Abstract: A stealthy, one-hand keyboard suitable for pedestrians is implemented as a frame held between thumb and palm, to which is attached an adjustable array of keyswitches. The configuration is such that the fingers play no part in supporting the keyboard against gravity, nor in retaining it within the hand. This property facilitates faster typing. The keyboard is strapless and leaves the fingers near their relaxed positions. The hand hides the keyboard on one side and chords are entered by small motions of the fingers, actuating contact being via the flesh on the palm sides of the middle and distal phalanges. These properties reduce the keyboard's observability.

Abstract: A radio unit (12) for communication over a communication channel (300) having repeating frames. The radio unit has a memory (131) with a table (280) of time locations in a frame and indications of the availability of time locations for transmission. A time is selected from the table and a cell of data is transmitted on the channel at the selected time. If an acknowledgement to the cell is received at a receiver (102) the transmitter sends a series of further cells at corresponding times in later frames. Otherwise a different time is selected for a new access attempt. A sequence of ATM cells is prepared for transmission by forming data into cells each having synchronization information (230), a physical layer field (251), a sequence number (253) and an error check number (254). Error coding cells (245) are added, with error coding which is spread across the cells such that a lost cell is recoverable from adjacent cells.

Abstract: An adaptive matched filter is described as a replacement for a signal replica filter of a maximum likelihood (ML) demodulator, the filter normally receiving an input data vector having signal and noise components. A symbol-justified input data vector is produced from the input data vector. This vector is then used to generate a weight vector. In a time-domain embodiment, the symbol-justified data vector is multiplied by the weight vector on a symbol-by-symbol basis to estimate the signal components of the output of a filter. In a frequency-domain implementation, multiplication is carried out on a symbol block-by-symbol block basis.