38 research outputs found
Future Evolution of CSMA Protocols for the IEEE 802.11 Standard
In this paper a candidate protocol to replace the prevalent CSMA/CA medium
access control in Wireless Local Area Networks is presented. The proposed
protocol can achieve higher throughput than CSMA/CA, while maintaining
fairness, and without additional implementation complexity. Under certain
circumstances, it is able to reach and maintain collision-free operation, even
when the number of contenders is variable and potentially large. It is backward
compatible, allowing for new and legacy stations to coexist without degrading
one another's performance, a property that can make the adoption process by
future versions of the standard smooth and inexpensive.Comment: This paper has been accepted in the Second IEEE ICC Workshop 2013 on
Telecommunication Standards: From Research to Standard
On the Performance of Packet Aggregation in IEEE 802.11ac MU-MIMO WLANs
Multi-user spatial multiplexing combined with packet aggregation can
significantly increase the performance of Wireless Local Area Networks (WLANs).
In this letter, we present and evaluate a simple technique to perform packet
aggregation in IEEE 802.11ac MU-MIMO (Multi-user Multiple Input Multiple
Output) WLANs. Results show that in non-saturation conditions both the number
of active stations (STAs) and the queue size have a significant impact on the
system performance. If the number of stations is excessively high, the
heterogeneity of destinations in the packets contained in the queue makes it
difficult to take full advantage of packet aggregation. This effect can be
alleviated by increasing the queue size, which increases the chances to
schedule a large number of packets at each transmission, hence improving the
system throughput at the cost of a higher delay
Capacity Analysis of IEEE 802.11ah WLANs for M2M Communications
Focusing on the increasing market of the sensors and actuators networks, the
IEEE 802.11ah Task Group is currently working on the standardization of a new
amendment. This new amendment will operate at the sub-1GHz band, ensure
transmission ranges up to 1 Km, data rates above 100 kbps and very low power
operation. With IEEE 802.11ah, the WLANs will offer a solution for applications
such as smart metering, plan automation, eHealth or surveillance. Moreover,
thanks to a hierarchical signalling, the IEEE 802.11ah will be able to manage a
higher number of stations (STAs) and improve the 802.11 Power Saving
Mechanisms. In order to support a high number of STAs, two different signalling
modes are proposed, TIM and Non-TIM Offset. In this paper we present a
theoretical model to predict the maximum number of STAs supported by both modes
depending on the traffic load and the data rate used. Moreover, the IEEE
802.11ah performance and energy consumption for both signalling modes and for
different traffic patterns and data rates is evaluated. Results show that both
modes achieve similar Packet Delivery Ratio values but the energy consumed with
the TIM Offset is, in average, a 11.7% lower.Comment: Multiple Access Communications 201
Towards a Collision-Free WLAN: Dynamic Parameter Adjustment in CSMA/E2CA
Carrier Sense Multiple Access with Enhanced Collision Avoidance (CSMA/ECA) is
a distributed MAC protocol that allows collision-free access to the medium in
WLAN. The only difference between CSMA/ECA and the well-known CSMA/CA is that
the former uses a deterministic backoff after successful transmissions.
Collision-free operation is reached after a transient state during which some
collisions may occur. This article shows that the duration of the transient
state can be shortened by appropriately setting the contention parameters.
Standard absorbing Markov Chain theory can be used to describe the behaviour of
the system in the transient state and to predict the expected number of slots
to reach the collision-free operation.
The article also introduces CSMA/E2CA, in which a deterministic backoff is
used two consecutive times after a successful transmission. CSMA/E2CA converges
quicker to collision-free operation and delivers higher performance than
CSMA/CA in harsh wireless scenarios with high frame error rates.
To achieve collision-free operations when the number of contenders is large,
it may be necessary to dynamically adjust the contention parameter. The last
part of the article suggests an approach for such parameter adjustment which is
validated by simulation results
Implementation and Experimental Evaluation of a Collision-Free MAC Protocol for WLANs
Collisions are a main cause of throughput degradation in Wireless LANs. The
current contention mechanism for these networks is based on a random backoff
strategy to avoid collisions with other transmitters. Even though it can reduce
the probability of collisions, the random backoff prevents users from achieving
Collision-Free schedules, where the channel would be used more efficiently.
Modifying the contention mechanism by waiting for a deterministic timer after
successful transmissions, users would be able to construct a Collision-Free
schedule among successful contenders. This work shows the experimental results
of a Collision-Free MAC (CF-MAC) protocol for WLANs using commercial hardware
and open firmware for wireless network cards which is able to support many
users. Testbed results show that the proposed CF-MAC protocol leads to a better
distribution of the available bandwidth among users, higher throughput and
lower losses than the unmodified WLANs clients using a legacy firmware.Comment: This paper was submitted to the IEEE International Conference on
Communications 2015 and it is waiting for approva