Enabling SWIPT via OFDM-DC

This thesis presents two original ontributions on orthogonal frequency division multiplexing (OFDM). The first is a thorough investigation of the error performance and channel capacity of asymmetrically clipped optical OFDM (ACO-OFDM). ACO-OFDM is a modulation scheme designed specifically for optical communications. The second concerns the use of multiple-input multiple-output (MIMO) OFDM in radio frequency (RF) systems. A new scheme which uses polynomial cancellation coding (PCC) OFDM with time offsets is proposed. This new scheme is robust to both carrier frequency offset (CFO) and channel estimation errors. OFDM has been used extensively to reduce the effect of dispersion in wired and wireless RF systems. Although dispersion is also a problem in optical wireless systems, OFDM has not until recently been considered for use in these. This is because optical wireless systems use intensity modulation (IM) and so the transmitted signals must be nonnegative and as a result conventional OFDM signals which are bipolar cannot be used directly. ACO-OFDM and DC biased optical OFDM (DCO-OFDM) are two non-negative forms of OFDM developed for optical systems. Both are robust to ISI but ACO-OFDM is in most cases much more power efficient. In this thesis results are presented for the performance of ACO-OFDM, DCO-OFDM and conventional optical modulation schemes such as on-off keying (OOK) and pulse position modulation (PPM) for both dispersive and non-dispersive channels. These show that ACO-OFDM is more tolerant to dispersion and requires less optical power than the other modulation schemes. To investigate the theoretical limits of an ACO-OFDM system, closed form analytical expressions for the channel capacity of ACO-OFDM are derived both for a flat channel and for representative dispersive optical wireless channels. The capacity of ACO-OFDM cannot be compared with the general case of an intensity modulated signal, because no general solution for this has yet been found. Instead the mutual information of an ACO-OFDM signal is calculated and compared with two other signal distributions: an exponential distribution and a clipped-Gaussian distribution. The combination of OFDM and MIMO has been used in several radio standards. However, MIMO OFDM systems like single-input single-output (SISO) OFDM systems are very sensitive to CFO. An improved MIMO PCC OFDM system is proposed in this thesis. In this system, the signals transmitted from different antennae have different time offsets. At the receiver, OFDM symbols are demodulated by using each of these time offsets in a matched detection window. This system shows better performance than a MIMO PCC OFDM system without time offsets in two cases: when there are channel estimation errors and in MIMO systems with more transmit antennae than receive antennae.

This paper applies wavelet transform (WT) on Orthogonal Frequency Division Multiplexing (OFDM) and single carrier (SC) digital signals twice (WT-T) to extract the transient characteristics of them, and then by using the transient characteristics in WT-T domain, it is easy to identify the two types of signals. The simulations show that the proposed identification algorithms can obtain good performances in low signal to noise ratio (SNR) and multipath Rayleigh fading channel. In addition, the effects of sample rate and symbol rate on the identification algorithms are analyzed and simulated. To obtain the best performances of the identification algorithms, sample rate is set to be equal to 2.4 times of carrier frequency approximately, therefor, the difference of characteristics between OFDM and SC signals reaches maximum, while OFDM and SC signals can be well separated if only the symbol rate is greater than 20 kHz.

With simultaneous wireless information and power transfer, the energy of RF signal can be used effectively for the self-sustained operation of wireless devices. In practical applications, power splitting method can be used for simultaneous wireless information and power transmission (SWIPT) between base station and multi-user. Different user systems have different energy consumption, so users with insufficient power need more energy transmission to supplement their power. Nowadays, the beamforming strategy of simultaneous wireless information and energy transmission does not consider the problem of insufficient power at the terminal. This paper proposes a energy state feedback method to optimize simultaneous wireless information and power transmission system. Through the joint design optimization of beamforming and power splitting, the power transmission of users with insufficient power is added, and the minimized transmission power optimization is done under the conditions of satisfying SINR and energy harvesting constraints by utilizing the channel state information and node power information of each node. This optimization model is difficult to solve. In order to solve this problem, the concept of reserve group is introduced. When the optimization model cannot be solved, the users with the worst channel state of the node are put into the reserve group. These users do not participate in the optimization first. After the new channel state information is obtained, the optimization model is established again. If the problem can be solved, the transmission power of base station doesn’t reach the maximum power, some users in the reserve group is added to continue to optimize, if it has reached the maximum power of base station transmission, it is not optimizing, so as to maximize the optimization of all users and improve system performance.

