Qualcomm
40+ Starmark Interview Questions and Answers
Q1. In real time operating systems which scheduling strategy will you choose?
The choice of scheduling strategy in real-time operating systems depends on the system requirements and constraints.
Priority-based scheduling is commonly used in real-time operating systems.
Earliest Deadline First (EDF) scheduling is suitable for systems with strict deadlines.
Rate Monotonic Scheduling (RMS) is appropriate for systems with periodic tasks.
Shortest Job First (SJF) scheduling can be used for systems with non-periodic tasks.
The choice of scheduling strategy should...read more
Q2. you have various strings each associated with an arbitrary 32-bit integer.what data structure will you choose if you need to search for a string given its number?
Use a hash table to store the strings with their associated integers.
Create a hash table with the integers as keys and the strings as values.
Use a hash function to map the integers to their corresponding buckets in the table.
To search for a string, compute the hash of its associated integer and look it up in the table.
Q3. hy do we have two modes of execution in operating systems?what are they?
Two modes of execution in operating systems are user mode and kernel mode.
User mode is a restricted mode where user applications run.
Kernel mode is a privileged mode where the operating system kernel runs.
User mode has limited access to hardware and system resources.
Kernel mode has full access to hardware and system resources.
Switching between modes requires a system call or interrupt.
Examples of system calls include opening a file or creating a process.
Kernel mode is more po...read more
Q4. How many parallelograms are there in a grid of mxn parallel lines?
The number of parallelograms in a grid of mxn parallel lines can be calculated using a formula involving combinations.
The formula to calculate the number of parallelograms is (m * (m + 1) * n * (n + 1)) / 4
For example, in a 2x3 grid, there are (2 * 3 * 3 * 4) / 4 = 18 parallelograms
The formula is derived by considering all possible combinations of 4 points on the grid to form a parallelogram
Q5. How does the frequency spectrum change if alternate samples in the time domain are negated?
Negating alternate samples in time domain results in spectral inversion.
Negating alternate samples in time domain is equivalent to multiplying the signal by a square wave with alternating values of +1 and -1.
This multiplication in time domain results in spectral convolution in frequency domain.
The frequency spectrum is inverted around the Nyquist frequency due to the spectral convolution.
This technique is used in some audio effects like flangers and phasers.
It can also be use...read more
Q6. How do you construct a 4x16 decoder from 2x4 decoders with enable pins
To construct a 4x16 decoder from 2x4 decoders with enable pins, you can use the enable pins of the 2x4 decoders to control the output of the 4x16 decoder.
Use one 2x4 decoder to decode the first 2 bits of the input and the other 2x4 decoder to decode the last 2 bits of the input.
Connect the enable pins of the 2x4 decoders to the same control signal, which will act as the enable pin for the 4x16 decoder.
Combine the outputs of the 2x4 decoders to form the 16 outputs of the 4x16 ...read more
Q7. what topology do you have in your LAB and why?
My LAB has a star topology because it provides centralized control and easy troubleshooting.
Star topology has a central hub that connects all devices
All communication goes through the hub
Easy to add or remove devices without affecting the rest of the network
Commonly used in LANs
Examples: Home networks, small businesses
Q8. What is the distribution of product of N normal RVs
The product of N normal RVs is a non-central chi-squared distribution with N degrees of freedom.
The distribution is non-central chi-squared with N degrees of freedom
The non-centrality parameter is the product of the means of the RVs
The variance of the distribution is the product of the variances of the RVs
This distribution is commonly used in signal processing and communication systems
Q9. write full and working code to sort a linked list with minimum time complexity
Sort a linked list with minimum time complexity
Use merge sort or quick sort for O(n log n) time complexity
Implement the sorting algorithm recursively
Use a temporary linked list to merge the sorted sub-lists
Consider edge cases like empty list or list with only one element
Q10. write a code to print all the connected components in a graph.
Code to print all connected components in a graph.
Implement Depth First Search (DFS) algorithm to traverse the graph.
Maintain a visited array to keep track of visited nodes.
For each unvisited node, perform DFS and add all visited nodes to a connected component.
Repeat until all nodes are visited.
Print all connected components.
