Communicating system, communicating method, base station, and mobile station Number:7,436,809 from the United States Patent and Trademark Office (PTO) owispatent A communicating system is disclosed. The communicating system has a base station and a plurality of mobile stations that radio-communicate through an uplink channel and a downlink channel with frames each of which is composed of a plurality of time divided slots, each of the frames of the uplink channel and the downlink channel being transmitted in accordance with OFDM transmitting system. An OFDM sub carrier used in the OFDM transmitting system is divided in accordance with a predetermined diving method, each of the frames of the uplink channel or downlink channel being allocated to the divided portions of the OFDM sub carrier, a plurality of frames of the uplink channel or downlink channel being radio-communicated between one base station and a plurality of mobile stations.<H communicating, Communicating, Communicating, s, 7436809.html, Patent, pto, 7436809

Title: Communicating system, communicating method, base station, and mobile station

Abstract: A communicating system is disclosed. The communicating system has a base station and a plurality of mobile stations that radio-communicate through an uplink channel and a downlink channel with frames each of which is composed of a plurality of time divided slots, each of the frames of the uplink channel and the downlink channel being transmitted in accordance with OFDM transmitting system. An OFDM sub carrier used in the OFDM transmitting system is divided in accordance with a predetermined diving method, each of the frames of the uplink channel or downlink channel being allocated to the divided portions of the OFDM sub carrier, a plurality of frames of the uplink channel or downlink channel being radio-communicated between one base station and a plurality of mobile stations.

Patent Number: 7,436,809 Issued on 10/14/2008 to Harada, et al.

Inventors: Harada; Hiroshi (Kanagawa, JP), Ahn; Chang-Jun (Kanagawa, JP), Takahashi; Satoshi (Kanagawa, JP), Kamio; Yukiyoshi (Tokyo, JP), Sampei; Seiichi (Osaka, JP)
Assignee: National Institute of Information and Communications Technology, Incorporated Administrative Agency (Tokyo, JP)
N/A (

Appl. No.: 11/030,920

Filed: January 6, 2005

Foreign Application Priority Data


Mar 08, 2004 [JP]			2004-063984

Current U.S. Class: 370/338 ; 370/319; 370/329; 370/348; 370/447; 455/450; 455/509

Current International Class: H04Q 7/00 (20060101)

Field of Search: 455/450-453,509,517,522,69 370/329-330,315-322,341,347-348,470,478,458,447

References Cited [Referenced By]

U.S. Patent Documents


6151329	November 2000	Berrada et al.
6434122	August 2002	Barabash et al.
6567383	May 2003	Bohnke
6791475	September 2004	Yamashita
6829531	December 2004	Lee
7003301	February 2006	Sawada et al.
7339919	March 2008	Harada
2003/0021245	January 2003	Haumonte et al.
2004/0081123	April 2004	Krishnan et al.
2005/0020211	January 2005	Takikita

Foreign Patent Documents


2003-32171	Jan., 2003	JP
2003032171	Jan., 2003	JP
2003-234688	Aug., 2003	JP
2003234688	Aug., 2003	JP

Other References

Harada et al., New Generation Mobile Communication System by Dynamic Parameter Controlled OF/TDMA, IEICE Technical Report, vol. 103, No. 553, 9 pages including pp. 41-46, Jan. 9, 2004. cited by other.

Primary Examiner: Afshar; Kamran
Attorney, Agent or Firm: Bell, Boyd & Lloyd LLP

Claims

The invention claimed is:

1. A communicating system having a base station and a plurality of mobile stations that radio-communicate through an uplink channel and a downlink channel with frames each of which is composed of a plurality of time divided slots, each of the frames of the uplink channel and the downlink channel being transmitted in accordance with OFDM transmitting system, an OFDM sub carrier used in the OFDM transmitting system being divided, each of the frames of the uplink channel and the downlink channel being allocated to the divided portions of the OFDM sub carrier to form a plurality of sub channels that are independent from each other, a plurality of frames of the uplink channel and downlink channel being radio-communicated between one base station and the plurality of mobile stations through the sub channels, a frame control message slot (FCMS) being allocated to each frame of the sub channel of the downlink channel, slot allocation information of the uplink channel, slot allocation information of the downlink channel, response information against data transmitted through the uplink channel, response information against connection setup--connection release request transmitted from one of the mobile stations, and response information against registration--deregistration request transmitted from one of the mobile stations being transmitted from the base station to one of the mobile stations with the frame control message slot, an activation slot (ACTS) being allocated to each frame of the sub channel of the uplink channel, the connection setup--connection release request and the registration--deregistration request transmitted from one of the mobile stations being transmitted from one of the mobile stations to the base station with the activation slot (ACTS), one of the mobile stations receiving all the divided portions of the OFDM sub carrier transmitted in accordance with the OFDM transmission system from the base station through the downlink channel, the frame message control slot allocated to all the received sub channels being received, the allocated information of the frames of the uplink and downlink channels being received, an available one of the sub channels being determinable based on the allocated information, a registration request being performed for the activation slot of the available sub channel, a communication being performed with the frames of the uplink and the downlink channels allocated to the sub channel that has been registered.

2. The communicating system as set forth in claim 1, wherein download request, upload request, and user data transmitted from one of the mobile stations and response information against data transmitted through the downlink channel are transmitted from one of the mobile stations to the base station with a message data slot (MDS) allocated in a frame of the uplink channel, the frame being transmitted with the sub channels.

3. The communicating system as set forth in claim 1, wherein when the base station receives the download request from the plurality of mobile stations through the uplink channel, the slots of the downlink channel and the slots of the uplink channel are allocated to the plurality of mobile stations in accordance with a predetermined rule.

