WO2009101159A1 - Satellite signal reception system - Google Patents

Abstract

The invention relates to a satellite reception system for receiving N signals, including, combined with a satellite reception antenna, an outdoor unit and an indoor unit connected to each other. The outdoor unit of the system includes an intermediate-frequency conversion unit for converting the N signals received on N channels into N intermediate-frequency signals, a switching matrix NXM controlled by signals from a control unit, in order to select, for each of the M output paths and from the N transposed signals, the signal from which the information must be extracted, M frequency-adjustable filters controlled by signals from the control unit and each associated with a path for selecting a frequency band corresponding to a single channel in the intermediate-frequency band, a block of M tuners and M demodulators respectively associated with the M paths for extracting the information from the transmitted channels, and a combination unit for combining the signals to be transmitted and supplied by the different demodulators.

Description

 SYSTEM FOR RECEIVING SATELLITE SIGNALS

The present invention is in the field of information transmissions transmitted by a satellite and particularly relates to satellite receivers.

Satellite receivers usually include an outdoor outdoor unit consisting of a receiving antenna and a LNB (low noise block) conversion block placed at the antenna focus. The outdoor unit is connected for example by a cable to an indoor unit indoor unit also called STB (commonly called "Set top box").

The first function of the LNB block is to convert microwave signals from the satellite into intermediate frequency signals using fixed frequency oscillators. A universal "Quad LNB" block corresponds to an LNB block equipped with four independent outputs. This allows the connection of several receivers if necessary.

Intermediate frequency bands are derived from this transposition. Each of these frequency bands includes a set of frequency-separated channels. Each channel may include several television programs.

By using a diversity of polarization, the number of information transmitted by the satellite is doubled.

With microwave signals from the satellite between

10.7 and 11.7GHz, or 11.7 and 12.75GHz, depending on the case, and fixed frequency oscillators (9.75GHz and 10.6GHz, respectively). The intermediate frequency bands resulting from this transposition are between 950 MHz and 1950 MHz, in the first case, between 1100 MHz and

2150MHz in the second case.

It is understood that the frequency of the oscillators may be different, thus varying the intermediate frequency bands.

It is common for a user to want to have access to different programs at the same time, for example to be able to view a video program while recording a second program. The different programs to receive can be transported by channels from different blocks of transposition or come from different satellites, the channels to be transported between the LNB and Set-Top-Box can be at the same frequency.

It follows therefore a problem of interference between these signals.

From the state of the art, this problem is solved by complex switching modules called FTM (for frequency translation module) for example the RF5210 IC circuit. These modules of relatively high cost, which consist of a switching matrix, of frequency transposition elements associated with SAW filters makes it possible to select a signal coming from the various LNBs, to transpose it at a chosen frequency, in order to avoid interference. These new transposition frequencies are in the same frequency band as initially planned for the connection between the LNB and the Set-Top-Box. The combined signal from this circuit is transmitted via a cable to the STB, which includes tuners and demodulators to demodulate and extract information from the transmitted channels.

Since a tuner and a demodulator are used per channel to be demodulated in the Set-Top-Box and in order to be able to extract information from the transmitted channels, the tuner / demodulation part can be positioned near the antenna within the LNB. By positioning this tuner / demodulator part near the antenna, the signals will then be transported on a single cable to the indoor unit or set top box.

Figure 1 summarizes this concept. The signals received by the satellite antenna (not shown) are transmitted to different sources of an LNB block of the outdoor unit whose outputs are filtered signals, amplified and transposed into intermediate frequency. The intermediate frequency signals S1 - S4 issued from this LNB block are applied to the TD block formed by a set of T1-T4 tuner, associated with a set of demodulator D1-D4 respectively. The demodulated signals are then combined by combining means to be transmitted to an STB by the cable.

