Abstract
Grant-free access is an attractive approach to enable spectrum-efficient low-latency access for systems with massive number of users. Pilot design plays a crucial role for grant-free access as it needs to provide a large number of access codes with fast collision detection capability and good channel estimation performance. Recently, pilot designs with fast collision detection capability have been proposed for compressed sensing (CS) based channel estimation. But the existing designs are not optimized for the estimation of highly sparse and block-sparse channels. In this paper, we present several propositions related to the performances of the CS based sparse and block-sparse channel estimation. Utilizing these propositions, we develop a novel non-orthogonal pilot design with fast collision detection capability for grant-free access in block-sparse channels. We also propose two methods to optimize the Peak-to-Average Power Ratio (PAPR) of the proposed non-orthogonal pilot codes. The simulation results illustrate that the proposed design provides similar or better channel estimation and collision detection performances with much better pilot resource efficiency when compared to the existing designs. Finally, we investigate the trade-offs among different design parameters and the channel estimation performances to facilitate better design choices.
Highlights
T HE EMERGENCE of new/future wireless applications in various sectors including self-driving cars, video broadcasting on social media and smart cities are driving the demand for higher uplink capacity in terms of data throughput and user access with low latency in wireless communication systems
NON-ORTHOGONAL PILOT DESIGN FOR GRANTFREE ACCESS IN SPARSE AND BLOCK-SPARSE CHANNELS we develop a novel non-orthogonal pilot design with fast collision detection capability for grant-free access which is optimized for block-sparse channels
These results indicate that when needed according to system requirements, a higher number of grant-free access codes could be generated by the proposed design using more pilot resources without degrading the average channel estimation performances
Summary
T HE EMERGENCE of new/future wireless applications in various sectors including self-driving cars, video broadcasting on social media and smart cities are driving the demand for higher uplink capacity in terms of data throughput and user access with low latency in wireless communication systems. The orthogonal pilot design in [34] is optimized for single user scenario and does not support large number of pilot codes with similar channel estimation performances as needed for grant-free access in multiuser scenario. QUAYUM and MINN: COMPRESSED SENSING BASED NON-ORTHOGONAL PILOT DESIGNS FOR MULTI-ANTENNA GRANT-FREE ACCESS SYSTEMS in terms of the cyclic differences of the pilot tone indexes within structured pilot codes for sparse and block-sparse channels. We illustrate the tradeoffs among different pilot configurations in terms of the total number of pilot resources, the number of available grant-free access codes and the channel estimation performances Such trade-off flexibility is not available for the existing pilot design in [15] where only a single configuration is possible for any specific system. A is a matrix, a is a vector, {A} is a set and a is a scalar. aij represents the element in i-th column and j-th row of the matrix A and ak represents the k-th column of the matrix A. ||a|| represents the Euclidean norm of a and |a| is the absolute value of a. diag{a} is a square diagonal matrix with the vector a as the diagonal elements. (.)T and (.)H represent the transpose and hermitian operators, \ indicates the set difference, · denotes the ceiling operation, · denotes the floor operation and · denotes the rounding operation to the nearest integer
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