Vertical roaming in wireless networks through improved quality of service measures

• US 20050068982A1
• Filed: 10/18/2004
• Published: 03/31/2005
• Est. Priority Date: 02/28/2003
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Guo, Zihua, Zhang, Qian, Zhu, Wenwu, Yao, Richard
• Granted Patent: US 7,092,405 B2
• Time in Patent Office: Days
• 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 improved vertical handoff between different types of wireless network. Network allocation vector occupation and packet collision probability are used as quality of service measures, enabling vertical handoffs to be delayed until actually beneficial to quality of service. Improved wireless network cell boundary detection in vertical handoff scenarios is achieved with a Fourier-based technique in conjunction with an adaptively determined minimum operating signal strength threshold. Improved wireless network cell boundary detection enables vertical handoffs from high quality of service networks to be delayed as long as possible. Together, practical wireless network quality of service measures and improved detection of wireless network cell boundaries in vertical handoff scenarios reduce the rate of unnecessary vertical handoff resulting in higher overall quality of service experienced by a mobile computing device roaming between wireless network types.

Claims

1. A computer-implemented method, comprising:

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

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

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 a first type of wireless network to a second type of wireless network if the calculated wireless network quality of service measure in the second type of wireless network is greater than the observed wireless network quality of service in the first type of wireless network.

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

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

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

12. The method according to claim 8, further comprising initiating a vertical handoff from the second type of wireless network to the first type of wireless network if a signal strength received at a wireless network interface to the second type of wireless network is determined to be decreasing and an arithmetic mean of samples of signal strength received at the wireless network interface to the second type of 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.

14-27. -27. (Canceled)

28. 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; and

calculate a wireless network quality of service measure as a function of the network allocation vector occupation.

29. The computerized system according to claim 28, 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.

30. The computerized system according to claim 28 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.

31. The computerized system according to claim 28, wherein:

the system further comprises a second wireless network of a second type; and

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 wireless network quality of service in the second wireless network.

32. The computerized system according to claim 31, 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.

33. A computer-readable medium having thereon a data structure comprising a wireless network quality of service measure, 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 a wireless network.

34. The computer-readable medium according to claim 33 wherein the wireless network quality of service measure is calculated as a linear function of network allocation vector occupation.

35. The computer-readable medium according to claim 33 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.

36. The computer-readable medium according to claim 33 wherein the wireless network quality of service measure comprises an estimated residual bandwidth in the wireless network.

37. The computer-readable medium according to claim 33 wherein the wireless network quality of service measure comprises a wireless medium access control transmission delay.