29 research outputs found
Large-Scale MIMO versus Network MIMO for Multicell Interference Mitigation
This paper compares two important downlink multicell interference mitigation
techniques, namely, large-scale (LS) multiple-input multiple-output (MIMO) and
network MIMO. We consider a cooperative wireless cellular system operating in
time-division duplex (TDD) mode, wherein each cooperating cluster includes
base-stations (BSs), each equipped with multiple antennas and scheduling
single-antenna users. In an LS-MIMO system, each BS employs antennas not
only to serve its scheduled users, but also to null out interference caused to
the other users within the cooperating cluster using zero-forcing (ZF)
beamforming. In a network MIMO system, each BS is equipped with only
antennas, but interference cancellation is realized by data and channel state
information exchange over the backhaul links and joint downlink transmission
using ZF beamforming. Both systems are able to completely eliminate
intra-cluster interference and to provide the same number of spatial degrees of
freedom per user. Assuming the uplink-downlink channel reciprocity provided by
TDD, both systems are subject to identical channel acquisition overhead during
the uplink pilot transmission stage. Further, the available sum power at each
cluster is fixed and assumed to be equally distributed across the downlink
beams in both systems. Building upon the channel distribution functions and
using tools from stochastic ordering, this paper shows, however, that from a
performance point of view, users experience better quality of service, averaged
over small-scale fading, under an LS-MIMO system than a network MIMO system.
Numerical simulations for a multicell network reveal that this conclusion also
holds true with regularized ZF beamforming scheme. Hence, given the likely
lower cost of adding excess number of antennas at each BS, LS-MIMO could be the
preferred route toward interference mitigation in cellular networks.Comment: 13 pages, 7 figures; IEEE Journal of Selected Topics in Signal
Processing, Special Issue on Signal Processing for Large-Scale MIMO
Communication
Safeguarding Massive MIMO Aided HetNets Using Physical Layer Security
This paper exploits the potential of physical layer security in massive
multiple-input multiple-output (MIMO) aided two-tier heterogeneous networks
(HetNets). We focus on the downlink secure transmission in the presence of
multiple eavesdroppers. We first address the impact of massive MIMO on the
maximum receive power based user association. We then derive the tractable
upper bound expressions for the secrecy outage probability of a HetNets user.We
show that the implementation of massive MIMO significantly improves the secrecy
performance, which indicates that physical layer security could be a promising
solution for safeguarding massive MIMO HetNets. Furthermore, we show that the
secrecy outage probability of HetNets user first degrades and then improves
with increasing the density of PBSs
Transmit Beamforming in Dense Networks-A Review
Communication technology has prospered in manifolds over the last decade. The scarcity of spectrum as well as the demand for higher data rates and increase in capacity has become a matter of concern. Newer technologies have evolved time and again, the latest of which is Long Term Evolution (LTE) and Long Term Evolution Advanced (LTE-A) systems more commonly known as 4G technology. The striking feature of LTE/LTE-A is the deployment of smaller cells (femto cells) in the vicinity of a large macro cells resulting in a dense network. As a result the data rate as well as capacity has increased in manifolds but the detrimental factor is the issue of interference between the various cells. Beamforming provides a solution in removing the issues of interference in dense networks. This paper focuses on the interference scenario in LTE dense networks and gives an overview of different beamforming methods that can provide a solution to the interference problem. Further, a review of several such methods so far proposed in available literature has been presented in this paper.Keywords:LTE/LTE-A, Dense Network, Interference,Beamformin
Throughput and Energy Efficiency for S-FFR in Massive MIMO Enabled Heterogeneous C-RAN
This paper considers the massive multiple-input multiple-output (MIMO) enabled heterogeneous cloud radio access network (C-RAN), in which both remote radio heads (RRHs) and massive MIMO macrocell base stations (BS) are deployed to potentially accomplish high throughput and energy efficiency (EE). In this network, the soft fractional frequency reuse (S-FFR) is employed to mitigate the inter-tier interference. We develop a tractable analytical approach to evaluate the throughput and EE of the entire network, which can well predict the impacts of the key system parameters such as number of macrocell BS antennas, RRH density, and S-FFR factor, etc. Our results demonstrate that massive MIMO is still a powerful tool for improving the throughput of the heterogeneous C-RAN while RRHs are capable of achieving higher EE. The impact of S-FFR on the network throughput is dependent on the density of RRHs. Furthermore, more radio resources allocated to the RRHs can greatly improve the EE of the network
28GHz multiple input multiple output planar antenna for 5G mobile communication
v ABSTRACT Fifth generation (5G) is the next major phase of mobile telecommunications standards beyond the current 4G, which will operate at millimeter-wave frequency band. This thesis presents designs for MIMO planar antennas (single element and arrays at 28 GHz) Based on the best optimized single element patch, antenna array is designed at 28 GHz. An array theoretically offers higher gain compared to single antenna and offers more directive beam. The planar antennas are designed on Rogers RT Duroid with permittivity of 2.2 and the thickness of 0.381 mm. All structures are simulated and optimized using CST software. The performance are analyzed by means of the S parameters and the radiation pattern of the planar antenna. For single element antenna, are well matched at 28 GHz with S11 of -25.54 db in inset feed, and with S11 of -13.53 db in aperture coupled feed. The gain of single element antenna using inset feed is 7.721 db, while the gain of single element antenna using aperture coupled feed is 7.084 db. For 2x1 elements MIMO antenna using different two feeding techniques. The antenna is well matched at 28 GHz with S11 of -17.69 db, S21 of -34.78 db in inset feed, and with S11 of -17.3 db, S21 of -39.03 db in aperture coupled feed. The gain of single element antenna using inset feed is 8.169 db, while the gain of single element antenna using aperture coupled feed is 7.899 db. For 2x2 elements antenna array using aperture coupled feeding techniques. The antenna is well matched at 28 GHz with S11 of -10.2 db. The gain of 2x2 elements MIMO antenna using aperture coupled feed is 10.16 db
Edge Caching in Dense Heterogeneous Cellular Networks with Massive MIMO Aided Self-backhaul
This paper focuses on edge caching in dense heterogeneous cellular networks
(HetNets), in which small base stations (SBSs) with limited cache size store
the popular contents, and massive multiple-input multiple-output (MIMO) aided
macro base stations provide wireless self-backhaul when SBSs require the
non-cached contents. Our aim is to address the effects of cell load and hit
probability on the successful content delivery (SCD), and present the minimum
required base station density for avoiding the access overload in an arbitrary
small cell and backhaul overload in an arbitrary macrocell. The massive MIMO
backhaul achievable rate without downlink channel estimation is derived to
calculate the backhaul time, and the latency is also evaluated in such
networks. The analytical results confirm that hit probability needs to be
appropriately selected, in order to achieve SCD. The interplay between cache
size and SCD is explicitly quantified. It is theoretically demonstrated that
when non-cached contents are requested, the average delay of the non-cached
content delivery could be comparable to the cached content delivery with the
help of massive MIMO aided self-backhaul, if the average access rate of cached
content delivery is lower than that of self-backhauled content delivery.
Simulation results are presented to validate our analysis.Comment: Accepted to appear in IEEE Transactions on Wireless Communication