Patent Application
20240292362
Messages sent between a base station and a communication device encounter a delay between the sending and receipt of the message due to the time taken for messages to travel between the devices. It is desirable to mitigate the effects that this propagation delay has on communication between devices. It is desirable to provide effective mitigation of the effects of the propagation delay even as the distance between devices, and therefore the propagation delay, increases, in order to enable effective long range communication between a base station and a communication device.
In one example arrangement, there is provided a base station apparatus, comprising:
In a further example arrangement, there is provided a method for a base station apparatus, comprising:
In a still further example arrangement, there is provided a base station apparatus, comprising:
Further aspects, features and advantages of the present technique will be apparent from the following description of examples, which is to be read in conjunction with the accompanying drawings, in which:
As introduced above, messages sent between a base station and a communication device encounter a delay between the sending and receipt of the message due to the time taken for messages to travel between the devices. This propagation delay will affect messages sent from the base station to the communication device (downlink messages) and messages sent to the base station from the communication device (uplink messages). The larger the distance between the base station and the communication device, the longer the propagation delay will be due to the finite speed at which messages travel. Messages sent between the base station (BS) and communication devices (such as user equipment (UE) or intermediate devices between a BS and a UE) are often separated into temporal segments. For example, a message according to a 3GPP Standard such as LTE or 5G NR may be separated into frames and sub-frames. A base station may send and receive messages at certain times based on the boundaries between the segments in uplink and downlink messages. For example, a frequency-division duplexing (FDD) base station may send and receive messages at the same time and may operate to align segments in the uplink and downlink messages for timing purposes, so that the base station receives uplink messages at expected times. A time-division duplexing (TDD) base station may send and receive messages at different times so that uplink and downlink messages do not overlap at the base station, for example if the antenna is only able to receive or transmit at a given time, and may align boundaries between segments in uplink and downlink messages to do so. It will be appreciated that the alignment may not need to be exact, but an alignment to within a particular tolerance. Therefore, the base station may transmit messages such that the segments in the transmitted messages align with segments in messages it expects to receive from a communication device.
However, since the arrival time of messages is dependent on the distance between the base station and a communication device, boundaries between segments in received uplink messages may be shifted by an amount which depends on the location of the communication device, and alignment between messages sent to the communication device and messages received from the communication device may be disrupted. Furthermore, a base station may communicate with several target devices at once. Since the devices may be located at different distances from the base station, messages sent by each device to the base station may be delayed by differing amounts and therefore the boundaries between segments in uplink messages received from different devices may be shifted by different amounts. Not only does this make it difficult to align all uplink messages received at the base station with the downlink messages sent by the base station, this may also lead to interference between different uplink messages received at the base station, since the segments in the different uplink messages may not be aligned with each other. It would be desirable to avoid interference between uplink and downlink messages, and interference between different uplink messages, at the base station.
A base station apparatus according to the present technique therefore provides propagation delay determination circuitry configured to determine an indication of a propagation delay in messages sent between the base station apparatus and a target communication apparatus. The indication of the propagation delay could take a variety of forms, for example, an indication of a time representing the propagation delay or an indication of a distance corresponding to the propagation delay. This determination can be made based on a request received from the target communication apparatus requesting to initiate a communication session with the base station apparatus. The timing of the request may be indicative of the propagation delay, since the request has itself travelled between the communication device and the base station. For example, the request may have been sent by the communication device at a time known to the propagation delay determination circuitry, and the delay between a predicted time of arrival and the time of actual arrival of the request may be indicative of the propagation delay in messages sent between the base station apparatus and the target communication apparatus. The indication of a propagation delay may be a round trip propagation delay, which is a time equal to twice the measured delay of the request, and is equivalent to the combined delay of one downlink message and one uplink message.
