Methods and Apparatus to Account for Effective Downlink Channels Arising from Beamforming Uplink Reference Signals

Abstract

According to the teachings herein, a wireless device enhances uplink channel estimation at a node in a supporting wireless communication network by beamforming its uplink reference signal transmission towards the node, and correspondingly compensates for the effect of that beamforming when receiving a downlink transmission that was adapted in dependence on the uplink channel transmission. Such processing provides significant advantages in Multiple-Input-Multiple-Output, MIMO, systems that use a potentially large number of antennas for downlink MIMO transmissions and assume reciprocity between the uplink and downlink channels. In particular, uplink beamforming increases the received signal quality of the uplink reference signal used for estimating the uplink channel, while “automatic” compensation by the wireless device of the corresponding downlink transmission obviates the need for the network to know which precoder was used for uplink beamforming, or even that uplink beamforming is in use.

What is claimed is: 
     
         1 . A method at a wireless device configured for operation in a wireless communication network comprising:
 receiving a downlink transmission from a network node of the wireless communication network, the downlink transmission being beamformed by the network node in dependence on channel estimates determined from reception of an uplink reference signal transmitted from the wireless device; and   performing compensation processing on the received downlink transmission, in dependence on whether the uplink reference signal was transmitted by the wireless device using uplink beamforming;   said compensation processing compensating the received downlink transmission for the effects of the uplink beamforming on the channel estimates determined by the network node.   
     
     
         2 . The method of  claim 1 , wherein, for a case where the uplink reference signal was transmitted by the wireless device using uplink beamforming, the method comprises obtaining a compensated received transmission by performing the compensation processing on the received downlink transmission, and demodulating the compensated received transmission to recover information conveyed in the downlink transmission, and further wherein, for a case where the uplink reference signal was transmitted by the wireless device without using uplink beamforming, the method comprises demodulating the received downlink transmission to recover information conveyed in the downlink transmission, without performing the compensation processing. 
     
     
         3 . The method of  claim 1 , wherein performing the compensation processing on the received downlink transmission comprises linearly transforming the received downlink transmission, to account for the uplink beamforming. 
     
     
         4 . The method of  claim 3 , wherein linearly transforming the received downlink transmission comprises applying a transpose of a precoder matrix to the received downlink transmission, the precoder matrix being used by the wireless device for the uplink beamforming of the uplink reference signal. 
     
     
         5 . The method of  claim 1 , further comprising deciding to use uplink beamforming for transmitting the uplink reference signal in dependence on at least one of:
 a location of the wireless device with respect to the network node;   channel conditions observed at the wireless device with respect to the network node;   configuration information stored at the wireless device; and   control signaling received from the wireless communication network.   
     
     
         6 . The method of  claim 1 , wherein, for a case where the wireless device decided to use uplink beamforming for transmission of the uplink reference signal, the method further includes the wireless device selecting a precoder matrix to use for the uplink beamforming according to at least one of: control signaling received from the wireless communication network, and channel estimate information determined by the wireless device with respect to the network node. 
     
     
         7 . The method of  claim 1 , further comprising maintaining linking information in the wireless device that logically links the received downlink transmission to the uplink reference signal and indicates whether or not uplink beamforming was used for transmission of the uplink reference signal, and performing the compensation processing in dependence on the linking information. 
     
     
         8 . The method of  claim 1 , further comprising, for any given downlink transmission received at the wireless device, determining whether the given downlink transmission corresponds to a prior transmission of a beamformed uplink reference signal by the wireless device and, if so, obtaining a corresponding compensated received transmission from the given received downlink transmission for demodulation, according to a precoder matrix used for the beamformed reference signal. 
     
     
         9 . A wireless device configured for operation in a wireless communication network, the wireless device comprising:
 a communication interface comprising a radiofrequency transmitter and receiver and configured for receiving a downlink transmission from a network node of the wireless communication network, the downlink transmission being beamformed by the network node in dependence on channel estimates determined from reception of an uplink reference signal transmitted from the wireless device; and   processing circuitry operatively associated with the communication interface and configured to:
 perform compensation processing on the received downlink transmission, in dependence on whether the uplink reference signal was transmitted by the wireless device using uplink beamforming; 
 said compensation processing compensating the received downlink transmission for the effects of the uplink beamforming on the channel estimates determined by the network node. 
   
     
     
         10 . The wireless device of  claim 9 , wherein, for a case where the uplink reference signal was transmitted by the wireless device using uplink beamforming, the processing circuitry is configured to obtain a compensated received transmission by performing the compensation processing on the received downlink transmission, and demodulate the compensated received transmission to recover information conveyed in the downlink transmission, and further wherein, for a case where the uplink reference signal was transmitted by the wireless device without using uplink beamforming, the processing circuitry is configured to demodulate the received downlink transmission to recover information conveyed in the downlink transmission, without performing the compensation processing. 
     
     
         11 . The wireless device of  claim 9 , wherein the processing circuitry is configured to perform the compensation processing on the received downlink transmission by linearly transforming the received downlink transmission, to account for the uplink beamforming. 
     
     
         12 . The wireless device of  claim 11 , wherein the processing circuitry is configured to linearly transform the received downlink transmission by applying a transpose of a precoder matrix to the received downlink transmission, the precoder matrix being used by the wireless device for the uplink beamforming of the uplink reference signal. 
     
     
         13 . The wireless device of  claim 9 , wherein the processing circuitry is configured to decide to use uplink beamforming for transmitting the uplink reference signal in dependence on at least one of:
 a location of the wireless device with respect to the network node;   channel conditions observed at the wireless device with respect to the network node;   configuration information stored at the wireless device; and   control signaling received from the wireless communication network.   
     
     
         14 . The wireless device of  claim 9 , wherein, for a case where the wireless device decided to use uplink beamforming for transmission of the uplink reference signal, the processing circuitry is configured to select a precoder matrix to use for the uplink beamforming according to at least one of: control signaling received from the wireless communication network, and channel estimate information determined by the wireless device with respect to the network node. 
     
     
         15 . The wireless device of  claim 9 , wherein the processing circuitry is configured to maintain linking information in the wireless device that logically links the received downlink transmission to the uplink reference signal and indicates whether or not uplink beamforming was used for transmission of the uplink reference signal, and perform the compensation processing in dependence on the linking information. 
     
     
         16 . The wireless device of  claim 9 , wherein, for any given downlink transmission received at the wireless device, the processing circuitry is configured to determine whether the given downlink transmission corresponds to a prior transmission of a beamformed uplink reference signal by the wireless device and, if so, obtain a corresponding compensated received transmission from the given received downlink transmission for demodulation, according to a precoder matrix used for the beamformed reference signal. 
     
     
         17 . A wireless device configured for operation in a wireless communication network, the wireless device comprising:
 a communication interface configured for transmitting uplink signals for reception by a network node in the wireless communication network, and for receiving downlink signals from the network node; and   processing circuitry operatively associated with the communication interface and configured to:
 transmit an uplink reference signal using uplink beamforming; 
 receive a downlink signal from the network node, the downlink signal being beamformed by the network node in dependence on channel estimates generated at the network node from the uplink reference signal, the channel estimates being affected by the uplink beamforming; and 
 compensate for the affected channel estimates at the network node by applying a linear transformation to the received downlink signal, the linear transformation being based on the uplink beamforming used for transmission of the uplink reference signal.