US 6,651,031 B2Granted

Method for providing time using a multiple-clock model and a clock system using such a model

AssigneeNokia Corporation

InventorDavid Akopian

Life of this patent

Estimating the term…

Loading patent…

Abstract

An N-clock system, for use for example in a ranging receiver using a Kalman filter. The clock system uses N clocks (to save power by using some clocks that consume less power) with a schedule for switching from one clock to another (so that only one clock is on at any instant of time). It uses an N-clock model that, in case of an application using clock 1 for time interval Δt1, clock 2 for time interval Δt2, . . . , and clock N for time interval ΔtN, provides a state update equation for updating the N-clock system state (the state components being typically time and fractional frequency). The state update equation results from propagating the state of the assembly of N clocks (providing a single output, i.e. acting as a single clock) forward from interval to interval until the entire interval of Δt1+Δt2+ . . . +ΔtN is covered.

Claims10

Dependent claims

A method of providing an estimate of a current state of a clock assembly of at least two clocks including a first clock and a second clock, each clock having a clock phase and a clock fractional frequency, the method comprising:

a) a step (51), responsive to a schedule of operations indicating a first time period in a cycle of operation when the first clock is operative and a second time period when the second clock is operative, of providing a clock measurement (z) indicating information about the clock assembly, and
b) a step (52), responsive to the clock measurement (z) and also responsive to the schedule of operations, for providing the a estimate of a current state (x′) of the clock assembly using a state filter adapted to use a clock model for the clock assembly, the clock model indicating a state (x′) of the clock assembly via a state update process that includes a measure of process noise ({overscore (w)}(k+1,k)) and that propagates the state of the first clock to the end of the first time period in accordance with the schedule of operations using a state update process for the first clock, uses the state so obtained as the starting state for the second clock at the start of a second time period, and propagates the starting state for the second clock to the end of the second period using a state update process for the second clock, and also for providing a corresponding measure of process noise covariance (Q′).

A clock system (40) for providing an estimate of a current state of a clock assembly (32) including at least two clocks, the clock system comprising:

a) the clock assembly (32), responsive to a schedule of operations indicating when in a cycle of operation each of the two clocks is operative, for providing clock signals indicating a clock measurement (z) conveying information about the clock assembly;
and
b) a state filter (41), responsive to the clock signals indicating the clock measurement (z), and further responsive to the schedule of operations, for providing the estimate of the current state (x′) of the clock assembly, wherein the state filter is adapted to use a clock model for the clock assembly, the clock model indicating the state (x′) of the clock assembly via a state update process that includes a measure of process noise ({overscore (w)}(k+1,k)) and that propagates the state of a first one of the clocks of the clock assembly to the end of a first time period in accordance with the schedule of operations using a state update process for the first clock, uses the state so obtained as the starting state for a second clock of the clock assembly at the start of a second time period, and propagates the starting state for the second clock to the end of the second period using a state update process for the second clock, and also for providing a corresponding measure of process noise covariance (Q′).

Dependencies are inferred from the claim text.