GB2288714A - Data transmission in television microwave signal broadcasting - Google Patents

Abstract

Data (such as encryption data for satellite TV decoders) is transmitted in a broadcasting system without reducing the number of available TV channels. An aerial 2 receives satellite 4 and local radio frequency signals. A master transmitter 5(a) broadcasts a multi-channel television signal generated at a transmitter system 3. This transmitter 5(a) also transmits a 6 GHz signal incorporating data received via a leased line 13 from a computer 14. The data is inserted on a 7.5 MHz subcarrier. The data is dropped off at a next successive headend and the 6 GHz signal is re-transmitted. A television signal is broadcast from each successive headend, which signal includes directly received satellite signals. Extracted data is inserted at the Nicam carrier frequency at a lower bit rate than the usual Nicam bit rate, thereby not effecting the number of TV channels. <IMAGE>

Description

n Improvements in and Relating to Microwave Signal Broadcasting N The invention relates to the broadcasting of television channels using microwave signals.

Microwave broadcasting systems, generally referred to as multi-point microwave distribution systems (MMDS) at present broadcast a number of different television channels from microwave transmitters or headends located at different geographical sites. These signals are picked up by a microwave antenna at each household, the frequency of the signal being substantially reduced at a downconverter connected to the antenna. A decoder reads the output of the downconverter and transmits the resulting signals to a television set for viewing of the television channels.

Broadcasting of television signals generally is becoming more complex in that data must be communicated between sites. This data includes, for example, the encryption data which is required of decoders at the reception sites, in addition to data which is required for different parts of the broadcasting organisation. Where data has been transmitted using the microwave signals, it has generally been necessary to use up a television channel. This is the case, for example in the system described in PCT Patent Specification No. 85/04543 (A. C. Nielsen Co.).

The invention is directed towards providing an improved television signal distribution method which provides for communication of data in a versatile manner and in a manner which involves relatively little cost.

According to the invention, there is provided a broadcasting method carried out by a system comprising a primary aerial for reception of RF television signals, a transmitter system connected to the aerial, a master microwave transmitter connected to the transmitter system, a set of microwave transmitters located at geographically remote sites, and equipment located at each reception site including a microwave antenna and a decoder, the method comprising the steps of: the aerial receiving radio frequency signals from a satellite; the aerial receiving local radio frequency television signals; the transmitter system combining the received signals and generating an MMDS microwave multi channel television signal which is broadcast by the master transmitter at a microwave frequency in the range of 2.5 to 2.7 GHz band, this step involving insertion of a data signal received from a control computer at a substantially lower bit rate than a stereo information signal in that bandwidth of a channel reserved for stereo information; the master microwave transmitter transmitting at least one of the television signals together with data received from the control computer as a high frequency link at a frequency in the range of five to seven GHz, in which data is inserted in one of a plurality of channels; another microwave headend receiving the high frequency link signals, dropping-off the data channel for use in local broadcasting and re transmitting the link for reception by a next successive microwave headend, wherein for local broadcasting each of the microwave headends inserts the data signal received from the high frequency link at a stereo information carrier frequency on a channel at a substantially lower bit rate than that which is recognised by the reception equipment for stereo information; and at each reception site, the downconverter converting the data signal to a frequency recognisable by the reception equipment.

Preferably, the data signal is inserted on a sub-carrier in a channel of the high frequency link together with TV signals.

In one embodiment, the data signal is in biphase format and is fed directly into one side of an electronically balanced input having a shunt capacitor.

Preferably, the resistance of the balanced input is approximately 300 Ohm per side.

In one embodiment, each headend includes a satellite receiver for reception of the satellite TV signals for use in the local MMDS broadcast.

Preferably, the high frequency link has a frequency of approximately six GHz.

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which: Fig. 1 is a schematic representation of portion of a broadcasting system of the invention; Fig. 2 is a schematic representation of a local part of the broadcasting system; and Fig. 3 is a flow chart indicating the manner in which the system operates.

Referring to the drawings and initially to Fig. 1, there is shown portion of a broadcasting system of the invention, indicated generally by the reference numeral 1.

The system 1 comprises a main radio frequency aerial 2 connected to a transmitter system 3. The aerial 2 is for reception of television signals, in this embodiment four local channels received via local RF signals. In addition, it receives seven channels from a satellite 4.

The transmitter system 3 is connected between the aerial 2 and a master microwave transmitter 5(a). The system 3 comprises an RF frequency receiver connected to a microwave transmitter, the latter being constructed for microwave transmission at baseband frequencies. Referring also to Fig. 2, there is a series of microwave transmitters 5(b) to 5(d) located on hilltops for distribution of television signals to the local area around the transmitter or headend 5.

As shown in Fig. 2, a microwave headend 5 transmits signals to a number of households, each of which has a microwave antenna 7 with a downconverter 8. The downconverter 8 is connected to a decoder 9 which transmits decoded signals to television sets 12. A power supply 11 is connected to the various units.

The system 1 also comprises a leased line 13 connected to a television signal data control computer 14. This computer 14 is programmed to generate encryption data for the decoders 9 at each reception site.

In operation, the system 1 carries out the method 20 shown in Fig. 3 for broadcasting of television signals and communication of data. Radio frequency signals carrying in this embodiment seven television channels are received in step 21 from the satellite 4 at the aerial 2. These signals are all in the PALI format and are received in the 11.0 to 12.5 GHz frequency band.

In addition, local radio frequency television signals are received at the mast 2 in step 22. In this embodiment there are four signals, all of which are in the PALI format, being UHF broadcasts operating at 479.25 MHz, 503.25 MHz, 527.25 MHz, and 559.25 MHz.

