(SEM VII) THEORY EXAMINATION 2024-25 WIRELESS & MOBILE COMMUNICATION

WIRELESS & MOBILE COMMUNICATION (KEC076) – COMPLETE SOLVED PAPER

Time: 3 Hours  Max Marks: 100
Instructions: Attempt all Sections

SECTION A (2 × 10 = 20 Marks)

Attempt all questions in brief

a) Cluster size (i = 2, j = 1)

N=i2+ij+j2=4+2+1=7N = i^2 + ij + j^2 = 4 + 2 + 1 = \boxed{7}N=i2+ij+j2=4+2+1=7​

b) Doppler effect
Frequency shift due to relative motion between transmitter and receiver; causes Doppler spread and fast fading.

c) Channel estimation
Estimating channel parameters (gain, phase, delay) to enable accurate detection and equalization.

d) Spread spectrum modulation
Spreads signal over wide bandwidth for interference resistance, security, and multipath mitigation.

e) Orthogonality in OFDMA
Subcarriers are orthogonal (Δf = 1/T), yielding zero inter-carrier interference with precise synchronization.

f) Persistent CSMA methods
1-persistent, Non-persistent, p-persistent CSMA.

g) GSM frequency bands
Uplink: 890–915 MHz; Downlink: 935–960 MHz.

h) LEO / MEO / GEO
LEO: <2000 km; MEO: 2000–35,786 km; GEO: 35,786 km.

i) Bluetooth vs ZigBee
Bluetooth: higher data rate, short-range audio/data.
ZigBee: very low power, low data rate, sensor/IoT.

j) Air interface
Defines radio link specs: modulation, coding, multiple access, power control between MS and BS.

SECTION B (10 × 3 = 30 Marks)

Attempt any three

a) Rayleigh fading channel
No LOS; envelope pdf:

p(r)=rσ2e−r2/(2σ2), r≥0p(r)=\frac{r}{\sigma^2}e^{-r^2/(2\sigma^2)},\ r\ge0p(r)=σ2r​e−r2/(2σ2), r≥0

Models multipath with many scatterers.

b) Diversity mechanisms (advantages)
Time, Frequency, Space, Polarization diversity → reduces deep fades, improves reliability.

c) Equalization & Adaptive Equalizers
Combat ISI. Adaptive equalizers (LMS/RLS) auto-tune taps to channel variations.

d) GSM architecture
MS, BSS (BTS, BSC), NSS (MSC, HLR, VLR), OSS.

e) NGN
Packet-based converged network offering voice/data/video with QoS, mobility, service independence.

SECTION C (10 × 5 = 50 Marks)

Attempt one from each question

Q3

(a) Increasing coverage & capacity
Cell splitting, sectoring, microcells/picocells, power control, smart antennas, frequency reuse.

(b) Hand-off mechanisms
Hard, Soft, Softer; Horizontal vs Vertical handoff—maintains call continuity.

Q4

(a) FHSS types & DSSS comparison
FHSS: Slow/fast hopping (time-based hops).
DSSS: Wideband spreading with PN code; higher processing gain.

(b) Vocoders
Waveform, Parametric, Hybrid vocoders—speech compression for mobile systems.

Q5

(a) Multiple access comparison
FDMA (frequency slots), TDMA (time slots), CDMA (codes)—capacity and flexibility trade-offs.

(b) Pooling & CSMA
Pooling dynamically allocates channels; CSMA senses carrier to reduce collisions.

Q6

(a) GPRS architecture (over GSM)
Adds SGSN, GGSN; packet switching, higher data rates, always-on connectivity.

(b) UMTS architecture
UE, UTRAN (Node B, RNC), Core Network—supports 3G multimedia.

Q7

(a) WiMAX
IEEE 802.16d/16e; protocol stack, broadband MANs; compares with Wi-Fi (range/QoS).

(b) Bluetooth topology & stack
Piconet/Scatternet; RF, Baseband, L2CAP, upper profiles.