WO2009095832A1

WO2009095832A1 - Ieee 802.11 wlan client device with two wireless interfaces for improving scanning performance during roaming

Info

Publication number: WO2009095832A1
Application number: PCT/IB2009/050283
Authority: WO
Inventors: Ruediger Schmitt
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-01-31
Filing date: 2009-01-23
Publication date: 2009-08-06
Also published as: TW200944015A

Abstract

A wireless mobile device interacts with a proximate wireless Local Area Network (WLAN) and Access Points (APs), and uses a scanning interface configured to perform scanning; and, a communication interface configured to perform at least data communication. The two interfaces are expediently co-located in the same wireless device. If the scanning device is dedicated for performing scanning operations, it will free the communication interface from vacating its channel to perform scanning. The dedicated scanning interface generates a more thorough 'picture' of the wireless environment or neighborhood which the wireless device is operating in. This neighborhood information compiled by the scanning interface is then used by the communication interface for making effective decisions on which target AP to connect to during roaming. The invention is applicable to wireless systems that require seamless mobility support, such as in WUSB, 4G cellular and IEEE 802.11. Applications include patient monitoring and VoIP.

Description

IEEE 802 . 11 WLAN CLIENT DEVICE WITH TWO WIRELESS INTERFACES FOR IMPROVING SCANNING PERFORMANCE DURING ROAMING

A claim of priority under 35 USC § 119(e) is made to U.S. Provisional Patent Application No. 61/024,931, filed on January 31, 2008.

This invention relates generally to wireless mobile devices, and more particularly to a system and method for reliably discovering proximate WLAN access points for an IEEE 802.11 device during roaming, without support of the network infrastructure.

A brief discussion of the deployment of IEEE 802.11 WLANs in general is believed to be conducive to a better understanding of the present invention.

802.11 and 802.1 Ix refer to a family of specifications developed by the IEEE for wireless LAN technology. 802.11 specifies an over-the-air interface between a wireless client and a base station or between two wireless clients. The IEEE accepted the specification in 1997.

There are several specifications in the 802.11 family, including:

802.1 Ia — an extension to 802.11 that applies to wireless LANs and provides up to 54 Mbps in the 5GHz band. 802.11a uses an orthogonal frequency division multiplexing encoding scheme rather than FHSS or DSSS.

802.1 Ib — an extension to 802.11 that applies to wireless LANs and provides 11 Mbps transmission (with a fallback to 5.5, 2 and 1 Mbps) in the 2.4 GHz band. 802.11b uses only DSSS and was a 1999-ratification to the original 802.11 standard, allowing wireless functionality comparable to Ethernet.

802.1 Ig — applies to wireless LANs and provides upto 54 Mbps in the 2.4 GHz band.

The 802.1 \a standard is the wireless LAN standard using OFDM, with upto 54 Mbps designed to operate in the 5 GHz range band. Although segmented, the total bandwidth available for IEEE 802.1 Ia applications is almost four times that of the ISM band; the ISM band offers only 83 MHz of spectrum in the 2.4 GHz range, while the newly allocated UNII band offers 300 MHz. The 802.1 Ib spectrum is plagued by saturation from wireless phones, microwave ovens and other emerging wireless technologies, such as Bluetooth. In contrast, 802.1 Ia has an advantage in that its spectrum is relatively free of interference, at least for now.

For implementers, use of the same MAC in 802.1 lα as well as 802.1 Ib means one less component to design. For adopters, this means that upgrading from 802.1 Ib to 802.11a technology will not have significant impact on network operations. MAC in 802.1 Ib uses CSMA/CA technology and implements a number of options to improve throughput, especially in congested areas.

IEEE 802.11 wireless LANs (WLANs) have been widely deployed to provide wireless connectivity in home, enterprises and public hot spots. Usually, the WLANs are set up in infrastructure mode, where a centralized controller called access point (AP) acts as a bridge between wireless stations (STAs) and the wired network/internet. Due to the propagation characteristics of WLANs, multiple access points (APs) are deployed to ensure even coverage of the service area. IEEE 802.11 refers to an AP and the STAs connected to it as a basic service set (BSS). FIG 1 depicts and exemplary AP deployment in an office building or a similar facility.

