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With improvement of the automation level, wireless sensors are widely used, but various kinds of interference lead to problems in the application. In order to deal with co-channel interference, a throughput efficient scheme based on Extended Binary Phase Shift Keying (EBPSK) modulation is introduced in physical layer. On this basis, the corresponding transmission scheme and the important impacting filter are presented. Effects of co-channel interference on the EBPSK waveform in different cases are analyzed. Simulation results illustrate the excellent anti-interference performance of the EBPSK system itself, when the initial phase of the co-channel interference is small.

With recent developments in modern science technology, various types of sensors have been widely used in industry, agriculture, aerospace, aviation and other fields, to allow the production process a high level of automation. However, the interference suppression in the application of wireless sensors is a very difficult problem, which affects the control precision and accuracy of the whole system. Therefore, a variety of anti-interference measures to improve system stability and accuracy are inevitable, which has been a subject of intense research. The usual methods include shielding technology, filtering technology, isolation measure and grounding technology,

This paper considers this problem in physical layer directly in order to remove the complicated anti-interference module. In our research, we have found that the Ultra Narrow Band (UNB) system [

All in all, aiming at the interference problem in wireless sensors networks, this paper proposes a simple solving scheme of physical layer, which is based on EBPSK modulation with ultra narrow bandwidth. Simultaneously, the anti-interference performance of the EBPSK system itself is mainly discussed. When the initial phase of the co-channel interference is small, the EBPSK system has good anti-interference characteristics, which has been analyzed by intuition and proved by simulation results. While with the increasing of the initial phase, the anti-interference performance of system itself decreases, so the usual anti-interference methods can be considered to solve it.

The paper is organized as follows. The EBPSK modulation and the analysis of the related parameters are introduced in Section 2. Section 3 presents the scheme of EBPSK transmission system. The effects of co-channel interference are analyzed and verified experimentally in Section 4. Then BER simulation results are given in Section 5. Finally, Section 6 gives some conclusive remarks.

EBPSK [_{0} (_{1} (_{c}_{c}_{c}_{c}_{c}

In EBPSK modulation, the modulated waveforms corresponding to “0” and “1” have a very tiny difference, and the most parts of the waveform are sine components, therefore, having compact power spectra [

The modulation waveform corresponding to code “1” can be regarded as the superposition of all-zero sequence (

Reference [_{1} = −4.5781931992746454, _{2} = 9.6546659241157258, _{3} = −11.692079 480819313, _{4} = 8.5756341567768217, _{5} = −3.6121554794765309, _{6} = 0.70084076 00731199

Considering co-channel interference, if its initial phase is 0, the added interference can be thought of as the amplitude increasing of all-zero sequence in the decomposed sequences,

When signal power remains unchanged, the amplitude of the interference decreases with the increasing of SIR,

In this section, computer simulation results of bit error rate (BER) are given to illustrate the good anti-interference characteristics of the EBPSK system, where the transfer function of the filter is chosen as (2), _{c}

First, we consider BER performances in different SIR cases. Outwardly, according to Section 3.2, the impulse amplitude of jumping part increases with the decrease of SIR, but simultaneously the amplitude of non-jumping part corresponding to “0” is also improved, _{0} (_{1} (_{0} increases, _{0} (_{1} (

In this section, the effects of the co-channel interference with different initial phases on BER performance are simulated.

Obviously, in both cases, BER curves have almost the same change tendency with the increasing of the initial phase. When the initial phase of the interference is from 0 to 0.4

When the initial phase of the interference is small, the interference plays the enhancement role for the signal, analyzing as Section 4.1, so the BER performances are similar in the different SIR cases. On the other hand, when the initial phase becomes larger, the interference has negative effect on the original signal, especially greater on the amplitude of the jumping part, so that the waveform amplitude after filtering decreases greatly, and the amplitude difference between jumping part and non-jumping part decreases thereupon, also as shown in

^{−4}, the required SNR is given for the different initial phase, which indicates the effects of the initial phase on BER more clearly.

In this paper, aiming at the interference problem in wireless sensor networks, a simple solving scheme of physical layer is proposed, which is based on EBPSK modulation.

EBPSK modulation as a new idea, which takes some current binary modulations as its special examples, has good flexibility, universality and good possibilities for new high speed and high efficiency transmission [

The special impacting filter can transform the tiny waveform difference into amplitude impacting, so that the receiver structure can be simplified by threshold detection [

This paper discusses the anti-interference performance of EBPSK system itself. When the initial phase of the co-channel interference is small, EBPSK system has good anti-interference characteristics, which has been analyzed by intuition and proved by simulation results. While with the increasing of the initial phase, the anti-interference performance of system itself decreases, so the usual anti-interference methods can be considered to solve it. Therefore, the anti-interference performance may extend the use of EBPSK system in interference environments. Researches on this problem are underway, so for the case of the large interference initial phase, the detailed anti-interference scheme based on the EBPSK system would be given in the forthcoming papers.

The authors would like to thank the National Foundation of China (60872075), the Natural Science Foundation of Jiangsu Province (BK2007103), China Postdoctoral Science Foundation (20080441015), Jiangsu Planned Projects for Postdoctoral Research Funds (0802005B) and Southeast University Planned Projects for Postdoctoral Key Research Funds.

The decompose of the EBPSK signal. (a) EBPSK signal. (b) Pure sine wave. (c) Jumping sequence.

The response of the decomposed sequence to the filter. (a) The response of the EBPSK signal to the filter. (b) The response of the pure sine sequence to the filter. (c) The response of the jumping sequence to the filter.

The effect of different initial phase on impulse amplitude. (a) No interference. (b) The initial phase of the interference is 0. (c) The initial phase of the interference is

Effects of different SIR on time-domain waveform. (a) EBPSK modulation signal. (b) EBPSK signal after filter (no interference). (c) Interfered EBPSK signal after filter (

The sketch map of the detection performance by pdf.

BER performances in different SIR.

Effects of different initial phases on BER performance.

The SNR loss produced by co-channel interference.