Find the frame length with derivative

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Discussion Overview

The discussion revolves around finding the optimum frame length (nf) that maximizes transmission efficiency for various ARQ protocols (Stop-and-Wait, Go-Back-N, and Selective Repeat) by taking derivatives and setting them to zero. Participants are working through mathematical derivations and addressing potential errors in their calculations.

Discussion Character

  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant seeks to find the optimum frame length nf for maximizing transmission efficiency using derivatives.
  • Another participant suggests that there is an error in the last factor involving nf and proposes checking the derivative calculation using the product rule.
  • Participants discuss the use of u substitution in their derivative calculations, with one participant specifying u = nf - n0 and v = (nf+B)-1.
  • There is a suggestion that the differentiation process may have been incorrectly applied, specifically regarding the product rule for derivatives.
  • One participant expresses uncertainty about the correctness of their answer and asks how it compares to a book answer.
  • Another participant recommends simplifying the expression further by extracting common factors and finding a common denominator.
  • Participants inquire about the clarity of the posted answers and whether further simplification is necessary.

Areas of Agreement / Disagreement

Participants are engaged in a collaborative effort to identify and correct errors in their calculations, but there is no consensus on the correctness of the answers or the necessity for further simplification.

Contextual Notes

There are unresolved issues regarding the application of the product rule in differentiation and the specific forms of the derivatives being used. The discussion also reflects uncertainty about the relationship between their results and any book answers.

DODGEVIPER13
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Find the optimum frame length nf that maximizes transmission efficiency for a channel with random bit erros by taking the derivative and setting it to zero for the following protocols:
(a) Stop-and-Wait ARQ
(b) Go-Back-N ARQ
(c) Selective Repeat ARQ

My work has been uploaded I am a bit rusty on derivative, so I am pretty sure I made a mistake just unsure of where.
 

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The last factor with nf is wrong I think. I used the duv = u*dv + v*du rule with v= (nf+B)^-1 and got a different factor from yours so check it again and post your result.
 
What did you use for u? I guess you did a u substitution to do this then so if I find u I can do the derivative.
 
u = nf - n0 your numerator and v= (nf+B)^-1
 
EPSON001.JPG
 
My apologies, I must have done something wrong. Yours looks correct. How is the book answer different? That might tell you where the real error is.
 
Okay I think I see your error. You differentiated the a^nf and multiplied it to the differentiated version of the second factor. Don't you have to apply the duv product rule here too?

With u=a^nf and v= the rest.
 
Sorry if the post is a bit confusing and my slow responses.
EPSON002.JPG
 
Is my answer improved at all?
 
  • #10
Yes, it looks right but you can do more by extracting out the a^nf factor and by finding a common denominator so you can combine numerator terms ie multiply the second term by (nf+B)/(nf+B).
 
  • #11
Posted this with my phone sorry if it is hard to read
1412268926261.jpg
 
  • #12
So should this be simplified further?
 
  • #13
I can't see anything further. Does this differ from some book answer you have? or were you expecting it to be much simpler?
 

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