Time aligning in a distributed antenna system downlink data originating from two different types of donor base stations

1 . A distributed antenna system (DAS) serving a digital interface base station and a radio frequency (RF)-interface base station and configured to time align contemporaneous time division duplexing (TDD) radio frames from the digital interface base station and the RF-interface base station in a radio unit, the DAS comprising:

a digital donor interface circuit configured to couple the digital interface base station to the DAS and to communicate digital data for radio frames between the digital interface base station and the DAS;

an RF donor interface circuit configured to couple the RF-interface base station to the DAS and to communicate data in radio frames in analog radio frequency (RF) signals between the RF-interface base station and the RF donor interface circuit;

a first DAS propagation path;

a second DAS propagation path; and

the radio unit communicatively coupled to the digital donor interface circuit through the first DAS propagation path and communicatively coupled to the RF donor interface circuit through the second DAS propagation path, wherein the radio unit is configured to be coupled to a set of coverage antennas;

wherein the DAS is configured to:

obtain a first propagation time delay for the first DAS propagation path and a second propagation time delay for the second DAS propagation path;

obtain at least one of a time delay of the RF donor interface circuit and the digital donor interface circuit;

determine a first downlink time delay value equal to (i) a largest propagation delay (a) from an antenna port of the radio unit through the digital donor interface circuit or (b) from the antenna port of the radio unit through the RF donor interface circuit, minus (i) a shortest propagation time delay (x) from the antenna port of the radio unit through the digital donor interface circuit or (y) from the antenna port of the radio unit through the RF donor interface circuit; and

transmit the first downlink time delay value to a delay adjustment circuit in a downlink path of the DAS having the shortest propagation time delay (p) from the antenna port of the radio unit through the digital donor interface circuit or (q) from the antenna port of the radio unit through the RF donor interface circuit, wherein the delay adjustment circuit is configured to delay TDD downlink data in the downlink path by the first downlink time delay value.

2 . The DAS of claim 1 , further comprising time base circuitry configured to generate a time base;

wherein the DAS is further configured to:

determine an occurrence of when downlink digital data for a radio frame commences in the digital donor interface circuit;

determine an occurrence of when a radio frame commenced in downlink analog RF signals, contemporaneous with the downlink digital data, in the RF donor interface circuit; and

using the time base, determine a first start time for the downlink digital data and a second start time for the radio frame in the downlink analog RF signals;

wherein the determined first downlink time delay value is determined using a difference between the first start time and the second start time.

3 . The DAS of claim 1 , wherein the determined first downlink time delay value is a first downlink time delay value by which downlink digital data received from the digital interface base station have been advanced, by the digital interface base station in time by a digital downlink propagation time delay between the digital interface base station and the antenna port of the radio unit; and

wherein the DAS is further configured to:

determine a first uplink time delay value; and

transmit the first uplink time delay value to the digital interface base station and which is configured to be stored in the digital interface base station and to be used by the digital interface base station to determine a time of arrival of uplink data delayed by the first uplink time delay value.

4 . The DAS of claim 1 , wherein the DAS is further configured to:

provide, to the RF-interface base station, a constant delay value configured to be added to an RF downlink propagation time delay value stored in a second downlink antenna delay, wherein radio frames of data in downlink analog RF signals received by the DAS from the RF-interface base station are advanced, by the RF-interface base station, in time by the RF downlink propagation time delay value, and wherein a time delay value stored in a second uplink antenna delay is configured to be used by the RF-interface base station to determine a time of arrival of uplink data; and

transmit the constant delay value to the digital interface base station to increase the first downlink time delay value by the constant delay value.

5 . The DAS of claim 1 , wherein the determined first downlink time delay is a first downlink time delay value when downlink digital data received from the digital interface base station has not been advanced in time by the digital interface base station.

6 . The DAS of claim 1 , wherein the radio unit comprises a first delay adjustment circuit in a downlink path from the digital donor interface circuit and a second delay adjustment circuit in a downlink path from the RF donor interface circuit;

wherein the delay adjustment circuit is one of the first and the second delay adjustment circuits.

7 . The DAS of claim 1 , wherein the DAS comprises the delay adjustment circuit.

8 . A method for time aligning, in a distributed antenna system (DAS), contemporaneous time division duplexing (TDD) radio frames from a digital interface base station and a radio frequency (RF)-interface base station in the DAS, the method comprising:

obtaining a first propagation time delay for a first DAS propagation path and a second propagation time delay for a second DAS propagation path;

obtaining at least one of a time delay of an RF donor unit and a digital donor unit;

determining a first downlink time delay value equal to (i) a largest propagation delay (a) from an antenna port of a radio unit through the digital donor unit or (b) from the antenna port of the radio unit through the RF donor unit, minus (i) a shortest propagation time delay (x) from the antenna port of the radio unit through the digital donor unit or (y) from the antenna port of the radio unit through the RF donor unit; and

transmitting the first downlink time delay value to a delay adjustment circuit in a downlink path of the DAS having the shortest propagation time delay (p) between the antenna port of the radio unit and through the digital donor unit or (q) between the antenna port of the radio unit and through the RF donor unit, wherein the delay adjustment circuit is configured to delay TDD downlink data in the downlink path by the first downlink time delay value.

