Digital radio

A digital portable or mobile radio for pseudo-duplex radio communication, comprising:

• (i) signal transmission means for time division duplex signal transmission over a single radio channel;
• (ii) signal reception means for time division duplex signal reception over the said single radio channel;
• (iii) a controller, for controlling the signal transmission means and the signal reception means, the controller being adapted to transmit and receive signals in a plurality of pre-defined frame formats, each pre-defined frame format having a pre-defined time division duplex duty cycle, the controller being adapted to select the particular one of the plurality of pre-defined frame formats for use over the communication link;
• and
• (iv) a voice activity detector operable coupled to the controller to provide to the controller an output having more than two possible values each indicating a different likelihood of speech of a user being present,
• wherein, with the digital radio using a second frame format for communication over the said single radio channel with a second digital radio, the second frame format comprising substantially equal time for transmission by both the first digital radio and the second digital radio, each frame of the second frame format having at least two time slots for the first digital radio to transmit and at least two time slots for the second digital radio to transmit, the time slots for the first and second radios alternating within the frame, during the time slots of the second frame for the first radio to transmit, the controller of the first radio can in response to the output of the voice activity detector unilaterally change the pre-defined frame format selected, from the second frame format to a third frame format, without consulting the second digital radio, the third frame format having a higher time division transmitting duty cycle for the first digital radio than the second frame format.

A method of pseudo-duplex digital radio communication, comprising:

• transmitting a time division duplex signal over a single radio channel;
• receiving a time division duplex signal over the said single radio channel;
• selecting a particular one of a plurality of pre-defined frame formats for use over the single radio channel, each pre-defined frame format having a pre-defined time division duplex duty cycle;
• when a digital radio is in communication over the said single radio channel with a second digital radio and the digital radio is transmitting at a lower time division duplex duty cycle than the second digital radio,
• in response to an output from a voice activity detector having at least three different output values each indicating a different likelihood of speech of a user being present unilaterally changing the particular one of the plurality of pre-defined frame formats selected for use over the single radio channel from a first frame format to a second frame format, the second frame format having a higher time division transmitting duty cycle for the digital radio than the first frame format, without consultation with the second digital radio.

A method of pseudo-duplex digital radio communication between a first mobile or portable radio and a second mobile or portable radio, comprising:

• (i) transmitting a time division duplex signal over a single radio channel;
• (ii) receiving a time division duplex signal over the said single radio channel;
• (iii) wherein the transmission and reception are in a particular, second one of a plurality of pre-defined frame formats, each pre-defined frame format having a pre-defined time division duplex duty cycle, the second frame format comprising substantially equal time for transmission by both the first digital radio and the second digital radio, each frame of the second frame format having at least two time slots for the first digital radio to transmit and at least two time slots for the second digital radio to transmit, the time slots for the first and second radios alternating within the frame;
• and
• (iv) during the time slots of the second frame for the first radio to transmit, the first radio can, in response to an output from a voice activity detector having at least three different output values each indicating a different likelihood of speech of a user being present, unilaterally change the pre-defined frame format selected, from the second frame format to a third frame format, without consulting the second digital radio, the third frame format having a higher time division transmitting duty cycle for the first digital radio than the second frame format.