Q11. Pdf of sum and max of two iid uniform rvs in the range 0 to 1
Pdf of sum and max of two iid uniform rvs in the range 0 to 1
The sum of two uniform random variables is a triangular distribution
The maximum of two uniform random variables is also a uniform distribution
The joint pdf can be derived using convolution and differentiation
The resulting pdf will have piecewise functions
Q12. How would you find the impulse response of a system?
The impulse response of a system can be found by applying a short impulse input and measuring the output.
Apply a short impulse input to the system
Measure the output of the system
Take the Fourier transform of the input and output signals
Divide the output Fourier transform by the input Fourier transform to get the transfer function
Take the inverse Fourier transform of the transfer function to get the impulse response
Q13. Why wireless channel is modelled as Rayliegh
Rayleigh fading is a statistical model for the effect of a propagation environment on a radio signal.
Rayleigh fading is a common model for wireless channels because it accurately represents the random fluctuations in signal strength caused by multipath propagation.
It assumes that the signal is scattered by many objects in the environment, resulting in a large number of reflected signals arriving at the receiver with different phases and amplitudes.
This randomness is modeled b...read more
Q14. what are the issues in topology ?
Topology deals with the study of properties of space that are preserved under continuous transformations.
Classification of surfaces
Homotopy theory
Fundamental group
Manifolds
Knot theory
Q15. Explain coherence time, coherence bandwidth, delay spread and Doppler spread
Coherence time is the time duration over which a signal remains correlated. Coherence bandwidth is the frequency range over which a signal remains correlated. Delay spread is the time difference between the arrival of the first and last multipath components. Doppler spread is the frequency difference between the maximum and minimum Doppler shifts.
Coherence time and coherence bandwidth are important parameters in wireless communication systems.
Delay spread is a measure of the ...read more
Q16. Explain relationship between coherence time and subcarrier spacing
Coherence time and subcarrier spacing are inversely proportional.
Coherence time is the time duration over which a wireless channel remains constant.
Subcarrier spacing is the frequency difference between adjacent subcarriers in an OFDM system.
The coherence time and subcarrier spacing are inversely proportional to each other.
If the subcarrier spacing is decreased, the coherence time increases and vice versa.
This relationship is important in designing OFDM systems for wireless c...read more
Q17. x1,x2,x3...xn has fourier transform X (bandwidth Fb) Find the fourier transform of x1,0,x2,0,x3,0
The Fourier transform of x1,0,x2,0,x3,0 is X(f) + X(-f)
The Fourier transform of a shifted signal is the original transform multiplied by a complex exponential
The Fourier transform of x1,0,x2,0,x3,0 is the sum of the Fourier transforms of x1,x2,x3 shifted by 0
The Fourier transform of a real signal is symmetric about the origin
Therefore, the Fourier transform of x1,0,x2,0,x3,0 is X(f) + X(-f)
Q18. what is symbolic link in OS ?
A symbolic link is a file that acts as a pointer to another file or directory.
Symbolic links are similar to shortcuts in Windows.
They allow for easy access to files and directories located in different parts of the file system.
Symbolic links can be created using the 'ln -s' command in Unix-based systems.
They can be identified by the 'l' flag in the output of the 'ls -l' command.
Symbolic links can be used to create a backup of a file or directory without duplicating the data.
Q19. What is cramer Rao's bound, explain
Cramer Rao's bound is a lower bound on the variance of any unbiased estimator of a parameter.
It is used in statistical signal processing to determine the accuracy of parameter estimation.
It is based on the Fisher information matrix, which measures the amount of information a random variable carries about a parameter.
The bound is tight when the estimator is efficient, meaning it achieves the minimum variance possible.
It is useful for comparing the performance of different esti...read more
Q20. Use the sampling theorem for unsymmetrical signals and find the nyquist frequency
The Nyquist frequency for unsymmetrical signals can be found using the sampling theorem.
The Nyquist frequency is half of the sampling rate.
For unsymmetrical signals, the highest frequency component should be considered when determining the Nyquist frequency.
Nyquist frequency = 0.5 * highest frequency component
Q21. Find the number of parallelograms in an mXn set of parallel lines
The number of parallelograms in an mXn set of parallel lines can be calculated using a formula.
Use the formula: (m * (m + 1) * n * (n + 1)) / 4
For example, in a 2x3 set of parallel lines, there are 18 parallelograms
Q22. Derive optimal threshold for BPSK detection
Optimal threshold for BPSK detection can be derived using the likelihood ratio test.
