Abdelmohsen Ali

Next generation M2M cellular networks: challenges and practical considerations

In this article we present the major challenges of future machine-to-machine (M2M) cellular networks such as spectrum scarcity, and support for a large number of low-power, lowcost devices. As an integral part of the future Internet-of-Things (IoT), the true vision of M2M communications cannot be reached with conventional solutions that are typically cost inefficient. The cognitive radio concept has emerged to address spectrum under-utilization and scarcity. The heterogeneous network model is another alternative to relax the number of covered users. To this extent, we present a complete fundamental understanding and the engineering details of cognitive radios, the heterogeneous network model, and power and cost challenges in the context of future M2M cellular networks.

Advances on Spectrum Sensing for Cognitive Radio Networks: Theory and Applications

Due to the under-utilization problem of the allocated radio spectrum, cognitive radio (CR) communications have recently emerged as a reliable and effective solution. Among various network models, this survey paper focuses on the enabling techniques for interweave CR networks which have received great attention from standards perspective due to its reliability to achieve the required quality-of-service. Spectrum sensing provides the essential information to enable this interweave communications in which primary and secondary users are not allowed to access the medium concurrently. Several researchers have already considered various aspects to realize efficient techniques for spectrum sensing. In this direction, this survey paper provides a detailed review of the state-of-the-art related to the application of spectrum sensing in CR communications. Starting with the basic principles and the main features of interweave communications, this paper provides a classification of the main approaches based on the radio parameters. Subsequently, we review the existing spectrum sensing works applied to different categories such as narrowband sensing, narrowband spectrum monitoring, wideband sensing, cooperative sensing, practical implementation considerations for various techniques, and the recent standards that rely on the interweave network model. Furthermore, we present the latest advances related to the implementation of the legacy spectrum sensing approaches. Finally, we conclude this survey paper with some suggested open research challenges and future directions for the CR networks in next generation Internet-of-Things applications.

Spectrum Monitoring Using Energy Ratio Algorithm for OFDM-Based Cognitive Radio Networks

This paper presents a spectrum monitoring algorithm for Orthogonal Frequency Division Multiplexing (OFDM) based cognitive radios by which the primary user reappearance can be detected during the secondary user transmission. The proposed technique reduces the frequency with which spectrum sensing must be performed and greatly decreases the elapsed time between the start of a primary transmission and its detection by the secondary network. This is done by sensing the change in signal strength over a number of reserved OFDM sub-carriers so that the reappearance of the primary user is quickly detected. Moreover, the OFDM impairments such as power leakage, Narrow Band Interference (NBI), and Inter-Carrier Interference (ICI) are investigated and their impact on the proposed technique is studied. Both analysis and simulation show that the energy ratio algorithm can effectively and accurately detect the appearance of the primary user. Furthermore, our method achieves high immunity to frequency-selective fading channels for both single and multiple receive antenna systems, with a complexity that is approximately twice that of a conventional energy detector.

Low Power Wideband Sensing for One-Bit Quantized Cognitive Radio Systems

We propose an ultra low power wideband spectrum sensing architecture by utilizing a one-bit quantization at the cognitive radio (CR) receiver. The impact of this aggressive quantization is quantified and it is shown that the proposed method is robust to low signal-to-noise ratios (SNR). We derive closed-form expressions for both false alarm and detection probabilities. The sensing performance and the analytical results are assessed through comparisons with respective results from computer simulations. The proposed method provides significant saving in power, complexity, and sensing period on the account of an acceptable range of performance degradation.

Employing Broadcast Channel for Frequency Tracking in LTE-MTC Systems

To support machine type communication (MTC), new challenges for the system design have emerged. For instance, the device shall be able to setup a call at a signal-to-noise ratio (SNR) of -15dB in the extended coverage mode with only one receive antenna and almost no frequency diversity. Maintaining frequency synchronization is one of the main challenges. In this letter, we present, analyze, and evaluate a frequency tracking technique that relies on the repetitive nature of the MTC broadcast channel. Results show that this method does not only provide better performance at very low SNRs when compared to conventional techniques, but also it saves the amount of time required to lock to the network.