4. The communicating system as set forth in claim 3, wherein the predetermined rule is one of the round robin method, the FIFO method, and the modified FIFO method.

5. The communicating system as set forth in claim 1, wherein when the base station and each of the plurality of mobile stations transmit data, the modulating system and the transmission power can be selected for each slot of the uplink channel and the downlink channel.

6. The communicating system as set forth in claim 1, wherein the slots of each frame allocated to the divided portions of the OFDM sub carrier and transmitted through the downlink channel are independent from those through the downlink channel.

7. A communicating method of a base station and a plurality of mobile stations that radio-communicate through an uplink channel and a downlink channel with frames each of which is composed of a plurality of time divided slots, each of the frames of the uplink channel and the downlink channel being transmitted in accordance with OFDM transmitting system, an OFDM sub carrier used in the OFDM transmitting system being divided, each of the frames of the uplink channel and the downlink channel being allocated to the divided portions of the OFDM sub carrier to form a plurality of sub channels that are independent from each other, a plurality of frames of the uplink channel and downlink channel being radio-communicated between one base station and the plurality of mobile stations through the sub channels, comprising the steps of: transmitting slot allocation information of the uplink channel, slot allocation information of the downlink channel, response information against data transmitted through the uplink channel, response information against connection setup--connection release request transmitted from one of the mobile stations, and response information against registration--deregistration request transmitted from one of the mobile stations from the base station to one of the mobile stations with the frame control message slot; allocating an activation slot (ACTS) to each frame of the sub channel of the uplink channel; transmitting the connection setup--connection release request and the registration--deregistration request transmitted from one of the mobile stations to the base station with the activation slot (ACTS); causing one of the mobile stations to receive all the divided portions of the OFDM sub carrier transmitted in accordance with the OFDM transmission system from the base station through the downlink channel; receiving the frame message control slot allocated to all the received sub channels and the allocated information of the frames of the uplink and downlink channels and determining an available one of the sub channels based on the allocated information; and performing a registration request for the activation slot of the available sub channel and communicating with the frames of the uplink and the downlink channels allocated to the sub channel that has been registered.

8. The communicating method as set forth in claim 7, wherein download request, upload request, and user data transmitted from one of the mobile stations and response information against data transmitted through the downlink channel are transmitted from one of the mobile stations to the base stations with a message data slot (MDS) allocated in a frame of the uplink channel, the frame being transmitted with the sub channels.

9. The communicating method as set forth in claim 7, wherein when the base station receives the download request from the plurality of mobile stations through the uplink channel, the slots of the downlink channel and the slots of the uplink channel are allocated to the plurality of mobile stations in accordance with a predetermined rule.

10. The communicating method as set forth in claim 9, wherein the predetermined rule is one of the round robin method, the FIFO method, and the modified FIFO method.

11. The communicating method as set forth in claim 9, wherein when the base station and each of the plurality of mobile stations transmit data, the modulating system and the transmission power can be selected for each slot of the uplink channel and the downlink channel.

12. The communicating method as set forth in claim 9, wherein the slots of each frame allocated to the divided portions of the OFDM sub carrier and transmitted through the downlink channel are independent from those through the downlink channel.

13. A base station in a communicating system having a base station and a plurality of mobile stations that radio-communicate through an uplink channel and a downlink channel with frames each of which is composed of a plurality of time divided slots, each of the frames of the uplink channel and the downlink channel being transmitted in accordance with OFDM transmitting system, an OFDM sub carrier used in the OFDM transmitting system being divided, each of the frames of the uplink channel and the downlink channel being allocated to the divided portions of the OFDM sub carrier to form a plurality of sub channels that are independent from each other, a plurality of frames of the uplink channel and downlink channel being radio-communicated between one base station and the plurality of mobile stations through the sub channels, a frame control message slot (FCMS) being allocated to each frame of the sub channel of the downlink channel, slot allocation information of the uplink channel, slot allocation information of the downlink channel, response information against data transmitted through the uplink channel, response information against connection setup--connection release request transmitted from one of the mobile stations, and response information against registration--deregistration request transmitted from one of the mobile stations being transmitted from the base station to one of the mobile stations with the frame control message slot, an activation slot (ACTS) being allocated to each frame of the sub channel of the uplink channel, the connection setup--connection release request and the registration--deregistration request transmitted from one of the mobile stations being transmitted from one of the mobile stations to the base station with the activation slot (ACTS), one of the mobile stations receiving all the divided portions of the OFDM sub carrier transmitted in accordance with the OFDM transmission system from the base station through the downlink channel, the frame message control slot allocated to all the received sub channels being received, the allocated information of the frames of the uplink and downlink channels being received, an available one of the sub channels being determinable based on the allocated information, a registration request being performed for the activation slot of the available sub channel, a communication being performed with the frames of the uplink and the downlink channels allocated to the sub channel that has been registered.

14. The base station as set forth in claim 13, wherein download request, upload request, and user data transmitted from one of the mobile stations and response information against data transmitted through the downlink channel are transmitted from one of the mobile stations to the base station with a message data slot (MDS) allocated in a frame of the uplink channel, the frame being transmitted with the sub channels.

15. The base station as set forth in claim 13, wherein when the download request is received from the plurality of mobile stations through the uplink channel, the slots of the downlink channel and the slots of the uplink channel are allocated to the plurality of mobile stations in accordance with a predetermined rule.

16. The base station as set forth in claim 15, wherein the predetermined rule is one of the round robin method, the FIFO method, and the modified FIFO method.

17. The base station as set forth in claim 13, wherein when data are transmitted, the modulating system and the transmission power can be selected for each slot of the uplink channel and the downlink channel.

