DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention embodies several aspects of radio network connection management, and offers connection management techniques that may be particularly beneficial in certain types of radio networks. More particularly, certain of these connection management techniques support connection management where an access terminal that has connected to a radio network momentarily suspends that connection, and then returns to the network an uncertain time later.

[0022] On that basis, the discussion below begins with a description of certain aspects of the present invention in the context of two particular types of radio networks, an cdma2000 radio network and a cdma2000 high rate packet data radio network. The Telecommunication Industry Association/Electronic Industry Association (TIA/EIA) Interim Standard 2000 (IS-2000) covers the cdma2000 radio network, while the TIA/EIA IS-856 standard describes the packet data radio network. It should be understood that connection management as presented herein has applicability well beyond these two types of radio networks.

[0023] Turning now to the drawings, FIG. 1 is a diagram of a wireless communication system 10 comprising a first access network 12 providing communication between an access terminal 14 and a packet data network 16 , such as the Internet. A second access network 18 provides communication between the access terminal 14 and the Public Switched Telephone Network (PSTN) 20 . Note that access network 18 may also provide connection with the packet data network 16 for some types of communication with the access terminal 14 .

[0024] Access network 12 comprises a radio network 22 operating in accordance with IS-856 and provides high data rate packet-based communications between the Internet 16 and the access terminal 14 by interfacing with a Packet Data Serving Node (PDSN) 24 through an access network interface 26 . In the illustrated embodiment, the access network interfaces comply with the IS-634 and IS-2001 standards, the details of which are not material to the invention.

[0025] Access network 18 comprises a radio network 28 operating in accordance with IS-2000 and provides communication between the access terminal 14 and the PSTN 20 by interfacing with a mobile switching center (MSC) 30 through the access network interface 26 . Access network 18 may also provide communication between the access terminal 14 and the Internet 16 via the access network interface 26 , however the data rates supported with this type of connection are generally lower than those available with access network 12 , which is explicitly intended to support high packet data rates.

[0026] In operation, a subscriber connects with the access network 12 by establishing a connection with the radio network 22 . To establish a connection, the radio network 22 allocates network resources to support the connection. The network resources include a reverse traffic channel and a reverse power control (RPC) channel used for reverse link power control, which is described in greater detail below.

[0027] FIG. 2 illustrates a plurality of access terminals 14 engaged in open packet data connections with the radio network 22 . Each access terminal 14 has both forward and reverse communication links established with the radio network 22 , which support data transfer to and from the access terminals 14 , as well as providing control and status information used to manage signaling between the access terminals 14 and the radio network 22 . Note that some forward link channel information transmitted by the radio network 22 is commonly used by all of the access terminals 14 that are active within a given sector of the radio network 22 .

[0028] Forward link channels include the pilot channel, medium access control (MAC) channel, common control channel, and data channels, which are time multiplexed into the forward traffic channel. The MAC channel includes multiple reverse power control (RPC) channels, which are code multiplexed into the MAC channel. The different RPC channels carry power control information for different access terminals 14 connected with the radio network 22 . At any given time, only one access terminal 14 is allocated to any given RPC channel.

[0029] A given RPC channel is used to transmit power control information to a specific access terminal 14 . The power control information is in the form of a power control bit that instructs the access terminal 14 to either increase or decrease its transmit power. By keeping the transmit power of each active access terminal 14 constrained to the minimum level necessary to maintain reliable signal demodulation, the radio network 22 minimizes interference between all active access terminals 14 operating in a given region. Thus, reverse link power control maximizes the total number of subscribers that can simultaneously use the radio network 22 .

[0030] When an access terminal 14 has an open connection with the radio network 22 , it is expected to continuously transmit to the radio network 22 on its assigned reverse link traffic channel. The reverse traffic channel actually comprises several sub-channels that are used to send data traffic and control information from the access terminal 14 to the radio network 22 . Thus, the radio network 22 continuously receives information from the access terminal 14 during an open packet data connection.

[0031] An access terminal 14 engaged in an open packet data connection with the IS-856 radio network 22 appears to be in an idle state from the perspective of the IS-2000 radio network 28 . As defined by the IS-2000 standard, an access terminal 14 that is in idle state must perform certain functions from time to time to maintain its registration with the radio network 28 . Typically, this entails periodically monitoring certain paging or control channels transmitted by the radio network 28 for incoming paging, messaging, or other call information. Additionally, the access terminal 14 must handle idle state handoff procedures and other registration procedures as needed.

[0032] Because there is no inter-network communication between the two radio networks 22 and 28 , the access terminal 14 must suspend its communication with the IS-856 radio network 22 to monitor the paging channel and to perform needed idle state processing on the IS-2000 radio network 28 . The typical time of suspension ranges from something on the order of 100 ms, to times in excess of several seconds. The time of suspension depends on what idle state processing is required. For example, simply checking a paging channel will take less time than handling an idle state handoff. When the access terminal 14 completes idle state processing in the IS-2000 radio network 28 , it resumes communication with the IS-856 radio network 22 by transmitting on the reverse link channel and demodulating its assigned RPC channel.