On the Cell Search and Initial Synchronization for NB-IoT LTE Systems

In the Narrowband Internet-of-Things (NB-IoT) LTE systems, the device shall be able to blindly lock to a cell within 200-KHz bandwidth and with only one receive antenna. In addition, the device is required to setup a call at a signal-to-noise ratio (SNR) of −12.6 dB in the extended coverage mode. A new set of synchronization signals have been introduced to provide data-aided synchronization and cell search. In this letter, we present a procedure for NB-IoT cell search and initial synchronization subject to the new challenges given the new specifications. Simulation results show that this method not only provides the required performance at very low SNRs, but also can be quickly camped on a cell, if any.

Cell search evaluation: A step towards the next generation LTE-MTC systems

The main features for future Machine Type Communication (MTC) cellular networks enable low-power, low-cost, narrow band, and extended coverage system. To support these features, new challenges for the system design have emerged. For instance, the device shall be able to setup a call at a signal to noise ratio (SNR) of -15dB in the extended coverage mode with only one receive antenna and almost no frequency diversity. For these reasons, we present an evaluation to the conventional cell search and initial synchronization algorithms subject to these new hard requirements. The performance of most of the algorithms can be enhanced by utilizing time averaging on the account of increasing the processing time. By simulating exact LTE-MTC system, the performance of various algorithms is obtained with the expected time budget to meet LTE-MTC specifications, if applicable.

A novel one-bit quantization design for correlation-based low-power wideband sensing

We propose an ultra low power wideband spectrum sensing architecture by utilizing a one-bit quantization at the cognitive radio (CR) receiver. A window-based autocorrelation is utilized to provide the power spectral density of the quantized signal. Closed-form expressions are derived for the 1-bit quantized correlation. It is shown that the introduced method can still provide full information about the sparse spectrum even at low signal-to-noise ratios (SNR). An optimized detection algorithm is presented to sense whether an individual sub-band is occupied or vacant. The sensing performance is justified through computer simulations. When compared to other methods, in addition to the significant saving in power and complexity, results indicate that the proposed method provides better performance even though an aggressive quantization has been applied.

A Novel Spectrum Monitoring Algorithm for OFDM-Based Cognitive Radio Networks

-This paper introduces a novel spectrum monitoring algorithm for Orthogonal Frequency Division Multiplexing (OFDM) based cognitive radios so that the primary user activity can be detected during the secondary user transmission. The presented technique fully utilizes the performance of both primary and secondary networks. This is done by sensing the variations in signal power over a number of reserved OFDM sub-carriers so that the reappearance of the primary user is quickly detected and the throughput of both primary and secondary networks are kept high. Both analysis and simulation show that the energy ratio algorithm not only effectively and accurately detects the appearance of the primary user in frequency selective channels, but also offers immunity to the traditional OFDM challenges like the sensitivity of Inter Carrier Interference (ICI) effects.

A multi-mode IFFT/FFT processor for IEEE 802.11ac: design and implementation

In this paper, we present 64/128/256/512-point inverse fast Fourier transform IFFT/FFT processor for single-user and multi-user multiple-input multiple-output orthogonal frequency-division multiplexing based IEEE 802.11ac wireless local area network transceiver. The multi-mode processor is developed by an eight-parallel mixed-radix architecture to efficiently produce full reconfigurability for all multi-user combinations. The proposed design not only supports the operation of IFFT/FFT for 1-8 different data streams operated by different users in case of downlink transmission, but also, it provides different throughput rates to meet IEEE 802.11ac requirements at the minimum possible clock frequency. Moreover, less power is needed in our design compared with traditional software approach. The design is carefully optimized to operate by the minimum wordlengths that fulfill the performance and complexity specifications. The processor is designed and implemented on Xilinx Vertix-5 field programmable gate array technology. Although the maximum clock frequency is 377.84i¾źMHz, the processor is clocked by the operating sampling rate to further reduce the power consumption. At the operation clock rate of 160i¾źMHz, our proposed processor can calculate 512-point FFT with up to eight independent data sequences within 3.2~µs meeting IEEE 802.11ac standard requirements. Copyright