Since Ultra Wideband Impulse Radio (UWB-IR) systems can resolve many paths and are thus rich in multipath diversity, the use of the Rake diversity combining is very effective. In the Rake diversity combining, the bit error rate (BER) is improved with the increase of the number of fingers. The Pre-Rake diversity combining is known as another technique to achieve the performance equivalent to the Rake diversity combining without increasing the receiver complexity. In the Pre-Rake diversity combining, the transmitted signals are scaled and delayed according to the delay and strength of the multipath. In this paper, we propose the Pre-Rake diversity combining techniques for UWB systems, the All-Pre-Rake (A-Pre-Rake) diversity combining using perfect channel information, the Selective-Pre-Rake (SPre-Rake) diversity combining using the information on the L strongest paths, and the Partial-P re-Rake (PPre-Rake) diversity combining using the information on the first L paths. From the results of our computer simulation for UWB-IR systems in IEEE 802.15 UWB multipath channel model, we show that the proposed Pre-Rake diversity combining techniques are effective for the UWB-IR systems to achieve good error rate performance, while keeping the complexity of the receiver low. We also show that the S-Pre-Rake diversity combining is effective to achieve good error rate performance with less amount of the channel information.
