Narrowband communication

The term narrow band , also narrow band communication , English narrow band , is handled with different meanings depending on the context in the field of communications technology and in the field of Internet access .

Communications engineering

In the field of communications technology, the term narrowband describes a transmission channel whose bandwidth is so small that the frequency response can be assumed to be almost constant. This is equivalent to a group delay that is constant over the entire band . In the case of narrowband transmission, it is in principle possible, because of the frequency-independent group delay, to manage without channel equalization. If a transmission channel does not have a constant frequency response, as is the case in broadband communication , the transmitted useful signals are distorted differently depending on the level of their frequencies. Equalizers that reverse this distortion at the receiver of the useful signals can be implemented, for example, by means of adaptive filters .

In the case of digital data transmissions, a narrowband transmission using the symbol rate is also specified. Each transmitted symbol requires a certain symbol duration for transmission . If the symbol duration is longer than the transmission time on the transmission channel, there is narrowband communication: ${\displaystyle T_{s}}$ ${\displaystyle \tau _{\mathrm {max} }}$

${\displaystyle T_{s}\gg \tau _{\mathrm {max} }}$

It is essential that the definition of a narrowband transmission is not fixed on concrete numerical values ​​of a certain bandwidth, but is based on the respective peripheral circumstances, such as the physical parameters of a radio link.

Internet access

From the field of telephone networks and with the emergence of Internet access from the 1990s, the term narrowband is used for narrowband networks or narrowband access, which are characterized by a bandwidth of less than or equal to 3.1 kHz or a data transfer rate of at most 64  kbit / s . This rigid definition is based, on the one hand, on the bandwidth of analog landline telephony . For the transmission of analog voice signals over copper wires in good quality was of technical transmission a frequency band of 300 Hz to 3.4 kHz specified reasons already in the early days of telephony. A pair of the same type is also used for the U _K0 interface for the digital transmission of voice signals in ISDN ; the required bandwidth is 40 kHz (with the 2B1Q code with 80 k baud ) or more, depending on the coding. In addition to the signaling channel ( D-channel ), two so-called basic channels can be transmitted in it, each with a data transmission rate of 64 kbit / s. In ITU-T recommendation I.113, the term narrowband service with a data transmission rate of a base channel of less than or equal to 64 kbit / s is specified. In mobile communications , also a narrowband service, digital voice is transmitted at a much lower data transmission rate - with the full rate codec in GSM , it is 13 kbit / s. (The required bandwidth is 2 x 200 kHz, whereby it can be used by eight connections at the same time.)

In addition to analog telephone systems and telephone modems , the narrowband services for Internet access also include ISDN and cellular networks such as GSM with GPRS . Internet access systems such as DSL are broadband Internet access types . They require wider frequency bands of more than 40 kHz - with corresponding restrictions on the part of the network operator with regard to the cable length.

literature

• Karl-Dirk Kammeyer, Martin Bossert: message transmission . 5th edition. Vieweg + Teubner, Wiesbaden 2011, ISBN 978-3-8348-0896-7 .

Individual evidence

1. ↑ Jochen Seitz, Maik Debes, Michael Heubach, Ralf Tosse: Digital voice and data communication: networks, protocols, switching . Carl Hanser Verlag, 2006, ISBN 978-3-446-22979-2 , pp. 183 .