Uplink frequency selective precoder
Disclosed herein is an apparatus that receives, from a network, an uplink reference signal configuration, receives, from the network, an indication on an uplink reference signal precoding method, receives, from the network, a downlink reference signal, estimates uplink channel wideband information based on the received downlink reference signal, transmits, to the network, an uplink reference signal based on the received uplink reference signal configuration, the estimated uplink channel wideband information and the indicated uplink reference signal precoding method, receives, from the network, uplink frequency selective precoding information, the uplink frequency selective precoding information having been determined based on the uplink reference signal and the indicated uplink reference signal precoding method, and constructs an uplink frequency selective precoder based on the estimated uplink channel wideband information and the received uplink frequency selective precoding information.
1 . An apparatus comprising at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to:
receive, from a network, an uplink reference signal configuration;
receive, from the network, an indication on an uplink reference signal precoding method;
receive, from the network, a downlink reference signal;
estimate uplink channel wideband information based on the received downlink reference signal;
transmit, to the network, an uplink reference signal based on the received uplink reference signal configuration, the estimated uplink channel wideband information and the indicated uplink reference signal precoding method;
receive, from the network, uplink frequency selective precoding information, the uplink frequency selective precoding information having been determined based on the uplink reference signal and the indicated uplink reference signal precoding method; and
construct an uplink frequency selective precoder based on the estimated uplink channel wideband information and the received uplink frequency selective precoding information,
wherein the apparatus is further caused to:
receive, from the network, an indication of a timing offset for transmission of the uplink reference signal, wherein the uplink reference signal is transmitted based on the received indication of the timing offset,
wherein the timing offset refers to:
a timing offset between the time of the reception of downlink control information triggering the transmission of the downlink reference signal and the time of the transmission of the uplink reference signal,
wherein the indicated uplink reference signal precoding method is one of a set of precoding methods comprising:
a precoding method based on an estimated channel spatial support and an estimated channel delay support of the uplink channel,
wherein the apparatus is further caused to:
receive an uplink frequency selective precoding configuration via a higher layer wherein construction of the uplink frequency selective precoder is further based on the received uplink frequency selective precoding configuration.
2 . The apparatus of claim 1 , wherein the indication of the timing offset:
is received via a medium access control configuration element;
selects a timing offset of a list of multiple timing offsets;
refers to a number of slots;
refers to a number of uplink occasions; and
comprises an indication of the downlink reference signal.
3 . The apparatus of claim 1 , wherein the uplink frequency selective precoding configuration comprises information on:
a number of uplink reference signal ports to be used;
a number of bits for quantization of amplitude scaling coefficients;
a number of bits for quantization of co-phasing coefficients;
a port selection sampling size;
a number of frequency domain components; and
a number of non-zero coefficients for amplitude scaling and/or co-phasing coefficients.
4 . The apparatus of claim 1 , wherein:
the downlink reference signal is a synchronization signal block; and
the uplink reference signal is a periodic, aperiodic or semi-persistent reference signal.
5 . The apparatus of claim 1 , wherein the uplink frequency selective precoding information is received via two or more of:
a physical downlink shared channel;
a physical downlink control channel; and
a medium access control configuration element.
6 . The apparatus of claim 1 , wherein the uplink frequency selective precoding information comprises:
an indication of one or more amplitude scaling coefficients for the construction of the uplink frequency selective precoder;
an indication of one or more co-phasing coefficients for the construction of the uplink frequency selective precoder;
a bitmap indicating selected ports to be used for constructing the uplink frequency selective precoder;
a combinatorial indicator indicating selected ports to be used for constructing the uplink frequency selective precoder; and
an indication of a first selected port to be used for constructing the uplink frequency selective precoder.
