Ju-Lan Hsu

Performance analysis of directional CSMA/CA MAC protocol in mobile ad hoc networks

In this paper, we consider a shared wireless medium as employed in a mobile ad hoc wireless network. We develop an analytical approach to evaluate the single-hop performance of IEEE 802.11 DCF (Distributed Coordination Function) based MAC (Medium Access Control) algorithm that is combined with the use of directional transmitting and receiving antenna beams at each mobile entity. We characterize the saturation throughput performance of such directional CSMA/CA (Carrier Sensing Multiple Access with Collision Avoidance) protocol in terms of the number of channel contenders, packet size, selected beamwidth and location tracking imprecisions induced by entity mobility. The presented analytical framework provides valuable insights on the use of directional contention-based MAC protocols in mobile ad hoc wireless networks. Using our analytical, as well as simulation evaluations, we present an extensive set of performance results. We show that the directional CSMA/CA system can provide a significant upgrade of network performance when the beamwidth is properly selected.

Performance analysis of directional random access scheme for multiple access mobile ad-hoc wireless networks

It has been proposed to upgrade the performance of medium access control (MAC) schemes through the use of beamforming directional antennas, to achieve better power and bandwidth utilization. In this paper, we consider a shared wireless medium as employed in a mobile ad hoc wireless network. We present and analyze a random access MAC algorithm that is combined with the use of directional beamforming formed by each transmitting mobile entity. Mathematical equations are derived to characterize the throughput performance of such a directional-ALOHA (D-ALOHA) algorithm. We describe the interferences occurring at each receiving node by considering both distance based and SINR based interference models. The D-ALOHA protocol includes the establishment of a (in-band or out of band) control sub-channel that is used for the transmission of location update messages. The latter is used for allowing mobile nodes to track the location of their intended destination mobiles. We employ our derived mathematical equations, as well as carry out simulation evaluations, to present an extensive set of performance results. We characterize the throughput performance of such a beamforming based MAC protocol in terms of the systems traffic loading conditions, the selected beamwidths of the antennas at the transmitting mobiles, and the mobility levels of the nodal entities. We show that the D-ALOHA protocol can provide a significant upgrade of network performance

On the performance of randomized power control algorithms in multiple access wireless networks

In this paper, we develop and investigate a novel power control algorithm (the fair randomized power control algorithm; FRPC) to enhance the throughput level of the slotted Aloha medium access control mechanism. FRPC is developed based on the analysis of the capture effect for which the transmitter captures the channel only if the observed signal-to-interference and noise ratio (SINR) at the receiver is above a certain threshold. We first analyze the sensitivity of the generic randomized power control algorithm with respect to expected value and standard deviation of the power density function. In particular, based on the one-tailed version of Chebyshevs inequality, we derive a closed-form expression for an upper bound on the probability of capture (and an upper bound on the aggregate throughput) in the network. We then apply the latter result to the process of designing the FRPC algorithm for the slotted Aloha MAC mechanism. Our simulation results indicate that the FRPC algorithm leads to significant throughput gain while providing fairness for different mobile users in the system.

The D-ALOHA protocol for MANETs using beamforming directional antennas

It has been proposed to upgrade the performance of medium access control (MAC) schemes through the use of directional antennas, to achieve better power and bandwidth utilization. In this paper, we present and study directional random access algorithms that form the basis for MAC schemes employed by mobile nodes that share multiple access radio channels through the use of transmitter based beamforming. We characterize and represent the network throughput performance as a product of two factors: 1) a stationary factor that represents the system throughput performance under a perfect receiver location update process, and 2) a mobility factor that embeds the user mobility and location update processes in expressing the level of throughput degradation caused due to location update errors. A Directional-ALOHA (D-ALOHA) protocol is introduced and extensive performance results based on our analytical evaluations as well as on simulations are presented. We show that the DALOHA protocol can significantly improve performance when the beamwidth is properly selected in accordance with the underlying user mobility level.

Performance Analysis of Multi-Rate Capable Random Access Mac Protocols in Wireless Multi-Hop Networks

In this paper, we study an ad hoc wireless network system in which multiple access wireless channels are shared in accordance with a random access (ALOHA type) MAC protocol. We assume that a modulation/coding scheme (MCS) can be selected from a list of available such structures, each of which is associated with a transmission data rate and an acceptable SINR level that yields a prescribed BER value. The use of such different MCSs impacts the achievable value of the systems spatial reuse factor level and of the realized end-to-end lengths of flow paths. Consequently, as the traffic loading level increases, the use of such different schemes yields different throughput capacity levels. We present mathematical models that enable the selection of the MCS that yields the highest level of throughput performance. For the multi-hop network system, we demonstrate that the link range and the employed MCS can be jointly selected to yield the highest throughput capacity level. We show that for the system under consideration it is generally preferable for a node to use a high data rate MCS while jointly selecting its neighbours from a usually reasonably short range level

Cross-Layer Multi-Rate Routing Strategies in Wireless Multi-Hop Random Access Networks

In this paper, we develop and study combined multi- rate and packet forwarding and routing operations in the context of multi-hop ad hoc wireless networks. Nodes are assumed to employ a software controlled radio that is programmed to use several modulation/coding schemes (MCSs) that operate at different data rates. The underlying MAC scheme is assumed to be based on a random access (pure ALOHA type) protocol. We propose a distributed QoS-aware cross-layer joint routing and rate control algorithm. It is used by nodal stations to jointly select, for each packet that traverses multi-hop routes across the network, the transmit data rate and the neighboring node to which the packet should be routed towards its destination. Each station monitors certain station and network activity states, and uses these data to adapt the selection of its parameter vectors. The mechanism strives to ensure that flow throughput and end- to-end packet delay target levels are met. Once satisfied, the algorithm selects parameters that serve to enhance the transport throughput level, thus occupying limited overall network wide resources. Simulation results demonstrate the significant performance enhancements that are achieved under the use of the proposed scheme. Our analytical models and mechanisms provide important guidelines for the design of such joint channel rate, MAC and routing based operations algorithms.

