Abstract:
A method of communicating with mobile stations operating in an area covered by a wide-area wireless network and a wireless local area network (WLAN). The method comprises the steps of: i) receiving in a packet data server node of the wide-area wireless network data traffic statistics associated with each of a plurality of base stations associated with the wide-area wireless network; ii) receiving in the packet data server node of the wide-area wireless network data traffic statistics associated with each of a plurality of access points associated with the WLAN; iii) identifying a first base station handling a high level of data traffic; and iv) transmitting a handoff direction message to a first mobile station communicating with the first base station, the handoff direction message capable of causing the first mobile station to access a selected first access point of the WLAN.

Description:
TECHNICAL FIELD OF THE INVENTION 
   The present invention generally relates to wireless networks and, more specifically, to methods and apparatuses for interworking CDMA2000 wireless networks and wireless local area networks (WLANs). 
   BACKGROUND OF THE INVENTION 
   Businesses and consumers use a wide variety of fixed and mobile wireless terminals, including cell phones, pagers, Personal Communication Services (PCS) systems, and fixed wireless access devices (i.e., vending machine with cellular capability). Wireless service providers continually try to create new markets for wireless devices and expand existing markets by making wireless devices and services cheaper and more reliable. The price of wireless devices has decreased to the point where these devices are affordable to nearly everyone. 
   A conventional public wide area network (WAN), such as a CDMA cellular network, covers a large geographical area (on the order of 1 to 100 plus square miles), but has a relatively low bit-rate between each mobile station and each base station. These public wireless networks use regulated portions of the radio spectrum and are shared by many users. The infrastructure costs of public wireless networks are relatively high due to the size and complexity of the base station equipment. 
   Newer wireless networks, such as CDMA2000-EV-DO/DV networks, offer higher bit-rates (on the order to 2.4 MBps) and enhanced data services, such as web browsing. These networks pack many users into a relatively small portion of the regulated spectrum. Other types of radio networks, such as wireless local area networks (WLANs), try to improve spectral efficiency and to increase bit-rates by using unregulated frequencies and smaller coverage areas. For example, an IEEE 802.xx wireless LAN (i.e., a WI-FI network) may transmit at speeds up to 11 MBps in Direct Sequence Spread Spectrum (DSSS) mode or at speeds up to 54 MBps in Orthogonal Frequency Division Multiplexing (OFDM) mode. 
   An access point (or base station) in an IEEE 802.xx (e.g., IEEE 802.11) network may cover an area only a few hundred feet in diameter. Each access point is connected to the core network (e.g., Internet). In order to cover the same geographical area as a base station of a public wireless network, a large number of IEEE 802.xx network access points and a large wireline back haul network are required. Thus, there are always tradeoffs between and among the coverage areas, the maximum bit-rates, and the costs of different types of wireless networks. 
   In order to reduce the number of wireless devices a consumer must carry, equipment vendors have developed dual mode transceivers that allow a user to access both public wireless (e.g., CDMA2000) networks and wireless LANs. However, the usefulness of these devices because it is not technically feasible to perform reliably a seamless handoff between a CDMA2000 network and a wireless LAN. Thus, if a user is mobile, the user may repeatedly drop data sessions with one type of network and be forced to search for and access another type of network. 
   Also, there is no control mechanism that can efficiently distribute traffic loads between CDMA2000 networks and wireless LANs. A user in a CDMA2000 wireless network may have difficulty browsing websites and receiving e-mail during peak traffic conditions. At the same time, the user could easily access a lightly loaded 802.11 wireless LAN. There currently is no mechanism that can cause the user&#39;s mobile station to automatically handoff from the busy CDMA2000 wireless network to the underutilized 802.11 wireless LAN. 
   Therefore, there is a need in the art for an improved wireless network architecture that overcomes the limitations of the above-described conventional wireless networks. In particular, there is a need for a system and method that provides a handoff capability between CDMA2000 networks and wireless LANs. More particularly, there is a need for a wireless network architecture that uses this handoff capability to distribute data traffic between CDMA2000 networks and wireless LANs. 
   SUMMARY OF THE INVENTION 
   The present invention provides a system and method for performing a reliable hard handoff between a CDMA2000 wireless network and a wireless local area network (WLAN), such as an 802.11 (i.e., WiFi) network. The present invention also performs an effective load balancing between the CDMA2000 network and the WiFi network. These objectives are achieved by modifying the air interface messages, the wired network messages, and some network functions. 
