Viterbi generator by Piotr Krysik.

7 files changed, 564 insertions, 0 deletions

diff --git a/viterbi_generator/tests/utils/make_increment.m b/viterbi_generator/tests/utils/make_increment.m
new file mode 100644
index 0000000..91cc0ae
--- /dev/null
+++ b/viterbi_generator/tests/utils/make_increment.m
@@ -0,0 +1,70 @@
+function [ INCREMENT ] = make_increment(SYMBOLS,NEXT,Rhh)
+%
+% MAKE_INCREMENT:
+%           This function returns a lookuptable containing the
+%           metric increments related to moving from state n to m.
+%           The data is arranged so that the increment accosiated 
+%           with a move from state n to m is located in 
+%           INCREMENT(n,m). To minimize computations only legal
+%           transitions are considdered.
+%
+% SYNTAX:   [ INCREMENT ] = make_increment(SYMBOLS,NEXT,Rhh)
+%
+% INPUT:    SYMBOLS: The table of symbols corresponding the the state-
+%                    numbers.
+%           NEXT:    A transition table containing the next legal
+%                    states, as it is generated by the code make_next.
+%           Rhh:     The autocorrelation as estimated by mf.m.
+%
+% OUTPUT:   INCREMENT:
+%                    The increment table as described above.
+%
+% SUB_FUNC: None
+%
+% WARNINGS: There is no syntax checking on input or output.
+%
+% TEST(S):  By hand, against expected values.
+%
+% AUTOR:    Jan H. Mikkelsen / Arne Norre Ekstrøm
+% EMAIL:    hmi@kom.auc.dk / aneks@kom.auc.dk
+%
+% $Id: make_increment.m,v 1.6 1997/09/22 11:39:34 aneks Exp $
+
+% IN THIS PEACE OF CODE THE SYNTAX CHECKING IS MINIMAL
+% THIS HAS BEEN CHOSEN TO AVOID THE OVERHEAD. RECALL THAT
+% THIS CODE IS EXECUTED EACH TIME A BURST IS RECEIVED.
+
+% FIND THE NUMBER OF SYMBOLS THAT WE HAVE
+%
+[M,Lh]=size(SYMBOLS);
+
+% INITIALIZE THE INCREMENT MATRIX
+%
+INCREMENT=zeros(M);
+
+% RECALL THAT THE I SEQUENCE AS IT IS STORED IN STORED AS:
+% [ I(n-1) I(n-2) I(n-3) ... I(n-Lh) ]
+%
+% ALSO RECALL THAT Rhh IS STORED AS:
+% [ Rhh(1) Rhh(2) Rhh(3) ... Rhh(Lh) ]
+%
+% THE FORMULA TO USE IS:
+% INCREMENT(n,m)
+% =
+% real(conj(I(n))*(I(n-Lh)*Rhh(Lh)+I(n-Lh+1)*Rhh(Lh-1)+...+I(n-1)*Rhh(1))
+%
+% THEY CAN THUS BE MULTIPLIED DIRECTLY WITH EACH OTHER
+
+% LOOP OVER THE STATES, AS FOUND IN THE ROWS IN SYMBOLS.
+%
+for n=1:M, 
+  % ONLY TWO LEGAL NEXT STATES EXIST, SO THE LOOP IS UNROLLED
+  %
+  m=NEXT(n,1);
+
+  INCREMENT(n,m)=real((conj(SYMBOLS(m,1))*SYMBOLS(n,:))*Rhh(2:Lh+1).');
+  m=NEXT(n,2);
+
+  INCREMENT(n,m)=real((conj(SYMBOLS(m,1))*SYMBOLS(n,:))*Rhh(2:Lh+1).');
+end
+
diff --git a/viterbi_generator/tests/utils/make_next.m b/viterbi_generator/tests/utils/make_next.m
new file mode 100644
index 0000000..f5af8dc
--- /dev/null
+++ b/viterbi_generator/tests/utils/make_next.m
@@ -0,0 +1,54 @@
+function [ NEXT ] = make_next(SYMBOLS)
+%
+% MAKE_NEXT:
+%           This function returns a lookuptable containing a mapping
+%           between the present state and the legal next states.
+%           Each row correspond to a state, and the two legal states
+%           related to state n is located in NEXT(n,1) and in
+%           NEXT(n,2). States are represented by their related 
+%           numbers.