Directional random access scheme for mobile ad hoc networking using beamforming antennas

It has been proposed to upgrade the performance of medium access control (MAC) schemes through the use of beamforming directional antennas, to achieve better power and bandwidth utilization. In this paper, we consider a shared wireless medium as employed in a mobile ad hoc wireless network. We present and analyze a random access MAC algorithm that is combined with the use of directional beamforming formed by each transmitting mobile entity. Mathematical equations are derived to characterize the throughput performance of such a directional-ALOHA (D-ALOHA) algorithm. We describe the interferences occurring at each receiving node by considering both distance based and SINR based interference models. The D-ALOHA protocol includes the establishment of a (in-band or out-of-band) control sub-channel that is used for the transmission of location update messages. The latter is used for allowing mobile nodes to track the location of their intended destination mobiles. We present a separation property result that allows us to express the network throughput performance as a product of two factors: (1) a stationary factor that represents the system throughput performance under a perfect receiver location update process, and (2) a mobility factor that embeds the user mobility and location update processes in expressing the level of throughput degradation caused due to location update errors. We employ our derived mathematical equations, as well as carry out simulation evaluations, to present an extensive set of performance results. The throughput performance of such a beamforming based MAC protocol is characterized in terms of the systems traffic loading conditions, the selected beamwidths of the antennas at the transmitting mobiles, the mobility levels of the nodal entities and the bandwidth capacity allocated to the control channel used for location update purposes. We show that the D-ALOHA protocol can provide a significant upgrade of network performance when the transmitting nodes adapt their beamwidth levels in accordance with our presented control scheme. The latter incorporates the involved tradeoff between the attained higher potential spatial reuse factors and the realized higher destination pointing process errors, and consequently uses nodal mobility levels and channel loading conditions as key parameters.

On Routing and Rate Control Strategies in Wireless Multi-Hop Random Access Networks

In this paper, we investigate in the context of multi- hop ad hoc wireless networks the impact of combined multi-rate and packet forwarding and routing operations on the throughput performance of the system. Our models and analysis results reveal key performance and design options involving the cross- layer operation of such networks. We carry out mathematical analysis in computing the transport throughput performance of the network under the use of different modulation/coding schemes (MCSs) that operate at different data rates. The medium access control (MAC) scheme is assumed to be based on a random access (pure ALOHA type) protocol. In configuring the parameters of the employed MCS, we use the Information theoretic (Shannons) capacity formula, as well as settings that are based on IEEE 802.11 implementations. The results provide characterizations of the networks (end to end) throughput performance in terms of the underlying physical (and certain MAC) layer parameters in combination with the setting of the link and network layer involved packet forwarding range and routing scheme configuration. Our models provide important guidelines for the design of such rate adaptation algorithms and for the selection of the involved parameters and schemes at the physical, link and network layers.

Cross-layer routing and rate control strategies for datagram-based wireless multi-hop CSMA/CA networks

We investigate multi-hop wireless ad hoc networks in which nodes use 802.11-based MAC and PHY. Each node independently selects its cross-layer parameter vector for each packet that it forwards. The latter consists of the setting of the transmission data rate and the identification of the neighboring node to which the packet is forwarded (and thus the selection of the route). We present an analytical model to calculate, for each candidate parameter vector, the corresponding attainable throughput and transport throughput capacity rates. To enable the network to transport traffic in a throughput-effective manner, we present cross-layer schemes under which each node configures its parameter vector by using the corresponding link transport capacity measure as a key metric. We present two such datagram-based cross-layer parameter vector selection schemes. We compare the throughput performance behavior attained through these schemes, as well as with that of schemes that do not use the link transport capacity as a metric. Our results confirm the precision of our analysis and demonstrate the distinct effectiveness of schemes that employ the link transport capacity measure.

Cross layer on-demand routing algorithm for mutli-hop wireless CSMA/CA networks

We investigate the impact of combined multi-rate and routing operations in multi-hop wireless ad hoc networks in which nodes employ 802.11-based CSMA/CA MAC protocols. To measure the ability of the network to transport traffic in a throughput effective manner, we employ the link-flow transport throughput capacity measure as a key routing metric. The latter measure considers multi-rate operations as well as instantaneous topological, loading and capacity availability conditions. We develop on-demand cross layer schemes that employ these transport throughput metrics for route discovery purposes. We compare the performance behavior of our schemes with that exhibited by those that do not use the link-flow transport throughput capacity function as a routing metric. We demonstrate the performance effectiveness of these schemes by evaluating three distinct network scenarios.