We leveraged an unsupervised deep learning (DL) network for blind noise attenuation in a massive multi-input multi-output (MIMO) system without prior knowledge or labeled data. Initially, the real and imaginary parts of the received signal are concatenated in a 2-channel matrix, which is then partitioned into antenna-group patches to improve denoising efficiency. Afterward, our proposed gated recurrent unit (GRU) U-Net (GRUU-Net) network is applied to patch-wise real/imaginary data. The GRUU-Net network consists of gated recurrent units arranged in a U-Net architecture; the encoder extracts salient features from the input, while the decoder reconstructs the input patches. The main idea of GRUU-Net is that it combines the structural denoising capability of U-Net with the sequence modeling strength of GRUs and incorporates attention mechanisms to enhance feature integration within an iterative architecture. The numerical evaluation shows that our proposed model outperforms the benchmark methods across different signal-to-noise ratios (SNRs) and numbers of base station antennas (BSs). Additionally, we confirmed that applying the model simultaneously across multiple subsystems, where each patch can be considered a subsystem serving the same users in the same environment, results in better performance.

In a full-duplex (FD) multiuser multiple-input-multiple-output (MU-MIMO) base station system with imperfect channel state information (ICSI), there are challenges, such as co-channel interference, residual self-interference (SI), channel estimation errors, multiuser interference, and noise. To maximize the spectral efficiency (SE) of a system affected by interference, we proposed an efficient signal-to-leakage-plus-noise-ratio precoding scheme (SLNR-PS). The optimal precoding vectors that maximize the sum rates were obtained by solving the signal-to-leakage-noise ratio (SLNR) optimization problem using the generalized eigenvalue decomposition method. The SE is then calculated by combining the sum rates of the downlink and uplink transmissions. By developing an efficient power consumption model and precoding design schemes, we investigate the maximum energy efficiency (EE) of these systems. The results of the simulation indicate that SLNR-PS outperforms zero-forcing and block-diagonalization methods at all SNR levels. Additionally, it has been verified that the SE enhancement of the FD system compared to the half-duplex system relies on the suggested SLNR-PS technique, considering various factors, such as the number of antennas, Rician factors, and channel state information (CSI) inaccuracies. Through the utilization of these proposed methodologies, we have further demonstrated that the achievable EE of the FD system exceeds that of the half-duplex system, taking into account transmit power, circuit power consumption, power amplifier efficiency, and CSI inaccuracies.

In this paper, we study an optimal load balancing association scheme for a C-RAN (Cloud-based Radio Access Network) with mobile IoT (Internet of Things) devices. In C-RANs, short-range low-complex RRHs (Remote Radio Heads) are densely deployed to provide coverage. However, due to their limited processing power, it is critical to evenly distribute the traffic load. In addition, when user devices are mobile, frequent handovers can generate significant amount of control messages. In this regard, we propose an optimal load balancing association scheme between RRHs and mobile devices that minimizes the handovers as well. We first formulate an optimal load-balancing problem. Then, we revise the formulation such that an occurrence of handovers is penalized. We implement a discrete-time network simulator to evaluate and compare the performance of the proposed algorithm to conventional load balancing schemes. The evaluation results show that the proposed scheme can evenly distribute the traffic load, while minimizing the handovers.

The Internet of Things (IoT) paradigm has been proposed to assist and automate various activities such as environment monitoring by connecting physical devices in the area of our interest. Low- cost, battery-operated, and resource-limited IoT devices usually are densely deployed for robustness against node failures as well as for providing desired quality of monitoring. One of the effective ways to prolong the lifetime of an IoT network is to schedule selected IoT devices to enter the sleep mode and activate them later in a future time. However, this must be done carefully in order not to violate application-specific requirements. In this paper, we study the scheduling problem of IoT devices to prolong the network lifetime while satisfying both report- accuracy and timely-update requirements. We model and analyze the network as a Markov process, and derive system parameters. We formulate an optimal node activation scheduling problem and propose a low-complex greedy algorithm to expedite the scheduling process. Evaluation results demonstrate the effectiveness of both optimal and greedy algorithms.

Recent advances in signal processing have demonstrated in-band full-duplex capability at WiFi ranges. In addition to simultaneous two-way exchange between two nodes, full-duplex access points can potentially support simultaneous uplink and downlink flows. However, the atomic three-node topology, which allows simultaneous uplink and downlink, leads to inter-client interference. In this paper, we propose a random-access medium access control protocol using distributed power control to manage inter-client interference in wireless networks with full-duplex-capable access points that serve half-duplex clients. Our key contributions are two-fold. First, we identify the regimes in which power control provides sum throughput gains for the three-node atomic topology, with one uplink flow and one downlink flow. Second, we develop and benchmark PoCMAC, a full 802.11-based protocol that allows distributed selection of a three-node topology. The proposed MAC protocol is shown to achieve higher capacity as compared to an equivalent half-duplex counterpart, while maintaining similar fairness characteristics in single contention domain networks. We carried out extensive simulations and software-defined radio-based experiments to evaluate the performance of the proposed MAC protocol, which is shown to achieve a significant improvement over its half-duplex counterpart in terms of throughput performance.

