NUSC Technical Document 639

IF II f . ..

30 March 1961

Sign Polar Return-To-ZeroTelemetry and Coding Logic

Gerald L. AssardSurface Ship Sonar Department

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N- I fI

Naval Underwater Systems CenterNewport, Rhode Island/New London, Connectc

Appr'vld for public releee, distribution unlimited. 81 5 26 OR7

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Preface

This document was prepared under the Ocean Measurements and ArrayTechnology (OMAT) Program portion of the SEAGUARD Program sponsored bythe Defense Advanced Research Projects Agency (ARPA Order No. 2976),Program Manager, V. Simmons, Tactical Technology Office, NUSC Project No.A69600, Program Manager, R. F. LaPlante (Code 33492).

The author gratefully acknowledges the contribution of Mr. Charles Veitch ofMAR, Incorporated, for his assistance in the development, preparation, and editingof this technical document.

IReviewed and Approved: 30 March 1981

D. WaltersHead, Surface Ship Sonar Department

The author of this document is located at theNew London Laboratory, Naval Underwater Systems Center

New London, Connecticut 06320

i 4i I I - I I I - -

TD 6399

FOREWORD

An existing Navy digital time division multiplexing telemetry systememploys pulse-code modulation of companded towed array hydrophone channelinformation. The existing scheme assigns 8 binary data bits per channelword and allocates these bits as follows: I bit for the argument sign, 3bits for its exponent and 4 bits for its mantissa. An improvement in datatransfer efficiency is described herein that is a characteristic of theexisting scheme and results in the availability of an additional bit perchannel word.

The existing scheme employs Bipolar Return-to-Zero (BPRZ) logine toencode binary information for telemetry transfer using a pseudoternarycode format. The BPRZ logic provides for trilevel waveform pulse-codemodulation: positive voltage pulses, zero voltage (no pulses), and negativevoltage pulses. This particular encoding scheme assigns to any BPRZ timedivision window one binary state to all nonzero levels (all pulses bothpositive and negative) and the other binary state to all zero voltagelevels (no pulse). As can be seen, the binary encoding does not use thefull ternary capacity of the BPRZ logic; therefore, this implementation isreferred to as pseudoternary encoding.

Pulse polarity encoding, as shown herein, provides an additionalbit transfer per channel word. The implementation chosen as an example inthis discussion assigns the bit required for the sign of each telemetrychannel argument to be transferred by polarity encoding of the existingeight pulse waveform. The first nonzero pulse within each pulse-encodedwaveform channel argument transfers the argument sign information by way ofits polarity. This technique simply extends the incompletely exploitedinformation capacity of the ternary format, yet retains the BPRZ logic. Itis called Sign Polar Return-to-Zero (SPRZ) because of the polarity encodingof argument sign information. Examples used in this description retain the8 binary pulse-encoded bits per channel word and allocate the additional bitto exponential use, thereby increasing system dynamic range. Similar schemescould assign the additional bit to the mantissa, realizing an increase inquantizing accuracy or simply require only 7 pulse-encoded bits per word toincrease the system capacity for channels proportionally. The novel tech-nique described represents an effective and efficient use of existing digitalcircuit technology to perform a function not being accomplished using aconventional approach.

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TABLE OF CONTENTS

Section Page

1 BACKGROUND ............... . . 1

2 TECHNICAL DESCRIPTION ................ 7

3 SUbMRY .. .. .. .. . . ... .. ... 13

LIST OF ILLUSTRATIONS

Figure Page

1 BPRZ Logic Pseudoternary Waveform Encoding . . . . . . 22 Inverted BPRZ Logic Pseudoternary Waveform Encoding. . 33 Compandng Block Diagram ............... 54 Companding A/D Converter Bit Identification . o . . . 55 SPRZ Block Diagram. .. .. ............. . 86 SPRZ Logic Pseudoternary Waveform Encoding . o o . .. 97 Inverted SPRZ Pseudoternary Waveform Encoding. . . . . 108 Two Simulated 9-Bit Words and Their Pulse