18. The base station as set forth in claim 13, wherein the slots of each frame allocated to the divided portions of the OFDM sub carrier and transmitted through the downlink channel are independent from those through the downlink channel.

19. A mobile station in a communicating system having a base station and a plurality of mobile stations that radio-communicate through an uplink channel and a downlink channel with frames each of which is composed of a plurality of time divided slots, each of the frames of the uplink channel and the downlink channel being transmitted in accordance with OFDM transmitting system, an OFDM sub carrier used in the OFDM transmitting system being divided, each of the frames of the uplink channel and the downlink channel being allocated to the divided portions of the OFDM sub carrier to form a plurality of sub channels that are independent from each other, a plurality of frames of the uplink channel and downlink channel being radio-communicated between one base station and the plurality of mobile stations through the sub channels, a frame control message slot (FCMS) being allocated to each frame of the sub channel of the downlink channel, slot allocation information of the unlink channel, slot allocation information of the downlink channel, response information against data transmitted through the uplink channel, response information against connection setup--connection release request transmitted from one of the mobile stations, and response information against registration-- deregistration request transmitted from one of the mobile stations being transmitted from the base station to one of the mobile stations with the frame control message slot, an activation slot (ACTS) being allocated to each frame of the sub channel of the uplink channel, the connection setup--connection release request and the registration--deregistration request transmitted from one of the mobile stations being transmitted to the base station with the activation slot (ACTS), all the divided portions of the OFDM sub carrier transmitted in accordance with the OFDM transmission system being received from the base station through the downlink channel, the frame message control slot allocated to all the received sub channels being received, the allocated information of the frames of the uplink and downlink channels being received, an available one of the sub channels being determinable based on the allocated information, a registration request being performed for the activation slot of the available sub channel, a communication being performed with the frames of the uplink and the downlink channels allocated to the sub channel that has been registered.

20. The mobile station as set forth in claim 19, wherein download request, upload request, and user data and response information against data transmitted through the downlink channel are transmitted to the base station with a message data slot (MDS) allocated in a frame of the uplink channel, the frame being transmitted with the sub channels.

21. The mobile station as set forth in claim 19, wherein when data are transmitted, the modulating system and the transmission power can be selected for each slot of the uplink channel and the downlink channel.

Description

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2004-063984 filed on Mar. 8, 2004, the disclosure of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to a communicating system, a communicating method, a base station, and a mobile station applicable for an inter-vehicle communicating system for transmitting for example multimedia data from the base station to a vehicle and vice versa.

In the inter-vehicle communicating system, there are needs for multimedia communication. In the multimedia communication, mobile stations send requests for information to the base station so that it downloads multimedia data such as video data and music data to the mobile stations. The multimedia communication has a feature of which the amount of data that are transmitted (uplinked) from the mobile station to the base station are smaller than the amount of data that are transmitted (downlinked) from the base station to the mobile station. Thus, to accomplish the multimedia communication with the inter-vehicle communicating system, a radio communicating system that can effectively transmit a large amount of data that are generated as burst data to mobile stations is required. In addition, when photographed video data are transmitted from a mobile station to the base station, it cannot be always said that the amount of photographed video data is small. Thus, it is desired to effectively transmit video data.

To suitably perform inter-vehicle multimedia radio communication, a communicating method for forming both a frame of the uplink channel and a frame of the downlink channel with TDMA (Time Division Multiple Access) frames has been proposed (Patent Document 1).

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2003-32171

Next, the communicating method described in the Patent Document 1 will be described with reference to FIGS. 31A and 31B. In FIGS. 31A and 31B, BS represents a base station (or an access point (AP)). T1 to Tn represent n mobile stations (MS). As shown in FIG. 31A, one frame of downlink channel transmitted through the downlink channel is composed of one notification slot (shaded slot) and one or a plurality of (for example, seven) data slots. A process for dividing a successive period at constant intervals is referred to as slot segmentation. Each portion of which a successive period is divided is referred to as a slot. In the notification slot, a notification packet is allocated. In the data slots, data packets are allocated. A notification packet and data packets transmitted from the base station are received by the mobile stations T1 to Tn.

A notification packet contains information of statuses of the data slots of the current frame of the downlink channel, information of statuses of the data slots of the subsequent frame of the downlink channel, information of statuses of the data slots of the current frame of the uplink channel, information of statuses of the data slots of the subsequent frame of the uplink channel, and information of the reception statuses of the base station against uploaded packets that the mobile stations have transmitted in the immediately preceding frame of the uplink channel.

FIG. 31B shows an example of the structure of a frame of the uplink channel. A frame of the uplink channel is composed of one or a plurality of (for example, five) data slots, at least one download request slot for a download request packet, at least one upload request slot for an upload request packet, and a plurality of acknowledgement (ACK) slots. ACK slots corresponds to seven data slots that are downloaded from the base station BS.

Although at least one download request slot and at least one upload request slot are needed, if the number of request slots is small, when each mobile station transmits a request packet to the base station BS at a time, the possibility of which the request packets transmitted from mobile stations collide becomes high. However, when the number of request slots is increased, the number of data slots is decreased. Thus, in the example shown in FIG. 31B, the number of download request slots and the number of upload request slots are set to 7 and 5, respectively.

Next, the relation between timing of a frame of the downlink channel and timing of a frame of the uplink channel will be described. When a download request packet and an upload request packet are transmitted, the base station needs to be able to generate notification packets of the subsequent frame against the request packets. In addition, ACK packets that represent information about the reception statuses of data packets of the frame of the downlink channel should be transmitted before the subsequent frame is uploaded so as to prevent the ACK packets from colliding with the subsequent frame. In addition, after the notification packet is received from the base station, the upload data packets and the request packets should be transmitted.

