Low PAPR Channel Estimation for OTFS with Scattered Superimposed Pilots

Orthogonal time frequency space(OTFS)modulation has been proven to be superior to traditional orthogonal frequency division multiplexing(OFDM)systems in high-speed communication scenarios.However,the existing channel estimation schemes may results in poor peak to average power ratio(PAPR)performance of OTFS system or low spectrum efficiency.Hence,in this paper,we propose a low PAPR channel estimation scheme with high spectrum efficiency.Specifically,we design a multiple scattered pilot pattern,where multiple low power pilot symbols are superimposed with data symbols in delay-Doppler domain.Furthermore,we propose the placement rules for pilot symbols,which can guarantee the low PAPR.Moreover,the data aided iterative channel estimation was invoked,where joint channel estimation is proposed by exploiting multiple independent received signals instead of only one received signal in the existing scheme,which can mitigate the interference imposed by data symbols for channel estimation.Simulation results shows that the proposed multiple scattered pilot aided channel estimation scheme can significantly reduce the PAPR while keeping the high spectrum efficiency.

Assessing the maturity of China's seven carbon trading pilots

Indicators based on the developed version of the Capability Maturity Model were set up to access the maturity degree of China's seven pilot carbon markets from 2013 to 2017. Results show that the maturity degree of Shenzhen and Beijing pilot carbon markets ranks first;while those of Guangdong, Hubei, and Shanghai rank second. Tianjin and Chongqing rank lowest. Most of pilot markets failed to perform well on price efficiency except Shenzhen. There is significant disparity in the scores that the pilot carbon markets got, with a range from 9 to 73. The drivers to maintain market maturity is different among the pilot markets, either with a good performance on market structure, scale, or efficiency could lead to a certain score. Much could be done to increase the maturity level of the carbon market. Further downscaling the firm size, raising the legislation level, and increasing the participation of the third party entities may help the carbon market to grow healthier.

Spectral Efficiency of Superimposed Pilots in Cell-Free Massive MIMO Systems with Hardware Impairments

In this paper,the spectral efficiency(SE)of an uplink hardware-constrained cell-free massive multi-input multi-output(MIMO)system with maximal ratio combining(MRC)receiver filters in the context of superimposed pilots(SPs)is investigated.Tractable closed-form SE expressions for the considered system are derived,which share us with opportunities to explore the impacts of the hardware quality coefficient,the length of coherence interval,and the power balance factor between pilot and data signals.Numerical results indicate that the achievable SE deteriorates as the hardware quality decreases and is more susceptible to the hardware impairments at the user equipments(UEs).Besides,we observe that SPs outperform regular pilots(RPs)in terms of SE and this performance gain is heavily dependent on the values of power balance factor and coherence interval.However,the superiorities of SPs over RPs have vanished when severe hardware imperfections are considered.

Comparison of Antioxidant Status between Pilots and Non-flight Staff of the Army Force: Pilots May Need More Vitamin C

Objective To compare the blood antioxidant levels and dietary antioxidant intakes between pilots and non-flight staff of the Army Force in The Islamic Republic of Iran. Methods Thirty-seven helicopter pilots and 40 non-flight staff were included in this study. Their general characteristics were recorded and their weight, height, and waist circumference were measured. Their daily intake of energy and nutrients including antioxidants was assessed using a semi-quantitative food frequency questionnaire. Serum levels of total antioxidant capacity （TAC）, malondialdehyde （MDA）, and glutathione reductase （GR）, glutathione peroxidase （GPx）, superoxide dismutase （SOD）, and catalase （CAT） in red blood cells were also measured. Results The median erythrocytes SOD, serum MDA level and the mean serum level of TAC and erythrocytes GPx were significantly higher in pilots than in non-flight staff. The median vitamin C intake was significantly lower in pilots than in non-flight staff. The serum MDA levels were similar in non-flight staff and pilots when their vitamin C intake was 〈168 mg and significantly lower in non-flight staff than in pilots when their vitamin C intake was 〉168 mg. Conclusion The serum MDA level is lower in non-flight staff than in pilots when their vitamin C intake level is high, indicating that pilots need more vitamin C than non-flight staff.

