CN112997417A - Mimo (multiple input multiple output) inter-stream interference cancellation - Google Patents

Mimo (multiple input multiple output) inter-stream interference cancellation Download PDF

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CN112997417A
CN112997417A CN201880094648.6A CN201880094648A CN112997417A CN 112997417 A CN112997417 A CN 112997417A CN 201880094648 A CN201880094648 A CN 201880094648A CN 112997417 A CN112997417 A CN 112997417A
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antennas
transmit
receive
transmit antennas
channel
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瞿麒
帕丁亚雷曼尼尔·萨姆·亚历克斯
阿里·亚兹丹·帕纳赫
阿布舍克·蒂瓦里
闫妍
周宏宇
普拉迪普·邦达拉帕蒂
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Meta Platforms Inc
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Facebook Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
    • H04B7/0891—Space-time diversity
    • H04B7/0894—Space-time diversity using different delays between antennas
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
    • H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
    • H04B7/0842—Weighted combining
    • H04B7/0845—Weighted combining per branch equalization, e.g. by an FIR-filter or RAKE receiver per antenna branch

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Abstract

Apparatus, methods, and systems for inter-MIMO stream interference cancellation are disclosed. One method comprises the following steps: determining a channel matrix between a plurality of transmit antennas of a transmitter and a plurality of receive antennas of a receiver; determining a plurality of channel propagation delays based on propagation delays between each of the plurality of transmit antennas and each of the plurality of receive antennas; pre-processing, by a transmitter, a symbol stream for each transmit antenna for transmission based on a plurality of channel propagation delays and based on a channel matrix; and transmitting, by the transmitter, the pre-processed symbol streams through the plurality of transmit antennas.

Description

Mimo (multiple input multiple output) inter-stream interference cancellation
Field of the described embodiments
The described embodiments relate generally to wireless communications. More particularly, the described embodiments relate to systems, methods, and apparatus for inter-stream interference cancellation (MIMO inter-stream interference cancellation).
Background
Wireless networks that include long-range propagation of wireless signals are being deployed. Long-range MIMO (multiple-input multiple-output) channel wireless systems suffer from different interference scenarios than typical short-range MIMO systems, such as LTE (long term evolution) and WiFi (wireless fidelity) wireless systems.
It is desirable to have a method, apparatus and system for canceling interference between MIMO streams.
SUMMARY
One embodiment includes a method. The method comprises the following steps: determining a channel matrix between a plurality of transmit antennas of a transmitter and a plurality of receive antennas of a receiver; determining a plurality of channel propagation delays based on propagation delays between each of the plurality of transmit antennas and each of the plurality of receive antennas; pre-processing, by a transmitter, a symbol stream for each transmit antenna for transmission based on a plurality of channel propagation delays and based on a channel matrix; and transmitting, by the transmitter, the pre-processed symbol streams through the plurality of transmit antennas.
One embodiment includes another method. The method includes determining a channel matrix between a plurality of transmit antennas of a transmitter and a plurality of receive antennas of a receiver, determining a plurality of channel propagation delays based on propagation delays between each of the plurality of transmit antennas and each of the plurality of receive antennas, receiving a stream of symbols over the channel by each of the plurality of receive antennas, and processing, by the receiver, the stream of symbols for each receive antenna based on the plurality of channel propagation delays and based on the channel matrix.
Another embodiment includes a transmitter. The transmitter includes a plurality of Radio Frequency (RF) chains, wherein the plurality of RF chains are connected to a plurality of transmit antennas. The transmitter also includes a controller. The controller operates to determine a channel matrix between the plurality of transmit antennas and a plurality of receive antennas of the receiver, determine a plurality of channel propagation delays based on propagation delays between each of the plurality of transmit antennas and each of the plurality of receive antennas, pre-process a symbol stream for each transmit antenna for transmission based on the plurality of channel propagation delays and based on the channel matrix, and transmit the pre-processed symbol streams through the plurality of transmit antennas.
