There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

Orthogonal frequency division multiplexing (OFDM) is a modulation technique which is now used in most new and emerging broadband wired and wireless communication systems because it is an effective solution to intersymbol interference caused by a dispersive channel. Very recently a number of researchers have shown that OFDM is also a promising technology for optical communications. This paper gives a tutorial overview of OFDM highlighting the aspects that are likely to be important in optical applications. To achieve good performance in optical systems OFDM must be adapted in various ways. The constraints imposed by single mode optical fiber, multimode optical fiber and optical wireless are discussed and the new forms of optical OFDM which have been developed are outlined. The main drawbacks of OFDM are its high peak to average power ratio and its sensitivity to phase noise and frequency offset. The impairments that these cause are described and their implications for optical systems discussed.

OFDM for Optical Communications

Visible Light Communications: Theory and Applications

https://www.jstage.jst.go.jp/article/itej/64/8/64_1219/_pdf

Introduction of LTE

This paper implement Wireless Sensor Networks (WSNs) in agriculture, especially for hydroponics plants. In agriculture with hydroponic method, water becomes the main nutrient for plants. Water and surroundings are become the important factors for plant growth. WSN is used to remotely monitor the quality of water in hydroponic plants. Zigbee is one of wireless technology usually used in WSN since it is suitable for low data rate, low costs, and low power consumption, while a widely used wireless gateway is using WiFi based. This proposed design combines Zigbee and WiFi technology in WSN system. Zigbee based transceiver is used in the sensor nodes side and the WiFi based gateway is used in the coordinator side. The experiment is conducted to test the WSN performance in the presence of Zigbee and WiFi, includes testing the Received Signal Strength Indicator (RSSI), Packet loss and error, and Throughput. The results show that the RSSI value and throughput in network with the interconnected Zigbee - WiFi are decreased about −10 dBm and 0.13 kbps respectively compared to the not-interconnected Zigbee - WiFi. The farther the distance between nodes the throughput is decreased.

Hybrid ZigBee and WiFi Wireless Sensor Networks for Hydroponic Monitoring

Klaten City which is famous for its tourist attractions invites foreign and local tourists to visit the place. However, 4G LTE (Long Term Evolution) telecommunications services in the tourist city have not been maximally felt by the public and tourists who visit because based on data from Provider X, the number of sites installed is only concentrated in densely populated areas, while many tourist objects have not been installed. This study aims to improve the efficiency and coverage of LTE networks in the city of Klaten, Central Java using the ACP optimization function with the 1800 MHz Frequency Division Duplex (FDD) modulation technique. This network simulation uses Atoll software to perform several measurements including link budget calculation, final signal quality comparison on existing and new site data. The result of comparing existing sites when a site has been added is that the signal quality improves and the covered area becomes wider than the previous area. The results of the simulation data with the percentage of 642.8 km2 Klaten area covered by the Existing site, RSRP with 85.6% covered area and RSRQ with 55.3% covered area. New Site RSRP with 100% covered area and RSRQ with 100% covered area. Automatic Cell Planning RSRP with 93.9% covered area and RSRQ with 96.2% covered area.

Automatic Cell Planning of LTE FDD 1800 MHz Network in Klaten, Central Java

The development of telecommunications system in modern technology is increasing widely so that the process can take place more quickly and efficiently, one of which was the use of Software Defined Radio (SDR). SDR is a radio communication system where the components that have been typically implemented in hardware (mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software on computer or embedded system supported by GNU Radio Companion and USRP. This research is designing the video transmission using based on Software Defined Radio using GNU Radio and USRP. Some hardware function is replaced by the software in GRC block in GNU Radio. USRP B200 is used to translate the signal to the exact radio frequency. In testing the video transmission, the parameters of the FFT length of OFDM, 128, 256, and 512 and with different type of modulation was tested. The video transmission with the best result was performed using 512 FFT lengths.

Implementation of SDR for video transmission using GNU radio and USRP B200

This paper investigate implementation of unequal power for downlink multiple access for visible light communication. A straightforward allotment of power in regard to fairness is used to differentiate the user access, while the modulation is performed using discrete cosine transform, pulse amplitude modulation and DC bias. The system performance is examined by the bit error rate on tapered condition of VLC channel. The uneven power allocation had shown distinctive performance, in compare with transmission of equally powered signals.

Discrete Cosine Transform and Pulse Amplitude Modulation for Visible Light Communication with Unequally Powered Multiple Access

This paper discusses human voice filtering. The filtering was done by attenuating human voice's frequencies within a song's frequencies using filter design. Band-stop filter design is one of filter design that is used in this research. The band-stop filter design uses one type of windowing that is the Butterworth windowing. The method for the human voice filtering is offered by using a band-stop filter design simulated in MATLAB. The specified stop-band is based on the human voice's frequencies. The algorithm was done to filter the human voice from an audio. The result is then optimized to find the optimal result for the filtering. The methods for the optimization are used to simulate the band-stop filter design with different stop-band, FFT the result to show its frequency spectrum, and repeat the process until the heard voice has the optimal result. Based on the methods, a comparison between various stop-band specifications is presented to find the most optimal one. The chosen stop-band is used for male voice filtering and female voice filtering to see if it is suitable for both kind of voices.

Dwi Astharini

Papers

Hybrid ZigBee and WiFi Wireless Sensor Networks for Hydroponic Monitoring

Automatic Cell Planning of LTE FDD 1800 MHz Network in Klaten, Central Java

Implementation of SDR for video transmission using GNU radio and USRP B200

Discrete Cosine Transform and Pulse Amplitude Modulation for Visible Light Communication with Unequally Powered Multiple Access

Human voice filtering with band-stop filter design in MATLAB