Abstract
One of the key requirements for next generation wireless or cellular communication systems is to efficiently support a large number of connections for Internet of Things (IoT) applications, and uplink non-orthogonal multiple access (NOMA) schemes can be used for this purpose. In uplink NOMA systems, pilot symbols, as well as data symbols can be superimposed onto shared resources. The error rate performance can be severely degraded due to channel estimation errors, especially when the number of superimposed packets is large. In this paper, we discuss uplink NOMA schemes with channel estimation errors, assuming that quadrature phase shift keying (QPSK) modulation is used. When pilot signals are superimposed onto the shared resources and a large number of devices perform random accesses concurrently to a single resource of the base station, the channels might not be accurately estimated even in high SNR environments. In this paper, we propose an uplink NOMA scheme, which can alleviate the performance degradation due to channel estimation errors.
Highlights
Generation wireless and cellular communication systems are expected to support a variety of services requiring high data rates, low delays, high availabilities, high reliabilities, and large connection densities [1–4]
non-orthogonal multiple access (NOMA) systems, there is no exact limit on concurrent random accesses, and superimposed signals from many devices can be decoded with the help of interference cancellation techniques
Unlike orthogonal multiple access systems, channel estimates in uplink NOMA systems might not be accurate even in high signal-to-noise ratio (SNR) environments due to the interference from other devices, and it is desirable to alleviate the performance degradation caused by channel estimation errors
Summary
Generation wireless and cellular communication systems are expected to support a variety of services requiring high data rates, low delays, high availabilities, high reliabilities, and large connection densities [1–4]. The prosperity of IoT services can greatly increase the density of devices, which will require massive IoT technologies to support simultaneous random accesses from a large number of devices to a single base station (BS) [4–9]. For this purpose, one can use non-orthogonal multiple access (NOMA) schemes, in which signals from devices can be superimposed onto the shared resource and distinguished by spreading or interleaving patterns [10–17]. NOMA systems, there is no exact limit on concurrent random accesses, and superimposed signals from many devices can be decoded with the help of interference cancellation techniques.
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