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Orthogonal frequency division multiplexing/offset quadrature amplitude modulation (OFDM/OQAM) has the advantage of high spectral efficiency due to non-requirement of cyclic prefix (CP) and guard band. However, the high direct current (DC) used in OFDM/OQAM is power inefficient for visible light communication (VLC). In this letter, an enhanced OFDM/OQAM (EO-OFDM/OQAM) scheme is proposed for VLC, which is inspired by the idea of the pulse-amplitude-modulation based hybrid optical OFDM (PHO-OFDM) scheme. In this system, the half of subcarriers of the normal branch carry useful data while the remaining subcarriers are selected to carry negative clipping noise instead of useful data for improving the power efficiency, and a flexible power allocation method is introduced. The simulation results show that compared with the PHO-OFDM, the proposed scheme has a better bit error rate (BER) performance under the same average bit rate without additional operations of interference regeneration and cancellation.

Folded quad-mode stub-loaded loop resonators (QMSLLRs) are proposed for realizing both bandpass and dual-band bandpass filters with compact dimensions. The QMSLLR is a folded square loop loaded with four short stubs, providing structure symmetry in both transversal and longitudinal directions. Determined by the lengths of the loaded stubs, the four resonant frequencies as analyzed with even-odd mode method can be either distributed in one passband with equal space, or in two passbands with a guard band in between, for realizing a single-band bandpass filter or a dual-band bandpass filter, respectively. For both the input and output couplings, two perpendicular feeding lines are parallel coupled to the QMSLLR at one corner. The measure results prove that the structure is suitable for the design of a medium band or even narrow band bandpass filters with compact dimensions.

Filtered orthogonal frequency division multiplexing (f-OFDM) is considered one of the candidates for future mobile communication because of its flexible parameter configuration for different scenarios. However, the interference analysis of f-OFDM is considerably challenging due to its special transceiver structure, especially in the uplink with non-ideal synchronization. The uplink interference of f-OFDM systems under non-ideal synchronization, in which carrier frequency offset (CFO) and timing offset (TO) of multiple user equipment (UE) are considered, is investigated in this study. The interference is classified into several sub-interferences. The closed-form expressions of each sub-interference and its variance are first derived, and then verified via simulations. On the basis of the derived closed-form expressions, first, the influences of non-ideal factors and system parameters, such as CFO, TO, guard band (GB), and subcarrier spacing (SCS), on the uplink interference of f-OFDM systems, are simulated and analyzed. This study is verified by computer simulations, and the theoretical derivation of interference agrees with the simulation result. Second, Hanning window filters are employed by previous f-OFDM systems, resulting in bit error rate (BER) imbalance between sub-bands. Hence, the effect of waveform filter on the interference and BER is also investigated in this research. Results indicate that better interference and BER performances than Hanning window filters can be obtained by employing reasonable filter settings. Furthermore, several filter design rules are concluded. Overall, the analysis and simulations reveal many intrinsic interference characteristics of f-OFDM, which will benefit the future f-OFDM system designs.

This study has investigated the mitigations necessary for successful compatibility between International Mobile Telecommunications (IMT) services and Fixed Satellite Service (FSS) Earth Stations operating in adjacent frequency bands. We consider a problem where IMT services operate in the 3.4–3.6 GHz frequency band and FSS Earth Stations operate in the adjacent 3.6–3.8 GHz band (both bands are within the frequency range designated C-band). The results presented in this paper are applicable to other boundaries between IMT and FSS operating in C-band. This is an adjacent band compatibility problem, hence the mitigation considered is based on frequency separation. We firstly perform a co-frequency interference analysis and then determine the Net Filter Discrimination available for a range of possible frequency separations including Guard Bands. These calculations rest on some assumptions regarding the IMT transmitter and FSS receiver spectrum masks. We present some results which show that an 18 MHz Guard Band is sufficient to mitigate interference. This analysis is based on the median aggregate interference-to-noise ratio $$\Sigma I/N$$ delivered by our co-frequency analysis, using a − 10 dB threshold and covering all of the spectrum mask combinations considered in the study.

Filter bank multicarrier (FBMC) is one of the effective candidates for the fifth generation of wireless communication networks. 5G (5th-generation wireless systems) is accepted as the next major stage of mobile telecommunication technology. The extent of 5G will be expanded mobile broadband services to next-generation automobiles and connected machines. In particular, filter bank multicarrier with offset quadrature amplitude modulation (FBMC/OQAM) is determined as the future generation 5G air interface by researchers recently. Filter bank multicarrier (FBMC) is admitted as one of the alternative technologies for multicarrier modulation. Compared to orthogonal frequency-division multiplexing (OFDM), FBMC has better spectrum shape and supports mobility. Therefore, efficient hardware implementations have highly interested researchers. Cyclic prefix (CP) and guard band are used for orthogonal frequency-division multiplexing (OFDM) and this causes loss of spectral efficiency, but FBMC applications do not need CP and guard band. Due to the fact that FBMC has offset QAM (OQAM) and band-limited filtering features on each subcarrier, the need for CP and guard band is eliminated. In this paper, novel pipelined hardware architecture of the filter design of FBMC/OQAM modulator has been proposed.

Cognitive radio (CR) is a promising technology that allows devices to effectively utilize the underutilized or unutilized portions of the licensed spectrum. In literature, several channel assignment and spectrum sharing algorithms for CR Networks (CRNs) have been developed to improve spectrum efficiency without considering the problem of Adjacent Channel Interference (ACI). Guard-Band (GB)-aware mechanisms have been proposed in CRNs to prevent ACI and improve spectrum efficiency. However, most of the existing GB-aware algorithms assume having channels with fixed-rate and employ a sequential channel assignment paradigm. Unfortunately, this assumption is not realistic, because channel’s conditions may vary over time. In this work, we propose a GB-aware channel assignment that considers the channel-dependent achieved transmission rates (due to Rayleigh fading time-varying conditions) at different time slots while simultaneously assigning channels to several CR transmissions. This batch based proposal aims at increasing network capacity and minimizing the number of assigned channels per user subject to rate demand and interference constraints. Simulation experiments demonstrate the effectiveness of our proposed scheme, which show a significant improvement in network performance in terms of the number of served CR users.

