A Novel Ultra-Wide Band Signal Generation Scheme Based on Carrier Interference and Dynamics Suppression
© Luyong Zhang et al. 2010
Received: 15 December 2009
Accepted: 6 April 2010
Published: 16 May 2010
This paper initiatively puts forward a novel synthesis design for generating UWB narrow pulse by using CI (Carrier Interference) subcarrier waveform synthesis and Bessel function expansion. Through adaptively adjusting the initial phases of multiple sub-carriers according to the location information, CI (Carrier Interference) sub-carrier waveform synthesis signal could achieve better performance. More specifically, when the carrier arrives at the receiver with a particular phase, the dynamic change of this signal amplitude can be significantly reduced by introducing sinusoidal frequency modulation signals. The method has significance for improving the overall performance of UWB communication system. This paper gives theoretical analysis and computer simulation results as well as the functional block diagram.
Ultra-wide bandCI pulse waveform method is one of the current UWB signal generation methods based on the idea of multiband UWB signal design. In sensor networks, there is always a large dynamic change on the communication signals between cluster head and inner-cluster node when multiple wireless sensors communicate using UWB signals because of the uncertainty of node location distribution . This dynamic change of signal amplitude can be significantly reduced by introducing sinusoidal frequency modulation signals which has very important significance on improving the transmission performance of wireless sensor networks and reducing the device costs of nodes. CI can produce narrow pulse signals synthesized by multiple coherent carriers, and adaptively adjust the initial phase of multiple sub-carriers by location information so that the carrier amplitude could get the maximum when the carrier arrives at specified location which means the carrier amplitude may be too low when the carrier arrives at distant specified location.
The low dynamic interference telecommunication signal methods based on BESEL function expansion, which has the advantage of low dynamic and multicarrier interference superposition, has a strong penetrating and low intercept probability.
where represents the unit amplitude gate function with the period , A is a scale factor in order to ensure the unit energy. The Interferometry CI time-domain pulse waveform is simplified as CI waveform because it is introduced by Interferometry method.
2. Proposed UWB Signal Generation Scheme
The UWB signal has a relationship with primary users in spectrum reuse. Thus, the transmit power of UWB signal is strictly limited in order to avoid the interference to primary users, which requires low Bit Error Rate(BER) in the situation of low Signal to Noise Ratio (SNR) . This invention proposes a scheme of UWB signal generation based on distance awareness. We should determine the distance between transmitted end and its intended end in order to adaptively adjust multiple sub-carriers' initial phases and assemble their peak in a specified location. The scheme adds sinusoidal frequency modulation signal while adjusting sub-carriers' phases and introduces the first-order Bessel function in order to cancel out space spread channel fading. Receiver receives signals in specified location in order to get an excellent BER performance even in the situation of low SNR.
We can adjust the initial phase ofn th subcarrier as , and generate the pulse signal, followed by the process of frequency modulation. Thus, the initial phase ofn th subcarrier is modified as , where is the modulation index, the term is the baseband frequency modulation signal, and the related parameters must satisfy the inequalities; and .
- (4)We adopt the IFFT transform for the signals which have finished the phase and frequency modulation. The transformed time-domain signal can be expressed as follows :
Then through the multicarrier-tuned filter, we can derive the first-order Bessel function expansion components, thus mitigate the transmission attenuation for the UWB transmission scheme.
At the intended receiver, we can demodulate the received signal as follows: first we sample the received signal at the time , if , where is a predefined threshold, then we determine the received data , otherwise, .
The scheme of UWB signal generation is based on distance awareness. The distance awareness module is used to measure the distance between transmits end and its intended end. UWB signal generation module is used to generate the signal which is available to the communication between transmits end and its intended end.
Multiple sub-carriers' initial phases are adjusted adaptively according to the result of distance awareness module. At the same time, the scheme introduces the first-order Bessel function in order to generate multicarrier signals with sinusoidal frequency modulation.
The distance awareness module can be obtained by UWB distance measure system. UWB pulse has a strong ability to be time-resolved for the duration is as short as nanoseconds because of its very high bandwidth. The UWB distance measure system usually gets the distance between transmit end and its intended end by estimating the time of arrival (TOA) of first component among receiving signals and then calculates the distance of two ends. The TOA algorithm gets the transmission time interval between two ends by estimating the direct path (DP) of receiving signals and thus calculates the distance. According to the recent research, the TOA algorithm can reach centimeter-level accuracy.
In the following subsection, we give the details about the above signal generation scheme.
where is the initial phase, and denote the frequency lower bound and upper bound of the transmitted signal, respectively. Here we adjust the initial phase according to the distance-aware based information, thus ensure each sinusoidal sub-carrier to reach the peak value at the intended receiver.
It is noted that from (13), the signal attenuation is sufficiently reduced.
3. Simulation Results
The UWB signal has flexible spectrum characteristics. The carriers of the UWB signal consists of multiple sub-carriers which results in flexible spectrum characteristics. This feature makes the UWB signal available to the flexible spectrum allocation strategy of Cognitive Radio. We can adjust the parameters of sub-carriers such as number, distribution, frequency interval and other parameters according to the available spectrum hole, the distance between two ends, the requirements of ranging accuracy the information transmission rate and so on. Thus the UWB signal can be better applied to realistic communication environment.
The peak value overlap of multiple sub-carriers based on distance measuring greatly improve the BER performance of communication system.
By adjusting the initial phase, the peak values of multiple sub-carriers are overlapped at the receiver end, and the sub-carriers at any location between transmitter and receiver are cancelled each other. Modern distance measuring technique can achieve centimeter order precision, and the correlation demodulation at receiver end can greatly increase the processing gain, so the system BER performance can be significant improved on the basis of precise distance measurement.
Through the adjustment of multiple sub-carriers' initial phases, the interference UWB signals based on distance awareness enable receiver to receive maximum amplitude of synthetic signals which brings great benefits for reducing interception probability and improving the received signal to noise ratio (SNR). The UWB signals can inhibit channel fading and reduce the dynamic changes of received signals as well as costs of receiver by introducing low frequency sinusoid frequency modulation signals and first-order Bessel function expansion. The simulation results have verified the theoretical analysis in this paper. The further research includes relationship between parameter design and realistic communication environment and improvement of whole system performance to make it more flexible and adaptive.
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