The threshold should be set such that the probability of false alarm is equal to the probability of detection.
The threshold can be derived by finding the point where the likelihood ratio crosses a certain threshold value.
The threshold can also be derived by maximizing the signal-to-noise ratio.
Simulation and testing can be done to verify the performance of the threshold.
Q23. what is computer networking?
Computer networking is the practice of connecting devices together to share resources and information.
It involves the use of hardware and software to create and manage networks
Networking protocols such as TCP/IP are used to facilitate communication between devices
Examples of computer networks include LANs, WANs, and the internet
Networking allows for sharing of resources such as printers and files
Security measures such as firewalls and encryption are used to protect networks a...read more
Q24. Example of linear time varient system(wireless comm channel)
A wireless communication channel is an example of a linear time variant system.
Wireless communication channels experience time-varying fading due to changes in the environment.
The channel impulse response changes over time, making it a linear time variant system.
Examples of wireless communication channels include Wi-Fi, cellular networks, and satellite communication.
The channel can be modeled as a linear time variant system using techniques such as channel estimation and equa...read more
Q25. Design OFDM system for given scenario
Design an OFDM system for a given scenario.
Determine the bandwidth and carrier frequency
Choose the number of subcarriers and their spacing
Select a suitable cyclic prefix length
Implement modulation scheme and error correction coding
Optimize system performance through simulation and testing
Q26. What is linear time invarient systems
Linear time invariant systems are systems whose output is proportional to the input and is not affected by time.
Linear time invariant systems have constant coefficients and do not change over time.
The output of the system is a scaled version of the input signal.
Examples of LTI systems include RC circuits, mass-spring-damper systems, and filters.
LTI systems are important in signal processing and control theory.
They can be analyzed using techniques such as Laplace transforms an...read more
Q27. Differentiate between call by value and reference
Call by value passes a copy of the value while call by reference passes a reference to the value.
Call by value creates a new copy of the value being passed, while call by reference passes a reference to the original value.
In call by value, changes made to the parameter inside the function do not affect the original value, while in call by reference, changes made to the parameter inside the function affect the original value.
Call by value is used for simple data types like int...read more
Q28. why qualcomm?
Qualcomm is a leading technology company with a strong focus on innovation and cutting-edge solutions.
Qualcomm is a leader in the mobile technology industry
The company has a strong reputation for innovation and research
Qualcomm's products and solutions are used by millions of people worldwide
The company has a diverse portfolio of products, including processors, modems, and wireless technologies
Qualcomm is committed to sustainability and social responsibility
Q29. Trailing zero problem in factorials
Trailing zero problem in factorials
Trailing zeros in a factorial are the number of zeros at the end of the factorial's decimal representation
The number of trailing zeros is equal to the number of times 10 can be divided from the factorial
To find the number of trailing zeros, divide the number by 5 and add the quotient to the result of dividing the quotient by 5, and so on
For example, the factorial of 10 has 2 trailing zeros, while the factorial of 25 has 6 trailing zeros
Q30. What is your experience with Java Programming?
Q31. Explain OFDM and need of CP
OFDM is a modulation technique that divides a high-speed data stream into multiple subcarriers. CP is added to prevent inter-symbol interference.
OFDM stands for Orthogonal Frequency Division Multiplexing
It is used in high-speed data transmission over wireless and wired networks
OFDM divides the data stream into multiple subcarriers that are orthogonal to each other
CP or Cyclic Prefix is added to each OFDM symbol to prevent inter-symbol interference
CP is a copy of the end of th...read more
Q32. relocation problems ?
Relocation problems can be challenging but can also offer new opportunities.
Adjusting to a new environment can be difficult
Finding new housing and schools can be stressful
Making new friends and building a support system takes time
Exploring a new city can be exciting and offer new experiences
Relocation can offer career advancement and new opportunities
Q33. Design a 4:16 decoder using 2:4 decoders
Design a 4:16 decoder using 2:4 decoders
Use two 2:4 decoders to decode the 4 input bits into 16 output bits
Connect the enable input of each 2:4 decoder to the complement of the other decoder's enable input
Connect the outputs of the two 2:4 decoders to form the 16 output bits
Q34. Explain Nyquist sampling theorem
Nyquist sampling theorem states that a signal must be sampled at least twice its highest frequency component to be accurately reconstructed.
The theorem is named after Harry Nyquist.