[0033] When the access terminal 14 suspends communication with the IS-856 radio network 22 , the IS-856 radio network 22 will detect a loss of the signal on the reverse link traffic channel and initiate a fade timer to time the duration of the inactivity. The fade timer is a mechanism used by the radio network 22 to free up unused resources. When the access terminal 14 resumes communication the fade timer is reset. However, if the fade timer expires before the access terminal 14 resumes communication, the radio network 22 terminates the connection and releases the network resources supporting the dormant access terminal's connection, including the forward and reverse link channels and the RPC channel. Those resources can then be reassigned to another access terminal 14 requesting a connection with the radio network 22 . The returning access terminal 14 may be unaware that its prior connection with the radio network 22 was terminated.

[0034] Potential problems arise if an access terminal 14 returning from a period of suspended communication, whose connection has been terminated by the radio network 22 , resumes communication with the radio network 22 using its prior connection setup. The resources supporting the connection with the returning access terminal 14 , including the RPC channel, may have been reallocated by the radio network 22 to another access terminal 14 . The particular type and severity of problems associated with the returning access terminal 14 inadvertently resuming communication using reassigned resources may vary depending upon the particulars of the radio network involved. At the least, the transmissions of the returning access terminal 14 will increase the level of radio interference. In radio networks that use individually assigned channels to control the transmit power of the active access terminals 14 , such as those based on IS-856, the problems are potentially severe.

[0035] As noted above, a situation may arise where the returning access terminal 14 resumes its reverse link power control operations based on an RPC channel that has be reallocated to another access terminal 14 , causing the returning access terminal 14 to erroneously control its transmit power. Its erroneous power control may interfere with the radio network 22 and the other active access terminals 14 in a manner that can result in a loss of service.

[0036] FIG. 3 illustrates a potential power control problem arising with two or more access terminals 14 using the same RPC to receive reverse link power control information. The primary horizontal access denotes time, while the left and right vertical axes denote access terminal transmit power and base station noise floor, respectively. The radio network 22 includes one or more base stations (not shown) that provide the RF signaling between the radio network 22 and the access terminals 14 .

[0037] Assume that an access terminal 14 denoted as AT1 had previously established a connection with the radio network 22 , but then suspended communication with the radio network 22 to perform idle state procedures required by radio network 28 . Further assume that the time of suspension exceeds that permitted by the radio network 22 , and that the associated network resources dedicated to that connection are released.

[0038] A new access terminal 14 denoted as AT2 then establishes a connection with the radio network 22 and is assigned the RPC channel previously assigned to AT1. When AT1 returns from suspension, it responds to power control information intended for AT2. Depending on the distance between the involved base station and AT1, AT1 may transmit at a power level dramatically higher than it should.

[0039] This action causes the signal noise floor at the involved base station to increase. An increase in the noise floor results in a commensurate decrease in the received signal-to-noise ratio of all access terminals 14 with an open connection to the base station. This results in the base station commanding the access terminals 14 , including AT1 and AT2, to increase reverse link transmit signal power. This is reflected by the sudden and continuing upward trend in the transmit power from AT1 and AT2, and in the illustrated sequence of reverse channel power control bits in the RPC channel assigned to AT1. Typically, the power control bit sequences average out to a equal mix of 1's and 0's, which maintains the transmit power at a given level. To increase transmit power, the radio network 22 transmits more 1's than 0's. Similarly, to decrease power, more 0's than 1's are transmitted.

[0040] As the interference from AT1 continues raising the noise floor of the base station, the radio network 22 continues commanding AT2 (and any other affected access terminals 14 ) to increase their reverse link transmit power, creating a positive feedback relationship. As the noise floor increases, the base station begins losing the reverse communication links with the various access terminals 14 in its coverage area. These losses result because the access terminals 14 are power-limited and will at some point be unable to increase transmit power enough to overcome the noise floor. The access terminals 14 furthest away from the base station are typically the first to drop out of communication.

[0041] Depending on the base station itself, it may continue operating even in the presence of escalating noise and dropped connections, or may implement some form of jamming detection which causes it to suspend or halt operation once signal conditions deteriorate beyond a given threshold. In any case, the net effect of the above scenario is that the service area supported by the affected base station is lost, resulting in the attendant loss of the access terminals 14 supported by that base station.

[0042] The above failure scenario may be avoided if the returning access terminal 14 is prevented from using its previously assigned channels after its connection is terminated. Existing protocols have a mechanism to notify an access terminal 14 when its connection is terminated. In current systems, this is accomplished by transmitting a connection release message to the access terminal 14 . This mechanism is not available in the above-described scenario, however, since the access terminal 14 is inaccessible to radio network 22 while it is communicating with the IS-2000 radio network 22 . Therefore, the access terminal 14 will not receive the connection release message.

