Q&A Hero

Communication

Q: Subchannels are further grouped into ________, which can be allocated to wireless users. A) links B) chips C) signals D) bursts
Q: Like OFDM, _______ employs multiple closely spaced subcarriers, but the subcarriers are divided into groups of subcarriers. A) CDMA B) IFFT C) QPSK D) OFDMA
Q: FFT is a family of algorithms that form a special case of the __________ , which refers to any algorithm that generates a quantized Fourier transform of a time-domain function. A) DFT B) IFT C) IFFT D) QPSK
Q: The relationship among the subcarriers in the OFDM scheme is referred to as ________ . A) modulation B) B) subchannels C) orthogonality D) spread spectrum
Q: With __________ , each bit in the original signal is represented by multiple bits in the transmitted signal, using a spreading code. A) IFFT B) DSSS C) CDMA D) FHSS
Q: With ________ it is possible to simultaneously transmit either from or to different users by allocating the subcarriers during any one-time interval to multiple users. A) OFDMA B) SC-FDMA C) SC-TDMA D) all of the above
Q: One prominent advantage of _______ over OFDMA is the lower peak-to-average power ration of the transmit waveform, which benefit the mobile user in terms of battery life and power efficiency. A) PAPR B) IFFT C) FMDA D) SC-FDMA
Q: OFDMA subcarriers are divided into groups and each group is named a ______ . A) chip B) hop C) subchannel D) SCG
Q: _________ is a common modulation scheme used with OFDM. A) QPSK B) FFT C) IFFT D) ISI
Q: The ________ scheme uses advance digital signal processing techniques to distribute the data over multiple carriers at precise frequencies. A) SC-FDMA B) OFDM C) OFDMA D) CDMA
Q: ________ is used on the downlink channel to enable the base station to transmit different data streams to multiple users over the same frequency band. A) OFDM B) SC-FDMA C) MIMO-BC D) all of the above
Q: ________ is used on the uplink channel to provide multiple access to subscriber stations. A) MIMO-MAC B) MIMO-MU C) MIMO-DS D) MIMO-BC
Q: __________ is when a source data stream is divided among the transmitting antennas.A) SC-FDMAB) Spatial multiplexingC) OFDMD) None of the above
Q: With __________ the same data is coded and transmitted through multiple antennas.A) spatial multiplexingB) CDMAC) spatial diversityD) SC-FDMA
Q: MIMO exploits the space dimension to improve wireless systems in terms of _________. A) range B) capacity C) reliability D) all of the above
Q: Spread spectrum is an important form of encoding for wireless communications.
Q: Subchannelization is not useful for battery-powered devices.
Q: Orthogonal Frequency-Division Multiple Access employs multiple closely spaced subcarriers.
Q: MU-MIMO techniques are used in both Wi-Fi and 4G cellular networks.
Q: The IFFT operation has the effect of ensuring that the subcarriers do not interfere with each other.
Q: OFDM cannot overcome intersymbol interference in a multipath environment.
Q: MIMO systems are characterized by the number of antennas at each end of the wireless channel.
Q: In OFDM all of the subcarriers are dedicated to a single data source.
Q: MIMO-MAC systems outperform point-to-point MIMO.
Q: A disadvantage of MU-MIMO is that the available capacity cannot be shared to meet time-varying demands.
Q: Spatial diversity can be used when transmitting conditions are favorable and for relatively short distances compared to spatial multiplexing.
Q: In a multipath scenario where each receiving antenna would experience a different interference environment, there is a high probability that if one antenna is suffering a high level of fading, another antenna has sufficient signal level.
Q: Diverse multipath fading offers multiple views of the transmitted data at the receiver, thus increasing robustness.
Q: In a MIMO scheme the transmitter employs a single antenna.
Q: Together, MIMO and OFDM technologies are the cornerstone of emerging broadband wireless networks.
Q: LDPC codes exhibit performance in terms of bit error probability that is veryclose to the ________ limit and can be efficiently implemented for high-speed use.
Q: ________ codes make highly efficient use of redundancy and block lengths and symbol sizes can be easily adjusted to accommodate a wide range of message sizes.
Q: (A) Process received bits to compute the syndrome code in exactly the same fashion as the encoder processes the data bits to produce the check code; (B) if the syndrome bits are all zero, no error has been detected; and (C) if the syndrome is nonzero, perform additional processing on the syndrome for error correction, -- is the procedure for the decoding of a _________ code.
Q: For a parity-check code there are three functions to perform: encoding, error detection, and __________ .
Q: The ________ is a measure of how much additional bandwidth is required to carry data at the same data rate as without the code.
Q: The ratio of redundant bits to data bits, (n - k)/k, is called the _______ of the code.
Q: The m * n matrix H = [hij] is called the _______ .
