WO2003060542A2

WO2003060542A2 - System for the efficient utilization of navigation satellites

Info

Publication number: WO2003060542A2
Application number: PCT/IL2003/000028
Authority: WO
Inventors: Joseph Nir; Baruch Shayevich; Hanoch Cohen; Eiran Duchovni
Original assignee: Cellguide
Priority date: 2002-01-16
Filing date: 2003-01-09
Publication date: 2003-07-24
Also published as: AU2003207954A1; WO2003060542A3; AU2003207954A8

Abstract

A procedure for using mobile receivers of navigation satellites, utilizing an energy conservation scheme (ECS) in a snap data acquisition environment. Two separable schedules are employable during which some or all the components of the receiver are powered up. During a data collection schedule session associated with a snap, the receiving circuitry is powered up (20) and a FIFO memory field is filled up (24). During a data retrieval session,_a processor is powered up and the FIFO is searched and data stored in it is processed. In one embodiment, the data collection schedule session initiates a snap.

Description

SYSTEM FOR THE EFFICIENT UTILIZATION OF NAVIGATION SATELLITES

FIELD OF THE INVENTION

The invention relates generally to navigation technologies employing navigation satellites. More specifically the present invention relates to snap oriented systems for satellite signal acquisition.

BACKGROUND OF THE INVENTION

GPS receivers sensitivity has improved appreciably in the last years. Receivers with sensitivity of down to -155dBm were developed. However, even with such high sensitivity the navigation capability using such receivers implemented inside buildings is still quite limited. One common method of obtaining a navigation fix inside buildings is by using the last calculated position as a substitution for the present position. Thus, for example, a mobile receiver which receives enough satellites outdoors to determine successfully the current position, upon entering a building, may not be able to receive the sufficient number of satellites to determine a position. Inside the building, the situation is typically unpredictable with respect to the number of satellites received at any one place. Therefore, there may be places inside buildings in which the number of satellites received is indeed sufficient to allow effective calculations to determine the current location of the receiver. However, a continuous search of satellites within buildings may prove to be a heavy burden on the energy budget of the mobile receiver. The approach to solving the problem of insufficiency of satellites by keeping the last position effective until an updated position can be determined, requires a continuous search for satellite signals, if not too large a deviation is permitted. If the receiver is powered down for a relatively long period of time to reduce power consumption, the last calculated position may be for practical purposes too far off the actual position of the receiver.

Presently, a new generation of "snap" based receivers is used for mobile units GPS navigation. In this technique, a snap, i.e. a short period of receiving activity, a GPS IF or baseband signal is recorded. Later, this snap data is processed to extract pseudo-ranges to the satellites, followed by a position determination. As explained in Fig. 1 to which reference is now made, feasible calculations of the receiver's position can be made when enough satellites are received. Thus, when a position determination is required, a snap is initiated following which in step 12 satellites are received, and the signals thereof stored in a snap memory. In step 14 the number of satellites received in the snap is verified. If the number of satellites received is above a certain minimum, typically 4, the position of the receiver is calculated in step 16. If the number of satellites received is smaller than the minimal number allowing position fix, another snap can be initiated in step 18.

DESCRIPTION OF THE INVENTION

The present invention optimizes the use of snap based GPS receivers by utilizing a previously calculated position without consuming power on repetitive updating of the position. The system of the invention is suited for implementation in built - up areas or inside buildings in which the number of satellites that can be received concomitantly is seriously decreased by the physical obstruction associated with the buildings. The procedure of the invention can also be employed regularly.

In a preferred embodiment of the present invention, snaps are scheduled, and in every snap, the GPS receiver downconverts the GPS RF signal to IF (or baseband). The IF signal is then sampled and stored in a snap memory. Signal processing is performed on the snap data, independent of the satellite data acquisition schedule. Processing is implemented by a general purpose DSP or RISC processor, or by combination of dedicated hardware and a general purpose processor. Subsequently, pseudo-ranges to the satellites are extracted followed by position calculation. The duration of a snap depends on the required sensitivity and on the algorithm implemented for processing the signal. A typical snap ranges from a few milliseconds up to a few seconds. A snap is triggered by at least one of the following events:

• Predetermined periodic snap recording - typically every about 10- 60 seconds. • Predetermined periodic position fix request - typically every 10-

60 minutes.

• Independent navigation request.

When energy conservation scheme (ECS) is employed in accordance with the present invention, most of the time the RF front - end, down-converter, interface logic and signal processor are powered down. Typically, only a low power consumption controller and a real time clock are powered up, consuming some power. Periodically, the necessary components in the receiver are powered up, the RF front end, the down - converter, an A/D converter and the interface logic to the memory are powered up and a snap recording is made. This is described in Fig. 2 to which reference is now made. During the snap, the satellites' signals are recorded and added to a FIFO memory. Typically, up to 100 snaps are stored in such a FIFO memory. During this phase no signal processing is carried out, to significantly reduce power consumption. The purpose of such ECS snap is to store the downconverted signals in the FIFO memory, without applying signal processing to the received data.

