MCA : Practice Questions and Answers

The mean excess delay, excess delay spread and rms delay spread are some multipath channel parameters. They can be determined from a power delay profile. Doppler spread is a measure of spectral broadening caused by time rate of change of mobile radio channel.

The main problem with RF pulse system is that it is subject to interference and noise. This is due to wide passband filter required for multipath time resolution.

Rapid changes in signal strength over a small travel distance are caused due to multipath. It causes random frequency modulation due to varying Doppler shifts on different multipath signals. Time dispersion is also caused by multipath propagation delays.

Okumura’s model is one of the most widely used models for signal prediction in urban areas. This model is applicable for frequencies in the range 150 MHz to 1920 MHz (Extrapolated upto 3000 MHz).

Log normal shadowing, log distance path loss model and determination of percentage of coverage area are practical pat loss estimation techniques. Hata model is only valid for exterior environment.

The concept of diffraction loss is a function of the path difference around an obstruction. It can be explained by Fresnel zones. Fresnel zones represent successive regions where secondary waves have a path length from Tx to Rx which are nλ/2 greater than total path length.

Reflection occurs when a propagating electromagnetic wave impinges upon an object which has very large dimensions when compared to the wavelength of the propagation wave. Reflection occurs from the surface of the Earth and from buildings and walls.

EM signals when traveling through wireless channels experience fading effects due to various effects. But in some cases the transmission is with no obstruction and direct line of sight such as in satellite communication, microwave and wireless line of sight radio links.

Micro cell zone concept distributes the coverage of the cell and extends the cell boundary to hard-to reach places. It is the solution for the problem of increased number of handoffs when sectoring which results in an increase of load on switching.

One of the main problems with adjacent channel interference is the near-far effect. It occurs when a mobile close to a base station transmits on a channel close to one being used by a weak mobile.

Locator receiver is a spare receiver in each base station. It is used to scan and determine signal strengths of mobile users which are in neighbouring cells.

Hexagonal cell shape is a simplistic model of radio coverage for each base station. It has been universally adopted since the hexagon permits easy and manageable analysis of a cellular system.

Bluetooth uses GFSK (Gaussian Frequency Shift Keying). When GFSK is used for Bluetooth modulation, the frequency of the carrier is shifted to carry the modulation. By doing this the Bluetooth modulation achieves a bandwidth of 1 MHz with stringent filter requirements to prevent interference on other channels.

IEEE 802.11 is a set of media access control and physical layer specification for implementing WLAN computer communication. It was founded in 1987 to begin standardization of spread spectrum WLANs for use in the ISM bands.

3G Cdma2000 is based on the original IS-95 and IS-95A CDMA standards, as well as the 2.5G IS-95B air interface. While upgrading, Cdma2000 maintains backward compatibility with existing IS-95, IS-95A and IS-95B equipments. Thus, Cdma2000 allow wireless carriers to introduce a family of new high data rate Internet access capabilities within existing systems.

The 3G evolution for GSM, IS-136 and PDC systems leads to W-CDMA (Wideband CDMA). It is based on the network fundamentals of GSM, as well as merged versions of GSM and IS-136 through EDGE. GPRS, EDGE and HSCSD are 2.5G networks.

GSM (Global System for Mobile) is a TDMA standard for 2G network. HSCSD (High Speed Circuit Switched Data), GPRS (General Packet Radio Service) and EDGE (Enhanced Data rates for GSM Evolution) are TDMA standards of 2.5G technology.

Interim Standard 95 (IS-95) is the most popular CDMA standard of second generation networks. IS-136 is a TDMA standard of 2G. EDGE is a standard of 2.5G and ETACS is a 1G standard.

FCC (Forward Control Channel) and RCC (Reverse Control Channel) are control channels responsible for initiating mobile calls.

Cordless telephone systems are wireless, but they have a disadvantage of limited coverage area with cell size of approx. 300 m. Being digital, they have very less chance of eaves dropping.