Encoded Waveforms ............... .. . 12

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Section 1. BACKGROUND

Digital data telemetry systems must efficiently transfer the maximumamount of information possible. An existing time division multiplexingtelemetry system employed in U. S. Navy sonar applications utilizes BipolarReturn-to-Zero (BPRZ) logic in a pulse-code-modulation scheme to transmitcompanded digital data. The use of BPRZ logic provides a trilevel pulselogic capable of supporting a ternary code; however, only binary data areencoded, leaving unused degrees of freedom in the BPRZ logic. Because thetristate (ternary) logic is used only to transfer bistate (binary) data,this application of BPRZ is referred to as a pseudoternary code. The SignPolar Return-to-Zero (SPRZ) technique improves the data transfer capacityby exploiting an unused degree of freedom available in the BPRZ logic.

The existiag telemetry system application of BPRZ logic provides forbinary data transfer of 8 bits per channel word using pulse-code modulation.For bit encoding, the binary data requires two states, "a" and ti."

The available trilevels in the BPRZ logic are allocated as follows:

1. BPRZ binary bit-state "a" encoded by transmitting, at thatparticular bit's time division windoiy, either a positive ornegative voltage pulse. The pulse polarity is alternated suchthat the sequential occurrence of pulse-encoded binary state"a" within any serial bit stream provides a pulse of oppositepolarity to the preceding state "a" encoded pulse modulation.

2. BPRZ binary bit-state "I" encoded by not transmitting anypulse during that bit's time division window, thereby main-taining the zero voltage level.

A typical sequential pair of binary words, J and J+l, 8 bits each, areshown in figure 1, with the corresponding BPRZ pulse-code-modulation wave-form. Note that all three voltage levels, +A, 0, and -A, are used to encodebinary information because the absence of a pulse during a bit time divisionwindov indicates a binary state. Note also that the example given associatesBPS" state "a," as defined above, with the binary value 12' and BPRZ state "I"with the binary value 02.1 An equally efficient encoding could reverse theorder of association between BPRZ logic states "a" and "I" and the binaryvalues 02 and 12. The encoded waveform with this inverted logic wouldappear as in figure 2, where words J and J+l contain the same binary valuesas in figure 1. (Both BPRZ and inverted BPRZ logic pseudoternary encoding areemployed in the existing telemetry system.) Lastly, the polarity of the firstnonzero pulses in word J+l in figures 1 and 2 are negative and the polarity ofthe last nonzero pulses in word J in both figures are positive since polarityalternation is preserved from word to word. In these examples, the pulsewaveform for both J words has an odd number of transmitted pulses. Note,however, if a word pulse waveform included a last pulse of negative polarity,

lSubscript notation for base 2, binary values.

