RF wireless communication – Analog VS DIgital

Communication

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Radio Frequency (RF) wireless communication is the leading form of wireless communication as it is being used in TV, radio, cellular phone systems, wireless networking and several other applications. The advent of RF communications had seen the rise of analog systems which have now mostly been replaced by digital systems due to the advantages offered by the digital technologies. This article will present an overview of RF wireless technology, analog and digital wireless communication and will draw a comparison between the two RF technologies.

RF Wireless Technology

RF wireless communication systems have a transmitter and a receiver. Since the size of antenna has to be as large as one-fourth of the wavelength, the original signal (normally voice) cannot be transmitted without transferring it onto a higher frequency (smaller wavelength) that reduces size of the antenna. On the transmission side, the original signal (normally voice) is superimposed on a locally generated RF signal called a carrier – a process termed as modulation. The carrier signal containing the information, is then transmitted by the antenna; and then received at receiver where the information is extracted from the modulated carrier – a process called demodulation. During propagation of the signal in free space the signal becomes weaker and gets distorted due to noise and propagation effects like reflection, diffraction and scattering. Distortion effects are worse in mobile systems where the environment is changing from one moment to the other. The analog and digital RF technologies are in fact used to enable the transmission and reception while reducing the problems of distortion during propagation.

Analog Wireless Technology

In analog systems, signals of varying frequency or amplitude are used to modulate the carrier waves. Analog signals are continuously changing (infinite values) and are represented as a series of sine waves. The AM and FM radio transmissions are the most common examples of analog transmission.

Figure 1

Figure 1 – Original Signal, AM and FM Modulated Signals

In AM (Amplitude Modulation) the amplitude of the original signal (voice) is used to modulate the carrier and the transmitted signal has the information in the amplitude of the carrier wave. Whereas, in FM (Frequency Modulation) the frequency of the original signal (voice) is used to modulate the carrier and the transmitted signal has the information in the changing frequency of the carrier wave.

The first generation (1G) mobile cellular standards like AMPS (Advanced Mobile Phone System) and NMT (Nordic Mobile Telephone) were based on analog communication technologies. These were introduced in 1980s and were replaced by 2G standards which were based on digital cellular technologies by end 1990s or early 2000s.

Figure 2

Figure 2 – AMPS Phone

Digital Wireless Technology

In digital systems, signals are discrete (finite or limited set of values) in time and value and are represented by binary numbers, “0” or “1” (each called a bit).

Figure 3

Figure 3 – Original Signal, Analog and Digital Signal

The digital signals can be generated by sampling of continuous (analog) signal where the digital signal tries to approximate the values of analog signal in small discrete steps.

Figure 4

Figure 4 – Analog to digital conversion

The modulation techniques of digital wireless signal are more complicated than those of analog signals. Since the frequency spectrum is required to be shared among users in an area, digital RF technologies provide a number of multiple access techniques.

  • In FDMA (frequency division multiple access), spectrum is divided into frequency slots where each slot is assigned to a single user at any one time.

  • In TDMA (Time Division Multiple Access), frequency spectrum is divided into time slots where each slot is assigned to a single user at any one time.

  • In CDMA (Code Division Multiple Access) all users use the same carrier frequency and may transmit simultaneously. Each user has its own pseudorandom code word which is used at the receiver to identify the sender. CDMA is a digital technique which allows 8-15 times more users to be accommodated in the same bandwidth as compared to analog technologies.

The latest cellular technologies GSM, 3G and 4G LTE all are examples of digital technologies. Digital technologies offer several advantages over analog systems especially a large number of users can be accommodated in the available bandwidth.

Comparison – Analog vs Digital RF Wireless Technologies

  • Noise: Analog signals are less tolerant to noise whereas digital signals are much more tolerant to noise.

  • Data Integrity: Using analog technologies, errors during transmission can corrupt the message. In Error correction techniques are used to regenerate message and provide immunity against noise.

  • Bandwidth: Analog signals require less bandwidth whereas digital signals require more bandwidth. However, digital technologies can accommodate more users in the same bandwidth as compared to analog signals.

  • Users / Multiple Access: In analog techniques, less users can be accommodated in a given bandwidth whereas using digital techniques more users can be accommodated in a given bandwidth due to more efficient multiple access techniques.

  • Multiplexing: More channels can be multiplexed in a given bandwidth in digital technologies as compared to analog.

  • Flexibility of hardware: In analog systems, hardware is not flexible. It is specific and required to be changed with change in frequency. However, in digital systems the hardware is flexible where RF Signals can be handled by simple, standardized receivers and transmitters, and the digital signal can be then dealt with in baseband or software.

  • Size of Hardware: The transmitter and receiver in analog systems are large in size whereas digital systems are much small in size.

  • Services: Analog systems are used for voice and video services. Digital systems are used for voice, video and data.

  • Storage: Analog signals cannot be stored on computer whereas digital signals can be easily processed and stored on computer.

  • Signal mixing: Analog signals cannot be easily mixed whereas multiple digital signals can be easily mixed.

  • Packet networks / Internet: Analog signals cannot be packetized (unless digitized). Whereas digital signals can be packetized to send over packet networks like Internet.

  • Compression: Limited compression is possible in analog signals whereas higher compression can be achieved in digital signals.

Serial

Factor

Analog

Digital

1

Data Continuous Discrete (finite)

2

Representation Uses continuous range of values to represent information Uses discrete or discontinuous values to represent information

3

Signalling Continuously varying electromagnetic wave Sequence of voltage pulses

4

Waves Denoted by sine waves Denoted by square waves

5

Noise Less tolerant to noise More tolerant to noise

6

Data Integrity Errors during transmission can corrupt the message Error correction techniques are used to regenerate message and provide immunity against noise

7

Bandwidth Low bandwidth High bandwidth

8

Users / Multiple Access Less users can be accommodated in a given bandwidth More users can be accommodated in a given bandwidth due to better multiple access techniques

9

Multiplexing Less channels can be multiplexed More channels can be multiplexed

10

Flexibility of hardware Hardware is not flexible. It is specific and required to be changed with change in frequency Flexible. RF Signals can be handled by simple, standardized receivers and transmitters, and the digital signal can be then dealt with in baseband or software.

11

Hardware size -Transmitter and receiver Large in size Small in size

12

Services Voice and video Voice, video and data

13

Storage Not easily stored on computer Easily stored on computer

14

Signal mixing Cannot be mixed Can be easily mixed

15

Packet networks / Internet Cannot be packetized Can be packetized to send over packet networks like Internet

16

Compression Limited compression possible Higher compression can be achieved