Multiplex communications – Communication over free space
Reexamination Certificate
1998-08-10
2003-01-14
Nguyen, Steven (Department: 2665)
Multiplex communications
Communication over free space
C370S469000, C455S557000, C455S574000, C358S426100
Reexamination Certificate
active
06507566
ABSTRACT:
TECHNICAL FIELD
The present invention relates to mobile data communication, and more specifically, to a mobile communication device and a method for mobile data communication which are suitably employed in the beneficial utilization of a wireless communication channel. The technique, device and method also reduce power consumption in wireless communication units. The present invention also relates to a storage medium wherein a program for executing the method is stored.
TECHNICAL BACKGROUND
A typical data-communication mobile station device used for mobile data communication systems has the structure shown in FIG.
15
. In
FIG. 15
, data processing terminal
11
is, for example, a computer in which an application is processed. Wireless communication unit
12
is, for example, a wireless mobile station device which can transmit data via a wireless channel. As shown in
FIG. 16
, there is another type of data-communication mobile station device, in which data processing terminal
11
is connected with a wireless communication unit
12
via a data-processing-terminal-interface
13
, which functions as an adapter or interface for data transformation between data processing terminal
11
and wireless communication unit
12
.
FIG. 17
represents the reference model for OSI (open systems interconnection).
FIG. 18
represents a frame format transmitted and received in the HDLC (high-level data link control) protocol. HDLC is the usual communication protocol used between data-link layers
21
in the OSI reference model devices shown in FIG.
17
. HDLC is a widely-used protocol; e.g., the point to point protocol (PPP) complies with HDLC. As may be clearly understood from
FIG. 18
, a transmitting device, in which data processing terminal
11
is accommodated to HDLC, forms a frame such that data for transmission is inserted between two fields of flag sequence
31
having a prescribed bit pattern. The transmitting device then transmits the formed frame, thereby sending the subject data. Flag sequences
31
may be used as a signal to synchronize the frame operations of the transmitting device and the receiving device; i.e., the receiving device, in which data processing terminal
11
is adapted to HDLC, detects flag sequence fields
31
, thereby recognizing the beginning and end of the frame. Furthermore, in accordance with HDLC, when a series of frames is transmitted continuously, at least one of flag sequences
31
may denote the end of one frame and the beginning of the next frame.
As mentioned above, in HDLC, flag sequences
31
are detected for synchronous frame operations. Consequently, it is possible to supervise whether the wireless link according to HDLC is maintained or not. Therefore, it is possible to prepare an application which monitors the link establishment, and an application in which the process changes due to the link condition, e.g., an application which ends in response to recognition that the link has been disconnected. Accordingly, the HDLC protocol prescribes that the transmitting device should transmit flag sequences periodically in order to prevent the receiving device's application from carrying out an undesirable operation when the interval between the frames from the transmitted device is too long (hereinafter, this type of interval is referred to as “inter-frame time”). In other words, a plurality of flag sequences
33
are transmitted as inter-frame-time fills in HDLC as represented in FIG.
19
.
A system wherein the frames and flag sequences
33
are transmitted independently to the wireless channel is possible. However, the data-link layer of wireless communication unit
12
, which is linked to the data-link layer of data processing terminal
11
, is usually adapted to a protocol which requires wireless communication unit
12
to form a frame such that any data from data processing terminal
11
is inserted between the flag sequences having a prescribed bit pattern, and the frame is transmitted to the wireless channel. Therefore, not only the usual data, but flag sequences
33
are also loaded in the information field of the frame in such a protocol, and then are transmitted to the wireless channel.
For example, under the PDC system, the frame adapted to a data-link layer protocol (HDLC) of data processing unit
11
is loaded in the information field of the LAPDM (link access procedure for digital mobile channel) frame at wireless communication unit
12
, and then transmitted to the wireless channel. As described above, the protocol to which the data-link layer of data processing terminal
11
is adapted, prescribes that the flag sequences be transferred to wireless communication unit
12
in order to maintain the synchronization of frame operations, even if no essential data to be transferred exists. Therefore, wireless communication unit
12
loads the flag sequences into the information field of the LAPDM frame, and then transmits the frame to the wireless channel. In the receiving device, wireless communication unit
12
receives the LAPDM frame loaded with the flag sequences accordingly.
Unlike devices which are always connected to commercial power supplies and may be applied to LANs (local area networks) and so on, mobile station devices, which are driven by small voltage batteries, have been required to reduce the consumption of electric power. In order to reduce power consumption, with reference to development of protocols and applications, attempts have been made to eliminate the transmission and reception of unnecessary frames in which data is not stored since such unnecessary frames increase the electric power used when transmitting. Furthermore, the limited number of usable frequency bands available has also required that transmission and reception of such unnecessary frames via the wireless channel be eliminated.
If a new protocol and a new application specialized for data communication in mobile communication systems were developed, the above problem would be solved. However, in view of the wide utilization of data communication in mobile. communication systems, it is preferable that the protocols and applications which have been used in LAN and cable network techniques be carried over into the mobile communication technique.
However, as mentioned above, in the existing techniques for LANs and cable networks, the protocol requires that frames without data be transmitted and detected (e.g., HDLC requires flag sequences) so as to synchronize the frame operations and to supervise the maintenance of the wireless link. In addition, it is possible that the application at the uppermost layer of the OSI reference model changes the process due to the link condition. If such an application and protocol are utilized for a mobile communications system, then the transmission and receipt of frames containing no data via the wireless channel is inevitable. In summary, if an application which operates in existing LANs or cable networks is carried over into the conventional mobile communication system (i.e., the application assets are passed on), then power consumption is increased and the use of the wireless channel is not effective.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to realize effective data communication for a mobile communication system, so as to reduce the power consumption of wireless mobile station devices and the like, and realize effective use in the radio frequency band.
In order to solve the above-described problems, the present invention includes a method for mobile data communication in which a communication protocol is used which prescribes that data prepared by an application be transmitted to a receiving device via a wireless communication channel and that unnecessary data other than the aforementioned data be prepared and transmitted to the wireless channel. The method generally is characterized in deleting the unnecessary data which is prepared according to the communication protocol, so that the unnecessary data is not transmitted to the wireless communication channel. If the mobile data
Hattori Hiroyuki
Noda Chie
Okajima Ichiro
Takami Tadao
Nguyen Steven
NTT DoCoMo Inc.
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