Another embodiment includes a receiver. The receiver includes a plurality of receive antennas, wherein the plurality of receive antennas are connected to the plurality of RF chains. The receiver also includes a controller. The controller operates to determine a channel matrix between a plurality of transmit antennas of the transmitter and a plurality of receive antennas of the receiver, determine a plurality of channel propagation delays based on propagation delays between each of the plurality of transmit antennas and each of the plurality of receive antennas, receive a stream of symbols through each of the plurality of receive antennas, and process the stream of symbols for each receive antenna based on the plurality of channel propagation delays and based on the channel matrix.
Other aspects and advantages of the described embodiments will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the described embodiments.
Brief Description of Drawings
Fig. 1A illustrates a long-range MIMO system according to one embodiment.
Fig. 1B illustrates a long-range MIMO system according to another embodiment.
Fig. 2 shows a MIMO system and a channel matrix of the MIMO system according to one embodiment.
Fig. 3 illustrates a MIMO system and propagation delays associated with the MIMO system in accordance with one embodiment.
Fig. 4A shows a MIMO long-range system including a transmitter located on a hovering drone (circling drone), according to another embodiment.
Fig. 4B is a graph depicting varying time delay differences between the transmit signals of the hovering drone of fig. 4A, according to one embodiment.
Fig. 5A is a graph depicting delay times of multipath components after an inter-stream interference cancellation process, in accordance with one embodiment.
Fig. 5B is a graph depicting delay times of multipath components after an inter-stream interference cancellation process, in accordance with one embodiment.
Fig. 6 shows a transmitter including transmit preprocessing according to one embodiment.
Fig. 7 illustrates a receiver including post-receive processing according to one embodiment.
Figure 8 is a flow diagram of the actions of a method including transmitter pre-processing, according to one embodiment.
Figure 9 is a flow diagram of the actions of a method including receiver post-processing in accordance with one embodiment.
Detailed Description
The described embodiments include methods, apparatus and systems for inter-MIMO stream interference cancellation for time-offset channels in long-range wireless systems. For at least some embodiments, symbol streams for transmission over a MIMO system or symbol streams received over a MIMO system are processed using differences in propagation delays between different ones of multiple transmit and receive antennas of the MIMO system and a channel matrix of the MIMO system.
Fig. 1A illustrates a long-range MIMO system according to one embodiment. This embodiment includes a satellite 110 and a plurality of antennas 122, 124 located on the ground, with the satellite 110 including a plurality of antennas 112, 114. In addition, the receive antennas are physically spaced apart by a large distance. This MIMO system differs from a typical MIMO system in that the distance between the transmit and receive antennas is large, and the antenna spacing is large, and therefore the difference in signal flight time between the transmit and receive antennas of the wireless transmission signal is much greater than the duration of the symbols of the symbol stream of the wireless transmission signal. That is, for one embodiment, for example, the time of flight of a symbol transmitted from antenna 112 of satellite 110 and received by antenna 122 on the ground differs from the time of flight of a symbol transmitted from antenna 114 of satellite 110 and received by antenna 122 on the ground by a multiple of the duration of the transmitted symbol. As will be described, this results in time-offset interference that is not experienced by typical LTE and WiFi systems. That is, long-range wireless systems may suffer from time-offset interference due to misalignment of the received streams due to differences in-flight travel times of different transmitted streams. For one embodiment, a long-range wireless system is one in which the difference in-flight propagation delays for different streams is greater than a multiple of the duration of the symbols of the symbol stream.
For the embodiment shown in fig. 1A, an exemplary distance between the transmit and receive antennas is 1200 kilometers, and the distance between the receive antennas (on the ground) is 1200 meters. As described, the distance traveled by the wireless signal is large enough such that the difference in the time traveled by the symbol streams transmitted by the different transmit antennas and received by the receive antennas is greater than a multiple of the duration of the symbols of the symbol streams. Furthermore, the satellites are in motion and, therefore, the travel time may also change.
