Frequency assignment for multi-cell IEEE 802.11 wireless networks

• US 7,206,586 B2
• Filed: 09/28/2005
• Issued: 04/17/2007
• Est. Priority Date: 11/08/2001
• Status: Expired due to Term

• Current Assignee: AT&T Corporation (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Kim, Byoung-Jo J., Leung, Kin K
• Primary Examiner(s): Feild; Joseph
• Assistant Examiner(s): Nguyen; Huy D.
• Application Number:
  US11/237,337
• Publication Number:
  US 20060025150A1
• Time in Patent Office: 566 Days
• Field of Search: 455/52, 455/63.1, 455/63.3, 455/447, 455/450, 455/452.1, 455/453, 455/560, 455/561, 455/451, 455/452.2, 455/446, 370/329, 370/431, 370/445
• US Class Current: 455/450
• CPC Class Codes: H04W 16/04 Traffic adaptive resource partitioning
• CPC Class Codes: H04W 28/16 Central resource management; Negotiation of resources or communication parameters, e.g. negotiating bandwidth or QoS [Quality of Service]
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information
• CPC Class Codes: H04W 72/541 using the level of interference
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A frequency planning method for use in an IEEE 802.11 wireless network is described. The frequency planning method obtains traffic load information associated with access points belonging to a multi-cell wireless network and assigns channels to the access points based on the traffic load information.

Claims

1. A method for frequency planning in wireless networks comprising:

obtaining traffic load information for access points belonging to a wireless network having a plurality of Access Points (APs) where a channel between a terminal and an AP of said network is employed to communicate both traffic and control information and communication is established between said terminal and said AP by use of a protocol that supports a Point Coordination Function (PCF) that provides contentions-free access, and a Distributed Coordination Function (DCF) that uses a carrier sense multiple access with collision avoidance (CDMA/CA) mechanism for contention-based access; and

assigning channels to the access points based on the traffic load information where traffic load information for a considered AP includes load of traffic between the considered AP and terminals that communicate with the considered AP, and effective load that results from detections of channel busy conditions due to interfering communication by terminals with other APs of said network, wherein the step of assigning comprises;

determining, for each considered AP, at least one set of interferers from among the other APs relative to said considered AP based on interference signal strength;

generating random channel assignments for the access points;

determining effective channel utilization values for each access point;

modifying the random channel assignment for interferers in the at least one set of interferers such that the highest one of the effective channel utilization values is minimized;

repeating said step of modifying until the highest one of the effective channel utilization values cannot be reduced by further modification; and

saving the modified random channel assignment as a final assignment.

2. The method of claim 1 wherein the step of determining comprises:

determining, for each of the other access points, if any co-channel interference by any of the other access points is greater than or equal to a detection threshold, the detection threshold indicative of an additional perceived load arising from the CSMA protocol; and

if it is determined that the co-channel interference is greater than or equal to the detection threshold, identifying the other access point as belonging to the set of interferers for the access point that increases the load that is considered to burden the access point.

3. The method of claim 2 wherein the co-channel interference between an access point and another access point is derived from values of signal path loss between the access point and the other access point and transmission power of the other access point.

4. The method of claim 2 wherein the at least one set of interferers comprises a second set of interferers, and wherein the step of determining comprises:

determining, for any pair of the other access points, if any combined co-channel interference by such pair is greater than or equal to a detection threshold, the detection threshold indicative of an additional perceived load arising from the CSMA protocol; and

if it is determined that the combined co-channel interference is greater than or equal to the detection threshold, identifying the other access points in such pair as belonging to the second set of interferers for the access point that increases the load that is considered to burden the access point.

5. The method of claim 1 wherein the step of assigning further comprises:

providing the final assignment to the access points.

6. The method of claim 1 wherein the step of assigning further comprises:

assigning randomly a channel to each of the access points; and

computing, based on the random channel assignment, an effective channel utilization value for each access point, the effective channel utilization value representing the sum of an offered load associated with the access point and total traffic load associated with each set of interferers.

7. The method of claim 6 wherein the step of assigning further comprises:

determining which access point has the highest effective channel utilization value;

identifying which channel is assigned to the access point having the highest effective channel utilization value; and

for each access point in the first set of interferers, modifying the random channel assignment;

recomputing the effective channel utilization value for the modified random channel assignment; and

repeating modifying and recomputing for each available channel other than the channel assigned to the access point having the highest effective channel utilization value;

determining a minimum effective channel utilization from among the recomputed effective channel utilization values;

comparing the minimum effective channel utilization and the recomputed effective channel utilization values; and

replacing the highest effective channel utilization with the determined minimum effective channel utilization and saving the modified random channel assignment as a best solution if the determined minimum effective channel utilization is lower than the highest effective channel utilization.

