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In this work, coordinated beamforming and power allocation schemes are proposed for multicell downlink non-orthogonal multiple access (NOMA) systems. Beamforming is adopted at the base-station to mitigate both intercell and intracell interference whereas power-domain multiplexing between a pair of users is considered in each spatial dimension. Given the beamforming vectors, intra-pair power allocation...
This work examines a cross-layered caching problem for distributed estimation in wireless sensor networks (WSNs). In WSNs, large amounts of data are produced continuously over time, and storing all the data collected from the sensors can be costly. In distributed estimation applications, sensors first gather information about a common phenomenon, and then forward the information to a fusion center...
This work proposes a jamming-resistant frequency hopping (FH) system that utilizes local channel observations for secret key generation (SKG). FH is a spread spectrum technique used in both military and consumer wireless applications to avoid jamming attacks, but requires pre-shared secret keys among communicating terminals, say Alice and Bob, to ensure that the same FH sequence is used at both sides...
This work examines the user-pair selection problem for distributed-input distributed-output (DIDO) wireless systems. A DIDO system refers to a network of densely deployed transmitter and receiver pairs, where the transmitters are connected to and coordinated by a DIDO server. The system sum rate is known to grow without bound as the number of transmitter-receiver pairs increases. However, when zero-forcing...
Cooperative communications refer to systems or techniques that allow users to help transmit each other’s messages to the destination. Most cooperative transmission schemes involve two phases of transmission: a coordination phase, where users exchange their own source data and control messages with each other and/or the destination, and a cooperation phase, where the users cooperatively retransmit...
Wireless communications have gained much popularity in recent years due to its ability to provide untethered connectivity and mobile access. However, before the turn of the century, many attempts to achieve reliable and high data-rate communication over the wireless channel have been unsuccessful due to multipath fading, shadowing, and path loss effects. These effects result in random variations of...
Previously, we focused on cooperative systems where only one user is allowed to act as the source at any instant in time while the other users serve as relays of the source. However, in multiuser systems, multiple sources may be accessing the cooperative channel simultaneously and, thus, multiple access strategies must be devised to separate their signals in either time, frequency, code, or space...
Most works in the literature on cooperative communications have focused mainly on the physical layer aspects such as coding, modulation, MIMO signal processing techniques etc, as described in the previous chapters. However, in practical systems, there may be multiple users that have the need to access the channel and therefore a proper design of medium access control (MAC) protocols is necessary to...
In this chapter, cooperative transmission schemes are introduced for networks that consist of more than two users. Following the assumptions made in the previous chapter, we assume that, at each instant in time, only one user acts as the source while the other users serve as relays that help forward the source’s message to the destination. In this case, the relays can together form a distributed antenna...
In previous chapters, different cooperative relaying schemes have been introduced under the basic setting where relays are each equipped with a single antenna and transmit over a single-carrier channel. However, cooperative diversity can actually be exploited on top of many other transmission technologies. In particular, the use of cooperation in orthogonal frequency-division multiplexing (OFDM) and...
In the previous chapter, we have examined medium access control (MAC) layer issues in cooperative networks and have introduced several cooperative MAC protocols to help exploit cooperative advantages from the MAC layer. In this chapter, we take a further look at other higher-layer issues in cooperative networks, including quality-of-service (QoS), routing, and security. First, we examine the advantages...
To facilitate the understanding of the cooperative strategies introduced throughout this book, we provide in this chapter a brief review of wireless communications and MIMO techniques. First, we introduce some basic characteristics of the wireless environment, including path loss, shadowing, and multipath fading, and describe popular diversity techniques that are often used to combat these channel...
In this chapter, the fundamental limits of relay networks are introduced under different channel settings, including Gaussian channels and wireless fading channels. For each scenario, we will study the information-theoretic capacities, diversity-multiplexing tradeoffs, and scaling laws of large networks accordingly. In Section 5.1, we first examine the case of the single-relay Gaussian channel. When...
In this chapter we discuss cooperative source and channel coding strategies and their performance in very dense sensor networks. In particular we investigate how the efficient acquisition of correlated data mandates that the node transmit cooperatively, instead of contending to report their local information. This is important as correlated information it is one of the remaining resource to tap into,...
Cooperative and relay communications have recently become the most widely explored topics in communications, whereby users cooperate in transmitting their messages to the destination, instead of conventional networks which operate independently and compete among each other for channel resources. As the field has progressed, cooperative communications have become a design concept rather than a specific...
This work proposes a learning-based energy management policy that takes into consideration the trade-off between the depth-of-discharge (DoD) and the lifetime of batteries. The impact of DoD on the energy management policy is often neglected in the past due to the inability to model its effect on the marginal cost per battery usage. In this work, a novel battery cost evaluation method that takes into...
We propose a new protocol, named Pulse coupled Synchronization and Scheduling (PulseSS), inspired by the dynamics of pulse coupled oscillators (PCO). PulseSS coordination signaling mechanism provides both decentralized network synchronization and time division multiple access scheduling for clustered networks. Contrary to previous PCO based protocols proposed for scheduling, PulseSS can resolve conflicts...
This work examines the charging power allocation and beam selection problem for distributed estimation in wireless passive sensor networks, where the sensors are charged over the air by RF-enabled energy sources. A two-phase replenishment and transmission cycle is considered. In the replenishment phase, each wireless charger emits power over the air through a carefully selected beam and power to replenish...
We consider the problem of multicasting information from a source to a destination over a multihop network of intermediate relays. However, some of the relays are untrustworthy and may be subject to eavesdropping. The source wishes to enlist their help while keeping the message secret against the eavesdropper. By employing random linear network coding at the relays, the problem is modeled as a noncoherent...
In this paper, we develop an analytical framework to evaluate the network throughput and traffic offloading efficiency in heterogeneous cellular networks (HCNs) with multiple energy-harvesting personal cells. The network consists of a tier of power-grid connected base-stations (BSs) and multiple tiers of energy-harvesting (personal) small cell access points (EH-SAPs). Each EH-SAP is personally owned...
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