WO2006063273A1

WO2006063273A1 - System and method capable of implicit feeback for the devices with an unequal number of transmitter and receiver chains in a wireless local area network

Info

Publication number: WO2006063273A1
Application number: PCT/US2005/044700
Authority: WO
Inventors: Qinghua Li; Xintian Lin
Original assignee: Intel Corp
Current assignee: Intel Corp
Priority date: 2004-12-07
Filing date: 2005-12-07
Publication date: 2006-06-15
Anticipated expiration: 2007-06-07
Also published as: KR101087482B1; GB0711667D0; TWI292660B; DE112005003118T5; DE112005003118B4; US20110053545A1; GB2437192A; KR20070086675A; US7830980B2; TW200633412A; JP4663734B2; JP2008523666A; KR20100080571A; GB2437192B; US8279972B2; US20060120476A1

Abstract

An embodiment of the present invention provides a wireless station (STA) capable of implicit feedback in a wireless local area network, comprising at least one power amplifier, a plurality of antennas capable of being connected with said at least one power amplifier, and a switch capable of switching the connection between said plurality of antennas and said at least one power amplifier thereby enabling said wireless station to sound a complete channel matrix for an access point (AP) in communication with said wireless station (STA).

Description

SYSTEM AND METHOD CAPABLE OF IMPLICIT FEEDBACK FOR THE

DEVICES WITH AIM UNEQUAL NUMBER OF TRANSMITTER AND RECEIVER

CHAINS IN A WIRELESS LOCAL AREA NETWORK

BACKGROUND

[0001 ] Wireless communications has become prevalent

throughout society creating the need for faster and more reliable wireless

communication techniques. Although not limited in this respect, one such

technique, 802.1 1 n is designed to increase WLAN speeds to at least 1 00M

bps for data and actual throughput rates. Unlike current ratified standards —

802.1 1 a, 802.1 1 b and 802.1 1 g- 802.1 1 n focuses on throughput at the

MAC (media access control) interface, rather than as a signaling bit rate in the

physical layer. This means the throughput rates will more likely match the

highest-possible data rates. This standard may operate in the 5GHz range

along with 802.1 1 a, although the present invention is not limited to these

frequency ranges.

[0002] One technique used in 802.1 1 n includes calibration and

implicit feedback for closed loop multiple input multiple output (MIMO), which

depends on the radio calibration to establish the channel reciprocity.

However, there are shortcomings to current attempts at implicit feedback.

[0003] Thus, a strong need exists for an apparatus, system and

method capable of improved wireless communication techniques that overcome the aforementioned shortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] The subject matter regarded as the invention is particularly

pointed out and distinctly claimed in the concluding portion of the

specification. The invention, however, both as to organization and method of

operation, together with objects, features, and advantages thereof, may best

be understood by reference to the following detailed description when read

with the accompanying drawings in which:

[0005] FIG. 1 illustrates a protocol for data exchange in an

embodiment of the present invention;

[0006] FIG. 2 depicts how the wireless station (STA) sounds the

channel and the access points (AP) obtains the 4x2 uplink channel matrix in

an embodiment of the present invention;

FIG. 3 depicts the channel as seen by the STA in a 3x4 channel

matrix in the downlink;

FIG. 4 depicts the short and long preamble format in the MIMO

packet header wherein the system has 3 transmit and receive chains. FIG. 5 illustrates a 1 + 1 x2 switch scheme;

FIG. 6 illustrates a 2x3 switch scheme to connect any two of the

3 antennas to the 2 PAs;

FIG. 7 depicts the preambles for the "2x3" switch of FIG. 6; and

FIG. 8 depicts the preambles for the "1 + 1 x2" switch scheme of

FIG. 5.

[0009] It will be appreciated that for simplicity and clarity of

illustration, elements illustrated in the figures have not necessarily been drawn

to scale. For example, the dimensions of some of the elements are

exaggerated relative to other elements for clarity. Further, where considered

appropriate, reference numerals have been repeated among the figures to

indicate corresponding or analogous elements.

