Communication complexity

About: Communication complexity is a research topic. Over the lifetime, 3870 publications have been published within this topic receiving 105832 citations.

Efficient Two-dimensional Data Allocation in IEEE 802.16 OFDMA

Abstract: The IEEE 802.16 standard uses Orthogonal Frequency Division Multiple Access (OFDMA) for mobility support. Therefore, the medium access control frame extends in two dimensions, i.e., time and frequency. At the beginning of each frame, i.e., every 5~ms, the base station is responsible both for scheduling packets, based on the negotiated quality of service requirements, and for allocating them into the frame, according to the restrictions imposed by 802.16 OFDMA. To break down the complexity, a split approach has been proposed in the literature, where the two tasks are solved in separate and subsequent stages. In this paper we focus on the allocation task alone, which is addressed in its full complexity, i.e., by considering that data within the frame must be allocated as bursts with rectangular shape, each consisting of a set of indivisible sub-bursts, and that a variable portion of the frame is reserved for in-band signaling. After proving that the resulting allocation problem is NP-hard, we develop an efficient heuristic algorithm, called Recursive Tiles and Stripes (RTS), to solve it. RTS, in addition to handle a more general problem, is shown to perform better than state-of-the-art solutions via numerical analysis with realistic system parametrization.

Coordinated User Scheduling for Multi-Cell Distributed Antenna Systems

Abstract: In this paper, we address the problem of coordinated user scheduling for the downlink of a multi-cell distributed antenna system (DAS). With the practical assumption that only large-scale channel state information (CSI) is known at the transmitter, a low-complexity greedy scheduling scheme is proposed. In order to provide fairness among users, the proposed scheme adopts round-robin scheduling within each cell and optimizes the scheduling order for each cell to maximize the minimum ergodic capacity of the users. For each user, the selection transmission scheme (just the distributed antenna element (DAE) with the largest channel gain to the user is selected for transmission) is implemented and each selected DAE transmits with equal power. Simulation results demonstrate that the proposed greedy scheme promises much better performance than that without inter-cell coordination and its performance is quite close to the optimal one. Moreover, by simulations we find that the proposed scheme achieves nearly the same system ergodic sum capacity with the one targeted to maximize the system ergodic sum capacity.

An Introduction to Quantum Complexity Theory

Abstract: We give a basic overview of computational complexity, query complexity, and communication complexity, with quantum information incorporated into each of these scenarios. The aim is to provide simple but clear definitions, and to highlight the interplay between the three scenarios and currently-known quantum algorithms. Complexity theory is concerned with the inherent cost required to solve information processing problems, where the cost is measured in terms of various well-defined resources. In this context, a problem can usually be thought of as a function whose input is a problem instance and whose corresponding output is the solution to it. Sometimes the solution is not unique, in which case the problem can be thought of as a relation, rather than a function. Resources are usually measured in terms of: some designated elementary operations, memory usage, or communication. We consider three specific complexity scenarios, which illustrate different advantages of working with quantum information: 1. Computational complexity

On Self-Healing Key Distribution Schemes

Abstract: Self-healing key distribution schemes allow group managers to broadcast session keys to large and dynamic groups of users over unreliable channels. Roughly speaking, even if during a certain session some broadcast messages are lost due to network faults, the self-healing property of the scheme enables each group member to recover the key from the broadcast messages he has received before and after that session. Such schemes are quite suitable in supporting secure communication in wireless networks and mobile wireless ad-hoc networks. Recent papers have focused on self-healing key distribution, and have provided definitions, stated in terms of the entropy function, and some constructions. The contribution of this paper is the following: We analyze current definitions of self-healing key distribution and, for two of them, we show that no protocol can achieve the definition. We show that a lower bound on the size of the broadcast message, previously derived, does not hold. We propose a new definition of self-healing key distribution, and we show that it can be achieved by concrete schemes. We give some lower bounds on the resources required for implementing such schemes, i.e., user memory storage and communication complexity. We prove that the bounds are tight

Quantum and Approximate Privacy

Abstract: This paper studies privacy and secure function evaluation in communication complexity. The focus is on quantum versions of the model and on protocols with only approximate privacy against honest players. We show that the privacy loss (the minimum divulged information) in computing a function can be decreased exponentially by using quantum protocols, while the class of privately computable functions (i.e., those with privacy loss 0) is not enlarged by quantum protocols. Quantum communication combined with small information leakage on the other hand makes certain functions computable (almost) privately which are not computable using either quantum communication without leakage or classical communication with leakage. We also give an example of an exponential reduction of the communication complexity of a function by allowing a privacy loss of o(1) instead of privacy loss 0.