Techniques for improving the spatial reuse of wireless networks

A method (400) for improving the spatial reuse of a wireless network, comprising selecting a medium access slot (MAS) type for scheduling concurrent transmissions in the wireless network (S410); assigning reservations to the selected MAS (S420); and applying the selected MAS to source nodes and sink nodes of the wireless network (S430).

The invention relates generally to block transmission techniques.

In wireless networks, nodes located at a distance from each other can successfully transmit at the same time on the same frequency. This ability is typically referred to as spatial reuse. Spatial reuse is an important feature for wireless networks to support multiple concurrent transmissions, thereby enabling an increase in the network throughput.

The spatial reuse is further described with reference toFIG. 1which shows a WiMedia based wireless network100that includes ten nodes110-1through110-10. Each node110-X (X is an integer greater than or equal to 1) may be either in a sink mode, source mode, or idle mode. A node110-X operating in a source mode (hereinafter “source node”) transmits DATA and request to send (RTS) frames and receives clear to send (CTS) and acknowledgment (ACK) frames. A node110-X operating in a sink mode (hereinafter “sink node”) transmits ACK and CTS frames and receives RTS frames. A node110-X in an idle mode (hereinafter “idle node”) neither receives nor transmits frames.

The network100operates according to the WiMedia standard specification, which governs several rules with regard to concurrent transmissions. One of the rules determines that neighbouring nodes of a source node110-X and a sink node100-Y (Y is an integer greater than or equal to 1) are idle nodes. That is, neighbours of transmitting nodes cannot transmit any frames and neighbours of receiving nodes cannot receive frames. For example, applying this rule in the wireless network100implies that the spatial reuse is limited only to two pairs of nodes110-1and110-2, as well as110-7and110-8, where110-1and110-7are source nodes. Obviously, this significantly reduces the throughput of the network100.

A distributed reservation protocol (DRP), defined as part of the WiMedia MAC specification, provides a mechanism for concurrent communications between nodes110-X. Specifically, the DRP enables a device to gain scheduled access to the wireless medium within a negotiated reservation. Generally, a reservation type may be a hard reservation or a soft reservation. In hard reservations, nodes110-X other than the reservation owner and target(s) are not allowed to transmit frames. In soft reservations, neighbours of a reservation target that are not neighbours of the reservation owner are not allowed to access the wireless medium. For all kinds of transmissions, neighbours of a source node110-X are not allowed to transmit MAC frames.

Simply canceling the concurrent transmissions rules and the reservation provisions of the DRP will not improve the performance of the network as frames may collide at some nodes for the reason that the transmission is often bi-directional. That is, ACK frames sent from a sink node100-Y and DATA frames sent from a source node110-X will probably collide.

Certain embodiments of the invention include a method for improving the spatial reuse of a wireless network. The method comprises selecting a medium access slot (MAS) type for scheduling concurrent transmissions in the wireless network; assigning reservations to the selected MAS; and applying the selected MAS to source nodes and sink nodes of the wireless network.

Certain embodiments of the invention also include a computer readable medium having stored thereon computer executable code. The execution of the code causing a computer to perform the process of: selecting a medium access slot (MAS) type for scheduling concurrent transmissions in the wireless network; assigning reservations to the selected MAS; and applying the selected MAS to source nodes and sink nodes of the wireless network.

The invention further includes a wireless network adapted for enabling concurrent transmissions. The wireless network comprises a plurality of source nodes for transmitting at least DATA frames according to a predefined medium access slot (MAS) type and according to pre-assigned reservations; and a plurality of sink nodes for receiving at least DATA frames according to a predefined MAS type and according to the pre-assigned reservations.

The invention also includes a DRP information element data structure adapted to improve the spatial reuse of wireless networks. The DRP information element includes a DRP availability status bitmap information element including at least a medium access slot (MAS) type to be used; a control element for describing the content in the DRP information element; a MAS timing information element for supporting any type of MAS; and a length element including the length of the DRP availability status bitmap information element, the control element, and the MAS timing information element.

