% Determine sample (1) echo delay times, (2) norm. Doppler frequencies
% and (3) initial phases of the Rayleigh portions of a (time-variant)
% physical transmission channel according to the European standard COST-
% 207 (COoperation in the field of Science & Technology, Project #207).
%
% function [tau_MHz, fD_norm, psi, tau_pdf] = ...
% COST207 (mPDS[, N_echo[, rseed]]])
% ----------------------------------------------------------------------
% INPUT:
% ----------------------------------------------------------------------
% mPDS : String designating the desired propagation environment,
% i.e. the physical channel, according to COST-207:
% - 'TU': "Typical Urban" (non-hilly urban environment),
% - 'RA': "Rural Area" (non-hilly rural environment),
% - 'BU': "Bad Urban" (hilly urban environment),
% - 'HT': "Hilly Terrain" (hilly rural environment).
% Note: These environments correspond to different mean power
% delay spectra (PDS, "Verzoegerungsleistungsspektren").
% N.B.: To obtain environments NOT standardized by COST-207, mPDS
% can also be a matrix with entries as in tau_pdf (see o/p).
% [N_echo]: Desired number of echo paths (Default: 100).
% [rseed] : If this parameter is given, rseed is used to set the
% seeds for the random numbers generator. In this way,
% the function outputs can be reproduced.
% ----------------------------------------------------------------------
% OUTPUT:
% ----------------------------------------------------------------------
% tau_MHz: (Length N_out) col. vector of delay times of the echo paths.
% The values of tau_MHz := tau*1MHz = tau/1us are in the range
% 0..7 (TU), 0..0.7 (RA), 0..10 (BU), 0..2 and 15..20 (HT).
% The histogramm of tau_MHz approaches the pdf of tau, which
% is prop. to the mean power delay spectrum indicated by mPDS.
% N.B.: N_out may slightly differ from N_echo to satisfy the relative
% power ratio between echo clusters (for 'BU' and 'HT', only).
% fD_norm: (Length N_out) column vector with norm. Doppler frequencies
% fD/max{fD} resulting from echos impinging isotropically on
% the mobile unit. The values are in the range -1.0...1.0 and
% approximate the Jakes pdf. To unnormalize, multiply by the
% maximum Doppler frequency max{fD}:= v*f0/c0, where
% - v is the speed of the mobile unit [m/s]
% - f0 is the carrier frequency [Hertz]
% - c0=3e8 is the speed of light in empty space [m/s].
% psi : (Length N_out) column vector containing the initial phases.
% The values are uniformly distributed in the range 0..2pi.
% tau_pdf: Complete set of parameters describing the pdf of echo delay
% times, where row n refers to the n-th echo cluster:
% tau_pdf(n,1): exp. decay factor for the echo delay times,
% tau_pdf(n,2): minimum of this cluster's delay times [us],
% tau_pdf(n,3): range of this cluster's delay times [us],
% tau_pdf(n,4): total channel energy portion of this cluster.
% If mPDS was a matrix, tau_pdf is identical to mPDS.
% ----------------------------------------------------------------------
% DERIVATION: M. Benthin, PhD thesis, TU Hamburg-Harburg, 1996, Kap. 3.1
% ----------------------------------------------------------------------
% AUTHOR : Marcus Benthin, 01.07.92 (name of m-file: "chan207w.m")
% Dieter Boss, 01.07.96
% ----------------------------------------------------------------------
% <------------------------------- max. linewidth for atops ------------------------------------->|
function [tau_MHz, fD_norm, psi, tau_pdf] = COST207 (mPDS, N_echo, rseed)
% ##### 1. Verzoegerungszeiten tau_MHz #####
if nargin<2, N_echo = 100; end; % Das mittlere Verzoegerungs-Leistungsspektrum (mean power
% delay spectrum (mPDS) ist proportional zur Verteilungs-
if isstr(mPDS) % dichte der Echo-Laufzeiten tau_MHz, die durch uc be-
mPDS = mPDS(find(isletter(mPDS))); % schrieben wird. Der Prototyp fuer ein einfaches Echo-
mPDS = upper(mPDS(1:2)); % Cluster hat die Gestalt: p(tau) = alpha*exp(-beta*tau),
% 0<=tau<=tauD. Kompliziertere Echo-Profile werden aus
% mehreren solcher Cluster superponiert (vgl. BU oder HT).