Fig. 1B illustrates a long-range MIMO system according to another embodiment. This embodiment includes a drone hovering over the earth. Similar to the system of fig. 1A, the distance traveled by the wireless signal is large enough that the difference in the time traveled by the symbol streams transmitted by the different transmit antennas and received by the receive antennas is greater than the duration of the symbols of the symbol streams. Furthermore, the drone is in motion, so the transit time can also change.
The MIMO system of the described embodiments may include unique characteristics. For example, carrier frequencies are as high as 70 to 85 gigahertz for at least some embodiments. Further, for at least some embodiments, the distance between the transmitter and the receiver is 30-1200 kilometers. Further, the spacing distance between antennas can be large based on the rayleigh criterion of LOS (line of sight) MIMO systems. The combination of large distances results in large propagation delays between the transmit and receive antennas. To satisfy the rayleigh criterion, the following equation is satisfied:
dr × Dt — Drt × λ/a, where Dr is the distance between the receiving antennas, Dt is the distance between the transmitting antennas, Drt is the distance between the transmitter (transmitting antennas) and the receiver (receiving antennas), λ is the wavelength of the carrier signal of the transmitted data stream, and where a is the minimum of the number of transmitting antennas or the number of receiving antennas. For the case of two transmitter antennas and two receiver antennas, a equals 2.
Channel matrix
Fig. 2 shows a MIMO system and a channel matrix of the MIMO system according to one embodiment. Dt denotes a physical distance between the transmitting antennas, and Dr denotes a physical distance between the receiving antennas. As shown, at the transmit antenna Tx1、TxNAnd a receiving antenna Rx1、RxMForming a channel matrix H. As shown in fig. 2, the channel matrix comprises an element h11、hlM、hN1、h22. That is, for an ideal LOS MIMO system:
Figure BDA0002834606500000051
for example, the channel matrix may be determined by training of the channel, which includes transmitting known pilot symbols and measuring the effect of the channel on the pilot symbols at the receiver. For one embodiment, the channel matrix is determined periodically. For one embodiment, the channel matrix is determined at the receiver and passed back to the transmitter. That is, the controller of the transmitter obtains the channel matrix by receiving or acquiring the channel matrix from some other place. For one embodiment, reciprocity of the transmission channel is assumed and the channel matrix is determined by the transmitter. Further, for one embodiment, the propagation delay is determined at the receiver. The transmitter then obtains the propagation delay by accessing the propagation delay from some other place. For one embodiment, reciprocity of the transmission channel is assumed and the transmitter obtains the propagation delay by directly determining the propagation delay.
Fig. 3 illustrates a MIMO system and propagation delays associated with the MIMO system in accordance with one embodiment. As shown, t11 represents the propagation delay of a wireless signal transmitted from transmit antenna Tx 1310 and received by receive antenna Rx 1330, t12 represents the propagation delay of a wireless signal transmitted from transmit antenna Tx 2320 and received by receive antenna Rx 1330, t21 represents the propagation delay of a wireless signal transmitted from transmit antenna Tx 1310 and received by receive antenna Rx 2340, and t22 represents the propagation delay of a wireless signal transmitted from transmit antenna Tx 2320 and received by receive antenna Rx 2340.
For the long-range wireless systems shown in fig. 1A and 1B, the difference between the propagation travel times is greater than a multiple of the duration of the symbols of the symbol stream of the transmitted signal. For example, for the system of FIG. 1A, the difference between the propagation delays (t)12-t11And t2l-t22) May be as large as the duration of 40 symbols of the symbol stream.
The difference in propagation times may cause unwanted interference. E.g. from transmit antenna Tx2Delayed versions of the transmitted symbol stream may undesirably interfere with the Tx from the transmit antenna1Transmitting and receiving at an antenna Rx1To the received symbol stream. That is, as previously described, long-range wireless systems may suffer from time-offset interference due to misalignment of received streams due to differences in-flight travel times of different transmitted streams, which is not experienced by typical MIMO LTE (long term evolution) and WiFi (wireless fidelity) systems. As previously described, for one embodiment, a long-range wireless system is one in which the differences in-flight propagation delays for different streamsGreater than a multiple of the duration of the symbols of the symbol stream.