DETAILED DESCRIPTION

[0010] In the following detailed description, numerous specific

details are set forth in order to provide a thorough understanding of the

invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other

instances, well-known methods, procedures, components and circuits have

not been described in detail so as not to obscure the present invention.

[0011] Some portions of the detailed description that follows are

presented in terms of algorithms and symbolic representations of operations

on data bits or binary digital signals within a computer memory. These

algorithmic descriptions and representations may be the techniques used by

those skilled in the data processing arts to convey the substance of their

work to others skilled in the art.

[0012] An algorithm is here, and generally, considered to be a

self-consistent sequence of acts or operations leading to a desired result.

These include physical manipulations of physical quantities. Usually, though

not necessarily, these quantities take the form of electrical or magnetic

signals capable of being stored, transferred, combined, compared, and

otherwise manipulated. It has proven convenient at times, principally for

reasons of common usage, to refer to these signals as bits, values, elements,

symbols, characters, terms, numbers or the like. It should be understood,

however, that all of these and similar terms are to be associated with the

appropriate physical quantities and are merely convenient labels applied to

these quantities.

[0013] Unless specifically stated otherwise, as apparent from the

following discussions, it is appreciated that throughout the specification

discussions utilizing terms such as "processing," "computing," "calculating," "determining," or the like, refer to the action and/or processes of a computer

or computing system, or similar electronic computing device, that manipulate

and/or transform data represented as physical, such as electronic, quantities

within the computing system's registers and/or memories into other data

similarly represented as physical quantities within the computing system's

memories, registers or other such information storage, transmission or display

devices.

[0014] Embodiments of the present invention may include

apparatuses for performing the operations herein. An apparatus may be

specially constructed for the desired purposes, or it may comprise a general

purpose computing device selectively activated or reconfigured by a program

stored in the device. Such a program may be stored on a storage medium,

such as, but not limited to, any type of disk including floppy disks, optical

disks, compact disc read only memories (CD-ROMs), magnetic-optical disks,

read-only memories (ROMs), random access memories (RAMs), electrically

programmable read-only memories (EPROMs), electrically erasable and

programmable read only memories (EEPROMs), magnetic or optical cards, or

any other type of media suitable for storing electronic instructions, and

capable of being coupled to a system bus for a computing device.

[0015] The processes and displays presented herein are not

inherently related to any particular computing device or other apparatus.

Various general purpose systems may be used with programs in accordance

with the teachings herein, or it may prove convenient to construct a more specialized apparatus to perform the desired method. The desired structure

for a variety of these systems will appear from the description below. In

addition, embodiments of the present invention are not described with

reference to any particular programming language. It will be appreciated that

a variety of programming languages may be used to implement the teachings

of the invention as described herein. In addition, it should be understood that

operations, capabilities, and features described herein may be implemented

with any combination of hardware (discrete or integrated circuits) and

software.

[0016] Use of 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 indicate that two or more elements are in direct

physical or electrical contact with each other. "Coupled" my be used to

indicated that two or more elements are in either direct or indirect (with other

intervening elements between them) physical or electrical contact with each

other, and/or that the two or more elements co-operate or interact with each

other (e.g. as in a cause an effect relationship).

[0017] It should be understood that embodiments of the present

invention may be used in a variety of applications. Although the present invention is not limited in this respect, the devices disclosed herein may be used in many apparatuses such as in the transmitters and receivers of a radio system. Radio systems intended to be included within the scope of the present invention include, by way of example only, cellular radiotelephone communication systems, satellite communication systems, two-way radio communication systems, one-way pagers, two-way pagers, personal communication systems (PCS), personal digital assistants (PDA's), wireless local area networks (WLAN), personal area networks (PAN, and the like).

[0018] Multiple-input multiple-output (MIMO) antenna technology

is a promising candidate for IEEE 802.1 1 n high throughput and 802.16d

standard. It is understood that these standards are just a couple of many

wireless communication techniques that are intended to fall within the scope

of the present invention and any standards illustrated herein are intended to

merely exemplify techniques which may obtain benefits by utilizing the

present invention.

