SE516564C2 - Method and apparatus for data packet communication - Google Patents

Abstract

A method and apparatus are provided for improving packet data communications in a point to multi-point communication system (1) having a primary node (BS) and secondary nodes (SU1-SU5). Data packets, which are to be transmitted from the primary node to one or more of the secondary nodes, are stored by the primary node. A time interval for transmitting a first data packet (111) from one of the secondary nodes to the primary node is established. After establishing the time interval for the transmission of the first data packet, a second data packet (113) is selected from the stored data packets. The transmission of the second data packet over a first downlink is timed so that an acknowledgement packet (115) acknowledging a receipt of the first data packet can be transmitted promptly over the first downlink from the primary node after the receipt of the first data packet.

Description

25 30 u u n u oo .m 6 56, w 2 Today, however, there is a growing interest in data communication, e.g. electronic mail, Internet, fl delivery transfers etcetera. For many types of data communication, however, circuit switching is not the optimal solution. Data packet transmission is an alternative type of connection, which is often more suitable for data communication. The information, which is to be transmitted through a data packet network using data packet switching, is divided into packets, which do not have to be the same length. Each data packet contains an address indicating its destination. When the data packets reach a node in the data packet network, the data packets are sometimes checked for bit errors, e.g. by means of cyclic redundancy check (CRC), which could have occurred during the transmission, and a retransmission is requested if bit errors are detected. Today, however, it is not uncommon for the error check to be performed only when the package has reached its destination. However, error checking and retransmission cause delays in the transmission of information. If no bit errors are detected, the address of the packet is read and the packet is forwarded to a next node. This is repeated until the package reaches its destination. At the destination, the package is collected and the original information is compiled from the packages. In data packet transmission, there is no assigned connection (channel) for each user. The transmission of information requires only as much (or as little) of the channel resources (eg bandwidth or time) as is necessary. Packet data transfer is not normally the best choice for voice and video communications, due to the delays involved. Data packet transmission is instead very suitable for most types of data communication, thanks to the high accuracy that error checking and retransmission results in.

Wireless data packet networks have also been designed. The wireless data packet networks are usually designed as overlay systems on the existing PLMN, e.g. CDPD (English: Cellular Digital Packet Radio, English: Cellular Digital Packet Radio) for the AMPS and D-AMPS systems and GPRS (English: General Packet Radio Service) for the GSM system. However, there are also wireless communication systems, which have been designed more exclusively for data packet communication, e.g. mobitex, Hiperlan / 2 or systems according to the wireless LAN standard 10 15 20 25 conc nu u à (S16, (564 3 IEEE 802.11. In wireless data packet systems, the base stations are normally connected (directly or via an intermediate node such as a mobile telephone exchange) to a The PDBN (English: Packet Data Backbone Network) The said PDBN comprises one or more node (s) for performing the data packet processing within the country system. Internet, Intranet, PSTN, ISDN or mobile networks, the PDBN can also be connected to individual computers (Lex. PCs).

The base station and the connected subscriber units constitute a kind of point-to-point system where the base station is a primary node and the subscriber units are secondary nodes. Of course, only a limited amount of bandwidth can be used when the base station is to deliver data packet services to the connected subscriber units. Since there are several subscriber units that are to share the data packet services provided by the base station, it is desirable to use the available communication resources efficiently, so that the data packet services delivered to the subscriber units are of good quality.

Summary of the Invention The present invention addresses the problem of improving data packet communication in a point-to-point communication system having a primary node and secondary nodes, which nodes perform data packet communication over an uplink and a downlink, wherein at least the primary node is arranged to acknowledge receipt of a data packet by sending a receipt packet.

The problem presented above is solved, in short, by introducing methods and devices for an improved coordination of the transmission of data and control information in the point-to-point communication system. 10 15 20 25 30 516 56-? ::: = 4 An object of the invention is therefore to deliver improved data packet communication in a point-to-point communication system and the invention comprises both methods and devices for achieving this object.

