Ali Hazmi

Feasibility study of IΕΕΕ 802.11ah radio technology for IoT and M2M use cases

In this paper we study the feasibility of IEEE 802.11ah radio technology for internet of things (IoT) and machine to machine (M2M) use cases. Devices in internet of things and machine to machine networks are foreseen to communicate wirelessly. Therefore, it is of foremost importance to have a reliable, low-energy wireless technology available that may be used anywhere and anytime without draining the device battery and could achieve satisfactory coverage and data rate. Here we study the link budget, achievable data rate and packet size design of the IEEE 802.11ah radio technology in different channel scenarios. System design and simulation results show that when using this technology the system parameters can be selected to satisfy in most of the cases a reliable communication link while providing better coverage and relatively comparable throughput when compared to other existing solutions like ZigBee.

Efficient BER Reduction Technique for Nonlinear OFDM Transmission Using Distortion Prediction

This paper presents an efficient technique for reducing the bit error rate (BER) of orthogonal frequency-division multiplexing (OFDM) signals transmitted over nonlinear solid-state power amplifiers (SSPAs). The proposed technique is based on predicting the distortion power that an SSPA would generate due to the nonlinear characteristics of such devices. Similar to the selective-mapping or partial-transmit-sequence (PTS) schemes, the predicted distortion is used to select a set of phases that minimize the actual SSPA distortion. Simulation results confirmed that the signal-to-noise ratio that is required to obtain a BER of ~ 10-4 using the proposed technique is less by about 8 dB when it is compared to the standard PTS utilizing 16 partitions. Moreover, complexity analysis demonstrated that the proposed system offers a significant complexity reduction of about 60% compared to state-of-the-art methods.

Performance evaluation of IEEE 802.11ah and its restricted access window mechanism

In this paper we provide an analytical model to compute the throughput and energy consumption of IEEE 802.11ah, the new Sub-1 GHz WiFi standard. The analytical model assumes known collision and error probabilities and applies to both basic and RTS/CTS access mechanisms. Comparison with simulation results shows that the model is extremely accurate in predicting the system throughput and energy consumption. We also investigate the IEEE 802.11ah system including the new restricted access window (RAW) mechanism, and compare it to the basic scheme. The obtained results show that the RAW mechanism can provide substantial improvements in the system performance, in terms of throughput, packet delay and energy consumption, in particular in highly-loaded dense network scenarios. These findings affirm and substantiate the prospects of IEEE 802.11ah as one of the key enabling technologies for wide-scale low-cost and energy-efficient M2M deployments and IoT applications in the future.

Impulse burst position detection and channel estimation schemes for OFDM systems

A new method for compensating the effects of impulse noise in OFDM systems has been presented by Rinne, Henriksson and Hazmi (see Proc. 7th International OFDM Workshop, Hamburg. Germany, p.183-187, Sept. 2002). It is shown that in the AWGN case, the method can effectively cancel the impulse noise. However in the time-frequency selective channel further measures are needed. The purpose of this paper is to present an enhanced channel estimation scheme for the standard method to overcome its sensitivity to the time frequency selective channel estimates. The scheme uses the impulse free pilots to estimate the corrupted ones. Three different alternatives are discussed. Their performances in mean squared error (MSE) versus Doppler frequency are studied analytically. Bit error rate ratio (BER) simulations results are given, in the cases of SFN hilly terrain static and mobile channels. Additionally, results on simple practical impulse burst position detection method are also presented.

Efficient interleaving technique for OFDM system over impulsive noise channels

In this work, an efficient interleaving process is proposed for orthogonal frequency division multiplexing (OFDM) systems over impulsive noise channels. Unlike the conventional OFDM systems where the interleaving process is implemented before the inverse discrete Fourier transform (IDFT), the proposed scheme is based on performing the interleaving process post the IDFT. The aim of this process is to average the effect of the impulsive noise burst over a large number of OFDM symbols, which can reduce its impact on the bit error rate (BER) significantly. For the system and channel models considered in the work, simulation results have confirmed that the proposed system can effectively reduce the BER degradation due to the impulsive noise to about 1 dB as compared to the impulsive noise-free case.