The propagation delay t can be estimated or measured11、tl2、t2lAnd t22. For example, based on the known locations of the transmit antennas 310, 320 and the known locations of the receive antennas 330, 340, the distance between each of the transmit antennas 310, 320 and each of the receive antennas 330, 340 may be estimated. The propagation delay t may be estimated based on the estimated distance11、tl2、t2lAnd t22. For one embodiment, the position of the transmit antenna and/or the position of the receive antenna is determined by a GPS (global positioning system) receiver located at the transmit antenna and/or the receive antenna.
For one embodiment, the propagation delay t may be estimated or measured by transmitting symbols with known characteristics by each of the transmit antennas 310, 32011、tl2、t2lAnd t22. The signals received by the receive antennas 330, 340 may be correlated to determine the propagation delay.
Fig. 4A shows a MIMO long-range system including transmit antennas a1, a2 located on a hovering drone 410 according to another embodiment. The top view depicts the radius R of the convoluted path 420 of the drone 410. Further, the distance D depicts the offset between the ground positions G1, G2 of the receive antennas and the center point of the spiral path 420 of the drone 410. The side view depicts the distance H of the hovering drone 410.
Fig. 4B is a graph depicting varying time delay differences between the transmit signals of the hovering drone of fig. 4A, according to one embodiment. That is, due to the motion of the drone, the propagation delay time of the transmission signal varies over time. For example, the graph of FIG. 4B shows at t when the drone hover angle changes as the drone hovers21-t22And t12–t11The difference between them.
For at least some embodiments, the rate at which the difference in propagation delay changes is very small relative to absolute time, and it is easy to perform real-time estimation of the propagation delay. For one embodiment, the propagation delay varies less than a predetermined rate. For one embodiment, the rate at which the difference between the propagation delays changes is less than a threshold.
Transmitter pre-processing
For one embodiment, the first symbol stream is associated with a first transmit antenna and the second symbol stream is associated with a second transmit antenna. As described, for at least some embodiments, the difference in propagation delay between the first transmit antenna and the first receive antenna and the second transmit antenna and the first receive antenna is greater than a multiple of the duration of the symbols of the first symbol stream and the second symbol stream. As described, for at least some embodiments, the difference in propagation delay between the first transmit antenna and the second receive antenna and the second transmit antenna and the second receive antenna is greater than a multiple of the duration of the symbols of the first symbol stream and the second symbol stream. The transmit and receive antennas are physically located such that this relationship between propagation delays holds true. It is apparent that at least some embodiments include N symbol streams associated with N transmit antennas.
At least some embodiments include preprocessing, by a transmitter, a stream of symbols (assuming one stream for each transmit antenna) for transmission based on a plurality of channel propagation delays and based on a channel matrix. As will be described, the propagation delay may be determined in one or more ways. Further, the channel matrix may be determined in one or more ways. For one embodiment, once the symbol stream is pre-processed, at least some embodiments include transmitting, by the transmitter, the pre-processed symbol stream over a plurality of transmit antennas.
For at least some embodiments, pre-processing, by a transmitter, a stream of symbols for transmission comprises: for the symbol stream for each transmit antenna, the scaled version of the symbol stream is linearly combined with scaled and delayed versions of one or more symbol streams for other transmit antennas of the plurality of transmit antennas, wherein delays of the delayed versions of the symbol streams for the other transmit antennas of the plurality of transmit antennas are determined based on the plurality of channel propagation delays.