[0043] According to the present invention, the access terminal 14 may, for example, be configured with a suspension timer that corresponds to the maximum inactivity time-out or fade timer used by the radio network 22 . The network's inactivity timer or fade timer is simply a defined duration of time after loss of reverse link traffic from a given access terminal 14 that may pass before the radio network 22 releases the dedicated communication resources. Thus, if the access terminal 14 keeps track of how long its communication with the radio network 22 was suspended, it can determine whether or not its suspension exceeded the maximum allowed time. If so, the access terminal 14 will request a new connection rather than use previously allocated resources.

[0044] A number of different approaches are available for providing maximum suspension time information to the access terminal 14 . In one approach, a suspension time-out value may be stored in the access terminal 14 manually or automatically, as part of its configuration information. In a more flexible approach, the access terminal 14 receives the information from the radio network 22 . For example, the radio network 22 might broadcast suspension time-out information as part of the control channel information. Such information may be included in the sector parameters message defined by the IS-856 standard. Alternatively, the radio network 22 might include suspension time-out information when access terminal 14 establishes a connection with the radio network 22 . For example, the suspension or time-out value may be included as part of the traffic channel assignment message.

[0045] FIG. 4 is a diagram of exemplary radio network connection management in accordance with the present invention. The access terminal 14 sends a connection request and route update message to the access network 12 , which supports high rate packet data communication in accordance with IS-856. This connection request is for a new connection between the radio network 22 and the access terminal 14 so normal connection setup information is used.

[0046] The radio network 22 responds to the connection request by returning an access acknowledgement message to the access terminal 14 via a forward control channel. Then, the radio network 22 transmits a Unicast traffic channel assignment (TCA) message to the access terminal 14 that contains information needed to set up the connection between the access terminal 14 and the radio network 22 . Upon receiving the TCA message, the access terminal 14 begins transmitting on its reverse link traffic channel. The radio network 22 acquires and locks with the reverse link traffic signal from the access terminal 14 and sends a reverse link traffic channel acknowledgement in response via the forward link control channel.

[0047] At some later point in time, the access terminal 14 suspends its reverse link traffic channel communication with the radio network 22 so that it can perform idle state processing associated with the IS-2000 radio network 28 . Upon suspending IS-856 communication, the access terminal 14 begins monitoring its time of suspension.

[0048] At roughly the same point in time, the radio network 22 detects loss of the reverse link traffic channel and begins timing the duration that the link is inactive. The radio network 22 may use a fade timer for this purpose. The fade timer typically serves to time reverse link time-outs regardless of whether the loss stems from an access terminal 14 actually suffering from signal fade, or because it intentionally suspended its communication.

[0049] Once the fade timer expires, the radio network 22 sends a directed message (a Unicast message) to the access terminal 14 that its connection has been released. In this example, the access terminal 14 remains busy with idle state processing in the IS-2000 environment and misses the connection release message.

[0050] Upon completion of IS-2000 idle state processing the access terminal 14 returns to the IS-856 environment in a manner dependent upon whether its suspension timer has expired. If its timer has not expired, the access terminal 14 resumes communication with the access network 12 using the communication resources previously assigned to it by the radio network 22 . If the timer has expired, the access terminal 14 issues a connection request so that a new connection between it and the radio network 22 may be established. The access terminal 14 may provide information to the radio network 22 indicating that it is returning from a period of suspension longer than that allowed by the radio network 22 . This may have value in terms of performance monitoring at the radio network 22 .

[0051] Radio network operators necessarily monitor the network performance and dropped connections may be a key measure of network performance or reliability. With a potentially substantial number of access terminals 14 periodically suspending communication with the radio network 22 to perform IS-2000 idle state processing, it may be expected that some percentage of dropped connections stem from excessively long suspensions, rather than actual signal reception problems. Absent an opportunity to discriminate between drops caused by intentional suspension versus drops caused by signal reception problems, network operators would be unable to develop an accurate picture of true network performance.

[0052] To request a connection with the radio network 22 , the access terminal 14 sends a “ConnectionRequest” message to the radio network 22 . The ConnectionRequest message as defined by IS-856 has a set of fields, including a Message ID, a Transaction ID, and a Request Reason.

[0053] Current defined values of the RequestReason field may be extended to include a provision for indicating when the access terminal 14 is returning from a suspended connection with the radio network 22 . Of course, such information may be conveyed to the radio network 22 using a message other than the ConnectionRequest message. For example, the IS-856 standard may be extended to include some other defined message type or format for conveying such information.

[0054] Also, the information received by the access terminal 14 from the radio network 22 may be extended to include a value for the suspension timer relevant to the particular radio network 22 to which the access terminal 14 is connected. This may simply require the radio network 22 to transmit its fade timer value to the access terminal 14 . In any case, receiving the required time out value from the radio network 22 is flexible in that the access terminal 14 does not need to be configured with any default suspension timer information and the value is free to vary across different radio networks 22 .

[0055] FIG. 5 is an exemplary logic flow diagram for an access terminal 14 in accordance with the present invention. Processing begins with the assumption that the access terminal 14 has an open packet data connection with the radio network 22 but is required to maintain registration within a separate IS-2000 radio network 28 (block 200 ). If IS-2000 idle state procedures are not yet required (block 202 ), the access terminal 14 continues with its packet data connection (block 204 ). However, if IS-2000 idle state processing is necessary, the access terminal 14 suspends communication on its connection with the radio network 22 (block 206 ), starts its suspension timer (block 208 ), and performs the idle state processing needed (block 210 ).

[0056] As noted earlier, idle state processing may require comparatively little time, or may be a relatively lengthy undertaking. In short, idle state processing may require the access terminal to suspend IS-856 communication for no more than a few tens of milliseconds, or for as much as several seconds. In any case, when idle state processing is completed, the access terminal 14 checks its suspension timer (block 212 ) to see if it has exceeded the maximum suspension time permitted by the IS-856 radio network (e.g., radio network 22 ) (block 214 ).

[0057] If the maximum permissible suspension time is not exceeded, the access terminal 14 returns to the IS-856 radio network 22 using its previously assigned communication channels (block 216 ). If the maximum suspension time is exceeded, the access terminal 14 issues a completely new connection request based on the assumption that its previously assigned communication resources have been released and possibly reused (block 218 ). The access terminal 14 may attempt several connection requests (blocks 218 to 220 ), or may perform other processing (not shown) if its connection request is denied.

[0058] FIG. 6 is an exemplary logic flow diagram from the perspective of the radio network 22 . It receives a new connection request from an access terminal 14 that is establishing a new connection with the access network 12 (block 230 ). In response, communication resources, including assigned communication channels, are assigned to the access terminal 14 . Part of the information transmitted to the access terminal 14 includes the maximum suspension time value, as discussed above (block 234 ). This information may optionally be sent as part of the communication setup procedures, or may be broadcast generally by the radio network 22 .

[0059] The access network 12 , and more specifically, the radio network 22 , monitors the reverse link traffic channel from the access terminal 14 for loss of communication (block 236 ). If the reverse traffic channel from the access terminal 14 remains active (block 238 ), the radio network 22 clears or resets the associated timing function (block 240 ) and continues monitoring. If the reverse traffic channel is lost, the radio network 22 begins timing the duration of the loss (block 242 ). If communication is lost for more than the allowed period of time (block 244 ), the radio network 22 releases the resources that were assigned to the dropped access terminal 14 (block 246 ) and processing ends. If the time period has not expired, the radio network continues monitoring and timing operations (blocks 238 through 244 ).

[0060] FIG. 8 is an exemplary diagram for a physical implementation of the access networks 12 and 18 introduced in FIG. 1 . It should be understood that access network implementation is subject to significant variation and may or may not involve the simplified resource sharing depicted. The arrangement depicted is illustrative only.

[0061] Two or more radio base stations (RBS) 50 provide RF signaling with one or more access terminals 14 . The RBSs 50 interface the access terminal 14 with a base station controller 52 that provides interconnection with the MSC 30 and the PDSN 24 . With regard to FIG. 1 , the upper RBS 50 , the BSC 52 , and the MSC 30 may comprise access network 18 , while the lower RBS 50 , the BSC 52 , and the PDSN 24 may comprise access network 12 . As noted, many other sharing or segregation arrangements are possible.

[0062] In operation, the BSC 52 manages communication resource allocation for the RBSs 50 , and provides numerous interface and call/session management functions supporting interaction between the access terminal 14 and the PSTN 20 , and any available packet data networks 16 (e.g., the Internet).

[0063] Within the above framework, it should be understood that the access terminal 14 may be one of a broad range of device types. The access terminal 14 , might, for example, be a cellular telephone with packet data capability, or may be a personal digital assistant (PDA) with wireless communication capability. The access terminal 14 may take on many other forms, for example, it may be a radio interface module adapted to provide wireless capability to a portable computing and communication device.

[0064] As with the many variations of types of access terminals, the present invention is itself subject to much variation. It is not dependent on specific implementations or architectures for the access networks. While it may have particular value within the IS-856/IS-2000 framework discussed in detail above, it is not limited to implementations involving these specific network types. Thus, the foregoing discussion and associated drawings should be considered exemplary rather than limiting. Indeed, the present invention is limited only by the scope of the claims and their reasonable equivalents.