Performance Analysis And Evaluation Of Ultra Narrow Band System

With the rapid development of wireless communication technology, the limitation and scarcity of radio spectrum resources are increasingly outstanding, due to the contradiction between demand and supply of radio spectrum. Generally, the frequency bandwidth efficiency of the traditional wireless communication system stays around5bit/s/Hz. Utilizing high-order modulation can improve frequency bandwidth efficiency dramatically, while requiring exponential growth of transmitting power, which brings a limit in a real system. Hence, seeking another efficient modulation technology is always the hot spot in the field of communications research all over the world. Traditional modulation method just relies on sacrificing spatial complexity of signal or increasing transmitting power to improve frequency bandwidth efficiency, however, UNB (Ultra Narrow Band) modulation technology employs the mutation of carrier phase to carry symbol information. On one hand, it can raise frequency bandwidth efficiency tremendously, on the other hand, the output SNR (Signal to Noise Ratio) of receiver climbs up a lot as a consequence of the rather narrow bandwidth of system. This can be used to design the high-sensitivity receiver, promoting the value of simplicity and better anti-interference ability of UNB transmission. According to this significance, this paper focuses on the process of UNB transmission, analyzes and evaluates the performance of UNB modulation method.Firstly, this paper introduces the formation, development and research status in domestic and international field, and illustrates some primary UNB modulation methods. Taking the example of EBPSK (Extended Binary Phase Shift Keying), I analyze the waveform characteristics in time domain and frequency domain, simulate PSD (power spectral density) and determine indices (such as bandwidth, etc.) according to PSD.Secondly, two options of filters in transmitting terminal are studied and their theories are elaborated. This paper also compares two demodulation methods referring to the choice of modulation filter and decides proper demodulation method to judge receiving signal, with detailed analysis of the utilized integral amplitude decision algorithm. As a result, I conclude that adopting integral amplitude decision algorithm to demodulate signal can make the system performance derive optimal result, by placing digital impulse filter in both transmitting and receiving terminals.Finally, the paper researches the impact of the modulation parameters of UNB signal on performance and the improvement of anti-noise performance compared with other ways. And then simulates the Rayleigh channel by using Matlab and the Shadow fading channel by using a method combining the channel correlation distance with the channel correlation time selection, afterwards, analyzes the bit error performance of UNB signal in these two kinds of common fading channel.The innovations of this paper are listed as follows:First, this paper compares two demodulation schemes that digital phase-locked loop and amplitude integration decision algorithm, deriving the decision of using amplitude integration decision algorithm, which is simple as a demodulation scheme, and also improves the amplitude integration decision algorithm.Second, this paper improves transmission scheme of the system by adding the digital impulse filter to both the transmitter and the receiver. Compared to other schemes that only adds digital impulse filter to the transmitter or the receiver, this improvement makes BER performance better.Third, this paper uses Matlab to simulate the performance of UNB signal under fading channel and presents a selection method of parameters in shadow fading channel, and evaluates the performance of UNB signal.