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Implementation of Wireless Channel Model in MATLAB: Simplified

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Implementation of Wireless Channel Model in MATLAB: Simplified

  1. 1. IMPLEMENTATION OF WIRELESS CHANNEL MODEL IN MATLAB: SIMPLIFIED Dr. Rosdiadee Nordin Wireless Networks and Communications Group MATLAB Workshop, 22nd Dec, 2011 Faculty of Engineering and Built Environment Universiti Kebangsaan Malaysia
  2. 2. LAYOUT • What is a wireless channel? • Impairment in wireless • Basic of channel model • SISO • MIMO • OFDM • Share of experience
  3. 3. What is a wireless channel? • Performance of wireless comm sys governed by the wireless channel environment • Wireless channel is dynamic and unpredictable, analysis often difficult • Unique characteristic in a wireless channel is a phenomenon called ‘fading’  variation of signal amplitude over time and frequency • Fading may either be due to multipath propagation, or shadow fading • Broadly classified into two different types: (i) large- scale fading and (ii) small-scale fading
  4. 4. What is a wireless channel? Distortion: amplitude or phase ‘flat’ effect baseband signal variation
  5. 5. Impairment in wireless • Small-scale fading often referred to as fading • Rapid variation of the received signal level in the short term as the user terminal moves a short distance • Multiple signal paths induce interference when arrive with varying phases in the receive antenna • Variation of the received signal level depends on the relationships of the relative phases among the number of signals reflected from the local scatters • Small-scale fading is attributed to multi-path propagation, mobile speed, speed of surrounding objects, and transmission BW of signal
  6. 6. Impairment in wireless • Characteristics of a multipath fading channel are often specified by a power delay profile (PDP) • Useful parameters provide reference of comparison among the different multipath fading channels: ▫ Mean excess delay ▫ RMS delay spread • General guideline to design a wireless transmission system • Wireless channels characterized by different channel parameters: ▫ Multipath delay spread: frequency dispersion (frequency-selective fading) ▫ Doppler spread: time dispersion (time-selective fading)
  7. 7. Basic of Channel Models • Generation of fading channels ▫ LOS (Line-of-Sight): Rician ▫ NLOS (Non Line-of-Sight): Rayleigh 4 x 10 2.5 Rayleigh Ricean near Rayleigh Rician, K=-40dB Rician, K=15dB 2 Ricean near Gaussian 1.5 Occurrence 1 0.5 0 0 0.5 1 1.5 2 2.5 3 3.5 4 x
  8. 8. Basic of Channel Models • Geographical profile: indoor, outdoor, urban, sub- urban, macro, micro, etc • Accurate channel model in specific environment, need knowledge on the characteristics of reflectors, including situation, movement, and the power of the reflected signal at any specified time • Reference to specific channel model that represent a typical or average channel condition in the given environment. • Analysis in static channel: environment in which a channel condition does not change for the duration of data transmission at the given time and location
  9. 9. Basic of Channel Models • Complete opposite to time-varying environment, i.e. objects or people surrounding the transmitter or receiver are steadily moving even while a terminal is not in motion • Degree of time variation in signal strength relative to symbol duration - relatively small with respect to symbol duration • Referred to as a quasi-static channel condition • Channels usually modeled under the assumption of static or quasi-static channel conditions
  10. 10. SISO • Can be categorized into: ▫ Indoor channel:  Small coverage areas inside the building, e.g. office and mall  Completely enclosed by wall – power azimuth spectrum (PAS) tends to be uniform, i.e. scattered components will be received from all directions with same power  Static due to extremely low mobility of the terminals inside the building ▫ Outdoor channel:  Characterized by time variation of the channel gain, subject to mobile speed of terminals  Governed by Doppler spectrum – determines time-domain correlation in the channel gain.  Channel model can be implemented in both frequency-flat and frequency-selective channels
  11. 11. SISO – Common Implementation Indoor Outdoor • Two – ray • FWGN • Exponential • Clarke/ Gan • IEEE 802.11 • Jakes • Saleh-Valenzuela (S-V) • Ray-based • UWB • Frequency selective fading • ETSI HiperLAN • Tapped delay line • Stanford Uni Interim (SUI)
  12. 12. SISO (Indoor): Two – ray Channel Model • Two rays, one for a direct path with zero delay (t > 0) , and the other for a 2-ray Model Ideal 0.6 Simulation path which is a reflection with delay of t1 > 0 0.5 • Delay of second path is the only Channel Power[linear] parameter determines the 0.4 0.3 characteristics of model 0.2 • Not accurate: magnitude of second 0.1 path is less than that of the first path in practice 0 0 20 40 60 Delay[ns] 80 100 120 140 • Acceptable only when there is a significant loss in the first path
