Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1999-08-03
2001-09-18
Trost, William (Department: 2746)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S524000, C455S445000, C455S456500, C370S335000, C370S342000
Reexamination Certificate
active
06292671
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to wireless telecommunications, and in particular, to a method of providing dispatch mode calling in a code division multiple access wireless network.
2. Description of the Prior Art
“Dispatch mode” is a radio communications technique where one radio communicates to many other radios using short bursts of communications. Many groups such as taxi drivers and police officers desire to communicate with dispatch mode radio devices because it allows them to speak with a number of other people at the same time without initiating a plurality of separate phone calls. Until recently, dispatch mode services were only available in two-way radio systems such as walkie talkies. Although these radio systems work effectively when all of the users are located close together, they become ineffective once the users travel beyond the range of the radio transceivers.
Nextel has recently begun offering dispatch mode operations in its enhanced specialized mobile radio (ESMR) systems. ESMR can be deployed on a cellular network and, therefore, supports network features that enable users to operate in dispatch mode over greater distances. ESMR systems use time division multiple access (TDMA) technology which allocates a discrete amount of frequency band width to each user of the system to permit many simultaneous conversations. Each caller is allowed to transmit in predetermined time slots so that channelization of users in the same band is achieved through separation in time. Unfortunately, the capacity of these networks is limited by the number of available time slots. TDMA networks also suffer from poor call clarity, “hard” call hand-offs and minimal call security.
Companies such as Sprint PCS have recently begun offering wireless communication services using code division multiple access (CDMA) techniques. CDMA is a digital spread-spectrum modulation technique which digitizes wireless conversations and tags them with special codes. The digitized data is spread across the frequency band in a pseudo random pattern. Receiving mobile phones are instructed to decipher only the data corresponding to particular codes to reconstruct the signal. CDMA networks offer advantages over TDMA networks including increased network capacity, fewer dropped calls because of better hand-off methods, improved voice clarity, improved privacy and transmission security, and enhanced services such as text messaging and data transmissions. However, until now, CDMA wireless networks have not included dispatch mode calling capabilities.
SUMMARY OF THE INVENTION
The present invention solves the above-described problems and provides a distinct advance in the art of wireless telecommunications networks. More particularly, the present invention provides a method of providing dispatch mode calling in a CDMA wireless network.
The method of the present invention is implemented by first defining at least one talk-group consisting of a plurality of mobile phones in a CDMA network operated by users who wish to communicate with each other in a dispatch mode. To initiate a dispatch mode call, an originating phone sends a dispatch mode call request to the network. The dispatch mode call request is validated, then the location of the destination mobile phones in the talk-group is determined. Voice channels are then assigned to the members of the talk-group and a group code or mask is sent to each destination phone that enables the phones to demodulate or decode communications from the originating phone. Voice packets are received from the originating mobile phone, encoded, and sent to the destination phones. The destination mobile phones then decipher the encoded voice packets with the received mask.
The present invention permits dispatch mode calling between a plurality of users in a talk-group all located within the same sector of a telecommunications cell without adversely affecting the capacity of the cell. Specifically, the method assigns a first Walsh code to the forward traffic channel for the originating mobile phone that all mobiles listen to if they are located in the same sector, and a second Walsh code to the forward traffic channel for all other destination mobile phones that are located in a different sector. Thus, a dispatch mode call between mobile phones in the same sector of a telecommunications cell utilizes the same network capacity as a conventional wireless call between only two mobile phones.
The method of the present invention also provides dispatch mode calling for members of a talk-group even when the members are located in more than one telecommunications cell. This is achieved by replicating the encoded voice packets and routing a copy of the voice packets to each base station serving a cell in which any destination mobile phone is located. For example, if destination phones are located in three different telecommunications cells, the present invention includes the step of replicating the encoded voice packets and routing the voice packets to each of the three base stations serving the three cells.
REFERENCES:
patent: 4191860 (1980-03-01), Weber
patent: 5247571 (1993-09-01), Kay et al.
patent: 5303285 (1994-04-01), Kerihuel et al.
patent: 5353331 (1994-10-01), Emery et al.
patent: 5416770 (1995-05-01), Stoner et al.
patent: 5694463 (1997-12-01), Christie et al.
patent: 5850611 (1998-12-01), Krebs
patent: 5852781 (1998-12-01), Ahvenainen
patent: 5924041 (1999-07-01), Alperovich et al.
patent: 5930723 (1999-07-01), Heiskari et al.
patent: 5970417 (1999-10-01), Toyryla et al.
patent: 5983099 (1999-11-01), Yao et al.
patent: 6005848 (1999-12-01), Grube et al.
patent: 6021326 (2000-02-01), Nguyen
Hovey Williams Timmons & Collins
Milord Marceau
Sprint Spectrum L.P.
Trost William
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