Abstract: A method of transmitting signals from a mobile unit to a base station in the reverse link direction using multi-tone techniques includes the step of dividing a frequency band into a plurality of generally even spaced tones. The tones are partitioned into a predetermined number of tone sets which each contain a predetermined number of tones. Each unit within a given sector is assigned a tone set for transmitting information signals. The tones within each tone set are selected so that the modulated signals transmitted by each unit are orthogonal with respect to all other tone sets assigned to units in that sector. Adjacent cells have no more than one tone in common.

Abstract: A speech scrambling system using discrete prolate spheroidal sequence coefficients (PC). The problem is to provide high fidelity and high security in a scrambling system while limiting the bandwidth of the scrambled signal to the bandwidth of the original speech signal. The disclosed system uses PC to solve this problem. The analog speech signal is digitally sampled (100), converted to PC (203, 204, 205), scrambled (208, 209), and converted to scrambled samples (211, 212, 213). The scrambled samples are transmitted using pulse amplitude modulation (102) in the same bandwidth as the original signal. At the receiving end, the inverse steps are performed to recover the original speech. The scrambling is periodically modified (220, 320) to improve security.

Abstract: Pulse amplitude modulated data systems typically utilize linear combinations of Nyquist pulses to transmit data signals. Ideally, required bandwidth for the transmitted signal is 1/(2T)=.rho./2L where .rho. is the data rate, T the signaling interval, and L the number of bits per signal. In practice, however, an "excess bandwidth" of at least 10-20 percent is required.According to the invention, data signals are encoded to produce an encoded signal which can be transmitted over a communications channel having excess bandwidth of merely 2-4 percent. The encoding scheme utilizes linear combinations of characteristic sequences which are known as discrete prolate spheroidal sequences. A transmitter and a corresponding receiver are disclosed.

Abstract: Error-correcting code theory is utilized in a video signal interframe coding system which requires no transmitter frame memory. In the transmitter, each of a plurality of n-bit words representing respective portions of the current frame is transformed into the corresponding k-bit syndrome of a selected (n,k) error-correcting code. As the syndrome of each word is received at the receiver, the corresponding word from the previous frame is read out of a receiver frame memory and its syndrome is formed. The received and formed syndromes are subtracted from one another and passed through an error-correcting code decoder. The previous-frame word is added to the decoder output, yielding the current-frame n-bit word.