CE L Technical Memorandum No. 104 03604-1-M OPERATOR'S MANUAL for the M4 COMMUNICATIONS EXPERIMENT by D. Jaarsma Approved by:.-4 c e/ for COOLEY ELECTRONICS LABORATORY Department of Electrical Engineering The University of Michigan Ann Arbor, Michigan Contract No. N00014-67-A-0181-0032 Office of Naval Research (Code 468) Department of the Navy Washington, D. C. 20360 August 1970 Reproduction in whole or in part is permitted for any purpose of the U. S. Government

TABLE OF CONTENTS Page L INTRODUCTION 1 IL PURPOSE 3 III SYSTEM COMPONENTS 4 IV. CONNECTION OF COMPONENTS 6 V. SYSTEM OPERATION 11 Figures 1. Test setup at CEL 7 2. Experimental setup at Bimini 8 3. LMSG settings for normal mode 9 4. Mimi - Preprocessor settings 10 iii

I. INTRODUCTION The M4 Communication System is a complete revision of the M3 Communication System as constructed by C. V. Kimball in June 1969. The M4 system operates under the control of CPS (Cooley Programming System) and is designed to be run on the Field8 computer. The M4 system operates only in a reference mode, i.e., it is not set up to operate in a communication mode. The M4 system is considerably more versatile than the M3 system: 1) it utilizes 8K of memory, 2) it operates under CPS, 3) software support is readily available at CEL. The transmitter is the LMSG. The reference word transmitted is a 15 digit maximal length pseudo-random sequence. The LMSG can transmit each bit of information, i.e., each digit of the sequence, either in the normal mode (no subsequence) or in a bandspreading mode (each digit of the sequence is characterized by a particular subsequence). The "receiver" is the Field-8 computer. The program consists basically of two parts, the synchronization procedure and the receiver itself. Major improvements over the M3 system are: -1

-21) automation of synchronization procedure, 2) conversion to double precision, 3) more detailed computation of system parameters, 4) simplicity of operation (one program only).

II. PURPOSE The goals of the M4 Communication Experiment are: 1. To calculate P(E) versus S/N. 2. Compare band-spreading with the normal mode of operation. 3. Study effect of exponential weighting in computing the reference. -3

III. SYSTEM COMPONENTS Operating the M4 system requires the following system components. 3.1 Field-8 Computer, an 8K DEC PDP-8/L with tape controller modified to operate under CPS. Additional hardware needed for the M4 system and for general purpose signal processing include: 1) external interrupt for timing control from clock (or oscillator), 2) A/D converter for sampling, 3) 2 D/A converters for display purposes, 4) 4 mechanical relays for computer attenuator control. 3.2 Logically Modulated Signal Generator (LMSG), a function generator (designed and built by P. Nuspl of CEL) used to generate periodic sequence transmissions. It is capable of transmitting the reference word (the 15 bit periodic sequence) in either the normal mode or in the bandspreading mode. 3.3 Mimi Preprocessor, an analog unit which contains a line-to-line transformer, a bandpass filter (140 Hz about 420 Hz) and a 3 dB per step attenuator. The attenuator has a built-in gain of 40 dB and can be controlled either manually at the unit or remotely by the Field-8 mechanical relays. 3.4 Precision Oscillator, the source for maintaining a -4

-5coherent reference. A 1680 Hz, 5 volt square wave is required. 3.5 RMS Voltmeter, for monitoring input voltage level to A/D converter. 3.6 x, y Oscilloscope, for observing synch display and receiver reference. 3.7 8K-CPS Tapes, operating system tapes which contain the binary versions of the M4 system. There are currently two operating versions. The binary file COMS4 contains the program for the "simple" version. The binary file COMM4 contains the program for the Markov version (or the arersion which exponentially weights the reference).

IV. CONNECTION OF COMPONENTS Figure 1 illustrates the setup for laboratory simulation of the M4 Communication Experiment. Figure 2 shows the connections used in the experiment of July, 1970 for the Mimi channel, Miami to Bimini. Figures 3 and 4 depict the proper settings for the LMSG and MIMI preprocessor, respectively. -6

-74f I 0 LMSG mod l |G.R. Signal Conditioner, 1/3 Octave at 420 Hz Noise Generator, Variable Gain Display | Simulated Inp t SiEnal _ Scope 1.-(1o^ W. i s, Krohnhite Filter,' = t Eo 370-470 Hz 1680 Hz ~ Oscillator -- -- -= I < IRMS Qna aQs!Voltmeter |Analog__ | Mimi In Pre-processor Clock Field/8 jComputer Fig. 1.TestsetupatCE Teletype Fig. l. Test setup at CEL

-8Receiving Hydrophone Line 100 Hz Bandpass Filter Display Scope CJ -M~.^ ^ -Adjustable --------..rg =f'~'~~Amplifier 1680 Hz - L I _ I. Oscillator Voltmeter Analog Mimi in l | Feld8 |Pre-processor Clock Field/8 Computer Fig. 2Exei<mni Teletype Fig. 2. Experimental setup at Bimini

-9The settings given in Fig. 3 are for operating the Communications Experiment in the normal mode. To operate in the bandspreading mode requires that switch Dl. be in the down position and the BS/NORM switch should be in the BS position. A word of caution is in order. When changing from the normal mode to the bandspreading mode, the "receiver" must be restarted since synchronization is lost in the switching process. Fig. 3. LMSG settings for normal mode 3 2 2 2 2 MSRG TAPS Dl D2 D3 D4 AO Al A2 A3 A4 A5 O SEQ CW AM BPM CPM EXT SO Sl 3 MESS 7 NORM 0 4FO MESS MOD SYNC SYNC SRCF B2 B3 INQ Q OUTO 0 0

-10To Field-8 A/D Converter _- (Analog In) Receiving ( Hydrophon Filter Line Int Ext o 0 0 0 Q. Man I 24 12 6 3 ~!iiiiii.? To Field-8 Normally Open Relays 2, 3, 4, 5. (Switches in up position, control cable leaves plug from right side.) Fig. 4. Mimi - Preprocessor settings

V. SYSTEM OPERATION 5.1 Connect system components. 5.2 Load CPS. 5.3 Type RUN COMS4 or RUN COMS4P [or RUN COMM4] (CR) (COMS4 computes Dl and D2, COMS4P computes D1 and D3.) 5.4 Adjust amplifier gain so that the input voltage to the A/D converter is approximately.05 volts RMS. [For COMM4 set MAN/REMOTE switch to MAN and adjust gain to.05 volt RMS. ] 5. 5 Enter data number N, (CR) Enter group number M, (CR) [For COMM4 enter weight factor I, (CR).] 5.6 Synch mode: Wait about 2 ~ n ~ m seconds for display to appear and the word SYNCHED to be typed. If display is "triangularlike," synchronization is satisfactory. If display is bi-modal (indicative of two distinct paths) or "noise-like," synchronization is doubtful. Wait until conditions improve (path structure changes or SNR increases) or increase averaging times (increase N and/ or M) and restart program at loc 200. A program option in the synch mode is: 1) Type D to view the distribution of energy in the received symbol (it should be "pulse-like"). Type D again to view the original display. -11

-125.7 Receive mode: Type R to enter receive mode if synchronization is deemed satisfactory. Program options in the receive mode are: 1) Type C to change from computer control of attenuator to manual control or vice versa (only for COMS4). 2) Type P to change from normal printing mode to minimal printing mode or vice versa. Have patience since these changes will occur only at the end of a block, one at a time. GOOD LUCK!