8 research outputs found
The Price of Local Power Control in Wireless Scheduling
We consider the problem of scheduling wireless links in the physical model, where we seek an assignment of power levels and a partition of the given set of links into the minimum number of subsets satisfying the signal-to-interference-and-noise-ratio (SINR) constraints. Specifically, we are interested in the efficiency of local power assignment schemes, or oblivious power schemes, in approximating wireless scheduling. Oblivious power schemes are motivated by networking scenarios when power levels must be decided in advance, and not as part of the scheduling computation.
We present the first O(log log Delta)-approximation algorithm, which is known to be best possible (in terms of Delta) for oblivious power schemes, where Delta is the longest to shortest link length ratio. We achieve this by representing interference by a conflict graph, which allows the application of graph-theoretic results for a variety of related problems, including the weighted capacity problem. We explore further the contours of approximability and find the choice of power assignment matters; that not all metric spaces are equal; and that the presence of weak links makes the problem harder. Combined, our results resolve the price of local power for wireless scheduling, or the value of allowing unfettered power control
Power control for predictable communication reliability in wireless cyber-physical systems
Wireless networks are being applied in various cyber-physical systems and posed to support
mission-critical cyber-physical systems applications. When those applications require reliable and
low-latency wireless communication, ensuring predictable per-packet communication reliability is a
basis. Due to co-channel interference and wireless channel dynamics (e.g. multi-path fading), however,
wireless communication is inherently dynamic and subject to complex uncertainties. Power
control and MAC-layer scheduling are two enablers. In this dissertation, cross-layer optimization
of joint power control and scheduling for ensuring predictable reliability has been studied. With an
emphasis on distributed approaches, we propose a general framework and additionally a distributed
algorithm in static networks to address small channel variations and satisfy the requirements on
receiver-side signal-to-interference-plus-noise-ratio (SINR). Moreover, toward addressing reliability
in the settings of large-scale channel dynamics, we conduct an analysis of the strategy of joint
scheduling and power control and demonstrate the challenges.
First, a general framework for distributed power control is considered. Given a set of links
subject to co-channel interference and channel dynamics, the goal is to adjust each link\u27s transmission
power on-the-fly so that all the links\u27 instantaneous packet delivery ratio requirements
can be satised. By adopting the SINR high-delity model, this problem can be formulated as
a Linear Programming problem. Furthermore, Perron-Frobenius theory indicates the characteristic
of infeasibility, which means that not all links can nd a transmission power to meet all the
SINR requirements. This nding provides a theoretical foundation for the Physical-Ratio-K (PRK)
model. We build our framework based on the PRK model and NAMA scheduling. In the proposed
framework, we dene the optimal K as a measurement for feasibility. Transmission power and
scheduling will be adjusted by K and achieve near-optimal performance in terms of reliability and
concurrency.
Second, we propose a distributed power control and scheduling algorithm for mission-critical
Internet-of-Things (IoT) communications. Existing solutions are mostly based on heuristic algorithms
or asymptotic analysis of network performance, and there lack eld-deployable algorithms
for ensuring predictable communication reliability. When IoT systems are mostly static or low mobility,
we model the wireless channel with small channel variations. For this setting, our approach
adopts the framework mentioned above and employs feedback control for online K adaptation and
transmission power update. At each time instant, each sender will run NAMA scheduling to determine
if it can obtain channel access or not. When each sender gets the channel access and sends a
packet, its receiver will measure the current SINR and calculate the scheduling K and transmission
power for the next time slot according to current K, transmission power and SINR. This adaptive
distributed approach has demonstrated a signicant improvement compared to state-of-the-art
technique. The proposed algorithm is expected to serve as a foundation for distributed scheduling
and power control as the penetration of IoT applications expands to levels at which both the
network capacity and communication reliability become critical.
Finally, we address the challenges of power control and scheduling in the presence of large-scale
channel dynamics. Distributed approaches generally require time to converge, and this becomes a
major issue in large-scale dynamics where channel may change faster than the convergence time
of algorithms. We dene the cumulative interference factor as a measurement of impact of a single
link\u27s interference. We examine the characteristic of the interference matrix and propose that
scheduling with close-by links silent will be still an ecient way of constructing a set of links
whose required reliability is feasible with proper transmission power control even in the situation of
large-scale channel dynamics. Given that scheduling alone is unable to ensure predictable communication
reliability while ensuring high throughput and addressing fast-varying channel dynamics,
we demonstrate how power control can help improve both reliability at each time instant and
throughput in the long-term. Collectively, these ndings provide insight into the cross-layer design
of joint scheduling and power control for ensuring predictable per-packet reliability in the presence
of wireless network dynamics and uncertainties
Algorithms for Efficient Communication in Wireless Sensor Networks - Distributed Node Coloring and its Application in the SINR Model
In this thesis we consider algorithms that enable efficient communication in wireless ad-hoc- and sensornetworks using the so-called Signal-to-interference-and-noise-ratio (SINR) model of interference. We propose and experimentally evaluate several distributed node coloring algorithms and show how to use a computed node coloring to establish efficient medium access schedules