Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Reexamination Certificate
2001-06-14
2004-08-31
Banks-Harold, Marsha D. (Department: 2686)
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
C455S249100, C455S253200
Reexamination Certificate
active
06785524
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device and method for ensuring that the amplitude of signals fall within a predetermined range.
In particular, but not exclusively, the device and method can be used in a receiver for a wireless telecommunication network.
BACKGROUND TO THE INVENTION
FIG. 1
illustrates a known wireless telecommunication network
2
. The area covered by the network
2
is divided into a number of cells
4
. Each cell
4
has associated therewith a base transceiver station
6
. Each base transceiver station
6
is arranged to communicate with the terminals
8
located in the cell
4
associated with that base transceiver station
6
. The terminals
8
may be mobile stations which are able to move between the cells
4
.
Each base transceiver station is, in the GSM standard (Global System for Mobile Communications), arranged to receive N channels out of M available channels C
1
. . . CM, as illustrated in
FIG. 2
a.
The M channels C
1
. . . CM occupy a bandwidth of XMHz. Each channel therefore has a width of X/M MHz. Typically this will be around 200 KHz. Each channel is divided into frames F one of which is shown in
FIG. 2
b.
Each frame is divided into eight slots S
1
. . . S
8
. The GSM standard is a time division multiple access (TDMA) system and accordingly different mobile stations will be allocated different slots. Thus, the base transceiver station will receive signals from different mobile stations in different time slots in the same channel. N is usually much less than M.
There are two forms of GSM, E_GSM and GSM1800. E_GSM operates in the frequency band of 880-915 MHz for the receipt of signals by the base station. GSM 1800 operates in the frequency band of 1710 to 1785 MHz for the receipt of signals by the base station. E_GSM 900 and GSM
—
1800 operate with bandwidths of 35 MHz and 75 MHz respectively. For E_GSM M=125 and for GSM 1800 M=375.
Reference is made to
FIG. 3
which shows part of a known base transceiver station
9
which is arranged to receive N channels at the same time. For clarity, only the receiving part of the base transceiver station
9
is shown. The base transceiver station
9
has an antenna
10
which is arranged to receive signals from mobile stations in the cell served by the base transceiver station
9
. The base transceiver station comprises N receivers R
1
, R
2
. . . RN. Thus one receiver is provided for each channel which is to be received by the base station
9
. All of the receivers R
1
-RN are the same and accordingly the components of the first receiver R
1
only are shown.
The first receiver R
1
comprises a first bandpass filter
12
which is arranged to filter out signals which fall outside the bandwidth in which the M available channels are located. The filtered output is input to a first low noise amplifier
14
which amplifies the received signals. The amplified signal is then passed through a second bandpass filter
16
which attenuates spurious frequencies, noise, and harmonics or the like introduced by the first amplifier
14
. The output of the second bandpass filter is connected to a mixer
18
which receives a second input from a local oscillator
20
. The frequency of the output of the local oscillator
20
will depend on the frequency of the channel allocated to the particular receiver. The output of the second bandpass filter
16
is mixed with the output of the local oscillator
20
to provide a signal at an intermediate frequency IF, which is less than the radio frequency at which the signals are received. The intermediate frequency IF output by the mixer
18
of each receiver will be the same for all receivers.
The output of the mixer
18
is input to a third bandpass filter
22
which filters out spurious signals and the like generated by the mixer
18
. The output of the third bandpass filter
22
is amplified by a second amplifier
24
and output to a surface acoustic wave (SAW) filter
26
. The surface acoustic wave filter
26
filters the adjacent signals and interfering signals within the bandwidth X except that of the channel allocated to that particular receiver. In other words, all the channels received by the antenna
10
with the exception of the channel allocated to the receiver will be filtered by a combination of the first to third bandpass filters and the surface acoustic wave filter
26
. The output of the surface acoustic wave filter
26
is connected to an automatic gain control unit
28
which alters the gain of the signal so that it falls within the dynamic range of an analogue to digital converter
30
.
If the amplitude of the signal input to the analogue to digital converter
30
is too high, then the converter
30
will become saturated, giving rise to phase errors, recovery time problems and unwanted noise. By the same token, if the signal input to the analogue to digital converter
30
is too low, then the received signal may be below the noise floor of the converter
30
. In other words, if the signal is too small, it will be swamped by the noise floor and information carried by the signal may be lost.
One problem with the known architecture is that it is necessary to provide a receiver for each channel. This is to ensure that each signal which is input to an analogue to digital converter is within the dynamic range of that converter. The need to provide a receiver for each channel increases substantially the costs of the base transceiver station. It is therefore an aim of embodiments of the present invention to solve or at least mitigate this problem.
Another problem with the known receiver is that it is necessary to use a SAW filter to filter out the adjacent channels and high power interferers which compromise the dynamic range of the converter
30
. SAW filters are expensive. It is therefore also an aim of embodiments of the present invention to provide a device for ensuring that signals fall within the dynamic range of, for example, an analogue to digital converter. It is preferred that this device not require the use of SAW filters.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided a device for ensuring that the amplitude of signals fall within a predetermined range, said device comprising input means for receiving a plurality of input signals at substantially the same time; a first path for increasing the amplitude of any of the input signals having an amplitude below a first threshold; a second path for decreasing the amplitude of any of the input signals having an amplitude which exceeds a second threshold; and combining the outputs of the first and second paths to provide the plurality of signals having amplitudes between said first and second thresholds.
Thus, it can be ensured that signals which are too large are reduced to a lower amplitude whilst signals which are too small are increased to a larger amplitude. In this way, the device is able to ensure that the amplitude of signals fall within a predetermined range.
The first and second thresholds may be the same or different.
Preferably, the second path comprises attenuator means. Preferably, signals which have an amplitude below the second threshold are removed by the second path. Those signals may be removed by reducing those signals to substantially zero. This can, for example, be achieved by the attenuator means and is both simple and cost effective.
Preferably, the first path comprises amplifier means.
Removing means may be provided to remove signals from said first path having an amplitude exceeding said first threshold. An output of the second path may be introduced in the first path and the output of the second path may be used by said removing means to cancel out the signals in the first path having an amplitude exceeding the first threshold. A phase shift may be provided so that one of the signals output by the second path introduced into the first path and signals on the first path is 180° out of phase with respect to the other of the signals output by the second path introduced into the first path and the signals o
Banks-Harold Marsha D.
Moore James
Nokia Corporation
Squire Sanders & Dempsey L.L.P.
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