Downlink coordinated transmission in OFDMA systems
View Patent ↗Embodiments described herein include methods for improving the SINR, and therefore communication quality or rate, in the downlink of a cellular communication system. In an embodiment, the system is an orthogonal-frequency-division multiple-access (OFDMA) system. In an embodiment, a set of terminals is designated a coordinated-transmission group. The set of terminal is chosen such that the slot-allocations of the set are given special treatment to alleviate interference from other sectors or cells. All terminals within a coordination group generally use the same slot, but embodiments are not so limited.
1. A cellular communication method, the method comprising:
identifying a distressed terminal of a plurality of terminals in a cellular network, wherein the distressed terminal is identified as receiving downlink transmission signals having an signal to interference and noise ratio (SINR) less than a threshold; and
coordinating downlink transmission to the plurality of terminals based on at least the identified distressed terminal, wherein the network comprises cells, and each cell comprises sectors; wherein
coordinating the downlink transmission comprises multiple base stations transmitting a same signal to the identified distressed terminal; and the distressed terminal receiving a copy of the same signal from each of the multiple base stations, comprising selecting pseudo-random bit sequences (PRBS), and aligning the PRBS of the multiple sectors and multiple cells, wherein the aligning comprises assigning a time-frequency slot for the identified distressed terminal;
wherein the plurality of terminals comprises distressed terminals with a low SINR relative to sacrificial terminals, and sacrificial terminals with a high SINR relative to distressed terminals, the method further comprising:
a sector transmitting data to a terminal in an allocated slot; and
pairing a distressed terminal with one or more sacrificial terminals such that transmit power for the distressed terminal is increased while transmit power for the sacrificial terminal is decreased;
designating a distressed terminal in a serving sector and a distressed terminal in an interfering sector as being in the plurality of terminals; and
using beams to reduce interference between the distressed terminal in the serving sector and the distressed terminal in the interfering sector.
2. The method of claim 1 , wherein coordinating downlink transmission comprises:
designating the plurality of terminals as a group, wherein a terminal comprises a cellular communication device; and
handling communications involving a terminal in the group in a preferential manner.
3. The method of claim 2 , wherein the plurality of terminals in the group use a same slot, wherein a slot comprises a subset of available symbols and available subcarriers in a sector of a terminal.
4. The method of claim 2 , wherein designating the plurality of terminals comprises:
receiving base station reports from multiple sectors, wherein the reports comprise one or more of signal strength and SINR for terminals in the sectors; and
analyzing the reports to determine terminals to designate.
5. The method of claim 2 , wherein handling communications comprises handling pilot subcarriers in a same manner as data subcarriers.
6. The method of claim 1 , wherein the cellular communication method comprises an orthogonal-frequency-division multiple-access (OFOMA) method.
7. The method of claim 1 , wherein the plurality of terminals comprises boundary terminals that are on one or more of a sector boundary and a cell boundary.
8. The method of claim 1 , wherein the plurality of terminals comprises terminals with a relatively low signal-to-interference ratio (SINR) with respect to other terminals of the plurality of terminals.
9. The method of claim 1 , wherein the plurality of terminals comprises:
distressed terminals with a low SINR relative to sacrificial terminals; and
sacrificial terminals with a high SINR relative to distressed terminals.
10. The method of claim 1 , wherein the plurality of terminals comprises distressed terminals with a low SINR relative to sacrificial terminals, and sacrificial terminals with a high SINR relative to distressed terminals, the method further comprising selecting slot allocations of a sector comprising a distressed terminal to correspond with slots in which other sectors are not transmitting.
11. The method of claim 1 , wherein the plurality of terminals comprises a single terminal that has a relatively low SINR compared to other terminals of the plurality of terminals, the method further comprising:
multiple base stations transmitting a same signal to the single terminal; and
the single terminal receiving copies of the same signal from each of the multiple base stations.
12. The method of claim 11 , wherein each of the multiple base stations weights its transmission by a scaling factor.
13. The method of claim 11 , further comprising coordinating beams from two different sectors to the single terminal.
14. The method of claim 11 , further comprising coordinating beams from two different cells to the single terminal.
15. The method of claim 1 , further comprising:
steering a beam toward a distressed terminal in a serving sector; and steering a beam away from a distressed terminal in an interfering sector.
16. The method of claim 15 , wherein steering comprises beamforming using multiple antennas from at least one of a sector and a cell.
17. The method of claim 15 , wherein steering comprises beamforming using multiple antennas from across at least one of one or more sectors and one or more cells.
18. The method of claim 1 , further comprising:
performing space-time coding of the data to be transmitted; and
transmitting the coded data using available antennas, wherein the available antennas comprise multiple antennas from at least one of a sector and a cell.
19. The method of claim 1 , further comprising:
performing space-time coding of the data to be transmitted; and
transmitting the coded data using available antennas, wherein the available antennas comprise multiple antennas from at least one of one or more sectors and one or more cells.
20. An orthogonal-frequency-division multiple-access (OFDMA) communication method, comprising:
identifying a distressed terminal of a plurality of terminals in a cellular network, wherein the distressed terminal is identified as receiving downlink transmission signals having an signal to interference and noise ratio (SINR) less than a threshold; and
coordinating downlink transmission to the plurality of terminals based on at least the identified distressed terminal, wherein the network comprises cells, and each cell comprises sectors; wherein
coordinating the downlink transmission comprises multiple base stations transmitting a same signal to the identified distressed terminal; and the distressed terminal receiving a copy of the same signal from each of the multiple base stations, comprising selecting pseudo-random bit sequences (PRBS), and aligning the PRBS of the multiple sectors and multiple cells, wherein the aligning comprises assigning a time-frequency slot for the identified distressed terminals;
wherein the plurality of terminals comprises distressed terminals with a low SINR relative to sacrificial terminals, and sacrificial terminals with a high SINR relative to distressed terminals, the method further comprising:
a sector transmitting data to a terminal in an allocated slot; and
pairing a distressed terminal with one or more sacrificial terminals such that transmit power for the distressed terminal is increased while transmit power for the sacrificial terminal is decreased;
designating a distressed terminal in a serving sector and a distressed terminal in an interfering sector as being in the plurality of terminals; and
using beams to reduce interference between the distressed terminal in the serving sector and the distressed terminal in the interfering sector.
21. The method of claim 20 , wherein coordinating downlink transmission comprises:
designating the plurality of terminals as a group, wherein a terminal comprises a cellular communication device; and
handling communications involving a terminal in the group in a preferential manner.
22. The method of claim 21 , wherein the plurality of terminals in the group will use a same slot, wherein a slot comprises a subset of available symbols and available subcarriers in a sector of a terminal.
23. The method of claim 20 , wherein the plurality of terminals comprises boundary terminals that are on one or more of a sector boundary and a cell boundary.