Massive Machine Type Communications (mMTC) is one of the main features supported by the 3GPP New Radio (NR) technology. The new system specifications render multiple challenges for radio designers. Machine terminals are required to setup a call at signal-to-noise ratio (SNR) as low as -10dB in the extended coverage mode. Further, only one receive antenna is to be used with almost no frequency diversity. Maintaining timing and frequency synchronization with such requirements is a challenging task. In this work, we present, and evaluate the potential timing and frequency offset tracking algorithms subject to the new system requirements. The performance of the presented algorithms can be improved at low SNR regimes by employing the time averaging approach on the account of increasing the processing time. A comparison of the performance of different algorithms using system simulations is presented for different channel conditions.

In this paper, we maximize the benefits from the ultra low power wideband sensing approach based on FFT-based 1-bit quantization by addressing the practical limitations to this method. Unlike the conventional architecture that assumes a fully synchronized and coordinated Primary User (PU) network, the proposed system relaxes these limitations by providing an analytical framework for an uncoordinated asynchronous FFT-based 1-bit quantization system. For this system, we analytically derive the sub-band power which is the main parameter for the closed-form expressions representing the false alarm and detection probabilities. Further, improving the system performance through cooperative sensing is considered. While respecting the decision fusion cooperation, the optimum threshold for the generalized FFT-based 1-bit quantization system is derived such that the aggregate error rate is minimized. In addition to its significant power and complexity reduction, the presented analysis expands the use of the FFT-based 1-bit quantization wideband sensing approach in practical deployments. The sensing performance and the analytical results are assessed through comparisons with respective results from computer simulations.

The future Machine Type Communication (MTC) forces new requirements on cellular networks such as low-power, low-cost, narrow band, and extended coverage. To support these features, the 3GPP LTE-A introduced a new user equipment (UE) category, namely CAT-M1 raising new challenges for the system designers. For instance, the device should be able to setup a call at a signal-to-noise ratio (SNR) of -15 dB in the extended coverage mode with only one receive antenna and almost no frequency diversity. A new Physical Downlink Control Channel (PDCCH), namely MPDCCH, is introduced to satisfy the new system requirements. The new design relies on signal repetition to enhance the detection performance under very low SNRs. While the performance of this control channel will mainly depend on the channel estimation techniques used for coherent equalization during transmission, the choice of such technique will affect both the complexity and the performance of the UE. In this paper, we propose a channel estimation for MPDCCH that depends on linear processing of the pilot symbols and first-order polynomial interpolations. In order to enhance the performance of this technique we use a de-noising step using decision-feedbacks to help the UE reduce the power consumption of the reception and detection of the MPDCCH. The proposed scheme is able to use less than 30% of the supported repetitions in enhanced coverage modes to achieve the required detection error rate at moderate and low SNRs.

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.

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.

Abstract 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 377.84 MHz, the processor is clocked by the operating sampling rate to further reduce the power consumption. At the operation clock rate of 160 MHz, our proposed processor can calculate 512‐point FFT with up to eight independent data sequences within 3.2~μsmeeting IEEE 802.11ac standard requirements. Copyright © 2015 John Wiley & Sons, Ltd.

-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.

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.