When a mobile station needs to download or upload, the mobile station transmits a request packet with any download request slot or any upload request slot of the subsequent frame to the base station BS through the uplink channel in accordance with the contents of which the base station has noticed.

When the base station receives a download request packet from a mobile station, the base station performs a data slot allocating process for a frame of the downlink channel. When the base station receives an upload request packet from a mobile station, the base station performs a data slot allocating process for a frame of the uplink channel. The base station generates a notification packet in accordance with the statues of the data slots of the current frame and the subsequent frame and the reception statuses of upload packets received in the immediately preceding frame of the uplink channel.

The base station transmits data packets with data slots of a frame of the downlink channel to a mobile station that has transmitted a download request packet to the base station. The mobile station receives a notification packet and data packets from the base station and transmits the reception statuses thereof with an ACK slot to the base station.

A mobile station that has transmitted an upload request packet receives a notification packet from the base station. The mobile station transmits data packets to the base station with an allocated data slot. When the base station has completely transmitted data packets to a mobile station and has completely received data packets from the mobile station, the base station unallocates the data slot assigned to the mobile station.

While the base station is transmitting data packets to a mobile station, if the base station receives a request packet from another mobile station, the base station allocates one data slot to each mobile station and the other blank data slots to each mobile station in accordance with a predetermined rule for the subsequent frames. An example of the predetermined rule is as follows.

When the base station receives download requests from mobile stations, the base station allocates all blank data slots to a mobile station whose data packets to be transmitted are the smallest in these mobile stations. When the base station receives upload requests from mobile stations, the base station allocates all blank data slots to a mobile station whose data packets to be received are the smallest in these mobile stations. When there are still blank data slots, the base station allocates these data slots to a mobile station whose data packets to be received are the next smallest in these mobile stations. The base station performs the allocating process until there is no blank data slot or there is no mobile station to assign a data slot.

Next, the allocating rule for data slots that are downloaded will be described in detail. Likewise, this rule can be applied for data slots that are uploaded. The rule consists of a first rule and a second rule. The first rule describes that while the base station is transmitting data packets to a particular mobile station, when the base station does not receive a download request packet from another mobile station (at least one mobile station), the base station allocates all blank data slots to the particular mobile station. The second rule describes that while the base station is transmitting data packets to a particular mobile station, when the base station receives a download request packet from another mobile station (at least one mobile station), the base station allocates one data slot of each of the subsequent frames to each mobile station that has transmitted a request packet to the base station, allocates blank data slots of each of the subsequent frames to a mobile station whose data packets to be transmitted are the smallest in these mobile stations, and when each frame has blank data slots, allocates the blank data slots to mobile stations whose data packets to be transmitted are smaller than these mobile stations. The base station performs the process in accordance with the second rule until there is no blank data slot or there is no mobile station to allocate a data slot. The second rule can have several modifications. The data slot allocating process for frame of the uplink channels is the same as the data slot allocating process for frames of the downlink channel.

When the base station notifies a mobile station that the subsequent frame has a blank slot, the mobile station transmits a download request packet or an upload request packet to the base station with any download slot or any upload slot.

When a mobile station receives a notification packet from the base station, if the notification packet is a download request packet, the mobile station determines whether or not the subsequent frame of the downlink channel has a blank data slot in accordance with the notification packet. When a mobile station receives notification packet that is a upload request, the mobile station determines whether or not the subsequent frame of the uplink channel has a blank data slot in accordance with the notification packet. At this point, if the mobile station has determined that the subsequent frame of the uplink channel does not have a blank data slot, the mobile station does not transmit the request packet, but just stands by.

When the determined result represents that the subsequent frame of the uplink channel has a blank data slot, the mobile station allocates any request slot for a request packet and transmits the request packet with the allocated request slot. The mobile station transmits a download request packet to the base station with a download request slot. Likewise, the mobile station transmits an upload request packet to the base station with an upload request slot.

The mobile station receives the subsequent notification packet. The mobile station determines whether or not the base station has received the request packet in accordance with the information of the received notification packet. When the determined result represents that the base station has received the request packet that is a download request packet, the mobile station receives a data packet from the base station. When the mobile station has completely received the data packet of the frame, the mobile station transmits an ACK packet that represents information of the reception status with an ACK slot. After the mobile station has completely received all data packets, the mobile station stands by.

When the request packet is an upload request packet, the mobile station transmits data packets to the mobile station with a data slot of a frame of the uplink channel. When the mobile station has completely transmitted all data packets to the base station, the mobile station stands by. When the base station has completely received all data packets from the mobile station, the base station disallocates the data slot allocated to the mobile station.

According to this communicating method, when the base station downloads data packets to a mobile station, the base station can allocate at least one data slot of one frame to the mobile station. Thus, this method has a higher throughput than the method for allocating one data slot of one frame to one mobile station. Likewise, when a mobile station uploads data packets to the base station, it can allocate at least one data slot to the mobile station. As a result, a mobile station can upload a large amount of data to the base station in a short time.

However, according to the communicating method of the Patent Document 1, ACK slots are allocated in each frame of the uplink channel. When a mobile station has completely received data packets of a frame of the downlink channel, the mobile station transmits an ACK packet to the base station. In this system, although data communication can be safely performed, since the mobile station side needs to have a buffer having a large capacity for storing data packets of the frame and needs to perform a complicated process for transmitting an ACK packet.