A mobile WLAN node will move in and out of the coverage area of APs and to ensure uninterrupted connectivity a handoff process takes place in which the node changes its association from one AP to another.

A handoff occurs when a mobile station moves beyond the radio range of one AP, and enters another BSS at the MAC layer. During the handoff, management frames are exchanged between the station and the AP. The APs involved may exchange certain context information (credentials) specific to the station. Consequently, ordinarily, there may be latency involved in the handoff process during which the station is unable to send or receive traffic.

The handoff process in 802.11 can be split into three phases namely, detection, scanning and execution. The detection phase is a continuous process, during which the STA evaluates, whether it should roam to a new AP based on MAC or PHY layer parameters. Details of this process are not defined by any 802.11 standard, i.e. the implementation is up to the vendors. In the scanning phase, after the STA has made the decision to initiate roaming, it needs to search for another AP to connect to. This phase is also referred to as discovery and probe or search phase. Lastly, once a target AP has been found, the STA has to connect to the target AP and the network in the execution phase. The execution phase consists of a series of message exchanges between the STA and the target AP.

In IEEE 802.11, it is stated that the APs can work in a number of specified channels depending on the regulatory domain. There are twelve non- overlapping channels in 802.11a and 11 channels in 802.1 lb/g as used in the US, three of which are non- overlapping. A wireless station can only work in one wireless channel at a time.

IEEE 802.11 (Wireless LAN medium access control (MAC) and physical layer (PHY) specifications, 1999 (Reaff) edition, sections 11.1.3.1 and 11.1.3.2) describes two methods for scanning, passive and active scanning:

Passive Scanning is wherein the STA moves to a channel and listens for beacons and probe response frames from APs operating in that channel. Beacon periods are usually 100 ms and the STA has to decide how long to wait on a specific channel.

Active Scanning is wherein the STA transmits a probe request frame which causes the AP to return a probe response frame. If the station has not received channel-busy indication in MinChannel-time it moves to the next channel. Otherwise, it moves to the next channel after MaxChannel-time. MinChannel-and MaxChannel-time are implementation dependent.

This invention proposes a system and method for a wireless mobile device (e.g., mobile IEEE 802.11 device) to reliably discover nearby WLAN access points (APs) and the traffic load in their respective BSSs without support of the network infrastructure. This invention proposes to use two wireless interfaces co-located in the same wireless device, one being generally responsible for data communication and the other for mainly scanning. The deployment of the two wireless interfaces allows for more accurate scanning and prevents loss of connection from the current AP.

One embodiment of the invention resides in a mobile IEEE 802.11 device for interacting with a proximate wireless Local Area Network (WLAN) and Access Points (APs), comprising: a first scanning interface configured to perform scanning; and, a second communication interface configured to perform at least data communication. The scanning interface and the communication interface may be placed in the same mobile device and interconnected to interact.

A second embodiment of the invention resides in a mobile IEEE 802.11 type device for selective use for patient monitoring and VoIP applications, wherein the device interacts with a proximate wireless Local Area Network (WLAN) and Access Points (APs), comprising: a first scanning interface dedicated to performing scanning (preferably but not necessarily) without data communication; and, a second communication interface configured to perform at least data communication.

In a third form, the invention resides in a wireless mobile device for applications requiring seamless mobility such as in WUSB (Wireless Universal Serial Bus) and 4G cellular applications, said wireless mobile device interacting with a proximate wireless Local Area Network (WLAN) and Access Points (APs), and comprising: a first scanning interface dedicated to performing scanning without data communication; and, a second communication interface configured to perform at least data communication, wherein the scanning interface uses hardware similar to that contained in the communication interface, but uses a modified version of software and firmware from the communication interface, and wherein the scanning interface is configured to do active or passive scanning operation continuously.

