Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-09-08
2002-06-04
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S422100, C455S439000, C455S513000
Reexamination Certificate
active
06400952
ABSTRACT:
CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. § 119 arising from an application entitled, METHOD AND APPARATUS FOR IDLE HANDOFF IN A CELLULAR YSTEM, earlier filed in the Korean Industrial Property Office on Sep. 9, 1998, and there duly assigned Ser. No. 1998-36976.
FIELD OF INVENTION
The current invention relates to a method for executing an idle handoff in a cellular system and an apparatus thereof. More particularly, a method for executing a hard handoff when a mobile telephone in an idle state moves between base stations having other frequency assignments (FA) in a conventional code division multiple access (CDMA) system and an apparatus thereof.
DESCRIPTION OF THE RELATED ART
In a cellular system, there are a plurality of cells within a service area, a plurality of base stations for controlling the cells, and a mobile switching center for controlling the base stations. When a mobile telephone moves between cells, it is possible to maintain the continuity of the transmission traffic by using a handoff function.
A handoff function permits a mobile telephone to continue transmission over a channel to a current base station as the mobile telephone moves into another base station's coverage region.
FIG. 1
depicts a conventional cellular system using the CDMA technology. As shown in
FIG. 1
, a conventional cellular system comprises a mobile telephone (MT)
40
for providing call service to user, a base transceiver station (BTS)
30
,
31
for providing service to the mobile telephone, a base station controller (BSC)
20
for controlling the BTS, and a mobile switching center (MSC)
10
for connecting between the BSC and a public switched telephone network (PSTN)
11
. The MSC
10
receives information on the user from a home location resistor (HLR)
12
and visitor location resistor (VLR)
13
.
During an idle state, a mobile telephone monitors the strength of the paging channels transmitted from different base stations.
A mobile telephone receives a message by using one of the paging channels when either receiving an incoming call or initializing an outgoing call. The mobile telephone monitors the various paging channels when moving from a coverage area of a current base station to another coverage area of a neighboring base station. This function for monitoring the paging channels is referred to as an idle handoff.
In a CDMA system, each of the channels transmitted from a base station has a same pseudo-random noise (PN) sequence offset value, which is called a pilot signal, so that the base station is identified by the PN signal. Accordingly, a mobile telephone identifies each of the base stations from the different pilot signals.
A mobile telephone monitors the pilot signal having the strongest intensity from all of the neighboring base stations. When the strength of pilot signal monitored from one of the neighboring base stations is stronger, over a predetermined value (for example, 3 dB), than the strength of the pilot signal of the current base station which is connected to the mobile telephone via the paging channel, the mobile telephone executes the idle handoff at the frequency of the monitored pilot signal and recognizes itself as entering into the new base station.
In a CDMA system, the number of frequency assignments (FA) assigned to a base station is increased as the demand for increased capacity grows.
When a mobile telephone moves from a first base station having a specific channel with a channel frequency into a neighboring base station, which does not have call service at the specific channel frequency of the first base station, or into a neighboring base station which does not have an available channel at the specified channel frequency, a hard handoff is executed. The hard handoff process first cuts off the channel connected between the mobile telephone and base station and makes a new channel connection within a short time in an attempt to prevent a user from recognizing that the hard handoff has occurred.
Although not providing call service at the specified channel frequency, the neighboring base station transmits a dummy pilot signal to the mobile telephone on the specified channel frequency in order to make it possible for the mobile telephone to receive pilot signals at its current specified frequency. Therefore, the mobile telephone can recognize that it has entered into a new coverage area of another base station as soon as it detects a dummy pilot signal.
The current base station, to which the mobile telephone is connected, transmits information on the neighboring base stations to the mobile telephone through a paging channel. This information is called an extended neighbor list.
If the mobile telephone detects a pilot signal from a new base station, and the detected new base station is included in an extended neighbor list, the mobile telephone executes the idle handoff to the new base station. If the new base station is not included in the list, the mobile telephone does not execute the idle handoff.
In
FIG. 1
, a base station
30
provides call service to a first cell
1
, which has two frequency assignments (1FA, 2FA), and is connected to a mobile telephone with a paging channel at the 2FA frequency. A neighboring base station
31
provides call service to a second cell
2
at a frequency assignment (1FA), and the neighboring base station
31
uses the frequency assignment at 2FA for a dummy pilot signal.
As the mobile telephone, which monitors the 2FA frequency paging channel, moves from cell
1
to cell
2
, the mobile telephone receives the 2FA dummy pilot signal from the base station
31
; this reception indicates that the mobile telephone has entered into the transmission area of cell
2
. The mobile telephone subsequently monitors the paging channel of the base station
31
with at the 2FA dummy pilot signal at first and thereafter monitors a paging channel of the base station
31
at the 1 FA frequency so that both an inter-cell handoff (from cell
1
to cell
2
), and an inter-frequency handoff (from frequency 2FA to 1 FA) can occur.
As described above, the prior art idle handoff method has some complexities owing to executing two step handoff process including (1) an inter-cell handoff and (2) an inter-frequency handoff within the new cell. Moreover, if a call from a base station or initiated by the mobile telephone user occurs before the inter-cell handoff and inter-frequency handoff are finished, it is impossible to set up the call properly.
SUMMARY OF THE INVENTION
It is an object of the current invention to provide an idle state handoff method and a handoff apparatus for a mobile station, which performs a handoff between base stations having different frequency assignments in a cellular system. If a mobile telephone, in an idle state, detects the pseudo pilot signal of the neighboring base stations, then the handoff is directly performed with the frequency provided by the neighboring base stations.
It is another object of the current invention to provide an idle state handoff method and a handoff apparatus for a mobile station in a cellular system, which continuously transmits information to the mobile telephones about the channels and the frequencies of the neighboring base stations.
According to a first preferred embodiment of the present invention, a method for an idle state handoff between base stations having different frequency assignments in a cellular system, the method comprising the steps of:
(a) transmitting information by the current base station to a mobile telephone regarding a frequency assignment of each of a plurality of neighboring base stations and a list of the neighboring base stations building up a channel with the mobile telephone;
(b) detecting a pilot signal from one of the plurality of neighboring base station by the mobile telephone;
(c) determining whether the pilot signal detected from the one of the neighboring base stations is included in the received list of the neighboring base stations;
(d) recognizing that
Kim Sang-tae
Lim Young-sik
Klauber & Jackson
Samsung Electronics Co,. Ltd.
Tran Congvan
Trost William
LandOfFree
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