Vertical roaming in wireless networks through improved quality of service measures

• US 7,092,405 B2
• Filed: 10/18/2004
• Issued: 08/15/2006
• Est. Priority Date: 02/28/2003
• Status: Expired due to Fees

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Guo, Zihua, Zhang, Qian, Zhu, Wenwu, Yao, Richard
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): ABELSON, RONALD B
• Application Number:
  US10/968,602
• Publication Number:
  US 20050068982A1
• Time in Patent Office: 666 Days
• Field of Search: 370/465, 370/468, 370/477
• US Class Current: 370/468
• CPC Class Codes: H04W 36/0088 Scheduling hand-off measurements
• CPC Class Codes: H04W 36/04 Reselecting a cell layer in multi-layered cells
• CPC Class Codes: H04W 36/14 Reselecting a network or an air interface
• CPC Class Codes: H04W 36/22 for handling the traffic

Abstract

A system and method for vertical handoff between different types of wireless networks. A network allocation vector of a first wireless network is sampled for a period of time. The network allocation vector may include a transmission time advertised by a sender in the first wireless network. A network allocation vector occupation is calculated. The calculation of the network allocation vector may include calculating a ratio of an amount of time that the network allocation vector is busy during the time period to a total amount of time during the time period. A wireless network quality of service measure is calculated as a function of the network allocation vector occupation. A vertical handoff may be initiated from a second wireless network to the first wireless network based at least in part on the calculated wireless network quality of service measure.

Claims

1. A computer-implemented method, comprising:

sampling a network allocation vector of a first wireless network for a period of time, the network allocation vector comprising a transmission time advertised by a sender in the first wireless network;

calculating a network allocation vector occupation comprising calculating a ratio of an amount of time that the network allocation vector is busy during the time period to a total amount of time during the time period;

calculating a wireless network quality of service measure as a function of the network allocation vector occupation; and

determining whether to initiate a vertical handoff from a second wireless network to the first wireless network based at least in part on the calculated wireless network quality of service measure.

2. The method according to claim 1, wherein calculating the wireless network quality of service measure as a function of network allocation vector occupation comprises calculating the wireless network quality of service measure as a linear function of network allocation vector occupation.

3. The method according to claim 2, wherein a low network allocation vector occupation corresponds to a high wireless network quality of service measure and a high network allocation vector occupation corresponds to a low wireless network quality of service measure.

4. The method according to claim 3, wherein the wireless network quality of service measure comprises an estimated residual bandwidth in the wireless network.

5. The method according to claim 4, wherein a high level of network allocation vector occupation corresponds to zero estimated residual bandwidth in the wireless network.

6. The method according to claim 3, wherein the wireless network quality of service measure comprises a wireless medium access control transmission delay.

7. The method according to claim 1, wherein calculating the wireless network quality of service measure as a function of network allocation vector occupation comprises looking-up the wireless network quality of service measure in a network allocation vector occupation to wireless network quality of service measure look-up table.

8. The method according to claim 1, further comprising initiating a vertical handoff from the second wireless network to the first wireless network when the calculated wireless network quality of service measure for the first wireless network is greater than an observed wireless network quality of service in the second wireless network.

9. The method according to claim 8, wherein the second wireless network is a wireless wide area network.

10. The method according to claim 9, wherein the first wireless network is a wireless local area network.

11. The method according to claim 8, wherein the first wireless network is a wireless local area network.

12. The method according to claim 1, further comprising initiating a vertical handoff from the first wireless network to the second wireless network when a signal strength received at a wireless network interface to the first wireless network is determined to be decreasing and an arithmetic mean of samples of signal strength received at the wireless network interface to the first wireless network is less than a minimum operating signal strength threshold.

13. A computer-readable medium having thereon computer executable instructions for performing the method of claim 1.

14. A computerized system comprising:

a first wireless network of a first type;

a plurality of senders of transmissions in the first wireless network; and

a connection manager configured to, at least;

sample a network allocation vector of the first wireless network for a period of time, the network allocation vector comprising a transmission time advertised by ones of the plurality of senders;

calculate a network allocation vector occupation comprising calculating a ratio of an amount of time that the network allocation vector is busy during the time period to a total amount of time during the time period;

calculate a wireless network quality of service measure for the first wireless network as a function of the network allocation vector occupation; and

determine whether to initiate a vertical handoff from a second wireless network of a second type to the first wireless network based at least in part on the calculated wireless network quality of service measure for the first wireless network.

15. The computerized system according to claim 14, wherein calculating the wireless network quality of service measure as a function of network allocation vector occupation comprises calculating the wireless network quality of service measure as a linear function of network allocation vector occupation.

16. The computerized system according to claim 14 wherein calculating the wireless network quality of service measure as a function of network allocation vector occupation comprises looking-up the wireless network quality of service measure in a network allocation vector occupation to wireless network quality of service measure look-up table.

17. The computerized system according to claim 14, wherein:

the connection manager is further at least configured to initiate a vertical handoff from the second wireless network to the first wireless network if the calculated wireless network quality of service measure in the first wireless network is greater than an observed wirelessnetwork quality of service in the second wireless network.

18. The computerized system according to claim 17, wherein the connection manager is further at least configured to initiate a vertical handoff from the first wireless network to the second wireless network if a signal strength received at a wireless network interface to the first wireless network is determined to be decreasing and an arithmetic mean of samples of signal strength received at the wireless network interface to the first wireless network is less than a minimum operating signal strength threshold.

19. A computer-readable medium having thereon a data structure comprising a wireless network quality of service measure for determining whether to initiate a vertical handoff to a wireless network, the wireless network quality of service measure calculated as a function of a network allocation vector occupation, the network allocation vector occupation calculated as a ratio of an amount of time that a sampled network allocation vector is busy during a time period to a total amount of time during the time period, the network allocation vector comprising a transmission time advertised by a sender in the wireless network.

20. The computer-readable medium according to claim 19 wherein the wireless network quality of service measure is calculated as a linear function of network allocation vector occupation.

21. The computer-readable medium according to claim 19 wherein the wireless network quality of service measure is calculated by looking-up the wireless network quality of service measure in a network allocation vector occupation to wireless network quality of service measure look-up table.

22. The computer-readable medium according to claim 19 wherein the wireless network quality of service measure comprises an estimated residual bandwidth in the wireless network.

23. The computer-readable medium according to claim 19 wherein the wireless network quality of service measure comprises a wireless medium access control transmission delay.