For example, for a MIMO system comprising 2 transmit antennas and 2 receive antennas, the channel matrix may be given as:
Figure BDA0002834606500000071
and the precoding matrix T may be given as:
Figure BDA0002834606500000072
and the linearly scaled version of the symbol stream combined with the linearly scaled and delayed version of the one or more symbol streams of the other transmit antennas of the plurality of transmit antennas may be given as:
Figure BDA0002834606500000073
(symbols of the first symbol stream);
Figure BDA0002834606500000074
(symbols of the second symbol stream);
where Δ t1＝t12-t11And Δ t21＝t21-t22。
For one embodiment, T is selected such that:
Figure BDA0002834606500000081
thus, the first transmit antenna Tx1 transmits:
s1＝c*s1(t)-a*s2(t-(t12-t11))；
and the second transmit antenna Tx2 transmits:
s2＝d*s2(t)-b*s1(t-(t21-t22))。
at the receive antennas, the received symbol stream is:
r1(t)＝h11*c*s1(t)-h12*b*s1(t-t21-t12+t22+t11) (ii) a And
r2(t)＝h22*d*s2(t)-h21*a*s2(t-t21-t12+t22+t11)。
for the first receive antenna, the received symbol r1The interference part of (t) is: -h12*b*s1(t-t21-t12+t22+t11)。
For the second receive antenna, the received symbol r2The interference part of (t) is: -h21*a*s2(t-t21-t12+t22+t11)。
Although a2 transmit antenna and 2 receive antenna system is described, it should be understood that the descriptions may be extended to include an N x M antenna system.
Fig. 5A is a graph depicting delay times of multipath components after an inter-stream interference cancellation process, in accordance with one embodiment. That is, fig. 5A is a graph of the interference portion of the system of fig. 1A.
Fig. 5B is a graph depicting delay times of multipath components after an inter-stream interference cancellation process, in accordance with one embodiment. That is, fig. 5B is a graph of the interference portion of the system of fig. 1B.
As can be observed from the graphs of fig. 5A and 5B, the transmit process reduces the inter-stream interference to be negligible. That is, inter-stream interference is mitigated (mathematically eliminated for the ideal case) when negligible multipath components are introduced. That is, the transmit process reduces the interference portion of the reduced signal to less than the threshold amount.
The values (t) of FIGS. 5A and 5B22+t11–t12-t21) On the order of picoseconds, while the propagation delay of the proposed multi-transmit antenna, multi-receive antenna system is on the order of nanoseconds. Thus, the inter-symbol interference is reduced to a relatively low (less than threshold) level. Propagation delay is caused byThe physical location and distance between the transmitter antenna and the receiver antenna is determined. The symbol duration is set by the communication system. For one embodiment, the communication system comprises a millimeter wave communication system having a bandwidth of up to 2GHz and a sampling rate of up to 2 GHz.
Thus, for one embodiment, each receive antenna operates independently. That is, each antenna receives a symbol stream and does not need to perform any post-processing of another symbol stream that depends on another receive antenna.
Receiver post-processing
The two previously described embodiments for pre-processing at the transmitter may alternatively be implemented at the receiver. That is, one embodiment includes a receiver processing a received symbol or stream, including inter-stream interference cancellation.
At least some embodiments include receiving a symbol stream over a channel by each of a plurality of receive antennas, and processing, by a receiver, the symbol stream for each receive antenna based on a plurality of channel propagation delays and based on a channel matrix.
Similar to the transmit processing, for one embodiment, the difference in propagation delay between the first transmit antenna and the first receive antenna and the second transmit antenna and the first receive antenna is greater than a multiple of the duration of the symbols of the symbol stream.
For one embodiment, processing the symbol stream by the receiver comprises: for each symbol stream for each receive antenna, linearly combining the scaled version of the symbol stream with scaled and delayed versions of the symbol streams for other ones of the plurality of receive antennas, wherein delays of the delayed versions of the symbol streams for the other ones of the plurality of receive antennas are determined based on the plurality of channel propagation delays.
Delay estimation
As previously described, the propagation delay between the transmit and receive antennas may be estimated or measured. For example, based on the known locations of the transmit antennas and the known locations of the receive antennas, the distance between each of the transmit antennas and each of the receive antennas may be estimated. A Global Positioning System (GPS) may be used to monitor the position of the transmitting or receiving antenna if the transmitting or receiving antenna is in motion. For example, the drone 410 of fig. 4 may include a GPS receiver that determines the exact location of the transmit antenna. The receiving antenna may be fixed on the ground. Thus, the distance between the transmit antenna and the receive antenna can be constantly (repeatedly) estimated. The propagation delay may be estimated based on the estimated distance.
