Ondrej Krajsa

A comparative study of the modern access networks

A great extension of the Fiber To The Home (FTTH) services is provided by Internet service providers through using the Passive Optical Networks (PON) technology. Another technology offered by telecommunication companies is VDSL2. These providers offer not only data services, but also voice and video services, which are sensitive to latency, jitter, throughput and other network parameters. This article discusses the transmission capacity of metallic and optical (PON) networks for VoIP and video services. We used defined PON network topologies and VDSL network topologies for the measuring scenarios, utilizing PBX Asterisk for VoIP benchmarking. Tests based on RFC 2544, ITU-T Y.156sam and bit-error-test were performed. The parameters we compared in this article are jitter, call setup time, latency, throughput and frame-loss. Optical Networks are considered as the best choice, however, in this article we found that the VDSL2 networks show comparable performance, and sometimes they show better results in some parameters.

Filterbank modulation techniques and its utilization in ADSL systems

The multicarrier modulations (MCM) became widely used and have been applied to wire and wireless transmission systems in recent years. This modulation techniques enable a near-perfect utilization of the provided frequency band on metallic cables and they also eliminate multipath propagation effect in terrestrial transmission. Mainly used implementations of MCM are Discrete MultiTone (DMT) and Orthogonal Frequency Division Multiplexing (OFDM). These approaches have also disadvantages, which have led to seeking new approaches to the implementation of the MCM modulation scheme. One of them is the Filtered MultiTone Modulation (FMT). In the article, the channel equalization in half-overlapped and non-overlapped FMT modulation will be compared.

On Location Estimation Technique Based of the Time of Flight in Low-power Wireless Systems

Abstract This study deals with the distance estimation issue in low-power wireless systems being usually used for sensor networking and interconnecting the Internet of Things. There is an effort to locate or track these sensor entities for different needs the radio signal time of flight principle from the theoretical and practical side of application research is evaluated. Since these sensor devices are mainly targeted for low power consumption appliances, there is always need for optimization of any aspects needed for regular sensor operation. For the distance estimation we benefit from IEEE 802.15.4a technology, which offers the precise ranging capabilities. There is no need for additional hardware to be used for the ranging task and all fundamental measurements are acquired within the 15.4a standard compliant hardware in the real environment. The proposed work examines the problems and the solutions for implementation of distance estimation algorithms for WSN devices. The main contribution of the article is seen in this real testbed evaluation of the ranging technology.

Half-overlap Subchannel Filtered MultiTone Modulation and Its Implementation

Multitone modulations are today frequently used modulation techniques that enable optimum utilization of the frequency band provided on non-ideal transmission carrier channel (Bingham, 2000). These modulations are used with especially in data transmission systems in access networks of telephone exchanges in ADSL (asymmetric Digital Subscriber Lines) and VDSL (Very high-speed Digital Subscriber Lines) transmission technologies, in systems enabling transmission over power lines PLC (Power Line Communication), in systems for digital audio broadcasting (DAB) and digital video broadcasting (DVB) [10]. And, last but not least, they are also used in WLAN (Wireless Local Area Network) networks according to IEEE 802.11a, IEEE 802.11g, as well as in the new WiMAX technology according to IEEE 802.16. This modulation technique makes use of the fact that when the transmission band is divided into a sufficient number of parallel subchannels, it is possible to regard the transmission function on these subchannels as constant. The more subchannels are used, the more the transmission function approximates ideal characteristics (Bingham, 2000). It subsequently makes equalization in the receiver easier. However, increasing the number of subchannels also increases the delay and complication of the whole system. The dataflow carried by individual subchannels need not be the same and the number of bytes carried by one symbol in every subchannel is set such that it maintains a constant error rate with flat power spectral density across the frequency band used. The mechanism of allocating bits to the carriers is referred to as bit loading algorithm. The resulting bit-load to the carriers thus corresponds to an optimum distribution of carried information in the provided band at a minimum necessary transmitting power. In all the above mentioned systems the known and well described modulation DMT (Discrete MultiTone) (Bingham, 2000) or OFDM (Orthogonal Frequency Division Multiplexing) is used. As can be seen, the above technologies use a wide spectrum of transmission media, from metallic twisted pair in systems ADSL and VDSL, through radio channel in WLAN and WiMAX to power lines in PLC systems. Using multitone modulation, in this case DMT and OFDM modulations, with adaptive bit loading across the frequency band efficient data transmission is enabled on higher frequencies than for which the transmission medium was primarily designed (xDSL, PLC) and it is impossible therefore to warrant here its transfer characteristics. In terrestrial