WO2016120615A1

WO2016120615A1 - A mobile device and method of control thereof

Info

Publication number: WO2016120615A1
Application number: PCT/GB2016/050173
Authority: WO
Inventors: Zohar Bogin; Richard Malinowski
Original assignee: Kofinder Technologies, Inc.; Harding, Andrew
Priority date: 2015-01-27
Filing date: 2016-01-27
Publication date: 2016-08-04

Abstract

A method of controlling a mobile device operating in a signal environment, the signal environment comprising at least one remote signal source operable to emit wireless signals within a plurality of time frames, each time frame of a predetermined duration F, at least one signal containing a data packet of a predetermined size S and the or each remote signal source emitting the data packet at a predetermined data transfer rate R, wherein S/R is shorter than F, wherein a time delay between the wireless signal being emitted by the remote source and being received at the receiver is within the range D₁ to D₂, the method comprising the steps of: activating the receiver; detecting the start of a first data packet being received at the receiver; detecting the completion of the first data packet being received at the receiver; deactivating the receiver; reactivating the receiver no later than at a predetermined time T after the start of the first data packet being received, wherein T is substantially equal to: F - (D₂ - D₁)

Description

A mobile device and method of control thereof Field of the invention

The present invention relates to a method of controlling a mobile device, particularly, but not exclusively, to a method of managing power usage in a cell (mobile) phone. The present invention further relates to a mobile device.

Background of the invention

The use of Global Navigation Satellite Systems (GNSS), e.g. GPS, to locate and/or track the movement of a mobile device, e.g. a cell/mobile phone, is well known and well documented.

A known GNSS, such as GPS, uses a constellation of orbiting satellites which each continuously transmit data. The data transmitted by a given satellite includes the current time and position of the satellite relative to a known reference point. The number of satellites in the constellation is chosen, and their respective orbits arranged, at least in the case of GPS, such that any location on earth always has a clear line of sight to at least a predetermined number of satellites. The receiver of the GNSS-enabled device receives data from a plurality of satellites in view and processes the data to determine the co-ordinates of the device within a particular degree of accuracy.

GNSS, particularly GPS, has been extensively adopted for both civilian and military use. In outdoor situations, GNSS offers a reasonably accurate means of locating a GNSS-enabled device (particularly so with military GNSSs). However, an acknowledged drawback with GNSS, particularly GPS, is that it is not reliable in built-up or indoor environments, which tend to attenuate, reflect or block signals to the extent that they cannot be used to accurately track the location/movement of the device.

It an attempt to improve the accuracy of GNSS, it is known to combine GNSS positioning with additional methods of positioning. Many mobile/cell phones utilise 'assisted-GNSS', which processes signals from a plurality of mobile cell transceivers. The location of the device may be determined by triangulating the signals received from each transceiver, which may verify, replace or correct the location estimated using the GNSS.

Although assisted-GNSS offers an improvement to standard GNSS, it is effectively just a way of compensating for inherent problems with known GNSSs.

More recently, the iridium constellation of satellites has been proposed for use in locating a mobile device.

In some GNSSs, such as GPS, the constellation of orbiting satellites (remote signal sources) each continuously transmit data. The GPS receiver, when determining the location of the device, may continuously read the signals received from the visible satellites, to accurately locate the device at all times. In other embodiments, it may be acceptable for the device only to periodically sample and process GNSS signals. The sampling period will be determined by the GNSS enabled device, and may change over time. For example, when the device is determined to be moving, the sampling frequency may be altered according to the speed of movement. When the device is deemed to be stationary, the sampling frequency may be lower.

In other GNSSs, such as Boeing Time and Location (BTL) which uses the Iridium constellation, the satellites may not transmit a continuous signal.

