Reducing location-dependent interference in distributed antenna systems operating in multiple-input, multiple-output (mimo) configuration, and related components, systems, and methods

Abstract

Components, systems, and methods for reducing location-based interference in distributed antenna systems operating in multiple-input, multiple-output (MIMO) configuration are disclosed. Interference is defined as issues with received MIMO communications signals that can cause a MIMO algorithm to not be able to solve a channel matrix for MIMO communications signals received by MIMO receivers in client devices. These issues may be caused by lack of spatial (i.e., phase) separation in the received MIMO communications signals. Thus, to provide phase separation of received MIMO communication signals, multiple MIMO transmitters are each configured to employ multiple transmitter antennas, which are each configured to transmit in different polarization states. In certain embodiments, one of the MIMO communications signals is phase shifted in one of the polarization states to provide phase separation between received MIMO communication signals. In other embodiments, multiple transmitter antennas in a MIMO transmitter can be offset to provide phase separation.

What is claimed is: 
     
         1 . A multiple-input multiple-output (MIMO) remote unit configured to wirelessly distribute MIMO communications signals to wireless client devices, comprising:
 a first MIMO transmitter configured to:
 receive a first downlink MIMO communications signal in a first phase over a first downlink communications medium, and wirelessly transmit the first downlink MIMO communications signal in a first polarization to a wireless client device; and 
 receive a second downlink MIMO communications signal in the first phase over a second downlink communications medium, and wirelessly transmit the second downlink MIMO communications signal in a second polarization different from the first polarization to the wireless client device; and 
   a second MIMO transmitter configured to:
 receive a third downlink MIMO communications signal in the first phase over a third downlink communications medium, and wirelessly transmit the third downlink MIMO communications signal in the first polarization to the wireless client device; and 
 receive a fourth downlink MIMO communications signal over a fourth downlink communications medium, and wirelessly transmit the fourth downlink MIMO communications signal in a second phase shifted from the first phase in the second polarization to the wireless client device. 
   
     
     
         2 . The MIMO remote unit of  claim 1 , wherein:
 the first MIMO transmitter comprises a first MIMO transmitter antenna configured to transmit the first downlink MIMO communications signal in the first polarization and a second MIMO transmitter antenna configured to transmit the second downlink MIMO communications signal in the second polarization; and   the second MIMO transmitter comprises a third MIMO transmitter antenna configured to transmit the third downlink MIMO communications signal in the first polarization and a fourth MIMO transmitter antenna configured to transmit the fourth downlink MIMO communications signal in the second polarization.   
     
     
         3 . The MIMO remote unit of  claim 1 , wherein the first, second, third, and fourth downlink MIMO communications signals are optical downlink MIMO communications signals and wherein:
 the first MIMO transmitter further comprises a first optical-to-electrical (O/E) converter configured to convert the first optical downlink MIMO communications signal to the first downlink MIMO communications signal and a second O/E converter configured to convert the second optical downlink MIMO communications signal to the second MIMO downlink communications signal; and   the second MIMO transmitter further comprises a third O/E converter configured to convert the third optical downlink MIMO communications signal to the third downlink MIMO communications signal and a fourth O/E converter configured to convert the fourth optical downlink MIMO communications signal to the fourth downlink MIMO communications signal.   
     
     
         4 . The MIMO remote unit of  claim 1 , further comprising at least one phase shifter configured to phase shift the fourth downlink MIMO communications signal to the second phase. 
     
     
         5 . The MIMO remote unit of  claim 1 , wherein the second MIMO transmitter is configured to receive the fourth downlink MIMO communications signal in the second phase as a result of a phase shift of the fourth downlink MIMO communications signal in a central unit. 
     
     
         6 . The MIMO remote unit of  claim 1 , wherein the second MIMO transmitter is configured to receive the fourth downlink MIMO communications signal in the second phase as a result of a phase shift of the fourth downlink MIMO communications signal in the fourth downlink communications medium. 
     
     
         7 . The MIMO remote unit of  claim 6 , wherein the fourth downlink communications medium is positioned between a central unit of a wireless communications system and the second MIMO transmitter. 
     
