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

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.

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.

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).