We propose the use of the specific form of the integrated device known as the boxcar filters for big data transmission, where the advantage of such device is the number of roll-off (bandwidth) can be increased to meet the large demand of the future bandwidth requirements. A boxcar filter system is formed by the serial Panda-ring resonators, where the initial and end rings are used to form the whispering gallery mode beams for the light fidelity (LiFi) up-down-link conversion. There are 5 boxcar circuits within the system. Each of boxcar devices has the electro-optic connection that can be used to perform the external signal processing applications, where all electronic signals are changed to be the light signals and connected to the network via the free-space up-down link nodes. In a simulation, the selected light source is fed into the boxcar filters via the input port, in which the single roll-off bandwidth of 300 THz is obtained. The frequency guard band is given by each boxcar separation. In applications, the electromagnetic immunity interference (EMI) signals can be obtained by the electro-optic conversion circuit, which is the medical instrument specification requirement. The low EMI signals can be connected to the network and transmission using the LiFi network to the remote area. In addition, the medical information to home using the big data via the ad hoc LiFi network and the internet of thing platform arrangements are also proposed.

A novel beat interference cancellation receiver (BICR) is proposed to cancel the signal-signal beat interference (SSBI) for polarization division multiplexed (PDM) optical orthogonal frequency division multiplexing (OOFDM) system, where two single sideband (SSB) OOFDM signals are polarization multiplexed along with their offset optical carriers (OCs) located at opposite sides. At receiver, the PDM SSB-OOFDM signal is equally power split into four beams with one or two OCs filtered out, and then fed into two balanced photodiode pairs for recovering the RF-OFDM signals with SSBI cancellation. The PDM SSB-OOFDM system is insensitive to fiber polarization mode dispersion since the proposed BICR is implemented without polarization-sensitive devices. Moreover, the spectral efficiency is greatly improved because of PDM and the small guard band since the SSBIs are eliminated. The proposed BICR scheme is validated with a simulation link of 112 Gbps 16-QAM PDM SSB-OOFDM signals. After 120km SSMF transmission, the EVM keeps below forward error correction limit of 16.3%.

A considerable part of latency in the baseband of massive multiple-input multiple-output (MIMO) systems is introduced by orthogonal frequency division multiplexing (OFDM) (de)modulation. To address the low-latency demand of massive MIMO systems, a fast Fourier transform (FFT) processor and corresponding reordering scheme are proposed, which reduce the processing latency and reordering latency of OFDM-based systems, respectively. The main idea is to utilize the OFDM guard bands to decrease the number of required computations and thus the processing time. In case of a 2048-point IFFT, the proposed scheme leads to 42% reduction in latency compared to the reported pipelined schemes at the cost of 4% additional memory, which is around 2.4% of the total chip area. To realize this idea, a modified pipelined architecture with a reorganized memory structure and also an efficient data scheduling mechanism for memories and butterflies are developed. Using the proposed scheme, a 2048-point FFT/IFFT processor has been implemented in a 28-nm complementary metal-oxide-semiconductor technology. The post-layout simulations show that our design achieves a throughput of 0.6 GS/s and 1200 clock cycles latency, the lowest latency reported to-date for single-input pipelined FFT/IFFT architectures.

In this letter, a signal-to-signal beating interference (SSBI) cancellation technique is proposed in direct detection transmission system based on balanced photodiodes. We use a pilot-supported single-sideband direct detection scheme to transmit up to 400-Gb/s signal in three branches through a 10-km 7-core fiber. Using the manner of transmitting the signal in one core and the combination of signal and pilot in another core, the SSBI terms can be efficiently mitigated in both 100-Gb/s and 400-Gb/s direct detection optical orthogonal frequency division multiplexing transmission systems. Compared to the conventional pilot-supported direct detection scheme, no guard band is required based on our proposed SSBI elimination technique. The efficiency of the receiver’s bandwidth is significantly enhanced.

We experimentally demonstrate the generation of a single-sideband orthogonal frequency division multiplexed (OFDM) signal using an on-chip silicon photonics microring-based IQ modulator. Over 18-dB sideband suppression ratio is achieved for the wideband OFDM: 15.7-GHz data band and 2.7-GHz guard band. The 31.4-Gb/s signal was transmitted over 20 km of standard single-mode fiber with a bit error rate below the forward error correction threshold. While single-sideband continuous-wave signals have been produced with such hardware, this is the first demonstration of stable data transmission on the single sideband carrier.

Filtered-orthogonal frequency division multiplexing (F-OFDM) is a candidate for 5G new waveform, which has flexible numerologies to support various scenarios and can combat interference of multi-users effectively with filters. However, although longer filter length and higher roll-off factor can suppress out of band radiation, inter-symbol interference (ISI) and inter-carrier interference (ICI) will increase at the same time. Meanwhile, the wider guard band reduce inter-user interference (IUI) at the cost of higher spectrum occupancy. To meet target bit error rate (BER) requirements of all users and maximize the spectrum efficiency, a filter parameter and guard bandwidth optimization model was proposed to design related parameters dynamically for uplink asynchronous F-OFDM system, where users are allocated with different numerologies. We present a detailed theoretical derivation on ISI, ICI, and IUI for BER calculation, and the theoretical derivation of IUI in multi-user scenario with different subcarrier spacing between users is first presented. The formulated problem is proved to be a non-convex NP hard problem and Imperialist Competitive Algorithm (ICA) is applied for a desirable solution. The simulation results show that the theoretical derivations are valid and the proposed filter parameter and guard bandwidth optimization model can achieve higher spectrum efficiency than the fixed filter parameters in F-OFDM while outperforms traditional OFDM.

