Huiswerkopgaven 5b - numerical problems

10 important questions on Huiswerkopgaven 5b - numerical problems


The American Standard Code for Information Interchange (ASCII) uses 128 distinct characters, each encoded in binary. A computer generates 120 000 characters per second
(a) How many bits are required to represent one ASCII character

(a) n = log2 128 = 7 bits per character.


The American Standard Code for Information Interchange (ASCII) uses 128 distinct characters, each encoded in binary. A computer generates 120 000 characters per second.


(b) What bit rate (bits/s) is needed to transmit the computer output? What is the minimum transmission bandwidth


(b) Bit rate: 120,000 × 7 = 840,000 bit/s = 840 kbps. By the Nyquist criterion the minimum bandwidth is BT = Rb/2 = 420 kHz.




The American Standard Code for Information Interchange (ASCII) uses 128 distinct characters, each encoded in binary. A computer generates 120 000 characters per second.

(a) n = log2 128 = 7 bits per character.
(b) Bit rate: 120,000 × 7 = 840,000 bit/s = 840 kbps. By the Nyquist criterion the minimum bandwidth is BT = Rb/2 = 420 kHz.
(c) A single parity bit is appended to each character for error detection. Recalculate
your answers to parts (a) and (b)


(c) With the parity bit, 8 bits per character. Bit rate: 120,000 × 8 = 960 kbps.
Minimum bandwidth: 480 kHz
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A telephone channel carries a voice signal band-limited to 4 kHz. The signal is encoded using PCM with a uniform quantizer.
(a) What is the minimum sampling rate

(a) fs = 2 × 4 kHz = 8 kHz (Nyquist rate).


A telephone channel carries a voice signal band-limited to 4 kHz. The signal is encoded using PCM with a uniform quantizer.
(b) If 256 quantization levels are used, how many bits are required per sample

(b) n = log2 256 = 8 bits per sample


A telephone channel carries a voice signal band-limited to 4 kHz. The signal is encoded using PCM with a uniform quantizer(c) What is the resulting bit rate?

(c) Rb = fs × n = 8000 × 8 = 64 kbps.


A telephone channel carries a voice signal band-limited to 4 kHz. The signal is encoded using PCM with a uniform quantizer
(d) What is the minimum channel bandwidth required to transmit this PCM signal

d) Minimum bandwidth: BT = Rb/2 = 32 kHz.



A telephone channel carries a voice signal band-limited to 4 kHz. The signal is encoded using PCM with a uniform quantizer
(e) If the quantizer uses 8-bit words but the channel bandwidth is limited to 32 kHz, what is the maximum number of voice channels that can be time-division multiplexed on this channel?


(e) Each PCM voice channel requires 64 kbps. A bandwidth of 32 kHz supports a maximum bit rate of 2 × 32,000 = 64 kbps (Nyquist). This exactly accommodates one channel – the channel is fully occupied by a single 64 kbps stream, leaving no capacity for additional channels. (In practice, oversampling margins and framing overhead would reduce this further

A compact disc (CD) records stereo audio, each channel band-limited to 20 kHz.


a) fs,min = 2 × 20 kHz = 40 kHz.
(b) n = log2 65536 = 16 bits per sample.
(c) Per channel: 44100 × 16 = 705.6 kbps. Both channels: 2 × 705.6 = 1.4112 Mbps.
(d) Minimum bandwidth: 1,411,200/2 = 705.6 kHz.
(e) For a sinusoid S = m2p/2. Using SNR = 3L2S/m2p with L = 216:


A 10-bit digital-to-analogue (D/A) converter has an output range of 0 V to 10 V.
(a) How many discrete output voltage levels does it produce?
(b) What is the voltage resolution (smallest voltage step)?
(c) A signal is reconstructed with a maximum voltage error of ±1/2 LSB. Express this error in millivolts.


(a) 2^10 = 1024 levels.
(b) Resolution = 10 V/(2^10−1) = 10/1023 ≈ 9.77 mV.
(c) 1/2 * LSB = 1/2 × 9.77 ≈ 4.89 mV

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