In a modification, the scanning interface is configured also to execute the handoff procedure on behalf of the communication interface by performing the operations of association, authentication, while the communication interface still operates in the other channel. Only after the authentication and associated steps would the communication interface switch to the new AP.

In another embodiment, both the scanning interface and the communication interface are able execute handoff (scanning, association and authentication) and data transfers. While at a given time the first interface is connected to an AP and performs data communication, the second interface attempts to find a new AP which provides better connectivity (higher signal strength, less contention) than the currently used AP. If such an AP is found, the second interface associates and authenticates with the new AP. The data communication is then switched from the first to the second interface. The first interface proceeds to scan the wireless environment for a better wireless connection. It is noted that the references to the first and second interfaces in this embodiment are not absolute, but interchangeable.

Problems and disadvantages overcome by the present approach:

It is commonly reported in related literature and standards, that the scanning phase is the most time-consuming phase in the handoff process (vide: An Empirical analysis of the IEEE 802.11 MAC layer Handoff Process, ACM computer communications Review, vol. 33, no 2, April 2003). This is true, provided that advanced authentication mechanisms, introduced to improve WLAN security (Amendment to part 11 of IEEE standard 802.11), are used in a way suggested in the draft amendment to IEEE 802.1 lrelating to fast roaming, i.e., when techniques such as pre- authentication etc. are employed.

Active scanning is faster than passive scanning. During the active scanning process the station (STA) leaves the currently used communication channel to sweep through available channels in order to find neighboring APs. The time the STA dwells in other channels should be at least long enough to receive all probe responses from APs in a particular channel. For a station to acquire knowledge about the traffic pattern or channel utilization the dwell time would need to be even longer in order for the STA to observe the ongoing transmissions. For the duration of the dwell time, the data communication is interrupted, i.e. the STA cannot exchange data frames with the AP it is associated with. This causes increased delays or even packet loss (buffer overflow) for the application data which is transmitted from the STA to the AP, and it prevents the STA from receiving data from the AP. The situation results in QoS degradations which may not be acceptable for time-critical applications such as patient monitoring or VoIP connections.

While the new IEEE standard 802.1 Ik (Wireless LAN MAC and PHY specifications: Radio Resource Measurement, July 2004) defines mechanisms such as neighboring reports which can assist in optimizing scanning, the availability of IEEE 802.1 Ik support in new WLAN STA modules and new APs cannot always be relied on. Upgrading the firmware in large numbers of currently installed APs and STA modules to add IEEE 802.1 Ik capability is not always practical.

Functional features of the present approach:

This invention as described above proposes to use two wireless networking interfaces expediently co-located in the same wireless device. One of the interfaces is dedicated to mainly scanning operations, while the other networking interface is used for data communication. Such strategy will free the data communication interface from the need to vacate its channel to perform scanning. Furthermore, a dedicated scanning interface would be able to generate a more thorough "picture" of the wireless environment or neighborhood the wireless device is operating in. This neighborhood information compiled by the scanning interface can then be used by the data communication interface for making effective decisions on which target AP to connect to during roaming.

A more detailed understanding of the invention may be had from the following description of embodiment/s given by way of example and to be understood in conjunction with the accompanying drawing wherein:

FIG 1 illustrates the floor plan of premises with exemplary AP locations for deploying the present invention;

FIG 2 shows an exemplary wireless node block diagram in the context of the present invention; and,

FIG 3 shows exemplary scanning and communication interface details in the practice of the present invention.

A detailed description of one or more embodiments of the invention is provided below in the context of the accompanying figures that illustrate by way of example the principles of the invention. While the invention is described in connection with such embodiments, it should be understood that the invention is not limited to any embodiment. On the contrary, the scope of the invention is limited only by the appended claims and the invention encompasses numerous alternatives, modifications and equivalents. For the purpose of example, numerous specific details are set forth in the following description in order to provide a thorough understanding of the present invention.