The apparatus further provides time adjustment determination circuitry configured to determine a time adjustment to be communicated to the target communication apparatus in response to the request. For example, the base station apparatus may use antenna circuitry to transmit a response to the request, wherein the response includes a value indicating the time adjustment. The time adjustment is to be applied to uplink messages by the target communication apparatus by shifting the time of transmission of the uplink messages by an amount equal to the time adjustment. The time adjustment is determined based on the indication of the propagation delay such that when an uplink message to which the time adjustment has been applied is received at the base station apparatus, the boundaries between temporal segments in the received uplink message align with reference boundaries. Therefore, the timing of messages sent by the communication apparatus may be adjusted based on the measured propagation delay in a way which causes boundaries in the uplink messages received by the base station to align with reference boundaries. As will be discussed in further detail below, shifting messages by an amount which depends on the propagation delay they are expected to experience enables interference to be reduced at the base station, both between uplink and downlink messages, and between uplink messages arriving from different communication apparatuses.
In one example technique, the time adjustment may be calculated such that a given boundary in a received uplink message aligns with a given reference boundary. Therefore, the time adjustment could be calculated so that a given segment of the uplink message arrives at the same time regardless of the distance between the base station and a target communication apparatus. For example, when the time adjustment is applied with respect to the boundaries between downlink messages as received at the target communication device, the time adjustment could be a timing advance equal to a round trip propagation delay so that, from the perspective of the base station, it would appear as though the target communication apparatus is at zero distance from the base station, and messages encounter no propagation delay at all. Whilst the uplink message itself will only encounter half of the round-trip propagation delay, if the adjustment is applied to a message which has already been delayed by half of the round-trip propagation delay then a full round-trip propagation delay will eliminate the effect of propagation delay. It will be appreciated that based on the particular implementation, different time adjustments may be applied to mitigate the effect of propagation delay but in each case the delay encountered by the uplink message will be half of the round-trip propagation delay.
However, the inventors have recognised that this technique encounters problems at large distances. At large distances, with large propagation delays, the target communication device may be required to advance messages by a large time adjustment so that they are sent considerably before the time they would be sent were no time adjustment to be applied. However, circuitry applying the timing advance may have a maximum time adjustment limit beyond which it can advance the uplink messages no further. In addition, the response sent by the base station to the target communication apparatus which includes the time adjustment may need to adhere to a particular format. The format may restrict the maximum size of the time adjustment, such that larger timing adjustments would be too large to encode in the format of the response. These issues mean that applying a time advance to align a given boundary in an uplink message with a given reference boundary is limited by range. Beyond a maximum range, circuitry in the target communication apparatus may be unable to apply a large enough timing advance to cause the two given boundaries to align, and/or the base station apparatus may be unable to communicate a large enough timing advance to the target communication apparatus.
The inventors recognised that the problems discussed above could be mitigated if a time adjustment were selected so that a given boundary in the uplink message to which the time adjustment has been applied aligns with a reference boundary which is not a predetermined reference boundary, but is a reference boundary selected in dependence on which of a plurality of defined ranges the indication of the propagation delay falls within. For example, the time adjustment could be selected so that a given boundary in the uplink message aligns with any of a first, second, third, and so on reference boundary depending on the size of the indication of the propagation delay. Then, rather than making the time adjustment larger and larger the further the target communication apparatus is from the base station in an effort to still align with a given reference boundary, a different, smaller, time adjustment could be applied which instead aligns an uplink message with a later reference boundary. As discussed further below, this technique can be used at any range since it can be used with a finite maximum time adjustment, and therefore lifts the restriction on maximum range which the alternative technique could impose.
This technique may appear counter-intuitive since it may lead to messages being received an integer number of segments later than they would be received if there were no propagation delay. Whilst the alternative technique discussed above aims to cause messages to arrive as if there were no propagation delay at all, the inventors have determined that to avoid interference between messages it is sufficient that boundaries between segments align, even if the segments are received later than expected.
In some examples, the defined ranges for the indication of the propagation delay may each correspond to one of the reference boundaries. In addition, adjacent ranges may correspond to adjacent reference boundaries such that first and second time adjustments determined for indications of the propagation delay falling within adjacent defined ranges may be determined such that the given boundary within an uplink message to which the first time adjustment has been applied and the given boundary within an uplink message to which the second time adjustment has been applied align with adjacent reference boundaries.
