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In the global effort to curb energy consumption and promote a sustainable lifestyle for our societies, we must strive to lower our energy needs in all aspects of our lives. One of the biggest contributors to our energy requirements are the buildings we spend most of our time inside. Buildings’ energy consumption can take many forms, such as, air conditioning, heating, ventilation, and lighting systems in order to create a comfortable environment for the users. One way of reducing buildings’ energy consumption is the use of renewable resource for energy. The main aim of this research is to measure and assess the public perceptions, knowledge and awareness of the concept of renewable energy, with specific regards to the use of solar photovoltaic cells, as well as investigate the desire to spend on the installation of renewable energy sources. Data was collected through a survey questionnaire applied in Irbid governorate in the north of Jordan. The statistical SPSS program was used to analyze closed-ended questionnaires and obtain numerical results based on arithmetical averages and percentages. The results show people are adequately aware of the benefits of renewable energy and most would like to have photovoltaic cells installed. However, 54.35% of the study sample live in apartments and do not have the space for the installation. 70.1% are open to the idea of sharing the solar energy system with their neighbors. 50% thought that the photovoltaic cells affected the aesthetics of the architecture style of the buildings especially the more traditional styles. It is concluded that the government needs to build a large-scale solar energy project to sustainably produce electricity instead of relying on individuals who generally lack the ability or the space for such systems, taking in note that the general public supports such concepts.

Background Progress has been made in the reduction of morbidity and mortality of cervical cancer by the implementation of human papillomavirus (HPV) vaccination programs. This study aimed to assess the awareness of Palestinian women about HPV as well as their knowledge and acceptability of the HPV vaccine and to examine the factors associated with good awareness. Methods This was a national cross-sectional study. Adult women were recruited from hospitals, primary healthcare centers, and public spaces in 11 Palestinian governorates using convenience sampling. A structured questionnaire was used for data collection. For each correctly answered question, one point was given. The total score was calculated and categorized into poor (0–10) and good awareness (11–21). Results The questionnaire was completed by 7223 women out of 8086 who were approached (response rate = 89.3%). A total of 7058 questionnaires were included in the final analysis; 4403 from the West Bank and Jerusalem (WBJ) and 2655 from the Gaza Strip. Women recruited from the Gaza Strip were younger, getting lower monthly incomes, and with fewer chronic diseases than women recruited from the WBJ. Only 33 women (0.5%) displayed good awareness of HPV and its vaccine with 0.7% of women from WBJ and only 0.2% of women from the Gaza Strip. Completing post-secondary education, being employed or a student, and having a higher monthly income were associated with an increase in the likelihood of having good awareness. Among women who had heard of HPV (n = 571, 8.1%), only 46 women (8.1%) reported familiarity with its vaccine. Women from the WBJ were more likely than women from the Gaza Strip to have heard about the HPV vaccine (0.9% vs. 0.2%). Most women agreed to receive the HPV vaccine themselves or for their daughters if it was given without cost or with a co-payment. No differences were found in the likelihood of agreeing to receive the HPV vaccine among women in the WBJ versus the Gaza Strip. Conclusion The overall awareness of HPV and its vaccine was extremely low. Inclusion of the HPV vaccine in the national immunization program could change this, especially as the HPV vaccine appeared to be acceptable.

"Background: Timely presentation and diagnosis of cervical cancer (CC) are crucial to decrease its mortality especially in low- and middle-income countries like Palestine. This study aimed to evaluate the knowledge of Palestinian women about CC warning signs and determine the factors associated with good knowledge. Methods: This was a national cross-sectional study conducted between July 2019 and March 2020 in Palestine. Stratified convenience sampling was used to recruit adult women from hospitals, primary healthcare centers, and public spaces of 11 governorates. A translated-into-Arabic version of the validated CC awareness measure (CeCAM) was used to assess women’s knowledge of 12 CC warning signs. Results: Of 8086 approached, 7223 participants completed the CeCAM (response rate = 89.3%). A total of 7058 questionnaires were included in the analysis: 2655 from the Gaza Strip and 4403 from the West Bank and Jerusalem (WBJ). The median age [interquartile range] for all participants was 34.0 [24.0, 42.0] years. Participants recruited from the WBJ were older, getting higher monthly income, and having more chronic diseases than those recruited from the Gaza Strip. The most frequently identified warning sign was ‘vaginal bleeding after menopause’ (n = 5028, 71.2%) followed by ‘extreme generalized fatigue’ (n = 4601, 65.2%) and ‘unexplained weight loss’ (n = 4578, 64.9%). Only 1934 participants (27.4%) demonstrated good knowledge of CC warning signs. Participants from the Gaza Strip were slightly more likely than participants from the WBJ to have a good level of knowledge. Factors associated with having good knowledge included having a bachelor or postgraduate degree, being married, divorced, or widowed as well as knowing someone with cancer. Conclusion: The overall awareness of CC warning signs was low. Educational interventions are needed to increase Palestinian women’s awareness of CC warning signs. Keywords: Cervical cancer, Early detection, Survival, Symptom, Warning sign, wareness, Knowledge, Early presentation, Palestine" "الخلفية: يعد تشخيص سرطان عنق الرحم وتشخيصه في الوقت المناسب أمرًا بالغ الأهمية لتقليل معدل الوفيات خاصة في البلدان المنخفضة والمتوسطة الدخل مثل فلسطين. هدفت هذه الدراسة إلى تقييم معرفة النساء الفلسطينيات بعلامات التحذير الخاصة بسرطان عنق الرحم وتحديد العوامل المرتبطة بالمعرفة الجيدة. الطرق: كانت هذه دراسة مقطعية وطنية أجريت بين تموز 2019 وآذار 2020 في فلسطين. تم استخدام عينات من النساء البالغات من المستشفيات ومراكز الرعاية الصحية الأولية والأماكن العامة في 11 محافظة. تم استخدام نسخة مترجمة إلى العربية من مقياس الوعي (CeCAM) الذي تم التحقق من صحته لتقييم معرفة النساء بـ 12 علامة تحذير من سرطان عنق الرحم. النتائج: أكمل 7223 مشاركًا CeCAM (معدل الاستجابة = 89.3 ٪). تم تضمين ما مجموعه 7058 استبانة في التحليل: 2655 من قطاع غزة و 4403 من الضفة الغربية والقدس. كان المشاركون من الضفة الغربية و القدس أكبر سناً ، ويحصلون على دخل شهري أعلى ، ولديهم أمراض مزمنة أكثر من أولئك الذين من قطاع غزة. كانت علامة التحذير الأكثر تحديدًا هي ""النزيف المهبلي بعد انقطاع الطمث"" (العدد = 5028 ، 71.2٪) يليه ""التعب الشديد العام"" (العدد = 4601 ، 65.2٪) و ""فقدان الوزن غير المبرر"" (العدد = 4578 ، 64.9٪) . أظهر 1934 مشاركًا (27.4 ٪) معرفة جيدة بعلامات التحذير من سرطان عنق الرحم. كان احتمال حصول المشاركين من قطاع غزة على مستوى جيد من المعرفة أكثر بقليل من المشاركين من الضفة الغربية. تشمل العوامل المرتبطة بالحصول على معرفة جيدة الحصول على درجة البكالوريوس أو الدراسات العليا ، والحالة الاجتماعية وكذلك معرفة شخص مصاب بالسرطان. الخلاصة: كان الوعي العام بعلامات التحذير من سرطان عنق الرحم منخفضًا. هناك حاجة إلى تدخلات تثقيفية لزيادة وعي المرأة الفلسطينية بعلامات التحذير من سرطان عنق الرحم. "

