Pulse or digital communications – Systems using alternating or pulsating current – Angle modulation
Patent
1996-06-28
1998-06-09
Chin, Stephen
Pulse or digital communications
Systems using alternating or pulsating current
Angle modulation
375219, 370280, 455 78, 455 84, H04B 144, H04L 514, H04L 2710
Patent
active
057647003
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This application claims benefit of international application PCT/F194/00426, filed Sep. 22, 1994.
The invention relates to a radio link system and to a radio link terminal.
A radio link system usually operates on the duplex principle, which means that two radio link terminals establish together a two-way connection so that the traffic propagates in both directions simultaneously.
A two-way simultaneous connection is established by using a different radio frequency in the outbound and inbound directions. This, however, causes certain problems, which will be discussed under the following points A to D:
A. In both of the radio link terminals, the transmitter and receiver signals have to be separated from each other so that the receiver will not be overloaded. In practice, the only way to accomplish this objective is to use a band division filter (antenna branching unit), which connects the transmitter at one frequency band and the receiver at another frequency band to the antenna. This kind of filter is a very complicated component and thus also is expensive.
B. An antenna branching unit requires either channel-associated tuning or tuning that covers only a frequency range portion, which complicates the manufacture of both the filter itself and its spare parts.
C. As the equipment at the ends of a radio hop are reverse to each other with respect to frequencies, it is difficult to make them similar in structure. At least, it is necessary to modify the antenna branching unit with respect to the reversed transmitting and receiving frequencies, but the radio parts themselves may need to be varied in accordance with the reversed frequencies.
D. As the transmitter and the receiver of the radio link terminal operate at different frequencies, they contain several oscillators operating at different frequencies and possibly causing interfering mixing results within the radio link terminal.
The following ways, among others, have been used in an attempt to solve the problems described above (references A to D correspond to the points set forth above):
A. In the case of a digital radio link, the band division filter (antenna branching unit) is used all the time, and it has been possible to reduce its high cost mainly only in ways relating to the manufacturing technique. In certain applications, e.g., in a wireless telephone system described in PCT Application WO 84/00455, the duplex operation has been achieved by the use of a single channel where communication takes place alternately in both directions at a rate higher than the normal rate. The rates can be evened out by a suitable elastic buffer, and the antenna branching unit can be replaced with a less expensive switch.
B. and C. The antenna branching unit is replaced in the same way as set forth above under item A.
D. The receiver can be made such that it operates on the principle of direct conversion, so that the number of frequency-selective parts and disadvantageous mixing results diminishes. The wireless telephone system disclosed in the above-mentioned PCT Application WO 84/00455 also employs direct conversion.
SUMMARY OF THE INVENTION
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
REFERENCES:
patent: 3219931 (1965-11-01), Lennon, III et al.
patent: 5020076 (1991-05-01), Cahill et al.
patent: 5319799 (1994-06-01), Morita
Chin Stephen
Gluck Jeffrey W.
Nokia Telecommunications Oy
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