The present invention is useful in spatial reuse of wireless networks and particularly of WiMedia based wireless networks by providing a new medium access slot (MAS) scheduling transmission mechanisms. Accordingly, in certain embodiments a node in the wireless network can only transmit or only receive frames in fixed intervals of the MAS or during the entire MAS.

In order to use the MAS transmission scheduling mechanisms and to avoid collisions of frames when neighboring nodes concurrently transmit, new concurrent transmission rules are defined. The first rule provides that only one sink node can be in each source node's neighborhood, and that there is only one source node in each sink node's neighborhood. The second rule determines that neighboring nodes (i.e., either sink nodes or source nodes) involved in concurrent transmissions in the same MAS must adopt the same MAS type, i.e., follow exactly the same transmission and reception intervals. Accordingly, all source nodes in each other's neighborhood can transmit DATA frames and receive ACK frames at the same time. Similarly, all sink nodes in each other's neighborhood can receive DATA frames and transmit ACK frames at the same time. Therefore, the new concurrent transmission rules are useful in avoiding collisions between DATA frames and ACK frames and increasing successful concurrent transmissions.

FIG. 2shows a topology of a wireless network200demonstrating how the new communication rules may improve the spatial reuse. The network200includes ten nodes210-1through210-10where nodes connected with an edge are neighbors. In accordance with the invention, the optimal spatial reuse is achieved when nodes210-2,210-3,210-5,210-8and210-10are source nodes and all others are sink nodes. This complies with the first rule mentioned above. For example, the node210-6is a sink node as only one sink node can be in the neighborhood of source nodes210-2,210-3and210-5. The number of concurrent transmissions that can be achieved in such configuration is five, i.e., node210-2to node210-1, node210-3to node210-4, node210-5to node210-6, node210-8to node210-7, and node210-10to node210-9. In comparison to the conventional concurrent transmissions mechanism disclosed in the related art, for such topology no concurrent transmissions are allowed at the same MAS other than transmissions from node210-5to node210-6. Therefore, as shown, this example embodiment significantly improves the spatial reuse.

In accordance with the certain embodiments of the invention, three different types of MASs can be utilized to facilitate the concurrent transmissions. Regardless to its type, a MAS is divided into one or more intervals with predefined lengths. There are two kinds of intervals: a transmission interval and a reception interval. In transmission intervals, source nodes transmit RTS or DATA frames, and sink nodes receive RTS or DATA frames. In reception intervals, sink nodes transmit CTS or ACK frames and source node receive those frames.

FIG. 3Ashows an exemplary diagram of a single directional transmission MAS310for scheduling concurrent transmissions constructed in accordance with an embodiment of the invention. The MAS310includes a single transmission interval311and no reception interval. Therefore, when utilizing the MAS310for scheduling the transmissions, a source node only transmits DATA frames and a sink node only receives DATA frames. No other medium access is allowed.

FIG. 3Bshows an exemplary diagram of a bi-directional transmission MAS320for scheduling concurrent transmissions constructed in accordance with another embodiment of the invention. The MAS320is divided into a transmission interval321and a reception interval322. In addition, there is an interval spacing323between the intervals321and322to allow the turnaround from transmitting to receiving and from receiving to transmitting. In the transmission interval321a source node transmits DATA frames, and a sink node receives DATA frames. In the reception interval322a sink node transmits an ACK frame (may be a block acknowledgement), and a source node receives an ACK frame.

FIG. 3Cshows an exemplary diagram of a bi-directional transmission MAS330for scheduling concurrent transmissions constructed in accordance with another embodiment of the invention. This type of MAS includes two transmission intervals331and333and two reception intervals332and334and in between there are interval spacings335. Always after a transmission interval there is a reception interval. According to one embodiment of the invention, in the interval331a source node transmits a RTS frame and a sink node receives a RTS frame. In the interval332a sink node transmits a CTS frame and a source node receives a CTS frame. In the interval333a source node transmits DATA frames and a sink node receives DATA frames. In the interval334a sink node transmits an ACK frame and a source node receives an ACK frame. It is appreciated that one of ordinary skill in the art can adopt the teachings disclosed herein to define other type of MASs.