Instead, discrete signals are transmitted within a predetermined time interval, referred to as a time frame, having a duration F. The time frames may be synchronised across all satellites, such that the beginning of a time frame of one satellite begins at the same time as that of every other satellite. Within a time frame, a data packet of a predetermined size S is transmitted at a predetermined data transfer rate R. The time taken for the data packet to be transmitted (S/R) is shorter than the time frame interval F. An active receiver of the GNSS-enabled device will therefore only periodically receive data from the satellite. For the rest of the time, the receiver will receive no useable data until another data packet is transmitted. The next data packet may be transmitted in the immediately subsequent time frame, or there may be a delay of several time frames before another data packet is transmitted.

A typical receiver of a GNSS-enabled device will contain multiple hardware, firmware and software modules. These may comprise an RF frontend module, an IF processing module, baseband signal processing module and location processing module. When these modules are activated, they consume power, even when no signal is being received.

When a signal is being received, certain modules of the receiver may be idle (i.e. on but not being used). For example, while the RF and IF frontend sub system operate on an incoming signal, the backend location processing module may remain idle. Similarly, after a signal has been received and is being processed by the backend sub system, the frontend RF and IF sub systems may fall idle. In other words, during the receipt and processing of a given data packet, the operation times of each of the modules may not necessarily be synchronised. Keeping components powered on but not using them leads to power being wasted unnecessarily.

US7277737, US8867419, US8861415, US879791 1 and US2014/01 12229 all disclose methods for power saving by deactivating a receiver after a data packet has been received. Before being able to receive the next data packet, the receiver must receive a signal from the transmitter informing it to reactivate. In order to receive this reactivation signal, the receiver must be in a standby state (i.e. idle) and not truly off, which wastes power.

US8897188 and EP0473465 generally relate to methods that deactivate components of a system for a period of time after a data packet has been received. The systems then reactivate at the anticipated beginning of the next time frame in order to receive the next data packet. It is desirable to be able to deactivate components of a receiver in order to save power, while also ensuring that reactivation occurs in time to receive the whole data packet.

It is an object of the present invention to provide an improvement to the known systems or at least an alternative.

Brief summary of the invention

Accordingly, in one aspect of the present invention there is provided a method of controlling a mobile device having a receiver operating in a signal environment, the signal environment comprising at least one remote signal source operable to emit wireless signals within at least one of a plurality of time frames, each time frame of a predetermined duration F, at least one signal containing a data packet of a predetermined size S and the or each remote signal source emitting the data packet at a predetermined data transfer rate R, wherein S/R is shorter than F, wherein a time delay between the wireless signal being emitted by the remote source and being received at the receiver is within the range Di to D₂, the method comprising the steps of: activating the receiver;

detecting the start of a first data packet being received at the receiver; detecting the completion of the first data packet being received at the receiver;

deactivating the receiver;

reactivating the receiver no later than at a predetermined time T after the start of the first data packet being received, wherein T is substantially equal to:

F - (D₂ - Di)

In one embodiment, the method further comprises:

detecting the start of a second data packet being received at the receiver;

detecting the completion of said second data packet being received at the receiver; deactivating the receiver; and

reactivating the receiver at said predetermined time T after the start of the second data packet being received.

In one embodiment, the method further comprises:

detecting that a subsequent data packet has not been received at the receiver;

deactivating the receiver; and

reactivating the receiver no later than a time F after the previous reactivation.

In one embodiment, T is equal to:

F - (D₂ - D₁) - E

wherein E is a predetermined error compensation value.

In one embodiment, deactivating the receiver is performed a predetermined time P after detecting the completion of the data packet being received at the receiver.

In one embodiment, the receiver at least partially processes the received data packet during a least a part of time P.

In one embodiment, the method further comprises processing the received data packet

In one embodiment, the receiver is deactivated after the data packet has been processed.

In one embodiment, deactivating the receiver comprises deactivating at least one part of the receiver.

In one embodiment, the receiver includes an RF frontend module, an IF processing module, baseband signal processing module and location processing module, and wherein deactivating the receiver comprises deactivating at least one of said modules.

In one embodiment, F is substantially 90ms, R is substantially 50kbps, S is substantially 1000 bits, D₂ is substantially 1 1 s and D is substantially 2.5s.

