Adaptive radio system

Details Adaptive radio system Adaptive radio system

2000-02-17

2002-08-06

Hunter, Daniel (Department: 2749)

Telecommunications

Transmitter and receiver at same station

Radiotelephone equipment detail

C455S073000, C455S277100, C455S277200, C455S279100

Reexamination Certificate

active

06430421

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to an adaptive radio system and a method for assigning transmitting and receiving branches in a radio system. The radio system comprises a plurality of mobile stations and at least one base station. In the radio system, at least the base station comprises a plurality of independent transmitting and receiving branches to transfer signals between the base station and the mobile stations.
BACKGROUND OF THE INVENTION
FIG. 1
in the accompanying drawing shows a simplified block diagram of the UMTS (Universal Mobile Telecommunication System). A mobile station (MS) communicates over the radio path with a base transceiver station (BTS), in the case of
FIG. 1
, with BTS
1
. The base station sub-system (BSS) consists of a base station controller (BSC) and base stations (BTS) under its control. A mobile services switching centre (MSC) usually controls a plurality of base station controllers BSC. The MSC communicates with other MSCs, and via a gateway mobile services switching centre (GMSC), the UMTS network is connected to other networks such as the public switched telephone network PSTN, another mobile communications network PLMN or an ISDN network ISDN. The mobile communications system shown by the figure is e.g. the pan-European GSM system or the UMTS system (Universal Mobile Telecommunication System). The GSM system is implemented with the TDMA technology (Time Division Multiple Access) and the UMTS system is proposed to be implemented with the time division multiple access technology (TDMA) or with the code division multiple access technology (CDMA) or a combination of these two, i.e. a so-called hybrid system.
In digital radio systems implemented with the TDMA technique, such as the GSM or the UMTS system, a group of mobile stations MS may, according to the time-division principle, use the same carrier frequency i.e. radio channel for communication with the base station BTS. The carrier is divided into successive frames that are further divided into timeslots, e.g. 8, 16 or 64 timeslots, that are allocated to users as required. From the network point of view, one carrier wave can consequently be used to establish e.g. 8, 16 or 64 traffic channels. In e.g. the GSM system, the channel width is 200 kHz and in the UMTS system 1.6 MHz, according to a proposal.
Code division multiple access CDMA radio systems are based on spread spectrum communication. The data signal to be transmitted is multiplied by a special hash code assigned to the subscriber, whereby the transmission spreads out onto the broadband radio channel, which is e.g. 1.25; 6.4 or 20 MHz. This means that the same broadband radio channel may be used by several users for simultaneous transmission of CDMA signals processed with different hash codes. Therefore, the unique hash code of each subscriber in CDMA systems produces the traffic channel of the system in the same sense as the timeslot does in TDMA systems. At the receiving end, the CDMA signal is despread by the subscriber's hash code, whereby a narrowband data signal is obtained. At the receiver, the other subscribers' broadband signals represent noise to the desired signal.
In radio systems, it is of prior art to use so-called SDMA technology (Space Division Multiple Access) employing adaptive antennas, in which subscribers can be distinguished on the basis of their geographical direction as seen from the base station, when e.g. antenna lobes are adjusted at the base station to desired directions according to the location of the mobile stations. Employing SDMA technology thus improves the signal to interference ratio C/I or the signal to noise ratio S/N of the radio connection between the base station BTS and the mobile station MS whereby the overall capacity of the system increases. SDMA technology further improves the frequency efficiency of the network as the transmission is beamed to a narrow geographical area, which means that the same frequency can be reused for another connection in another direction, possibly even at the same base station. Due to the antenna lobe aimed at the subscriber, the disturbing effects of multipath propagation on the radio link are reduced.
The SDMA technology is based on using a number of parallel receivers and transmitters on the same radio connection, e.g. for a base station transmission and reception, and signal processing that generally is performed digitally. The improvement in the signal to interference ratio and/or signal to noise ratio is usually the better the larger number of parallel transmitting and receiving branches are in use. So-called adaptive antennas, i.e. antennas having variable directional pattern, and processing of received signals are used to monitor mobile stations that communicate with the base station via a radio connection, for example by beaming the base station antenna lobe to a narrow geographical area with some prior art method, for example as regards CDMA systems, the antenna lobe can be beamed to the direction or directions from which the best signal components of the connection in question are received.
An adaptive antenna is comprised of an antenna array consisting of several antenna elements, the directional pattern of the antenna array being dynamically changed by phasing the signals of the antenna elements. Such an antenna array may consist of omnidirectional or directional antenna elements that may be arranged e.g. in a linear or planar manner. Signals arriving from outside the main lobe of an adaptive directional antenna are attenuated in proportion determined by the antenna directional pattern in relation to the signals received from main lobe. When adaptive antenna are utilized, the selected mobile station MS may transmit its signal at lower transmit power than normally due to the better antenna gain and signal processing at reception. The transmit and receive antennas may be separate, or the transmission and reception may be arranged to be carried out via a common antenna by separating the receiving and transmitting circuit from one another with a duplex filter.
Adaptive antennas contribute to lower level of interference due to the narrow antenna lobe as interference from other subscribers is reduced and interference caused to other subscribers is lower. Simultaneously, the coverage of the base station is increased towards the antenna main lobe. The antenna signal transmitted by a single mobile station MS can also be received via more than one antenna lobe, in which case signal components caused by e.g. multipath propagation can be combined or the signal from the mobile station, received at different antennas, can be processed in other ways, e.g. by weighting the received signals differently so that the signal is amplified in comparison to other signals that have been received. The directional pattern of an adaptive antenna can thus be changed by receiving a signal via more than one fixedly directed antenna lobes and by suitably weighting the signals thus received.
FIGS. 2
a
and
2
b
illustrate a block diagram for receiving and transmitting section of a base station employing SDMA technology. In the example of the figures, four parallel receiving and transmitting branches are tuned to the same channel CH
1
and frequency f
1
. In the SDMA implementation, it is possible to set up as many parallel transmitting and receiving branches as the particular system requires. By increasing the number of transmitting and receiving branches set up in parallel, the antenna lobe can be directed to a narrower geographical area and at the same time to extend the coverage area further from the base station.
FIG. 2
a
illustrates the structure of a base station consisting of four parallel receiving branches. In the block diagram of the receiving section in
FIG. 2
a
, all four receiving branches have a common signal processing unit
201
in which the signals are processed as desired so that just one processed signal CH
1
is conveyed from the signal processing unit
201
to other parts of the base station. The structure of one of the receiving branche

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