The existence of inter-numerology interference (INI) is a major drawback for the flexible multi-numerology frame structure proposed for the upcoming fifth generation New Radio (5G-NR). Insertion of a guard band (GB) between adjacent numerologies has been widely used in the literature as one of the effective ways to reduce the INI. However, the conventional way of implementing GBs is inefficient in terms of spectrum usage. In this letter, we exploit the inherent INI characteristics of the scalable multi-numerology structure to propose a more spectrally efficient way of implementing GBs. It is shown through simulations that the proposed GB insertion technique enhances the GB utilization up to 50% while achieving the same bit error rate performance as the conventionally implemented GB. 218E035

The final publication is available at Springer via http://dx.doi.org/10.1007/s11107-020-00890-z Filterless optical networks (FONs) have been proposed as a feasible solution for optical metro networks. In addition, as a result of the shorter distance compared to core optical networks, direct detection optical transmission systems can be used in metro FONs, which reduces costs, as compared to coherent detection systems. In this work, we present two optical signal tracking approaches for FONs that allow to detect small frequency laser drift problems and enable safely reducing channel spacing. Additionally, we study the most proper resolution for optical spectrum analyzers continuously scanning the whole C-band. Proposed approaches are: (1) feature-based tracking and (2) residual-based tracking. Experiments are carried out to compare the performance of the approaches for both direct detection and coherent detection systems, in the case of a single optical signal with no neighboring signals nearby in the spectrum, as well as in the case of a group of optical signals closely allocated in the spectrum. The results show that the residual-based approach enriched with contextual information enables to better track and correct the wavelength drifts before they reach their limits (e.g.,¿±¿2.5 GHz), leading to the guard band reduction for what concerns wavelength drifts. The research leading to these results has received funding from the European Commission for the H2020-ICT-2016-2 METRO-HAUL project (G.A. 761727), from the AEI/FEDER TWINS project (TEC2017-90097-R), and from the Catalan Institution for Research and Advanced Studies (ICREA).

We propose a signal-to-signal beating interference (SSBI) cancellation scheme in two-mode fiber (TMF) transmission system based on balanced detection without requirement of a guard band. The SSBI can be eliminated based on the mode selectivity characteristic of mode coupler. The mode selectivity in mode coupler relies on the coupling behavior between the fundamental mode LP01 and the first-order mode LP11, which is highly dependent on the spatial orientation of the fiber modes. We design and fabricate a fused-type fiber mode coupler (FFMC) based on circular-core TMF. Based on the fabricated FFMC, we experimentally demonstrate a multi-band 100-Gb/s optical orthogonal frequency division multiplexing signal transmission over 10-m TMF with SSBI cancellation. Significant performance improvement is observed when compared with conventional direct detection scheme under the condition of insufficient bandwidth of a guard band.

A 5G communication system includes massive machine-type communication, enhanced mobile broadband, and ultra-reliable low-latency communication. To meet the requirements of 5G applications, researchers have considered various scalable subcarrier spacings and transmission time intervals. In this article, we introduce the concept of waveform multiplexing, which is a resource management system for numerology multiplexing that employs appropriate waveforms to various numerologies. It also possesses both a dynamic cyclic prefix and a minimum guard band, which are the key features for achieving high spectral efficiency. We verify the significant gain produced by proposed waveform multiplexing by performing extensive 3D ray-tracing- based system-level evaluations in realistic 3D environments. Finally, we provide guidelines on waveform multiplexing design by considering the time-domain and frequency-domain characteristics of the new radio waveform candidates.

In this paper, we have proposed a polarization-division multiplexing (PDM) single-sideband optical orthogonal frequency division multiplexing (SSB-OOFDM) scheme with signal-signal beat interference cancellation receivers with balanced detection (ICRBD). This system can double channel capacity and improve spectrum efficiency (SE) with the reduced guard band (GB) due to the PDM. Multiple input multiple output (MIMO) technique is used to solve polarization mode dispersion (PMD) associated with channel estimation and equalization. By simulation, we demonstrate the efficacy of the proposed technique for a 2 × 40 Gbit/s 16-QAM SSB-PDM-OOFDM system according to the error vector magnitude (EVM) and the constellation diagrams.

Body area networks (BANs) are systems of wearable computing devices for long-term monitoring of personal health care. BAN is an emerging technology for the worldwide ageing population. In the BAN system, the transceiver is the most energy-consuming part of a sensor node and radio transmission in the vicinity of the human body is highly lossy and inefficient. Therefore, the energy of the sensor node constraints the life cycle and quality of service of the network; consequently, low-cost protocol shaves attracted wide interest. This study proposes a frame structure model of a self-adaptive guard band protocol, which introduces a GB in each time slot according to the allowed maximum time drift of the crystal, adaptively adjusts the value of the GB based on the actual time drift, and then ensures that the node simultaneously maintains the sleeping state and synchronisation with the coordinator during beacon transmission, thus reducing the energy consumption.

This study suggests the optimization of the acceptance in testing from the economic point of view. For this purpose, a type of the global consumer's risk different from that expressed in JCGM 106 is used. The consumer's risk in this study considers the risk of market-available items, and may be helpful for the economical assessment. We have developed a mathematical expression of the revenue increasing by testing items under the existence of the measurement uncertainty. The acceptance can be optimized in terms of the maximization of the revenue. A simple but accurate approximate solution is given.

To further improve receiver sensitivity of spectrally-efficient guard-band direct-detection optical orthogonal frequency-division multiplexing (OFDM) with twin single-side-band (SSB) modulation technique, an optical IQ modulator (IQM) is employed to optimize optical carrier-to-signal power ratio (CSPR). The CSPRs for the guard-band twin-SSB-OFDM signal generated by using dual-drive Mach–Zehnder modulator (DD-MZM) and optical IQM are theoretically analyzed and supported by simulations. The optimal CSPR for the two types of guard-band twin-SSB-OFDM are identified. The simulations exhibit that the error vector magnitude (EVM) performance of the IQM-enabled guard-band twin-SSB-OFDM is improved by more than 4-dB compared to that of the twin-SSB-OFDM enabled by DD-MZM after 80-km single-mode fiber (SMF) transmission. In addition, more than 3-dB and 10 dB receiver sensitivity improvements in terms of received optical power (ROP) and optical signal-to-noise ratio (OSNR) are also achieved, respectively.

