Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1999-12-09
2003-11-04
Urban, Edward F. (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S003050, C455S502000, C725S062000
Reexamination Certificate
active
06643518
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the transmission of a reference signal necessary for the mutual synchronization of telecommunications devices in a transmission network.
BACKGROUND OF THE INVENTION
For any synchronous transmission between two telecommunications devices, the devices involved must always be synchronized. Among other things, synchronization is required for compensation of frequency errors between the devices. Typically, synchronization is carried out using a reference signal relayed to all the devices involved in transmission. Terminal devices may receive this reference signal from the transmission network they are using. Alternatively, one of the devices involved transmits a reference signal that the other devices can then use for synchronization.
An example of an arrangement where one of the two transmission devices in a system synchronizes with another device by means of a reference signal transmitted by the former is transmission between a Base Transceiver Station BTS and its distributed Antenna Unit AU in a telecommunications network. Traditionally, such transmission is carried out by means of special cabling laid between the Base Transceiver Station and the Antenna Unit. However, if one Base Transceiver Station is to be connected to several distributed Antenna Units, the cost of cabling may prove prohibitive.
Data can also be transmitted between the Base Transceiver. Station and its Antenna Unit via a separate, already existing transmission network. An example of such a transmission network that is readily available is the cable television network. At present, the cable television network is fairly extensive and offers unused capacity, making it possible to use it for the transmission of data other than just the television signal. As it is, in addition to television signals, the cable television network is also being used, for example, for transmitting other data using the so-called cable modems.
FIG. 1
shows an example of a system where the signal between the base transceiver station BTS
101
and the antenna unit AU consisting of the transmitter TX
105
and receiver
111
is transmitted via a separate transmission network. The transceiver unit (not shown) is connected to an antenna, by means of which the mobile stations can communicate with the base transceiver station and make use of -the services offered by the network. For the sake of clarity, the figure only shows one antenna unit AU, but the same base transceiver station can communicate simultaneously with several transceivers. In this example, the transmission network is a cable television network, where the signal is transmitted following conversion for the frequency of the television channel used for transmission.
The modulated signal with a bandwidth of 200 kHz on the 1930-1990 MHz band in an air interface traffic channel conforming to the mobile communications system specifications and which is to be transmitted from the base transceiver station to the transmitter TX of the antenna unit AU is converted in the adapting unit
102
for the free channel on the band used for the connection in a transmission network. For the connection, the band 180-810 MHz may be selected, with the exception for certain narrow bands that are disallowed. At the receiving end, the signal is converted by the adapting unit
104
into its original band of 1930-1990 MHz.
The signal in the 1850-1910 MHz band to be transmitted by the antenna unit receiver RX to the base transceiver station BTS is converted in the adapting unit
112
for the band 10-105 MHz to be used for the connection in the transmission network. At the receiving end, the signal is re-converted in the adapting unit
114
into its original band 1850-1910 MHz. In addition to the traffic channel signal, the reference signal S
REF
required for the synchronization of the terminal devices must also be transmitted over the transmission network.
The frequency ranges to be used are not critical to the use of the system, and so the GMS-1900 frequencies used in this example can be replaced by GSM frequencies, in which case the signal from the base transceiver station to the transmitter TX is in the 935-960 MHz band and the signal from the receiver-to the base transceiver station in the 890-915 MHz band, or DCS-1800 frequencies, in which case the signal from the base transceiver station to the transmitter TX is in the 1805-1880 MHz band and the signal from the receiver to the base transceiver station in the 1710-1785 MHz band.
The operation of the transmitting-end adapting units
102
and
112
is discussed below.
Generally, the task of the adapting units is to convert the signal modulated to the frequency f
1
into such a form that the signal can be transmitted over a channel operating in the frequency f. Let us first examine the processing of just the modulated signal to be transmitted over a traffic channel. The operation of the adapting unit
102
in
FIG. 1
is illustrated in FIG.
2
. Except for the frequency bands to be used, the adapting unit
112
operates in an identical manner. The unit input consists of the modulated downlink signal S
201
in the band 1930-1990 MHz obtained by modulating the signal s(t) to be transmitted by the base transceiver station over the traffic channel. In the adapting unit
102
, the signal S
201
is first converted in the mixer
202
by means of the mixing signal S
MIX
having another frequency of f
MIX
. Thus, the signal S
202
is obtained in addition to the input signals,
S
202
=S
201
·S
MIX
, (1)
where two frequencies are present, f
TCH
+f
MIX
and f
TCH
−f
MIX
(f
TCH
being the frequency of the modulated traffic channel signal S
201
and f
MIX
the frequency of the mixing signal S
MIX
). f
MIX
is selected so that one of the two frequency components of the mixed signal is consistent with the frequency channel of the transmission network to be used (such as a cable television network). If, for example, a modulated traffic channel signal with a frequency of 1951 MHz is to be adapted for transmission in a cable television network at a frequency of 546 MHz, the mixing frequency f
MIX
of 1405 MHz will be selected. At the same time, the other signal components remain outside the frequency range of the channel reserved for transmission, and so they must be filtered. This is achieved by means of the band-pass filter
203
, which filters the signal components that fall outside the frequency range of the channel operating at the frequency f (e.g. 545 MHz<f<555 MHz). The signal S
203
obtained from the band-pass filter is fed into the transmission network.
The signal s(t) travels in the transmission network in its original bandwidth but at a new center frequency f=f
TCH
−f
MIX
=546 MHz. The signal S
203
conforms to the band reserved in the cable television network for the connection between the transceiver station BTS and transmitter TX and can be fed into the cable television network as it is.
At the receiving end, the modulated traffic channel signal S
201
sent from the base transceiver station BTS to the transmitter TX and converted by the adapting unit
102
will be reconstructed by the adapting unit
104
,
FIG. 1
, whose operation is explained in FIG.
3
. Similarly, the signal from the receiver RX to the base transceiver station BTS converted- by adapting unit
112
is reconstructed by unit
114
in exactly the same way, except for the frequency bands. Several signals are being transmitted in the transmission network (such as a cable television network) simultaneously over several channels, the individual signals constituting the total signal S. The channel for the transmission connection is selected by suppressing the other signals by means of the band-pass filter
301
. The signal S
301
with a center frequency of f
TCH−f
MIX
=546 MHz obtained must be re-converted for its original frequency band of f
TCH
. To accomplish this, the signal is mixed in the mixer
302
using the mixing signal S′
MIX
with a frequency of f
MIX
gen
Craver Charles R.
Nokia Corporation
Squire Sanders & Dempsey LLP
Urban Edward F.
LandOfFree
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