Realization of a Second Harmonic Antenna for Rural Communications*

In this research, an active antenna operated at the second harmonic frequency is investigated, and is implemented using microstrip antenna material. The antenna consists of a FET oscillator which plays as a fundamental frequency oscillator and a frequency multiplier, and a patch antenna resonated at the second harmonic frequency as the radiator. A maximum second-harmonic output power can be extracted when the load impedance of the oscillator is optimized both at the fundamental and at the second harmonic frequencies. A rectangular patch antenna is used to radiate the second harmonic output power from the oscillator. The patch impedance is matched resistively at the second harmonic frequency. The patch antenna is fabricated using Diclad 522 microstrip substrates (relative permitivity r = 2.5) with a dielectric thickness of 1.57 mm. A GaAs FET AT-8250 transistor is used as an oscillator and a frequency multiplier and acts as the active component. Fundamental frequency is designed at 2,4 GHz band, so that the second harmonic frequency operates at 4,8 GHz band. The frequency is chosen to facilitate and to extend the needs of communications in rural areas using the unlicensed Industrial Scientific, and Medical (ISM) band. Operating the communication infrastructures intended for the use at 2.4 GHz band at its second harmonic frequency, is intended to alleviate interference levels at 2.4 GHz

Improved Predictive Power Control of Cdma System in Rayleigh Fading Channel

In this paper an improved prediction-based power control is proposed for code division multiple access (CDMA)systems in Rayleigh fading channel environments. One of the most serious problems which degrades the performanceof power control algorithm is the effect of feedback delay. To overcome the effect of feedback delay, power controlneeds to employ prediction algorithm which utilises the correlation property of the past channel samples measurementsto predict the future sample values. In CDMA power control, however, the correlation property of channelmeasurements is destroyed because the transmit power is continuously updated for each power control interval. Theprediction algorithm in this paper uses the recursive least square (RLS) technique and an improved predictor algorithmis proposed to compensate for the channel correlation. The result shows that the performance of improved predictivepower control proposed in this paper evaluated in terms of bit error rate (BER) as a function of bit energy-tointerferencepower density ratio Eb/Io improved significantly from that of the conventional predictor

Variable Step Closed Loop Power Control with Space Diversity for Low Elevation Angle High Altitude Platforms Communication Channel [Langkah Variabel Kontrol Daya Loop Tertutup Dengan Keragaman Ruang Untuk Sudut Elevasi Rendah Pada Kanal Komunikasi HAPs]

This paper proposes variable step closed loop power control algorithm combined with space diversity to improve the performance of High Altitude Platforms (HAPs) communication at low elevation angle using Code Division Multiple Access (CDMA). In this contribution, we first develop HAPs channel model which is derived from experimental measurement. From our experiment, we found HAPs channel characteristic can be modeled as a Ricean distribution because the presence of line of sight path. Different elevation angle resulting different K factor value. This value is then used in Signal to Interference Ratio (SIR) based closed loop power control evaluation. The variable step algorithm is simulated under various elevation angles with different speed of mobile user. The performance is presented in terms of user elevation angle, user speed, step size and space diversity order. We found that the performance of variable step closed-loop power control less effective at low elevation angle. However our simulation shows that space diversity is able to improve the performance of closed loop power control for HAPs channel at low elevation angle.*****Kajian ini mengusulkan suatu algoritma kontrol daya langkah variabel loop tertutup dikombinasikan dengan keragaman ruang untuk meningkatkan kinerja komunikasi High Altitude Platforms(HAPs) pada sudut elevasi rendah menggunakan Code Division Multiple Access (CDMA). Kami berkontribusi untuk mengembangkan model kanal HAPs yang berasal dari pengukuran eksperimental sebelumnya. Dari percobaan tersebut, kami menemukan karakteristik kanal HAPs yang dapat dimodelkan sebagai distribusi Ricean karena kehadiran jalur tanpa penghalang. Eksperimen menunjukkan bahwa perbedaan sudut elevasi menghasilkan perbedaan nilai factor K. Nilai ini kemudian digunakan dalam Signal to Interference Ratio (SIR) berbasiskan evaluasi kontrol daya loop tertutup. Algoritma langkah variabel disimulasikan dibawah sudut elevasi yang berbeda dengan kecepatan yang berbeda dari pengguna vobile. Kinerja tersebut disajikan dalam hal sudut elevasi pengguna, kecepatan pengguna, ukuran langkah dan ketertiban ruang keanekaragaman. Kami menemukan bahwa kinerja langkah variabel kontrol daya loop tertutup kurang efektif pada sudut elevasi rendah. Namun simulasi kami menunjukkan bahwa ruang keragaman mampu meningkatkan kinerja kontrol daya loop tertutup untuk kanal HAPs di sudut elevasi rendah

