Narrowband-physical random access channel techniques
Disclosed are narrowband (NB)-physical random access channel (PRACH) techniques for NB-long term evolution (LTE) systems supporting cellular internet of things (CloT) and machine-type communications (MTC) deployments. Apparatus and methods are described for generating, transmitting, or receiving an NB-PRACH defined by an NB-PRACH physical structure and an NB-PRACH numerology.
1. Electronic device circuitry for a user equipment (UE) configured to use a narrowband (NB) bandwidth when performing random access of a cellular network associated with an evolved Node B (eNB) providing the NB bandwidth at a frequency band of a repurposed deployment using global systems for mobile communications (GSM) spectrum, an in-band deployment using a physical resource block (PRB) of a larger-bandwidth long term evolution (LTE) system, or a guard-band deployment using a guard band of the larger-bandwidth LTE system, the electronic device circuitry comprising:
control circuitry configured to generate an NB-physical random access channel (NB-PRACH) defined by an NB-PRACH physical structure and an NB-PRACH numerology;
the NB-PRACH physical structure including a cyclic prefix (CP), a guard time (GT), and an NB-PRACH sequence between the CP and the GT; and
the NB-PRACH numerology configured to size components of the NB-PRACH physical structure such that a beginning of the CP and an end of the GT temporally correspond with a beginning and an end of one or more LTE subframes that each have a one millisecond (1 ms) duration, and the NB-PRACH numerology configured to maintain a number of subcarriers at a subcarrier spacing to establish the NB-PRACH as having an NB-PRACH bandwidth within the NB bandwidth,
wherein the control circuitry is further configured to randomly select one NB-PRACH preamble signature and a scheduling request (SR) transmission opportunity for transmission of the NB-PRACH and an SR within one LTE subframe.
2. The electronic device circuitry of claim 1 , further comprising transmit circuitry coupled to the control circuitry, the transmit circuitry configured to transmit the NB-PRACH in the frequency band and within the NB-PRACH bandwidth of about 200 kHz or less.
3. The electronic device circuitry of claim 1 , in which the NB-PRACH further includes coded bits that carry information related to the SR.
4. The electronic device circuitry of claim 3 , in which control circuitry is further configured to generate, in a time dimension, the SR between the NB-PRACH sequence and the GT, or after the GT.
5. The electronic device circuitry of claim 1 , in which a length of the CP is different from that of a CP used for transmission of an NB-physical uplink shared channel (NB-PUSCH) and/or an NB-physical uplink control channel (NB-PUCCH).
6. The electronic device circuitry of claim 1 , in which a design of the NB-PRACH sequence is based on one or more Zadoff-Chu (ZC) sequences of prime-number length.
7. The electronic device circuitry of claim 1 , in which the control circuitry is further configured to select a combination of an NB-PRACH preamble signature and a scheduling request (SR) transmission opportunity based on a single selection defining a one-to-one mapping between the NB-PRACH preamble signature and the SR transmission opportunity.
8. The electronic device circuitry of claim 1 , in which the NB-PRACH bandwidth is 90 kHz.
9. The electronic device circuitry of claim 1 , in which the NB-PRACH includes a scheduling request (SR), and the control circuitry is configured to multiplex the NB-PRACH with the SR by frequency division multiplexing (FDM) such that the SR is configured for simultaneous transmission in an NB-physical uplink shared channel (NB-PUSCH) and/or an NB-physical uplink control channel (NB-PUCCH).
10. The electronic device circuitry of claim 1 , in which the subcarrier spacing for the LTE subframe carrying the NB-PRACH is set to a smaller value than 15 kHz and is equal to that of an NB-physical uplink control channel (NB-PUCCH) and/or an NB-physical uplink shared channel (NB-PUSCH).
11. The electronic device circuitry of claim 10 , in which a subcarrier spacing for a legacy PUSCH is an integer multiple of the subcarrier spacing for one or both of the NB-PRACH and the NB-PUSCH.
