Alaa Muqattash

Power controlled dual channel (PCDC) medium access protocol for wireless ad hoc networks

In this paper, we propose a comprehensive solution for power control in mobile ad hoc networks (MANETs). Our solution emphasizes the interplay between the MAC and network layers, whereby the MAC layer indirectly influences the selection of the next-hop by properly adjusting the power of route request packets. This is done while maintaining network connectivity. Directional and channel-gain information obtained mainly from overheard RTS and CTS packets is used to dynamically construct the network topology. By properly estimating the required transmission power for data packets, our protocol allows for interference-limited simultaneous transmissions to take place in the neighborhood of a receiving node. Simulation results indicate that compared to the IEEE 802.11 approach, the proposed protocol achieves a significant increase in the channel utilization and end-to-end network throughput, and a significant decrease in the total energy consumption.

CDMA-based MAC protocol for wireless ad hoc networks

We propose a CDMA-based power controlled medium access protocol for mobile ad hoc networks (MANETs). Unlike previously proposed protocols, ours accounts for the multiple access interference (MAI), thereby addressing the notorious near-far problem that undermines the throughput performance in MANETs. Channel-gain information obtained from overheard RTS and CTS packets over an out-of-band control channel is used to dynamically bound the transmission power of mobile terminals in the vicinity of a receiver. By properly estimating the required transmission power for data packets, the proposed protocol allows for interference-limited simultaneous transmissions to take place in the neighborhood of a receiving terminal. Simulation results indicate that compared to the IEEE 802.11 approach, the proposed protocol achieves a significant increase in network throughput at no additional cost in energy consumption.

Transmission power control in wireless ad hoc networks: challenges, solutions and open issues

Recently, power control in mobile ad hoc networks has been the focus of extensive research. Its main objectives are to reduce the total energy consumed in packet delivery and/or increase network throughput by increasing the channels spatial reuse. In this article, we give an overview of various power control approaches that have been proposed in the literature. We discuss the factors that influence the selection of the transmission power, including the important interplay between the routing (network) and the medium access control (MAC) layers. Protocols that account for such interplay are presented.

POWMAC: a single-channel power-control protocol for throughput enhancement in wireless ad hoc networks

Transmission power control (TPC) has great potential to increase the throughput of a mobile ad hoc network (MANET). Existing TPC schemes achieve this goal by using additional hardware (e.g., multiple transceivers), by compromising the collision avoidance property of the channel access scheme, by making impractical assumptions on the operation of the medium access control (MAC) protocol, or by overlooking the protection of link-layer acknowledgment packets. In this paper, we present a novel power controlled MAC protocol called POWMAC, which enjoys the same single-channel, single-transceiver design of the IEEE 802.11 ad hoc MAC protocol but which achieves a significant throughput improvement over the 802.11 protocol. Instead of alternating between the transmission of control (RTS/CTS) and data packets, as done in the 802.11 scheme, POWMAC uses an access window (AW) to allow for a series of request-to-send/clear-to-send (RTS/CTS) exchanges to take place before several concurrent data packet transmissions can commence. The length of the AW is dynamically adjusted based on localized information to allow for multiple interference-limited concurrent transmissions to take place in the same vicinity of a receiving terminal. Collision avoidance information is inserted into the CTS packet and is used to bound/ the transmission power of potentially interfering terminals in the vicinity of the receiver, rather than silencing such terminals. Simulation results are used to demonstrate the significant throughput and energy gains that can be obtained under the POWMAC protocol.

A distributed transmission power control protocol for mobile ad hoc networks

In this paper, we propose a comprehensive solution for power control in mobile ad hoc networks (MANETs). Our solution emphasizes the interplay between the MAC and network layers, whereby the MAC layer indirectly influences the selection of the next-hop by properly adjusting the power of route request packets. This is done while maintaining network connectivity. Channel-gain information obtained mainly from overheard RTS and CTS packets is used to dynamically construct the network topology. Unlike the IEEE 802.11 approach and previously proposed schemes, ours does not use the RTS/CTS packets to silence the neighboring nodes. Instead, collision avoidance information is inserted in the CTS packets and sent over an out-of-band control channel. This information is used to dynamically bound the transmission power of potentially interfering nodes in the vicinity of a receiver. By properly estimating the required transmission power for data packets, our protocol allows for interference-limited simultaneous transmissions to take place in the neighborhood of a receiving node. Simulation results indicate that, compared to the IEEE 802.11 approach, the proposed protocol achieves a significant increase in the channel utilization and end-to-end network throughput and a significant decrease in the total energy consumption.