   To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide a method of communicating with mobile stations operating in an area covered by a wide-area wireless network and a wireless local area network (WLAN). According to an advantageous embodiment of the present invention, the method comprises the steps of: i) receiving in a packet data server node of the wide-area wireless network data traffic statistics associated with each of a plurality of base stations associated with the wide-area wireless network; ii) receiving in the packet data server node of the wide-area wireless network data traffic statistics associated with each of a plurality of access points associated with the WLAN; iii) identifying a first base station handling a high level of data traffic; and iv) transmitting a handoff direction message to a first mobile station communicating with the first base station, the handoff direction message capable of causing the first mobile station to access a selected first access point of the WLAN. 
   According to one embodiment of the present invention, the handoff direction message comprises signal parameters associated with the forward and reverse channels of the WLAN. 
   According to another embodiment of the present invention, the method further comprises the step of transmitting a request message to the first mobile station, the request message capable of causing the first mobile station to transmit to the first base station a list of access points of the WLAN from which the first mobile station receives signals. 
   According to still another embodiment of the present invention, the method further comprises the step of selecting the selected first access point of the WLAN from the list of access points of the WLAN from which the first mobile station receives signals. 
   According to yet another embodiment of the present invention, the wide-area wireless network is a CDMA2000 wireless network. 
   According to further embodiment of the present invention, the handoff direction message is a Universal Handoff Direction message. 
   According to a still further embodiment of the present invention, the request message transmitted to the first mobile station is a Pilot Signal Measurement message. 
   According to a yet further embodiment of the present invention, the WLAN is an IEEE-802.xx-compatible wireless local area network. 
   Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
       FIG. 1  illustrates an exemplary CDMA2000 wireless network and an exemplary wireless local area network (WLAN) that are capable of handing off mobile stations in both directions according to the principles of the present invention; 
       FIG. 2  is a message flow diagram illustrating selected control messages in the exemplary CDMA2000 wireless network in  FIG. 1  according to an exemplary embodiment of the present invention; and 
       FIG. 3  illustrates selected portions of the CDMA2000 wireless network in greater detail according to the principles of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 through 3 , discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged wireless network. 
     FIG. 1  illustrates exemplary CDMA2000 wireless network  100  and exemplary wireless local area network (WLAN)  160 , which are capable of handing off mobile stations  111 - 114  in both directions according to the principles of the present invention. Mobile stations  111 - 114  may be any suitable wireless devices, including conventional cellular radiotelephones, PCS handset devices, personal digital assistants, portable computers, telemetry devices, and the like, which are capable of communicating with the base stations and access points via wireless links. According to the exemplary embodiment, mobile stations  111 - 114  operate in two or more modes that enable mobile stations  111 - 114  to access both CDMA2000 wireless network  100  and wireless local area network (LAN)  160 . 
   Wireless network  100  comprises a plurality of cell sites  121 - 123 , each of which contains one of the base stations, BS  101 , BS  102 , or BS  103 . Wireless local area network (WLAN)  160  comprises a plurality of cell sites  161  and  162 , each of which contains a base station or access point (AP), such as AP  171  and AP  172 . Base stations  101 - 103  are capable of communicating with mobile stations (MS)  111 - 114  over code division multiple access (CDMA) channels according to the IS-2000-C standard (i.e., Release C of CDMA2000). Access points  171  and  172  are capable of communicating with one or more of mobile stations (MS)  111 - 114  using Direct Sequence Spread Spectrum (DSSS) techniques or Orthogonal Frequency Division Multiplexing (OFDM) techniques. 
   The present invention is not limited to mobile devices. Other types of wireless access terminals, including fixed wireless terminals, may be used. For the sake of simplicity, only mobile stations are shown and discussed hereafter. However, it should be understood that the use of the term “mobile station” in the claims and in the description below is intended to encompass both truly mobile devices (e.g., cell phones, wireless laptops) and stationary wireless terminals (e.g., monitoring devices with wireless capability). 
   Dotted lines show the approximate boundaries of the cell sites  121 - 123  and  161 - 162  in which base stations  101 - 103  and access points  171 - 172  are located. The cell sites are shown approximately circular for the purposes of illustration and explanation only. It should be clearly understood that the cell sites may have other irregular shapes, depending on the cell configuration selected and natural and man-made obstructions. 
   As is well known in the art, cell sites  121 - 123  are comprised of a plurality of sectors (not shown), where a directional antenna coupled to the base station illuminates each sector. The embodiment of  FIG. 1  illustrates the base station in the center of the cell. Alternate embodiments position the directional antennas in corners of the sectors. The system of the present invention is not limited to any particular cell site configuration. 
