1

Common TerminologySummary

NASA CCSDS Optical Communications Working Group

May 8, 2015

May 8, 2015

2

Definitions of Terms

May 8, 2015

Term Definition

Bit A unit of information transferred between data link protocol sublayer and the sync and channel coding sublayer

Code symbol An indivisible entity transferred between the sync and channel coding sublayer and the physical layer

Channel symbol An optical waveform used to transmit information within a unit interval (i.e., indivisible output of physical layer)

Off time Unit time interval between channel symbols or groups of channel symbols in which no information is conveyed via an optical transmission

Burst period Periodic interval including a single off time and an associated preceding channel symbol or group of channel symbols

Data rate The average rate of bit transmission

Channel symbol rate The average rate of channel symbol transmission

Bandwidth expansion The ratio of the channel symbol rate to the data rate

Channel clock rate The maximum instantaneous rate of channel symbol transmission

3

Suggested Notation

May 8, 2015

Notation DefinitionChannel symbol duration

Off time duration

Burst period duration*

Number of channel symbols per burst period*

Channel symbol rate ()

Bandwidth expansion ()

Channel clock rate ()

* For non-burst-modulations such as BPSK and OOK , and .

4

Next Steps

May 8, 2015

• Each proposed recommended standard, and associated documentation, should be updated to use this terminology

• Examples of needed updates– Fix incorrect use of “bit” (all proposals for all regimes)

• The word “bit” is used in many places to refer to the make-up of the ASM, unique word, control data, and header (all proposals)

• According to our definition, these aren’t bits since they are not passed from data link protocol sublayer, they originate in the coding sublayer, and they do not convey information to the end user (the markers are removed before data makes it to the user) and do not contribute to data rate

• The interleaver in NASA’s proposal is described as operating on “bits,” but it really operates on code symbols.

• “Mbps” is used in many places in ESA/DLR proposal where bits are not present; may refer instead to symbol rate, e.g., “Msps”. Also, LPC is described as operating on “bits”. (Also, CCSDS books use “octets” not “bytes” to avoid historical ambiguity with length of byte.)

– All proposals could use suggested notation, for clarity across proposals

5

Backup

6

OSI layers CCSDS layers CCSDS protocols

Physical layer Physical layer

Data link layer

Network andupper layers

Network andupper layers

Data linkprotocolsublayer

Synchronization andchannel coding

sublayer

data link protocolTM or AOS space

Synchronization

Communications

Optical

Coding &

Opt. Physical Layer

Suggested Definitions

Bits

Code symbolsChannelsymbols

• Bits occur at the boundary between the Data link protocol sublayer and the Synchronization and channel coding sublayer

• Code symbols occur at the boundary between the Synchronization and channel coding sublayer and the physical layer

• Channel symbols occur at the output of the physical layer, and they have a physical manifestation (light).

7

Consistency with Prior CCSDS Terminology

Previous definitions are consistent with CCSDS Prox-1 Blue Book (211.2-B-1):

•Data rate = bit rate = Rd (bits / second)•Code symbol rate = Rcs (code symbols / second)•Channel symbol rate = Rchs (channel symbols / second)•Photon efficiency: photons/bit•Bandwidth expansion (BWE): Rchs / Rd (channel symbols / bit)

8

Channel Symbols in Current White Books

Guard Slots

0 1 1 0 0 1 0 1

0 0 0 0 0 00BM-RZ-DPSK*

0 0 0 0 BPSK

OOK

PPM + Guard Slots*

Off Time

*Note: parameters for burst duration, off time, and guard slots were selected for illustration purposes only. They do not necessarily reflect parameter proposals in the current White Books for these signaling formats.

9

Proposed Definitions (1 of 2)

TCHS

0 1 1 0 0 1 0 1

0 0 0 0 0 00BM-RZ-DPSK

0 0 0 0 BPSK

OOK

PPM + Guard Slots

TOT

TOT

TCHS

TCHS

TOT = off time duration

Channel Symbol = An optical waveform used to transmit information within a unit interval

TCHS

TCHS = channel symbol durationOff Time = Unit time interval between channel symbols or groups of channel symbols in which no information is conveyed via an optical transmission

NCHS = number of channel symbols transmitted per burst period (=1 for non-burst modulations)

TB (NCHS=4)

TB (NCHS=16)

Burst Period = Periodic interval including a single off time and an associated preceding channel symbol or group of channel symbols

TB = Burst period duration (=TCHS for non-burst modulations)

10

Proposed Definitions (2 of 2)

• The channel symbol rate is the average rate of channel symbol transmission

• Bandwidth expansion is the ratio of the channel symbol rate to the data rate

• The channel clock rate is the maximum instantaneous rate of channel symbol transmission