Analysis of two naval pilots’ ejection injuries: Two case reports

BACKGROUND Recently,two naval pilots in a two-seat trainer jet were forced to eject urgently due to sudden mechanical failure during night-time training.They were both successfully rescued and sent to the hospital for emergency treatment.In this study,we investigate their ejection injuries and recovery process.CASE SUMMARY We analyzed the clinical data of the traumatic condition and recovery process from ejection injuries of two pilots who ejected from a failed trainer jet and survived.After being successfully rescued and sent to the hospital,they were diagnosed with multiple ejection injuries,including eye trauma,limb bone and joint injury,rib and spine injury,and so on.Both cases underwent fluid replacement,acid suppression,nutritional support,hemostasis,bone metabolism improvement,phlegm elimination,psychological measurement,blood circulation promotion and detumescence,physical therapy,and external fixation with braces for 1 mo before being discharged from hospital.They then recuperated in a sanatorium for 2 mo,and the related laboratory tests and supplementary examinations show that they recovered from all the above injuries.After successfully passing the psychological test and physical examination,they returned to flight duty 3 mo after ejection.CONCLUSION The causes and conditions of ejection injury in the pilots were very complex.Although they finally recovered quickly and were released,it also serves as a reminder that attention should be paid to pilots’ejection and parachute training in order to significantly reduce ejection injury and improve the ejection success rate.In addition,air defense support personnel should strengthen search and rescue and on-site emergency measures,and locate and rescue pilots in distress as early as possible to reduce subsequent injuries.

Research on Pilots Development Planning

Pilot is one of the most important factors to ensure aviation safety. The article focuses on the Pilots Development Planning (PDP) problem. It is different from other countries that pilots are developed by airways themselves in China. Promotion of every pilot needs specified quantity of flight experience hours which are accumulated in daily flights. In the same time, the promotion routes of pilots are diversified. So keys of PDP problem are to estimate the number of pilots who have promotion qualification in different planning period and to optimize their promotion and transfer in all routes. After analyzing characteristics of pilot training, a PDP road map is drawn which shows the typical process for pilots’ promotion and transfer. An optimization model which has promotion qualification constraints is built to solve PDP problem. According to different pilot development patterns, the method is proved to be effectively by a case study. The research has practical significance for Chinese airways.

US Pilots' Remains Homeward Bound

On December 7.1993,as|soon as an airplane landed at the Uhasa airport,sever-al Americans dashed down from it.Burning with impatience,they were in no mood to enjoy the wonderful scenery in this city on the heights,but asked in haste,"Where?Where ane they?"

Chinese Female Jet-Fighter Pilots Change New Uniforms

Prior to the 60th anniversary of founding of People’s Republic of China that marks calendar day of Oct.1st this year, Chinese armed forces stage on a new change of uniforms to welcome the birthday of the New China that was

Hybrid pilots assisted channel estimation algorithm for MIMO-OFDM systems

A hybrid pilots assisted channel estimation algorithm for multiple input multiple output（MIMO） orthogonal frequency division multiplexing（OFDM） systems under low signal-to-noise ratio（SNR） and arbitrary Doppler spread scenarios is proposed.Motivated by the dissatisfactory performance of the optimal pilots（OPs） designed under static channels over multiple OFDM symbols imposed by fast fading channels,the proposed scheme first assumes that the virtual pilot tones superimposed at data locations over specific subcarriers are transmitted from all antennas,then the virtual received pilot signals at the corresponding locations can be obtained by making full use of the time and frequency domain correlations of the frequency responses of the time varying dispersive fading channels and the received signals at pilot subcarriers,finally the channel parameters are derived from the combination of the real and virtual received pilot signals over one OFDM symbol based on least square（LS） criterion.Simulation results illustrate that the proposed method is insensitive to Doppler spread and can effectively ameliorate the mean square error（MSE） floor inherent to the previous method,meanwhile its performance outmatches that of OPs at low SNR region under static channels.

Must pilots permanently quit flying career after treatment for colorectal cancer?-Medical waiver for Air Force pilots with colorectal cancer: Three case reports

BACKGROUND Colorectal cancer(CRC)could seriously threaten the physical and mental health of pilots.Shall they end their flying after treatment of CRC?With this study,we investigated the possibility of a gradual medical waiver for such pilots to fly aircrafts again after treatment of CRC.CASE SUMMARY We analyzed the medical waiver and clinical data of 3 pilots with CRC,who had accepted the treatment at the Department of General Surgery,Air Force Medical Center(formerly,Air Force General Hospital)between 2013 and 2018.All 3 cases underwent a series of comprehensive treatment courses,including radical resection of CRC,sequential radiotherapy,and chemotherapy.The follow-up results were satisfactory.After passing through the high-risk period of recurrence and metastasis of CRC,they all were given a medical waiver for flying again.Medical observation showed that their flying operations were safe.CONCLUSION The CRC treatment shall follow the guidelines for diagnosis and treatment and should simultaneously protect the combating capabilities of pilots as much as possible.It is safe for pilots with CRC,who are continuously monitored under medical observation after passing through the high-risk period of recurrence and metastasis,to undertake military flight missions again.