The problem presented above is solved, in a little more detail, as follows. Data packets to be transferred from the primary node to one or more secondary nodes are stored by the primary node. A time interval for transmitting a first data packet from one of the secondary nodes to the primary node is determined. After determining the time interval for the transmission of the first data packet, a second data packet is selected from the stored data packets. The transmission of the second data packet over the first downlink is timed so that an acknowledgment packet acknowledging receipt of the first data packet can be transmitted over the first downlink from the primary node immediately after receiving the first data packet. A retransmission of the first data packet is avoided. The opposite fl fates of data packets over the first uplink and the first downlink are, therefore, better organized and deliver efficient full duplex data packet communication.

A main advantage of the invention is that available communication resources are used more efficiently and thus provide users of the data packet communication systems with higher speed and quality.

The invention will now be further described by means of preferred embodiments and with references to the figures.

Brief description of the figures Figure 1 shows a block diagram of a communication system comprising WLAN.

Figure 2 shows a block diagram of a base station in adjacent WLANs.

Figure 3 shows a block diagram of a typical subscriber unit in said WLAN.

Figure 4 shows a diagram of a structure on an RTS packet. 10 15 20 25 30. Figure 5 shows a diagram of a structure on a CTS packet.

Figure 6 shows a diagram of a structure on a data packet.

Figure 7 shows a diagram of a structure on an ACK package.

Figure 8 shows a number of time diagrams illustrating a coordination of data packet communication in the WLAN.

Preferred Embodiments Figure 1 shows a block diagram of a WLAN 1 (Wireless Local Area Network) according to an embodiment of the invention. The WLAN 1 comprises a (radio) base station BS and a number of subscriber units SU1-SU5, for example computers with associated radio communication equipment, radio telephones (fixed or mobile) or cordless screen telephones and so on. The base station BS and the subscriber units SU1-SU5 are arranged to perform data packet communication by using a first radio channel rcl and a second radio channel rc2. The first radio channel functions as an uplink, i.e. as a communication link for data packet communication from the subscriber units SU1-SU5 to the base station BS. The subscriber units SU1-SU5 take turns using the first radio channel rcl. The second radio channel rc2 is used by the base station BS for data packet communication to any of the subscriber units SU1-SU5. The base station BS is connected to a PDBN 4 (eng: Packet Data Backbone Network, sve: Datapaketryggradsnätverk) via a data communication link 3. The data communication link 3 can e.g. be a landline connection (for example, an optical cable or a coaxial cable), an xDSL connection, or a microwave link. DSL stands for Digital Subscriber Line; xzet is used to indicate the different variations of DSL, such as ADSL, HDSL and VDSL. Communications over the data communication link 3 are performed by using appropriate data packet protocols, such as Ethernet (a widely used technology for local area networks, now Standardized in IEEE 802.3), ATM (English: Asynchronous Transfer Mode) or IP (Asynchronous Transfer Mode). eng: Intemet Protocol, sve: Internetprotokoll). The PDBN 4 is connected to a number of communicators; -s f;: = 6 tion networks. In the particular example in Figure 1, the networks connected to said PDBN are: Internet 5; a PSTN 6 (Public Switched Telephone Network), i.e. a regular fixed telephone network; an ISDN 7 (eng: Integrated Services Digital Network, eng: Integrated Services Digital Network); and a CN 8 (eng: Corporate Network, sve: Företagsnätverk), e.g. an intranet. Accordingly, the subscriber units SULSUS can participate in data packet communication with each other via the base station BS or via the base station BS and the PDBN 4, with other communication units (not shown) connected to the communication networks 5-8.

Figure 2 is a block diagram describing the base station BS in more detail according to a preferred embodiment. The base station BS comprises a (radio) transceiver 21 having a transmitter 23 and receiver 25. The transmitter 23 is arranged to transmit radio signals on the second radio channel rc2 (downlink). In the particular example of Figure 2, the transmitter 23 includes an up-converter 29 and a D / A converter 27. The up-converter is connected to an antenna 35 and to the D / A converter 27. The D / A converter 27 is also connected to a data packet control unit 37 and is arranged to receive digitally modulated baseband signals from the data packet control unit 37.

