Adaptive Sub-Carrier Control for IFDMA Frequency Diversity
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Solution Overview
Problem
Interleaved Frequency Division Multiple Access (IFDMA) systems do not always activate all possible sub-carriers, resulting in sub-optimal performance due to limited frequency diversity gain when the number of requested sub-carriers is less than the maximum, leading to inefficiencies in wireless communication systems.
Innovation Solution
Adaptive control of sub-carriers by adjusting the Repetition Factor (RF) and repetition block size (Q) based on the number of users and requested sub-carriers, along with controlling the Spreading Factor (SF) to maximize the number of active sub-carriers, ensuring orthogonality and increasing frequency diversity gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the system bandwidth and sub-carrier spacing are kept constant, then the maximum number of sub-carriers is constant and system simplicity is maintained, but the number of active sub-carriers cannot be maximized when total requested sub-carriers is less than maximum, resulting in sub-optimal frequency diversity gain
Solution Approach 1:
The patent applies dynamics by making the system configurable between two operational modes: a first mode where system bandwidth and sub-carrier spacing are constant, and a second mode where these parameters can be dynamically adjusted. This allows the system to adapt the number of active sub-carriers to match the total requested sub-carriers, maximizing frequency diversity gain when needed while maintaining simplicity during normal operation.
Solution Approach 2:
The patent implements parameter changes by allowing modification of system bandwidth and sub-carrier spacing parameters. When the total number of requested sub-carriers is less than the maximum, the system can adjust these parameters to activate exactly the needed number of sub-carriers, thereby achieving full frequency diversity gain without permanently increasing system complexity.
2Reliability
If all possible sub-carriers are activated, then full frequency diversity gain is achieved, but the system cannot accommodate scenarios where the total number of requested sub-carriers is smaller than the maximum, leading to resource waste
Solution Approach 1:
The patent enables dynamic adjustment of the number of active sub-carriers based on actual demand. By switching between operational modes and adjusting system bandwidth and sub-carrier spacing, the system activates exactly the number of sub-carriers needed (matching total requested sub-carriers), ensuring full frequency diversity gain for reliability while avoiding activation of excess sub-carriers that would waste resources.
3Productivity
If narrow frequency bands are allocated to low-rate users in FDMA systems, then resource allocation efficiency is improved, but frequency diversity gain is not available to these users
Solution Approach 1:
The patent segments the frequency band into multiple sub-carriers and uses IFDMA to interleave sub-carrier assignments across users. This segmentation allows low-rate users to receive multiple non-contiguous sub-carriers distributed across the frequency spectrum, providing frequency diversity gain while maintaining efficient resource allocation. The interleaved structure ensures that users obtain frequency diversity without requiring contiguous narrowband allocation.
Data Source
AI summary
A method and system for adaptive control of sub-carriers is useful for increasing frequency diversity gain to improve bit error rate performance in an Interleaved Frequency Division Multiple Access (IFDMA) system. The method includes selecting a combination of a Repetition Factor (RF) and a repetition block size (Q), from possible combinations of a RF and a Q, based on a number of users (Nu) (step 1405). A Spreading Factor (SF), Forward Error Correction (FEC) coding rate (R), or modulation order (M) based on the Nu is then determined (step 1410). Control signals are then provided based on the RF and Q, and based on the SF, R, or M (step 1415).