To solve such a problem, another communicating method has been proposed. In this method, an ACK slot is not allocated in each frame. When data such as an EOD (End Of Data) of a sequence of data of downlink channel are received, an ACK (with a data slot) is sent back to the base station. This communicating method has been proposed in Patent Document 2

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2003-234688

According to the communicating method of the Patent Document 2, with the benefit of the Patent Document 1, a large amount of data can be communicated in a relatively short time, the mobile station side can simplify the communicating process and decrease the circuit scale. In this method, a response signal is sent back as a block of a predetermined amount of data. Thus, the normal transmitting process becomes the same as the re-transmitting process. As a result, the storage capacity of the buffer on the mobile station side can be decreased. In addition, the process can be simplified. In this example, the block of data represents for example an IP packet transmitted through the Internet or the like. Data are basically communicated in accordance with the TCP/IP.

Because the so-called MAC layer protocol has been improved, multimedia communication between vehicles has become more effective than before. However, it cannot be said that such communication is sufficient from a point of view of transmission and reception of multimedia data. It is essential to further improve the transmission rates and transmission quality without need to enlarge frequency bands.

Since transmission rates of inter-vehicle multimedia radio communication are 100 Mbps or higher, a frequency band of around 100 MHz should be secured. To have as a large cell radius as possible, a frequency band ranging from 3 GHz to 10 GHz microwave band will be mainly used. However, so far, the frequency band has become tight. To enlarge the communication area, it is necessary to take effective countermeasures against interference and suppress the frequency band as much as possible.

In addition, the mobile communicating system needs to provide effective countermeasures against multi-path interference. This leads to the improvement of transmission rates and transmission quality. In addition, considering connectivity with the IP network, as one possible solution, a communicating system that accomplishes the MAC layer protocol described in the Patent Document 2 could be accomplished on the basis of the Orthogonal Frequency Division Multiplexing (OFDM).

OBJECT AND SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a communicating system, a communicating method, a base station, and a mobile station that allow high transmission rates to be accomplished in mobile communication using TDMA frames on the basis of the OFDM system.

A first aspect of the present invention is a communicating system having a base station and a plurality of mobile stations that radio-communicate through an uplink channel and a downlink channel with frames each of which is composed of a plurality of time divided slots, each of the frames of the uplink channel and the downlink channel being transmitted in accordance with OFDM transmitting system, an OFDM sub carrier used in the OFDM transmitting system being divided in accordance with a predetermined diving method, each of the frames of the uplink channel or downlink channel being allocated to the divided portions of the OFDM sub carrier, a plurality of frames of the uplink channel or downlink channel being radio-communicated between one base station and a plurality of mobile stations.

A second aspect of the present invention is a communicating method of a communicating system having a base station and a plurality of mobile stations that radio-communicate through an uplink channel and a downlink channel with frames each of which is composed of a plurality of time divided slots, each of the frames of the uplink channel and the downlink channel being transmitted in accordance with OFDM transmitting system, an OFDM sub carrier used in the OFDM transmitting system being divided in accordance with a predetermined diving method, each of the frames of the uplink channel or downlink channel being allocated to the divided portions of the OFDM sub carrier, a plurality of frames of the uplink channel or downlink channel being radio-communicated between one base station and a plurality of mobile stations.

A third aspect of the present invention is a base station of a communicating system having a base station and a plurality of mobile stations that radio-communicate through an uplink channel and a downlink channel with frames each of which is composed of a plurality of time divided slots, each of the frames of the uplink channel and the downlink channel being transmitted in accordance with OFDM transmitting system, an OFDM sub carrier used in the OFDM transmitting system being divided in accordance with a predetermined diving method, each of the frames of the uplink channel or downlink channel being allocated to the divided portions of the OFDM sub carrier, a plurality of frames of the uplink channel or downlink channel being radio-communicated between one base station and a plurality of mobile stations.

A fourth aspect of the present invention is a mobile stable of a communicating system having a base station and a plurality of mobile stations that radio-communicate through an uplink channel and a downlink channel with frames each of which is composed of a plurality of time divided slots, each of the frames of the uplink channel and the downlink channel being transmitted in accordance with OFDM transmitting system, an OFDM sub carrier used in the OFDM transmitting system being divided in accordance with a predetermined diving method, each of the frames of the uplink channel or downlink channel being allocated to the divided portions of the OFDM sub carrier, a plurality of frames of the uplink channel or downlink channel being radio-communicated between one base station and a plurality of mobile stations.

According to the present invention, a communicating system, a communicating method, a base station, and a mobile station that allow high transmission rates to be accomplished in mobile communication using TDMA frames on the basis of the OFDM system are provided. Thus, a limited frequency band can be more effectively used than before.

These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, wherein similar reference numerals denote similar elements, in which:

FIG. 1 is a block diagram showing an example of the structure of a base station;

FIG. 2 is a block diagram showing an example of the structure of a mobile station;

FIG. 3 is a schematic diagram showing an outline of an inter-vehicle communicating system;

FIGS. 4A, 4B, and 4C are schematic diagrams showing the structures of a frame of the downlink channel and a frame of the uplink channel and the structure of data of one slot;

FIG. 5 is a schematic diagram showing an example of data stored in a transmission buffer;

FIG. 6 is a schematic diagram showing an example of a slot allocating system;

FIG. 7 is a schematic diagram showing an example of another slot allocating system;

FIG. 8 is a schematic diagram showing an example of a further slot allocating system;

FIG. 9 is a schematic diagram showing the format of a packet FCMP;

FIGS. 10A, 10B, 10C, and 10D are schematic diagrams showing data formats of a payload of the packet FCMP;

FIG. 11 is a schematic diagram showing the format of a packet MDP;

