Description of the Patent
131 The 355 Patent is entitled 'Method and system of scanning a TDMA channel'. It has a priority date of 26 July 2004. The patent describes the field of the invention as relating generally to 'wireless communications systems and more specifically to scanning in a time division multiple access (TDMA) system'. The patent describes the background of the invention in these terms:
A wireless communications system may generally comprise a set of "subscriber units," typically subscriber units are the endpoints of a communication path, and a set of "base radios," (also known as "repeaters") typically stationary and the intermediaries by which a communication path to a subscriber unit (SU) may be established or maintained. One such type of system is a time division multiple access (TDMA) communication system where the radio medium (or RF frequency) is divided into time slots to carry the communications of the system. Because the communication system carries many communications at one time, a subscriber unit may want to monitor other communications in the system. Scan is a feature that allows a subscriber unit to monitor other communications in the system.
SUs of the wireless communications system utilize a feature termed "scan" where an SU locks on to specific RF frequencies in a preprogrammed list in the SU. The RF frequencies in the scan list may be associated with more than one wireless communications system. For example, an SU may have RF frequencies from the Schaumburg fire department and the Rolling Meadows fire department in its scan list. If the preprogrammed scan list is very long and has many RF frequencies, then the scan feature takes a long time. Further, in the usual case, when many of the RF communications are normally of no interest to the scanning SU, the scanning SU spends a lot of time listening to communications that are of no interest to it. For example, this occurs when an RF frequency is included in the preprogrammed scan list, but the current communication is addressed to a SU or group of SUs that are of no interest to the scanning SU.
Accordingly, there exists a need for scanning a TDMA channel which improves the amount of time that an SU spends scanning.
132 A summary of the invention is then given in these terms:
According to one aspect of the present invention there is provided a method for scanning a TDMA channel by a subscriber unit in a wireless communications landscape, wherein the subscriber unit is operationally connected to at least one base radio over a plurality of channels, the method including the steps of:
locking onto a channel of the plurality of channels by the subscriber unit wherein a subset of the plurality of channels is preprogrammed in a list in the subscriber unit;
transmitting from at least one base radio a control message to the subscriber unit wherein the control message has a first information which informs the subscriber unit of activity present on the channel of the plurality of channels;
receiving and decoding the control message for the first information by the subscriber unit; and
if the first information indicates that activity is present on the channel of the plurality of channels, then determining whether the activity is of interest to the subscriber unit by comparing a second information in the control message with a third information preprogrammed in the subscriber unit and
if the activity is of interest to the subscriber unit, then remaining on the channel of the plurality of channels to receive the activity present on the channel.
According to a further aspect of the present invention there is provided in a TDMA system whereby the TDMA system includes a plurality of subscriber units and a plurality of base radios, a method for scanning, the method including the steps of:
locking onto a channel preprogrammed in a list of a subscriber unit whereby the channel carries activity on one timeslot of the TDMA system;
receiving an activity update message from a base radio of the plurality of base radios wherein the activity update message indicates in a first information the activity on the channel and indicates in a second information at least one characteristic of the activity on the channel;
determining whether the activity is of interest to the subscriber unit by comparing the at least one characteristic with preprogrammed third information in the subscriber unit; and
if the activity is of interest, then remaining on the channel to receive the activity; otherwise moving to the next channel in the list.
133 As will be seen, a significant issue which divides the parties is the relationship between the invention disclosed in the claims and the invention which appears in the detailed description of the invention in the body of the specification. Under the heading 'Brief Description of the Figures' there appears references to three figures in these terms:
An illustrative embodiment of the invention is now described, by way of example only, with reference to the accompanying figures in which:
FIG. 1 is a block diagram of an example wireless communications landscape in accordance with an embodiment of the invention.
FIG. 2 is a flow diagram of an example method for providing channel access for voice transmissions.
FIG. 3 is an example of a specific Common Announcement Channel message called an Activity Update.
…
134 The three figures are then explained in the remaining body of the specification under the heading 'Detailed Description'. Figure 1 is as follows:
135 So far as this case is concerned, little controversy attends Figure 1. It is described in these terms at p 2 line 18 to p 3 line 20:
Referring now to FIG. 1, there is shown an example of the method and apparatus of the present invention as it may be employed and incorporated into a typical wireless communications landscape 100 having system 100, system 120, and system 130. The illustrated example has three systems 110, 120, 130 whereby a system is comprised of a multiplicity of communication resources of RF frequencies, base radios (BRs) and subscriber units (SUs) optionally managed by system controllers (not shown) whereby the SUs send and receive communications with BRs (also known as "repeaters").
System 110 comprises a plurality of cells, each with a BR 3, 5, 7, 9, 11, 13 typically located at the center of the cell, and a plurality of SUs 12, 14, 16, 18, 20, 22 all of which are communicating on RF frequencies assigned to system 110. The SUs 12, 14, 16, 18, 20, 22 in system 110 may include all the RF frequencies associated with the BRs 3, 5, 7, 9, 11, 13 in system 110 in their preprogrammed scan lists. System 120 comprises a plurality of cells, each with a BR 26, 28, 30 typically located at the center of the cell, and a plurality of SUs 34, 36, 38 all of which are communicating on RF frequencies assigned to system 120. The SUs 34, 36, 38 of system 120 may include all the RF frequencies associated with BRs 26, 28, 30 in their preprogrammed scan lists. Further, SU 36 may include RF frequencies associated with the BRs in system 110 and with the BR in system 130 since the SU 36 is sufficiently close to all three systems 110, 120, 130. System 130 comprises a cell with a BR 24 and SUs 32, 40 all of which are communicating on RF frequencies assigned to system 130. Further, BRs 3, 13, 24, 28 may all be operating on the same RF frequency, but using a different color code since the BRs are separated by great geographical distance.
