~69~62 26P5C~
The present invention relates to RF repea-ter arrangements for use 5 in wireless telephone systems and, more particularly, for linking basestations to wireless handsets in such systems.
The invention is useful in particular in wireless telephone systems using cable television plant for the transport of radio frequency signals to and from a wireless handset and a basestation linked to a public switched telephone network.
10 Such basestations have RF signal transmitting and receiving equipment and control equipment and can be connected through a coaxial cable or other RF
signal conduit to one or more RF repeaters, which interface with the wireless handsets, i.e transmit signals from the basestation to wireless handsets as off-air signals and also receive off-air signals from the handsets and pass them to the 15 basestation. In this way, the RF repeaters can be utilized to increase substantially the area which can be served by the basestation.
It is in many cases advantageous to make such an RF repeater in two parts, i.e. a first part which interfaces with the basestation and a second partwhich interfaces with the handset. These two parts may be physically separated 20 from one another by a long distance, e.g. several kilometres, and cannected by a signal conduit in the form of co-axial cable or optical fiber cable.
In practice, the second or handset part of the RF repeater is often one of a number of such handset interface parts provided at different locations and connected through a common signal conduit, in the form of a coaxlal cable or a 25 fiber optic cable, to the first or basestation interface part. In this way, there is provided an RF repeater arrangement which ena,bles the basestation to serve a number of wireless handsets in many different locations.
However, a problem that may arise with such an arrangement is that the sharing of the cornmon signal conduit by a number of R~ repeaters results in 30 excessive noise in the common signal conduit.
According to the present invention, there is provided an RF repeater arrangement for interfacing with a wireless handset and a basestation in a wireless telephone system, comprising a first RF repeater part for interfacing with the , 20~94fi2 basestation, a plurality of second RF repeater parts for interfacing with the handsets and means including a common signal conduit for connecting the first RF repeater parts to the second RF repeater parts, the second RF repeater parts each comprising rneans for transmitting signals from the first RF repeater part to S the handsets, means for receiving off-air signals from the handsets and feeding the received signals to the first RF repeater part, means for determining the level of the received signals and means for inhibiting the feeding through the common signal conduit of the received signals having a level less than a predetermined value.
For counteracting noise on the common signal conduit, the second RF
repeater parts include means for frequency multiplexing the received signals onto the common signal conduit, and the first RF repeater part compr;ses rneans ~or demultiplexing the received signals.
The present invention will become more readily apparent to those skilled lS in the art from the following description of embodiments of the invention when taken in conjunction with the accompanying drawings, in which:
Figures 1 and 2 show diagrammatic views of an RF repeater arrangement embodying the invention during different operational phases;
Figure 3 shows a view corresponding to Figures 1 and 2 but of a modified 20 RF repeater arrangement embodying the invention;
Figure 4 shows a block diagram of a handset inter~ace part of the RF
repeater arrangement of Fig~lres I and 2 or ~s;
Fig-lre 5 shows a block diagram of a signal processor circuit forming part of the apparatus of Figure 4;and Figures 6, 7 and 8 show three different ba~estation interface parts for use in the arrangement of Figures 1 and 2 or Figure 3.
As shown in Figure 1 of the accompanying drawings, a basestation 10 is connected by a coaxial cable 12 to a first or basestation interface part 14 of an RF repeater arrangement.
The basestation 10 contains transmitter and receiver equipment and control equipment ~or transmitting and receiving signals through the coaxial cable 12 and is connected to the public switched telephone system 15. Since such 206~62 basestations and systems are well known in the art, they will not be described in greater detail herein.
The basestation interface part 14 of the RF repeater arrangement is connected to three second or handset interface parts 16a, 16b and 16c o-f the 5 arrangement by a common signal conduit 18 in the form of coa1~ial cable or optical fiber cable. Typically, these cables form parts of a cable television distribution plant. It is to be understood that, in practice, the number of the handset interface parts will be substantially greater than the three illustrated in Figures 1 and 2 or the four shown in Figure 3.
The handset interface parts have antennas 20 for exchanging off-air signals with any of a plurality of handsets æ (Figure 4), of which only two are illustrated.
As shown in Figure 1, the handset interface parts 16a, 16b and 16c are simultaneously translating the received off-air spectrum to approximately 30 MHzThe summation of these off-air spectra passes along the common signal conduit 15 18 at 30 MHz to the basestation interface part 14. Excessive noise may occur on the signal conduit 18, which may effectively limit the number of handset interface parts which can be utilized.
The present invention overcomes this problem, as diagrammatically illustrated in Figure 2, by inhibiting the feeding of received off-air spectra to the 20 signal conduit 18 by all except the handset interface parts that ar~ receiving a signal from a handset. In Figllre 2, the handset parts 16b and 16c are shown as being squelched, in the manner described in greater detail below, while the handset interface part 16a remains unsquelched and thus feeds its signal throughthe signal conduit 18.
Figures 4 and 5 show in greater detail tl~le components of the handset interface part 16a, and it is to be understood that the handset interface parts 16b and 16c have components similar to those shown in Figure 4 and described below.
