This paper addresses robust link adaptation for a precoded downlink multiple input single output (MISO) system, for guaranteeing ultra-reliable (99.999%) transmissions to mobile users served by a small cell network (e.g. slowly moving machines in a factory). Effects of inaccurate channel state information (CSI) caused by user mobility and varying precoders in neighboring cells are mitigated. Both of these impairments translate to changes of received signal-to-noise plus interference ratios (SINRs), leading to CSI mispredictions and potentially erroneous transmissions. Knowing the statistics of the propagation channels and the precoder variation, backoff values can be selected to guarantee robust link adaptation. Combining this with information on the current channel state, transmissions can be adapted to have a desired reliability. Theoretical analysis accompanied by simulation results show that the proposed approach is suitable for attaining 5G ultra-reliability targets in realistic settings.
Cooperative communication is one of the major diversity techniques which exploit spatial diversity through a virtual antenna array. In addition to cooperation, transmitting the same symbols through different sub carriers (Multi-Carriers) introduces frequency diversity as well. The objective of this paper is to investigate cooperative diversity performance in Multi-Carrier Code Division Multiple Access (MC-CDMA) systems with orthogonal and non-orthogonal spreading codes. We evaluate the Symbol Error Rate (SER) of cooperative transmission in frequency-selective Rayleigh faded uplink channel. We focus on the use of despreading-combining (DC) receiver and coherent detection with Maximal Ratio Combining for the above selected criteria respectively. It is shown that the orthogonal spreading code cancels Multiple-Access Interference (MAI) and the performance is completely independent of the length of the spreading code. The approximate SER derived here for the the transmission scheme is well matched with the increasing number of users in the system. Hence the Gaussian approximation is acceptable for systems which are operating with their maximum user capacities at lower SNR values.Keywords Cooperative communication · MC-CDMA · Rayleigh fading channel · Symbol error rate (SER)
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