l, / I I l l I I . .. . ... .. .. . .. .. . .1

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WORD + .1+1

I

8-BIT IDENTIFIERS iD, 6 5 % 3 S2 1 O 7 6 35 34 33 B2 B1 SO

BIT~ ~ ~~I SL.1ATOE2 El ED '3 M2 MI M 0 S E2 El E031 N~ M2M

DV .UES BNRY 0 1 0 1 0 1 10 1 0 1 1 1

TRANSFER OF BINARYDATA TO BPZ LOGIC

-PULSE IDENTIFIER- IP7 P6 p5 P4 p3 P21 P P 6 A P P 4 P P PI ! i:t JTRISTATE VOLTAGE 1+ 0 0 + 0 + - + -+

ASSIGNMENT

BPRZ WAVEFORM4

PULSE CLOCK RATE n

PUSECDE TIME DIVISION

BI - £th BIT _ I'OID SYNC

S - SIGNE, . I

th EPNN

145 . I th

MANTISSA

Figure 1. BPRZ Logic PseudoternaryWaveform Encoding

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WORD + I* I* II

8-BIT IDENTIFIERS I B7 B6 B 5 4 B3 B2 s1 B0 i 7 B6 15 B4 153 B2 15 1

sE 2 E 1 0 ZIs 3 2 "1 No E E1 E0 H3 M2 Ml No

BIT ALLOCATIONS E2 |- D' 2M.M

sIGN AND BINARY l1 0 1 0 1 0 1 10 0 1 1

DATA VALUES

TRANSFER OF BINARYDATA TO BPRZ LOGIC

S-PULSE IDENTIFIERS IP7 6 P5 P4 P3 P2 1 P0 7 P6 P5 P4 P3 P2 P1 PO

TRISTATE VOLTAGE 1o + 0 - 0 + 0 - 0 + 0 0 0 0 0

ASSICGtE4

BPRZ WAVEFORM 0 VOLTAGE

! nr H- +2A, ,.

PULSE CLOCKC RATE0

, PULSE CODE TIME DIVISIONWINDOW

±1 ih BIT WORD SYNC

S - SIGN

E - iCh EXpONENT

Hi I 1 th MANTISSA

Figure 2. Inverted BPRZ Logic PseudoternaryWaveform Encoding

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the first pulse of the next word waveform would be positive, again preservingpolarity alternation from word to word.

BPRZ logic transmitting and receiving codes have been employed for anumber of years. These transmitting schemes normally employ word formatsconsisting of 4, 8, 12, or 16 bits. The existing Navy telemetry system usesa BPRZ 8-bit word code to transfer data input from companding analog-to-digital (A/D) converter electronics.

Analog signals are input to a linear 12-bit A/D converter that providesan output of I sign bit and 11 magnitude bits. A compander reduces the11 bits of magnitude to the following 7 bits: 3 bits for exponential valuesthat identify the value of the most significant bit (MSB) and 4 bits ofmantissa value to further define the analog signal amplitude at the sacri-fice of precision because of lost least significant bits (LSB's). The signbit is transferred by an 8th bit through the companded circuitry. The de-companded value at an expander output provides a linear value to 5 mostsignificant bits: 1 bit transferred by the exponential set of 3 compandedbits and 4 bits transferred by the mantissa set of 4 companded bits. Note,by design the exponential set of 3 companded bits identify the position andbinary value of the most significant bit of the li-bit magnitude value atthe output of the 12-bit A/D converter. The system functional details areshown in figure 3, and the specifics of companded encoding are shown infigure 4. The expander output reformats the binary word into a 12-bit value:1 bit sign and 11 bits magnitude. However, the expander output only contains5 significant bits of information. The block diagram of the companding shownin figure 3 indicates the bit transfers between functions. The BPRZ logicpseudoternary encoding is used to transfer the 8 data bits between the digitalcompander and the digital expander.

The transfer characteristics for the 12-bit A/D converter code and theresultant companded 8-bit code are shown in figure 4. The top of the figureshows the enumerated 12 bits from the A/D converter: bits number 0 through 10for magnitude and bit number 11 for sign encoding. The bottom of the figuredemonstrates the allocation of companded bits: bits 0c2 through 3c iden-tify mantissa, bits 4c through 6c are for exponent encoding transferring theMSB, and bit 7c is for sign encoding. Figure 4 presents three regions:

1. Region of No Data - a region of no error, since it carries no infor-mation and all bits are zero.

2. Region of Lost Data - a region of 12's and 02's, but is not carriedthrough the system and can represent a maximum quantizing error of 3.125percent.

3. Region of Mantissa - a region occurring between the Regions of No Dataand Lost Data that presents the highest energized bits (MSB of the mantissa)and the following 4 lower significant bits. This region presents a linearmeasure of the data, but is limited to 5 significant bits of precision.

21c denotes the ith companded form binary bit.

