The present disclosure relates generally to multi-mode communications networks wherein various radio technologies are employed at the physical layer, and wherein Internet Protocol/Transport Control Protocol is used at the transport layer, and more particularly to methods and apparatuses for enabling a mobile station to perform measurements prior to handing over between the various radio technologies.
Wireless communications systems wherein a single radio technology (or physical layer technology with respect to the OSI Seven Layer Reference Model) is used generally support handover of a mobile station from one base station coverage area to another.
Coverage areas may be determined or defined in various ways such as, but not limited to, radio coverage areas as determined by a base station antenna beam width, allocated channels corresponding to such antenna beam widths, levels of radio signal strength perceived at the mobile station, channel congestion at a specific point in time, or any other appropriate criteria. Regardless of the specifics of the defined coverage areas, a mobile station in general must measure parameters of one or more candidate coverage areas when handover is needed due to some parameter of the serving coverage area failing to meet a threshold, for example.
Therefore, various radio technologies have provisions for a mobile station to make the necessary measurements, without being disruptive to ongoing communications such as an in-progress file transfer. For example, UMTS provides a compressed mode wherein transmission gaps are created in the mobile station's data transmission sequence. These gaps in time may then be used as intervals in which the mobile station may make the necessary measurements, of a neighboring base station radio signal for example.
Unfortunately, not all radio technologies employ this approach and therefore, in a multi-mode network environment, a mobile station may not have the needed measurement opportunity when attempting to handover between different radio technologies.
Thus, there is a need for a method and apparatus to provide a mobile station, handing over from a first radio technology to a second different radio technology, with an opportunity to make measurements of the candidate channels of the second different radio technology.
In accordance with the embodiments, a mobile station may use Layer 4, the transport layer of the mobile station protocol stack, and specifically TCP/UDP to determine when receive data from a first physical layer communication is not expected. Further, in some embodiments the transport layer may be used to create opportunities to allow the mobile station physical layer to perform needed neighbor measurements.
The embodiments makes use of TCP acknowledgement scheduling techniques to create holes in the expected receive data stream. The created holes are thus measurement opportunities for situation wherein the signal conditions of a current radio link reach a level where a handover may be required. Thus the various embodiments use higher layers of a mobile station protocol stack to either determine the existence of, or create, an opportunity for the mobile station physical layer to perform alternate work, for example, the work of measuring signal strength on neighboring Radio Access Technologies.
Turning now to the drawings wherein like numerals represent like components,
In
In the various embodiments herein disclosed, mobile station 101 may also collect measurement data 113 for a radio interface, physical layer type II 109, that is different from physical layer type I 105, such that handovers between the technologies may be better facilitated.
In addition, mobile station 200 has interoperation module 201, which may be separate or may be integrated into any of the other components/layers. The mobile station 200 interoperation module 201 may send and receive messages between the physical layer 203, 205, 207, etc. and the transport layer 213. The mobile station may transmit and receive various messages to and from the base station on the physical layer air interface 227.
The mobile station 201 interoperation module 201 enables the transport control layer 213 to create measurement opportunities for the mobile station in circumstances wherein a handover for one physical layer to another is warranted. The action of the interoperation module 201 is explained in further detail below.
The base station 217, similar to mobile station 200, has an RLC 221, MAC 223 and PHY 225. The modules shown in
It is to be understood that
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Memory 305 is for illustrative purposes only and may be configured in a variety of ways and still remain within the scope of the present disclosure. For example, memory 305 may be comprised of several elements each coupled to the processor 303. Further, separate processors and memory elements may be dedicated to specific tasks such as rendering graphical images upon a graphical display. In any case, the memory 305 will have at least the functions of providing storage for an operating system 307, applications 309 and general file storage 311 for mobile station 300. In some embodiments, and as shown in
Also in the various embodiments, applications 309 may include an interoperations module 319 for coordinating the transport layer and various physical layer activities.
The receiving entity may implement flow control by setting the Window field and the Acknowledgement field with values that inform the sending entity that no further data should be sent. The transport layer in the mobile station will then inform the physical layer that it is free to disconnect from the currently active physical interface and perform necessary functions such as neighbor measurements, neighbor resource reservation, etc. The transport layer should provide specific timing parameters to the physical layer so that the device will be back on the currently active physical interface before data reception and/or transmission is to resume. The transport layer should consider the calculated Round Trip Time (RTT) of the current transport session to limit the amount of time the device is off the physical channel.
When the type of session is well known, such as a file transfer, the receiving device may use the knowledge that a continual stream of data is expected to set a more deterministic schedule of opportunities, as well as minimizing the time that the data flow is disrupted.
This may be accomplished in some embodiments, by reducing the window size value in acknowledgement packets until the available window size is small enough that the next received packet will fill the window. The receiving device will then know that when this packet is received, no more data is expected until a new acknowledgement packet is sent. In this case, the transport layer informs the physical layer of the opportunity to disconnect from the currently active interface.
Prior to disconnecting the physical interface, the transport layer will send a new acknowledgement packet to open the receiver window again. The transport layer may then provide the physical layer with the idle slot time of something less then RTT, since it knows no more data will arrive until the sender receives the new ACK packet, and sends the new data packet.
The above examples assume that the primary data transfer is from the network to the device. When the primary transfer is from the device to the network, the device may create opportunities as frequently as it needs by delaying the generation of a new data packet. Care should be taken to make sure the physical interface is not disconnected while there is an outstanding ACK packet, since this would result in a lost acknowledgement requiring retransmission, and involvement of TCP congestion mechanisms which would have a detrimental impact on data throughput.
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In
While various embodiments have been illustrated and described, it is to be understood that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.