Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Patent
1996-06-07
1998-10-06
Eisenzopf, Reinhard J.
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
4552342, 4552772, 455561, H04B 110, H04B 708
Patent
active
058191674
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to radio receiving apparatus.
Radio Systems such as GSM/PCN (Groupe Systeme Mobile/Personal Communication Network) use time division multiple access (TTDMA) to carry several channels of information on a single radio frequency channel by sending separate bursts of information in successive time slots. When a base station receives such transmissions from several different mobile handsets some signals may be much stronger than others. These can cause the filters in the base station receiver to "ring" (ie to suffer persistence of vibration) and hence some of the signal energy can still be present in the subsequent time slot. This can cause blocking of a weak signal in the subsequent time slot and hence a degradation of the system performance. This is adjacent channel interference in the time domain.
SUMMARY OF THE INVENTION
This invention provides a way of utilising the diversity receiver often found in such systems to reduce the affect of such interference.
According to the invention radio receiving apparatus comprises a main receiver, a diverse receiver and means for altering the sensitivity of one of the receivers in dependence upon the strength of signal received by the other of the receivers.
Preferably, said means are operative to reduce the sensitivity of the diverse receiver if the strength of signal received by the main receiver exceeds a predetermined threshold and to reduce the sensitivity of the main receiver if the strength of signal received by the diverse receiver exceeds a predetermined threshold.
The radio receiving apparatus may employ time division multiple access using a plurality of time slots to constitute a frame of received information, and said means are then operative to reduce the sensitivity for a terminal part of each time slot, to prevent ringing of a filter of the corresponding receiver in the subsequent time slot.
The invention thus relies on the principle that when a strong signal is known to be present, it is less likely that the diverse receiver is contributing to the link performance since there is likely to be sufficient signal in the main receiver. Thus it is possible to reduce the sensitivity of the diverse receiver during the strong signal transmission so that in the subsequent time slot its sensitivity can be reset and the receiver used to receive a weak signal without the loss of sensitivity associated with the strong signal still ringing in the filters.
Clearly this process is symmetrical in that a strong signal in the diverse receiver would allow muting of the main receiver. Suitable logic is required to decide if and when to mute one or other receiver depending on the signal levels in each receiver.
In this way it should be possible to reduce the adjacent (time) channel interference.
The preferred embodiment of radio receiving apparatus comprises two receivers, a main receiver and a diversity receiver. The gain of each is controlled firstly to provide a constant signal level at the detector as is usual in a receiver and secondly to reduce the sensitivity of the diversity receiver when the signal strength in the time slot is sufficient for the main receiver to provide adequate reception.
BRIEF DESCRIPTION OF THE DRAWING
Radio receiving apparatus according to the invention will now be described, by way of example, with reference to the accompanying drawing wherein:
FIG. 1 shows the apparatus in block circuit form;
FIG. 2 shows locations of handsets relative to a base station; and
FIG. 3 shows a TDMA time frame relating to transmission of signals between the handsets and the base station of FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
The apparatus is incorporated in a base station and includes a main receiver 10 and a diversity receiver 12. The main receive path includes a main receive antenna 14, an automatic gain control circuit 16, a filter 18 and a detector 20 the output of which feeds a further automatic gain control circuit 22. The diversity receive path includes a diversity antenna 24 and components
REFERENCES:
patent: 3831095 (1974-08-01), Mounce
patent: 4969207 (1990-11-01), Sakamoto et al.
patent: 5119501 (1992-06-01), Perry et al.
patent: 5203026 (1993-04-01), Ekelund
patent: 5361404 (1994-11-01), Dent
Eisenzopf Reinhard J.
Kincaid Lester G.
Nokia Telecommunications Oy
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