Each indication of a propagation delay may be associated with a time adjustment, and the association may be continuous within a given range. Between adjacent ranges there may be a discontinuity between the time adjustments associated with successive indications of the propagation delay. In some examples, the size of the ranges is not limited. As long as the ranges are finite, an advantage is provided over the technique in which time adjustments are calculated to align with a single reference boundary. However, smaller ranges may mean that a smaller time adjustment needs to be communicated to a target communication apparatus and applied by the target communication apparatus, which means that the circuitry requirements are reduced and less encoding space is used to communicate the timing adjustment. In some examples, the smallest range which still enables alignment of every message with a reference boundary may be used, which is provided when the difference between a minimum time adjustment corresponding to the smallest indication of the propagation delay in a given defined range and a maximum time adjustment corresponding to the largest indication of the propagation delay in the given defined range is equal to the length of one temporal segment.
The limits between ranges, that is the values of the indication of the propagation delay which lie at the point between two ranges, may in some cases be adjusted freely. In some examples, the limits may be set at periodic values of the indication of the propagation delay starting from zero based on the selected size of the range. However, this is not necessary and in particular the ranges do not need to be the same size as each other. Since each range may correspond with aligning a given boundary in an uplink message with a particular reference boundary, devices having propagation delays falling within different ranges may have their uplink messages aligned with different reference boundaries. If a particular device lies at a distance having a propagation delay which is on the limit between two ranges, and which moves between the two ranges, then as the device moves over the limit there may be a gap or overlap in the communication between devices as the uplink messages begin to be aligned with a later or earlier reference boundary. If the target device fails to decode a timing advance message, for example, then the target device may transmit in an incorrect uplink slot for a short time after the particular reference boundary has changed as it is attempting to align with an incorrect reference boundary. The incorrect uplink slot may have been allocated to a different user, so the transmitted information may not be correctly received by the base station and some information could be lost. This may be detected and corrected by the base station (for example, by re-triggering a Random Access procedure to recalculate a timing adjustment to be transmitted to the target device), but the correction will not be immediate and undesirable loss of information may occur as a result of the device moving between two ranges. Hence, it can be useful if a device is located at a position which is associated with a propagation delay that does not fall near to a limit between ranges, so that movement of the device can occur whilst the device remains in the same range. In cases where there are several communication devices communicating with one base station, it may not be possible to ensure that this is true for every device if the same ranges are used for every device. However, since the range limits may be moved, in some examples the range limits of the defined ranges may be set in dependence on an estimated distribution of target communication apparatuses.
In particular, the range limits may be selected to seek to maximise the number of target communication apparatuses for which the indication of the propagation delay falls within a single range having regard to the estimated distribution of target communication apparatuses. The range limits may be therefore selected to minimise the number of target communication apparatuses located at a position which is near to a boundary between ranges of the propagation delay. The estimated distribution of target communication apparatuses could be determined by the base station apparatus based on observed indications of the propagation delay or may be predetermined and provided to the base station apparatus. The estimated distribution of target communication apparatuses may vary over time, and therefore may be updated periodically.
In some examples, the time adjustment may be entirely positive (a timing advance). That is, the time adjustment may be a shift which causes the uplink messages to which the time adjustment is applied to be sent earlier than if no time adjustment were applied. Larger positive time adjustments cause messages to be shifted further forwards, and therefore sent earlier, than smaller positive time adjustments. As long as the range of time adjustments is at least as large as the time duration of one segment, then a time adjustment can be used to align uplink messages with any reference boundary. This can allow uplink messages which are sent by devices at any range to be aligned with reference boundaries at a base station, which avoids the problems associated with attempting to align to a single reference boundary, particularly signalling and applying large time advances.
However, the inventors have realised that when it is acceptable to align a given uplink boundary with a later reference boundary, it is possible to apply a negative time adjustment. A negative time adjustment corresponds to delaying the transmission of uplink messages so they are sent later than if no time adjustment were applied. Applying a negative time adjustment may cause an uplink message to align with reference boundaries at the base station. However, this is highly counter-intuitive, since one would usually expect that the time adjustment should be made to mitigate the effect of propagation delay. A negative time adjustment acts to increase the delay that a given message experiences, which therefore appears to be counterproductive since it has a completely opposite effect to a typical intention of a time adjustment. However, since interference can be mitigated as long as boundaries in an uplink message align with any reference boundaries, interference can be mitigated even by applying a negative time adjustment.