A BR preferably comprises fixed equipment for communicating data/control and voice information to and from the SUs for facilitating communications between the SUs in the wireless communication landscape 100. A subscriber unit (SU) preferably comprises mobile or portable devices (such as an in-car or handheld radios or radio telephones) capable of communicating with a BR using time division multiple access (TDMA) or time division duplex (TDD) techniques as further described herein, in which specified time segments are divided into assigned time slots for individual communication. As is known in the art, each RF frequency in the system carries time slots whereby each time slot is known as a "channel." Thus, for the BRs shown in FIG. 1, each BR has two channels associated with the coverage area.
136 The description then turns to an illustrative embodiment of the invention. The first part of this is at p 3 line 21 to line 29:
In an illustrative embodiment of the present invention, the wireless communications landscape 100 assumes a two slot TDMA communications system; however, other slotting ratios may be used in the TDMA communications system and still remain within the spirit and scope of the present invention. In an illustrative embodiment, the SU determines time slot numbering by decoding a TDMA channel field in a Common Announcement Channel (CACH) burst whereby the CACH burst is used for signalling information in the wireless communications landscape 100. In the illustrative embodiment of a two slot TDMA communications systems, the CACH burst is common to timeslot 1 and to timeslot 2.
137 The priority date for the 355 Patent is 26 July 2004. By this time, the DMR Standard had not yet come into effect and would not come into effect until 2005. That standard prescribed a two timeslot TDMA system. The illustrative embodiment proceeds on the same basis. An important aspect of this paragraph is its reference to the Common Announcement Channel ('CACH') burst. The CACH burst is used for signalling information and, in the illustrative embodiment, is common to both channels. Later in the description it becomes important to know this fact - the illustrative embodiment proceeds on the basis that the CACH burst is the same for both channels. An implication of this, borne out later in the description, is that the CACH burst carries signalling information for both channels.
138 The description then continues at p 3 line 30 to p 4 line 9:
As is known in the art, "color code" is a common identifier used by a group of SUs which utilize the same BR. For example, as shown in FIG. 1, SUs 12, 14, 22 are in one color code because they utilize the same BR, namely BR 9. Further, a color code field may be present in an embedded signaling message and a general data burst to provide a means of addressing a radio network or a specific repeater so that cochannel interference may be rejected. Further known in the art, a "talkgroup" is a group of SUs that share an RF frequency and timeslot and have the same color code. In an illustrative embodiment, a talkgroup is identified by a 16-bit talkgroup identifier (TGID and an individual subscriber unit is identified by a 24-bit subscriber unit identifier (SUID). Thus, in an illustrative embodiment, SUs that share a color code are further subdivided into talkgroups so that SUs in one talkgroup do not hear SUs in another talkgroup.
139 This accords with the discussion of colour coding set out above in Chapter II. Important concepts are the ideas of the Talkgroup Identification ('TGID') and Subscriber Unit Identification ('SUID'). It will be noted that in the illustrative embodiment, these are 16 bit and 24 bit fields respectively. As will be seen later in the discussion of the CACH burst, the length of the SUID and TGID are important elements of the debate between the parties.
140 The description then continues at p 4 line 10 to line 21:
As used herein, the terms "communication" and "transmission" are used interchangeably and refer to contiguous TDMA bursts emanating from one radio in one timeslot. As such, transmissions may generically refer to voice, data or control information relating to the wireless communications landscape 100. The term "call" refers to related voice transmissions between SUs in the wireless communications landscape 100.
As is known in the art, the term "burst" refers to the smallest standalone unit of a TDMA transmission. In an illustrative embodiment, for a burst found in a Motorola Low Tier Digital system, a defined transmission is 216 bits of payload and 48 bits of synchronization or embedded signaling. The defined transmission takes 27.5 msec to transmit and may be followed by 2.5 msec of guard time or the CACH burst. Thus, a "burst" in such a Motorola Low Tier Digital system is 30 msec.
141 Again, this is important for some of the disputes between the parties. The defined transmission used in the illustrative embodiment is 264 bits in length. It takes 27.5 msec to transmit. It is followed by a period of 2.5 msec which can be used as guard time or for a CACH burst, it being recalled from the above that the CACH burst is used for signalling information and is transmitted on both slots 1 and 2. The total burst is therefore 30 msec. A little later in the description there is a discussion of a particular kind of CACH message known as an 'activity update message' which is transmitted by means of four CACH bursts: page 6 line 24. What this means is that the activity update message is transmitted in the last 2.5 msec in each of four 30 msec bursts. It is not clear from the description at this stage whether these bursts are successive or whether other signalling information is conveyed by means of the CACH bursts. Later in the description, however, it becomes apparent that more signalling information in the form of seven CACH bursts, known as the full LC message, also utilise this 2.5 msec portion. I will return to the activity update message shortly, but it may be noted that, as Professor Rangan confirmed at T806.1-4, in the illustrative embodiment, the activity update message is itself 28 bits in length:
MR BURGESS: Thank you, Professor. And the activity update message described in the body of the 355 patent is 28 bits in size; correct?