In one embodiment, the wireless signal is emitted by the iridium satellite constellation.

In one embodiment, the frequency of the wireless signal is within 1618 to 1627 MHz.

In one embodiment, the receiver is activated for around one third of the predetermined time interval F, and deactivated for around two thirds of the predetermined time interval F.

In one embodiment, the receiver is deactivated substantially twice as long as it is activated.

In one embodiment, the method further comprises determining the location of the mobile device using at least one received data packet.

The present invention further provides a mobile device comprising:

a receiver operable to receive wireless signals within a plurality of time frames from at least one remote signal source, each time frame of a

predetermined duration F, at least one signal containing a data packet of a predetermined size S and the or each remote signal source emitting the data packet at a predetermined data transfer rate R, wherein S/R is shorter than F, wherein a time delay between the wireless signal being emitted by the remote source and being received at the receiver is within the range D to D₂,

a control module configured to:

activate the receiver;

detect the start of a first data packet being received at the receiver; detect the completion of the first data packet being received at the receiver;

deactivate the receiver; and

reactivate the receiver no later than at a predetermined time T after the start of the first data packet being received, wherein T is substantially equal to F - (D₂ - D-i )

In one embodiment, the control module is further configured to:

detect the start of a second data packet being received at the receiver; detect the completion of said second data packet being received at the receiver;

deactivate the receiver; and

reactivate the receiver at said predetermined time T after the start of the second data packet being received.

The present invention further a method of controlling a mobile device having a receiver operating in a signal environment, the signal environment comprising at least one remote signal source operable to emit wireless signals during a subset of a plurality of predetermined time frames, the method comprising the steps of:

receiving or generating a schedule of the subset of timeframes;

activating the receiver during the or each timeframe within said subset; and deactivating the receiver during all other timeframes.

Brief description of the drawings

Embodiments of the invention will now be described, by way of non-limiting example only, with reference to the accompanying figures in which:

FIGURE 1 schematically illustrates a mobile device in a signal environment receiving signals from satellites; FIGURE 2 schematically illustrates the functional modules of a receiver of a mobile device embodying the present invention;

FIGURE 3 schematically illustrate signals being transmitted by the remote signal source(s) and received by the mobile device.

FIGURES 3 to 5 schematically illustrate various scenarios comprising the transmission of data packets from a remote signal source(s) over time frames, their receipt by a receiver, and the status of the receiver according to embodiments of the present invention.

FIGURE 6 illustrates a method embodying the present invention. FIGURE 7 illustrates another method embodying the present invention. Detailed description Intra-frame power management

Figure 1 schematically illustrates a mobile device 1 in a signal environment 2. The signal environment 2 comprises a plurality of remote signal sources 3, e.g. satellites. Two signal sources 3A, 3B are shown for illustrative purposes only. The remote signal sources 3A, 3B transmit signals 4A, 4B, which are received by the mobile device 1 .

Figure 2 schematically illustrates part of a mobile device 1 according to the present invention. The mobile device includes a receiver 5. The receiver 5 includes an antenna 6 connected to an RF frontend module 7, an IF

processing module 8, baseband signal processing module 9 and a location processing module 10. All the modules 7 to 10 are connected so as to allow communication therebetween. Additionally, each of the modules 7 to 10 of the receiver 5 are connected to a control module 1 1 . The control module 1 1 is configured to control the operation of each of the modules 7 to 10. In another embodiment, at least the location processing module 10 may not form a physical part of the receiver 5, but may form part of another system, circuit or module which is functionally connected to the receiver 5. The precise physical form, arrangement and connection of each of the modules 7 to 10 of the receiver 5 is not of concern.

Figure 3 denotes, at section (a), the transmission of data packets 21 from the remote signal source(s) 3. The beginning of each predetermined time frame 20 is denoted on the X-axis: F-i , F₂, F₃, etc. Section (b) denotes the receipt of the respective data packet 21 at the receiver 5 of the mobile device. Section (c) denotes the status of the receiver 5 of the mobile device 1 , as determined by the present invention.

