Preamble detection and time-of-arrival estimation for a single-tone frequency hopping random access preamble

Patent metadata

Field	Value
Publication number	US-10148461-B2
Application number	US-201615148691-A
Country	US
Kind code	B2
Filing date	May 6, 2016
Priority date	May 6, 2016
Publication date	Dec 4, 2018
Grant date	Dec 4, 2018

Abstract

A receiver baseband processor and method for performing preamble detection and Time-of-Arrival, ToA, estimation for a single-tone frequency hopping random access preamble. The processor FFT processes a received signal and identifies logical tones. For each logical tone, the processor reads received symbols; determines a ToA estimate; forms a statistic based on the ToA estimate; compares the statistic to a preamble threshold; and when the statistic is greater than or equal to the threshold, determines a preamble is present and utilizes the ToA estimate for a timing advance command.

First claim

The invention claimed is:

1. A method in a baseband processor of a receiver for performing preamble detection and time-of-arrival, ToA, estimation for a single-tone frequency hopping random access preamble, said method comprising:
Fast Fourier Transform, FFT, processing a received signal and identifying logical tones; and
for each logical tone:
reading received symbols;
determining a ToA estimate and a residual Carrier Frequency Offset, CFO, estimate;
forming a statistic based on the ToA estimate and the residual CFO estimate;
comparing the statistic to a preamble threshold; and
when the statistic is greater than or equal to the threshold, determining a preamble is present and utilizing, by the baseband processor of the receiver, the ToA estimate for a timing advance command.

2. The method according to claim 1 , further comprising determining the preamble is not present and discarding the ToA estimate when the statistic is less than the threshold.

3. The method according to claim 1 , wherein the random access preamble is transmitted on a Narrowband Internet of Things, NB-IoT, Physical Random Access Channel, NPRACH.

4. The method according to claim 1 , wherein determining a ToA estimate includes jointly determining the ToA estimate and the residual CFO estimate.

5. The method according to claim 4 , wherein jointly determining the ToA estimate and the residual CFO estimate includes:
element-wise multiplying the received symbols and a conjugate of pilot symbols to create L symbol groups;
dividing the L symbol groups into L/Q blocks, each block having Q symbol groups;
for every block of Q symbol groups, forming a two-dimensional array with zero value elements;
when the position of an element in the two-dimensional array corresponds to the position, in a two-dimensional time-frequency grid, of a symbol in the Q symbol groups, updating the zero value element to the value of the symbol;
for every two-dimensional array, performing a two-dimensional FFT to obtain a two-dimensional FFT output;
non-coherently combining L/Q two-dimensional FFT outputs to obtain a two-dimensional array;
finding the position of the maximum value in the two-dimensional array; and
converting the position of the maximum value in the two-dimensional array to the ToA and the residual CFO estimates.

6. The method according to claim 1 , wherein determining a ToA estimate and a residual CFO estimate includes separately determining a residual CFO estimate and then determining the ToA estimate.

7. The method according to claim 6 , wherein determining the residual CFO estimate includes:
element-wise multiplying received symbols and a conjugate of pilot symbols to create L symbol groups;
dividing the L symbol groups into L/Q blocks, each block having Q symbol groups;
for every block of Q symbol groups, forming a two-dimensional array with zero value elements;
when the position of an element in the two-dimensional array corresponds to the position, in a two-dimensional time-frequency grid, of a symbol in the Q symbol groups, updating the zero value element to the value of the symbol;
for every row in the two-dimensional array, performing a one-dimensional FFT to obtain a one-dimensional FFT output;
non-coherently combining all the one-dimensional FFT outputs to obtain a one-dimensional array;
finding the position of the maximum value in the one-dimensional array; and
converting the position of the maximum value in the one-dimensional array to the residual CFO estimate.

8. The method according to claim 6 , wherein determining the residual CFO estimate includes:
performing differential processing of the symbols 0, 1, 2, 3, 4 in each symbol group, wherein beginning with symbol 1, each symbol in the symbol group is multiplied by the conjugate of the previous symbol in the group to produce an output symbol;
summing all the output symbols from the differential processing in each symbol group, resulting in a single symbol value for each symbol group;
summing the single symbol values for all of the symbol groups to obtain a final symbol; and
estimating the residual CFO based on a phase of the final symbol.