if strcmp(mPDS,'TU')==1 % COST-207 Mobilfunk-Kanalmodell TYPICAL URBAN
uc = [ 1.0 0.0 7.0 1.0 ];
elseif strcmp(mPDS,'RA')==1 % COST-207 Mobilfunk-Kanalmodell RURAL AREA
uc = [ 9.2 0.0 0.7 1.0 ];
elseif strcmp(mPDS,'BU')==1 % COST-207 Mobilfunk-Kanalmodell BAD URBAN
uc = [ 1.0 0.0 5.0 2/3
1.0 5.0 5.0 1/3 ]; % rel. Amplitude: 0.5
elseif strcmp(mPDS,'HT')==1 % COST-207 Mobilfunk-Kanalmodell HILLY TERRAIN
uc = [ 3.5 0.0 2.0 0.88
1.0 15.0 5.0 0.12]; % rel. Amplitude: 0.04
else
error (sprintf('ERROR (COST207.m): Unknown COST-207 propagation environment "%s"!', mPDS));
end;
% Beliebige Mobilfunk-Kanalmodelle
else
if size(mPDS,2)~=4,
error('ERROR (COST207.m): First argument must be a string or a matrix with 4 columns.');
end;
uc = mPDS;
end;
beta = uc(:,1); % Abklingkonstante(n) der Exponentialverteilung(en)
tauS = uc(:,2); % Startzeit(en) der Exponentialverteilung(en) in us
tauD = uc(:,3); % Dauer der/des Echocluster(s) in us
% \int_0^tauD p(tau) dtau =
% \int_0^tauD alpha*exp(-beta*tau) dtau =
alpha = beta./(1-exp(-beta.*tauD)); % alpha(1-exp(-beta*tauD))/beta != 1 => alpha.
% s. Marcus Benthin, Diss., Gl. (3.16)
N = round(uc(:,4)*N_echo); % Prozentuale Verteilung von N_echo Exp.Schwingungen
N_out = sum(N); % auf die Echogruppen. Damit ist nur die Leistung
no_clusters = size(uc,1); % der Rayleigh-Streuung beruecksichtigt.
if nargin > 2
rand('seed', rseed); % Generate reconstructable seeds for the uniform
end; % random numbers generator (uniformly distributed
useeds = round(1e8*rand(no_clusters+2,1)); % between 0 and 1e8).
tau_MHz = []; % Auswuerfelung von Echozeiten tau in us (Rayleigh-Anteile)
for cl_no = 1:no_clusters % cl_no = cluster number
rand('seed', useeds(cl_no)); % s. Marcus Benthin, Diss., Gl. (3.17)
tau_MHz = [tau_MHz; -1/beta(cl_no)*log(1-beta(cl_no)/alpha(cl_no)*rand(N(cl_no),1)) + tauS(cl_no)];
end;
if nargout > 1 % ##### 2. Norm. Dopplerfrequenzen fD_norm #####
rand('seed', useeds(no_clusters+1));
alpha = pi*rand(N_out,1); % Gleichverteilte Einfallswinkel in (0..pi)
fD_norm = cos(alpha); % Jakes-verteilte normierte Dopplerfrequenzen
end; % im Intervall -1.0 < fD_norm < 1.0
if nargout > 2
rand('seed', useeds(no_clusters+2)); % ##### 3. Startphasen psi #####
psi = 2*pi*rand(N_out,1); % Gleichverteilte Startphasen in (0..2pi)
end
if nargout > 3 % ##### 4. Parameters describing the pdf of tau #####
tau_pdf = uc;
end;
end;
% EOF
