Analog Vs Digital Data
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Electromagnetic Signals • • •
An electromagnetic Signal varies from time to time It may be represented as a – Function of time Also, it may be represented as a – Function of frequency
The information carrying signals are divided into two broad classes; 1. Analog (Voice , images) 2. Digital (Text, Digitize Voice or images) Analog signals
Analog signals are continuous electrical signals that vary in time as shown in figure. Most of the time, the variations follow that of the non-electric (original) signal. Therefore, the two are analogous hence the name analog. Not all analog signals vary as smoothly as the waveform shown in Figure 4a. Analog signals represent some physical quantity and they are a ‘MODEL’ of the real quantity.
Example: Telephone voice signal is analog. The intensity of the voice causes electric current variations. At the receiving end, the signal is reproduced in the same proportion. Hence the electric current is a ‘MODEL’ but not one’s voice since it is an electrical representation or analog of one’s voice. Digital Signal Digital signals are non-continuous, they change in individual steps. They consist of pulses or digits with discrete levels or values. The value of each pulse is constant, but there is an abrupt change from one digit to the next. Digital signals have two amplitude levels called nodes. The value of which are specified as one of two possibilities such as 1 or 0, HIGH or LOW, TRUE or FALSE and so on. In reality, the values are anywhere within specific ranges and we define values within a given range. Digital Data • Represented as a sequence of discrete symbols from a finite “alphabet” of text and/or digits • Rate and capacity of a digital channel measured in bits per second (bps) • Digital data is binary: uses 1s and 0s to represent everything • Data encoded in strings – ASCII, Unicode (UTF), etc • Data is often redundant – the same information is repeated several times
Channel Capacity • •
The rate at which data can be transmitted over a given path, under given conditions Four concepts (Data rate, Bandwidth, Noise, Error rate)
Bandwidth • • •
Width of the spectrum of frequencies that can be transmitted – if spectrum=300 to 3400Hz, bandwidth=3100Hz Greater bandwidth leads to greater costs Limited bandwidth leads to distortion
Impairments and Capacity • • •
Impairments exist in all forms of data transmission Analog signal impairments result in random modifications that impair signal quality Digital signal impairments result in bit errors (1s and 0s transposed)
•
Attenuation – loss of signal strength over distance
•
Distortion – the shape of a signal changes as it travels further Noise – Thermal Noise (White noise) – Impulse Noise – Crosstalk: interference from adjacent signals
•
•
Refraction – Refraction is the bending of radio waves due to changes in atmospheric conditions. – Typically, radio waves travel faster at higher altitudes causing the waves tend to bend downward.
Period (T): amount of time it takes for one repetition Phase (φ): relative position in time, measured in degrees Frequency (f): repetition rate, no of cycles per second or Hertz ( T = 1/f) Amplitude (A): signal value, measured in volts
An electromagnetic Signal varies from time to time It may be represented as a – Function of time Also, it may be represented as a – Function of frequency
The information carrying signals are divided into two broad classes; 1. Analog (Voice , images) 2. Digital (Text, Digitize Voice or images) Analog signals
Analog signals are continuous electrical signals that vary in time as shown in figure. Most of the time, the variations follow that of the non-electric (original) signal. Therefore, the two are analogous hence the name analog. Not all analog signals vary as smoothly as the waveform shown in Figure 4a. Analog signals represent some physical quantity and they are a ‘MODEL’ of the real quantity.
Example: Telephone voice signal is analog. The intensity of the voice causes electric current variations. At the receiving end, the signal is reproduced in the same proportion. Hence the electric current is a ‘MODEL’ but not one’s voice since it is an electrical representation or analog of one’s voice. Digital Signal Digital signals are non-continuous, they change in individual steps. They consist of pulses or digits with discrete levels or values. The value of each pulse is constant, but there is an abrupt change from one digit to the next. Digital signals have two amplitude levels called nodes. The value of which are specified as one of two possibilities such as 1 or 0, HIGH or LOW, TRUE or FALSE and so on. In reality, the values are anywhere within specific ranges and we define values within a given range. Digital Data • Represented as a sequence of discrete symbols from a finite “alphabet” of text and/or digits • Rate and capacity of a digital channel measured in bits per second (bps) • Digital data is binary: uses 1s and 0s to represent everything • Data encoded in strings – ASCII, Unicode (UTF), etc • Data is often redundant – the same information is repeated several times
Channel Capacity • •
The rate at which data can be transmitted over a given path, under given conditions Four concepts (Data rate, Bandwidth, Noise, Error rate)
Bandwidth • • •
Width of the spectrum of frequencies that can be transmitted – if spectrum=300 to 3400Hz, bandwidth=3100Hz Greater bandwidth leads to greater costs Limited bandwidth leads to distortion
Impairments and Capacity • • •
Impairments exist in all forms of data transmission Analog signal impairments result in random modifications that impair signal quality Digital signal impairments result in bit errors (1s and 0s transposed)
•
Attenuation – loss of signal strength over distance
•
Distortion – the shape of a signal changes as it travels further Noise – Thermal Noise (White noise) – Impulse Noise – Crosstalk: interference from adjacent signals
•
•
Refraction – Refraction is the bending of radio waves due to changes in atmospheric conditions. – Typically, radio waves travel faster at higher altitudes causing the waves tend to bend downward.
Period (T): amount of time it takes for one repetition Phase (φ): relative position in time, measured in degrees Frequency (f): repetition rate, no of cycles per second or Hertz ( T = 1/f) Amplitude (A): signal value, measured in volts
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