[Paper Review] Joint Routing and STDMA-based Scheduling to Minimize Delays in Grid Wireless Sensor Networks

Ichrak Amdouni, Cédric Adjih+1 more|arXiv (Cornell University)|Feb 27, 2014

Mobile Ad Hoc Networks18 references3 citations

TL;DR

This paper proposes ORCHID, a joint routing and STDMA scheduling scheme for grid-based wireless sensor networks that minimizes end-to-end delay and energy consumption by co-designing hierarchical routing based on spatially periodic colorings with optimized slot ordering in the TDMA cycle. Results show ORCHID reduces delay and energy use compared to shortest-path routing with delay as a heuristic, and it generalizes to arbitrary topologies under the SINR model using VCM++ for interference-aware cell coloring.

ABSTRACT

In this report, we study the issue of delay optimization and energy efficiency in grid wireless sensor networks (WSNs). We focus on STDMA (Spatial Reuse TDMA)) scheduling, where a predefined cycle is repeated, and where each node has fixed transmission opportunities during specific slots (defined by colors). We assume a STDMA algorithm that takes advantage of the regularity of grid topology to also provide a spatially periodic coloring ("tiling" of the same color pattern). In this setting, the key challenges are: 1) minimizing the average routing delay by ordering the slots in the cycle 2) being energy efficient. Our work follows two directions: first, the baseline performance is evaluated when nothing specific is done and the colors are randomly ordered in the STDMA cycle. Then, we propose a solution, ORCHID that deliberately constructs an efficient STDMA schedule. It proceeds in two steps. In the first step, ORCHID starts form a colored grid and builds a hierarchical routing based on these colors. In the second step, ORCHID builds a color ordering, by considering jointly both routing and scheduling so as to ensure that any node will reach a sink in a single STDMA cycle. We study the performance of these solutions by means of simulations and modeling. Results show the excellent performance of ORCHID in terms of delays and energy compared to a shortest path routing that uses the delay as a heuristic. We also present the adaptation of ORCHID to general networks under the SINR interference model.

Motivation & Objective

• Address the under-explored problem of delay degradation due to suboptimal slot ordering in STDMA-based WSNs.
• Design a cross-layer solution that jointly optimizes routing and scheduling to minimize end-to-end delay.
• Ensure all nodes can deliver data to the sink within a single STDMA cycle.
• Improve energy efficiency by minimizing active transmission slots and idle listening.
• Extend the solution to general network topologies under the SINR interference model.

Proposed method

• Use a spatially periodic graph coloring (VCM) to partition the grid into colored cells, enabling spatial reuse.
• Construct a hierarchical dominating tree rooted at color-based aggregators to guide data collection.
• Order color transmissions in the STDMA cycle based on routing proximity to minimize end-to-end delay.
• Introduce CO-Routes and CO-Highways for color ordering, prioritizing nodes closer to the sink.
• Adapt the VCM method to the SINR model (VCM++) by computing interference-limited transmission ranges and maximizing spatial reuse.
• Form the global STDMA cycle as a sequence of Routes period followed by Highways period, ensuring single-cycle delivery.

Experimental results

Research questions

• RQ1 How does random slot ordering in STDMA cycles affect end-to-end delay in grid WSNs?
• RQ2 Can joint optimization of routing and slot ordering reduce delay and energy consumption compared to shortest-path routing with delay as a metric?
• RQ3 What is the impact of hierarchical routing based on color-based aggregators on cycle efficiency and delay?
• RQ4 How can ORCHID be adapted to general graphs under the more realistic SINR interference model?
• RQ5 What is the trade-off between spatial reuse (number of colors) and successful transmission range in interference-limited environments?

Key findings

• ORCHID reduces the number of required slots in the STDMA cycle compared to shortest-path routing with delay as a heuristic.
• ORCHID achieves lower energy consumption by minimizing active transmission slots and reducing idle listening.
• All nodes can deliver data to the sink within a single STDMA cycle, ensuring minimal end-to-end delay.
• The normalized delay per range under random color ordering is analytically modeled and validated via simulation.
• VCM++ enables adaptation of ORCHID to general graphs by computing interference-aware cell coloring with optimal generator vectors.
• The proposed method ensures a trade-off between spatial reuse and reliable transmission under the SINR model.