Q: _________ codes are a widely used subclass of nonbinary BCH codes.
Q: In the case of the CRC, a particular cyclic code can be represented by a polynomial divisor, called the ___________ .
Q: Reed-Solomon is an example of a ________ code.
Q: Bose-Chaudhuri-Hocquenghem is an example of a _________ code.
Q: Cyclic codes can be easily encoded and decoded using __________ registers.
Q: Frequency modulation and phase modulation are special cases of _________ modulation.
Q: _________ modulation is the simplest form of modulation.
Q: __________ has been defined as the process of combining an input signal m(t) and a carrier at frequency fc to produce a signal s(t) whose bandwidth is (usually) centered on fc.
Q: __________ proposed an approach for the construction of LDPC codes by defining the LDPC parity-check matrix. A) MacKay B) Reed C) Gallager D) Neal
Q: To compute an error-locator polynomial and solve for its roots is a technique for BCH decoding proposed by ________ . A) Berlekamp B) Reed-Solomon C) Bose D) Chaudhuri
Q: Special cases of angle modulation are frequency modulation and ________ modulation. A) VSB B) repeat-accumulate C) code rate D) phase modulation
Q: An LDPC construction technique that results in a systematic code is called a __________ code. A) Tanner B) irregular LDPC C) regular LDPC D) repeat-accumulate
Q: The ratio of data bits to total bits, k/n, is called the _________ . A) code rate B) parity-check matrix C) systematic code D) redundancy
Q: With __________ codes, data are processed in chunks of m bits, called symbols. A) FEC B) systematic C) Reed-Solomon D) all of the above
Q: __________ codes are among the most powerful cyclic block codes and are widely used in wireless applications.A) Parity checkB) B) BCHC) LPDCD) Repeat-accumulate
Q: A ____________ code takes a fixed-length input and produces a fixed-length check code. A) cyclic error-correcting B) cyclic redundancy check C) cyclic logic check D) none of the above
Q: A _________ code takes an input of arbitrary length and produces a fixed-length CRC check code. A) BCH B) LFS C) VSB D) CRC
Q: Many of the error-correcting block codes that are in use are in a category called ________ . A) cyclic codes B) logic codes C) linear codes D) BCH codes
Q: ___________ rule demonstrates that both FM and PM require greater bandwidth than AM.A) Reed'sB) Carson'sC) Chaudhuri'sD) Solomon's
Q: ________ uses one sideband and a reduced power carrier. A) SSB B) DBS C) VSB D) BTC
Q: The _________ is the ratio of the amplitude of the input signal to the carrier. A) modulation index B) frequency phase C) division rate D) none of the above
Q: __________ is a basic characteristic of a signal used for modulation. A) Frequency B) Amplitude C) Phase D) All of the above
Q: Voice signals are transmitted over telephone lines at their original spectrum, which is referred to as __________ transmission. A) modulation B) baseband C) frequency D) parity
Q: Stop-and-wait flow control is more efficient than sliding-window flow control.
Q: With the exception of the repeat-accumulate code, the LDCP code is systematic.
Q: With a nonsystematic code it is more difficult to determine a technique for generating a codeword from a block of data bits.
Q: The syndrome indicates which of the individual parity-check equations do not equal 0.
Q: LDPC codes cannot be efficiently implemented for high-speed use.
Q: RS codes are well suited for burst error correction.
Q: The LFSR implementation of a cyclic error-correcting encoder is the same as that of the CRC error-detecting code.
Q: Amplitude modulation is a linear process and produces frequencies that are the sum and difference of the carrier signal and the components of the modulating signal.
Q: DSBSC filters out the carrier frequency and sends both sidebands but does not use as much power and bandwidth as DSBTC.
Q: The spectrum of the AM signal consists of the original carrier plus the spectrum of the input signal translated to fc.
Q: SSB is a variant of AM that requires only half of the bandwidth.
Q: The principal techniques for modulation using analog data are amplitude modulation, frequency modulation, and phase modulation.
Q: For unguided transmission it is virtually impossible to transmit baseband signals.
Q: Modulation does not permit frequency-division multiplexing.
Q: When only analog transmission facilities are available, modulation is required to convert the digital data to analog form.
Q: In addition to TCP, the ________ is the other transport-level protocol that is commonly used as part of the TCP/IP protocol suite.
Q: RTT Variance Estimation, also known as ________, is the technique specified in the TCP standard that enables a TCP entity to adapt to changes in round-trip time.
Q: A TCP implementation may employ one of three retransmission strategies: First-only, Individual, and ________.
Q: TCP mechanisms can be grouped into the categories of data transfer, connection termination, and ________.
Q: The ________ field in the TCP header contains the sequence number of the next data octet that the TCP entity expects to receive.
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