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12 BIT S IGN # - SIGN / ._ SIGN / _ SIGN 12 BIT

DIGITAL I B-it DI I A fI I ALC DIGITAL

IPT MAGNITUDE e _COKPANDE.R #/ -EXPANDER /1 l MAGN

ITUDE

OUTOUTIN U 1 i ENCODER 7 BI -s DECODER fI110

Figure 3. Companding Block Diagram

-M 12-BIT

SIGN , - IAGNITUDE ?-- LINEAR

10 9 8 7 6 5 4 3 2 1 0 FORMREGION OF MANTISSA

S 000 REGION OF 0 0 0 0 0

S 000 0 1 1 1 1NO DATA

S 001 1 0 0 0 0NO ERROR

S 001 1 1 1 1 1

S 010 1 0 0 0 0

S 010 1 1 1 1 1

S 011 1 0 0 0 0

S 011 1 1 1 1 1

S 100 1 0 0 0 0 REGION OF

S 100 1 1 1 1 1 LOST DATA

S 101 1 0 0 0 0

S 101 1 1 1 1 1

S 110 1 0 0 0 0MAXIM.4 ERROR

S 110 1 1 1 1 11 3.125

S 111 1 0 0 0 0 3

1 ill1e Id Ib 1c CI

REGION OF MANTISSA

7 654 * 3 2 1 0?c 6ccc c c c c S-BIT

SIGN EXPONENT MANTISSA FORM

-- CO?'TANDER -

* THIS BIT IDENTIFIED IN POSITION AND VALUEBY EXPONENT COMPANDED BITS; 6 5 4 .

Figure 4. Companding A/D ConveterBit Identification

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The BPRZ pseudoternary code allocation for the 8 companded bits can beshown as follows:

7c3 6c 5c 4c 3c 2c Ic 0c

S E2 E1 E0 M3 M2 MI M0,

whereS Sign +

En Exponent (Identifies the location of the highest orderbinary value, 12, of the 11 magnitude bits from a 12-bit(sign + 11 magnitude) A/D conversion for the noncompandedtelemetry receiver output.

Mn Mantissa (carries the magnitude to 4 additional binaryplaces).

It became necessary to increase the dynamic range of the A/D convertersystem. One such system to accomplish this is described in NUSC TD 6317.

4

This system requires data transfer capacity for 4 bits of mantissa infor-mation, 4 bits of exponential information, and I bit of sign information.The existing BPRZ pseudoternary telemetry system has no space for the re-quired additional exponential bit per word. SPRZ logic digital encoding wasdeveloped to accommodate this extension of dynamic range. This method out-puts at the transmitter a conventional BPRZ waveform polarized for sign iden-tification to present a 9-bit code at the telemetry receiver expander input.

As indicated above, recently developed underwater acoustic arrays thatuse BPRZ digital logic to transfer data over coaxial cable are not being uti-lized as efficiently as possible. By using an inexpensive encoding/decodingtechnique, we can take advantage of a BPRZ logic polarity modulation char-acteristic to transfer the information content of an additional bit in thetransmitted digital word. The example presented demonstrates the extractionof the sign (+) information of an electrical (acoustic) signal without trans-ferring this information by using a conventional pulse-encoded bit in thetransmitted digital word.

The purpose of the SPRZ digital encoder/decoder is to present a conven-tional N-pulse logic, enhanced by polarity sign encoding, to a BPRZ transmit-ter and, thereby, extract an N+l-bit code at the receiver. The SPRZ logicdescribed increases the telemetry system's information capacity for datatransmission; however, the same number of time division windows for binarypulse encoded modulation is used. Because BPRZ logic is being employed inexisting Navy digital transmission systems, any cost effective improvementin information transfer efficiency is of great interest.

31c denotes the ith companded form binary bit.

4 G. L. Assard, A Gain Step Companding (COMpressing ExPANDING) Analog-to-Digital Converter, NUSC Technical Document 6317, Naval Underwater SystemsCenter, New London, CT, 30 March 1981.

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Section 2. TECHNICAL DESCRIPTION

The block diagram in figure 5 presents the functional blocks requiredto transform an N+l-bit binary word into a sign polar enhanced conventionalN-bit format that can be reconstructed into the original N+l-bit word at acorresponding telemetry receiver. In this specific case,

N = 8.

