MIMO Reference Signal Signaling Overhead Reduction
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Solution Overview
Problem
Current MIMO techniques in LTE-Advanced systems face inefficiencies in signaling reference signals, leading to increased signaling overhead, limited flexibility in resource assignment, and poor support for multi-user MIMO scenarios, especially with dense scheduling and unequal bandwidth allocations.
Innovation Solution
The implementation of a method to efficiently signal cyclic shifts and orthogonal cover codes using a pattern index, allowing for larger tables and increased flexibility by borrowing unused bits from other signaling fields, enabling better mapping of reference signals to transmission layers and supporting both single-user and multi-user MIMO scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If explicit signaling of B=log2(N) bits is performed using the uplink grant message to identify cyclic shift and orthogonal cover code patterns, then reference signal assignment flexibility is improved, but signaling overhead increases
Solution Approach 1:
The patent combines multiple signaling functions into a single uplink grant message by merging the B-bit pattern index with existing signaling fields. This allows the network to signal cyclic shift and orthogonal cover code patterns for multiple transmission layers simultaneously while utilizing the same signaling resources, thereby improving reference signal assignment flexibility without proportionally increasing overhead.
Solution Approach 2:
The uplink grant message is designed to serve multiple purposes: it not only schedules uplink transmissions but also carries the B-bit pattern index for reference signal assignment. This multi-functional approach allows the same signaling mechanism to handle both resource allocation and reference signal configuration, reducing the need for separate dedicated signaling channels.
2Adaptability or versatility
If larger tables with more reference signal patterns are implemented, then resource assignment flexibility is improved, but device complexity increases
Solution Approach 1:
The patent segments the reference signal configuration space by using B bits to index into a table of N predefined patterns. Instead of requiring devices to handle all possible cyclic shift and orthogonal cover code combinations simultaneously, the system divides the configuration space into N discrete patterns, each representable by a unique B-bit index. This segmentation reduces device complexity while maintaining flexibility through the pattern selection mechanism.
Solution Approach 2:
The system pre-defines N reference signal patterns in lookup tables before transmission occurs. These patterns are prepared in advance and stored at both the network side and the user equipment. During operation, the network simply signals the appropriate pattern index via the B-bit field, and the device retrieves the pre-configured pattern parameters, avoiding the need for real-time complex calculations and reducing device complexity.
3Productivity
If multiple UEs are co-scheduled in the same bandwidth for MU-MIMO, then system throughput is improved, but inter-layer interference increases
Solution Approach 1:
The patent applies different cyclic shifts and orthogonal cover codes to reference signals of different layers and different users through the signaled patterns. This creates local differentiation in the signal characteristics for each layer while maintaining overall system coordination. By varying the local signal properties (cyclic shift values and orthogonal codes) based on the assigned patterns, the system enables multiple UEs to share the same bandwidth with reduced inter-layer interference while maintaining high system throughput.
Data Source
AI summary
Systems and methods for signaling a pattern of cyclic shifts and orthogonal cover codes for use by a wireless device in multi-layer transmissions are presented. In one exemplary embodiment, a method includes receiving a signal that includes B bits for identifying a reference signal. Each of several available reference signals are defined by a cyclic shift and an orthogonal cover code. Further, the method includes using the B bits to identify the cyclic shift and orthogonal cover code according to pre-determined tables that map each value of the B bits to a pattern of cyclic shift and orthogonal cover code combinations for a multi-layer transmission scheme. The patterns for the multi-layer transmission scheme include first and second patterns based on the same cyclic shifts, but where some, but not all, of the cyclic shifts in the first pattern are associated with the same corresponding orthogonal cover codes in the second pattern. In addition, the method includes transmitting each of the one or more spatially multiplexed data streams using a corresponding reference signal for each data stream.