This study proposes adaptive downlink association schemes for controlled device-to-device (D2D) communication in cellular networks. The proposed schemes utilise active devices under specific conditions to improve the network performance. Specifically, active devices are classified into two disjoint groups according to their individual quality of service (QoS) requirements from their base station (BS). The BS adaptively allocates downlink physical channels to meet individual QoS of devices using a minimal number of these available channels. The unused channels at each served device (in the first class) can be then utilised by that device to serve other devices from the second class, which are not served by the BS, via controlled D2D associations. Herein, D2D pair discovery as well as the conditions for establishing successful D2D association between the classified devices are treated. Furthermore, two D2D association schemes that vary in terms of their performance and implementation complexity to meet certain objectives at the device of interest are presented. The developed analytical results address the scenarios of idealised perfect and practical imperfect D2D association. Numerical results are provided to further explain the performance variations between the proposed association schemes under perfect and imperfect operation scenarios.

"Background: High awareness of cervical cancer (CC) risk factors is important to decrease the morbidity and mortality associated with CC. This study aimed to assess the knowledge level of Palestinian women about CC risk factors and to determine the factors associated with good knowledge. Methods: This was a national cross-sectional study. Adult women from hospitals, primary healthcare centers, and public spaces of 11 governorates in Palestine were recruited using a stratified convenience sampling. A translated-into-Arabic version of the validated CC awareness measure (CeCAM) was used to assess the knowledge about the 11 CC risk factors. For each correctly identified risk factor, the participant was given one point. The total score was calculated and was categorized into three categories: poor knowledge (0–3), fair knowledge (4–7), and good knowledge (8–11). Results: A total of 7223 participants completed the Arabic CeCAM (response rate = 89.3%) and 7058 questionnaires were included in the final analysis: 2655 from the Gaza Strip and 4403 from the West Bank and Jerusalem. Participants recruited from the Gaza Strip were younger, getting lower monthly incomes, and with less chronic diseases than participants recruited from the West Bank and Jerusalem. The most frequently identified risk factor was ‘having a weakened immune system’ (n = 5458, 77.3%) followed by ‘infection with a sexually transmitted infection’ (n = 5388, 76.3%). The least identified risk factor was ‘having many children’ (n = 1597, 22.6%). Only 1670 women (23.7%) had good knowledge of CC risk factors. Women living in the Gaza Strip were more likely than women living in the West Bank and Jerusalem to have good knowledge (25.2% vs 22.7%). Completing a secondary or diploma degree, being employed, and having a monthly income of ≥ 1450 NIS (around $450) were all associated with lower likelihood of having good knowledge of CC risk factors. Conversely, knowing someone with cancer was associated with higher likelihood of having good knowledge. Conclusion: The overall awareness of CC risk factors was low. There is a substantial need to establish educational programs to promote Palestinian women’s awareness of CC." "خلفية البحث: الوعي العالي بعوامل الخطر لسرطان عنق الرحم مهم لتقليل نسبة المرض والوفيات المرتبطة بسرطان عنق الرحم. هدفت هذه الدراسة إلى تقييم مستوى معرفة النساء الفلسطينيات حول عوامل خطر الإصابة بسرطان عنق الرحم وتحديد العوامل المرتبطة بالمعرفة الجيدة. منهجية البحث: كانت هذه دراسة مقطعية وطنية. تم اختيار المشاركات في هذا البحث من النساء البالغات و تم جمع البيانات من النساء من المستشفيات ومراكز الرعاية الصحية الأولية والأماكن العامة في 11 محافظة في فلسطين باستخدام عينة ملائمة طبقية. تم استخدام نسخة مترجمة إلى العربية من مقياس الوعي لسرطان عنق الرحم (CeCAM) لتقييم المعرفة حول عوامل الخطر ذات العلاقة بسرطان عنق الرحم. لكل عامل خطر تم تحديده بشكل صحيح ، تم إعطاء المشارك نقطة واحدة. تم حساب النتيجة الإجمالية وتم تصنيفها إلى ثلاث فئات: ضعف المعرفة (0-3) ، ومتوسطة (4-7) ، والمعرفة الجيدة (8-11). النتائج: أكمل ما مجموعه 7223 مشاركًا اختبار CeCAM باللغة العربية (معدل الاستجابة = 89.3٪) وتم تضمين 7058 استبيانًا في التحليل النهائي: 2655 من قطاع غزة و 4403 من الضفة الغربية والقدس. كان المشاركون من قطاع غزة أصغر سناً, ويحصلون على دخل شهري أقل ، ولديهم أمراض مزمنة أقل من المشاركين من الضفة الغربية والقدس. كان عامل الخطر الأكثر تحديدًا هو ""ضعف الجهاز المناعي"" (العدد = 5458 ، 77.3٪) متبوعًا بـ ""الإصابة بعدوى تنتقل عن طريق الاتصال الجنسي"" (العدد = 5388 ، 76.3٪). كان عامل الخطر الأقل تحديدًا هو ""إنجاب العديد من الأطفال"" (العدد = 1597 ، 22.6٪). فقط 1670 امرأة (23.7٪) لديهن معرفة جيدة بعوامل خطر الإصابة بالسكري. كانت النساء اللواتي يعشن في قطاع غزة أكثر عرضة من النساء في الضفة الغربية والقدس للحصول على معرفة جيدة (25.2٪ مقابل 22.7٪). إن إكمال الشهادة الثانوية أو الدبلوم ، والتوظيف ، والحصول على دخل شهري قدره 1450 شيكل إسرائيلي جديد (حوالي 450 دولارًا) ، كلها مرتبطة بانخفاض احتمالية امتلاك معرفة جيدة بعوامل خطر الإصابة بسرطان عنق الرحم. على العكس من ذلك ، ارتبطت معرفة شخص مصاب بالسرطان بارتفاع احتمالية امتلاك معرفة جيدة. الخلاصة: كان الوعي العام لعوامل الخطر ذات العلاقة بسرطان عنق الرحم منخفض. هناك حاجة جوهرية لإنشاء برامج تثقيفية لتعزيز وعي النساء الفلسطينيات ببرنامج سرطان عنق الرحم."

