40+ Qualcomm Interview Questions and Answers for Freshers

The number of ways to arrange sets of coloured balls in a line.

• The number of ways to arrange the red balls is the factorial of the number of red balls.

• The number of ways to arrange the blue balls is the factorial of the number of blue balls.

• The number of ways to arrange the green balls is the factorial of the number of green balls.

• To find the total number of arrangements, multiply the number of arrangements for each set.

Overlap-add method of convolution is implemented by dividing the input signal into overlapping segments and convolving each segment with a filter.

• Divide the input signal into overlapping segments

• Apply the filter to each segment

• Add the convolved segments together to get the output signal

• The length of each segment should be greater than or equal to the length of the filter

• The overlap between adjacent segments should be greater than or equal to the length of the filter minus one

The in-phase and quadrature components of a real pass-band signal can be obtained using a complex mixer.

• A complex mixer is used to convert the real pass-band signal to a complex baseband signal.

• The in-phase component is obtained by multiplying the pass-band signal with a local oscillator signal in-phase with the carrier frequency.

• The quadrature component is obtained by multiplying the pass-band signal with a local oscillator signal 90 degrees out of phase with the carrier fre...read more

The bit-rate for quantization of a band-limited signal can be obtained by considering the Nyquist-Shannon sampling theorem.

• The Nyquist-Shannon sampling theorem states that in order to accurately represent a band-limited signal, the sampling rate must be at least twice the highest frequency component of the signal.

• The bit-rate for quantization is determined by the number of bits used to represent each sample. It is typically calculated as the product of the sampling rate and t...read more

Interpolation in discrete-time domain involves estimating values between known data points.

• Interpolation is used to fill in missing data or estimate values between known data points.

• Common interpolation techniques include linear interpolation, polynomial interpolation, and spline interpolation.

• Linear interpolation calculates values along a straight line between two known data points.

• Polynomial interpolation uses a polynomial function to estimate values between data points.

• Spl...read more

Nyquist sampling frequency for unevenly distributed band-limited signal.

• Determine the highest frequency component in the signal

• Use Nyquist theorem to calculate the minimum sampling frequency

• Sampling frequency should be at least twice the highest frequency component

Maximal Ratio Combining (MRC) is a technique used in MIMO systems to improve signal quality by combining multiple received signals.

• MRC combines the received signals from multiple antennas to maximize the signal-to-noise ratio (SNR)

• Quantization noise power refers to the noise introduced during the process of converting analog signals to digital signals

• In MIMO systems, MRC can be used to mitigate the effects of quantization noise

• MRC calculates the weights for each received sign...read more

The minimum number of steps needed to find the value of an nth order polynomial is n+1.

• To find the value of a 1st order polynomial, we need 2 steps (1 multiplication and 1 addition).

• For an nth order polynomial, we need to compute n 1st order polynomials and perform n-1 additions.

• Therefore, the minimum number of steps is n+1.

• If parallel processing is allowed, we can compute the value of each 1st order polynomial simultaneously, reducing the time taken.

• In this case, the number ...read more

Demodulating a QAM signal involves separating the amplitude and phase components to recover the original data.

• QAM signals combine amplitude and phase modulation

• Demodulation involves separating the amplitude and phase components

• Techniques like coherent demodulation and quadrature demodulation are used

• Coherent demodulation uses a local oscillator to recover the phase component

• Quadrature demodulation separates the in-phase and quadrature components

Modulation is the process of varying a carrier signal to transmit information. Different types include AM, FM, PM, and QAM.

• Modulation is used to transfer information by varying a high-frequency carrier signal.

• Amplitude Modulation (AM) varies the amplitude of the carrier signal to encode information.

• Frequency Modulation (FM) varies the frequency of the carrier signal to encode information.

• Phase Modulation (PM) varies the phase of the carrier signal to encode information.

• Quadra...read more

The Nyquist criterion states that in order to accurately sample a signal, the sampling rate must be at least twice the highest frequency component of the signal.

