Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-01-07
2001-10-23
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S437000, C455S440000, C455S441000, C370S331000, C370S335000, C370S337000
Reexamination Certificate
active
06308066
ABSTRACT:
FIELD OF THE INVENTION
The object of the invention is a method to determine the neighbour cell information in a cellular system where user information is carried in information frames transmitted by the base station of the current cell, and in which method information, for instance neighbour cell information, of the neighbour cell base station is received in order to synchronise to the base station of the neighbour cell or in order to perform level measurements. The method is preferably used to speed up or to enable determination of channel information during handover from one base station area to another.
BACKGROUND ART
It is important that a mobile cellular station can get information about the cells surrounding the cell corresponding to its current location, so that it can move to the next cell (MAHO, Mobile Assisted Handover). The information which must be determined in this context is i.a. the signal levels, signal strengths and the synchronisation information of the base stations of neighbour cells. For instance in the GSM system (Global System for Mobile communications) the synchronisation information is the frequency correction channel (FCCH) and the synchronisation channel (SCH) of the neighbour cell. The object is to acquire the information without causing interference in the user information during a call.
In continuous transmission systems (CDMA, Code Division Multiple Access; FDMA, Frequency Division Multiple Access) and in time division systems (TDMA, Time Division Multiple Access), when all time slots are used for the communication of information, a problem is the second receiver required for the determination. In a TDMA system, such as the GSM system, where one or more idle frames are reserved for the determination of neighbour cell information, the idle time is used for reception. There is a problem in that the idle time is barely sufficient for the reception. Due to this it is not always possible to obtain the FCCH and SCH information during the idle time. On the average, this information is obtained only after several unsuccessful reception during the idle frames, when the location in time of the FCCH and the SCH is unknown, or it is necessary to wait over several idle frames, even when the location of the FCCH and the SCH is known.
Prior art is illustrated with the aid of FIG.
1
. There the frames
101
,
103
and
104
are normal TDMA information frames of the GSM system. The frame
102
is an idle frame, during which neighbour cell information is received
105
in a well known way. The time slots
0
,
1
,
2
, . . .
7
of the information frames are used in the following way: the time slot
0
transmits received information RX of the downlink transmission direction: the time slot
3
transmits the transmitted information TX of the uplink transmission direction, and neighbour cell signal level measurements are made during the time slots
5
and
6
at a monitoring moment M, which is not tied to the time slots. The other time slots are used i.a. for changing the synthesiser frequency. RX and TX are information signals, which can be speech or data information. The so called discontinuous transmission method (DTX) is not used during the period shown in the figure.
When the SCH time slot appears in the determination period
105
it is read during the idle frame
102
. However, as mentioned above, this happens very seldom, and in this way the time slot is not usually found at the first attempt. Several systematically unsuccessful attempts are required in order to success, if the FCCH and SCH locations in time are unknown, or a delay over several idle frames is required, even when the FCCH and SCH locations are known.
SUMMARY OF THE INVENTION
The object of the invention is to create a solution for the determination of neighbour cell information, with which the above mentioned prior art problems can be avoided.
The characteristic features of the method according to the invention are presented in the characterizing part of claim
1
. Preferred embodiments of the invention are presented in the characterizing parts of claims
2
to
7
. The mobile station according to the invention is characterised by the features presented in the characterizing part of claim
11
.
In the method according to the invention the reception/transmission of user information is preferably interrupted during reception of the neighbour cell information, which can be i.a. the signal level, the base station identity code (BSIC). Then said information can be received sufficiently often in an urgent situation, during a rapid handover from one cell to another, that is, also when no idle frame can be favourably received. The reception of neighbour cell information is not made simultaneously with reception/transmission of user information, and thus only one receiver is required. The invention makes it possible that in future systems the idle frame is not required at all. Also in delay nonsensitive packet reservation multiple access systems it is possible to delay the transmission during measurements.
The advantage of the method according to the invention is that the reception of neighbour cell information is made faster and more efficient when it uses time from the communication channel. Communication channel means the transmission path formed by the RX and TX time slots in the information frame. A channel encoding may reduce decreasing of the quality of the actual speech and data. The length of the interruption in reception is short compared to the interleaving time. The invention is preferable particularly in data services having long interleaving depths, for instance
19
bursts in GSM. Further the packet retransmission (automatic repeat request, ARQ) in GSM data services will correct the errors of the transmission path. Thus it is usually possible to correct all transmission errors regarding data communication. The reception moment can be random or deterministic, so that the method utilises as much as possible the active periods of the discontinuous transmission, in other words those periods during which no active speech is transmitted during a call. When an active period of the discontinuous transmission has begun, it is possible to determine with a rather high reliability that the speech will not recommence at once, because the information reception time is rather short compared to human reactions. Said information can then be received when a period just has begun, and still one can be almost sure not to interfere with the speech. During about 50% of the time the speech service will need no transmission.
The interval between repeated reception of neighbour cell information can be controlled on the basis of e.g. the signal quality, such as strength and correctness. When the signal quality is high there is a low probability of cell handover, and the reception can be reduced. When the signal quality is low there is a high probability of cell handover, and the reception of neighbour cell information is increased. Thus it is possible to minimise interruptions in the reception of the information signal.
A cell handover has a high probability i.a. when there is a long distance between the mobile station and the base station or when the attenuation on the radio path from the base station is high, when the signal strength from neighbour base stations starts to increase compared to the current base station, or when the mobile station moves at a high speed.
Preferably the reception of neighbour cell information can also be controlled so that information from different neighbour cells is received at different repetition rates. Further the neighbour cell information can be received at different repetition rates for different services and/or operating modes of the system.
The invention is preferably applied in connection with the discontinuous transmission (DTX) method of the GSM system. In this method transmission is interrupted when the voice activity detection (VAD) does not detect any speech to be transmitted. Then a so called SID frame (SIlence Descriptor) will be transmitted, which indicates the n
Ranta Jukka
Ranta Pekka
Nokia Mobile Phones Ltd.
Perman & Green LLP
Smith Sheila
Trost William
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