Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1999-05-10
2003-06-10
Urban, Edward F. (Department: 2685)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S404200, C455S435100
Reexamination Certificate
active
06577874
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of communications and more particularly to radiotelephone communications methods and systems.
BACKGROUND OF THE INVENTION
Conventional cellular communications systems (such as systems operating according to the IS-136 standard) generally provide one-to-one communications from one mobile terminal to another mobile terminal or to a landline telephone coupled to a public switched telephone network. A conventional cellular communications system is illustrated in FIG.
1
. This system includes a mobile switching center (MSC)
31
and a home location register
33
.
The MSC is coupled to a plurality of radio base stations (RBS)
32
wherein each RBS
32
defines a cell
35
. In addition, the MSC can be coupled to a public switched telephone network (PSTN)
36
. As will be understood by those having skill in the art, the conventional cellular communications system of
FIG. 1
can provide cellular radiotelephone communications for one or more cellular mobile terminals (MT)
37
. More particularly, the cellular radiotelephone communications can be provided using conventional cellular standards wherein a telephone is dialed to place a call to another communications device.
Each radio base station provides radio frequency transmit and receive functions and supports low level protocol functions. Moreover, a radio base station can be considered a dumb peripheral of the MSC
31
wherein the MSC provides central intelligence for the system. Each radio base station can be coupled to the MSC
31
via communications links
39
. These communications links can be T
1
links provided, for example, via landline or microwave. The MSC
31
provides voice path switching between two cells or a cell and the PSTN
36
. The MSC
31
provides central system intelligence to control the radio base stations and to process high level protocol messages from mobile terminals
37
relayed by the radio base stations. In other words, the MSC handles call setup, paging, handoff, and call connection.
The home location register
33
keeps track of the current status of the mobile terminals. For each mobile terminal, for example, the home location register can record whether that terminal is on, off, or busy, as well as the location area (including a group of cells) within which the mobile terminal is located. The home location register can also include a database of restrictions and allowed service features for each mobile terminal. The home location register can also be considered a portion of the MSC.
The setup of a call between mobile terminals
37
using the system of
FIG. 1
is illustrated in FIG.
2
. As shown, the originating mobile terminal
37
a
issues an origination message which is received by the radio base station
32
a
for the cell
35
a
in which the mobile terminal
37
a
is located. According to the IS-136 standard, a conventional origination message may be sent over time slots in a plurality of time division multiple access (TDMA) time frames. The radio base station
32
a
checks the origination message for errors, and if no significant errors are detected, the radio base station
32
a
forwards the message to the mobile switching center. The mobile switching center authenticates the originating mobile terminal
37
a
and analyses the called number. If the originating mobile terminal and the called number are valid, the mobile switching center instructs the radio base station
32
a
to assign a Digital Traffic Channel (DTC) to the originating mobile terminal. Origination and channel designation messages are discussed, for example, in TR45, TIA/EIA-136-123-A Draft Text, Digital Control Channel. Layer
3
, Aug. 31, 1998, the disclosure of which is hereby incorporated herein in its entirety by reference.
Because the called party is another mobile terminal, the mobile switching center checks the HLR to determine the current location area (LA) for the called mobile terminal
37
b
if the called mobile terminal is active. A plurality of cells is assigned to a location area, and a mobile terminal updates its location with the cellular system only when the mobile terminal enters a new location area. Accordingly, location area updates are not needed every time a mobile terminal enters a new cell. While Digital Control Channel (DCCH) traffic may be reduced, pages for a called mobile terminal may need to be transmitted in all cells assigned to the location area.
The mobile switching center then issues a page message to all radio base stations supporting cells in the location area of the called mobile terminal
37
b
. Each of these radio base stations issues a page message on an appropriate paging subchannel. Because of the DCCH paging structure, however, a period of time as long as 1.28 seconds may pass before the page message can be issued. The page message wakes the called mobile terminal from its battery sleep mode, and the called mobile terminal
37
b
responds to the appropriate radio base station (now referred to as the called radio base station
32
b
) with a page response message to indicate the same.
The page response message is relayed from the called radio base station
32
b
to the mobile switching center, and the mobile switching center instructs the called radio base station
32
b
to assign a digital traffic channel to the called mobile terminal
37
b
. The mobile switching center then completes a communications path between the originating mobile terminal
37
a
and the called mobile terminal
37
b
using the two digital traffic channels.
The conventional cellular communications system of
FIG. 1
, however, may not support dispatch oriented group calls (also referred to as conference calls). Radio dispatch group communications systems are commonly used by emergency service providers such as police and/or fire departments to provide communications between a dispatcher and emergency personnel. For example, a police dispatcher can simultaneously call all on-duty police officers using a radio dispatch communications system. Alternately, a police office can quickly establish communications with other police officers and/or dispatchers simply by pressing a push-to-talk button on his radio. Similar radio dispatch communications systems may also be used by businesses such as trucking and/or taxi businesses.
In general, radio dispatch group communications systems provide one-to-many group communications as opposed to one-to-one communications provided by conventional cellular radiotelephone communications systems. Radio dispatch group communications are also preferably provided without the call setup delays that may be common in a conventional cellular radiotelephone communications system. For example, the time required to setup a call in a conventional IS-136 cellular radiotelephone system may be as long as 6 or 7 seconds including up to 1.28 seconds just to page the receiving cellular radiotelephone. This setup time, however, may be unacceptable for police and other radio dispatch group communications systems.
With the proliferation of cellular communications systems, there has been an effort to provide hybrid communications systems that can support both cellular radiotelephone communications as well as dispatch oriented group communications. Such a system has been developed, for example, by Motorola with service being offered by Nextel. A similar system has been developed by Ericsson (the assignee of the present application) under the name DAMPS-PRO. In particular, the DAMPS-PRO product provides cellular communications according to the IS-136 cellular communications standard, as well as dispatch oriented group communications for predefined user groups.
In the DAMPS-PRO system, intelligent group communications functionality is added to an IS-136 cellular communications system as shown in FIG.
3
. This intelligent group communications functionality is provided by adding a group server
41
, a group bridge
43
, a local area network
45
, and a group database
47
. The cells, mobile switching center, home location register, public swit
Ericsson Inc.
Gesesse Tilahun
Myers Bigel & Sibley & Sajovec
Urban Edward F.
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