System and method for beam indexing reference signal design for initial access

A method for wireless communications, the method comprising:

• receiving, by a user equipment (UE), a first synchronization signal from a first network node during a first time interval and a second synchronization signal from the first network node during a second time interval that is different than the first time interval;
• decoding, by the UE, the first synchronization signal in accordance with a first spreading sequence to identify a first beam index associated with the first spreading sequence, the first beam index corresponding to a first beam direction used to transmit the first synchronization signal;
• decoding, by the UE, the second synchronization signal in accordance with a second spreading sequence to identify a second beam index associated with the second spreading sequence, the second beam index corresponding to a second beam direction used to transmit the second synchronization signal, the second beam index being different than the first beam index;
• and
• transmitting, by the UE, an indication of the first beam index to the first network node or a second network node.

A method for beam-scanning, the method comprising:

• receiving, by a user equipment (UE), beamformed reference signals and at least a first instance of a common physical broadcast channel (PBCH) signal during an initial sequence of time intervals, wherein each of the beamformed reference signals are received during a different time interval in the initial sequence of time intervals;
• performing blind decoding on the beamformed reference signals using a common spreading sequence until at least a first instance of a specific one of the beamformed reference signals is decoded using the common spreading sequence, the first instance of the specific beamformed reference signal being received during a specific time interval in the initial sequence of time intervals, the specific time interval in the initial sequence of time intervals being mapped to a specific time interval in a subsequent sequence of time intervals;
• and
• receiving, by the UE, a second instance of the beamformed reference signal and a second instance of the common PBCH signal during the specific time interval of the subsequent sequence of time intervals, the first instance of the common PBCH signal transmitted over a different beam direction than the second instance of the common PBCH signal;
• performing blind decoding on the second instance of the beamformed reference signal using different spreading sequences in a set of spreading sequences, each spreading sequence in the set of spreading sequences being associated with a different beam index;
• identifying a beam index based on a specific spreading sequence used to successfully decode the beamformed reference signal;
• transmitting, by the UE, an indication of the beam index to a network node;
• combining first instance bits in the first instance of the common PBCH signal with second instance bits in the second instance of the common PBCH signal to obtain a soft combination of bits corresponding to the common PBCH signal;
• and
• decoding the soft combination of bits corresponding to the common PBCH signal to obtain control information carried by the common PBCH signal.

A method for wireless communications, the method comprising:

• transmitting, by a network node, a first synchronization signal during a first time interval, the first synchronization signal encoded with a first spreading sequence generated by permutating a root sequence based on a first permutation parameter associated with a first index, the first synchronization signal identifying the first index by virtue of the first synchronization signal being encoded with the first spreading sequence;
• transmitting, by the network node, a second synchronization signal during a second time interval, the second synchronization signal encoded with a second spreading sequence generated by permutating the root sequence based on a second permutation parameter associated with a second index, the second synchronization signal identifying the second index by virtue of the second synchronization signal being encoded with the second spreading sequence, the second permutation parameter associated with the second index being different than the first permutation parameter associated with the first index;
• and
• receiving, by the network node, an indication of either the first index or the second index from a user equipment (UE).

A network node comprising:

• a processor;
• and
• a non-transitory computer readable storage medium storing programming for execution by the processor, the programming including instructions to:
• transmit a first synchronization signal during a first time interval, wherein the first synchronization signal is encoded with a first spreading sequence generated by permutating a root sequence based on a first permutation parameter associated with a first beam index, the first synchronization signal identifying the first beam index by virtue of the first synchronization signal being encoded with the first spreading sequence;
• transmit a second synchronization signal during a second time interval, wherein the second synchronization signal is encoded with a second spreading sequence generated by permutating the root sequence based on a second permutation parameter associated with a second beam index, the second synchronization signal identifying the second beam index by virtue of the second synchronization signal being encoded with the second spreading sequence, the second permutation parameter associated with the second beam index being different than the first permutation parameter associated with the first beam index;
• and
• receive an indication of either the first beam index or the second beam index from a user equipment (UE).

A user equipment (UE) comprising:

• a processor;
• and
• a non-transitory computer readable storage medium storing programming for execution by the processor, the programming including instructions to:
• receive a first synchronization signal from a first network node during a first time interval and a second synchronization signal from the first network node during a second time interval that is different than the first time interval;
• decode the first synchronization signal in accordance with a first spreading sequence to identify a first beam index associated with the first spreading sequence, the first beam index corresponding to a first beam direction used to transmit the first synchronization signal;
• decode the second synchronization signal in accordance with a second spreading sequence to identify a second beam index associated with the second spreading sequence, the second beam index corresponding to a second beam direction used to transmit the first synchronization signal, the second beam index being different than the first beam index;
• and
• transmit an indication of the first beam index to the first network node or a second network node.