+%
+% SYNTAX:   [ NEXT ] = make_next(SYMBOLS)
+%
+% INPUT:    SYMBOLS: The table of symbols corresponding the the state-
+%                    numbers.
+%
+% OUTPUT:   NEXT:    The transition table describing the legal next
+%		     states asdescribed above.
+%
+% SUB_FUNC: None
+%
+% WARNINGS: None
+%
+% TEST(S):  The function has been verified to return the expected
+%           results.
+%
+% AUTOR:    Jan H. Mikkelsen / Arne Norre Ekstrøm
+% EMAIL:    hmi@kom.auc.dk / aneks@kom.auc.dk
+%
+% $Id: make_next.m,v 1.3 1997/09/22 08:13:29 aneks Exp $
+
+% FIRST WE NEED TO FIND THE NUMBER OF LOOPS WE SHOULD RUN.
+% THIS EQUALS THE NUMBER OF SYMBOLS. ALSO MAXSUM IS NEEDED FOR
+% LATER OPERATIONS.
+%
+[ states , maxsum ]=size(SYMBOLS);
+
+search_matrix=SYMBOLS(:,2:maxsum);
+maxsum=maxsum-1;
+
+% LOOP OVER THE SYMBOLS.
+%
+for this_state=1:states,
+  search_vector=SYMBOLS(this_state,1:maxsum);
+  k=0;
+  for search=1:states,
+    if (sum(search_matrix(search,:)==search_vector)==maxsum)
+      k=k+1;
+      NEXT(this_state,k)=search;
+      if k > 2,
+	error('Error: identified too many next states');
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/viterbi_generator/tests/utils/make_previous.m b/viterbi_generator/tests/utils/make_previous.m
new file mode 100644
index 0000000..678fa43
--- /dev/null
+++ b/viterbi_generator/tests/utils/make_previous.m
@@ -0,0 +1,54 @@
+function [ PREVIOUS ] = make_previous(SYMBOLS)
+%
+% MAKE_PREVIOUS:       
+%           This function returns a lookuptable containing a mapping
+%           between the present state and the legal previous states.
+%           Each row correspond to a state, and the two legal states
+%           related to state n is located in PREVIOUS(n,1) and in
+%           previous(n,2). States are represented by their related 
+%           numbers.
+%
+% SYNTAX:   [ PREVIOUS ] = make_previous(SYMBOLS)
+%
+% INPUT:    SYMBOLS: The table of symbols corresponding the the state-
+%                    numbers.
+%
+% OUTPUT:   PREVIOUS:
+%                    The transition table describing the legal previous
+%		     states asdescribed above.
+%
+% SUB_FUNC: None
+%
+% WARNINGS: None
+%
+% TEST(S):  Verified against expected result.
+%
+% AUTOR:    Jan H. Mikkelsen / Arne Norre Ekstrøm
+% EMAIL:    hmi@kom.auc.dk / aneks@kom.auc.dk
+%
+% $Id: make_previous.m,v 1.3 1997/09/22 08:14:27 aneks Exp $
+
+% FIRST WE NEED TO FIND THE NUMBER OF LOOPS WE SHOULD RUN.
+% THIS EQUALS THE NUMBER OF SYMBOLS. ALSO MAXSUM IS NEEDED FOR
+% LATER OPERATIONS.
+%
+[ states , maxsum ]=size(SYMBOLS);
+
+maxsum=maxsum-1;
+search_matrix=SYMBOLS(:,1:maxsum);
+
+% LOOP OVER THE SYMBOLS.
+%
+for this_state=1:states,
+  search_vector=SYMBOLS(this_state,2:maxsum+1);
+  k=0;
+  for search=1:states,
+    if (sum(search_matrix(search,:)==search_vector)==maxsum)
+      k=k+1;
+      PREVIOUS(this_state,k)=search;
+      if k > 2,
+	error('Error: identified too many previous states');
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/viterbi_generator/tests/utils/make_start.m b/viterbi_generator/tests/utils/make_start.m
new file mode 100644
index 0000000..83275fd
--- /dev/null
+++ b/viterbi_generator/tests/utils/make_start.m
@@ -0,0 +1,63 @@
+function [ START ] = make_start(Lh,SYMBOLS)
+%
+% MAKE_START:
+%           This code returns a statenumber corresponding to the start
+%           state as it is found from Lh. The method is to use the table
+%           of symbolic start states as it is listed in the report made 
+%           by 95gr870T. For the table lookups are made in SYMBOLS. in 
+%           order to map from the symbol representation to the state number 
+%           representation.