[0019] The 802.1 1 n standards group has been working on a

closed loop MIMO technique which may have significant advantages over the

mandatory open loop MIMO systems. An "implicit" feedback, which depends

on radio calibration to establish the channel reciprocity, may be used in the

802.1 1 n wireless communication standard and requires calibration. This

method has an advantage of potential lower cost on the wireless station

(STA) side.

In an embodiment of the present invention are described 2 switch

schemes and the associated short and long preamble structures used for

(automatic gain control) AGC setting and channel training for a 2x3 MIMO

system. However, it is understood that although a 2X3 system is exemplified herein, the principles and methodologies of the present invention can be

utilized in many different systems and may be extended to other MIMO

system with unequal number of transmitter and receiver chains all of which

are intended to be within the scope of the present invention. Since 2x3 is a

very popular scheme to extend the range of MIMO spatial multiplexing, these

schemes may be put in place to support implicit feedback closed-loop MIMO

to further extend the range of the 2x3 system.

In an embodiment of the present invention at least 2x2 MIMO may be

provided as a baseline. Further, in an embodiment of the present invention

and not limited in this respect, is provided a 2x3 system as well. This

notation indicates 2 transmitting chains and 3 receiving chains on the device

- again, it is understood that the 2X3 scheme is but one of many schemes

and is provided herein for illustrative purposes only. It may be noted that the

2X3 may have a better eigen value distribution compared to that of a 2x2

channel matrix, which makes the multiplexing mode usable over a much

longer distance.

In an embodiment of the present invention, and as mentioned above

not limited in this respect, there are currently two issues with such 2x3

systems and the present invention articulates schemes to mitigate them.

Channel reciprocity is one such issue. The close-loop MIMO may send back

the Channel State Information (CSI) to the transmitter. Based on the CSI, the

transmitter may form spatial beams, which offers a 4 - 10 dB advantage

depending on number of transmitting and receiving antennas. "Implicit" feedback takes advantage of the channel reciprocity when the radios are

properly calibrated - which is to say that the downlink channel may be the

transpose of the uplink channel. Therefore, the CSI does not need to be sent

back "explicitly"; it can be estimated from the reverse traffic.

FIG. 1 , shown generally as 100, illustrates a protocol for data exchange

in an embodiment of the present invention. In an embodiment of the present

invention it is assumed the AP 105 needs to send a data packet to the STA

1 10. The AP 105 initiates the Request To Send (RTS) 1 1 5 packet when the

media is idle. The STA 1 10 sends back the Clear To Send (CTS) with channel

sounding packet 1 20 to let the AP 105 obtain the uplink channel. From the

reciprocity, the AP 105 also gets the downlink channel and subsequently

sends the DATA with beam forming 1 25. The STA 1 10 sends back ACK at

130.

However, in the case of a 2x3 system, the reciprocity does not hold.

To illustrate this, assume that an AP has 4 transmit and receive chains and a

STA has 2 transmit and 3 receive chains as shown in Fig. 2, which depicts

generally at 200 that the STA 210 sounds the channel 280 and the AP 205

obtains the 4x2 uplink channel matrix. 21 5 - 250 illustrate the AP side with

the 4 transmit and receive chains and 255 - 275 illustrate the STA 2 and 3

receive chains.

As shown in FIG. 3 at 300 is the downlink. The channel 380 as seen

by the STA 310 is the 3x4 channel matrix. An embodiment of the present

invention provides adding an RF switch to switch a Power Amplifier to the third STA antenna 375 in order to sound the complete channel matrix for the

AP 305. 31 5 - 350 illustrate the AP side with the 4 transmit and receive

chains and 355 - 375 illustrate the STA 3 and 4 receive chains.

An embodiment of the present invention provides (automatic gain

control) AGC Level Setting and Channel State Measurement. Most of the

modern receivers may be able to handle an input signal power between -

9OdBm to -20 dBm. The typical 8 bit (analog-to-digital converter) ADC does

not have enough dynamic range to resolve the full scale. The front end AGC

is essential to set the gain level such that the averaged base band signal is in

the appropriate ADC range for maximum accuracy. The short preamble may

thus be used for the receiver to choose the appropriate AGC setting. The

long preambles may be used for channel state measurement.