PROF RANGAN: I believe that's correct.
142 It may be surmised from Figure 3 that each of the four CACH bursts occurs as the last 2.5 msec of the burst, that three of the four bursts contain 8 bits, and that one of the bursts contains 4 bits:
143 Very important also is the fact recorded at p 6 line 24 to 27 that the activity update message (transmitted by means of the four CACH bursts) is 'used to assist in identifying whether there is an active transmission (also termed "activity") on the channel'. It also 'provides information that indicates whether the scanning SU should dwell on the channel or should resume scanning'. Jumping ahead a little, determining that there is no active transmission on the channel would be a good reason for resuming scanning. But even if there is activity on the channel, the information contained in the activity update message may indicate to the subscriber unit that the activity is not of interest to it. That observation will in due course feed into the question of the meaning of some of the claims. Part of the controversy between the parties concerns the nature of the information contained in the activity update message. For present purposes it will be seen, however, that the illustrative embodiment proceeds on the basis that the activity update message both indicates whether there is activity on the channel and also provides unspecified (at this stage) information to determine whether to 'dwell' on the channel or move to the next channel. The word 'dwell' does not appear in the claims and prefigures one of the debates between the parties which concerns whether the decision to dwell is a permanent decision or whether the subscriber unit, once confronted with further information, might decide to stop dwelling on the channel and move on to scanning for the next channel. Hytera's construction case is that this is not permissible.
144 The description then continues to discuss the nature of scanning at p 4 line 22 to 28:
In an illustrative embodiment, a scan is performed in at least one of three situations: 1) when the SU powers on where the receiver automatically changes "channels" in a set order with a list preprogrammed in the SU, 2) when a user of the SU manually taps a button or turns a dial to manually step through frequencies preprogrammed in the SU, and 3) when a user of the SU sets the SU to scan mode where the receiver automatically changes frequencies in a set order with a list preprogrammed in the SU.
145 At p 4 line 29 to p 5 line 14, an important connection is made, in the case of the illustrative embodiment, between scanning and the concept of a characteristic of a communication:
Further, there may be different types of scanning that a SU performs. An SU may be programmed to perform scan based upon a characteristic of the active transmission such as whether the active transmission is voice, data, group, individual, emergency, and non-emergency. For example, a scanning SU may be programmed to scan for channels only carrying voice transmissions. Further, a scanning SU may be programmed to scan for channels only carrying data transmissions. Further yet, a scanning SU may be programmed to scan for channels carrying voice transmissions that are addressed to individual SUs and not voice transmissions that are addressing talkgroups. Further yet, a scanning SU may be programmed to scan for channels carrying data transmissions that are addressed to individual SUs and not data transmissions addressing talkgroups. Another example, a scanning SU may be programmed to scan for channels carrying any emergency transmissions regardless of the group that the active transmission is associated with. Yet another example, a scanning SU may be programmed to scan for channels carrying only non emergency transmissions regardless of the group that the active transmission is associated with. As can be imagined, there are numerous examples combining the characteristics to program a scanning SU to only search for specific active transmissions and the examples listed above are only illustrative and not exhaustive.
146 There appear to be six characteristics discussed but in fact they may be grouped into three sets of pairs each member of which is complimentary. For example, a communication is either a voice communication or a data communication. It is either addressed to a group or to an individual. It is either an emergency transmission or it is not. These binary pairs and their susceptibility to being represented by bits is a matter to which it will be necessary to return. As the passage describes, the scan function can be set so as to scan for channels which are only carrying voice transmissions. Or it could be set to scan for communications which are both voice transmissions and addressed to an individual subscriber unit. By doing this, the scan function is able to exclude communications which are not of interest to the subscriber unit. For example, if it is set to scan for voice communications addressed to an individual subscriber unit, the fact that the communication is not of that nature can be discerned from the characteristics. I return below to how the illustrative embodiment in fact does this.
147 The description then introduces Figures 2A and 2B which are important for the debate between the parties. Between the two figures is a single flow chart. Figure 2A is concerned with how the illustrative embodiment processes a voice transmission and Figure 2B deals with a data transmission. They are as follows:
148 It will be seen that Figure 2A is connected to Figure 2B at Block 226. The explanation of Figure 2A occupies much of the specification. It begins at p 5 lines 15 to 30:
Referring to FIG. 2, in operation, an SU performs the function of scanning by tuning to a specified channel enumerated in a scan list preprogrammed in the scanning SU (Block 202). As is known in the art, a channel is also known as a "personality" where a personality is typically a radio frequency (RF) with additional qualifying information. The scanning SU pauses on the selected personality for a specified time period and tests whether an RF carrier is detected (Block 204). In one embodiment, a scanning SU which is programmed to scan only for voice transmissions pauses for 25 msecs before continuing.
As is known in the art, the specified time period depends upon the type of signal expected to be received by the scanning SU such as analog voice, FDMA digital, and TDMA digital. Further, the specified time period may depend upon the type of scan being performed. As mentioned above, the type of scan may depend upon a characteristic of the active transmission such as whether the active transmission is voice, data, group, individual, emergency, and non-emergency. For example, if the scanning SU is programmed to scan for channels only carrying data transmissions, then it may wait for 65 msecs before continuing.