Performance comparison between slotted IEEE 802.15.4 and IEEE 802.1 lah in IoT based applications

In this paper, we present a performance comparison between IEEE 802.15.4 which specifies the physical and media access control layers for low-rate wireless personal area networks (LR-WPANs) like ZigBee, and IEEE 802.11ah, a new global WLAN standard using sub-1 GHz frequency band, in terms of throughput and energy consumption. Both standards are targeting low power applications with relatively high number of nodes as in IoT and M2M applications. The simulations results demonstrate the better performance of IEEE 802.11ah throughput mainly in congested networks. However in particular cases, the IEEE 802.15.4 outperforms the IEEE 802.11ah from energy consumption point of view.

Enhanced Algorithm for Digital Mitigation of ICI Due to Phase Noise in OFDM Receivers

In this letter, an enhanced yet computationally efficient algorithm is proposed for suppressing ICI due to phase noise in OFDM receivers. The method is particularly targeted to improve the detection error rate performance when high-order constellation size and long cyclic prefix are used. The approach optimizes the interpolation of estimated excess phase between adjacent OFDM symbols and re-compensates for residual CPE after interpolation. The proposed enhancement is verified in OFDM system with 64-QAM subcarrier modulation and 1/4 cyclic prefix, and shown to outperform state-of-the-art. Implementation complexity and its optimization are also discussed.

Efficient OFDM Symbol Timing Estimator Using Power Difference Measurements

This paper presents an efficient blind symbol timing estimation scheme for orthogonal frequency-division multiplexing (OFDM) systems with constant modulus constellation. The proposed technique is designed to estimate symbol timing offsets by minimizing the power difference between subcarriers with similar indices over two consecutive OFDM symbols based on the assumption that the channel slowly changes over time. The proposed power difference estimator (PDE) is totally blind because it requires no prior information about the channel or the transmitted data. Monte Carlo simulation is used to assess the PDE performance in terms of the probability of correct timing estimate Plock-in. Moreover, we propose a new performance metric denoted as the deviation from safe region (DSR). Simulation results have demonstrated that the PDE performs well in severe frequency-selective fading channels and outperforms the other considered estimators. The complexity of the PDE can be significantly reduced by incorporating a low-cost estimator to provide initial coarse timing information. The proposed PDE is realized using feedforward and early-late gate (ELG) configurations. The new PDE-ELG does not suffer from the self-noise problem inherent in other ELG estimators reported in the literature.

PAPR Reduction Scheme using Maximum Cross Correlation

This letter presents an efficient technique to reduce the impact of nonlinear power amplifiers on the bit error rate (BER) of orthogonal frequency division multiplexing (OFDM) systems. The proposed technique is based on the well-established Partial Transmit Sequence (PTS), a power amplifier model, and a simple single point cross correlator. Unlike the conventional PTS, the optimum phase sequence in the proposed system is selected by maximizing the correlation between the input and output of the power amplifier model. Simulation results have confirmed that the BER using the proposed technique is almost identical to the state-of-the-art while the complexity of the proposed optimization metric is significantly reduced.

Performance analysis of IoT-enabling IEEE 802.11ah technology and its RAW mechanism with non-cross slot boundary holding schemes

IEEE 802.11ah task group is working on a new amendment of the IEEE 802.11 standard, suitable for high density WLAN networks in the sub 1 GHz band. It is expected to be the prevalent standard in many Internet of Things (IoT) and Machine to Machine (M2M) applications where it will support long-range and energy-efficient communication in dense network environments. Therefore, significant changes in the legacy 802.11 standards have been proposed to improve the network performance in high contention scenarios, most important of which is the Restricted Access Window (RAW) mechanism described in the amendment. In this paper we analyze the performance of the RAW mechanism in the Non-Cross Slot Boundary case under various possible holding schemes. We propose new holding schemes as well as a new grouping scheme for RAW mechanism based on backoff states of the stations. The proposed schemes are shown to improve the saturation throughput and energy efficiency of the network through extensive simulations. These schemes can therefore be adapted in practical deployment scenarios of the IEEE 802.11ah use cases to improve the overall network performance. Overall, these advanced features make 802.11ah standard a true IoT-enabling technology towards seamless integration of massive amount of connected devices in the future.