KR20130103276A - Medium access control for wireless networks - Google Patents

Abstract

PURPOSE: A medium access controlling method of a wireless network and an apparatus thereof are provided to decide a first measurement and a second measurement. CONSTITUTION: A wireless network includes a source node (2), a destination node (8) and at least one relay nodes (4,6). The wireless network decides a first measurement and a second measurement. The first measurement is a measurement about the signal quality related to a direct link between the source node and the destination node. The second measurement is a measurement about the signal quality related to a link passing at least one of a first relay node between the source node and the destination node. [Reference numerals] (2) Source; (4) Relay 1; (6) Relay 2; (8) Destination

Description

MEDIUM ACCESS CONTROL FOR WIRELESS NETWORKS

FIELD OF THE INVENTION The present invention relates generally to wireless networks and, more particularly, to methods and apparatus related to medium access control (MAC) for wireless local area networks, although not excluding anything else.

Wireless networks, such as wireless local area networks (WLANs), are widely used in accordance with IEEE.802.11 norms and generally provide the advantages of low cost, simple use, and high speed data communications. In WLAN networks, the physical layer of IEEE 802.11 a / b / g / n is generally used to transmit and receive data packets over a shared wireless medium. IEEE 802.11 Media Access Control (MAC) generally provides a reliable delivery mechanism for user data over wireless channels that may be subject to interference and fading. IEEE 802.11 Distributed Coordination Function (DCF) is a Carrier Sense Multiple approach to Collision Avoidance (CSMA / CA) with a handshaking mechanism that is typically used to avoid the effects of collisions and to enable the transmission of large data packets. It is a general MAC protocol based on Access. In this DCF scheme, when the source node is ready to transmit a packet, it first detects activity until the same idle interval as the Distributed Inter Frame Space (DIFS) is detected in the transport channel. In this case, the source waits for another random backoff interval before transmission to avoid collisions with other nodes. At that time, the source starts transmission by sending an RTS (Request-to-Send) control packet. If the control packet is received correctly, the destination sends a clear-to-send (CTS) control packet after a Short Inter Frame Space (SIFS) interval. When a CTS frame is received, the source sends a data packet after an SIFS interval. If the data packet was received correctly, the destination responds by sending an acknowledgment (ACK) packet after the SIFS interval. IEEE 802.11 DCF also uses Network Vector (NAV) for virtual carrier sensing. The NAV is generally maintained by nodes that are not involved in any transmission or reception of current packets and tracks of updates remaining according to the information received in any persistent data transmission and control / data packets.

As an extension of the use of wireless mesh networks using ad-hook routing between nodes via other nodes used as relay nodes, MAC schemes such as IEEE 802.11 DCF can route through beneficial multi-hop routes to the MAC layer. For example, a slow single hop transmission can be replaced by a fast two or more hop transmissions, since it has been extended to a so-called cooperative MAC scheme that allows for cooperation between nodes.

MAC protocols for cooperative communications include CoopMAC (Cooperative MAC), relay enabled DCF (rDCF) and Robust Cooperative Relaying.

However, prior art cooperative MAC protocols may be inefficient in terms of signaling overhead and data capacity complexity. For example, a database of signal qualities of links between nodes may be maintained to select the appropriate multi-hop route as the associated signaling. In addition, the selection of routes may be mutually exclusive due to potential interference, since prior art cooperative MAC protocols may be limited in capacity by the need to limit interference between concurrent transmissions of interfering data. This may limit the achievable bandwidth.

It is an object of the present invention to alleviate the problems of the prior art system.

In a method for transmitting signals in a wireless network according to the first aspect of the invention, the wireless network comprises a source node, a destination node and at least one first relay node, the wireless network comprising the source node and the Determine a first measurement of signal quality with respect to a direct link between a destination node and a second measurement of signal quality with respect to a link via the at least one first relay node between the source node and the destination node. Configured to

The method comprises at least one relay node;

Determining a duration of an incoming slot within which the relay node may send a recruitment message indicating the availability of the relay node to relay, wherein the duration of the incoming slot is the signal. Determined on the basis of including the first measure of quality.

The ingress of the relay has the advantage that it can depend on the signal quality of the direct link from the source node to the destination node. If the signal quality of the direct link is better than the case, the relay may be less likely to enter.

In an embodiment of the present invention, if it is determined that the incoming message is transmitted, determining the delay interval for the transmission of the incoming message from the first relay that depends on a second measurement of the signal quality. It may include.

The ingress of a relay node has the advantage that it can depend on the signal quality of the link via the relay from the source node to the destination node. If the signal quality of the direct link from the source node to the destination node is better than if it is bad, the relay may be more likely to be introduced.

In an embodiment of the invention, data may be transmitted from the source node to the destination node in at least one first mode or second mode, the first mode being directly from the source node to the destination node. Wherein the second mode comprises a transmission from the source node to a destination node via a first path via a relay,

Selecting an operation of the second mode on a basis comprising a first measurement and a second measurement of the signal quality.

Data is passed from the source to the destination by the comparison of the measurement of the quality of the link via the one relay with the measurement of the signal quality of the direct link via the first path via the one relay. There is an advantage that it can be transmitted in a suitable mode for transmission from a node to the destination node and in a suitable format for the second mode, for example suitable addressing.

In an embodiment of the invention, the method comprises;

Sending a first message from the source node indicating that data is ready for transmission;

Receiving the first message at the destination node; And

And determining a first measurement of the signal quality from the signal quality of the first message received at the destination node.

The first measure of signal quality has the advantage that it can be determined on the basis of the reception of existing signaling without the need for providing additional signaling.

