Optis Cellular Technology LLC and Others v Apple Retail UK Ltd and Others
| Jurisdiction | England & Wales |
| Judge | Lord Justice Birss,Lord Justice Phillips,Lord Justice Arnold |
| Judgment Date | 13 June 2022 |
| Neutral Citation | [2022] EWCA Civ 792 |
| Court | Court of Appeal (Civil Division) |
| Docket Number | Case No: CA-2021-000725 |
[2022] EWCA Civ 792
Lord Justice Arnold
Lord Justice Phillips
and
Lord Justice Birss
Case No: CA-2021-000725
IN THE COURT OF APPEAL (CIVIL DIVISION)
ON APPEAL FROM BUSINESS AND PROPERTY COURTS
INTELLECTUAL PROPERTY LIST
Mr Justice Meade
CP2019000006
Royal Courts of Justice
Strand, London, WC2A 2LL
Tom Moody-Stuart QC and Thomas Jones (instructed by EIP LLP) for the Respondent/Claimant
Lindsay Lane QC and Jeremy Heald (instructed by Wilmer Hale LLP) for the Appellant/Defendant
Hearing dates: 4th & 5th May 2022
Judgment Approved
This appeal concerns the validity of European Patent (UK) No. 2 229 744 B1 entitled “Method and Arrangement in a Wireless Communication Network”. The patent was filed on 7 October 2008 claiming priority from 8 January 2008 and granted on 22 May 2013. It has been declared essential to the relevant standards. The sole question on appeal is whether the patent is anticipated by a prior art document referred to as InterDigital (TDoc R2-071618). That question turns on the construction of three claims (claims 1, 6 and 9).
The action began as an infringement claim brought by the respondents (“Optis”) against the appellants (“Apple”) in February 2019. The action was split into a number of trials, including a FRAND trial. This appeal is from the judgment of Meade J given on 25 June 2021 [2021] EWHC 1739 (Pat). The same patent was previously litigated in ( Unwired Planet v Huawei [2015] EWHC 3366 (Pat) and on appeal [2017] EWCA Civ 226). I was the trial judge, and my lord Arnold LJ was a member of the Court of Appeal in that case. There were no overlapping issues with the present case.
By the time of the judgment of Meade J, it was common ground that the patent was essential/infringed. The patent issues were all concerned with validity. There was also an issue about proprietary estoppel. The judge rejected Apple's case that the patent lacked novelty or was obvious over the cited prior art. He gave permission to appeal on novelty. The judge also rejected Apple's proprietary estoppel case and refused permission to appeal. Apple's application for permission to this court on the proprietary estoppel ground was refused.
The technical background
A detailed exposition of the undisputed technical background and common general knowledge is set out in the judgment from paragraph [40] to [79]. As the judge explained, those passages were based on the earlier judgment of mine in the Unwired Planet case (cited above). No purpose would be served in setting them all out again here. In order to understand the issues in this appeal, what one needs to know is the following.
The case is about modern mobile telecommunications networks. These systems are specified by international standards which are set by standards setting organisations. In sequence the various digital systems specified by these standards are known as GSM (2G), UMTS (3G) and LTE (4G). Today there is also 5G, but that is irrelevant. The standards specify how the different entities in the network behave so that they can communicate effectively. This case is about the behaviour of the entity which is transmitting data to a receiver by radio waves (the radio link). An example would be the transmitter at a mobile phone mast, and a mobile phone as the receiver. The relevant protocol for this transmission is called the Radio Link Control or RLC.
The stream of data to be sent is divided up into separate units called PDUs (Protocol Data Units). As an example, a single PDU can be about 1,500 bits in length. Every PDU consists of a small string of bits called a header followed by the remaining bits which represent the data to be sent. The header contains control information. One piece of control information is a sequence number. The sequence number uniquely identifies the PDU. The fundamental problem is that the radio link is unreliable and so one cannot guarantee that a PDU which is transmitted will be received. The sequence numbers allow the receiver to reassemble the data stream correctly using the individual PDUs. They also allow the receiver to identify if a PDU is missing. The receiver can therefore acknowledge (ACK) receipt of given PDUs and can also indicate that a given PDU has not been received (called a NACK — a negative acknowledgement). The way the receiver provides this acknowledgement information to the transmitter is by sending a status report. All control signalling, such as status reports, uses up bandwidth which might otherwise be used to send data. Therefore, in designing these systems there is a balance between having enough signalling to make them work efficiently, but not too much signalling which reduces the data capacity.