Franchise Cellular Operator in Rural Areas (Operator Seluler Model Franchise di Daerah Rural)

The rapid development in telecommunication motivates organizations or business person to gain some profits in telco-based business. However, very limited Indonesian villagers had access to these technologies.  This problem was caused by the less attractive condition (even  unfeasible) to invest in the rural areas because the cost to build a conventional telecommunication infrastructure was very high, eventhough this was a potential new market. The other is the limitations of the spectrum allocated for new wireless access operator. This study formulated a new network cellular business model that met the rural needs, called franchise operator which is able to solve the problem of the frequency spectrum limitations, because new operators could make use of the frequency spectrum of the legal operators, though a new proposed business scheme, whereby the new operator does not require a new frequency allocation. However, the implementation of this franchising model is highly dependent on telecommunication regulation in Indonesia. So that further studies is needed regarding the regulation that will permit the creation of franchising operator. Open BTS technology as selected village cellular technology, requires an investment only of Rp 223 million to build telecommunication infrastructure in rural areas. This is much cheaper than to deploy a conventional infrastructure. Supported by franchise business model, operating cost could be decreased, making this model feasible to be implemented as a breakthrough of the telecommunication infrastructure development in rural areas.Perkembangan teknologi mendorong pelaku perdagangan beralih membentuk bisnis telekomunikasi dan berkompetisi dengan menawarkan berbagai produk telekomunikasi. Namun sangat disayangkan, 50,21% dari total penduduk Indonesia yang tinggal di pedesaan (Badan Pusat Statistik Indonesia, 2010) hampir tidak terjangkau akses telekomunikasi. Masalahnya adalah para operator merasa berat berinvestasi di pedesaan karena biaya pembangunan jaringan seluler konvensional yang sangat tinggi dan tidak sebanding dengan keuntungan yang diperoleh. Selain itu keterbatasan spektrum menjadi kendala bagi calon operator baru yang ingin mengambil peran. Guna mengatasi masalah tersebut, dihasilkan sebuah model operator berbasis kerjasama franchise yang disesuaikan dengan kebutuhan pedesaan. Operator model franchise yang dimaksud dapat memberi solusi keterbatasan spektrum frekuensi karena operator hanya perlu memanfaatkan spektrum frekuensi dari operator berlisensi sehingga tidak membutuhkan alokasi frekuensi yang baru. Namun pelaksanaan franchising ini sangat tergantung pada regulasi atau peraturan telekomunikasi yang berlaku di Indonesia. Sehingga diperlukan kajian lebih lanjut mengenai Undang-Undang maupun Peraturan Pemerintah yang dapat berdampak bagi franchising operator ini. Teknologi openBTS yang dipilih sebagai solusi teknologi seluler pedesaan hanya memerlukan biaya investasi sekitar Rp 223 juta untuk membangun satu site infrastruktur di daerah terpencil. Biaya investasi ini jauh lebih murah dibandingkan biaya pembangunan infrastruktur seluler konvensional. Didukung dengan model bisnis franchise yang akan mengurangi biaya operasional operator, maka desain ini dapat menjadi peluang bisnis baru bagi operator eksisting maupun untuk memberi dukungan dalam meningkatkan produktifitas dan efisiensi infrastruktur telekomunikasi dan informasi di pedesaan. 