In an embodiment of the invention, the method comprises;

Receiving the first message at the first relay node; And

Determining a second measurement of the signal quality from the signal quality of the first message received at the first relay node.

The second measure of signal quality has the advantage that it can be determined on the basis of the reception of the existing signaling without the need for providing additional signaling.

In an embodiment of the invention, the method comprises;

Sending a second message from the destination node that includes an indication of the duration of the incoming slot within a time at which the relay node can send a message, the duration of the signal quality for the received first message; It may be determined from the basis.

The duration of the incoming slot may be effectively transmitted to other nodes in the network using the second message, which may modify a message of a request that may be sent for other purposes, such as indicating a clear to send (CTS). There is an advantage to that.

In an embodiment of the invention, the method comprises;

Receiving the second message at the first relay node;

Determining the second measurement of the signal quality may be a method that depends on at least the signal quality of the second message received at the first relay node.

The second measure of signal quality has the advantage that it can be determined on the basis of the constant reception of the signaling present.

In an embodiment of the invention, the method comprises;

And transmitting a third message depending on the determined delay period that is less than or equal to the duration of the inflow slot, wherein the third message is an inflow message from the first relay node after the determined delay period, and the determined delay period. May be from the end of the reception of the second message at the first relay node.

When the delay period is later than the inflow slot, the inflow message is not transmitted, so the inflow of the relays is advantageously suppressed on the basis of the signal quality at the direct link from the source node to the destination node.

In an embodiment of the invention, the third message may comprise an indication of a second measurement for the signal quality.

Since the second measure of signal quality can be sent to the source node using the incoming message, there is an advantage that can provide efficient use of signaling resources.

In an embodiment of the invention, the method comprises;

And selecting an operation of the second mode on a basis including always receiving the third message.

In an embodiment of the invention, the method comprises;

Determining a data rate for transmission of data from the source node on the basis of including the indication of the second measurement of the signal quality in the third message.

The data rate has the advantage that it can be suitably determined for the link via the relay node from the source node to the destination node.

In an embodiment of the invention, data may be transmitted from the source node to the destination node in a third mode, wherein the third mode is additional to the first path via the first relay node and from the source node. The method comprising transmitting to the destination node via a combination of a second path via a relay node;

Receiving the first message at the additional relay node;

Determining a fourth measure of signal quality of the first message received at the additional relay node;

Receiving the second message at the additional relay node; And determining a fifth measure of signal quality, wherein the fifth measure of signal quality is a measure of signal quality of the second message received at the additional relay node;

Determining a second delay interval for transmission of a fourth message in dependence on a fourth measurement and a fifth measurement of the signal quality;

Receiving the third message from the first relay node; And

Transmitting the fourth message after the determined second delay period, depending on the determined delay period that is less than or equal to the duration of the inflow slot;

The determined second delay period may begin from the end of reception of the third message at the additional relay node.

The data capacity of the wireless network has the advantage that it can be increased by the simultaneous transmission of data via at least two relays.

In an embodiment of the present invention, the fourth message may include an indication of received signal quality based on a fourth measurement and a fifth measurement of the signal quality.

The signaling has the advantage that it can be effectively transmitted without requiring additional messages to be transmitted.

In an embodiment of the invention, the method comprises;

Selecting the third mode of operation for transmission of data from the source node on a basis comprising the receipt of the third message and a fourth message; And

Determining a data rate for transmission of data from the source node on a basis comprising an indication in the third message and a fourth message of received signal quality,

The received signal quality may be based on second, third and fourth measurements of the signal quality.

The source node has the advantage of being able to set a data rate suitable for the link over which the data can be transmitted.

In an embodiment of the present invention, the method may include transmitting data simultaneously via the first path and the second path.

The data capacity of the wireless network has the advantage that it can be increased.

In an embodiment of the invention, the method may comprise relaying data in accordance with Quantise Map and Forward (QMF) protocol at the first relay node and the additional relay node.

It is an advantage to provide efficient transmission with media access control implemented in accordance with an embodiment of the present invention.

In an embodiment of the present invention, the first message may be a ready-to-send (RTS) message, the second message may be a clear-to-send (CTS) message, and the third message may be a ready-to-relay (RTR) message. Message, and the fourth message may be a ready-to-relay (RTR) message.

In an embodiment of the invention, the basis for determining the incoming slot duration may include an allowed modulation scheme.

The incoming slot duration has the advantage that it can be set according to the target data rate taking into account the allowed modulation or coding scheme.

In an embodiment of the invention, the method may comprise receiving an indication of the allowed modulation or coding scheme from the source node.

The source node has the advantage of being able to communicate the allowed modulation scheme with other nodes.

In an embodiment of the invention, the wireless network may be operating in accordance with IEEE 802.11.

In a relay node for transmitting signals in a wireless network according to a second aspect of the invention, the wireless network comprises a source node, a destination node and at least one relay node, the wireless network comprising the source node and the Determine a first measurement of signal quality with respect to a direct link between a destination node and a second measurement of signal quality with respect to a link via the at least one first relay node between the source node and the destination node. Configured to

The relay node;

Determine a duration of an inlet slot through which the relay node can send a receipt message indicating the availability of the relay node to relay, the duration of the inlet slot being a first measure of the signal quality It may be a relay node based on.

In an embodiment of the invention, the relay node;

If it is determined to transmit the incoming message, it may be a relay node that determines a delay interval for the transmission of the incoming message from the first relay depending on a second measurement of the signal quality.

Additional features and advantages of the invention will be apparent from the following description of the preferred embodiments of the invention. However, such embodiments are given only by way of example.

