The present invention relates generally to wireless communications, and in particular to wireless communications using multiple antennas to wirelessly transmit multiple downlink traffic streams to multiple receiving stations.
In a typical wireless network utilizing a coordination function for coordinating transmissions among wireless stations, such a coordination function may be implemented in one of the wireless stations such as a wireless access point (AP) functioning as a coordinator. The wireless stations may communicate via directional transmissions using sector antennas and beam-forming antenna arrays. The coordinator may use omnidirectional transmissions for broadcasts to all wireless stations in all directions (e.g., 360 degrees range).
Alternatively, the coordinator may use quasi-omnidirectional transmissions for broadcasts to a wide range, but not necessarily in all directions. In many wireless area networks (WLANs) such as those according to IEEE 802.11 standards, a coordinator is used in infrastructure mode for providing contention-free access to a wireless communication medium to support Quality of Service (QoS) for certain applications.
Embodiments of the present invention provide multi-user (MU) multiple-input-multiple-output (MIMO) communication in a Power Save Multi-Poll (PSMP) sequence for a wireless communication system such as wireless network to support multiple downlink traffic streams to multiple receiver wireless stations simultaneously.
Wireless communication in a wireless communication system, comprises maintaining data blocks at a wireless transmitting station for transmission to multiple wireless receiving stations over a shared wireless communication medium, and simultaneously transmitting data blocks from the transmitting station over multiple spatial streams to multiple destination wireless receiving stations in a power save multi-poll (PSMP) sequence, via the wireless communication medium.
These and other features, aspects and advantages of the present invention will become understood with reference to the following description, appended claims and accompanying figures.
The present invention relates to wireless communications using multiple antennas to wirelessly transmit multiple downlink traffic streams from a transmitting station to multiple receiving stations.
Generally in the absence of a coordinator, contention-free access to a shared wireless communication (e.g., a radio frequency (RF) channel) may be implemented using announcement or information exchange among wireless stations in a network to negotiate/reserve the use of the communication medium.
Embodiments of the present invention provide multi-user (MU) multiple-input-multiple-output (MIMO) communication in a Power Save Multi-Poll (PSMP) sequence for a wireless communication system such as wireless network to support multiple downlink traffic streams to multiple receiver wireless stations simultaneously.
In one embodiment, the present invention provides a communication system and protocol for wireless communication in a wireless local area network, wherein multiple antennas wirelessly transmit multiple downlink traffic streams (spatial streams) from a transmitting station to multiple receiving stations. In one embodiment, a communication protocol according to the present invention is useful with PSMP in the IEEE 802.11 wireless communication standard.
One implementation of said communication protocol according to the present invention provides an enhancement to said PSMP mechanism, wherein said communication protocol supports downlink (DL) multi-user (MU) multiple-input-multiple-output (MIMO) communication in one or more PSMP downlink transmission times (DTTs) in a PSMP sequence.
A frame structure is used for data transmission between wireless stations such as a transmitter station and a receiver station. In one example, a frame structure in a Media Access Control (MAC) layer and a physical (PHY) layer is utilized, wherein in a transmitter station, a MAC layer receives a MAC Service Data Unit (MSDU) and attaches a MAC header thereto, in order to construct a MAC Protocol Data Unit (MPDU). The MAC header includes information such as a source address (SA) and a destination address (DA). The MPDU is a part of a PHY Service Data Unit (PSDU) and is transferred to a PHY layer in the transmitter to attach a PHY header (i.e., PHY preamble) thereto to construct a PHY Protocol Data Unit (PPDU). The PHY header includes parameters for determining a transmission scheme including a coding/modulation scheme. The PHY layer includes transmission hardware for transmitting data bits over a wireless link. Before transmission as a frame from the transmitter station to the receiver station, a preamble is attached to the PPDU, wherein the preamble can include channel estimation and synchronization information.
PSMP is used by an AP to schedule time periods to access the wireless communication medium for downlink transmission target STAs, as well as schedule time periods for target STAs to access the medium for uplink transmission to the AP. PSMP operation is under the control of a Hybrid Coordinator (HC), operating under a centralized access control scheme, and it is only available when traffic specifications (TSPECs) have been established between an AP and its target (associated) STAs. TSPECs are used by the AP to reserve resources within the AP and to modify the AP's scheduling behavior. The parameters in the TSPEC can be grouped into two categories for two purposes: PSMP scheduling and PSMP reservation.
The PSMP mechanism is controlled using a PSMP Action frame. PSMP Downlink Transmission Time (PSMP-DTT) is a period of time described by a PSMP frame during which the AP transmits. PSMP Uplink Transmission Time (PSMP-UTT) is a period of time described by a PSMP frame during which a non-AP station may transmit. A PSMP sequence is a sequence of frames where the first frame is a PSMP frame, followed by transmissions in zero or more PSMP-DTTs and then by transmissions in zero or more PSMP-UTTs. The schedule of the PSMP-DTTs and PSMP-UTTs is defined in the PSMP frame.
