KR20010023207A - Radio communication system - Google Patents

Abstract

The present invention relates to a wireless communication system, and more particularly to a wireless communication system for use with a local area network having at least one receiver transmitter device coupled to a local area network for communicating with one or more wireless mobile devices. Data transmission occurs via a wireless communication system between at least one reference base station and at least one far base station. When the far base station is within a predetermined range, the reference base station may transmit and receive a signal with the far base station. Priority is assigned to each type of data transmitted and the priority of each subsequent transmission is determined and stored. Thereafter, the highest priority data type is transmitted in advance of the data type having the lower priority. If there is more than one reference base station, there will be multiple overlapping communication cells. The reference base station transmits a signal in a first time period, and the far base station transmits a signal in a second time period. The reference base station is coupled to a central control unit that synchronizes first and second time periods used by the reference base station in adjacent cells. The number of transmissions in each cell is monitored and the duration of each of the first and second time periods is adjusted to improve the use of the effective transmission bandwidth. The transmission from the far base station to the reference base station may be sent after a predetermined delay that varies with the distance of the far base station from the reference base station.

Description

Wireless communication system {RADIO COMMUNICATION SYSTEM}

The present invention has been developed in connection with an asynchronous transmission mode (ATM) network infrastructure using wireless communications capable of supporting multimedia data exchange at speeds of 25 Mb / s to 2.4 Gb / s at near and far distances. However, the present invention can also be used with other network infrastructure.

In a standard ATM network, all devices operating on the network are connected to the network by cable. However, there is an increasing demand for mobile devices that can communicate with the network. The mobile device may include articles such as laptop and notebook portable computers, cameras, and the like. The basic wireless network system is described in a paper entitled "The ORL Radio ATM System, Architecture and Implementation" dated January 16, 1996 and is published on the website www.orl.co.uk.

In the proposed system, the network is a plurality of base stations or access points (APs) connected to a standard wired network or a plurality of mobile base stations or radios connected to portable laptop and laptop computers, for example. It has a terminal (wireless terminal). 1 schematically illustrates a set of access points and wireless terminals operating in a network. The network 2 has an access point 4 connected thereto. The access points are physically separated and each access point may send and receive messages, for example, in a limited range of up to 30 meters. The range covered by transmission between a single access point is called a pico-cell 6. The pico-cells overlap to ensure that all desired areas are covered by the wireless system. The channels through which the access point 4 sends and receives messages are chosen so that adjacent contacts use different radio channels and do not interfere with each other.

The wireless terminal 8 operates within the pico-cell 6 and can move between pico-cells. The wireless terminal transmits and receives data from an access point 4 which controls the pico-cell to which the wireless terminal belongs. When a wireless terminal approaches a neighboring pico-cell boundary, handshaking and cross-over operations occur as the wireless terminal moves to the neighboring pico-cell and begins transmitting and receiving with the radio channel of the pico-cell. Happens.

Multiple access points will be located in the building to provide full coverage.

Each access point communicates with a wireless terminal in its pico-cell using a frame transmission structure. The frame structure provides time division multiple access to the wireless channel. The frame is divided into a first part that the access point transmits and two parts that the wireless terminal can transmit.

The access point first transmits a preamble comprising a number of data and control messages following the frame description message. During the time reserved for a wireless terminal, many other wireless terminals may transmit. Such transmissions include data and control messages. The wireless terminal is assigned a time slot when trying to send a data message. The wireless terminal may be assigned a specific periodic time slot when transmitting. The access point and the wireless terminal exchange request and assignment messages with the WT for a future time slot.

In addition to assigning time slots to specific transmissions, the access point must prioritize other data types and thus manage the allocation of time slots. Some data types, such as voice data, require high priority to ensure that they are sent in real time without interruption over the wireless link. Managing such a configuration presents various problems with the wireless communication configuration.

Another problem exists in such systems in that splitting prediction between upstream transmissions (WT to AP) and downstream transmissions (AP to WT) is difficult to predict. This will depend on your needs at some point. With a fixed frame structure this prevents the full use of the effective bandwidth, especially when there are a small number of WTs within the AP range.

This can be overcome by using variable frame length and variable partitioning between upstream and downstream data transmissions depending on the total call volume. However, since neighboring APs have overlapping coverage areas, this can cause problems with crosstalk between devices in the system.

