Pulse or digital communications – Spread spectrum – Hybrid form
Reexamination Certificate
1999-02-11
2002-03-26
Pham, Chi (Department: 2631)
Pulse or digital communications
Spread spectrum
Hybrid form
C375S132000, C370S329000, C370S335000, C370S341000, C370S441000
Reexamination Certificate
active
06363099
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a physical channel assignment method and a transmitter, and more particularly, is preferably applicable to a cellular radiocommunication system such as a portable telephone system.
2. Description of the Related Art
In the cellular radiocommunication system, an area for providing a communication service has been divided into cells with desired size. A base station has been provided as a fixed station in each of the cells and a communication terminal unit as a mobile station has been designed to perform a radiocommunication with the base station whose communication state seems to be most desirable.
There have been proposed various types of systems as a communication system between the communication terminal unit and the base station. A representative communication system is called a frequency hopping scheme. With this frequency hopping scheme, assuming that, for instance, eight frequency channels f
0
to f
7
are prepared for communication from the base station to the communication terminal unit, as shown in
FIG. 1
, the frequency channels used at the time of communication are sequentially changed in terms of time. For example, as shown in
FIG. 1
, the frequency channels employed are sequentially changed in such a manner that a frequency channel f
3
is used in an interval (called a time slot T
0
, hereinafter) from time t
0
to time t
1
, a frequency channel f
1
is used in an interval of time t
1
to time t
2
(namely, a time slot T
1
), a frequency channel f
5
is used in an interval of time t
2
to time t
3
(that is to say, a time slot T
2
) and a frequency channel
2
is used in an interval of time t
3
to time t
4
(namely, a time slot T
3
). Since the frequency channels are changed as described above in terms of time, even if an interference wave exists in a certain frequency channel, the influence of an interference only on the same channel can be reduced, because that the frequency channel is not always used.
In such a frequency hopping scheme, a frequency channel determined by a physical parameter such as frequency is looked up as a physical channel. A channel formed by successively combining the frequency channels in terms of time, in other words, a channel formed by the frequency channels f
3
, f
1
, f
5
, f
2
, . . . in an example shown in
FIG. 1
, is called a logical channel. In this case, if there are, for instance, eight frequency channels, the number of frequency channels available for each time slot may be eight. Therefore, when the frequency channels are combined together in terms of time, eight logical channels may be also formed. Consequently, even in accordance with the frequency hopping system, if there exist eight frequency channels, the eight logical channels can be formed and eight communications can be carried out simultaneously.
Here, it is assumed that the eight frequency channels f
0
to f
7
are prepared for communication from the base station to the communication terminal unit. Further, as shown in
FIG. 2
, it is assumed that eight communication terminal units MS
0
to MS
7
are present in the service area of an arbitrary base station BS
1
and the base station BS
1
performs a communication with the eight communication terminal units MS
0
to MS
7
by using logical channels #
0
to #
7
formed based on the frequency hopping scheme.
Under these conditions, in the conventional base station, the frequency channels f
0
to f
7
are respectively assigned to the eight logical channels #
0
to #
7
in accordance with a method described below.
That is to say, the base station has an offset value V
0
peculiar to each of the communication terminal units. The frequency channels of the channel numbers fN obtained as a result of a remainder computation as shown in the following Equation are assigned to the respective logical channels #
0
to #
7
based on the offset value V
0
and a random number value V
R
changing with time generated in a prescribed random number generator.
fN=
(
V
0
+V
R
)mod8 (1)
Where, mod indicates a remainder computation. Further specifically, as shown in
FIG. 3
, it is assumed that the offset values V
0
assigned to the communication terminal units MS
0
to MS
7
are respectively 0, 1, 2, 3, 4, 5, 6 and 7, and the random number values V
R
are 0, 3, 5, 7, 2, 1, . . . , the frequency channels f
0
, f
3
, f
5
, f
7
, f
2
, f
1
, . . . are assigned to the logical channel #
0
used for the communication with the communication terminal unit MS
0
based on the above described Equation (1). The frequency channels f
1
, f
4
, f
6
, f
0
, f
3
, f
2
, . . . are assigned to the logical channels #
1
used for the communication with the communication terminal unit MS
1
.
The frequency channels f
0
to f
7
are assigned to the logical channels #
0
to #
7
in accordance with the above method, hence the frequency channels can be assigned to the logical channels #
0
to #
7
so that the same frequency channels are not employed at the same time.
In the above mentioned conventional channel assignment, however, although the different frequency channels f
0
to f
7
are respectively assigned to the logical channels #
0
to #
7
at the same time, there exists an inconvenience that the same logical channels are always assigned to the adjacent frequency channels. For instance, when the channel assignment shown in
FIG. 3
is represented again by providing the frequency channels on the abscissa axis, this channel assignment can be changed to one as illustrated in FIG.
4
. As can be seen from
FIG. 4
, the logical channels #
0
and #
2
are always assigned to the frequency channels adjacent to the frequency channel #
1
to which the logical channel #
1
is assigned. In such a way, if the same logical channels are always located at adjacent positions on a frequency axis, they always undergo an interference wave of the same level (this is called an adjacent channel interference wave) from the adjacent logical channels. As a result, there arises a problem that an interference with adjacent channels is always fixed.
As mentioned above, when the interference with adjacent channels is fixed, this causes a serious problem particularly when transmitted power is controlled. Usually, in the cellular radiocommunication system, parties of communication mutually monitor the received power of a signal sent from one party to the other party and inform him of the monitored result so that the transmitted power is controlled. Accordingly, in the cellular radiocommunication system, the communication can be always performed with minimum transmitted power as required. When the transmitted power is controlled in such a manner, the transmitted power differs every communication (namely, for each of logical channels).
The power state of the logical channels at prescribed time under the control of the transmitted power is illustrated in FIG.
5
. As shown in
FIG. 5
, when the power of the logical channel #
1
is low and the power of the logical channels #
0
and #
2
located at the adjacent positions thereto in terms of frequency is high, the adjacent channel interference waves to the logical channel #
1
from the logical channels #
0
and #
2
are increased because the power of the logical channels #
0
and #
2
is high under this state. As a result, there arises a risk that a communication cannot be performed through the logical channel #
1
because a signal component sent originally from the logical channel #
1
is buried in the adjacent channel interference waves. This phenomenon is not generated only at a prescribed time and may be generated at all timings when the same logical channels are always located at the adjacent positions as mentioned above.
According to the conventional channel assignment method as described, since the same logical channels are always located at the adjacent positions, the adjacent channel interference wave is fixed. Conseque
Sakoda Kazuyuki
Suzuki Mitsuhiro
Maioli Jay H.
Nguyen Dung X.
Pham Chi
Sony Corporation
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