Uttar Pradesh Technical University (UPTU) 2007-8th Sem B.Tech Electronics and Communications Engineering ,wireless communication. - Question Paper

B.Tech.
8th Semester Examination,2007-2008
Wireless Communication(TEC-801)

Note:Attempt ALL ques..All ques. carry equal marks.

Q.1.Attempt any 4 parts of the following:

(a)For LOS transmission,show that the received power(relative to transmitted power)decreases

by six dB for every doubling of distance and also for every doubling of the radio frequency.

(b)Using the ground reflection 2 ray model and the method images,find total electric field

at any yime t at a distance d.

(c)How the percentage of coverage area is determined within a cell?Calculate the percentage

of area with a received signal that is equal or greater than threshold gamma.

(d)What are the factors influencing small scale fading?Show that the mobile radio channel

can be modeled as a linear filter with time varying impulse response.

(e)With the help of block diagram,explain the spread spectrum channel impulse response

measurement system and provide its advantages and disadvantages.

(f)What is the concept of multipath shape factors for fading channels?Define the 3

multipath shape factors and provide the fading rates variance relationships in terms of the

shape factors.

Q.2.Attempt any 4 parts of the following:

(a)Why spread spectrum modulation is used in mobile radio environment?Draw and discuss the

block diagram of a DS-SS system and show how interference is minimized at the receiver.

(b)Compare similarities and differences ranging from basic concepts of DS-SS versus FH-SS

system.Analyze the performance of a synchronous frequency hopping spread spectrum system and

show that the irreducible fault rate due to multiple access interference is equal to

1/2[(k-1)/M]where k is number of MA users and M is number of possible hopping slots.

(c)What is diversity technique?What are the drawbacks of selection diversity?How maximal

ratio combining overcomes them?Show that the avg. signal to noise ratio at detector input

of a maximal ratio combiner is provided by gamma bar M=MI where M is the number of diversity

branches and I is avg. SNR of every branch.

(d)What is the need of equalization?With the help of block diagram,explain a communication

system using an adaptive equalizer at the receiver and show that the equalizer is an inverse

filter of the channel.

(e)How transversal filter can be used as an adaptive equalizer?Show that the optimum weight

is provided by W=R^(-1)P,where R is input correlation matrix and P is cross-correlation vector.

(f)Derive the probability of fault expressions for DPSK and non coherent orthogonal binary

FSK in a slow flat fading channel where the received signal envelope has a Ricean

probability distribution.

Q.3.Attempt any 2 parts of the following:

(a)Give the model foe Human speech production.Draw the block diagram of a linear predictive

coder (LPC)system and discuss it.How the predication coefficients are determined?Describe a

code-excitedLPC.

(b)Why non-uniform quantization is necessary for speech signals?Give the u legal regulations and A legal regulations

compandings and plot them.For PCM with u legal regulations compander,the output signal to quantization

noise ratio is provided by (s/nq)=3L^2/[In(1+u)]^2 where L is the number of quantization

levels.Show that for u=255, (S/Nq)dB=6.02n-10.1dB where n is the number of binary digits in

PCM.

(c)List the multiple excess techniques used in various wireless communication

systems.Explain the TDMA scheme,its salient features and the frame structure.Find the

expressions for the efficiency and number of channels in TDMA system.

Q.4.Attempt any 4 parts of the following:

(a)Explain the principle of frequency reuse in a cellular network.Show that the frequency

reuse factor is provided by k/s where k is the avg. number of channels per cell and s is the

total number of channels available.

(b)Name the technique used to increase the capacity of a cellular system and compare

them.Explain cell sectoring and show how co-channel interference is decreased in this.

(c)What is handoff in cellular systems?List the performance matrices used to make handoff

decisions and provide the different handoff strategies.

(d)Differentiate co-channel and adjacent channel interference in a cellular system and

mention their causes.Find out the expression for signal to co-channel interference

ratio(S/I) and show that a minimum cluster size of 7 is needed to meet an S/I

requirement of atleast 18 dB.Assume path loss exponent n=4.

(e)What is GSM?Mention the GSM services and features.Give the GSM system architecture and

the different interfaces used in this.

(f)List the key specifications of leading 2G Technologies.How 2G GSM technology can be

upgraded to 2.5G HSCSD(High Speed Circuit Switched Data)?

Q.5.Attempt any 2 parts of the following:

(a)What are the advantages and disadvantages of using CDMA for cellular network?Discuss the

frequency and channel specification of CDMA digital cellular standard(IS-95)and discuss the

forward CDMA channel.How power control is done in IS-95?

(b)Mention the vision and capabilities of 3G Wireless networks as described by ITU in IMT-2000

standard.Give the spectrum allocation,radio transmission technologies(RTT)and functional

network architecture for IMT-2000 and illustrate the class of functions to be supported by

IMT-2000.

(c)Explain the United States digital Cellular USDC(IS-136)standard under the subsequent

headings:
1.Radio interface 2.USDC channels
3.Frame structure on forward and reverse link. 4.Speech and channel coding.

Earning:   Approval pending.