Two-dimensional magnetic recording (TDMR), which combines shingled magnetic recording (SMR) with 2-D signal processing attracts attention from the hard disk drive industry. SMR is a magnetic recording system in order to increase the track density by writing tracks without the guard band. Therefore, the influences of writing and reading intertrack interferences (ITIs) deteriorate the quality of reproducing waveforms. Additionally, degradation of track due to overwriting and crosstalk from the adjacent tracks due to the width of reader sensitivity. The equalization using 2-D finite impulse response filter for the waveforms from three adjacent tracks is proposed as a method to reduce the influence of reading ITIs. In this paper, we evaluate the bit aspect ratio (BAR) in TDMR read/write channel under a specification of 4 Tb/in2 using bit error rate of the low-density parity-check (LDPC) coding and iterative decoding system obtained by computer simulation. The results show that the suitable BAR in array head reading is 2.0.

One of the fundamental problems in cryptography is the generation of a common secret key between two legitimate parties to prevent eavesdropping. In this paper, we propose an information-theoretic secret key generation (SKG) method for time division duplexing (TDD)-based orthogonal frequency-division multiplexing (OFDM) systems over multipath fading channels. By exploring physical layer properties of the wireless medium, i.e., the reciprocity, randomness, and privacy features of the radio channel, an SKG method is proposed to maximize the number of secret bits given a target secret key disagreement ratio (SKDR). In the proposed SKG method, the phase information of the estimated channel state information (CSI) is distilled for SKG, and a special guard band (GB) scheme is designed to achieve the target SKDR with a small phase information loss. The proposed GB consists of both the amplitude GB (AGB) and phase GB (PGB), where the AGB is determined by the average signal-to-interference plus noise ratio (SINR), whereas the PGB adapts itself to the instantaneous SINR and thus incurs a smaller phase information loss in the higher SINR region. Analyses show that this GB scheme trades off a small loss of channel phase information for a better SKDR performance, and achieves a much larger number of quantization levels for a given SKDR due to the fact that the PGB decreases quickly as the SINR increases. Based on the performance analysis on the SKDR, the average secret key length, the phase information loss percentage (PILP), and the optimal GB and quantization level of the adaptive quantizor are derived for a given target SKDR. Both analytical and simulation results are presented to demonstrate the superiority of the proposed scheme for TDD-OFDM systems over frequency-selective fading channels.

Semiconductor aging is a serious threat to the reliability of a system. We address the aging level of semiconductor components by describing the degree of semiconductor aging under certain operating conditions, including voltage, frequency, temperature, and usage rate. Aging level information can be used to follow the real aging rate of a device, predict the remaining life, and control the device performance under certain degradation conditions by balancing the operation of various device components. Such applications can improve the reliability of automotive semiconductor systems, which should have longer lives than mobile systems. In this brief, we present an aging level estimating flip-flop (FF) that can be used for these and other applications as well. Moreover, we can control the operation of the proposed FF by controlling its clock and control signals. We demonstrate an application of the proposed FF for aging-monitoring, showing that, by halting the operation of the proposed FF, the power consumption is significantly reduced compared with other approaches.

Service diversity is expected in the upcoming fifth-generation (5G) cellular networks, which poses great challenges to the underlying waveforms to accommodate heterogeneous service requirements in a flexible way. By dividing the bandwidth into several subbands, each having a different numerology, this paper reports a field trial in time division duplex downlink conducted on a configurable test bed in a real-world environment for the performance evaluations of orthogonal frequency-division multiplexing (OFDM)-based 5G waveform candidates, i.e., cyclically prefixed OFDM (CP-OFDM), windowing OFDM (W-OFDM), and filtered OFDM (f-OFDM), in the presence of mixed numerologies. Field trial results confirm the feasibility of mixed numerologies and reveal the impact of several important system parameters, e.g., guard bandwidth, data bandwidth, signal-to-noise ratio (SNR), and transmit power. The results also suggest that f-OFDM outperforms CP-OFDM and W-OFDM in terms of both the spectrum efficiency and robustness in a high SNR regime, and the gain increases with a higher inter-numerology out-of-band interference. In some specific scenarios, ideal spectrum utilization can be realized by f-OFDM which completely removes the guard band.

In this paper, a novel seamless guard band (SGB) technique for charge sharing mitigation is studied using 3-D TCAD numerical simulations. The simulations results in 65-nm twin-well bulk CMOS technology indicate that the SGB technique can not only mitigate the single-event transient pulsewidth greatly but also mitigate the charge sharing between logical nodes or logical cells significantly. The simulation results also indicate that the SGB technique is superior to the conventional guard band (GB) technique, for it is more beneficial for parasitic bipolar effect mitigation. Using SGB technique, the single-event double-transient (SEDT) generation is mitigated completely under low LET particle (LET $\le \text{40}\ \text{MeV}\cdot \text{cm}^{2}/\text{mg}$ ) radiation, and the SEDT pulsewidth is mitigated > 50% even with the LET of 80 $\text{MeV}\cdot \text{cm}^{2}/\text{mg}$ , which is > 25% from GB technique. Finally, the SGB technique can be applied to the construction of a radiation-hardened standard cell library conveniently, and its area penalty is 1–1.67 $\times$ , which is the same with that of the GB technique.

A low-power 2-Mb Resistance random access memory (ReRAM) macro is developed in a 90-nm CMOS platform with a 3-nm-thick TaO x /Ta2O5 switching layer of the active area of $0.01~\mu \text{m}^{2}$ . Instability of the ON-state minority bits degrades the high-temperature retention lifetime. The oxygen vacancies in the filament are annihilated by oxygen ions, which have been generated mainly by the OFF-write bias repeated in the ON/OFF switching cyclesbefore the retention. This instability is improved by decreasing the oxygen concentration near Ru bottom electrode as well as lowering the OFF-write bias. Instability of the OFF-state minority bits narrows the memory window by random telegraph noise (RTN). Setting a statistically derived guard band with a pulse-modulated verify sequence is able to handle RTN to ensure the memory window. The 2-Mb ReRAMmacro with 1-b error-correcting code is confirmed to ensure ten years’ retention from −40 °C to 85 °C after 1E3 ON/OFF cycles.

