1. A method for operating a wireless multiple input multiple output (MIMO) device, the method comprising:
communicating with a first communication device via a first communication link and with a second communication device via a second communication link;
determining respective channel conditions of the first communication link and the second communication link;
selecting a first preamble format from a plurality of preamble formats, each including a respective format of a high throughput signal field, for a first preamble of a first data frame for the first communication link based on the channel conditions of the first communication link; and
selecting a second preamble format from the plurality of preamble formats for a second preamble of a second data frame for the second communication link based on the channel conditions of the second communication link;
wherein the plurality of preamble formats includes a QPSK preamble format, a BPSK preamble format and a rotated BPSK preamble format, the high throughput signal field of the QPSK preamble format including one QPSK OFDM symbol, the high throughput signal field of the BPSK preamble format including two BPSK OFDM symbols, one of which is rotated by 90 degrees and the high throughput signal field of the rotated BPSK preamble format including two BPSK OFDM symbols that are both rotated by 90 degrees.
2. The method of claim 1, wherein the channel conditions include respective channel signal to noise ratios (SNRs) on the first communication link and the second communication link.
3. The method of claim 2, wherein each of the selecting further includes:
when a relatively higher channel SNR exists, using a relatively higher order modulation for the high throughput signal field; and
when a relatively lower channel SNR exists, using a relatively lower order modulation for the high throughput signal field.
4. The method of claim 2, wherein each of the selecting further includes:
when a relatively higher channel SNR exists, using a relatively shorter high throughput signal field; and
when a relatively lower channel SNR exists, using a relatively longer high throughput signal field.
5. The method of claim 1, wherein:
the QPSK preamble format includes a legacy short training field, a legacy long training field, a legacy signal field, the high throughput signal field having a first duration and modulation, and a high throughput long training field;
the rotated BPSK preamble format includes a legacy short training field, a legacy long training field, a legacy signal field, the high throughput signal field having a second duration and modulation, and a high throughput long training field; and
the BPSK preamble format includes a legacy short training field, a legacy long training field, a legacy signal field, the high throughput signal field having a third duration and modulation, and at least one high throughput long training field.
6. The method of claim 1, wherein:
the first preamble format includes a legacy short training field, a legacy long training field, a legacy signal field, the high throughput signal field having a first duration, and a high throughput long training field; and
the second preamble format includes a legacy short training field, a legacy long training field, a legacy signal field, the high throughput signal field having a second duration, and a high throughput long training field, the second duration greater than the first duration.
7. The method of claim 6, wherein:
the high throughput signal field of the first preamble format includes one QPSK OFDM symbol; and
the high throughput signal field of the second preamble format includes two BPSK OFDM symbols.
8. The method of claim 1, wherein each of the plurality of preamble formats includes a differing modulation of the high throughput signal field.
9. The method of claim 1, wherein each of the selecting further includes:
when the respective preamble is used for clear channel assessment by a non-data-receiving MIMO wireless device, using a relatively longer preamble; and
when the respective preamble is not used for clear channel assessment by a non-data-receiving MIMO wireless device, using a relatively shorter preamble.
10. An apparatus providing multiple input multiple output (MIMO) wireless communication, comprising:
a plurality of RF transmitters operable to communicate with a first communication device via a first communication link and a second communication device via a second communication link; and
a processing module coupled to the plurality of RF transmitters and operable to:
determine respective channel conditions of the first communication link and the second communication link;
select a first preamble format from a plurality of preamble formats, each including a respective format of a high throughput signal field, for a first preamble of a first data frame for the first communication link based on the channel conditions of the first communication link; and
select a second preamble format from the plurality of preamble formats for a second preamble of a second data frame for the second communication link based on the channel conditions of the second communication link;
wherein the plurality of preamble formats includes a QPSK preamble format, a BPSK preamble format and a rotated BPSK preamble format, the high throughput signal field of the QPSK preamble format including one QPSK OFDM symbol, the high throughput signal field of the BPSK preamble format including two BPSK OFDM symbols, one of which is rotated by 90 degrees and the high throughput signal field of the rotated BPSK preamble format including two BPSK OFDM symbols that are both rotated by 90 degrees.
11. The apparatus of claim 10, wherein the apparatus is an access point.
12. The apparatus of claim 10, wherein the channel conditions include respective channel signal to noise ratios (SNRs) on the first communication link and the second communication link.
13. The apparatus of claim 12, wherein the processing module is further operable to:
when a relatively higher channel SNR exists, use a relatively higher order modulation for the high throughput signal field; and
when a relatively lower channel SNR exists, use a relatively lower order modulation for the high throughput signal field.
14. The apparatus of claim 12, wherein the processing module is further operable to:
when a relatively higher channel SNR exists, use a relatively shorter high throughput signal field; and
when a relatively lower channel SNR exists, use a relatively longer high throughput signal field.