149 The significance of the time delays was not something which the evidence touched upon and appears immaterial to the debates between the parties. It is not obvious to me why the pause times might vary depending on the nature of the signal expected to be received or why the description includes reference to FDMA and analogue systems when it is concerned only with TDMA systems. In any event, this does not matter.
150 The description then continues at p 5 line 31 to p 6 line 12:
If an RF carrier is present, then the scanning SU remains on the selected personality and performs synchronization (Block 206). In an illustrative embodiment, performing synchronization between the BR and the SU involves waiting a predetermined period of time for detecting a time slot synchronization signal. The time slot synchronization signal is a 48 bit (also known as 24 symbols) frame sync word. The time slot synchronization signal identifies the center of a TDMA burst and the type of communication present on the TDMA channel so that a receiver in the scanning SU may be able to receive transmissions on the TDMA channel. Performing synchronization is complete upon detection of the time slot synchronization signal within a predetermined period of time. In one embodiment, the scanning SU must receive the time slot synchronization signal within 335 msecs. If the communication between the SU and the BR is in synchronization or the SU is successfully able to perform synchronization between the BR and the SU, then the SU determines a color code for the active transmission on the channel (Block 208).
151 Synchronisation is, as I explained above in Chapter II, an essential element of TDMA architecture. The reference to colour code at p 6 lines 11 to 12 harks back to the explanation of colour codes at p 3 line 30 (discussed above). The description then continues at p 6 lines 13 to 20:
As is known in the art, regardless of whether a carrier is detected (Block 202), a scanning SU that receives a frame synchronization message further decodes the personality. Thus, if frame synchronization is performed, then the scanning SU remains on the personality an additional amount of time to determine whether there is a match of the color code for the active transmission on the channel (Block 208). If there is not a match of the color code (Block 208), frame synchronization (Block 206), or carrier detect (Block 204), then the scanning SU tunes to the next channel in the preprogrammed scan list (Block 220).
152 At least for the illustrative embodiment, a failure to establish the presence of a carrier on the RF, or if having done so, if frame synchronisation is not achieved or, if it is, if the colour associated with the communication does not match the colour of the subscriber unit, then it moves to the next channel. If all of those matters are, on the other hand, satisfied then it follows that the subscriber unit has detected a carrier signal, has achieved frame synchronisation, and has determined that the subscriber unit and the base radio sending the communication are part of the same colour group. In this circumstance, the illustrative embodiment then decodes what it refers to as an 'activity update message'. This appears from p 6 lines 21 to 27:
If there is a match of the color code for the active transmission on the channel, then the scanning SU remains on the channel and decodes a specific CACH message termed an "activity update" message 300 (Block 210). In an illustrative embodiment, the activity update message 300 is a 4-burst CACH message used to assist in identifying whether there is an active transmission (also termed "activity") on the channel. The activity update message 300 provides information that indicates whether the scanning SU should dwell on the channel or should resume scanning.
153 The nature of the four CACH bursts is described a little later. The description then continues to describe the activity update message used in the illustrative embodiment in more detail. It does so by reference to Figure 3 which is extracted above at [142].
154 This diagram is not easy to follow. However, it is reasonably clear that its four horizontal layers represent the four CACH bursts which, as I have said, are either 8 or 4 bits in length (or 2.5 msec). Although, as will shortly be seen, the description of the illustrative embodiment explains the lower three horizontal layers in terms which are clear, this is not so in relation to the first layer. It is not clear, for example, what the '4-BURST CACH MSG. OPCODE (4 bits)' is. Since it is an opcode, I am inclined to conclude that it is an instruction to the subscriber unit to receive the following three CACH bursts as data. The view that the opcode is part of an instruction set is supported by an observation appearing later in the description where it is contrasted with the balance of the activity update message which is said to be data ('besides the opcode field 302, the rest of the activity update message 300 is considered to be data': p 7 lines 19 to 20).
155 Returning then to the explanation of Figure 3, the description continues in these terms at p 6 line 28 to p 7 line 14:
As shown in FIG. 3, the activity update message 300 includes an activity field 304, 306 specific to each timeslot that indicates whether the channel is presently supporting a call or transmission on either of the timeslots. For example, as shown in FIG. 3, one-bit field 304 indicates whether timeslot one is supporting a call or transmission and one-bit field 306 indicates whether timeslot two is supporting a call or transmission where a value of "0" indicates that the timeslot is not active and "1" indicates an active transmission on the time slot. If there is an active transmission on the timeslot (Block 211), then the scanning SU determines whether the active transmission is of interest to the scanning SU. Otherwise, the scanning SU moves to the next personality in the preprogrammed scan list (Block 220).
Further, if an active transmission is present, then the activity update message 300 also has other information to identify the type of transmission. For example, the transmission may be voice, data, an emergency, talkgroup or individual transmission as shown in FIG. 3. As shown in FIG. 3, a voice or data transmission is signaled by one-bit fields 314, 318 where a value of "0" indicates that the active transmission is a voice transmission and "1" indicates that the active transmission is a data transmission. As shown in FIG. 3, an emergency or non emergency is signaled by one-bit fields 312, 316 where a value of "0" indicates that the active transmission is a non emergency transmission and "1" indicates that the active transmission is an emergency transmission.
