Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-09-11
2004-11-30
Cumming, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S452100, C455S551000, C455S552100, C455S553100, C455S574000, C370S329000, C370S350000, C370S352000, C380S044000
Reexamination Certificate
active
06826400
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to wireless communication devices, and more particularly to portable subscriber stations operable between two or more divergent wireless communication systems.
2. Description of Related Art
The modern analog cellular system for mobile wireless duplex voice transmission is called “Advanced Mobile Phone Service” (AMPS). The AMPS cellular network 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 using up to one watt of power. Hand-held cellular units using battery power supplies transmit voice signals to a cellular base station within a given cell using up to one quarter watt of transmission power.
The AMPS system was designed to communicate the analog human voice signal. The AMPS system 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 a higher carrier frequency range (800 MHZ-900 MHZ) is achieved through a cellular arrangement of base stations whereby a user's signal is handed off to the next cell site as the user moves into a new cell. This cellular hand-off can cause a temporary loss in transmission or reception. However, temporarily losing a voice signal is not critical because a user can easily detect a loss of voice signals and the voice information can be readily retransmitted upon request. However, signal loss, even though temporary, poses special problems for the transmission of digital data. Other examples of inherent AMPS shortcomings which can cause loss in voice signals are diminished signal strength, reflections, Rayleigh fading, and cellular dead spots.
The availability of portable computers has given rise 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 first be converted so that it can be transmitted and received using the analog AMPS system. The baud rates available using an AMPS system disadvantageously is, limited due to inherently narrow channel bandwidths and transmission errors.
Heretofore, providing efficient wireless communication of both voice and data signals in an integrated package has been difficult. It has been difficult to integrate the features of AMPS voice transmission with applications such as data transmission, electronic mail, duplex paging, as well as the provision of a circuit-switched cellular data interface such as a wireless fax-modem, into a single hand-held battery operated wireless unit. Some degree of integration of these functions has been facilitated by the development of the Cellular Digital Packet Data (CDPD) system described in the CDPD specification, Version 1.1, hereinafter referred to as the “CDPD Specification”. 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 base unit or mobile data base station (MDBS
1
, as illustrated in FIG.
1
), of a CDPD system utilizes a channel within an AMPS cell to establish a link and to communicate with a user's mobile end system (M-ES
2
). The MDBS
1
may use frequencies outside the scope of the AMPS frequencies. The M-ES
2
may be a portable computer, hand-set or some other portable electronic device containing a communication unit. The MDBS
1
serves as a communication link between the user of the M-ES
2
and a service provider's network of wire lines, microwave links, satellite links, AMPS cellular links, and other CDPD links. For example, the MDBS
1
facilitates communication between the M-ES
2
and a mobile data intermediate system (MD-IS)
3
, intermediate systems
4
,
5
,
6
to convey data to another mobile end system, computer network, or non-mobile or fixed end-user system (e.g. F-ES
7
,
8
).
As described in the CDPD specification, the CDPD network is designated to operate as an extension and overlay of existing communication networks, such as AMPS networks and the Internet. From the mobile subscriber's perspective, the CDPD network is 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.
As defined in the CDPD specification, 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 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 simultaneously to many users 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 comprises 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 just a portion of the cell. This portion of the second type of cell is 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 mobile end system can maintain continuous service by switching from one cell to an adjacent cell in a manner roughly analogous to the standard hand-off in the 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 M-ES
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 plurality of mobile data base stations can be controlled by a single MD-IS. The MD-ISs are connected to each other through intermediate systems such as system
4
and system
5
in FIG.
1
.
The intermediate systems comprise at least one node connected to more than one sub-network (e.g., MD-IS
3
). The intermediate system has a primary role of forwarding data from one sub-network to another. Specifically, the MD-IS
3
performs data packet routing based on knowledge of the current location of each mobile end system 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 has knowledge of the location of any of the mobile end systems. However, under some circumstances (as defined in the CDPD specification) particular mobile data base stations track the behavior of specific subscriber stations. A CDPD-specific Mobile Network Location Protocol (MNLP) is operated between each MD-IS (through the intermediate system) to exchange location information regarding the mobile end systems.
The overall CDPD network is controlled by a network management system (NMS)
10
having an interface with at least one
Cashman Russell P.
Schwartz Richard A.
Cumming William
Lin, Esq. Steven
Pacific Communication Sciences, Inc.
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