This study aimed to test the effect of corporate social responsibility through activities towards society and environmental activities on financial leverage and corporate performance, the study population consists of all companies listed on the Amman Stock Exchange. The study sample reached 187 companies for the period 2014-2017, to achieve the goals of the study; regression analysis was used to find out the effect of social and environmental responsibility on leverage and performance, the study reached the results that the social responsibility towards the society affects the financial leverage of the company while the environmental activities did not affect the financial leverage, responsibility for social and environmental activities did not affect the performance of companies, and there was a positive correlation between social and environmental responsibility and financial leverage, and a negative link was found between financial leverage and performance.

Semi-Transparent conductive films (semi-TCFs) were fabricated from sustainable onion quercetin and functionalized carbon nanotubes (F-CNTs) in presence of different metal ion crosslinking agents via layer-by-layer technique. Moreover, 3D printing inks and injectable hydrogels were fabricated from sustainable onion quercetin and functionalized carbon nanotubes (F-CNTs) in presence gelatin. Synthesis and characterization of sustainable quercetin and functionalized CNTs were performed using spectroscopic, thermal, microscopic techniques; 1H-NMR, and ATR-FTIR for chemical structure, XRD for crystal structure, TGA and DTG for thermal stability, and SEM for morphologic nanostructure. Layer-by-layer semi-TCFs were fabricated in presence of crosslinking agent of metal ions like Ca2+, Ti2+, Sn2+, and Fe3+ ions, where transmittance was in the range of 41-67%, sheet resistance in 17-1567 kΩ/sq, and σdc/σop in 0.0005-0.02 range, which undoubtly confirm their semi-TCFs characteristics. Optimum performance of single-layer F-CNTs semi-TCFs was as follows; transmittance= 46.6%, sheet resistance= 6.5 kΩ/sq, and σdc/σop= 0.06. On the other hand, 3D printing ink of sustainable quercetin and Functionalized CNTs in presence of gelatin was fabricated. Semi-Interpenetrating network hydrogel was verified through spectroscopic ATR-FTIR technique. The injectable hydrogel showed promising characteristics of robustness, elasticity, anti-microbial activity, biocompatibility with human body, and stretchable low cost that adapt them to be successfully employed in biomedical and surgical applications.

Additional file 2.

In the present study, the concentrations of nine heavy metals (Fe, Zn, Mn, Cu, Mg, Cr, Ni, Cd, and Pb) in six different imported dried fruit samples of different brands (Mangoes, black raisins, figs, apricots, plums, and cranberries) were determined by Flame Atomic Absorption Spectroscopy (FAAS) after wet digestion. Samples were collected from different stores in Amman, Jordan. The average concentration of the selected metals in the analyzed samples were found to be in the range of 1.70-8.70 (Fe), 0.15-0.72 (Zn), 0.09-0.59 (Mn), 0.07-0.46 (Cu), 2.5-53.4 (Mg), 0.06-0.15 (Cr), 0.17-0.29 (Ni), 0.01-0.05 (Cd), and 0.11-0.57 (Pb) µg/g. The highest concentrations of Fe, Zn, Mn, Mg, and Ni were found in dried figs, highest concentrations of Cr, Cd, and Pb were found in dried apricots, and highest concentrations of Cu was found in dried black raisins. The results obtained in this study showed that Mg and Fe have the highest concentrations in all analyzed samples, whereas, the lowest concentrations obtained were for Cd and Cr. The concentrations of the highly toxic metals (Pb and Cd) in the all analyzed samples were found to be below or in good agreement with the permissible limits set by different health organizations. The figures of merit obtained for the FAAS calibration curves are brilliant with good linearity (r2 > 0.99). The FAAS method was validated by determining limit of detection (LOD), limit of quantitation (LOQ), and percent recovery (%R) for all investigated metals. The results obtained in this work were compared with the literature reported values.

