Abstract
Agriculture is one of the main economic industries of a country. Application of information technologies in agriculture, smart agriculture, aims to realize precision control of irrigation, fertilizer, diseases, and insect pests prevention in the growing of crops. For the sake of obtaining the interest data, wireless sensor networks (WSNs) are used to collect the interest data in the farm field and send the obtained data to the servers via wireless communication. Since the WSNs usually operate in the unlicensed spectrum, the available resource elements (REs) are scarce especially when a large number of sensor nodes are deployed in the farm field. To accommodate more sensor nodes and prolong the lifetime of the WSNs in agriculture, relay-aided non-orthogonal multiple access is introduced into the uplink transmission stage of the direct transmission from the sensor nodes to the sink node. Non-orthogonal multiple access (NOMA) can transmit multiple symbols simultaneously on the same RE by splitting them in the power domain and distinguish them according to diverse power levels of different symbols. The average sum data rate and outage probability of the relay-aided NOMA in uplink transmission are theoretically analyzed. The numerical simulation results show that the WSNs with relay-aided NOMA outperforms the traditional OMA scheme in uplink transmission in WSNs in agriculture.
Highlights
Agriculture is one of the basic sources of livelihood for people and plays a key role in the development of the rural economy in China
The performance of relay-aided Non-orthogonal multiple access (NOMA) in uplink transmission is compared with wireless sensor networks (WSNs) in agriculture with traditional orthogonal multiple access (OMA)
The signal wavelength is given by λ = c/fsig, where c is the speed of light and fsig = 2.4GHz is the signal frequency used in WSNs in agriculture
Summary
In NOMA based uplink transmission, the first symbol can be detected directly by subtracting the received second symbol from the relay This detecting process can reduce the calculation complexity at the sink node and fully exploits the signals from the relay. A SIC receiver is employed to detect the second transmitted symbol from the processed signal based on the obtained estimate of the first symbol This process exploits the space diversity and improves the sum data rate at the sink node side. For the sake of balancing the power consumption of the sensor nodes that act as relays in uplink transmission and maximizes the lifetime of the WSNs, same target data rates are set to the sensor nodes that can communicate with the sink node directly. The power allocation and route information are broadcast to all the sensor nodes in WSNs before data transmission
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