In this context status reports are not sent all the time because that would be inefficient. Rather the standard specifies events which trigger them. The transmitter may realise it wants to receive a status report and so needs to ask the receiver to do it. This request is called a poll. One of the bits in the header of a PDU is defined as a poll bit. The way the transmitter polls the receiver to send a status report is by “setting” the poll bit in a PDU which is transmitted to the receiver. Every time the receiver receives a PDU, it will check the status of the poll bit. If the poll bit is set, then the receiver knows it is being asked for a status report. When the status report is received by the transmitter it will know which PDUs are ACKed and which are NACKed.
When the transmitter sends a PDU, it will need to keep a copy in a memory buffer until it knows that that PDU has been ACKed. Once the PDU is ACKed, the copy can be deleted, freeing up space in the memory buffer. If that PDU is NACKed then the transmitter knows to send it again.
The meaning of the various bits in the header of a PDU are defined by the standard and as part of this the number of bits used for the sequence number is defined. In UMTS 12 bits were used, giving 4096 possible numbers. Therefore the sequence number cycles back to zero when PDU number 4095 is sent. One cannot re-use a sequence number unless one is sure that the previous PDU with that number has been received. Therefore, if the transmitter runs out of available sequence numbers it cannot send any more PDUs. The system is said to stall.
In the standards at the time various criteria were specified which might trigger a poll. The two important ones in the relevant standard specification were a counter-based trigger and window-based trigger. A counter-based poll trigger counts the number of PDUs transmitted and when that number reaches a predetermined value a poll is triggered. The predetermined value is in a defined field called Poll_PDU. A window-based trigger keeps track of the percentage of the available sequence number resource which has actually been used, and so indicates how much is still available. The percentage was defined in the standard as a parameter J in the following equation:
VT(S), VT(A) and VT(WS) are state variables. VT(S) is the sequence number of the next PDU to be transmitted. VT(A) is the sequence number of the last in-sequence acknowledged PDU. In other words, all the PDUs with a sequence number lower than VT(A) must have been ACKed. There may also be ACKed PDUs with sequence numbers higher than VT(A) but they will not form a continuous sequence because of the presence of at least one NACKed PDU. VT(WS) is the pre-defined size of the transmission window.
The equation determines the difference between VT(S) and VT(A) as a proportion of the predefined window size VT(WS) expressed as a percentage. Because sequence numbers cycle round 4096 values the calculation is done modulo 4096. Thus by specifying a value for J which triggers a poll, the window-based method allows one to trigger a poll when the window is near to filling up ( say 70% full) but has not yet filled up.
The purpose of both of these poll triggers is to poll periodically during continuous operation so as to avoid stalling. The window-based approach is more complicated to implement but more accurate than the counter-based method.
Originally PDUs had a fixed length. This meant that the PDU sequence number resource and the amount of memory buffer taken up by transmitted but unacknowledged PDUs were directly related to one another. However, before the priority date, the idea of variable length PDUs was introduced. These still had fixed headers, but the amount of data held in a PDU could vary. Therefore, one now needs to keep track of two resources, sequence numbers and memory space. Running out of either causes a stall.
This is the problem which the patent relates to. All of the above was common general knowledge.
The patent
In its background section (paragraphs [0006] and [0007]) the patent describes two existing criteria used to trigger a poll: one trigger is the transmission of the last PDU available, the other is the expiry of a poll retransmission timer. Then at paragraph [0008] the patent explains their limitations and describes how counter-based and window-based methods can be used to prevent stalling when transmitting continuous data:
“[0008] Such criteria for setting poll bits may work well for bursty traffic, where the poll is sent for the last PDU in each burst. For continuous transmission however, additional triggers may has to be considered. A properly designed polling procedure can be used to limit the number of outstanding, i.e. transmitted but not acknowledged, PDUs, or bytes, and to avoid stalling situations. Two mechanisms, counter-based and window-based, have been identified to avoid protocol stalling. Protocol stalling is an expression signifying that no more new data can be transmitted. Further, the...
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