We investigate the secrecy performance of a multiuser diversity scheme for an interference-limited wireless network with a base station (BS), $N$ legitimate users, and an eavesdropper in the presence of a single dominant interferer. Assuming interference dominates noise power at the eavesdropper and at each legitimate user's receiver, the BS transmits information to the legitimate user with the $k$ th best (highest) signal-to-interference ratio. We derive a closed-form expression for the secrecy outage probability for an arbitrary $N$ and an asymptotic expression for a fixed $k$ and large $N$ . Furthermore, we derive a closed form asymptotic expression for the ergodic secrecy capacity of the $k$ th best user and shows that it scales like $O\left(\log (N)\right)$ for a fixed $k$ and large $N$ .

In this paper, we study the outage performance of multiuser mixed underlay radio frequency (RF)/multidestinations free-space optical (FSO) links. For RF links, we consider a secondary network with multiple users that can communicate with multiple destinations through a relaying node. The relay is equipped with an antenna array at the RF side, and it uses the amplify-and-forward (AF) protocol. The primary users (PUs) are equipped with multiple antennas at transmit and receive nodes. The RF link is subjected to the aggregate PUs interference effect on the secondary network. To reduce the effect of PUs interference on secondary network at the relay node, two interference cancellation (IC) schemes are adopted, which vary in terms of complexity and achieved performance. On the other hand, the multidestination FSO links can be exploited to further enhance the quality of the second hop, and their associated channel models account for pointing errors, intensity modulation/direct detection, and heterodyne detection. For the aforementioned system model, we obtain exact and asymptotic closed-form expressions for the end-to-end outage probability. To further enhance system performance, optimal power allocation between the two hops is obtained based on the derived asymptotic outage probability expressions.

This paper investigates the impact of primary network interference on the performance of cognitive multihop secondary network under various multiple-input multiple-output MIMO approaches per hop. Specifically, the cognitive system involves a secondary network with MIMO relays that use the amplify-and-forward (AF) protocol, and each of which shares the same spectrum resources of multiple primary users (PUs) transmit and receive stations. Two different receive array conditions, and hence processing approaches, per hop in the secondary network are treated separately, which are maximal ratio combining (MRC) for sufficiently spaced receive antennas to provide receive diversity gain and interference cancellation (IC) for insufficiently spaced antennas to reduce the effect of PUs interference. The latter approach involves two different algorithms that vary in terms of complexity and achieved performance, which are dominant receive interference cancellation (DRIC) and adaptive receive interference cancellation (ARIC). Moreover, for both approaches, the transmit array gain is achieved per hop through the low-complexity transmit antenna selection (TAS). In doing so, new analytical results for multihop secondary network’s end-to-end outage probability are developed. Moreover, simple asymptotic results for this outage performance in high SNR regime are provided, from which the achieved diversity and coding gains and the diversity-multiplexing trade-off can be extracted. In addition, to further enhance the secondary network, optimal power allocation among hops is obtained based on the asymptotic outage performance under the constraints of transmit power of a secondary transmit station and interference limit on the primary network. The developed analytical results in this work are validated through numerical and simulation results.

Small-signal models are useful tools to preliminary understand the dynamics of interconnected systems like modular dc-dc converters which find a wide range of industrial applications. This work proposes a state-space-based averaged small-signal model in symbolic form for a peak current-mode controlled parallel-input/parallel-output buck converter operating in the continuous-conduction mode. In modeling the converter power-stage each module is independently represented. For modeling the current-mode control the state-space algebraic approach is used to incorporate the current-mode control-law into the power-stage equations. For each module two parasitic elements in addition to the current-loop sampling action are included in the derivation. Furthermore, the control-to-output voltage transfer functions are presented in symbolic form for two cases of interest: the first when the converter has two non-identical modules to study the effect of inductor mismatch, and the second when the converter is composed of n-connected identical modules to assess the effect of varying the number of modules. All responses from PSIM cycle-by-cycle simulations are in good agreement with the mathematical model predictions up to half the switching frequency.

This paper studies the achievable secrecy performance of multiple-input multiple-output wiretap channels in the presence of imperfect channel state information (CSI) with practical low-complexity transmission schemes. In particular, we propose a general order transmit antenna selection and power-efficient output-threshold maximal ratio combining scheme. Two separate cases depending on the availability of the eavesdropper’s CSI at the transmitter are considered. New closed-form expressions of the secrecy outage probability and the average secrecy rate are obtained. In addition, the secrecy diversity order and array gains, high signal-to-noise ratio slope, and power offset are characterized through asymptotic analysis, which enables the characterization of the effect of imprecise transmit antenna selection, output-threshold, and imperfect CSI on the secrecy performance. Numerical results are presented to validate the main outcomes of this paper.

