This preview shows page 1. Sign up to view the full content.
Unformatted text preview: l
and cannot recognize the next CLTU's START sequence which follows immediately.
Although the Start Sequence of the next CLTU is NOT part of a codeblock and so has a high
probability of causing CODEBLOCK REJECTION, this attribute is of no help at this point,
since the start sequence has already passed. As a result, the entire CLTU which follows is
missed.
The probability of missing a tail sequence when using the TED decoding mode is the
probability that 2 or more changes are introduced into the tail sequence during transmission:
PTA = 1  [(1  p)n + np(1  p)n1] [EQ. G] where n = length of tail sequence in bits.
Issue 6 Page D16 January 1987 CCSDS REPORT CONCERNING TELECOMMAND: SUMMARY OF CONCEPT AND SERVICE The probability of missing a tail sequence when using the SEC decoding mode is the
probability that one or more changes are introduced into the tail sequence during transmission:
PTB = 1  (1  p)n [EQ. H] It should be noted that Equations G and H are conservative approximations, since changes in
certain locations may not result in a missed tail. Values are tabulated in Table D7.
Table D7: Probability of Missing Tail Sequence, PTA (TED) and PTB (SEC)
___________________________________________________________________________
Probability of missing a tail,
Tail Sequence
Decoding
for a Channel BER of
4
105
106
length, bits
mode
10
___________________________________________________________________________
1.95x105
1.95x107
1.95x109
64
TED (PTA)
SEC (PTB)
6.28x103
6.30x104
6.30x105
56 TED (PTA)
SEC (PTB) 1.48x105
5.49x103 1.48x107
5.50x104 1.48x109
5.50x105 48 TED (PTA)
SEC (PTB) 1.08x105
4.69x103 1.08x107
4.70x104 1.08x109
4.70x105 TED (PTA)
7.39x106
7.41x108
7.41x1010
SEC (PTB)
3.89x103
3.90x104
3.90x105
___________________________________________________________________________
40 The probability of rejection of the last frame in a CLTU which follows another CLTU (without
reacquisition) may be evaluated as the probability of missing the tail of the preceding CLTU
(PTA or PTB) OR the probability of rejecting the last frame of the subject CLTU.
That is,
<Prob. of frame rejection in
subsequent CLTU, TED decoding> = PF2A
= PTA + (1PTA)PFA
= PTA + (1PTA)[(PSA + (1PSA)PCA] [EQ. I] where PFA refers to the frame performance as previously calculated in Equation E (independent
of a previous CLTU); and Issue 6 Page D17 January 1987 CCSDS REPORT CONCERNING TELECOMMAND: SUMMARY OF CONCEPT AND SERVICE <Prob. of frame rejection in
subsequent CLTU, SEC decoding> = PF2B
= PTB + (1PTB)PFB
= PTB + (1PTB)[(PSB + (1PSB)PCB] [EQ. J] where PFB refers to the frame performance as previously calculated in Equation F (independent
of a previous CLTU).
Given equal length CLTUs, one can see that each subsequent CLTU will have a higher
probability of rejection than the previous CLTU.
Example. Two maximum length frames could be packaged into two separate but contiguous
CLTUs in an organization as shown in Figure D5. The probability of rejection of the first
(PF1) and second (PF2) frames in this organization may be compared...
View
Full
Document
This document was uploaded on 03/06/2014.
 Spring '14

Click to edit the document details