A negative time adjustment can be useful because it can enable a smaller magnitude of time adjustment to be applied to uplink messages. Rather than only advancing uplink messages to align with a reference boundary, selectively advancing or retarding uplink messages to align with reference boundaries which are closer in time to boundaries between segments in uplink messages received at a base station, regardless of whether the reference boundaries are earlier or later than the boundaries in the uplink messages, can allow smaller magnitude time adjustments to be used to achieve alignment between messages. For example, at some distances the magnitude of a time retard for achieving alignment at the base station may be smaller than the magnitude of a time advance. This can reduce the complexity of circuitry for applying the time adjustment at the target communication apparatus since the amount that a message needs to be adjusted by can be reduced. In particular, some hardware may only be able to apply a timing adjustment up to a maximum magnitude, for example a maximum value imposed by a Standard. In particular, this timing advance may be smaller than the size of a segment in the messages. Rather than updating the hardware to allow a larger advance to be applied, the existing hardware may in some cases be configured to apply a timing retard in addition to a timing advance, whilst keeping the maximum magnitude of adjustment unchanged. Therefore, the difference between the minimum and maximum timing adjustment can be increased to enable the present technique to be implemented without increasing the magnitude of time adjustment which can be applied, by configuring the circuitry to apply a timing retard in addition to a timing advance.
In addition, the use of a negative time adjustment can enable the ranges to be moved with increased freedom.
As discussed above, the maximum value of time adjustment in some apparatus may be a value imposed by a Standard. For example, it may be set according to the maximum value of a timing advance representable in a Random Access Response (RAR) message according to a 3GPP Standard such as LTE (4G) or NR (5G). Therefore, the maximum positive time adjustment which can be determined by the time adjustment determination circuitry may be set equal to the largest timing advance representable in an encoding of the RAR message. This may enable hardware configured to comply with the 3GPP Standard to be reused to apply the technique described above.
To enable communication between devices made by different manufacturers, the request received from the target communication apparatus and the response to the request may both adhere to message formats defined by a Standard (in particular a 3GPP Standard). For example, the time adjustment may be signalled in a RAR message according to a 3GPP Standard such as LTE (4G) or NR (5G). The response message may have a field which can represent a timing advance between 0 and a threshold value. However, the response message may not have sufficient room for a spare bit in addition to representing the threshold value, and therefore there may not be encoding space in the timing advance field of the response message to encode a negative timing adjustment having a magnitude up to the threshold value. However, there may be sufficient encoding space, between the threshold value represented by the response message and the maximum value representable in a field having the number of bits used to represent the threshold value, to represent the negative timing adjustment values. Therefore, the base station may be configured to encode a negative time adjustment value as a positive time adjustment having a magnitude larger than the threshold value. This means that the response message is backwards compatible, since values lower than the threshold value represent the same positive time adjustment values as if no negative time adjustment were encoded, however the message is also able to reuse the spare encoding space above the threshold value to represent the negative time adjustments. Therefore, an existing message format can be used to communicate a negative timing adjustment.
The negative time adjustment may be communicated in further ways, however. In particular, if the field typically used to represent the timing advance does not have a spare bit to use as a sign bit, then in some message encodings having a separate unused bit, the unused bit can be considered to be an additional bit and used to represent the sign of the value in the timing advance field. Therefore, the timing advance field can be used to represent a magnitude of a timing adjustment and an additional bit can be used to represent a sign of the timing adjustment.
Alternatively, the additional bit can be considered to be appended to the timing advance field and the entire field including the additional bit can be used to represent the timing advance in two's complement.
In both cases, the message format is backwards compatible since the positive timing adjustment would be encoded in the message in the same way whether or not a negative timing advance could be applied.
For the additional bit, a reserved bit in the format of the RAR message according to a 3GPP standard could for example be used.
