ENCS300 Communication Systems Assessment 2026 | University of Dubai Module Title ENCS300 Communication Systems Academic Year 2026 ENCS300 Assessment Course Learning Outcomes (CLO) Identify building blocks of communication systems and the basic principles that are used in the analysis and design of analogue communication systems Identify building blocks of communication systems and the basic principles that are used in the analysis and design of analogue communication systems Question 1 [20 points] (1)An available channel bandwidth is 1.2 MHz. Each voice channel requires 25 kHz of bandwidth. In addition, a 5 kHz guard band is required between adjacent channels. Assume no guard band is required at the two outer edges of the 1.2 MHz band.
A.[2 points] Derive an expression for the total required bandwidth in terms of the number ofchan- nelsN. B.[2 points] Determine the maximum integer number of channels that can fit. (2)A receiver has a sensitivity of−72 dBm when operating at a bit rate ofRb =2 Mb/s. Assume the sensitivity is the minimum average received power required for reliable detection.
(1)[2 points] Convert the sensitivity−72 dBm to watts.(2) (2) [2 points] Compute the minimum bit energy Eb at this operating point using E b =PminTb,Tb =1Rb
3)[2 points] A second system operates atRb =8 Mb/s with sensitivity−66 dBm. Compute its minimum Eb.
(4) [2 points] Which system requires a lower energy per bit? By what factor?
(5) A point-to-point microwave communication link operates at a carrier frequency of fc = 12 GHz and a data rate of Rb = 150 Mb/s. The transmitter and receiver are separated by a line-of-sight distance of 45 km through free space. Use c = 3 × 10⁸ m/s.
A. [2 points] Compute the carrier wavelength λ. B. [2 points] Compute the one-way propagation delay tprop. C. [3 points] Compute the number of bits in flight on the link (the bandwidth–delay product) Nflight = Rb tprop. D. [1 point] Briefly interpret what Nflight means in words. Question 2 [24 points] (1) Let the message signal be
m(t) = 2 cos(2πfmt), fm = 2 kHz,
and let the carrier frequency be fc = 100 kHz. A DSB-SC (double-sideband suppressed-carrier) signal is generated as
sDSB-SC(t) = m(t) cos(2πfct).
A. [2 points] Write sDSB-SC(t) as a sum of cosines at the appropriate frequencies using trigonometric identities. B. [2 points] From your expression in (a), identify all spectral lines (their frequencies and amplitudes) in the spectrum SDSB-SC(f). C. [2 points] Sketch the amplitude spectrum |SDSB-SC(f)|. Clearly label the frequency axis and the line amplitudes. D. [2 points] Sketch the power spectrum SDSB-SC(f) (power per spectral line). Clearly label the frequency axis and the line powers. (2) A conventional AM signal is given by
sAM(t) = Ac [1 + μ cos(2πfmt)] cos(2πfct),
with Ac = 5, μ = 0.6, message frequency fm = 3 kHz, carrier frequency fc = 100 kHz, and load resistance R = 1Ω.
A. [2 points] Expand sAM(t) into a sum of cosines and identify:
the carrier component (frequency and amplitude). the upper sideband (USB) and lower sideband (LSB) components (frequencies and amplitudes). B. [2 points] Sketch the amplitude spectrum |SAM(f)|, showing the carrier and the two sidebands at fc ± fm.
C. [2 points] Compute the carrier power Pc, the total sideband power Pside, and the total transmitted power PT using the standard AM power formulas in terms of the modulation index μ.
D. [2 points] Determine the percentage transmission efficiency, defined as
η = (Psideband / PT) × 100%.
(3) Let the carrier be given by
c(t) = 8 cos(2πfct),
and let the message signal be
m(t) = cos(40πt).
Further assume that the message signal is used to frequency modulate the carrier with kf = 30, and that the transmitted power is 31.7 W. Find:
A. [1 point] The modulation index B. [1 point] The expression for the modulated signal C. [3 points] The number of transmitted harmonics D. [3 points] Express the modulated signal in terms of the selected harmonics