Wireless Communication Networks PDF

CCCN 422 Wireless Communication Networks Dr. Mohammed Balfaqih Assistant Professor [email protected] @modditto Lecture Outline ▪ Wireless Transmission Fundamentals • • • • • • • • • Signals for Conveying Information Spectrum Considerations Cells and Antennas Signal and Propagation Analog and...

CCCN 422 Wireless Communication Networks Dr. Mohammed Balfaqih Assistant Professor [email protected] @modditto Lecture Outline ▪ Wireless Transmission Fundamentals • • • • • • • • • Signals for Conveying Information Spectrum Considerations Cells and Antennas Signal and Propagation Analog and Digital Data Transmission Signal Encoding Techniques Channel Capacity Transmission Media Multiplexing Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Signals for Conveying Information Physical representation of data Function of time and location Signal parameters: parameters representing the value of data Classification continuous time/discrete time continuous values/discrete values analog signal = continuous time and continuous values digital signal = discrete time and discrete values Signal parameters of periodic signals: period T, frequency f=1/T, amplitude A, phase shift  sine wave as special periodic signal for a carrier: s(t) = At sin(2  ft t + t) Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Signals for Conveying Information Fourier representation of periodic signals   1 g (t ) = c +  an sin( 2nft ) +  bn cos(2nft ) 2 n =1 n =1 1 1 0 0 t ideal periodic signal Dr. Mohammed Balfaqih t real composition (based on harmonics) CCCN 422: Wireless Communication Networks Signals for Conveying Information Real technical systems are always bandwidth-limited attenuation threshold 0 Dr. Mohammed Balfaqih bandwidth frequency [Hz] CCCN 422: Wireless Communication Networks Signals for Conveying Information • Different representations of signals • amplitude (amplitude domain) • frequency spectrum (frequency domain) • constellation diagram (amplitude M and phase  in polar coordinates) Q = M sin  A [V] A [V] t[s]  I= M cos   f [Hz] • Composed signals transferred into frequency domain using Fourier transformation • Digital signals need • infinite frequencies for perfect transmission • modulation with a carrier frequency for transmission (analog signal!) Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Spectrum Considerations Spread spectrum technology Problem of radio transmission: frequency dependent fading can wipe out narrow band signals for duration of the interference Solution: spread the narrow band signal into a broad band signal using a special code - protection against narrow band interference power interference power spread signal detection at receiver f signal spread interference f Side effects: - coexistence of several signals without dynamic coordination - tap-proof Alternatives: Direct Sequence, Frequency Hopping Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Spectrum Considerations Effects of spreading and interference dP/df i) dP/df ii) f sender dP/df iii) f dP/df dP/df iv) f receiver Dr. Mohammed Balfaqih user signal broadband interference narrowband interference v) f f CCCN 422: Wireless Communication Networks Spectrum Considerations Spreading and frequency selective fading channel quality 1 2 5 3 6 narrowband channels 4 frequency narrow band signal guard space channel quality 1 Dr. Mohammed Balfaqih spread spectrum 2 2 2 2 2 spread spectrum channels frequency CCCN 422: Wireless Communication Networks Spectrum Considerations DSSS (Direct Sequence Spread Spectrum) I XOR of the signal with pseudo-random number (chipping sequence) - many chips per bit (e.g., 128) result in higher bandwidth of the signal Advantages - reduces frequency selective fading - in cellular networks - base stations can use the same frequency range - several base stations can detect and recover the signal - soft handover tb user data 0 1 XOR tc chipping sequence 01101010110101 = resulting signal 01101011001010 Disadvantages - precise power control necessary Dr. Mohammed Balfaqih tb: bit period tc: chip period CCCN 422: Wireless Communication Networks Spectrum Considerations DSSS (Direct Sequence Spread Spectrum) II user data X spread spectrum signal modulator chipping sequence transmitted signal radio carrier transmitter correlator received signal demodulator radio carrier Dr. Mohammed Balfaqih lowpass filtered signal products X sampled sums integrator data decision chipping sequence receiver CCCN 422: Wireless Communication Networks Spectrum Considerations FHSS (Frequency Hopping Spread Spectrum) I • Discrete changes of carrier frequency - sequence of frequency changes determined via pseudo random number sequence • Two versions - Fast Hopping: several frequencies per user bit - Slow Hopping: several user bits per frequency • Advantages - frequency selective fading and interference limited to short period - simple implementation - uses only small portion of spectrum at any time Dr. Mohammed Balfaqih • Disadvantages - not as robust as DSSS - simpler