FIG. 12 is a schematic diagram showing the format of a packet ACTP;

FIGS. 13A and 13B are schematic diagrams showing an example of a slot allocation management table and an example of slot allocation of a frame of the downlink channel, respectively;

FIG. 14 is a first part of a flow chart describing an operation of a slot allocating process for a frame of downlink channel;

FIG. 15 is a second part of the flow chart shown in FIG. 14;

FIG. 16 is a schematic diagram showing an example of slot allocation of a frame of the uplink channel;

FIG. 17 is a first part of a flow chart describing an operation of a slot allocating process of a frame of the uplink channel;

FIG. 18 is a second part of the flow chart shown in FIG. 17;

FIG. 19 is a schematic diagram describing an example of an operation of a re-transmitting process;

FIG. 20 is a schematic diagram showing each sub-channel of a TDMA frame as a frame of the downlink channel according to the present invention;

FIG. 21 is a schematic diagram showing each sub-channel of a TDMA frame as a frame of the downlink channel according to the present invention;

FIGS. 22A and 22B are tables showing common characteristics and characteristics of the FCMS of an example of the structure of a TDMA frame, respectively;

FIGS. 23A and 23B are tables showing characteristics of the MDS and ACTS of an example of the structure of a TDMA frame, respectively;

FIG. 24A and FIG. 24B are schematic diagrams showing an image of radio communication and the MDS of a frame of the downlink channel according to the present invention, respectively;

FIG. 25 is a block diagram showing the structure of a transmitting portion of the base station according to the present invention;

FIG. 26 is a block diagram showing the structure of a receiving portion of the base station according to the present invention;

FIG. 27 is a block diagram showing the relation of transmitting and receiving functions of the base station according to the embodiment of the present invention and the MAC layer;

FIG. 28 is a block diagram showing the structure of a transmitting portion of the mobile station according to the embodiment of the present invention;

FIG. 29 is a block diagram showing the structure of a receiving portion of the mobile station according to the embodiment of the present invention;

FIG. 30 is a block diagram showing the relation of transmitting and receiving functions of the mobile station according to the embodiment of the present invention and the MAC layer; and

FIGS. 31A and 31B are schematic diagrams showing a frame of the downlink channel and a frame of the uplink channel of a conventional communicating method.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a communicating system, a communicating method, a base station, and a mobile station that accomplish the modified MAC layer protocol described in the Patent Document 2 in accordance with the OFDM. The MAC layer protocol is almost the same as that described in the Patent Document 2. Thus, first of all, the contents of the protocol will be described.

According to the protocol of the present invention, two channels referred to as an uplink channel and a downlink channel are used. They are communicated simultaneously in accordance with the OFDM system. The protocol uses the frequency division duplexing (FDD) system that uses different frequencies for the downlink channel (a channel from the base station to a mobile station) and the uplink channel (a channel from a mobile station to the base station).

In FIG. 1, a base station 1 is composed of a network controlling portion 2 connected to a network, a message data packet (MDP) generating portion 3, a frame control message packet (FCMP) generating portion 4, a selector 5 that selectively outputs the MDP and the FCMP, a transmitting portion 7 that receives an output signal of the selector 5 and that is included in a radio device 6, an antenna 8 that radiates a radio signal from the transmitting portion 7 to mobile stations, a receiving portion 9 that receives signals from mobile stations through the antenna 8, and a received packet determining portion 10. The MDP corresponds to a data packet of the Patent Document 1. The FCMP corresponds to a notification packet and contains control data of the frame. The MDP is transmitted with a message data slot (MDS) of a frame of the downlink channel. On the other hand, the FCMP is transmitted with a frame control message slot (FCMS) of a frame of the downlink channel.

Multimedia data are supplied from the network to the MDP generating portion 3 through the network controlling portion 2. The MDP generating portion 3 generates the MDP. The FCMP generating portion 4 generates the FCMP. A received packet determined by the received packet determining portion 10 is sent to the network through the network controlling portion 2. The network may be a cellular phone network, a broadcasting network, the Internet, or the like.

The base station 1 notifies mobile stations of slot allocation statuses of a frame of the downlink channel and a frame of the uplink channel with the FCMP at the beginning of each frame. Each mobile station can determine a data slot from which the mobile station can receive in accordance with the contents of the FCMP. Each mobile station can determine a data slot with which the mobile station can transmit data in accordance with the contents of the FCMP that represents the allocated status of data slots of the frame of the uplink channel. In addition, the FCMP contains information of the reception status of the base station against the frame of the uplink channel. In other words, the FCMP contains information that represents whether or not upload packets have been normally received by the base station.

Next, with reference to FIG. 2, an example of the structure of each mobile station will be described. A mobile station 21 corresponds to each terminal of the Patent Document 1. In FIG. 2, a data device is connected to a network controlling portion 22. The data device uses received data or generates transmission data. The data device is for example a cellular phone terminal, a personal computer, a digital broadcasting receiver, a digital camera, a car navigation device, a global positioning system (GPS), a display, an audio system, or the like.

Connected to the network controlling portion 22 are an activation packet (ACTP) generating portion 23 and an MDP generating portion 24. Disposed between the ACTP generating portion 23 and the MDP generating portion 24 and a transmitting portion 28 included in a radio device 27 is a selector 26. Data selected by the selector 26 are supplied to the transmitting portion 28. A radio signal supplied form the transmitting portion 28 is radiated from an antenna 29 and uploaded to the base station 1. The MDP is transmitted with a message data slot (MDS) of a frame of the uplink channel. On the other hand, the ACTP is transmitted with an activation slot (ACTS) of a frame of the uplink channel.

