Vertical roaming in wireless networks through improved quality of service measures

• US 7,499,432 B2
• Filed: 10/18/2004
• Issued: 03/03/2009
• Est. Priority Date: 02/28/2003
• Status: Expired due to Fees

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Yao, Richard, Guo, Zihua, Zhang, Qian, Zhu, Wenwu
• Primary Examiner(s): ABELSON, RONALD B
• Application Number:
  US10/968,696
• Publication Number:
  US 20050083874A1
• Time in Patent Office: 1,597 Days
• Field of Search: 370/458, 370/459, 370/345, 370/442, 370/465, 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 36/1446 wherein at least one of the networks is unlicensed
• 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:

transmitting probing data packets from a mobile computing device in a wireless network, the probing data packets transmitted in accordance with an IEEE 802.11 wireless network standard by a wireless network interface in compliance with a wireless Network Driver Interface Specification;

calculating a probing data packet collision probability for the wireless network based upon the probing data packets, the calculating comprising calculating a ratio of a number of unacknowledged probing data packets to a total number of probing data packets transmitted, wherein the ratio is calculated by dividing a Network Driver Interface Specification Acknowledge Failure Count statistic by the sum of the Network Driver Interface Specification Acknowledge Failure Count statistic and a Transmitted Fragment Count statistic;

calculating a wireless network quality of service measure as a function of the probing data packet collision probability; and

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 in the second type of wireless network is greater than observed wireless network quality of service in the first type of wireless network.

2. The method according to claim 1, wherein calculating the probing data packet collision probability comprises calculating the ratio of a number of unacknowledged probing data packets to a total number of probing data packets transmitted.

3. The method according to claim 2, wherein the probing data packets are transmitted in accordance with an IEEE 802.11 wireless network standard by a wireless network interface in compliance with a wireless Network Driver Interface Specification, wherein the ratio is calculated by dividing a Network Driver Interface Specification Acknowledge Failure Count statistic by the sum of the Network Driver Interface Specification Acknowledge Failure Count statistic and a Transmitted Fragment Count statistic.

4. The method according to claim 1, wherein a low probing data packet collision probability corresponds to a high wireless network quality of service measure and a high probing data packet collision probability corresponds to a low wireless network quality of service measure.

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

6. The method according to claim 5, wherein a high level of probing data packet collision probability 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 a wireless medium access control transmission delay.

8. The method according to claim 1, wherein calculating the wireless network quality of service measure as a function of probing data packet collision probability comprises looking-up the wireless network quality of service measure in a probing data packet collision probability to wireless network quality of service measure lookup table.

9. The method according to claim 1, wherein the first type of wireless network comprises a wireless wide area network.

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

11. The method according to claim 1, wherein the second type of wireless network comprises a wireless local area network.

12. The method according to claim 1, further comprising initiating a vertical handoff from the second type of wireless network to the first type of wireless network if 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.

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