A method of operating one of a plurality of end nodes to communicate with a central node over an unlicensed spectrum, the method comprising: wirelessly receiving, an instance of a non-hopping beacon signal, B, periodically-transmitted from the central node; each instance B(i) of the beacon signal including: a frame number, FN(i), of a frame corresponding thereto; and an identification, IDCN, of the central node; interpreting a frequency-block hopping guide according to the frame number FN(i) and the identification IDCN thereby to determine a corresponding set, CSET(i), of at least two channels available to the end node for transmission thereover, respectively, during the frame number FN(i); wherein the frequency-block hopping guide establishes: a total of L frames; a set of channels CSET for each frame, respectively; and that, for any two consecutive ones of the L frames, FN(j) and FN(j+1), corresponding sets CSET(j) and CSET(j+1) will be different, CSET(j)≠ CSET(j+1); wherein the frequency-block hopping guide, for any given frame FN(j), further establishes: a corresponding set of channels CSET(j) includes N blocks, 2 ≤ N; each block in the corresponding set of channels CSET(j) includes P contiguous channels, 2 ≤ P; each channel in the corresponding set of channels CSET(j) is a member of only one of the blocks of the corresponding set of channels CSET(j); and N and P are positive integers; wherein the frequency-block hopping guide further establishes: how, for any two consecutive ones of the L frames, FN(j) and FN(j+1), channels comprising only one of the N blocks, block BK H, change between the corresponding sets CSET(j) and CSET(j+1) such that BK H (j) ≠ BK H (j+1), thereby establishing how the block BK H hops between the corresponding sets CSET(j) and CSET(j+1); and selecting, at least pseudo-randomly, at least one channel amongst the corresponding set CSET(i); and wirelessly transmitting at least one message from the end node using the at least one selected channel, respectively, wherein i and j are non-negative integers, L is an integer and 2 ≤ L. wirelessly receiving, an instance of a non-hopping beacon signal, B, periodically-transmitted from the central node; each instance B(i) of the beacon signal including: a frame number, FN(i), of a frame corresponding thereto; and an identification, IDCN, of the central node; a frame number, FN(i), of a frame corresponding thereto; and an identification, IDCN, of the central node; interpreting a frequency-block hopping guide according to the frame number FN(i) and the identification IDCN thereby to determine a corresponding set, CSET(i), of at least two channels available to the end node for transmission thereover, respectively, during the frame number FN(i); wherein the frequency-block hopping guide establishes: a total of L frames; a set of channels CSET for each frame, respectively; and that, for any two consecutive ones of the L frames, FN(j) and FN(j+1), corresponding sets CSET(j) and CSET(j+1) will be different, CSET(j)≠ CSET(j+1); a total of L frames; a set of channels CSET for each frame, respectively; and that, for any two consecutive ones of the L frames, FN(j) and FN(j+1), corresponding sets CSET(j) and CSET(j+1) will be different, CSET(j)≠ CSET(j+1); wherein the frequency-block hopping guide, for any given frame FN(j), further establishes: a corresponding set of channels CSET(j) includes N blocks, 2 ≤ N; each block in the corresponding set of channels CSET(j) includes P contiguous channels, 2 ≤ P; each channel in the corresponding set of channels CSET(j) is a member of only one of the blocks of the corresponding set of channels CSET(j); and N and P are positive integers; a corresponding set of channels CSET(j) includes N blocks, 2 ≤ N; each block in the corresponding set of channels CSET(j) includes P contiguous channels, 2 ≤ P; each channel in the corresponding set of channels CSET(j) is a member of only one of the blocks of the corresponding set of channels CSET(j); and N and P are positive integers; wherein the frequency-block hopping guide further establishes: how, for any two consecutive ones of the L frames, FN(j) and FN(j+1), channels comprising only one of the N blocks, block BK H, change between the corresponding sets CSET(j) and CSET(j+1) such that BK H (j) ≠ BK H (j+1), thereby establishing how the block BK H hops between the corresponding sets CSET(j) and CSET(j+1); and selecting, at least pseudo-randomly, at least one channel amongst the corresponding set CSET(i); and wirelessly transmitting at least one message from the end node using the at least one selected channel, respectively, wherein i and j are non-negative integers, L is an integer and 2 ≤ L.