In this paper, we examine transmit antenna selection with receiver maximal ratio combining (TAS/MRC), and selection combining (TAS/SC) in underlay multiple-input multiple-output cognitive relay networks with decode-and-forward relaying protocol, considering optimal and suboptimal cases. The considered secondary user (SU) network consists of a source, a relay and a destination each equipped with multiple correlated antennas. On the other hand, the primary network is composed of L primary users (PU) destinations, each of which is equipped with multiple correlated antennas. The SU transmission power is limited to the minimum between the maximum allowable power for transmission and the maximum interference power allowed by the PU network. In the analysis, all the channel coefficients between the PU and SU networks and between the SU nodes are assumed to follow independent and identically distributed (i.i.d.) Rayleigh fading distribution. Hence, new exact closed-form expressions are derived to study the outage performance of the considered CRN system. Moreover, for the high SNR values, simple asymptotic expressions for the outage probability are obtained to get more insights on the characterization of the achievable diversity orders and coding gains. The impact of antenna correlation on the system outage probability is investigated for special correlation cases. To enhance SU network performance, a power allocation optimization problem is formulated to minimize the SU asymptotic outage probability by optimally distributing the SU power budget between the SU source and SU relay under the constraints of total allowable SU transmission power and maximum allowable PU interference limit. The derived analytical formulas herein are supported by numerical and simulation results to clarify the main contributions. The results show that although the antenna correlation harms the system coding gain, the considered system can still achieve a full diversity order. Also, The results show that although the outage performance of optimal case outperforms the suboptimal case, the optimal case is more complicated compared to the suboptimal one. Moreover, the optimal power allocation solutions enhance the system outage performance compared to equal distribution model.

This paper studies the performance of a multiuser mixed radio frequency (RF)/free space optical (FSO) relay network with transmit opportunistic scheduling. The outdated channel information (OCI) on the first relaying hop and its effect on the system performance is also studied in this paper. Furthermore, a power allocation scheme is proposed for optimizing the overall system performance. The considered system includes $K$ sources (users), one amplify-and-froward relay and one destination. The users are connected with the relay node through RF links and the relay is connected with the destination through an FSO link. In the analysis, the first hop channels are assumed to follow Rayleigh fading model and the second hop channel is assumed to follow Gamma–Gamma fading model with considering the effect of pointing errors. Closed-form expressions are derived for the outage probability, average symbol error probability, and ergodic channel capacity. Furthermore, the system performance is studied at high signal-to-noise ratio regime, where the diversity order and coding gain are derived and analyzed. Using the asymptotic results, the power of users and relay are determined to minimize the system outage probability under a total power constraint. Monte–Carlo simulations are provided to validate the achieved exact and asymptotic results. Main results show that under weak atmospheric turbulence conditions, the system performance is dominated by the RF channels and a diversity order of $K$ is achieved by the system, whereas under severe atmospheric turbulence conditions, the system is dominated by the FSO channel and the diversity order is determined by the minimum value of the turbulence fading and pointing error parameters.

This paper investigates the effect of various operation parameters on the downlink user performance in overlaid small-cell networks. The case study considers closed-access small cells (e.g., femtocells), wherein only active authorized user equipment (UE) can be served, each of which is allocated a single downlink channel at a time. On the other hand, the macrocell base station can unconditionally serve macrocell UEs that exist inside its coverage space. The available channels can be shared simultaneously in the macrocell network and the femtocell network. Moreover, a channel can be reused only at the macrocell base station. The analysis provides quantitative approaches to model UE identities, their likelihoods of being active, and their likelihoods of producing interference, considering UE classifications, locations, and access capabilities. Moreover, it develops models for various interference sources observed from effective interference femtocells, considering femtocells capacities and operation conditions. The associated formulations to describe a desired UE performance and the impact of the number of available channels and the adopted channel assignment approach are thoroughly investigated. The results are generally presented for any channel models of interference sources and the desired source of the served UE. Moreover, specific channel models are then adopted, for which generalized closed-form analytical results for the desired UE outage probability performance are obtained. Numerical and simulation results are presented to further clarify the main outcomes of the developed analysis.

This study aimed to test the effect of corporate social responsibility through activities towards society and environmental activities on financial leverage and corporate performance, the study population consists of all companies listed on the Amman Stock Exchange. The study sample reached 187 companies for the period 2014-2017, to achieve the goals of the study; regression analysis was used to find out the effect of social and environmental responsibility on leverage and performance, the study reached the results that the social responsibility towards the society affects the financial leverage of the company while the environmental activities did not affect the financial leverage, responsibility for social and environmental activities did not affect the performance of companies, and there was a positive correlation between social and environmental responsibility and financial leverage, and a negative link was found between financial leverage and performance.

This paper presents generalized modeling and analysis of the impact of imperfect device-to-device (D2D) association for direct D2D communication in spectrum-shared downlink cellular networks. It also addresses practical interference and energy constraints that are imposed on the underlying D2D communication network. Specifically, new decentralized schemes to identify and then establish point-to- point D2D communication links between well-identified groups of active devices when downlink cellular resources can be accessed by the underlying D2D network are proposed. Through the analysis, detailed characterization of devices that can serve others are first presented, wherein each of which is required to meet a specific transmit power constraint it can dedicate to serve others. Then, the downlink resources (i.e., physical channels) that can be used by serving devices to serve others via D2D communication links are identified cooperatively in the D2D network, while meeting an interference constraint per channel as imposed by the primary cellular network. The analysis then proceeds to analyze the proposed D2D association, which aims to simultaneously improve the desired link quality while minimizing the effect of interference at each served device, considering various practical but imperfect operating scenarios. Numerical results are presented to clarify some of the main outcomes of this work.

This letter proposes a low-complexity antenna selection scheme based on large-scale fading to enhance the secrecy performance in independent and non-identical generalized- $\mathcal{K}$ fading channels. New analytical results for the secrecy outage probability and the probability of non-zero secrecy capacity are derived when the receiving terminals employ the maximum ratio combining scheme. In addition, simple and insightful approximations are obtained for the secrecy outage probability in the high signal to noise ratio regime, which shed light on the impact of key system parameters on the secrecy performance. Simulation results are provided to validate the analytical expressions.