The timing block (1) in figure 5 consists of binary circuitry that willgenerate the required timing functions to format the N+l-bit word stored inthe transmit register (2) through the SPRZ codes (3) into the N-bit trans-mitter similar to the existing BPRZ format.

The N+l-bit word transmit register stores the N+l-bit word and presentsthe bits serially into the SPRZ encoder (3).

The SPRZ encoder (3) polarizes the bit stream to be transmitted so thatthe first nonzero voltage pulse encoded bit of each word contains two piecesof binary information: first, its own bit identity and, second, the polar-ization (a second degree of freedom) that identifies the additional bitstate. Thereafter, the SPRZ encoder (3) alternates the polarization of theremaining bits of the word to produce a pulse-encoded waveform entirelysimilar to the existing BPRZ format.

For example, two typical 9-bit words, K and K+l, can be used to demon-strate waveform pulse encoding. These words are shown in figure 6, where thebit allocation per word is as follows: 1 bit for sign state identification,4 bits for exponential precision, and 4 bits for mantissa precision. Notethat the first nonzero pulse in words K and K+l transfers sign information aswell as binary state. This sign information is carried in the first pulse-time-division window, i. e., pulse P7 in word K. In word K+l, where the 9-bitword binary value +000000012 is similarly encoded, its sign is transferredby the polarity of the last word pulse, Po. It also should be observed thatwhile positive and negative pulse encoding alternates within the 8-pulse trainof a word, the particular data now may require two consecutive identicalpolarity pulses occurring in the last nonzero pulse of word K and the firstnonzero pulse of word K+l. Moreover, figure 7 demonstrates the possibilityof inverse SPRZ logic application, as was demonstrated for BPRZ logic infigure 2. As mentioned earlier, certain telemetry system electronic areasuse this inverting flexibility to enhance performance.

The N-bit transmitter (4) in figure 5 is a conventional BPRZ transmitterwith polarization under the control of the SPRZ encoder (3). The transmitter(4) drives the transmission line (5) with the SPRZ N-bit code. The bits areextracted from the transmission line (5) at the recgiver N-bit detector (6).The detector (6) provides the receiver timing (7) block with the conventionalsynchronizing pulses to maintain synchronization with the transmitted digitalbit stream. The second function of the detector is to present the SPRZ decoder(8) with the polarity of the first nonzero voltage encoded bit along with the

7

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w &4 0

Ln

001-4cnI.

