�� ��� � � �� �� ������ �������������� ������� ����� �� � �������� � ������� ���� ��� � � ��� Channel Models and Signaling Schemes Department of Electrical & Computer Engineering The University of British Columbia Elham Torabi Supervisor: Dr. Robert Schober
Outline 2 1. Overview and Introduction to the IEEE 802.15.4a Standard 2. Channel Models • Generic Channel Model • UWB Model Parametrization and Simulation Results for 2-10 GHz 3. Signaling Schemes • Time-Hopping UWB (TH-UWB) • RAKE Receivers • UWB Transmitted-Reference (UWB-TR) • UWB Differential Transmitted-Reference (UWB-DTR) • Comparison Elham Torabi: Low-Power Low-Rate Ultra-Wideband Communication
1. Overview and Introduction to the IEEE 802.15.4a Standard 3 • The IEEE 802.15 low-rate alternative PHY task group 4a (TG4a) for WPANs, named subgroup IEEE 802.15.4a, has the mandate to develop an alternative physical layer for sensor networks and similar devices that work with the IEEE 802.15.4 MAC layer. • Technical characteristics summary – Topology – Bit Rate – Range – Coexistence and Interference Resistance – Power Consumption – Quality of Service – Antenna – Complexity – Location Awareness Elham Torabi: Low-Power Low-Rate Ultra-Wideband Communication
1. Overview and Introduction to the IEEE 802.15.4a Standard 4 • The principle interest of this subgroup is in providing communications for WPAN applications such as 1. Sensors networks 2. High precision positioning 3. Security/authentication 4. Smart home systems 5. Networks of wearable mobile devices 6. Real time location services Elham Torabi: Low-Power Low-Rate Ultra-Wideband Communication
2. Channel Models 5 Different Proposed Channel Models in the IEEE 802.15.4a standard • UWB channel models covering the frequency range from 2 to 10 GHz, con- sidering indoor residential, indoor office, industrial, outdoor, and open out- door environments (usually with a distinction between line-of-sight (LOS) and none-LOS (NLOS) properties) • UWB channel model for the frequency range from 100 to 1000 MHz, consid- ering a model for indoor office-type environments • UWB channel model for the frequency range from 2 to 6 GHz, considering a model for body area networks (BANs) Main Goals are modeling the • Attenuation • Delay Dispersion Elham Torabi: Low-Power Low-Rate Ultra-Wideband Communication
2. Generic Channel Model 6 • Used for the 2-10 GHz frequency range. • model treats only channel, while antenna effects should be modeled separately. • block fading is assumed, i.e., channel stays constant over data burst duration. • modified Saleh-Valenzuela (SV) model is adapted. Elham Torabi: Low-Power Low-Rate Ultra-Wideband Communication
2. Generic Channel Model: Pathloss - Preliminary Comments 7 • The pathloss for a narrowband system is conventionally defined as PL ( d ) = E { P RX ( d , f c ) } , P TX where P TX and P RX are transmit and receive power, respectively, d is the distance between transmitter and receiver, f c is the center frequency. Note that E {·} = E lsf { E ssf {·}} , where ‘ lsf ’ and ‘ ssf ’ indicate large-scale fading and small-scale fading, respectively. • The pathloss related to wideband pathloss is defined as �� f +∆ f / 2 � 2 � � �� ˜ d ˜ PL ( f , d ) = E � H f , d , f � � � f − ∆ f / 2 � � ˜ where H f , d is the transfer function from antenna connector to antenna connector. Elham Torabi: Low-Power Low-Rate Ultra-Wideband Communication
2. Generic Channel Model: Pathloss - Preliminary Comments 8 • To simplify computations, we assume PL ( f , d ) = PL ( f ) · PL ( d ) • The frequency dependence of the pathloss is given as � PL ( f ) ∝ f − k , where k is the frequency dependence coefficient of the pathloss. • The distance dependence of the pathloss in dB is described by � d � PL ( d ) = PL 0 + 10 n log 10 , d 0 where the reference distance d 0 is set to 1 m, PL 0 is the pathloss at the reference distance, and n is the pathloss exponent. Elham Torabi: Low-Power Low-Rate Ultra-Wideband Communication
2. Generic Channel Model: Pathloss - Recommended Model 9 • According to the proposed model the pathloss is found to be � − 2( k+1 ) � f P TX − amp ( f ) = 1 P r ( d, f ) f c PL ( f, d ) = 2 PL 0 · η TX − ant ( f ) · η RX − ant ( f ) , � n � d d 0 where P TX − amp ( f ) is the output spectrum of the transmit amplifier, P r ( d , f ) is the received frequency-dependent power, η TX − ant ( f ) is the frequency depen- dent transmit antenna efficiency, and η RX − ant ( f ) is the frequency dependent receive antenna efficiency. Elham Torabi: Low-Power Low-Rate Ultra-Wideband Communication