Being capable of serving multiple users with the same radio resource, non-orthogonal multiple access (NOMA) can provide desirable performance enhancements in a fair and spectral efficient manner. In this paper, we investigate the resource allocation (RA) and cluster formation (CF) aspects of NOMA for downlink (DL) uplink (UL) decoupled (DUDe) heterogeneous networks (HetNets). A non-ideal NOMA scheme is considered with power disparity and sensitivity constraints (PDSCs), delay tolerance, and residual interference after cancellation. Taking the PDSCs into account, we analytically show that using the DL decoding order limits UL-NOMA performance by that of OMA, while employing an inverse order result in a performance gain that is mainly determined by the channel gain disparity of users. Thereafter, a generic CF method is proposed for any type of user graph, which iteratively forms clusters using Blossom algorithm. Finally, highly non-convex RA problem is converted into a convex form by employing geometric programming (GP) where power and bandwidth are optimized to maximize network sumrate and max-min fairness objectives.

Non-orthogonal multiple access (NOMA) has recently drawn attentions on its ability to fairly serve multiple users on the same radio resource with a desirable performance. However, achievable NOMA gain is primarily limited by channel gain disparity and successive interference cancellation (SIC) receiver characteristics. Accordingly, we introduce an imperfect SIC receiver model considering the power disparity and sensitivity constraints, delay tolerance, and residual interference due to detection and estimation errors. Then, a generic cluster formation (CF) and Power-Bandwidth Allocation (PBA) is formulated as a mixed-integer non-linear programming (MINLP) problem for downlink (DL) heterogeneous networks (HetNets). After dividing the MINLP problem into mixed-integer and non-linear sub- problems, we first transform CF into a multi-partite matching problem, which is solved sequentially using bi-partite matching techniques. For sumrate maximization, max-min fairness, and energy & spectrum efficiency objectives, we secondly put highly non-convex joint PBA into a convex form using geometric programming (GP). Extensive simulations unleash the potential of NOMA to handle large number of users, traffic offloading, and user fairness.

This paper presents new approaches to characterize the achieved performance of hybrid control-access small cells in the context of two-tier multi-input multi-output (MIMO) cellular networks with random interference distributions. The hybrid scheme at small cells (such as femtocells) allows for sharing radio resources between the two network tiers according to the densities of small cells and their associated users, as well as the observed interference power levels in the two network tiers. The analysis considers MIMO transceivers at all nodes, for which antenna arrays can be utilized to implement transmit antenna selection (TAS) and receive maximal ratio combining (MRC) under MIMO point-to-point channels. Moreover, it tar-gets network-level models of interference sources inside each tier and between the two tiers, which are assumed to follow Poisson field processes. To fully capture the occasions for Poisson field distribution on MIMO spatial domain. Two practical scenarios of interference sources are addressed including highly-correlated or uncorrelated transmit antenna arrays of the serving macrocell base station. The analysis presents new analytical approaches that can characterize the downlink outage probability performance in any tier. Furthermore, the outage performance in high signal-to-noise (SNR) regime is also obtained, which can be useful to deduce diversity and/or coding gains.

In this paper, resource allocation and co-tier/cross-tier interference management are investigated for D2D-enabled heterogeneous networks (HetNets) where tiers 1, 2, and 3 consist of macrocells, smallcells, and D2D pairs, respectively. We first propose a D2D-enabled fractional frequency reuse scheme for uplink (UL) HetNets where macrocell subregions are preassigned to different subbands (SBs) in order to mitigate the tier-1↔tier-1 interference. Nevertheless, cell-edge macrocell user equipments (MUEs) with high transmission powers still form dead-zones for nearby smallcell UEs (SUEs) and D2D UEs (DUEs). One of the simple but yet novel means of the dead-zone alleviation is associating the cell-edge MUEs with nearby smallcells, which is also known as downlink (DL)/UL decoupling (DUDe). Subject to quality of service (QoS) requirements and power constraints, we formulate a joint SB assignment and resource block (RB) allocation optimization as a mixed integer non-linear programming (MINLP) problem to maximize the D2D sum rate and minimize the co-tier/cross-tier interference. Based on tolerable interference limit, we propose a fast yet high-performance suboptimal solution to jointly assign available SBs and RBs to smallcells. A D2D mode selection and resource allocation framework is then developed for DUEs. As traditional DL/UL Coupled (DUCo) scheme generates significant interference proportional to cellular user density and user association bias factor, results obtained from the combination of proposed methods and developed algorithms reveal the potential of DUDe for co-tier/cross-tier interference mitigation which opens more room for spectrum reuse of DUEs.

This paper studies power allocation for performance constrained dual-hop variable-gain amplify-and-forward (AF) relay networks in Nakagami-$m$ fading. In this context, the performance constraint is formulated as a constraint on the end-to-end signal-to-noise-ratio (SNR) and the overall power consumed is minimized while maintaining this constraint. This problem is considered under two different assumptions of the available channel state information (CSI) at the relays, namely full CSI at the relays and partial CSI at the relays. In addition to the power minimization problem, we also consider the end-to-end SNR maximization problem under a total power constraint for the partial CSI case. We provide closed-form solutions for all the problems which are easy to implement except in two cases, namely selective relaying with partial CSI for power minimization and SNR maximization, where we give the solution in the form of a one-variable equation which can be solved efficiently. Numerical results are then provided to characterize the performance of the proposed power allocation algorithms considering the effects of channel parameters and CSI availability.