In high volume manufacturing, conventional approach to deal with inverse-temperature dependence (ITD) and aging is to add a postsilicon flat voltage guard band to all dies based on testing a small random sample of dies. Although this scheme guarantees error-free operation, it significantly degrades energy efficiency, as it penalize all dies for the maximum delay degradation due to ITD and aging as seen by the worst case die, while also assuming maximum aging condition. In this paper, a graphics execution core implemented in 22 nm trigate process uses per-die tunable replica circuit (TRC) to monitor delay degradation due to ITD and actual aging conditions. TRC triggers adaptive voltage scaling to dynamically adjust $V_{\mathrm {CC}}$ as needed during run time to maintain correct operation at minimum additional voltage. Measured data show up to 33% (14%) energy savings at 0.4 V (0.8 V) compared with baseline scheme. The TRC is also utilized in a dynamic power gating (DPG) scheme to lower energy overhead due to fast droop guard band. DPG introduces a load line effect during normal operation, thus saving energy, while deactivating this load line upon droop detection by the TRC to maintain ISO performance as baseline. Silicon data show that DPG can improve energy efficiency by 14.5% (7%) at 0.8 V (0.6 V).

The phenomenon of four-wave mixing in passive optical networks with wavelength-division multiplexing of channels has been studied. This paper presents the results of modeling the distribution of combination frequencies over the spectrum as a function of the number of channels and the channel frequency spacing. To suppress crosstalk between the channels at combination frequencies, it is proposed to divide the spectrum into two parts and select a guard band between them. The effect of combination frequencies on the signal transmission quality is considered as a function of the channel power, channel frequency spacing, and transmission length.

A secret key can be generated between two legitimate parties from observations of the common wireless channel. However, key disagreement usually occurs due to the estimation errors. Considering a guard band, the key disagreement rate (KDR) is firstly derived in a closed-form expression. Although increasing the size of the guard band can decrease KDR; the length of the raw key bit sequence is also shortened. To evaluate such an effect, the raw key generation rate is defined and derived. The simulation results verify the theoretical analysis and are useful for the determination of pilot power and guard band size.

On the basis of coherent optical orthogonal frequency-division-multiplexing (CO-OFDM), CO-OFDM/ offset quadrature amplitude modulation (CO-OFDM/OQAM) improves the spectrum efficiency by utilizing specially designed filter banks to eliminate the cyclic prefix (CP) inserted between consecutive OFDM blocks and decreases the demanding of guard band between two channels, being a promising candidate for the next generation optical transmission link. Due to the relaxation of the orthogonal condition from the complex field to the real field, chromatic Dispersion (CD) and polarization mode dispersion (PMD) bring serious intrinsic imaginary interference (IMI) to an optical OFDM/OQAM system. Channel estimation schemes based on the interference approximation method (IAM) have been proved to be effective in suppressing the IMI with low complexity. For the IAMs, increasing the power of the pseudo pilot could decrease the effects of amplified spontaneous emission (ASE) noise and other frequency domain residual error on the channel estimation accuracy. In most of the previous reported IAM works, pilot blocks were designed according to the structure of the center pilot block loaded, while the two side pilots nulled for simplicity. However, the power of the pseudo pilot under this method did not reach the maximum, resulting in non-optimal channel estimation accuracy. In this paper, channel estimation method based on the combined phase offset (CMPO) is proposed and systematically discussed. For the proposed method, three consecutive full loaded blocks are treated as the pilot blocks and the optimal pilot structure have been obtained by utilizing the maximum likelihood algorithm. As validated by numerous Montel Carlo simulations results, system robustness against IMI, phase noised induced interference, and nonlinear effect have been improved significantly, thanks to CMPO.

Among the theory and design of oversampled nonuniform filter banks (NUFBs), most of the existing works only consider the cases with integer decimators, and up to now the issue with rational sampling factors has not been discussed yet. In this paper, we generalize the partial modulation technique to realize arbitrary rational frequency partitioning of oversampled NUFBs with highly desired linear-phase (LP) property. Further for the subbands with sampling factors violating the guard band restriction, a phase-modification scheme is derived to avoid uneliminable large aliasing and meanwhile preserving the LP characteristics of shifted analysis/synthesis filters. By using the proposed method, the design issue of LP oversampled NUFBs can be reduced to that of several prototypes, decreasing the design complexity largely. As illustrated by examples, the proposed algorithm is more general in terms of arbitrary rational decimation and thus has broad application prospects.

In this paper, we propose an emergency wake-up alert system (EWAS) for providing accurate and rapid emergency information. The proposed system can provide an emergency wake-up alert service without an additional frequency allotment by utilizing the guard band of the Advanced Television Systems Committee (ATSC) Terrestrial Digital Television (DTV) system. The design target of the proposed system is to match the indoor reception coverage of EWAS with the outdoor reception coverage of the ATSC DTV system. To achieve this, the proposed system should be about 35.65 dB more robust than the ATSC DTV system. The simulation results show that the proposed system offers an emergency wake-up alert service supporting a data rate of up to 23 bps.

Offset quadrature amplitude modulation-based orthogonal frequency division multiplexing (OFDM) systems cannot be directly combined with the Alamouti code because of the intrinsic imaginary interference. In this paper, we propose a block-wise space-frequency block coding (SFBC) scheme and a block-wise space-time block coding (STBC) scheme for offset quadrature amplitude modulation-based OFDM systems, which achieve bit error rate performances that are close to OFDM systems. The proposed schemes satisfy the orthogonality condition of the Alamouti code in the complex field with guard band/intervals. To improve the spectral efficiency of the block-wise SFBC scheme, we also consider the case without the guard band. It is observed that only the two innermost subcarriers do not satisfy the complex orthogonality condition when the guard band is removed. Then, a simple equalization scheme is proposed to independently equalize the two innermost subcarriers. Simulation results show that the block-wise SFBC scheme works well under channels with mild-to-moderate frequency selectivity, and the block-wise (STBC ) scheme suffers less than 1 dB loss under severe frequency selective channels at the bit error rate of 10 − 3, when only a simple one tap zero-forcing equalizer is employed. Copyright © 2016 John Wiley & Sons, Ltd.