+%
+% SYNTAX:   [ START ] = make_start(Lh,SYMBOLS)
+%
+% INPUT:    SYMBOLS: The table of symbols corresponding the the state-
+%                    numbers.
+%           Lh:      Length of the estimated impulseresponse.
+%
+% OUTPUT:   START:   The number representation of the legal start state.
+%
+% SUB_FUNC: None
+%
+% WARNINGS: The table of symbolic representations has not been verified
+%           but is used directly as it is listed in the report made 
+%           by 95gr870T.
+%
+% TEST(S):  The function has been verified to return a state number
+%           which matches the symbolic representation.
+%
+% AUTOR:    Jan H. Mikkelsen / Arne Norre Ekstrøm
+% EMAIL:    hmi@kom.auc.dk / aneks@kom.auc.dk
+%
+% $Id: make_start.m,v 1.2 1997/09/22 11:40:17 aneks Exp $
+
+% WE HAVEN'T FOUND IT YET.
+%
+START_NOT_FOUND = 1;
+
+% OBTAIN THE SYMBOLS FROM Lh. THIS IS THE TABLE LISTED IN THE REPORT MADE 
+% BY 95gr870T. (SATEREPRESENTATION IS SLIGHTLY CHANGED).
+%
+if Lh==1,
+  start_symbols = [ 1 ];
+elseif Lh==2,
+  start_symbols = [ 1 -j ];
+elseif Lh==3,
+  start_symbols = [ 1 -j -1 ];
+elseif Lh==4,
+  start_symbols = [ 1 -j -1 j ];
+elseif Lh==5,
+  start_symbols = [ 1 -j -1 j 1];
+else
+  fprintf('\n\nError: Illegal value of Lh, terminating...');
+end
+
+% NOW MAP FROM THE SYMBOLS TO A STATE NUMBER BY SEARCHING 
+% SYMBOLS.
+%
+START=0;
+while START_NOT_FOUND,
+  START=START+1;
+  if sum(SYMBOLS(START,:)==start_symbols)==Lh,
+    START_NOT_FOUND=0;
+  end
+end
diff --git a/viterbi_generator/tests/utils/make_stops.m b/viterbi_generator/tests/utils/make_stops.m
new file mode 100644
index 0000000..98734c9
--- /dev/null
+++ b/viterbi_generator/tests/utils/make_stops.m
@@ -0,0 +1,67 @@
+function [ STOPS ] = make_stops(Lh,SYMBOLS)
+%
+% MAKE_STOPS:
+%           This code returns a statenumber corresponding to the set of
+%           legal stop states as found from Lh. The method is to use the table
+%           of symbolic stop states as it is listed in the report made 
+%           by 95gr870T. For the table lookups are made in SYMBOLS. in 
+%           order to map from the symbol representation to the state number 
+%           representation.
+%
+% SYNTAX:   [ STOPS ] = make_stops(Lh,SYMBOLS)
+%
+% INPUT:    SYMBOLS: The table of symbols corresponding the the state-
+%                    numbers.
+%           Lh:      Length of the estimated impulseresponse.
+%
+% OUTPUT:   STOPS:   The number representation of the set of legal stop 
+%                    states.
+%
+% SUB_FUNC: None
+%
+% WARNINGS: The table of symbolic representations has not been verified
+%           but is used directly as it is listed in the report made 
+%           by 95gr870T.
+%
+% TEST(S):  The function has been verified to return a state number
+%           which matches the symbolic representation.
+%
+% AUTOR:    Jan H. Mikkelsen / Arne Norre Ekstrøm
+% EMAIL:    hmi@kom.auc.dk / aneks@kom.auc.dk
+%
+% $Id: make_stops.m,v 1.2 1997/09/22 11:44:21 aneks Exp $
+
+% OBTAIN THE SYMBOLS FROM Lh. THIS IS THE TABLE LISTED IN THE REPORT MADE 
+% BY 95gr870T. (SATEREPRESENTATION IS SLIGHTLY CHANGED).
