System and method for adaptive rate selection for wireless networks

• US 20050286440A1
• Filed: 06/24/2005
• Published: 12/29/2005
• Est. Priority Date: 06/24/2004
• Status: Abandoned Application

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: MeshNetworks, Inc. (Motorola Solutions, Inc.)
• Inventors: Strutt, Guenael T., Ozer, Sebnem Z.
• Application Number:
  US11/166,578
• Publication Number:
  US 20050286440A1
• Time in Patent Office: Days
• US Class Current: 370/253
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04W 28/22 Negotiating communication rate

Abstract

A system and method for dynamic rate adaptation in wireless networks is presented. A dynamic adjustment scheme adapts quickly to channel variation characteristics where adjustment values depend on the target data packet completion rates that maximizes the effective throughput. The required information is an estimate of the Medium Access Controller overhead including channel access delay. This a priori information can also be measured by the system a posteriori. Although the invention can be applied to both cellular and non-cellular systems, the exemplary embodiment is given for a carrier sense multiple access with collision avoidance (CSMA/CA) network.

Claims

1. A method for selecting a data rate by a node in a wireless communication network, the method comprising:

predicting a traffic throughput at the node for each of a plurality of potential data rates;

converting each of the predicted traffic throughputs into a respective target packet completion rate for each of a respective potential data rate; and

selecting the data rate based on an assessment of the actual packet completion rate in comparison with the respective target packet completion rates.

2. A method as claimed in claim 1, wherein:

the predicting step comprises predicting the traffic throughput for said each potential data rate based on at least one condition at the physical layer.

3. A method as claimed in claim 2, wherein the at least one condition comprises at least one of the following:

expected packet completion rate at each said data rate;

transmission time of each data rate, including overhead and variations due to packet length;

time lost due to failed packet transmissions at each said data rate; and

queuing delays at each said data rate.

4. A method as claimed in claim 1, wherein the converting step determines the respective target packet completion rate that maximizes the throughput at its corresponding respective potential data rate.

5. A method as claimed in claim 4, wherein the target packet completion rate is calculated according to the following equation:

$\mathrm{PCR}<br><br>\left(r,l\right)=\begin{array}{c}\mathrm{Effective}\\ \mathrm{Throughput}\end{array}<br><br>\left(r_0,l\right)·<br><br>\frac{t_s<br><br>\left(r,l\right)+t_e}{l+t_e·<br><br>\begin{array}{c}\mathrm{Effective}\\ \mathrm{Throughput}\end{array}<br><br>\left(r_0,l\right)}$

where;

Effective Throughput (ET) (r₀, l)=the predicted traffic throughput for a particular data rate and packet length;

l=packet length;

r=data rate;

r₀ =reference data rate used to determine the predicted effective throughput;

PCR=packet completion rate;

t_s=duration of a successful packet transmission; and

t_e=extra time required if the packet transmission fails, including estimated channel access delay.

6. A method as claimed in claim 1, wherein the selecting step comprises adjusting the respective data rate threshold values.

7. A method as claimed in claim 6, wherein said adjusting data rate threshold values is performed according to the following equations:

${\mathrm{Adjust}}_{\mathrm{NACK}}={\mathrm{Adjust}}_{\mathrm{ACK}}\times <br><br>\left(\frac{\mathrm{Target}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{PCR}}{\mathrm{Target}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{PCR}-1}\right)$ ${\mathrm{Adjust}}_{\mathrm{ACK}}={\mathrm{Adjust}}_{\mathrm{NACK}}\times <br><br>\left(\frac{1}{\mathrm{Target}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{PCR}}-1\right)$

where Target PCR represents a target packet completion rate, Adjust_AcK represents an adjustment applied to the data rate thresholds when the node successfully transmits a packet at a selected data rate and Adjust_NACK represents an adjustment applied to the data rate thresholds when the node fails to transmit a packet at a selected data rate.

8. A method as claimed in claim 6, wherein said adjusting the data rate threshold values comprises increasing the selected data rate when the actual packet completion rate is higher than the target packet completion rate, and wherein said adjusting the data rate threshold values comprises decreasing the selected data rate when the actual packet completion rate is lower than the target packet completion rate.

9. A method as claimed in claim 6, wherein the selecting step further comprises selecting the data rate by comparing a current condition at the physical layer to the data rate threshold values.

10. A method as claimed in claim 9, wherein the current condition at the physical layer comprises at least one of the received signal strength, the signal-to-noise ratio, and the error vector magnitude.

12. A node as claimed in claim 1, wherein:

the controller is adapted to predict the traffic throughput for said each potential data rate based on at least one condition at the physical layer.

13. A node as claimed in claim 12, wherein the at least one condition comprises at least one of the following:

expected packet completion rate at each said data rate;

transmission time of each data rate, including overhead and variations due to packet length;

time lost due to failed packet transmissions at each said data rate; and

queuing delays at each said data rate.

11. A node, adapted for communication in a wireless communication network, and capable of adjusting its rate of communication, the node comprising:

a controller, adapted to predict traffic throughput at the node for each of a plurality of potential data rates, convert each of the predicted traffic throughput into a respective target packet completion rate for each of a respective potential data rate, and select the data rate based on an assessment of the actual packet completion rate in comparison with the respective target packet completion rates.

14. A node as claimed in claim 11, wherein the converting determines the respective target packet completion rate that maximizes the throughput at its corresponding respective potential data rate.

15. A node as claimed in claim 14, wherein the target packet completion rate is calculated according to the following equation:

$\mathrm{PCR}<br><br>\left(r,l\right)=\mathrm{ET}<br><br>\left(r_0,l\right)·<br><br>\frac{t_s<br><br>\left(r,l\right)+t_e}{l+t_e·<br><br>\mathrm{ET}<br><br>\left(r_0,l\right)}$

where;

Effective Throughput (ET) (r₀, l)=the predicted traffic throughput for a particular data rate;

l=packet length;

r=data rate;

PCR=packet completion rate;

t_s=duration of a successful packet transmission; and

t_e=extra time required if the packet transmission fails, including estimated channel access delay.

16. A node as claimed in claim 11, wherein the selecting step comprises adjusting the respective data rate threshold values.

17. A node as claimed in claim 16, wherein said adjusting data rate threshold values is performed according to the following equations:

${\mathrm{Adjust}}_{\mathrm{NACK}}={\mathrm{Adjust}}_{\mathrm{ACK}}\times <br><br>\left(\frac{\mathrm{Target}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{PCR}}{\mathrm{Target}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{PCR}-1}\right)$ ${\mathrm{Adjust}}_{\mathrm{ACK}}={\mathrm{Adjust}}_{\mathrm{NACK}}\times <br><br>\left(\frac{1}{\mathrm{Target}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{PCR}}-1\right)$

where Target PCR represents a target packet completion rate, Adjust_AcK represents an adjustment factor applied to the data rate thresholds when the node successfully transmits a packet at a selected data rate and Adjust_NACK represents an adjustment applied to the data rate thresholds when the node fails to transmit a packet at a selected data rate.

18. A node as claimed in claim 16, wherein said adjusting the data rate threshold values comprises increasing the selected data rate when the actual packet completion rate is higher than the target packet completion rate, and wherein said adjusting the data rate threshold values comprises decreasing the selected data rate when the actual packet completion rate is lower than the target packet completion rate.

19. A node as claimed in claim 16, wherein:

the controller is adapted to select the data rate by comparing a current condition at the physical layer to the data rate threshold values.

20. A node as claimed in claim 19, wherein the current condition at the physical layer comprises at least one of the received signal strength, the signal-to-noise ratio, and the error vector magnitude.