Unsaturated Throughput Analysis of IEEE 802.11 in Presence of Non Ideal Transmission Channel and Capture Effects

In this paper, we provide a throughput analysis of the IEEE 802.11 protocol at the data link layer in non-saturated traffic conditions taking into account the impact of both transmission channel and capture effects in Rayleigh fading environment. The impact of both non-ideal channel and capture become important in terms of the actual observed throughput in typical network conditions whereby traffic is mainly unsaturated, especially in an environment of high interference. We extend the multi-dimensional Markovian state transition model characterizing the behavior at the MAC layer by including transmission states that account for packet transmission failures due to errors caused by propagation through the channel, along with a state characterizing the system when there are no packets to be transmitted in the buffer of a station. Finally, we derive a linear model of the throughput along with its interval of validity. Simulation results closely match the theoretical derivations confirming the effectiveness of the proposed model.Comment: To appear on IEEE Transactions on Wireless Communications, 200

Protocols for dynamic spectrum access in cognitive radio networks

Spectrum access protocols permit secondary users to transmit on frequency bands that are not being utilized by the primary owners. A cognitive radio that wishes to transmit in a band must first decide if the band is available (i.e., not being used by the owner) and then it must periodically re-evaluate the band\u27s availability once it begins transmitting in the band to ensure that a signal from a primary owner has not emerged. To accomplish these tasks, spectrum access protocols employ periodic sensing of the channel. Frequent sensing intervals are required to ensure that cognitive radios wishing to access the band are not disrupting transmissions by the owners of the band. Because spectrum sensing requires that radios cease transmission to observe the channel, the potential for throughput by the secondary users is reduced. A proposed enhancement to standard spectrum access protocols is presented that permits secondary users to monitor the frequency bands while communicating. This capability increases the amount of time that radios can transmit on the band and it decreases the amount of time required to detect the emergence of transmissions by a primary owner. Both improvements are obtained via a protocol that observes statistics obtained in the receiver of the cognitive radio during packet reception. The statistics are obtained with little or no additional hardware and do not require complicated channel measurements or pilot symbols. The proposed protocol for spectrum access is applicable to both single-link networks and multi-link cooperative networks

Saturation Throughput Analysis of IEEE 802.11 in Presence of Non Ideal Transmission Channel and Capture Effects

In this paper, we provide a saturation throughput analysis of the IEEE 802.11 protocol at the data link layer by including the impact of both transmission channel and capture effects in Rayleigh fading environment. Impacts of both non-ideal channel and capture effects, specially in an environment of high interference, become important in terms of the actual observed throughput. As far as the 4-way handshaking mechanism is concerned, we extend the multi-dimensional Markovian state transition model characterizing the behavior at the MAC layer by including transmission states that account for packet transmission failures due to errors caused by propagation through the channel. This way, any channel model characterizing the physical transmission medium can be accommodated, including AWGN and fading channels. We also extend the Markov model in order to consider the behavior of the contention window when employing the basic 2-way handshaking mechanism. Under the usual assumptions regarding the traffic generated per node and independence of packet collisions, we solve for the stationary probabilities of the Markov chain and develop expressions for the saturation throughput as a function of the number of terminals, packet sizes, raw channel error rates, capture probability, and other key system parameters. The theoretical derivations are then compared to simulation results confirming the effectiveness of the proposed models.Comment: To appear on IEEE Transactions on Communications, 200

REED-SOLOMON CODED FREQUENCY-HOPPED PACKET RADIO NETWORKS WITH RECEIVER MEMORY, THROUGHPUT-DELAY ANALYSIS

This paper investigates the performance of frequency hopped packet radio networks which employ a memory at the receiver. The main feature of the memory is that all successive transmissions are utilized for packet reconstruction. Two schemes based on RS codes are investigated. System performance is analyzed in both slotted and unslotted channels. Fixed and adaptive packet lengths are considered. It is demonstrated that it is possible to achieve high throughput even in dense jamming environments

Carrier Sense Random Packet CDMA Protocol in Dual-Channel Networks

Code resource wastage is caused by the reason that many hopping frequency (FH) sequences are unused, which occurs under the condition that the number of the actual subnets needed for the tactical network is far smaller than the networking capacity of code division net¬working. Dual-channel network (DCN), consisting of one single control channel and multiple data channels, can solve the code resource wastage effectively. To improve the anti-jamming capability of the control channel of DCN, code division multiple access (CDMA) technology was introduced, and a carrier sense random packet (CSRP) CDMA protocol based on random packet CDMA (RP-CDMA) was proposed. In CSRP-CDMA, we provide a carrier sensing random packet mechanism and a packet-segment acknowledgement policy. Furthermore, an analytical model was developed to evaluate the performance of CSRP-CDMA networks. In this model, the impacts of multi-access interference from both inter-clusters and intra-clusters were analyzed, and the mathematical expressions of packet transmission success probability, normalized network throughput and signal interference to noise ratio, were also derived. Analytical and simulation results demonstrate that the normalized network throughput of CSRP-CDMA outperforms traditional RP-CDMA by 10%, which can guarantee the resource utilization efficiency of the control channel in DCNs