1 is a schematic diagram illustrating a network with two relay nodes according to an embodiment of the invention.
2 is a timing diagram illustrating the flow of messages in a scenario in which two relays are introduced according to an embodiment of the present invention.
3 is a timing diagram illustrating the flow of messages in a scenario in which one relay is introduced according to an embodiment of the present invention.
4 is a timing diagram illustrating the flow of messages in a scenario where there is no incoming relay in accordance with an embodiment of the present invention.
5 is a flow diagram illustrating processes at the source node according to an embodiment of the invention.
6 is a flow diagram illustrating processes at the destination node in accordance with an embodiment of the present invention.
7 is a flow diagram illustrating processes in the relay node according to an embodiment of the present invention.
8 is a diagram illustrating messaging in accordance with an embodiment of the present invention.
9 is a schematic diagram illustrating RTS and CTS signaling fields according to an embodiment of the present invention.
10 is a schematic diagram showing the selection of a transmission mode when the source-destination link is an advantageous choice in an embodiment of the invention.
11 is a schematic diagram showing the selection of a transmission mode when cooperative transmission via one relay is an advantageous choice in an embodiment of the invention.
12 is a schematic diagram showing the selection of a transmission mode when cooperative transmission via two relays is an advantageous choice in an embodiment of the invention.

Embodiments of the invention may be described in the context of a wireless local area network system operating in accordance with IEEE 802.11 protocols.

It will be understood that this is only an exemplary method, and that other embodiments may be applicable to other wireless systems; That is, embodiments are not limited to the use of wireless local area network systems.

1 illustrates an embodiment of the invention of a wireless network in an example of a WLAN network operation comprising a source node 2, a destination node 8, a first relay node 4 and a second relay node 6 in accordance with IEEE 802.11. Data can be sent from the source node to the destination node, usually in the form of data frames. Referring to FIG. 1, data may be sent directly from source node 2 to destination node 8 and / or via one or two relay nodes 4, 6. Since the network is configured to operate according to an embodiment of the present invention, the route of the data depends on the signal quality at the links via each relay and the signal quality at the direct link from the source node to the destination node. The combination or link of links via which data is transmitted may be determined on the frame by the basis of the frame, for example, by nodes moving or by changes in the radio frequency environment, eg by a change in interference or fading characteristics. Relay nodes are not introduced for use in the link from the source node to the destination node, but are generally introduced on a frame-by-frame basis. This is configured by showing in FIG.

2 is a timing diagram illustrating the flow of a message between a source node, a destination node and two relay nodes, for example in a scenario where nodes of two relays are introduced for transmission of one or more data frames. The wireless network is a signal associated with a first measurement of signal quality associated with a direct link between source node 2 and destination node 8 and a link between source node 2 and destination node 8 via at least one first relay node 4. Configured to determine a second measure for quality. The first measure of signal quality is from a first node sent from the source node indicating a message received at the destination node, eg, data ready to be sent, from the source node, such as an RTS (Ready to Send) message 34. Can be determined from the signal quality. The first message may also be received at the first relay node, and the second measure of signal quality may be determined from at least one signal quality of the first message received at the first relay node.

Two inlet slots of inlet slot 1 12 and inlet slot 2 14 in the frame format diagram of FIG. An inflow slot is a period within which a relay node may transmit an inflow message indicating the validity of the relay node for relaying, such as a ready-to-relay (RTR) signal RTR1 38 and RTR2 40. The relay node may be sent to the destination node to relay from the source node on the basis of receipt of the incoming message at the source node.

In an embodiment of the invention, the duration of the inlet slot is determined on the basis of the first measurement of the quality of the direct link from the source node to the destination node, ie the signal quality. In general, the higher the signal quality of the direct link, the shorter the inlet slot. Each relay node back-off, that is, the transmission of incoming messages by delay and delay intervals, and also the back-off interval in accordance with a second measure of the quality of the link via the relay node, ie the signal quality, from the source node to the destination node. Indicates. As a result, the relay node with the best link sends the incoming message first. In receipt of an incoming message, other relays inhibit transmission of an incoming message in the incoming slot, and the other relays may have another attempt in the second incoming slot, and in that second incoming slot, the already introduced relay will be silent. will be.

In this method, a relay node with a high quality link is introduced first, and the relay node is generally only introduced if the direct link is bad enough compared to the link via the relay, which is advantageous for using the relay.

So, if the direct link is bad, the inlet slot will be long because the relays send inlet messages after a long period of time with the chance to ingress. However, if a direct link is good, the inlet slot will be shortened, since relays send an ingress message after a short interval with the chance to ingress. This prevents relays from introducing bad links and reduces signaling time overhead. The duration of the inlet slot can be zero if the quality of the direct link is good enough. In this case, since the link via the relay node contains two or more hops rather than a single hop from the source node to the destination node, even though the signal quality for the link to the relay node is good, the relay nodes may have radio resources. No relay nodes can be introduced because they are expected to provide an inefficient use of these devices.

Data may be sent from the source node to the destination node in at least a first mode or a second mode, the first mode comprising a direct transfer from the source node to the destination node, and the second mode relays the relay from the source node. And transmission to the destination node via the first path through. For example, the destination address of the data may be indicated in a header appropriate for the mode suitable for the route between the source node and the destination node. The operation of the second mode may be selected instead of the first mode on a basis that includes a first measurement and a second measurement for signal quality. Thus, the mode of operation in which data is relayed is selected on the basis of a measurement of the quality of the direct link and the link via the relay.

