Multiplex communications – Communication over free space – Combining or distributing information via time channels
Reexamination Certificate
2000-12-26
2002-06-04
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Communication over free space
Combining or distributing information via time channels
C370S348000, C455S277200, C455S450000
Reexamination Certificate
active
06400704
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a control channel placement method in which control channels for establishing wireless communication between a base station and a terminal station in a wireless communication system are placed in optimal time slots within a TDMA-TDD frame. The terminal station could be a vehicle telephone, a portable telephone or the like.
2. Discussion of the Background
A cellular system is generally used for providing a communication service for vehicle telephones or portable telephones. This cellular system comprises a plurality of base stations and small zones (referred to hereafter as cells) around each base station. The cells are so constructed that there is no gap between then.
In the cellular system, same channel is repeatedly used in zones under the condition that no mutual interference obstruction is generated. Therefore, it is possible provides a service in a very wide area with less number of channels. When the antenna of the base station is non-directional within the horizontal plane, and if the effects of topography and ground based obstructions are ignored, then the shape of the area covered by each base station will be circular. These circular cells are called omnicells. Switching of channels is performed in the portions where adjacent omnicells overlap.
On the other hand, sector cell structure zones are also known. In case of sector cell structure zones, directional antennas are provided in each base station. The beam width of each antenna is set so as to divide a circular area into a plurality of fan-shaped cells (referred to hereafter as sector cells) each having the same size.
Since directional antennas are used, it is possible to remove the effect of interference waves that arrive from directions other than the direction to which the antenna is pointed. In addition, there is no possibility of interfering waves broadcast towards base stations using the same channel but situated in a direction other than the one to which the antenna is pointed. As a result, it is possible to decrease the distance between base stations to which the same channel has been allocated and to improve the spatial channel usage efficiency. Moreover, the overall channel usage efficiency is improved in comparison with omnicells using non-directional antennas.
Because of reasons such as this, in wireless communication systems for performing mobile communication such as vehicle telephones and portable telephones, as the number of users increases, there is currently a transition underway from employing a zone structure that uses omnicells having a small radius to employing a zone structure that uses sector cells.
In the meanwhile, time division multiple access (TDMA) mode is known as the representative mode among digital wireless access modes employed in vehicle telephones and portable telephones. In TDMA mode, signals having a predetermined frequency bandwidth are divided along a time axis and communication is performed by cyclically allocating the divided time band to each user as one channel. Using this TDMA mode, a user can perform communication in time slots allocated into short cycles in the same frequency having a predetermined bandwidth.
The characteristics of this TDMA mode are described below. Firstly, a plurality of users can perform communication simultaneously using a single transreceiving device, therefore, the base station can be constructed with a small size and at a low cost. Secondly, open time is generated because the communication time only needs to be the time of the allocated time slot, thus allowing the state of peripheral bands to be observed at this time. Thirdly, because the operating time during communication is intermittent, the power consumption in the terminal station can be reduced.
Furthermore, when the TDMA mode is employed as a wireless access mode, it is possible to use the time division duplex (TDD) mode in combination with the TDMA mode. The TDD mode uses the same frequency for both, reception and transmission, between a terminal station and a base station and performs the transmission and reception by dividing the time. In the TDD mode, the characteristics of the wave propagation are the same going “up” (i.e. from the terminal station to the base station) as they are going “down” (i.e. from the base station to the terminal station). Therefore, it is possible to only have to carry out countermeasures against variations in the wave propagation at the base station side only.
The frame structure of the transmission and reception using this TDMA-TDD may be one structured, for example, from four pairs of time slots (one up and one down). In this case, the first pair is used as a control channel with the remaining three pairs being used as notification channels. As a result, in this example, three terminal stations can perform communication with one base station at the same time.
In this case, it is possible to divide the control channels into “down control channels” going in the direction from the base station to the terminal station and “up control channels” going in the direction from the terminal station to the base station. The down control channels are formed from a broadcast channel (BCCH) for notifying a terminal station as to the ID of the host base station and about information peculiar to the base station such as the control channel frequencies of peripheral base stations and the like, and from a paging channel (PCH) for transmitting incoming message information, and the like.
The up control channels are formed from a random access type of signal control channel (SCCH) for performing tasks such as receiving transmissions and specifying wireless channels.
FIG. 14
is an explanatory diagram showing the frame structure in a conventional TDMA-TDD mode. In
FIG. 14
, in accordance with the above example, four pairs of time slots comprising up and down are set as one TDMA-TDD frame.
In particular, in this example, the up control channel is a multiframe structure in which 20 frames are set as one new frame, while the down control channel is a super frame structure in which 12 multiframes are set as one new frame.
The TDMA-TDD mode has commonly been applied as a wireless access mode in portable telephones and vehicle telephones. Various control channel setting methods which should be able to realize higher quality communication are provided in a wireless communication system that employs this TDMA-TDD mode.
For example, according to the “Control Channel Setting Method” disclosed in Japanese Patent Application Laid-Open (JP-A) No. 7-245780, in order to reduce interference in its own down control channel, a parent station (a base station) measures the reception levels of all channels of frequencies used for control signals (control channels), and selects, for setting as control channels, usable combinations from the reception levels of each channel from among combinations of up control channels and down control channels that form pairs in the TDMA-TDD mode, such that up control channels and down control channels of peripheral base stations do not overlap.
As another example, according to the “Radio Control System” explained in U.S. patent application No. 09/236,392, by the same assignee as the present application in the wireless communication system of a sector cell zone structure that uses directional antennas, when a particular base station performs communication, interference is reduced by not using antennas transmitting in the same direction as the antennas used for communication by base stations adjacent to that particular base station, based on tables that have been prepared in advance.
Moreover, as the channel allocation method, a fixed channel allocation method may be used in which the channels to be used by each cell are fixed in advance with consideration given to mutual interference between zones. Alternatively, a dynamic channel allocation method in which the channel allocation is changed time-wise in accordance with the demands of the calls in each cell may be used.
In the channel
Kawabata Takashi
Mikuni Yuko
Toyota Norihiko
Hsu Alpus H.
Mitsubishi Denki & Kabushiki Kaisha
Qureshi Afsar M.
LandOfFree
Control channel placement method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Control channel placement method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Control channel placement method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2919582