How much information can be carried over a wireless network with a multiplicity of nodes? What are the optimal strategies for information transmission and cooperation among the nodes? We obtain sharp information theoretic scaling laws under some conditions.

Capacity improvement is one of the principal challenges in wireless networking. We present a link-layer protocol called Slotted Seeded Channel Hopping, or SSCH, that increases the capacity of an IEEE 802.11 network by utilizing frequency diversity. SSCH can be implemented in software over an IEEE 802.11-compliant wireless card. Each node using SSCH switches across channels in such a manner that nodes desiring to communicate overlap, while disjoint communications mostly do not overlap, and hence do not interfere with each other. To achieve this, SSCH uses a novel scheme for distributed rendezvous and synchronization. Simulation results show that SSCH significantly increases network capacity in several multi-hop and single-hop wireless networking scenarios.

Selfish hosts in wireless networks that fail to adhere to the MAC protocol may obtain an unfair share of the channel bandwidth. We present modifications to the IEEE 802.11 backoff mechanism to simplify detection of such selfish hosts. We also present a correction scheme for penalizing greedy misbehavior which attempts to restrict the misbehaving nodes to a fair share of the channel bandwidth. Simulation results indicate that our detection and correction schemes are fairly successful in handling MAC layer misbehavior.

We address the problem of how throughput in a wireless network scales as the number of users grows. Following the model of Gupta and Kumar, we consider n identical nodes placed in a fixed area. Pairs of transmitters and receivers wish to communicate but are subject to interference from other nodes. Throughput is measured in bit-meters per second. We provide a very elementary deterministic approach that gives achievability results in terms of three key properties of the node locations. As a special case, we obtain O ( √ n) throughput for a general class of configurations. Results for random node locations can also be derived as special cases of the general result by verifying the growth rate of three parameters. For example, as a simple corollary of our result we obtain a stronger (almost sure) version of the √ n / √ log n throughput for random node locations obtained by Gupta and Kumar. Results for some other interesting non-i.i.d. node distributions are also provided.

Recent advances in wireless technology have brought us closer to the vision of pervasive computing where sensors/actuators can be connected through a wireless network. Due to cost constraints and the dynamic nature of sensor networks, it is undesirable to assume the existence of base stations connected by a wired backbone. In this paper, we present a network architecture suitable for sensor networks along with a medium access control protocol based on Earliest Deadline First. The key idea consists of exploiting the periodic nature of the traffic in sensor networks. Hence, medium access control can be achieved using implicit prioritization instead of relying on control packets. The robustness of our protocol is proved in spite of packets loss and its effectiveness is shown by experimental results.

Abstract—An admission control algorithm must coordinate between flows to provide guarantees about how the medium is shared. In wired networks, nodes can monitor the medium to see how much bandwidth is being used. However, in ad hoc networks, communication from one node may consume the bandwidth of neighboring nodes. Therefore, the bandwidth consumption of flows and the available resources to a node are not local concepts, but related to the neighboring nodes in carrier-sensing range. Current solutions do not address how to perform admission control in such an environment so that the admitted flows in the network do not exceed network capacity. In this paper, we present a scalable and efficient admission control framework—Contention-aware Admission Control Protocol (CACP)—to support QoS in ad hoc networks. We present several options for the design of CACP and compare the performance of these options using both mathematical analysis and simulation results. We also demonstrate the effectiveness of CACP compared to existing approaches through extensive simulations. Index Terms—Admission control, ad hoc network, multihop, QoS routing, Quality of Service, contention-aware, simulations. 1

Sensor networks can be considered distributed computing platforms with many severe constraints including limited CPU speed, memory size, power, and bandwidth. Individual nodes in sensor networks are typically unreliable and the network topology dynamically changes, possibly frequently. Sensor networks can also be considered a form of ad hoc network. However, here also many constraints in sensor networks are different or more severe. Sensor networks also differ because of their tight interaction with the physical environment via sensors and actuators. Due to all of these differences many solutions developed for general distributed computing platforms and for ad hoc networks cannot be applied to sensor networks. Many new and exciting research challenges exist. This paper discusses the state of the art and presents the key research challenges to be solved, some with initial solutions or approaches.

Abstract — We consider networks consisting of nodes with radios, and without any wired infrastructure, thus necessitating all communication to take place only over the shared wireless medium. The main focus of this paper is on the effect of fading in such wireless networks. We examine the attenuation regime where either the medium is absorptive, a situation which generally prevails, or the path loss exponent is greater than 3. We study the transport capacity, defined as the supremum over the set of feasible rate vectors of the distance weighted sum of rates. We consider two assumption sets. Under the first assumption set, which essentially requires only a mild time average type of bound on the fading process, we show that the transport capacity can grow no faster than  ¢¡¤£¦ ¥ , where £ denotes the number of nodes, even when the channel state information (CSI) is available non-causally at both the transmitters and the receivers. This assumption includes common models of stationary ergodic channels; constant, frequency selective channels; flat, rapidly varying channels; and flat slowly varying channels. In the second assumption set, which essentially features an independence, time average of expectation, and nonzeroness condition on the fading process, we constructively show how to achieve transport capacity of § even when the CSI is unknown to both the transmitters and the receivers, provided that every node has an appropriately nearby node. This assumption set includes common models of i.i.d. channels; constant, flat channels; and constant, frequency selective channels. The transport capacity is achieved by nodes only communicating with neighbors, and only using point-to-point coding. The thrust of these results is that the multi-hop strategy, towards which much protocol development activity is currently targeted, is appropriate for fading environments. The low attenuation regime is open. Index Terms — Wireless networks, fading channels, capacity, transport capacity.

Wireless sensor networks are considered the sensing technology of the future. Large numbers of untethered sensor nodes can be used for tracking small animals and targets, environmental monitoring, enforcing security perimeters, etc. A major problem for many sensor network applications is determining the most efficient way of conserving the energy of the power source. Some networks use batteries, while others suggest different methods of gathering energy (e.g., solar cells). Regardless of the powering method, energy conservation is of prime importance for sensor networks. The best way to conserve energy is to turn the sensor nodes off; however, since an inactive sensor node is no longer part of the network, the network can become disconnected. This creates a fundamental trade-off. In this paper, we propose a deterministic, schedule-based energy conservation scheme. In the proposed approach, time-synchronized sensors form on-off schedules that enable the sensors to be awake only when necessary. The schedule establishment is fully distributed and thus appropriate for large sensor networks. The performance of the proposed approach is evaluated through the use of simulations.

This paper presents a distributed implementation of RAND, a randomized time slot scheduling algorithm, called DRAND. DRAND runs in O(δ) time and message complexity where δ is the maximum size of a two-hop neighborhood in a wireless network while message complexity remains O(δ), assuming that message delays can be bounded by an unknown constant. DRAND is the first fully distributed version of RAND. The algorithm is suitable for a wireless network where most nodes do not move, such as wireless mesh networks and wireless sensor networks. We implement the algorithm in TinyOS and demonstrate its performance in a real testbed of Mica2 nodes. The algorithm does not require any time synchronization and is shown to be effective in adapting to local topology changes without incurring global overhead in the scheduling. Because of these features, it can also be used even for other scheduling problems such as frequency or code scheduling (for FDMA or CDMA) or local identifier assignment for wireless networks where time synchronization is not enforced.