Driven by advances in the signal processing and antenna technology, it has become possible for wireless nodes to simultaneously transmit and receive a packet through self-interference cancellation using multiple antennas. This is known as a full-duplex communication. In this paper, we propose a MAC protocol with immediate acknowledgement (ACK) for single-channel full-duplex wireless networks. The proposed scheme in a full-duplex communication can solve the hidden terminal problem by using the immediate ACK. That is, the proposed scheme ensures that the transmission of a packet that is being correctly received is continued, and prevents the transmission of an already failed packet. To evaluate the performance of the proposed scheme, we carried out extensive simulations and subsequently showed that the proposed scheme significantly improves the network throughput.

In real-time networked control systems, the end-to-end path delays on the communication network should be bounded in order to satisfy the stringent timing constraints of physical system. While the packet delivery on a single path could be significantly affected by network congestion levels, transmitting duplicate packets along multiple paths can overcome fluctuations of the time delay on a specific path by exploiting the diversity of multiple paths. As such, we propose a multi-path selection scheme that selects an appropriate number of multiple paths while minimizing the network traffic overhead due to multiple paths.

Abstract Robust and efficient data delivery in vehicularad hocnetworks (VANETs) with high mobility is a challenging issue due to unstable wireless links and dynamic topology changes. In this vehicular environment, the exchanges of topology information and discoveries of routing paths on an end‐to‐end basis are not desired, because the network topology changes rapidly and the information is out‐of‐date in short. In this paper, we propose a contention based forwarding mechanism, which locally exploitsgeographiclocation information in order to achieve robustness of data delivery for vehicular communications. A node that is closer to the destination node has a higher priority in competing for the wireless channel, and forwards packets as a relay node earlier than other adjacent nodes. When a packet is forwarded by a relay node, its preceding node informs adjacent nodes that it has been already relayed to prevent the duplications of packet delivery. Through ns‐2 simulations, we show that the proposed scheme can significantly improve the network performance in terms of the packet delivery ratio and the end‐to‐end delay in various synthetic and trace‐based realistic VANET scenarios with a wide range of vehicle speed and density. Copyright © 2010 John Wiley & Sons, Ltd.

Driven by advances in signal processing and multiuser detection (MUD) technologies, it has become possible for a wireless node to simultaneously receive multiple signals from other transmitters. In order to take full advantage of MUD in multi-packet reception (MPR) capable wireless networks, it is highly desirable to make the compounded signal from multiple transmitters more separable on its constellation at the receiver by coordinating the carrier phase offsets of the transmitters. In this paper, we propose a feedback-based carrier phase adjustment scheme that estimates the carrier phase offset for each user's received signal, computes the optimal phase shift to maximize the minimum Euclidean distance between the constellation points, and finally feeds the phase shift information back to the transmitters. We then evaluate the performance of the proposed carrier phase adjustment scheme and compare it to that of the no carrier phase adjustment case for QPSK and 8PSK with 2-4 users, and subsequently show that the proposed scheme significantly reduces the error probability in a multiuser communication system having MPR capability.

This paper addresses the power control problem in wireless multiple access communication systems with a multi-packet reception (MPR) channel. Driven by advances in signal processing and multiuser detection (MUD) technologies such as UWB and MIMO, it has become possible for a wireless node to simultaneously receive several packets from other transmitters. In this case, the receiver node can determine the set of transmitters from which it wants to receive data and instruct them to adjust their transmit power levels in order to maximize the overall network capacity by exploiting the MPR capability. We first show that the efficiency of the MPR channel utilization can be maximized by equalizing the transmission durations of simultaneously transmitting nodes, and then propose a power control that increases/decreases the transmit power of the nodes to equalize the transmission durations. Under the proposed power control, a node with a long transmission duration is allowed to use a higher transmit power if the next higher transmission rate is achievable with the increased transmit power. Through extensive simulations, we show that the proposed power control significantly improves the overall network capacity in multiple access.

In vehicular ad-hoc networks (VANETs), mobility is one of key characteristics that have a significant effect on routing performance because it causes dynamic changes of network topology. In this paper, we propose a contention based forwarding protocol that exploits geographic or virtual location information. A node that is closer to the destination node has a higher priority in competing for the wireless channel, and forwards packets as a relay node earlier than other adjacent nodes. When a packet is forwarded by a relay node, its preceding node informs adjacent nodes that it has been already relayed to prevent duplication of packet delivery. Through ns-2 simulations, we show that the proposed scheme can significantly improve the network performance in terms of the packet delivery ratio and the end-to-end delay in various VANET scenarios.