Solving the near-far problem in CDMA-based ad hoc networks

Abstract In this paper, we propose a distributed CDMA-based medium access protocol for mobile ad hoc networks (MANETs). Our approach accounts for multiple access interference (MAI) at the protocol level, thereby addressing the notorious near–far problem that undermines the throughput performance in MANETs. Collision avoidance information is inserted in the clear-to-send (CTS) packets and broadcasted over an out-of-band control channel. This information is used to dynamically bound the transmission power of possible interfering nodes in the vicinity of a receiver. Data packets are transmitted at a power level such that interference-limited simultaneous transmissions can take place in the vicinity of a receiving terminal without disturbing its reception. Simulation results indicate that the proposed protocol achieves a significant increase in network throughput relative to the 802.11 approach, at no additional cost in energy consumption. Finally, we show that variable processing gain may be used to increase the capacity of the proposed protocol.

Directional medium access protocol (DMAP) with power control for wireless ad hoc networks

Protocols for mobile ad hoc networks (MANETs) are often designed with the assumption that nodes are equipped with omnidirectional antennas. Spatial reuse in such networks can be significantly improved by using directional antennas, leading to higher system capacity. This gain is associated with a substantial energy saving that results for beamforming the transmitter and/or receiver antennas in the appropriate directions. However, several medium access problems (e.g., hidden terminal, deafness) resurface when directional antennas are integrated into existing MAC protocols. In this paper, we propose a power-controlled MAC protocol for directional antennas that ameliorates many these problems. Our protocol uses separate control and data channels to reduce collisions. It allows for dynamic adjustment of the data-packet transmission power, such that this power is just enough to overcome interference at the receiver. Simulation results demonstrate that the combined gain from using directional antennas and power control results in significant energy saving and improved throughput performance.

CONSET: a cross-layer power aware protocol for mobile ad hoc networks

In this paper, we present a novel scheme for power control in mobile ad hoc networks called the CONSET (connectivity set) protocol. CONSET is a cross-layer solution in which the MAC layer indirectly influences the selection of the next hop along the end-to-end path by manipulating the transmission power of the route request (RREQ) messages. These messages are commonly used in on-demand (reactive) routing protocols, such as DSR and AODV. In CONSET, network topology is dynamically constructed from channel-gain and directional information obtained from overheard RTS and CTS packets. RREQ messages are broadcast at the minimum power required to maintain network connectivity, leading to longer end-to-end paths at the network layer but with less distance per hop. This results in a significant reduction in the overall end-to-end energy consumption per delivered packet. Extensive simulations are used to compare the CONSET protocol with a DSR-based power-aware routing protocol that uses the transmission energy as its routing metric. The results indicate that CONSET achieves significant improvements in network throughput, energy consumption, and packet delay.

Performance enhancement of adaptive orthogonal modulation in wireless CDMA systems

Recent research in wireless code-division multiple-access systems has shown that adaptive rate/power control can considerably increase network throughput relative to systems that use only power or rate control. In this paper, we consider joint power/rate optimization in the context of orthogonal modulation (OM) and investigate the additional performance gains achieved through adaptation of the OM order. We show that such adaptation can significantly increase network throughput, while simultaneously reducing the per-bit energy consumption relative to fixed-order modulation systems. The optimization is carried out under two different objective functions: minimizing the maximum service time and maximizing the sum of user rates. For the first objective function, we prove that the optimization problem can be formulated as a generalized geometric program (GGP). We then show how this GGP can be transformed into a nonlinear convex program, which can be solved optimally and efficiently. For the second objective function, we obtain a lower bound on the performance gain of adaptive OM (AOM) over fixed-modulation systems. Numerical results indicate that relative to an optimal joint rate/power control fixed-order modulation scheme, the proposed AOM scheme achieves significant throughput and energy gains.

A power control scheme for MANETs with improved throughput and energy consumption

We propose a new power-control protocol for medium access control (MAC) in mobile ad hoc networks. Compared with the EEEE 802.11 approach, the proposed protocol achieves significant improvement in both throughput and energy consumption. The protocol relies on dynamic adjustment of the data-packet transmission power, while maintaining a fixed (maximum) transmission power for control (RTS/CTS) packets. Furthermore, it allows nodes to control the transmission power of the route request (RREQ) packets, which indirectly influences the next-hop selection at the upper routing layer. This is done by dynamically computing a node-dependent connectivity set. RREQ packets are broadcasted only to nodes within the connectivity set. The connectivity set guarantees the nodes connectivity to the rest of the network, while at the same time enabling a simple (min-hop) routing algorithm to provide power-efficient routes. Channel gain and directional information obtain from overheard RTS/CTS exchanges are used to compute the connectivity set. Our protocol allows for concurrent yet interference-limited transmissions to take place in the vicinity of a receiver. A modified RTS/CTS exchange allows nodes to broadcast their interference margins and requested transmission powers.