to detect CCCN 422: Wireless Communication Networks Spectrum Considerations FHSS (Frequency Hopping Spread Spectrum) II tb user data 0 1 f 0 1 1 t td f3 slow hopping (3 bits/hop) f2 f1 f t td f3 fast hopping (3 hops/bit) f2 f1 t tb: bit period Dr. Mohammed Balfaqih td: dwell time CCCN 422: Wireless Communication Networks Spectrum Considerations FHSS (Frequency Hopping Spread Spectrum) III spread transmit signal narrowband signal user data modulator modulator frequency synthesizer transmitter received signal narrowband signal demodulator hopping sequence Dr. Mohammed Balfaqih frequency synthesizer hopping sequence data demodulator receiver CCCN 422: Wireless Communication Networks Spectrum Considerations Software Defined Radio Basic idea (ideal world) - Full flexibility wrt. modulation, carrier frequency, coding… - Simply download a new radio! - Transmitter: digital signal processor plus very fast D/A-converter - Receiver: very fast A/D-converter plus digital signal processor Real world - Problems due to interference, high accuracy/high data rate, low-noise amplifiers needed, filters etc. Examples - Joint Tactical Radio System, GNU Radio, Universal Software Radio Peripheral, … - see e.g. SDR – 20 Years Later, IEEE Communications Magazine, Sept. 2015 and Jan. 2016 Application Signal Processor Application Dr. Mohammed Balfaqih D/A Converter Signal Processor A/D Converter CCCN 422: Wireless Communication Networks Cells and Antennas Antennas: isotropic radiator - Radiation and reception of electromagnetic waves, coupling of wires to space for radio transmission. - Isotropic radiator: equal radiation in all directions (three dimensional) - only a theoretical reference antenna. - Real antennas always have directive effects (vertically and/or horizontally). - Radiation pattern: measurement of radiation around an antenna y z z y x Dr. Mohammed Balfaqih x ideal isotropic radiator CCCN 422: Wireless Communication Networks Cells and Antennas Antennas: simple dipoles Real antennas are not isotropic radiators but, e.g., dipoles with lengths /4 on car roofs or /2 as Hertzian dipole ➔ shape of antenna proportional to wavelength /4 /2 Example: Radiation pattern of a simple Hertzian dipole y y x side view (xy-plane) z z side view (yz-plane) x simple dipole top view (xz-plane) Gain: maximum power in the direction of the main lobe compared to the power of an isotropic radiator (with the same average power) Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Cells and Antennas Antennas: directed and sectorized Often used for microwave connections or base stations for mobile phones (e.g., radio coverage of a valley) y y z x z side view (xy-plane) x side view (yz-plane) top view (xz-plane) z z x x top view, 3 sector Dr. Mohammed Balfaqih directed antenna sectorized antenna top view, 6 sector CCCN 422: Wireless Communication Networks Cells and Antennas Antennas: diversity Grouping of 2 or more antennas - multi-element antenna arrays Antenna diversity - switched diversity, selection diversity - receiver chooses antenna with largest output - diversity combining - combine output power to produce gain - cophasing needed to avoid cancellation /2 /4 /2 + Dr. Mohammed Balfaqih ground plane /4 /2 /2 + CCCN 422: Wireless Communication Networks Cells and Antennas MIMO Multiple-Input Multiple-Output - use of several antennas at receiver and transmitter - increased data rates and transmission range without additional transmit power or bandwidth via higher spectral efficiency, higher link robustness, reduced fading Examples - IEEE 802.11n, LTE, HSPA+, … Functions - “beamforming”: emit the same signal from all antennas to maximize signal power at receiver antenna - spatial multiplexing: split high-rate signal into multiple lower rate streams and transmit over different antennas - diversity coding: transmit single stream over different antennas with (near) orthogonal codes t1 t3 3 sender Dr. Mohammed Balfaqih 1 2 Time of flight t2=t1+d2 t3=t1+d3 t2 Sending time 1: t0 2: t0-d2 3: t0-d3 receiver CCCN 422: Wireless Communication Networks Signal and Propagation Signal propagation ranges Transmission range - communication possible - low error rate Detection range - detection of the signal possible - no communication possible sender transmission Interference range - signal may not be detected - signal adds to the background noise distance detection interference Warning: figure misleading – bizarre shaped, time-varying ranges in reality! Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Signal and Propagation Signal propagation Propagation in free space always like light (straight line) Receiving power proportional to 1/d² in vacuum – much more attenuation in real environments, e.g., d3.5…d4 (d = distance between sender and receiver) Receiving power additionally influenced by - fading (frequency dependent) - shadowing - reflection at large obstacles - refraction depending on the density of a medium - scattering at small obstacles - diffraction at edges Dr. Mohammed Balfaqih shadowing reflection refraction scattering diffraction CCCN 422: Wireless Communication Networks Signal and Propagation Real world examples www.ihe.kit.edu/index.php Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Signal and Propagation Multipath propagation Signal can take many different paths between sender and receiver due to reflection, scattering, diffraction LOS pulses multipath pulses LOS (line-of-sight) signal at sender signal at receiver Time dispersion: signal is dispersed over time - interference with “neighbor” symbols, Inter Symbol Interference (ISI) The signal reaches a receiver directly and phase shifted - distorted signal depending on the phases of the different parts Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Signal and Propagation Effects of mobility Channel characteristics change over time and location - signal paths change - different delay variations of different signal parts - different phases of signal parts ➔ quick changes in the power received (short term/fast fading) power Additional changes in - distance to sender - obstacles further away ➔ slow changes in the average power received (long term/slow fading) Dr. Mohammed Balfaqih long term fading t short term fading CCCN 422: Wireless Communication Networks Analog and Digital Data Transmission Examples of Analog and Digital Data • Analog • Video • Audio • Digital • Text • Integers Acoustic Spectrum of Speech and Music Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Analog and Digital Data Transmission Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Analog and Digital Data Transmission Analog Signals • A continuously varying electromagnetic wave that may be propagated over a variety of media, depending on frequency • Examples of media: • Copper wire media (twisted pair and coaxial cable) • Fiber optic cable • Atmosphere or space propagation • Analog signals can propagate analog and digital data Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Analog and Digital Data Transmission Digital Signals • A sequence of voltage pulses that may be transmitted over a copper wire medium • Generally cheaper than analog signaling • Less susceptible to noise interference • Suffer more from attenuation • Digital signals can propagate analog and digital data Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Analog and Digital Data Transmission Reasons for Choosing Data and Signal Combinations • Digital data, digital signal • Equipment for encoding is less expensive than digital-to-analog equipment • Analog data, digital signal • Conversion permits use of modern digital transmission and switching equipment • Digital data, analog signal • Some transmission media will only propagate analog signals • Examples include optical fiber and satellite • Analog data, analog signal • Analog data easily converted to analog signal Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Analog and Digital Data Transmission Analog Transmission • Transmit analog signals without regard to content • Attenuation limits length of transmission link • Cascaded amplifiers boost signal’s energy for longer distances but cause distortion • Analog data can tolerate distortion • Introduces errors in digital data Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Analog and Digital Data Transmission Digital Transmission • Concerned with the content of the signal • Attenuation endangers integrity of data • Digital Signal • Repeaters achieve greater distance • Repeaters recover the signal and retransmit • Analog signal carrying digital data • Retransmission device recovers the digital data from analog signal • Generates new, clean analog signal Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Analog and Digital Data Transmission Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Signal Encoding Techniques • • • Encoding is the process of converting the data or a given sequence of characters, symbols, alphabets etc., into a specified format, for the secured transmission of data. Decoding is the reverse process of encoding which is to extract the information from the converted format. The data encoding technique is divided into the following types, depending upon the type of data conversion. - Analog data to Analog signals − The modulation techniques such as Amplitude Modulation, Frequency Modulation and Phase Modulation of analog signals, fall under this category. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Signal Encoding Techniques - Analog data to Digital signals − This process can be termed as digitization, which is done by Pulse Code Modulation PCM. Hence, it is nothing but digital modulation. - Digital data to Analog signals − The modulation techniques such as Amplitude Shift Keying ASK, Frequency Shift Keying FSK, Phase Shift Keying PSK, etc., fall under this category. - Digital data to Digital signals − These are in this section. There are several ways to map digital data to digital signals such as Non-Return to Zero (NRZ). Dr. Mohammed Balfaqih Pulse Code Modulation CCCN 422: Wireless Communication Networks Channel Capacity About Channel Capacity • Impairments, such as noise, limit data rate that can be achieved • For digital data, to what extent do impairments limit data rate? • Channel Capacity – the maximum rate at which data can be transmitted over a given communication path, or channel, under given conditions Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Channel Capacity Concepts Related to Channel Capacity • Data rate - rate at which data can be communicated (bps) • Bandwidth - the bandwidth of the transmitted signal as constrained by the transmitter and the nature of the transmission medium (Hertz) • Noise - average level of noise over the communications path • Error rate - rate at which errors occur • Error = transmit 1 and receive 0; transmit 0 and receive 1 Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Channel Capacity Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Channel Capacity Nyquist Bandwidth • For binary signals (two voltage levels) • C = 2B • With multilevel signaling • C = 2B log2 M • M = number of discrete signal or voltage levels • As an example, - consider a voice channel being used, via modem, to transmit digital data. Assume a bandwidth of 3100 Hz. Then the capacity, C, of the channel is 2B = 6200 bps. - for M = 8, a value used with some modems, a bandwidth of B = 3100 Hz yields a capacity C = 18,600 bps . Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Channel Capacity Signal-to-Noise Ratio • Ratio of the power in a signal to the power contained in the noise that’s present at a particular point in the transmission • Typically measured at a receiver • Signal-to-noise ratio (SNR, or S/N) signal power ( SNR)dB = 10 log10 noise power • A high SNR means a high-quality signal, low number of required intermediate repeaters • SNR sets upper bound on achievable data rate Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Channel Capacity Shannon Capacity Formula • Equation: C = B log 2 (1 + SNR ) • Represents theoretical maximum that can be achieved • In practice, only much lower rates achieved • Formula assumes white noise (thermal noise) • Attenuation distortion or delay distortion not accounted for • Here the channel capacity C is the upper bound on the rate of information transmission per second. • In other words, C is the maximum number of bits that can be transmitted per second with a probability of error arbitrarily close to zero; that is, the transmission is as accurate as one desires. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Channel Capacity • Shannon's equation clearly brings out the limitation on the rate of communication imposed by B and SNR. • If there is no noise on the channel (assuming SNR = ∞), then the capacity C would be ∞, and communication rate could be arbitrarily high. We could then transmit any amount of information in the world over one noiseless channel. This can be readily verified. • In conclusion, Shannon's capacity equation demonstrates qualitatively the basic role played by B and SNR in limiting the performance of a communication system. These two parameters then represent the ultimate limitation on the rate of communication. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Channel Capacity Example of Nyquist and Shannon Formulations • Spectrum of a channel between 3 MHz and 4 MHz ; SNRdB = 24 dB B = 4 MHz − 3 MHz = 1 MHz SNR dB = 24 dB = 10 log 10 (SNR ) SNR = 251 • Using Shannon’s formula C = 106  log2 (1 + 251)  106  8 = 8Mbps C = 2 B log 2 M ( ) 8 106 = 2  106  log 2 M 4 = log 2 M Dr. Mohammed Balfaqih M = 16 CCCN 422: Wireless Communication Networks Transmission Media Classifications of Transmission Media • Transmission Medium • Physical path between transmitter and receiver • Guided Media • Waves are guided along a solid medium • E.g., copper twisted pair, copper coaxial cable, optical fiber • Unguided Media • • • • • Provides means of transmission but does not guide electromagnetic signals Usually referred to as wireless transmission E.g., atmosphere, outer space Transmission and reception are achieved by means of an antenna Configurations for wireless transmission: Directional & Omnidirectional Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Multiplexing • Capacity of transmission medium usually exceeds capacity required for transmission of a single signal • Multiplexing - carrying multiple signals on a single medium • More efficient use of transmission medium • There are three ways to improve communication throughput 1. Increase the transmitter’s power or reduce system loss to improve at receiver (Link analysis) 2. Provide more channel bandwidth. 3. Make the allocation of the communication resource more efficient (multiple access) • Reasons for Widespread Use of Multiplexing Cost per kbps of transmission facility declines with an increase in the data rate Cost of transmission and receiving equipment declines with increased data rate Most individual data communicating devices require relatively modest data rate support Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Multiplexing • Multiple Access Techniques 1. Frequency Division Multiplexing/Multiple Access (FDMA): specified sub-band or frequency are allocated. 