1,375 research outputs found
Iterative Joint Channel Estimation and Symbol Detection for Multi-User MIMO OFDM
Multiple-Input-Multiple-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) systems have recently attracted substantial research interest. However, compared to Single-Input-Single-Output (SISO) systems, channel estimation in the MIMO scenario becomes more challenging, owing to the increased number of independent transmitter-receiver links to be estimated. In the context of the Bell LAyered Space-Time architecture (BLAST) or Space Division Multiple Access (SDMA) multi-user MIMO OFDM literature, no channel estimation technique allows the number of users to be higher than the number of receiver antennas, which is often referred to as an “overloaded” scenario. In this contribution we propose a new Genetic Algorithm (GA) assisted iterative joint channel estimation and multiuser detection approach for MIMO SDMA-OFDM systems, which exhibits a robust performance in the above-mentioned overloaded scenario. Furthermore, GA-aided Multi-User Detection (MUD) techniques found in the literature can only provide a hard-decision output, while the proposed GA is capable of providing “soft” outputs, hence achieving an improved performance with the aid of channel decoders. Finally, a range of simulation results are provided to demonstrate the superiority of the proposed scheme
Uniquely Decodable Ternary Codes for Synchronous CDMA Systems
In this paper, we consider the problem of recursively designing uniquely
decodable ternary code sets for highly overloaded synchronous code-division
multiple-access (CDMA) systems. The proposed code set achieves larger number of
users than any other known state-of-the-art ternary codes that
offer low-complexity decoders in the noisy transmission. Moreover, we propose a
simple decoder that uses only a few comparisons and can allow the user to
uniquely recover the information bits. Compared to maximum likelihood (ML)
decoder, which has a high computational complexity for even moderate code
length, the proposed decoder has much lower computational complexity. We also
derived the computational complexity of the proposed recursive decoder
analytically. Simulation results show that the performance of the proposed
decoder is almost as good as the ML decoder.Comment: arXiv admin note: text overlap with arXiv:1806.0395
Fast Decoder for Overloaded Uniquely Decodable Synchronous CDMA
We consider the problem of designing a fast decoder for antipodal uniquely
decodable (errorless) code sets for overloaded synchronous code-division
multiple access (CDMA) systems where the number of signals K_{max}^a is the
largest known for the given code length L. The proposed decoder is designed in
a such a way that the users can uniquely recover the information bits with a
very simple decoder, which uses only a few comparisons. Compared to
maximum-likelihood (ML) decoder, which has a high computational complexity for
even moderate code length, the proposed decoder has a much lower computational
complexity. Simulation results in terms of bit error rate (BER) demonstrate
that the performance of the proposed decoder only has a 1-2 dB degradation at
BER of 10^{-3} when compared to ML
Random Access Protocols for Massive MIMO
5G wireless networks are expected to support new services with stringent
requirements on data rates, latency and reliability. One novel feature is the
ability to serve a dense crowd of devices, calling for radically new ways of
accessing the network. This is the case in machine-type communications, but
also in urban environments and hotspots. In those use cases, the high number of
devices and the relatively short channel coherence interval do not allow
per-device allocation of orthogonal pilot sequences. This article motivates the
need for random access by the devices to pilot sequences used for channel
estimation, and shows that Massive MIMO is a main enabler to achieve fast
access with high data rates, and delay-tolerant access with different data rate
levels. Three pilot access protocols along with data transmission protocols are
described, fulfilling different requirements of 5G services
Frequency Domain Backoff for Continuous Beamforming Space Division Multiple Access on Massive MIMO Wireless Backhaul Systems
This paper newly proposes a frequency domain backoff scheme dedicated to continuous beamforming space division multiple access (CB-SDMA) on massive antenna systems for wireless entrance (MAS-WE). The entrance base station (EBS) has individual base band signal processing units for respective relay stations (RSs) to be accommodated. EBS then continuously applies beamforming weight to transmission/reception signals. CB-SDMA yields virtual point-to-point backhaul link where radio resource control messages and complicated multiuser scheduling are not required. This simplified structure allows RSs to work in a distributed manner. However, one issue remains to be resolved; overloaded multiple access resulting in collision due to its random access nature. The frequency domain backoff mechanism is introduced instead of the time domain one. It can flexibly avoid co-channel interference caused by excessive spatial multiplexing. Computer simulation verifies its superiority in terms of system throughput and packet delay
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