     
         8 . The MIMO remote unit of  claim 2 , wherein the third MIMO transmitter antenna is phase offset from the fourth MIMO transmitter antenna by the third MIMO transmitter antenna being positioned in distance from the fourth MIMO transmitter antenna. 
     
     
         9 . The MIMO remote unit of  claim 2 , wherein the first MIMO transmitter antenna is position offset from the second MIMO transmitter antenna by positioning the first MIMO transmitter antenna in distance from the second MIMO transmitter antenna. 
     
     
         10 . A method of transmitting multiple-input multiple-output (MIMO) communications signals to wireless client devices, comprising:
 receiving a first downlink MIMO communications signal in a first phase over a first downlink communications medium at a remote unit;   transmitting the first downlink MIMO communications signal wirelessly in a first polarization to a wireless client device;   receiving a second downlink MIMO communications signal in the first phase over a second downlink communications medium at the remote unit;   transmitting the second downlink MIMO communications signal wirelessly in a second polarization to the wireless client device;   receiving a third downlink MIMO communications signal in the first phase over a third downlink communications medium at the remote unit;   transmitting the third downlink MIMO communications signal wirelessly in the first polarization to the wireless client device;   receiving a fourth downlink MIMO communications signal over a fourth downlink communications medium; and   transmitting the fourth downlink MIMO communications signal wirelessly in a second phase shifted from the first phase in the second polarization to the wireless client device.   
     
     
         11 . The method of  claim 10 , further comprising receiving the fourth downlink MIMO communications signal in the second phase from a central unit that phase shifts the fourth downlink MIMO communications signal from the first phase to the second phase. 
     
     
         12 . The method of  claim 10 , further comprising receiving the fourth downlink MIMO communications signal in the second phase via the fourth downlink communications medium configured to phase shift the fourth downlink MIMO communications signal from the first phase to the second phase. 
     
     
         13 . The method of  claim 10 , wherein:
 the first MIMO transmitter comprises a first MIMO transmitter antenna configured to transmit the first downlink MIMO communications signal in the first polarization and a second MIMO transmitter antenna configured to transmit the second downlink MIMO communications signal in the second polarization;   the second MIMO transmitter comprises a third MIMO transmitter antenna configured to transmit the third downlink MIMO communications signal in the first polarization and a fourth MIMO transmitter antenna configured to transmit the fourth downlink MIMO communications signal in the second polarization; and   wherein the method further comprises phase offsetting the third MIMO transmitter antenna from the fourth MIMO transmitter antenna by positioning the third MIMO transmitter antenna in distance from the fourth MIMO transmitter to phase shift the fourth downlink MIMO communications signal to the second phase.   
     
     
         14 . The method of  claim 10 , wherein:
 the first MIMO transmitter comprises a first MIMO transmitter antenna configured to transmit the first downlink MIMO communications signal in the first polarization and a second MIMO transmitter antenna configured to transmit the second downlink MIMO communications signal in the second polarization;   the second MIMO transmitter comprises a third MIMO transmitter antenna configured to transmit the third downlink MIMO communications signal in the first polarization and a fourth MIMO transmitter antenna configured to transmit the fourth downlink MIMO communications signal in the second polarization; and   wherein the method further comprises position offsetting the first MIMO transmitter antenna from the second MIMO transmitter antenna by positioning the first MIMO transmitter antenna in distance from the second MIMO transmitter antenna.   
     