15. The apparatus of claim 10, wherein:
the QPSK preamble format includes a legacy short training field, a legacy long training field, a legacy signal field, the high throughput signal field having a first duration and modulation, and a high throughput long training field;
the rotated BPSK preamble format includes a legacy short training field, a legacy long training field, a legacy signal field, the high throughput signal field having a second duration and modulation, and a high throughput long training field; and
the BPSK preamble format includes a legacy short training field, a legacy long training field, a legacy signal field, the high throughput signal field having a third duration and modulation, and at least one high throughput long training field.
16. The apparatus of claim 10, wherein the processing module is further operable to:
use a relatively longer preamble for the first preamble or the second preamble when the respective preamble is used for clear channel assessment by a non-data-receiving MIMO wireless device, and
use a relatively shorter preamble for the first preamble or the second preamble when the respective preamble is not used for clear channel assessment by a non-data-receiving MIMO wireless device.
17. The apparatus of claim 10, further comprising:
a plurality of RF receivers coupled to the processing module and operable to receive an OFDM data frame on one of the first communication link and the second communication link, the OFDM data frame including a preamble and a data field; and wherein the processing module is further operable to:
determine a modulation format of a high throughput signal field of the preamble;
when the high throughput signal field has a first modulation format, determining that the preamble is of a first preamble format and that the data frame is of a first type;
when the high throughput signal field has a second modulation format, determining that the preamble is of a second preamble format and that the data frame is of a second type; and
when the high throughput signal field has a third modulation format, determining that the preamble is of a third preamble format and that the data frame is of a third type.
18. The apparatus of claim 17, wherein the processing module is further operable to, when the high throughput signal field has the first modulation format and a legacy signal field of the preamble indicates a particular data rate, determine that the preamble is of a legacy preamble format and that the data frame is of a legacy type.
19. An apparatus providing multiple input multiple output (MIMO) wireless communication, comprising:
a plurality of antennas;
a plurality of RF transmitters coupled to the plurality of antennas operable to communicate with a first communication device via a first communication link formed using a first number of the plurality of antennas and a second communication device via a second communication link formed using a second number of the plurality of antennas; and
a processing module coupled to the plurality of RF transmitters and operable to:
determine respective channel conditions of the first communication link and the second communication link;
select a first preamble format from a plurality of preamble formats, each including a respective format of a high throughput signal field, for a first preamble of a first data frame for the first communication link based on the channel conditions of the first communication link; and
select a second preamble format from the plurality of preamble formats for a second preamble of a second data frame for the second communication link based on the channel conditions of the second communication link;
wherein the plurality of preamble formats includes a QPSK preamble format, a BPSK preamble format and a rotated BPSK preamble format, the high throughput signal field of the QPSK preamble format including one QPSK OFDM symbol, the high throughput signal field of the BPSK preamble format including two BPSK OFDM symbols, one of which is rotated by 90 degrees and the high throughput signal field of the rotated BPSK preamble format including two BPSK OFDM symbols that are both rotated by 90 degrees.
20. The apparatus of claim 19, wherein:
the QPSK preamble format includes a legacy short training field, a legacy long training field, a legacy signal field, the high throughput signal field having a first duration and modulation, and a high throughput long training field;
the rotated BPSK preamble format includes a legacy short training field, a legacy long training field, a legacy signal field, the high throughput signal field having a second duration and modulation, and a high throughput long training field; and
the BPSK preamble format includes a legacy short training field, a legacy long training field, a legacy signal field, the high throughput signal field having a third duration and modulation, and at least one high throughput long training field.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. An inclination angle detection device comprising:
a chart drawing unit which draws an equal distance sequential pattern chart, which has patterns so that bright sections are sequentially placed in equal distances, by sequentially projecting the projection light of the equal distance sequential pattern chart to a projection surface, while shifting the patterns;
sensor units which comprise a plurality of light receiving units that are placed having predetermined distances from each other, setting a center line as the center, and sequentially receives the reflection light of the equal distance sequential pattern charts, that are drawn on the projection surface, at the plurality of light receiving units; and
inclination angle obtaining units wherein the sensor units sequentially obtain the average distance between the projection point of the projection light and equal distance sequential pattern charts, based on a plurality of phase differences at the time when the reflection light of the equal distance sequential pattern chart is received, the sum of each lag amount between the imaging position on the light receiving unit when the sensor unit receives a parallel light, and the imaging position on the light receiving unit when the sensor unit receives the reflection light of the equal distance pattern chart being set as the phase difference, and obtain the inclination angle of the projection surface based on the obtained average distance.