2. Generic Channel Model: Shadowing 10 • Large-scale fading or shadowing is defined as the variation of the local mean around the pathloss, and has log-normal distribution about the mean. The pathloss, averaged over the small-scale fading in dB, can be written as � d � PL ( d ) = PL 0 + 10 n log 10 + S , d 0 where S is a Gaussian-distributed random variable with zero mean and stan- dard deviation σ S . • If shadowing effects come into play, the overall channel is no longer wide sense stationary (WSS), therefore, for the simulation procedure according to the se- lection criteria document, shadowing shall not be taken into account. Elham Torabi: Low-Power Low-Rate Ultra-Wideband Communication
2. Generic Channel Model: Power Delay Profile (PDP) 11 • A statistical model for indoor multipath propagation is introduced, known as SV (Saleh-Valenzuela) model. • The physical realization: received signal rays arrive in clusters. • The cluster arrival times are modeled as a Poisson arrival process with some fixed rate Λ l . • Subsequent rays arrive according to a Poisson process within each cluster, with another fixed rate. • T l : arrival time of the l th cluster l = 0 , 1 , 2 , ... • τ k,l : arrival time of the k th ray measured from the beginning of the l th cluster k = 0 , 1 , 2 , ... (aka Excess Delay) Elham Torabi: Low-Power Low-Rate Ultra-Wideband Communication
2. Generic Channel Model: Power Delay Profile (PDP) 12 • According to this model, the distribution of the cluster arrival times are given by a Poisson process p ( T l | T l-1 ) = Λ l exp [ − Λ l ( T l − T l-1 )] , • Ray arrival times are modeled with mixtures of two Poisson processes � � �� � � � p ( τ k , l | τ (k-1) , l ) = βλ 1 exp − λ 1 τ k , l − τ (k-1) , l +( β − 1) λ 2 exp − λ 2 τ k , l − τ (k-1) , l where β is the mixture probability, λ 1 and λ 2 are the ray arrival rates. • The number of clusters L is assumed to be Poisson-distributed � L exp � ¯ − ¯ � � L L P L ( L ) = L ! Elham Torabi: Low-Power Low-Rate Ultra-Wideband Communication
2. Generic Channel Model: Pathloss - Preliminary Comments 13 • The complex, low-pass impulse response of the channel L K � � h ( t ) = a k , l exp ( j φ k , l ) δ ( t − T l − τ k , l ) , l =0 k =0 where a k , l is the gain of the k th ray of the l th cluster and the phases φ k , l are uniformly distributed in the interval [0 , 2 π ] . • The Power Delay Profile (PDP) of the channel is defined by taking the spatial average of | h ( t ) | 2 over a local area, in general P ( t ) ≈ K | h ( t ) | 2 . • For the SV model, and for the LOS case, the PDP, which is the mean power of the different paths, is found to be 1 � | a k , l | 2 � E = Ω l γ l [(1 − β ) λ 1 + βλ 2 + 1] exp ( − τ k , l /γ l ) , Elham Torabi: Low-Power Low-Rate Ultra-Wideband Communication
2. Generic Channel Model: Power Delay Profile (PDP) 14 where Ω l is the integrated energy of the l th cluster,and γ l is the intra-cluster decay time constant. γ l ∝ k γ T l + γ 0 , where k γ describes the increase of the decay constant with delay. k γ and γ 0 are intra-cluster decay time constant parameters. 10 log (Ω l ) = 10 log (exp ( − T l / Γ)) + M cluster , where M cluster is a normally distributed variable with standard deviation σ cluster around it and Γ is the inter-cluster decay constant. Elham Torabi: Low-Power Low-Rate Ultra-Wideband Communication
2. Generic Channel Model: Small-scale Fading 15 • The distribution of the small-scale amplitudes a k , l , is Nakagami 2 � m � m − m x 2 m − 1 exp � Ω x 2 � P X ( x ) = Γ ( m ) Ω m ≥ 1 / 2 is the Nakagami m -factor, Γ ( m ) is the gamma function, and the parameter Ω corresponds to the mean power, and its delay dependence is thus given by the power delay profile. • The m -parameter is modeled as a lognormally distributed random variable, whose logarithm has a mean µ m and standard deviation σ m . Both of these can have a delay dependence µ m ( τ ) = m 0 − k m τ m 0 − ˆ σ m ( τ ) = ˆ k m τ m 0 and ˆ m 0 and k m are Nakagami- m factor mean and ˆ k m are Nakagami- m factor variance. Elham Torabi: Low-Power Low-Rate Ultra-Wideband Communication
2. Generic Channel Model: Auxilary Parameters 16 • Mean Excess Delay: First moment of the PDP � ∞ −∞ P ( τ ) τdτ τ = ¯ � ∞ −∞ P ( τ ) dτ • RMS Delay Spread: Square root of the second central moment of the PDP � τ 2 − (¯ ¯ τ ) 2 σ τ = � ∞ −∞ P ( τ ) τ 2 dτ τ 2 = ¯ � ∞ −∞ P ( τ ) dτ Elham Torabi: Low-Power Low-Rate Ultra-Wideband Communication
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