Portable radio telephone data terminal using cdpd

Details Portable radio telephone data terminal using cdpd Portable radio telephone data terminal using cdpd

1995-06-07

2002-10-08

Cumming, William (Department: 2684)

Telecommunications

Radiotelephone system

Emergency or alarm communication

Reexamination Certificate

active

06463271

ABSTRACT:

TECHNICAL FIELD
This invention relates generally to wireless voice and data communication systems. More particularly, the invention relates to wireless communication systems integrating voice mode and data mode operations.
BACKGROUND 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 analog human voice was the signal that the AMPS system was first designed to communicate. The AMPS system has been 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 whereby a user's signal is handed off to the next cell site as he or she moves into a different cell area. This cellular hand-off can cause a temporary loss in transmission or reception. 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. However, signal loss, even though temporary, poses special problems for transmission of digital data. Some other AMPS cellular problems causing loss in voice signals are drops in signal strength, reflections, Rayleigh fading, and cellular dead spots.
The availability of portable computers naturally results in 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 to using the AMPS system for data transmission is that a narrow channel bandwidth and errors in transmission limit the baud rate for transmitting and receiving the digital data. As previously stated, loss of raw digital data may be caused by other problems in the AMPS mobile cellular system.
Another problem of data transmission with a mobile subscriber station occurs when a subscriber station is moving at the edge of a cell or coverage area. Such circumstances can result in a substantial loss of data, or substantial delays due to the necessity of re-transmitting the data. These problems have been addressed in part by the Cellular Digital Packet Data (CDPD) system described in the CDPD specification, Version 1.1, incorporated herein as background information. Version 1.0 of the CDPD specification is included as Appendix VII of the parent application. The CDPD communication system shares the same carrier frequencies assigned to the AMPS channels as indicated in the subject CDPD specification.
The base unit or mobile data base station (MDBS
1
, as illustrated in FIG.
1
), of an exemplary CDPD system utilizes a channel within an AMPS cell to establish an RF link and communicate to a user's mobile end system. The MDBS may use other frequencies outside of AMPS that are made available to it by service providers. The mobile end system or subscriber station (M-ES
2
) is a portable computer, hand-set or other portable electronic device containing a subscriber communication unit. The MDBS 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, or other CDPD links (such as 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 (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 transmitter/receiver in a particular 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 which the RF transmission between an M-ES and an MDBS are received at acceptable levels of signal strength. It is not sufficient that the subscriber receive an adequate signal level. The base station must also receive a good signal from the subscriber station (M-ES) for the subscriber to be considered within the cell. 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 transmission carried out via a directional antenna. This second type of cell is also 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 moving 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 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 mobile end system
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 various public and private data networks. One example is 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 mobile end system within the range of the mobile data base stations under the control of the MD-IS. The MD-IS is usually the only network entity that is “aware” of the location of any of the mobile end systems. However, under some circumstances (as defined by the CDPD specification) particular mobile database stations will keep track of the behavior of specific subscriber stations. A CDPD-specific Mobile Network Location Protocol (MNLP) is operated between each MD-IS (thro

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