2. The inclination angle detection device according to claim 1, wherein the inclination angle obtaining unit obtains the average phase difference, based on the plurality of phase differences at the time when the sensor unit sequentially receives the reflection of the equal distance sequential pattern charts, and obtains the average distance between the projection point of the projection light and the equal distance sequential pattern charts, based on the obtained average phase difference.
3. The inclination angle detection device according to claim 1, wherein the chart drawing unit is constituted so as to draw the charts by shifting the patterns of the projection light of the charts by a number which is equal to or larger than 4 and is in multiples of 2, and sequentially projecting the patterns to the projection surface.
4. The inclination angle detection device according to claim 1, wherein the chart drawing unit is constituted so as to draw the charts by selecting at least two sets of sets of four values divided by 90 degrees, as the angle to be shifted, setting the pitch of the brightdark section as 360 degrees, and sequentially projecting the patterns of the projection light of the charts to the projection surface, while shifting the patterns of the projection light of the charts by the predetermined angles.
5. The inclination angle detection device according to claim 2, wherein:
the chart drawing unit projects the projection light of an un-sequential chart wherein the brightdark sections are placed only in a predetermined range on left and right sides respectively so that there is only one local maximum value of a correlation function value that indicates the correlation of the sensor data that each light receiving unit receives, to the projection surface, before projecting the equal distance sequential pattern charts to the projection surface; and
the inclination angle obtaining units are constituted to obtain the local maximum value of the correlation function value, by obtaining sensor data at the time reflection light from the un-sequential chart is received from the sensor units, and obtain the average phase difference, by setting the search range of the average phase difference so that the average phase difference at the time the sensor units receive the reflection light of the equal distance sequence charts, is specified based on the obtained local maximum value.
6. The inclination angle detection device according to claim 2, wherein:
the chart drawing unit projects the projection light of the twice pitched equal distance sequential pattern charts that have a pitch twice as large as the pitch of the equal distance sequential pattern charts, wherein the distances of the brightdark sections are set so that the local maximum value of correlation function value indicating the correlation of the sensor data that each light reception unit of the sensor units receives, is at least twice the local maximum value of correlation function value at the time the sensor units receive the reflection light of the equal distance sequential chart, on the projection surface, before projecting the equal distance sequential pattern charts on the projection surface; and
the inclination angle obtaining units are constituted to obtain the local maximum value of the correlation function value, by obtaining sensor data at the time reflection light from the twice pitched equal distance sequential pattern charts is received from the sensor units, and obtain the average phase difference, by setting the search range of the average phase difference so that the average phase difference at the time the sensor units receive the reflection light of the equal distance sequence charts, is specified based on the obtained local maximum value.
7. The inclination angle detection device according to claim 1, wherein the chart drawing unit draws the equal distance sequential pattern charts by sequentially projecting the projection light of the equal distance sequential pattern charts, wherein the brightness of the brightdark sections are adjusted, on the projection surface, while shifting the pattern.
8. A method comprising:
a drawing step of drawing an equal distance sequential pattern chart, which has patterns so that bright sections are sequentially placed in equal distances, by sequentially projecting the projection light of the equal distance sequential pattern chart to a projection surface, while shifting the patterns;
a light receiving step of sequentially receiving reflection light from the equal distance sequential pattern charts drawn on the projection surface, at receiving units that are placed having predetermined distances from each other; and
an inclination obtaining step of sequentially obtaining the average distance between the projection point of the projection light and equal distance sequential pattern charts, based on a plurality of phase differences at the time when the reflection light of the equal distance sequential pattern chart is received, the sum of each lag amount between the imaging position on the light receiving unit when the sensor unit receives a parallel light, and the imaging position on the light receiving unit when the sensor unit receives the reflection light of the equal distance pattern chart being set as the phase difference, and obtaining the inclination angle of the projection surface based on the obtained average distance; and
a correction step of correcting an image signal to be projected to the projection surface based on the obtained inclination angle of the projection surface.
9. The inclination angle detection device according to claim 1, wherein each of the sensor units receives the reflection light from left-hand and right-hand distance measuring windows on the projection surface, and each of the distance measuring windows includes a point serving as a distance measuring point such that a line from the sensor unit measuring the distance measuring point to the distance measuring point is at an angle \u03b8w with respect to the center line of the sensor units, and wherein the inclination angle obtaining units obtain an inclination angle Os of the projection surface for each of the sensor units by calculating the formula:
\u03b8
\u2062
\u2062
s
=
arctan
\u2062
\u2062
(
R
–
L
R
+
L
\xb7
cot
\u2062
\u2062
\u03b8
\u2062
\u2062
w
)
Formula
\u2062
\u2062
9
based on an average distance L and average distance R from a projector which projects the projection light to a left-hand one of the distance measuring points and a right-hand one of the respective distance-measuring points, respectively, in the two distance-measuring windows on the projection surfaces, and based on the angle \u03b8w.