A Random Access Protocol for Pilot Allocation in Crowded Massive MIMO Systems

Abstract

Abstract-The Massive MIMO (multiple-input multipleoutput) technology has great potential to manage the rapid growth of wireless data traffic. Massive MIMO achieves tremendous spectral efficiency by spatial multiplexing of many tens of user equipments (UEs). These gains are only achieved in practice if many more UEs can connect efficiently to the network than today. As the number of UEs increases, while each UE intermittently accesses the network, the random access functionality becomes essential to share the limited number of pilots among the UEs. In this paper, we revisit the random access problem in the Massive MIMO context and develop a reengineered protocol, termed strongest-user collision resolution (SUCRe). An accessing UE asks for a dedicated pilot by sending an uncoordinated random access pilot, with a risk that other UEs send the same pilot. The favorable propagation of Massive MIMO channels is utilized to enable distributed collision detection at each UE, thereby determining the strength of the contenders' signals and deciding to repeat the pilot if the UE judges that its signal at the receiver is the strongest. The SUCRe protocol resolves the vast majority of all pilot collisions in crowded urban scenarios and continues to admit UEs efficiently in overloaded networks.

Performance Analysis of Random Access Protocol in Crowded LTE Network over Nakagami Fading Channel

“…Step 4: Termed by contention resolution and comprises of one or multiple steps that are envisioned to avoid collision [8], [9]. …”

“…techniques are reviewed, over traditional techniques for pilot allocation in MIMO based network and random-access protocol techniques used for pilot allocation in over-crowded Long term evolution (LTE) network [8], [9].Future of mobile network is facing immense numbers of linked user equipment's or UE's that mutually request for immense data volumes [12]. As the allotted cellular frequency resources are limited, hence, magnifying improvements are required in the spectral efficiency [13].…”

“…The attainable Uplink (UL) and Downlink (DL) data outputshave been examined broadly in recent years; for example, in [4].On contrary, the network access functionality has acknowledged little devotion in crowded MIMO [16], in spite of the circumstance that the enormous numbers of UE's with intermittent action need scalable and efficient solutions [8]. Random access has a vital role in crowded MIMO network [8], [9].…”

Uncoordinated pilot decontamination in massive MIMO systems

“…Recent work utilizing temporal correlation for channel estimation is found in [13], although not in combination with pilot hopping and not with the purpose of mitigating pilot contamination. Random selection of pilot sequences is also explored in [14] and [15]. Both works consider the random access problem in cellular networks.…”

“…Both works consider the random access problem in cellular networks. In [14], pilot contamination is avoided through a distributed collision detection algorithm, which enables users with weak channels to detect that they are contaminators of a user with a strong channel and as a result postpone their transmission. The work in [15] considers codeword transmissions that are spread across multiple time slots, each with a different contaminator.…”