Delay correction system for wireless telephone system

Details Delay correction system for wireless telephone system Delay correction system for wireless telephone system

2000-02-14

2003-10-07

Yao, Kwang Bin (Department: 2662)

Multiplex communications

Communication techniques for information carried in plural...

Combining or distributing information via time channels

C370S337000, C370S350000

Reexamination Certificate

active

06631142

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to delay correction systems, and more particularly to a delay correction system for a wireless telephone system which employs time division multiple access (TDMA), designed to provide a wireless telephone service in a sparsely populated region which is distant from a densely populated region.
Recently, telephone services are essential for everyday life, and there are demands to expand the range of the telephone services to the sparsely populated regions which are distant from the densely populated regions.
In an extremely sparsely populated region, it is not realistic to construct a wired network as in the case of the densely populated region. For this reason, there are expectations to apply the TDMA wireless telephone system to such an extremely sparsely populated region.
2. Description of the Related Art
FIG. 1
is a system block diagram showing an example of a TDMA wireless telephone system. In
FIG. 1
, a base station apparatus
410
is coupled to a base station control apparatus
401
via an integrated services digital network (ISDN) interface
411
. Further, the base station apparatus
410
is coupled to an existing network via the base station control apparatus
401
.
In addition, a maintenance management system
402
shown in
FIG. 1
is coupled via a communication line to each base station control apparatus
401
which is set in a maintenance management area. Hence, the maintenance management system
402
centrally manages each base station control apparatus
401
and each base station apparatus
410
coupled thereto.
In the base station apparatus
410
, a TDMA LSI
412
extracts information of each channel forming the TDMA frame received via a transmission and reception processor
413
, and sends the extracted information to the base station control apparatus
401
via the ISDN interface
411
. In addition, the TDMA LSI
412
inserts the information of each channel received via the ISDN interface
411
into the TDMA frame, and sends the TDMA frame via the transmission and reception processor
413
.
A control channel analyzer
414
analyzes control channel information received from the ISDN interface
411
and the TDMA LSI
412
. Based on an analysis result of the control channel analyzer
414
, a base station control processor
415
controls the operation of the TDMA LSI
412
.
On the other hand, in a subscriber apparatus
424
shown in
FIG. 1
, a TDMA LSI
421
controls the exchange of information between a speech converter
422
and a transmission and reception processor
423
in conformance with the TDMA system, similarly as in the case of the control carried out by the TDMA LSI
412
described above.
A subscriber control processor
424
controls the operation of the TDMA LSI
421
depending on an analysis result of a control channel analyzer
425
which operates similarly to the control channel analyzer
414
described above.
According to the TDMA system, 1 frame period is divided into a transmission period made up of time slots TS
1
through TS
4
, and a reception period made up of time slots TS
1
through TS
4
, as shown in
FIG. 2. A
plurality of subscriber apparatuses
420
carry out the transmission and reception operations using the base station apparatus
410
as the synchronization reference, and use the allocated time slots to communicate with the base station apparatus
410
.
For example, suppose that a time slot
1
(TS
1
) is allocated to a subscriber apparatus
1
and a time slot
2
(TS
2
) is allocated to a subscriber apparatus
2
. In this case, if the base station apparatus
410
sends transmitting information S
1
addressed to the subscriber apparatus
1
at the timing of the time slot
1
of the transmission period on one hand, and sends transmitting information S
2
addressed to the subscriber apparatus
2
at the timing of the time slot
2
of the transmission period, the transmitting information S
1
is received by the subscriber apparatus
1
as received information R
1
and the transmitting information S
1
is received by the subscriber apparatus
2
as received information R
2
.
In addition, in this case, the base station apparatus
410
simply needs to receive, as the information from the subscriber apparatus
1
, the received information R
1
which is received at the timing of the time slot
1
of the reception period, and to receive, as the information from the subscriber apparatus
2
, the received information R
2
which is received at the timing of the time slot
2
, and process the received information.
The information exchanged between the base station apparatus
410
and the subscriber apparatus
420
has a structure shown in
FIG. 3
, for example. In
FIG. 3
, a start symbol (SS), a control signal (CAC), a unique word (UW) and an error check code (CRC) are sandwiched between 4-bit ramp bits (R) and 16-bit guard bits (G).
When applying the TDMA wireless telephone system to the region in which the base station apparatuses are set at a high density, as in the case of a metropolitan region, there is virtually no transmission delay between the base station apparatus
410
and the subscriber apparatus
420
. Hence, the transmission delay can be absorbed sufficiently by the ramp bits and the guard bits described above, and it is possible to realize a normal communication.
On the other hand, when applying the wireless telephone system to the sparsely populated region, it is necessary to enlarge the area covered by (area coverage of) each base station apparatus.
However, according to the conventional wireless telephone system described above was developed in a direction so as to reduce the cell size in order to improve the frequency band utilization efficiency in the metropolitan area or the like. In other words, it is a precondition that the base station apparatus
410
covers an area in a relatively limited range, and no consideration was given as to the transmission delay generated between the base station apparatus
410
and the subscriber
420
.
For this reason, when the conventional wireless telephone system is applied as it is to the sparsely populated region, the area coverage of the base station apparatus
410
becomes limited to a range in which the ramp bits and the guard bits can absorb the transmission delay.
Suppose that the subscriber apparatus
1
is distant from the base station apparatus
410
and the subscriber apparatus
2
is close to the base station apparatus
410
, as shown in FIG.
4
. Further, suppose that the time slot
1
(TS
1
) is allocated for the distant subscriber apparatus
1
, and the time slot
2
(TS
2
) is allocated for the close subscriber apparatus
2
, as shown in FIG.
5
. In this case, because of the transmission delay between the subscriber apparatus
1
and the base station apparatus
410
, the information transmitted from the subscriber apparatus
1
at the transmitting timing (TS
1
) and the information transmitted from the subscriber apparatus
2
at the transmitting timing (TS
2
) interfere during the reception period of the base station apparatus
410
as indicated by the hatching in FIG.
5
.
As a technique for preventing the interference caused by the transmission delay, there is a proposed method which uses a remote type subscriber apparatus for the subscriber apparatus which is located at a distant location from the base station apparatus.
FIG. 6
is a system block diagram showing the construction of the remote type subscriber apparatus. In the remote type subscriber apparatus shown in
FIG. 6
, the TDMA LSI
421
is designed to supply the transmitting information to the transmission and reception processor
423
via a timing adjuster
431
. The timing adjuster
431
adjusts the timing of the transmitting information to become advanced by a time corresponding to a symbol number n specified by a symbol number setting unit
432
.
In other words, the timing adjuster
431
receives transmitting information D
1
which is sent from the TDMA LSI
421
during the time slot of the transmission perio

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