This imposes a limit on the sensor detection speed, http://www.selleckchem.com/products/Imatinib(STI571).html number of sensors, and maximum distance between sensors [5]. The CDMA system utilizes the autocorrelation property to separate individual sensors from the multiplexed output of many sensors [6]. To identify each sensor, a pseudo-random binary sequence (PRBS) code is sent as a random signal into the FBG sensor array, and the information of the corresponding sensor is decoded in the electrical domain [7].In this paper, we report a CDMA sensor network based on a sliding correlation method [8,9] that provides a higher scanning rate than a conventional CDMA scheme [7]. Further, a wavelength-to-time conversion technique is introduced to provide a wide dynamic range to FBG sensors.
This conversion is implemented using a wavelength dispersive medium, so the change in the center wavelength of each sensor is converted into a time shift in the correlation peak. Moreover, by using a wideband reflective semiconductor optical amplifier (RSOA) as an optical source, WDMA can be integrated with FBG sensors having different center wavelengths.2.?Proposed CDMA Sensor NetworkThe basic concept of a proposed FBG sensor network system is to use a wavelength shift caused by external strain. The grating period of the FBG is changed when the external strain is applied to the sensor. As a result, the center wavelength of the reflected light is also changed. Depending on the distance between FBG sensor and photodetector (PD), the incoming sensor information has a time delay and it is merged into the PD through the wavelength-to-time converter, which changes the wavelength shift into a time shift.
For a CDMA application based on a correlation technique, an electrical signal with a random data pattern is split into two signals: one is applied to the optical source and the other is applied to the mixer at the detector to obtain the autocorrelation peak. In conventional CDMA, time delays from all sensors should be compensated for before mixing. This makes it difficult to expand a system to accommodate new sensors in a practical application. To overcome this, a sliding correlation method is employed in the proposed sensor system.A proposed conceptual diagram of a CDMA sensor network using sliding correlation is shown in Figure 1. To cover the whole wavelength band of all sensors, a broadband light source is used.
Then, we apply two different random signals, with the same data patterns, but slightly different frequencies, to the optical modulator and the mixer. This slight difference in frequency has a scanning effect Anacetrapib and thereby gives an autocorrelation output without any information about the time delay between the two signals fed towards the PD. As a result, whenever sensors are added to the network, Trichostatin A cost the time delays from the source to the mixer need not be measured.