Another synchronization problem occurs because some WTs are further away from the AP than others. This means that the WT receives data from the nearest AP. Assuming these are the same delay between transmission from AP to WT and transmission from WT to AP as a remote WT, this will cause lack of synchronization in transmission from WT to AP.

Summary of the Invention

The preferred embodiment provides an apparatus for allocating time slots for data transmission in accordance with the priority given to the data type for transmission from AP to WT and transmission from WT to AP. Such devices can be implemented using field programmable gate arrays (FPGAs) and storage devices. It assigns slots to the WTs by the WT and prioritizes the transmission for each WT.

Another embodiment provides, for example, a configuration for synchronizing the frame structure used by adjacent access points that provide the same frame length and split between upstream and downstream transmissions to each AP and synchronize the transmissions. However, the frame structure (length and division) can be changed as the user's request by the data transmission change, thereby making the optimum use of the effective bandwidth.

Preferably, the WT in proximity to the AP inserts a variable delay before transmitting data to the AP to synchronize transmissions with data transmitted by the WT at a greater distance from the AP.

The invention is defined in various aspects in more detail in the appended claims, which should be referenced.

The present invention relates to a wireless communication system, and more particularly to a wireless communication system for use with a local area network having at least one receiver transmitter device coupled to a local area network for communicating with one or more wireless mobile devices.

The invention will be described in detail by way of examples with reference to the drawings.

1 is a schematic diagram of a network access point and a wireless terminal for use in practicing the present invention as described above.

FIG. 2 shows a timing diagram for a series of frames received and transmitted by the WT and AP in the schematic diagram of FIG. 1.

3 shows a table stored in a storage device for determining transmission priority.

4 illustrates a register bank used in conjunction with the table of FIG. 3 for transmission scheduling.

5 shows a set of synchronized frames transmitted in an adjacent pico-cell.

The form of data transmission between the access point 4 and the wireless terminal 8 can be best understood with reference to FIG. 2. The transmission comprises a series of frames having a downstream portion which the wireless terminal transmits to the access point after the upstream access point 4 transmits to the WT in its pico-cell. A null period (TTn) is provided while the access point and the wireless terminal switch between reception and transmission modes. In FIG. 2, the left column shows events that occur in the WT and the right column shows events that occur in the AP. The bright part is the transmission from the AP to the WT, and the dark part is the transmission from the WT to the AP.

The identifier used in the example of FIG. 3 is as follows.

TTO: Return time from WT to AP.

PRE: full access point (not shown)

FD: frame descriptor map

RG: Reservation approval

DACK: downstream confirmation

DCELL: Downstream data cell transmission

TT1: Return time from AP to WT

RR: Upstream Reservation Request

UACK: Upstream Check

UCELL: Upstream data cell (start of burst)

In the present embodiment, the first part of the frame is followed by a field descriptor (FD) followed by a field descriptor (FD) transmitted to all mobile devices in the pico-cell 6 controlled by the particular access point 4. -Not shown). The frame descriptor informs all wireless terminals 8 and frames of subsequent formats.

Following the frame descriptor, there is a reserved grant slot (RG) which is used to contend with an undetermined transmission slot in the frame for data transmission to the access point and inform the approved WT. This is a confirmation of the reservation request and informs the WT of the number of recently allocated data cell transmission opportunities. This is the basic information included in all transmissions from the access point to the wireless terminal. After this step, an upstream data cell transmission from the mobile device and a downstream acknowledgment (DACK) of the downstream data cell transmission (DCELL) are performed.

The access point is then switched from transmit to receive mode and the wireless terminal is followed by a null period TT1 while switching from receive to transmit mode. The wireless terminal 8 may then send an upstream reservation request RR in the next slot of the frame. If more than one terminal transmits an upstream reservation request at the same time, contention may exist and the reservation request may be lost. As such, this can be done after any upstream data cell (UCELL) that needs to be sent upstream of the downstream data cell and transmitted.

There is then an additional null period while the access point switches back to transmit mode and the wireless terminal switches back to receive mode before the start of the next frame. The above is the basic frame structure.

As shown, the minimum frame is as follows.

TTO PRE FD RG TT1 TTO

The reservation request is as follows.