The following illustrates the process in the following 3x3 system. Fig

4_r generally at 400, illustrates the short 41 5 and long 420, 425, 430

preamble format in the MIMO packet header as frequency 405 vs. time 410.

The system has 3 transmit and receive chains. The different grayscales or

color denote different antennas (i.e., first, second and third antennas in one

embodiment). Only 6 tones are shown in the drawing to reduce the clutter,

however, in typical use, such as the 802.1 1 a/g standard there may be 52

tones - although the present invention is not limited to specific numbers of

tones.

When the STA 125 of FIG. 1 sends the CTS packet 1 20, the AP 105

needs to measure the uplink channel matrix accurately. The measurement is done in the short and long preamble portion of the packet shown in FIG. 4. In

an exemplary embodiment and not limited in this respect, an AP may be a

4x4 system.

In the short preamble, all antennas and tones may be on so the AGC of

the AP may settle to the most appropriate gain level to maximize accuracy.

The next 3 long preambles train the 4x3 channel matrix for every tone. The

tone interleaving at each time slot is used to make sure the average power

stay close to the average. The thicker lines indicate a factor of 3 higher

power in each tone in order to make the total output power the same.

If the STA is a 2x3 system, the scheme indicated in Fig. 4 will not

work due to the lack of a third transmitter. In another embodiment of the

present invention is provided an interleaving scheme to mitigate this problem.

For a 2x3 system, the present invention may use an extra switch to connect

the third antenna to a Power Amplifier (PA) so the channel reciprocity may be

used in implicit feedback. Also provided is a short preamble and long

preamble format to facilitate the channel state measurement by the device i communicating with this system.

As shown in FIG. 5, generally at 500, is a first switch topology of one

embodiment of the present invention where one PA 555 serves the first

antenna 570 and another PA 560 serves the other 2 antennas 575 and 580

alternatively through a 1 x2 switch (SPDT). The receive chain on the STA

510 side is omitted to simplify the picture. Illustrated at 51 5 - 550 are the

transmit and receive antennas and PAs of AP 505 with channel shown at 565.

Turning now to FIG. 6, illustrated generally at 600, is a second switch

scheme which uses a 2x3 switch 612 to connect any two of the three

antennas 670, 675 and 680 to the 2 PAs 655 and 660. The channel is

generally illustrated at 665 and at 51 5 - 650 are the transmit and receive

antennas and PAs of AP 605.

Looking now at FlG. 7, generally at 700 as frequency 705 vs. time

710, the short 71 5 preambles and long 720, 725 and 730 preambles are

designed according to the "2X3" switch scheme. First, the system keeps

track of the power received by each antenna in previous packets from the AP

and then ranks them accordingly. From the reciprocity, the antenna that

receives the most power also appears stronger to the AP. Therefore, the

strongest and the weakest antennas are used to send the short preamble in

order to set the AGC in the AP to the appropriate level.

Turning now to FIG. 8, the gray scales represent the stronger of

antenna 2 and 3. Further, the pair of antennas, 1 and the stronger of 2 and

3 are selected for long preamble 820 and 825. And the other antenna is

selected for long preamble 830, such that all tones and antennas are

exercised once and only once. The thicker lines indicate a factor of 2 higher

power in each tone so that the total emitted power are constant - although

the present invention is not limited in this respect.

The switch scheme A outlined in FIG. 4 is less flexible than that of FIG.

5 as it has one PA serving antenna 1 only. The other PA serves either antenna 2 or 3. The short preamble 81 5 may be sent using antenna 1 and

the stronger of antenna 2 and antenna 3. The long preambles 820, 825 and

830 may be sent with the tone interleaving scheme as if it is a two antenna

system. The third long preamble may be sent with the PA switched to the

third antenna.

[0032] While certain features of the invention have been

illustrated and described herein, many modifications, substitutions, changes,

and equivalents will now occur to those skilled in the art. It is, therefore, to

be understood that the appended claims are intended to cover all such

modifications and changes as fall within the true spirit of the invention.

