Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1999-05-10
2002-09-10
Urban, Edward F. (Department: 2685)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S519000, C455S520000, C455S426100, C455S447000, C455S450000
Reexamination Certificate
active
06449491
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to wireless communications systems (apparatus) and methods, and more particularly, to systems and methods for communicating among terminals in wireless communication systems.
BACKGROUND OF THE INVENTION
Wireless communications systems are commonly employed to provide voice and data communications to subscribers. For example, analog cellular radiotelephone systems, such as those designated AMPS, ETACS, NMT-450, and NMT-900, have been long been deployed successfully throughout the world. Digital cellular radiotelephone systems such as those conforming to the North American standard IS-54 and the European standard GSM have been in service since the early 1990's. More recently, a wide variety of wireless digital services broadly labeled as PCS (Personal Communications Services) have been introduced, including advanced digital cellular systems conforming to standards such as IS-136 and IS-95, lower-power systems such as DECT (Digital Enhanced Corpses Telephone) and data communications services such as CDPD (Cellular Digital Packet Data). These and other systems are described in The Mobile Communications Handbook, edited by Gibson and published by CRC Press (1996).
Included among the wireless communications systems in use today are low-power private wireless systems that are used to cover a limited geographic area, such as office, a building or a campus. An example of such a private wireless system is the Digital Wireless Office System (DWOS) developed by Ericsson Inc., the assignee of the present invention. As illustrated in
FIG. 1
, the DWOS
110
is designed for use by wireless terminals
150
that are also configured to access a public cellular network
130
, such as a cellular network complying with IS-41, IS-136 or other standards. The DWOS
110
includes a plurality of radio heads
118
, i.e., transceiver units that function in a manner similar to base stations of the public cellular network
130
. The radio heads
118
are networked with a private cellular radio exchange (CRE)
114
that handles air interface and switching functions, and a mobility server
116
that provides such functions as home location registration, authentication, interfacing the DWOS to the public cellular network
130
, as well as other operation and maintenance functions. The DWOS
110
also includes one or more scanning heads
119
, receiver units that monitor the radio frequency (RF) environment and determine which frequencies the DWOS
110
can use with the least interference. The DWOS
110
also includes a public exchange (PBX) that connects the radio infrastructure to regular wireline telephones
111
and to the public switched telephone network (PSTN)
120
.
The Ericsson DWOS system described is specifically designed to operate according to an IS-136 time division multiple access (TDMA) air interface. An IS-136 TDMA system is implemented by communicating over a plurality of carrier frequency bands during repeating series of time slots, with each repeating series of time slots constituting a “physical channel.” “Logical channels” are mapped onto the physical channels by assigning selected slots of a physical channel to selected channels in repeating frame, superframe and hyperframe structures, in a manner well known to those skilled in the art.
Typically included among the channels are dedicated control channels, including forward (downlink) control channels for conveying information from base stations (or radio heads, in the DWOS) to terminals, and reverse control channels for conveying information from terminals to base stations. The information broadcast on a forward control channel may include such things as an identification of a geographic cell served by a transmitting base station, and associated network identification, system timing and other information needed to access the wireless system. Reverse control channels are typically used for transmitting access requests and page acknowledgments from terminals.
An exemplary slot allocation utilized by wireless systems complying with the IS-136 standard is illustrated in FIG.
2
. For groups of three repeating slots on the uplink and downlink carrier frequency bands used by a base station, a “slot pair” on one pair of carrier frequency bands is reserved for the provision of a forward (downlink) Digital Control Channel (FDCCH) and a reverse (uplink) DCCH (RDCCH). Other slot pairs may be assigned to Digital Traffic Channels (DTCs), i.e., channels assigned to particular terminals on a dynamic basis for communication of voice or other data.
As illustrated in
FIG. 3
, an IS-136 FDCCH has a plurality of logical channels mapped thereon, including a multiplexed Broadcast Channel (BCCH) designed to convey information about system configuration and system access rules, and a multiplexed point-to-point short message service (SMS), paging and access response channel (SPACH). The BCCH is further divided into a Fast Broadcast Channel (F-BCCH) for conveying time-critical information such as system identification (ID) and registration information, an Extended Broadcast Channel (E-BCCH) for conveying less time critical information such as neighboring cell lists, and an SMS Broadcast Channel (S-BCCH). The SPACH comprises a short message service channel (SMSCH) for carrying messages, a paging channel (PCH) for conveying system pages, and an access response channel (ARCH) for providing system response to queries from subscriber units and other administration information. A Shared Channel Feedback (SCF) field contains information about the reservation status of an associated Random Access Channel (RACH) on the RDCCH. The RACH is used by terminals to transmit requests to access the wireless system.
A call between terminals
150
in a standard wireless system such as the DWOS
110
of
FIG. 1
is typically initiated by one of the terminals
150
transmitting a call origination message that identifies the number the originating terminal desires to call. This origination message is received by one of the radio heads
118
, and conveyed to other elements of the DWOS for authorization and traffic channel designation. Once the call request is authorized, the system transmits a traffic channel designation message to the originating terminal, designating a traffic channel for use by that terminal. The DWOS
110
also transmits a page message addressed to the called terminal from selected radio heads
118
, typically based on location information maintained by the mobility server
116
. The called terminal acknowledges the page by transmitting a page acknowledgment message, which typically is received by more than one of the radio heads. Typically based on relative signal strengths of the acknowledgments received at the radio heads, one of the radio heads is selected to communicate with the called terminal, and an appropriate traffic channel designation message is transmitted to the called terminal, designating a traffic channel for its use.
Communications between the terminals are then conducted over the designated traffic channels. During the call, both voice and control information may be communicated over the designated channels using so-called “in-band” signaling channels mapped onto the designated traffic channels. Signals communicated over the designated traffic channels are also typically monitored for signal quality. This in-band signaling and monitoring is typically used to guide handoffs as terminals
150
move among areas served by different radio heads
118
.
This call setup procedure may also be used to setup a group call among more than two terminals. However, the above-described call setup procedure may be too cumbersome for some group call applications, such as emergency police or other safety applications, due to the overhead associated with paging multiple terminals.
SUMMARY OF THE INVENTION
In light of the foregoing, it is an object of the present invention to provide efficient apparatus and methods for group calling.
It is another object of the present invention to provide apparatus and metho
Davis Temica M.
Ericsson Inc.
Myers Bigel & Sibley & Sajovec
Urban Edward F.
LandOfFree
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