9 . The method of claim 8 , further comprising:

determining an occurrence of when downlink digital data for a radio frame commenced in the digital donor unit;

determining an occurrence of when a radio frame commenced in downlink analog RF signals, contemporaneous with the downlink digital data in the RF donor unit; and

using a time base generated, determining a first start time for the downlink digital data and a second start time for the radio frame in the downlink analog RF signals;

wherein the determined first downlink time delay value is determined using a difference between the first start time and the second start time.

10 . The method of claim 8 , further comprising:

determining a first uplink time delay value; and

transmitting the first uplink time delay value to the digital interface base station and which is configured to be stored in the digital interface base station and to be used by the digital interface base station to determine a time of arrival of uplink data delayed by the first uplink time delay value;

wherein the determined first downlink time delay value is a first downlink time delay value by which downlink digital data received from the digital interface base station have been advanced, by the digital interface base station in time by a digital downlink propagation time delay between the digital interface base station and the antenna port of the radio unit.

11 . The method of claim 8 , further comprising:

providing, to the RF-interface base station, a constant delay value configured to be added to an RF downlink propagation time delay value stored in a second downlink antenna delay, wherein radio frames of data in downlink analog RF signals received by the DAS from the RF-interface base station are advanced, by the RF-interface base station, in time by the RF downlink propagation time delay value, and wherein a time delay value stored in a second uplink antenna delay is configured to be used by the RF-interface base station to determine a time of arrival of uplink data; and

transmitting the constant delay value to the digital interface base station to increase the first downlink time delay value by the constant delay value.

12 . The method of claim 8 , wherein the determined first downlink time delay value is a first downlink time delay value when digital downlink data received from the digital interface base station has not been advanced in time by the digital interface base station.

13 . A non-transitory computer readable medium storing a program causing at least one processor to execute a process to time align, in a distributed antenna system (DAS), contemporaneous time division duplexing (TDD) radio frames from a digital interface base station and a radio frequency (RF)-interface base station in the DAS, the process comprising:

obtaining a first propagation time delay for a first DAS propagation path and a second propagation time delay for a second DAS propagation path;

obtaining at least one of a time delay of a RF donor unit and a digital donor unit;

determining a first downlink time delay value equal to (i) a largest propagation delay (a) from an antenna port of a radio unit through the digital donor unit or (b) from the antenna port of the radio unit through the RF donor unit, minus (i) a shortest propagation time delay (x) from the antenna port of the radio unit through the digital donor unit or (y) from the antenna port of the radio unit through the RF donor unit; and

causing transmission of the first downlink time delay value to a delay adjustment circuit in a downlink path of the DAS having the shortest propagation time delay (p) from the antenna port of the radio unit through the digital donor unit or (q) from the antenna port of the radio unit through the RF donor unit, wherein the delay adjustment circuit is configured to delay TDD downlink data in the downlink path by the first downlink time delay value.

14 . The non-transitory computer readable medium of claim 13 , wherein the process further comprises:

determining an occurrence of when downlink digital data for a radio frame commenced in the digital donor unit;

determining an occurrence of when a radio frame commenced in downlink analog RF signals, contemporaneous with the downlink digital data, in the RF donor unit; and

using a time base generated, determining a first start time for the downlink digital data and a second start time for the radio frame in the downlink analog RF signals;

wherein the determined first downlink time delay value is determined using a difference between the first start time and the second start time.

15 . The non-transitory computer readable medium of claim 13 , wherein the process further comprises:

determining a first uplink time delay value; and

causing transmission of the first uplink time delay value to the digital interface base station and which is configured to be stored in the digital interface base station and to be used by the digital interface base station to determine a time of arrival of uplink data delayed by the first uplink time delay value;

wherein the determined first downlink time delay value is a first downlink time delay value when downlink digital data received from the digital interface base station has been advanced, by the digital interface base station, in time by a digital downlink propagation time delay between the digital interface base station and the antenna port of the radio unit.

16 . The non-transitory computer readable medium of claim 13 , wherein the process further comprises:

providing, to the RF-interface base station, a constant delay value configured to be added to an RF downlink propagation time delay value stored in a second downlink antenna delay, wherein radio frames of data in downlink analog RF signals received by the DAS from the RF-interface base station are advanced, by the RF-interface base station, in time by the RF downlink propagation time delay value, and wherein a time delay value stored in a second uplink antenna delay is configured to be used by the RF-interface base station to determine a time of arrival of uplink data; and

transmitting the constant delay value to the digital interface base station to increase the first downlink time delay value by the constant delay value.

17 . The non-transitory computer readable medium of claim 13 , wherein the determined first downlink time delay value is a first downlink time delay value when a digital downlink data received from the digital interface base station has not been advanced in time by the digital interface base station.