Abstract: Efficient utilization of spectrum resources is a
fundamental issue of wireless communications due to its scarcity.
To improve the efficiency of spectrum utilization, the spectrum
sharing for unlicensed bands is being regarded as one of key
technologies in the next generation wireless networks. A number
of schemes such as Listen-Before-Talk(LBT) and carrier sensor
adaptive transmission (CSAT) have been suggested from this aspect,
but more efficient sharing schemes are required for improving
spectrum utilization efficiency. This work considers an opportunistic
transmission approach and a dynamic Contention Window (CW)
adjustment scheme for LTE-U users sharing the unlicensed spectrum
with Wi-Fi, in order to enhance the overall system throughput. The
decision criteria for the dynamic adjustment of CW are based on
the collision evaluation, derived from the collision probability of the
system. The overall performance can be improved due to the adaptive
adjustment of the CW. Simulation results show that our proposed
scheme outperforms the Distributed Coordination Function (DCF)
mechanism of IEEE 802.11 MAC.
Abstract: The use of wireless technology in industrial networks
has gained vast attraction in recent years. In this paper, we have
thoroughly analyzed the effect of contention window (CW) size on
the performance of IEEE 802.11-based industrial wireless networks
(IWN), from delay and reliability perspective. Results show that the
default values of CWmin, CWmax, and retry limit (RL) are far from
the optimum performance due to the industrial application
characteristics, including short packet and noisy environment. In this
paper, an adaptive CW algorithm (payload-dependent) has been
proposed to minimize the average delay. Finally a simple, but
effective CW and RL setting has been proposed for industrial
applications which outperforms the minimum-average-delay solution
from maximum delay and jitter perspective, at the cost of a little
higher average delay. Simulation results show an improvement of up
to 20%, 25%, and 30% in average delay, maximum delay and jitter
respectively.
Abstract: The quality-of-service (QoS) support for wireless
LANs has been a hot research topic during the past few years. In this paper, two QoS provisioning mechanisms are proposed for the employment in 802.11e EDCA MAC scheme. First, the proposed call
admission control mechanism can not only guarantee the QoS for the higher priority existing connections but also provide the minimum reserved bandwidth for traffic flows with lower priority. In addition, the adaptive contention window adjustment mechanism can adjust the
maximum and minimum contention window size dynamically according to the existing connection number of each AC. The collision
probability as well as the packet delay will thus be reduced effectively.
Performance results via simulations have revealed the enhanced QoS property achieved by employing these two mechanisms.