A communications terminal comprising: an encoder configured to encode a source digital data signal to generate an encoded signal, wherein the source digital data signal comprises a source bit stream; a scrambler configured to scramble the encoded signal based on a scrambling signature associated with the communications terminal, and to format the scrambled signal into a sequence of data frames, wherein each data frame comprises a data payload that includes a block of the scrambled encoded signal, and a frame header that includes a unique word, UW, segment associated with the scrambling signature; a modulator configured to modulate the sequence of data frames to generate a transmission signal; and a transmitter configured to transmit the transmission signal via respective time slots of a random access channel of a wireless communications system; wherein the communications terminal is one of a group of communications terminals, wherein the scrambling signature is associated with each communications terminal of the group, wherein the communications terminals are mapped among the groups of communications terminals in order to distribute the respective uinque word segments in a mannerthat reduces data collision probabilities within a contention channel, wherein the unique word, UW, segment for each frame of the sequence of data frames is configured as a reference for synchronization by a receiving communications terminal on frame boundaries and to designate the associated scrambling signature for use by the receiving communications terminal in descrambling the data payload of the data frame, and wherein the unique word, UW, segment for each frame of the sequence of data frames is configured for identification by a receiving terminal via correlation process and thereby to distinguish the data frame from at least one data frame originating from at least one further communications terminal, transmitted via a common time slot of the random access channel, for which a different scrambling signature was used to scramble a respective encoded signal thereof. an encoder configured to encode a source digital data signal to generate an encoded signal, wherein the source digital data signal comprises a source bit stream; a scrambler configured to scramble the encoded signal based on a scrambling signature associated with the communications terminal, and to format the scrambled signal into a sequence of data frames, wherein each data frame comprises a data payload that includes a block of the scrambled encoded signal, and a frame header that includes a unique word, UW, segment associated with the scrambling signature; a modulator configured to modulate the sequence of data frames to generate a transmission signal; and a transmitter configured to transmit the transmission signal via respective time slots of a random access channel of a wireless communications system; wherein the communications terminal is one of a group of communications terminals, wherein the scrambling signature is associated with each communications terminal of the group, wherein the communications terminals are mapped among the groups of communications terminals in order to distribute the respective uinque word segments in a mannerthat reduces data collision probabilities within a contention channel, wherein the unique word, UW, segment for each frame of the sequence of data frames is configured as a reference for synchronization by a receiving communications terminal on frame boundaries and to designate the associated scrambling signature for use by the receiving communications terminal in descrambling the data payload of the data frame, and wherein the unique word, UW, segment for each frame of the sequence of data frames is configured for identification by a receiving terminal via correlation process and thereby to distinguish the data frame from at least one data frame originating from at least one further communications terminal, transmitted via a common time slot of the random access channel, for which a different scrambling signature was used to scramble a respective encoded signal thereof.