Channel state information (CSI) request procedures are disclosed for use in wireless communication systems. The serving base station transmits an identifier, which signals that the aperiodic reference signal will be transmitted, either in the same subframe or a future subframe, and then transmits the aperiodic reference signal in the designated subframe. UEs served by the base station will receive the identifier, identify a CSI request, either implicitly through the identifier signal received from the base station or explicitly through a UE-specific CSI request, and then generate a CSI report based on the aperiodic reference signal for transmission back to the serving base station.

Systems and methods are disclosed for determining a first downlink control indicator (DCI) and a second DCI, determining a set of active aperiodic channel state information reference signals (A-CSI-RSs) based on the first DCI, and determining a subset of the set of active A-CSI-RSs based on the second DCI. A WTRU may perform resource element (RE) muting based on a set of active A-CSI-RSs. A WTRU may perform channel state information (CSI) measurement based on a subset of a set of active A-CSI-RSs.

Methods, systems, and devices for wireless communications are described. Generally, a user equipment (UE) may indicate one or more uplink beams that the UE is capable of generating where grating and main lobes of the one or more uplink beams satisfy a permissible exposure constraint. The UE may operate in an intra-band or inter-band carrier aggregation (CA) mode, and the UE may indicate an uplink beam per band of the CA mode that the UE is capable of generating to satisfy the permissible exposure constraint. Frequency dependent beam training may be initiated by the base station to support intra-band CA modes and inter-band CA modes. The base station may indicate a frequency band and uplink beam to the UE, and the UE may indicate one or more parameter values that the UE may use to generate the uplink beam in the band that satisfies the permissible exposure constraints.

Example implementations are directed to methods and systems employing a solicited sounding protocol that includes an efficient communication sequence for operating a wireless transceiver transmitting a sounding trigger to one or more beamformees via a forward channel, receiving at least one dedicated training signal from the one or more beamformees via a reverse channel in response to the sounding trigger, and for each of the received dedicated training signal. The method also includes estimating forward CSI derived based on the dedicated training signal from an associated beamformee; and where subsequent packets are precoded with precoding derived from the forward CSI for transmission to the associated beamformee via the forward channel. Example aspects including scheduling multiple dedicated training signals from one or more beamformees based on a single sounding trigger.

Example implementations are directed to methods and systems employing a solicited sounding protocol that includes an efficient communication sequence for operating a wireless transceiver transmitting a sounding trigger to one or more beamformees via a forward channel, receiving at least one dedicated training signal from the one or more beamformees via a reverse channel in response to the sounding trigger, and for each of the received dedicated training signal. The method also includes estimating forward CSI derived based on the dedicated training signal from an associated beamformee; and where subsequent packets are precoded with precoding derived from the forward CSI for transmission to the associated beamformee via the forward channel. Example aspects including scheduling multiple dedicated training signals from one or more beamformees based on a single sounding trigger.

The present disclosure relates to a wireless base station and a terminal device that can shorten time required for sounding information collection by a plurality of wireless base stations and suppress deterioration of following accuracy. When a wireless base station as a master performs channel measurement with a terminal device, it is possible to transmit channel measurement frames in wireless base stations including the wireless base station at the same timing or at different timings only by instructing another wireless base station to perform a channel measurement, and also transmitting a Sounding Trigger frame including a transmission timing and a transmission stream of a channel measurement frame once. The present disclosure can be applied to communication systems in wireless LAN.

Methods, apparatuses and systems are provided for transmission of a CSI report. A WTRU may receive an aperiodic CSI reporting request on a PDCCH. The WTRU may determine a time gap between a last symbol of the PDCCH of which the aperiodic CSI reporting request is received and a first uplink symbol of a designated uplink channel for transmission of a corresponding aperiodic CSI report. The determination of the time gap may include consideration of a timing advance value. A determination may be made as to whether a time threshold is shorter than the determined time gap. If the determined time gap is not shorter than the time threshold, the WTRU may transmit the CSI report. If the determined time gap is shorter than the threshold, the WTRU may not transmit the CSI report.

Channel state information (CSI) request procedures are disclosed for use in wireless communication systems. The serving base station transmits an identifier, which signals that the aperiodic reference signal will be transmitted, either in the same subframe or a future subframe, and then transmits the aperiodic reference signal in the designated subframe. UEs served by the base station will receive the identifier, identify a CSI request, either implicitly through the identifier signal received from the base station or explicitly through a UE-specific CSI request, and then generate a CSI report based on the aperiodic reference signal for transmission back to the serving base station.

Systems and methods are disclosed for determining a first downlink control indicator (DCI) and a second DCI, determining a set of active aperiodic channel state information reference signals (A-CSI-RSs) based on the first DCI, and determining a subset of the set of active A-CSI-RSs based on the second DCI. A WTRU may perform resource element (RE) muting based on a set of active A-CSI-RSs. A WTRU may perform channel state information (CSI) measurement based on a subset of a set of active A-CSI-RSs.

This disclosure provides systems, methods and apparatus, including computer programs encoded on computer storage media, for group formation and sounding for distributed multi-user multiple input multiple output (MU-MIMO). Some implementations include a method of wireless communication. The method includes transmitting, from a first access point of a plurality of access points, an announcement frame for performing a beamforming procedure for a distributed transmission. The distributed transmission includes a transmission from the plurality of access points. The announcement frame includes at least one identifier of a user terminal in a different basic service set than a basic service set of the first access point. The method further includes transmitting a packet for measuring a channel. The method further includes receiving feedback information from the user terminal based on the packet for measuring the channel. The method further includes transmitting the distributed transmission using the beamforming procedure.