It is used in digital signal processing and communication systems.
Sampling rate must be greater than or equal to 2 times the highest frequency component.
If the sampling rate is less than 2 times the highest frequency component, aliasing occurs.
Aliasing can be avoided by using a low-pass filter befo...read more
Q35. Why Qualcomm?
Qualcomm is a leading semiconductor and telecommunications equipment company with a strong focus on innovation.
Qualcomm is a leader in 5G technology and has been instrumental in the development of this technology.
The company has a strong patent portfolio and is known for its innovative products.
Qualcomm has partnerships with many major technology companies, including Apple and Samsung.
The company has a strong commitment to sustainability and has set ambitious goals for reduci...read more
Q36. Draw the CMOS layout of inverter
A CMOS inverter consists of a PMOS and an NMOS transistor connected in series.
The PMOS and NMOS transistors are connected in series with their gates connected together.
The output is taken from the connection between the two transistors.
The input is applied to the gate of the NMOS transistor.
The PMOS transistor is connected to VDD and the NMOS transistor is connected to GND.
The layout consists of two complementary transistors and their interconnects.
The layout is designed to m...read more
Q37. RC circuits with diodes
RC circuits with diodes involve the combination of resistors, capacitors, and diodes to control the flow of current.
RC circuits with diodes are commonly used in electronic circuits to control the flow of current and voltage.
The diode in the circuit allows current to flow in only one direction, preventing reverse current flow.
The time constant of the circuit is determined by the values of the resistor and capacitor, affecting the charging and discharging of the capacitor.
Examp...read more
Q38. Describe an LTI system
An LTI system is a linear time-invariant system that produces an output signal from an input signal.
LTI systems have constant parameters that do not change over time
The output of an LTI system is a linear combination of the input signal and the system's impulse response
Examples of LTI systems include electronic filters, audio equalizers, and control systems
Q39. Derive the sampling theorem
The sampling theorem states that in order to accurately reconstruct a continuous signal from its samples, the sampling frequency must be at least twice the highest frequency component of the signal.
The sampling theorem, also known as Nyquist-Shannon theorem, was developed by Claude Shannon and Harry Nyquist in the 1940s.
It states that in order to accurately reconstruct a continuous signal from its samples, the sampling frequency must be at least twice the highest frequency co...read more
Q40. Find CTFT of a periodic signal
CTFT of a periodic signal involves decomposing the signal into its frequency components.
CTFT stands for Continuous-Time Fourier Transform
Periodic signals have discrete frequency components
CTFT of a periodic signal results in a frequency spectrum with Dirac delta functions at the harmonic frequencies
Q41. Prove convolution equation
Convolution equation states that the output of a linear time-invariant system is the convolution of the input and impulse response.
Convolution is a mathematical operation that combines two functions to produce a third function.
The convolution of two functions f and g is denoted by (f * g).
The convolution equation is given by y(t) = x(t) * h(t), where x(t) is the input signal, h(t) is the impulse response, and y(t) is the output signal.
Convolution is used in signal processing,...read more
Q42. Prove the sampling theorem
The sampling theorem states that a continuous signal can be perfectly reconstructed from its samples if the sampling rate is at least twice the highest frequency component of the signal.
The sampling theorem, also known as Nyquist-Shannon sampling theorem, is a fundamental concept in signal processing.
It states that in order to accurately reconstruct a continuous signal from its samples, the sampling rate must be at least twice the highest frequency component of the signal.
For...read more
Q43. Find DTFT of a signal
DTFT of a signal is a continuous function that represents the frequency content of the signal.
DTFT stands for Discrete-Time Fourier Transform
It is used to analyze the frequency content of a discrete-time signal
The DTFT of a signal x[n] is defined as X(e^jw) = Σ x[n]e^(-jwn)
Example: DTFT of a rectangular pulse signal
Q44. What is process and thread
Q45. Draw CMOS NAND gate
A CMOS NAND gate is a digital logic gate that produces an output that is the inverse of the logical AND of its inputs.
A CMOS NAND gate consists of two complementary MOSFETs connected in series.
The gate of one MOSFET is connected to the input A, while the gate of the other MOSFET is connected to the input B.
The drains of both MOSFETs are connected together to form the output.
The sources of both MOSFETs are connected to the ground.
When both inputs are high, both MOSFETs are off...read more
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