Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1999-06-24
2002-12-03
Urban, Edward F. (Department: 2685)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S245100, C455S069000
Reexamination Certificate
active
06490461
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to wireless communication systems, and more particularly, to a method and apparatus for efficiently controlling power levels in a mobile radio.
BACKGROUND AND SUMMARY OF THE INVENTION
In a typical cellular radio system, a geographical area is divided into cell areas served by base stations which are connected to a radio network. Each user (mobile subscriber) in the cellular radio system is provided with a portable, pocket, hand-held, or car mounted mobile station which communicates voice and/or data with the mobile network. Each base station includes a plurality of channel units including a transmitter, a receiver, and a controller and may be equipped an omni-directional antenna for transmitting equally in all directions or with directional antennas, each directional antenna serving a particular sector cell. Each mobile station also includes a transmitter, a receiver, a controller, and a user interface and is identified by a specific mobile station identifier. Each mobile subscriber is identified by another identifier, e.g., an international mobile subscription number (IMSI).
The present invention is described in the non-limiting, example context of a universal mobile telecommunications (UMTS)
10
shown in
FIG. 1. A
representative, connection-oriented, external core network, shown as a cloud
12
may be for example the Public Switched Telephone Network (PSTN) and/or the Integrated Services Digital Network (ISDN). A representative, connectionless-oriented external core network shown as a cloud
14
, may be for example the Internet. Both core networks are coupled to corresponding service nodes
16
. The PSTN/IDSN connection-oriented network
12
is connected to a connection-oriented service node shown as a Mobile Switching Center (MSC) node
18
that provides circuit-switched services. In the existing GSM model, the MSC
18
is connected over an interface A to a Base Station Subsystem (BSS)
22
which in turn is connected to radio base station
23
over interface A′. The Internet connectionless-oriented network
14
is connected to a General Packet Radio Service (GPRS) node
20
tailored to provide packet-switched type services sometimes referred to as the serving GPRS service node (SGSN). Each of the core network service nodes
18
and
20
connects to a UMTS Terrestrial Radio Access Network (UTRAN)
24
over a radio access network (RAN) interface. UTRAN
24
includes one or more radio network controllers
26
. Each RNC
26
is connected to a plurality of base stations (BS)
28
and to any other RNCs in the UTRAN
24
.
Preferably, radio access is based upon wideband, Code Division Multiple Access (WCDMA) with individual radio channels allocated using CDMA spreading codes. Of course, other access methods may be employed. WCDMA provides wide bandwidth for multimedia services and other high transmission rate demands as well as robust features like diversity handoff and RAKE receivers to ensure high quality.
The mobile stations
30
use transmission codes so base station
28
can identify transmissions from that particular MS
30
. In the current WCDMA standard, codes are supposed to be allocated as follows for the dedicated channels:
a) the uplink and downlink transmission is using channelization codes, and on top of that a scrambling code;
b) the channelization code determines e.g., the spreading factor, and the spreading factor determines the maximum bitrate;
c) mobiles in the same cell using the same frequency and the same spreading factor use different channelizations codes for the downlink channels but the same scrambling code; and
d) mobiles in other cells use the same channelization codes but different scrambling codes.
The scrambling codes secure the integrity, between downlink transmissions using the same channelization code but in different cells. The scrambling code used in uplink secure the integrity between uplink transmissions from different mobile stations in the same or in other cell.
Thus, the MS gets its own scrambling code while the BS transmission to a specific mobile on a dedicated channel will use a common scrambling code but a unique channelization code. The MS have the ability to combine a downlink transmission using a different scrambling codes and different channelization codes (one limitation today is that the spreading factor of the channelization codes must be the same from all cells).
The radio network controller
26
and base station
28
shown in
FIG. 2
are radio network nodes that each include a corresponding data processing and control unit
32
and
33
for performing numerous radio and data processing operations required to conduct communications between the RNC
26
and the mobile stations
30
. Part of the equipment controlled by the base station data processing and control unit
33
includes plural radio transceivers
34
connected to one or more antennas
35
. The mobile station
30
shown in
FIG. 3
also includes a data processing and control unit
36
for controlling the various operations required by the mobile station. The mobile's data processing and control unit
36
provides control signals as well as data to a radio transceiver
37
connected to an antenna
38
.
The present invention may be employed in the context of the example mobile communications system
10
shown in
FIG. 1
in which the radio network controllers
26
and base stations
28
form a radio access network between a core network node (like the MSC
16
) and the mobile stations
30
.
It is important for the mobile stations
30
to maintain appropriate power levels when communicating with the base station
28
in order to prevent one mobile station from overwhelming communications from other mobile stations in the transmission area. Because the power level for mobile stations is a critical parameter for maintaining good communication quality within a particular cell, is valuable for power control to be performed as often as possible. Ideally, each mobile station is continually monitored to ensure that its power levels are high enough to provide good transmission quality yet no higher than necessary to provide that transmission quality and no higher than will create unreasonable interference with other mobile station communications. The invention also applies to maintenance of proper power level in the base station transmission.
In prior systems, very fast power control of mobile station communications was typically performed by the network in
FIG. 1
using signal-to-interference (E
b
/I
o
) measurements. The signal-to-interference measurements were typically performed over a couple of pilot symbols contained in each slot. The measured E
b
/I
o
for the uplink slot is compared to a target and Transmission Power Control (“TPC”) bits in the next downlink slot are set to order a one step increase or decrease of the mobile station power.
Although signal-to-interference measurements can be made very rapidly, and therefore, are useful in fast power control, varying and different propagation conditions cause the E
b
/I
o
parameter to be less than accurate in determining whether a mobile station should be commanded to increase or decrease its transmit power. There are several possible reasons for this inaccuracy:
If the E
b
/I
o
is changing too fast, e.g., due to a fast moving mobile, the power control delay will be too large and the power adjustment wvill come too late to be able to counteract the changed E
b
/I
o
.
Also, the measured E
b
/I
o
estimate will not be valid for the whole slot since the true E
b
/I
o
changes during non-measured time periods during a slot.
The radio propagation conditions, e.g., rapid variation in the number of radio paths used, will affect the E
b
/I
o
estimate in a negative manner.
In addition to the inaccuracy of the E
b
/I
o
based power control, the E
b
/I
o
estimate's inability to reflect the true, end user perceived quality also creates a problem. The end-user perceived quality is more accurately estimated by using estimated frame error rate.
To increase accura
Craver Charles
Nixon & Vanderhye
Telefonaktiebolaget LM Ericsson (publ)
Urban Edward F.
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