TTO PRE FD RG TT1 RR TTO PRE FD RG TT1

The burst of four data cells from one mobile device is shown below.

RG TT1 rr UCELL (× 4) TTO PRE FD RG DACK TT1

… … …

The processing sequence continues indefinitely.

The preceding field descriptor is a preamble (not shown).

This includes certain basic housekeeping information such as synchronization data. The access point and the wireless terminal use the full text to synchronize the reception and adjust the automatic gain control for the reception.

When the AP receives a reservation request, it responds to the reservation grant transmission as described above. This means that time slots are allocated to mobile devices. The WT then notifies this when it is allowed to send a message included in the FD of a subsequent frame, and then transmits a preset number of data cells in that frame. If the WT has more data cells than can be adjusted within a particular frame, another permission will be included in subsequent frames to send the message. This will continue until the WT has sent all its data.

Prioritize Delivery

The manner in which the AP handles data transmissions having different priorities is shown with reference to FIGS. 3 and 4.

The AP stores the table of the type shown in FIG. 3 in its local storage. This includes for the WT to AP transmission record of the data type (DTN) that can be transmitted and for the AP to WT transmission record. The flag F indicates whether a particular WT requires or requires transmission for each data type in an upstream or downstream transmission, where N is the number of data cells required for that particular transmission.

The data type has a different priority. This embodiment shows only three data types but more data types may be used. DT1 has the highest priority and DT3 has the lowest priority. An entry is made in the stored table for the next transfer. Entries in the table correspond to reservations and this corresponds to any number of transfers. The reservation is maintained until it is removed by the WT and continues to generate transmission opportunities.

Each time a new entry is made in the table of FIG. 3, the corresponding entry is made in the register bank shown in FIG. It contains a shift register for each data type for upstream and downstream transmissions. Thus, the column corresponds to the column of the table of FIG. 3 where the column representing the shift register of FIG. These registers are used to queue the next transfer when they are requested.

The counter is provided with a register bank for indicating the start and end points of entries in registers for each data type. This ensures that the new entry is in the correct location. The register acts like a first-in first-out (FIFO) register.

When allocating a data cell in a frame, the access point will first allocate the first request from the WT to the highest priority transmission. In the given example, this is a request from WT4 for upstream transmission and an assignment to WT5 for downstream transmission. The data cell is assigned to the field descriptor on the next frame and the data will be transmitted. On the next frame, the highest priority DT1 request will be allocated by WT3 to the data cell accordingly. The number of data cells is taken from the table of FIG. 3 stored in storage. There will be no allocation of data cells to DT2 and DT3 type data of either upstream or downstream transmission until all DT2 allocations have been processed respectively. After these have been processed, the DT2 data is transmitted. When no outstanding problem exists, DT3 type data will be transmitted. Thus, data is prioritized and scheduled to ensure optimal transmission.

If a particular WT requires transmitting more than the number of data cells available in a single frame, the excess data cells will remain until the next frame. If the request for DT1 transmission is repeated upstream or downstream to such an extent that DT2 and DT3 are not transmitted at all, the system is subject to periodic transmission of data of DT2 and DT3 type to ensure that they actually reach their destination. It can be changed to ensure that.

The apparatus may be implemented in a direct manner using random access memory (RAM), a register bank and an FPGA, and the control circuit may be preferably implemented using software control.

The additional entries shown in the table of FIG. 3 are for the antenna used in the transmission between the AP and each WT. The AT is preferably provided with at least two antennas and periodically checks the quality of transmission to each WT within its particular defendant-cell. A value is then stored that indicates which antenna provides the best communication with each WT. This information is then used for upstream and downstream transmissions between the AP and each WT.

This entry may change if any of the WTs move.

A given WT will generate data at a fixed rate, for example audio data. In order to coordinate such data, the configuration may be modified such that the AP pre-allocates a time slot for the type of data transmission and uses it in addition to the queue of data types shown in FIG. The table of FIG. 3 may be extended to include an entry for the WT requiring constant bit-rate transmission on the upstream or downstream side. An entry for such a transmission can then be made in every frame to ensure data loss.

