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computer science
introduction wireless mobile systems

Questions and Answers of Introduction Wireless Mobile Systems

During a busy hour, the number of calls per hour for each of the 12 cells of a cellular cluster is 2220, 1900, 4000, 1100, 1000, 1200, 1800, 2100, 2000, 1580, 1800 and 900. Assume that 75% of the car
A TDMA-based system shown in the Figure, has a total bandwidth of 12.5 MHz and contains 20 control channels with equal channel spacing of 30 kHz. Here, the area of each cell is equal to 8 km2, and
For the following cell pattern,(a) Find the reuse distance if radius of each cell is 2 km.(b) If each channel is multiplexed among 8 users, how many calls can be simultaneously processed by each cell
A cellular scheme employed a cluster of 16 cells. Later on, it was decided to use two different clusters of 7 and 9 cells. Is it possible to replace each original cluster by two new clusters? Explain
The size and shape of each cluster in a cellular need to be designed carefully so as to cover adjacent spoke in a non-overlapped manner. Define such patterns for the following cluster sizes:(a)
Prove that N = i2 + j2 + ij.
Prove that D = √3NR.
If each user keeps a traffic channel busy for an average of 5% time and an average of 60 requests per hour is generated, what is the Erlang value?
Two adjacent BSs i and j are 30 km apart. The signal strength received by the MS is given by the following expressions.Whereand x is the distance of the MS from BS i. Assume unity gain for Gr and Gt,
A new wireless service provider decided to employ a cluster of 19 cells as the basic module for frequency reuse.(a) Can you identify one such cluster structure?(b) Repeat (a) for N = 28.(c) Can you
An octagon shaped cell is closer to a circle than a hexagon. Explain why such a shape is not used as an ideal shape of the cell?
If the number of mechanics in Example 2.4 is increased to 3, what is the impact on the performance parameters?
The density for X is given in the table of Problem 7.(a) Find E[X](b) Find E[X-](c) Find Var[X](d) Find the standard deviation for X.
Compare a block with a convolutional interleaver.
In Stop-and-Wait ARQ, let the probability of the transmitting side receiving an ACK after exactly one loss of ACK be P = 0.021. Find the Average transmission time in terms of a block duration
Prove that the average transmission time in terms of block duration, TSR, for Selective-Repeat ARQ is given by:Where PACK is the probability to return an ACK in the transceiver side. Also, solve the
Describe briefly syndrome decoding and incomplete decoding?
What is an RSC code? Why are these codes called be systematic?
Develop the encoder and syndrome calculator with 1+x2 + x3 as generator polynomial in Problem P4.18.In ProblemPolynomial 1 + x7 can be factorized into three irreducible polynomials (1 + x)(1 + x +
Repeat Problem P4.18 with 1 + x2 + x3 as generator polynomial and compare the results.Repeat ProblemPolynomial 1 + x7 can be factorized into three irreducible polynomials (1 + x)(1 + x + x3)(1 + x2 +
Polynomial 1 + x7 can be facted into threeoriz irreducible polynomials (1 + x) (1+ x + x3)(1 + x2 + x3) with (1 + x + x3) and (1 + x2 + x3) as primitive polynomials. Using 1 + x + x3 as generator
Under what scenarios would cyclic codes be preferred over interleaving and vice ersa?
In a two-stage coding system, the first stage provides (7, 4) coding while the second stage supports (11, 7) coding. Is it better to have such a two-stage coding scheme as compared to a single-stage
Why do you need both error correction capability and ARQ in a cellular system? Explain clearly.
Can you interleave an interleaved signal? What do you gain with such a system?
Consider the block diagram of a typical digital transmission system. Speculate where one would use source coding and channel coding. Differentiate between them. Would they increase or decrease the
Compare and contrast GBN ARQ and SR ARQ schemes.