Light emitting diode (LED) nonlinearities have a significant impact on the performance of optical wireless (OW) communication systems based on orthogonal frequency division multiplexing (OFDM) modulation. In this paper, different techniques to compensate for the induced nonlinearity distortions are presented and analyzed. First, single-carrier frequency division multiple access (SC-FDMA) is proposed instead of OFDM for OW systems. In SC-FDMA, some of the major OFDM problems such as high peak-to-average power ratio are inherently resolved. It is shown that the performance of OW OFDM systems and their counterpart SC-FDMA systems are traded off for certain input signal powers and modulation orders. Second, OW OFDM systems with hard, soft, and turbo channel coding techniques are considered. It is reported that significant performance gains can be achieved through channel coding. Finally, a novel method to reduce signal clipping distortion through the use of iterative signal clipping (ISC) and multiple transmit LEDs is proposed. The ISC technique is based on iterative clipping of the time domain OFDM signal and transmission from a multiple LED transmitter. Transmit LEDs are synchronized, located close to each other, and placed to emit light in the same direction. Hence, the channel path gains from each LED to the receiver photodiode are similar. The received signals from the different LEDs add coherently at the receiver. Reported results demonstrate that the effect of distortion is eliminated or significantly reduced based on the considered number of transmit LEDs.

Cooperative relaying (CoR) is extensively utilized to extend the communication range, spectral efficiency, and system capacity. To achieve a highly reliable and sustainable CoR, the antenna system at energy-constrained relay nodes should provide broader coverage with the capability to replenish its battery. This work proposes a 2×2 reconfigurable simultaneous wireless information and power transmission (SWIPT) antenna array comprising four frequency-splitting antenna elements. A reconfigurable feed network is designed to achieve pattern and polarization reconfigurable wireless information transmission (WIT) in 5 GHz WiFi band. On the other hand, WPT is implemented at 5 GHz utilizing a completely integrated conjugate impedance-matched full wave rectification circuit. Moreover, the DC outputs of all four SWIPT antenna elements are combined in parallel to enhance the overall harvested DC power with negligible circuit losses. The performance of the proposed antenna system is validated using software-defined radio to showcase its capability to implement battery-assisted cooperative relaying in IoT networks.

Multi-level modulation on orthogonal frequency division multiplexing (OFDM) signals is experimentally demonstrated by an integrated silicon Mach-Zehnder modulator. The measured bit error rate is well below the forward error correction (FEC) threshold.

In this paper, we study a multi-hop amplify-and-forward (AF) simultaneous wireless information and power transmission (SWIPT) relay system. Each relay node harvests power using a power split (PS) method from a portion of the received signal, amplifies the remaining received signal, and passes it to the next relay. Based on this system model and signal flow, we derived and solved the convex power minimization problem with the optimal PS ratio. In this case, it was found that using the optimal PS ratio consumed a lower amount of power than when using a fixed PS ratio (0.5). We then investigated the impact of processing cost on the AF-SWIPT system using decoding and forwarding SWIPT as benchmarks, and found that AF-SWIPT was superior.

A novel ranging technique based on orthogonal frequency division multiplexing (OFDM) is proposed for the ranging systems in space by using the properties of OFDM in time and frequency domains. The coarse estimation of the time delay is obtained by the correlation of the waveforms of OFDM signals in the time domain, and the fine estimation of the time delay is obtained by the phase differences between the subcarriers in the frequency domain by the proposed method. The simulation results show that the performance of the proposed technique is better than that of the pseudonoise ranging method and that of the phase ranging method.

Simultaneous wireless information and power transmission (SWIPT)-enabled vehicle-to-vehicle (V2V) systems use radio frequency (RF) signals for both information transmission and power. It reduces energy consumption, increases spectrum efficiency, and optimizes resource allocation to improve overall system performance. In this article, we investigate the physical-layer security (PLS) for a SWIPT enabled V2V cooperative communication system in which a source vehicle (S) transmits information to a destination vehicle (D) through an intermediate vehicle treated as relay node (R). During analysis, it is assumed that two independent vehicular nodes in the same road, i.e., eavesdroppers (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E_{1}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E_{2}$ </tex-math></inline-formula>) are trying to intercept the information from different legitimate channels. The communication links are assumed to follow the double Nakagami-m (DNm) fading distribution. The study examines the security performance of the networks by calculating the secrecy outage probability (SOP), strictly positive secrecy capacity (SPSC), intercept probability (IP), and connection outage probability (COP). Next, we extend to the analysis of tradeoff between security and reliability as well as tradeoff between secrecy rate and secrecy outage which are termed as security and reliability tradeoff (SRT) and effective secrecy throughput (EST). For a comprehensive analysis, the results are produced for different values of the fading parameter <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(m)$ </tex-math></inline-formula>, power splitting factor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(\rho)$ </tex-math></inline-formula>, and secrecy thresholds. The results clearly indicate that an increase in m leads to an enhancement in the secrecy performance. Additionally, the results show that secrecy performance improves as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho $ </tex-math></inline-formula> decreases. Finally, the Monte-Carlo simulation results are presented to verify our proposed analytical models.

