The proposed intermittent Channel State Information (CSI) estimation scheme can be extended to frequency-selective channels by adapting the estimation intervals for each subcarrier based on the unique channel characteristics associated with frequency-selective fading. In frequency-selective channels, different subcarriers experience varying levels of multipath fading, which necessitates a more granular approach to CSI estimation.
To implement this, the following steps can be taken:
Subcarrier-Specific Estimation Intervals: Instead of using a uniform estimation interval for all users and targets, the scheme can dynamically adjust the CSI estimation intervals for each subcarrier based on the channel's temporal correlation and the Doppler shift associated with each user. This allows for more efficient use of resources by focusing on subcarriers that exhibit rapid changes in channel conditions.
Adaptive Pilot Transmission: The scheme can incorporate adaptive pilot transmission strategies where the pilot symbols are transmitted on specific subcarriers that require more frequent updates. This can be determined by analyzing the channel's coherence bandwidth and the rate of change in the channel state.
Multi-Carrier Modulation Techniques: Utilizing Orthogonal Frequency Division Multiplexing (OFDM) can facilitate the separation of channels into multiple subcarriers, each of which can be treated independently. The intermittent CSI estimation can then be applied to each subcarrier, allowing for tailored estimation strategies that account for the unique fading characteristics of each frequency.
Feedback Mechanisms: Implementing feedback mechanisms from users can help the base station (BS) to understand the channel conditions better and adjust the CSI estimation intervals accordingly. This feedback can include information about the perceived quality of the received signals on different subcarriers.
By employing these strategies, the intermittent CSI estimation scheme can effectively manage the complexities introduced by frequency-selective channels, thereby enhancing the overall performance of Integrated Sensing and Communication (ISAC) systems.