The Tight Bound for the Number of Pilots in Channel Estimation for OFDM Systems

Coherent detection in OFDM systems requires accurate channel state information (CSI) at the receiver. Channel estimation based on pilot-symbol-assisted transmissions provides a reliable way to obtain CSI. Use of pilot symbols for channel estimation, introduces overhead and it is desirable to keep the number of pilot symbols as minimum as possible. This paper introduces a new tight bound for the number of pilots in channel estimation using adaptive scheme in OFDM systems. We calculate the minimum number of necessary pilots using two approaches. The first approach for the number of pilots is obtained based on Doppler frequency shift estimation and the second approach is acquired based on channel length estimation using second order statistics of received signal. Finally we obtain the tight bound for the number of pilots using attained values.

Fundamental issues and solutions in the design of China's ETS pilots:Allowance allocation,price mechanism and state-owned key enterprises

This paper analyzes the three main fundamental issues in the design of China's ETS pilots,including allowance allocation,price mechanism and state-owned key enterprises,and proposed suggested solutions.For the issue of allowance allocation,we suggest that the gradual hybrid mode could be applied at the beginning,which starts with mainly free allocation and then increases auction ratio gradually.And grandfathering is a suitable method of free allocation.For the issue of price mechanism,we suggest a price floating zone with open market operation to reduce the uncertainty of prices.For the issue of state-owned key enterprises,we suggest a good coordination with SASAC,defining the state-owned property right and supervision right when state-owned key enterprises are involved into the carbon market,and the local government can set rules of allocation and transaction to limit their potential market power.

Analysis of 3 565 healthy pilots'rest recording ECGs using Minnesota code

ECGs of 3 565 clinically normal male pilots,aged from 21 to 51 years,were classi-fied and analyzed by Minnesota code.Among the 3 565 pilots,there were 1 315 coded pilots,making up 36.89％ of the total number.The results were as follows:abnormal Q/QS wave0.14％,electrocardial axis deflection 5.11％,high voltage of left ventricle 10.58％,chargedST-T segment 2.07％,atrioventricular conduction block 1.71％,intraventricular conductionblock 4.60％,arrhytmias 10.66％ and other abnormalities 13.04％.The research showed thatthere were various changes in the coded pilots,although no abnormal alteration of the cardio-vascular system was discovered by physical examination,the ECG exercise stress test and otherrelevant clinical tests.This suggests that most of ECG abnormalities in clinically normal pilotsare normal physiological and functional variations.

Preliminary Studies on the Relationship betweenAutoantibodies to Heat Stress Proteins and Heat Injury of Pilots during Acute Heat Stress

Comparison in the heart rate, oral temperature and lymphocyte DNAdamage during heat stress was made in pilots with negative antibodies to heatstress proteins (HSPs) and those with positive antibodies in the man-made climate room with Western blot and comet assay. Our results showed that the increase in oral temperature, heart rate and lymphocyte DNA damage in pilots with the posi-tive antibodies to HSPs were higher than those in pilots with the negative antibod-ies during heat stress. These results indicated that the presence of autoantibodies in plasma of pilots might reflect heat damage and high sensitivity to heat.

Clinical diagnosis,treatment,and medical identification of specific pulmonary infection in naval pilots:Four case reports

BACKGROUND Specific pulmonary infection could seriously threaten the health of pilots and their companions.The consequences are serious.We investigated the clinical diagnosis,treatment,and medical identification of specific pulmonary infections in naval pilots.CASE SUMMARY We analyzed the medical waiver and clinical data of four pilots with specific pulmonary infections,who had accepted treatment at the Naval Medical Center of Chinese People’s Liberation Army between January 2020 and November 2021,including three cases of tuberculosis and one of cryptococcal pneumonia.All cases underwent a series of comprehensive treatment courses.Three cases successfully obtained medical waiver for flight after being cured,while one was grounded after reaching the maximum flight life after being cured.CONCLUSION Chest computed tomography scanning should be used instead of chest radiography in pilots’physical examination.Most pilots with specific pulmonary infection can be cured and return to flight.

An Exploratory Factor Analysis of Quality of Work Life of Pilots

This study aims to explore dimensions of quality of work life (QWL) of pilots by using an exploratory factor analysis (EFA). The sample was 400 pilots who are currently working for an airline based in Thailand. The items using in this study were generated using input from three sources. First, using input from commercial pilots who had a minimum of total 5,000 flying hour and currently working for either premium or low cost airlines in Thailand. Second, translated quality of work life items from a published research on Quality of Work Life of Personnel at Dhurakij Pundit University by Chatthai (2016). After the content analysis, the left items for the EFA analysis were 30 items. The Kaiser-Meyer-Olkin (KMO) demonstrated at 0.93. The exploratory factor analysis was to examine the loading patterns of QWL items. A principal component and orthogonal rotation (Verimax method) were chosen. It showed there were five structural factor patterns. The five factors were labored as “Human Resource Management”;“Social Relation”;“Safe Working Environment”;“Work-Life Balance”;and “Fairness and Respect”. Discussion and future research are also discussed.

