Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2000-06-01
2004-10-12
Vanderpuye, Kenneth (Department: 2661)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S328000
Reexamination Certificate
active
06804212
ABSTRACT:
The invention relates to a method and arrangement for establishing a connection between a base station and mobile station. The invention is especially applicable to digital TDMA (Time Division Multiple Access) and CDMA (Code Division Multiple Access) cellular systems which utilize extended cell operating ranges. One such TDMA cellular system is the GSM (Global System for Mobile telecommunications) which uses the 450-MHz frequency band.
In its active state a terminal of a cellular radio system always attempts to select a coverage area, or cell, of a given base station to camp on. Conventionally, the selection of the cell has been based on measuring the strength of a received radio signal either at the terminal or at the base station. In the GSM, for example, each base station transmits a signal on a so-called Broadcast Control Channel (BCCH) which is given different frequencies for adjacent base stations, and the terminals measure the strengths of the BCCH signals received, and decide on the basis of the measured strengths which cell is the most advantageous in regard to the radio link quality. The base stations also transmit to the terminals information about the BCCH frequencies used in the neighboring cells so that the terminals know what frequencies they have to listen to in order to find the BCCH transmissions of the neighboring cells. In each cell the BCCH transmission also includes information about how the terminals can make so-called random access requests in that particular cell in order to establish connections for calls. The base stations use the System Information message, for example, to transmit the information.
In TDMA systems, information is usually transmitted in time slots of a TDMA frame at a certain operating frequency. In order for the bursts transmitted by a mobile station to be timed correctly for the right time slot the transmission moment of the mobile station must be determined also on the basis of the distance between the mobile station and base station in such a manner that the propagation delay of the burst provides for a timing advance for the mobile station's transmission time. For example, in the GSM the maximum timing advance is 233 &mgr;s, corresponding to a 35-km propagation delay. The mobile station's timing advance parameter may take values from 0 to 63, where 63 corresponds to the maximum timing advance 233 &mgr;s.
FIG. 1
shows in the form of a flow diagram a procedure according to the GSM for establishing a connection with a base station. The procedure may start e.g. when a call directed to a given mobile station arrives at the switching center MSC of the traffic area in which the called subscriber is located at that moment. The switching center transmits a paging request to one or more base stations in that particular traffic area, which base stations are those to whose coverage areas the called subscriber is registered. The base stations transmit a paging message onto the radio path through their paging channels PCH, phase
10
. A mobile station that notices a subscriber identifier belonging to it on the paging channel that it monitors will transmit a CHANNEL REQUEST message to the base station,
12
. If the user of the mobile station wants to establish a connection, it is initiated by transmitting to the base station a corresponding CHANNEL REQUEST message,
12
. This message is transmitted in a random access type burst on a RACH channel. Having received the CHANNEL REQUEST message the base station determines a timing advance value for the mobile station and transmits it and other information concerning the connection to the mobile station in an IMMEDIATE ASSIGNMENT message,
14
. The mobile station then starts using the traffic channel and timing advance value indicated by the base station,
16
.
FIG. 2
is a flow diagram depicting a procedure according to the GSM for making handover between the serving base stations. First, the current serving base station sends a HANDOVER COMMAND message to the mobile station, phase
20
. This message indicates the new serving base station. Then the mobile station sends to the new base station HANDOVER ACCESS bursts, phase
22
. These random access type bursts are transmitted on a Dedicated Control CHannel (DCCH). Having received the HANDOVER ACCESS message the new base station determines a timing advance value for the mobile station and transmits it and other related information to the mobile station in a PHYSICAL INFORMATION message, phase
24
. If the handover is synchronous, however, the mobile station already knows the timing advance. The mobile station then starts using the traffic channel and timing advance value indicated by the base station, phase
26
. Finally, the mobile station transmits to the new serving base station a HANDOVER COMPLETE message, phase
28
, whereafter the old base station no longer serves the mobile station.
In some cases it has become necessary in TDMA systems to introduce so-called extended cells in which the operating range could be greater than the normal range 35 km (for example). One reason for this need is the introduction of lower frequencies. For instance, a 450-MHz GSM system could operate at a distance of up to 120 km from base station as far as the allowable transmission power is concerned because signal attenuation in relation to the distance is smaller than at higher operating frequencies. However, problems are then caused by the fact that the maximum timing advance is not sufficient to compensate for the propagation delay of the signal.
FIG. 3
shows two base stations BTS
1
301
and BTS
2
311
of a cellular system according to the prior art and their operating ranges. Cells
302
and
312
of the base stations are conventional cells in which the maximum operating range is 30 km from the base station. At that distance the timing advance is 54. Cells
303
and
313
of the base stations are conventional cells, too, with a maximum operating range of 35 km from the base station, in which case the timing advance is 63. As said, this timing advance is the maximum timing advance in a conventional GSM system. Cells
304
and
314
are extended cells in which the maximum operating range from the base station is 120 km. The maximum timing advance parameter required in this case is 215.
FIG. 3
also shows a mobile station MS
320
. When the mobile station is moving in the direction of the arrow it is first connected with base station BTS
1
and, after a while, it has to make handover from BTS
1
to BTS
2
. If the system allows for timing advance parameters greater than 63, the problem is how to transmit an access request from the mobile station to base station in such a manner that the base station is able to receive it. Normally the mobile station sends the random access request with a timing advance parameter value 0. If, however, the correct timing advance parameter value were greater than 63, the random access request would not arrive at the base station within the time window reserved for the message.
FIG. 4
illustrates a situation in which a mobile station becomes connected to a base station/makes handover serving base stations. The figure shows a TDMA frame in a possible current cell
1
,
410
, comprising time slots
411
to
418
. Time slot
411
contains a control channel CCCH. The potential traffic channel of the mobile station MS is located in time slot
415
in this cell. Let us consider a situation in which the mobile station establishes a connection with cell
2
,
420
. In this case the extended cell comprises TDMA time slots
421
to
428
. The mobile station transmits a CHANNEL REQUEST or HANDOVER ACCESS burst to the control channel of cell
2
. This is depicted by arrow
431
. When the mobile station after that learns the correct timing advance of cell
2
, it can transmit on the traffic channel TCH allotted to it, located in this case in time slot
425
. This is depicted by arrow
432
.
In the case of an extended cell, the second time slot
422
of the TDMA frame cannot be used as a traffic channel because the HANDOVER ACCESS burst
Jokinen Harri
Vallstrom Jari
Vihriälä Jaakko
Nokia Mobile Phones Ltd.
Vanderpuye Kenneth
LandOfFree
Method and arrangement for establishing a connection between... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and arrangement for establishing a connection between..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and arrangement for establishing a connection between... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3278041