CN1853373A - Back-end alignment to avoid SDMA ack time-out - Google Patents

Abstract

In a base station using spatial division multiple access communications, different length transmissions directed from a base station to different multiple mobile devices substantially simultaneously may have their start times adjusted so that the transmissions end at approximately the same time. The mobile devices may then respond during a response period with acknowledgments at approximately the same time. Thus all the acknowledgments may be received within the same time period from the end of the transmissions, reducing the likelihood of missed acknowledgments in responses to the shorter transmissions.

Description

Backend calibration to avoid SDMA acknowledgment timeout

background

In order to address the increasing bandwidth demands faced by wireless data communication systems, various techniques are being developed to allow multiple devices to communicate with a single base station by sharing a single channel. In one such technique, the base station can transmit separate signals to or receive separate signals from multiple mobile devices simultaneously on the same frequency if the mobile devices are located in sufficiently different directions from the base station. For transmission from the base station, different signals can be transmitted simultaneously from each of multiple spatially separated antennas, such that the combined transmission is directional, i.e., the signal intended for each mobile device can Relatively strong in the direction of the mobile device and relatively weak in other directions. Similarly, a base station can simultaneously receive combined signals from multiple independent mobile devices on the same frequency via each of multiple spatially separated antennas, and combine the signals received from the multiple antennas with appropriate signal processing. The combined signal is split into separate signals from each mobile device so that reception is also directional.

Under the currently developing specifications, such as IEEE 802.11 (IEEE is the abbreviation of the Institute of Electrical and Electronics Engineers located at 3 Park Avenue, ^17th floor, New York, New York), the base station can basically send different information to different mobile devices at the same time. block of variable length, and then waits for the designated mobile device to respond with an acknowledgment, each acknowledgment indicating that the respective mobile device has received the block. Because each mobile can respond shortly after it receives its intended transmission from the base station, a mobile receiving a short block may send its own while the base station is still sending a longer block to a different mobile. response. If the base station transmits and receives on the same frequency, and thus cannot transmit and receive at the same time, acknowledgments for short blocks may be lost because the base station is still transmitting. The base station may then assume that the short data block was never received by the intended mobile device, and subsequently retransmit the data block. Such unnecessary retransmissions can lead to overall inefficiency in data communication and, in some circumstances, even disruption of service.

Description of drawings

The present invention can be understood by reference to the following description and the accompanying drawings, which illustrate embodiments of the invention. In the attached picture:

Fig. 1 shows a diagram of a communication network according to an embodiment of the present invention.

Figure 2 shows a timing diagram of a communication sequence involving a base station and multiple mobile devices, according to an embodiment of the present invention.

Figure 3 shows a flowchart of a method of adjusting transmissions to end nearly simultaneously, according to an embodiment of the present invention.

Fig. 4 shows a block diagram of a base station according to an embodiment of the present invention.

Detailed ways

Numerous specific details are set forth in the following description. However, it is understood that embodiments of the invention may be practiced without these specific details. In addition, well-known methods, structures and techniques have not been shown in detail in order not to obscure the understanding of this description.

References to "one embodiment," "an embodiment," "an exemplary embodiment," "various embodiments," etc., mean that the embodiments of the invention so described may include a particular feature, structure, or characteristic, but not Every embodiment must include that specific feature, structure or characteristic. Furthermore, repeated use of the phrase "in one embodiment" does not necessarily refer to the same embodiment, although it may.

In the following description and claims, the terms "coupled" and "connected," along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Rather, in particular embodiments, "connected" may be used to mean that two or more elements are in direct physical or electrical contact with each other. "Coupled" may mean that two or more elements are in direct physical or electrical contact with each other, or that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other.

As used herein, unless otherwise specified, common adjectives such as "first", "second", "third", etc., when used to describe common things, merely mean that different instances of similar things are referred to, while It is not meant that things so described necessarily have a given order in time, space, in rank, or in any other way.

