Method and apparatus for load sharing in wireless access networks based on dynamic transmission power adjustment of access points

• US 20040229621A1
• Filed: 05/16/2003
• Published: 11/18/2004
• Est. Priority Date: 05/16/2003
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Misra, Archan
• Granted Patent: US 7,162,250 B2
• Time in Patent Office: Days
• US Class Current: 455/445
• CPC Class Codes: H04W 16/08 Load shedding arrangements
• CPC Class Codes: H04W 36/22 for handling the traffic
• CPC Class Codes: H04W 52/283 Power depending on the position of the mobile
• CPC Class Codes: H04W 52/34 TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading

Abstract

A load balancing system and methodology for packet-based wireless cellular networks, whereby wireless access points are dynamically reconfigured by altering their transmission power level to modify their area of coverage. The modification function is based on the localized traffic load or congestion at each individual access point, or the collective load experienced by groups of access points. This modification to the cellular layout is used as an implicit load-balancing technique. When an overloaded access point reduces its coverage area, it forces some wireless client devices that were earlier within its footprint, but no longer within its coverage area, to attach to alternative access points. Similarly, when an underloaded access point increases its coverage area, it provides an opportunity to wireless devices, which were earlier outside its footprint, but now within the expanded coverage area, to switch attachment to this access point. By changing the access point to which a wireless device attaches, the load-levels on the individual access points are indirectly changed.

Claims

1. A method for relieving the traffic load on one or more wireless access points (APs) in a wireless cellular network, the method comprising the steps of:

a) detecting one of;

a traffic overload or underload condition at one or more APs;

b) modifying a transmission power level associated with said one or more APs, thereby modifying the size of the associated coverage area of each AP; and

,

c) initiating switching of one or more of the current wireless devices from their current attachment to a first of said one or more APs to an alternative AP, thereby modifying the traffic load at said first and alternative APs.

2. The method as recited in claim 1, wherein said wireless cellular network is packet-based, said detecting step comprising monitoring one or more of:

traffic related metrics and various performance metrics associated with packets transmitted via said AP, and generating overload condition signals at said AP when said overload or underloaded condition at an AP is detected.

3. The method as recited in claim 2, wherein said modifying step b) comprises one of:

increasing or decreasing the transmission power level associated with one or more APs, said transmission power being decreased at an overloaded AP to a lower power level, and transmission power being correspondingly increased at a neighboring AP to ensure appropriate overlap of coverage areas.

4. The method as recited in claim 3, wherein said detecting further comprises:

tracking the number of attached users at each access point and, generating an overload condition signal if these values exceed a threshold value.

5. The method as recited in claim 3, wherein said performance metric includes one or more of:

a packet delay, a packet loss rate, and AP processor utilization, said detecting further comprising;

comparing one or more of said packet delay, packet loss rate and AP processor utilization against a respective threshold value and generating an overload condition signal at said AP if these values exceed a threshold value.

6. The method as recited in claim 3, wherein said traffic related metric includes total traffic rate or the number of users at one or more access points, said detecting further comprising:

comparing said total traffic rate or the number of users at one or more access points against a threshold value and generating an overload indication signal at said AP if the total traffic rate or the number of users at one or more access points exceed a threshold value.

7. The method as recited in claim 3, further comprising providing a centralized load balancing means for receiving overload condition signals generated by an AP, and controlling modification of said power levels at said AP and alternative APs in response thereto.

8. The method as recited in claim 1, wherein said initiating switching step c) comprises one of:

explicitly instructing a client device to switch to another identified access point, or enabling a client device to initiate a search for a new AP and then switch to that new AP.

13. The system as recited in claim 1, further comprising a centralized load balancing means for receiving overload condition signals generated by one or more AP, and controlling modification of said power levels at said AP and alternative APs in response thereto.

14. The system as recited in claim 13, wherein said wireless cellular network comprises an local access domain network linking said one or more access points (APs), said local access domain network linked to a wide-area network, wherein said centralized load balancing means is in communication with one of said local access domain network or said wide-area network.

9. A system for relieving the traffic load on one or more wireless access points (APs) of a wireless cellular network comprising:

means for detecting one of;

a traffic overload or underload condition at one or more APs;

means for modifying a transmission power level associated with said one or more APs, thereby modifying the size of the associated coverage area of each AP; and

,

means for switching of one or more of the current wireless devices from their current attachment to a first of said one or more APs to an alternative AP, thereby modifying the traffic load at said first and alternative APs.

10. The system-as recited in claim 9, wherein said wireless cellular network is packet-based, said detecting means comprising:

means for monitoring one or more of;

traffic related metrics and various performance metrics associated with packets transmitted via said AP;

means for comparing said traffic and packet performance related metric values with threshold values to determine said overload or underloaded condition; and

,

means for generating overload condition signals at said AP when an overload and underload condition at an AP is detected.

11. The system as recited in claim 10, wherein said means for modifying a transmission power level performs one of:

increasing or decreasing the transmission power level, said transmission power being decreased at an overloaded AP to a lower power level, and transmission power being correspondingly increased at an alternative AP to ensure appropriate overlap of coverage areas.