Franchise Cellular Operator in Rural Areas (Operator Seluler Model Franchise di Daerah Rural)

The rapid development in telecommunication motivates organizations or business person to gain some profits in telco-based business. However, very limited Indonesian villagers had access to these technologies.  This problem was caused by the less attractive condition (even  unfeasible) to invest in the rural areas because the cost to build a conventional telecommunication infrastructure was very high, eventhough this was a potential new market. The other is the limitations of the spectrum allocated for new wireless access operator. This study formulated a new network cellular business model that met the rural needs, called franchise operator which is able to solve the problem of the frequency spectrum limitations, because new operators could make use of the frequency spectrum of the legal operators, though a new proposed business scheme, whereby the new operator does not require a new frequency allocation. However, the implementation of this franchising model is highly dependent on telecommunication regulation in Indonesia. So that further studies is needed regarding the regulation that will permit the creation of franchising operator. Open BTS technology as selected village cellular technology, requires an investment only of Rp 223 million to build telecommunication infrastructure in rural areas. This is much cheaper than to deploy a conventional infrastructure. Supported by franchise business model, operating cost could be decreased, making this model feasible to be implemented as a breakthrough of the telecommunication infrastructure development in rural areas.Perkembangan teknologi mendorong pelaku perdagangan beralih membentuk bisnis telekomunikasi dan berkompetisi dengan menawarkan berbagai produk telekomunikasi. Namun sangat disayangkan, 50,21% dari total penduduk Indonesia yang tinggal di pedesaan (Badan Pusat Statistik Indonesia, 2010) hampir tidak terjangkau akses telekomunikasi. Masalahnya adalah para operator merasa berat berinvestasi di pedesaan karena biaya pembangunan jaringan seluler konvensional yang sangat tinggi dan tidak sebanding dengan keuntungan yang diperoleh. Selain itu keterbatasan spektrum menjadi kendala bagi calon operator baru yang ingin mengambil peran. Guna mengatasi masalah tersebut, dihasilkan sebuah model operator berbasis kerjasama franchise yang disesuaikan dengan kebutuhan pedesaan. Operator model franchise yang dimaksud dapat memberi solusi keterbatasan spektrum frekuensi karena operator hanya perlu memanfaatkan spektrum frekuensi dari operator berlisensi sehingga tidak membutuhkan alokasi frekuensi yang baru. Namun pelaksanaan franchising ini sangat tergantung pada regulasi atau peraturan telekomunikasi yang berlaku di Indonesia. Sehingga diperlukan kajian lebih lanjut mengenai Undang-Undang maupun Peraturan Pemerintah yang dapat berdampak bagi franchising operator ini. Teknologi openBTS yang dipilih sebagai solusi teknologi seluler pedesaan hanya memerlukan biaya investasi sekitar Rp 223 juta untuk membangun satu site infrastruktur di daerah terpencil. Biaya investasi ini jauh lebih murah dibandingkan biaya pembangunan infrastruktur seluler konvensional. Didukung dengan model bisnis franchise yang akan mengurangi biaya operasional operator, maka desain ini dapat menjadi peluang bisnis baru bagi operator eksisting maupun untuk memberi dukungan dalam meningkatkan produktifitas dan efisiensi infrastruktur telekomunikasi dan informasi di pedesaan. 

Antioxidant, Antidiabetic, and Anti-obesity Potential of Ipomoea Reptans Poir Leaves

Ipomoea reptans Poir or kangkung is a popular leafy vegetable, a favorite to people in Asian countries. However, limited information is available on their bioactivities. In the present study, the antioxidant, antidiabetic, and anti-obesity potential of I. reptans leaves were investigated. Different fractions (ethanol, ethyl acetate, and hexane) of I. reptans leaves were evaluated for their scavenging activity on DPPH radicals, whereas their reducing potential was investigated by cupric reducing antioxidant capacity (CuPRAC), total antioxidant, and reducing power assays. The antidiabetic potential was investigated by their inhibition effect on α-glucosidase. Total phenolic and flavonoid contents of I. reptans leaves were solvent dependent. Ethyl acetate contained the highest phenolic content, followed by ethanol and hexane fractions. However, for flavonoid content, the order was ethanol > ethyl acetate > hexane. All fractions showed DPPH scavenging activity in a concentration-dependent manner, with activities weaker than standards ascorbic acid and BHT, in the order of ethanol > ethyl acetate > hexane. All fractions showed reducing capacity, but only hexane and ethanol fractions of I. reptans leaves showed inhibition on α-glucosidase, with hexane showed more potent inhibition compared to acarbose. The study also found that fractions of I. reptans inhibit lipase and trypsin, enzymes related to lipid metabolism. Findings in this study offer a prospect for I. reptans leaves as a functional food source for antioxidant, antidiabetic, and anti-obesity purposes