Unless otherwise indicated, it will be clear from the following discussion that terms such as "processing," "computing," "computing," and the like are used in discussions throughout this specification to refer to a computer or computing system, or similar electronic computing device. Actions and/or processes by which a computer or computing system, or similar electronic computing device, manipulates and/or converts data expressed as a physical quantity (eg, electrical quantity) into other data similarly expressed as a physical quantity.

Similarly, the term "processor" may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory. A "computing platform" may include one or more processors.

In the context of this document, the term "wireless" and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communication channels, etc., that can use modulated electromagnetic radiation to transmit data over a non-solid medium. The term does not imply that the associated equipment does not contain any wired wiring, although in some embodiments it might be.

Consistent with common industry terminology, the terms "base station," "access point," and "AP" are used interchangeably herein to describe an electronic device that can communicate wirelessly and substantially simultaneously with multiple other electronic devices, while the term "Mobile device" and "STA" are used interchangeably to describe any of the various other electronic devices that may have the ability to communicate while moving, although movement is not a requirement. However, the scope of the present invention is not limited to devices labeled with these terms. Similarly, the terms "spatial division multiple access" and SDMA are used interchangeably. As used herein, these terms are intended to include communications techniques in which different signals may be transmitted from the same device substantially simultaneously through a combination of multiple antennas such that combining the transmitted signals results in different signals destined for different devices being transmitted at the same frequency transmit in substantially different directions; and/or include communication techniques in which different signals can be received substantially simultaneously at the same frequency from different devices in different signals are separated from each other. The term "same frequency" as used herein may include slight deviations at a precise frequency due to bandwidth tolerances, Doppler Shift adaptation, parameter drift, and the like. Two or more transmissions to different devices are considered substantially simultaneous as long as at least part of each transmission to different devices occurs simultaneously, but it does not imply that the different transmissions necessarily start and/or end at the same time , though it can be. Similarly, two or more receptions from different devices are considered to be substantially simultaneous as long as at least part of each reception from different devices occurs simultaneously, but it does not imply that the different transmissions necessarily start at the same time and/or Or end at the same time, though it can be. Words represented by the term SDMA may sometimes use other variants, such as but not limited to replacing "spatial" with "space" and "division" with "diversity". The scope of the various embodiments of the present invention is intended to embrace these differences in nomenclature.

Fig. 1 shows a diagram of a communication network according to an embodiment of the present invention. The illustrated embodiment of an SDMA-based network shows an AP 110 that can communicate with multiple STAs 131-134 in different directions from the AP while avoiding the problems associated with sending transmissions of different lengths to different STAs. The acknowledgment timed out. While AP 110 is shown with four antennas 120 to communicate with up to four STAs at a time, other embodiments may have other arrangements (e.g., AP 110 may have two, three, or more than four antennas). Each STA may have one or more antennas to communicate with AP 110. In some embodiments, one or more STA antennas may be adapted to function as omnidirectional antennas, but in other embodiments, one or more STA antennas may be adapted to function as directional antennas. In some embodiments, STAs may be located at fixed locations, but in other embodiments at least a portion of STAs may move during a communication sequence and/or between communication sequences. In some embodiments, the AP 110 may be located in a fixed location, but in other embodiments, the AP 110 may be mobile.

Figure 2 shows a timing diagram of a communication sequence involving an AP and two STAs (labeled STA1 and STA2), according to an embodiment of the present invention. Although the illustrated embodiment shows only two STAs, other embodiments may include other numbers of STAs. In the AP part of FIG. 2 , a row labeled 1 indicates directed transmission from AP to STA1 , and a row labeled 2 indicates directed transmission from AP to STA2 . The two rows of STA1 and STA2 respectively indicate the transmission from STA1 to the AP and from STA2 to the AP. In some embodiments, outbound transmissions from STA1 and STA2 may be nominally omnidirectional (e.g., no direction is intentionally dominant - reception is possible within a 360-degree circumference around STA), But in other embodiments, the outbound transmissions from STA1 and STA2 may be directed.

