Analog and Digital Technology: A Comparison

Analog and Digital Technology: A Comparison

NTC362

University of Phoenix

Analog and Digital Technology: A Comparison

Analog to digital conversions techniques begin with the transmission of the information without reproduction of the original information minus the degradation with signal distortion or noise by the binary signal. T. T. (2011). "The binary signal consists of two values characterized by binary digits or bits 1 and 0. Unless the noise and distortion is picked up during transmission then the binary signal will not change. The value is measure by the receiver so that the reception is clear. If the information to be transferred is already in binary form as in data communications there isn't any need for the signal to be encoded. Voice communication thru the method of the telephone is not in binary form. These signals vary in range of values are analog and within the digital communications system analog signals must be converted to digital form."

Digital to Analog conversions involve a conversion process with DAC. This devise takes the binary code converting it to the analog signal. Digital to analog signals can compromise the quality of the signal, if it is not actively monitored. Analog lines, which are also known as POTS lines usually support standard phone lines, fax machines or alarm lines, keeping them separate from the digital PBX equipment. An example of digital to an analog signal would be the use of a modem for Internet use that converts computer digital signals using POTS lines.

Advantages and Disadvantages of Common Modulation Techniques

Amplitude Modulation

Analogsignals have four modulation techniques. The most simple of the four is Amplitude Modulation (AM). AM transmits data by varying the intensity of the waves. The most common use for AM is transmitting radio stations. AM is very simple by design thatmakes it the least costly method of transmitting data. The main disadvantage with AM is how easily the transmission can contain interference. AM signals also use more energy than other types of modulation methods.

Frequency Modulation

Frequency Modulation (FM) is also most commonly used in broadcasting radio stations. FM transmits data by using multiple frequencies of the signal as opposed to the varying the intensity wave. Using multiple frequencies makes FM transmissions less susceptible to line interference. Disadvantages of FM are the amount of bandwidth required. It is much higher than that of other methods. FM is also much more complicated and requires more complicated equipment.

Phase Modulation

Phase Modulation (PM) is similar to FM. PM; however, uses two waves, whereas FM only uses one. The first wave sends out the signal normally, and the second sends out the signal up to 180 degrees out of phase. PM is much simpler than FM because only the phase varies, not the frequencies. Many of the complex circuits needed to measure the frequencies in FM are not needed in PM. A disadvantage of PM is the creation of phase ambiguity when the modulation signal exceeds 180 degrees.

Quadrature Amplitude Modulation

Quadrature Amplitude Modulation (QAM) can send multiple signals on one carrier. When using QAM in modems both the amplitude and the phase of the signals vary, this causes the transmissions to be much faster than any of the other modulation techniques. A disadvantage is how susceptible QAM is to noise and interference. Another disadvantage is that QAM requires the use of linear amplifiers. Linear amplifiers use much more energy and makes them not very popular in mobile devices.

Applications of Modern Modulation Techniques

From dial-up to DSL to Wi-Fi, modulation techniques continue to increase throughput and improve quality through optimization. The current networking technologies are 100 plus years in the making, but it seems as though each year brings about a new advancement, and each new generation of networking technology can be marked by a new or improved modulation technique. Although hardware is significant, as it often makes new modulation techniques possible, with the current developmental state of communication technology, it is advancements in modulation that get noticed as significant.

V.90

Starting with dial-up connections, as it was a major milestone of information technology as it is know today, the creation of the 56k (V.90) modem marked the peak of the technology. If fact, after a decade, V.90 modems are still widely used still. V.90 modems use a very simple PAM consisting of 8000 symbols per second each coded from seven bits of each eight bit PCM word. The result is 128 amplitude levels in the signal. Upstream of V.90 modems are limited to the older V.34 modulation and is only capable of 33.6 Kbps.

ADSL

Asymmetric Digital Subscriber Lines (ADSL) marked a huge step forward in consumer connectivity, and the best part about it was that it made use of current twisted pair telephone lines, which at the time almost every home in America already had active. The advancement from Dial-up to DSL was made possible by a combination of modulation techniques. Carrierless Amplitude Phase CAP, a form of QAM developed by AT&T, was used in early implementations of ADSL; however, it has been replaced by Discrete Multi-tone Modulation (DMT), which is currently the universally standardized ADSL modulation method. Therefore, only DMT is covered in detail.

DMT, also a form of multicarrier modulation, splits available bandwidth into sub-channels, each using QAM modulation on a separate carrier to maximize throughput. DMT for ADSL divides the downstream bandwidth into 4.3125 kHz wide channels and the upstream bandwidth into 32 4.3125 kHz wide channels (Alturayef & Rodriguez, 2007). The result is a throughput of about 8.1 Mbps downstream and a 1.5mbps upstream.Because it has to coexist with POTS, the first six channels are reserved for voice allowing ADSL and POTS to function simultaneously.

802.11(x)

802.11 commonly referred to as Wi-Fi, marked a huge step forward in modern connectivity, one people are still working to build upon. Once again, modulation has played a very important role in the development of 802.11 from its original throughput of one to two Mbps to the 504 Mbps capabilities of today's standard 802.11n. The first widely adopted Wi-Fi standard was 802.11b operating in the 2.4 GHz spectrum. To reach its top speed of 11Mbs, 802.11b used