This paper computes the distortion power at the receiver side of an FBMC/OQAM-based OFDMA uplink channel under strong frequency selectivity and/or user timing errors. More precisely, it provides a distortion expression that is valid for a wide class of prototype pulses (not necessarily perfect-reconstruction ones) when the number of subcarriers is sufficiently large. This result is a valuable instrument for analyzing how users interfere to one another and to justify, formally, the common choice of placing an empty guard band between adjacent users. Interestingly, the number of out-band subcarriers contaminated by each user only depends on the prototype pulses and not on the channel nor on the equalizer. To conclude, the distortion analysis presented in this paper, together with some simulation results for a realistic scenario, also provide convincing evidence that FBMC/OQAM-based OFDMA is superior to classic circular-prefix OFDMA in the case of asynchronous users., 27 pages, 12 figures; new version corrects few minor typos and reports final reference

In this paper, we present a new method to implement beat interference cancellation receiver (BICR) for single-sideband optical orthogonal frequency division multiplexing (SSB-OOFDM) signal, which improves the spectral efficiency (SE) by reducing the guard band (GB) between the optical carrier and the OOFDM signal while mitigating the impact of signal–signal beat interference (SSBI). This BICR structure is relatively simple using only an optical interleaver (IL), a 3×3 optical coupler (OC) and three photodiodes (PDs). A system simulation for the 40 Gbit/s 16-QAM SSB-OOFDM signal with the reduced GB is carried out to prove the feasibility of this new scheme. The simulation results show that our proposed BICR has a better performance to suppress SSBI and a higher SE than the conventional direct-detection receiver (CDDR) according to the EVMs and the constellations.

Spectral efficiency is one of the critical issues in passive optical networks (PONs). Thus, next generation PON systems must employ advanced modulation techniques and channel compensation to improve the network performance and provide more bandwidth for end users. In this letter, we have experimentally demonstrated a spectral efficiency improvement in PONs based on the bandwidth scalable orthogonal frequency division multiplexing (BSOFDM-PON), considerably reducing the recommended optical guard band of such direct detection systems. The experimental results show that this efficiency can be achieved in a 33.5-Gb/s BSOFDM-PON on one wavelength channel when subcarrier pre-emphasis is used.

A light-trail in a traditional ITU − T fixed wavelength grid optical network is a generalization of a lightpath. Multiple nodes in a light-trail are allowed to communicate each other along the light-trail, leading to sub-wavelength granularity utilized traffic grooming. Architecturally, a light-trail is analogous to a shared wavelength optical bus. Moreover, a new light-trail is always equipped by a guard band for non-interference of optical signals. Therefore, multiple light-trails must be accompanied by multiple guard bands, which indeed is an absolute wastage of optical spectrum resources. In the recent years, besides RWA (Routing and Wavelength Assignment) in WDM (Wavelength Division Multiplexing) optical networks, the Routing and Spectrum Assignment (RSA) algorithm is widely being adopted in many new and emerging elastic optical mesh networks to perform traffic grooming. In such networks, Orthogonal Frequency Division Multiplexing (OFDM) technology is a promising candidate to execute a RSA algorithm and implement an elastic lightpath as a result. The algorithm is capable of transmitting high-speed data stream using multiple low-speed spectrum overlapped sub-carriers (mini-grids). Hereafter, in this paper we have introduced a novel concept (based on our knowledge and belief) elastic light-trail (a variant of an elastic lightpath) in elastic optical networks and proposed an algorithm “Multi-hop Elastic Light-Trail – MELT” that performs an elastic light-trail expansion and/or contraction (in frequency domain), instead of creating a new elastic light-trail where applicable. Otherwise, the algorithm creates a new elastic light-trail that facilitates required data transportation. In this work, we investigate optical spectrum utilization efficiency for proposed elastic light-trail, existing elastic lightpath (Multi-hop Elastic Lightpath algorithm – MEL) and ITU − T wavelength grid fixed lightpath (Multi-hop Lightpath algorithm – ML) and perform comparison measurements.

The adjacent channel interference (ACI) resulting from imperfect filtering can severely degrade the performance of any wireless communication system. Despite this fact, most of previously proposed medium access control (MAC) protocols for cognitive radio networks (CRNs) were designed while ignoring the effects of ACI (assuming ideal filtering). The effect of ACI can be reduced by introducing guard bands (GBs). However, this solution comes at the expense of degrading spectrum efficiency. In this paper, we develop an efficient GB-aware MAC protocol that attempts at maximizing network throughput while improving fairness in CRNs. Unlike most of previously proposed GB-aware MAC protocols that perform channel assignment sequentially, our MAC performs the channel assignment for multiple CR links simultaneously (the so-called batch method). Batching enables concurrent channel assignment for multiple CR links, which consequently allows for concurrent data transmissions. Batching can be realized by introducing an admission control phase for CR users to share their control information. The batch method can effectively provide distributed decisions that achieve better throughput while reducing the number of GBs. Our MAC also allows the CR users to utilize the reserved GBs of primary networks under predefined FCC power constraints. Simulation results indicate that our protocol achieves significant performance improvement compared to previous GB-aware protocols.

