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Ambient backscatter is a new technology that utilizes environmental wireless signals to enable battery-free devices to communicate with each other. In this paper, we investigate the problem of signal detection for the full duplex wireless system utilizing ambient backscatter. Since one of the key technologies of full duplex wireless system is self-interference cancellation, we first estimate the channel...
Recently backscatter networks have received booming interest because, they offer a battery-free communication paradigm using propagation radio waves as opposed to active radios in traditional sensor networks while providing comparable sensing functionalities, ranging from light and temperature sensors to recent microphones and cameras. While sensing data on backscatter nodes has been seen on a clear...
In this paper, we consider a time-slotted energy harvesting (EH) cognitive radio (CR) network, where the secondary user (SU) is powered by a continual source of energy harvested from ambient environment. Jointly considering the primary user activity on the primary channel, diversity of channel conditions, energy replenishment process as well as the imperfection of spectrum sensing, the SU aims to...
In most Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) systems, channel estimation is required for equalization and symbol detection. It often exploits the specified pilot symbols consuming not only a large part of the throughput but also significant power resources. This paper quantifies the theoretical maximum power reduction of the transmitted pilots when...
This paper proposes a new spectrum access algorithm based on the Partially Observable Markov Decision Process (POMDP) for Cognitive Radio Networks (CRNs). The proposed algorithm uses the Maximum Likelihood to estimate the licensed channel state transition probabilities based on historical statistics information of the channels. Then, the number of channels sensed by the secondary users in each time...
In this paper, we analyze the performance of the fractional pilot reuse (FPR) scheme with pilot contamination mitigation in massive multiple-input multiple-output (MIMO) system. In FPR, users are classified into the cell- center and the cell-edge ones according to their signal-to- interference-plus-noise ratios (SINRs) at the receiver side. Then, the cell- edge users with low SINRs in different cells...
We propose a decentralized multi-cell aware opportunistic random access (MA-ORA) protocol that almost achieves the optimal throughput scaling in a K-cell random access network with one access point (AP) and N users in each cell. Under our MA-ORA protocol, users opportunistically transmit with a predefined physical layer data rate in a decentralized manner if the desired signal power to the serving...
Due to the difficulty of coordination in multi-cell random access, it is a practical challenge how to achieve the optimal throughput with decentralized transmission. In this paper, we propose a decentralized multi-cell aware opportunistic random access (MA-ORA) protocol that almost achieves the optimal throughput scaling in a multi-cell random access network with one access point (AP) and multiple...
Hybrid ARQ (HARQ) and link adaptation (LA) are two powerful techniques to improve the data throughput in wireless communication systems. However, when integrated with LA, conventional HARQ does not provide much gain over LA without significantly increasing the number of retransmissions and initial coding rate. In this paper, we explore the feasibility of achieving high throughput by combining HARQ...
MIMO beamforming provides high throughput for WiFi networks, but it also leads to high computation and communication overhead due to Channel State Information (CSI) feedback. Explicit CSI feedback provides high beamforming gains, but it introduces extremely high overhead. Implicit CSI feedback has low overhead, but it provides very low beamforming gains. We propose EliMO to completely Eliminate CSI...
Human and animal societies exhibit complex cognitive and social processes of coordination, cooperation, and competition among their members. Among other functions, these processes can facilitate fairer sharing of resources among community members and enhance individual survival outcomes. In this work, three bio-socially inspired models for secondary users of spectrum in cognitive radio networks are...
Transmit beamforming and Multi User MIMO (MU MIMO) are key features in the 802.11ac WLAN standard. In this paper, we study these features and analyze the approaches suggested in the literature for enhancing the performance of 802.11ac WLANs using these features.
In massive multiple-input multiple-output (MIMO) systems, superimposed (SP) and time-multiplexed (TM) pilots exhibit a complementary behavior, with the former and latter schemes offering a higher throughput in high and low inter-cell interference scenarios, respectively. Based on this observation, in this paper, we propose an algorithm for partitioning users into two disjoint sets comprising users...
MIMO-OFDM is the generally accepted standard in all WLAN systems. However, this method increases training signals required to estimate the propagation matrix of multi-antenna system. In this study, we investigate methods of shortening VHT-LTF training signal in WLAN systems. Simulation results have shown that 1/2 and 3/4 reduction in VHT-LTF training signal is possible while maintaining a considerable...
LTE in Unlicensed band (LTE-U) has gained intensive attention recently due to its capability to offload mobile data to unlicensed bands. In order to use unlicensed band, LTE-U has to coexist with WiFi - another wireless technology that operates in unlicensed bands. This coexistence is riddled with several challenges as these technologies use different core networks, backhauls and deployment plans...
This paper is devoted for designing and investigation of some algorithms for direct sequence spread spectrum (DSSS) signal processing with time-shift keying for underwater communication. The results of marine experiments for developed system performance evaluation in shallow sea (depth ∼ 20–30 m) on distances up to 10 km on frequency of 12 kHz (bandwidth of 4 kHz) are supplemented.
We derive for the first time closed-form expressions for the Cramér-Rao lower bounds (CRLBs) of the joint channel phase, and carrier frequency offset (CFO) estimates from turbo-coded (TC) Pulse-amplitude modulation (PAM) and rectangular-QAM (RQAM) modulated signals over flat-fading channels. After wisely exploiting the properties of Gray mapping, we are able to simplify the log-likelihood...
This paper presents initial results for a novel 128-antenna massive Multiple-Input, Multiple- Output (MIMO) testbed developed through Bristol Is Open in collaboration with National Instruments and Lund University. We believe that the results presented here validate the adoption of massive MIMO as a key enabling technology for 5G and pave the way for further pragmatic research by the massive MIMO community...
We consider training-based channel estimation for cloud radio access networks (CRANs), in which a large amount of remote radio heads (RRHs) and users are randomly scattered over a certain service area. In this model, assigning orthogonal training sequences to all users, if possible, will cause a substantial overhead to the overall network. Instead, we introduce the notion of local orthogonality, in...
In high mobility environment, the carrier frequency offset (CFO) introduced by Doppler shifts can severely degrade the system performance. On the other hand, orthogonal pilot sequence which is utilized in conventional frame structure for CFO and channel estimation induces large pilot resource consumption as the number of users increases, resulting in low achievable throughput. In this paper, we propose...
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