Slot assignment algorithm

• US 20030002518A1
• Filed: 04/05/2001
• Published: 01/02/2003
• Est. Priority Date: 04/05/2001
• Status: Active Grant

• Current Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Original Assignee: DOCOMO Communications Laboratories USA, Inc.
• Inventors: Shibutani, Akira
• Granted Patent: US 6,940,824 B2
• Time in Patent Office: Days
• US Class Current: 370/442
• CPC Class Codes: H04W 24/10 Scheduling measurement reports ; Arrangements for measurement reports
• CPC Class Codes: H04W 72/00 Local resource management
• CPC Class Codes: H04W 72/0446 Resources in time domain, e.g. slots or frames
• CPC Class Codes: H04W 72/541 using the level of interference
• CPC Class Codes: H04W 72/542 using measured or perceived quality

Abstract

The present invention provides scheduling algorithms that guarantee minimum data transport service for even ATs with poor channel conditions. Data-requesting ATs are divided into a number (N_g1) of AT groups according to their channel conditions. Also, a recurring sequence of time slots is defined on the TDMA channel and partitioned into a number (N_g2) of slot groups, where N_g2 is made larger than N_g1. Generally, slot assignment according to the present invention is a two-step process. First, in the sequence, the slot groups are allocated to the AT groups so that AT groups with better channel conditions will receive more slot groups while each AT group will receive at least one slot group. Second, in each AT group, the time slots allocated to an AT group are assigned to the individual ATs in the group. By assigning more slot groups to AT groups with better channel conditions, the algorithm will optimize the overall data throughput. By assigning at least one slot group to each AT groups, the algorithm will guarantee minimum service to ATs with poor channel conditions.

Claims

1. A method for dynamically scheduling communications to a plurality of receivers over a TDMA channel that is partitioned into frames each consisting of slots, comprising the steps of:

measuring a channel condition of each receiver;

dividing the receivers into receiver groups according their channel conditions;

partitioning the TDMA channel into a recurring sequence of slots;

dividing each sequence into a certain number of slot groups; and

allocating the slot groups to the receiver groups according to the receivers'"'"' channel conditions.

2. A method according to claim 1, wherein more slot groups are allocated to the receiver groups having receivers with good channel conditions.

3. A method according to claim 1, further comprising the step of assigning receivers in a receiver group slots in the slot group allocated to the receiver group.

4. A method according to claim 3, wherein more slots are assigned to receivers with better channel conditions.

5. A method according to claim 1, wherein the channel condition is indicated by any one of SIR, SNIR, SNR, CI, E/N, FER, BER and DRC.

6. A method according to claim 1, wherein the receivers are grouped based on statistically predicted signal reception conditions.

7. A method according to claim 1, wherein the TDMA channel is implemented on a CDMA channel.

8. A method according to claim 1, wherein the receivers are grouped in an equal number.

9. A method according to claim 1, wherein the receivers are grouped based on threshold levels of channel condition.

10. A method according to claim 8, wherein at least one of the upper and lower threshold levels defining a group is changed to try to keep constant the number of receivers in the group.

11. A method according to claim 8, wherein at least one of the upper and lower threshold levels defining a group is changed to try to keep constant an average of the signal reception conditions of the receivers in the group.

12. A method according to claim 1, wherein as a number of receivers in a group increases or decreases, more or less slots are allocated to the group.

13. A method according to claim 1, wherein when a group becomes comprised only of receivers whose current channel conditions are lower than a minimum channel condition, a slot that has been allocated to the group will be made an idle slot.

14. A method according to claim 1, wherein when a group becomes comprised only of receivers whose current channel conditions are lower than a minimum channel condition, a slot that has been allocated to the group will be reallocated to another group.

15. A method according to claim 1, wherein slots that have been allocated to a group are assigned more favorably to receivers in the group that require higher QoS.

16. A method according to claim 1, wherein the channel condition is measured at a receiver based on a pilot symbol received from the sender.

17. A method according to claim 1, wherein the channel condition is measured at the sender based on data received from a receiver.

18. A method according to claim 1, wherein a data rate for a receiver is adaptively changed according to the channel condition of the receiver.

19. A method according to claim 1, wherein data to be multicasted to a plurality of receivers in at least one group are not multicasted to the receivers unless all or most of the receivers have channel conditions higher than a predetermined multicast channel condition.

20. A method according to claim 1, wherein each receiver is notified of slots assigned thereto and puts itself in a sleep mode during timings of slots assigned to the other receivers.