   In one embodiment of the present invention, BS  101 , BS  102 , and BS  103  comprise a base station controller (BSC) and at least one base transceiver subsystem (BTS). Base station controllers and base transceiver subsystems are well known to those skilled in the art. A base station controller is a device that manages wireless communications resources, including the base transceiver subsystems, for specified cells within a wireless communications network. A base transceiver subsystem comprises the RF transceivers, antennas, and other electrical equipment located in each cell site. This equipment may include air conditioning units, heating units, electrical supplies, telephone line interfaces and RF transmitters and RF receivers. For the purpose of simplicity and clarity in explaining the operation of the present invention, the base transceiver subsystem in each of cells  121 ,  122 , and  123  and the base station controller associated with each base transceiver subsystem are collectively represented by BS  101 , BS  102  and BS  103 , respectively. 
   BS  101 , BS  102  and BS  103  transfer voice and data signals between each other and the public switched telephone network (PSTN) (not shown) via communication line  131  and mobile switching center (MSC)  140 . BS  101 , BS  102  and BS  103  also transfer data signals, such as packet data, with the Internet (not shown) via communication line  131  and packet data server node (PDSN)  150 . Packet control function (PCF) unit  190  controls the flow of data packets between base stations  101 - 103  and PDSN  150 . PCF unit  190  may be implemented as part of PDSN  150 , as part of base stations  101 - 103 , or as a stand-alone device that communicates with PDSN  150 , as shown in  FIG. 1 . Line  131  also provides the connection path to transfer control signals between MSC  140  and BS  101 , BS  102  and BS  103  used to establish connections for voice and data circuits between MSC  140  and BS  101 , BS  102  and BS  103 . 
   Communication line  131  may be any suitable connection means, including a T1 line, a T3 line, a fiber optic link, or any other type of data connection. The connections on line  131  may transmit analog voice signals or digital voice signals in pulse code modulated (PCM) format, Internet Protocol (IP) format, asynchronous transfer mode (ATM) format, or the like. According to an advantageous embodiment of the present invention, line  131  also provides an Internet Protocol (IP) connection that transfers data packets between the base stations of wireless network  100 , including BS  101 , BS  102  and BS  103 . Thus, line  131  comprises a local area network (LAN) that provides direct IP connections between base stations without using PDSN  150 . 
   AP  171  and AP  172  transfer voice and data signals to and from an Internet protocol (IP) network, such as the Internet. The ability to access the Internet enables AP  171  and AP  172  to communicate with PDSN  150  and wireless network  100 . Because of this ability, it is possible to perform handoffs and to load share data traffic between wireless network  100  and WLAN  160 . 
   MSC  140  is a switching device that provides services and coordination between the subscribers in a wireless network and external networks, such as the PSTN or Internet. MSC  140  is well known to those skilled in the art. In some embodiments of the present invention, communications line  131  may be several different data links where each data link couples one of BS  101 , BS  102 , or BS  103  to MSC  140 . 
   The present disclosure allows handoffs to be performed between a WiFi network (e.g., WLAN  160 ) and a public cellular wireless network (e.g., CDMA2000 wireless network  100 ). To achieve this air interface messages between base station  101 - 103  and mobile stations  111 - 114  must be modified. Also, network control messages and some of the network functions of wireless network  100  have been modified. 
   There are three possible types of handoffs in a geographical area in which a number of between CDMA2000 wireless networks and a number of wireless LANs are operating. One type of handoff operation is a handoff between CDMA2000 networks. This type of handoff is performed using conventional techniques and is not affected by the present invention. A second type of handoff is a handoff between wireless LANs. This type of handoff also is performed using conventional techniques and is not affected by the present invention. The third type of handoff is a handoff between a WLAN and a CDMA2000 network. This type of handoff is performed according to the principals of the present invention. 
   For the purposes of the present invention, it is assumed that mobile stations  111 - 114  have the capability to switch between the Wi-Fi network and the CDMA2000 network. It also is assumed that there is a loose coupling between WLAN  160  and CDMA2000 network  100 . The access gateways (e.g., PDSN  150 ) are the point of coupling between WLAN  160  and wireless network  100 . 
   According to one example, MS  112  is operating in CDMA2000 network  100  in cell site  121 . Cell sites  161  and  162  overlap cell site  121 . Both wireless LAN  160  and CDMA2000 network  100  are coupled to PDSN  150 . MS  112  is currently communicating with BS  101 . PDSN  150  monitors the RF link for BSC of BS  101  and the output of WLAN  160 . If WLAN  160  is lightly loaded and CDMA2000 network  100  is becoming heavily loaded, PDSN  150  sends a notification message to BS  101  to trigger a handoff to WLAN  160 . WLAN  160  operates in a different frequency band than wireless network  100 . Hence the handoff will be hard handoff. The handoff can be performed even if MS  112  determines that the RF link to BS  101  to be of good signal strength. This, the present invention discloses a forced hard handoff scheme. 
