Virtual Carrier Allocation for MTC Receiver Complexity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current mobile telecommunications systems face challenges in efficiently supporting low capability machine type communication (MTC) devices due to the need for complex receivers capable of processing full bandwidth, which increases costs and complexity, and direct conversion receivers are prone to self-mixing interference when using conventional OFDM-based radio access technologies.
Innovation Solution
A base station is configured to detect the bandwidth status of MTC devices and allocate unused subcarriers to virtual channels, allowing for communication using a narrower frequency bandwidth, thereby reducing the complexity of receivers and avoiding self-mixing interference by using unused subcarriers as virtual carriers that do not share the same central frequency as the host carrier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional OFDM-based radio access technology is used for MTC devices, then full bandwidth communication is achieved, but receiver complexity and cost increase
Solution Approach 1:
The patent divides the conventional wideband OFDM system into multiple narrowband virtual carriers. Each MTC device is assigned to a specific virtual carrier with a subset of subcarriers, allowing the receiver to process only a narrow bandwidth while maintaining communication capability. This segmentation resolves the contradiction by enabling full system bandwidth utilization through multiple narrowband partitions.
Solution Approach 2:
The patent introduces a new dimension of virtual carrier indexing and assignment. Instead of all devices competing for the same wideband resources, devices are differentiated by their assigned virtual carrier indices and subcarrier sets. This dimensional separation allows multiple narrowband devices to coexist in the same physical bandwidth without requiring complex wideband receivers.
2Device complexity
If direct conversion receivers are used for MTC devices, then receiver simplicity and cost are reduced, but self-mixing interference occurs
Solution Approach 1:
The patent extracts and removes the DC subcarrier (center frequency) from the available subcarrier set for MTC device assignment. By explicitly excluding the center frequency subcarrier from allocation to any virtual carrier, the system eliminates the source of self-mixing interference while allowing direct conversion receivers to be used. This extraction resolves the contradiction by removing the harmful frequency component.
Solution Approach 2:
The patent converts the potential harm of DC offset in direct conversion receivers into a beneficial resource allocation constraint. The unused DC subcarrier is systematically excluded from MTC assignments, and this constraint is used to define the boundaries of virtual carriers. The harm is transformed into a structured resource management rule that simplifies interference avoidance.
3Device complexity
If virtual carriers are assigned to MTC devices, then receiver complexity is reduced, but bandwidth utilization efficiency decreases
Solution Approach 1:
The patent creates a universal resource allocation framework where the same physical OFDM bandwidth serves multiple functions: wideband services use the full bandwidth, while MTC services are assigned to specific virtual carriers with subsets of subcarriers. The DC subcarrier serves as a universal exclusion zone for all MTC virtual carriers. This multi-functionality resolves the contradiction by enabling flexible bandwidth sharing between different service types.
Solution Approach 2:
The patent implements dynamic virtual carrier assignment where MTC devices can be allocated to different virtual carriers based on traffic demand and device capabilities. The system can dynamically adjust which subcarrier sets are assigned to which virtual carriers, optimizing bandwidth utilization while maintaining narrowband receiver simplicity. This dynamic allocation resolves the efficiency concern.
Data Source
AI summary
An apparatus and method for allocating transmission resources to MTC-type terminals and transmitting data in mobile telecommunication systems in dependence upon the capability of the RF receiver equipment of those terminals. Where a virtual carrier is established to carry data for a given MTC-type device, the position of the center frequency for that virtual carrier is assigned on the basis of both the capability of the RF receiver equipment of that terminal and the degree of traffic congestion on the frequency band at which the virtual carrier has been established.