This paper studies generalized single-stream transmit beamforming employing receive array co-channel interference reduction algorithms under slow and flat fading multiuser wireless systems. The impact of imperfect prediction of channel state information for the desired user spatially uncorrelated transmit channels on the effectiveness of transmit beamforming for different interference reduction techniques is investigated. The case of over-loaded receive array with closely-spaced elements is considered, wherein it can be configured to null specified interfering sources. Both dominant interference reduction and adaptive interference reduction techniques for statistically ordered and unordered interferers powers, respectively, are thoroughly studied. The effect of outdated statistical ordering of the interferers powers on the efficiency of dominant interference reduction is studied and then compared against the adaptive interference reduction. For the system models described above, new analytical formulations for the statistics of combined signal-to-interference-plus-noise ratio are presented, from which results for conventional maximum ratio transmission and single-antenna best transmit selection can be directly deduced as limiting cases. These results are then utilized to obtain quantitative measures for various performance metrics. They are also used to compare the achieved performance of various configuration models under consideration.

This paper proposes a reduced-complexity multichannel assignment scheme for short-range cellular systems. It treats the scenario when a number of small-cell (e.g., femtocell) access points (APs) can be shared to serve active scheduled users. The APs employ isotropic antenna arrays and operate using an open-access control strategy. To improve the reuse ratio of physical resources, the APs are assumed to occupy a single physical channel, wherein coordination among them is infeasible. On the other hand, to improve the spatial coverage, a scheduled user can be served by a single transmit channel from an AP at a time. For the case of overloaded APs and when the feedback links are capacity limited, the scheme attempts to identify the suitable transmit channels from the deployed APs in an adaptive manner such that certain performance and/or processing load limits are satisfied. The effects of some system and design parameters on the outcomes of the scheme are thoroughly discussed. Novel results for the statistics of the resulting interference power are presented, from which results for some performance measures and processing loads are obtained. Numerical and simulations results are provided to clarify the achieved gains, as compared with related models under different operating conditions.

This paper proposes adequate methods to improve the interference mitigation capability of a recently investigated switched-based interference reduction scheme for single downlink channel assignment in over-loaded small-cell networks. The model assumes that the available orthogonal channels for small cells are distributed among access points in close vicinity, where each access point knows its allocated channels a priori. Each cell has a single antenna, employs the open access strategy, and can reuse its allocated channels simultaneously, while scheduling concurrent service requests. Moreover, the access points can not coordinate their transmissions, and can receive limited feedback from active users. The paper presents low-complexity schemes to identify a suitable channel to serve the scheduled user by maintaining the interference power level within a tolerable range. They attempt to either complement the switched-based scheme by minimum interference channel selection or adopt different interference thresholds on available channels, while reducing the channel examination load. The optimal thresholds for interference mitigation at the desired receive station are quantified for various performance criteria. The performance and processing load of the proposed schemes are obtained analytically, and then compared to those of the single-threshold scheme via numerical and simulation results.

Femtocells can be employed in cellular systems to enhance the indoor coverage, especially in the areas with high capacity growing demands and high traffic rates. In this paper, we propose an efficient resource utilization protocol, named as shared access protocol (SAP), to enable the unauthorized macrocell user equipment to communicate with partially closed-access femtocell base station to improve and enhance the system performance. The system model considers a femtocell that is equipped with a total of N separated antennas or channels to multiplex independent traffic. Then, a set of N1 channels is used for closed access only by the authorized users, and the remaining set of channel resources can be used for open access by either authorized or unauthorized users upon their demands and spatial locations. For this system model, we obtain the signal-to-interference ratio characteristics, such as the distribution and the moment generating function, in closed forms for two fading models of indoor and outdoor environments. The signal-to-interference ratio statistics are then used to derive some important performance measures of the proposed SAP in closed form, such as the average bit error rate, outage probability, and average channel capacity for the two fading models under consideration. Numerical results for the obtained expressions are provided and supported by Monte Carlo simulations to validate the analytical development and study the effectiveness of the proposed SAP under different conditions. Copyright © 2013 John Wiley & Sons, Ltd.

This letter studies the ergodic capacity of channel state information (CSI)-assisted two-hop amplify-and-forward (AF) relaying system, in which the relay and the destination undergo independent sources of co-channel interference. The fading envelopes associated with the desired and interfering users are assumed to follow independent but non-identically distributed (i.n.d.) Nakagami-m fading models. Through the analysis and by assuming the fading parameter m of the two hop channels being integer, exact and approximate results for the system average ergodic capacity under different conditions are derived. They are valid for arbitrary numbers of interfering signals, and can be used to study the case of independent and identically distributed (i.i.d.) channels as a limiting application. Simulation results are provided to validate the analytical development, and to clarify the average ergodic capacity under different conditions.

© 2016 IEEE. This paper investigates low-complexity joint interference avoidance and desired link improvement for single-channel allocation in multiuser multiantenna access points (APs) for open-access small cells. It is considered that an active user is equipped with an antenna array that can be used to suppress interference sources but not to provide spatial diversity. On the other hand, the operation of APs can be coordinated to meet design requirements, where each of which can unconditionally utilize assigned physical channels. Moreover, each AP is equipped with uncorrelated antennas that can be reused simultaneously to serve many active users. The analysis provides new approaches to exploit physical channels, transmit antennas, and APs to mitigate interference, while providing the best possible link gain to an active user through the most suitable interference-free channel. The event of concurrent service requests placed by active users on a specific interference-free channel is discussed for either interference avoidance through identifying unshared channels or desired link improvement via multiuser scheduling. The applicability of the approaches to balance downlink loads is explained, and practical scenarios due to imperfect identification of interference-free channels and/or the scheduled user are thoroughly investigated. The developed results are applicable for any statistical and geometric models of the allocated channel to an active user, as well as channel conditions of interference users. They can be used to study various performance measures. Numerical and simulation results are presented to explain some outcomes of this paper.

