T 0594/91 18-11-1993

1. The appeal is admissible.

2. Allowability of the amendments

The Board agrees with the view expressed by the Opposition Division in the minutes of the oral proceedings of 9 April 1991 that the omission of the words "having a predetermined minimum orbital spacing" from Claims 1 and 16 of the second auxiliary request gives rise to objection under Article 123(3) EPC. As will be seen from paragraph 4 below the Board considers that these words have a limitative effect, so that their omission extends the protection conferred. The Board has accordingly considered the modified second auxiliary request.

3. Requests

The claims of the main, first auxiliary and modified second auxiliary requests differ in language rather than substance. It follows that a finding on novelty and inventive step on the claims of one request will apply to the claims of the other requests. The Board has accordingly considered below the claims of the request which in its opinion are most clearly expressed, namely those of the modified second auxiliary request.

4. Clarity of Claims 1 and 16

4.1. In the decision under appeal the issue has been raised as to whether the reference to a minimum orbital spacing of satellites might lead to a third party infringing the patent without any act of his own if further satellites were launched. Infringement is however exclusively a matter for national jurisdictions. The Board will therefore confine itself strictly to a consideration of whether the claims are clear in themselves.

4.2. As pointed out by the Opposition Division in the contested decision, it can be argued that the size of the earth station antenna is indeterminate, in that its beamwidth is defined with respect to the orbital spacing of geosynchronous satellites, a parameter over which the earth station builder has no control and which can be changed by administrative fiat.

4.3. It is noted that an analogous question arose in case T 636/88, the disclosure of which made reference to "standard container dimensions"; this expression was considered by an opponent to be insufficient on the grounds that the skilled man was not told which set of standards was relevant and that standards were constantly being revised. In that case the Board held that the skilled person would recognise which standard was applicable and that a change in standards did not happen overnight, so that at any one point in time the skilled person would have no difficulty in choosing. The Board furthermore refused to comment on the issue of infringement.

4.4. In the present case, the spacing of satellites is a matter of international agreement and any changes would have to be the subject of extensive consultations; moreover, antenna sizes are largely standardised and the skilled person would know what size of antenna is normally considered the minimum acceptable for any given band. Thus, the reference to satellite spacing does not render the scope of the independent claims indeterminate since when directing any given antenna at any given satellite the skilled person would be aware of the satellite spacing for the band and hence what antenna size would be likely to give rise to interference from neighbouring satellites.

5. Novelty and Inventive Step

5.1. The subject-matter of Claims 1 and 16 is novel, in that no single document discloses the use of spread-spectrum modulation in the context of a geostationary satellite system in which the receiving station antenna beamwidth is such that the antenna receives interfering signals from adjacent satellites.

5.2. The Board considers that the correct starting point for the present invention is spread spectrum rather than satellite technology. The Board also considers that the cited documents show that at the claimed priority date the advantages to be gained from the general use of spread spectrum were part of the common general knowledge in the communications art. Reference is directed to D6, which in a discussion on land mobile radio systems refers at page 224, central column, to a "possible vast improvement in spectral efficiency" from using spread spectrum, a theoretical user density of five times that of narrow-band f.m. being mentioned. The same document indicates at page 222, left hand column, that "only in recent years... the necessary high-speed digital hardware has become available, enabling serious consideration to be given to practical systems". D7 discusses spread spectrum in avionics systems and gives as advantages "capability to reject jamming by interfering signals" and "multiple access by many signals in a common RF channel". D56 refers at page 21, right hand column to spread spectrum techniques having a "high interference rejection capability"; D59 makes clear that this capability is not merely with respect to intentional jamming but also unintentional interference from other users (page 11, right hand column).