156 There is much which is important in this passage for an understanding of what the dispute between the parties is. The first matter to understand concerns the second row which contains 8 bits marked as A1, E1, D1, I1, A2, E2, D2 and I2. It will be recalled that the illustrative embodiment concerns a two timeslot TDMA system. The first four bits concern timeslot 1 and the second four concern timeslot 2. The bits A1 and A2 (the 'activity indicators') indicate whether activity is present on timeslot 1 and 2 respectively, 1 signifying activity and 0 signifying no activity. The bits E1 and E2 signify the presence of an emergency broadcast if set to 1 or no emergency broadcast if set to 0. The bits D1 and D2 signify a data communication if set to 1 or a voice communication if set to 0. The bits I1 and I2 indicate whether the transmission is intended for an individual if set to 1 or a talkgroup if set to 0.
157 It will be seen from the nature of some of these fields that the decoding of the four burst CACH message and the rendering of these 8 bits is unlikely, except perhaps in the case of the emergency bit, to provide enough information to the subscriber unit to ascertain that the communication to which the activity update message relates is, in fact, a communication which the subscriber unit wishes to receive. What most of them do is to operate either in a negative fashion to indicate that the communication is not one in which the subscriber unit is interested, or alternatively, in a provisional fashion, to indicate that the communication could be of interest. For example, if the activity bit is set to no activity then the subscriber unit may move on to the next channel. Similarly, if the subscriber unit is not interested in data transmissions the fact that the D1 bit is set to 1 provides the subscriber unit with sufficient information to know to move on to the next channel.
158 Because it will be relevant when it comes to the claims, it is to be noted also that the activity bit has the consequence that the subscriber unit will not continue scanning on a timeslot which is indicated to be inactive. This activity indicator is important for the debate between the parties. Also important are the other bits in the second row in Figure 3 which, in various ways, signify the presence or absence of communications with certain characteristics. It is possible to think of these separate signifiers as a form of information. It is also possible to think of the activity indicator as a form of information. As will be seen in due course, the claims in the 355 Patents speak in terms of a 'first information' (signifying whether activity is present on a timeslot) and the existence of a 'second information' (which signifies whether the communication is of interest to the subscriber unit).
159 Another matter worth noting at this stage is an implication flowing from the inclusion of the activity update message in the 2.5 msec interval at the end of each 30 msec burst. Plainly enough, the activity indicator is useful for saving the subscriber unit from wasting time scanning an inactive timeslot. The other bits (E, D and I) perform a similar although less dramatic purpose. In terms of the signal architecture in the illustrative embodiment, the 2.5 msec is used not just to signal activity but also to convey other information about the communication. Whether this is a feature of the invention as claimed, as opposed to a feature of the illustrative embodiment, is an issue between the parties.
160 The description then continues at p 7 lines 19 to 23:
Further, besides the opcode field 302, the rest of the activity update message 300 is considered to be data and is populated by information from a full Link Control (LC) message for a voice transmission and from a data header for a data transmission. For example, the emergency one bit fields 312, 316, the group one bit fields 320, 322, and the addresses 308, 310 are recovered from the LC message or a data header.
161 Here will be seen the reference to the opcode not being data which I have mentioned above. It appears from this that in the illustrative embodiment, the data in the activity update message is populated by information from a full LC message for a voice transmission or from a data header for a data transmission. The description does not explain at this point what a full LC message or a data header is. However, it would appear that it contains at least all of the information which is in the activity update message. I return to the topic of the full LC message shortly.
162 The description then continues at p 7 line 24 to p 8 line 2:
If an active transmission is present and if the scanning SU is programmed to check the active transmission (Block 222) for a transmission addressed to a SU of interest, then the scanning SU determines whether the active transmission is addressed to a SU of interest (Block 212). Otherwise, the scanning SU checks to see if the scanning SU is programmed to receive the active transmission (Block 224). For example, the scanning SU may be programmed to receive all emergency calls regardless of identification (ID) of the source or destination of the active transmission. If the active transmission is of interest to the scanning SU, then the speaker is unmuted and audio is rendered to the user of the scanning SU (Block 218). Otherwise, the scanning SU moves to the next personality in the preprogrammed scan list (Block 220).
163 This passage and Blocks 222, 212 and 224 are, at first blush, a little obscure. However, they are important and it is necessary to dispel the obscurity. First, it will be noted that Block 222 is only reached after it has been determined at Block 211 that there is an active transmission on the timeslot. Translated back into Figure 3, this means that bit A1 (or if timeslot 2 is involved, bit A2) has been set to 1. Secondly, Block 222 reflects the programming of the subscriber unit. It will either be programmed to check for identification or it will not. Thirdly, if is programmed to check for identification, then the subscriber unit proceeds to Block 212. Block 212 is further expanded upon in the following paragraph. Fourthly, if the subscriber unit is not programmed to check for identification then it proceeds to Block 224 and checks to see if the transmission is nevertheless of interest. This it does by checking the remaining bits in the same row of Figure 3. As the description notes, if the subscriber unit is programmed to receive emergency transmissions and the emergency bit is set in the second row then the speaker is unmuted and the audio rendered (Block 218).