9. The method according to claim 6 , wherein determining the residual CFO estimate includes:
element-wise multiplying received symbols and a conjugate of pilot symbols to create L symbol groups;
dividing the L symbol groups into L/4 blocks, each block having four symbol groups (0, 1, 2, 3);
for every block of four symbol groups, performing differential processing of symbols in symbol groups 0 and 1, and symbol groups 2 and 3, respectively, wherein each symbol in group 0 is multiplied by the conjugate of the symbol in group 1 having the same relative position in the group to produce an output symbol, and each symbol in group 2 is multiplied by the conjugate of the symbol in group 3 having the same relative position in the group to produce an output symbol;
for every block of four symbol groups, summing the output symbols obtained from the differential processing, resulting in a new symbol;
summing the L/4 new symbols obtained by summing the products, resulting in a final symbol; and
estimating the residual CFO based on a phase of the final symbol.

10. The method according to claim 6 , wherein determining the ToA estimate includes:
element-wise multiplying received symbols and a conjugate of pilot symbols to create L symbol groups;
correcting a phase shift using the residual CFO estimate;
dividing the L symbol groups into L/Q blocks, each block having Q symbol groups; and
searching for a ToA value that yields a maximum statistic, which is a summation of absolute values of the statistics from the L/Q blocks.

11. The method according to claim 6 , wherein determining the ToA estimate includes:
determining a coarse timing estimate based on 1-tone hopping; and
determining a fine timing estimate based on 6-tone and/or random hopping.

12. The method according to claim 11 , wherein determining the coarse timing estimate includes:
element-wise multiplying received symbols and a conjugate of pilot symbols to create L symbol groups;
dividing the L symbol groups into L/4 blocks, each block having four symbol groups (0, 1, 2, 3);
for every block of four symbol groups, performing differential processing of symbols in symbol groups 0 and 1, and symbol groups 2 and 3, respectively, wherein each symbol in group 0 is multiplied by the conjugate of the symbol in group 1 having the same relative position in the group to produce an output symbol, and each symbol in group 2 is multiplied by the conjugate of the symbol in group 3 having the same relative position in the group to produce an output symbol;
for every block of four symbol groups, summing the output symbols obtained from the differential processing, resulting in a new symbol;
for every block of four symbol groups, conjugating the new symbol when the 1-tone hopping is DOWN-UP, otherwise keeping the symbol unchanged, wherein the 1-tone hopping is DOWN-UP when a tone index decreases from symbol group 0 to symbol group 1 due to hopping, and the tone index increases from symbol group 2 to symbol group 3 due to hopping;
summing the L/4 symbols after conjugating, resulting in a final symbol; and
generating the coarse timing estimate based on a phase of the final symbol.

13. The method according to claim 11 , wherein determining the fine timing estimate includes:
element-wise multiplying received symbols and a conjugate of pilot symbols to create L symbol groups;
correcting a phase shift using the residual CFO estimate;
dividing the L symbol groups into L/4 blocks, each block having four symbol groups (

Assignees

• Ericsson Telefon Ab L M
• Ericsson Telefon Ab L M

Inventors

• Lin Xingqin
• Wang Yi-Pin Eric
• Adhikary Ansuman

Classifications

• H04W74/08 Primary

  Non-scheduled access, e.g. ALOHA (hybrid access H04W74/02) · CPC title

• H04B1/7136

  Arrangements for generation of hop frequencies, e.g. using a bank of frequency sources, using continuous tuning or using a transform · CPC title

• H04J11/0023

  Interference mitigation or co-ordination (direct sequence spread spectrum [DSSS] systems H04B1/7097; frequency hopping H04B1/713; allocation criteria for ingress interference avoidance H04L5/0062; frequency allocation criteria for requirements on out-of-channel emissions H04L5/0066; arrangements for removing intersymbol interference or baseband equalisers H04L25/03006; peak power aspects in multicarrier modulation H04L27/2614; power management H04W52/00; traffic scheduling H04W72/54, H04W72/541) · CPC title

• H04B2201/71353

  Fast frequency hopping · CPC title

• H04L27/2675

  Pilot or known symbols · CPC title