Ammar Abu-Hudrouss Islamic University Gaza ١ Course Syllabus Text Boo Andrea Goldsmith,, Cambridge University Press 005. References 1. Rappaport, : Principles and Practice, Prentice Hall nd Ed. D. N. C. Tse and P. Viswanath, Fundamentals of Wireless Communication, Cambridge, U.K., 005 Slide ١
Course Syllabus Course Content: Statistical multipath channel models (ch. 3). Capacity of wireless channel: (ch 4). Diversity techniques for the receiver and the transmitter (ch 7). Multiple antenna and space time communications (ch. 10) Orthogonal Frequency Division Multiplexing (OFDM) (ch. 1) Spread spectrum : DSSS and FSSSS (ch. 13) Multiple access, Random access, power control (ch. 14) Cellular systems and infrastructure-based wireless networs (ch. 15) Slide 3 Course Syllabus Grading Policy The final course grade will be distributed as follows: Quizzes and class activity 10 % Programming and simulation assignments 0 % Research topic and presentation 15% Midterm exam 5 % Final exam 30 % Plagiarism will not be tolerated at any case. Copying homewor from your colleagues or project from any source will lead to severe consequences. Slide 4 ٢
Satellite TV Cordless phone Cellular phone Wireless LAN, WIFI Wireless MAN, WIMAX Bluetooth Ultra Wide Band Wireless Laser Microwave GPS Ad hoc/sensor Networs Slide 5 Basic Concepts Simplex, half-duplex, and full duplex Base Station Mobile Station Subscriber Transceiver Mobile Switching centre Control Channel Roamer Handoff Page Slide 6 ٣
Pager System Slide 7 Pager System Broad coverage for short messaging Message broadcast from all base stations Simple terminals Optimized for 1-way transmission Overtaen by cellular Slide 8 ٤
Cordless phone DC and DECT standards Slide 9 Bluetooth Cable replacement RF technology (low cost) Short range (10m, extendable to 100m).4 GHz band (crowded) 1 Data (700 Kbps) and 3 voice channels, up to 3 Mbps Widely supported by telecommunications, PC, and consumer electronics companies Few applications beyond cable replacement Slide 10 ٥
IEEE 80.15.4 / ZigBee Radios Low-Rate WPAN Data rates of 0, 40, 50 Kbps Support for large mesh networing or star clusters Support for low latency devices CSMA-CA channel access Very low power consumption Frequency of operation in ISM bands Focus is primarily on low power sensor networs Slide 11 Satellite Systems Cover very large areas Different orbit heights GEOs (39000 Km) versus LEOs (000 Km) Optimized for one-way transmission Most two-way systems struggling or banrupt Global Positioning System (GPS) use growing Satellite signals used to pinpoint location Popular in cell phones, PDAs, and navigation devices Slide 1 ٦
Cellular System Mobile identification number (MIN) electronic serial number (ESN) Slide 13 G to 3G evolution Slide 14 ٧
4G and LTE (long term evolution) OFDM/MIMO Much higher data rates (50-100 Mbps) Greater spectral efficiency (bits/s/hz) Flexible use of up to 100 MHz of spectrum Low pacet latency (<5ms). Increased system capacity Reduced cost-per-bit Support for multimedia Slide 15 Wireless Local Area Networs (WLANs) 01011011 0101 1011 Internet Access Point WLANs connect local computers (100m range) Breas data into pacets Channel access is shared (random access) Bacbone Internet provides best-effort service Poor performance in some apps (e.g. video) Slide 16 ٨
Wifi Networs (Supporting Multimedia) 80.11n++ Streaming video Gbps data rates High reliability Coverage in every room Slide 17 Wireless HDTV and Gaming Wimax (80.16) Wide area wireless networ standard System architecture similar to cellular Hopes to compete with cellular OFDM/MIMO is core lin technology Operates in.5 and 3.5 MHz bands Different for different countries, 5.8 also used. Bandwidth is 3.5-10 MHz Fixed (80.16d) vs. Mobile (80.16e) Wimax Fixed: 75 Mbps max, up to 50 mile cell radius Mobile: 15 Mbps max, up to 1- mile cell radius Slide 18 ٩
Characteristic of Wireless Channel Slide 19 Channel Impulse Response x(t) y(t) Channel Slide 0 ١٠
Channel Impulse Response Response of channel at t to impulse at t-: N jn ( t ) c(, t) n( t) e ( n1 ( t)) t is time when impulse response is observed t- is time when impulse put into the channel is how long ago impulse was put into the channel for the current observation path delay for MP component currently observed n Slide 1 Received Signal Characteristics Received signal consists of many multipath components Amplitudes change slowly Phases change rapidly Constructive and destructive addition of signal components Amplitude fading of received signal (both wideband and narrowband signals) Slide ١١
Major Categories of Fading Large Scale Fading : This is the loss that propagation models try to account for mostly dependant on the distance from the transmitter to the receiver also nown as Large Scale Path Loss, Log-Normal Fading or Shadowing Small Scale Fading : Could be 0-30 db over a fraction of a wavelength. It is Caused by the superposition or cancellation of multipath propagation signals, the speed of the transmitter or receiver or the bandwidth of the transmitted signal. It is also nown as Multipath Fading or Rayleigh Fading Slide 3 Small Scale Fading: The type of fading experienced by a signal propagating through a channel can be determined by the nature of the transmitted signal with respect to the characteristics of the channel. Factors influencing small scale fading: Factors influencing small scale fading: Multipath propagation. Speed of the mobile. Speed of the surrounding objects. Transmission bandwidth of the signal. Slide 4 ١٢