In some examples, the time adjustment determination circuitry is arranged to determine a time adjustment which is periodic with respect to the indication of the propagation delay. That is, the same time adjustment is calculated for values of the indication of the propagation delay separated by an amount equal to the period. Therefore, even as the indication of the propagation delay increases due to a large separation between the base station and the target communication apparatus, the time adjustment remains within a finite range of values. The periodicity may be selected such that the time adjustment remains within a range equal to the length of one segment of a message. A time adjustment which is periodic with respect to the indication of the propagation delay can be achieved when one no longer attempts to align with one particular reference boundary and instead decides to align with any reference boundary, and allows the problem of extremely large time adjustments to be avoided.
The reference boundaries may be freely chosen by the base station apparatus. However, when the antenna circuitry is configured to communicate with two or more target communication apparatuses, it is advantageous for the same reference boundaries to be used to determine a time adjustment for each target communication apparatus. This means that the incoming messages from different target communication apparatuses will be adjusted to align with the same reference boundaries, and therefore align with each other. This reduces the interference between uplink messages received at the base station from different target communication apparatuses.
The reference boundaries may also be selected to depend on the boundaries between segments in downlink messages transmitted by the base station apparatus. In particular, the reference boundaries may be selected to align with the boundaries between temporal segments in the downlink messages. In certain base stations such as Time-Division Duplexing (TDD) base stations, aligning the reference boundaries with the downlink boundaries can be useful to avoid overlap between downlink messages and uplink messages. In TDD, the antenna may be configured to either transmit downlink messages (transmitted by the BS in transmission segments) or receive uplink messages (received by the BS in receiving segments), but not both at once. If the reference boundaries were not aligned with the downlink boundaries, then uplink messages could arrive as downlink messages are being transmitted, which could cause loss of information as the antenna may not be configured to receive the uplink messages. However, by aligning reference boundaries so that segments do not overlap, and assigning certain segments to uplink and certain segments to downlink, the risk of loss of information may be reduced. In other base stations, such as Frequency-Division Duplexing (FDD) base stations, alignment between uplink and downlink segments may be desirable to ensure that uplink messages arrive at the correct time as expected by the base station.
The time adjustment may be applied by the target communication apparatus in several ways. For example, it could be applied with respect to periodic reference transmission times based on a clock or other timing circuitry. However, in one example the time adjustment is applied as an offset with respect to boundaries in a downlink message received at the target communication apparatus. That is, the boundaries in a downlink message received at the target communication apparatus (which will have been delayed since the downlink message was transmitted by the base station) are treated as intermediate reference boundaries from which the timing adjustment is applied. This means that the timing at which the timing adjustment is applied ultimately depends on both the downlink boundaries as communicated by the base station, and the propagation delay, which are both times known to the base station. Therefore, the timing adjustment can be determined by the base station apparatus such that uplink messages arrive at a given time, since the factors affecting time of arrival are known to the base station.
As discussed above, in some examples, the propagation delay determination circuitry is configured to determine an indication of the propagation delay based on an elapsed time between a reference time and receipt of the request. However, alternative methods for determining the propagation delay may be possible, including determinations made based on a measured distance of the target communication apparatus with respect to the base station, such as by reference to co-ordinates of both apparatuses. An indication of the propagation delay may itself be a measurement of the distance, the indication of the propagation delay may be a time calculated based on the distance, or the indication of the propagation delay may be some other value based on the measurement of the distance.
As mentioned above, the temporal segments into which the uplink and downlink messages are split may in one example implementation be sub-frames of messages according to a 3GPP Standard. However, in other examples the temporal segments may for example be frames of messages.
Whilst the type of target communication apparatus is not particularly limited by the above described technique, the technique may be particularly useful when the target communication apparatus is mounted on a moving vehicle, for example an aeroplane in an air-to-ground (ATG) communication network. This is because the above technique may increase the maximum range between the base station and target communication apparatus, enabling a moving target communication apparatus to remain connected with a single base station for longer, which reduces the burden of handing over communication to different base stations during a journey. The increased range also reduces the number of base stations which are required to cover a particular area, which can reduce installation and maintenance costs in rolling out communication networks to remote areas to support communication with moving vehicles, such as networks for supporting communication with aeroplanes overflying remote areas.