When the mobile station 21 has entered the communication area of the base station 1, the ACTP generating portion 23 generates the ACTP and transmits it to the base station 1 with the ACTS of a frame of the uplink channel. When the base station 1 has successfully registered the mobile station 21, it can communicate with the base station 1 using the uplink channel. When the base station 1 has allocated a slot of a frame of the uplink channel to the mobile station 21, the MDP generating portion 24 generates the MDP.

The base station 1 receives an upload request, a download request, and user data from the mobile station 21, and response information against data transmitted through the downlink channel with the MDP. The base station 1 exchanges the response data with the mobile station 21 against data transmitted with the FCMS using slots of a frame of the uplink channel and a frame of the downlink channel. The ACTP contains information necessary for registering the mobile station 21 to the base station 1.

When the mobile station 21 downloads data from the base station 1, the mobile station 21 receives the FCMP and the MDP from the base station 1 through the antenna 29 with the FCMS and MDS, respectively. A signal received by the antenna 29 is supplied to a received packet determining portion 31. The received packet determining portion 31 determines whether the received packet is the FCMP or MDP. In addition, the received packet determining portion 31 determines whether the received packet is for the mobile station 21 or another mobile station. The received packet determining portion 31 supplies the received packet to the data device through the network controlling portion 22.

The base station 1 (shown in FIG. 1) and the mobile station 21 (shown in FIG. 2) correspond to for example a base station and a mobile station disposed in a vehicle in an inter-vehicle communicating system, respectively. In reality, the present invention can be applied to an inter-vehicle communicating system shown in FIG. 3. The system shown in FIG. 3 is composed of an integrated base station 41, optical fibers 421, 422, . . . and so forth, and a plurality of local base stations 43.sub.1, 43.sub.2, . . . , and so forth. The local base stations 43.sub.1, 43.sub.2, . . . , and so forth are disposed along for example a road at predetermined intervals. The local base stations 43.sub.1, 43.sub.2, . . . , and so forth can communicate with a mobile station disposed in a vehicle 44. Other than the antenna are disposed in the integrated base station 41. Antennas are disposed in the local base stations 43.sub.1, 43.sub.2, . . . , and so forth.

In the inter-vehicle communicating system, the integrated base station 41 generates the MDP and FCMP that have been modulated in accordance with the predetermined radio modulating system. The resultant radio frequency signal is converted into an optical signal by a radio frequency signal--optical signal converting device. The radio frequency signal--optical signal converting device converts an optical signal of for example a laser diode. Alternatively, the radio frequency signal--optical signal converting device converts a radio frequency signal into an optical signal using an optical converter. The optical signal is transmitted to at least one of the local base stations 43.sub.1, 43.sub.2, . . . , and so forth through the optical fibers 42.sub.1, 42.sub.2, . . . and so forth. In the local base stations 43.sub.1, 43.sub.2, . . . , and so forth, an optical signal--radio frequency signal converting device typified by a photo diode converts an optical signal into a radio frequency signal. The radio frequency signal is transmitted with the MDP and FCMP from an antenna disposed along the road to the mobile station.

The mobile station disposed in the vehicle 44 has an antenna that receives a radio signal radiated from the road-side antenna and a connecting portion that sends the radio signal received by the antenna to a cellular phone or a broadcasting receiver. When data are uplinked, the ACTP and MDP modulated in accordance with a predetermined radio modulating system are received from the mobile station by the local base stations 43.sub.1, 43.sub.2, . . . , and so forth. The received ACTP and MDP are converted into an optical signal by a radio frequency signal--optical signal converting device that operates in the same theory as the foregoing radio frequency--optical signal converting device. The optical signal is transmitted to the integrated base station 41 through the optical fibers 42.sub.1, 42.sub.2, . . . and so forth. In the integrated base station 41, an optical signal--radio frequency signal converting device that operates in the same theory as the foregoing optical signal--radio frequency signal converting device converts the optical signal into a radio frequency signal. As a result, the ACTP and MDP transmitted from the mobile station are received.

Radio frequencies and intermediate frequencies modulated for cellular phones and broadcasts by a frequency converting, multiplexing, and demultiplexing device disposed in the integrated base station 41 may be multiplexed so that they are contained in a particular frequency band for example a millimeter wave band and radiated from a rode-side antenna. In this case, the mobile station disposed in the vehicle 44 has an antenna having sensitivity in a common frequency band, a frequency converting and demultiplexing device that converts a radio frequency signal received from the antenna into discrete radio frequency signals and intermediate frequency signals and distributes the converted signals, and a connecting portion that sends the discrete radio frequency signals and intermediate frequency signals to the cellular phone and the broadcasting receiver.

The base station 1 shown in FIG. 1 corresponds to all the integrated base station 41 and local base stations 43.sub.1, 43.sub.2, . . . , and so forth of the system shown in FIG. 3. The mobile station 21 shown in FIG. 2 corresponds to the mobile station disposed in the vehicle 44. In this example, the downlink channel from the base station 1 to the mobile station 21 and the uplink channel from the mobile station 21 to the base station 1 are simultaneously communicated.

The protocol of the present invention corresponds to the second layer (data link layer) of the OSI reference model. The data link layer is further divided into a media access control (MAC) layer and an logical link control (LLC) layer disposed above the MAC layer. FIG. 4A shows an example of the structure of a TDMA frame. One TDMA frame of the downlink channel is composed of one FCMS and a plurality of (n) MDSS.

One TDMA frame of the uplink channel is composed of one ACTS and a plurality of MDSs. The ACTS is composed of a plurality of mini slots. The frame period of a frame of the downlink channel is the same as that of a frame of the uplink channel. However, the slot period of a frame of the downlink channel is different from that of a frame of the uplink channel. Next, each slot will be described.