12. A method performed by a user equipment (UE) configured to use a narrowband (NB) bandwidth when performing random access of a cellular network associated with an evolved Node B (eNB), the method comprising:
receiving from the eNB an indication of availability of the NB bandwidth at a frequency band of a repurposed deployment using global systems for mobile communications (GSM) spectrum, an in-band deployment using a physical resource block (PRB) of a larger-bandwidth long term evolution (LTE) system, or a guard-band deployment using a guard band of the larger-bandwidth LTE system; and
generating an NB-physical random access channel (NB-PRACH) defined by an NB-PRACH physical structure and an NB-PRACH numerology;
the NB-PRACH physical structure including a cyclic prefix (CP), a guard time (GT), and an NB-PRACH sequence between the CP and the GT;
the NB-PRACH numerology configured to size components of the NB-PRACH physical structure such that a beginning of the CP and an end of the GT temporally correspond with a beginning and an end of one or more LTE subframes that each have a one millisecond (1 ms) duration, and the NB-PRACH numerology configured to maintain a number of subcarriers at a subcarrier spacing to establish the NB-PRACH as having an NB-PRACH bandwidth within the NB bandwidth; and
selecting a combination of an NB-PRACH preamble signature and a scheduling request (SR) transmission opportunity based on a single selection defining a one-to-one mapping between the NB-PRACH preamble signature and the SR transmission opportunity.
13. The method of claim 12 , in which the subcarrier spacing for the NB-PRACH is different from that used for other uplink (UL) transmissions for a larger-bandwidth LTE system physical uplink control channel (PUCCH), a larger-bandwidth LTE system physical uplink shared channel (PUSCH), and/or a larger-bandwidth LTE system PRACH.
14. The method of claim 12 , in which the NB-PRACH includes guard bands at its edges, and in which a size of a guard band for the NB-PRACH is smaller than that of a larger-bandwidth LTE system PRACH.
15. The method of claim 12 , in which the NB-PRACH sequence comprises multiple repetitions of an NB-PRACH preamble sequence.
16. The method of claim 15 , further comprising applying a cover code to the NB-PRACH preamble sequence.
17. The method of claim 15 , further comprising, in response to a failure to receive a random access response (RAR) from the eNB after NB-PRACH transmissions at a first NB-PRACH repetition level, transmitting at a second NB-PRACH repetition level that is different from the first NB-PRACH repetition level.
18. An apparatus of a user equipment (UE) for accessing a narrowband (NB)-long term evolution (LTE) network connection, the apparatus comprising:
control circuitry configured to generate an NB-physical random access channel (NB-PRACH) preamble and a scheduling request (SR), the NB-PRACH preamble being for transmission in an NB-PRACH and the SR being for transmission in a physical uplink (UL) channel having a frequency band that is different from that of the NB-PRACH, the NB-PRACH having a frequency bandwidth of up to 200 kilohertz (kHz) and a transmission time duration of one or more LTE transmission time intervals (TTIs); and
the control circuitry further configured to multiplex the NB-PRACH and SR by frequency division multiplexing (FDM) for simultaneous transmission during the transmission time duration and through, respectively, the NB-PRACH and the physical UL channel,
wherein a minimum distance between cyclic shifts (NCS) for the NB-PRACH sequence is reduced compared to those of larger-bandwidth LTE PRACH sequences.
19. The apparatus of claim 18 , in which the control circuitry selects NB-PRACH resources based on repetition levels or coverage classes, the NB-PRACH resources being separated based on either time-division multiplexing (TDM) for transmission in one or multiple subframes, code-division multiplexing (CDM) having different NB-PRACH preambles reserved for each repetition level or coverage class, or frequency-division multiplexing (FDM) for transmission in one or more NB bandwidths.
20. The apparatus of claim 18 , in which the UE is configured to receive NB-LTE system information blocks (NB-LTE SIBs) as part of an NB-PRACH configuration signaling, and the UE, in response to the NB-PRACH configuration signaling, is configured to transmit by using a power ramping mechanism to adjust NB-PRACH transmit power based on a selected number of repetitions of the NB-PRACH sequence.