As previously described, for one embodiment, the propagation delay t may be estimated or measured by transmitting symbols with known characteristics by each of the transmit antennas 310, 32011、t12、t21And t22. The signals received by the receive antennas 330, 340 may be correlated to determine the propagation delay.
Fig. 6 shows a transmitter 610 including transmit preprocessing according to one embodiment. For one embodiment, transmitter 610 receives N symbol streams for transmission. The transmitter 610 pre-processes the N symbol streams based on the estimated propagation delays and the channel matrix. For one embodiment, the pre-processing comprises: for the symbol stream for each transmit antenna, the scaled version of the symbol stream is linearly combined with scaled and delayed versions of one or more symbol streams for other transmit antennas of the plurality of transmit antennas, wherein delays of the delayed versions of the symbol streams for the other transmit antennas of the plurality of transmit antennas are determined based on the plurality of channel propagation delays.
The pre-processed symbol stream is then transmitted through the transmit antennas (Antl to AntN).
Fig. 7 illustrates a receiver 720 including post-receive processing according to one embodiment. It should be understood that the embodiment of fig. 7 may be operationally exclusive from the embodiment of fig. 6. That is, for one embodiment, a system comprising a transmitter and a receiver may include pre-processing of a symbol stream as described or post-processing of a symbol stream as described.
Receiver 720 receives the M symbol streams through receive antennas (Ant1 through Ant M). Receiver 720 post-processes the M received symbol streams based on the estimated propagation delays and the channel matrix. For one embodiment, the post-processing comprises: for each symbol stream for each receive antenna, linearly combining the scaled version of the symbol stream with scaled and delayed versions of the symbol streams for other ones of the plurality of receive antennas, wherein delays of the delayed versions of the symbol streams for the other ones of the plurality of receive antennas are determined based on the plurality of channel propagation delays.
Figure 8 is a flow diagram of the actions of a method including transmitter pre-processing, according to one embodiment. A first step 810 includes determining a channel matrix. For one embodiment, a transmitter receives a channel matrix. For one embodiment, the transmitter acquires a channel matrix. For one embodiment, the channel matrix is determined by training transmission channels between a plurality of transmit antennas of a transmitter and a plurality of receive antennas of a receiver. For one embodiment, training includes transmitting known pilot symbols by the transmit antennas, and characterizing the channel based on reception of the known pilot symbols at the receiver of the receive antennas. The receiver then passes the channel matrix back to the transmitter.
A second step 820 includes determining a plurality of channel propagation delays based on the propagation delay between each of the plurality of transmit antennas and each of the plurality of receive antennas. For one embodiment, the transmitter receives a plurality of channel propagation delays. For one embodiment, the transmitter acquires a plurality of channel propagation delays. For one embodiment, determining the propagation delay includes transmitting known pilot symbols by the transmit antennas, and determining the propagation delay based on reception of the known pilot symbols at a receiver of the receive antennas. The receiver then passes the propagation delay back to the transmitter.
A third step 830 includes preprocessing, by the transmitter, the symbol stream for each transmit antenna for transmission based on a plurality of channel propagation delays and based on a channel matrix. A fourth step 840 includes transmitting, by the transmitter, the pre-processed symbol streams over a plurality of transmit antennas.
For one embodiment, a difference in propagation delay between the first transmit antenna and the first receive antenna and the second transmit antenna and the first receive antenna is greater than a multiple of a duration of symbols of the symbol stream. Further, for one embodiment, a difference in propagation delay between the second transmit antenna and the first receive antenna and the second transmit antenna and the second receive antenna is greater than a multiple of a duration of symbols of the symbol stream.
