HomeInsightsHigh Court invalidates patent relating to digital Distributed Antenna System and rules that the court has no jurisdiction to amend a patent after proceedings have been discontinued

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CommScope Technologies LLC (CommScope) issued proceedings against Solid Technologies Inc (SOLiD) for infringement of its digital Distributed Antenna System (DAS) European patent designating the UK (the Patent).

Mr Justice Mellor explained that a DAS is used in a cellular wireless communication system (in the forward or downlink direction) to distribute radio frequency (RF) signals transmitted from a base station into areas where the signal has been significantly attenuated, so that mobile devices in such areas can continue to operate effectively. A DAS is bi-directional, so (in the reverse or uplink direction) it is used to gather wireless signals from mobile devices and transmit them back to the base station. Analogue DASs were known at the time the Patent was filed. The Patent provided a digital DAS, so that the internal handling of the analogue RF signals was digitised.

In response to the infringement claim, SOLiD counterclaimed for invalidity, arguing that Claim 1 of the Patent was anticipated by or was obvious over a single piece of prior art called “Oh”, which was a Korean patent application entitled “Digital optical repeater” published on 5 August 1999, i.e., before the priority date of the Patent which was 19 July 2000. SOLiD also said that Claim 7 of the Patent was obvious over “Oh”.


The Patent

The Patent was entitled “A method for point-to-multipoint communication using digital radio frequency transport”.

Claim 1 explained the technical field of the invention as, “… related to high capacity mobile communications systems, and more particularly to a point-to-multipoint digital micro-cellular communication system”.

Claim 6 described the core issue the Patent sought to address, which was, instead of using a point-to-point architecture, which required multiple RF units and remote antenna units on each floor of a tall building, the Patent taught incorporation of the benefits of digital RF transport into a point to multipoint architecture.

The Patent then offered two solutions: (i) a single host unit that transmitted to multiple remote units, using a star arrangement; or (ii) a single host unit using a tree arrangement where the host unit transmitted the digital signals either directly to the remote units or via an “expansion unit” (Claim 7), allowing further branching to a set of remote units.

Mellor J found that the Claims were widely drawn, and he dismissed CommScope’s argument for a narrow Claim construction. Mellor J found that the Patent was not limited to a single-channel system, as argued by CommScope, but also described a multi-channel arrangement, as argued by SOLiD.

SOLiD said that if Claims 1 and 7 were construed according to its analysis, no issue of infringement arose, as both were invalid.


CommScope argued that the disclosure in “Oh” was limited to a multi-channel arrangement. Mellor J disagreed, finding that “Oh” disclosed both a multi-channel arrangement, a single channel arrangement and one involving two slave units.

Accordingly, having found that Claim 1 of the Patent was not limited to a single channel arrangement and given that “Oh” was also a multi-channel arrangement, Mellor J found that “Oh” anticipated Claim 1.

As for obviousness, which only arose if the findings on anticipation were wrong, assuming that “Oh” only disclosed a multi-channel arrangement (as argued by CommScope) and that Mellor J was wrong on his construction of Claim 1 and it was, in fact, limited to a single-channel system, CommScope argued that there was no motivation for the skilled person to dispense with the multi-channel arrangement in “Oh” and modify it to implement a single processing pipeline.

However, SOLiD presented evidence of various examples of applications where the skilled person might do just that, e.g., emergency service radio systems. Further, in terms of the steps required, SOLiD showed that the skilled person would be able readily to create a single channel system from the “preferred embodiment” in “Oh” simply by dispensing with the components required for the other three channels. This would involve using dividers and combiners, but the changes required would have been entirely obvious to do. Accordingly, Mellor J found that Claim 1 was obvious over “Oh”.

Mellor J also found that Claim 7, which taught the use of expansion units, was obvious over “Oh”. On the evidence, he rejected CommScope’s contention that the skilled person was not aware of expansion units at the relevant time. In fact, there were potentially many arrangements using expansion units that were obvious, of which Claim 7 claimed just one class of them.


Mellor J concluded that had the Patent been valid, SOLiD’s system would have infringed. However, since the Patent was invalid and should be revoked, SOLiD had not infringed.

Application to amend

Originally, CommScope sued SOLiD for infringement of two patents: the Patent (discussed above) and another European Patent designating the UK relating to a digital DAS with “daisy chain” topology in which the signal would be demodulated before and modulated after each node (the Second Patent). CommScope reacted to SOLiD’s counterclaim for invalidity by applying to amend each of the patents unconditionally.

The action for infringement of the Second Patent and the corresponding counterclaim to invalidate it were settled on terms and resulted in two court orders, the effect of which was that each side undertook to carry out a staged discontinuance of the relevant claims, CommScope undertook not to sue on the Second Patent in the UK, SOLiD undertook not to oppose CommScope’s unconditional application to amend and the amendment application for both the Patent and the Second Patent was ordered to be heard at the trial of the Patent.

The Comptroller subsequently provided a lengthy report on the proposed amendments. CommScope’s initial reaction was to suggest to SOLiD that it would withdraw its application to amend. The parties were unable to agree whether the amendment application was still live or not, so the issue had to be decided by the court.

Mellor J concluded that the court did not have jurisdiction to decide the amendment application because:

  1. when the application to amend was issued there were “proceedings” (under s 75 of the Patents Act 1977) in which the validity of the Second Patent was in issue, so the court had jurisdiction at that point; however, CommScope then served a notice of discontinuance of its infringement claim and SOLiD served a notice of discontinuance of its counterclaim for invalidity; there was no qualification to either notice of discontinuance: each concerned the whole of the relevant claim or counterclaim relating to the Second Patent; therefore, by the time of the trial, there were no extant proceedings in which it could be said that the validity of the Second Patent was or might be put in issue under s 75;
  2. the fact that a different judge had made an order by consent directing that the application to amend the Second Patent should be heard at the trial of the Patent did not create an exception to either notice of discontinuance, which were both unqualified; those notices put an end to the application to amend;
  3. there was no reason to strain to find jurisdiction as CommScope could still apply to the Comptroller to amend and SOLiD was not at risk due to the provisions of the Consent Order; and
  4. although the court did have jurisdiction at the time the application to amend was made, it was necessary to establish jurisdiction both when an application to amend is first made and when it is determined by the court.

(CommScope Technologies LLC v SOLiD Technologies Inc [2022] EWHC 769 (Pat) (1 April 2022) — to read the judgment in full, click here).