As shown in Figure 4, the handset interface part 16a has a transmi-tter 24 for transmitting off-air signals to the handsets 22 through the antenna 20, and a 30 receiver 28 for receiving off-air signals from the handsets.
More particularly, the input of the receiver 28 and the olltpUt of the transmitter 24 are connected to the antenna 20 through a transmit/receive sv~ritch 20~946~
30 and the OUtpllt of the receiver 28 and the input of the transmitter are connected through a transmit/receive coupler 32 and a line coupler 34 to -the signal conduit 18. The transmit/receive switch 30 and the transmit/receive coupler 32 may be replaced by diplexers.
Local oscillators 36 are connected to the transmitter 24 and to first and second mixers 38 and 40 in the receiver 28. The first and second rr~ixers 38 and4û are provided between the output and input, respectively, of the receiver 28 and a signal processing circuit 42, which is illustrated in g~eater detail in Figure 5.
As shown in Figure 5, the signal processing circuit 42 has a input narrowband filter 44, an amplifier circuit 46, a output narrowband filter 48 anda squelch gate 50. An automatic gain control/squelch circuit 52 is connected to the amplifier circuit 46 and to the squelch gate 50.
In operation, a received signal from one of the handsets 22 is m;xed with a predetermined frequency, generated by one of the local oscillators 36, at the 15 first mixer 38 to form an intermediate frequency signal, which is then filtered by the narrowband filter 44 and the filtered signal passes to the amplifier circuit 46.
The gain of the amplifier circuit 46 is controlled by the automatic gain control/squelch circuit 52t the squelch portion of which disengages the squelch gate 50 when the filtered received signal has an amplitude above a predetermined20 value and engages the squelch gate 50 when the received signal has an amplitude below this value. In this way, all handset interface parts can be squelched, except those receiving a valid signal, as illustrated in Figure 2, thus correspondinglyreducing the noise on the signal conclu;t 18.
The squelch circuit should disengage quickly, in order to allow a handset 25 to initiate a call with a minimal loss of signal, but should be engaged s]owly, so that normal multipath fades do not cause the squelch action to disengage the call.
This can be achieved by forming the squelch circuit as illustrated in Figure 6, which shows an energy detector circuit indicated generally by reference numeral 60, having its input cormected by conductor 62 to the output of the 30 narrowband filter 48 of Figure 5.
The output of the energy deteetor circuit 60 is connected to a buffer amplifier 64, having an output cormected to a resistor R1 and to one input of a 20~9~62 comparator 66, the other input of which is connected to a variab]e resistor 68 providing a variable reference voltage. The output of the comparator 66 is applied to the amplifier 46 (Figure 5) for effecting gain control thereo-f.
The resists)r Rl is in series with another energy detector circ~lit which is 5 indicated generally by reference numeral 70 and comprises a diode Dl, a resistor 1~2 and a capacitor C. The energy detector circuit 70 is in turn connected to one input of a high input impedance comparator 72, the other input of which is supplied with a variable reference voltage by a variable resistor indicated generally by reference numeral 74 and the output of which controls the squelch 10 engagement and disengagement operation of the squelch switch 50 (Figure 5).
Adjustment of the variable resistor 74 serves to control the energy trip point at which the squelch engagement and disengagement occur.
The squelch engagement reaction time will be determined by the product of the values of the resistor Rl and the capacitor C, while the squelcl disengagement reaction time will depend on the product of the ~alues of the resistor R2 and the capacitor C. l`hus, by appropriate selection of these values, the quick squelch disengagement and the slow squelch engagement referred to above can be ensured.
Another possibili~r for counteracting noise on the signal conduit 18 is to frequency multiplex the received signals from interfaces 16a, 16b, 16c and 16d, as shown in Figure 3, in which these interfaces are illustrated as feeding receivedspectra to the signal conduit 18 at 30MHz, 20MHz, lOMHz and lOM~Iz, respectively. Sllch multiplexing may be effected with or without the squelching represented in Figure 2.
This can be effected in the handset interface part by changing the local oscillator frequency fed to the mixer 40 shown in Figure 4.
The basestation interface part 14 is in that case modified as illustrated in Figure 7, which shows three bandpass filters 52a - 52c for separating the three frequency bands centered on 30 MHz, 20 MHz and 10 MHz. The outputs of the bandpass filters 52a - 52c are fed through frequency translators 58a - 58c to respective basestations lOa - lOc.
~odifications of the apparatus shown in Figure 7 are possible, based on 2069~62 the fact that it is unlikely that all basestations are required to handle valid telephony signals at the same instant of time.
Figure 8 shows an extreme example, in which three separate frequency translators 58a, 58b, 58c and 58d are connected as shown between bandpass filters S 52a-52d and signal-to-noise ratio detector circuits 54a - 54d for determining the signal-to-noise ratios of the thus separated signals.
A computer 56 supplied with signal-to-noise ratio data from the detectors 54a - 54c controls a switch 57 so as to connect the active frequency band to thebasestation 14.
As will be apparent to those skilled in the art, various modifications of the present invention may be made within the scope of the invention as defined in the appended claims.
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