoding unit to exploit channel state information obtained through feedback from the wireless client devices to compute MU-MAS IQ-aware precoding weights, the MU-MAS IQ-aware precoding unit precoding the complex symbols obtained from the mapping units using the weights to pre-cancel interference due to I/Q gain and phase imbalances and/or inter-user interference.

8. The system as in claim 7 further comprising:

one or more orthogonal frequency division multiplexing (OFDM) units to receive the precoded signals from the MU-MAS IQ-aware precoding unit and to modulate the precoded signals according to an OFDM standard.

9. The system as in claim 8 wherein the OFDM standard comprises computing an inverse fast Fourier transform (IFFT) and adding a cyclic prefix.

10. The system as in claim 8 further comprising one or more D/A units to perform digital to analog (D/A) conversion on the output of the OFDM units to generate an analog baseband signal;

and

one or more radio frequency (RF) units to upconvert the baseband signal to radio frequency and transmit the signals using a corresponding one or more transmit antennas.

11. The system as in claim 7 wherein the MU-MAS IQ-aware precoding unit is implemented as a minimum mean square error (MMSE), a weighted MMSE or a zero-forcing (ZF) precoder.

12. The system as in claim 7 wherein the MU-MAS precoding unit is implemented as a minimum mean square error (MMSE), a weighted MMSE, a zero-forcing (ZF) or a block diagonalization (BD) precoder.

13. The system as in claim 7 wherein the MU-MAS communication comprises DIDO communication and wherein the system comprises a DIDO IQ-aware precoding unit to exploit channel state information obtained through feedback from the wireless client devices to compute DIDO IQ-aware preceding weights, the DIDO IQ-aware preceding unit precoding the complex symbols obtained from the mapping units using the weights to pre-cancel interference due to I/Q gain and phase imbalances and/or inter-user interference.

22. The system as in claim 13 wherein the MU-MAS communication comprises DIDO communication and wherein the one or more RF units receive signals transmitted from one or more DIDO transmitter units, and downconvert the signals to baseband.

14. A wireless client device for use in a system for compensating for in-phase and quadrature (I/Q) imbalances for MU-MAS communication comprising:

one or more RF units to receive signals transmitted from one or more MU-MAS transmitter units, and downconvert the signals to baseband;

one or more analog to digital (A/D) conversion units to receive the downconverted signals and to convert the signals from analog signals to digital signals;

one or more OFDM units to remove cyclic prefix and perform a fast Fourier transform (FFT) on the digital signals to report the signals in the frequency domain;

an I/Q-aware channel estimate unit which receives a signal output from the one or more OFDM units during a training period and responsively calculates channel estimate data; and

a feedback generator unit to transmit the channel estimate data to a base station for use in preceding signals prior to transmission to the wireless client device.

15. The system as in claim 14 where the channel estimates are computed in the time domain by using the input to the OFDM units

16. The wireless client device as in claim 14 wherein the feedback generator unit further comprises logic for quantizing the channel estimates prior to transmission to the base station.

17. The wireless client device as in claim 14 further comprising:

an I/Q-aware receiver unit which receives outputs from the OFDM units and responsively computes the IQ receiver and demodulates/decodes the signal to obtain the estimate of the transmitted data.

18. The wireless client device as in claim 16 wherein the I/Q-aware receiver unit is a minimum mean square error (MMSE) receiver, zero-forcing (ZF) receiver, a maximum likelihood (ML) or a MAP receiver.

19. The wireless client device as in claim 16 wherein the I/Q-aware receiver unit comprises an MMSE or ZF filter to cancel inter-carrier interference (ICI) caused by I/Q imbalance on mirror tones.

20. The wireless client device as in claim 16 wherein the I/Q-aware receiver unit comprises a nonlinear detector (i.e., ML) to jointly detect symbols on mirror tones.

21. The wireless client device as in claim 16 wherein the I/Q aware channel estimate unit calculates coefficients usable by the I/Q-aware receiver unit to remove inter-carrier interference (ICI).