  13. 13. SISO (Indoor): Exponential Model • Average channel power decreases exponentially with channel delay 1  /  d P ( )  e (1) d • More appropriate for an indoor channel environment
  14. 14. SISO (Indoor): IEEE 802.11 • Representation of 2.4 GHz indoor channel by IEEE 802.11b Task Group • Channel impulse response can be represented by the output of finite impulse response (FIR) filter • Each channel tap is modeled by an independent complex Gaussian random variable with its average power that follows the exponential PDP • Time index of each channel tap by the integer multiples of sampling periods.
  15. 15. SISO (Indoor): IEEE 802.11 • Maximum number of paths determined by the RMS delay spread,   and sampling period, T s 10 .  p max  (2) Ts • maximum excess delay is fixed to 10 times the RMS delay spread – as oppose to exponential model (max. excess delay computed by a path of the least non- negligible power level) • In this case, the power of each channel tap is given as  pT s /     0e 2 2 p (3)
  16. 16. SISO (Indoor): IEEE 802.11 • where  0 is the power of the first tap, which is 2 determined so as to make the average received power equal to one • Thus: T / 1 e s    (4) 2 0  ( p max  1 ) T s /   1 e • Sampling period must be at least as small as 1/4
  17. 17. SISO (Indoor): IEEE 802.11 Average channel power Channel frequency response IEEE 802.11 Model,  =25ns, TS=50ns Frequency response,  =25ns, TS=50ns 1 0 Ideal 0.9 Simulation 0.8 -2 Average Channel Power[linear] 0.7 -4 Channel power[dB] 0.6 0.5 -6 0.4 -8 0.3 0.2 -10 0.1 0 -12 -1 0 1 2 3 4 5 6 7 -10 -8 -6 -4 -2 0 2 4 6 8 10 channel tap index, p Frequency[MHz]
  18. 18. MIMO • Multi-Input and Multi-Output (MIMO) systems: channel model vary with antenna config • Different channel model is required to capture their spatio-temporal characteristics (e.g., correlation between different paths among multiple transmit and receive antennas). • Correlation between transmit and receive antenna is an important aspect of the MIMO channel. • Depends on the angle-of-arrival (AoA) of each multi-path component
  19. 19. MIMO • Two common methods: ▫ I-METRA MIMO ▫ SCM MIMO • Recall: delay spread and Doppler spread are the most important factors to consider in characterizing the SISO system • MIMO however relies on the correlation between transmit and receive antenna • Depends on the angle-of-arrival (AoA) of each multi-path component • AoA: azimuth angle of incoming path with respect to the broadside of the antenna element
  20. 20. MIMO
  21. 21. MIMO: SCM Channel Model • Proposed by a joint work of Ad Hoc Group (AHG) in 3GPP and 3GPP2. • Aimed at specifying the parameters for spatial channel model and developing a procedure for channel modeling • Combination of (sum) the arriving plane waves • Ray-based channel model, which superposes sub- ray components on the basis of PDP, PAS, and antenna array structure • Model the plane waves incoming from an arbitrary direction around the mobile terminal - can deal with the various scattering environments
  22. 22. MIMO: SCM Channel Model • Spatial channel model (SCM) for a MIMO channel in 3GPP is one of the ray-based channel models • Channel with the given PAS can be modeled by allocating the angle and power to each subray in accordance with the PAS. • Two different methods have been considered: ▫ uniform power subray method ▫ discrete Laplacian method
  23. 23. MIMO: SCM Channel Model • Uniform power subray method allocates the same power to each subray while arranging the subray angles in a non-uniform manner • Given M subrays, each of their angles is determined such that the area of each section subject to each subray is equally divided under PAS • Equal power allocation (EPA) simplifies the modeling process • Propagation environments defined in SCM: ▫ Suburban macro ▫ Urban macro ▫ Urban micro
  24. 24. MIMO: SCM Channel Model • Some of the advantages: ▫ Directly models the statistical characteristics of MIMO channel ▫ Maintains the statistical characteristics in the time, space, and frequency domains ▫ Simple ▫ Flexibility - various types of PDP and PAS ▫ Supports both LOS and NLOS channels ▫ Effective rank of H depending on the number of sub-rays in each path, M
  25. 25. MIMO: SCM Channel Model 1 0.9 Parameters Urban Micro 0.8 Environment Outdoor urban NLOS 0.7 Normalised power 0.6 Bandwidth 5 MHz 0.5 Excess Delay Spread 923 ns 0.4 0.3 Mean Delay Spread 251 ns 0.2 Carrier Frequency 2 GHz 0.1 200 300 400 500 600 700 800 900 1000 Excess delay (ns)
  26. 26. Share of (limited) experience • Nobody is a great teacher • Learn from mistakes • Learn from examples: • http://www.mathworks.com/matl abcentral/fileexchange/ • Sharing is caring: • http://www.edaboard.com/ • Patience is a virtue!
  27. 27. THANK YOU & GOOD LUCK!

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