One TDMA frame always has one FCMS. The slot FCMS is allocated at the beginning of a TDMA frame. The FCMS is a slot dedicated for the downlink channel. The FCMS contains information about the base station, slot allocation information for frames of the downlink and uplink channels, acknowledgment (ACK) information against data of the uplink channel (user data). If the base station 1 detects an error, the base station 1 sends back negative acknowledgment (NACK) to the mobile station with the FCMS. In this case, the mobile station re-transmits the data from which the base station 1 has detected an error.

At least one MDS is allocated to one TDMA frame of the uplink channel and one TDMA frame of the downlink channel. In the downlink channel, the base station multiplexes the MDSs. In the uplink channel, a plurality of mobile stations MS multiplex the MDSs. The MDS is used for normal data communication. In the downlink channel, the base station uses the MDS to transmit registration--deregistration response (notification) and connection setup--connection release response (notification). In the uplink channel, the mobile station uses the MDS to transmit the ACK against data of the downlink channel (user data) to the base station.

The ACTS is allocated to one TDMA frame of the uplink channel. The ACTS is a random accessible slot. The mobile station uses the ACTS to transmit a registration--deregistration request to the base station. The mobile station may use the ACTS to transmit a connection setup--connection release request and so forth to the base station. The ACTS is composed of a plurality of mini slots. When the mobile station transmits a request to the base station, the mobile station randomly selects one of the mini slots of the ACTS and transmits the request to the base station in the selected time period of the ACTS.

Like the Patent Document 1 (see FIG. 31), a frame of the downlink channel has an FCMS that contains slot allocation information and a data slot MDS. However, unlike the Patent Document 1, a frame of the uplink channel does not have a slot for the ACK. In the uplink channel, the ACK against data of the downlink channel is transmitted with the MDS. In addition, slots for a download request and a upload request slot are not provided. A request is transmitted with the ACTS at the beginning of a frame of the uplink channel.

FIG. 4B shows a basic packet format of the FCMP, MDP, and ACTP. One slot is composed of a preamble PR, a unique word UW, a packet, and a guard time GT arranged in the order. The preamble and the unique word may be referred to as a header portion. In addition, the packet is a portion of which the preamble, the unique word, and the guard time are excluded from the slot. As shown in FIG. 4C, the packet is composed of a header having a fixed length and a payload having a variable length.

The guard time is disposed to prevent bursts from colliding due to the difference between transmission delays of terminals. Since the slot period of a frame of the uplink channel is different from the slot period of a frame of the downlink channel, their guard time lengths may differ from each other. However, the guard times of slots of a frame of the uplink channel are the same. Likewise, the guard times of slots of a frame of the downlink channel are the same.

The length of the header portion composed of the preamble and the unique word is decided in accordance with the desired reliability for the FCMS, MDS, and ACTS.

Next, the slot allocation system and the transmission of the ACK in the downlink channel will be described. FIG. 5 shows an example of the contents of a transmission buffer of the base station. Recipient addresses (addresses of mobile stations) are designated by A, B, C, . . . , and so forth. Data (1-1, 1-2, 1-3, . . . , and 1-6) stored in the first one line of the transmission buffer are a block of data (hereinafter referred to as a sequence) transmitted to the recipient address A. The last packet 1-6 contains an EOD that represents the end of the data. This sequence is also referred to as an upper layer protocol data unit (PDU). The sequence corresponds to one Ethernet packet or an IP packet to be transmitted, to each mobile station. Likewise, data (2-1, 2-2, . . . , and 2-5) are data of sequence number 2 to be transmitted to the recipient address B. Likewise, data to be transmitted to the recipient addresses A, B, and C are shown. In the drawing, 1-1, 1-2, . . . and so forth represent packets (MDPs) allocated in the MDSs.

When data to be transmitted are stored in the transmission buffer, there are three methods for allocating slots of frames of the downlink channel. The first method is called the FIFO (First-In First-Out) method. The second method is called the round robin method. The third method is called the modified FIFO method. Next, these three methods will be described in succession.

FIG. 6 shows the FIFO method. In the downlink channel, packets are allocated in slots of a TDMA frame in the order that these packets have been stored in the transmission buffer. In the example, one TDMA frame of the downlink channel is composed of one FCMS and eight MDSs. When the mobile station of the recipient address A normally receives one sequence of data, the mobile station sends back the ACK to the base station with the MDS of a frame of the uplink channel. When the mobile station receives data (1-1, . . . , and 1-6) of the sequence number 1, the mobile station sends back 1-ACK to the base station with the MDS. Likewise, whenever each mobile station receives each sequence of data, the mobile station sends back the ACK to the base station.

FIG. 7 shows the round robin method. In the round robin method, the base station asks each mobile station of recipient address whether or not the transmission buffer stores data to be transmit to each mobile station. When the transmission buffer stores data to be transmitted to the mobile stations, the data are transmitted to the mobile stations with slots of frames of the downlink channel. In this example, the transmission buffer stores data to be transmitted to the mobile stations of the recipient addresses A, B, and C, the base station repeatedly and successively asks the mobile stations of the recipient addresses A, B, and C whether or not to the transmission buffer stores data to be transmitted to the mobile stations. In the example shown in FIG. 5, the base station completes the transmission of data of sequence number 5 to the mobile station of the recipient address C at first. Thereafter, the base station repeatedly and successively asks the mobile stations of the recipient addresses A and B whether or not to the transmission buffer stores data to be transmitted to the mobile stations. After the base station has completely transmitted data of sequence num