Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1999-09-24
2003-07-01
Le, Thanh Cong (Department: 2684)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S462000, C370S357000
Reexamination Certificate
active
06587694
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to electronic devices, such as a cordless telephone. More particularly, it relates to a method and device to synchronize clocks of two wireless devices, e.g., a wireless portable device with its base device.
2. Background of Related Art
A wireless device, e.g., a cordless telephone, wireless keyboard, wireless mouse, a digital personal assistant (PDA), or a notebook computer, etc., must keep its own internal clock in synchronization with an associated base unit or station, e.g., a telephone base unit, or a desk top computer, for communications therebetween.
As a particular example, a cordless telephone system, e.g., shown in
FIG. 5
, generally includes a stationary unit, e.g., a base unit
10
, which communicates with a telephone network (not shown), e.g., public switching telephone network (PSTN). A telephone circuit
160
of the base unit
10
typically communicates with a telephone network by wired communication means, i.e., through the tip and ring lines,
101
and
102
, respectively.
The base unit
10
includes a control unit
110
, which may be for example, any microprocessor, microcomputer or microcontroller known in the art and readily available from a manufacturer such as Lucent Technologies Inc. of Murray Hill, N.J. The control unit
110
controls the operation of the base unit including the communication to and from the telephone network and to and from a wireless remote handset
20
. The interface unit and display
165
provides a user I/O interface to the base unit
10
.
The base unit
10
is typically connected to a conventional household AC power outlet via a power circuit
190
, which provides an appropriate power level to the base unit
10
derived from the household AC power. The power circuit
190
also provides appropriate power level to a charge circuit
170
that provides a charging signal to one or more charging contacts (not shown) for providing a charging power to a cradled external device, e.g., a wireless remote handset
20
.
A conventional cordless telephone system, e.g., the one shown in
FIG. 5
, also typically includes one or more portable devices, e.g., the wireless remote handset
20
, which communicates with the base unit
10
via a radio frequency (RF) link through respective RF front ends including RF circuits
150
,
250
and RF transceivers
130
,
230
. A user of a cordless telephone system may initiate or receive a telephone call using the interface and display unit
265
of the remote handset
20
through the base unit
10
, to and from the telephone network.
The remote handset
20
also includes a control unit
210
, which may be for example, any microprocessor, microcomputer or microcontroller known in the art and readily available from a manufacturer such as Lucent Technologies, Inc of Murray Hill, N.J. The control unit
210
controls the operation of the base unit including the communication to and from the base unit
10
. The interface unit and display
265
provides a user I/O interface to the remote handset
20
.
The remote handset
20
typically includes a rechargeable battery
260
. The rechargeable battery
260
provides power for the remote handset
20
, and may be charged when one or more charge contacts (not shown) of the remote handset
20
are made to be in contact with one or more charge contacts (not shown) of the base unit
10
, i.e., when the remote handset
20
is “cradled” in the base unit
10
.
The frequency of the handset clock
215
must be in synchronization with the frequency of the base clock
115
in order to establish an RF communication link between the remote handset
20
and the base unit
10
. Because of the differences in characteristics of the respective oscillators of the remote handset
20
and the base unit
10
, the respective clocks
115
and
215
have a tendency to drift away from each other over time, and thus are required to be synchronized frequently.
The frequency synchronization of the clocks
115
and
215
may be performed at the start of each communication session between the remote handset
20
and the base unit
10
. Alternatively, the synchronization may be performed periodically to maintain a reasonable alignment between the clocks in order to be able to quickly establish the RF communication link for each communication session.
Typically, in a conventional radio communication device pair, e.g., comprising the remote handset
20
and the base unit
10
of a cordless telephone system, frequency synchronization therebetween is achieved by one of the pair transmitting a radio frequency synchronization signal that is received by the other one of the pair continuously until the respective oscillators are brought into alignment using known alignment techniques. One common technique uses a Phase Locked Loop (PLL).
For example, the base unit
10
of a cordless telephone system may transmit an RF signal representing a train of pulses at its own clock rate. The remote handset
20
receives the RF signal, and “tunes” its oscillator by aligning its own clock signal to the received pulse rate. A more detailed description of an exemplary clock synchronization via RF signal transmission may be found in U.S. Pat. No. 5,841,823 entitled “METHOD AND APPARATUS FOR EXTRACTING A CLOCK SIGNAL FROM A RECEIVED SIGNAL” issued on Nov. 24, 1998 to Tuijin, the entirety of which is hereby expressly incorporated by reference. A more detailed description of a conventional oscillator alignment method, e.g., a PLL method, may be found in U.S. Pat. No. 5,463,351 entitled “NESTED DIGITAL PHASE LOCK LOOP” issued on Oct. 31, 1995 to Marko et al., the entirety of which is hereby expressly incorporated by reference.
Unfortunately, the above described conventional frequency (or clock) synchronization techniques require that an RF communication channel be tied up for the purpose of the synchronization, thus making the channel unavailable for user communications at least for the duration of the synchronization process.
Because the conventional synchronization is performed by transmission of signals over an RF channel, the conventional techniques are prone to error due to an RF interference. Thus, when there are many sources of RF interference, e.g. other cordless telephones in close proximity, for example, in cordless telephone manufacturing facilities or busy offices, etc., it may be impossible or at least extremely difficult to achieve clock synchronization using the above described conventional technique.
Moreover, because the operation of the RF circuit
250
consumes a significant amount of the power from the battery
270
, repeated synchronization may drain the battery
270
, and thus shortens the duration that the remote handset
20
may remain portable before a recharge is required.
Furthermore, under rules established by the Federal Communications Commission (“FCC”), a cordless telephone must employ spectrum spreading techniques (frequency hopping) if the power level exceeds a threshold level, e.g., one milliwatt, to minimize interference with other devices using the frequency band. Thus, a high power (i.e., greater than 1 mW) cordless telephone may need to continue an ongoing synchronization effort in another frequency channel thereby adding delay, consuming more power and tying up more frequency channels.
An error during the frequency hopping in a high power cordless telephone as described above may result in the handset hopping to a frequency channel different from the frequency channel of the base unit. In this case, the handset and the base unit must (during a process often referred to as the “registration” process) establish a common frequency channel in order to communicate to each other. Without a common communication channel between the handset and the base unit, the above described conventional frequency synchronization technique cannot be used for the synchronization of the clocks of the handset and the base unit, which may be a required part of the registration process.
Thus, there is a need in the art for a synchro
Grundvig Jeffrey P.
McDowell Richard L.
Mooney Philip D.
Wu Jian
Agere Systems Inc.
Bollman William H.
Cong Le Thanh
Corsaro Nick
LandOfFree
Clock synchronization between wireless devices during... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Clock synchronization between wireless devices during..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Clock synchronization between wireless devices during... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3083500