21. The apparatus of claim 18 , in which the minimum distance between cyclic shifts is given by an expression NCS≥ceil((2*R/c+DS)*(NZC/TSEQ))+gs;
where R, c, DS, NZC, TSEQ, and gs are, respectively, the target cell radius, speed of light, target maximum delay spread, NB-PRACH sequence length, NB-PRACH sequence duration, and additional guard samples.
22. The apparatus of claim 18 , in which the control circuitry is configured to establish an NB-PRACH configuration based on an NB-PRACH configuration index that is less than six bits in size and code-points of the NB-PRACH configuration index that indicate an NB-PRACH preamble format among multiple NB-PRACH preamble formats, and/or that indicate time resources available for NB-PRACH transmission.
23. The apparatus of claim 22 , in which the time resources available for NB-PRACH transmission are based on an expression k*f*10 ms, where k and f are, respectively, an integer value greater than or equal to one, and a ratio of downlink (DL) to uplink (UL) subcarrier spacing.
24. Electronic device circuitry for a user equipment (UE) configured to use a narrowband (NB) bandwidth when performing random access of a cellular network associated with an evolved Node B (eNB) providing the NB bandwidth at a frequency band of a repurposed deployment using global systems for mobile communications (GSM) spectrum, an in-band deployment using a physical resource block (PRB) of a larger-bandwidth long term evolution (LTE) system, or a guard-band deployment using a guard band of the larger-bandwidth LTE system, the electronic device circuitry comprising:
control circuitry configured to generate an NB-physical random access channel (NB-PRACH) defined by an NB-PRACH physical structure and an NB-PRACH numerology;
the NB-PRACH physical structure including a cyclic prefix (CP), a guard time (GT), and an NB-PRACH sequence between the CP and the GT;
the NB-PRACH numerology configured to size components of the NB-PRACH physical structure such that a beginning of the CP and an end of the GT temporally correspond with a beginning and an end of one or more LTE subframes that each have a one millisecond (1 ms) duration, and the NB-PRACH numerology configured to maintain a number of subcarriers at a subcarrier spacing to establish the NB-PRACH as having an NB-PRACH bandwidth within the NB bandwidth; and
the NB-PRACH includes a scheduling request (SR), and the control circuitry is configured to multiplex the NB-PRACH with the SR by frequency division multiplexing (FDM) such that the SR is configured for simultaneous transmission in an NB-physical uplink shared channel (NB-PUSCH) and/or an NB-physical uplink control channel (NB-PUCCH).
25. An apparatus of a user equipment (UE) for accessing a narrowband (NB)-long term evolution (LTE) network connection, the apparatus comprising:
control circuitry configured to generate an NB-physical random access channel (NB-PRACH) preamble and a scheduling request (SR), the NB-PRACH preamble being for transmission in an NB-PRACH and the SR being for transmission in a physical uplink (UL) channel having a frequency band that is different from that of the NB-PRACH, the NB-PRACH having a frequency bandwidth of up to 200 kilohertz (kHz) and a transmission time duration of one or more LTE transmission time intervals (TTIs); and
the control circuitry further configured to multiplex the NB-PRACH and SR by frequency division multiplexing (FDM) for simultaneous transmission during the transmission time duration and through, respectively, the NB-PRACH and the physical UL channel,
wherein the control circuitry is further configured to establish an NB-PRACH configuration based on an NB-PRACH configuration index that is less than six bits in size and code-points of the NB-PRACH configuration index that indicate an NB-PRACH preamble format among multiple NB-PRACH preamble formats, and/or that indicate time resources available for NB-PRACH transmission.
26. The apparatus of claim 25 , in which the time resources available for NB-PRACH transmission are based on an expression k*f*10 ms, where k and f are, respectively, an integer value greater than or equal to one, and a ratio of downlink (DL) to uplink (UL) subcarrier spacing.