Consider a SAW ARQ system between two nodes: A (transmitting node) and B (receiving node). Assume that data frames are all of the same length and require τ seconds for transmission. Acknowledgement
The following figure shows the encoder for a 1/2 rate convolutional code. Determine the encoder output produced by the message sequence 1011... Flip Flop (shift register) O Modnlo 2 adder У1 Output
Find the state diagram for Problem P4.8.Consider the rate r = 1/2 in the convolutional encoder shown below. Find the encoder output (Y1 Y2) produced by the message sequence 10111. . . Modulo 2 adder
Consider the rate r = 1/2 in the convolutional encoder shown below. Find the encoder output (Y1Y2) produced by the message sequence 10111. . . Modulo 2 adder First bit Flip Flop X Output 11101 Y2
Repeat Problem P4.6 if g(x) = 1 + x for a (7, 4) code.Repeat Problem P4.6Find the linear block code generator matrix G, if the code generator polynomial is g(x) = 1 + x2 + x3 for a (7, 4) code.
Find the linear block code generator matrix G, if the code generator polynomial is g(x) = 1 + x2 + x3 for a (7, 4) code.
The following matrix represents a generator matrix for a (7, 4) block code.What is the corresponding parity check matrix H? 100 0 1 1 0] 0 10 0 0 1 1 G = 0 0 10 1 1 1 0 0 0 1 10 1
If the code generator polynomial is g(x) = 1 + x2 for a (5, 3) code. Find the linear block code generator matrix G.
What is the main idea behind channel coding? Does it improve the performance of mobile communication?
Can channel coding be considered as a post detection technique?
Explain why channel coding reduces bandwidth efficiency of the link in high signal-to-noise ratio conditions.
What causes the inter-symbol interference and how can you reduce the intersymbol interference in the wireless communication system?
Consider two random variables X and Y that are independent and Gaussian mean and the other is of mean μ. Prove that the density function of Z =√ X + Y is Rician distributed.
An MS is not in the direct line of sight of a BS transmitting station. How is the signal received? Explain.
What is the inter-symbol interference (ISI)? Does it affect the transmission rate of a digital channel? Explain clearly.
What is the role or usefulness of reflected and diffracted radio signals in a cellular system? Explain with suitable examples.
What is the diversity reception? How can it be used to combat multipath?
A BS has a 900 MHz transmitter and a vehicle is moving at the speed of 50 mph. Compute the received carrier frequency if the vehicle is moving(a) Directly toward the BS.(b) Directly away from the
Path loss, fading, and delay spread are the three important radio propagation issues. Explain why those issues are important in a cellular system?
What are the differences between fast fading and slow fading?
How is radio propagation on land different from that in free space?
How can you compensate for the impact of Doppler Effect in a cellular system? Explain.
Describe the consequence of the Doppler Effect on the receiver in an isotropic scattering environment. Based on your description, speculate on the meaning of the term “Doppler Spread”.(a) Is the
Repeat Problem P3.6. Calculate the average fading duration if ρ = 0.1.Repeat ProblemWhat does a small delay spread indicate about the characteristics of a fading channel? If the delay spread is 1
Consider an antenna transmitting at 900 MHz. The receiver is traveling at a speed of 40 km/h. Calculate its Doppler shift.
What does a small delay spread indicate about the characteristics of a fading channel? If the delay spread is 1 microsecond, will two different frequencies that are 5 MHz apart, experience correlated
A receiver is tuned to 1 GHz transmission and receives signals with Doppler frequencies ranging from 10 Hz to 50 Hz when moving at a speed of 80 km/hr. What is the fading rate?
The transmission power is 40 W, under a free-space propagation model, (a) What is the transmission power in unit of dBm?(b) The receiver is in a distance of 1000 m; what is the received power,
In a cellular system, diffraction, reflection, and direct path take different amount of time for the signal to reach an MS. How do you differentiate and use these signals? Explain clearly. Compute
Consider an antenna transmitting a power of 5 W at 900 MHz. Calculate the received power at a distance of 2 km if propagation is taking place in free space.
A wireless receiver with an effective diameter of 250 cm is receiving signals at 20 GHz from a transmitter that transmits at a power of 30 mW and a gain of 30 dB.(a) What is the gain of the receiver
In the M/M/1/ queuing system, suppose λ and μ are doubled. How are Ls and Ws changed?
