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This paper proposes a low-complexity algorithm to calculate log likelihood ratios (LLRs) of coded bits, which is necessary for channel decoding in coded MIMO-OFDM mobile communications. An approximate LLR needs to find a pair of transmitted signal candidates that can maximize the log likelihood function under a constraint that a coded bit be equal to either one or zero. The proposed algorithm can...
The growth in broadband access and increases in terminal capability have enabled us to provide large-scale multimedia services. The traditional unicast architecture cannot support such a service because the transportation from a content server to many end hosts causes the overload to a content server. Overlay multicast techniques have been proposed to solve this problem. This high-layer technology...
In this paper, we propose a distributed contention resolution algorithm for multi-packet reception slotted ALOHA systems, which is based on backlog estimation. In the algorithm, a base station broadcasts a binary-valued collision indicator and the identifications of the packets successfully received, when some of packets simultaneously transmitted collide. Then, mobile terminals (MTs) estimate the...
In this paper, we propose an adaptive forwarding scheme for achieving efficient message delivery in the mobile sensor delay-tolerant network (DTN). By adaptively adjusting the probability of replicating a message based on the information about the number of existing message copies in the network, the proposed scheme can achieve nice balance between the delivery delay and the average message copy....
The problem of resource allocation (RA) in a downlink OFDMA system with minimum user rate requests is examined under the realistic scenario of partial (imperfect) channel state information (CSI) at the base station. The challenge in this setting is the non-zero probability of outage events which may lead to significant performance degradation if algorithms assuming perfect CSI are utilized. In this...
In this paper, we propose a novel medium access control (MAC) protocol called flow-driven MAC (FD-MAC) for mobile ad hoc networks (MANETs). FD-MAC is a slotted MAC protocol that combines random access and reservation-based access, and introduces the concept of "data flow" and a flow-driven mechanism for resource reservation. For short-duration data flows, it employs a random access protocol,...
The Guard Channel (GC) scheme is an extensively deployed handover prioritization policy in wireless mobile networks due to its appealing properties of easy implementation and flexible control. Self-similar traffic has been demonstrated to be a ubiquitous phenomenon in modern communication networks and many measurement studies have demonstrated that the call holding times in wireless mobile networks...
In this paper, the network deployment problem for IEEE 802.16j networks is studied. We consider jointly deploying a number of base stations and relay stations to serve mobile stations distributed arbitrarily in a given geographic area such that the cost is within the budget and the system capacity is maximized. This problem is formulated as an integer linear programming (ILP) model. We analyze the...
Due to their nature, vehicular ad hoc network (VANET) is vulnerable to denial of service (DoS) attacks, such as jamming attack. The objective of a jammer is to interfere with legitimate wireless communications, and to degrade the overall QoS of the network. In this paper, we propose a model to detect a particular class of jamming attack, in which the jammer transmits only when valid radio activity...
The performance of prevalent MAC protocols in MANETs relies on the level of contention in networks. While contention-based MAC protocols such as CSMA suffer from inefficiency under high contention, slot-based MAC protocols such as TDMA perform in the opposite way. In this paper, we propose a hybrid protocol to which we refer as Load-Adaptive MAC (LA-MAC) protocol for MANETs. By adaptively switching...
This paper proposes a three-dimensional (3-D) model for wideband multiple-input multiple-output (MIMO) vehicle-to-vehicle (V-to-V) multipath fading channels that accounts for mutual coupling among both, transmit and receive antenna elements. From the 3-D model, the spatial correlation is derived for a 3-D non-isotropic scattering environment. Finally, this model is used to evaluate the effect of mutual...
The present study investigates a Medium Access Control (MAC) protocol for reliable inter-vehicle communications (IVC) to support safe driving with the goal of reducing road traffic accidents. A number of studies have evaluated the performance of the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol. However, the communication quality provided by the CSMA/CA protocol is degraded...
Clustering has been used as a fundamental tool to improve scalability in large wireless ad hoc networks. Techniques based on clustering, such as routing, self-organization, context management, service discovery, etc., ensure QoS in wireless ad hoc networks when the number of devices increases. The crucial issue of clustering is the overhead generated during the cluster formation and maintenance phases...
In this paper, we present a spatiotemporal multicast, called a mobicast, protocol for supporting applications which require spatiotemporal coordination in VANETs. The spatiotemporal character of a mobicast is to forward a mobicast message to vehicles located in some geographic zone at time t, where the geographic zone is denoted as zone of relevance (ZOR). Vehicles located in ZOR at the time t must...
The delay tolerant mobile sensor network (DTMSN) is a new type of sensor network for pervasive information gathering. Although similar to conventional sensor networks in hardware components, DTMSN owns some unique characteristics such as sensor mobility, intermittent connectivity, etc. Therefore, traditional data gathering methods can not be applied to DTMSN. In this paper, we propose an efficient...
The connectivity properties of a mobile linear network with high speed mobile nodes, dynamic node population, and a strict delay constraint are investigated. A new mobility model is developed to represent the steady state node distributions in terms of random node location and random node population. The model accurately captures the statistical properties of random node arrival, time-varying node...
We consider a Delay Tolerant Network (DTN) whose users (nodes) are connected by an underlying Mobile Ad hoc Network (MANET) substrate. Users can declaratively express high-level policy constraints on how "content" should be routed. For example, content can be directed through an intermediary DTN node for the purposes of preprocessing, authentication, etc., or content from a malicious MANET...
Routing of data packets in vehicular ad hoc networks (VANETs) is challenging due to dynamic changes in the network topologies. As nodes in VANETs can obtain accurate position information from onboard Global Positioning System receivers, position-based routing is considered to be a very promising routing strategy for VANETs. This paper presents a novel position-based directional vehicular routing (PDVR)...
Multiple base station (Multi-BS) cooperation has been considered as a promising mechanism to suppress cochannel interference and boost the capacity for cellular networks. However, the large feedback and signaling overhead hinder it from practice. Therefore, limited cooperation among BSs is recognized as a good tradeoff between the performance gain and the relevant cost. In this paper, the whole network...
Progressive image and scalable video have gradual differences of importance in their bitstreams, which can benefit from multiple levels of unequal error protection (UEP). Though hierarchical modulation has been intensively studied as an UEP approach for digital broadcasting and multimedia transmission, methods of achieving a large number of UEP levels have rarely been studied. In this paper, we propose...
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