Bandwidth efficient QAM on a TDM-FDM system for wireless communications

A radio system capable of accommodating pre-defined frequency channels of differing bandwidths, each pre-defined frequency channel having a center frequency, comprising:

• a data source providing at least N independent communication signals;
• a transmitter coupled to the data source and configured to transmit N independent communication signals to N mobile units over N sub-channels of a broad pre-defined frequency channel when available;
• each of the N sub-channels having a frequency offset from the center frequency of the broad pre-defined frequency channel, but falling entirely within the bandwidth of the broad pre-defined frequency channel, and no two of the N sub-channels having the same frequency offset;
• the transmitter being configured to transmit M independent signals to M mobile units over a each of a N/M narrow pre-defined frequency channels when a broad pre-defined frequency channel is unavailable, wherein N is an integer multiple of M;
• each of the M sub-channels for each of the plurality of narrow pre-defined frequency channels having a frequency offset from the center frequency of the narrow pre-defined frequency channel, but falling entirely within the bandwidth of the narrow pre-defined frequency channel;
• wherein the frequency offsets for the sub-channels of the narrow pre-defined frequency channels comprise a subset of the frequency offsets for the broad pre-defined frequency channel.