Digital radio link system and radio link terminal

DETAILED DESCRIPTION The object of the present invention is to avoid the above-described disadvantages and at the same time provide a radio link terminal and radio link system which can be realized as economically as possible, i.
e.
, with a minimal number of parts while the link terminals are also as similar as possible.
The idea of the invention is to apply alternate communication at a single frequency to the radio link system while the transmitter employs direct modulation to a radio frequency and the receiver employs direct conversion from the radio frequency to the baseband so that (a) the transmission and reception use a single common quadrature mixer which is controlled by means of one and the same local oscillator, and (b) the transmitting and receiving branches are separated at the baseband.
In principle, the system according to the invention contains no high-frequency frequency-selective parts, such as an antenna branching unit.
The link terminal or link system according to the invention does not either contain any separate high-frequency switches, but these can be replaced with an inexpensive baseband switch.
In addition, less tuning is required.
Savings in costs will be considerable as the transmitter and the receiver of the radio link terminal share the same mixer and local oscillator.
As the transmitter and receiver both operate on the principle of direct modulation/conversion and alternate at the same frequency, there is no risk of disadvantageous mixing results occurring between the transmitter and the receiver.
As the system according to the invention does not use two channels but a single channel twice as broad, the spectral efficiency will, in principle, not change.
Alternation between transmission and reception, however, requires a predetermined recovery time, which, in practice, deteriorates the spectral efficiency to some extent.