In a transition diagram of M/M/5 model, write the state transition equations and find a relation for the system to be in each state.
Consider a cellular system in which each cell has only one channel (single server) and an infinite buffer for storage the calls. In this cellular system, call arrival rates are discouraged, that is,
Consider a cellular system with an infinite number of channels. In such a system, all arriving calls begin receiving service immediately. The average call holding time is 1/nμ when there are n calls
What should be a relationship between call arrival rate and service rate when a cellular system is in a steady state? Explain clearly.
A Poisson process exhibits a memoryless property and is of great importance in traffic analysis. Prove that this property is exhibited by all Poisson processes.Explain clearly every step of your
A gambler has a regular coin and a two-headed coin in his packet. The probability of selecting the two-head coin is given as p = 2/3. He select a coin and flips it n = 2 times and obtains heads both
In a wireless office environment, all calls are made between 8 am and 5 pm over the period of 24 hours. Assuming the number of calls to be uniformly distributed between 8 am and 5 pm, find the pdf of
Given that the number of arrivals of data packet in the receiver follows a Poisson distribution on which arrival rate is 10 arrivals per second. What is the probability that the number of arrivals is
The number of calls arrive under a particular time in a cell has been established to be a Poisson distribution. The average number of calls arriving in a cell in 1 millisecond is 5. What is the
Find the distribution function of the maximum of a finite set of independent random variables {X1, X2, ..., Xn}, where Xi has distribution function Xi F . What is this distribution when Xi is
Find the probability when(a) k = 2 and λ = 0.01 for Poisson distribution.(b) p = 0.01 and k = 2 for geometric distribution.(c) Repeat (b) when binomial distribution is used and n = 10.
The following table shows the density of the random variable X.(a) Find p(8)(b) Find the table for CDF F(x)(c) Find P(3 ‰¤ X ‰¤ 5)(d) Find P(X ‰¤ 4) and P(X <
Consider an experiment consisting of tossing two true dice. Let X, Y, and Z be the numbers shown on the first die, the second die, and total of both dice, respectively. Find P (X ≤ 1, Z ≤ 2) and
There are three red balls and seven white balls in box A, and six red balls and four white balls in box B. After throwing a die, if the number on the die is 1 or 6, then pick a ball from box A.
A department survey found that 4 of 10 graduate students use CDMA cell phone service. If 3 graduate students are selected at random, what is the probability that 3 graduate students use CDMA cell
A snapshot of the traffic pattern in a cell with 10 users of a wireless system is given as follows:(a) Assuming the call setup/connection and call disconnection time to be zero, what is the average
A random digit generator on a computer is activated three times consecutively to simulate a random three-digit number.(a) How many random three-digit numbers are possible?(b) How many numbers will
A random number generator produces numbers between 1 and 99. If the current value of the random variable is 45, then what is the probability that the next randomly generated value for the same random
If a total of 33 MHz of bandwidth is allocated to a particular cellular telephone system which uses two 25 kHz simplex channels to provide full duplex voice channels, compute the number of
What are the similarities between frequency hopping and TDMA?
In an airplane in the air, what happens if you use(a) A walkie-talkie?(b) A satellite phone?(c) A cell phone?
How do you compare a cell phone with a satellite phone?
Why do you have difficulty in using your cell phone inside an elevator?
What are the pros and cons of having different size cells for wireless networking?
Why is “anytime anywhere” access not required for all applications? Explain clearly.
What are the limitations if a network is mobile with no wireless support?
Can a network be wireless, but not mobile? Explain your answer carefully.
What are the advantages of different wireless service provoders in an area? Explain clearly.
List some prospective application areas for sensor networks?
How is an ad hoc network different from a cellular network?
How many cellular service providers are present in your area? Which of the multiple access technique supported by each system? What are the cell size and transmitting power level? What are the number
What are the household applications that use wireless schemes to control functionally?
What are the unconventional applications of wireless networks?
What are the challenges for wireless networking?
Why do you need wireless services when adequate wired infrastructure exists in most parts of the United States?

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