**2. Telemetry system**

Telemetry is a technology that allows remote measurement, control, and reporting of information. In order to transmit the data throughout radiation, concept of the modulation have to be known.

#### **2.1 Modulation methods**

Modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with respect to a modulating signal. Fig. 1 shows block diagram of the modulation where the signal is modulated by the carrier signal. There are the three key parameters of the modulation, which is amplitude, phase, and frequency. Typically a high-frequency sinusoid waveform is used as carrier signal, but a square wave pulse train may also occur. Fig. 2 (a) depicts the modulation result that the baseband signal (*m*(*t*)) is up converted by carrier frequency (cos(*wct*)). The negative frequency is generated and bandwidth of the signal is remained.

Fig. 1. Block diagram of the modulation.

Fig. 2. Spectrum of frequency up converting.

Due to success of the capsule endoscopy, there are many trails to develop the capsule that has surgical operation, medical treatment, and locomotion abilities [27-33]. Most of researches are focused to give locomotion ability by using a magnet, actuator, and electrical stimuli. The aim of locomotion research is to observe a suspicious area because the capsule is naturally goes down to the aboral direction. Other researches do increasing friction to stop the capsule at the suspicious area [34, 35]. Also, there are many interesting capsules are developing such as a bleeding detection [36], assembling capsule[37], and biopsy [37]. From above description, application of the swallowable telemetry capsule is abundant and it is rapidly cutting its edges. In order to transmit the physiological data or control the capsule, a telemetry system is essential part for stable module. In this chapter, a basic telemetry methods are describe in 2.1 to 2.2 and describe important points for swallowable capsule in the 2.6. Therefore, the reader who is familiar of a communication technique should skip the

Telemetry is a technology that allows remote measurement, control, and reporting of information. In order to transmit the data throughout radiation, concept of the modulation

Modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with respect to a modulating signal. Fig. 1 shows block diagram of the modulation where the signal is modulated by the carrier signal. There are the three key parameters of the modulation, which is amplitude, phase, and frequency. Typically a high-frequency sinusoid waveform is used as carrier signal, but a square wave pulse train may also occur. Fig. 2 (a) depicts the modulation result that the baseband signal (*m*(*t*)) is up converted by carrier frequency (cos(*wct*)). The negative frequency is generated

2.1~2.5 and read the 2.6 directly.

**2. Telemetry system** 

**2.1 Modulation methods** 

and bandwidth of the signal is remained.

Fig. 1. Block diagram of the modulation.

Fig. 2. Spectrum of frequency up converting.

have to be known.

Fig. 3 depicts common analog modulation methods that is known as amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM). The latter two types of modulation are similar, and belong to the class of modulation known as the angle modulation.

The AM is characterized by the fact that amplitude of carrier signal is varied in proportion to the baseband signal. In the fig. 3 (c) depicts modulated AM signal and it could be easily see the amplitude of the signal is varying with the baseband signal. The FM conveys information over a carrier wave by varying its instantaneous frequency. In the fig. 3 (d) depicts the frequency of the carrier signal is changed from the baseband signal. The PM is a form of modulation that represents information as variations in the instantaneous phase of a carrier wave. In the fig. 3 (e) depicts that the phase of the signal is varying with the baseband signal.

Fig. 3. Simple example of the modulated signal.

With using analog modulation system, the super heterodyne system is widely used due to its simplicity, cheap, and high performance. Fig. 4 depicts the super heterodyne system that uses frequency mixing or heterodyning to convert a received signal to a fixed intermediate frequency (IF). With using the IF, it is easily tuning the channel and can reduce performance of the band filters.

Communication Strategies for Various Types of Swallowable Telemetry Capsules 45

With help the I/Q modulator, various digital modulation is generated such as BPSK, O-PSK, GMSK, and QAM. The Fig. 6 depicts that the BPSK signal that vary with input baseband signal. Unlike analogy modulation, the digital modulation uses digitalized baseband signal

A spread-spectrum system is a process other than the information signal to expand, or spread, the bandwidth of the signal. The spread-spectrum method is that breaks the data signal into little pieces using some kind of code, and the transmitted signal with wide bandwidth. Therefore, it is hard to tap and find the signal. There are four types are used for spectrum spreading such as direct sequence, frequency hopping, time hopping, and

Fig. 7 depicts a direct sequence spread spectrum (DSSS) technique is that multiply the data by the pseudonoise (PN) code, and spreading the energy of the original signal into a much wider band. The spread signal resemble the white noise, which looks like wide band noise,

Another method to spread spectrum is using frequency-hopping spread spectrum (FHSS). The FHSS is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence. Fig. 8 depicts the block diagram of the FHSS. Unlike the DSSS, the spectrum the FHSS shows vary shape impulses

and the modulated signal is discontinued.

Fig. 6. I/Q modulator and demodulator.

and it could be dispreading when PN code is known.

Fig. 7. Diagram of direct-sequence spread spectrum.

and disappear immediately.

**2.2 Spread spectrum** 

frequency chirp.

Fig. 4. Block diagram of traditional super heterodyne detection system.

Unlike analogy modulation, the digital modulation uses digitalized baseband signal and inphase/quadrature (I/Q) modulator, which can actually create the AM, FM, and PM modulation with in one hardware. The fig. 5 depicts the I/Q modulator and demodulator system that has two mixer with same carrier signal with –pi/2 lag. The I/Q modulator can modulate a carrier with a waveform that changes the carrier's frequency slightly; you can treat the modulating signal as the phasor. It has both a real and an imaginary parts, or an inphase (I) and a quadrature (Q) part. Now construct a receiver that locks to the carrier, and you can decipher information by reading the I and Q parts of the modulating signal.

Fig. 5. I/Q modulator and demodulator.

With help the I/Q modulator, various digital modulation is generated such as BPSK, O-PSK, GMSK, and QAM. The Fig. 6 depicts that the BPSK signal that vary with input baseband signal. Unlike analogy modulation, the digital modulation uses digitalized baseband signal and the modulated signal is discontinued.

Fig. 6. I/Q modulator and demodulator.
