Search

We address the problem of joint downlink beamforming and power control in wireless communication systems. The goal is to minimise the overall transmission power radiated from the base station while satisfying individual signal-to-interference levels at the mobiles. Several iterative algorithms have been proposed for this non-linear optimisation task. One important problem in this context is that for certain scenarios the problem has no feasible solution. One of the main contributions of this paper is to derive a necessary and sufficient condition for the existence of a solution. This not only gives new insight into the analytical structure of the problem, but also provides a unifying framework by which several optimisation criteria known from literature can be compared. Finally, simulations are carried out using a deterministic multi-path channel model.

We consider the combined control problem of connection admission, flow rate, and bandwidth allocation (capacity, service-rate) under nonstationary conditions. A fluid flow model in state variable form describes the time varying mean behaviour of Available Bit Rate (ABR) traffic, which competes with Guaranteed Traffic for network resources. Using nonlinear control we derive an integrated control strategy, for the finite buffer and finite server case, that is insensitive to any propagation delay. We also derive bounds on mix between ABR and Guaranteed traffic to ensure that control strategy is effective, and select control design variables which can be used to influence the delivered QoS. The performance of proposed scheme is evaluated using analysis and simulation. Simulation results show that it achieves effective server and buffer utilisation (as predicted by analysis) and by appropriate choice of control design variables achieves prescribed bounded delays (for Guaranteed traffic only) and zero cell loss (even for ABR traffic demands exceeding server capacity, which if not controlled would cause losses). Hence proposed scheme delivers guaranteed QoS to user and avoids retransmissions, thus increasing network utilisation. 2 785 793 Sponsors: IEEE Conference code: 44643 Cited By :7

Multistage networks are strong candidates for implementation of ATM switching fabrics in B-ISDN networks. Among a number of proposed multistage networks, the Banyan network with its self-routing property, modular structure and suitability for VLSI implementation has received much attention. But the Banyan network suffers from internal link blocking and output port blocking. The Batcher sorting network was proposed to prevent internal link blocking, but it cannot prevent output port blocking. In this paper, we present a new 'Relay Chain' (RC) contention control network to prevent output port blocking. A parallel input buffer is adopted, with a special relay chain controller to solve the head of line (HOL) blocking problem normally associated with the input buffer strategy. The relay chain bus structure has a simple topology and makes the contention control network easy to implement. Performance analysis shows that this switch architecture achieves low cell loss rate together with the high throughput normally associated with output buffering. 3 2097 2101 Sponsors: IEEE GLOBECOM TAS NUS NTU et al Conference code: 44561 Cited By :2

In this paper, we use adaptive feedback and adaptive feedforward control methodologies to avoid congestion at high server utilisation. This addresses the combined connection admission and flow control problem (generic functions for managing and controlling traffic and congestion in BISDN). Using a novel control concept, based on only two groups of traffic (controllable and uncontrollable) we formulate a problem aimed at high (unity) utilisation of resources while maintaining quality of service at prescribed levels. Bounds on operating conditions are derived, and using simulation we show that high utilisation can be achieved as suggested by the theory, together with robustness for unforeseen traffic connections and disconnections. Even with such a high efficiency and strong properties on the quality of service, the only traffic descriptor required from the user is that of the peak rate of the uncontrollable traffic. 3 1083 1091 Sponsors: IEEE Computer Society Conference code: 21445 Cited By :7

This paper adopts a hierarchical multilayer/ multilevel approach for the allocation, management and control of B-ISDN resources. This approach seems appropriate to present a vertical decomposition of control layers, having different time-scales in addition to a horizontal decomposition, derived from the geographical distribution of control units. The paper outlines the layers proposed and explains the integrated structure derived. For virtual path allocation and management a Linear Programming model is derived. For connection admission control we suggest schemes which can handle connection types having different quality of service requirements. In addition, as fast and a fair dynamic cell-rate control scheme is presented. 1320 1324 Sponsors: IEEE Conference code: 18808 Cited By :7

Analytic expressions have been derived for the probability density functions of the total signal-to-interference ratio when considering mixed-type interference sources in the reverse link of a DS/CDMA packet radio system with Rayleigh fading. Four different scenarios were studied, and the corresponding expressions are presented for each situation. The users are divided into two groups: those that apply a closed-loop power control and those that only use an open-loop power control. By making use of these expressions, the mean block error probability is derived as a function of the number of total interfering users in each group.

Floating Car Data (FCD) applications are based on the collection of geo-localized information updates that are issued by vehicles roaming in a given area. These data are an essential source for traffic information and are widely employed by Intelligent Transportation Systems (ITS). We present and examine a hybrid networking architecture and protocol that are used for the efficient execution of such a collection process. We employ a VANET-based multihop dissemination logic to spread control messages and elect designated nodes. Those nodes are exploited to report vehicular data via LTE communications. The performance behavior of the proposed protocol is evaluated through the consideration of two real urban scenarios. In comparing with performance bounds that characterize the performance behavior attained by state-of-theart hybrid integrated VANET and LTE mechanisms, we show our approach to offer a substantial reduction in the traffic load rates induced over the LTE cellular radio access system.

In the process of bringing ATM traffic control into reality, the ATM Forum has proposed to adopt the sustainable cell rate (SCR) and its cell delay variation tolerance (CDVT/sub SCR/) as traffic descriptors, besides the peak cell rate (PCR) and its cell delay variation tolerance (CDVT/sub PCR/). The introduction of the SCR and the CDVT/sub SCR/ aims at obtaining a more efficient multiplexing of source traffic streams than PCR can provide. In this paper we provide guidelines for the choice of the SCR and CDVT/sub SCR/ values. We evaluate the impact of specific SCR and CDVT/sub SCR/ values on the usage parameter control (UPC) performance in case of measured MPEG and LAN traffic. A main result is the definition of conservative CAC rules at the access multiplexer that are easily implementable and yield guaranteed performance. The potential for further efficiency improvements is also explored.

An essential function for achieving security in computer networks is reliable authentication of communicating parties and network components. Such authentication typically relies on exchanges of cryptographic messages between the involved parties, which in turn implies that these parties be able to acquire shared secret keys or certified public keys. Provision of authentication and key distribution functions in the primitive and resource-constrained environments of low-function networking mechanisms, portable, or wireless devices presents challenges in terms of resource usage, system management, ease of use, efficiency, and flexibility that are beyond the capabilities of previous designs such as Kerberos or X.509. This paper presents a family of light-weight authentication and key distribution protocols suitable for use in the low layers of network architectures. All the protocols are built around a common two-way authentication protocol. The paper argues that key distribution may require substantially different approaches in different network environments and shows that the proposed family of protocols offers a flexible palette of compatible solutions addressing many different networking scenarios. The mechanisms are minimal in cryptographic processing and message size, yet they are strong enough to meet the needs of secure key distribution for network entity authentication. The protocols presented have been implemented as part of a comprehensive security subsystem prototype called KryptoKnight, whose software and implementation aspects are discussed in [16], and which is the basis for the recently announced IBM Network Security Program product.