Multiplex communications – Communication over free space – Combining or distributing information via time channels
Reexamination Certificate
1999-04-29
2002-07-23
Vu, Huy D. (Department: 2665)
Multiplex communications
Communication over free space
Combining or distributing information via time channels
C370S322000, C370S422000, C370S468000, C370S512000, C375S285000, C375S365000
Reexamination Certificate
active
06424645
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to assignment of a time division multiplexed radio channel, and particularly to a radio communication method capable of changing the frame structure that is specified by a boundary between downward and upward TDMA channels, or by the boundary information between multiple access protocols of a random access channel and a DA-TDMA channel.
2. Description of Related Art
Conventionally, DA-TDMA (Demand Assignment-Time Division Multiple Access) is known as one of multiple access methods which establish channels as needed in channel resources shared by a base station and multiple terminal stations, as disclosed in Chapter 6.2 of Yamamoto and Kato, “TDMA COMMUNICATIONS”, published by the institute of electronics, information and communication engineers of Japan, for example. The DA-TDMA, which assigns channels in response to demands of the terminal stations, can make effective use of the channels having traffic fluctuations. As a transmission method, a variety of multiple access schemes are used such as a random access method allowing collision, and a collision avoidance method employing assigned channels.
FIG. 7
shows the entire configuration of a TDMA communication system. A base station
3
is connected with terminal stations
2
(
2
a
,
2
b
and
2
c
) via radio channels. Terminal units
1
(
1
a
,
1
b
and
1
c
) are connected to the corresponding terminal stations
2
. The base station
3
manages the channel resources between it and the terminal stations
2
connected thereto, and establishes channels between them in response to channel establishment requests from the terminal stations
2
. The channel resources are time-divided, and the channel establishment is carried out at a TDMA frame period consisting of a plurality of time slots.
FIG. 8
shows a TDMA frame structure disclosed in Japanese patent application laid-open No. 9-18435/1997, for example. Various types of channels are assigned to a plurality of time slots constituting a TDMA frame. Upward control channels are used when the terminal stations
2
make a request for channel establishment or release to the base station
3
, and downward control channels are used when the base station
3
issues a command to perform channel establishment or release to the terminal stations
2
. Downward and upward traffic channels are assigned to the terminal stations as needed, and are used for the data communications between the base station
3
and terminal stations
2
. The present example employs in the downward channels the TDM (Time Division Multiplex), and in the upward control channels the DA-TDMA using the slotted ALOHA (Additive Links On-line Hawaii Area). The upward traffic channels can be divided into subframes associated with services such as ABR (Available Bit Rate), VBR (Variable Bit Rate) and CBR (Constant Bit Rate). In addition, it will be able to vary, in accordance with traffic, boundaries such as a boundary between the upward channel and downward channel, or between the control channel and traffic channel, and a boundary between the multiple access protocols such as S-ALOHA and DA-TDMA, or between subframes corresponding to various services.
FIG. 9
is a sequence diagram illustrating channel assignment disclosed in Japanese patent application laid-open No. 9-214459/1997, for example. Horizontal axes are a time axis, and the processings are carried out sequentially from the left-hand side. Blocks at the top of this figure represent TDMA frames, on the basis of which the processings are carried out. When the data to be transmitted takes place in
FIG. 9
, the terminal station
2
transmits assignment request information to the base station
3
. Receiving the request, the base station
3
assigns the requested number of slots from among the available slots in a TDMA frame, and sends to the terminal station
2
channel assignment information obtained as a result of the assignment. The terminal station
2
begins data communications in accordance with the instructions.
FIG. 10
shows a TDMA frame structure disclosed in Japanese patent application laid-open No. 10-51406/1998, for example. In this example, upward control channels, which are used for requesting the channel establishment or release from the terminal station
2
to the base station
3
, precede the downward control channels, which are used for requesting the channel establishment or release from the base station
3
to the terminal station
2
. Downward and upward traffic channels are allotted between the upward and downward control channels.
FIG. 11
is a sequence diagram illustrating channel assignment, in which the horizontal axes are a time axis, and the processings are carried out sequentially from the left-hand side. Blocks at the top of this figure represent TDMA frames, on the basis of which the processings are carried out. When the data to be transmitted takes place in
FIG. 11
, the terminal station
2
a
transmits assignment request information to the base station
3
. Receiving the request, the base station
3
assigns the requested number of slots from among the available slots in a TDMA frame at a downward/upward traffic channel period, and sends to the terminal station
2
channel assignment information obtained as a result of the assignment through the downward control channel of the same frame. The terminal station
2
begins data communications from the next frame in accordance with the instructions.
Finally,
FIG. 12
shows a method for assigning a plurality of slots disclosed in Japanese patent application laid-open No. 8-265836/1996, for example.
FIG. 12
illustrates only a single frame on a upward traffic channel, in which the frame consists of five slots designated by S
1
-S
5
. At stage 1, the slots S
1
, S
4
and S
5
are assigned to the terminal station
2
a
, the slot S
3
is assigned to the terminal station
2
b
and the slot S
2
is assigned to the terminal station
2
c
. Discontinuous slots thus assigned will result in divided transmission bursts. Generally, since an overhead like guard time or an alignment symbol is required for each transmission burst, assigning continuous slots is preferable to improve the efficiency. Stage 2 illustrates a state in which the terminal station
2
c
completes its call. At stage S
3
, the slot S
2
, which becomes available owing to the call completion, is reassigned to the terminal station
2
b
instead of the slot S
3
. At stage 4, continuous slots S
3
, S
4
and S
5
are reassigned to the terminal station
2
a
. Thus, the conventional reassignment is achieved by independently changing the assignment of the slots to the individual terminal stations
2
in accordance with the timings of originating or terminating a call.
As described above, the conventional TDMA radio communication systems achieve the channel assignment by assigning a channel to each terminal station
2
, by changing the assignment and by reassigning a channel. Therefore, it is very difficult for them to consider the entire terminal stations
2
belonging to the base station
3
to carry out the channel assignment or reassignment at the same time. Thus, it is difficult for them to implement optimum channel assignment considering characteristics of the entire terminal stations and the channel assignment requests. In particular, it is not unlikely that the entire channel assignment of all the terminal stations
2
must be changed to vary in accordance with the traffic the boundary such as the boundary between the upward channel and downward channel, between the control channel and traffic channel, between the multiple access protocols, or between subframes corresponding to various services. Accordingly, it is necessary to design a TDMA radio communication system capable of changing the channel assignment of all the terminal stations
2
at the same time.
The simultaneous change of the channel assignment to all the terminal stations
2
is difficult in the conventional TDMA radio communication system because it is not rare that only insufficie
Hamada Tomokazu
Kawabata Takashi
Moritani Youichi
Sogabe Tohru
Phan M.
Vu Huy D.
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