Methods and systems for scheduling a virtual MIMO communication environment
A system and method for scheduling cooperative uplink transmissions in a virtual multiple input multiple output (MIMO) wireless communication environment are provided. More specifically, both random and channel aware orthogonal scheduling techniques for identifying a sub-set of N mobile terminals to provide cooperative uplink transmissions for each transmit time interval are provided.
1. An apparatus for scheduling uplink transmissions comprising:
at least one network interface; and
a control system associated with the at least one network interface and configured to:
determine at least one channel transfer function for a plurality of sub-carriers for each of a plurality of mobile terminals served by a base station;
identify a select group of mobile terminals from the plurality of mobile terminals for cooperative uplink transmission with one another, wherein the select group of mobile terminals are identified based on orthogonality of the channel transfer functions;
assign at least one sub-channel comprising one or more of the plurality of sub-carriers to the select group of mobile terminals to be simultaneously used by each mobile terminal in the select group of mobile terminals; and
schedule at least one mobile terminal from the plurality of mobile terminals for a single input multiple output (SIMO) transmission rather than cooperative uplink transmission,
wherein the select group of mobile terminals are scheduled for cooperative uplink transmission based on determining that the select group of mobile terminals comprise mobile terminals having channel transfer functions that are orthogonal to each other, and wherein the at least one mobile terminal is scheduled for the SIMO transmission based on determining that a channel quality associated with the at least one mobile terminal is below a predetermined threshold.
2. The apparatus of claim 1 , wherein the control system is further configured to assign different pilot signals for each mobile terminal in the select group of mobile terminals.
3. The apparatus of claim 1 , wherein the control system is further configured to receive sounding signals from each mobile terminal in the select group of mobile terminals.
4. The apparatus of claim 3 , wherein the control system is further configured to receive pilot signals from each mobile terminal in the select group of mobile terminals.
5. The apparatus of claim 1 , wherein the control system is further configured to remove at least one mobile terminal from the select group of mobile terminals.
6. The apparatus of claim 5 , wherein the mobile terminal is removed based on a performance criteria.
7. The apparatus of claim 6 , wherein the criterion is long term signal to noise ratio.
8. The apparatus of claim 1 , wherein the control system is further configured to determine the orthogonality of the channel transfer functions for one or more of the plurality of mobile terminals in each of a plurality of potential groups including the select group.
9. The apparatus of claim 8 , wherein, in order to identify the select group of mobile terminals, the control system is further configured to:
select a first mobile terminal from the plurality of mobile terminals based on round-robin scheduling; and
select one of the plurality of potential groups including the first mobile terminal as the select group based on the orthogonality of the channel transfer functions for the one or more of the plurality of mobile terminals in each of the plurality of potential groups.
10. The apparatus of claim 8 , wherein, in order to identify the select group of mobile terminals, the control system is further configured to:
select one of the plurality of potential groups based on proportional fairness scheduling.
11. The apparatus of claim 10 , wherein, in order to select one of the plurality of potential groups based on proportional fairness scheduling, the control system is further configured to:
determine proportional fairness values for the plurality of potential groups, each of the proportional fairness values being a sum of ratios of transmission rates and average throughputs for mobile terminals in an associated one of the plurality of potential groups; and
select one of the plurality of potential groups as the group of mobile terminals based on the proportional fairness values for the plurality of potential groups.
12. The apparatus of claim 8 , wherein, in order to identify the select group of mobile terminals, the control system is further configured to:
for each one of the plurality of mobile terminals, identify at least one group including the one of the plurality of mobile terminals from the plurality of potential groups based on the orthogonality of the channel transfer functions for the one or more of the plurality of mobile terminals in each of the plurality of potential groups including the one of the plurality of mobile terminals; and
select the select group from the at least one group for each of the plurality of mobile terminals based on proportional fairness scheduling.
13. The apparatus of claim 12 , wherein, in order to select the select group from the at least one group for each of the plurality of mobile terminals based on proportional fairness scheduling, the control system is further configured to:
determine proportional fairness values for the at least one group for each of the plurality of mobile terminals, each of the proportional fairness values being a sum of ratios of transmission rates and average throughputs for mobile terminals in an associated one of the at least one group for each of the plurality of mobile terminals; and
select one of the at least one group for each of the plurality of mobile terminals as the select group based on the proportional fairness values for the at least one group for each of the plurality of mobile terminals.
14. The apparatus of claim 1 , wherein, in order to assign the at least one sub-channel, the control system is further configured to:
assign the at least one sub-channel via downlink transmission.
15. The apparatus of claim 1 , wherein, in order to assign the at least one sub-channel, the control system is further configured to:
assign the at least one sub-channel to the select group of mobile terminals to be simultaneously used by each mobile terminal in the select group of mobile terminals during a common uplink transmit time interval.
16. The apparatus of claim 1 , wherein the control system is further configured to:
instruct one of the plurality of mobile terminals to artificially rotate a phase of sub-carrier waveforms transmitted by the one of the plurality of mobile terminals in order to improve the orthogonality of the channel transfer functions for the one of the plurality of mobile terminals with at least one other of the plurality of mobile terminals.
17. The apparatus of claim 1 , wherein the uplink transmissions are Orthogonal Frequency Division Multiplexing (OFDM) transmissions.
18. The apparatus of claim 1 , wherein the uplink transmissions are Single-Carrier Frequency Division Multiple Access (SC-FDMA) transmissions.
19. The apparatus of claim 1 , wherein the control system is further configured to form the select group of mobile terminals by selecting a first mobile terminal and one or more mobile terminals for cooperative uplink transmission with the first mobile terminal, the first mobile terminal being selected based on round-robin scheduling and the one or more mobile terminals being selected based on channel aware orthogonal scheduling.
20. The apparatus of claim 1 , wherein the control system is further configured to schedule a second group of mobile terminals from the plurality of mobile terminals for random user scheduling (RUS), the second group of mobile terminals being identified based on a velocity of each mobile terminal in the second group.
21. A method for scheduling uplink transmissions, the method comprising:
determining at least one channel transfer function for a plurality of sub-carriers for each of a plurality of mobile terminals served by a base station;
identifying a select group of mobile terminals from the plurality of mobile terminals for cooperative uplink transmission with one another, wherein the select group of mobile terminals are identified based on orthogonality of the channel transfer functions;
assigning at least one sub-channel comprising one or more of the plurality of sub-carriers to the select group of mobile terminals to be simultaneously used by each mobile terminal in the select group of mobile terminals; and
scheduling at least one mobile terminal from the plurality of mobile terminals for a single input multiple output (SIMO) transmission rather than cooperative uplink transmission,
wherein the select group of mobile terminals are scheduled for cooperative uplink transmission based on determining that the select group of mobile terminals comprise mobile terminals having channel transfer functions that are orthogonal to each other, and wherein the at least one mobile terminal is scheduled for the SIMO transmission based on determining that a channel quality associated with the at least one mobile terminal is below a predetermined threshold.
22. The method of claim 21 , further comprising assigning different pilot signals for each mobile terminal in the select group of mobile terminals.
23. The method of claim 21 , further comprising receiving sounding signals from each mobile terminal in the select group of mobile terminals.
24. The method of claim 23 , further comprising receiving pilot signals from each mobile terminal in the select group of mobile terminals.
25. The method of claim 21 , further comprising removing at least one mobile terminal from the select group of mobile terminals.