Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1998-08-07
2001-03-06
Nguyen, Lee (Department: 2746)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S067150, C455S426100
Reexamination Certificate
active
06198941
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a method of operating a portable communication device such as a laptop or palmtop computer, a personal digital assistant (PDA), or a cellular telephone (or the like), and more particularly, to a method of effectuating a change in the operation of the device (implemented in changes in parameters in the transport and/or application protocol layer in the device), in accordance with anticipated or predicted changes in the communications arrangement (i.e., changes in the network or link level protocol parameters) that the device is using.
BACKGROUND OF THE INVENTION
Modern portable telecommunication devices, such as laptop or palmtop computers, personal digital assistants (PDA's), or cellular telephones, are now capable of operating using more than one different communications arrangement, depending upon various external factors. For example, a handheld digital terminal may transmit data to, and receive data from a remote server or host via a wireless local area network (e.g., Wavelan) when the device is indoors. When the device is later moved to an outdoor location, the device may then be arranged to communicate via a cellular (e.g., GSM) network. In the aforementioned example, when the device is moved outdoors, it may transition from a high-bandwidth environment to a low-bandwidth environment, and various other of its communications properties (e.g. bit error rate, delay, jitter, loss, etc.) may also change. These changes typically are evidenced by network or link level protocol signals in the processor that controls the operation of the device.
In prior art portable devices, when an abrupt change or discontinuity, such as a bandwidth reduction, occurs in the communications arrangement, the performance of the device degrades, causing, for example, graphical images to become fuzzy or received signals to become noisy or distorted. In some existing arrangements, this degradation is then sensed, and steps are taken to correct to problem, such as by intentionally permitting a reduction in the precision of the received and/or transmitted signals, decreasing the resolution of the display or reducing the size of the image. Such an approach is reactive, in that the change in the communication arrangement occurs first, and the change in the operation of the portable device occurs later, in response to the detection of the fact that performance has become degraded. In a reactive approach, data can be lost, since the transition itself may take a not insignificant amount of time, and during that time, the device operation is sub-optimum and the quality of service, as perceived by the user, will be degraded.
One example of a previous reactive approach is described generally in a paper entitled “Renegotiable Quality of Service—A New Scheme for Fault Tolerance in Wireless Networks, presented by R-W Chen, P. Krzyzanowski, M. Lyu, C. Sreenan and J. Trotter (all of Lucent Technologies) at the 27
th
PTCS, June 1997, Seattle, Wash. This reference relates to a device in which the link layer protocol is arranged to determine that the bandwidth available to the device has changed. The link layer protocol can then signal this change to upper layers of the protocol stack, including, the application layer protocol, responsive to which the application may, for example, change its data rate.
Other reactive approaches have been used in modems, in Internet applications, and in images processed in accordance with MPEG standards. In connection with certain “intelligent” modems, the bit rate at which a modem operates can be changed reactively, in response to channel conditions that are inferred, for example, from a measurement of error rate or constellation dispersion. In connection with the Internet, it is also known in a general way that the TCP/IP protocol stack can be arranged to adapt, over time, to the fact that the available bandwidth available to an Internet device has changed. This adaptation can be used to thereafter cause the application to change its rate, or to at least cause the application's data to be buffered, so that data is not lost in the network due to inadequate bandwidth. With respect to image processing, the MPEG standard contemplates an application protocol layer that can be structured in such a way as to be able to provide outputs at different bit rates, based on being told what bandwidth is available.
In each of the reactive approaches described above, changes occurring in the communications arrangement that a device is using are first observed. Then, changes to the operation of the device itself are brought about by changes in the applications layer protocol. This reactive process takes time, during which data may be lost and/or performance may suffer. Thus, the problem in the prior art is the inability to provide a speedy transition so as to minimize or eliminate data loss or to at least provide a transition that is as unobjectionable as possible, even in the face of some data loss during the transition.
SUMMARY OF THE INVENTION
In accordance with the present invention, a portable communication device can communicate with a remote host or server using one of two or more different communication arrangements. A change in the communications arrangement used by the portable communication device is anticipated or predicted, by monitoring various signals indicative of the environment in which the device is operating. If the change is determined to be both imminent and significant, the operation of the portable device is altered, typically by adjusting parameters in the application or transport layer protocol. Thus, changes in the operation of the device occur virtually simultaneously with changes in the communications arrangement.
In one embodiment of the invention, a signal or flag is generated in response to significant changes in signal strength occurring in the communications arrangements with which the device can be used. The flag is then used to explicitly signal or announce the change to one or more applications running on the device, and/or to the communications transport protocol layer. Where the characteristics of one or more applications are to be changed, the application protocol layer is involved. For example, the changes may affect the characteristics by which an image is displayed on a display screen that is part of the device, such as by changing the window size, the resolution, frame rate, or other characteristics of the pictorial image. Where the transport protocol layer is involved, changes may affect the size of the packets with which information is conveyed, or the characteristics by which information is buffered or stored. In either event, by virtue of the present invention, when there is a transition in the communication arrangement used by the device, there is also an almost simultaneous change in the operation of the device itself.
As an example, in a laptop computer communicating with a remote host via a wireless communications link, if the laptop is being moved from one location to another, a falling signal strength is detected in a first communications arrangement (e.g., a Wavelan communications arrangement used indoors) at the same time that an increasing signal strength is detected in a second communications arrangement (e.g. a GSM network used outdoors). This indicates that there is a strong likelihood that a change in the communication channel between the laptop and a remote host or server is imminent. Because this change may lead to a corresponding transition from a high bandwidth (e.g., 10 Mbps) to a low bandwidth transmission channel (e.g., 10 Kbps), the present invention causes an almost simultaneous change in the data rate of the display driver running on the laptop computer, so that the display resolution is reduced to accommodate the reduced bandwidth without any data loss.
In another embodiment of the invention, the fact that a change in the communications arrangement may be in the offing is anticipated or predicted, based upon observed operational changes in other communication ch
Aho Alfred Vaino
Gitlin Richard Dennis
Ramjee Ramachandran
Woo Thomas Yat Chung
Freedman Barry H.
Lucent Technologies - Inc.
Nguyen Lee
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