Beam-space time coding methods are being extensively investigated, since they provide levels of performance appropriate for the next and future generations of wireless communication systems. In this paper, we focus on beam-domain space-time coding, especially considering the case when transmit beams have inter-beam interference (IBI). A new beam-space time coding scheme that takes into account the overlap amount among beams is proposed. We observe that the overlap of beams introduces an amount of correlation to the channels in a similar way to the well-known Partial Response (PR) channel in magnetic recording. Based on that observation, the proposed system can make use of IBI to encode and decode the signals. We evaluate the proposed system both via theoretical upper bound and via computer simulations. The Bit Error Rate (BER) performance of the proposed system using IBI is better than that of the system with no-IBI because the proposed system delivers more coding gain. However, the overlap of beams decreases the diversity gain. The tradeoff relationship between diversity gain and coding gain is investigated.

In this paper we present a novel method for improving RAKE receiver reception in UWB systems. Due to the fact that practical pulses that can be produced for UWB-IR (Ultra Wideband-Impulse Radio) may occupy a longer time than the typical multipath resolution of the actual UWB channel, multiple channel components may arrive within this typical pulse width. Performance degradation may occur due to the resulting intrapulse (overlapping received pulses) interference. We here propose an adaptive, pilot aided RAKE receiver for UWB communications in the multipath environment. The proposed system estimates the actual received signal with intrapulse interference in each RAKE finger using projections onto a Hadamard-Hermite subspace. By exploiting the orthogonality of this subspace it is possible to decompose the received signal so as to better match the template waveform and reduce the effects of intrapulse interference. By using the projections onto this subspace, the dimension of the received signal is effectively increased allowing for adaptive correlator template outputs. RAKE receivers based on this proposal are designed which show significant performance improvement and require less fingers to achieve required performance than their conventional counterparts.

The worldwide availability of the Industrial Scientific and Medical (ISM) bands has prompted the proposal of several communication systems for indoor application at the 2.4 and 5 GHz bands. Although adaptive array antennas have been thoroughly investigated for various outdoor scenarios, their application to indoor communications has been overlooked. Experimental results indicating that conventional array antenna techniques exhibit poor performance when implemented indoors have recently been published. An important peculiarity of the indoor channel is the coexistence of both near-field and far-field propagating waves. Therefore, algorithms that can indifferently cope with both near-field and far-field wavefronts for source location and beamforming are desirable. In this paper, the following are presented. First, a mathematical analysis of the performance of array antennas in the indoor environment is taken up. Second, a new, simple, cost-effective and statistically coherent scheme, the Adaptive Sampling algorithm, is proposed for location estimation of sources anywhere from near field to far field. It is shown that the proposed algorithm achieves ubiquitous source location, allowing for symmetric uplink/downlink beamforming with seamless performance. Finally, the performance of the proposed Adaptively Sampled Array Antenna is performance analyzed via computer simulations under the specifications of the IEEE802.11b DS Wireless Local Area Network (W-LAN).