For at least some embodiments, pre-processing, by a transmitter, a stream of symbols for transmission comprises: for the symbol stream for each transmit antenna, the scaled version of the symbol stream is linearly combined with scaled and delayed versions of one or more symbol streams for other transmit antennas of the plurality of transmit antennas, wherein delays of the delayed versions of the symbol streams for the other transmit antennas of the plurality of transmit antennas are determined based on the plurality of channel propagation delays. For one embodiment, scaled versions of the symbol stream and scaled versions of the symbol stream for other transmit antennas of the plurality of transmit antennas are determined based on a precoding matrix, where the precoding matrix is determined based on a channel matrix. Further, for one embodiment, the precoding matrix is determined additionally based on a zero forcing function. Further, for one embodiment, the precoding matrix is determined additionally based on a SINR (signal to interference and noise ratio) maximization criterion.
At least some embodiments also include receiving the symbol streams independently at each of the receive antennas.
At least some embodiments further include continuously estimating the position of one or more transmit antennas and updating the values of the plurality of channel propagation delays.
At least some embodiments further include: continuously updating the values of the plurality of propagation delays comprises transmitting a signal from at least one transmit antenna and correlating versions of the signal received at a plurality of receive antennas.
For at least some embodiments, the plurality of transmit antennas are located on a flying drone that surrounds a central point. For at least some embodiments, multiple transmit antennas are located on one or more satellites.
Figure 9 is a flow diagram of the actions of a method including receiver post-processing in accordance with one embodiment. A first step 910 includes determining a channel matrix between a plurality of transmit antennas of a transmitter and a plurality of receive antennas of a receiver.
A second step 920 includes determining a plurality of channel propagation delays based on the propagation delay between each of the plurality of transmit antennas and each of the plurality of receive antennas. A third step 930 includes receiving a stream of symbols over the channel through each of a plurality of receive antennas. A fourth step 940 includes processing, by the receiver, the symbol stream for each receive antenna based on the plurality of channel propagation delays and based on the channel matrix.
For at least some embodiments, a difference in propagation delay between the first transmit antenna and the first receive antenna and the second transmit antenna and the first receive antenna is greater than a multiple of a duration of symbols of the symbol stream.
For at least some embodiments, processing the symbol stream by the receiver comprises: for each symbol stream for each receive antenna, linearly combining the scaled version of the symbol stream with scaled and delayed versions of the symbol streams for other ones of the plurality of receive antennas, wherein delays of the delayed versions of the symbol streams for the other ones of the plurality of receive antennas are determined based on the plurality of channel propagation delays. For one embodiment, scaled versions of the symbol stream and scaled versions of the symbol streams for other ones of the plurality of receive antennas are determined based on a precoding matrix, wherein the precoding matrix is determined based on a channel matrix and a zero forcing function.
At least some embodiments further include continuously estimating the position of one or more transmit antennas and updating the values of the plurality of channel propagation delays.
At least some embodiments further include: continuously updating the values of the plurality of propagation delays comprises transmitting a signal from at least one transmit antenna and correlating versions of the signal received at a plurality of receive antennas.
For at least some embodiments, the plurality of transmit antennas are located on a flying drone that surrounds a central point. For at least some embodiments, multiple transmit antennas are located on one or more satellites.
Although specific embodiments have been described and illustrated, the embodiments are not to be limited to the specific forms or arrangements of parts so described and illustrated. The described embodiments are limited only by the claims.

Claims (19)

1. A method, comprising:
determining a channel matrix between a plurality of transmit antennas of a transmitter and a plurality of receive antennas of a receiver;
determining a plurality of channel propagation delays based on a propagation delay between each of the plurality of transmit antennas and each of the plurality of receive antennas;
pre-processing, by the transmitter, a symbol stream for each transmit antenna for transmission based on the plurality of channel propagation delays and based on the channel matrix; and
transmitting, by the transmitter, the pre-processed symbol streams through the plurality of transmit antennas.
2. The method of claim 1, wherein a difference in propagation delay between the first transmit antenna and the first receive antenna and the second transmit antenna and the first receive antenna is greater than a multiple of a duration of symbols of the symbol stream.
