Common Terminology Summary NASA CCSDS Optical Communications Working Group May 8, 2015 May 8, 2015

Definitions of Terms 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 May 8, 2015

Suggested Notation Notation Definition 𝑇 𝐶𝐻𝑆 Channel symbol duration 𝑇 𝑂𝑇 Off time duration 𝑇 𝐵 Burst period duration* 𝑁 𝐶𝐻𝑆 Number of channel symbols per burst period* 𝑅 𝐶𝐻𝑆 Channel symbol rate (≡ 𝑁 𝐶𝐻𝑆 / 𝑇 𝐵 ) 𝐵𝑊𝐸 Bandwidth expansion ( ≡𝑅 𝐶𝐻𝑆 / 𝑅 𝐷 ) 𝑅 𝐶𝐻𝐶 Channel clock rate (≡1/ 𝑇 𝐶𝐻𝑆 ) * For non-burst-modulations such as BPSK and OOK , 𝑇 𝐵 = 𝑇 𝐶𝐻𝑆 and 𝑁 𝐶𝐻𝑆 =1. May 8, 2015

Next Steps 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 May 8, 2015

Backup

Suggested Definitions 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). Bits Code symbols Channel symbols

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)

Channel Symbols in Current White Books 1 1 1 1  BM-RZ-DPSK* Off Time  BPSK OOK PPM + Guard Slots* *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. Guard Slots

Proposed Definitions (1 of 2) Channel Symbol = An optical waveform used to transmit information within a unit interval 1 1 1 1  BM-RZ-DPSK TCHS = channel symbol duration Off Time = Unit time interval between channel symbols or groups of channel symbols in which no information is conveyed via an optical transmission TCHS TOT TB (NCHS=4)  BPSK TOT = off time duration TCHS Burst Period = Periodic interval including a single off time and an associated preceding channel symbol or group of channel symbols OOK TCHS TB = Burst period duration (=TCHS for non-burst modulations) PPM + Guard Slots NCHS = number of channel symbols transmitted per burst period (=1 for non-burst modulations) TCHS TOT TB (NCHS=16)

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) BWE = RCHS/RD RCHC = 1/TCHS

Channel Symbol Rate Examples RCHS = NCHS/TB 1 1 1 1 RCHS = 4/(4*TCHS + 4*TCHS) = 1 / (2*TCHS)  BM-RZ-DPSK TCHS TOT TB (NCHS=4)  BPSK RCHS = 1 / TCHS TCHS OOK RCHS = 1 / TCHS TCHS PPM + Guard Slots RCHS = 16/(16*TCHS + 2*TCHS) = 8 / (9*TCHS) TCHS TOT TB (NCHS=16)

Channel Symbol Rate Example: BM-RZ-DPSK RCHS = NCHS/TOB NASA Proposed High Data Throughput Modes (for Rate ½ DVB-S2 FEC) Mode Name User Data Rate (Mbps) Duty Cycle Q Repetition RCHS (GHz) BWE RCHS/RD U-1244 1244 1 2.88 2.27 U-622 622 1/2 1.44 U-311 311 1/4 0.72 U-155 155.5 1/8 0.36 U-51.8 51.8 1/24 0.12 U-16 16 1/40 2 0.072 4.38 U-8 8 4 8.76 U-4 17.52 U-2 35.04

Channel Symbol Rate Example: BM-RZ-DPSK Photon Efficiency vs Channel Symbol Rate Example: BM-RZ-DPSK Photon Efficiency vs. Bandwidth Expansion U-2 U-4 U-1244 U-622 U-311 U-155 U-51.8 U-8 U-16

Alternate Definition for Channel Symbol Rate, RCHS The channel symbol rate is the maximum instantaneous rate of channel symbol transmission RCHS = 1/TCHS

Alternate Definition Examples RCHS = 1/TCHS 1 1 1 1 RCHS = 1/TCHS  BM-RZ-DPSK TCHS TOT NCHS=4  BPSK RCHS = 1 / TCHS TCHS OOK RCHS = 1 / TCHS TCHS PPM + Guard Slots RCHS = 1/TCHS TCHS TOT NCHS=16

Alternate Definition Example: BM-RZ-DPSK RCHS = 1/TCHS NASA Proposed High Data Throughput Modes (for Rate ½ DVB-S2 FEC) 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) 4.54 U-311 311 (Max/4) 9.08 U-155 155.5 (Max/8) 18.17 U-51.8 51.8 (Max/24) 54.50 U-16 16 2 175.18 U-8 8 4 350.35 U-4 700.70 U-2 1401.41

Alternate Definition Example: BM-RZ-DPSK Photon Efficiency vs Alternate Definition Example: BM-RZ-DPSK Photon Efficiency vs. Bandwidth Expansion U-4 U-8 U-16 U-1244 U-622 U-155 U-51.8 U-311

Alternate Definition Example: BM-RZ-DPSK Photon Efficiency vs Alternate Definition Example: BM-RZ-DPSK Photon Efficiency vs. Bandwidth Expansion U-4 U-8 U-16 U-1244 U-622 U-155 U-51.8 U-311