As illustrated in figure 3, signals are transmitted from remote sources 3 within a predetermined time interval F, which is referred to as a time frame 20.

A new time frame 20 starts immediately after the previous time frame 20, such that the beginning of each time frame 20 is spaced by a time interval F. The time interval F may be, for example, 100ms (milliseconds). The start times of each time frame 20 of each remote signal source 3 are preferably

synchronised. That is to say that the start of a time frame 20 of one remote signal source 3 will start at the same time as a corresponding time frame 20 of all other remote signal sources 3 in the signal environment. The

synchronisation is maintained principally by the use of highly accurate timing means, e.g. atomic clocks, on board each remote signal source 3. The synchronisation may periodically be verified between the remote signal sources 3, and realigned if necessary.

Within each time frame 20, a data packet 21 of a predetermined size S is transmitted at a predetermined data transfer rate R. In a known GNSS the size of the data packet 21 , the transfer rate R and the time interval F are chosen such that the time taken for the data packet to be transmitted is shorter than the time interval F of the time frame 20. The time taken for a data packet of size S to be transmitted, at a predetermined data transfer rate R is: s

R

Therefore, in this known GNSS:

S

^{F >} R

Accordingly, during a given time frame 20, a data packet 21 will only be transmitted for a portion of that time frame 20. For the rest of the time frame 20, no useful data will be transmitted.

In a known GNSS, there is a slight lag 22 (e.g. 1 ms) between the start of the time frame 20 and the start of transmission of a data packet 21 from the signal source 3. Preferably, the lag 22 is fixed for each time frame 20.

There is also a variable delay 23 (propagation) between the data packet 21 being transmitted by the signal source 3 and being received at the receiver 5. The delay 23 depends on various factors, including the physical distance between the remote signal source 3 and the receiver 5, and any

environmental delays (including atmospheric and ionospheric delays). For a known signal environment, it can be measured, calculated or observed that the total delay 23 between a signal being transmitted by a remote signal source 3 and received at the receiver 5 is within a range of Di and D₂, where Di is the minimum delay and D₂ is the maximum delay.

Over time, for a given signal environment, the values of D1 and D2 may change. For example, D1 and D2 may increase when the mobile device is in particular environments (such as built-up areas, mountainous terrain etc). They may also change due to alterations in the orbits of the satellites, or other changes to the constellation. In one embodiment, the values of D1 and D2 stored on the mobile device are regularly updated - they are adaptive. For example, if D2 was set based on a signal arriving with a significant delay, and such a delay was not experienced again within a subsequent period of time, D2 may be reset to a lower value. Outliers of D1 and D2 as measured by the mobile device may be ignored. D1 and D2 may be set based on the average minimum and maximum delays measured.

During some time frames 20, no data packets 21 are emitted by a particular signal source 3.

Preferably, F = 90ms, the lag is 1 ms, the data packet 21 comprises 1000 bits, and data transfer rate is 50Kbps and so the transmission is completed within about 20ms (preferably 20.32 ms). D is 2.5ms, D₂ is 1 1 ms.

Of all GNSS, BTL is unique in that the active data transmission time (data packet) is a subset of the frame time.

Knowing, or having assessed, the above parameters, the inventor has determined that it is possible to estimate the earliest possible arrival time of the next data packet 21 . The present invention seeks to adopt this estimate to provide a method of saving power in a mobile device.

According to a method embodying the present invention, the receiver 5 of the mobile device may be placed in at least two states - a full power mode and a low power mode. Low power does not necessarily mean 'zero' power, but rather that at least one module of the mobile device has been deactivated or turned off.

Initially, when the mobile device is in a 'cold' state, the receiver 5 is activated (placed in high power mode). The receiver 5 is then active and ready to receive data.

The receiver 5, and or associated control circuitry, detects the start of a first data packet 21 being received at the receiver 5.