Particular examples will now be described with reference to the figures.
In modern communications systems, including those according to a 3GPP standard such as LTE (4G) or NR (5G), a target communication apparatus may communicate with a base station. The base station may communicate with several different target communication apparatuses. In one example system (an air-to-ground (ATG) system), the target communication apparatus is mounted on a moving vehicle such as an aeroplane and the base station is located at a fixed position on the ground. An example is shown in
Messages sent between the target device 10 and the base station 20 may be separated into temporal segments. This is illustrated in
As shown in
This is illustrated in
The effect of the propagation delay is that uplink messages received at the base station do not align with downlink messages sent by the base station. That is, the boundaries between sub-frames in uplink and downlink messages do not align. In TDD systems this can cause issues as the antenna 80 may be configured at certain points in time to transmit downlink messages but not receive uplink messages, and therefore be unable to receive uplink messages from the target devices when they arrive during a time the antenna is configured for downlink communication. In FDD systems, unaligned boundaries between sub-frames can cause interference between downlink messages being transmitted by the base station 20 and uplink messages being received at the base station 20. Further, since uplink messages arriving from different target devices can be shifted by different amounts, the boundaries in the uplink messages do not align with each other and the different uplink messages can therefore also interfere.
In one example technique, the effect of propagation delay can be reduced by applying a timing advance to uplink messages sent by the target devices. When the target device initiates a communication session, it may send a request to the base station 20. For example, the request may be a Physical Random Access Channel (PRACH) preamble according to a 3GPP standard. The timing of the PRACH may be predefined so that, when the base station 20 receives the PRACH, it can determine how much the PRACH message has been delayed by propagation. For example, the base station 20 may comprise propagation delay determination circuitry 84 for determining an indication of the propagation delay, such as a round-trip propagation delay time, based on the timing of receipt of the PRACH message and knowledge of a time at which an invite to send a PRACH was previously sent by the base station. The base station 20 may also comprise time adjustment determination circuitry 86 to calculate a timing advance based on the indication of the propagation delay. In some cases, the timing advance could be equal to the round-trip propagation delay time, for example. Under the control of control circuitry 82, the antenna circuitry 80 of the base station 20 may then communicate the timing advance to the target device 10. For example, the timing advance may be signalled in a Random Access Response (RAR) message (as illustrated in
This gives a maximum signalled time advance of 0.67 ms. If this is the maximum round-trip propagation delay, then the maximum range of communication according to this format is 100 km (200 km total round-trip distance), since larger distances are associated with timing advances that cannot be signalled to the target communication apparatus. Therefore, both the format of communication and the limitations of the timing advance application circuitry 94 may impose a maximum range of communication, since any larger range may require a timing advance that is too large to be signalled and/or applied. Even if the format of the RAR message allowed a larger advance to be signalled, this would still have a maximum at a certain point, beyond which the timing advance would be too large to be signalled and/or applied.
However, the inventors have recognised that the size limitations of timing advances need not limit the maximum range of communication between a base station 20 and a target device 10.