8. The method of claim 7 wherein the step of assigning further comprises:

with a pre-specified probability, replacing the highest effective channel utilization with the determined minimum effective channel utilization and saving the modified random channel assignment as a best solution if the determined minimum effective channel utilization is equal to the highest effective channel utilization.

9. The method of claim 1 wherein the step of assigning further comprises:

computing an effective utilization value for each access point based on the final assignment; and

determining if the effective utilization value for each access point is less than a value of one.

10. The method of claim 9, where the effective utilization of a channel by an access point is a sum of channel utilization by said access point, plus interference in said channel by units belonging to a first class of interferers, plus interference in said channel by units belonging to a second class of interferers, where said units in said first class are characterized by an interference level that is sufficiently high to cause a conclusion that said channel is busy, and said units in said second class are characterized by an interference level that requires two of the second class units to transmit concurrently to cause a conclusion that said channel is busy.

11. The method of claim 1 wherein the channels comprise non-overlapping channels.

12. The method of claim 1 wherein the channels comprise overlapping and non-overlapping channels.

13. The method of claim 1 wherein the access points employ the CSMA/CA protocol.

14. The method of claim 1 wherein the step of assigning comprises:

seeking to minimize effective channel utilization of a most heavily loaded of the access points.

15. The method of claim 1 wherein the step of assigning comprises:

seeking to minimize total effective channel utilization of all access points.

16. The method of claim 1 wherein the step of assigning comprises:

seeking to maximize network throughput.

17. The method of claim 1 where multiple access protocol is able to carry communication in frequency bands centered about 1.9 GHz, or 5.4 GHz, for a link distance of at most several hundred meters.

18. The method of claim 1 where the step of assigning executes a process that minimizes channel utilization by an AP, where channel utilization corresponds to the fraction of time at which the channel can be sensed busy or is used for transmission.

19. An article comprising:

a storage medium having stored thereon instructions that when executed by a machine result in the following;

obtaining traffic load information for access points belonging to a wireless network having a plurality of Access Points (APs) where a channel between a terminal and an AP of said network is employed to communicate both traffic and control information and communication is established between said terminal and said AP by use of multiple access protocol; and

assigning channels to the access points based on the traffic load information where traffic load information for a considered AP includes load of traffic between the considered AP and terminals that communicate with the considered AP, and effective load that results from detections of channel busy conditions due to interfering communication by terminals with other APs of said network, wherein the step of assigning comprises;

determining, for each considered AP, at least one set of interferers from among the other APs relative to said considered AP based on interference signal strength;

generating random channel assignments for the access points;

determining effective channel utilization values for each access point;

modifying the random channel assignment for interferers in the at least one set of interferers such that the highest one of the effective channel utilization values is minimized;

repeating said step of modifying until the highest one of the effective channel utilization values cannot be reduced by further modification; and

saving the modified random channel assignment as a final assignment.

20. An apparatus comprising:

a processor; and

a memory storing a computer program product residing on a computer-readable medium comprising instructions to cause a computer to;

obtain traffic load information for access points belonging to a multi-cell IEEE 802.11-type wireless network; and

assign channels to the access points based on the traffic load information where traffic load information for a considered AP includes load of traffic between the considered AP and terminals that communicate with the considered AP, and effective load that results from detections of channel busy conditions due to interfering communication by terminals with other APs of said network, wherein the step to assign channels to the access points comprises;

determining, for each considered AP, at least one set of interferers from among the other APs relative to said considered AP based on interference signal strength;

generating random channel assignments for the access points;

determining effective channel utilization values for each access point;

modifying the random channel assignment for interferers in the at least one set of interferers such that the highest one of the effective channel utilization values is minimized;

repeating said step of modifying until the highest one of the effective channel utilization values cannot be reduced by further modification; and

saving the modified random channel assignment as a final assignment.

21. An access point for use in wireless network comprising:

a logic module configured to obtain traffic load information for access points belonging to the wireless network having a plurality of Access Points (APs) where a channel between a terminal and an AP of said network is employed to communicate both traffic and control information and communication is established between said terminal and said AP by use of multiple access protocol; and

a logic module configured to assign channels to the access points based on the traffic load information where traffic load information for a considered AP includes load of traffic between the considered AP and terminals that communicate with the considered AP, and effective load that results from detections of channel busy conditions due to interfering communication by terminals with other APs of said network, wherein assigning channels to the access points comprises;

determining, for each considered AP, at least one set of interferers from among the other APs relative to said considered AP based on interference signal strength;

generating random channel assignments for the access points;

determining effective channel utilization values for each access point;

modifying the random channel assignment for interferes in the at least one set of interferers such that the highest one of the effective channel utilization values is minimized;

repeating said step of modifying until the highest one of the effective channel utilization values cannot be reduced by further modification; and

saving the modified random channel assignment as a final assignment.