Transmit power dependent reduced emissions from a wireless transceiver
View Patent ↗Methods and apparatus for reducing out of band emissions through selective resource allocation, transmit power control, or a combination thereof. A resource controller, such as a base station, can allocate uplink resources to a requesting subscriber station based in part on an expected transmit power. The base station can allocate uplink bandwidth to the subscriber station based on an expected subscriber station uplink transmit power and a frequency of a restricted emissions band. Those subscriber stations having higher expected transmit powers are allocated bandwidth further from the restricted emissions band. The subscriber station can perform complementary transmit power control based on allocated uplink resources. The subscriber station can limit a transmit power based in part on a bandwidth allocation, modulation type allocation, or some combination thereof.
1. A method of reducing out of band emissions, performed by a base station, the method comprising:
transmitting a downlink transmission;
receiving from a subscriber station a request for uplink transmission resources;
receiving, from the subscriber station, a feedback message including a power control metric based on the downlink transmission;
determining an expected power level at which the subscriber station is expected to transmit in an uplink transmission responsive to the power control metric received from the subscriber station;
determining a position of a portion of an available bandwidth for uplink transmissions based on the determined expected power level and based on a probability that the subscriber station transmitting at the expected power level will result in distortion products exceeding an emissions constraint associated with an emissions band; and
allocating to the subscriber station the portion of the available bandwidth for uplink transmissions, responsive to the request for uplink transmission resources and the determined expected power level.
2. The method of claim 1 , further comprising:
configuring an uplink allocation message including an indication of uplink transmission resources that have been allocated to the subscriber station; and
transmitting the uplink allocation message to the subscriber station.
3. The method of claim 2 , wherein the configuring the uplink allocation message comprises configuring an uplink map (UL-MAP) message.
4. The method of claim 1 , wherein the feedback message is a Received Signal Strength Indication (RSSI) feedback message.
5. The method of claim 1 , wherein the allocating the uplink transmission resources comprises:
determining a modulation type and a signal bandwidth responsive to the request for uplink transmission resources; and
allocating at least one Orthogonal Frequency Division Multiplex (OFDM) symbol subcarrier to the subscriber station responsive to the modulation type and the signal bandwidth.
6. The method of claim 1 , wherein the base station allocating the uplink transmission resources to the subscriber station further comprises:
the base station allocating the uplink transmission resources such that a location of the portion of the available bandwidth that is allocated to the subscriber station with respect to an emissions band depends on the expected power level at which the subscriber station is expected to transmit in the uplink.
7. The method of claim 1 , wherein the determining the position of the portion of the available bandwidth further comprises positioning the portion of the available bandwidth at frequencies further away from the emissions band for uplink transmissions for a subscriber station having a higher expected power level.
8. A method of reducing out of band emissions performed by a subscriber station, the method comprising:
receiving a downlink transmission from a base station;
determining a power control metric responsive to the downlink transmission received from the base station;
transmitting a request for uplink transmission resources from the base station;
transmitting a feedback message including the determined power control metric to the base station, the power control metric being useable by the base station to determine an expected power level at which the subscriber station is expected to transmit;
receiving an allocation of a portion of an available bandwidth for the uplink transmission resources from the base station, the portion of the available bandwidth allocated for uplink transmissions received from the base station being responsive to the request for uplink transmission resources and the determined expected power level,
the allocated portion of the available bandwidth for uplink transmission being positioned away from at least one band of interest to reduce out-of-band emissions therein; and
determining a transmit power constraint responsive to the allocation of the portion of the available bandwidth for the uplink transmission resources received from the base station, the transmit power constraint being based on a position of the allocated portion of the available bandwidth.
9. The method of claim 8 , wherein receiving the downlink transmission comprises receiving at least one Orthogonal Frequency Division Multiplex (OFDM) symbol during a downlink Time Division Duplex (TDD) portion.
10. The method of claim 8 , wherein receiving the downlink transmission comprises receiving at least one Orthogonal Frequency Division Multiplex (OFDM) symbol having a fixed power density over a bandwidth of the OFDM symbol.
11. The method of claim 8 , wherein receiving the resource allocation comprises receiving at least one of a modulation type and a bandwidth allocation.
12. The method of claim 8 , wherein receiving the allocation of the uplink transmission resources comprises receiving an uplink map (UL-MAP) message including the allocation of the uplink transmission resources.
13. The method of claim 11 , wherein determining the transmit power constraint comprises:
determining a maximum transmit power responsive to at least one of the bandwidth allocation and the modulation type; and
transmitting an uplink transmission using the at least one of the bandwidth allocation and the modulation type and limiting a power of the uplink transmission to the maximum transmit power.
14. A base station comprising:
a transmitter configured to transmit a downlink transmission;
a receiver configured to receive a request for uplink transmission resources from a subscriber station, and to receive a feedback message comprising a power control metric from the subscriber station based on the downlink transmission; and
an uplink resource controller configured to:
determine an expected power level responsive to the power control metric received from the subscriber station at which the subscriber station is expected to transmit to the base station;
determine a position of a portion of an available bandwidth for uplink transmissions based on the determined expected power level and on a probability that the subscriber station transmitting at the expected power level will result in distortion products exceeding an emissions constraint associated with an emissions band;
allocate the portion of the available bandwidth for uplink transmissions to the subscriber station responsive to the request for uplink transmission resources and the determined expected power level; and
generate an uplink resource message including an indication of uplink transmission resources that have been allocated to the subscriber station;
the transmitter further configured to transmit the uplink resource message to the subscriber station.
15. The base station of claim 14 , further comprising:
a modulation subcarrier map configured to store a look up table that relates the power control metric to an uplink bandwidth portion, wherein the uplink resource controller is further configured to allocate the uplink transmission resources in accordance with the look up table.
16. The base station of claim 15 , wherein the look up table further relates a combination of an expected transmit power and a modulation type to the uplink bandwidth portion and the expected transmit power is responsive to the power control metric.
17. The base station of claim 14 , wherein the uplink resource controller is further configured to allocate the uplink transmission resources such that a location of the portion of the available bandwidth that has been allocated to the subscriber station with respect to an emissions band depends on the expected power level at which the subscriber station is expected to transmit in the uplink.
18. A subscriber station comprising:
a receiver configured to receive a downlink transmission and an allocation of a portion of an available bandwidth for uplink transmission resources from a base station;
a power detector configured to determine a power control metric based on the received downlink transmission; and
a transmitter configured to transmit to the base station a request for the uplink transmission resources and a feedback message containing the power metric,
wherein:
the power control metric is usable by the base station to determine a power level at which the subscriber station is expected to transmit in the uplink;
the portion of the available bandwidth allocated for uplink transmissions received from the base station is responsive to the request for uplink transmission resources and the determined expected power level, and is positioned away from at least one band of interest to reduce out-of-band emissions therein; and
the transmitter is constrained to a maximum transmit power responsive to the allocation of the portion of the available bandwidth, the maximum transmit power being based on a position of the portion of the available bandwidth allocated for uplink transmissions.
19. The subscriber station of claim 18 , further comprising:
a modulation subcarrier map configured to store a look up table that relates the maximum transmit power to a modulation type and an uplink allocation, wherein the transmitter is further configured to determine the maximum transmit power in accordance with the look up table.