     FIG. 2  depicts message flow diagram  200 , which illustrates selected control messages in exemplary CDMA2000 wireless network according to an exemplary embodiment of the present invention. In  FIG. 2 , it is assumed that PCF unit  190  functionality is integrated into the base station controller (BSC) portion of BS  101 . The present invention may be implemented by adding new Throughput Request data field to A10 Registration Request message  205 , which is transmitted from BSC/PCF  101 / 190  to PDSN  150 . The present invention also adds a new Throughput Response data field to A11 Registration Reply message  210 , which is transmitted from PDSN  150  to BSC/PCF  101 / 190 . Finally, the present invention adds new signal parameter information related to the access points of WLAN  160  to the Universal Handoff Direction message  215  transmitted from BSC/PDF  101 / 190  to MS  112 . 
     FIG. 3  illustrates selected portions of wireless network  100  in greater detail according to the principles of the present invention. Packet control function (PCF) unit  190  comprises A10/A11 interface (IF) controller  310  and packet data server node (PDSN)  150  comprises A10/A11 Interface (IF) controller  320  and traffic allocation controller  330 . Modifications to the control message interfaces of A10/A11 IF controller  310  and A10/A11 IF controller  320  enable handoffs and traffic load sharing between wireless network  100  and WLAN  160 . Traffic allocation controller  330  determines and controls the distribution of data traffic between wireless network  100  and WLAN  160  and triggers the forced handoffs that implement the traffic distribution. 
   According to an exemplary embodiment of the present invention, PDSN  150  is capable of accessing a database that tracks the total traffic demand on each base station (BS) in wireless network  100 . This database is represented by BS traffic statistics database  340 . BS traffic statistics database  340  may be directly coupled to or integrated into PDSN  150 . Alternatively, PDSN  150  may access remotely disposed BS traffic statistics database  340  via the Internet. 
   Similarly, PDSN  150  is capable of accessing a database that tracks the total traffic demand on each access point (AP) in wireless LAN  160 . This database is represented by WLAN traffic statistics database  350 . WLAN traffic statistics database  350  may be directly coupled to or integrated into PDSN  150 . Alternatively, PDSN  150  may access remotely disposed WLAN traffic statistics database  350  via the Internet. 
   According to the principles of the present invention, BS  101  and PDSN  150  are provisioned with the signal parameters of the forward and reverse channels of WLAN  160  (e.g., frequency, transmit power, etc.). These parameters may be provisioned by storing them in database  350 , for example. UHDM  215  is modified to include the parameters required for the handoff to be performed to WLAN  160 . Alternatively, a different handoff message or an entirely new handoff message may be used to transmit the WLAN  160  signal parameter information to MS  112 . 
   PDSN  150  monitors all access points and base stations to determine the throughput of each base station and access point. The throughput information is queried using A10 Registration Request message  205 . PDSN  150  responds to A10 Registration Request by transmitting A11 Registration Reply message  210 . BSC/PCF  101 / 190  is now aware of the throughput or bandwidth allocated to it. If the throughput is large, that means a large amount of data has been requested from BSC/PCF  101 / 190  and PDSN  150 . If the throughput exceeds a predetermined limit, BS  101  requests MS  112  to send a Pilot Strength Measurement message (PSMM). 
   If the PSMM values sent by MS  112  indicate that MS  112  also receives a strong signal from a particular access point of WLAN  160 , the BSC portion of BS  101  may initiate a forced handoff that forces MS  112  to access that particular access point. To accomplish this, BSC/PDF  101 / 190  sends UHDM  215  to MS  112 . UHDM contains the signal parameters of, for example, AP  172  in WLAN  160  as the target access point to which MS  112  will be handed off. After receiving UHDM  215 , MS  112  performs a hard handoff and moves on to WLAN  160 . 
   For handoffs between WLAN  160  and CDMA2000 network  100 , WLAN  160  is notified about the throughput (data traffic) being used. WLAN  160  then determines if the throughput level exceeds a predetermined limit. If predetermined limit is exceeded, WLAN  160  transmits a notification message to MS  112  causing MS  112  to search for CDMA2000 wireless network  100  and to perform a handoff to CDMA2000 wireless network  100 . 
   The present invention ensures that the user of MS  112  always gets the best available throughput by ensuring that mobile stations  111 - 114  are properly shared between WLAN  160  and CDMA2000 wireless network  100 . Advantageously, users get higher data rates and the service providers can handle more users. 
   Although the present invention has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as fall within the scope of the appended claims.