tn pa0

A7,LA

8

TD 6359

WORD S K K+ II II I

9-BIT IDENTIFIERS '8 B7 A 6 35 B4 B3 B2 B1 B0 IS B7 B6 B5 B4 B3 B2 Bl DO

IIBIT ALOCA IO S E I E 0 M I I MOIS E 3 El I E M3 M2 M 0

,' 0331 0 32 ,'SIGN AND BINARY M

DATA VALUES 1 0 0 1 0 1 0 + 0 0 0 0 0 0 0 is

TRANSFER OF BINARY IIDATA TO SPRZ LOGIC

8-PULSE IDENTIFIERS l7 P P P PP P P P P 1 P

TRISTATE VOLTAGE 0 + 0 0 0 0 0 0 0 0 VLA

ASS IGNMENT I

SPRZ WAVEFORM 0 -I - VOLTAGE

. I - -A

n lnr r r r r r-nnnr l + o ,PULSE CLOCK RATE - -- 0 VOLTAGE

It II

PULSE CODE TIME DIVISIONWINDOWS

B, - ith BIT WORD SYNC

S - SIGN

E1 - £th

EXPONENT

M1 - 1th MANTISSA

Figure 6. SPRZ Logic PseudotenaryWaveform Encoding

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WORD I J 341

9-BIT IDENTIFIERS 15 3 1~ B5 I4 B3 B2 a ~ 3 ti8 7 6 5 4 3 B2 B1 BO

BIT ALLOCATION IS E3 E2 E1 E0 M3 2 M1 M0 S E 3 E 2 El EO M3 M2 "1 "0

SIGN AND BINARY jlIIIIII~uDATA VALUES 1 0 1 0 1 0 1 0 + 0 0 0 0 0 0 0 1

TRANSFER OF BINARY 4 /DATA TO SPRZ LOGIC

8-PULSE IDENTIFIERS P7 P6 p5 P P P l I p p. P4 P3 P PIP 6 2107 65432 1 0I

,RTSTATE VOLTAGE 0 - 0 + 0 - 0 +8+ - 4 - + - 0'

SPRZ WAVEFORM VLTG

PULSE CLOCK RATEnnnni 0 O#ZUs, UI rrrr Ui:::~ U r U too

-PULSE CODE TIME DIVISION

________________________ WINDOWaS

WORD SYNC

S - SIGN

E, . Ath EXPONENT

KN.-I th MANTISSA

Figure 7. Inverted SPRZ PseudoternaryWaveform Encoding

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transmitted N-bit serial binary word. The polarity of the first nonzerovoltage encoded bit is processed within the SPRZ decoder (8) to identify theadditional transmitted bit state and reconstruct the original N+l-bit word.While the word is being decoded (8), it is being clocked (7) into the N+l-bitword receiver register (9) where it can be transferred to its intended desti-nation, thereby clearing the receiver for accepting the next serial word.

Figure 8 presents two simulated 9-bit words and their pulse-encoded wave-form as they appear at various points in the system block diagram, (figure 5).The simulated 9-bit word is first seen at the functional block (2) in figure 5.The B8 bit is encoded as the polarity of first nonzero pulse in the 8-pulsewaveform at blocks 4, 5, or 6. The B8 bit has been decoded from the polarityof the first nonzero voltage encoded bit to complete the original 9-bit wordand is again available at block (9) in figure 5.

In figure 5, the SPRZ decoder (6) must also provide for decoding the B8bit, (word argument sign) for the case when no pulses are transmitted; i.e.,B0 through B7 are all zero-pulse encoded. The all-zero pulse transmittedword can accommodate only one sign state of the B8 bit, as in the conventional2's complement format that would transfer to the receiver a decoded 40 wordstate. However, an alternative would be to never transmit the B0 through B7all-zero pulse-encoded state. This can easily be accomplished by forcing theall-zero pulse-encoded state to be modified by including a B0 pulse polar-ized to preserve the word argument sign information. This is a hard clippedsign implementation.

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4 0

'00

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'A0 0z +

apa

0l 0

C-4 4 am

~~0i +

000

00 ~- -3

al w 0n 0

do 04 1

'- K 0-4 on 0n .-4

1-4 = -4 + i -'Z" o '

- i w' 0D

1.-4

og'

21

TD 6399

Section 3. SU4RY

The Sign Polar Return-to-Zero (SPRZ) telemetry digital formatteremploys an inherent additional degree of freedom of the serial N-bit BPRZtransmitter. Use of this degree of freedom, previously unencoded, resultsin an advantage because the telemetry receiver is able to extract N+1 bitsof digital code from an otherwise conventional N-bit transmitted code. Thepolarization of the N-bit per word BPRZ logic has been employed to presentan N+1 bit per word code at the telemetry output.

In sumeary the SPRZ utilizes an encoded tristate voltage waveform totransmit binary inf( rmation over a telemetric link. It is more efficientthan the conventional Bipolar Return-to-Zero (BPRZ) format because the SPRZdoes not require a separate waveform state solely dedicated to transfer wordargument sign information. The sign information for each word is transferredby the polarity of the first nonzero waveform pulse in each word as describedherein. The SPRZ format reduces an N+1 bit format by one bit to an N-bit codefor waveform transfer because this coding has eliminated the requirement ofthe conventional BPRZ transmitted sign bit. This increase in telemetry effi-ciency is significant to multichannel digital telemetry circuit technology.

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