3. The method of claim 1, wherein pre-processing, by the transmitter, the symbol stream for transmission comprises:
for each transmit antenna's symbol stream, linearly combining the scaled version of the symbol stream with scaled and delayed versions of one or more symbol streams for other transmit antennas of the plurality of transmit antennas, wherein delays of the delayed versions of the symbol streams for the other transmit antennas of the plurality of transmit antennas are determined based on the plurality of channel propagation delays.
4. The method of claim 3, wherein the scaled version of the symbol stream and scaled versions of the symbol streams for other transmit antennas of the plurality of transmit antennas are determined based on a precoding matrix, wherein the precoding matrix is determined based on the channel matrix.
5. The method of claim 4, wherein the precoding matrix is determined based on the channel matrix and a selected precoding function.
6. The method of claim 1, further comprising:
a stream of symbols is received independently at each of the receive antennas.
7. The method of claim 1, further comprising continuously estimating a location of one or more of the transmit antennas and updating values of the plurality of channel propagation delays.
8. The method of claim 1, further comprising: continuously updating the values of the plurality of propagation delays comprises transmitting signals from at least one of the transmit antennas and correlating versions of the signals received at the plurality of receive antennas.
9. The method of claim 1, wherein the plurality of transmit antennas are located on flying drones that surround a central point.
10. The method of claim 1, wherein the plurality of transmit antennas are located on one or more satellites.
11. A method, comprising:
determining a channel matrix between a plurality of transmit antennas of a transmitter and a plurality of receive antennas of a receiver;
determining a plurality of channel propagation delays based on a propagation delay between each of the plurality of transmit antennas and each of the plurality of receive antennas;
receiving a stream of symbols over a channel through each of the plurality of receive antennas; and
processing, by the receiver, a symbol stream for each receive antenna based on the plurality of channel propagation delays and based on the channel matrix.
12. The method of claim 11, wherein a difference in propagation delay between the first transmit antenna and the first receive antenna and the second transmit antenna and the first receive antenna is greater than a multiple of a duration of symbols of the symbol stream.
13. The method of claim 11, wherein processing the symbol stream by the receiver comprises:
for each symbol stream for each receive antenna, linearly combining the scaled version of the symbol stream with scaled and delayed versions of the symbol streams for other receive antennas of the plurality of receive antennas, wherein delays of the delayed versions of the symbol streams for the other receive antennas of the plurality of receive antennas are determined based on the plurality of channel propagation delays.
14. The method of claim 13, wherein scaled versions of the symbol stream and scaled versions of symbol streams for other receive antennas of the plurality of receive antennas are determined based on a precoding matrix, wherein the precoding matrix is determined based on the channel matrix.
15. The method of claim 11, further comprising continuously estimating a location of one or more of the transmit antennas and updating values of the plurality of channel propagation delays.
16. The method of claim 11, further comprising: continuously updating the values of the plurality of channel propagation delays comprises transmitting signals from at least one of the transmit antennas and correlating versions of the signals received at the plurality of receive antennas.
17. The method of claim 11, wherein the plurality of transmit antennas are located on flying drones that surround a central point.
18. The method of claim 11, wherein the plurality of transmit antennas are located on one or more satellites.
19. A transmitter, comprising:
a plurality of Radio Frequency (RF) chains, wherein the plurality of RF chains are connected to a plurality of transmit antennas;
a controller operative to:
determining a channel matrix between the plurality of transmit antennas and a plurality of receive antennas of a receiver;
determining a plurality of channel propagation delays based on a propagation delay between each of the plurality of transmit antennas and each of the plurality of receive antennas;
pre-processing a symbol stream for each transmit antenna for transmission based on the plurality of channel propagation delays and based on the channel matrix; and
transmitting the pre-processed symbol streams through the plurality of transmit antennas.
CN201880094648.6A 2018-06-13 2018-06-13 Mimo (multiple input multiple output) inter-stream interference cancellation Pending CN112997417A (en)

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