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In this study, the authors introduce a new multiple access technique for ultra-wideband (UWB) communications called multi-scale (MS) direct sequence (DS)-UWB (MS/DS-UWB). In the MS/DS-UWB design, the dyadic-scaled orthogonal wavelets spread by DS codes create a dyadic-scaled multi-band structure which exhibits the scalability of the spectrum. Hence, it can be incorporated with cognitive radio by intelligent spectrum adaptation when part of the UWB spectrum cannot be used. MS/DS-UWB is a multi-rate system, where services are assigned to different orthogonal sub-bands with respect to their data rates. Compared with the conventional single-band DS-UWB, the increased pulse durations (or scaled sub-bands) relax the system design. Besides, it eliminates the disadvantages associated with orthogonal frequency division multiplexing-based UWB systems. The authors analyse the probability of error performance of the MS/DS-UWB system and compare it with a multi-processing gain (MPG) DS-UWB system over UWB channels. Numerical results show that the MS/DS-UWB performs much better than that of MPG/DS-UWB due to the low cross correlation among the scaled wavelets.