The digitally modulated baseband signals include data packets and communication control packets, which are to be transmitted from the base station to the subscriber units using the second radio channel rc2. In a manner well known to a person skilled in the art, the up-converter is arranged to supply a frequency change of an analog signal from the D / A-converter from a baseband frequency range to a frequency range belonging to the second radio channel rc2. In the particular example of Figure 2, the receiver 25 includes a down-converter connected to the antenna 35. The down-converter 33 is arranged, in a manner well known to those skilled in the art, to change the frequency of radio signals received by the antenna 35. The received the radio signals have their frequency changed from a frequency range belonging to the first radio channel rcl to the baseband frequency range. The receiver 25 also includes an A / D converter 31, which is connected to the down-converter 33 and the data packet control unit 37. The data packet control unit 37 is arranged to receive and demodulate digital signals from the A / D-10. u ~ ao v51 6 55.4 'š 2 .f ::: = 7 converter 31. The digital signals include both data packets and communication control packets. The data packet control unit 37 is also connected to a buffer system 39, which has one or two buffers in which data packets to be sent to one or two of the subscriber units SU1-SU5 are temporarily stored.

In addition to the examples given above, the subscriber units SUI-SU5 can also be communication providers of a more general type. Figure 3 shows a block diagram that describes in detail a type of subscriber unit with an ability to deliver communication services to many types of communication equipment. The subscriber unit in Figure 3 comprises a transceiver 42, which has a transmitter 45 and a receiver 47. The construction and function of the transmitter 45 in Figure 3 are similar to the construction and function of the transmitter in Figure 2. Of course, the transmitter 45 is arranged to broadcast on the first radio channel rcl (uplink). The transmitter 45 comprises an up-converter 29, which is connected to an antenna 57 and a D / A-converter 49. The D / A-converter is also connected to a data packet control unit 59, which is arranged to control data packet functions on the subscriber unit in Figure 3. The construction and function of the receiver 47 in the subscriber unit in Figure 3 is similar to the construction and function of the receiver 25 in Figure 2. Of course, however, the receiver 47 is arranged to receive radio signals on the second radio channel rc2 (downlink).

The receiver 47 comprises a down-converter 55, which is connected to the antenna 57 and to an A / D-converter 53, which A / D-converter 53 is also connected to the data packet control unit 59.

Furthermore, the data packet control unit 59 is connected to a number (in this example three) of CPEs 63 (eng: Customer Premises Equipment) via associated data links. Approximate CPEs 63 include equipment for communicating with the data packet controller 59 over the data links 61. The data links may be both wireless links and "wire" connections. In principle, any suitable data communication protocol can be used, e.g. Ethernet, POTS (Plain Old Telephone Service, Swedish: Standard Old Telephone Service), ISDN, WLAN protocol, wireless 10 15 20 25 30 g (516 564 8 short distance connections (eg based on the Bluetooth specification or similar Approximate CPEs 63 can be virtually any customer equipment, such as personal computers, landlines, cell phones, screen telephones, TVs or videos, household appliances (such as a refrigerator or freezer) and so on.

The WLAN 1 is a point-to-point system, where the base station BS constitutes a primary node, which controls the data packet communication over the radio channels rcl and rc2. Consequently, when one of the subscriber units is to transmit a data packet by using the first radio channel rcl, the transmission must be allowed by the data packet control unit 37 in the base station BS. Furthermore, a suitable time interval for the transmission must be determined. Below are the steps commonly used in WLANs to control the transmission of data packets from the subscriber units SU1-SU5.

- The subscriber unit transmits an RTS (Request To Send) package on the first radio channel rcl (uplink). The RTS packet indicates to the base station BS that the subscriber unit requests to transmit data packets of a special duration or size.