The indication of the duration of the incoming slot may be sent from the destination node in a second message, such as clear to cent (CTS) message 36, the duration of the incoming slot being the signal quality of the first message received at the destination node, i.e. The basis for the quality of the direct link is determined. At a relay node on receipt of a message sending an indication, the duration of the inlet slot within the relay node may send an incoming message that may be determined from the received indication.

Receipt of the second message, which may be a CTS message at the relay node, may additionally be used. The second measure of signal quality associated with the link via the relay node may be determined depending on the signal quality of at least the second message received at the first relay node.

The incoming message, i.e., the third message, may be sent from the relay node after the determined delay period depending on the determined delay period which is less than or equal to the duration of the incoming slot, the determined delay period being used to receive the second message which may be a CTS message at the relay node. Start from the end.

If the determined regional section is longer than the duration of the inflow slot, the inflow message may not be transmitted.

For example, a third message, such as an RTR message, may include an indication of a second measure for signal quality associated with the link via the relay node. The second mode of operation may then be selected, for example at the source node, on the basis of receiving the third message. In addition, the data rate may be selected for transmission of data from the source node on a basis that includes an indication of a second measure for signal quality in the third message. The modulation and / or coding scheme may also be selected on the basis of receipt for the third message at the source node.

A physical layer (PHY) transmission scheme that allows simultaneous transmission and reception of other data streams 44 and 46 in a shared medium, such as space-time coding, is shown in FIG. It can be used to utilize. Two or more links between the source and destination nodes may be established in parallel and may allow data to be relayed at once by two or more relays so that data capacity and throughput rate may increase. have. In an embodiment of the invention, a method of relaying data according to the Quantise Map and Forward (QMF) protocol which allows simultaneous transmission and simultaneous reception of different data streams 44, 46 on a shared medium at a first relay node and an additional relay node. It includes.

Thus, data can be transmitted from a source node to a destination node in a third mode via a combination of a first path via a first relay node and a second path via an additional relay node. In a third mode, a first message, for example an RTS message, is received at an additional relay node and a fourth measure of signal quality of the first message received at the additional relay node is determined. A second message, such as a CTS message, is also received at an additional relay node, a fifth measure of signal quality is determined, and a fifth measure of signal quality is received at an additional relay node related to the quality of the link via the additional relay. A measure of the signal quality of the second message.

The second delay interval is determined for the transmission of the fourth message, such as for example an RTR2 40 message, depending on the fourth and fifth measurements of signal quality.

A third message from the first relay node, for example RTR1 38, is received at the second relay node, and a fourth message, for example RTR2 40, is a second delay determined depending on the determined delay interval that is less than or equal to the duration of the time slot. The second delay interval, sent after interval 32, begins with the end of the reception of the third message at the additional relay node. The fourth message, such as RTR2 40, may include an indication of the received signal quality based on the fourth and fifth measurements of signal quality.

The third mode of operation for the transmission of data from the source node may be selected on a basis that includes receipt of third and fourth messages such as RTR1 38 and RTR2 40 and an indication of the signal quality of each carrier.

The data rate for the transmission of data from the source node includes an indication in the third message and the fourth message of the received signal quality based on the second measurement, the third measurement, the fourth measurement and the fourth measurement on the signal quality. Can be determined on the basis.

In an embodiment of the invention, the basis for determining the incoming slot duration includes the allowed modulation and / or coding scheme. In this way, signal qualities such as, for example, signal to noise ratio can be used to select the allowed modulation and / or coding schemes, and slot durations can be obtained using the allowed modulation and / or coding schemes. Can be made dependent on the data rate. Similarly, since the delay in the transmission of incoming messages from a relay node may depend on the allowed modulation and / or coding scheme, the delay may depend on the data rate obtainable using the allowed modulation and / or coding scheme. Can be. This may perform the operation of the MAC schema to select relays for more efficient ingress. An indication of the allowed modulation and / or coding scheme may be received from the source node. The allowed coding scheme may be, for example, a network coding scheme such as Quantize Map Forward (QMF), amplify and forward (AF) or Compress and Forward (CF).

As shown in FIG. 2, the Short Inter Frame Space (SIFS) intervals 10, 16, 18, and 20 are generally ACK between RTS 34 and CTS 36, between RTR2 40 and data 42 transmitted by the source node and from the destination node. It is provided between the reception of 48 and the data 44, 46 transmitted by the relay nodes. SIFS intervals allow for data transmission time to avoid collisions between signals.

FIG. 3 shows a situation similar to FIG. 2 except that relay 2 is experimenting with a poor quality link from the source node to the destination node via relay 2. FIG. As a result, since the delay period 32 for the inflow message transmission is superior to the duration of the inflow slot 2 14, the RTR 2 message is not transmitted and the relay 2 is not inflow. Thus, data 42 sent by the source node is not sent to relay 2 but only to relay 1, so that data is relayed only by relay 1 by sending data 44.

FIG. 4 shows a situation similar to FIG. 3 except that relay 1 and relay 2 both experiment with a poor quality link from the source node to the destination node via each relay. As a result, since the delay interval 30 for the incoming message is better than the duration of the incoming slot 1 12, the RTR 1 message is not transmitted and neither the relay 1 nor the relay 2 is introduced. Thus, data 42 sent from the source node is not sent to relay 1 or relay 2, so the data is received on the direct link to the destination node.

