Telecommunications – Carrier wave repeater or relay system – Directive antenna
Reexamination Certificate
2001-07-13
2004-11-30
Corsaro, Nick (Department: 2684)
Telecommunications
Carrier wave repeater or relay system
Directive antenna
C455S063400, C455S504000
Reexamination Certificate
active
06826386
ABSTRACT:
This application is based on application No. 2000-215098 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a radio information terminal (hereinafter “mobile station”) that connects to abase station, for example a telephone and a portable information communication device, and a radio communication system made up of the radio base station and the mobile station. In particular, the present invention relates to improved efficiency of frequency usage in the system.
(2) Description of the Related Art
Recently with the number of mobile stations, including portable telephones and portable communication devices, on the rise there is increasing demand in society for more effective use of frequency resources. Path division multiple access and the wireless zone system (the latter is also called the cellular system) are techniques which respond to this demand.
Path division multiple access is a system in which a radio base station uses a directional antenna to communicate with a plurality of mobile stations at the same time but in different directions using the same carrier wave frequency.
An example of a directional antenna that is used in the radio base station in path division multiple access is an adaptive array apparatus. The adaptive array apparatus is composed of a plurality of antenna devices which are provided fixed. The adaptive array apparatus forms a directivity pattern (also called “array antenna pattern”) for reception and transmission for the antenna as a whole by movably varying the amplitude and phase of the reception and transmission signals for each antenna device.
The adaptive array apparatus, in forming the directivity pattern, not only increases transmission strength and reception sensitivity towards a desired mobile station, but also reduces transmission strength and reception sensitivity toward other mobile stations. Note that details of an adaptive array apparatus are contained in “Adaptive Signal Processing in Space Areas and its Applied Technology Special Feature” (Journal of the Institute of Electronics, Information and Communication Engineers Vol. J75-B-2 No. 11).
The wireless zone system is a system in which a service area is divided into sectors called zones and a frequency to be used for a carrier wave is allocated to each zone. Each radio base station and mobile station in the zone communicates using the allocated frequency of a carrier wave, and the same frequency is allocated repeatedly to zones which are in positions in which interference does not occur.
FIG. 10
is a schematic drawing for explaining path division multiple access and the wireless zones.
900
shows a service area,
901
shows one wireless zone,
902
shows the frequency allocated to the wireless zone,
903
shows a radio base station,
904
and
905
show mobile stations,
906
and
907
show radio base station directivity patterns in relation to the mobile stations
904
and
905
respectively, and
908
and
909
show the respective directivity patterns of the mobile stations
904
and
905
.
Here the directivity patterns show, for communication within one wireless zone, a range in which transmission signals from the radio base station and the mobile station reach their destination with adequate strength, and a range in which the radio base station and the mobile station can receive signals with adequate sensitivity. These ranges are also understood to be ranges in which interference with communication in other wireless zones which use the same frequency occurs.
In the drawing the radio base station
903
communicates with the mobile stations
904
and
905
according to path division multiplexing using a carrier wave frequency f
1
by forming different directivity patterns
906
and
907
. The drawing shows schematically that the frequency f
1
is allocated again to a wireless zone outside of the directivity patterns of the radio base station
903
and the mobile stations
904
and
905
. Note that conventionally the mobile stations
904
and
905
transmit and receive signals with a uniform directionality in all directions.
In the path division multiple access system, the radio base station changes its directivity patterns following the movements of each mobile station using the adapter array apparatus, in order to avoid mixing of voices and to maintain communication quality. Control substance of the directivity pattern during reception and transmission according to minimum mean square error (MMSE) when there are N antenna devices is shown below.
The control of the directivity pattern during reception is for controlling extraction of a reception signal from a specific mobile station by suitably compositing signals received through each antenna device.
FIG. 11
is an outline showing control contents according to MMSE when a signal from the mobile station is received by the adaptive array apparatus.
y
(
t
)=
w
(
t−
1)*
x
(
t
)=
w
1
(
t−
1)*
x
1
(
t
)+
w
2
(
t
1)*
x
2
(
t
)+ . . . +
wN
(
t−
1)*
xN
(
t
) <Equation 1>
This control, as shown in the figure and in Equation 1, is performed to obtain a total sum y(t) by multiplying the reception signal vectors x
1
(t), x
2
(t), . . . , xN(t) which are constituted from each signal actually obtained through the antenna devices, with the weight vectors w
1
(t−1), w
2
(t−1), . . . , wN(t−1) which are constituted from each weight coefficient corresponding to each antenna. This control is for determining appropriate weight vectors so that y(t) includes a maximum of components of the reception signal from the mobile station from which the signal is being extracted, and so that y(t) includes a minimum of components of reception signals from other mobile stations.
Here, t shows the time that the signal reaches the radio base station and is, for example, a value showing an elapsed time within a timeslot in the PHS Standard and is used as a unit of time taken to receive 1 symbol. Therefore, the reception signal vector x, the weight vector w and so on are a signal series corresponding to values 1, 2, . . . . Furthermore, the weight vector w is a parameter for forming the directivity pattern, and the weight vector w and the reception signal vector x express as a complex vector a signal which has amplitude and phase.
The initial value of the weight vector is set appropriately, and the weight vector is updated each unit of time by being varied within a predetermined range in a manner explained below, so that the difference between a particular part of the signal (hereinafter “reference signal”) sent from the mobile station d(t) and the signal y(t) is a minimum. The particular part is a part of the signal which is predetermined and fixed, for example, a preamble and a UW (unique word) which are symbol synchronization codes in the PHS Standard.
e
(
t
)=
d
(
t
)−
y
(
t
)=
d
(
t
)−&Sgr;(
wi
(
t−
1)*
xi
(
t
)) <Equation 2>
As shown in Equation 2, in each time t the difference e(t) between the signal y(t) calculated using the weight vector in time t−1 and the reference signal d(t). Wi(t) is calculated by correcting wi(t−1) so that the difference is a minimum. Theoretically, by repeating this calculation each time, the value of the weight vector converges at a constant value, and the signal y(t) becomes close to the signal of the mobile station from which the signal is being extracted.
The preamble and the unique word that are represented by the reference signal are sent before target data, which is the content of the communication, therefore the signal y(t) shows substantially the signal of the mobile station that is being extracted at the point of reception of the target data. Note that after conversation starts, the last weight vector value obtained in the previous time slot, for example, is used as the initial value in the following time slot.
Control of the directivity pattern in reception is a process of dis
Corsaro Nick
Sanyo Electric Co,. Ltd.
Trinh Tan
LandOfFree
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