• Rationale– Channel symbol rate and bandwidth expansion definitions are consistent with

widely-accepted approaches for analyzing spectral and power efficiency– For optical links, cost in terms spectral efficiency of adding off time or guard slots is

negligible – New metric, channel clock rate, can be used to assess the cost of high-rate

electronic processing required for optical signal processing

RCHS = NCHS/TB = NCHS/(NCHS*TCHS + TOT)

RCHC = 1/TCHS

BWE = RCHS/RD

11

Channel Symbol Rate Examples

TCHS

0 1 1 0 0 1 0 1

0 0 0 0 0 00BM-RZ-DPSK

0 0 0 0 BPSK

OOK

PPM + Guard Slots

TOT

TOT

TCHS

TCHS

TCHS

RCHS = 4/(4*TCHS + 4*TCHS) = 1 / (2*TCHS)

RCHS = 1 / TCHS

RCHS = 1 / TCHS

RCHS = 16/(16*TCHS + 2*TCHS) = 8 / (9*TCHS)

RCHS = NCHS/TB

TB (NCHS=4)

TB (NCHS=16)

12

Channel Symbol Rate Example: BM-RZ-DPSK

Mode Name User Data Rate (Mbps)

Duty Cycle

Q Repetition RCHS (GHz)

BWE RCHS/RD

U-1244 1244 1 1 2.88 2.27

U-622 622 1/2 1 1.44 2.27

U-311 311 1/4 1 0.72 2.27

U-155 155.5 1/8 1 0.36 2.27

U-51.8 51.8 1/24 1 0.12 2.27

U-16 16 1/40 2 0.072 4.38

U-8 8 1/40 4 0.072 8.76

U-4 4 1/40 8 0.072 17.52

U-2 2 1/40 16 0.072 35.04

NASA Proposed High Data Throughput Modes (for Rate ½ DVB-S2 FEC)

RCHS = NCHS/TOB

13

100

101

102

103

2

4

6

8

10

12

14

Bandwidth Expansion

Eff

icie

ncy

at

Cap

acit

y (P

ho

ton

s P

er B

it, d

B)

Hard Decision Pre-Amplified DPSK

Channel Symbol Rate Example: BM-RZ-DPSKPhoton Efficiency vs. Bandwidth Expansion

U-1244U-622U-311U-155U-51.8

U-16

U-8

U-4

U-2

14

Alternate Definition for Channel Symbol Rate, RCHS

• The channel symbol rate is the maximum instantaneous rate of channel symbol transmission

RCHS = 1/TCHS

15

Alternate Definition Examples

TCHS

0 1 1 0 0 1 0 1

0 0 0 0 0 00BM-RZ-DPSK

0 0 0 0 BPSK

OOK

PPM + Guard Slots

TOT

TOT

TCHS

TCHS

TCHS

NCHS=4

NCHS=16

RCHS = 1/TCHS

RCHS = 1 / TCHS

RCHS = 1 / TCHS

RCHS = 1/TCHS

RCHS = 1/TCHS

16

Alternate Definition Example: BM-RZ-DPSK

Mode Name User Data Rate (Mbps)

Q Repetition

Def 2 RCHS

(GHz)

Def 2 BWE RCHS/RD

U-1244 1244 (Max) 1 2.88 2.27

U-622 622 (Max/2) 1 2.88 4.54

U-311 311 (Max/4) 1 2.88 9.08

U-155 155.5 (Max/8) 1 2.88 18.17

U-51.8 51.8 (Max/24) 1 2.88 54.50

U-16 16 2 2.88 175.18

U-8 8 4 2.88 350.35

U-4 4 8 2.88 700.70

U-2 2 16 2.88 1401.41

RCHS = 1/TCHS

NASA Proposed High Data Throughput Modes (for Rate ½ DVB-S2 FEC)

17

100

101

102

103

2

4

6

8

10

12

14

Bandwidth Expansion

Eff

icie

ncy

at

Cap

acit

y (P

ho

ton

s P

er B

it, d

B)

Hard Decision Pre-Amplified DPSK

Alternate Definition Example: BM-RZ-DPSKPhoton Efficiency vs. Bandwidth Expansion

U-16

U-8

U-4

U-51.8U-155

U-311

U-622U-1244

18

100

101

102

103

2

4

6

8

10

12

14

Bandwidth Expansion

Eff

icie

ncy

at

Cap

acit

y (P

ho

ton

s P

er B

it, d

B)

Hard Decision Pre-Amplified DPSK1/2 Duty Cycle1/4 Duty Cycle1/8 Duty Cycle1/24 Duty Cycle1/40 Duty Cycle

Alternate Definition Example: BM-RZ-DPSKPhoton Efficiency vs. Bandwidth Expansion

U-16

U-8

U-4

U-51.8U-155

U-311

U-622U-1244