For all MAS types described above, the time durations of the transmission, reception, and spacing intervals are predetermined according to the length of the transmitted frames. Specifically, the interval spacing is typically larger than or equal to the maximum value of a guard time interval (e.g., maximum synchronization error, or maximum clock drift among devices and a short inter-frame spacing). The reception intervals are based on the length of the ACK frame and RTS frame. The interval331and332are based on the lengths of the RTS and CTS frames and are typically fixed.

FIG. 4shows an exemplary and non-limiting flowchart400describing a method implemented in accordance with an embodiment of the invention. At S410, the type of MAS to be used by the source and sink nodes is selected. The selection is based on a communication application of a wireless network to achieve optimized performance. For example, if the application does not require acknowledgment of frames reception, then MAS310is selected. If should be noted that a combination of MASs can be utilized by the nodes. For example, if an ACK frame should be transmitted after DATA frames transmitted within a sequence of MASs, then in such case a combination of MAS310and MAS320is selected. At S420, reservations are assigned to the selected MAS to allow more concurrent transmissions in each MAS. The assignment of reservations comply with the rule that only one sink node can be in the neighbourhood of a source node and that only one source node can be in the neighbourhood of a sink node. At S430, the selected MAS or combination of MASs are applied to sink and source nodes in the network. It should be noted that idle nodes may or may not adopt the selected MAS type. It should be further noted that during the same MAS, two pairs of source nodes and sink nodes which are far away from each other could use different types of MASs as long as either one of the first pair of source node and sink node is not a neighbor of either one of the second pair of source node and sink node.

In one embodiment of the invention the teachings described herein can be adapted to be included in the WiMedia MAC specification, thereby improving the spatial reuse of WiMedia based wireless networks. To this end, two reserved bits in the DRP control field of the DRP information element (IE) are utilized to designate the type of MAS transmission scheduling. The MAS type may be either one of those described above or the MAS currently adopted by WiMedia standard. This allows backward compatibility with existing WiMedia based devices. In addition, the format of the DRP IE is modified to indicate the status of the MAS. A modified DRP IE data structure500is shown inFIG. 5. For each bit set as zero in a DRP availability bitmap of a DRP availability IE, there are two bits allocated in a DRP availability status bitmap IE510to designate the MAS type to be used. The DRP IE format500also includes a control IE520, a MAS timing IE530and a length IE540that designates the length of the elements510,520, and530.

The control IE520indicates how to decode the information in the modified DRP IE500and includes at least the following fields of information (not shown): a) an indication of whether the control element520is used to explain the MAS type of a reservation advertised by the reservation owner and target, or whether the IE520is used to explain the MAS type of the MAS availability information advertised by any device; b) an indication of whether all MASs have the same MAS type or not; c) an indication of whether the modified DRP IE500is used to explain a single reservation advertisement or all reservation advertisements; d) an indication of whether a device is in the range of a reservation owner or a reservation target; and e) the number of bits used to designate the MAS type.

The MAS timing IE530is used for any types of MASs other than the MASs shown inFIGS. 3A,3B and3C. To support additional types of MASs, the MAS timing IE530describes the locations and lengths of all transmission and reception intervals in a MAS. A pair of source node and sink node can use the MAS timing IE530to establish any new type of MASs.

All nodes that use the DRP for transmission or reception announce their reservations by including DRP IEs with the MAS type field in their beacons. In a reservation negotiation, if the reservation cannot be granted due to a conflict with its own or its neighbors' reservations, the reservation target includes a DRP availability IE as well as a DRP MAS status bitmap IE510in a DRP reservation response command frame. In a DRP reservation response command frame for a multicast reservation, the reservation target shall include a DRP availability IE as well as a DRP MAS status bitmap IE510for a reason code other than denied.

The improved spatial reuse techniques described herein can be implemented in communication systems including, but not limited to, a ultra wideband (UWB) based wireless personal area networks (PANs), WiMedia based wireless networks, or any time division multiple access (TDMA) or super-frame based wireless networks.

The foregoing detailed description has set forth a few of the many forms that the invention can take. It is intended that the foregoing detailed description be understood as an illustration of selected forms that the invention can take and not as a limitation to the definition of the invention. It is only the claims, including all equivalents that are intended to define the scope of this invention.