In an embodiment of the present invention, a medium access control (MAC) protocol of a wireless local area network (WLAN) such as an IEEE 802.11 WLAN is provided that allows cross layer cooperative communications. In accordance with an embodiment of the present invention, the MAC protocol shown in FIGS. 2, 3 and 4 is based on the ACCMAC utilizing the capabilities of the Adaptive Cross-layer Cooperative MAC (ACCMAC) and PHY protocols, in particular other data in the simultaneous transmission and shared media. Represents a Quantise Map and Forward (QMF) protocol that allows relaying with reception of streams. In this way, multiple relay paths can be used to increase the data capacity of the network in parallel. In addition, the ACCMAN schema according to an embodiment of the present invention serves as a basis for link quality measurements that enable automatic inflow of relays that provide optimal quality links without the need to maintain a database of link quality measurements and the need for high signaling overhead. It is effective with respect to signaling overhead using current transmissions such as RTS (Ready to Send) and CTS (Clear to Send). Relay ingress is via an inlet slot with a duration dependent on signal quality on the direct link between the source and destination nodes and a back-off interval for incoming messages from each relay depending on signal quality and via each relay from the source. Automatically based on the allowable modulation scheme on the link to the destination node. Signal level coordination at the PHY layer uses cooperative transmission to improve outage performance and bit error rate (BER). Packet-level cooperation at the MAC layer is one or more to serve as intermediate nodes for data between source and destination in two hop approaches where each hop can provide a higher transmission rate than the direct link between transmitter and receiver. It relates to the selection of relays. In an embodiment of the present invention, the MAC protocol is provided to enable cross-layer cooperative communication between the PHY and MAC layers allowing proper relay selection at the MAC layer and signal level coordination at the PHY layer. First, the MAC protocol is designed to 'inflow relays avoiding the overhead of maintaining a relay table at each node in the air'. Secondly, the MAC layer header is modified to accommodate the exchange of information among the nodes for proper transmission mode selection during single- or multiple-relay transmissions depending on the direct transmission and channel conditions. Third, once multiple relays are available, the MAC design allows simultaneous transmissions from relays instead of sequential transmissions from each relay. As above, the first, second and third aspects of the design use both PHY and MAC layer cooperative transmissions to enable other distributed systems to enable cross-layer cooperative communication or WLAN systems that potentially provide high transmission rates and low power consumption. Integrated into the new collaborative MAC for the network.

Embodiments of the present invention may use cooperative communication to take advantage of the broadcast nature of wireless media, which may limit the capability of prior art systems because of the potential for interference between parallel links. The diversity of broadcast and space can be utilized to improve the performance of the wireless link. At the PHY layer, cooperative communication is enforced by relayed protocols such as Amplify-and-Forward (AF), Decode-and-Forward (DF), Compress-and-Forward (CF), and Quantize-Map-Forward (QMF). Can be. QMF has been found to be particularly suitable in embodiments of the present invention. In particular, QMF supports the transmission of multiple relays at the same time, and additionally does not require relays to fully decode the received data, but also enables an effective implementation. However, since the prior art MAC system does not support relaying based QMF, the general prior art MAC layer of WLAN is designed to avoid simultaneous transmission from other nodes in case of impulse. In an embodiment of the invention, the capability for simultaneous transmission at the PHY layer and the broadcast nature of signaling messages is used.

In an embodiment of the present invention, the carrier sensing scheme of the IEEE 802.11 MAC is redesigned to allow relays to support good quality links that can join concurrent transmission networks. In addition, the handshaking mechanism and carrier sensing for the source node and destination node are modified to introduce relays 'at air' without having to maintain a relay table at each node. MAC header and frame networks have been redesigned to support the selection of the appropriate relay between direct transmission and single relay and multiple relay modes.

Referring back to FIG. 2 according to an embodiment of the present invention, the destination node retransmits the CTS 36 after the SIFS interval 10. Status information about the relay to provide better performance than direct transmission is transmitted in the CTS. This information can be used to set up 'inlet slots' for the next relay ingress process in both source and destination. The maximum incoming slot duration can be configured identically to SIFS duration 10, which matches the relay back-off depending on the minimum state for the relay to provide better performance than direct transmission. The minimum ingress slot is zero, which can be applied when the direct link achieves the transmission rate of the system most supported and no relay can join the transmission.

The relays may start back-off interval 30 after receiving CTS 36 while waiting for the incoming slot interval to introduce both relays to the source and destination. The back-off time at each relay may be set according to the aggregate target data rate for the transfer from source to destination via a relay with a high target data rate with a short back-off time. The target data rate may be indicated by measurements on the signal quality of the link and / or the allowable modulation of the link and / or the coding scheme that may be indicated by the signal quality, such as the signal to noise ratio. The target data rate can also be used as an indication of signal quality.

If the relay can complete the back-off interval in the inlet slot, it may send RTR1 (ready to relay) to respond to the inflow opportunity. In RTR1, the indication of the target transmission rate for the link using the relay, which may be an indication of signal quality, is broadcast to neighboring nodes.

The case of multiple-relay is supported based on the current information exchange, and nodes can start another ingress in the same way as the first inlet slot. Additional relays can transmit out of the RTR2 40. When the relay ingress interval is complete, the source transmits data frame 42 after SIFS interval 16. Incoming relays receive data frame 42 from the source and send data frames 44 and 46 to the destination node after signal level processing according to the PHY layer cooperative schema supported simultaneously after SIFS interval 18, for example QMF. send. If the destination correctly receives data by data co-processing received from the source and / or relays, the destination retransmits ACK 48 after SIFS interval 20.