A switching matrix K located between the tuners and the demodulators makes it possible to provide a single program to be processed at each demodulator. The number of outputs of the LNB blocks varies according to the use. The example of Figure 1 shows a block with 4 outputs. But this model also exists for a number N of outputs.

The principle is relatively simple, but has the disadvantage of providing the entire frequency spectrum of a signal from the first part of the LNB to the RF tuner.

However, a ratio of nearly 20 dB can exist between the total power supplied by an LNB and that of the unitary channel. The RF tuner must therefore be very linear and very broadband.

On the other hand, the different desired channels can be derived from the same RF transposition, some tuners can be unused while others must treat multiple channels.

In addition, each tuner being dedicated to a microwave transposition, and several programs to be demodulated that can be derived from the same transposition, it is necessary to make a switching matrix K between the tuners and the demodulators in order to provide a single program to deal with each demodulator.

The object of the invention is to avoid these disadvantages;

The invention consists of a satellite reception system of N signals comprising, associated with a satellite reception antenna, an outdoor unit and an indoor unit connected to each other.

The outdoor unit of this system is formed by: - an intermediate frequency conversion block to transform the

N signals received on N channels in N intermediate frequency signals;

a switching matrix NXM, controlled by signals from a control unit, for selecting for each of the M output channels 1-4, among the N signals transposed, the signal from which the information must be taken;

M frequency tunable filters, controlled by signals from the control unit, each associated with a channel for selecting a frequency band corresponding to a single channel in the intermediate frequency band;

A block of M tuners and M demodulators respectively associated with the M channels for extracting the information from the transmitted channels. a combination block for combining the signals to be transmitted from the different demodulators.

The invention has the advantage of reducing the overall consumption of the receiver.

Preferably, the reception system comprises M Digital Analog Converters (ADCs for Analog Digital Converter) associated with the N frequency tunable filters for digitizing the information to be transmitted.

The features and advantages of the invention mentioned above, as well as others, will appear more clearly on reading the following description, made with reference to the accompanying drawings, in which:

- Figure 1 already described, represents an example of an outdoor unit with 4 outlets as known from the state of the art connected to an indoor unit indoor unit through a cable.

- Figure 2 is a simplified representation of an outdoor unit according to the invention.

FIG. 3 is a more detailed representation of the outdoor unit according to the invention;

To simplify the description, the same references will be used in these last figures to designate elements fulfilling identical functions. The proposed architecture of an outdoor unit according to the invention is represented by FIG. 2. A conventional 3-head LNB block P1-P3 allows the reception of microwave signals transmitted by satellite and received by an antenna. These signals are filtered, amplified and transposed into intermediate frequency signals S1-S4. The intermediate frequency signals S1 - S4 from this first part of an LNB block are then applied to the inputs of an M4X4 switching matrix (4x4 in the example described). It will select by the control signal Sc for each associated channel, an RF signal transposed from which the information must be taken. The signals of each channel, coming from this matrix, are then filtered by frequency tunable filters F1-F4 making it possible to extract a single desired channel in the intermediate frequency band. The TD tuner / demodulator block, as described in FIG. 1, associates with each channel 1, 2, 3, 4 a tuner T1, T2, T3, T4 and a demodulator D1, D2, D3, D4 which makes it possible to select and demodulate the signals of the selected channel. The demodulated signals are then transmitted to an STB by one or more connections.

If only one wired link is used, the demodulated signals are combined by means of combination C. Thus, the various information streams are previously concatenated.

The frequency tunable filters F1-F4 significantly reduce the power received by the tuner, and adjust the gain of the latter on the only channel used.

When the choice of programs to be decoded is done by the user, the configuration of the switching matrix is programmed by the Set Top Box, and the number of demodulator tuner necessary for the demodulation of the information is thus determined.

Since several programs can be transmitted in the same channel, the number of channels necessary for the demodulation is less than the number of programs chosen. Each of the necessary tuners / demodulators (one per channel) is connected to the LNB, corresponding to the channel assigned to it. Each tunable filter is programmed at the corresponding channel frequency, and attenuates overall power by eliminating unwanted channels.

