Fast frequency hopping with a code division multiplexed pilot in an OFDMA system

• US 7,177,297 B2
• Filed: 12/03/2003
• Issued: 02/13/2007
• Est. Priority Date: 05/12/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Agrawal, Avneesh, Teague, Edward Harrison
• Primary Examiner(s): Vu; Huy D.
• Assistant Examiner(s): HO, CHUONG T
• Application Number:
  US10/726,944
• Publication Number:
  US 20040228267A1
• Time in Patent Office: 1,168 Days
• Field of Search: 370/342, 370/343, 370/345, 370/341, 370/335, 370/347, 370/324, 370/328, 370/331, 370/377, 375/377
• US Class Current: 370/342
• CPC Class Codes: H04B 1/713 using frequency hopping
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 2025/03509 fractionally spaced H04L2025/03515 takes precedence
• CPC Class Codes: H04L 2025/03789 Codes therefore
• CPC Class Codes: H04L 25/0232 by interpolation between sounding signals
• CPC Class Codes: H04L 25/03866 using scrambling
• CPC Class Codes: H04L 27/26134 Pilot insertion in the transmitter chain, e.g. pilot overlapping with data, insertion in time or frequency domain
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0016 Time-frequency-code
• CPC Class Codes: H04L 5/0041 Frequency-non-contiguous
• CPC Class Codes: H04L 5/0051 of dedicated pilots, i.e. pilots destined for a single user or terminal

Abstract

Techniques are provided to support fast frequency hopping with a code division multiplexed (CDM) pilot in a multi-carrier communication system (e.g., an OFDMA system). Each transmitter (e.g., each terminal) in the system transmits a wideband pilot on all subbands to allow a receiver (e.g., a base station) to estimate the entire channel response at the same time. The wideband pilot for each transmitter may be generated using direct sequence spread spectrum processing and based on a pseudo-random number (PN) code assigned to that transmitter. This allows the receiver to individually identify and recover multiple wideband pilots transmitted concurrently by multiple transmitters. For a time division multiplexed (TDM)/CDM pilot transmission scheme, each transmitter transmits the wideband pilot in bursts. For a continuous CDM pilot transmission scheme, each transmitter continuously transmits the wideband pilot, albeit at a low transmit power level. Any frequency hopping rate may be supported without impacting pilot overhead.

Claims

1. A method of receiving a wideband pilot in a wireless multi-carrier communication system, comprising:

obtaining a sequence of received chips that includes a time division multiplexed (TDM) sequence of received pilot and data chips;

demultiplexing the sequence of received chips to obtain a sequence of received pilot chips for the wideband pilot and a sequence of received data chips;

processing the sequence of received pilot chips with a pseudo-random number (PN) code to obtain a sequence of chip-spaced gain values based upon a plurality of channel gain estimates for a plurality of propagation paths for the wideband pilot and to obtain the plurality of channel response estimates for the plurality of subbands based upon transformations of the sequence of chip-spaced gain values; and

processing the sequence of received data chips in accordance with a multi-carrier demodulation scheme and with the plurality of channel response estimates to obtain recovered data symbols.

2. The method of claim 1, wherein the wireless multi-carrier communication system is an orthogonal frequency division multiple access (OFDMA) communication system, and wherein the multi-carrier demodulation scheme is for orthogonal frequency division multiplexing (OFDM).

3. The method of claim 1, wherein the plurality of channel gain estimates are obtained with a rake receiver having a plurality of finger processors, wherein each finger processor is operative to process a different one of to plurality of propagation paths to provide a channel gain estimate for the propagation path.

4. The method of claim 1, wherein the system includes a plurality of subbands, and wherein the recovered data symbols are obtained from different ones of the plurality of subbands in different time intervals as determined by a frequency hopping (FH) sequence.

5. A method of receiving a wideband pilot in a wireless multi-carrier communication system, comprising:

obtaining a sequence of received chips that includes a sequence of combined pilot and data chips transmitted by a transmitting entity, wherein the sequence of combined pilot and data chips is obtained by summing a sequence of pilot chips for the wideband pilot with a sequence of data chips at the transmitting entity;

processing the sequence of received chips with a pseudo-random number (PN) code to obtain a sequence of chip-spaced gain values based upon a plurality of channel gain estimates for a plurality of propagation paths for the wideband pilot and to obtain the plurality of channel response estimates for the plurality of subbands based upon transformations of the sequence of chip-spaced gain values; and

processing the sequence of received chips in accordance with a multi-carrier demodulation scheme and with the plurality of channel response estimates to obtain recovered data symbols for the transmitting entity.

6. The method of claim 5, wherein the plurality of channel gain estimates are obtained with a rake receiver having a plurality of finger processors, wherein each finger processor is operative to process a different one of the plurality of propagation paths to provide a channel gain estimate for the propagation path.

7. The method of claim 5, further comprising:

estimating interference due to the wideband pilot; and

canceling the estimated interference from the sequence of received chips to obtain a sequence of received data chips, and wherein the sequence of received data chips is processed to obtain the recovered data symbols.

8. The meted of claim 5, wherein the wireless multi-carrier communication system is an orthogonal frequency division multiple access (OFDMA) communication system, and wherein the multi-carrier demodulation scheme is for orthogonal frequency division multiplexing (OFDM).

9. An apparatus in a wireless multi-carrier communication system, comprising:

means for obtaining a sequence of received chips that includes a sequence of combined pilot and data chips transmitted by a transmitting entity, wherein the sequence of combined pilot and data chips is obtained by summing a sequence of pilot chips for a wideband pilot with a sequence of data chips at the transmitting entity;

means for processing the sequence of received chips with a pseudo-random number (PN) code to obtain a sequence of chip-spaced gain values based upon a, plurality of channel gain estimates for a plurality of propagation paths for the wideband pilot and to obtain the plurality of channel response estimates for the plurality of subbands based upon transformations of the sequence of chip-spaced gain values; and

means for processing the sequence of received chips in accordance with a multi-carrier demodulation scheme and with the plurality of channel response estimates to obtain recovered data symbols for the transmitting entity.