Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-07-28
2002-12-24
Le, Thanh Cong (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S067700, C455S069000
Reexamination Certificate
active
06498932
ABSTRACT:
DESCRIPTION
1. Field of the Invention
The present invention relates to a method and an apparatus for determining the pathloss between a base transceiver station and a mobile station of a cellular mobile radio network such as the GSM network.
2. Background of the Invention
In recent years, the use of mobile telephones has become increasingly popular. One such mobile telephone system which is used in Europe and which is implemented as a fully digital cellular network is the GSM network set up according to the specifications of the CEPT committee “Groupe Speciale Mobile”.
The GSM network belongs to the group of systems operating on the basis of TDMA (Time Division Multiple Access). In systems using TDMA, data are transmitted using successive TDMA frames. In many cases, each of these frames consists of eight time slots. In each time slot, a data packet is sent in the form of a radio frequency burst having a finite duration and consisting of a set of modulated bits. The time slots are used for transmitting control channels and traffic channels. On the control channels, signaling and synchronization information between a base station (BS) and a number of mobile stations (MS) is exchanged, whereas, on the traffic channels (TCH), data and speech are transmitted. See FIG.
1
. One time slot of a traffic channel is assigned to each mobile station so that a base station may be simultaneously connected in a parallel fashion to a number of mobile stations using the same carrier frequency.
According to the GSM standard, the number of mobile stations simultaneously connectable to a single station amounts to eight. The data transfer rates are 9.6 kbit/s for data or 13 kbit/s for speech (TCH/F) as user rates. In addition, half-rate traffic channels (TCH/H) are available at 4.8 kbit/s for data which offer a doubled capacity, i.e. up to 16 mobile stations can be simultaneously connected to a base station using a single carrier frequency.
In order to establish a proper communication between a mobile station and a base station, general information concerning the base station is transmitted from the base station (BS) to the mobile station, i.e. in the downlink direction, using the so called Broadcast Control Channel (BCCH), as shown in FIG.
1
. More particularly, the base station transmits TDMA frames which include one Broadcast Control Channel and at least seven full-rate traffic channels or 14 half-rate traffic channels. For transmission of signaling information, 51 frames are combined into a single multi-frame, while for transmission of traffic information, a multi-frame consists of only 26 frames. Such a multi-frame is shown in FIG.
2
. The idle frame after the last of the 24 frames used for the traffic channels is not used. Furthermore, as shown in
FIG. 2
, a Slow Associated Control Channel (SACCH) is provided as one of the dedicated channels and is associated with a traffic channel. The Slow Associated Control Channel is used by the mobile station for transmitting different measurement results to the base station in the uplink direction. Any of a full-rate traffic channel, a half-rate traffic channel and a Standalone Dedicated Control Channel (SDCCH) is always allocated together with a Slow Associated Control Channel. On the other hand, the base station uses the Slow Associated Control Channel to transmit commands related to power control to the mobile station in the downlink direction.
FIG. 1
shows a block circuit diagram illustrating the structure of the mobile radio network including a mobile station in a single cell according to the GSM specification. The Broadcast Control Channel including the eight time slots is transmitted on the BCCH carrier in all time slots continuously with a constant power and at a standard frequency according to the GSM specification, usually with the highest allowable power. As will be described in detail below, a mobile station periodically measures the signal strength of the BCCH carrier in neighboring cells. In addition, the mobile station also determines the connection quality to the serving cell, i.e. to its own base station, by means of the bit error ratio. The results obtained are used e.g. in the handover process. A handover is a transfer of a mobile station from one channel to another channel of the same cell (intracell handover) or a transfer of the mobile station from one cell to another (neighboring) cell (intercell handover) during an ongoing call.
The power control to be implemented both in the base station as well as in the mobile station serves for minimizing channel interference and for saving energy in the mobile station so as to increase the battery life of the mobile telephone handset. The power control process always precedes a handover process. The transmitting power levels of the mobile stations can be controlled from the maximum power to as low as 20 mW in steps of 2 dB.
For handover purposes, the mobile station controller (MS) measures the signal level received from up to 32 neighboring base stations and transmits the signal levels of its serving cell as well as of those neighboring cells having the six strongest received signal levels and the signal quality value of the serving cell to its own base station. The measured signal level of the serving cell is also to be used for downlink power control, i.e. for power control of the carrier transmitted from the base station to the mobile station. This transmission of the measurement results is even performed during an ongoing call during which speech data are transmitted. The base station conveys the measurement results received from all mobile stations linked thereto to a base station controller (BSC),
FIG. 1
, which performs averaging and weighting on the measurement data obtained from the base station. In detail, as described above, the transmitted measurement results which are regularly updated comprise the received signal level (RXLEV) and the received signal quality (RXQUAL) of the serving cell of the mobile station as well as the received signal levels of the neighboring cells.
According to the GSM recommendation, the measurement results must be reported at least once a second to the base station. The transmitted value RXLEV of the received signal level is the average of the samples measured in a period of 480 ms containing four multi-frames. The measurement results are transmitted in another cycle of 480 ms also containing four multi-frames. On the other hand, the base station measures only the received signal level on the associated traffic channel in all time slots. The base station controller which analyses the received measurement results decides on the basis of the received data e.g. whether a handover is to be effected.
More particularly, a handover is requested in cases where the transmitting power of a mobile station cannot be further increased, where the measured values are larger or smaller than the threshold values for effecting a handover, or where the transmission could be continued with another cell having a lower pathloss than the serving cell.
From WO-96/21 987 and WO-96/21 998 originating from the applicants of the present invention, mobile radio systems are known in which a power control of the transmitter of the base station as well as of the mobile station is effected. However, since, in these two conventional systems, intercell handovers are prevented due to the fact that a subscriber is only allowed to move within his home cell, the signal strength of the BCCH carrier of neighboring stations is not measured. Therefore, the BCCH carrier is not continuously transmitted, i.e. not in all time slots of a frame, which results in that this system cannot be used for a proper mobile communication between a fixed base station and moving subscribers not restricted to a particular cell.
Furthermore, due to the radio link pathloss between transmitter and receiver the received field strength RXLEV decreases with increasing distance from the transmitter. The pathloss is a critical factor for mobile radio systems since a handover has to be effected if the measured field s
Posti Harri
Silventoinen Marko
Cong Le Thanh
Heller Ehrman White & McAuliffe LLP
Nguyen Thuan T.
Nokia Telecommunications Oy
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