Inter symbol interference A A B D = A+B+C C Slide 5-90 Power delay Profile RMS Delay Spread ( ) = 46.4 ns Received Signal Level (dbm) -90-95 -100 Mean Excess delay () = 45 ns Maximum Excess delay < 10 db = 110 ns Noise threshold -105 0 50 100 150 00 50 300 350 400 450 Excess Delay (ns) Slide 6 ١٣
Delay Spread: Mean excess delay RMS delay spread Excess delay spread Mean excess delay is the first moment of the power delay profile and is defined by the equation a a h h P( ) P( ) Slide 7 RMS delay spread is the square root of the second central moment of the power delay profile and is defined by the equation: where ( ) a a h P( ) h P( ) Maximum excess delay is defined as the x 0,where, 0 is the first arriving signal and x is the maximum delay at which a multipath component is within X db of the strongest arriving multipath signal. Slide 8 ١٤
Example (Power delay profile) P r () 4.38 µs 1.37 µs 0 db -10 db -0 db -30 db 0 1 5 (µs) _ (1)(5) (0.1)(1) (0.1)() (0.01)(0) 4. 38s [0.010.1 0.11] _ (1)(5) (0.1)(1) (0.1)() (0.01)(0) 1.07s [0.010.10.11] 1.07(4.38) 1. 37s Slide 9 RMS delay spread and coherence b/w RMS delay spread and coherence b/w (B c ) are inversely proportional B c 1 Bc 1 50. For 0.9 correlation Bc 1 5. For 0.5 correlation Slide 30 ١٥
Coherence Bandwidth Time domain view x(t) Freq. domain view X ( f ) delay spread Range of freq over which response is flat B c High correlation of amplitude between two different freq. components Slide 31 Time dispersive nature of channel Delay spread and coherence bandwidth are parameters which describe the time dispersive nature of the channel. Time domain view Freq domain view signal 1 signal Signal Symbol Time (T s ) Signal bandwidth (B s ) channel 1 channel Channel channel 3 RMS delay spread ( ) Coherence b/w (B c ) Slide 3 ١٦
Revisit Example (Power delay profile) P r () 0 db 4.38 µs 1.37 µs _ 4. 38s -10 db -0 db -30 db _ 1.07s 1. 37s 0 1 5 (µs) 1 ( 50% coherence) Bc 146Hz 5. Signal bandwidth for Analog Cellular = 30 KHz Signal bandwidht for GSM = 00 KHz Slide 33 Coherence bandwidth: It is the range of frequencies over which two frequency components have a potential for amplitude correlation. If two sinusoids with a frequency separation of greater than B c are propagating in the same channel, they are affected quite differently by the channel. Slide 34 ١٧
Doppler Effect Slide 35 Doppler Shift v Doppler shift v cos f Example - Carrier frequency f c = 1850 MHz (i.e. = 16. cm) - Vehicle speed v = 60 mph = 6.8 m/s - If the vehicle is moving directly towards the transmitter 6.8 f 165 Hz 0.16 - If the vehicle is moving perpendicular to the angle of arrival of the transmitted signal f 0 Slide 36 ١٨
Doppler Spread and Coherence Time Doppler spread and Coherence Time tae into account the relative motion between mobile and base station, or by movements of objects in the channel. They describe the time varying nature of the channel in a small scale region. Slide 37 Doppler Spread B d : When a signal of frequency f c is transmitted, the received signal spectrum, called the Doppler spectrum, will have components f c - f d to f c + f d, where f d is the Doppler shift. Coherence time T c : It is used to characterize the time varying nature of the frequency depressiveness of the channel in the time domain Slide 38 ١٩
For high correlation T c 1 f m For correlation above 0.5 9 Tc 16 f m Mean of the previous two equation is usually used in digital communication systems T c 0.43 f m Slide 39 Time varying nature of channel Doppler spread and coherence time are parameters which describe the time varying nature of the channel. Time domain view Freq domain view signal 1 signal Signal Symbol Time (T S ) Signal bandwidth (B S ) channel 1 channel Channel channel 3 Coherence Time (T C ) Doppler spread (B D ) Slide 40 ٢٠
Small Scale Fading: Different types of transmitted signals undergo different types of fading depending upon the relation between the Signal Parameters: Bandwidth, Symbol Period and Channel Parameters: RMS Delay Spread, Doppler Spread In any mobile radio channel a wave can be dispersed either in Time or in Frequency. These time and frequency dispersion mechanisms lead to four possible distinct effects which depend on the nature of transmitted signal, the channel and the velocity. Slide 41 Flat Fading: A received signal is said to have underwent Flat Fading if The Mobile Radio Channel has a constant gain and linear phase response over a Bandwidth which is greater than the Bandwidth of the transmitted Signal Fading in which all frequency components of a received radio signal vary in the same proportion simultaneously Slide 4 ٢١
Here the multipath structure of the channel is such that spectral characteristics of the transmitted signal are preserved at the receiver But due to the fluctuations in the gain of the channel caused by multipath, the signal strength varies with time Slide 43 From the figure we can note that if the channel gain varies with time, a change of amplitude of the received signal occurs. From the figure we can note that the spectrum of the received signal r (t) is preserved even though there is a change in gain. Flat fading channels are also referred as amplitude varying channels or narrow band channels, since the bandwidth of the applied signal is narrow as compared to the channel flat fading bandwidth. Slide 44 ٢٢