164 It is then necessary to say a little more about the process of identification if the subscriber unit has been programmed to receive transmissions addressed to a subscriber unit of interest. As I have explained above, the process of identification does not take place at Block 222 which instead just reflects a programming choice which has been made in the subscriber unit. If it is programmed to see if the transmission is from a subscriber unit of interest, then the actual process of identification occurs at Block 212. Of this process the description then continues in these terms at p 8 lines 3 to 15:
Further yet, if an active transmission is present, the activity update message 300 also identifies the SUID or TGID of the active transmission. As shown in FIG. 3, the identification field 308, 310 is an 8-bit hashed field as shown in FIG. 3. Further, because there are a limited number of bits in the activity update message 300, the ID field 308, 310 is hashed. For example, if the active transmission on timeslot 1 is directed to SU 16 and SU 16 is identified by a 24 bit SUID, then the ID field 308 is hashed to 8 bits. Another example is an active transmission on timeslot 2 directed to an SU in a talkgroup, e.g. SU 12, where the talkgroup is identified by a 16 bit TGID.
Thus, the ID field 310 is hashed from the TGID of 16 bits to 8 bits. As is known in the art, there are many algorithms that can be used to perform the function of hashing and one such well known algorithm is a CRC-8 checksum with a generating polynomial of g(x)=x8+x2+x+1. With an input of a 16 bit TGID or a 24 bit SUID, the output is an 8 bit CRC hashed ID field 308, 310 as shown in FIG. 3.
165 This takes one back once again to Figure 3. The third and fourth rows of Figure 3 are 8 bits in length. The bottom row is for Channel (timeslot) 2 and the second from the bottom row is for Channel (timeslot) 1. As has previously been noted, the activity update message is sent across both timeslots. To that extent it contains redundant information, for the information in bits b0 to b3 concern timeslot 2 in the row which indicates the characteristics of the transmission whilst those at b4 to b7 concern timeslot 1. Similarly, the two 8 bit 'hashed IDs' are each only relevant to one of the two timeslots. As above, the SUID and TGID are shorthands for 'subscriber unit ID' and 'talkgroup ID'.
166 The immediate problem facing the illustrative embodiment is that the SUID is 24 bits long and the TGID is 16 bits long. The two ID fields in the activity update message are, however, only 8 bits long. The passage effectively teaches that the SUID and TGID are to be subject to a compression algorithm which will reduce them in length to an 8 bit structure. The expression 'hashed ID' therefore refers to a compressed form of the SUID and the TGID. As will be seen shortly, an ID match at Block 212 does not definitively determine that the transmission is for the subscriber unit of interest. As was accepted by all parties, this is because the compression algorithm can cause more than one subscriber unit identified by a 24 bit SUID to have the same 8 bit hashed ID (a similar problem affects subscriber units identified by a 16 bit TGID). It is therefore necessary for a complete ID check to be done. This is apparent from Blocks 213, 226 and 214 (if the transmission is a voice transmission) and from Blocks 213, 226 and, in Figure 2B, Blocks 228, 230, 232 and 234 (if the transmission is a data transmission).
167 The description returns to these matters shortly, but before it does so it notes that the activity update message may be received before the colour code of the active transmission is known. This it says at p 8 lines 16 to 22:
As is known in the art, the activity update message 300 may be received before knowing the color code for the active transmission on the channel. In any case, knowing the color code for the active transmission on the channel and whether it matches the color code of the scanning SU is important to deciding whether to stop scanning or not. As mentioned above, if there is not a match of the color code (Block 208), then the scanning SU tunes to the next channel in the preprogrammed scan list (Block 220).
168 Returning then to the process of identification, once it has been determined from the hashed IDs in rows 3 and 4 of Figure 3 that the subscriber unit the transmission is addressed to is of interest, the subscriber unit then asks whether the transmission is voice or data (Block 226). This it can do from the D bits in row 2 of Figure 3 which, it will be recalled, provide that information. So much is stated at p 8 lines 23 to 25:
If the ID field 308, 310 of the activity update message 300 matches the SUID or TGID of the scanning SU (Block 212), then the scanning SU determines whether the active transmission is voice or data (Block 213).
169 It is useful to pause at this point and to note what might not otherwise be obvious: that the flow chart in Figure 2A therefore uses all four of the characteristic bits in row 2 of Figure 3. The activity bit ('A bit') is used at Block 211 to determine whether there is activity on the channel or not. The emergency bit ('E bit') is used at Block 224 to determine, if the transmission is not directed to a subscriber unit of interest, whether it is an emergency transmission or not and, if it is an emergency transmission, unmutes the speaker. The individual bit ('bit I') is used at Block 224 to determine whether the transmission is directed to an individual or a talkgroup. Finally, the data bit ('D bit') is used at Block 226 to determine after identification at the level of the hashed IDs has occurred, whether the transmission is voice or data. The illustrative embodiment therefore deploys all four of the characteristic bits in the second row of the activity update message as well as the hashed IDs (and does so in respect of both timeslots).