An AP transmits a PSMP frame containing a schedule only for target STAs that are awake. A target STA with an established PSMP session is awake at the start of the session's service period (SP) and remains awake until the end of the SP unless permitted to return to sleep as regulated in PSMP. A PSMP sequence may be used to transmit group addressed frames along with individually addressed frames. Individually addressed frames are scheduled after group addressed frames. During a PSMP sequence, a STA is able to receive frames during its scheduled PSMP-DTT and is not required to be able to receive frames at other times. A STA that has frames to send that are valid for transmission within the PSMP-UTT starts transmission without performing CCA and regardless of NAV at the start of its PSMP-UTT. STAs can save power by only waking up for receiving and transmitting at the pre-scheduled times and sleep for the rest of the times.
PSMP allows an AP station to schedule DTTs for a wireless station (STA) to wake up, receive downlink data frames, and go back to sleep. The AP further schedules UTTs for a STA to wake up, transmit to the AP, and go back to sleep. The scheduling is based on the traffic specification the STAs negotiated with the AP. By using PSMP, a STA is able to wake up for receiving and transmitting only at the scheduled times and to sleep for the rest of the time. This saves the power consumption of the STA. The PSMP mechanism allows an AP to transmit to one STA at a time within one DTT in a PSMP sequence.
According to an embodiment of the invention, a MU-MIMO PSMP communication protocol enables multi-user downlink transmissions in a PSMP sequence.
Specifically,
In this example, there are three traffic streams (or queues) of data frames (packets) at the AP station 11 for transmission to receiver wireless stations 13 (i.e., STA-1, STA-2 and STA-3), respectively. In one embodiment, the system operates in hybrid coordination function controlled channel access (HCCA). For each STA that has uplink traffic to send to the AP, channel time is scheduled accordingly. Embodiments of the invention are useful with wireless devices where power saving is important, such as mobile wireless devices operating on battery power. A STA communicates with the AP and provides its traffic specification (TSPEC) to the AP for channel access scheduling.
Specifically,
Further,
Said MU-MIMO PSMP communication according to an embodiment of the invention allows one PSMP-DTT to be shared by a physical layer convergence procedure (PLOP) protocol data unit (PPDU) targeting at different receiving STAs by using multiple sets of spatial streams enabled by DL MU-MIMO. Further, MPDUs sent by an AP STA within a DTT in a MU-MIMO PSMP sequence may contain MPDUs of multiple TIDs. As such, in one embodiment the MU-MIMO PSMP mechanism provides flexibility of transmission scheduling and efficiency.
In one embodiment, the MU-MIMO PSMP mechanism provides DL MU-MIMO support for wireless devices implementing wireless communication based on IEEE 802.11ac standard. In one implementation of the MU-MIMO PSMP mechanism according an embodiment of the invention, PSMP Mixed Mode allows PSMP-DTTs and PSMP-UTTs for both IEEE 802.11n and IEEE 802.11ac devices, to be scheduled in the same PSMP sequence. As such, a MU-MIMO DTT and a conventional DTT can be transmitted in one single PSMP sequence (by using different STA_Info type). The word “Mixed” herein means mixing different type of STA_Info fields in the PSMP frame. Further, a PSMP Green Field Mode reduces control overhead and provides a way of DL MU-MIMO transmission under HCF Controlled Channel Access (HOCA) for IEEE 802.11ac. There is no need for a Group ID, providing less power consumption.
As such, according to embodiment of the invention, MU-MIMO PSMP is a PSMP sequence where at least one DTT is transmitted using the MU-MIMO technology. MU-MIMO DTT is a DTT during which the PPDUs are transmitted using the MU-MIMO technology. PSMP 11ac Green Field Mode is a PSMP operation mode which allows only MU-MIMO DTT(s) to be transmitted in a PSMP sequence. PSMP Mixed Mode is a PSMP operation mode which allows both legacy DTT (under IEEE 802.11n operation rules) and MU-MIMO DTT to be transmitted in the same PSMP sequence.
As shown by example in
For example in
For the uplink scheduling, the UTTs for STAs included in a MU-MIMO DTT can be determined by the AP flexibly. For example, in
To allow simultaneous transmissions of MU-MIMO PPDUs to multiple IEEE 802.11ac capable STAs, the AP can schedule the same PSMP-DTT Start Offset and PSMP-DTT Duration for the MU-MIMO DTT in a PSMP frame. All targeted STAs need to wake up for the length of this MU-MIMO DTT. Each STA has its own PSMP-UTT Start Offset and PSMP-UTT Duration scheduled in the PSMP frame. In case different STAs have different PPDU lengths, they can be scheduled into different PSMP-DTTs such that PPDUs of similar length can be grouped together to allow STAs to stay wake up only when necessary.