Variable frame structure

As described above, interference between transmissions in adjacent pico-cells can cause problems, particularly when variable frame lengths are used and transmissions in adjacent pico-cells are not synchronized. This can occur even if the frequencies used in adjacent pico-cells are different and the isolation between channels is limited.

The problem is that by providing a synchronized frame structure for neighboring pico-cells, i.e., the transmission in each pico-cell starts and ends at the same time, and the split between upstream and downstream exchanges as transmission in the neighboring pico-cell. Of course it can be overcome. This idea is shown schematically in FIG. 5. This shows a series of transmissions for two adjacent pico-cells named PC1 and PC2. Downstream transmissions from the AP to the WT are denoted A, and upstream transmissions from the WT to the AP are denoted B. Thus, each frame includes the sum of the portions A and B.

As can be seen from the figure, in each frame part A and part B start and end at exactly the same time in PC1 and PC2. For this reason, the interference between the two frames will be eliminated.

However, it will be appreciated that the overall length of the frame varies over time and the portion of the frame allocated for upstream and downstream transmissions also changes over time. This change in frame length monitors the upstream and downstream transmission needs of adjacent pico-cells at a central controller connected to an access point at a given time, and determines the optimal frame length and split between upstream and downstream transmissions. This is accomplished by using this.

Delay compensation

As described above, in communication with each other, the WTs remote from the AP will receive downstream data at a time delayed than the WT close to the AP. Thus, they will start calculating the return time (TT1 in FIG. 1) at the delayed time and perform their upstream transmission at the delayed time. This will cause contention at the AP with transmissions from other WTs.

To overcome this, a variable delay is provided in each of the WTs to insert between the reception of the downstream transmission and the AP. The system is configured to set a delay such that the WT proximate to the AP has an inserted delay to simulate the effect of the WT being at the maximum possible distance from the AP.

Initially, all mobile devices have no delay information. The first transmission that the mobile device can perform is in the reservation request slot state and the default transmission delay is O. This means that the reservation request may appear earlier than the AP, but may conflict with other reservation requests from other mobile devices in a normal manner. The acknowledgment of the reservation request and the data cell by the AP include delay correction information so that the mobile device can later synchronize at an appropriate delay.

Claims (6)

A method for determining the priority of data transmission in a wireless communication system having at least one reference base station and at least one far base station, the method comprising: A reference base station configured to transmit and receive signals with the remote base station while the remote base station is within a predetermined area, Assigning a priority to each type of data to be transmitted; Determining the type and priority of each next transmission; Storing data relating to the next transmission for each data type; And Transmitting the data type having the highest priority in advance of the data type having the lower priority. Method comprising a. 2. The transmission of claim 1, wherein the transmission between the reference base station and the far base station is performed by the reference base station transmitting data to the reference base station in a pre-allocated time slot in every time period and by the far base station. And a series of time periods each having a second portion to transmit, wherein time slots in each time period are allocated to data transmission according to priorities assigned to the data types to be transmitted and received with each remote base station. Way. 3. The method of claim 2, wherein the reference base station transmits and receives signals to and from a plurality of remote base stations, and the time slots in each time period depend on the priority assigned to the data type to be transmitted and the time for which the request for transmission is made. And assigned to transmission between the reference base station and the individual far base station. 4. The method of claim 2 or 3, further comprising: transmitting constant bit-rate data between the reference base station and at least one remote base station and allocating at least some of the time slots in every time period for transmission of the constant bit-rate data. And comprising a step. A method for wireless communication for use with a plurality of overlapping communication cells, the method comprising: Each cell includes a reference base station and at least one far base station, wherein the base station transmits a signal in a first time period and the far base station transmits a signal to the reference base station in a second time period, in each of the cells. Reference base station is connected to the central control unit, Synchronizing the first and second time periods used by a reference base station of an adjacent cell; Monitoring transmissions in each cell; And Adjusting each period of the first and second time periods to improve the use of effective transmission bandwidth while maintaining synchronization of the first and second time periods between adjacent cells. Method comprising a. A method for wireless communication between a reference base station and a plurality of distant base stations, A reference base station capable of transmitting and receiving signals with the plurality of remote base stations, Transmitting a signal from the reference base station to the far base station during a first time period; Transmitting a signal from the far base station to the reference base station after a predetermined delay; And Varying a delay according to the distance of the far base station from the reference base station Method comprising a.