Ultra-wideband (UWB) communications has emerged as a promising technology for high data rate wireless personal area networks (WPANs). Several proposals for UWB- based WPANs have been made. One widely popular proposal was standardized by ECMA-368, and is based on OFDM. In this paper, we address one of the important aspects that impact the performance of this standard, namely interference management between different uncooperative beacon groups operating simultaneously over the same area. We propose an interference management distributed reservation protocol (IM-DRP) for OFDM-based UWB communications. IM-DRP aims at improving the throughput achieved by WPANs by reducing interference between uncooperative beacon groups. Computer simulations are used to demonstrate the performance gain of the proposed protocol.

In this paper, we determine the maximum achievable "performance" of a wireless CDMA network that employs a conventional matched filter receiver and that operates under optimal link-layer adaptation where each user individually achieves the Shannon capacity. The derived bounds serve as benchmarks against which adaptive CDMA systems can be compared. We focus on two optimization criteria: minimizing the maximum service time and maximizing the sum of users rates (i.e., network throughput). We show that the problem of joint optimization of the transmission powers and rates so as to minimize the maximum service time can be formulated as a generalized geometric program (GGP), which can be transformed into a nonlinear convex problem and solved optimally and efficiently. When the goal is to maximize the sum of the rates, we show that the problem can be approximated as a GGP. Our derivation methodologies are applicable to both ad hoc and cellular networks. Numerical results are provided to show how well variable-rate, variable-power adaptation schemes perform relative to the performance bounds derived in this paper.

Adaptive rate/power control schemes have great po- tential to increase the throughput of wireless CDMA networks. In this paper, we investigate the additional gains achieved through adaptation of the orthogonal modulation (OM) order .W e show that adaptive orthogonal modulation (AOM) can significantly increase network throughput while simultaneously reducing the per-bit energy consumption (compared to variable-rate, variable-power, fixed-order OM schemes). We study the problem of joint rate/power control in AOM under two different objective functions: minimizing the maximum service time and maximizing the sum of users rates. For the first objective function, we show that the optimization problem can be formulated as a generalized geometric program (GGP), which can be transformed into a nonlinear convex problem and solved optimally and efficiently. In the case of the second objective function, we obtain a lower bound on the performance gain of AOM over fixed-order OM schemes. Unlike previous works on adaptive transmission, which have focused mainly on cellular networks, ours is applicable to both ad hoc and cellular networks. Numerical results indicate that relative to a variable-rate, variable- power fixed-order OM scheme, the proposed AOM scheme achieves significant throughput and energy gains.

Transmission power control has often been used in wireless packet networks to improve the channel reuse and reduce energy consumption. It has been mainly applied to single-input single-output (SISO) systems, where each node is equipped with a single antenna. In this paper, we propose a power-controlled channel access protocol for MIMO-capable wireless LANs with two antennas per node. Our protocol, called E-BASIC, is based on a modification of the classic CSMA/CA access scheme, where we dynamically adjust the "transmission mode" and the transmission power on a per-packet basis so as to minimize the total energy consumption. By "transmission mode" we mean one of the four possible transmit/receive antenna configurations: 1 x 1 (SISO), 2 x 1 (MISO), 1 x 2 (SIMO), and 2 x 2 (MIMO). Our energy model accounts for both the transmission and the circuit powers. While the MIMO mode requires less RF transmission energy than the other three modes, it also incurs the highest circuit energy consumption. Depending on the transmitter-receiver distance, any of the four modes can be the "optimal" one in terms of minimizing the total energy consumption. We study the performance of E-BASIC in ad hoc and infrastructure-based scenarios and compare it with two channel access protocols (802.11 and BASIC) that use a fixed transmission mode (SISO or MIMO) all the time. Our simulations show that E-BASIC often consumes much less total energy than the reference protocols. We further incorporate E-BASIC into the design of a power-aware routing (PAR) scheme that uses a variant of Dijkstra's algorithm to select the most energy-efficient end-to-end path between nodes.

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.

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.

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.

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.

Transmission power control (TPC) has a 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, or by imposing impractical requirements on the operation of the MAC protocol. In this paper, we present a novel power control MAC protocol, known as POWMAC, for MANETs that enjoys the same simple single-channel, single-transceiver design of the IEEE 802.11 ad hoc MAC protocol, but that achieves a significant throughput improvement over the 802.11 scheme. Collision avoidance is integrated into the design of POWMAC. 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 RTS/CTS exchanges to take place before multiple, concurrent data packet transmissions can commence. The length of the AW is dynamically adjusted (based on local traffic load information) to allow for concurrent interference-limited transmissions to take place in the same vicinity of a receiving node. Collision avoidance information is inserted into the CTS packet and is used to bound the transmission powers of potential interferers, rather than to silence such nodes. Simulation results for “random-grid” and “clustered ” topologies are used to demonstrate the significant throughput and energy gains that can be obtained under the POWMAC protocol.

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.

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.

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.