| With the development of communication technology, various mobile business and portable communication equipments are emerged constantly. Meanwhile, carriers of information are change a lot from simple text and voice data to multiple media, such as images and video. Since the high bandwith requirements of the the multimedia technology, modern wireless communications faces greater challenges. As a new short-range wireless communication technology, Ultra broadband attracts an extensive attention for its advantages such as low cost, low power consumption, high transmission rate and good multipath resolution. It will became as the physical layer implementation in wireless personal area network in the future.According to the provisions of FCC, the concept of Ultra-WideBand signals are defined as that: if the absolute signal bandwidth is greater than 500MHz, it can be realized as the ultra-wideband signal. In the definition, it doesn't limited its modulation. As a result, a variety of UWB implementations have been appeared. OFDM-UWB implementation proposed by WiMedia Alliance has gained a lot of supports for its advantage of spectrum flexible. It has proposed ECM368/369 standards.Currently, ECMA-369 standard has been formulated as the norm for the physical layer and Media access sublayer (MAC) for high-speed ultra-wideband technology. OFDM-UWB technology will become as the physical solutions for the wireless USB and next generation bluetooth standard.In accordance with the provisions of FCC, the power spectral density have been strictly limited. So how to reduce the power spectral density become a bottleneck to ultra-wideband. OFDM-UWB system distributes the high-speed tranfer data conversion to a number of sub-channels of relatively low transmission rate by parallel/serial. Each OFDM symbol are composed with several subcarriers which are mutually orthogonal when transmit. So it will be very meaningful to conduct research on effectively allocating system resources as power, subcarriers and bits for users.Our research is mainly on resource allocation techniques for OFDM-UWB system in multi-user environment. As we all know, subcarriers undergoing multipath environment will show different multipath fade, each user has different fade condition on different subcarrier, specially in UWB channel. Therefore, in this research, we use an adaptive technology to allocate resources. We can allocation system resources such as power, subcarriers and bits for user according to thechannel condition of different users in different subcarriers.The mainly details in this research are listed as followings: The wireless communication system of OFDM-UWB and several typical UWB wireless channel modes are analyed and simulated first. In this paper we used CM1 channel mode recommended by IEEE802.15.3a to allocate bits and subcarriers.Take the stringent limit on transmission power specified by FCC and different fade conditon on different subcarriers to each users into consideration, a new subcarrier allocation algorithm has been proposed to minimizes transmission power. Compare with ACG algorithm, this subcarrier allocation algorithm allocate subcarrier based on the contribution subcarriers gived to the user's rate in order to greatly satisfy users rate requirement and improve the system's performance. In bit allocation process, a fast bit allocation algorithm has been proposesd according to the rate requirments for each user. In order to minimize the transmission power and reduce the operation's complexity. Every bit is allocated based on the data rates requirment of the users and the subcarriers number the users need.In order to reduce the system complexity furthermore, in this paper we use subcarrier groups to allocate subcarriers and bits. Although subcarrier groups make the system a little performance losses, the resource allocation scheme's complexity can be effectively reduced. Through the simulation we can see that when the the number of the subcarriers in a group is not very large,the performance only has very little loss. |
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