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