Extremely short or long PPDUs should be transmitted without using MU-MIMO, if power consumption is the major concern. This is because STAs receiving short frames will be forced to stay awake longer than what it needs when using MU-MIMO DTT and STAs receiving long frames will force other STAs to stay awake longer than what they need, when using MU-MIMO DTT. The balance between throughput and power consumption is considered.
According to an embodiment of the invention, a new STA_INFO field 80 for the PSMP frame is provided to reduce control overhead, as illustrated in
Using DL MU-MIMO according to embodiments of the invention, multiple frames can be transmitted to different STAs in one DTT simultaneously, increasing network throughput. Further, multiple SIFSs can be saved between different DTTs, which saves network bandwidth. Using said DL MU-MIMO, the sleeping cycle can be reduced, which reduces transmission delay for delay sensitive applications.
Conventionally in one DTT, the transmitted frames must have the same RA. Each STA can be targeted only once by the AP in one PSMP sequence. When there are multiple DTTs, although STAs can save power during the sleeping period, transmission delay is also long since the AP takes turns to transmit to different STAs. Conventionally, individually addressed entries in the PSMP frame have their PSMP-DTT and PSMP-UTT start offsets scheduled to minimize the number of on/off transitions or to maximize the delay between their PSMP-DTT and PSMP-UTT periods.
According to embodiments of the invention, a STA need not go to sleep before its own DTT, and may transmit immediately after receiving a PSMP frame. This reduces number of On/Off (Wakeup/Sleep) transitions (power saving). Further, neither PSMP-DTT Start Time nor PSMP-DTT Duration are needed since each entry starts at the same time (SIFS after PSMP frame), and the end of the transmission can be detected by every receiver so it can go back to sleep until their UTT arrives. This simplifies scheduling of the start offsets of each addressed entry. Because PSMP operation relies on TSPEC, an AP can perform better scheduling for DL MU-MIMO transmission, based on the TSPEC parameters. An example involves determining which STAs should be grouped together into one PPDU for downlink transmission. In addition, backward compatibility is provided such that mixed IEEE 802.11n and IEEE 802.11ac transmissions can share the same PSMP sequence.
As is known to those skilled in the art, the aforementioned example architectures described above, according to the present invention, can be implemented in many ways, such as program instructions for execution by a processor, as software modules, microcode, as computer program product on computer readable media, as logic circuits, as application specific integrated circuits, as firmware, as consumer electronic devices, etc., in wireless devices, in wireless transmitters/receivers, in wireless networks, etc. Further, embodiments of the invention can take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment containing both hardware and software elements.
Information transferred via communications interface 107 may be in the form of signals such as electronic, electromagnetic, optical, or other signals capable of being received by communications interface 107, via a communication link that carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, an radio frequency (RF) link, and/or other communication channels. Computer program instructions representing the block diagram and/or flowcharts herein may be loaded onto a computer, programmable data processing apparatus, or processing devices to cause a series of operations performed thereon to produce a computer implemented process.
Embodiments of the present invention have been described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. Each block of such illustrations/diagrams, or combinations thereof, can be implemented by computer program instructions. The computer program instructions when provided to a processor produce a machine, such that the instructions, which execute via the processor create means for implementing the functions/operations specified in the flowchart and/or block diagram. Each block in the flowchart/block diagrams may represent a hardware and/or software module or logic, implementing embodiments of the present invention. In alternative implementations, the functions noted in the blocks may occur out of the order noted in the figures, concurrently, etc.
The terms “computer program medium,” “computer usable medium,” “computer readable medium”, and “computer program product,” are used to generally refer to media such as main memory, secondary memory, removable storage drive, a hard disk installed in hard disk drive, and signals. These computer program products are means for providing software to the computer system. The computer readable medium allows the computer system to read data, instructions, messages or message packets, and other computer readable information from the computer readable medium. The computer readable medium, for example, may include non-volatile memory, such as a floppy disk, ROM, flash memory, disk drive memory, a CD-ROM, and other permanent storage. It is useful, for example, for transporting information, such as data and computer instructions, between computer systems. Computer program instructions may be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks.
Furthermore, the computer readable medium may comprise computer readable information in a transitory state medium such as a network link and/or a network interface, including a wired network or a wireless network, that allow a computer to read such computer readable information. Computer programs (i.e., computer control logic) are stored in main memory and/or secondary memory. Computer programs may also be received via a communications interface. Such computer programs, when executed, enable the computer system to perform the features of the present invention as discussed herein. In particular, the computer programs, when executed, enable the processor multi-core processor to perform the features of the computer system. Such computer programs represent controllers of the computer system.
Though the present invention has been described with reference to certain versions thereof; however, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.
This application claims priority from U.S. Provisional Patent Application Ser. No. 61/443,681, filed Feb. 16, 2011, incorporated herein by reference.
Number | Date | Country | |
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61443681 | Feb 2011 | US |