Optimal Spacing Design for Pilots in OFDM Systems over Multipath Fading Channels

In wireless orthogonal frequency division multiplexing (OFDM) systems, the time-varying channel is often estimated by algorithms based on pilot symbols. Such an estimator, however, requires statistical prior knowledge that is not easily obtained. Therefore, the pilot tones have to be close enough to fulfill the sampling theorem. In this case the statistical knowledge of the channel is not required to reconstruct correctly the channel impulse response (CIR). This paper explores the optimal placement and number of pilot symbols, we investigate optimal training sequences in OFDM systems and we analyze the number of pilot symbols required to fulfill the sampling theorem. Using a general model for a multipath slowly fading channel, the approach is based on the LS as a criterion of channel estimation while the channel interpolation is done using the piecewise-constant interpolation compromising between complexity and performance. Simulation results demonstrate the good performance of our approach.

Design of integral sliding mode guidance law based on disturbance observer

With the increasing precision of guidance,the impact of autopilot dynamic characteristics and target maneuvering abilities on precision guidance is becoming more and more significant.In order to reduce or even eliminate the autopilot dynamic operation and the target maneuvering influence,this paper suggests a guidance system model involving a novel integral sliding mode guidance law(ISMGL).The method utilizes the dynamic characteristics and the impact angle,combined with a sliding mode surface scheme that includes the desired line-ofsight angle,line-of-sight angular rate,and second-order differential of the angular line-of-sight.At the same time,the evaluation scenario considere the target maneuvering in the system as the external disturbance,and the non-homogeneous disturbance observer estimate the target maneuvering as a compensation of the guidance command.The proposed system’s stability is proven based on the Lyapunov stability criterion.The simulations reveale that ISMGL effectively intercepted large maneuvering targets and present a smaller miss-distance compared with traditional linear sliding mode guidance laws and trajectory shaping guidance laws.Furthermore,ISMGL has a more accurate impact angle and fast convergence speed.

The"4+4"Medical Doctor(MD)Pilot Program at PUMC:Implementation,Performance,and Prospects

Peking Union Medical College(PUMC)launched the"4+4"Medical Doctor(MD)pilot program in 2018,admitting students with non-medical backgrounds from top universities,aligning with national medical talent training policies to foster diverse and eager learners in medicine.On the occasion of the graduation of the first class of the"4+4"MD pilot class at PUMC in 2023,we reviewed the teaching reform in the pilot program and carried out a systematic survey and interviews with students,faculties,and management staff of the pilot class.This article reports on the measures taken by the pilot class at PUMC in enrollment and curriculum setting,and demonstrates the achievements of the pilot class in terms of student academic background structure,knowledge acquisition and skill learning,scientific research ability,and course evaluation.The results indicated that the pilot class had met the national demand for the"Medicine+X"talent training model.More specifically,with a diverse academic backgrounds,the pilot class graduates had academic levels comparable to the eight-year medical education graduates,and their scientific research abilities were satisfactory.The pilot program at PUMC will optimize the curriculum setting,strengthen the construction of faculty,learning resources,and teaching facilities,and reform the academic evaluation methods,thus deepening the reform of medical education and improving the"4+4"MD program as a novel medical education model.

The Tenth Anniversary of Free Trade Pilot Zones in China:Fundamental Experiences and Enhancement Strategies

Since the 18th National Congress of the Communist Party of China,the country has established 21 Free Trade Pilot Zones(FTZs),achieving significant pioneering results in reform and opening up and creating a strong demonstrative effect nationwide.The basic experience from a decade of FTZs includes:adhering to the centralized and unified leadership of the CPC Central Committee;combining top-level design with encouragement of grassroots innovation;leveraging the distinct characteristics and strengths of FTZs to form a differentiated development pattern;maintaining the integration of opening up with domestic reforms;using openness to drive reforms;and organically combining openness with national security assurance.Under the current and future new circumstances,China’s FTZs face new challenges and tasks.In accordance with the directives of the 20th National Congress of the Communist Party of China,an enhancement strategy for the FTZs needs to be implemented.This involves the following:First,accurately understanding and responding to the changing situation to create strategic opportunities.Second,shifting paradigms to implement innovation-driven strategies,using the new development pattern concept to guide the reform experiments and construction of the FTZs.Third,granting more autonomy to FTZs for reforms,pursuing progress while maintaining stability,and solidly advancing the reform experiments in the FTZs.Fourth,orderly expanding the opening up of the service sector and cautiously advancing the internationalization of the renminbi.Fifth,promoting innovative development in trade to build a strong trade nation.Sixth,establishing synergy with bilateral FTZs,Belt and Road cooperation,and national diplomatic strategies to enhance the linkage effect.