• The Nyquist criterion is used in digital signal processing and communication systems.

• It ensures that the original signal can be accurately reconstructed from its samples.

• The sampling rate should be at least twice the bandwidth of the signal to avoid aliasing.

• For example, if a signal has a maximum frequency of 10 kHz, ...read more

Overlap-add is implemented by dividing the input signal into overlapping segments, applying a window function, and adding the segments together.

• Overlap-add is a method used in digital signal processing to efficiently convolve long signals with finite impulse response (FIR) filters.

• The input signal is divided into overlapping segments, typically with a length equal to the filter length.

• A window function, such as the Hamming window, is applied to each segment to reduce spectral...read more

Different types of analog modulation schemes can be found in various communication systems.

• Analog modulation schemes are used in radio broadcasting, television transmission, and wireless communication.

• Some common types of analog modulation schemes include amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM).

• AM is used in AM radio broadcasting, where the amplitude of the carrier signal is varied to transmit audio signals.

• FM is used in FM radio broadc...read more

The question is about calculating the probability density function (pdf) of the sum of two random variables (RV) following a Gaussian mixture distribution.

• A Gaussian mixture distribution is a combination of multiple Gaussian distributions.

• To calculate the pdf of the sum of two RVs, convolve the pdfs of the individual RVs.

• Convolution involves integrating the product of the pdfs over the entire range of possible values.

• The resulting pdf will also follow a Gaussian mixture distr...read more

Propagation delay is the time it takes for an electromagnetic wave to travel from one point to another.

• Propagation delay is determined by the distance between the two points and the speed of light.

• It is the time it takes for the wave to propagate through a medium or free space.

• Propagation delay can be calculated using the formula: delay = distance / speed of light.

• For example, if the distance between two points is 100 meters, and the speed of light is 3 x 10^8 meters per seco...read more

VSWR stands for Voltage Standing Wave Ratio. It is a measure of how well a transmission line is matched to the impedance of the connected devices.

• VSWR is a ratio of the maximum voltage to the minimum voltage along a transmission line.

• It is used to measure the efficiency of power transfer and the impedance matching in RF systems.

• A lower VSWR indicates better impedance matching and less power loss.

• VSWR is important in RF systems to prevent signal reflections, which can degrade ...read more

A standing wave in a transmission line is a wave that appears to be stationary, resulting from the interference of two waves traveling in opposite directions.

• A standing wave is formed when a wave traveling in one direction reflects back upon encountering an impedance mismatch in the transmission line.

• The interference between the incident and reflected waves creates regions of constructive and destructive interference, resulting in nodes and antinodes along the transmission li...read more

Amplitude modulation (AM) and frequency modulation (FM) waveforms can be represented graphically.

• AM modulation: The amplitude of the carrier signal is varied in proportion to the amplitude of the modulating signal.

• FM modulation: The frequency of the carrier signal is varied in proportion to the amplitude of the modulating signal.

• Waveforms can be drawn to show the variations in amplitude or frequency over time.

• AM waveform will have varying amplitudes while FM waveform will hav...read more

A transmitter and receiver are essential components of a communication system.

• Transmitter converts information into a suitable form for transmission.

• Receiver receives the transmitted signal and converts it back into the original form.

• Transmitter typically includes a modulator, power amplifier, and antenna.

• Receiver typically includes an antenna, demodulator, and audio or video output.

• Example: In a radio communication system, the transmitter converts audio signals into radio wa...read more

Histogram equalization is a technique to enhance the contrast of an image by redistributing pixel intensities.

• Histogram equalization stretches the histogram of an image to cover the entire range of pixel values.

• It increases the dynamic range of an image, making it visually more appealing.

• It improves the visibility of details in both dark and bright regions of an image.

• Histogram equalization can be used to enhance images with low contrast or uneven lighting conditions.

• For exam...read more

The asymptotic bound on capacity refers to the maximum amount of data that can be transmitted through a communication channel.

• Asymptotic bound on capacity is a theoretical limit that determines the maximum data rate of a channel.

