Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1999-12-29
2004-06-15
Tran, Sinh (Department: 2681)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S090200
Reexamination Certificate
active
06751468
ABSTRACT:
FIELD OF INVENTION
The field of this invention is wireless communication systems and methods of operating the same. More specifically, this invention relates to a system and method for providing a Push to Talk feature with a wireless communication system.
BACKGROUND
The dispatch or Push to Talk (“PTT”) feature is a method of communication over a speech circuit, e.g., a wireless unit, in which the talker is required to keep a designated switch operated while talking. The PTT feature is currently offered by some wireless service providers, e.g., the Direct Connect® service from Nextel Communications of Reston, Virginia. Typically, with the PTT feature, a caller must press a designated PTT button while speaking in order to be heard by the called party. The caller is generally heard by the called party in speaker phone mode. The called party then may respond in like manner by pressing a designated PTT button while speaking.
Currently, the PTT feature is most widely offered on Enhanced Specialized Mobile Radio (“ESMR”) systems. The PTT feature can be implemented on a Time Division Multiple Access (“TDMA”) system such as EIA/TIA standard IS-136, but the implementation of the PTT feature in a IS-136 system is not as spectrally efficient as with an ESMR system. As such, a current IS-136 system is not particularly well suited to handle the PTT functionality. An ESMR system is able to release the selected channel when no one is speaking during a PTT conversation, thereby allowing other users to utilize the channel.
With IS-136, for any type of call, a wireless unit utilizes a thirty kHz wide communication channel consisting of a frequency pair of signals to communicate with a base station. As shown in
FIG. 1
, the frequency pair includes an uplink or transmit (TX (F
1
)) frequency and a downlink or receive (RX (F
2
)) frequency. The signals are typically separated by the frequency duplex separation (for example, forty-five MHz for cellular transmission) and both transmit voice and control information. This is full duplex transmission. The wireless unit transmits control information such as signal strength and call quality data to the base station and receives control information such as handoff data and other call management information. Currently, the wireless unit holds the communication channel using both the TX and RX frequencies for the entirety of the call to the exclusion of other wireless units. As such, an IS-136 system is not as spectrally efficient as an ESMR system for providing a PTT function. Therefore, there is a need for a more efficient method and system of providing PTT on cellular systems such as TDMA systems.
SUMMARY OF THE INVENTION
Systems and methods are provided for allowing a first wireless unit and a second wireless unit to share a single communication channel including a transmit frequency and a receive frequency. The systems and methods include assigning the single communication channel to the first wireless unit and the second wireless unit, so that the first wireless unit and the second wireless unit may alternatively transmit on the transmit frequency, and the first wireless unit and the second wireless unit may monitor the receive frequency; receiving a first transmission from the first wireless unit on the transmit frequency; sending a signal to the first wireless unit indicating to the first wireless unit to stop transmitting; sending a signal to the second wireless unit that the second wireless unit can send a second transmission on the transmit frequency; and receiving the second transmission from the second wireless unit on the transmit frequency.
The systems include a first wireless unit, a second wireless unit, and a base station. The first wireless unit transmits on a transmit frequency of a communication channel and monitors a receive frequency of the communication channel. The second wireless unit monitors the receive frequency.
As a result of the disclosed systems and methods, a wireless unit in Push To Talk mode does not maintain a whole communication channel, i.e., both the transmit and receive frequency, for the entirety of a Push To Talk call. The systems and methods allow for a more spectrally efficient transmission of Push To Talk mode calls over a Time Division Multiple Access system or similar communication system by allowing two wireless units to share a single communication channel. Because of the increased efficiency, the disclosed systems and methods provide for more economically feasible systems and methods of providing a Push To Talk mode in a communication system.
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Austin Mark D.
Heubel Michael L
BellSouth Intellectual Property Corporation
Merchant & Gould
Ramos-Feliciano Eliseo
Tran Sinh
LandOfFree
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