Interference and noise estimation in an OFDM system

• US 20050002324A1
• Filed: 03/24/2004
• Published: 01/06/2005
• Est. Priority Date: 05/14/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Naguib, Ayman Faway, Agrawal, Avneesh, Sutivong, Arak
• Granted Patent: US 8,477,592 B2
• Time in Patent Office: Days
• US Class Current: 370/208
• CPC Class Codes: H04L 1/20 using signal quality detector
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

Noise and interference can be independently measured in a multiple user Orthogonal Frequency Division Multiplexing (OFDM) system. Co-channel interference is measured in a frequency hopping, multiple user, OFDM system by tracking the sub-carriers assigned to all users in a particular service area or cell. The composite noise plus interference can be determined by measuring the amount of received power in a sub-carrier whenever it is not assigned to any user in the cell. A value is stored for each sub-carrier in the system and the value of noise plus interference can be a weighted average of the present value with previously stored values. The noise component can be independently determined in a synchronous system. In the synchronous system, all users in a system may periodically be prohibited from broadcasting over a sub-carrier and the received power in the sub-carrier measured during the period having no broadcasts.

Claims

1. A method of estimating noise in an Orthogonal Frequency Division Multiplexing (OFDM) system, the method comprising:

receiving OFDM symbols; and

detecting a received power of a signal in an unassigned sub-carrier frequency band.

2. The method of claim 1, further comprising averaging the received power with at least one previously stored received power measurement for the unassigned sub-carrier frequency band.

3. The method of claim 1, further comprising, prior to detecting the received power, demodulating an unassigned sub-carrier corresponding to the unassigned sub-carrier frequency band.

4. The method of claim 1, further comprising determining the unassigned sub-carrier frequency band based in part on a received message.

5. The method of claim 1, further comprising determining the unassigned sub-carrier frequency band based in part on an internally generated sequence.

6. The method of claim 1, wherein receiving OFDM symbols comprises wirelessly receiving, from a base station transmitter, RF OFDM symbols.

7. The method of claim 1, wherein receiving OFDM symbols comprises:

converting wirelessly received RF OFDM symbols to baseband OFDM symbols;

removing a guard interval from the baseband OFDM symbols; and

transforming, using a Fast Fourier Transform (FFT), time domain OFDM baseband signals to modulated sub-carriers.

8. The method of claim 1, wherein detecting the received power comprises determining one of a magnitude, an amplitude, or a squared magnitude of the signal in the unassigned OFDM frequency band.

9. The method of claim 1, wherein detecting the received power comprises determining a sum of a square of a quadrature signal component with a square of an in-phase signal component.

10. The method of claim 1, further comprising:

determining if the unassigned sub-carrier frequency band comprises a system wide unassigned sub-carrier frequency band;

storing the detected received power as a noise plus interference estimate if the sub-carrier frequency band does not comprise the system wide unassigned frequency band; and

storing the detected received power as a noise floor estimate if the sub-carrier frequency band comprises the system wide unassigned frequency band.

11. The method of claim 10, further comprising synchronizing a time reference with a transmitter transmitting the OFDM symbols.

12. The method of claim 1, further comprising:

averaging the received power with at least one previously stored received power measurement to produce a noise estimate corresponding to the unassigned sub-carrier frequency band; and

communicating the noise estimate to a transmitter.

13. The method of claim 12, wherein communicating the noise estimate to the transmitter comprises transmitting the noise estimate from a terminal transmitter to a base transceiver station.

14. A method of estimating noise in an Orthogonal Frequency Division Multiplexing (OFDM) system, the method comprising:

receiving OFDM symbols in a wireless cellular communication system, the OFDM symbols corresponding to a symbol period;

determining an unassigned sub-carrier during the symbol period;

determining a power, during the symbol period, of a signal in a frequency band corresponding to the unassigned sub-carrier;

storing a value of the power of the signal in a memory; and

averaging the power of the signal with previously stored values to generate a noise estimate.

15. An apparatus for estimating noise in an Orthogonal Frequency Division Multiplexing (OFDM) system, the apparatus comprising:

a wireless receiver configured to wirelessly receive OFDM symbols corresponding to an OFDM symbol period;

a detector configured to detect a received power level of signals received by the wireless receiver during the OFDM symbol period;

a processor coupled to the detector and configured to determine an unassigned sub-carrier during the OFDM symbol period and determine a noise estimate based in part on a received power level in a frequency band corresponding to the unassigned sub-carrier.

16. The apparatus of claim 15, further comprising a memory coupled to the processor, the processor storing the noise estimate in the memory.

17. The apparatus of claim 15, further comprising a memory coupled to the processor and storing a predetermined number of previously determined noise estimates corresponding to the unassigned sub-carrier, the processor determining an average noise estimate based in part on the noise estimate and the previously determined noise estimates.

18. The apparatus of claim 15, wherein the wireless receiver comprises:

an RF receiver portion configured to wirelessly receive RF OFDM symbols and convert the RF OFDM symbols to the OFDM symbols;

a Fast Fourier Transform (FFT) module configured to receive the OFDM symbols from the RF receiver portion and transform the OFDM symbols to modulated sub-carriers; and

a demodulator coupled to the FFT module and configured to demodulate the modulated sub-carriers.

19. The apparatus of claim 18, wherein the detector detects the received power levels of an output of the demodulator.

20. The apparatus of claim 15, wherein the detector detects the received power level by determining one of a magnitude, an amplitude, or a squared magnitude of the signals received by the wireless receiver during the OFDM symbol period.