Enhanced PRACH scheme for power savings, range improvement and improved detection

A method for operating a base station to facilitate a random access procedure by a user equipment (UE) device, the method comprising:

• receiving a first symbol data set in response to a first transmission by the UE device, wherein the first transmission includes a first set of one or more instances of a Physical Random Access Channel (PRACH) respectively over a first set of one or more consecutive subframes, wherein said first transmission is performed according to a conventional format for transmission of PRACH;
• receiving a second symbol data set in response to a subsequent transmission by the UE device, wherein the subsequent transmission includes a second set of one or more consecutive subframes starting immediately after a last subframe of the first set of one or more subframes;
• performing correlation processing on a union of the first symbol data set and the second symbol data set to determine if the second set of one or more consecutive subframes contains one or more PRACH instances in addition to the first set of one or more PRACH instances, wherein the one or more additional PRACH instances, if present, are assumed to use to the same ZC sequence as the one or more PRACH instances of the first set;
• and
• in response to determining that the second set of one or more consecutive subframes contains one or more PRACH instances in addition to the first set of one or more PRACH instances, storing in memory an indication that the UE device is link budget limited.

A method for operating a first user equipment (UE) device to facilitate a random access procedure, the method comprising:

• receiving system information including a configuration index for Physical Random Access Channel (PRACH), a cyclic shift value (Ncs) and a logical root number;
• when the first UE device is link budget limited, performing operations including:
• computing a first physical root number based on the logical root number, wherein the first physical root number is different from a conventional physical root number corresponding to the logical root number;
• generating a first set of Zadoff-Chu sequences based on the cyclic shift value and one or more physical root numbers including the first physical root number;
• randomly selecting one of the Zadoff-Chu sequences of the first set;
• transmitting a first PRACH subframe that includes repetitions of the selected Zadoff-Chu sequence, wherein the first PRACH subframe is transmitted during a first radio frame.

A method for operating a base station to facilitate a random access procedure by a user equipment (UE) device, the method comprising:

• transmitting system information including a configuration index for Physical Random Access Channel (PRACH), a cyclic shift value (Ncs) and a logical root number;
• receiving symbol data over two or more subframes that are consistent with the PRACH configuration index;
• performing a correlation search process to determine whether the symbol data includes repetitions of any Zadoff-Chu sequence from a first set of Zadoff-Chu sequences, wherein the first set of Zadoff-Chu sequences is determined based on the cyclic shift value and one or more physical root numbers including a first physical root number, wherein the first physical root number is different from a conventional physical root number corresponding to the logical root number;
• in response to said correlation search process determining that the symbol data includes repetitions of a particular Zadoff-Chu sequence of the first set, storing in memory an indication that the UE device is link budget limited.

An apparatus configured for inclusion in a link budget limited user equipment (UE) device, comprising:

• one or more processing elements, wherein the one or more processing elements are configured to:
• transmit a first set of one or more instances of a Physical Random Access Channel (PRACH) respectively over a first set of one or more consecutive subframes, wherein said transmitting the first set of one or more PRACH instances is performed according to a conventional format for transmission of PRACH;
• and
• transmit a second set of one or more instances of the PRACH respectively over a second set of one or more consecutive subframes starting immediately after a last subframe of the first set of one or more subframes, wherein each of the one or more PRACH instances of the first set and each of the one or more PRACH instances of the second set use the same Zadoff-Chu sequence.