| Ultra-wideband (UWB) technique is a new wireless communication technique. Compared with traditional narrowband communication, it has many advantages such as low cost, low power consumption, high transmission rate and good multipath resolution. So it has fine prospect in commercial, household and personal multimedia network, which makes it attract extensive attention home and abroad. IEEE proposes UWB as the realizing scheme of physical layer in wireless personal area network.Although UWB technique has lots of advantages, there are still many technical challenges in UWB deployment, such as antenna design for and synchronization of very short pulses, performance degradation due to multiple access interference and narrowband jamming, how to employ higher order modulation schemes to improve capacity or throughput, how to develop link and network layers to take advantage of the UWB transmission benefits at the physical layer.Our research object is the adaptive techniques in OFDM-UWB. It's well known that the sub-carriers of the OFDM system undergoing multi-path will show different fade, because of the frequency selective of channels. Based on the level of fade of sub-carriers, the performance of system should be improved by changing the transmit power or bit number of different sub-carriers. The frequency selective fade of UWB will be more serious. The transmit power is very low and the power spectrum regulation is strict. All of the above-mentioned illustrate that there are some unique characters in the adaptive techniques of OFDM-UWB, different from classical adaptive techniques. Started with mis, an adaptive sub-carrier selection and power allocation scheme and two bit allocation schemes are obtained after analysis, and evaluated after simulation. |