7 . A method for a user equipment, the method comprising:
receiving, from a network, an uplink reference signal configuration;
receiving, from the network, an indication on an uplink reference signal precoding method;
receiving, from the network, a downlink reference signal;
estimating uplink channel wideband information based on the received downlink reference signal;
transmitting, to the network, an uplink reference signal based on the received uplink reference signal configuration, the estimated uplink channel wideband information and the indicated uplink reference signal precoding method;
receiving, from the network, uplink frequency selective precoding information, the uplink frequency selective precoding information having been determined based on the uplink reference signal and the indicated uplink reference signal precoding method; and
constructing an uplink frequency selective precoder based on the estimated uplink channel wideband information and the received uplink frequency selective precoding information,
wherein the method further comprises:
receiving, from the network, an indication of a timing offset for transmission of the uplink reference signal, wherein the uplink reference signal is transmitted based on the received indication of the timing offset,
wherein the timing offset refers to:
a timing offset between the time of the reception of downlink control information triggering the transmission of the downlink reference signal and the time of the transmission of the uplink reference signal,
wherein the indicated uplink reference signal precoding method is one of a set of precoding methods comprising:
a precoding method based on an estimated channel spatial support and an estimated channel delay support of the uplink channel,
wherein the method further comprises:
receiving an uplink frequency selective precoding configuration via a higher layer wherein construction of the uplink frequency selective precoder is further based on the received uplink frequency selective precoding configuration.
8 . The method of claim 7 , wherein the uplink frequency selective precoding information comprises:
an indication of one or more amplitude scaling coefficients for the construction of the uplink frequency selective precoder;
an indication of one or more co-phasing coefficients for the construction of the uplink frequency selective precoder;
a bitmap indicating selected ports to be used for constructing the uplink frequency selective precoder;
a combinatorial indicator indicating selected ports to be used for constructing the uplink frequency selective precoder; and
an indication of a first selected port to be used for constructing the uplink frequency selective precoder.
9 . An apparatus comprising at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to:
transmit, to a user equipment, an uplink reference signal configuration;
transmit, to the user equipment, an indication on an uplink reference signal precoding method;
transmit, to the user equipment, a downlink reference signal;
receive, from the user equipment, an uplink reference signal transmitted based on the uplink reference signal configuration, the indicated uplink reference signal precoding method and uplink channel wideband information estimated based on the downlink reference signal;
determine uplink frequency selective precoding information based on the received uplink reference signal and on the indicated uplink reference signal precoding method; and
transmit, to the user equipment, the uplink frequency selective precoding information, so that the user equipment can construct an uplink frequency selective precoder based on the estimated uplink channel wideband information and the uplink frequency selective precoding information,
wherein the apparatus is further caused to:
transmit an uplink frequency selective precoding configuration via a higher layer, wherein determining the uplink frequency selective precoding information is based on the uplink frequency selective precoding configuration,
wherein determining of the uplink frequency selective precoding information comprises:
compare a number of uplink reference signal ports and a number of ports to be used for constructing the uplink frequency selective precoder; and
in case the number of ports to be used for constructing the uplink frequency selective precoder is lower than the number of uplink reference signal ports, select ports to be used for constructing the uplink frequency selective precoder from the uplink reference signal ports,
wherein the ports to be used for constructing the uplink frequency selective precoder are selected based on a predefined rule.
10 . The apparatus of claim 9 , wherein determining the uplink frequency selective precoding information takes into account:
an uplink reference signal resource set;
an uplink reference signal frequency density;
an uplink reference signal port selection;
an uplink reference signal resource indication;
a frequency domain component indication;
a strongest port indication; a strongest coefficient indication; and
one or more co-phasing coefficients and/or scaling coefficients.
11 . The apparatus of claim 9 , wherein the uplink frequency selective precoding information comprises:
an indication of one or more amplitude scaling coefficients for the construction of the uplink frequency selective precoder;
an indication of one or more co-phasing coefficients for the construction of the uplink frequency selective precoder;
a bitmap indicating selected ports to be used for constructing the uplink frequency selective precoder;
a combinatorial indicator indicating selected ports to be used for constructing the uplink frequency selective precoder; and
an indication of a first selected port to be used for constructing the uplink frequency selective precoder.