The present invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the present invention is not unnecessarily obscured.

In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

Fig 1 shows an exemplary floor plan of premises with exemplary AP locations for deployment of the present wireless mobile device. The number and location of the different APs can be varied depending on the need of the user. FIG 2 shows a block diagram of a wireless node using two wireless interfaces as taught by the present approach. FIG 2 also shows components which are found in traditional wireless nodes. The applications, such as VoIP, patient monitoring use the network services (TCP/IP etc.) of the operating system (Vx Works, Linux etc.). The communications interface generally consists of hardware (HW, WLAN card) and software (SW) or firmware (FW) components which implement medium access control (MAC) and physical layer (PHY) protocols of IEEE 802.11. Expediently, the time critical or lower MAC functions are implemented in HW and the higher MAC functions are implemented in SW (Linux driver etc.) and/or FW. The communications interface expediently handles all the data transfers between the applications running on the wireless node and the network. It interfaces with the network subsystem of the operating system.

The scanning interface, which is the newly added component proposed herein, is shown in FIG 2. It can be implemented using the same hardware as the communication interface and a modified version of the software/firmware (SW/FW) of the communication interface. More particularly, FIG 2 shows the wireless medium interacting with the scanning interface and the communication interface. The communication interface, as shown interacts with the scanning interface for control purposes, and also interacts with the operating system/network subsystem as necessary. Exemplary modifications in the SW/FW are shown in FIG 3. As shown in FIG 3 by way of example, the scanning interface includes elements for scanning, a lower MAC and a RF transceiver. The scanning interface could include other components additionally as desired, which will be intelligible to those skilled in the art. The communication interface for example includes, as shown, a software portion comprising MAC management and MAC data service, and a hardware portion including lower MAC and RF transceiver. The communication interface could include other components as necessary, which will be intelligible to those skilled in the art.

Since the main functionality of the scanning interface is to sweep through the IEEE 802.11 channels and collect information about neighboring APs and the traffic load in their respective BSSs, it does not need to implement the entire IEEE 802.11 MAC functionality. Association, authentication, data transmission and reception services can be omitted from the scanning interface, thus reducing the memory and processing requirements. The scanning operation can be executed all the time or triggered by the communications interface. Upon request the scanning interface provides the neighborhood information to the communication interface.

Exemplary applications of the invention:

This invention is applicable to any wireless system or application that requires seamless mobility support, such as WUSB, 4G cellular, and IEEE 802.11.

This invention is particularly important for critical applications, such as patient monitoring, in which delay is unacceptable and packet loss requirements are strict.

In the foregoing detailed description of embodiments of the invention, various features are grouped together in a single exemplary embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the detailed description of embodiments of the invention, with each claim standing on its own as a separate embodiment. It is understood that the above description is intended to be illustrative, and not restrictive. It is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined in the appended claims. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should therefore be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms "including" and "in which" where present, are used as the plain-English equivalents of the respective terms "comprising" and "wherein," respectively. Moreover, the terms "first," "second," and "third," etc., where used are merely labels, and are not intended to impose numerical requirements on their objects.

Claims

Claims:

1. A mobile IEEE 802.11 device for interacting with a proximate wireless Local Area

Network (WLAN) and Access Points (APs), comprising: a first scanning interface dedicated to performing scanning; and, a second communication interface configured to perform at least data communication.

2. A mobile device as in claim 1, wherein the scanning interface is configured to generate a picture of a wireless environment in which said device is operating, said wireless environment selectively including neighboring APs and their corresponding channels, traffic load per channel and number of devices per channel, said scanning interface and said communication interface being located in the same said mobile device and configured to interact with each other.

3. A mobile device as in claim 1, wherein said scanning interface is connected to and configured to be controlled by said communications interface using neighborhood information generated by the scanning interface, wherein the scanning device is configured to perform association and authentication.

