Modulation digital

All of the digital modules are installed inside the industrial PC as shown in Figure 2. 2.10. The major functions of the MRI digital system are implemented by three commercially available ISA boards. 

A much simpler expression for the peak height is obtained, however, if a digital modulation of the form shown in Figure 4.2B is applied in which Av(r) jumps between peak positive and negative values Av with an intermediate pause at zero. This is synchronised to waveform A and detected by waveform C. If the source is tuned to the peak frequency Vq its modulated frequency simply jumps back and forth between the line peak and a symmetrical offset on each side, generating a square wave of angular frequency 2(o and amplitude ... 

Figure 4.2 Digital modulation strategies for phase-coherent detection. A is the synchronising waveform B C and D E are modulation and detection pairs. For full explanation see text...

This paper is organized as follows section 2 introduces the S-K analog filter circuit section 3 describes how to establish the numerical model for low-pass S-K filter section 4 shows a simulation and an application of this digital module in infrasound signal processing. Conclusions and some more future research work are drawn in Section 5. 

TABLE 12.9 Characteristics of Coherent Binary Digital Modulation Schemes... 

There are many other important digital modulation formats that have not been discussed here. In this section, several of these will be mentioned with appropriate references given so that the reader will have a place to start to learn more about them. 

Bandwidth efficiency The ratio of bit rate to bandwidth occupied for a digital modulation scheme. 

Digital modulation The variation of some attribute of a carrier, such as amplitude, phase, or frequency, in a one-to-one correspondence with a message taking on a discrete set of values. 

Power efficiency The energy-per-bit over noise power spectral density (Ej/No) required to provide a given probabihty of bit error for a digital modulation scheme. 

ProbabUity of (bit) (symbol) error The average number of symbol errors over a long string (ideally infinite) of transmitted signals for any digital modulation scheme. If expressed in terms of the number of bits per symbol, the probability of bit error results. 

Quadrature-amplitude-shift keying (QASK) A digital modulation scheme in which both the phase and... 

Frequency modulation (FM) has been the most widely used modulation. However, advances in digital voice and video compression have led to the widespread use of digital modulation methods such as quadrature phase shift keying (QPSK) and quadrature amplitude modulation (QAM) (Schwartz, 1990 Sklar, 1988). 

High-power direct broadcast satellites (DBS) or direct-to-home (DTH) satellites operate atKu-band. In the U.S., satellites operating in the broadcast sateUite service (BSS) with downlink frequencies of 12.2-12.7 GHz, deliver TV directly to home receivers having parabolic dish antennas as small as 46 cm (18 in) in diameter. DBS with digital modulation and compressed video is providing more than 150 National Television Systems Committee (NTSC) TV channels from a single orbital location having an allocation of 32 transponder channels, each with 24-MHz bandwidth. 

For digital modulation systems, bit error rate (BER) is related to the dimensionless ratio (decibel difference) of energy per bit, dB 1 to the total noise power density N = 10 log(fcT) dB J (Sklar, 1988). For thermal... 

The degradation to a digital link from interference follows a form similar to that of Eq. (16.67) but in terms of ey I tio, where the lower case quantities refer to numerical ratios. For a Hnk that is subject to a given additive white noisehke interference power expressed as a ratio of desired signal power to interference power c/i, and assuming digital modulation with m bits per symbol. 

Fast frequency shift keying (FFSK) A system of digital modulation where the digits are represented by different frequencies that are related to the baud rate, and where transitions occur at the zero... 

Frequency shift keying (FSK) A commonly used method of digital modulation in which a one and a zero (the two possible states) are each transmitted as separate frequencies. 

Because of the almost perfect accuracy, enormous amounts of digitally modulated information can be stored in small spaces. This is not because it is more efficient than analog methods — it is actually less efficient, in that it requires more operations to store the same amount of music, text, etc. However, the combination of photonic (Chapter 22) and integrated circuit (Chapter 23) technologies has allowed the inexpensive use of complexity crammed into small spaces, so using many operations to store or transmit data is no longer expensive. Some of the triumphs of these developments are apparent in Table 19.2. 

Although several of the latest inertial sensors contain the digital modules discussed here, we have opted to discuss those of accelerometers (such as the ADXL345 and the BMA150) as they both have promising features for wearable recognition tasks. 

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