2. Time Division Multiplexing/Multiple Access (TDMA): specified time slots are allocated. 3. Code division Multiplexing/Multiple Access (CDMA): users use mutually orthogonal code 4. Orthogonal Frequency Division Multiplexing/Multiple Access (OFDMA): Mutually orthogonal frequency domain signals are used by different users. 5. Space division Multiplexing/Multiple Access (SDMA): use beam antennas pointing to different direction. 6. Polarization division Multiplexing/Multiple Access (PDMA): orthogonal polarization are used to separate signals. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Multiplexing Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Multiplexing • Frequency Division Multiplexing/Multiple Access (FDMA) - Allocate different frequency bands to different users. Ideally, there is no overlapping between the frequency bands. Guard band: a buffer zone between adjacent channels to reduce adjacent channel interference. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Multiplexing • Time Division Multiplexing/Multiple Access (TDMA) • Frame and slots - Frame: time is segmented into short intervals - Slot: Each frame is further divided into slots. • Time division multiple access (TDMA) - Different users are assigned different time slots. - Can only be used in digital communication systems. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Multiplexing • Fixed-assignment TDMA - Each user is assigned one or more fixed time slots - Efficient when the data from users are heavy. - Inefficient when the data from users are bursty (sporadic) Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Multiplexing • Dynamic-assignment TDMA (packet switching) - A user is assigned a time-slot only when it has data to transmit - Advantage: better utilization of channel, efficient for bursty traffic. - Disadvantage: need extra control scheme (media access control, MAC) to determine which user should transmit Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Multiplexing • FDMA v.s. TDMA: Bit Rate - Bit rate equivalence: with the same communication resource and same number of channels, FDMA and TDMA can support the same data rate on each channel. - Assume the size of a packet is b bits, and there are M channels. • FDMA: - Bit rate of one channel: b/T bps - Total bit rate of M channels: R = M b /T bps • TDMA - Time are divided into M slots - b bits are transmitted in a duration of T/M: R = b/(T/M) = Mb/T bps Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Multiplexing • FDMA V.S. TDMA: Delay Dr. Mohammed Balfaqih CCCN 435: Digital Communication Systems Multiplexing • FDMA V.S. TDMA: Delay Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Multiplexing • Code Division Multiplexing/Multiple Access (CDMA) - The data of all users are transmitted on the same frequency band at the same time. Each user is assigned a unique signature code The receiver extract the information of one user by using the signature code of that user. Two types of CDMA 1. Direct sequence CDMA (DS-CDMA) 2. Frequency hopping CDMA (FH-CDMA) Dr. Mohammed Balfaqih CDMA frequency-hopping modulation process Multiplexing • OFDMA • Orthogonal Frequency Division Multiplexing (OFDM) is a digital multi-carrier modulation technique extending the concept of single subcarrier modulation by using multiple sub-carriers over the channel. • Rather than transmit a high‐rate stream of data with a single carrier, OFDM makes use of a large number of closely spaced orthogonal sub-carriers that are transmitted in parallel. Send a sample using the entire band Dr. Mohammed Balfaqih Send samples concurrently using multiple orthogonal sub-channels Figure: Transport analogy: One large delivery vehicle depicts ordinary FDM. Many small vehicles depict OFDM. CCCN 422: Wireless Communication Networks Multiplexing • FDMA - Not orthogonal - Need guard bands between adjacent frequency bands → extra overhead and lower throughput • OFDMA - Don’t need guard bands - Multiple sub-channels (sub-carriers) carry samples sent at a lower rate. - Only some of the sub-channels are affected by interferers or multi-path effect Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Multiplexing Why OFDM? • Imagine a channel having a relatively narrow coherence bandwidth 𝑓0 , as shown in Figure 15.2a. Suppose that the goal is to transmit a wide-bandwidth W (high-data-rate) signal, as shown in Figure 15.2b, over that channel, where 𝑊 > 𝑓0 . • Figure 15.2c is a sketch illustrating that OFDM’s mitigation stems from dividing or parsing the high-rate signal into a number 𝑁𝑐 of low-rate orthogonal subchannels. • In the scheme of resource assignment, the term subchannel is used to designate some predetermined number of subcarrier bands. • Each subchannel has a bandwidth (𝑊/𝑁𝑐 ) < 𝑓0 , thereby transforming one large frequency-selectivefading channel into many flatfading Subchannels. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Thank you Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Review Questions 1) maximum power in the direction of the main lobe compared to the power of an isotropic radiator (with the same average power) a. Directivity b. Radiation power density c. Gain of antenna d. Array Factor 2) An ideal source in which the power is radiated equally in all directions is called as ________ radiator. a. Isotropic b. Omni-directional c. Directional d. Transducer Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Review Questions 3) _________ of an antenna is the measurement of radiation around an antenna. a. Radiation pattern b. Directivity c. Beam width d. None of the above 4) As the beam area of an antenna decreases, the directivity of the antenna a. Increases b. Decreases c. Remains unchanged d. Depends on the type of the antenna Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Review Questions 5) If directivity of antenna increases, then the coverage area __________ a. decreases b. increases c. increases and then decreases d. remains unchanged 6) It occurs when signal can take many different paths between sender and receiver due to reflection, scattering, diffraction a. Radiation pattern b. Multipath propagation c. Beam width d. None of the above Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Review Questions 7) It is constrained by the transmitter and the nature of the transmission medium (Hertz) a. Bandwidth b. Error rate c. Noise d. Data rate 8) _____________ is the ratio of the power in a signal to the power contained in the noise that’s present at a particular point in the transmission a. Signal to noise ratio b. Error rate c. Noise d. Data rate Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Review Questions 9) It is defined as the maximum number of bits that can be transmitted per second with a probability of error arbitrarily close to zero a. Signal to noise ratio b. Channel capacity c. Bandwidth d. Data rate 10)In ________, the data of all users are transmitted on the same frequency band at the same time in which each user is assigned a unique signature code a. FDMA b. TDMA c. CDMA d. OFDM Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Review Questions 11) A combination of digital data and digital signal is chosen for data transmission because a. Equipment for encoding is less expensive than digital-to-analog equipment b. Conversion permits use of modern digital transmission and switching equipment c. Some transmission media will only propagate analog signals d. Analog data easily converted to analog signal Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Review Questions 12) What are the advantages of spread spectrum over a fixed-frequency transmission? List the types of spread spectrum? 13)Explain, in your own words, the distinction between path loss, shadow fading, and multipath fading? 14)Explain the difference between Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FSSS) in terms of concept, advantages, and disadvantages. 15)What is antenna diversity? requirements? diversity types? 16)Give a brief description about MIMO technique, its functions, example of technologies that use MIMO? 17)What is signal propagation? Explain different propagation ranges. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Review Questions 18) Explain the free space propagation model? and Path loss model? 19)What the effects of mobility on signal propagation? 20)Differentiate between an analog and a digital electromagnetic signal. 21)Describe the processes of encoding and decoding techniques? 22) Give an example of encoding technique of that is used for the following data conversion a. Analog data to Analog signals: b. Analog data to Digital signals c. Digital data to Analog signals d. Digital data to Digital signals Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Review Questions 23) A voice channel with 3100 Hz wide is used to transmit digital data. a. How many bits/sec can be sent if binary signals are used? Assume a noiseless channel. b. How many bits/sec can be sent if eight–level digital (M=8) signals are used? Assume a noiseless channel. 24) Television channels are 6 MHz wide. How many bits/sec can be sent if four–level digital signals are used? Assume a noiseless channel. 25)Television channels are 12 MHz wide. How many bits/sec can be sent if 8–level digital signals are used? Assume a noiseless channel. 26)What is the channel capacity for a teleprinter channel with a 300-Hz bandwidth and a signal-to-noise ratio of 3 dB? Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Review Questions 27) Spectrum of a channel between 3 MHz and 4 MHz ; 𝑺𝑵𝑹𝒅𝑩 = 𝟐𝟒 dB. Calculate the channel capacity C and signal levels M. 28)Differentiate between transmission media classes? 29)List four multiple access techniques? Give a brief description about FDMA and TDMA? 30)What is OFMA? Its advantages? What is the difference between OFDMA and FDMA? Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks