Multiplex communications – Communication over free space – Signaling for performing battery saving
Reexamination Certificate
1999-08-17
2003-06-10
Vuong, Quochien (Department: 2681)
Multiplex communications
Communication over free space
Signaling for performing battery saving
C370S342000, C370S441000, C455S343200, C455S574000
Reexamination Certificate
active
06577608
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to CDMA communication systems, and in particular, to a device and method for controlling slotted mode communication.
2. Description of the Related Art
In a code division multiple access (CDMA) communication system, a forward link includes a pilot channels, a sync channel, a paging channel and a traffic channel. By using these channels, a base station and a plurality of mobile stations acquire sync of PN spreading codes and establish call channels.
Upon power on, the mobile station acquires a pilot signal, having the highest power, out of plurality of pilot signals received over the forward channels, and demodulates a sync channel message to acquire a reference time. Once a reference time is established the mobile station will thereafter perform demodulation. After receipt of the sync channel message, the mobile station can operate in a slotted mode wherein the mobile station periodically monitors a paging channel to check whether a paging message has been transmitted from a base station. Upon receipt of a paging message from a base station, the mobile station makes a transition to an active state where the mobile station can provide the call service using a traffic channel. However, if the mobile station does not receive the paging message, the mobile station enters a sleep mode where it cuts off a power supply voltage being provided to demodulation-related hardware, such as an RF (Radio Frequency)/analog part, searcher, finger and combiner, to disable the demodulation-related hardware.
Upon entering the sleep mode, the mobile station checks whether a paging message for it has been received from a base station, as stated above. The base station can transmit a paging message to the mobile station in either a slotted mode or a non-slotted mode. In either mode the message is transmitted in a unit of superframe having a length of 80 ms, which is called a slot. The 80 ms superframe includes information about a paged mobile station, information about the base station and a list of neighbor sectors of the mobile station.
To determine whether a paging message for a specified mobile station has been received or not, the mobile station should monitor paging channel slots transmitted from the base station. If the mobile station does not know when the paging message for it will be received, the mobile station should monitor all the slots that the base station transmits. Such a paging mode is called a non-slotted mode in which a time slot, at which a paging message for a specific mobile station will be transmitted, is not specified, requiring that the mobile station s monitor all the slots.
However, when a paging message for a specific mobile station is transmitted only at a predetermined specific slot, the mobile station can monitor only the corresponding specific slot and, instead of demodulating a paging channel message for other time slots, and cut off a power supply voltage being provided to the CDMA demodulation-related hardware to enter the sleep mode. As stated above, in the slotted mode, the mobile station can operate in the sleep mode for the period of time that the receiving stage is disabled.
FIG. 1
illustrates a message slot assigned to a specific mobile station transmitted in one cycle from a base station for a communication system operating in the slotted mode, and a monitoring time for which the mobile station monitors the slot assigned to itself.
Referring to
FIG. 1
, a base station transmits a paging channel message for a specified mobile station at a specific slot for the paging channel (
11
). The specified mobile station then provides a power supply voltage to an RF/analog circuit beginning at a time preceding the start time of the specific slot for the paging channel (
12
), and enables a searcher (
13
). After search of the base station using the searcher, the mobile station assigns a finger to receive the paging channel message (
14
).
FIG. 2
illustrates a method for receiving the above-stated paging channel message.
FIG. 2
shows a case where a sixth slot is assigned to the mobile station and a slot cycle is 16 slots (i.e., 1.28 seconds). Further, for a duration A, the mobile station is awaken from the sleep mode several tens of milliseconds before the sixth paging slot, for demodulation of the paging slot, provides power to the RF/analog circuit, searches base station pilot signals, and assigns multipath signals for an acquired pilot signal to a finger.
In an existing IS-95 system, a base station can operate either in the slotted mode or the non-slotted mode, but it is a system designer's option whether to support the slotted mode or the non-slotted mode. However, when the base station operates in the slotted mode, the mobile station can increase the standby time by demodulating the paging channel at the pre-assigned time slot, taking into consideration the limited batter capacity of the mobile station. That is, the mobile station monitors only a slot at which a paging message for it is to be received and, for the other time slots, cuts off the power supply voltage of the RF/analog circuit and the demodulation-related module thereof, thereby to increase the standby time.
As previously stated,
FIGS. 1 and 2
illustrate a paging slot transmission time of a base station and an operating duration of a mobile station in an existing IS-95 system, wherein the base station and the mobile station both operate in the slotted mode. For demodulation of a paging slot assigned to it, the mobile station is awaken from the sleep mode several tens of milliseconds before the pre-specified paging slot, to search a base station from which the paging slot is to be transmitted.
The RF/analog circuit of the mobile station is awaken from the sleep mode to operate in a stable state (
12
). Thereafter, the searcher of the mobile station is awaken from the sleep mode to detect correlation and energy between a received signal and a PN (Pseudo Noise) spreading code of the mobile station so as to detect a pilot signal received with sufficiently high energy (
13
). The mobile station repeats the steps of energy detection and comparison of the detected energy with a threshold for those sectors registered in an active sector list and a neighbor sector list until a single pilot signal is acquired which exceeds the threshold in energy. Upon failure to acquire a pilot signal having sufficiently high energy, the mobile station cannot normally demodulate the paging slot. However, upon receipt of a pilot signal having a sufficiently high energy, the mobile station assigns the multipath components of the acquired pilot signal to a finger to attempt demodulation of the paging slot (
14
). Subsequent to a paging message being detected through demodulation, the mobile station then makes a transition to a traffic channel state to establish a communication link. However, when a paging message is not detected, the mobile station enters the sleep mode again till the next paging slot to save power.
Here, the mobile station determines the period between the slots at which a paging message for a specific mobile station is to be transmitted and notifies the determined period to the base station through a registration procedure. The paging slots are assigned with unique numbers from 0 to 2047, and a slot to be first monitored is determined by a Hash function unique to each mobile station.
A mobile station may alternately determine a period between slots by changing a slot cycle index (SCI) according to a reacquisition algorithm for a pilot signal. The relationship between an actual inter-slot period and the SCI is defined as
Slot Period=16*2SCI [slots], where SCI=0,1,2,3,4,5,6 and 7.
As illustrated in
FIG. 2
, when the sixth slot is to be first monitored and SCI=0 (i.e., the period between slots is 16), the mobile station enters the sleep mode for the slot time from the sixth slot to the twenty-second slot to save the power.
In enabling the mobile station to operate in the slotte
Ahn Jae-Min
Kim Young Ky
Lee Jeong-Gu
Moon Hi-Chan
Dilworth & Barrese LLP
Samsung Electronics Co,. Ltd.
Vuong Quochien
LandOfFree
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