- After receiving the RTS packet, the base station is arranged to evaluate the request and, if the request is deemed acceptable, to send a CTS packet (Clear To Send) on the other radio channel rc2 . The CTS packet indicates that the transmission of data packets is allowed and determines the time interval for transmission of the data packet.

- After receiving the data packet, the base station is arranged to send an ACK packet (English: Acknowledgment, sve: Kvittens) to the subscriber unit that has sent the data packet. The ACK packet indicates to the subscriber unit the receipt, at the base station BS, of the transmitted data packet and if any bit errors have occurred during the transmission of the data packet. If the subscriber unit does not receive the ACK packet in good time after the transmission, or if bit errors have occurred, the subscriber unit is arranged to perform a retransmission of the data packet. Figure 15 shows a diagram illustrating a typical structure of an RTS packet. The RTS packet in Figure 4 includes a synchronization sequence 71. , an address field 73 and a request field 75. The address field 73 includes a transmitter address identifying the subscriber unit transmitting the RTS packet.The address field also includes a recipient address identifying the base station BS as the recipient of the RTS packet.The request field includes a request to transfer a data packet of a particular size or duration.

Figure 5 shows a diagram illustrating a typical structure of a CTS packet. The CTS packet in Figure 5 includes a synchronization sequence 77, an address field 79 and a permission field 81. The address field 79 comprises a transmitter address, which identifies the base station BS. The address field 79 also includes a recipient address that identifies the subscriber unit that sent the RTS packet. The permission field 81 includes an indication that a transmission of a data packet is allowed. The permission field also determines an actual time interval when the subscriber unit is allowed to transmit the data packet. All subscriber units receive the CTS packet and consequently all subscriber units are informed about which of the subscriber units has been granted permission to transmit the data packet and also when the data packet will be transmitted.

Figure 6 shows a diagram illustrating a typical structure of a data packet. The data packet in Figure 6 includes a synchronization sequence 83, a message type field 85, an address field 87, a data field 89 and an error detection field 91. The message type field includes information identifying the message type and also a priority associated with the data packet. The address field 87 includes a transmitter address that identifies the node (base station or subscriber station) that transmits the data packet. The address field 87 also includes a recipient address, which identifies the receiving node (base station or subscriber unit). The data contained in data field 89 may in principle represent any type of information, such as text (eg e-mail), database information, images, sound (eg voice or music), program code, data relating to to distributed game playing, financial transaction and so on. Error detection 10 in 1515 »564 10 in the coverage field includes an error detection code, e.g. CRC (Cyclic Redundancy Check) or similar.

Figure 7 shows a diagram illustrating a typical structure of the ACK package. The ACK packet in Figure 7 includes a synchronization sequence 93, an address field 95 and an acknowledgment field 97. The address field 95 includes a transmitter address identifying the base station BS and a receiver address identifying the subscriber unit which transmitted over the data packet.

The above steps for controlling and performing data packet transmissions from the subscriber units SU1-SUS have hitherto been used in half-duplex systems. However, the WLAN 1 in Figure 1 is a full duplex system, in the sense that transmissions over the first radio channel rcl (uplink) and transmissions over the second radio channel rc2 (downlink) can be performed simultaneously. The first channel rcl is used when data packets and communication control packets (RTS and ACK) are transmitted from subscriber units SU1-SU5 to the base station BS. The second radio channel rc2 is used when the control packet is transmitted from the base station BS to the subscriber units SU1-SUS, e.g. CTS packets and ACK packets, which acknowledge receipt of data packets transmitted from the subscriber units SU1-SU5. However, the second radio channel rc2 is also used in transmitting data packets from the base station to the subscriber units SU1-SU5. In order to make efficient use of the radio channels rcl and rc2, there must be an appropriate coordination of the data packet communications over the radio channels rcl and rc2.

Figure 8 includes three timing diagrams illustrating the base station BS's coordination of the data packet communication over the first radio channel rcl (uplink) and the second radio channel rc2 (downlink).

