### On the transport capacity of Gaussian multiple access and broadcast channels

- Research Article in 3rd International ICST Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks
- Authors
- G.A. Gupta, S. Toumpis, J. Sayir, R.R. Muller
- Abstract
We study the transport capacity of a Gaussian multiple access channel, which consists of a set of transmitters and a single receiver. The transport capacity is defined as the sum, over all transmitters, of the product of the transmission rate with a reward r(x), which is a function of the distance …

more »We study the transport capacity of a Gaussian multiple access channel, which consists of a set of transmitters and a single receiver. The transport capacity is defined as the sum, over all transmitters, of the product of the transmission rate with a reward r(x), which is a function of the distance x between the transmitter and the receiver, and quantifies the usefulness of the transmitting information over a distance x. Assuming that the sum of the transmitter powers is upper bounded, we present in closed form the optimal power allocation among the transmitters, that maximizes the transport capacity. We then present simple expressions for the optimal power allocation and induced transport capacity, as the number of transmitters approaches infinity. We also study the transport capacity of a Gaussian broadcast channel, which consists of a single transmitter and multiple receivers. Here, the transport capacity is defined as the sum, over all receivers, of the product of the transmission rate with a reward r(x). We determine in closed form the maximum possible transport capacity and the distribution of the available transmitter power among the receivers that achieve it. Although this result has already been reported in the literature, our derivation is shorter, and leads to simpler expressions. Our results can be used to gain intuition and develop good design principles in a variety of settings. For example, they apply to the uplink and downlink channel of cellular networks, and also to sensor networks which consist of multiple sensors that communicate with a single central station.

### The effect of retransmitted packet size preservation property on TCP goodput over links with Bernoulli bit-errors

- Research Article in 3rd International ICST Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks
- Authors
- T. Ikegawa, Y. Takahashi
- Abstract
In this paper, we investigate the effect of the retransmitted packet size preservation (RPSP) property on TCP performance over links with Bernoulli bit-errors, where RPSP means that the sizes of all packets transferred over datalinks (referred to as transferred packets) with the same sequence-numbe…

more »In this paper, we investigate the effect of the retransmitted packet size preservation (RPSP) property on TCP performance over links with Bernoulli bit-errors, where RPSP means that the sizes of all packets transferred over datalinks (referred to as transferred packets) with the same sequence-number at retransmissions are equal to the size of a packet generated from a message at the original transmission (namely, generated packet). To achieve this, we present a Markov model for size-sequences of the generated and transferred packets, in which the TCP message-segmentation and error-recovery functions with RPSP are taken into account, respectively. Furthermore, we derive the round-trip time and the transferred packet corruption probability, which are the main parameters of TCP performance. Applying them to the conventional TCP-Reno send-rate formula, we discuss the effect of RPSP on TCP-Reno goodput. The key findings from the numerical results include that RPSP cannot be negligible for networks that suffer from a high bit-error rate (e.g., 1 × 10-4, which is the mean bit-error rate of a wireless link in an industrial environment), when the message-segmentation occurrence probability is relatively small.

### Transmission costs, selfish nodes, and protocol design

- Research Article in 3rd International ICST Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks
- Authors
- P. Marbach, Ran Pang
- Abstract
We study how selfish nodes react to transmission costs in wireless networks. Intuitively, it seems that transmission costs should have a stabilizing effect as (rational) nodes defer the packet transmissions when congestion develops and the cost for (successfully) transmitting a packet becomes high.…

more »We study how selfish nodes react to transmission costs in wireless networks. Intuitively, it seems that transmission costs should have a stabilizing effect as (rational) nodes defer the packet transmissions when congestion develops and the cost for (successfully) transmitting a packet becomes high. In this paper we investigate whether this intuition is true. We use slotted Aloha to model the communication channel.

### Analysis of a reputation system for mobile ad-hoc networks with liars

- Authors
- J. Mundinger, J.-Y. Le Boudec
- Abstract
Using decentralized reputation systems is a promising approach to ensuring cooperation and fairness in mobile ad-hoc networks. However, they are vulnerable to liars and robustness has not been analyzed in detail. With our work, we provide a first step to the analysis of a reputation system based on…

more »Using decentralized reputation systems is a promising approach to ensuring cooperation and fairness in mobile ad-hoc networks. However, they are vulnerable to liars and robustness has not been analyzed in detail. With our work, we provide a first step to the analysis of a reputation system based on a deviation test. Nodes accept second hand information only if this does not differ too much from their reputation values. Whereas our earlier paper [J. Mundinger and J.-Y. Le Boudec, 2005] dealt with a simplified one-dimensional model, we now consider the original two-dimensional system. We show that the system exhibits a phase transition. In the subcritical regime, it is robust and lying has no effect. In the supercritical regime, lying does have an impact. We compute the critical values via a mean-field approach and use simulations to verify our results. Thus, we obtain conditions for the deviation test to make the reputation system robust and provide guidelines for a good choice of parameters.

### Secure comparison of encrypted data in wireless sensor networks

- Authors
- M. Acharya, J. Girao, D. Westhoff
- Abstract
End-to-end encryption schemes that support operations over ciphertext are of utmost importance for commercial private party wireless sensor network implementations to become meaningful and profitable. For wireless sensor networks, we demonstrated in our previous work that privacy homomorphisms, whe…

more »End-to-end encryption schemes that support operations over ciphertext are of utmost importance for commercial private party wireless sensor network implementations to become meaningful and profitable. For wireless sensor networks, we demonstrated in our previous work that privacy homomorphisms, when used for this purpose, offer two striking advantages apart from end-to-end concealment of data and ability to operate on ciphertexts: flexibility by keyless aggregation and conservation and balancing of aggregator backbone energy. We offered proof of concept by applying a certain privacy homomorphism for sensor network applications that rely on the addition operation. But a large class of aggregator functions like median computation or finding maximum/minimum rely exclusively on comparison operations. Unfortunately, as shown by Rivest, et al., any privacy homomorphism is insecure even against ciphertext that only attacks if they support comparison operations. In this paper we show that a particular order preserving encryption scheme achieves the above mentioned energy benefits and flexibility when used to support comparison operations over encrypted texts for wireless sensor networks, while also managing to hide the plaintext distribution and being secure against ciphertext only attacks. The scheme is shown to have reasonable memory and computation overhead when applied for wireless sensor networks.