The receiver 5, and or associated control circuitry, then detects the

completion of the first data packet 21 being received at the receiver 5. After the data packet has been received, the receiver 5 is deactivated (placed in a low power mode). The receiver 5 may be left active for a period after the receipt of the data packet before being deactivated, to allow for additional processing.

When the receiver 5 is deactivated, or placed in low power mode, it is consuming less, or no, power.

However, there is a need for the receiver 5 to be reactivated (placed back into a high power mode) when another data packet 21 arrives. Since the receiver 5 is deactivated, and thus saving power, it is not possible for it to detect the arrival of the next data packet 21 . Leaving the receiver 5 activated would consume power.

In Figure 3, section (a) denotes the data packets 21 being transmitted from the remote signal source(s) 3. The beginning of each predetermined time frame 20 is denoted on the X-axis: F-i , F₂, F₃, etc.

The data packets 21 are transmitted by the remote signal source 3 with a fixed lag 22 after the start of the time frame 20. The lag 22 is constant in each time frame 20, so is not of concern.

Section (b) denotes the receipt of the respective data packet 21 at the receiver 5 of the mobile device 1 . With reference to time frame F-i , there is a delay 23 between the start of the transmission of the data packet 21 from the remote signal source 3, and its receipt at the receiver 5. For the purposes of this illustration, we suppose that there has been the maximum possible delay, D₂ for the data packet 21 of the first time frame Fi .

Section (C) denotes the status of the receiver 5 of the mobile device 1 . The status may either be high (normal) power, denoted by H; or low power, denoted by L. The receiver 5 is initially set to H power status. After the receiver 5 has received all of the data packet 21 , the receiver 5 may be placed into L power status (e.g. deactivated).

As discussed above, two neighbouring data packets 21 are transmitted by the signal source(s) 3 with a predetermined time interval F (owing to the constant lag 22). It could therefore be assumed that the next data packet 21 will start to arrive at the receiver 5 a period F after the first data packet 21 started to arrive at the receiver 5.

However, as observed above, a data packet 5 may be delayed within a range of Di to D₂ from leaving the remote signal source 5. Without knowing the delay, a subsequent data packet 5 may arrive earlier or later, relative to the beginning of the time frame 20, than the previous data packet 5. This may particularly be the case where the data packets of two neighbouring time frames are received from different remote sources, which may be located at different distances from the receiver 5.

If the receiver 5 is reactivated a period F after the first data packet started to arrive, and the second data packet happens to arrive earlier than the first data packet, the receiver 5 would then 'miss' the beginning of the (early-arriving) second data packet 21 .

So as to ensure that the receiver 5 is reactivated in time to receive the subsequent data packet 21 , we must assume that the first data packet arrived late (i.e. with a maximum delay D₂), and that the subsequent data packet 21 will arrive early (i.e. with a minimum delay D-i).

In order to ensure that all of the second data packet is received, the present invention reactivates the receiver 5 a predetermined time T after the start of the first data packet being received, wherein:

T = F - (D₂ - D₁) The calculation of time T takes place at the receiver, allowing reactivation to occur without the need for a signal from the satellite. Accordingly, when the first data packet is 'late' (i.e. experiences a delay of, or close to, D₂), and the subsequent data packet is 'early' (i.e. experiences a delay of, or close to, Di) this method ensures that the receiver 5 has been reactivated in time to receive all of the second data packet. When the first data packet experiences the largest delay possible, D2, and the second data packet 21 experiences the shortest delay possible, D1 , the receiver 5 should be reactivated almost exactly as the second data packet 21 starts to arrive at the receiver 5. In this situation, the receiver 5 has not unnecessarily been activated before the second data packet starts to arrive, unlike US'1 88 and EP'465 where the receiver is always activated by the start of the next timeframe irrespective of any delays. This has the advantage of reducing or removing the time that the receiver spends idle which saves power.

In one embodiment:

T = F - (D₂ - D₁) - E where E is a compensation value, to allow for errors (e.g. timing errors).