Communications between the AP and the STA may include other communication sequences not shown in FIG. 2, eg, communications that occur before and/or after the sequence shown. Such sequences may include, but are not limited to, such as training (communications that derive parameters needed to enable SDMA techniques), polling (request responses), data (substantial information), acknowledgments (information about previous transmissions being correct) Received verification information), etc.

In FIG. 2 , it may be assumed that the AP has established various SDMA parameters required to transmit different data to and receive different data from multiple STAs substantially simultaneously. Using this capability, the AP can transmit to both STA1 and STA2 during time period _t1 . In the illustrated embodiment, the AP sends a poll (POLL1) to STA1, requesting a response from STA1 including data (if available) and an acknowledgment (ACK1) to POLL1. Similarly, the AP sends a poll (POLL2) to STA2 at substantially the same time as sending the poll to STA1, requesting a response from STA2 including data (if available) and an acknowledgment (ACK2) to POLL2. In the embodiment illustrated in FIG. 2, the AP sends data to STA2 in addition to POLL2, making the transmission to STA2 longer than the transmission to STA1. If the transmission to both STAs starts at the same time, the transmission to STA1 may end earlier than the transmission to STA2, and the immediate response from STA1 may not be received by the AP because during the response AP is still sending to STA2. The AP may then start listening for a response from STA1, but the AP does not receive the response because it was sent too early.

In order to avoid such a timeout condition, the initiation of the transmission to STA1 may be delayed for a predetermined time such that the transmissions to STA1 and STA2 end nearly simultaneously, as shown in FIG. 2 . In this way, both STA1 and STA2 can respond within a specified time after their respective polls, and avoid timeout problems, even though the specified time may be much shorter than the duration sent out from STA1 and STA2. possible difference. The illustrated embodiment shows separate timeout periods for each STA being polled, and these separate timeout periods may be of the same or different duration (same duration shown). Alternatively, a single timeout period can be maintained within which all polled STAs are expected to send acknowledgments. The illustrated embodiment also shows an acknowledgment timeout period that is shorter than the response period _t2 , during which a given STA may deliver an acknowledgment verifiable by the remaining responses alone within the timeout period (e.g., even if the response The remainder of the acknowledgment can also be verified as correctly received by the AP), but other implementations can use other techniques (e.g., the acknowledgment timeout period can be as long as time period _t2 or longer, and the start of any response can is interpreted as an acknowledgment, etc.). A response can contain one or more transmissions that can be independently verified (eg, using CRC checks).

Control of the timeout period may be implemented in any feasible manner (eg, hardware counters, software counters, etc.). The embodiment illustrated in FIG. 2 shows a timeout period that starts immediately after the AP transmits and is controlled by the AP. Other embodiments may use other techniques (eg, the timeout period may start at a predetermined interval after the transmission starts or ends, the timeout period may be controlled by the STA, etc.).

In the illustrated embodiment of FIG. 2, the transmissions to STA1 and STA2 each include polling, but only one includes data, but other embodiments may use other techniques. For example: 1) all, some, or none of the outgoing transmissions from the AP may contain polling, 2) all, some, or none of the outgoing transmissions from the AP may contain data, 3) all outgoing transmissions from the AP All, some or none of the transmissions may contain training requests, 4) others, etc. In various embodiments, any transmission from the AP to the STA that has a different length and expects an acknowledgment from the STA may use the techniques described herein.