In this letter, energy-efficient transmission and power allocation for fixed-gain amplify-and-forward relay networks with partial channel state information (CSI) are studied. In the energy-efficiency problem, the total power consumed is minimized while keeping the signal-to-noise-ratio (SNR) above a certain threshold. In the dual problem of power allocation, the end-to-end SNR is maximized under individual and global power constraints. Closed-form expressions for the optimal source and relay powers and the Lagrangian multiplier are obtained. Numerical results show that the optimal power allocation with partial CSI provides comparable performance as optimal power allocation with full CSI at low SNR. © 2012 IEEE.

This paper investigates an adaptive scheduling algorithm for multiuser environments with statistically independent but nonidentically distributed (i.n.d.) channel conditions. The algorithm aims to reduce feedback load by sequentially and arbitrarily examining the user channels. It also provides improved performance by realizing postexamining best user selection. The first part of the paper presents new formulations for the statistics of the signal-to-noise ratio (SNR) of the scheduled user under i.n.d. channel conditions. The second part capitalizes on the findings in the first part and presents various performance and processing complexity measures for adaptive discrete-time transmission. The results are then extended to investigate the effect of outdated channel estimates on the statistics of the scheduled user SNR, as well as some performance measures. Numerical results are provided to clarify the usefulness of the scheduling algorithm under perfect or outdated channel estimates.

This letter studies the outage probability of fixed-gain amplify-and-forward dual-hop relaying system in the presence of co-channel interference (CCI). Assuming that the relay and the destination terminals are subject to both CCI and additive white noise, and the envelopes of the channels follow dissimilar Nakagami-m distributions, an exact expression for the outage probability of the system is derived. The result is applicable for arbitrary numbers of interfering signals at receiving terminals and can be efficiently evaluated. In addition, it enables us to study the effect of CCI at either the relay or the destination as special cases. The analytical results are validated by simulations. The simulated results show that the outage performance of the system is less sensitive to the interference at the destination.

This letter studies cognitive radio transceiver that can opportunistically use the available channels of primary user (PU). Specifically, we investigate and compare two different opportunistic channel access schemes. The first scheme applies when the secondary user (SU) has access to only one channel. The second scheme, based on channel switching mechanism, applies when the SU has access to multiple channels but can at a given time monitor and access only one channel. For these access schemes, we derive the exact analytical results for the novel performance metrics of average access time and average waiting time under general PU traffic models.

This paper proposes a collaborative-based scheme for a transmit antenna channel assignment in overloaded multiantenna femtocells, with the aim of reducing the overhead load. It is assumed that multiple femtocell access points (FAPs) are deployed to sequentially allocate the available resources to scheduled users while reducing the interference experienced by each active user. The FAPs operate concurrently and each of them is allocated an orthogonal channel and employs a transmit array of arbitrary size. The suitable FAP and its associated transmit channel are then identified based on the noncoherently predicted interference power levels on available channels when feedback links are capacity limited. The effect of possible FAP failure or infeasibility to collaborate is characterized for different operating conditions. The applicability of the proposed scheme for specific cases, such as the use of directional antennas in each FAP or shared channels among different FAPs, is also discussed. For arbitrary statistical models of interference power levels on different channels, the average numbers of collaboration requests and examined transmit antenna channels are quantified. Moreover, the statistics of the resulting interference power are derived, which are then used to study various system performance measures. The effect of the interference threshold on the aforementioned measures for processing load and achieved performance is investigated. Numerical and simulations results are presented to support the analytical development and to clarify the tradeoff between the achieved performance enhancement using the proposed scheme and the required processing load for different operating scenarios.

Femtocells have been proposed to enhance the spatial coverage and system capacity of existing cellular networks. However, this technology may result in significant performance loss due to the increase in co-channel interference, particularly when coordination between access points is infeasible. This paper targets interference management in such overlaid networks. It is assumed that the femtocells employ the open-access strategy to reduce cross-tier interference, and can share resources concurrently. It is also assumed that each end user (EU) can access one channel at a time, and transfer limited feedback. To reduce the effect of co-tier interference in the absence of the desired EU channel state information (CSI) at the serving access point as well as coordination between active access points, a switched scheme based on the interference levels associated with available channels is proposed. Through the analysis, the scheme modes of operation in under-loaded and over-loaded channels are studied, from which the statistics of the resulting interference power are quantified. The impact of the proposed scheme on the received desired power is thoroughly discussed. In addition, the effect of the switching threshold on the achieved performance of the desired EU is investigated. The results clarify that the proposed scheme can improve the performance while reducing the number of examined channels and feedback load.

This paper investigates the performance of two low-complexity combining schemes, which are based on one- or two-phase observation, to mitigate multipath fading in dual-hop amplify-and-forward relaying systems. For the one-phase-based combining, a single-antenna station is assumed to relay information from a multiple-antenna transmitter to a multiple-antenna receiver, and the activation of the receive antennas is adaptively performed based on the second-hop statistics, regardless of the first-hop conditions. On the other hand, the two-phase-based combining suggests using multiple single-antenna stations between the multiple-antenna transmitter and the single-antenna receiver, where the suitable set of active relays is identified according to the precombining end-to-end fading conditions. To facilitate comparisons between the two schemes, formulations for the statistics of the combined signal-to-noise ratio and some performance measures are presented. Numerical and simulation results are shown to clarify the tradeoff between the achieved diversity-array gain, the processing complexity, and the power consumption.