     
         15 . A multiple-input multiple-output (MIMO) remote unit configured to wirelessly distribute MIMO communications signals to wireless client devices in a distributed antenna system, comprising:
 a first MIMO transmitter comprising a first MIMO transmitter antenna configured to transmit MIMO communications signals in a first polarization and a second MIMO transmitter antenna configured to transmit MIMO communications signals in a second polarization different from the first polarization; and   a second MIMO transmitter comprising a third MIMO transmitter antenna configured to transmit MIMO communications signals in the first polarization and a fourth MIMO transmitter antenna configured to transmit MIMO communications signals in the second polarization;   the first MIMO transmitter configured to:
 receive a first downlink MIMO communications signal in a first phase over a first downlink communications medium, and transmit the first downlink MIMO communications signal wirelessly over the first MIMO transmitter antenna in the first polarization; and 
 receive a second downlink MIMO communications signal in the first phase over a second downlink communications medium, and transmit the second downlink MIMO communications signal wirelessly over the second MIMO transmitter antenna in the second polarization; 
   the second MIMO transmitter configured to:
 receive a third downlink MIMO communications signal in the first phase over a third downlink communications medium, and transmit the third downlink MIMO communications signal wirelessly over the third MIMO transmitter antenna in the first polarization; and 
 receive a fourth downlink MIMO communications signal over a fourth downlink communications medium, and transmit the fourth downlink MIMO communications signal wirelessly as a fourth electrical downlink MIMO communications signal over the fourth MIMO transmitter antenna in the second polarization, 
 wherein the fourth MIMO transmitter antenna is phase offset from the third MIMO transmitter antenna such that the fourth downlink MIMO communications signal is transmitted in a second phase shifted from the first phase. 
   
     
     
         16 . The MIMO remote unit of  claim 15 , wherein the third MIMO transmitter antenna is phase offset from the fourth MIMO transmitter antenna by the third MIMO transmitter antenna being positioned in distance from the fourth MIMO transmitter antenna. 
     
     
         17 . The MIMO remote unit of  claim 15 , wherein the first MIMO transmitter antenna is position offset from the second MIMO transmitter antenna by positioning the first MIMO transmitter antenna in distance from the second MIMO transmitter antenna. 
     
     
         18 . The MIMO remote unit of  claim 15 , wherein the first MIMO transmitter is position offset from the second MIMO transmitter. 
     
     
         19 . A wireless communications system for distributing multiple-input multiple-output (MIMO) communications signals to wireless client devices, comprising:
 a central unit comprising a central unit transmitter configured to transmit a first downlink MIMO communications signal over a first downlink communications medium, a second downlink MIMO communications signal over a second downlink communications medium, a third downlink MIMO communications signal over a third downlink communications medium, and a fourth downlink MIMO communications signal over a fourth downlink communications medium;   a plurality of remote units in communications with the central unit, at least one remote unit of the plurality of remote units comprising:
 a first MIMO transmitter configured to:
 receive a first downlink MIMO communications signal in a first phase over a first downlink communications medium, and wirelessly transmit the first downlink MIMO communications signal in a first polarization to a wireless client device; and 
 receive a second downlink MIMO communications signal in the first phase over a second downlink communications medium, and wirelessly transmit the second downlink MIMO communications signal in a second polarization different from the first polarization to the wireless client device; and 
 
 a second MIMO transmitter configured to:
 receive a third downlink MIMO communications signal in the first phase over a third downlink communications medium, and wirelessly transmit the third downlink MIMO communications signal in the first polarization to the wireless client device; and 
 receive a fourth downlink MIMO communications signal over a fourth downlink communications medium, and wirelessly transmit the fourth downlink MIMO communications signal in a second phase shifted from the first phase in the second polarization to the wireless client device; and 
 
   at least one phase shifter configured to phase shift the fourth downlink MIMO communications signal to the second phase.   
     
     
         20 . The wireless communications system of  claim 19 , wherein the central unit further comprises a signal processor configured to:
 receive at least one downlink MIMO communications signal;   split the at least one downlink MIMO communications signal into the first downlink MIMO communications signal, the second downlink MIMO communications signal, the third downlink MIMO communications signal, and the fourth downlink MIMO communications signal, wherein each of the first downlink MIMO communications signal, the second downlink MIMO communications signal, the third downlink MIMO communications signal, and the fourth downlink MIMO communications signal is associated with a separate communications channel of four communications channels.   
     
     
         21 . The wireless communications system of  claim 19 , wherein at least one of the first downlink communications medium, the second downlink communications medium, the third downlink communications medium, and the fourth downlink communications medium comprises at least one optical fiber.