Accordingly, in this embodiment, even in the 'worst case' scenario discussed above (figure 3), the receiver 5 will tend always to be reactivated before the second data packet starts 21 to arrive.

In the alternative situation, illustrated in Figure 4, the first data packet is 'early' (is delayed only by D-i ) and the second data packet is 'late' (delayed by D₂). According to a method embodying the present invention, the receiver 5 will be reactivated in time to receive the second data packet 21 . In fact, in this scenario, the receiver 5 will be activated before (by a period equal to around D2- D1 ) the second data packet 21 starts to arrive, as shown in Figure 4. Although the receiver 5 will therefore be active for a period when no signal is yet being received, power has still been saved by having previously

deactivated the receiver 5 for a predetermined period of time. In either of the situations illustrated in Figures 3 and 4, the receiver 5 is then deactivated after detecting the completion of the second data packet 21 being received at the receiver 5.

When the receiver 5 has been deactivated a second time, after receiving the second data packet 21 , the present invention reactivates the receiver 5 a predetermined time T after the start of the second data packet being received. Therefore, as each data packet 21 is received, the arrival time of that data packet is used as the new basis on which to reactivate the receiver 5 for the subsequent data packet.

In the situation illustrated in figures 3 and 4, data packets 21 are emitted from the remote signal source(s) in two consecutive time frames 20. In other situations, no data packet 21 may be transmitted during a given, or multiple, time frame(s). This is illustrated in figure 5.

With reference to figure 5, a data packet 21 is transmitted within the first time frame 21 , F-i . As described above, a method embodying the present invention reactivates the receiver 5 a predetermined time T after the start of the first data packet being received.

At this point, a method embodying the present invention detects whether a second data packet 21 is being received at the receiver 5. Preferably, the detection step is carried out for at least a period of time equal to D₂ - Di , to allow for the situation as illustrated in figure 4, where the first data packet was early and the second data packet was late.

Accordingly, the detection step must continue until at least a point where a data packet 21 may still arrive.

If it is established (detected) that no data packet 21 is being transmitted during the current time frame 20, a method embodying the present invention deactivates the receiver 5, to save power. The receiver 5 would otherwise remain active until receiving the next data packet (which may be in the subsequent time frame, or in a much later time frame). This has the

advantage of reducing or removing the time that the receiver spends idle which saves power.

Once the receiver 5 has been deactivated, it will be appreciated that it must be reactivated in case a new data packet is received in the subsequent time frame 20. However, since no data packet was received in the current time frame, a different basis from which to calculate the reactivation time must be chosen.

Accordingly, in an embodiment of the present invention, the receiver 5 is reactivated at a time F after the previous reactivation of the receiver 5, as illustrated in figure 5. This will ensure that the receiver 5 will be reactivated in time to receive a subsequent data packet 21 in the next time frame. This has the advantage of saving power while also ensuring that a data packet is not missed.

In Figure 5, there is only one time frame in which no data packet is

transmitted. It will be appreciated that regardless of the number of 'inactive' time frames, in which no data packet is transmitted, the method embodying the present invention will ensure that the receiver 5 is reactivated in time for the next 'active' time frame, in which a data packet is transmitted.

It will be appreciated that where multiple time frames 21 pass without any data packets 21 being transmitted, the receiver 5 will be active only for a period of around (D₂ - Di), and inactive for a period of around F - (D₂ - Di) for each time frame, thus saving power compared to having the receiver on permanently.

Figure 6 illustrates a method embodying the present invention.

At step, 30, the receiver 5 is activated. At step 31 , the start of a first data packet being received at the receiver 5 is detected. At step 32, the completion of the first data packet being received at the receiver 5 is detected. At step 33, the receiver 5 is deactivated. At step 34, the receiver 5 is reactivated no later than a predetermined time T after the start of the first data packet being received, wherein T is substantially equal to F - (D₂ - D-i).

