Video Transmission over wireless error channels

[Preface]

The examples are included in myNS2.

 

[Background]

1.      I don’t use the default error models provided in NS2. I add Prawit Chumchu’s work in themyNS2. The model is shown blow. The error model is implemented at the receiver side.

 

 

2.      wireless GE model --- shows the burst error pattern

In the “good” state (G) losses occur with lower probability  while in the “bad” state (B) they happen with higher probability. Also,  is the probability of the state transiting from a good state to a bad state, and is the transition from a bad state to a good state. The steady state probabilities of being in states G and B are

 and ,

respectively. The average packet loss rate produced by the GE error model is

.

 

 

 

3.      wireless random uniform model --- the errors are distributed uniformly.

 

4.      Unicast vs. Multicast over 802.11 wireless network

l   In unicasting, the MAC layer at a sender retransmits an unacknowledged packet at a maximum of N times before it gives up. The perceived correct rate at application-level is thus, where N is the maximum number of retransmission at the MAC layer and p is the packet error rate at the physical-level. As a consequence, the application-level error rate is peffective = pN. (The default value for N is 4)

l   Due to the absence of retransmissions in broadcasting and multicasting, the packet error rate at the physical-level is the same as at the application-level.

 

[Run the examples]

1.      Change the path to ns-allinone-2.28/ns-2.28/myexample/video-wireless_error/

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1.      Example 1: The video packets are delivered via multicast over a random uniform error model of wireless channels.

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Description:

a.       ns test_bsc_multicast.tcl 0 0 0.1 0 1 1024 (test_bsc_multicast.tcl: simulation script; 0: don’t care; 0: don’t care; 0.1:average error rate; 0:don’t care; 1: seed; 1024: the max packet size)

b.      the error rate = (163682-147621)/163682 = 0.098 ~ 0.1 (very close to the setting value)

 

2.      Example 2: The video packets are delivered via multicast over a GE error model of wireless channels.

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Description:

c.       ns test_ge_multicast.tcl 0.96 0.94 0.001 0.05 1 1024 (0.96: PGG; 0.94: PBB; 0.001:PG; 0.05:PB; 1: seed; 1024: the max packet size)

d.      the error rate = (163682-160391)/163682 = 0.02  [ theory value : 0.01*(1-0.94)+0.05*(1-0.96)/((1-0.96)+(1-0.94))= 0.0206]

 

5.      Example 3: The video packets are delivered via unicast over a random error model of wireless channels.

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Description:

e.       ns test_ge_multicast.tcl 0 0 0.5 0 1 1024 (0: don’t care; 0: don’t care; 0.5:average error rate at the physical  level; 0:don’t care; 1: seed; 1024: the max packet size)

f.       the error rate = (163682-153625)/163682=0.061  [ theory value : 0.5*0.5*0.5*0.5=0.0625]

 

Last modified date: 2006/3/3

 

Author: Chih-Heng, Ke (柯志亨)

Email: smallko@ee.ncku.edu.tw

MSN: smallko@hotmail.com