According to the schema shown in Figure 2, the destination node and the source node are introduced in the air to avoid the overhead of maintaining a relay table at each node, and the cross-layer design is random to allow simultaneous transmission from the relays at the PHY layer. PHY cooperative schemas such as distributed spatial time coding schemas and Quantize-Map-Forward relaying schemas are supported. For example, in a wireless system comprising one source node 2, one destination node 8 and two relays 4, 6 shown in FIG. 1, the system adaptively does so from the source node to the destination node. It is possible to switch between three transmission modes for transmitting data directly, via two relays, or via one relay or directly. This means that if direct transmission can achieve the maximum supported rate, the source transmits the data directly without any assistance from the relay in the first mode. If the transmission via one relay can provide improved performance, the source first sends data to the destination, and the relay then sends a copy to the destination node in the second mode. If the transmission via two relays can achieve additional performance gains, the relay can then send data to the destination node simultaneously in the third mode. In an embodiment of the invention, the destination and source inlet relay in air, which can avoid the need to maintain a relay table at each node. In an embodiment of the present invention, QMF based on PHY layer relaying protocol is used since it can provide good performance compared to AF and DF. Another embodiment of the present invention may use alternative PHY layer relaying protocols such as randomly distributed space time coding. In an embodiment of the present invention, a wireless system can support two or more relays simultaneously by providing additional inlet slots.

In an embodiment of the invention, the transmit power for the nodes may be modified, the RTS and CTS may be overhead by the transmitting node and other nodes except intended reception, and the channel state information (CSI or received SNR) is available on the receiving side and is replaced via RTS and CTS. In general, transmission in two directions between two nodes uses the same frequency, and the channels are symmetrical. In other words, the channels have the same characteristics for transmission in both directions.

5 is a flow diagram illustrating processors in a source node according to an embodiment of the invention. In an embodiment of the present invention, if at least one packet is buffered in a queue, the source node starts a random back-off before sending out the RTS to reserve the channel after the interval of DIFS. If the CTS from the destination has been received, the source may have a channel for transmission. In the CTS control frame, the destination also informs the source of the duration of the inlet slot to introduce the relays. The source waits idle for the duration of the inlet slot to enter the relay until an RTR control frame is received or the inlet slot expires and listens to the channel.

This ingress can be repeated to introduce more relays depending on system requirements. After the import process is complete, the source starts sending data frames. If an ACK has been received, the source will go back to idle or back to the IEEE 802.11 DCF norm, which is a random back-off step to find the next opportunity to transmit the data.

6 is a flow diagram illustrating a process at a destination node in accordance with an embodiment of the present invention. In an embodiment of the invention, upon receiving the RTS from the source node, the destination estimates the channel state between the source and the destination. Based on the channel conditions, additionally calculate the states that cooperative transmission via relays can help to improve the performance of the direct transmission. The destination also sends out a CTS control frame containing the setting of the inlet slots for inleting relays in the air. If the destination can receive RTR (1, 2) control frames from the relays before the inlet slot expires, the relays can join the transmission to provide better performance than direct transmission, or the destination can enter the inlet slot. Idle until the end of time. After receiving the data frame from the source and / or relays and the physical layer signal processing, detection, and cyclic redundancy check (CRC), the destination returns an ACK at the correct reception.

7 is a flow diagram illustrating processes in a relay node according to an embodiment of the invention. In an embodiment of the invention, the potential relay node starts the delay period, in other words, after receiving the CTS. The back-off time may be set according to the channel state from the relay to the source node and destination node. The relay node may estimate the channel quality based on the received RTS and CTS. The back-off time can be designed to ensure that relays can join the network when the overall target rate is increased before the inlet slot expires. If the back-off time in the relay is shorter than the inlet slot, the relay transmits an RTR (RTR2 or RTR1 depending on whether the incoming relay is first or second) to indicate whether the relay will participate in transmission. The relay receives the data frame from the source and sends the data to the destination after some processing following the use of the PHY relaying schemes.

The carrier sensing and handshaking scheme is shown in Figure 2, which is described in more detail in the following embodiment of the present invention. When the channel holds another node and there is no data in the buffer of the source node, the source can wait for the duration of the DIFS and can perform random back-off with the legacy IEEE 802.11 DCF schema. At that time, the source may hold the channel by sending a control frame RTS. After waiting for the SIFS interval, the destination may broadcast a CTS control frame. This frame can also provide information about the setting of inlet slots. Upon receipt of the CTS, both the source and destination can begin an inlet slot to enter the relays. At the same time, the relays may individually start back-off according to channel state information and / or channel state, channel quality, target data rate associated with one or more links from source to relay and from relay to destination. The back-off time may have a short back-off time so that the channels are of better quality. If the relay finishes back-off before the end of the incoming slot, the relay sends out a control frame RTR (Ready to Relay). This can be repeated to introduce more relays in the same way. In the exemplary case for the two relays, after the second ingress, the control frame handshaking process is completed. The source node may send relays data frame after SIFS, and the relays retransmit data received from the source after another SIFS. The destination may accept a successful reception on the ACK to complete this transmission. Hidden nodes, for example, other than the source node, the destination node and the relay node, can update the time of each of the network allocation vectors (NAVs) receiving control frames from the wireless network. Control frames can hold channels for duration, as shown in the following table.

Frame NAV Reservation Duration RTS TCTS + 2 * SIFS + RS1 + RS2 CTS RS1 + RS2 + 2 * TRTR + TDADAs + SIFS RTR1 RS2 + TDATAs + TDATAr + SIFS RTR2 TDATAs + TDATAr + 3 * SIFS + ACK DATAS TDATAr + 2 * SIFS + ACK DATAR SIFS + ACK ACK 0

In the table above, RS denotes 'inlet slot', respectively, TCTS and TRTR denote transmission durations of control frames CTS and RTR, and denote transmission durations of data frames from sources and relays. Inlet slots can be set to a minimum state below which relays can provide better performance.