12. The system as recited in claim 11, wherein said transmission power at an individual AP is modified according to the explicit location of wireless client devices to either determine the appropriate level of power increase necessary to allow certain client devices that are currently attached to alternative APs to switch to a first AP, or, determine the appropriate level of power decrease needed to ensure that certain client devices currently attached to the first AP are switched to alternative APs.

15. The system as recited in claim 12, wherein an AP generates signals explicitly instructing a client device to switch to another identified access point, or signals enabling a client device to initiate a search for a new AP to be switched to.

16. A method for modifying the transmission power levels at individual wireless access points (APs) of a wireless cellular network, the method comprising the steps of:

a) detecting one of;

a traffic overload or underload condition at one or more APs and generating one or more signals at said AP upon detection of said overload or underload condition;

b) communicating said overload and underload signals to a load balancing means for controlling modification of a transmission power level associated with an AP, thereby modifying the size of the associated coverage area of each AP; and

,

c) initiating switching of one or more of the current wireless devices from their current attachment to a first of said one or more APs to an alternative AP,

whereby the traffic load at said first and alternative APs becomes modified.

17. The method for modifying the transmission power levels as recited in claim 16, wherein AP transmission power levels at an individual AP is modified according to the explicit location of wireless client devices to either determine the appropriate level of power increase necessary to allow certain client devices that are currently attached to alternative APs to switch to a first AP, or, determine the appropriate level of power decrease needed to ensure that certain client devices currently attached to the first AP are switched to alternative APs.

18. A method for modifying the transmission power levels at individual wireless access points (APs) of a wireless cellular network, the method comprising the steps of:

a) detecting one of;

a traffic overload or underload condition at one or more APs and generating one or more signals at said AP upon detection of said overload or underload condition;

b) communicating said overload and underload signals to one or more neighboring APs, each AP equipped to modify its associated transmission power level in coordination with said one or more neighboring APs, thereby modifying the size of the associated coverage area of each AP; and

,

c) initiating switching of one or more of the current wireless devices from their current attachment to a first of said one or more APs to an alternative AP,

whereby the traffic load at said first and alternative APs becomes modified.

19. The method for modifying the transmission power levels as recited in claim 18, wherein AP transmission power levels at an individual AP is modified according to the explicit location of wireless client devices to either determine the appropriate level of power increase necessary to allow certain client devices that are currently attached to alternative APs to switch to a first AP, or, determine the appropriate level of power decrease needed to ensure that certain client devices currently attached to the first AP are switched to alternative APs.

20. A method for balancing traffic load at one or more wireless access points (APs) provided in a wireless cellular network, the method comprising the steps of:

a) detecting one of;

a traffic overload or underload condition at one or more APs;

b) modifying a transmission power level associated with said one or more APs, thereby modifying the size of the associated coverage area of each AP; and

,

c) initiating switching of one or more of the current wireless devices from their current attachment to a first of said one or more APs to an alternative AP, thereby modifying the traffic load at said first and alternative APs.

21. The method for balancing traffic load as recited in claim 20, where said modifying of transmission power at APs, further comprises one or more of actions comprising:

decreasing the transmission power of an overloaded AP, and increasing the transmission power of an underloaded AP.

22. The method for balancing traffic load as recited in claim 21, wherein said wireless cellular network is packet-based, said method further comprising the steps of:

monitoring, at each AP, one or more of;

traffic related metrics and various performance metrics associated with packets transmitted via said AP;

comparing traffic and packet performance related metric values with threshold values to determine said overloaded or underloaded condition; and

,

generating overload condition signals at said AP when an overload and underload condition at an AP is detected.

23. The method for balancing traffic load as recited in claim 21, wherein said transmission power at an individual AP is modified according to the explicit location of wireless client devices to either determine the appropriate level of power increase necessary to allow certain client devices that are currently attached to alternative APs to switch to a first AP, or, determine the appropriate level of power decrease needed to ensure that certain client devices currently attached to the first AP are switched to alternative APs.

24. The method for balancing traffic load as recited in claim 21, wherein the step of increasing AP transmission power further comprises:

increasing the transmission power of an AP beyond a level needed to support communication with its current set of attached devices.

25. The method for balancing traffic load as recited in claim 21, wherein the increasing or decreasing of AP transmission power further comprises:

increasing or decreasing the transmission power of one or more wireless client devices that are attached to, or is enabled to attach to, an AP.

26. The method for balancing traffic load as recited in claim 21, wherein the modifying of AP transmission powers further comprises:

enabling coverage area of one or more APs become entirely included within a larger coverage area of another access point.

27. The method for balancing traffic load as recited in claim 21, wherein the modifying of AP transmission powers further comprises one of:

adjusting the power levels of an overloaded AP in a manner independent of the load levels, or in a manner that is based on the actual or estimated load level.

28. The method for balancing traffic load as recited in claim 21, wherein said transmission power at an individual AP with one or more attached wireless client devices is reduced by generating signals for receipt by said client devices instructing said client devices to bind to another alternative access point.

29. The method for balancing traffic load as recited in claim 28, wherein the signals received by said attached wireless devices comprise:

signals instructing the wireless client device to explicitly switch to a particular alternative access point, or instructing it to switch to any alternative feasible access point, said instructed wireless device losing connectivity to the access point to which the wireless device is current attached, and subsequently binding to an alternative access point.