Frequency Domain Channel Estimation for SC-FDMA Multi-User Systems
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Solution Overview
Problem
Existing channel estimation and equalization techniques become complex when applied to scenarios with multiple simultaneous users, leading to increased system complexity without ensuring accuracy and reliability.
Innovation Solution
A method and receiver architecture that perform joint channel estimation and equalization for all users by storing the inverse of pilot sequences and using them for channel transfer function estimation and equalization, employing an MMSE technique, which reduces system complexity and facilitates accurate channel compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional channel estimation and equalization techniques are applied to scenarios with multiple simultaneous users, then channel estimation can be performed, but system complexity increases significantly
Solution Approach 1:
The patent segments the channel estimation process by assigning dedicated pilot sequences to different user groups (first group and second group of users). Each user group receives pilot sequences on specific subcarriers, allowing the receiver to estimate channels for different users separately through frequency-domain processing. This segmentation enables multi-user channel estimation without requiring complex time-domain processing for each user individually.
Solution Approach 2:
The patent uses orthogonal pilot sequences that are transmitted on all subcarriers for channel estimation purposes, even though not all subcarriers carry user data for every user. This excessive use of pilot sequences ensures that channel estimation can be performed accurately for all users simultaneously, and the orthogonality property allows the receiver to extract individual user channel responses from the combined signal without interference.
2Measurement precision
If pilot sequences are transmitted for channel estimation in multi-user scenarios, then channel transfer function can be estimated, but interference between users increases
Solution Approach 1:
The patent assigns different orthogonal pilot sequences to different user groups, where each pilot sequence has specific properties optimized for its assigned users. The first pilot sequence is assigned to the first group of users and the second pilot sequence to the second group, with each sequence having local orthogonality properties that minimize interference for its intended users while allowing the receiver to distinguish between different user groups through correlation processing.
Solution Approach 2:
The patent introduces orthogonal pilot sequences as intermediary signals that mediate between multiple users and the channel. These pilot sequences serve as known reference signals that the receiver can use to estimate channel responses for different users separately. The orthogonality property of the pilot sequences acts as a mathematical mediator that allows the receiver to separate and estimate individual user channels from the combined received signal without direct user-to-user interference.
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AI summary
A channel estimator (202) for use in a receiver node receiving signals (x(1), x(2),.... x(Nu)) from a plurality of user terminals wherein each user terminal is allotted a respective set of transmission subcarriers and respective test signal sequences (rp) for transmission over the channel to be estimated. The channel estimator (202) has stored therein (400) information as to the respective sets of transmission subcarriers allotted to the user terminals (TUi, TU2,..., TIW for transmission as well as the discrete spectra of the respective test signal sequences allotted to the user terminals. Upon receiving from a plurality of user terminals signals including the respective test signal sequences (rp) transmitted over the channel by using the respective sets of transmission subcarriers allotted thereto, the estimator generates (208) the discrete spectrum of the combined test signal received and performs channel estimation as a function of the discrete spectrum of the combined test signal and the discrete spectra of the test signal sequences allotted to the user terminals (TU1, TU2 TUNu). A frequency domain channel estimation is performed for a Single Carrier Frequency Division Multiple Access (SC-FDMA) system.