Pavel Silhavy

Half-Overlap Subchannel Filtered MultiTone Modulation with the Small Delay

In this contribution an analysis of MultiCarrier Modulation (MCM) is realized. The features of Discrete MultiTone modulation (DMT), Orthogonal Frequency Division Multiplexing (OFDM) and alternative modulation based on filter bank - Filtered MultiTone (FMT) will be mentioned. Based on this study the half sub-channel overlapped Filtered MultiTone Modulation will be introduced.

Time Domain Equalization in Modern Communication Systems Based on Discrete Multitone Modulation

The article deals with the implementation of the design algorithm of time-domain equalizer (TEQ) coefficients. This equalization principle is used in several modern transmission systems based on discrete multitone modulation (e.g. ADSL, VDSL, WLAN base on 802.11 g, PLC, etc.).

Time domain equalization for ADSL technology and its optimization

The methods for compensating unfavorable properties of the transmission path in ADSL are compared. On the basis of measuring the transmission properties of the telephone channel during ADSL initialization, the optimum coefficients of the FIR (finite impulse response) digital filter are calculated. The filter realizes the TEQ (time domain equalization) method and processes effectively the impulse response of transmission channel to the length of permitted cyclic prefix. All analyzed methods give roughly the same results and mainly differ in how the limiting assumptions are defined. The TEQ method is described and recommendations are given that should lead to achieving optimum transmission rate for a given interference in the ADSL transmission.

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.

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