Orthogonal frequency division multiplexing (OFDM) system with channel transfer function prediction

• US 20030232601A1
• Filed: 04/15/2003
• Published: 12/18/2003
• Est. Priority Date: 04/16/2002
• Status: Active Grant

• Current Assignee: Sony Deutschland GmbH (Sony Group Corp.)
• Original Assignee: Sony Deutschland GmbH (Sony Group Corp.)
• Inventors: Uno, Masahiro
• Granted Patent: US 7,386,072 B2
• Time in Patent Office: Days
• US Class Current: 455/67.11
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 27/2637 with direct modulation of individual subcarriers

Abstract

The underlying invention generally relates to the field of wireless communication systems with high-speed mobile access, especially to Orthogonal Frequency Division Multiplexing (OFDM) systems considering channel estimation and/or channel tracking. More particularly, the invention provides an adaptive subcarrier loading function for a mobile receiver (1310) in a wireless communication system based on OFDM that can advantageously be applied to predict the channel transfer function H(j·ω,t) of a multipath propagation channel (1320) being severely impaired by frequency-selective fading and an extremely time-variant behavior by detecting the position and/or movement of zero points (A, B, and C) of said transfer function H(j·ω,t), thereby reducing the probability of an incorrect assignment of the modulation scheme for each subcarrier (102), that is caused by mobile terminals (405) moving at high velocity.

Thereby, said zero points (A, B, C) of the estimated channel transfer function Ĥ(j·ω,t) are determined by detecting the position of deep notches on the associated amplitude response H(j·ω,t)| of the measured channel transfer function H(j·ω,t) caused by frequency-selective fading whose depths are larger than a predefined threshold.

Claims

1. A method for an adaptive subcarrier loading for a mobile receiver (1310) in a wireless communication system based on Orthogonal Frequency Division Multiplexing (OFDM) applied to predict the frequency-selective distortion of the channel transfer function for a multipath propagation channel (1320) impaired by attenuation fades and a time-variant behavior when said mobile receiver (1310) is moved, comprising:

a channel estimation (802), a channel equalization and/or a synchronization on the basis of at least one part of the received signal,

an adaptive subcarrier loading (803′

) technique in which different modulation schemes can be assigned to applied subcarriers (102),

characterized by the step of

estimating (802) said channel transfer function by evaluating (806) the position and movement of its zero points (A, B, C).

2. A method according to claim 1, characterized in that said zero points (A, B, C) of the estimated channel transfer function are determined by detecting the position of notches on the associated amplitude response of the channel transfer function caused by a frequency-selective fading whose depths are larger than a predefined threshold.

3. A method according to claim 2, characterized by

a prediction of said zero points (A, B, C) for succeeding downlink signal bursts (700) by evaluating the movement of said zero points (A, B, C).

4. A method according to anyone of the preceding claims, wherein the OFDM symbol stream of the associated downlink signal burst (700) is extended by multiplexing one preamble frame (701, 702 and/or 703) each after a predefined number of OFDM data symbols within the associated downlink signal burst.

5. A method according to anyone of the preceding claims, wherein channel estimates are steadily exploited during the reception of the OFDM symbol stream by weighting previously obtained channel estimates in order to reduce the effect of noise on the channel estimation.

6. A method according to anyone of the previous claims, characterized in that

reference symbols transmitted by means of said pilot patterns are scrambled by means of a pseudo-noise scrambling sequence generated by a generator polynomial, which is known to the mobile transmitter (1301) and the mobile receiver (1310), in order to randomize the reference symbols to be transmitted.

8. A method supporting a modulation scheme planning for a wireless communication scenario with at least one mobile terminal (405) and at least one access point (401) according to anyone of the preceding claims, in which the following steps are performed in the given order in case the access point (401) transmits (801) a downlink signal to the mobile terminal (405):

first, the mobile terminal (405) receives the downlink signal of the access point (401), estimates (802) the transfer function of the multipath propagation channel (1320), estimates (806) the position of zero points (A), predicts (807) the position of zero points (B, C) for succeeding downlink signal bursts (700), makes a proposal (803′

) for a modulation scheme according to said prediction, and sends this proposal to the access point (401);

then, the access point (401) receives the proposal and evaluates it (804), and—

if it is acceptable—

sends an acknowledgment message for the proposal, sets up (805) the modulation scheme of the downlink signal according to the proposal, and sends (801) the downlink signal; and

finally, the mobile terminal (405) receives the acknowledgment message for the proposal, sets up (805) a modulation scheme according to the proposal, and receives the downlink signal.

9. Software routine running on a mobile receiver (1310) designed for performing a method according to anyone of the preceding claims.

11. A mobile telecommunications device, characterized by a mobile receiver (1310) according to claim 10 designed for supporting a method according to anyone of the claims 1 to 8.

7. A method supporting a modulation scheme planning for a mobile transmitter (1301) in a wireless communication system based on Orthogonal Frequency Division Multiplexing (OFDM) in combination with an adaptive subcarrier loading technique which can be applied to predict the frequency-selective distortion of the channel transfer function for a multipath propagation channel (1320) impaired by attenuation fades and a time-variant behavior, in which a mobile receiver (1310) conducts the following steps for each downlink signal burst:

performing a first channel estimation (802) by means of a first preamble frame (1202) that serves as a pilot pattern for the current downlink signal burst (1201), and finding (806) zero points (A, B, C) of the estimated channel transfer function by detecting the position of notches on its associated amplitude response characteristic,

performing a second channel estimation (802) by means of a second preamble frame (1202) that serves as a pilot pattern for the succeeding downlink signal burst (1203), and finding (806) zero points (A, B, C) of the newly estimated channel transfer function by detecting the position of notches on its associated amplitude response characteristic,

estimation (808) and/or prediction (807) of the movement of zero points (A, B, C) of said channel transfer function with the aid of results obtained for the current downlink signal burst (1201) and the succeeding downlink signal burst (1203), and

making a proposal (803′

) for the execution of a modulation scheme based on the position and movement of zero points (A, B, C) of the estimated channel transfer function.

10. A mobile receiver supporting wireless communication over a mobile radio channel (1320) by means of Orthogonal Frequency Division Multiplexing (OFDM) systems, comprising:

means (1305, 1315) for performing an OFDM multi-carrier modulation and/or an OFDM multi-carrier demodulation,

means (1318) for performing a channel estimation (802), a channel equalization and/or a synchronization on the basis of at least one part of the received signal,

means (1319) for performing an adaptive subcarrier loading technique (803′

), in which different modulation schemes are assigned to the applied subcarriers (102) to increase the capacity usage of the underlying multipath propagation channel (1320),

characterized by

means (1319, 1321) for predicting a frequency-selective distortion of the channel transfer function for the underlying multipath propagation channel being severely impaired by attenuation fades and a time-variant behavior when the mobile receiver (1310) is moved, which calculate an estimation (802) of said channel transfer function-by evaluating (806) the position of its zero points (A, B, C).