In the example of Figure 8, the second subscriber unit SU2 has requested to transmit a first data packet 111. The base station BS has then determined a time interval when the second subscriber unit is to transmit the second data packet 111. The lower diagram in 10 15 20 25 30 o tesae 564 11 fi gur 8 illustrates the transmission of the first data packet 111 from the second subscriber unit SU2 during the determined time interval, i.e. between a time t1 and time t2. The first data packet 111 has been received completely by the base station at a time t3. Of course, time t2 precedes time t3 due to the limited propagation speed of radio waves.

After determining the time interval for the transmission of the first data packet 111, the base station BS is arranged to select a second 113 from the buffer system 39. In the particular example in Fig. 8, the selected second data packet 113 is to be transmitted to the first subscriber unit SU1. The base station BS is arranged to time a transmission of the second data packet 113 so that the base station BS, after receiving the first data packet 111, can directly transmit an ACK packet 115 to the second subscriber unit SU2, in order to avoid an unnecessary retransmitting the first data packet 111 from the second subscriber unit SU2. Preferably, the base station is arranged to time the transmission of the second data packet 113 so that it has been transmitted from the base station BS before the time t3, but preferably as close to the time t3 as possible. In the example of Figure 8, the ACK packet has been completely received by the second subscriber unit SU2 at a time t4. In order to facilitate the timing of the transmission of the second data packet 113, the base station is preferably arranged to select the second data packet 113 so that a duration of the second data packet 113 is equal to or less than the duration (t2-t1) of the first data packet 111. In the particular example of Figure 8, the second data packet 113 has a duration which is less than the duration of the first data packet 111.

In an embodiment where the base station BS is arranged to monitor transmission delays between the base station BS and the subscriber units SU1-SU5, the base station BS can easily calculate the time t3 and base the timing of the transmission of the second data packet on this calculation. In the example in Figure 8, however, another method is used. In Figure 8, the timing of the transmission of the second data packet 113 is such that the transmission of the second data packet 113 ceases simultaneously with the transmission. .. ..: .z - - -. . . .. - - »i .... . ; g; ; _. a, o '. :: 'r u:: nf :,,, I I t n. H'. 'Ö E I I I' none of the first data packet lll. The timing method in Figure 8 is advantageous because it can be used even when the base station BS is not provided for monitoring the transmission delays. After receiving the second data packet at time t5, the first subscriber unit SU1 is arranged to transmit an ACK packet 117 to the base station BS. The transmission of the ACK packet 117 is shown in the circuit diagram in Figure 8. The ACK packet 117 is completely received by the base station BS at a time t6. Thanks to the special timing of the transmission of the second data packet 113, the first subscriber unit SU1 can perform the transmission of the ACK packet 117 immediately after receiving the second data packet 114 and thus avoid an unnecessary retransmission of the second data packet 113. Alternatively, the BS is arranged to provide the second data packet 113 with an indication (preferably in the case type field 85) that the second data packet 113 is to be considered as a data packet which does not require acknowledgment, the first subscriber not sending the ACK packet 117.

When the second data packet 113 is selected from the buffer system 39, the base station BS can be arranged to take into account the priorities of the stored data packets. Accordingly, if there are fl your suitable candidates, which can be selected from the buffer system 39 as the second data packet 113, the base station BS is arranged to select the candidate with the highest priority. Furthermore, the buffer system 39 can be arranged so that the data packets having the same priority are stored in the same buffer. In that case, the base station is arranged to first search through the buffer associated with the highest priority for a suitable candidate. If no suitable candidate is found in the buffer with the highest priority, the base station BS is arranged to search the buffers with lower priority in turn until a suitable data package has been found and selected. This organization of the buffer system naturally makes the selection of a second data packet 113 faster.