FIG. 3 shows a flowchart of a method of adjusting transmissions to end at near-simultaneity, according to an embodiment of the present invention. In flowchart 300, at 310, indicators of expected durations of transmissions that will occur substantially simultaneously can be determined. At the time of determination, the transmission may not have started, so the determined duration may be referred to as an expected duration. Such indicators can be determined in any feasible unit, such as time, bytes, clock cycles, etc., which provide a common basis for the indicators so that they can be compared to determine how to adjust the start time, This allows the sending to end nearly simultaneously. If different transmissions will have different data rates, these data rates can be a factor in determining the expected duration of a transmission. In some embodiments, the time period allocated to the transmission (e.g., t ₁ in FIG. 2 ) may be determined based on the expected duration of the longest transmission, in which case the expected longest transmission may be determined at 320 The duration of the transmission and at 330 the length of the transmission period is set. In other embodiments, the time period allocated for transmission may be fixed, or may be set according to other parameters not described here. At 340, a start delay may be calculated for each of the plurality of different transmissions such that if the start of each transmission is delayed by its associated delay, all transmissions will end approximately simultaneously. Start delays can be measured from any feasible common reference point. At 350 , the actual transmissions can be started with a specified delay in the start time of the individual transmissions such that the transmissions end at 360 approximately simultaneously. Once these transmissions are received, the mobile devices can each respond, and at 370 the responses can be received.

In some embodiments where a fixed time is allocated for transmissions, the described process may include calculating and using the delay of the longest transmission. In some embodiments that match the time allotted to a send to the length of the longest send, the delay in computing and using the longest send can be eliminated.

Referring back to FIG. 2, during time period _t2 , STA1 and STA2 may send responses to the AP substantially simultaneously. In the illustrated embodiment, these responses each include data and an acknowledgment to the respective poll, but other embodiments may generate other types of responses. For example: 1) all, some, or none of the responses from a specific STA may contain acknowledgments, 2) all, some, or none of the responses from a specific STA may contain data, 3) any correctly received responses Presence can be interpreted as a confirmation, 4) other.

During time period _t3 , after all STAs have finished transmitting, the AP may acknowledge these responses one by one substantially simultaneously, as shown. ACK1 is shown as an acknowledgment of the response from STA1 and ACK2 is shown as an acknowledgment of the response from STA2. If a given STA does not receive an acknowledgment within a defined period of time, it can assume that the response was not correctly received by the AP and can resend the response when polled again. A variety of techniques can be used to set such defined time periods.

Between time periods _ti , _t2 and _t3 , the embodiment of Figure 2 shows an interframe space (IFS). Various embodiments may use such time intervals in all, some, or none of the places indicated. IFS can have a uniform duration, or can have different durations according to various criteria. These time intervals can be used for different purposes, such as: 1) to allow for differences in the timing of the AP and individual STAs, 2) to allow time for required processing between reception and transmission, 3) to allow time for the transceiver to Switch between send and receive mode, 4) Other.

In some embodiments, the delay in the start time of the outbound transmission from the base station may be calculated from the interframe space immediately preceding the transmission. In other embodiments, the delay in the start time of all but the longest transmissions may be calculated from the start of the longest transmission.

Various embodiments of the invention can be implemented in one or a combination of hardware, firmware and software. Embodiments of the present invention can also be implemented as instructions stored on a machine-readable medium, which can be read and executed by a computing platform to perform the operations described herein, such as those described in FIGS. 2 and 3 and their associated text. operations described in . A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (eg, a computer). For example, a machine-readable medium may include read-only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals). , digital signals, etc.), and other media.

Fig. 4 shows a block diagram of a base station according to an embodiment of the present invention. Computing platform 450 may include one or more processors, and in some embodiments at least one of the one or more processors may be a digital signal processor (DSP). In the illustrated embodiment, the AP 110 has four antennas 120, but other embodiments may have two, three, or more than four antennas. Base station 110 may have modulator/demodulator 420 , analog-to-digital converter (ADC) 430 , and digital-to-analog converter (DAC) 440 for each antenna. The demodulator-ADC combination can convert the radio frequency signal received from the antenna into a digital signal suitable for processing by the computing platform 450 . Similarly, a DAC-modulator combination may convert digital signals from computing platform 450 into radio frequency signals suitable for transmission through an antenna. Other not shown components may also be included in the illustrated block diagrams, such as but not limited to amplifiers, filters, oscillators, etc., if desired.

