OCC-UWB System Design For Multiple NBIs Suppression Based On Chirp Function

Ultra wideband (UWB) technology derived from impulse radio (IR) technology and was first used in military radar field. In 1989, the term of UWB was proposed by DARPA and was developed through IR. FCC didn’t allow UWB technology to be opened to civilian use under the specified power spectrum masking until 2002. And UWB signal is no longer limited to be generated through IR. This landmark event together with the advantages, such as high data rate, low power consumption, strong multipath resolution, etc, inspired chip manufactures and academic experts of great research interest. With the rapid development of wireless communication, people’s demands for service quality are growing. To meet the requirements for high data transfer rate of all kinds of short distance and high speed wireless communication networks, such as the family multimedia network, the hospital medical network, etc, a variety of short distance and high speed wireless technologies arise and UWB technology is one of the most attractive technologies.Faced with the shortage of radio spectral resource, FCC allows a wide frequency band (3.1GHz～10.6GHz) for UWB system. Such a wide bandwidth is based on power limitation. To prevent interference with other existed narrowband systems operating within the UWB spectrum band, the power spectral density (PSD) of UWB system is less than —41.3dBm/MHz. Meanwhile, due to the higher power compared with that of UWB signal, the narrowband systems will influence UWB system seriously, and some efficient narrowband interference (NBI) suppression technologies must be taken. While at the same time, considering the indoor dense multipath environment that UWB system works in, there must be multi-user interference (MUI) and multipath interference (MPI), and we must take measure to suppress and get acceptable performance. In this thesis, we mainly focus on the interference suppression problems in UWB system, and considering accelerating the data transfer rate and raising the utilization ratio of frequency band to achieve overall optimization. Aimed at the problem to be solved, the main work of this thesis is as follows.Firstly, based on the good time-frequency mapping relation of Chirp signal, we propose a kind of modified method to design non-linear Chirp waveform that can suppress two NBIs, and the time domain expressions of two kinds of non-linear Chirp waveforms are deduced according to the proposed method. Then, generalizing this method to any number of NBIs, we get a kind of method to design non-linear Chirp waveform that can suppress multiple NBIs adaptively by the aid of spectrum sensing technology. Based on the atan and asinh inverse trigonometric functions, we get the general forms of two kinds of non-linear Chirp waveforms that can suppress multiple NBIs. This design method has many merits, such as flexible design, low complexity, and so on. The time domain expression of the waveforms can be obtained through time domain processing. Simulation results under AWGN channel show that the waveforms designed according to the proposed method can suppress multiple NBIs efficiently.Secondly, except for NBIs, there exist MUI and MPI in the environment. We design a single band OCC-CDMA UWB system for multiple NBIs suppression that adopting the non-linear Chirp waveform designed before as the transmitted pulse to suppress multiple NBIs and using orthogonal complementary code (OCC) as spreading code to suppress MUI and MPI. Theoretical analysis and performance simulation under multipath channel indicate the system can keep lower bit error rate (BER) and better performance in the presence of aforesaid interference. The system can suppress NBIs, MUI, and MPI efficiently.Finally, to optimize UWB system jointly in terms of interference suppression and the improvement of spectrum utilization, we design a multiband OCC-CDMA UWB system based on Chirp waveform for multiple NBIs suppression. The data bits are transmitted through multiple bands simultaneously without carrier modulation. The system has the characteristic of simple implementation and low complexity. We put forward two kinds of implementation scheme about the multiband system. The first is the equant multiband scheme. Firstly, we divide the whole frequency band equally according to requirements on the rate of data transmission. Then we adopt spectrum sensing technology to detect the corresponding information about NBIs. In the sub-bands under the condition of NBIs, the non-linear Chirp waveform designed before is used to suppress NBIs. The second is the non-equant multiband scheme. NBIs are suppressed from another angle by this scheme. The idea of evasion of spectrum is adopted while dividing the frequency band. Firstly, we get information about the central frequencies and bandwidths of NBIs through spectrum sensing technology. Then, according to the information of NBIs and requirements on the rate of data transmission, divide the band by making full use of the good time-frequency mapping relation of Chirp signal to mitigate the NBIs. Meanwhile, OCC is adopted to suppress MUI and MPI. Theoretical analysis and simulation results show that the multiband OCC-CDMA UWB system can improve the data transmission rate, spectrum utilization, and global system performance as well as suppress NBIs, MUI, and MPI.