+%
+if Lh==1,
+  stop_symbols = [ -1 ];
+  count=1;
+elseif Lh==2,
+  stop_symbols = [ -1 j ];
+  count=1;
+elseif Lh==3,
+  stop_symbols = [ -1 j 1 ];
+  count=1;
+elseif Lh==4,
+  stop_symbols = [  [ -1 j 1 j ] ; [ -1 j 1 -j ] ];
+  count=2;
+elseif Lh==5,
+  stop_symbols = [ [ -1 j 1 j -1] ; [ -1 j 1 -j -1] ; [ -1 j 1 j 1] ; [ -1 j 1 -j 1] ];
+  count=2;
+else
+  fprintf('\n\nError: Illegal value of Lh, terminating...');
+end
+
+% NOW THAT WE HAVE THE SYMBOL REPRESENTATION THE REMAINING JOB IS
+% TO MAP THE MSK SYMBOLS TO STATE NUMBERS
+%
+index = 0;
+stops_found=0;
+while stops_found < count,
+  index=index+1;
+  if sum(SYMBOLS(index,:)==stop_symbols(stops_found+1,:))==Lh,
+    stops_found=stops_found+1;
+    STOPS(stops_found)=index;
+  end
+end
diff --git a/viterbi_generator/tests/utils/viterbi_detector.m b/viterbi_generator/tests/utils/viterbi_detector.m
new file mode 100644
index 0000000..31e8f93
--- /dev/null
+++ b/viterbi_generator/tests/utils/viterbi_detector.m
@@ -0,0 +1,218 @@
+function [ rx_burst METRIC] = viterbi_detector(SYMBOLS,NEXT,PREVIOUS,START,STOPS,Y,Rhh)
+%
+% VITERBI_DETECTOR:
+%           This matlab code does the actual detection of the
+%           received sequence. As indicated by the name the algorithm
+%           is the viterbi algorithm, which is a MLSE. At this time 
+%           the approch is to use Ungerboecks modified algorithm, and
+%           to return hard output only.
+%
+% SYNTAX:   [ rx_burst ] 
+%           = 
+%           viterbi_detector(SYMBOLS,NEXT,PREVIOUS,START,STOPS,Y,Rhh)
+%
+% INPUT:    SYMBOLS:  The table of symbols corresponding the the state-
+%                     numbers. Format as made by make_symbols.m
+%           NEXT:     A transition table containing the next legal
+%                     states, as it is generated by the code make_next.m
+%           PREVIOUS: The transition table describing the legal previous
+%		      states as generated by make_previous.m
+%           START:    The start state of the algorithm.
+%           STOPS:    The legal stop states.
+%           Y:        Complex baseband representation of the matched 
+%                     filtered and down converted received signal, as it
+%                     is returned by mf.m
+%           Rhh:      The autocorrelation as estimated by mf.m
+%
+% OUTPUT:   rx_burst: The most likely sequence of symbols.
+%
+% SUB_FUNC: make_increment
+%
+% WARNINGS: None.
+%
+% TEST(S):  Tested with no noise, perfect syncronization, and channel 
+%           estimation/filtering. (Refer to viterbi_ill.m)
+%
+% AUTOR:    Jan H. Mikkelsen / Arne Norre Ekstrøm
+% EMAIL:    hmi@kom.auc.dk / aneks@kom.auc.dk
+%
+% $Id: viterbi_detector.m,v 1.7 1997/11/18 12:41:26 aneks Exp $
+
+% KNOWLEDGE OF Lh AND M IS NEEDED FOR THE ALGORITHM TO OPERATE
+%
+[ M , Lh ] = size(SYMBOLS);
+
+% THE NUMBER OF STEPS IN THE VITERBI
+%
+STEPS=length(Y);
+% INITIALIZE TABLES (THIS YIELDS A SLIGHT SPEEDUP).
+%
+METRIC = zeros(M,STEPS);
+SURVIVOR = zeros(M,STEPS);
+
+% DETERMINE PRECALCULATABLE PART OF METRIC
+%
+INCREMENT=make_increment(SYMBOLS,NEXT,Rhh);
+%INCREMENT
+% THE FIRST THING TO DO IS TO ROLL INTO THE ALGORITHM BY SPREADING OUT 
+% FROM 	THE START STATE TO ALL THE LEGAL STATES. 
+%
+PS=START;
+
+% NOTE THAT THE START STATE IS REFERRED TO AS STATE TO TIME 0
+% AND THAT IT HAS NO METRIC.
