% Range-Lag Ambiguity Function toolbox
% 
% When called without arguments, these functions will show help text for
% themselves.  When called with the minimum number of arguments (interval
% sequence for multipulse codes, code set for alternating codes), they
% will create a plot in the current axis showing the range-lag ambiguity
% functions (Wtt') for a given modulation.  Where arguments are not given
% or given as an empty matrix, default values will be used instead.  For
% Barker code functions, the length of the Barker code can be specified,
% defaulting to 13.  (bc_wtt requires the length of the code to be
% specified.)  The baud length can be specified, defaulting to 3 for
% Barker coded modulations and 20 for all others.  All functions accept a
% lag argument, specifying for which lags (in units of bauds) range-lag
% ambiguity functions are computed.
% 
% The next argument for each function can be used to specify in what axis
% to draw the plot, e.g. for use in multi-panel plots.  If this argument
% is empty, (and plotfunction argument is not given, see below) the
% range-lag ambiguity function is returned (range along the vertical
% (first) dimension and lag along the horizontal (second) dimension) and
% no plots are made.
% 
% After the axis argument, the name of a 3-D plotting function can be
% given.  This function must accept arguments (X, Y, Z) with
% X and Y vectors, and dim(Z) == [ length(X) length(Y) ].
% 
% Any remaining arguments will be passed to the plot function after the
% X, Y, Z arguments
% 
% If a plot is made and an output argument is specified, the handle to the
% plot is returned.
% 
% For alternating codes (random or otherwise), each non-zero lag can be
% decoded in multiple ways, with different range contributions.
% The ac_lp_wtt and bcac_lp_wtt functions show a separate ambiguity
% function for each decoding possibility, corresponding to figure 6.6 in
% [Nygrén, 1996].  To an experimenter trying to interpret a set of
% measurements from an incomplete code set, it is more interesting to know
% what range-lag ambiguity to expect in a single range gate from a
% partially decoded or small random code set.  The functions ac_gate_wtt
% and bcac_gate_wtt average the ambiguity functions for all possible
% decodings of the desired lags, shifted such that the expected peaks
% coincide.  The range axis of the plot is centered at the center range of
% the gate.
% 
% For long pulses, the function lp_lp_wtt shows the range-lag ambiguity
% functions of the different lagged products that can be formed.  When
% creating range-gated autocorrelation functions (ACFs) from long pulse
% data, it is customary to average a number of lagged products, different
% for each lag, to form a range gate.  The function lp_gate_wtt (not
% implemented yet) shows the range-lag ambiguity functions for the
% different lags of such a range gate, centered at the nominal center
% range of the gate.
% 
% Long pulse plots
%  lp_lp_wtt     - Wtt' for a long pulse
%  lp_lph_wtt    - as above, but using a realistic filter impulse response
% 
% Alternating code plots
%  ac_lp_wtt     - Wtt' for an alternating code set
%  ac_gate_wtt   - as above, but for a completely decoded range gate
%  ac_wgate_wtt  - as above, but allowing for differently weighted pulses
%  ac_lph_wtt    - Wtt' for an alternating code set, using a realistic
%                  filter impulse response
% 
% Barker codes
%  bc_wtt        - Wtt' for a Barker code
% 
% Barker coded alternating code plots
%  bcac_lp_wtt   - Wtt' for a Barker coded alternating code set
%  bcac_gate_wtt - as above, but for a completely decoded range gate
% 
% Multipulse code plots
%  mp_lp_wtt     - Wtt' for a multipulse code
%  bcmp_lp_wtt   - Wtt' for a Barker coded multipulse code
% 
% Random codes
%  sign(randn(N, M)) generates a random code set with N scans of M bauds each,
%                    suitable as the codeset parameter to any of the
%                    alternating code plotting functions above
% 
% Supporting functions
%  multipulse    - converts an interval sequence to a multipulse code
%  tau0code      - generates the alternating code set for the tau0 experiment
%  altcode       - generates strong alternating code sets of arbitrary size
%  barkercode    - generates Barker codes of all known lengths
%  baudexpand    - expands a sign sequence to patterns or bauds of given length
%  convolve      - convolves its inputs along rows
%  walsh         - generates the Walsh matrix from which strong codes are drawn
%
%   Literature
%
%  Holt, J. M., Rhoda, D. A., Tetenbaum, D., and van Eyken, A. P.,
%  Optimal analysis of incoherent scatter radar data, Radio Sci., 27(3),
%  435--447, 1992.
%
%  Lehtinen, M. S., Statistical theory of incoherent scatter measurements,
%  Tech. Rep. 86/45, EISCAT Scientific Association, Kiruna, Sweden,
%  Ph. D. Thesis, University of Helsinki, Helsinki, Finland, 1986.
%
%  Nygrén, T., Introduction to incoherent scatter measurements, Invers
%  Publications, Sodankylä, Finland, 1996.
%
%  Nygrén, T., Huuskonen, A., and Pollari, P., Alternating-coded
%  multipulse codes for incoherent scatter experiments, J. Atmos. Terr.
%  Phys., 58(1-4), 465--477, doi:10.1016/0021-9169(95)00049-6, 1996.
%

%   $Id: Contents.m,v 1.4 2008-11-18 05:34:39 tom Exp $

%   Copyright © 2003-2008 Tom Grydeland <Tom.Grydeland@phys.uit.no>
%   This is free software, licensed under GNU GPL version 2 or later