Power Allocation for Downlink Short Packet Transmission with Superimposed Pilots in Cell-free Massive MIMO

SHEN Luyao; ZHOU Xingguang; XIA Wenchao; ZHU Hongbo

doi:10.11999/JEIT250655

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SHEN Luyao, ZHOU Xingguang, XIA Wenchao, ZHU Hongbo, . Power Allocation for Downlink Short Packet Transmission with Superimposed Pilots in Cell-free Massive MIMO[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT250655

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SHEN Luyao, ZHOU Xingguang, XIA Wenchao, ZHU Hongbo, . Power Allocation for Downlink Short Packet Transmission with Superimposed Pilots in Cell-free Massive MIMO[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT250655

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Power Allocation for Downlink Short Packet Transmission with Superimposed Pilots in Cell-free Massive MIMO

doi: 10.11999/JEIT250655 cstr: 32379.14.JEIT250655

College of Communication and Information Engineering, Nanjing University of Posts andTelecommunications, Nanjing 210003, China

Funds: the National Science and Technology Major Project of the Ministry of Science and Technology of Jiangsu Province(XXX), the National Natural Science Foundation for Young Scientists of China(62201285), Young Elite Scientists Sponsorship Program(2022QNRC001)

Received Date: 2025-07-11
Accepted Date: 2025-11-03
Rev Recd Date: 2025-11-03

Available Online: 2025-11-12

Abstract

Abstract

Objective With the advancement of 5th Generation mobile communication, the volume of communication service interactions has experienced a dramatic surge. To effectively accommodate this substantial increase in communication demands, Cell-Free Massive Multiple-Input Multiple-Output (CF-mMIMO) has emerged as a key enabling technology. However, supporting multi-user access in CF-mMIMO systems introduces significant complexity in channel estimation. Conventional channel estimation methods based on regular pilots incur large overhead, which considerably reduces the number of symbols available for data transmission, thereby leading to a decrease in transmission rates. This issue is particularly pronounced in short packet transmission scenarios. To address this challenge, this paper investigates a downlink short packet transmission scheme based on Superimposed Pilots (SP) in CF-mMIMO systems, aiming to improve the performance of short packet transmission. Methods This study addresses the SP-based downlink short packet transmission scenario in CF-mMIMO systems. A power allocation algorithm is proposed. Considering the energy consumption and resource constraints encountered in practical applications, a User-Centric (UC) approach is adopted. Based on the Maximum Ratio Transmission (MRT) precoding scheme, a closed-form expression for the downlink achievable rate is derived under imperfect Channel State Information (CSI) . Due to the cross-interference between pilot signals and data signals, an iterative optimization algorithm based on Geometric Programming (GP) and Successive Convex Approximation (SCA) is further proposed. Specifically, considering the minimum data rate requirement and uplink and downlink power constraints, the objective is to optimize the power allocation between pilot signals and data signals. By employing logarithmic function approximation and SCA methods, the non-convex optimization problem is transformed into a GP problem, then an iterative algorithm is proposed to solve it. Furthermore, this paper compares the SP scheme with the Regular Pilots (RP) scheme to demonstrate the superiority of SP scheme and the algorithm proposed. Results and Discussions Simulation results first confirm the accuracy of the closed-form expressions for the downlink sum-rate under both SP and Regular Pilots (RP) schemes (Fig. 2). To further demonstrate the superiority and effectiveness of the proposed algorithm, this paper conducts a comparative analysis of the weighted sum-rate performance. The comparison is performed among the proposed power allocation algorithm under both SP scheme and RP scheme, and fixed power allocation under SP scheme, with the number of antennas of APs (Fig 3), the number of users (Fig 4), block length (Fig 5), and decoding error probability (Fig 6) serving as variables. The results demonstrate that the weighted sum-rate achieved with the proposed power allocation algorithm under the SP scheme outperforms both the RP scheme and the fixed power allocation scheme. Conclusions This paper investigates the downlink power allocation problem under SP scheme in CF-mMIMO systems for short packet transmission scenarios. Firstly, the user-centric (UC) scheme is adopted to derive a closed-form expression for the lower bound of the downlink transmission rate under imperfect CSI and MRT precoding schemes. Subsequently, the downlink weighted sum-rate maximization problem for SP scheme is formulated, and the non-convex problem is transformed into a solvable GP problem using SCA method. Finally, an iterative algorithm is employed to obtain the solution. Simulation results further validate the correctness of the closed-form expression for the transmission rate and demonstrate the superiority of the proposed power allocation algorithm.
- Cell-free massive multiple-input multiple-output,
- Superimposed pilot,
- Short packet transmission,
- Power allocation

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References(21)

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