On the Achievable User Number of the Downlinks in Cellular-Based Machine-to-Machine Communications

Yingbo Li,Lin Bai,Ye Jin,Chen Chen

doi:10.1155/2012/714971

Abstract

In cellular-based machine-to-machine (M2M) networks, supporting large number of machine-type communications (MTC) users (devices) has become a critical challenge in both the uplink and downlink channels. In this paper, we focus on the downlink beamforming using zero-forcing dirty paper coding (DPC). In order to characterize the system's ability of user admission, we consider the achievable user number, which is defined as the number of users whose signal-to-interference plus-noise ratios exceed a target threshold. Due to the complexity of the optimal scheme, we propose two algorithms with random user scheduling and greedy user scheduling in maximizing the achievable user number by dynamical power assignment. Using the joint distribution of effective channel gains, we derive the achievable user number of both the scheduling schemes. An upper bound on the achievable user number of the greedy scheme is then derived which is shown to be tight when there are a large number of users. From numerical results, we show that both of the schemes enjoy a linear increase in the achievable user number as the number of transmitter antennas increases. The performance of the greedy scheduling scheme is close to the optimal scheduling scheme.

Highlights

Wireless machine-to-machine (M2M) networks are emerging as new types of communication, where cellular systems are expected to play an important role in wireless M2M networks [1]
When perfect channel state information is available at the base station (BS), the optimal downlink beamforming scheme is dirty paper coding (DPC) [5] where the interference known at the transmitter is pre-subtracted at the BS
The upper bound of the greedy scheduling scheme with dynamic power assignment is shown in Figure 2, with L = 4, N = 4, and P = 6 dB

Summary

Introduction

Wireless machine-to-machine (M2M) networks are emerging as new types of communication, where cellular systems are expected to play an important role in wireless M2M networks [1]. In cellular-based M2M networks, supporting large number of machine-type communications (MTC) users (devices) has become a critical challenge in both the uplink [2, 3] and downlink channels. We focus on improving the number of active users in the cellular-based M2M communications networks. In the cellular communications networks, beamforming techniques with multiple antennas at the base station (BS) are used for simultaneous transmission of multiple users. When perfect channel state information is available at the BS, the optimal downlink beamforming scheme is dirty paper coding (DPC) [5] where the interference known at the transmitter is pre-subtracted at the BS. The optimal beamforming weight vectors and encoding order of DPC can be found using a duality between the downlink and the corresponding uplink channel.

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Discussion

Conclusion