The above description is only exemplary and not restrictive. Numerous variations can be implemented by those skilled in the art. These variations are intended to be included in the various embodiments of the invention, which are limited only by the spirit and scope of the appended claims.

Claims (22)

1. device comprises:

First electronic equipment, this equipment is adapted to be:

Relatively to first designator of first expectation duration that sends of second electronic equipment with to second designator of second expectation duration that sends of the 3rd electronic equipment;

Adjust described first and second send at least one time started, make described first and second to send to be close to side by side and finish; And

Using the adjusted time started to send described first and second sends.

2. device as claimed in claim 1, wherein said first electronic equipment also is adapted to be from described second electronic equipment and receives first response and receive second response from described the 3rd electronic equipment, wherein said first response comprises first affirmation that sends described first, and described second response comprises to be confirmed second of described second transmission.

3. device as claimed in claim 1, wherein said first electronic equipment also are adapted to be in described first sends and comprise poll, and comprise poll and other data in described second sends.

4. device as claimed in claim 1, wherein said first electronic equipment also are adapted to be based on long in the described first and second expectation duration that the send transmit time segments that described first and second transmissions are set.

5. device as claimed in claim 1, wherein

Described first transmission and described second sends will have different data transfer rates; And

The described first and second expectation duration parts that send are based on described different data transfer rate.

6. device as claimed in claim 1, wherein said first electronic equipment comprises the computing platform of finishing described compare operation.

7. device as claimed in claim 6 also comprises at least four modulator/demodulator that are coupled to described computing platform.

8. device as claimed in claim 7 also comprises at least four antennas, and each in described at least four antennas all is coupled at least one in described at least four modulator/demodulator.

9. device as claimed in claim 1, wherein said first electronic equipment comprises the base station.

10. device as claimed in claim 1, the wherein said second and the 3rd electronic equipment comprises mobile device.

11. also being adapted to be, device as claimed in claim 1, wherein said first electronic equipment use space division multiple access technique to send described first and second transmissions.

12. a method comprises:

Compare at first designator of the expectation duration that sends to first of first electronic equipment with between second designator of second expectation duration that sends of second electronic equipment;

Begin long one transmission in described first and second transmissions; And

After being approximately equal to the two the delay of difference of the described first expectation duration that sends and the described second expectation duration that sends, begin described first and second send in short one transmission;

Wherein said first and second send the use space division multiple access technique.

13. method as claimed in claim 12 also comprises being close to and side by side finishes described first and second transmissions.

14. method as claimed in claim 13 also is included in described end first and second transmissions and begins to confirm afterwards timeout period.

15. method as claimed in claim 12 also comprises substantially side by side receiving from first response of described first electronic equipment with from second of described second electronic equipment responding.

16. comprising greatly sending about described first and second, method as claimed in claim 15, the operation of wherein said reception first and second responses receive the initial of described first and second responses when finishing a back interFrameGap.

17. method as claimed in claim 12 also comprises and uses data transfer rate to determine the described expectation duration.

18. the machine readable media that instruction is provided, described instruction causes described processing platform to finish following operation when being carried out by processing platform, and described operation comprises:

Determining will be from the expectation duration of the outside a plurality of transmissions that send of an electronic equipment;

Adjust in described a plurality of transmission the time started of at least some, make described a plurality of transmission be close to side by side and finish; And

Use the adjusted time started and use space division multiple access technique substantially side by side to send described a plurality of transmission.

19. comprising, medium as claimed in claim 18, wherein said definite operation use data transfer rate to determine the described expectation duration.

20. medium as claimed in claim 18, wherein said operation also comprises the response that substantially side by side receives described a plurality of transmissions.

21. medium as claimed in claim 20, wherein said operation also comprise for receiving at least one affirmation in described a plurality of transmissions, initiate a timeout period.

22. medium as claimed in claim 20, wherein said reception operation receive the initial of described response when comprising greatly interFrameGap after described a plurality of transmissions finish.

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