Optimal admission control in cellular DS-CDMA systems with multimedia traffic

The problem of jointly controlling the data rates and transmit powers of users, so as to maximize throughput in cellular direct-sequence code-division multiple-access (CDMA) networks is addressed. The multicode (MC)-CDMA system, where the processing gain of each code is fixed and high-rate users use multiple codes for transmission, and the variable gain (VG)-CDMA architectures are considered. The throughout maximization problem is formulated as a classical optimization problem, modeling the constraints arising from the data rate requirements and power budgets. Optimal strategies to maximize throughput in both systems are derived. While the MC-CDMA system has a simple optimal rate-power allocation algorithm, the VG-CDMA system has a more complex solution.     

The problem of medium access control in wireless sensor networks

In this article we revisit the problem of scheduled access through a detailed foray into the questions of energy consumption and throughput for MAC protocols in wireless sensor networks. We consider a static network model that rules out simultaneous transmission and reception by any sensor node and consequently requires partitioning of nodes into disjoint sets of transmitters and receivers at any time instant. Under the assumption of circular transmission (reception) ranges with sharp boundaries, a greedy receiver activation heuristic is developed relying on the network connectivity map to determine distinct receiver groups to be activated within disjoint time intervals. To conserve limited energy resources in sensor networks, the time allocation to each receiver group is based on the residual battery energy available at the respective transmitters. Upon activating each receiver group separately, the additional time-division mechanism of group TDMA is imposed to schedule transmissions interfering at the non-intended destinations within separate fractions of time in order to preserve the reliable feedback information. The two-layered time-division structure of receiver activation and group TDMA algorithms offers distributed and polynomial-time solutions (as required by autonomous sensor networks) to the problems of link scheduling as well as energy and throughput-efficient resource allocation in wireless access. The associated synchronization and overhead issues are not considered in this article.     

Cognitive Multiple Access Via Cooperation: Protocol Design and Performance Analysis

In this paper, a novel cognitive multiple-access strategy in the presence of a cooperating relay is proposed. Exploiting an important phenomenon in wireless networks, source burstiness, the cognitive relay utilizes the periods of silence of the terminals to enable cooperation. Therefore, no extra channel resources are allocated for cooperation and the system encounters no bandwidth losses. Two protocols are developed to implement the proposed multiple-access strategy. The maximum stable throughput region and the delay performance of the proposed protocols are characterized. The results reveal that the proposed protocols provide significant performance gains over conventional relaying strategies such as selection and incremental relaying, specially at high spectral efficiency regimes. The rationale is that the lossless bandwidth property of the proposed protocols results in a graceful degradation in the maximum stable throughput with increasing the required rate of communication. On the other hand, conventional relaying strategies suffer from catastrophic performance degradation because of their inherent bandwidth inefficiency that results from allocating specific channel resources for cooperation at the relay. The analysis reveals that the throughput region of the proposed strategy is a subset of its maximum stable throughput region, which is different from random access, where both regions are conjectured to be identical.     

Distributed Reservation Control Protocols for Random Access Broadcasting Channels

Two distributed reservation control protocols are described, analyzed, and simulated for the transmission of datagramtype messages, encoded into fixed length packets, over a synchronous communication satellite channel. These protocols are of a hybrid form between pure random access contention protocols of the ALOHA variety and reservation control protocols such as CPODA. Simulations have shown that certain versions of these protocols can support throughput rates in excess of 97 percent of the channel capacity, maintain stability even under overload conditions, and incur waiting time delays ranging from 0.5 s under light traffic load to 0.88 s for saturated traffic conditions.     

Linear innovation theorems

In this paper linear versions of the Innovations Theorem as used in the case of signal-in-additive-noise are presented. The concept of the multiplicity of a random process plays a central role in the development. The conditions for the applicability of these theorems are shown to be very general. Questions concerning further generalizations are then investigated.     

Linear Innovation Theorems

In this paper linear versions of the Innovations Theorem as used in the case of signal-in-additive-noise are presented. The concept of the multiplicity of a random process plays a central role in the development. The conditions for the applicability of these theorems are shown to be very general. Questions concerning further generalizations are then investigated.     

Joint MAC and rate control for stability and delay in wireless multi-access channels

In this paper, we investigate the stability and delay issues of a two-user multi-access channel at the bit level. The two users, have the option to transmit at a higher instantaneous rate separately, or to transmit simultaneously but at a lower individual instantaneous rate due to interference caused by concurrent transmissions. Traffic burstiness is considered by modeling random arrivals at the users, and the stability region in terms of bits/slot is derived. Further, we determine the condition under which the maximum stability region is achieved when the users always transmit if their queues are non-empty; in this case, the stability region is shown to be convex. Subsequently, we study the minimum delivery time problem where each user is allocated an initial amount of traffic volume to be sent to the destination. For any initial queue size vector, we explicitly characterize the optimal policy that empties the two users’ queues within the shortest time.     

Wireless Link Scheduling With Power Control and SINR Constraints

The problem of determining a minimal length schedule to satisfy given link demands in a wireless network is considered. Links are allowed to be simultaneously active if no node can simultaneously transmit and receive, no node can transmit to or receive from more than one node at a time, and a given signal-to-interference and noise ratio (SINR) is exceeded at each receiver when transmitters use optimally chosen transmit powers. We show that a) the general problem is at least as hard as the MAX-SIR-MATCHING problem, which is easier to describe and b) when the demands have a superincreasing property the problem is tractable     

Standard and quasi-standard stochastic power control algorithms

In an energy-efficient wireless communication system, transmit powers are minimized subject to predetermined signal-to-interference ratio (SIR) requirements. In this paper, a general framework for distributed stochastic power control (PC) algorithms is proposed, where the transmit powers are updated based on stochastic approximations. The proposed algorithms are distributed in the sense that no global information is needed in the power updates. Interference to each user is estimated locally via noisy observations. Two types of stochastic PC algorithms are studied: standard stochastic PC algorithms where the interference estimator is unbiased, and quasi-standard stochastic PC algorithms where the interference estimator is biased. The conditions under which the stochastic PC algorithms converge to the unique optimal solution are identified. Corresponding to two classes of iteration step-size sequences, two types of convergence, the probability one convergence and convergence in probability, are shown for both algorithms based on recent results in the stochastic approximation literature. Based on the theoretical results, some well-known stochastic PC algorithms, such as stochastic PC with matched filter receivers, and joint stochastic PC with blind minimum mean-squared error (MMSE) interference suppression, are revisited; several new stochastic PC algorithms, such as stochastic PC with minimum-power base-station assignment, and stochastic PC with limited diversity, are proposed. It is shown that these algorithms fall into either the standard or the quasi-standard stochastic PC framework. Simulation results are given to illustrate the performance of the proposed algorithms in practical systems.     

Algorithms for Energy-Efficient Multicasting in Static Ad Hoc Wireless Networks

In this paper we address the problem of multicasting in ad hoc wireless networks from the viewpoint of energy efficiency. We discuss the impact of the wireless medium on the multicasting problem and the fundamental trade-offs that arise. We propose and evaluate several algorithms for defining multicast trees for session (or connection-oriented) traffic when transceiver resources are limited. The algorithms select the relay nodes and the corresponding transmission power levels, and achieve different degrees of scalability and performance. We demonstrate that the incorporation of energy considerations into multicast algorithms can, indeed, result in improved energy efficiency.