170 This understanding of the invention depicted in Figure 2A is important for the construction issue between the parties. The language of claim 1 (to which I will return in more detail shortly), requires the invention to determine whether the activity is of interest to the subscriber unit and if it is, to remain on the channel to receive the activity. Hytera submits that the determination of whether the activity is of interest can happen only once and cannot be, as Block 212 suggests it can be, provisional. Put another way, under Hytera's construction, the subscriber unit cannot decide that the transmission might be of interest and then carry out further acts to determine whether it actually is of interest. It will be apparent from what has been said in the preceding paragraph that in Figure 2A, this is not what is happening except in the case of an emergency transmission. In that case, the determination that the transmission is an emergency transmission, because the E bit is set to 1, leads the subscriber unit to receive the audio. However, leaving aside the position of the activity bit itself (which fits into claim 1 in a different way), all of the other information in the activity update message leads to determinations which are at best provisional. Thus, the matching of the hashed IDs at Block 212 (of which more below) requires two further determinations to be made before any audio is received: a determination using the D bit (data or voice) that the transmission is a voice communication (Block 226) and a further determination that there is a full ID match after decoding the full LC message (Block 214) (I return to the full LC message in more detail below). The information in the D bit in the activity update message also requires further determination. If the transmission is voice (Block 226), then the full LC message must be received and an ID match performed (Block 216). On the other hand, if the transmission is data (Block 226), then the subscriber unit must go through the ballet in Figure 2B which involves several steps including potentially an ID match at Box 234. In any event, the point is the same: only in the case of the E bit does the invention in Figure 2A operate in accordance with claim 1 construed as Hytera would have it. Everything else in Figure 2A is outside claim 1 construed in that fashion.
171 The description then continues at p 8 line 26 to p 9 line 11 in these terms:
If the active transmission is data (Block 226), then the scanning SU remains on the channel to recover the data message (Block 228) and waits until the end of the data transmission to receive a data terminator (Block 230). In an alternative, the scanning SU remains on the channel to receive embedded qualifying information.
Continuing, the data terminator is decoded to identify addressing identification (or an "ID") (Block 232). If the ID is of interest to the scanning SU (Block 234), then the data message is further processed. Otherwise, the scanning SU tunes to the next channel in the preprogrammed scan list (Block 220). Continuing, the scanning SU determines whether confirmed delivery is requested (Block 236) for the data message.
If confirmed delivery is requested, then the data message is processed until the entire data message is recovered (Block 238). In one embodiment, recovering an entire data message is performed by sending Selective Automatic Repeat Request (SARQ) messages to the BR. When the entire data message is recovered, the scanning SU tunes to the next channel in the preprogrammed scan list (Block 220). If confirmed delivery is not requested, then the scanning SU waits on the channel a predetermined amount of time for a possible redundant or subsequent transmission (Block 242). At the expiration of the predetermined amount of time, the scanning SU tunes to the next channel in the preprogrammed scan list (Block 220).
172 These relate to what occurs if the transmission is a data transmission. The data aspect of Figure 2B was not the subject of contention between the parties and as such may be passed over. The description then continues at p 9 lines 12 to 28:
If the active transmission is voice (Block 226), then the scanning SU remains on the channel to perform a full link control (LC) qualification of the active transmission by decoding an LC message which identifies whether the active transmission is addressed to an individual SU or a talkgroup, an emergency or non emergency, and the source and destination of the active transmission (Block 214). In an illustrative embodiment, the LC message is a 7-burst CACH message. Performing full LC qualification means that the scanning SU waits for a LC message on the timeslot of interest and decodes an ID field of the LC message to determine whether the active transmission is of interest to the scanning SU. In an illustrative embodiment of the wireless communications landscape 100, because LC messages are available once every 360 msec, having to wait to decode a full LC message is time consuming for the scanning SU. If the ID field of the LC message is an ID of interest to the scanning SU (Block 216), then the speaker is unmuted and audio is rendered to the user of the scanning SU (Block 218). If the ID field of the LC message is not of interest to the scanning SU (Block 216), then the scanning SU tunes to the next channel in the preprogrammed scan list (Block 220).
173 It will be recalled from above that the full LC message at least includes the information in the activity update message. From this it also appears that it contains the full SUID or TGID. Consequently, it is apparent that the full LC is larger than the activity update message. This is confirmed by the fact that whereas the activity update message is transmitted as four bursts of 2.5 msec duration (at the end of each 30 msec burst), the full LC is transmitted in seven bursts (presumably of 56 bits). The statement that the full LC message is available every 360 msec suggests that it is available after 12 bursts (recalling that the bursts take 30 msec). The activity update message takes four bursts and the full LC message takes seven bursts. This suggests, but it is unclear, that the activity update message bursts and the full LC message bursts alternate at the end of the 30 msec block, i.e. one burst uses the 2.5 msec for the next burst of the activity update message and the following burst uses the 2.5 msec for the next burst of the full LC message. In any event, it is clear from what the description says in the next paragraph that the activity update message is received in full more often than the full LC message.
174 The description then continues at p 9 line 28 to p 10 line 3:
If the ID field 308, 310 of the activity update message 300 does not contain an id that is of interest to the scanning SU (Block 212), then the scanning SU moves to the next channel in the preprogrammed scan list. In such a case, the scanning SU does not have to wait for a LC message. Because the LC message only is sent once every 360 msec, not having to wait for a LC message improves the time that the scanning SU spends during the function of scanning. By not having to wait for a LC message, the scanning SU is able to quickly determine that the active transmission is not of interest and the scan function is improved.
