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is paramount for results evaluation and reliability of
performance of the entire network. Therefore, we
authenticate performance improvement in three aspects,
throughput, average delay and packet drop rate.
V. RESULTS AND ANALYSIS
A. Simulation results and analysis of throughput
A. Simulation parameters setting
For Simple, simulation model conforms to
IEEE802.11b standard, transfer rate of 2Mbit/s for all
simulations. The following is other parameters’ setting:
●Transmission delay: 1μs
●Timeslot size: 20μs
●SIFS: 10μs
●back-off stages: 5
●In each scenario, the number of station increases
from 10 to 60 at the increment of 10.
B. Simulation scenarios setting
Simulation scenarios as shown in figure 4.
Figure.5 Overall throughput without services differentiation
Fig.4 Simulation scenarios
All stations access a WLAN server, which has the
function of AP (Access Point), carrying FTP service,
transmitting in TCP protocols, and each data frame size is
fixed at 1000 bytes, 60 seconds for each simulation time
as well. In addition, for observing the stable state, we
should eliminate the impact caused by transient variables
generated in the course of initialization. Therefore, only
the states after 10 seconds of each simulation should be
considered.
C. Brief description
In simulation scenarios, in order to simplify the
model, we make sure that each station supports one grade,
that is to say, it only can send data frames in the same
type. What’s more, for the convenience of simulation,
both EDCF and EASDCF merely take two QoS grades
into consideration. Table 3 describes the parameter and
situations of division in detail.
Class 1
CWmin
Class 2
CWmin
Table 3: Parameter in three scenarios
DCF EDCF EASDCF
32 32 32
32 64 64
Class 1 RLmax 7 7 7
Class 2 RLmax 7 7 9
Figure.6 Throughput of TC1 and TC2
As is shown in figure 5 for the performance of
throughput, DCF is close to EDCF, but EASDCF is
superior to both of them. EDCF mechanism sacrifices
low priority services to satisfy the need of delay sensitive
services. However, it could not enhance the overall
throughput of the system.
From table 3 we know, TC1 and TC2 don’t
differentiate priority in DCF model, they have the same
contention window and maximal retry limit, so they have
the same probability in media access authority, TC1 and
TC2 have the same throughput, whose lines are two
superposition curves. Nevertheless, it differentiates
priority in EDCF and EASDCF, in comparison with TC2,
TC1 has a smaller contention window and a greater
opportunity to media access, which lead to a larger
throughput. The two services in EASDCF have larger
throughput than in EDCF, especially in the greater
enhancement of TC1. In this way, not only ensure the
priorities of transmission real-time services, but also
improve the overall throughput performance about 10% -
15%.
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