SummaryWireless Sensor Network (WSN) is an emerging lower cost and resourceful solution, which enables controlled observation of the environment. The high amount of energy is required in wireless networks during the transmission of data. Here, Golden Ant Lion Whale Optimization (GALWO) and Golden Taylor Sea Lion Optimization (GTSLnO) techniques are presented for cluster head (CH) selection and prediction of neighbor nodes' age. The six stages performed in this work are setup, steady‐state, prediction, power transfer, communication or route discovery, and route maintenance stages. In the setup level, CH selection is carried out by GALWO, which is the combination of Ant Lion Whale Optimization (ALWO) with Golden Search Optimization (GSO). Moreover, ALWO is an integration of Ant Lion Optimizer (ALO) with the Whale Optimization Algorithm (WOA). In the steady state, the distance, energy, delay, throughput, and trust update are considered as objective functions. In the prediction stage, the Deep Convolutional Neural Network (Deep CNN) is utilized for age prediction of neighbor nodes, wherein Deep CNN is tuned by employing GTSLnO. The GTSLnO is an incorporation of GSO and Taylor series with Sea Lion Optimization (SLnO). Then, the power transfer stage is done utilizing simultaneous wireless information and power transmission (SWIPT). Thereafter, the communication/route discovery stage is conducted for path selection through neighbor node, and lastly, the route maintenance stage is carried out. The GTSLnO–Deep CNN achieved a minimal delay of 0.089 s, maximal residual energy, throughput, and trust of 0.500 J, 98,843 kbps, and 0.452 for DoS attack.

Localization networks based on orthogonal frequency-division multiplexing (OFDM) ranging systems provide desirable location-awareness with commodity WiFi chipsets in harsh propagation conditions. Understanding the fundamental limits of OFDM ranging can guide the design and operation of these systems. Existing studies on these fundamental limits generally do not account for the processing impairments such as the estimation error of the phase offset and packet detection delay, yet ignoring processing impairments may lead to inaccurate evaluation of OFDM ranging accuracy. To address such inconsistency, we develop a framework to determine the fundamental limit of OFDM ranging, accounting for both channel parameters and processing impairments. In particular, we derive the equivalent Fisher information (EFI) for the propagation delay of the first path and quantify the effects of the number of multipaths, the number of channels, and processing impairments on the ranging accuracy through case studies. Numerical results verify the insights gained from the theoretical analysis.

The IEEE 802.16 standards are based on Orthogonal Frequency Division Multiplexing (OFDM) and multi-user OFDM (also known as OFDMA) for their desirable characteristics and potentials. Although well established, these standards only provide a framework of necessary mechanisms for deployable systems. Majority of the resource allocation issues are left unspecified. The conventional one-dimension scheduling cannot be readily applied in an 802.16 system. In this paper, a proportional fairness scheduling algorithm for 802.16 systems is proposed that utilizes the flexibility of frame division. Monte Carlo simulations are performed to evaluate these new methods in comparison to previously proposed techniques. The results indicate that the proposed methods lead to satisfactory performances, thanks to their improved two-dimensional feature.

This paper proposed a Guard Interval Less (GI-less) transmission on orthogonal frequency division multiplexing (OFDM) for Long Term Evolution (LTE). The system will utilise the application of parallel packet transmission and the useful operation of the characteristics of IFFT. In addition with perfect frequency equalizer FEQ, the intersymbol and interchannel interference can be eliminated. Therefore, the proposed system offered the similar performance of QOS at a reasonable complexity enhancement. In this paper, an in-depth overview of OFDM with focus on physical layer will be examined.

Turbo codes are well known to be one of the error correction techniques which achieve closer results to the Shannon limit. Nevertheless, the specific performance of the code highly depends on the particular decoding algorithm used at the receiver. In this sense, the election of the decoding algorithm involves a trade off between the gain introduced by the code and the complexity of the decoding process. In this work we perform a thorough analysis of the different iterative decoding techniques and analyze their suitability for being implemented in the user terminals of new cellular and broadcast systems which are based on orthogonal frequency division multiplexing (OFDM). The analyzed iterative decoding algorithms are the max-log-MAP and the soft output Viterbi algorithm (SOVA), since both of them have a relative low computational complexity, simplifying their implementation in cost efficient terminals. Simulation results have been obtained for different encoder structures, block sizes and considering realistic channel conditions (an OFDM transmission over a wireless channel).

14 - LTE radio access: An overview