175 The point being made here is that the activity update message operates as a rapid negative criterion of exclusion and is faster than waiting for a full identification through the full LC message. The description then continues at p 10 lines 4 to 12:
As is known in the art, the timing of events relating to color code, the activity update message 300, and the LC message may occur in any order. For example, the activity update message 300 may be received by the scanning SU before 1) the color code of the active transmission is known or 2) the full LC message is received. Also, a full LC message may be received before 1) the activity update message 300 is received by the scanning SU or 2) the color code of the active transmission is known. Further, as shown in FIG. 2, the color code of the active transmission may be known before 1) the activity update message 300 is received by the scanning SU or 2) the full LC message is received.
176 There was not a lot of discussion of this. However, it appears that its import is that where the subscriber unit actually receives the full LC message before the activity update message, it can use the full LC message.
177 The description then continues at p 10 lines 13 to 26:
In any case, determining whether to remain on the channel and render audio to the user of the scanning SU is based upon whether the received information is of interest to the user. Specifically, a match of the color code and the full LC message stops the function of scanning and renders audio to the user of the scanning SU. A match of the color code and ID field 308, 310 of the activity update message 300 stops the function of scanning but requires a match of the full LC message before rendering audio to the user of the scanning SU.
In an illustrative embodiment, a match of the ID field 308, 310 indicates that the active transmission may be of interest to the scanning SU. In such a case, the scanning SU remains on the channel and performs Link Control (LC) qualification of the active transmission before committing itself to remaining on the channel and rendering audio to the subscriber unit user. Alternatively, if there is not a match of the ID field 308, 310 then the scanning SU continues to scan with the next personality in the scan list.
178 This is an important passage and highlights the difference between the full LC message and the activity update message. The matching of colour codes, it will be recalled, relates to whether the subscriber unit is associated with the base radio which has sent the transmission. A matching of the 'ID field 308, 310' is a reference to a matching of the hashed ID codes in the activity message (that is, the last two rows of Figure 3). What appears from the last sentence reflects the fact, referred to above, that by compressing the SUID and TGID using a compression algorithm, a certain amount of information is lost in the process so that a match between the compressed 8 bit SUID or 8 bit TGID in the activity update message and the 24 bit SUID or 16 bit TGID which the subscriber unit is programmed to be interested in, does not entail with certainty that the SUID and TGID actually match. Only when the full LC message is received (and decoded) can a match be carried out using the full 24 bit SUID or 16 bit TGID. It is only then, according to this paragraph, that audio is rendered to the user.
179 This paragraph is important for the construction issues between the parties. As alluded to above, Hytera submits that on its proper construction, the expression in claim 1 'determining whether the activity is of interest to the subscriber unit' entails a decision making process that is once and for all; or, to put it another way, that once the subscriber unit has determined that activity is of interest to it, that is the end of the process and nothing more remains to be done but to remain on the channel to receive the communication. It is not necessary to say anything about the correctness of this argument at this stage, but it will be noted that the use of the activity update message as described in this paragraph (and more generally in the illustrative embodiment) does not accord with such a construction. The determination that the activity is of interest because there is a match in the hashed IDs is inherently provisional in this paragraph and there remains the further steps of checking the full LC message before the subscriber unit commits to remaining on the channel to receive the activity. For present purposes, what should be taken away from this paragraph is that it uses the expression 'is of interest to the user' (at p 10 lines 14 to 15) in a way which suggests that 'interest' may be a provisional state of affairs.
180 The description then continues at p 10 lines 27 to p 11 line 5:
By utilizing an activity update message 300 in the wireless communications landscape 100, the time spent while scanning is reduced. For example, in the embodiment described, a scanning SU is able to identify an active transmission of no interest on average in 152 msec. In a worst case, a scanning SU takes up to 335 msec to identify an active transmission of no interest. Without the use of an embodiment of the present invention, experimentation has shown that in an average TDMA system, a scanning SU is able to identify an active transmission is of no interest on average in 512 msec and in the worst case in 695 msec. Further, without the use of an embodiment of the present invention, experimentation has shown that in an average FDMA system, a scanning SU is able to identify an active transmission is of no interest on average in 360 msec and in the worst case in 540 msec.
181 This passage explains the point of the activity update message and confirms that its advantage lies in its ability more rapidly to conclude that a transmission is not of interest. The illustrative embodiment is able to determine that a transmission is not of interest on average in 152 msec whereas without the use of the activity update message this takes on average 512 msec. In other words, the illustrative embodiment shows that the use of the activity update message allows the subscriber unit to ascertain that a transmission is not of interest more than twice as fast.
182 The description then continues at p 11 lines 6 to 12:
Further yet, by utilizing an activity update message 300 in the wireless communications landscape 100, a SU that is a party to a call may quickly join the call if the SU is not currently a party to the call. Such an SU is called a late entry SU. For example, in the embodiment described, a late entry SU may join a call in a minimum of 120 msec. In a worst case, the late entry SU may join in about 300 msec. Without the use of an embodiment of the invention, experimentation has shown that a late entry SU takes about 360 msec and in the worst case about 720 msec to join a call.
183 This is a reference to the problem of late entry subscriber units. Nothing particularly turns on this. Finally, the description concludes at p 11 lines 13 to 21 in these terms:
While the invention has been described in conjunction with specific embodiments thereof, additional advantages and modifications will readily occur to those skilled in the art. The invention, in its broader aspects, is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. Various alterations, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Thus, it should be understood that the invention is not limited by the foregoing description, but embraces all such alterations, modifications and variations in accordance with the spirit and scope of the appended claims.
184 Nothing turns on this.