+%
+S=NEXT(START,1);
+
+METRIC(S,1)=real(conj(SYMBOLS(S,1))*Y(1))-INCREMENT(PS,S);
+SURVIVOR(S,1)=START;
+
+S=NEXT(START,2);
+METRIC(S,1)=real(conj(SYMBOLS(S,1))*Y(1))-INCREMENT(PS,S);
+SURVIVOR(S,1)=START;
+
+PREVIOUS_STATES=NEXT(START,:);
+
+% MARK THE NEXT STATES AS REAL. N.B: COMPLEX INDICATES THE POLARITY
+% OF THE NEXT STATE, E.G. STATE 2 IS REAL.
+%
+COMPLEX=0;
+
+for N = 2:Lh,
+  if COMPLEX,
+    COMPLEX=0;
+  else
+    COMPLEX=1;
+  end
+  STATE_CNTR=0;
+  for PS = PREVIOUS_STATES,
+    STATE_CNTR=STATE_CNTR+1;
+    S=NEXT(PS,1);
+    METRIC(S,N)=METRIC(PS,N-1)+real(conj(SYMBOLS(S,1))*Y(N))-INCREMENT(PS,S);
+    SURVIVOR(S,N)=PS;
+    USED(STATE_CNTR)=S;
+    STATE_CNTR=STATE_CNTR+1;
+    S=NEXT(PS,2);
+    METRIC(S,N)=METRIC(PS,N-1)+real(conj(SYMBOLS(S,1))*Y(N))-INCREMENT(PS,S);
+    SURVIVOR(S,N)=PS;    
+    USED(STATE_CNTR)=S;
+  end
+  PREVIOUS_STATES=USED;
+end
+% AT ANY RATE WE WILL HAVE PROCESSED Lh STATES AT THIS TIME
+%
+PROCESSED=Lh;
+
+% WE WANT AN EQUAL NUMBER OF STATES TO BE REMAINING. THE NEXT LINES ENSURE
+% THIS.
+%
+
+if ~COMPLEX,
+  COMPLEX=1;
+  PROCESSED=PROCESSED+1;
+  N=PROCESSED;
+  for S = 2:2:M,
+    PS=PREVIOUS(S,1);
+    M1=METRIC(PS,N-1)+real(conj(SYMBOLS(S,1))*Y(N)-INCREMENT(PS,S));
+    PS=PREVIOUS(S,2);
+    M2=METRIC(PS,N-1)+real(conj(SYMBOLS(S,1))*Y(N)-INCREMENT(PS,S)); 
+    if M1 > M2,
+      METRIC(S,N)=M1;
+      SURVIVOR(S,N)=PREVIOUS(S,1);
+    else
+      METRIC(S,N)=M2;
+      SURVIVOR(S,N)=PREVIOUS(S,2);
+    end
+  end
+end
+
+% NOW THAT WE HAVE MADE THE RUN-IN THE REST OF THE METRICS ARE
+% CALCULATED IN THE STRAIGHT FORWARD MANNER. OBSERVE THAT ONLY
+% THE RELEVANT STATES ARE CALCULATED, THAT IS REAL FOLLOWS COMPLEX
+% AND VICE VERSA.
+%
+N=PROCESSED+1;
+while N <= STEPS,
+  for S = 1:2:M-1,
+    PS=PREVIOUS(S,1);
+    M1=METRIC(PS,N-1)+real(conj(SYMBOLS(S,1))*Y(N)-INCREMENT(PS,S));
+    PS=PREVIOUS(S,2);
+    M2=METRIC(PS,N-1)+real(conj(SYMBOLS(S,1))*Y(N)-INCREMENT(PS,S)); 
+    if M1 > M2,
+      METRIC(S,N)=M1;
+      SURVIVOR(S,N)=PREVIOUS(S,1);
+    else
+      METRIC(S,N)=M2;
+      SURVIVOR(S,N)=PREVIOUS(S,2);
+    end   
+  end
+  N=N+1;
+  for S = 2:2:M,
+    PS=PREVIOUS(S,1);
+    M1=METRIC(PS,N-1)+real(conj(SYMBOLS(S,1))*Y(N)-INCREMENT(PS,S));
+    PS=PREVIOUS(S,2);
+    M2=METRIC(PS,N-1)+real(conj(SYMBOLS(S,1))*Y(N)-INCREMENT(PS,S)); 
+    if M1 > M2,
+      METRIC(S,N)=M1;
+      SURVIVOR(S,N)=PREVIOUS(S,1);
+    else
+      METRIC(S,N)=M2;
+      SURVIVOR(S,N)=PREVIOUS(S,2);
+    end   
+  end
+  N=N+1;
+end  
+
+
+% HAVING CALCULATED THE METRICS, THE MOST PROBABLE STATESEQUENCE IS
+% INITIALIZED BY CHOOSING THE HIGHEST METRIC AMONG THE LEGAL STOP 
+% STATES.