In the examples above, the coordination of data packet communication is performed over a pair of radio channels rcl and rc2 in a WLAN. Of course, this type of coordination can also be used in other types of wireless communication systems, e.g. in 13 short-range wireless communication systems (eg based on the Bluetooth specification or similar). Coordination is not really limited to wireless systems but can be used generally in point-to-point data packet communication systems, which have at least a first uplink and a first downlink, which can be used simultaneously, thus delivering full duplex capacity. The uplink (s) and downlink (s) can be based on wired connections, such as optical cables, coaxial cables, etc.

Claims (15)

10 15 20 25 30 5-16 '564 14 Patent claims A method for use in data packet communication in a point-to-point communication system (1) having a primary node (BS) and secondary nodes (SU1-SU5), which nodes have means (25, 45) for communication over at least one first uplink and means (23, 47) for communicating over at least one first downlink, the method comprising: determining a time interval for transmitting a first data packet (l 1 1) over the first uplink from one of the secondary nodes to the primary node ; and transmitting the first data packet from the secondary node during the determined time interval, which method is characterized by: storing data packets to be transmitted from the primary node to one or more of the secondary nodes; selecting a second data packet (113) from the stored data packets; and timing adjusting a transmission of the second data packet over the first downlink so that an acknowledgment packet (115) for acknowledging receipt of the first data packet can be transmitted over the first downlink from the primary node immediately after receiving the first data packet. The method of claim 1, wherein selecting the second data packet (113) comprises selecting the second data packet to have a duration less than or equal to the duration of the first data packet (111). A method according to any one of claims 1 or 2, wherein the selection of the second data packet (113) comprises selecting the second data packet with respect to a priority ranking of the stored data packets. A method according to any one of claims 1, 2 or 3, in which the timing of the second data packet (113) comprises that the transmission of the second data packet is time-wise (S1e s64ë “% fi fafa fi f ~ - - is adjusted so that the transmission of the second data packet ceases simultaneously with the transmission of the first data packet (111). A method according to any one of claims 1 to 4, wherein the method further comprises: delivering the second data packet (113) with an indication that no acknowledgment is to be performed upon receipt of the second data packet. A method according to any one of claims 1 to 5, in which the first uplink is a first radio channel (rc 1). A method according to any one of claims 1 to 6, in which the first downlink is a second radio channel (rc2). A primary node (BS) for a point-to-point data packet communication system (1), the primary node comprising: means (23) for performing data packet transmissions over at least a first downlink to a number of secondary nodes (SU1-SU5); means (25) for receiving data packet information transmitted to the primary node from the secondary nodes over at least a first uplink; means (37) for determining a time interval for transmitting a first data packet (1 l 1) over the first uplink from one of the secondary nodes to the primary node, characterized in that the primary node comprises means (39) for storing data packets to be transmitted from the primary node to one or fl era of the secondary nodes; the primary node includes means (37) for selecting a second data packet (113) from the stored data packets; and that the primary node comprises means (37) for time-adjusting a transmission of the second data packet over the first downlink so that an acknowledgment packet (115), for acknowledging a reception of the first data packet, can be transmitted over the first downlink from the primary node immediately after receiving the first data packet. The primary node of claim 8, wherein the means for selecting the second data packet (113) is arranged to select the second data packet so that it has a duration shorter than or equal to the duration of the first data packet (1 1). 1). A primary node according to any one of claims 8 or 9, in which the means for selecting the second data packet (113) are arranged so that the second data packet is selected with respect to a priority ranking of the stored data packets. A primary node according to any one of claims 8, 9 or 10, in which means for timing the transmission of the second data packet (113) are arranged so that the transmission of the second data packet is timed so that the transmission of the second data packet ceases simultaneously with the transmission of the first data packet (111). The primary node of any of claims 8 to 11, wherein the primary node further comprises: means (37) for providing the second data packet (113) with an indication that no acknowledgment is to be performed upon receipt of the second data packet. A primary node according to any one of claims 8 to 12, in which the first uplink is a first radio channel (rc1). A primary node according to any one of claims 8 to 13, in which the first downlink is a second radio channel. Point-to-point communication system comprising a primary node according to any one of claims 8 to 14.