In Fig. 3 the connection between the snaps in the ECS and the FIFO memory are described symbolically. Snap 20 is the first in a ECS session. The data from the snap 20 is kept in FIFO memory, such that it occupies a field 22 in the FIFO memory. Subsequently, after a period of time, typically lasting between 10 to 60 seconds, another snap is evoked, snap 24, during which time the receiver receives the satellite signal, which is passed to field 26 in the FIFO memory. After another power - down period, the relevant components of the receiver are powered up again during snap 28, the satellites' signals are acquired, and the downconverted signal data is passed to FIFO field 30. The FIFO memory fields are eventually filled up in a consecutive order of time which corresponds to the succession of data acquisition sequences in time. Since the time that the FIFO is filled up, for every new snap data entered, the oldest memory field is deleted.

Independently of the snaps data acquisition schedule, a retrieval of stored satellite signal for the purpose of position determination is carried out. In each instance of data retrieval, the receiver is powered up affecting the relevant components, memory interface and the processor in the receiver. In some embodiments of the invention, each time a data retrieval event takes place, all the components of the receiver are powered up and a snap is performed irrespective of the regular snaps data acquisition schedule. In other embodiments of the invention, a data retrieval event will only occur in connection with a snap of the regular snaps data acquisition schedule. The snaps data retrieval schedule usually employs a much lower frequency of powering up, typically every 10 to 60 minutes. To search the FIFO fields, any data search algorithm in computer science may be used. For example, binary search is employed, as explained in reference to Fig. 3. When the data retrieval schedule session is initiated, the n/2^th FIFO data field 32 is accessed, and subsequently data fetched and processed. If a viable navigation fix is obtained, half of the FIFO representing older snaps is deleted, providing data fields which can be used for the new snap data obtained in further employment of snaps data acquisition schedule. The updated navigation fix can be used as the new position until a more updated position is determined. If a viable navigation fix is not obtained using the n/2* data field, the n/4^th is accessed, the stored data is fetched and processed. If a viable navigation fix is obtained, all of the FIFO fields containing data older then the n/4^th data field, are then deleted. Another example of a search strategy that can be employed is simply going back in order from the newer data field to the older data field. If a non scheduled position request is initiated during the execution of ECS, the same search and processing procedures can take place as in the scheduled snaps data retrieval schedule. In a preferred embodiment of the invention, if a non scheduled request for a position is received, the newest available viable navigation fix can be obtained by a performing an ad hoc snap, to be processed first.

The method of the invention can be used also in client-server systems, where major parts of the position calculations can be performed in the server. In such a case, the decision about the viability of a snap can incorporate considerations regarding the number of received satellites, the reception quality (signal to noise, multipath indicators), DOP etc. As an alternative to storing the navigation fix for further use, the relevant data for this position calculation is stored i.e. GPS time, pseudo-ranges, Doppler measurements, reception quality etc.

While this is the general description of the algorithm, some parametric optimizations can be implemented, depending on the requirements of specific applications, such as:

• criteria for terminating the search for data in the FIFO memory,

• which search algorithm to use - linear, tree like depth-first etc.

• dividing the FIFO memory between the old part and the new one.

• period of the recurring processes. ECS can also be used with any other navigation signals such as pseudolites, other navigation satellites (Glonass, Galileo) or even communication signals used for navigation, such as cellular base stations transmissions used for E-OTD navigation.

Claims

1. A procedure for utilization by a mobile receiver of a navigation satellite system, wherein an energy conservation scheme (ECS) is employed during which relevant components are powered up in said receiver, comprising:

• employing a snaps data acquisition schedule, wherein navigation satellite signal of each snap is received and stored in a data field in a FIFO memory;

• employing a snaps data retrieval schedule in which memory data fields of said FIFO memory are searched;

• using a first viable navigation fix, and • deleting older data fields in said FIFO memory.

2. A procedure for utilization by a mobile receiver of a navigation satellite system as in claim 1, and wherein said snaps data retrieval schedule is employed independently of said snap data acquisition schedule.

3. A procedure for utilization by a mobile receiver of a navigation satellite system as in claim 1, and wherein at least an RF front end, a down- converter, a A/D converter and an interface logic to said FIFO memory are powered up during said snaps data acquisition schedule.

4. A procedure for utilization by a mobile receiver of a navigation satellite system as in claim 1, and wherein at least a processor is powered up during said snaps data retrieval schedule.

5. A mobile receiver of a navigation satellite network, wherein components of said receiver are powered down and wherein a controller means functionally comiected to a clock is capable of initiating snaps data acquisition schedule sessions and snaps data retrieval schedule sessions, during each of which sessions components of said receiver are powered up.

6. A mobile receiver of a navigation satellite network as in claim 5, and wherein a FIFO memory is connected to a signal sampling means for storing data of each of said snaps data acquisition schedule sessions consecutively.

7. A mobile receiver of a navigation satellite network as in claim 5, and wherein a server of a network to which said mobile receiver is connected provides for at least some of the calculations of the position of said receiver.