Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1995-09-27
2004-02-17
Cumming, William (Department: 2683)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S343100
Reexamination Certificate
active
06694146
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to wireless communication devices. More particularly, the invention relates to controlling the scanning operation of a wireless subscriber station to limit power consumption and extend the life of a battery powering the wireless subscriber station.
BACKGROUND OF THE INVENTION
The modern analog cellular system for mobile wireless duplex voice transmission called “Advanced Mobile Phone Service” (AMPS), uses the FCC assigned carrier frequency range of 800 to 900 MHz. Automobile-mounted cellular units transmit voice signals to a cellular base station within a given cell at up to one watt of power. Battery powered, hand-held cellular units transmit voice signals to a cellular base station within a given cell using up to one quarter watt of transmission power.
The analog human voice was the signal that the AMPS system was first designed to communicate. AMPS was optimized for carrying as many analog voice signals within a given bandwidth of a channel as possible. Mobility of the cellular telephone using low power mobile units, FM modulation, and the higher carrier frequency range (800 MHz-900 MHz) is achieved through a cellular arrangement of base stations, with a user's signal handed off to the next cell site as he or she moves outside the current cell area. This cellular hand-off can cause a temporary loss in transmission or reception. Whereas, temporarily losing a voice signal is not critical because a user knows when there is a signal loss and the voice information can be retransmitted, signal loss, even if temporary, poses special problems for digital data transmission. Other sources of loss in voice signal transmission are drops in signal strength, reflections, Rayleigh fading, and cellular dead spots.
The availability of portable computers naturally led to the desire to conduct wireless transmission of digital data from a remote location. Presently, the AMPS voice cellular system is being used to transmit digital data in the form of circuit-switched cellular data across AMPS carrier channels. Raw (baseband) digital data must be converted so that it can be transmitted and received across the analog AMPS system. One disadvantage of the AMPS system for data transmission is that narrow channel bandwidth and transmission errors limit the baud rate for transmitting and receiving digital data. Again, loss of raw digital data may also be caused by other sources in the AMPS mobile cellular system.
Efficient wireless communication of both voice and data signals in an integrated package accordingly has been difficult. Furthermore, it has been difficult to integrate AMPS voice transmission features with applications such as data transmission, electronic mail and duplex paging, as well as enable provisions of a circuit-switched cellular data interface such as a wireless fax-modem, into a single hand-held battery operated wireless unit. This has been accomplished in part by the systems disclosed in the common assignee's U.S. patent applications Ser. No. 08/117,913 (filed Sep. 8, 1993) and Ser. No. 08/152,005 (filed Nov. 12, 1993) using a Cellular Digital Packet Data (CDPD) system described in the CDPD specification, Version 1.1, incorporated herein by reference as background material. The CDPD communication system shares the same carrier frequencies assigned to the AMPS channels as described in Part 405, Version 1.1 of the CDPD specification (the CDPD specification is incorporated herein by reference).
The typical base unit or mobile data base station (MDBS
1
, as illustrated in
FIG. 1
herein), of a CDPD system utilizes a channel within an AMPS cell to establish a link and communicate to a user's wireless subscriber station. The MDBS may use other frequencies outside of AMPS that are made available to it by service providers. The wireless subscriber station (M-ES
2
) is a portable computer, hand-set or other portable electronic device containing a subscriber communication station. The MDBS serves as a communications link between the user of the wireless subscriber station M-ES
2
and a service provider's network of wire lines, microwave links, satellite links, AMPS cellular links, or other CDPD links (such as mobile data intermediate system MD-IS
3
and intermediate systems
4
,
5
,
6
) to convey data to another wireless subscriber station, computer network, or non-mobile or fixed end-user system (F-ES
7
,
8
).
The CDPD network is designed to operate as an extension of existing communication networks, such as AMPS networks and the Internet network. From the mobile subscriber's perspective, the CDPD network is simply a wireless mobile extension of traditional networks. The CDPD network shares the transmission facilities of existing AMPS networks and provides a non-intrusive, packet-switched data service that does not impact AMPS service. In effect, the CDPD network is entirely transparent to the AMPS network, which is “unaware” of the CDPD function.
The CDPD system employs connectionless network services (CLNS) in which the network routes each data packet individually based on the destination address carried in the packet and knowledge of current network topology. The packetized nature of the data transmissions from an M-ES
2
allows many CDPD users to share a common channel, accessing the channel only when they have data to send and otherwise leaving it available to other CDPD users. The multiple access nature of the system makes it possible to provide substantial CDPD coverage to many users simultaneously with the installation of only one CDPD station in a given sector (transmitting range and area of a standard AMPS base station transceiver).
The airlink interface portion of the CDPD network consists of a set of cells. A cell is defined by the geographical boundaries within the RF transmission range from a fixed transmission site such as MDBS
1
, which can be received at acceptable levels of signal strength by mobile subscribers such as M-ES
2
. The transmitter supporting the cell may be located centrally within the cell, with transmission being carried out via an omni-directional antenna, or the transmitter located at the edge of a cell and transmitted via a directional antenna to cover only a portion of the cell, referred to as a sector. In typical configurations, the transmitters for several sectors are co-located. The area served by a set of cells has some area overlap so that a roaming wireless subscriber station can maintain continuous service by switching from one cell to an adjacent cell in a manner roughly analogous to the standard hand-off in an AMPS system. The two cells are considered to be adjacent if an M-ES can maintain continuous service by switching from one cell to the other. This switching process, called cell transfer, is done independently of normal AMPS hand-off procedures.
In
FIG. 1
, the interface (A) between the wireless subscriber station
2
and the MDBS
1
is an “air interface” constituted by a radio frequency link using standard AMPS frequencies. The MDBS
1
is connected to other mobile data base stations through a mobile data intermediate system (MD-IS)
3
. A number of mobile data base stations can be under the control of a single mobile data intermediate system. The mobile data intermediate systems are connected to each other through intermediate systems such as
4
and
5
in FIG.
1
.
The intermediate systems are constituted by at least one node connected to more than one sub-network (such as intermediate system MD-IS
3
). The intermediate system has a primary role of forwarding data from one sub-network to another. The mobile data MD-IS
3
performs data packet routing based on knowledge of the current location of each wireless subscriber station within the range of the mobile data base stations under the control of the MD-IS. The MD-IS is the only network entity that is “aware” of the location of any of the wireless subscriber stations. However, under some circumstances (as defined by the CDPD specification, Version 1.1), particular mobile data base stations will
Balachandran Kumar
Hardin Carl Thomas
Petranovich James E.
Wright Andrew
Cumming William
Lin, Esq. Steven
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