Telecommunications – Receiver or analog modulated signal frequency converter – With particular receiver circuit
Reexamination Certificate
1993-09-27
2001-02-20
Le, Thanh Cong (Department: 2749)
Telecommunications
Receiver or analog modulated signal frequency converter
With particular receiver circuit
C455S517000, C455S574000, C370S311000
Reexamination Certificate
active
06192230
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to wireless data communication systems.
A recent development in the field of local area networks (LANs), has been the introduction of wireless communications in such networks. Another development has been the introduction of portable, battery-operated devices for use in such wireless networks.
International Patent Application No. WO 92/19059 discloses a wireless data communication system which includes a cable-based network to which are attached controllers which maintain a portable device in communication with the network for data transfer. The portable unit transmits polling packets at regular intervals. Normally, a response packet is received from the current controller. If no response packet is received for a predetermined number of attempts, the portable unit initiates a procedure for registering with a new controller. The portable unit is powered by a battery which supplies power to the unit's transceiver and packet processor via a switch. Following transmission of a polling packet, the portable unit remains fully active until a response packet is received, or until the expiry of a predetermined time period such as 10 milliseconds, and then operates the switch thereby disabling battery current to the packet processor and transceiver for a further predetermined time period, whereafter a new polling packet is transmitted. This procedure effects a power-saving function. Initially, the polling may be at a slow rate of about two second intervals, this rate being doubled each time a response packet is received. When the transmission rate is low, the polling rate is reduced, thereby reducing requirements for battery current. The power saving function is thus seen to be a complex procedure, involving the exchange of polling and response packets for each individual station, which results in inefficient use of the wireless communication medium. Furthermore, the two seconds response time is inadequate for normal network operation at current data rates. Thus, a 200 milliseconds interval is considered appropriate to ensure uninterrupted communication under the typical LLC (logical link control) layer protocols used in the majority of contemporary LAN networks. These protocols typically utilize a timeout timer having around 400 milliseconds duration, after which a transmitted packet is considered to have been lost. On expiry of such timer, the protocols will attempt a recovery procedure by retransmitting the packet a limited number of times.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for operating a wireless communication system having a power saving function, wherein efficient use of the wireless communication medium is achieved.
Therefore, according to one aspect of the present invention, there is provided a method of operating a wireless data communication system including a plurality of wireless stations, characterized by the steps of: broadcasting synchronizing messages from a selected one of said stations; identifying stations that are to receive data messages by transmitting traffic indicator information in association with said synchronizing messages; operating said stations in an awake state of relatively high power consumption while broadcasting said synchronizing messages and transmitting said traffic indicator information; changing the operating state of stations that are not to receive data messages to a doze state of relatively low power consumption after receiving a synchronizing message; and maintaining stations that are to receive data messages in said awake state for at least a time period during which one or more data messages are transmitted to those stations.
According to another aspect of the present invention, there is provided a wireless data communication system, including a plurality of wireless data communication stations, characterized in that a selected one of said stations includes synchronizing timing means adapted to control the transmission of synchronizing messages by the selected station; in that means are provided adapted to transmit traffic indicator information in association with said synchronizing messages, identifying stations that are to receive data messages; and in that said stations include switching means adapted to control the power supply applied to station transceiver means, such that said stations are controlled to be in an awake state of relatively high power consumption to receive said synchronizing messages and said traffic indicator information and any data messages to be received and are changed to a doze state of relatively low power consumption following receipt of said synchronizing messages and said traffic indicator information if no data messages are to be received.
It will be appreciated that in a method and apparatus according to the invention, the synchronous operation of the power saving function enables efficient use of the wireless medium to be achieved by reducing the number of messages transmitted over the wireless medium to effect the power saving function as compared with the system disclosed in the aforementioned International Patent Application No. WO 92/19059. Also, the synchronous operation is more power efficient since the earliest possible arrival time of the synchronizing message is known in advance.
REFERENCES:
patent: 4794649 (1988-12-01), Fujiwara
patent: 5241542 (1993-08-01), Natarajan et al.
patent: 5278831 (1994-01-01), Mabey et al.
patent: 0319219 (1989-06-01), None
patent: 0443516 (1991-08-01), None
patent: 0529269 (1993-03-01), None
patent: 9219059 (1992-10-01), None
Claessen Albertus M. G.
Diepstraten Wilhelmus J. M.
Haagh Johannes P. N.
Moelard Hendrik
Monteban Leo
Cong Le Thanh
Lucent Technologies - Inc.
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