Claims

Claims:What is claimed is:

1. A wireless station (STA) capable of implicit feedback in a

wireless local area network, comprising:

at least one power amplifier;

a plurality of antennas capable of being connected with said at

least one power amplifier; and

a switch capable of switching the connection between said

plurality of antennas and said at least one power amplifier thereby enabling

said wireless station to sound a complete channel matrix for an access point

(AP) in communication with said wireless station (STA).

2. The wireless station of claim 1 , wherein said plurality of

antennas is three antennas and said at least one power amplifier is two power

amplifiers.

3. The wireless station of claim 2, wherein a first of said two

power amplifiers is non-switchably connected to a first antenna of said three

antennas and a second of said two power amplifiers is switchably connected

to a second and third of said three antennas.

4. The wireless station of claim 1 , wherein all of said power

amplifiers are switchably connected to all of said antennas.

5. The wireless station of claim 2, wherein both said power

amplifiers are switchably connected to all three said antennas.

6. The wireless station of claim 1 , wherein said AP keeps track of

the power received by each of said plurality of antennas and ranks them

accordingly.

7. The wireless station of claim 6, wherein based on said ranking,

the strongest and the weakest antennas are used to send a short preamble in

order to set the automatic gain control (AGC) in said AP to an appropriate

level.

8. A method of providing implicit feedback by a wireless station

(STA) in a wireless local area network, comprising:

associating at least one power amplifier with a plurality of

antennas via a switch capable of switching the connection between said

plurality of antennas and said at least one power amplifier thereby enabling

said wireless station to sound a complete channel matrix for an access point

(AP) in communication with said wireless station (STA).

9. The method of claim 8, further comprising associating three

antennas and with two power amplifiers.

10. The method of claim 9, further comprising connecting non-

switchably a first of said two power amplifiers to a first antenna of said three

antennas and switchably connecting a second of said two power amplifiers to

a second and third of said three antennas.

1 1. The method of claim 8, further comprising connecting switchably

all of said power amplifiers to all of said antennas.

12. The method of claim 9, further comprising connecting switchably

both of said power amplifiers to all three said antennas.

13. The method of claim 1 , further comprising keeping track by said

AP of the power received by each of said plurality of antennas and ranking

them accordingly.

14. The method of claim 1 3, further comprising sending a short

preamble in order to set the automatic gain control (AGC) in said AP to an

appropriate level based on said ranking.

15. An article comprising a storage medium having stored thereon

instructions, that, when executed by a computing platform, results in providing implicit feedback by a wireless station (STA) in a wireless local area

network by associating at least one power amplifier with a plurality of

antennas via a switch capable of switching the connection between said

plurality of antennas and said at least one power amplifier thereby enabling

said wireless station to sound a complete channel matrix for an access point

(AP) in communication with said wireless station (STA).

16. The article of claim 1 5, wherein said plurality of antennas is

three antennas and said at least one power amplifier is two power amplifiers.

17. The article of claim 1 6, wherein a first of said two power

amplifiers is non-switchably connected to a first antenna of said three

antennas and a second of said two power amplifiers is switchably connected

to a second and third of said three antennas.

18. The article of claim 1 5, wherein all of said power amplifiers are

switchably connected to all of said antennas.

19. An implicit feedback system in a wireless local area network,

comprising:

a wireless station including at least one power amplifier and

a plurality of antennas capable of being switchably connected with said

at least one power amplifier; and an access point capable of sounding a complete channel matrix

with said wireless station (STA) .

20. The implicit feedback system of claim 1 9, wherein said plurality

of antennas is three antennas and said at least one power amplifier is two

power amplifiers.

21. The implicit feedback system of claim 1 9, wherein a first of said

two power amplifiers is non-switchably connected to a first antenna of said

three antennas and a second of said two power amplifiers is switchably

connected to a second and third of said three antennas.

22. The implicit feedback system of claim 1 9, wherein all of said

power amplifiers are switchably connected to all of said antennas.

23. The implicit feedback system of claim 1 9, wherein both said

power amplifiers are switchably connected to all three said antennas.