Multidimensional modulation for ultra-wideband multiple-access impulse radio in wireless multipath channels

In this paper, we develop multidimensional modulation for ultra-wideband (UWB) multiple-access (MA) impulse-radio communications in wireless multipath environments. An important advantage of multidimensional modulation over single-dimensional modulation is the possibility of higher power efficiency, and this may be critical in UWB communications. For this reason, we propose a 2MN-ary biorthogonal keying (BOK) scheme, in which N orthogonal pulse shapes in conjunction with M orthogonal codes are employed to construct MN-dimensional biorthogonal modulation. The direct sequence (DS) MA performance of the proposed scheme is analyzed. A closed-form bit-error-rate expression is derived and compared with simulations based on the Intel Labs´ UWB channel model. Orthogonal pulse shapes that comply with the Federal Communications Commission UWB indoor-emission limits are used in simulations. Our results confirm the power-efficiency improvement achieved by multidimensional modulation for UWB MA communications under multipath fading.