As shown in
The time adjustment which aims to cause the uplink message to align with the reference boundaries at the base station 20 may be positive, or it may be negative. This is shown in
After a communication session has been established between a base station and a target device (after the PRACH and RAR messages, and any subsequent session establishing messages have been sent), the target device may move. In particular, the target device may move closer to or further from the base station, which may affect the propagation delay affecting messages sent between the two devices. Timing adjustments are associated with particular propagation delays, so if the target device continues applying a previous timing adjustment to messages in the communication session, the uplink messages to which the timing adjustment has been applied which are received at the base station may no longer be aligned with the reference boundaries after the target device has moved. Therefore, in some examples, the base station may comprise circuitry (such as the propagation delay determination circuitry 84) to determine that the received uplink messages are no longer aligned with the reference boundaries. The circuitry may identify the amount by which the messages are no longer aligned. The base station apparatus may then communicate a timing adjustment update message to the target communication apparatus, the timing adjustment update message including a time adjustment update value. The target communication apparatus may then update the timing adjustment by the amount communicated in the timing adjustment update message to account for the effects of the movement of the target communication apparatus. The timing adjustment update message may or may not be a standalone message, and may be encoded as part of other messages sent to the target communication apparatus. In one example, the timing adjustment updates are provided using a Timing Advance MAC Control Element included as part of a MAC header. For example, the Timing Advance MAC Control Element may include a 6-bit timing advance command which encodes a value from 0 to 63. The signalled value of the timing adjustment update may be determined from the encoded value TAupdate as TAnew=TAold+(TAupdate−31) (with the timing adjustment being T=TA*16*TS). Therefore, TA may be increased or decreased by an amount depending on the signalled timing adjustment update. The target communication apparatus may comprise time adjustment update circuitry 96 for applying the time adjustment update.
Simply applying the timing adjustment update may cause the timing adjustment to exceed the finite range of time adjustment values. For example, if a target device is at 100 km and has a time adjustment given by a value of TA=1282 (which in some examples may be the maximum value, corresponding to a time advance of 0.67 ms), then if the device moves further away and the base station signals an update to increase TA by, for example, 17 (If TAnew is equal to TAold+17, then this can be achieved by signalling a value of TAupdate=17+31=48) then the updated value TA=1299 may exceed the maximum time adjustment (see
In an example where TAmax=1282 (the largest time advance is approximately 0.67 ms) and TAmin=−641 (the largest time retard is approximately −0.33 ms), the size of the range of TA is 1924 (the size of the range when converted to time is 1 ms, equal to the length of a sub-frame). Therefore, an updated time adjustment value can be calculated as TAnew=((TAtemp+641)mod 1924)−641 where TAtemp=TAold+(TAupdate−31). More generally, for a minimum value of D and a range of R, the time adjustment value can be calculated as TAnew=((TAtemp−D)modR)+D. In the above example where TAtemp=1299, this leads to TAnew=−625 (which lies within the range of allowed time adjustments since it is between −641 and 1282). Updating the time adjustment in this manner can allow the uplink messages to which the updated time adjustment has been applied to align with reference boundaries at the base station 20 (although since TAnew and TAtemp may be offset, the updated time adjustment does not necessarily cause the uplink message to align with the same reference boundary as the previous time adjustment) whilst remaining within a finite range of time adjustment values.
The point at which the base station apparatus chooses to switch from causing uplink messages to align with a first reference boundary to aligning with a second reference boundary (i.e., the range limits) may be adjusted. For example, if the circuitry and response message allow a larger time advance can be applied, then the limit may be larger. In some cases, as shown in
The use of 0.67 ms as the maximum time adjustment may allow the technique to be used on older equipment and with the same format of messages as the alternative technique shown in
Nevertheless, using different boundaries between ranges may be useful when communicating with devices at certain ranges. In particular, if a target device is at a range near to one of the boundaries, then relatively small movement of the device closer to or further from the base station may cause the target device to repeatedly cross the boundary. The timing adjustment update may be signalled to the target device as discussed above, causing the timing adjustment to cross over a range limit. On one side of the range limit, the timing adjustment causes a given boundary in the uplink messages to align with a first boundary at the base station, and on the other side of the range limit the timing adjustment causes the given boundary to align with a different, second boundary at the base station. Therefore, when the device crosses the range limit, the entire uplink message becomes shifted by an integer number of sub-frames at the base station. If the base station is not adequately prepared for the shift, this may cause a temporary loss of the information communicated in those sub-frames which are received at the base station as the shift takes place, or even a complete loss in the communication session between the base station and the target communication apparatus. It may therefore be advantageous to minimise the chance of a target communication apparatus being located at a distance which corresponds to a propagation delay near to the limit between two ranges. This can be achieved by adjusting the limits of the ranges, by changing the maximum and minimum values of the time adjustment. The adjustment of ranges may be restricted by the maximum time adjustment which can be signalled and/or applied by the system, but there may nevertheless be some freedom to adjust the limits.