Typical Flat fading channels cause deep fades To achieve low bit error rates during times of deep fades, Flat fading channels operate at 0 to 30dB more transmitter power compared to the systems operating over non-fading channels. Rayleigh distribution is the most common amplitude distribution. According to this distribution, Rayleigh Flat fading channel model assumes that the channel induces an amplitude which varies in time. Slide 45 Summary Signal undergoes Flat Fading if: B s <<B c where B s is bandwidth and B c is the coherence bandwidth of the channel And T s >> where T s is the reciprocal bandwidth and rms delay spread. Slide 46 ٢٣
Frequency Selective Fading: The channel creates frequency selective fading on the received signal when the channel possesses a constant gain and linear phase response over a bandwidth, which is smaller than the bandwidth of the transmitted signal Under these conditions the channel impulse response has a multipath delay spread which is greater than the reciprocal bandwidth of the transmitted message waveform So the received signal includes multiple versions of the transmitted waveform, which are attenuated and delayed in time, and hence the received signal is distorted. Slide 47 Frequency selective fading is much difficult to model than flat fading channels because each multipath signal must be modeled and the channel must be considered to be a linear filter. It is for this reason that wideband multipath measurements are made and models are developed from these measurements. When analyzing mobile communication systems, statistical impulse response models such as the -ray Rayleigh model or computer generated or measured impulse responses are generally used for analyzing frequency selective small-scale fading. Slide 48 ٢٤
Slide 49 For frequency selective fading, the spectrum S(f) of the transmitted signal has a bandwidth which is greater than the coherence bandwidth B c of the channel. Frequency selective fading is caused by multipath delays which approach or exceed the symbol period of the transmitted symbol. These channels are also nown as wideband channels since the bandwidth of the signal s(t) is wider than the bandwidth of the channel impulse response. As time varies, the channel varies in gain and phase across the spectrum of s(t),resulting in time varying distortion in the received signal r(t) Slide 50 ٢٥
Summary Signal undergoes Frequency Selective Fading if: B s >B c where B s is bandwidth and B c is the coherence bandwidth of the channel And T s < where T s is the reciprocal bandwidth and rms delay spread. Slide 51 Small scale fading Flat fading B S B C Multi path time delay Frequency selective fading B S B C fading Doppler spread Fast fading Slow fading T S T C T S T C Slide 5 ٢٦
Rayleigh Fading Distribution: Rayleigh Fading Distribution in mobile radio channels is commonly used to describe the statistical time varying nature of the received envelope of a flat fading signal or the envelope of an individual multipath component. r r p( r) exp (0 ) r 0 (r < 0) where is the rms value of the received voltage signal before envelope detection, is the time-average power of the received signal before envelope detection. Slide 53 Slide 54 ٢٧
The variance r of the Rayleigh distribution is given by r E[ r ] E [ r] r p( r) dr 0 0.49 which represents the ac power in the signal envelope. The rms value of the envelope is Slide 55 The median value of r is found by solving 1 r median r median 0 p( r) dr 1.177 Note: It is customary to use median values instead of the mean values, since fading data are usually measured in the field and a particular distribution cannot be assumed. By using median values instead of mean values it is easier to compare different fading distributions which have widely varying means Slide 56 ٢٨
Ricean Fading Distribution: When there is a dominant stationary (nonfading) signal component present, such as a line-of-sight propagation path, the small scale-scale fading envelope distribution is Ricean. Random multipath components arriving at different angles are superimposed on a stationary dominant signal At the output of an envelope detector this has the effect of adding a dc component to the random multipath Slide 57 The effect of a dominant signal arriving with many weaer multipath signals gives rise to Ricean distribution As the dominant signal becomes weaer, the composite signal gives resembles a noise signal which has an envelope that is Rayleigh Thus, the Ricean distribution degenerates to a Rayleigh distribution when the dominant component fades away Slide 58 ٢٩
The Ricean distribution is given by r p( r) e ( r A ) For A 0,r 0 I0 Ar 0 For r< 0 Where A denotes pea amplitude of the dominant signal I o (.) is the modified Bessel function of the first ind and zero order Slide 59 Ricean Factor K completes determines the Ricean distribution. As A 0, K - db, and as the dominant path decreases in amplitude, the Ricean distribution degenerates to Rayleigh distribution Slide 60 ٣٠