Patent Application
20130044696
This invention generally relates to wireless communications and more particularly to circuit switched fall back (CSFB).
The evolution of wireless communication technologies often requires that newer systems and networks be compatible with legacy systems and networks. A communication specification defining operation of new technology often provides requirements for the new system to interface with the legacy systems. For example, the 3GPP Long term Evolution (LIE) standard requires that a wireless communication device be able to use circuit switched networks for voice calls as well as utilize the LTE network. One aspect of the 3GPP LTE specification, referred to as Circuit Switched Fallback (CSFB), requires that a mobile wireless communication device be able to receive incoming calls from the circuit switched network, temporarily suspend any LTE session, engage in the circuit switched call, and return to the LTE network after the circuit switched network call is complete. Unfortunately, the specifications defining the operation of the different networks are often in conflict in certain circumstances.
A mobile wireless communication device, in response to a circuit switched page message, suspends an LTE session and engages in a circuit switched call without a determination of receipt of a connection release message from the LTE network. The mobile wireless communication device, therefore, suspends the LTE session before, or without, receiving any connection release message authorizing the suspension of the LTE session.
The circuit switched network 104 and the LTE network 106 provide communication services to wireless devices within a common geographical region although each network 104, 106 may provide services in some areas that the other cannot. Each network 104, 106 includes infrastructure such as base stations, communication management equipment, and backhaul. The circuit switched network 104 is any wireless communication network where a physical communication path is dedicated to communication with the mobile wireless communication device 102. For the examples herein, the circuit switched network 104 is a network that operates in accordance with 1x CDMA standards.
The LTE network 106 is a packet switched network where a physical path is shared between multiple communication devices. The information related to communication with a particular mobile wireless communication device is arranged into packets and interlaced with packets corresponding to communications with other mobile wireless communication devices.
As is known, in some circumstances, LTE networks may communicate with circuit switched networks allowing call management and other information to be exchanged between the networks. S2 signaling is often used in these circumstances. In this example, however, there is no S2 signaling capability between the LTE network 106 and the circuit switched network 104. Accordingly, the LTE network 106 cannot communicate, either temporarily or permanently, with the circuit switched network 104 using S2 signaling.
The mobile communication device 102 is capable of communicating with a circuit switched network 104 and with an LTE network 106 but does not simultaneously transmit signals to both networks 104, 106. The mobile wireless communication device 102 includes a circuit switched transmitter 108, an LTE transmitter 110, a circuit switched receiver 112, and a LTE receiver 114. The mobile wireless communication device 102, therefore, includes a circuit switched transceiver 116 and an LTE transceiver 118, where the circuit switched transceiver 116 includes the circuit switched transmitter 108 and the circuit switched receiver 112 and where the LTE transceiver 118 includes the LTE receiver 114 and the LTE transmitter 110. Although the receivers and transmitters are illustrated as separate blocks, the functions of these components may be implemented with common circuitry and devices. The LTE transmitter 110 transmits signals that are to be received by one or more base stations within the LTE network 106. The circuit switched transmitter 108 is configured to transmit signals in accordance with the circuit switched network protocol to be received by one or more base stations in the circuit switched network 104. In the examples discussed herein, the transmitters 108, 110 cannot transmit simultaneously. This may be due to any of several circumstances such as, for example, the transmitters sharing common elements or circuitry that does not allow simultaneous functionality of both transmitters 108, 110. In some situations, the transmitters 108, 110 cannot be used at the same time because transmission, spurious, and/or harmonic signals due to one of the transmitters may cause interference with transmission of the other transmitter. The receivers 112, 114 are configured such that the circuit switched receiver 112 is capable of receiving at least some messages from the circuit switched network 104 when the mobile wireless communication device 102 is communicating with the LTE network 106. The receivers 112, 114 may be able to simultaneously receive signals from the two networks 104, 106 in some circumstances. The circuit switched receiver 112, however, is at least capable of intermittently receiving signals from the circuit switched network 104 while the mobile wireless communication device 102 is receiving LTE signals during an LTE session. As a result, the mobile wireless communication device 102 can receive signals from the circuit switched network 104 while maintaining a communication session with the LTE network 106 but cannot transmit to the circuit switched network 104 while maintaining the LTE communication session. The mobile wireless communication device 102, therefore, cannot simultaneously maintain a voice call on the circuit switched network 104 and maintain a session on the LTE network 106.
As described above, the Circuit Switched Fallback (CSFB) of the 3GPP LTE specification requires that a mobile wireless communication device 102 be able to receive incoming calls from the circuit switched network 104, temporarily suspend any LTE session, engage in the circuit switched call, and return to the LTE network 106 after the circuit switched call is complete. Without S2 signaling (or other suitable signaling) between the networks, however, the circuit switched network 104 cannot inform the LTE network 106 of an incoming circuit switched call and that the LTE session should be suspended for a particular mobile wireless communication device. In addition, conventional techniques require that the mobile wireless communication device 102 receive a connection release message 120, such as a radio resource control (RRC) Connection Release Message before suspending the LTE session. In conventional systems, the mobile wireless communication device 102 sends an extended service request 122, such as an Extended Service Request message, to the LTE network 106 prior to responding to a call page (page message) 124 from a circuit switched network 104. The LTE network 106 generates the connection release message 120 authorizing the suspension of the LTE session. With the timing requirements of conventional protocols, the connection release message 120 may not be received before the mobile wireless communication device must respond to the page message 124 sent from the circuit switched network 104. In accordance with the examples discussed herein, however, the mobile wireless communication device 102 suspends the LTE session before, or without ever, receiving a connection release message 120 authorizing release of the LTE session.
A Paging Request message 202 is generated by a mobile switching center (MSC) 204 in the circuit switched network 104. The Paging Request message 202 is forwarded to the circuit switched base station 206 in the circuit switched network 104 invoking transmission of a corresponding General Page message 208 from the circuit switched base station 206 to the mobile wireless communication device 102 in accordance with known techniques. The General Page message 208 is, therefore, an example of a call page message 124 described above with reference to
In response to the General Page message 208 (page message 124), the mobile wireless communication device 102 determines whether the LTE session should be temporarily suspended. In accordance with known techniques, the mobile wireless communication device 102 evaluates the status of communications to determine, for example, whether the mobile wireless communication device 102 is connected to the LTE network. As described herein, the mobile wireless communication device 102 is determined to be connected to the LTE network 106 if it is registered on the LTE network 106 and is either in the LTE idle state or in the LTE transmission state. If it is determined that the LTE session should be temporarily suspended, appropriate instructions are provided to the LTE transceiver 118 to facilitate notification to the LTE network 106. The LTE network 106 is notified even if the mobile wireless communication device 102 is in the LTE idle state so that the LTE network 106 does not continue to expect responses of acknowledgments when the mobile wireless communication device 102 has suspended LTE communication and will temporarily not be transmitting LTE messages. For example, when in the idle state, the mobile wireless communication device 102 may still need to send messages such as LTE page responses. The suspend LTE instruction 210 in
The mobile wireless communication device 102 responds to the paging request 124 by transmitting an Extended Service Request message 212 to a Mobility Management Entity (MME) 214 in the LTE communication network 106 through the LTE base station 216. Therefore, the LTE transmitter 110 in the LTE transceiver 118 transmits the message 212 to the LTE base station 216 which then conveys the message 212 to the MME 214. The Extended Service Request message 212, therefore, is an example of the extended service request 122 discussed with reference to
In response to the Extended Service Request message 212, the MME 214 sends an S1-AP message 218 to the LTE base station 216. The S1-AP message 218 is an application protocol message that instructs the LTE base station 216 to send an RRC Connection Release message 220 to the mobile wireless communication device 102. In the TS 36.413 specification, the S1-AP message 218 is a UE Context Modification Request message that includes a CS Fallback indicator IE informing the LTE base station 216 to send the RRC Connection Release message 220. As described below with reference to
In response to the S1-AP message 218, the LTE base station 216 sends the RRC Connection Release message 220 (connection release 120). The RRC Connection Release message 220 is illustrated with dashed lines to indicate that the message is not considered by the mobile wireless communication device 102 in the embodiments discussed herein and that, in some situations, the message 220 is not sent. The RRC Connection Release message 220 is an example of a connection release message 120 discussed with reference to
An LTE suspended notification 222 in
The circuit switched transmitter 108 in the circuit switched transceiver 116 transmits a page response message 224 to respond to the page message 124 (General Page message 208) in accordance with conventional techniques. The circuit switched base station 206 responds with an alert with information message 226 in accordance with conventional techniques.
At event block 225, the circuit switched call is executed and terminated in accordance with known techniques before the mobile wireless communication device 102 resumes LTE connectivity. The Resume LTE indicator 228 in
For the example of
In situations where the RRC Connection Release message 220 is transmitted, the mobile wireless communication device 102 does not respond for the example of
Therefore, the example of
The LTE base station 216 forwards this Extended Service Request 301 with the LTE suspension indicator 302 to the MME 214. The LTE base station 216 does not parse this message and only passes it on to the MME 214. In response to this indicator 302, the MME 214 sends a S1-AP message 304 that indicates that the LTE base station 216 need not send a connection release message 120, such as an RRC Connection Release message 220, for example. The S1-AP message 304, therefore, includes an indicator 306 that may be implemented within a currently defined field or within an additional field within the S1-AP message. The indicator 302 provides information indicating the mobile wireless communication device 102 will not wait for a connection release message and/or that a connection release message should not be sent.
The LTE base station 216, therefore, does not send a connection release message 120 such as a RRC Connection Release message 220 in the example of
At step 402, a page message 124 is received from the circuit switched network 104 while the LTE transceiver 118 is maintaining an LTE session with the LTE network 106. The mobile wireless communication device 102 is engaged in the LTE session when the page message 124 is received through the circuit switched receiver 112 of the circuit switched transceiver 116.
At step 404, an extended service request 122 such as Extended Service Request message 212, is sent to the LTE network 106. In response to the page message 124, the circuit switched functions of the mobile wireless communication device 102 internally inform the LTE functions of the wireless communication device 102 that LTE session should be suspended. As discussed above, this notification can be described as a suspend LTE notification 210 sent internally from the circuit switched functions to the LTE functions although an actual defined message may not be sent. In response, the LTE transmitter 110 sends the Extended Service Request message 212 to the LTE base station 216 in the LTE network 106.
At step 406, a page response message 224 is sent to the circuit switched network 104. As contrasted to conventional techniques, the mobile wireless communication device 102 does not wait for a connection release 120, such as an RCC Connection Release message 220, before sending the page response 224. The Connection Release message 220 authorizes suspension of the LTE session. For the examples herein, however, the mobile wireless communication device 102 does not wait for a determination that a Connection Release message 220 was received before suspending the LTE session and transmitting the page response message 224. In some situations, the Connection Release message 220 may be received after the page response message 224 is transmitted. In other situations, a Connection Release message 220 may not be sent by the LTE network 106. For example, in one example, the Extended Service Request message 301 includes an LTE suspension indicator 302 indicating that the mobile wireless communication device 102 will not wait for a connection release 120 before suspending the LTE session. The LTE network 106 can be configured to not send an RRC Connection Release message 220 in these circumstances.
Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. The above description is illustrative and not restrictive. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.