A multiband direct-detected optical orthogonal frequency-division multiplexing (DDO-OFDM) system effectively enhance data capacity without high-end electrical devices. However, signals are optical-to-electrically converted with only one photodetector in a direct detecting scheme, signal–signal beating interference (SSBI) is meanwhile introduced. Traditionally, a large guard band can be applied to evade SSBI, however, it seriously restricts the precious spectral efficiency (SE). In this letter, we propose an iterative digital signal processing (DSP) in the receiving end of a multiband DDO-OFDM system to cope with the SSBI. With this iterative DSP, the corresponding SE theoretically approach to that of single polarization coherent optical OFDM systems. A total 65.4-Gb/s data rate is experimentally demonstrated with a three-band DDO-OFDM signal in 16-QAM format, and the SSBI reduction DSP saturates within two iterations. Various bandgaps and carrier-to-signal power ratios settings are also evaluated to investigate the feasibility of the proposed iterative DSP.

We experimentally demonstrate Nyquist wavelength-division-multiplexed (WDM) channels with a low signal-to-noise ratio (SNR) difference based on flat electro-optic combs (EOCs), which reduce the interchannel crosstalk penalty in Nyquist-WDM transmission with no guard band. The five Nyquist-WDM channels are generated through the insertion of uniform and coherent lines around each line of the EOCs from a dual-parallel Mach–Zehnder modulator. For the five channels, the normalized root-mean-square error of optical sinc-shaped pulses at a repetition rate of 9 GHz is between 1.23% and 2.04%. The SNRs of the Nyquist signal can be better than 30 dB by using flat EOCs with a narrow linewidth as WDM sources, and the difference in SNR is less than 0.6 dB for the WDM channels. The transmission performance of five Nyquist-WDM channels with no guard band is compared in a 56 km fiber link. The results show that our scheme provides a minimum interchannel sensitivity penalty of 0.7 dB at the forward-error-correction limit. The Nyquist-WDM channels with low SNR difference can effectively improve the communication performance of the Nyquist-WDM system.

In this letter, a quasi-gapless integrated visible light communication and positioning (VLCP) system is experimentally demonstrated for the first time, based on filter bank multicarrier- based subcarrier multiplexing (FBMC-SCM). Compared with orthogonal frequency division multiplexing-based SCM (OFDM- SCM), FBMC-SCM has lower out-of-band interference (OOBI) and therefore requires much smaller guard band (GB) spacing. A low-complexity transmit diversity transmission scheme is adopted here, where all the light emitting diode (LED) lamps transmit the same communication signal.Moreover, phase difference of arrival (PDOA) is applied for positioning. The experimental results show that, in a coverage area of 1.2×1.2 m2 with a height of 2.1 m, the mean position errors using OFDM–SCM and FBMC-SCM for a GB of 0.7 MHz are 10.91 and 6.08 cm, respectively. Moreover, a comparable bit error rate (BER) performance can be achieved for both OFDM–SCM and FBMC-SCM. Due to the negligible GBs when using FBMC-SCM, the effective bandwidth utilization ratio of the integrated VLCP system is improved from 72% to 98% when OFDM-SCM is replaced by FBMC-SCM. NRF (Natl Research Foundation, S’pore) Accepted version

We have investigated the fiber transmission performance of the single-sideband optical orthogonal frequency division multiplexing (SSB-OOFDM) signal with reduced guard band (GB) received by the beat interference cancellation receiver based on balanced detection (ICRBD). The simulation results show that the error vector magnitude (EVM) of the 40 Gb/s 16-QAM SSB-OOFDM with 2 GHz GB remains below the forward error correction (FEC) limit even after 5×100 km standard single-mode fiber (SSMF) transmission. The link has stable tolerance of both the laser linewidth and the linear channel imperfections.

Orthogonal frequency division multiplexing (OFDM) technology has been adopted in various communications and broadcasting systems, including LTE, WiMax, and DVB-T2. However, cyclic prefix (CP) and guard band are required to limit the inter-symbol and adjacent interference, which would cause loss of spectral efficiency. Filter bank multiple carrier (FBMC) technology is one of the alternative solutions of multicarrier modulation that mitigate such problems. FBMC applies offset-QAM (OQAM) and band-limited filtering on each subcarrier, which eliminates the need of CP and guard band. FBMC filtering could maintain the orthogonality in a real signal domain by using a well localized filter. However, due to the OQAM structure, the transmitted data is mixed with an intrinsic interference, therefore, conventional log likelihood ratio (LLR) calculation for OFDM system is not applicable to FBMC system. In this letter, we propose an efficient LLR calculation method for use in FBMC system. It is found that the proposed method does not increase the implementation complexity of FBMC receiver while it performs same as that of OFDM system.

Fading and shadowing along with the primary user dynamics make channel quality in dynamic spectrum access networks uncertain. Furthermore, the imperfect design of filters and amplifiers in wireless devices motivates the need for guard-bands (GBs) to prevent adjacent-channel interference. In this paper, we develop novel stochastic GB-aware sequential and batch channel assignment schemes that aim at maximizing the spectrum efficiency. In line with recent IEEE 802.11 and LTE standards, our schemes support bonding and aggregation. We propose two assignment models for each of the sequential and batch schemes: a static single-stage and an adaptive two-stage . In the static model, channel assignment is performed once such that the rate demands are probabilistically met. The adaptive model is a two-stage model, where the initial assignment may be corrected once uncertainties are partially revealed. We refer to our formulations of the sequential and batch static assignments as c hance-constrained stochastic s ubset- s um p roblem (CSSP) and c hance-constrained stochastic m ultiple s ubset- s um p roblem (CMSSP) , respectively. Moreover, we develop stochastic formulations for the sequential and batch adaptive assignments, which we refer to as two-stage CSSP with r ecourse (CSSPR) and two-stage CMSSP with r ecourse (CMSSPR) , respectively. Finally, we present computationally efficient simplified versions of CSSP and CSSPR with near-optimal performance.

OFDM has been regarded as a promising candidate for use in cognitive radio systems with dynamic spectrum reuse capability. However, conventional OFDM has significant OOBE, which can cause severe interference to systems operating in adjacent frequency bands. In addition to conventional techniques such as spectral shaping filtering, guard band insertion, and time domain windowing, new OOBE reduction techniques, including cancellation carrier and spectral precoding, have been proposed in recent years. This article reviews various OOBE reduction techniques and proposes a generalized lowcomplexity OOBE reduction framework for discrete Fourier transform precoded OFDM. With the allocation of explicit frequency domain cancellation subcarriers and data domain cancellation symbols, the proposed framework enables various configurations to achieve significant OOBE reduction with low implementation complexity, and provides flexibility in balancing OOBE reduction and other performance metrics such as peak-to-average power ratio.