일 수 있다. 소스-데스티네이션 링크의 채널 품질에 기초하여, 직접 링크의 목표 레이트는

이 소스-데스티네이션 링크의 수신된 SNR인

이다. 따라서 유입 슬롯의 듀레이션은 다음과 같이 설정된다.
In an embodiment of the present invention, the duration of the inlet slot can be set in the following manner. For WLAN, the maximum transmission supported by the PHY layer for cooperation is

Lt; / RTI > Based on the channel quality of the source-destination link, the target rate of the direct link is

Is the received SNR of this source-destination link

to be. Therefore, the duration of the inlet slot is set as follows.

.

.

보다 작다면, 예를 들어 일반적으로 유입 슬롯보다 긴 3*SIFS로의 백-오프 셋팅에 의해 유휴 상태를 유지한다. 만약 목표 레이트가

보다 크다면, 릴레이는 다음 같은 구간에서 백-오프를 시작한다.
The worse the source destination channel quality, the longer the inlet slot is, and the maximum duration of the inlet slot is equal to SIFS. In this case, the maximum back-off limit is the duration of the SIFS, and when the direct link is good enough, the minimum may be zero. This ensures to minimize transmission delays and help set up other relay NAVs. By listening to the CTS frame, each potential relay can know the channel state between the source node and the destination node itself. If you join the transmission to the relay, you can calculate the target rate. If the target rate is

If smaller, it will remain idle, for example, by setting back-off to 3 * SIFS which is generally longer than the inlet slot. If the target rate is

If greater, the relay starts back-off in the next same interval.

By this process, the higher the attainable rate that the relaying transmission can achieve, the shorter the back-off time. Thus, the following formula is defined.

,

,

.

.

Therefore, the back-off time is set as follows.

(단순화하여, 나타내기 위해

을 사용한다.)에 대한 정보를 방송한다. 멀티플 릴레이들의 경우에서, 이 정보에 기반하여, 제2 유입은 듀레이션을 가지고 시작한다.
In the case of multiple relays, each of the relays can be reset the back-off duration every RTR heard from the other relay. The reset back-off period may begin if transmission from another relay is interrupted. In the RTR1 control frame, the relay is also

(For simplicity, to indicate

Broadcasts information about In the case of multiple relays, based on this information, the second ingress begins with a duration.

Each relay resets the duration time.

가 제2 릴레이로써 전송에 참여하는 릴레이의 목표 레이트이다.

Is the target rate of the relay participating in the transmission as the second relay.

8 shows a diagram of the communication of receipt of messaging control messages, data and messages between a source, relays and destination in a manner according to an embodiment of the invention.

In an embodiment of the invention, where the source-destination link can achieve the maximum supported rate, the actual inlet slot is set to zero. In this case, the source may transmit a data frame after one SIFS slot. There is no additional time waiting for a response from the relays. This is different from other protocols in systems that require a fixed time allocation waiting for a relay response.

In an embodiment of the invention, the RTS may be the same as legacy IEEE 802.11. The CTS may have the format shown in FIG. 9. In an embodiment, the extra 8 bits are used in the duration field in the 802.11 frame, and the duration field is changed to include both the inlet slot information and the duration to inform the source to the inlet relays. The RTR may have the format shown in FIG. 9. In an embodiment, 16 bits are used in the duration field to set the transmission rate for both the source-relay and relay-destination links.

10 is a schematic diagram showing the selection of a transmission mode when the source-destination link is an advantageous choice in an embodiment of the invention. In the embodiment of FIG. 10, the high transmission rate of the system is limited to 11 Mbps by coding and modulation rate. Direct transmission can support high rates, and cooperative transmission is not required. In an embodiment of the invention, the inlet slot duration can be set to zero in this case, and the source can transmit without the ingress of any relays.

11 is a schematic diagram showing the selection of a transmission mode when cooperative transmission via one relay is an advantageous choice in an embodiment of the invention. In the embodiment of Fig. 11, since the source-destination can only support 2 Mbps, the inlet slot is set to an interval appropriate for that speed. Relay 1 can provide an aggregate rate higher than 2 Mbps, which transmits an RTR corresponding to the ingress. Relay 2 may be back-off for a longer time than relay 1 because relay 2 may provide a rate that is better than direct link but worse than relay 1, so a relay that may provide a high rate link may join the transmission first. If multiple-relay mode is allowed, relay 2 may respond in the second inlet slot and both relays may transmit data frames to the destination at the same time.

12 is a schematic diagram showing the selection of a transmission mode when cooperative transmission via two relays is an advantageous choice in an embodiment of the invention. In the embodiment of FIG. 11, relay 1 joins transmission first as a relay providing a high rate link, and relay 2 joins transmission in a second inlet slot since a high transmission rate can be provided with two relays. Join.

In an embodiment of the present invention, alternative relaying protocols such as decode and forward (DF) may be used in the PHY layer. In this case, the destination informs the source / relay CTS control frame about explicit modulation / coding combinations instead of transmission rate requirements. By receiving this information, the relays can determine themselves if they can transmit in the type of coding / modulation format to ensure reliable transmission. Qualified nodes can transmit to modulation / code for direct signal detection.

The above embodiments are described as examples shown by the accompanying drawings of the present invention. It is described that all of the functions described in connection with one embodiment may be used alone or in combination with other functions, and all of the functions may be used in combination with one or more functions or other combinations of embodiments. Moreover, equivalents and modifications not described above may be used without departing from the scope of the invention as defined in the accompanying claims.

