Subspace multiuser receivers for UWB communication systems

In a typical impulse radio ultra-wideband (UWB) communication environment, transmitted signal carries user´s information in pulse positions and undergoes fading from a number of propagation paths. A conventional RAKE receiver may explore path diversity for better performance, but is unable to suppress multiple access interference. Multiuser receiver can significantly improve detection performance. However, it requires channel state information. To seek this information, we adopt a channel input/output model that exhibits a structure similar to a code-division multiple access system. In particular, code matrices for each user can be defined from its unique time-hopping sequence. Then subspace technique is applied to estimate each channel after some necessary modification due to particular formats of defined inputs. Subsequently, zero-forcing and minimum mean-square-error receivers are designed, applicable for both uplink and downlink, and different from existing multiuser detection (MUD) methods that assume perfect channel knowledge.