Telecommunications – Radiotelephone system – Including personal numbering system
Reexamination Certificate
1999-04-01
2002-09-03
Vo, Nguyen (Department: 2682)
Telecommunications
Radiotelephone system
Including personal numbering system
C455S561000
Reexamination Certificate
active
06445929
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to telecommunications systems and more particularly to wireless communication systems and the conversion of an International Mobile Station Identity (IMSI) number from one format to another format to allow global roaming capability within a code division multiple access (CDMA) cellular communications system.
2. Description of the Related Art
CDMA wireless telephones, hereinafter referred to as mobile stations (MS), register with a Mobile Switching Center (MSC) via a base station (BS) by. transmitting an encoded associated identification number known as the International Mobile Station Identity (IMSI) number to the serving BS.
The IMSI number consists of up to fifteen numerical characters (
0
-
9
). An IMSI consists of a three digit mobile country code (MCC) and a variable length national mobile station identity (NMSI). The NMSI consists of two variable length parts: the mobile network code (MNC) and the mobile station identification number (MSIN). A Class
0
IMSI is fifteen digits in length. A Class
1
IMSI is less than fifteen digits in length.
In the United States the variable length MNC and MSIN are set by the FCC to three digits and nine digits respectively. This results in IMSI numbers having a length of fifteen digits. A country may set the length of the MNC to be either one, two or three digits and the length of the MSIN to be between one and eleven digits. The length of the MNC plus the length of the MSIN must be no more than twelve digits.
An IMSI number is stored in CDMA wireless telephones as three parameters: MCC, IMSI_
11
_
12
, and IMSI_S. These IMSI parameters are transmitted from the mobile station to the base station. Additional information that may be transmitted from the mobile station to the base station along with the IMSI number may include an IMSI length indicator, the IMSI Class and the IMSI Type, as described further below. To ensure compatibility between a mobile station and a base station from different manufacturers, the procedures and protocol for the format and transmission of messages from an MS to a BS have been standardized. For an identification of industry standards relating to CDMA cellular communications systems, reference is made to TIA/EIA Standard IS-95, entitled “Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System.” Accordingly, the IMSI number is transmitted in a format compliant with TIA/EIA/IS-95, and includes the three parameters MCC, IMSI_
11
_
12
, and IMSI_S.
FIG. 1
is a block diagram of a conventional mobile network illustrating a mobile station (MS)
14
communicating with a mobile switching center (MSC)
10
. System configuration and operation of a code division multiple access (CDMA) cellular communications system is well known to those skilled in the art. Accordingly, detailed information concerning CDMA system configuration and operation is not provided. However, technical information concerning this topic may be obtained by referring to a number of available documents. For example, for a description of the use of CDMA techniques in a multiple access communications system, reference is made to U.S. Pat. No. 4,901,307, entitled “Spread Spectrum Multiple Access Communication System Using Satellite or Terrestrial Repeaters.” Furthermore, for a description of the generation of signal waveforms for use in a CDMA communications system, reference is made to U.S. Pat. No. 5,103,459, entitled “System and Method for Generating Signal Waveforms in a CDMA Cellular System” and U.S. Pat. No. 5,883,888, entitled “Seamless Soft Handoff in a CDMA Cellular Communications System.” The disclosures of the foregoing references are expressly incorporated by reference herein.
The heart of a typical wireless telecommunications system is the Mobile Switching Center that is connected to a plurality of base stations that are dispersed throughout the geographic area serviced by the system. The geographic area serviced by a wireless telecommunications system is partitioned into a number of spatially distinct areas called “cells.” Each MSC is responsible for, among other things, establishing and maintaining calls between mobile stations and between a mobile station and a wireline terminal, which is connected to the system via the local and/or long-distance networks. Referring to
FIG. 1
, whenever the mobile station
14
activates or roams into a MSC coverage area, i.e., the “cell” for which the MSC is responsible, the mobile station transmits the stored IMSI number to the serving MSC
10
via a base station (BS)
20
. The IMSI number is transmitted over a radio channel
22
in a format complicate with TIA/EIA/IS-95 and detected by antenna
21
of BS
20
.
Base station
20
, in turn, transmits at least a portion of the IMSI number to the serving MSC
10
, such as for example via communication line
24
. The procedures and protocol for communication between the base station
20
and the MSC
10
have also been standardized. For an identification of industry standards relating to these communications, reference is made to TIA/EIA/IS634-A, “MSC-BS Interface for Public Wireless Communication Systems.” The format for messages between base station
20
and MSC
10
is a variable octet field.
In order to provide mobile service to the newly registered MS
14
, the serving MSC
10
transmits a Mobile Application Part (MAP) based signal, such as a location update signal, to a home location register (HLR)
12
via a signaling link
26
. Such a signal informs the HLR
12
of the network address associated with the MSC
10
currently serving the MS
14
and also requests requisite subscriber information for providing mobile service to the roaming MS
14
. The HLR
12
updates its database to store the netwvork address representing the serving MSC
10
and also copies the requesting subscriber information to a visitor location register (VLR)
30
associated with the serving MSC
10
. The net work address representing the serving MSC
10
stored in the HLR
12
is later utilized by the mobile network to reroute any incoming call intended for the mobile station
14
to the serving MSC
10
. Accordingly, whenever a telecommunications subscriber dials a telephone number for the mobile station
14
, the HLR
12
is queried by the mobile network to determine the current location of the MS
14
. Utilizing the stored network address in HLR
12
representing the serving MSC
10
, the HLR
12
requests a roaming number from the serving MSC
10
in response to the receipt of the query signal. The roaming number provided by the serving MSC
10
is then used by the telecommunications network to route the incoming signal towards the serving MSC
10
. The serving MSC
10
then pages the mobile station
14
and accordingly establishes a speech connection with the mobile station
14
, if available.
If MS
14
roams out of MSC
10
coverage area and into MSC
31
coverage area, MSC
10
will hand-off the communication to MSC
31
and base station
32
. To ensure compatibility between two MSCs, the procedures and protocol for the format and transmission of messages have been standardized. For an identification of industry standards relating to these communications, reference is made to ANSI/TIA/EIA Standard 41, “Cellular Radio telecommunications Intersystem Operations.” The format for messages between two MSCs, such as for example MSC
10
and MSC
31
for
FIG. 1
, as specified by ANSI/TIA/EIA-41 is an 8-octet structure as illustrated in
FIG. 2
, wherein each of locations A-H represents one bit in each of the eight rows. Additionally, some manufacturers utilize proprietary interfaces between an MSC and BS that utilize the ANSI/TIA/EIA-41 format.
There are some shortcomings, however, with conventional mobile systems used in the United States. Currently, only a portion of the information included in the IMSI number, specifically the IMSI_S parameter, is sent from the BS to the MSC. As such, information included in the MCC and IMSI_
11
_
Chandnani Vishal S.
Garvert Anita R.
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