17 research outputs found
Joint Power Control and Time Division to Improve Spectral Efficiency in Dense Wi-Fi Networks
Ubiquitous densification of wireless networks has brought up the issue of
inter-and intra-cell interference. Interference significantly degrades network
throughput and leads to unfair channel resource usage, especially in Wi-Fi
networks, where even a low interfering signal from a hidden station may cause
collisions or block channel access as it is based on carrier sensing. In the
paper, we propose a joint power control and channel time scheduling algorithm
for such networks, which significantly increases overall network throughput
while maintaining fairness. The algorithm is based on branch-and-bound global
optimization technique and guarantees that the solution is optimal with
user-defined accuracy
Effectiveness Analysis of Physical Carrier-sensing in IEEE 802.11 Wireless Networks
[[abstract]]Abstract: Physical carrier-sensing mechanism has been used as an effective way to alleviate interference in wireless networks, but it also constrains spatial reuse. The aggregate throughput in wireless ad hoc networks is a tradeoff between spatial reuse and interference avoidance. The influence of physical carrier-sensing on the aggregate network throughput has attracted several studies. Previous work investigated the interference with the packet reception at receivers and proposed the optimal carrier-sensing range to achieve the maximum aggregate throughput. However, the interference with the sender’s reception of the receiver’s acknowledgement (ACK) has been ignored. In this paper, we consider the influence of interference at both senders and receivers on the aggregate throughput in wireless ad hoc networks. We propose a spatiotemporal model that describes the effectiveness of the physical carrier-sensing mechanism.[[conferencetype]]國內[[conferencedate]]20120601~2012060
Minimizing Spatial and Time Reservation With Collision-Aware DCF in Mobile Ad Hoc Networks
Carrier sensing is widely adopted in wireless communication to protect data transfers from collisions. For example, distributed coordination function (DCF) in IEEE 802.11 standard renders a node to defer its communication if it senses the medium busy. For the duration of deferment, each frame carries, in its MAC header, a 16-bit number in microseconds during which any overhearing node must defer. However, even if the carrier signal is detected, both ongoing and a new communication can be simultaneously successful depending on their relative positions in the network or equivalently, their mutual interference level. Supporting multiple concurrent communications is important in multihop ad hoc networks in order to maximize the network performance. However, it is largely ignored in DCF of the 802.11 standards because it is primarily targeted at single-hop wireless LANs. In addition, in DCF, the time duration information mentioned above is not delivered to all potential interferers, particularly those in the distance. This paper proposes Collision-Aware DCF (CAD) that efficiently utilizes the available channel resource along with the spatial as well as time dimension. First, each node makes its deferment decision adaptively based on the feedback from the communication counterpart and the status of the medium rather than on a simple, fixed carrier sense threshold as DCF. Second, CAD embeds the spatial and time reservation requirements in the PHY header, which is transmitted at the lowest data rate, so that a larger group of neighbors become aware of the ongoing communication and thus avoid collisions. Extensive experiments based on ns-2 network simulator show that CAD consistently outperforms DCF regardless of node mobility, traffic intensity, and channel randomness. For practicality, this paper discusses the implementation of CAD based on the DCF specification
Understanding the Paradoxical Effects of Power Control on the Capacity of Wireless Networks
Recent works show conflicting results: network capacity may increase or
decrease with higher transmission power under different scenarios. In this
work, we want to understand this paradox. Specifically, we address the
following questions: (1)Theoretically, should we increase or decrease
transmission power to maximize network capacity? (2) Theoretically, how much
network capacity gain can we achieve by power control? (3) Under realistic
situations, how do power control, link scheduling and routing interact with
each other? Under which scenarios can we expect a large capacity gain by using
higher transmission power? To answer these questions, firstly, we prove that
the optimal network capacity is a non-decreasing function of transmission
power. Secondly, we prove that the optimal network capacity can be increased
unlimitedly by higher transmission power in some network configurations.
However, when nodes are distributed uniformly, the gain of optimal network
capacity by higher transmission power is upper-bounded by a positive constant.
Thirdly, we discuss why network capacity in practice may increase or decrease
with higher transmission power under different scenarios using carrier sensing
and the minimum hop-count routing. Extensive simulations are carried out to
verify our analysis.Comment: I refined the previous version in many places, including the title.
to appear in IEEE Transactions on Wireless Communication
Maximizing Communication Concurrency via Link-Layer Packet Salvaging in Mobile Ad Hoc Networks
Carrier-sense medium access control (MAC) protocols such as the IEEE 802.11 distributed coordination function (DCF) avoid collisions by holding up pending packet transmission requests when a carrier signal is observed above a certain threshold. However, this often results in unnecessarily conservative communication, thus making it difficult to maximize the utilization of the spatial spectral resource. This paper shows that a higher aggregate throughput can be achieved by allowing more concurrent communications and adjusting the communication distance on the fly, which needs provisions for the following two areas. On the one hand, carrier sense-based MAC protocols do not allow aggressive communication attempts when they are within the carrier senseable area. On the other hand, the communication distance is generally neither short nor adjustable because multihop routing protocols strive for providing minimum hop paths. This paper proposes a new MAC algorithm, called multiple access with salvation army (MASA), which adopts less sensitive carrier sensing to promote more concurrent communications and adjusts the communication distance adaptively via packet salvaging at the MAC layer. Extensive simulation based on the ns-2 has shown MASA to outperform the DCF, particularly in terms of packet delay. We also discuss the implementation of MASA based on the DCF specification
Measuring Transmission Opportunities in 802.11 Links
We propose a powerful MAC/PHY cross-layer approach
to measuring IEEE 802.11 transmission opportunities in
WLAN networks on a per-link basis. Our estimator can operate
at a single station and it is able to: 1) classify losses caused by
noise, collisions, and hidden nodes; and 2) distinguish between
these losses and the unfairness caused by both exposed nodes and
channel capture. Our estimator provides quantitative measures of
the different causes of lost transmission opportunities, requiring
only local measures at the 802.11 transmitter and no modification
to the 802.11 protocol or in other stations. Our approach is suited
to implementation on commodity hardware, and we demonstrate
our prototype implementation via experimental assessments. We
finally show how our estimator can help the WLAN station to
improve its local performance
Adaptive Medium Access Control for Distributed Processing in Wireless Sensor Networks
acceptedVersionNivå