Methods and systems for scheduling OFDM frames

• US 9,565,123 B2
• Filed: 10/05/2015
• Issued: 02/07/2017
• Est. Priority Date: 05/10/2006
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Mukherjee, Biswaroop
• Primary Examiner(s): RENNER, BRANDON M
• Application Number:
  US14/875,579
• Publication Number:
  US 20160028642A1
• Time in Patent Office: 491 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: H04B 7/04 using two or more spaced independent antennas
• CPC Class Codes: H04L 25/03891 Spatial equalizers MIMO diversity systems H04B7/0413
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04L 47/2441 relying on flow classification, e.g. using integrated services [IntServ]
• CPC Class Codes: H04L 47/50 Queue scheduling
• CPC Class Codes: H04L 47/527 Quantum based scheduling, e.g. credit or deficit based scheduling or token bank
• CPC Class Codes: H04L 47/564 Attaching a deadline to packets, e.g. earliest due date first
• CPC Class Codes: H04L 49/90 Buffering arrangements
• CPC Class Codes: H04L 49/901 using storage descriptor, e.g. read or write pointers
• CPC Class Codes: H04L 49/9057 Arrangements for supporting packet reassembly or resequencing
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/001 the frequencies being arranged in component carriers
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04L 5/0044 allocation of payload
• CPC Class Codes: H04W 28/02 Traffic management, e.g. flow control or congestion control
• CPC Class Codes: H04W 72/12 Wireless traffic scheduling
• CPC Class Codes: H04W 8/04 Registration at HLR or HSS [Home Subscriber Server]

Abstract

System and methods for scheduling OFDM frames are provided. Each packet is assigned to a frame bucket, this amounting to a temporary decision of when to transmit the packet. Each packet is marked with one or more metrics. The metrics are used to sort packets and make scheduling decisions. Packets are analyzed to determine their suitability for MIMO transmission.

Claims

1. A method for transmitting orthogonal frequency division multiplexing (OFDM) frames in a multi-access OFDM communication system, the method comprising:

by a base station of the multi-access OFDM communication system;

scheduling a set of packets in accordance with a plurality of scheduling metrics,

generating at least one ordering of packets to transmit in an OFDM frame; and

transmitting the OFDM frame using a plurality of transmit antennas,

wherein each OFDM frame is constructed from packets assigned to the OFDM frame, each packet being placed in a respective rectangular time-frequency burst within the OFDM frame, and wherein time-frequency bursts transmitted to a first set of mobile stations are grouped for simultaneous transmission using at least two of the plurality of transmit antennas,

wherein channel conditions for the first set of mobile stations have a higher orthogonality compared to channel conditions for a second set of mobile stations.

2. The method of claim 1, wherein the plurality of scheduling metrics includes at least one compulsory scheduling metric that remains static for multiple OFDM frames and at least one optional scheduling metric that dynamically changes for each OFDM frame.

3. The method of claim 1, wherein the set of packets are scheduled by temporarily assigning each packet to a particular OFDM frame using a deadline for departure for the corresponding packet.

4. The method of claim 1, wherein the plurality of scheduling metrics includes at least one scheduling metric selected from a group consisting of:

earliest time of departure, deadline for departure, user/operator priority, link condition, power save mode considerations, and frame fitting information.

5. The method of claim 4, wherein the frame fitting information is updated when there is a change in robustness of data transmission to be used for transmitting corresponding packets.

6. The method of claim 1, wherein the at least one ordering of packets comprises at least one of:

a head of line ordering that defines an ordering of a most recent packet for each connection identifier (CID);

a frame bucket wide ordering that defines an ordering of all packets temporarily assigned to a given OFDM frame;

or

an all packets wide ordering that defines an ordering of all packets.

7. The method of claim 1, further comprising:

allocating resources of at least one future OFDM frame for retransmission of packets that require multiple transmissions.

8. The method of claim 1, further comprising:

performing multiple orderings of the packets to select the set of packets to send in the OFDM frame to improve a frame packing of time-frequency bursts in the OFDM frame.

9. The method of claim 8, further comprising:

stop performing the multiple orderings of the packets when the corresponding OFDM frame can be constructed based on a most improved frame packing of time-frequency bursts and transmitted on time.

10. The method of claim 1, further comprising:

allocating at least some time-frequency bursts to a third set of mobile stations for simultaneous transmission in an uplink (UL) direction using UL collaborative multiple-input multiple-output (MIMO) transmission.

11. The method of claim 10, wherein allocation of the at least some time-frequency bursts to the third set of mobile stations comprises at least:

determining sets of time-frequency bursts that are appropriate for simultaneous transmission using MIMO;

determining mobile stations that have sufficient orthogonality of channel conditions for MIMO to include in the third set of mobile stations; and

determining a number of symbols that can be saved by using MIMO as opposed to not using MIMO for sets of time-frequency bursts allocated to the third set of mobile stations.

12. The method of claim 1, further comprising:

altering robustness of modulation and encoding for the OFDM frame based on available room in the OFDM frame.

13. A base station comprising:

an OFDM transmitter for transmitting OFDM frames and comprising at least one transmit antenna; and

a scheduling device comprising;

a classifier configured to classify packets in accordance with one or more scheduling metrics; and

a scheduler configured to schedule a plurality of OFDM frames by assigning each packet to a corresponding OFDM frame using a logical assignment or a physical assignment, wherein packets are assigned to different OFDM frames based on one or more types of ordering of packets, and wherein each OFDM frame is constructed from packets assigned to the corresponding OFDM frame, each packet being placed in a respective rectangular time-frequency burst within the corresponding OFDM frame.

14. The base station of claim 13, wherein the physical assignment of a particular packet to the corresponding OFDM frame includes storing the particular packet in a memory location associated with the OFDM frame.

15. The base station of claim 13, wherein the logical assignment of a particular packet to the corresponding OFDM frame includes storing the particular packet in an arbitrary location and assigning a pointer to the particular packet stored in the OFDM frame.

16. A method for scheduling OFDM frames for an OFDM communication system, the method comprising:

classifying a set of packets in accordance with one or more scheduling metrics;

generating at least one ordering of packets to send in an OFDM frame using the one or more scheduling metrics; and

transmitting the OFDM frame using an OFDM transmitter comprising a plurality of transmit antennas,

wherein each OFDM frame is constructed from packets assigned to the OFDM frame by placing each packet in a respective rectangular time-frequency burst within the OFDM frame, wherein transmissions are grouped for simultaneous transmission to a first set of mobile stations that have a higher orthogonality of channel conditions than a second set of mobile stations.

17. The method of claim 16, wherein the one or more scheduling metrics used for classifying the set of packets comprise a connection identifier (CID) that includes one or more of:

(i) a set of quality of service (QoS) parameters including a maximum committed rate and a minimum committed rate or (ii) a set of channel quality measurements including a carrier-to-interference-plus-noise ratio (CINR).

18. The method of claim 16, wherein a receiver of the OFDM communication system reports a state of physical conditions for radio paths between the OFDM communication system and mobile stations.

19. The method of claim 16, wherein the one or more scheduling metrics comprises one or more of:

an earliest time of departure, a deadline for departure, user/operator priorities, radio path conditions, or power save modes.

20. The method of claim 16, wherein each packet of the set of packets are temporarily assigned to a particular OFDM frame using a deadline for departure for the corresponding packet.