Dynamic frame size adjustment and selective reject on a multi-link channel to improve effective throughput and bit error rate

• US 6,236,647 B1
• Filed: 02/24/1998
• Issued: 05/22/2001
• Est. Priority Date: 02/24/1998
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Tantivy Communications Incorporated (InterDigital, Inc.)
• Inventors: Amalfitano, Carlo
• Primary Examiner(s): Ton, Dang
• Assistant Examiner(s): TON, ANTHONY T
• Application Number:
  US09/030,049
• Time in Patent Office: 1,183 Days
• Field of Search: 370/104, 370/314, 370/545, 370/505, 370/230, 370/233, 370/110, 370/235, 370/324, 370/329, 370/335, 370/336, 370/342, 370/464, 370/465, 370/470, 370/471, 370/431, 370/437, 370/441, 370/442, 370/458, 370/351, 370/352, 370/389
• US Class Current: 370/335
• CPC Class Codes: H04L 1/0007 by modifying the frame length
• CPC Class Codes: H04L 1/165 Variable formats
• CPC Class Codes: H04L 1/1809 Selective-repeat protocols
• CPC Class Codes: H04L 25/14 Channel dividing arrangements , i.e. in which a single bit stream is divided between several baseband channels and reassembled at the receiver

Abstract

A technique for implementing a sublayer of a protocol suitable for data transfer in a multichannel environment where each channel is assumed to be prone to a significant bit error rate such as in a wireless communication system. The invention may be used to provide a high speed data transfer such as at 128 kilobits per second or higher with a bit error rate of 10⁻⁶ or better using multiple channels. By keeping track of the number of frames received in error, the sender dynamically adjusts the subframe size for each channel to optimize the effective overall throughput. The subframes each carry preferably two types of sequence numbers including a position number related to an index into a larger frame to be transmitted as a single data entity. The second sequence number is related to the subchannel used so that the receiver can detect missing subframes. This then enables the receiver to submit retransmission requests for the missing pieces which can then be transmitted on the same channel or on another channel.

Claims

1. A method for communication of data between a sender and a receiver over one or more communication channels, the data being provided in a frame, the method comprising the steps of:

(a) dividing a frame into subframes according to an optimum subframe size;

(b) sending the subframes over a communication channel;

(c) determining the number of subframes received in error at the receiver by counting the number of selective reject orders made to the sender; and

(d) determining an optimum subframe size for the communication channel based upon a determined number of subframes received in error which were attempted to be communicated over that channel.

2. A method as in claim 1 wherein step (b) additionally comprises sending subframes over multiple distinct communication channels.

3. A method as in claim 2 wherein steps (c) and (d) additionally comprise determining an error rate in each channel and an optimum number of subframes for each channel individually.

4. A method as in claim 1 wherein step (d) determines an optimum number of frames according to a ratio of a number of subframes received in error to a number of subframes received correctly.

5. A method as in claim 1 wherein step (d) additionally comprises the step of determining an adjusted number of data bytes in a frame, X, from the formula:

$X=\stackrel{\_}{-H+\mathrm{SQR}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(X_{\mathrm{current}}+H_{\mathrm{current}}\right)}*H/R)$

where X_current is the present number of data bytes in a frame, H_current is the present frame overhead in bytes, H is the new overhead for the frame in bytes, and R is a ratio of subframes received in error to subframes received correctly.

6. A method as in claim 1 wherein step (d) additionally comprises the step of dynamically adjusting the optimum frame size as changes in transmission characteristics change the observed frame error rate.

7. A method as in claim 6 wherein step (d) additionally adjusts the frame size dynamically to optimize the effective throughput by determining a ratio of actual data transferred between the sender and receiver to the total number of bits of information, including frame overhead and re-transmissions.

8. A method as in claim 1 wherein step (b) additionally comprises the step of inserting a position number into the subframe to identify a position of the subframe within the frame.

9. A method as in claim 1 wherein step (b) additionally comprises the step of inserting a sequence number added into each subframe so that receiver can identify missing subframes.

10. A method as in claim 1 wherein step (d) additionally comprises the step of maintaining an average of the number of frames transmitted successfully between the sender and receiver and the number of frames that were not transmitted successfully.

11. A method for providing wireless communication of digital signals, the digital signals being communicated between a plurality of wireless subscriber units and a base station, the digital signals being communicated using at least one radio frequency channel via Code Division Multiple Access (CDMA) modulated radio signals, the digital signals also having a given nominal data rate, the method comprising the steps of:

(a) making available a plurality of subchannels within each CDMA radio channel, wherein a data rate of each subchannel is less than the nominal data rate of the digital signals;

(b) establishing a network layer session between terminal equipment connected to a subscriber unit through the base station to other terminal equipment connected to the base station; and

(c) during the network layer session, allocating available subchannels on an as-needed basis, with the number of subchannels allocated thereby changing during the duration of a given session; and

(d) dividing a network layer frame into subframes according to optimum subframe sizes for each subchannel.

12. A method as in claim 11 additionally comprising the step of:

(e) determining an optimum subframe size for each subchannel based upon a determined number of subframes received in error which were attempted to be communicated over that subchannel.

13. A method as in claim 12 wherein step (e) additionall comprises dynamically adjusting the frame size of a channel to optimize the effective throughput of the overall system based upon the ratio of actual data transferred to the number of bits actually used to carry information, including frame overhead and retransmissions.

14. A data communication system comprising:

a first multichannel transceiver to transmit data of a frame structure over one or more communication channels;

a second multichannel transceiver to receive the data of a frame structure over the one or more communication channels;

a first protocol converter connected to the first multichannel transceiver to divide a frame into subframes in an optimum subframe size; and

a second protocol converter connected to the second multichannel transceiver to reassemble the subframes transmitted by the first multichannel transceiver and received by the second multichannel transceiver into the frame, to determine the number of subframes received in error at the second multichannel transceiver by counting the number of selective reject orders made to the first protocol converter, to determine the optimum subframe size for each communication channel based upon a determined number of subframes received in error which were attempted to be communicated over each channel, and to determine an error rate in each channel and an optimum number of subframes for each channel individually.

15. A system as in claim 14 wherein the second protocol converter further comprises:

means for determining an optimum number of frames according to a ratio of a number of subframes received in error to a number of subframes received correctly.

16. A system as in claim 14 wherein the second protocol converter further comprises:

means for determining an adjusted number of data bytes in a frame, X, from the formula;

$X=\stackrel{\_}{-H+\mathrm{SQR}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(X_{\mathrm{current}}+H_{\mathrm{current}}\right)}*H/R)$

where X_current is the present number of data bytes in a frame, H_current is the present frame overhead in bytes, H is the new overhead for the frame in bytes, and R is a ratio of subframes received in error to subframes received correctly.

17. A system as in claim 14 wherein the first protocol converter further comprises:

means for adjusting the optimum frame size as changes in transmission characteristics change the an observed frame error rate.

18. A system as in claim 17 wherein the first protocol converter further comprises:

means for adjusting the frame size to optimize the effective throughput by determining a ratio of actual data transferred between the first multichannel transceiver and the second multichannel transceiver to the total number of bits of information, including frame overhead and re-transmissions.

19. A system as in claim 14 wherein the second protocol converter further comprises:

means for maintaining an average of the number of frames transmitted successfully between the first multichannel transceiver and the second multichannel transceiver and the number of frames that were not transmitted successfully.