Channel-access and routing protocols to utilize multiple heterogeneous channels for ad hoc networks

In this thesis, we consider a multi-channel ad hoc network employing frequency-agile radios that utilize direct-sequence spread-spectrum signaling. Two of the key distributed protocols for this type of network control channel access and routing. The channel-access protocol is responsible for controlling access to the channels available to the terminals in the network, and the routing protocol determines how packets are forwarded among the terminals in the network. To achieve reliable and efficient network performance, these protocols should cooperate with one another and take advantage of the multiple channels available to the network. In this thesis, we investigate a number of channel-access strategies for selecting a channel as well as various channel metrics to be used with routing. For our channel-access protocol, one channel is designated the control channel and is used to reserve access to one of the traffic channels. The channel-access protocol selects the traffic channel for a data packet transmission by examining the characteristics of the different traffic channels. New channel metrics are proposed to characterize the channels, and the metric values are used to assign a link resistance value for a link. Least-resistance routing utilizes the link resistances to calculate routes. The performance of the channel metrics for the routing protocol and the channel-access strategies are examined with a discrete-event simulation. From our investigations, we show that a jointly designed protocol that coordinates the channel-access strategies with the channel metrics results in network performance that is better than traditional channel-access and minimum-hop routing protocols

Alibi framework for identifying reactive jamming nodes in wireless LAN

Reactive jamming nodes are the nodes of the network that get compromised and become the source of jamming attacks. They assume to know any shared secrets and protocols used in the networks. Thus, they can jam very effectively and are very stealthy. We propose a novel approach to identifying the reactive jamming nodes in wireless LAN (WLAN). We rely on the half-duplex nature of nodes: they cannot transmit and receive at the same time. Thus, if a compromised node jams a packet, it cannot guess the content of the jammed packet. More importantly, if an honest node receives a jammed packet, it can prove that it cannot be the one jamming the packet by showing the content of the packet. Such proofs of jammed packets are called "alibis" - the key concept of our approach. In this paper, we present an alibi framework to deal with reactive jamming nodes in WLAN. We propose a concept of alibi-safe topologies on which our proposed identification algorithms are proved to correctly identify the attackers. We further propose a realistic protocol to implement the identification algorithm. The protocol includes a BBC-based timing channel for information exchange under the jamming situation and a similarity hashing technique to reduce the storage and network overhead. The framework is evaluated in a realistic TOSSIM simulation where the simulation characteristics and parameters are based on real traces on our small-scale MICAz test-bed. The results show that in reasonable dense networks, the alibi framework can accurately identify both non-colluding and colluding reactive jamming nodes. Therefore, the alibi approach is a very promising approach to deal with reactive jamming nodes.published or submitted for publicationnot peer reviewe

Cognitive MAC protocols for mobile Ad-Hoc networks

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The term of Cognitive Radio (CR) used to indicate that spectrum radio could be accessed dynamically and opportunistically by unlicensed users. In CR Networks, Interference between nodes, hidden terminal problem, and spectrum sensing errors are big issues to be widely discussed in the research field nowadays. To improve the performance of such kind of networks, this thesis proposes Cognitive Medium Access Control (MAC) protocols for Mobile Ad-Hoc Networks (MANETs). From the concept of CR, this thesis has been able to develop a cognitive MAC framework in which a cognitive process consisting of cognitive elements is considered, which can make efficient decisions to optimise the CR network. In this context, three different scenarios to maximize the secondary user's throughput have been proposed. We found that the throughput improvement depends on the transition probabilities. However, considering the past information state of the spectrum can dramatically increases the secondary user's throughput by up to 40%. Moreover, by increasing the number of channels, the throughput of the network can be improved about 25%. Furthermore, to study the impact of Physical (PHY) Layer errors on cognitive MAC layer in MANETs, in this thesis, a Sensing Error-Aware MAC protocols for MANETs has been proposed. The developed model has been able to improve the MAC layer performance under the challenge of sensing errors. In this context, the proposed model examined two sensing error probabilities: the false alarm probability and the missed detection probability. The simulation results have shown that both probabilities could be adapted to maintain the false alarm probability at certain values to achieve good results. Finally, in this thesis, a cooperative sensing scheme with interference mitigation for Cognitive Wireless Mesh Networks (CogMesh) has been proposed. Moreover, a prioritybased traffic scenario to analyze the problem of packet delay and a novel technique for dynamic channel allocation in CogMesh is presented. Considering each channel in the system as a sub-server, the average delay of the users' packets is reduced and the cooperative sensing scenario dramatically increases the network throughput 50% more as the number of arrival rate is increased