Overview:

Topology control in ad-hoc networks is the problem of adjusting the transmission power at network nodes in order to achieve the optimal topology that maximizes network performance. Several related works have shown that the optimal throughput per unit energy performance can be achieved when the network topology is minimally connected. A minimally connected topology is achieved when the transmission power used by nodes is the minimum required to keep the network connected.

In this work, we show that in contrast, for typical ad-hoc networks with a few hundred nodes distributed over a few square miles area, the optimal topology is a function of the load in the network, and is not always the minimally connected topology. We discuss the reason of the phenomenon through both detailed arguments and simulations. Finally, we present three load sensitive adaptive topology control (ATC) algorithms ATC-CP (ATC - common power), ATC-IP (ATC - independent power), and ATC-MS (ATC - master/slave) that use purely local state to make topology control decisions, but vary in the degree of coordination between nodes once the decisions are taken. The ATC schemes are shown to achieve better performance than that of static topology control schemes.

Results / Status:

Basic Scenario

To evaluate the performance of the proposed algorithms, we have implemented the algorithms in ns2. We simulate nine different samples, and the environment consists of 100 nodes randomly distributed in an 1000m by 1000m area. Each simulation uses varying traffic loads with the number of flows randomly changing from one to fifteen during the simulation. The simulation time is 900 seconds and the number of flows at any given point in time is shown in Figure 1. The data rate of each flow is 60Kbps.

Figure 1

Comparisons

Figure 2

Figure 3

Figures 2 and 3 show the aggregate throughput and the energy consumption; and throughput per unit energy, respectively. Although static control using maximum power achieves the best throughput, it also consumes the largest amount of energy. Therefore, it has the smallest throughput per unit energy.

Among adaptive schemes, ATC-MS outperforms ATC-CP and ATC-IP in terms of both throughput and throughput per unit energy. Since ATC-MS uses coordinated power control (unlike ATC-IP), it decreases the possibility of route failures, and also decreases the convergence time of the transmission power adaptation in the highly loaded portions of the network.

Publications & Presentations:

• S.-J. Park and R. Sivakumar,
  ``Quantitative Analysis of Transmission Power Control in Wireless Ad-hoc Networks.''
  International Workshop on Ad Hoc Networking (IWAHN), Vancouver, Canada, August 2002.
• S.-J. Park and R. Sivakumar,
  ``Load Sensitive Transmission Power Control in Wireless Ad-hoc Networks.''
  IEEE Global Communications Conference (GLOBECOM), Taipei, Taiwan, November 2002.
• S.-J. Park and R. Sivakumar,
  ``Adaptive Topology Control in Wireless Ad-hoc Networks.''
  Extended Abstract to appear in Proceedings of ACM International Symposium on Mobile Ad Hoc Networking and Computing (MOBIHOC), Annapolis, MD USA, June 2003.

Software Downloads:

People:

• Seung-Jong Park (Alumnus)
• Raghupathy Sivakumar (Professor)

References & Related Work:

• B. Chen, K. Jamieson, H. Balakrishnan and R. Morris, "Span: An Energy-Efficient Cooridination Algorithm for Topology Maintenance in Ad Hoc Wireless Networks," Proceedings of ACM MOBICOM, Rome, Italy, July 2001.
• J. Monks, V. Bharghavan and W. Hwu, "Transmission Power Control for Multiple Access Wireless Packet Networks," Proceedings of IEEE LCN, Tampa, FL USA, November 2000.
• R. Ramanathan and R. Rosales-Hain, "Topology Control of Multihop Wireless Networks Using Transmit Power Adjustment," Proceedings of IEEE INFOCOM, Tel-Aviv, Israel, March 2000.