4. A mobile device as in claim 1, wherein the scanning interface uses hardware similar to that contained in the communication interface, but uses a modified version of software (SW) and firmware from the communication interface, and wherein the scanning interface is configured to do scanning operation continuously.

5. A mobile device as in claim 5, wherein the scanning device is configured to perform the scanning operation based on a trigger from the communication interface.

6. A mobile device as in claim 2, wherein upon request from the communication interface, the scanning interface provides neighborhood information to the communication interface.

7. A mobile device as in claim 6, wherein the scanning interface is configured to selectively receive control signals from the communication interface, and wherein the communication interface includes a software/firmware portion comprising MAC management and MAC data service, and a hardware portion (HW) comprising lower MAC and a RF transceiver.

8. A mobile device as in claim3, wherein the scanning interface includes a scanning element, lower MAC (Medium Access Control) and a RF (Radio Frequency) transceiver.

9. A mobile device as in claim 3, wherein the scanning interface is configured to perform active scanning of the type defined in the IEEE 802.11 standard.

10. A mobile IEEE 802.11 device for interacting with a proximate wireless Local Area Network (WLAN) and Access Points (APs), comprising: first and second interfaces each being selectively capable of data communication function, and scanning function by finding and connecting to an AP (by performing scanning, association and authentication), wherein at a given time: said first interface is in a role of data communication, and is connected to an AP and exchanges data with said AP; said second interface is in a role of scanning to find a more suitable AP, and if a more suitable AP is found, said second interface connects by performing association and authentication, and after said connection, the data communication function is switched to said second interface; and, the scanning function is assumed by said first interface.

11. A mobile IEEE 802.11 type device as in claim 1 deployed and configured for selective use for patient monitoring and VoIP applications

12. A mobile device as in claim 11, wherein the scanning interface is configured to generate a picture of a wireless environment in which said device is operating, said wireless environment selectively including neighboring APs and their corresponding channels, traffic load per channel and number of devices per channel, said scanning interface and said communication interface being located in the same said mobile device and configured to interact with each other.

13. A mobile device as in claim 11 , wherein said scanning interface is connected to and configured to be controlled by said communication interface using neighborhood information generated by the scanning interface, wherein the scanning device is configured to perform association and authentication.

14. A mobile device as in claim 11, wherein the scanning interface uses hardware similar to that contained in the communication interface, but uses a modified version of software and firmware from the communication interface, and wherein the scanning interface is configured to do scanning operation continuously.

15. A mobile device as in claim 15, wherein the scanning device is configured to perform the scanning operation based on a trigger from the communication interface.

16. A mobile device as in claim 12, wherein upon request from the communication interface, the scanning interface provides neighborhood information to the communication interface.

17. A mobile device as in claim 16, wherein the scanning interface is configured to selectively receive control signals from the communication interface, and wherein the communication interface includes a software(SW)/firmware portion comprising MAC management and MAC data service, and a hardware portion (HW) comprising lower MAC and a RF transceiver.

18. A mobile device as in claim 13, wherein the scanning interface includes a scanning element, lower MAC (Medium Access Control) and a RF (Radio Frequency) transceiver, wherein the scanning device is configured to perform active scanning of the type defined in the IEEE 802.11 standard.

19. A mobile device as in claim 11, wherein the scanning interface and the communication interface are configured to interact in an infrastructure mode by going through a selected one of said APs, and after going through detection scanning and execution for a handoff as defined in IEEE 802.11.

20. A wireless mobile device for application requiring seamless mobility such as in WUSB (Wireless Universal Serial Bus) and 4G cellular applications, said wireless mobile device interacting with a proximate wireless Local Area Network (WLAN) and access Points (APs), and comprising: a first scanning interface dedicated to performing scanning only, without data communication; and, a second communication interface configured to perform at least data communication, wherein the scanning interface uses hardware similar to that contained in the communication interface, but uses a modified version of software and firmware from the communication interface, and wherein the scanning interface is configured to do scanning operation continuously.