### A game-theoretic analysis on the conditions of cooperation in a wireless ad hoc network

- Authors
- S. Bandyopadhyay
- Abstract
To enable proper functioning of wireless ad hoc networks, all nodes in the network are expected to cooperate in forwarding each other's packet. But relaying other nodes' packets involves spending energy without getting any immediate revenue. Hence, due to the constraints on available energy the nod…

more »To enable proper functioning of wireless ad hoc networks, all nodes in the network are expected to cooperate in forwarding each other's packet. But relaying other nodes' packets involves spending energy without getting any immediate revenue. Hence, due to the constraints on available energy the nodes usually have in such networks, from an individual node's point of view, the best response is always not to cooperate. We model this problem as a repeated game and show analytically that given a suitable punishment mechanism, individual nodes can be deterred from their selfish behavior, and cooperation can emerge as the best response. We also show that generosity by other nodes cannot be part of a credible deterrent mechanism.

### Preventing impersonation attacks in MANET with multi-factor authentication

- Authors
- D. Glynos, P. Kotzanikolaou, C. Douligeris
- Abstract
Existing MANET authentication schemes cannot fully protect nodes from well-known impersonation attacks. Although these schemes cryptographically link an entity to a claimed identity, the actual entity is never linked to the physical node device. However, the link is implicitly assumed. This shortco…

more »Existing MANET authentication schemes cannot fully protect nodes from well-known impersonation attacks. Although these schemes cryptographically link an entity to a claimed identity, the actual entity is never linked to the physical node device. However, the link is implicitly assumed. This shortcoming may be easily exploited within a MANET setting, due to the broadcast nature of the access medium. In this paper we propose a multifactor authentication framework that extends the cryptographic link, binding an entity to a physical node device. This is achieved by using two distinct authentication factors; certified keys and certified node characteristics. Although the proposed framework requires additional sensing capabilities from the MANET nodes, it provides the additional confidence level required for node authentication in critical applications.

### Minimum energy transmission scheduling subject to deadline constraints

- Authors
- A. Tarello, J. Sun, M. Zafer, E. Modiano
- Abstract
We consider the problem of transmission scheduling of data over a wireless fading channel with hard deadline constraints. Our system consists of N users, each with a fixed amount of data that must be served by a common deadline. Given that, for each user, the channel fade state determines the throu…

more »We consider the problem of transmission scheduling of data over a wireless fading channel with hard deadline constraints. Our system consists of N users, each with a fixed amount of data that must be served by a common deadline. Given that, for each user, the channel fade state determines the throughput per unit of energy expended, our objective is to minimize the overall expected energy consumption while satisfying the deadline constraint. We consider both a linear and a strictly convex rate-power curve and obtain optimal solutions, based on dynamic programming (DP), and tractable approximate heuristics in both cases. For the special non-fading channel case with convex rate-power curve, an optimal solution is obtained based on the shortest path formulation. In the case of a linear rate-power curve, our DP solution has a nice "threshold" form; while for the convex rate-power curve we are able to obtain a heuristic algorithm with comparable performance with that of the optimal scheduling scheme.

### Distributed power allocation and scheduling for parallel channel wireless networks

- Authors
- Xiangping Qin, R. Berry
- Abstract
In this paper, we develop distributed approaches for power allocation and scheduling in wireless access networks. We consider a model where users communicate over a set of parallel multi-access fading channels, as in an OFDM or multi-carrier system. At each time, each user must decide which channel…

more »In this paper, we develop distributed approaches for power allocation and scheduling in wireless access networks. We consider a model where users communicate over a set of parallel multi-access fading channels, as in an OFDM or multi-carrier system. At each time, each user must decide which channels to transmit on and how to allocate its power over these channels. We give distributed power allocation and scheduling policies where each user's actions depend only on knowledge of their own channel gains. We characterize an optimal policy which maximizes the system throughput and also give a simpler sub-optimal policy which is shown to have the optimal scaling behavior in several asymptotic regimes.

### Distributed fair resource allocation in cellular networks in the presence of heterogeneous delays

- Authors
- L. Ying, R. Srikant, A. Eryilmaz, G.E. Dullerud
- Abstract
We consider the problem of allocating resources at a base station to many competing flows, when each flow is intended for a different receiver. The channel conditions may be time-varying and different for different receivers. It has been shown in A. Eryilmaz and R. Srikant (2005) that in a delay-fr…

more »We consider the problem of allocating resources at a base station to many competing flows, when each flow is intended for a different receiver. The channel conditions may be time-varying and different for different receivers. It has been shown in A. Eryilmaz and R. Srikant (2005) that in a delay-free network, a combination of queue-length-based scheduling at the base station and congestion control at the end users can guarantee queue-length stability and fair resource allocation. In this paper, we extend this result to wireless networks where the congestion information from the base station is received with a feedback delay at the transmitters. The delays can be heterogeneous (i.e., different users may have different round-trip delays) and time-varying, but are assumed to be upper-bounded, with possibly very large upper bounds. We show that the joint congestion control-scheduling algorithm continues to be stable and continues to provide a fair allocation of the network resources.