• It is influenced by factors such as bandwidth, signal-to-noise ratio, and channel coding.

• Shannon's capacity formula is often used to calculate the asymptotic bound on capacity.

• For example, a channel with a bandwidth of 10 kHz and a signal-to-noise rat...read more

Function to return Fibonacci series of N elements

• Create an array to store the series

• Use a loop to generate the series

• Return the array

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

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

Perspective distortion is the distortion that occurs when objects appear differently due to the angle of view. It can be corrected using software or adjusting the camera position.

• Perspective distortion happens when objects appear distorted or skewed due to the camera's angle of view.

• It is commonly seen in architectural photography, where buildings may appear to lean or converge.

• To correct perspective distortion, software tools like Adobe Photoshop or Lightroom can be used to ...read more

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

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

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

S-matrix is a mathematical representation used in RF engineering to describe the relationship between input and output signals of a linear system.

• S-matrix is also known as scattering matrix.

• It is used to analyze the behavior of RF circuits and systems.

• S-matrix elements represent the complex amplitudes of the incident and reflected waves at each port of a network.

• S11 parameter represents the reflection coefficient at port 1, S21 represents the forward transmission coefficient ...read more

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

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

Technical questions related to programming concepts and memory management.

• To find indices of a multi-dimensional array using offset, divide the offset by the size of each element and use the quotient as the index for the first dimension. Repeat this process for each dimension.

• Bitwise operations are used to manipulate individual bits in a binary number. Examples include AND, OR, XOR, and bit shifting.

• Structure padding is the insertion of unused bytes into a structure to ensure...read more

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.

Binary search in a sorted rotated array with no duplicates.

• Find the pivot point where the array is rotated.

• Determine which half of the array to search based on the target value and pivot point.

• Perform binary search in the selected half of the array.

Binary search in a sorted rotated array with duplicates present.

• Perform a modified binary search by checking both ends of the array for duplicates

• Handle cases where duplicates are present at the start, end, or middle of the array

• Consider cases where the array is rotated multiple times

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

Find the next greater element for each element in an array.

• Use a stack to keep track of elements without a next greater element.

• Iterate through the array and compare elements with the top of the stack.

• Update the stack with the current element if it is greater than the top element.

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

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

Design a micro arch for a given problem

• Identify the specific problem that the micro arch needs to solve

• Consider the size and scale of the micro arch in relation to the problem

• Design the structure of the micro arch to efficiently address the problem

• Ensure that the materials used are suitable for the intended purpose

Verilog code for micro architecture design

• Define modules for different components of the micro architecture

• Implement data paths and control logic using Verilog

• Use registers, multiplexers, and other logic gates to design the micro architecture

• Test the functionality of the micro architecture using simulation tools

Homography is a transformation that maps points in one image to corresponding points in another image.

• Homography is a 3x3 matrix that represents a planar perspective transformation.

• It is used in computer vision to align images, stitch panoramas, and perform image registration.

• Homography can be estimated using feature matching techniques like SIFT or SURF.

• It assumes a projective transformation between two images.

• Example: Homography can be used to remove distortion in images ta...read more

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

A transformer is an electrical device that transfers electrical energy from one circuit to another through electromagnetic induction.

• Transformers are used to increase or decrease the voltage of an alternating current (AC) power supply.

• They consist of two coils of wire, known as the primary and secondary coils, which are wrapped around a magnetic core.

• When an AC voltage is applied to the primary coil, it creates a magnetic field that induces a voltage in the secondary coil.

• Tra...read more

Current is the flow of electric charge through a conductor.

• Current is measured in amperes (A).

• It is caused by the movement of electrons.

• The direction of current flow is from positive to negative.

• Current can be either direct current (DC) or alternating current (AC).

Voltage is the measure of electric potential difference between two points in a circuit.

• Voltage is measured in volts (V).

• It is the force that drives electric current through a circuit.

• Higher voltage means more energy is available to move electrons.

• Voltage can be either AC (alternating current) or DC (direct current).