Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-10-15
2002-03-05
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S347000, C455S452200, C455S509000, C455S524000
Reexamination Certificate
active
06353605
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to mobile networks, and particularly to transmission to be implemented in their fixed network part. A fixed network in this context denotes that part of a mobile network which extends in the uplink direction from the base stations. Even though a fixed network is referred to in this context, it is to be noted that this fixed network or part thereof may be implemented with radio links, for example.
BACKGROUND OF THE INVENTION
To illustrate the typical architecture of a mobile network,
FIG. 1
shows the structure of the known GSM mobile communications system (Global System for Mobile Communications), using abbreviations known from the context of the GSM system. The system comprises several open interfaces. The transactions relating to crossing of interfaces have been defined in the standards, in which context the operations to be carried out between the interfaces have also been largely defined. The network subsystem (NSS) of the GSM system comprises a mobile services switching centre (MSC) through whose system interface the mobile network is connected to other networks, such as a public switched telephone network (PSTN), an integrated services digital network (ISDN), other mobile networks (Public Land Mobile Networks PLMN), and packet switched public data networks (PSPDN) and circuit switched public data networks (CSPDN). The network subsystem is connected across the A interface to a base station subsystem (BSS) comprising base station controllers (BSC), each controlling the base transceiver stations (BTS) connected to them. The interface between the base station controller and the base stations connected thereto is the Abis interface. The base stations, on the other hand, are in radio communication with mobile stations across the radio interface.
The GSM network is adapted to other networks by means of the interworking function (IWF) of the mobile services switching centre. On the other hand, the mobile services switching centre is connected to the base station controllers with PCM trunk lines crossing the A interface. The tasks of the mobile services switching centre include call control, control of the base station system, handling of charging and statistical data, and signalling in the direction of the A interface and the system interface.
The tasks of the base station controller include, inter alia, the selection of the radio channel between the controller and a mobile station MS. For selecting the channel, the base station controller must have information on the radio channels and the interference levels on the idle channels. The base station controller performs mapping from the radio channel onto the PCM time slot of the link between the base station and the base station controller (i.e., onto a channel of the link). The establishment of the connection will be described in closer detail in the following.
The base station controller BSC schematically shown in
FIG. 2
comprises trunk interfaces
21
and
22
through which the BSC is connected to the mobile services switching centre across the A interface on the one hand and to the base stations across the Abis interface on the other hand. The transcoder and rate adaptation unit TRAU forms part of the base station system and may be incorporated into the base station controller or the mobile services switching centre. For this reason, the unit is shown in broken line in FIG.
2
. The transcoders convert speech from a digital format to another, for example convert the 64 kbit/s PCM signals arriving from the mobile services switching centre across the A interface into 13 kbit/s coded speech signals to be conveyed to the base station, and vice versa. Data rate adaptation is performed between the speed 64 kbit/s and the speed 3.6, 6, or 12 kbit/s. In a data application, the data does not pass through the transcoder.
The base station controller configures, allocates and controls the downlink circuits. It also controls the switching circuits of the base station via a PCM signalling link, thus enabling effective utilization of PCM time slots. In other words, a branching unit at a base station, which is controlled by the base station controller, connects the transmitter/receivers to PCM links. Said branching unit transfers the content of a PCM time slot to the transmitter (or forwards it to the other base stations if the base stations are chained) and adds the content of the receive time slot to the PCM time slot in the reverse transmission direction. Hence, the base station controller establishes and releases the connections for the mobile station. Multiplexing of the connections from the base stations to the PCM link(s) crossing the A interface is carried out in switching matrix
23
, as is the reverse operation.
The layer
1
physical interface between the base station BTS and the base station controller BSC is in this example a 2048 kbit/s PCM line, i.e. comprises 32 64 kbit/s time slots (=2048 kbit/s). The base stations are fully under the control of the base station controller. The base stations mainly comprise transmitter/receivers providing a radio interface towards the mobile station. Four full-rate traffic channels arriving via the radio interface can be multi-plexed into one 64 kbit/s PCM channel between the base station controller and the base station, and hence the speed of one speech/data channel over this link is 16 kbit/s. Hence, one 64 kbit/s PCM link may transfer four speech/data connections.
FIG. 1
also shows the transfer rates used in the GSM system. The mobile station MS transmits speech data across the radio interface on the radio channel for example at the standard rate 13 kbit/s. The base station receives the data of the traffic channel and switches it to the 64 kbit/s time slot of the PCM link. Three other traffic channels of the same carrier are also located in the same time slot (i.e., channel), and hence the transfer rate per connection is 16 kbit/s, as stated previously. The transcoder/rate adaptation unit TRAU converts the encoded digital information to the rate 64 kbit/s, and at this rate the data is transferred to the mobile services switching centre. If the transcoder/rate adaptation unit is incorporated into the mobile services switching centre, maximum advantage is gained from compressed speech in data transmission.
In mobile networks of the above kind, the coverage area of the base stations has conventionally been wide, and thus there have been no great variations in the number of users roaming in the area of an individual base station, but the average traffic on the base station has been relatively uniform. In other words, the radio path has been concentrative (less channels in the radio path than users in the base station area). However, with the increase in the number of users, there has been a shift to using base stations having ever smaller coverage areas. With reduced cell size, the relative traffic fluctuations at the base station gain in magnitude. While the base station network continues to increase in density, it has become a problem how new base stations can be added to the network with maximum rapidity, flexibility and economy (with maximum utilization of the existing transmission capacity). This problem will be described in detail in the following in light of the current technology and the requirements to be set on the network.
Present-day mobile networks as a rule have fixed channels from the base stations to the base station controller, and such channels have been allocated in accordance with the overall radio path capacity of the base station. For example in TDMA-type (Time Division Multiple Access) radio systems, the time slot of the radio path is directly bound to the time slot of the transmission network (or part thereof. The transmission capacity of the fixed network is additionally needed for signalling between the base station and the base station controller and for network management.
The use of permanently allocated transmission channels (time slots) between the base station and the base station controller is
Jaamies Juhani
Rautanen Esko T.
Vaitovirta Hannu
Altera Law Group
Hsu Alpus H.
Nokia Telecommunications Oy
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