5.3. These advantages were also appreciated in the field of satellite communications. D5, a paper on air-ground communications via satellite, highlights the advantages to be gained by the use of spread spectrum and concludes by saying that "...[spread spectrum] modulation has now matured to the point where it may very well prove to be the most efficient and least expensive satellite communications technique in existence." D11 and D13, a DoD handbook and a textbook respectively, show that at the priority date spread spectrum was used in satellite communications, D11 stating at page 6-4 that "By proper choice of codes other SSMA transmission simultaneously present at the receiver will cause relatively small interference". D13 states at page 265 that "In space systems, especially communications satellites, which may be stationary and therefore continuously accessible to interference, spread spectrum methods have proved effective". From table 9.1 at page 266 it appears that by "interference" is meant jamming; the same table however gives "Interference rejection" as an application of spread spectrum in the area of "Signal protection (non-military)". D4, in a comparison of spread spectrum and conventional modulation for satellite communication, states at page 242, right hand column, that an advantage of spread spectrum is that "Interference from signals using the same bandwidth is suppressed... This 'redundancy' property of the signal permits many signals to share a common, broad band". Interference with existing ground-based microwave links is said to be minimized (page 255, left hand column). D14 indicates at page 130, right hand column, that RFI caused by the use of low-gain antennas for satellite reception in an environment of shared frequency allocations between satellites and other equipment could be overcome by the use of spread spectrum. Finally, D50 refers at page 617, right hand column, to the employment in satellite communications of "spread spectrum techniques that improve the communication system's resistance to undesirable signals".

5.4. From the above analysis of the prior art the Board draws the conclusion that it was at the priority date common general knowledge to employ an earth satellite communications system including a satellite and a central earth station which transmits messages to the satellite with a spread spectrum processing to be relayed to a plurality of receiving earth stations each equipped with a directional antenna and means for detecting the messages, said spread spectrum processing using a characteristic code sequence allowing selection by the earth station of the particular satellite relaying said spread spectrum processed messages and providing a processing gain sufficient to substantially suppress interfering signals.

The only remaining subject-matter in Claims 1 and 16 is that the satellite is one of a plurality of repeating geostationary satellites having a predetermined orbital spacing, and that the antenna is of a size resulting in a beamwidth such that the earth station receives said spread spectrum processed messages along with interfering signals from at least one other geostationary satellite.

5.5. A predetermined minimum orbital spacing for geostationary orbital satellites was at the claimed priority date clearly also common general knowledge.

Furthermore, from D2 and D10, both review articles, and from D37, a book, it appears that at the priority date the skilled person would have been well aware of the conflict between on the one hand the limited spectrum resources and limited geostationary orbital space and on the other hand the desirability of smaller ground antennas in order to make satellite communication links more attractive commercially. D2 shows at page 34 how the effective radiated power (e.r.p) of satellites has increased over the years, permitting lower gain (i.e. smaller) antennas to be used, and explicitly states at page 37 that "the trend to smaller, less expensive antennas runs counter to conservation of the synchronous orbit". This document also points in the direction of digital transmission systems (article bridging pages 32 and 33; page 37, last paragraph). D10 states at page 595, left hand column, that "small earth antennas have an enormous future" and goes on to discuss the cost trade-off between e.r.p., antenna diameter and LNB (Low Noise Block) noise figure; the implication, see particularly page 597, "TV Broadcasting from Space", is that reduction of antenna diameter size is desirable in order to reduce costs. D37 refers at page 53 to "a trend toward smaller earth antennas, suggesting fewer satellite positions" and states at page 145 that "The larger the antennas, the smaller the beam angle, and the closer the satellites without mutual interference". In this textbook it is also considered that in a practical system some interference will occur, since the same page states that "satellite interference is treated as noise in the link calculations...". At pages 365 and 366 the factors that permit lower costs are enumerated and include the following:

"1. Small antenna. 6. Modulation technique which can tolerate a substantial level of noise and interference."

This appears to be a clear invitation to the skilled person, who is faced with the problem of interference from adjacent satellites, to make use of "a modulation technique which can tolerate a substantial level of noise and interference", i.e. spread spectrum.

5.6. The Board accordingly concludes that at the claimed priority date, the skilled person looking for solutions to the problem of reducing antenna size whilst avoiding interference from adjacent geosynchronous satellites would, without the exercise of invention, have appreciated that spread spectrum processing represented an answer to his problem.

5.7. It follows that the subject-matter of each of Claims 1 and 16 of the modified second auxiliary request lacks an inventive step.

5.8. Since the claims of the Appellant's main and first auxiliary requests do not differ in substance from those of the modified second auxiliary request it follows that the above conclusions apply to them also and that the patent as a whole is not allowable.