Precoder-Based Interference Cancellation in Wireless Systems
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Solution Overview
Problem
Existing wireless communication systems face challenges in achieving full diversity and low complexity without sacrificing bandwidth, particularly in multi-user scenarios with multiple transmit and receive antennas, where interference cancellation methods increase complexity exponentially and do not work for general cases with complex constellations and multiple users.
Innovation Solution
The method involves designing precoders using channel information to align signals along orthogonal spaces, allowing users to transmit over orthogonal directions, enabling interference cancellation without relying on receive antenna resources, thus achieving full diversity with linear low complexity decoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If receive antennas are used to cancel interference from other users, then interference cancellation is achieved, but the diversity is reduced and complexity increases exponentially
Solution Approach 1:
Instead of using receive antennas to cancel interference (traditional approach), the invention inverts the approach by using transmit antennas with precoders to pre-cancel interference before transmission. The precoders are designed such that signals from different users are orthogonalized at the transmitter side, eliminating interference at the receiver without requiring complex processing there.
Solution Approach 2:
The interference cancellation is performed in advance at the transmitter side through precoder design. The precoders are computed using channel state information to pre-orthogonalize the signals before they are transmitted, so that when they arrive at the receiver, the interference has already been eliminated. This preliminary action shifts the complexity from the receiver to the transmitter.
2Object-generated harmful factors
If a large number of receive antennas are used to cancel interference for J users with N transmit antennas, then interference cancellation is achieved, but the number of required receive antennas increases to NJ
Solution Approach 1:
The invention inverts the traditional interference cancellation approach by moving the cancellation function from the receiver side to the transmitter side. Instead of requiring NJ receive antennas to cancel interference from J users, the system uses N transmit antennas per user with specially designed precoders that orthogonalize the signals before transmission, reducing the receive antenna requirement to just N antennas.
Solution Approach 2:
The invention changes the system parameters by introducing precoders at the transmitter side that transform the signal space. By applying precoding matrices based on channel state information, the system transforms the multi-user interference problem into an orthogonal signal transmission problem, allowing interference-free reception with fewer antennas.
3Object-generated harmful factors
If orthogonal designs are used to cancel interference at the receiver, then interference cancellation is achieved for specific cases, but the method does not work for general cases with complex constellations and multiple users
Solution Approach 1:
The invention changes the approach from using fixed orthogonal designs at the receiver to using adaptive precoders at the transmitter. The precoders are computed based on the actual channel state information and can adapt to different constellations, numbers of users, and antenna configurations. This parameter-based adaptation allows the system to work for general cases rather than being limited to specific orthogonal design scenarios.
Solution Approach 2:
The system transitions from static orthogonal designs to dynamic precoding. The precoders are continuously adapted based on the current channel conditions, allowing the system to handle varying numbers of users, different constellation types, and changing environmental conditions. This dynamic approach provides universal applicability across different operational scenarios.
Data Source
AI summary
A method to achieve full diversity without sacrificing bandwidth and with a linear complexity in a wireless system includes the steps of orthogonally transmitting a plurality of signals utilizing multiple antennas using a corresponding plurality of precoders in a plurality of time slots, which precoders are designed using the channel information to cancel interference among the plurality of signals while achieving a maximum possible diversity of NM with low complexity for at least two users each having N transmit antennas and one receiver with M receive antennas, separating the signals in the receiver using the orthogonality of the transmitted signals, and decoding the signals independently to provide full diversity to the at least two users.