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Wireless channels create both intersymbol interference (ISI) and interchannel interference (ICI) on the transmitted signal. The OFDM-OQAM system with well localized prototype filter can reduce the interference caused due to the transmission over wireless channel, but it is not the optimal choice. In this paper, we propose a new structure for OFDM-OQAM system with hexagonal time-frequency lattice which...
In this paper, we consider one of the main disadvantages of Ergodic Interference Alignment, i.e., delay. We propose two methods to solve the open problem of finding the best choice of user sets in order to minimize the delay. With these methods we are able to find the best JAP-B scheme which aims to trade off rate for delay in Ergodic Interference Alignment. First, we provide the solution based on...
Multicell coordinated beamforming, where multiple base stations (BSs) collaborate with each other in the beam-vectors design to mitigate the intercell interference (ICI), has been a subject of great attention recently. With perfect channel information available at the base stations, we first present a fast converging algorithm that solves the weighted sum rate maximization (WSRM) problem. Then, the...
We consider a channel sensing game in a cognitive radio network, where secondary users aim on maximizing their own utility by deciding on which channel to sense. We propose an algorithm for deriving Nash equilibrium strategies, and analyze the worst-case complexity of the algorithm. Finally, we examine differences between multiple possible equilibria in terms of total system utility and fairness.
In cognitive multimedia mesh networks (CMMNs), unlicensed users (secondary users, SUs) can share the spectrum with licensed users (primary users, PUs) on a non-interfering basis. The main challenge in CMMN is how to implement an efficient optimal control policy that can allocate spectrum and transmission powers for the SUs efficiently and how to adapt these resources to the changing network conditions...
In this paper, we elaborated on a new interference alignment technique for downlink multi-user system in a MIMO-X channel with multiple antennas. We considered two transmitters, each equipped with M antennas, and L users, each equipped with K antennas. Here, we consider a MIMO-X scenario that some users are receiving transmissions from both transmitters. The proposed approach is focused on rank-1...
A network consisting of a point-to-point (P2P) link and a multiple access channel (MAC) sharing the same medium is considered. The resulting interference network, with three transmitters and two receivers is studied from degrees of freedom (DoF) perspective, with and without cognition. Several cognition variants are examined. Namely, the setup is studied with (1) no cognitive transmitters, (2) a cognitive...
With the spread of passive Radio Frequency Identification (RFID) systems, new applications will see the coexistence of more and more RFID readers in the same area. As for wireless devices, also RFID readers experience collisions whenever sharing the same communication channel. In this paper, an anti-collision protocol has been proposed in order to solve the reader collision problem. The aims of the...
Home area networks (HANs) promise to enable sophisticated home automation applications such as smart energy usage and assisted living. However, recent empirical study of HAN reliability in real-world residential environments revealed significant challenges to achieving reliable performance in the face of significant and variable interference from a multitude of coexisting wireless devices. We propose...
Most previous work on spectrum sharing in the cognitive radio (CR) networks did not take into account the influence of node mobility on link available time as well as the spectrum heterogeneity. In this paper, a spectrum sharing algorithm based on spectrum heterogeneity is presented for centralized CR network, meanwhile the individual CR users are free to be mobile. A prediction model of channel usage...
Resource allocation is an important issue in multiuser cognitive OFDM systems. In this paper, the highest achievable rate of each OFDM subchannel for a cognitive radio user (also referred to as secondary user, SU) is calculated by jointly considering the channel gain and the interference level. A low complexity algorithm is presented to allocate radio resource to the SUs. Each subchannel is assigned...
In cognitive radio networks, secondary users conduct local sensing to use underutilized spectrum bands. However, every secondary user's local sensing usually gives rise to much sensing overhead. Moreover, a globally synchronized quiet period cannot be determined in a decentralized network. In this paper, we propose a zone-based distributed sensing scheme, in which multiple secondary users alternate...
Feedback of channel state information (CSI) in wireless systems is essential in order to exploit multi-user diversity and achieve the highest possible performance. When each spatially distributed user in the wireless system is assumed to have i.i.d. scalar CSI values, the optimal fixed-rate and entropy-constrained point density functions are established in the high-resolution regime for the quantization...
Next generation wireless networks will be heterogeneous, where several primary users (PU e.g. licensed users) and secondary users (SU e.g. unlicensed users) can operate in the same dynamic and reconfigurable networks at a given time. The major challenge in this heterogeneous radio environment is to enable the coexistence between PU and SU which will further improve the efficient use of radio spectrum...
Wake-up radio technology is a means to improve energy efficiency in low-power wireless sensor networks. In such radios, low-power low-complexity designs are considered, often based on narrow-band transmission, simple modulation techniques, noncoherent detection and matched filter receivers. In order to improve the performance of wake-up radios in interference limited scenarios, while keeping the power...
Heterogeneous cellular networks (HetNets) - conventional macro base stations overlaid with low-power nodes-are being deployed for reasons of improved spectral efficiency, economy, and scalable network expansion. To optimally realize the benefits of HetNets, it is crucial to factor deployment aspects such as cell association, transmission power, spectrum allocation, and deployment density. This paper...
Supporting secondary users through a collateral network dedicated to spectrum sensing has been recently proposed as a mean to overcome spectrum sensing limitations of secondary devices. Building on this idea, we propose a protocol for a Wireless Sensor Network (WSN) to support secondary devices of an Opportunistic Spectrum Access (OSA) network. We examine the fundamental tradeoff between the statistics...
Channel reciprocity is regarded as one of the most important advantages of TDD systems. However, the RF front-ends contribute to the channel experienced, and their TX/RX mismatches might cause reciprocity error, and thus degrade system throughput. Therefore, channel reciprocity calibration is a crucial issue. Among the existing calibration methods, Over-the-air (OTA) calibration is a promising approach...
In this paper, we design an energy-efficient cooperative Medium Access Control (MAC) protocol combined with physical layer power / rate control in order to minimize the energy consumption. Based on the Channel State Information (CSI) and relay-to-destination distance, the potential candidate relays carry out autonomous decisions for minimizing the transmission power required for forwarding their data,...
In practice, the imperfect channel state information can degrade the optimization performance of a cognitive system, especially yielding the detrimental violation of the interference constraint perceived by the primary users. This paper investigates the linear transceiver design in cognitive downlink systems with the imperfect channel knowledge, aiming at minimizing the mean square error of the secondary...
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