+%
+BEST_LEGAL=0;
+for FINAL = STOPS,
+  if METRIC(FINAL,STEPS) > BEST_LEGAL,
+    S=FINAL;
+    BEST_LEGAL=METRIC(FINAL,STEPS);
+  end
+end
+
+% UNCOMMENT FOR TEST OF METRIC
+%
+% METRIC
+% BEST_LEGAL
+% S
+% pause
+
+% HAVING FOUND THE FINAL STATE, THE MSK SYMBOL SEQUENCE IS ESTABLISHED
+%
+
+IEST(STEPS)=SYMBOLS(S,1);
+N=STEPS-1;
+while N > 0,
+
+%  if(N>STEPS-40),
+%    previo=ceil(S/2)
+%  end
+  S=SURVIVOR(S,N+1);
+  IEST(N)=SYMBOLS(S,1);
+  N=N-1;
+end
+
+% THE ESTIMATE IS NOW FOUND FROM THE FORMULA:
+% IEST(n)=j*rx_burst(n)*rx_burst(n-1)*IEST(n-1)
+% THE FORMULA IS REWRITTEN AS:
+% rx_burst(n)=IEST(n)/(j*rx_burst(n-1)*IEST(n-1))
+% FOR INITIALIZATION THE FOLLOWING IS USED:
+% IEST(0)=1 og rx_burst(0)=1
+%
+rx_burst(1)=IEST(1)/(j*1*1);
+for n = 2:STEPS,
+  rx_burst(n)=IEST(n)/(j*rx_burst(n-1)*IEST(n-1));
+end
+
+% rx_burst IS POLAR (-1 AND 1), THIS TRANSFORMS IT TO
+% BINARY FORM (0 AND 1).
+%
+
+rx_burst=(rx_burst+1)./2;
+
diff --git a/viterbi_generator/tests/utils/viterbi_init.m b/viterbi_generator/tests/utils/viterbi_init.m
new file mode 100644
index 0000000..a43b801
--- /dev/null
+++ b/viterbi_generator/tests/utils/viterbi_init.m
@@ -0,0 +1,38 @@
+function [ SYMBOLS , PREVIOUS , NEXT , START , STOPS ] = viterbi_init(Lh)
+% VITERBI_INIT:
+%           This function returns the tables which are used by the 
+%           viterbi demodulator which is implemented in the GSMsim
+%           package.
+%
+% SYNTAX:   [ SYMBOLS , PREVIOUS , NEXT , START , STOPS ]
+%           = 
+%           viterbi_init(Lh)
+%
+% INPUT:    Lh:       The length of the channel impulse response
+%                     minus one.
+%
+% OUTPUT:   SYMBOLS:  Statenumber to MSK-symbols mapping table.
+%           PREVIOUS: This state to legal previous state mapping table.
+%           NEXT:     This state to legal next state mapping table.
+%           START:    The start state of the viterbi algorithm.
+%           STOPS:    The set of legal stop states for the viterbi 
+%                     algorithm.
+%
+% GLOBAL:   None
+%
+% SUB_FUNC: make_symbols,make_previous,make_next,make_start,make_stops
+%
+% WARNINGS: None
+% 
+% TEST:     Verified that the function actually runs the subfunctions.
+%
+% AUTHOR:   Jan H. Mikkelsen / Arne Norre Ekstrøm
+% EMAIL:    hmi@kom.auc.dk / aneks@kom.auc.dk
+%
+% $Id: viterbi_init.m,v 1.4 1998/02/12 10:52:15 aneks Exp $
+
+SYMBOLS = make_symbols(Lh);
+PREVIOUS = make_previous(SYMBOLS);
+NEXT = make_next(SYMBOLS);
+START = make_start(Lh,SYMBOLS);
+STOPS = make_stops(Lh,SYMBOLS);