Claims (26)

In a method for transmitting signals in a wireless network,
The wireless network includes a source node, a destination node and at least one first relay node, wherein the wireless network includes a first measure of signal quality and a source of a signal related to a direct link between the source node and the destination node. Configured to determine a second measure of signal quality with respect to a link via the at least one first relay node between a node and the destination node,
The method comprises at least one relay node;
Determining a duration of an incoming slot within which the relay node may send a recruitment message indicating the availability of the relay node for relaying
Lt; / RTI >
The duration of the inlet slot is determined on a basis that includes a first measure of the signal quality. The method of claim 1,
If it is determined to transmit the incoming message, determining a delay interval for transmission of the incoming message from the first relay that relies on a second measurement of the signal quality
≪ / RTI > The method according to claim 1 or 2,
Data may be transmitted from the source node to the destination node in at least one first or second mode, the first mode comprising a direct transmission from the source node to the destination node, Two modes include transmission from the source node to the destination node via a first path via a relay;
Selecting an operation of the second mode on a basis comprising a first measurement and a second measurement of the signal quality
≪ / RTI > 4. The method according to any one of claims 1 to 3,
Sending a first message from the source node indicating that data is ready for transmission;
Receiving the first message at the destination node; And
Determining a first measurement of the signal quality from the signal quality of the first message received at the destination node
≪ / RTI > 5. The method of claim 4,
Receiving the first message at the first relay node; And
Determining a second measurement of the signal quality from the signal quality of the first message received at the first relay node
≪ / RTI > The method of claim 5,
Sending a second message from the destination node that includes an indication of the duration of the incoming slot within the time that the relay node can transmit the message;
Wherein the duration is determined on the basis of the signal quality for the received first message. The method according to claim 6,
Receiving the second message at the first relay node
Lt; / RTI >
Determining the second measure of signal quality comprises
And at least the signal quality of the second message received at the first relay node. The method of claim 7, wherein
Transmitting a third message depending on the determined delay interval that is less than or equal to the duration of the incoming slot
Lt; / RTI >
The third message is an inflow message from the first relay node after the determined delay period, and the determined delay period starts from the end of reception of the second message at the first relay node. 9. The method of claim 8,
The third message comprises an indication of a second measurement of the signal quality. 10. The method of claim 9,
Selecting an operation of the second mode on a basis comprising the receipt of the third message
≪ / RTI > 11. The method according to claim 9 or 10,
Determining a data rate for transmission of data from the source node on a basis comprising the indication of a second measurement of the signal quality in the third message
≪ / RTI > 12. The method according to any one of claims 9 to 11,
Determining a modulation scheme for transmission of data from the source node on the basis of including the indication of a second measure of signal quality in the third message
≪ / RTI > 13. The method according to any one of claims 4 to 12,
Data may be transmitted from the source node to the destination node in a third mode,
The third mode comprises transmission from the source node to the destination node via a combination of the first path via the first relay node and a second path via an additional relay node,
Receiving the first message at the additional relay node;
Determining a fourth measure of signal quality of the first message received at the additional relay node;
Receiving the second message at the additional relay node;
Determining a fifth measure of signal quality, wherein the fifth measure of signal quality is a measure of signal quality of the second message received at the additional relay node;
Determining a second delay interval for transmission of a fourth message in dependence on a fourth measurement and a fifth measurement of the signal quality;
Receiving the third message from the first relay node; And
Transmitting the fourth message after the determined second delay interval, depending on the determined delay interval that is less than or equal to the duration of the incoming slot.
Lt; / RTI >
And the determined second delay period begins with the end of reception of the third message at the additional relay node. The method of claim 13,
The fourth message includes an indication of received signal quality based on a fourth measurement and a fifth measurement of the signal quality. 15. The method of claim 14,
Selecting the third mode of operation for transmission of data from the source node on a basis comprising the receipt of the third message and a fourth message; And
Determining a data rate for transmission of data from the source node on a basis comprising an indication in the third message and a fourth message of received signal quality;
Lt; / RTI >
The received signal quality is based on a second measurement, a third measurement, a fourth measurement and a fourth measurement on the signal quality. 16. The method according to any one of claims 13 to 15,
And transmitting data simultaneously via the first path and the second path. 17. The method of claim 16,
Relaying data in accordance with Quantise Map and Forward (QMF) protocol at the first relay node and the additional relay node;
≪ / RTI > 18. The method according to any one of claims 4 to 17,
And the first message is a ready-to-send (RTS) message. The method according to any one of claims 6 to 18,
The second message is a clear-to-send (CTS) message. The method according to any one of claims 8 to 19,
The third message is a ready-to-relay (RTR) message. The method according to any one of claims 13 to 20,
And the fourth message is a ready-to-relay (RTR) message. The method according to any one of claims 1 to 21,
The basis for determining the incoming slot duration includes an allowed modulation or coding scheme. The method of claim 22,
Receiving an indication of the allowed modulation or coding scheme from the source node
≪ / RTI > 24. The method according to any one of claims 1 to 23,
The wireless network operating in accordance with IEEE 802.11. In a relay node for transmission signals in a wireless network,
The wireless network comprises a source node, a destination node and at least one relay node, the wireless network comprising a first measurement of signal quality relating to a direct link between the source node and the destination node and the source node. And determine a second measure of signal quality with respect to a link via the at least one first relay node between the destination nodes,
The relay node;
Determine a duration of an inlet slot through which the relay node can send a receipt message indicating the availability of the relay node to relay, the duration of the inlet slot being a first measure of the signal quality Relay node based on. 26. The apparatus of claim 25, wherein the relay node;
And if it is determined to transmit the incoming message, determine a delay interval for the transmission of the incoming message from the first relay that depends on a second measure of the signal quality.

Images