Figure 7 illustrates a method embodying the present invention. Preferably, the method of figure 7 is carried out after that of figure 6. The first step 35 of the method of figure 7 comprises detecting whether a data packet is being received at the receiver 5 (following the reactivation of the receiver 5 from step 34). If a data packet is detected, then step 37 comprises detecting the start of the data packet being received at the receiver 5. Step 38 comprises detecting the completion of the data packet being received at the receiver 5. At step 39, the receiver 5 is deactivated. At step 40, the receiver 5 is reactivated at time T after the start of the data packet being received at the receiver 5. Then, step 35 is repeated.

If, at step 35, it is determined that no data packet is being received at the receiver 5, step 41 comprises deactivating the receiver 5. Step 42 comprises reactivating the receiver 5 at a time F after the previous reactivation of the receiver 5. Then step 35 is repeated.

The method illustrated in Figure 6 may be seen as a 'calibration' step. After the calibration, the method illustrated in Figure 7 may subsequently be performed for multiple iterations (time frames).

It will be noted that step 40 of Figure 7 reactivates the receiver 5 at time T after the start of the current data packet being received. Accordingly, as each new (valid) data packet is received, the time basis from which the subsequent reactivation is calculated is effectively reset. In an alternative embodiment, the reactivation time for a given time frame may be calculated from the

reactivation time of the receiver 5 following the first data packet being received, wherein reactivation of the receiver 5 occurs every period F after the first reactivation. The above methods and systems may be referred to as relating to 'intra- frame' power management, in that power savings are made by deactivating the receiver 5 during a portion of a given time frame.

Cross-frame power management

In the GNSS discussed above, there are multiple remote signal sources which transmit data packets within time frames. As described, a given remote signal source may not always transmit a data packet within each time frame. For example, for a given number of time frames X, only a selection Y of those time frames may contain a data packet. X may be a multiple of Y. For example, within 50 time frames, only 2 or 3 time frames may contain a data packet. A mobile device may only need to receive one data packet from a remote data source to calculate its position.

In some GNSSs, the sequence of when each remote signal source transmits a data packet and when it is in inactive (i.e. does not transmit a data packet), during a given time frame, is known. The remote signal sources may all be configured so as to provide a defined sequence of activation of the remote signal sources and thus the transmission of each data packet. The sequence of activation/deactivation may be controlled by the operator of the signal environment. It is beneficial for the mobile devices to have knowledge of the sequence, to assist in the management of the mobile device. For example, in an embodiment of the invention, if it is known that a given remote source will not transmit a data packet in the next N time frames, there is no need to reactivate the receiver 5 in the known dormant time frames.

Information relating to the sequence may be transmitted by the remote signal sources, which information is then stored locally on the mobile device. Storing the sequence information on the mobile device requires increased local memory. In one embodiment of the present invention, the sequence data may be compressed on the mobile device, to reduce the required local memory. The information transmitted may be limited to a certain period of time or geographical area, thus reducing the memory requirements of the mobile device. However, there is still a need for the mobile device to acquire activation information from the remote signal source. Even if the activation information is received via other channels, such as via the internet, it is still a requirement that the system has cloud connectivity.

Accordingly, according to an embodiment of the present invention, the mobile device may calculate the activation sequence of each of the remote signal sources, based on predetermined criteria. Accordingly, there is no need for the mobile device to connect to a remote information source to retrieve the sequence information. Moreover, the mobile device does not need extensive memory in which to store the sequence, as it can be calculated on an 'ad hoc' basis.

The present invention provides a method of controlling a mobile device having a receiver operating in a signal environment, the signal environment comprising at least one remote signal source operable to emit wireless signals during a subset of a plurality of predetermined time frames, the method comprising the steps of:

receiving or generating a schedule of the subset of timeframes;

In one embodiment, there are 50 time frames, and the subset comprises 2 time frames. It will be appreciated that, in this example, only 4% of the total number of time frames are 'active' (i.e. contain a data packet). Accordingly, by deactivating the receiver 5 during the known 96% of inactive frames, significant power savings can be made.