Examples are shown in
The bottom graph in each Figure illustrates an expected distribution of target communication devices in communication with the base station. This distribution may be fixed or may be variable, and may vary between different base stations based on the typical distance devices are located from that base station. The base station may collect information from the propagation delay determination circuitry 84 to construct the expected distribution of target devices, or the information may be predetermined and provided to the base station apparatus. For example, the information defining the expected distribution could be stored in storage circuitry 88 of the base station apparatus 20. It will be seen that the example expected distributions of target devices show peaks in user device density at certain distances. In the examples of
As discussed above, the maximum time adjustment value TAmax may be adjusted by the base station apparatus (for example, to reduce the likelihood of target communication devices from being located near to the limits between ranges). Since the target communication apparatus updates the time adjustment in dependence on the maximum and minimum limits of the time adjustment value, as indicated above, in some examples the base station apparatus may communicate a value to the target communication apparatus indicative of this range. This can be useful for the first time a particular target communication apparatus communicates with a particular base station, or if the ranges are modified during a communication session, so that calculations are performed using the correct range of time adjustment values. As will be discussed below, it can also be important to know the maximum time adjustment value for decoding a time adjustment value from a RAR message. The time adjustment limits may be communicated in several ways. For example, a maximum time adjustment value may be communicated (with the size of the range being implied, or in addition to the size of the range being communicated) or a minimum time adjustment may be communicated.
The time adjustment determination circuitry 86 calculates a time adjustment based on an indication of a propagation delay. In some examples, the time adjustment determination circuitry 86 may use a relationship such as that illustrated in
As discussed above, an example message format for signalling the time adjustment is illustrated in
In the examples given above, TAmax=1282, and the range of TA is from −641 to 1282, so the largest value that will need to be signalled is 1923, which will fall within the range of values representable with 11 bits. It will be appreciated that the details of the specific examples given are not required, and the example is merely used to illustrate that negative timing adjustments can be encoded as positive timing adjustments larger than a threshold value. This technique is particularly useful when there is sufficient space in the encoding of a message to encode the negative timing adjustments between the threshold and the maximum representable value, but not sufficient space to provide a spare bit to use as a sign bit. This takes advantage of spare encoding space in a format which may be restricted by a Standard.
Therefore, the reserved bit may be treated as an additional bit which can be combined with the 11 bits of the Timing Advance Command field 100 to provide a 12 bit field for encoding a signed timing adjustment. In particular, if the maximum signalled value of the timing adjustment requires only 11 bits (e.g. if the maximum signalled value is 1282), then there is an unused bit in the extended field which may be used to represent the sign of the value. When the reserved bit takes its usual value (the value it would take if unused for the timing adjustment value), then the value in the timing advance command field may be interpreted by the target communication apparatus as a positive value. This allows backwards compatibility with previous message formats, since positive time adjustments can be interpreted as they would be if negative time adjustments were not provided for. However, when the reserved bit 102 takes a different value, then the value encoded in the 11 bits of the timing advance command field 100 may be interpreted as a negative value (e.g., a value between 0 and −2047). This therefore enables the RAR message format to be used to encode both positive and negative timing adjustments.
Further, rather than using the additional bit 102 to signal the sign of the value in the field 100, the bit 102 could be concatenated with the field 100 to provide a 12 bit field, and the timing adjustment could be calculated as a two's complement value. The two's complement timing adjustment could then be encoded in the 12 bit extended field, and used for transmitting both positive and negative timing adjustments.
In this way, both a positive and negative timing adjustment can be communicated from the base station to a target communication apparatus using an existing message format.
In the present application, the words “configured to . . . ” are used to mean that an element of an apparatus has a configuration able to carry out the defined operation. In this context, a “configuration” means an arrangement or manner of interconnection of hardware or software. For example, the apparatus may have dedicated hardware which provides the defined operation, or a processor or other processing device may be programmed to perform the function. “Configured to” does not imply that the apparatus element needs to be changed in any way in order to provide the defined operation.
Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2302666.9 | Feb 2023 | GB | national |
