Methods and apparatus for random access in multi-carrier communication systems

• US 9,565,700 B2
• Filed: 05/21/2013
• Issued: 02/07/2017
• Est. Priority Date: 03/09/2004
• Status: Active Grant

• Current Assignee: Neo Wireless LLC (f/k/a CFIP NCF LLC) (FIG LLC (d/b/a Fortress Investment Group LLC))
• Original Assignee: Neocific Incorporated
• Inventors: Li, Xiaodong, Lo, Titus, Li, Kemin, Huang, Haiming
• Primary Examiner(s): Phillips, Hassan
• Assistant Examiner(s): Wei, Siren
• Application Number:
  US13/899,226
• Publication Number:
  US 20130250907A1
• Time in Patent Office: 1,358 Days
• US Class Current: 1/1
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 5/0044 allocation of payload
• CPC Class Codes: H04W 52/50 at the moment of starting communication in a multiple access environment
• CPC Class Codes: H04W 74/08 Non-scheduled access, e.g. ALOHA hybrid access H04W74/02
• CPC Class Codes: H04W 74/0833 Random access procedures, e.g. with 4-step access

Abstract

A method at a base station of determining a time delay associated with a mobile station in a multiple access wireless communication system. A signal is received from a mobile station over a selected random access subchannel in a selected random access time slot. A Fast Fourier Transform is applied to the received signal to generate a transformed signal in the frequency domain. The transformed signal is then processed in the frequency domain by computing a dot-product to identify a random access sequence carried in the received signal. The received signal is then processed in the time domain by computing a correlation between a time-shifted version of the received signal and the identified random access sequence to determine a time delay associated with the mobile station.

Claims

1. In a multiple access wireless communication system having a plurality of base stations covering a plurality of cells, a method by a base station to determine a time delay associated with a mobile station using a random access subchannel, the method comprising:

allocating, within a communication channel, a random access (RA) subchannel selected from a plurality of frequency subchannels and a RA time slot selected from a plurality of time slots, the RA time slot and RA subchannel associated with the cell in which the base station is located;

receiving a signal from a mobile station over the selected RA subchannel in the selected RA time slot;

processing the received signal by;

applying a Fast Fourier Transform (FFT) to the received signal to generate a transformed signal in the frequency domain;

computing, in the frequency-domain, a dot-product between the transformed signal and an RA sequence specific to the cell in which the base station is located;

analyzing the computed frequency-domain dot-product to identify the RA sequence carried in the received signal;

computing, in the time-domain, a correlation between a time-shifted version of the received signal and the identified RA sequence; and

analyzing the computed time-domain correlation to determine a time delay associated with the mobile station;

identifying the mobile station associated with the RA sequence; and

transmitting to the identified mobile station an indication of a time advance based on the determined time delay associated with the mobile station.

2. The method of claim 1, wherein the RA subchannel is comprised of subcarriers that are contiguous in frequency.

3. The method of claim 1, wherein processing the received signal further comprises computing, in the frequency-domain, a dot-product between the transformed signal and a second RA sequence specific to the cell in which the base station is located.

4. The method of claim 1, wherein analyzing the computed frequency-domain dot-product to identify the RA sequence carried in the received signal comprises comparing a value of the computed frequency-domain dot-product with a threshold value.

9. The method of claim 1, wherein the frequency-domain dot-product is computed in a segment-wise fashion.

10. The method of claim 1, wherein the time-domain correlation is computed in a sliding-window fashion.

5. In a multiple access wireless communication system having a plurality of base stations covering a plurality of cells, a base station configured to communicate with a mobile station over a random access (RA) subchannel selected from a plurality of frequency subchannels and a RA time slot selected from a plurality of time slots, the RA time slot and RA subchannel associated with the cell In which the base station is located, the base station comprising:

a receiver configured to;

receive a signal from a mobile station over the selected RA subchannel in the selected RA time slot; and

a processor configured to process the received signal by;

applying a Fast Fourier Transform (FFT) to the received signal to generate a transformed signal in the frequency domain;

computing, in the frequency-domain, a dot-product between the transformed signal and an RA sequence specific to the cell in which the base station is located;

analyzing the computed frequency-domain dot-product to identify the RA sequence carried in the received signal;

computing, in the time-domain, a correlation between a time-shifted version of the received signal and the identified RA sequence;

analyzing the computed time-domain correlation to determine a time delay associated with the mobile station; and

identifying the mobile station associated with the RA sequence; and

a transmitter configured to transmit to the identified mobile station an indication of a time advance based on the determined time delay associated with the mobile station.

6. The base station of claim 5, wherein the RA subchannel is comprised of subcarriers that are contiguous in frequency.

7. The base station of claim 5, wherein, to process the received signal, the receiver is further configured to compute, in the frequency-domain, a dot-product between the transformed signal and a second RA sequence specific to the cell in which the base station is located.

8. The base station of claim 5, wherein analyzing the computed frequency-domain dot-product to identify the RA sequence carried in the received signal comprises comparing a value of the computed frequency-domain dot-product with a threshold value.

11. The base station of claim 5, wherein the frequency-domain dot-product is computed in a segment-wise fashion.

12. The base station of claim 5, wherein the time-domain correlation is computed in a sliding-window fashion.