These methods and systems may be referred to as relating to 'cross-frame' power management, in that power savings are made by deactivating the receiver 5 for the entirety of selected ones of a plurality of time frames. Further power savings can be achieved by combining both the cross-frame and intra-frame power management methods. For example, in an

embodiment of the intra-frame management method of claim 1 , the receiver 5 may be activated for roughly one third (33.33%) of a timeframe, as the data packet is being received. By combining both the cross-frame and intra-frame methods of power management for this example (for one remote signal source), the receiver 5 may be activated only 1 .33% of the time ((100 - 96) x 0.33%), resulting in a 98.67% power saving as compared to an arrangement in which the receiver 5 is always on. Even when there are multiple remote signal sources, the power savings are significant.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

What is claimed is:

1 . A method of controlling a mobile device having a receiver operating in a signal environment, the signal environment comprising at least one remote signal source operable to emit wireless signals within at least one of a plurality of time frames, each time frame of a predetermined duration F, at least one signal containing a data packet of a predetermined size S and the or each remote signal source emitting the data packet at a predetermined data transfer rate R, wherein S/R is shorter than F, wherein a time delay between the wireless signal being emitted by the remote source and being received at the receiver is within the range Di to D₂, the method comprising the steps of: activating the receiver ;

deactivating the receiver;

F - (D₂ - Di)

2. A method according to claim 1 , further comprising:

detecting the start of a second data packet being received at the receiver;

detecting the completion of said second data packet being received at the receiver;

deactivating the receiver; and

3. A method according to claim 1 , further comprising:

detecting that a subsequent data packet has not been received at the receiver; deactivating the receiver; and

4. A method according to claim 1 , wherein T is equal to:

F - (D₂ - D₁) - E

wherein E is a predetermined error compensation value.

5 A method according to any preceding claim, wherein deactivating the receiver is performed a predetermined time P after detecting the completion of the data packet being received at the receiver.

6. A method according to claim 5, wherein the receiver at least partially processes the received data packet during a least a part of time P.

7. A method according to any preceding claim, further comprising processing the received data packet

8. A method according to any preceding claim, wherein the receiver is deactivated after the data packet has been processed.

9. A method according to any preceding claim, wherein deactivating the receiver comprises deactivating at least one part of the receiver.

1 0. A method according to any preceding claim, wherein the receiver includes an RF frontend module, an IF processing module, baseband signal processing module and location processing module, and wherein deactivating the receiver comprises deactivating at least one of said modules.

1 1 . A method according to any preceding claim, wherein F is substantially 90ms, R is substantially 50kbps, S is substantially 1 000 bits, D₂ is

substantially 1 1 ms and Di is substantially 2.5ms.

12. A method according to any preceding claim, wherein the wireless signal is emitted by the iridium satellite constellation.

13. A method according to any preceding claim, wherein the frequency of the wireless signal is within 1618 to 1627 MHz.

14. A method according to any preceding claim, wherein the receiver is activated for around one third of the predetermined time interval F, and deactivated for around two thirds of the predetermined time interval F.

15. A method according to any preceding claim, wherein the receiver is deactivated substantially twice as long as it is activated.

16. A method according to any preceding claim, further comprising determining the location of the mobile device using at least one received data packet.

17. A mobile device comprising:

a control module configured to:

activate the receiver;

detect the start of a first data packet being received at the receiver;

detect the completion of the first data packet being received at the receiver;

deactivate the receiver; and reactivate the receiver no later than at a predetermined time T after the start of the first data packet being received, wherein T is substantially equal to F - (D₂ - D-i)

18. A mobile device according to claim 17, wherein the control module is further configured to:

deactivate the receiver; and

19. A method of controlling a mobile device having a receiver operating in a signal environment, the signal environment comprising at least one remote signal source operable to emit wireless signals during a subset of a plurality of predetermined time frames, the method comprising the steps of: receiving or generating a schedule of the subset of timeframes;