Multicarriertekniikka

Multicarriertekniikka, often translated as multicarrier technology, is a broad term encompassing various communication techniques that divide a data stream into multiple sub-carriers, each modulated and transmitted independently. This approach offers several advantages over single-carrier systems, particularly in combating the detrimental effects of frequency-selective fading encountered in wireless and wired channels.

The most prominent example of multicarrier technology is Orthogonal Frequency Division Multiplexing (OFDM). OFDM divides the available bandwidth into many narrow, closely spaced sub-carriers that are orthogonal to each other. This orthogonality ensures that the sub-carriers do not interfere with each other, even though their spectra overlap significantly. By using a large number of slow sub-carriers instead of a single fast one, OFDM effectively transforms a frequency-selective channel into a collection of many flat-fading sub-channels. This makes equalization much simpler and more efficient.

Another related technique is Discrete Multitone (DMT), which is essentially OFDM applied to digital subscriber line (DSL) technologies. DMT dynamically assigns data rates to different sub-carriers based on their channel quality, maximizing the achievable data throughput over a given telephone line. Other multicarrier techniques exist, but OFDM and DMT are the most widely deployed and influential.

The benefits of multicarrier technology include robustness against multipath propagation, efficient spectral utilization, and simplified receiver design compared to complex equalizers needed for high-speed single-carrier systems. These advantages have led to its widespread adoption in various communication standards, including Wi-Fi (IEEE 802.11a/g/n/ac/ax), cellular mobile communications (LTE, 5G), digital television broadcasting (DVB-T/T2), and DSL.