In this paper, we present techniques for mitigating the Negative Bias Temperature Instability (NBTI) effect on extensible processors. Firstly, the effect of NBTI on the extended instruction set architecture and the arithmetic logic unit of extensible processors is studied. The study includes modeling the circuit delay increase due to the NBTI and analyzing its impact on the processor lifetime. The study shows that in some cases, the lifetime is decreased while in other cases, it is increased compared to that of a baseline processor. Next, to lower the impact of the NBTI on the extensible processor lifetimes, we present four different techniques. The first technique is based on injecting proper input vectors during the idle time of the custom instructions such that the NBTI effect is reduced. The lifetime improvement, however, is limited by the delay increase reduction of the applied input vectors. In the second technique, the guard band delay of extensible processor is extended. This is effective because the rate of lifetime increase due to extending the guard band delay is much higher than the rate of speedup reduction. For the third technique, we duplicate the critical custom instructions to increase the processor lifetime without losing any speedup. The last technique estimates the delay increase of candidate custom instructions (CIs) and selects those that do not reduce the lifetime. The efficacies of the aforesaid techniques are evaluated and compared against each other by using benchmarks from different application domains. Studying the impact of the NBTI on the lifetime of the extensible processors.Proposing architectural techniques to improve the lifetime of the extensible processors under the NBTI effect, and studying their efficacy.Proposing system-level technique to increase the lifetime of the extensible processors.

The modulation technique of $N$ -continuous orthogonal frequency division multiplexing (OFDM) has lower sidelobes than those of the original OFDM as a result of the continuous connection with higher-order derivatives between the OFDM symbols. Compared with the other sidelobe suppression schemes, for example, cancellation carrier insertion, and windowing, $N$ -continuous OFDM does not require an extended guard interval nor the insertion of a wide guard band or cancellation carriers. However, $N$ -continuous OFDM requires an iterative algorithm to remove the correction symbols from received symbols at the receiver and the large power of the correction symbols in the high-frequency area results in unavailable bandwidth. Here, we propose an extension of the $N$ -continuous OFDM precoder matrix that flattens the bias power caused by the correction symbols in all frequency areas. Numerical experiments show that the proposed method improves the error rate performance without degrading the sidelobe suppression performance. The proposed method can also reduce the unavailable bandwidth.

Communication is one of the main aspects of life. With the advancement in age and its growing demands, there has been rapid growth in the field of communications. Signals, which were initially sent in the analog domain, are being sent in the digital domain. For better transmission, still the single carrier waves are being replaced by multi carriers. Multi carrier systems like CDMA and OFDM are now a day being implemented normally. In the OFDM system, orthogonally placed sub carriers are used to carry the data from the transmitter end to the receiver end. Presence of guard band in this system deals with the problem of ISI and noise is minimized by larger number of sub carriers. But the large peak to average power ratio (PAPR) of these signal have some undesirable effects on the system. This paper focuses on presenting the basics of an OFDM system and various methods to reduce the PAPR. High peak to average power ratio of the transmit signal is a major drawback of multicarrier transmission in OFDM. This article describes some of the important PAPR reduction techniques for multicarrier transmission including amplitude clipping and filtering, coding, partial transmit sequence, selected mapping, interleaving, tone reservation, tone injection and active constellation extension. Finally the criterion for PAPR reduction technique selection has been discussed.

Measurement uncertainty has important economic consequences for calibration and inspection activities. In calibration reports, the magnitude of the uncertainty is often taken as an indication of the quality of the laboratory. In industrial measurements, uncertainty has an economic impact through the decision rule employed in accepting and rejecting products. With significant economic interests at stake, manufacturers and consumers have to guard against accepting bad products and rejecting good ones. While the evaluation of measurement uncertainty is a pure technical activity well described in the GUM, the selection of a decision rule is a business decision that involves cost considerations. Recently, several national and international standards bodies have addressed the decision rule issue to provide a uniform, unambiguous terminology for documenting a decision rule and to describe the relationship between conforming characteristics and acceptable measurement results. Similarly, the issue of risk analysis addresses the problem of determining the gauging limits that define the boundaries of acceptable measurement results. Gauging limits are chosen to balance the risks of the two types of decision errors (accepting nonconforming products and rejecting conforming products), whose relative magnitudes depend upon product-specific economic factors. This paper reviews recent standardization developments in these areas.

In traditional multicarrier systems, the pilot carriers used to estimate the channel are placed as uniform as possible over the bandwidth. However, with the raise of cognitive radio systems, where the multicarrier system is used by the secondary users, parts of the bandwidth are not available for transmission as primary users are active in these bands. Therefore, the multicarrier system must introduce guard bands in which the carriers may not be used. Hence, a problem might occur when placing the pilot carriers. In this paper, we investigate the effect of the positions of the pilot carriers on the MSE performance of channel estimation, and look for the pilot carrier placement that minimizes the MSE. We do not restrict our attention to multicarrier systems with a cyclic prefix, but we also consider other types of guard interval that are used for multicarrier transmission. It is known that an equidistantly-spaced distribution of the pilot carriers is in general not the optimal placement of the pilot carriers, as the corresponding MSE can become very high. In this paper, we use a heuristic algorithm to search for the best pilot placement, which is able to deliver a pilot carrier placement that outperforms the maximum distance distribution from [S. Song and A. C. Singer, “Pilot-Aided OFDM Channel Estimation in the Presence of the Guard Band,” IEEE Trans. Commun., vol. 55, no. 8, pp. 1459-1465, Aug. 2008] in terms of the MSE, and results in an MSE that is close to the case where no guard bands are present. Based on the results of the algorithm, we can derive some simple rules of thumb to select the positions of the pilot carriers.