Vertical roaming in wireless networks through improved quality of service measures

• US 6,944,144 B2
• Filed: 02/28/2003
• Issued: 09/13/2005
• 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
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): ABELSON, RONALD B
• Application Number:
  US10/377,494
• Publication Number:
  US 20040170191A1
• Time in Patent Office: 928 Days
• Field of Search: 370458-459, 370/345, 370/442, 370/465, 370/468, 370331-333
• US Class Current: 370/332
• 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;

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

calculating a wireless network quality of service measure as a linear function of network allocation vector occupation, 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, the wireless network quality of service measure comprising a wireless medium access control layer transmission delay.

2. The method according to claim 1, wherein the wireless network quality of service measure comprises an estimated residual bandwidth in the wireless network.

3. The method according to claim 2, wherein a high level of network allocation vector occupation corresponds to zero estimated residual bandwidth in the wireless network.

4. A computer-implemented method, comprising:

sampling a network allocation vector of a wireless network for a period of time;

calculating a network allocation vector occupation comprising calculating the ratio of the amount of time that the network allocation vector is busy during the time period to the 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, 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, the wireless network quality of service measure comprising a wireless medium access control layer transmission delay.

5. The method according to claim 4, 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.

6. 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.

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

8. A computer-implemented method, comprising:

sampling a network allocation vector of a wireless network for a period of time;

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

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; and

initiating a vertical handoff from the second type of wireless network to the first type of wireless network if the signal strength received at the 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.

9. The method according to claim 8, 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.

10. The method according to claim 8, wherein a high level of network allocation vector occupation corresponds to zero estimated residual bandwidth in the wireless network.

11. The method according to claim 8, wherein the wireless network quality of service measure comprises an estimated residual bandwidth in the wireless network.

12. The method according to claim 8, wherein the wireless network quality of service measure comprises a wireless medium access control transmission delay.