The transmitter system 3 combines the received signals to generate a multi-channel television signal which is broadcast in step 23 via the master microwave headend 5(a). This broadcast incorporates data received on the leased line 13 in step 24. This is described in more detail below. There are available for the system 1 twenty-two RF frequencies in the 2.5 to 2.686 GHz band, of which eleven are used at each headend 5.

An important aspect of the invention is the fact that in addition to transmitting MMDS broadcasts, the master headend 5(a) transmits television signals together with data at a high frequency in the range of 5 to 7 GHz, in this embodiment 6 GHz in step 25. This is the data received via the leased line 13 from the control computer 14. The 6 GHz link has four channels, each taking 30 MHz of the bandwidth, and using FM modulation. The first channel transmits a TV signal of 5.5 MHz and a sound subcarrier of 6.5 MHz. In addition, however, this channel includes the data received from the leased line 13, this data being inserted on a 7.5 MHz sub-carrier. The data on the sub-carrier includes a series of serial number addresses for the decoders 12 at the reception sites. The data is in biphase format and is fed directly (unbalanced) into one side of a 600 ohm electronically balanced input (i.e. into 300 ohm) with a shunt capacitor of approximately 8200 pF. The remaining three channels carry T.V. signals.

The 6 GHz link signal is received at the next microwave headend 5 which "drops-off" the data for use in its own MMDS broadcast. In addition, the relevant headend 5 retransmits in step 28 the signals to the next microwave headend 5 and this is repeated for each successive headend 5. This provides a 6 GHz communications link between the various headends.

At each of the microwave headends 5, in addition to retransmitting the signal to the next headend, an MMDS broadcast is made at a frequency in the range of 2.5 to 2.7 GHz. Each successive headend 5 includes a satellite reception dish for reception directly in step 26 of the satellite TV channels, also received by the master headend 5(a). The relevant headend 5 combines the four TV channels received on the 6 GHz link and the received satellite signals to provide the input for the MMDS transmitter. From a commercial viewpoint, the number of TV channel signals broadcast must be maximised at each headend 5. The maximum of 11 channels is achieved because the data extracted from the 6 GHz link is inserted at the Nicam carrier frequency on the first channel at a substantially lower bit rate than a Nicam signal bit rate.

In this embodiment, the Nicam bit rate is 728 kb/s and the signal uses a QPSK modulation technique. The data is inserted at a bit rate of only 14 kb/s per second using FM modulation. This ensures that the various household equipment will not confuse the data with the Nicam data.

At each of the households, the signal is received at the antenna 7. The data frequency is converted by the downconverter 8 to 229.802 MHz. The decoder 9 receives the data which contains the encryption information regarding each television channel and the output is connected to the television set for display. The data which is received includes encryption signals for every decoder 12. The incoming data stream at 14 kb/s is continuously monitored by each encoder 12 for identification of the associated serial number address.

By transmitting data in this way the following advantages are achieved: 1. the headend equipment may operate in a simple and reliable manner with little chance of data corruption because it is not required to extract data for its associated reception sites, and 2. The number of TV channels which may be broadcast is not reduced.

It will be appreciated that the invention provides a relatively simple broadcasting method which provides for communication of data between different microwave headends and ultimately from a control computer to each of the reception units in the broadcasting network. Although the invention is quite simple, it leads to considerable cost savings in that there is no need to provide leased-line data communication between the various sites in the broadcasting organisation. In addition, there is no overhead on the number of microwave television channels which may be distributed as a Nicam carrier is used for encryption data.

The invention is not limited to the embodiments hereinbefore described, but may be varied in construction and detail.

Claims (7)

CLAIMS:

1. A broadcasting method carried out by a system comprising a primary aerial for reception of RF television signals, a transmitter system connected to the aerial, a master microwave transmitter connected to the transmitter system, a set of microwave transmitters located at geographically remote sites, and equipment located at each reception site including a microwave antenna and a decoder, the method comprising the steps of: the aerial receiving radio frequency signals from a satellite; the aerial receiving local radio frequency television signals; the transmitter system combining the received signals and generating an MMDS microwave multi-channel television signal which is broadcast by the master transmitter at a microwave frequency in the range of 2.5 to

2.7 GHz band, this step involving insertion of a data signal received from a control computer at a substantially lower bit rate than a stereo information signal in that bandwidth of a channel reserved for stereo information; the master microwave transmitter transmitting at least one of the television signals together with data received from the control computer at a high frequency link at a frequency in the range of five to seven GHz, in which data is inserted in one of a plurality of channels; another microwave headend receiving the high frequency link signals, dropping-off the data channel for use in local broadcasting and re transmitting the link for reception by a next successive microwave headend, wherein for local broadcasting each of the microwave headends inserts the data signal received from the high frequency link at a stereo information carrier frequency on a channel at a substantially lower bit rate than that which is recognised by the reception equipment for stereo information; and at each reception site, the downconverter converting the data signal to a frequency recognisable by the reception equipment.

2. A method as claimed in Claim 1, wherein the data signal is inserted on a sub-carrier in a channel of the high frequency link together with TV signals.

3. A method as claimed in claim 2, wherein the data signal is in biphase format and is fed directly into one side of an electronically balanced input having a shunt capacitor.

4. A method as claimed in claim 3, wherein the resistance of the balanced input is approximately 300 Ohm per side.

5. A method as claimed in any preceding claim wherein each headend includes a satellite receiver for reception of the satellite TV signals for use in the local MMDS broadcast.

6. A method as claimed in any preceding claim wherein the high frequency link is at a frequency of approximately six GHz.

7. A method substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.