As indicated above, a gain in power of 20 dB can be obtained.

The advantages of such a configuration are:

- cost reduction in comparison with the complex transposition system represented by the MTFs, - Reduction of linearity constraints on the receiver, which may result in a reduction in the overall consumption of the receiver.

Figure 3 is a more detailed representation of an outdoor unit according to the invention.

A more detailed representation of the LNB block includes the filters f1-f4, the amplifiers a1-a4, fixed frequency oscillators o1-o2 (for example 9.75GHz and 10.6GHz, respectively) and the mixers m1 -m4 make it possible to transpose the 4 microwave signals into intermediate frequency signals S1 -S4.

The number of signals received by the LNB depends as previously explained on the user and the number of selected programs.

The intermediate frequency bands resulting from this transposition are for example between 950 MHz and 1950 MHz, or between 1100 MHz and 2150 MHz.

The switching matrix can be implemented by one or more active components. An M4X4 matrix can for example be made by a set of

4 buffer circuits B1, B2, B3, B4 with one input and 4 outputs associated with 4 SP4T (Single port 4 Throw) switching circuits Sp1, SP2, SP3, SP4 and thus allowing to choose among the 4 inputs of the SP4T circuit one of them and thus select on the channels, the RF transposition from which the information must be taken.

These circuits are preferably silicon circuits for cost reasons, but other component technologies may be used.

The tunable filters F1, F2, F3, F4 are bandwidth filters of for example 40-50 MHz and are tunable on 1 GHz for example, which covers the bandwidth of the intermediate band signals.

The filtering technology could be, without limitation, active silicon or a realization based on varactors.

The switching matrix M4x4 as well as the tunable filters F1-F4 are controlled by control signals Sc originating from a programmable microcontroller (not shown). The filtered signals are applied to the inputs of the block comprising 4 tuners T1, 12, T3, T4 associated respectively with 4 demodulators D1, D2, D3, D4 via amplifiers A1 -A4.

This channel preselection principle can be applied for analogue tuners or digital tuners for which the filtered intermediate frequency signal (F1) is directly converted to digital using ADC (analog / digital converter). In the case of digital tuners with a direct conversion of the intermediate frequency signal F1 by ADCs, the gain provided by the invention has a strong influence on reducing the number of bits necessary for this conversion. Thus, if 8 bits are needed without filtering, only 6 bits are necessary with this tunable filtering and 2 bits can thus be saved. The consumption of the converters, which is relatively high because of the high sampling frequency necessary to convert the intermediate frequency spectrum F1, is considerably reduced. The gain in power obtained by the only filtering of the signal is between 10 and 15 dB, to which are added a gain of about 1 OdB, related to the power regulation on the only channel used making it possible to eliminate the differences of level between canals.

Each power reduction of 6dB is equivalent to one bit saved for the analog / digital converter, and therefore to a reduction of a ratio 2 of the converter's surface area and consumption.

Claims

claims 1. N signal satellite reception system comprising associated with a satellite reception antenna an outdoor unit and an indoor unit connected to each other and characterized in that the outdoor unit is formed by: an intermediate frequency conversion block for transforming the N signals received on N channels into N intermediate frequency signals; an NXM switching matrix, controlled by signals from a control unit, for selecting for each of the M output channels, among the N transposed signals, the signal from which the information must be taken; - M frequency tunable filters, controlled by signals from the control unit, each associated with a channel for selecting a frequency band corresponding to a single channel in the intermediate frequency band; A block of M tuners and M demodulators respectively associated with the M channels for extracting the information from the transmitted channels. a combination block for combining the signals to be transmitted from the different demodulators. 2. receiving system according to claim 1 characterized in that M analog digital converters (ADC for Analog digital converter) are associated with M frequency tunable filters for digitizing the information to be transmitted