1. Frequency Reuse Trade-off and System Capacity in Small Cell Networks in the Millimetre Wavebands
Emanuel S. B. Teixeira, Sofia C. Sousa, Rui R. Paulo and Fernando J. Velez
Instituto de Telecomunicações, Universidade da Beira Interior, Faculdade de Engenharia, Covilhã, Portugal
Introduction and Motivation
The millimetre wavebands can provide high bit rates in short range applications. Although, generally they suffer from higher path loss but also may have the advantage of additional O2 absorption to reduce interference. In real environments, cellular mobile connections are simultaneously affected by noise and co-channel interference, also, the understanding of the variation of the carrier-to-noise-plus-interference ratio (CNIR) for mobile communications. This work performs a comparison of the CNIR and the equivalent supported throughput among different frequency bands, for regular shaped cellular topologies, like main roads or highways. In fact, it is straightforward to show that, in the downlink (DL), the worst-case bounds from a Manhattan grid in terms of CNIR are similar to the ones from a linear cellular topology. Study of cell coverage and propagation models, analysis of the influence path loss by oxygen and rain at 60 GHz, study of carrier-to-noise-plus-interference ratio, and underlying throughput, was shown. Assuming the use of LTE, bandwidth of 20MHz, 100 resource blocks (100 RBs), Xσ= 0.04 for 28 GHz and Xσ= 4.4 for 38 GHz, 60GHz and 73 GHz.
Variation of the specific oxygen and H2O attenuation as a function of the frequency
Worst-case bounds from a Manhattan grid in terms of CNIR are similar to the ones from a linear cellular topology
Carrier-to-interference ratio
Parameters considered in the analysis
Variation of C/I with R (the coverage length) while considering different reuse factors, rcc=D/R=2K, where K is the reuse pattern
Power
0 dBW
Transmitter gain
3 dBi
Receiver gain
0 dBi
Carrier
20 MHz
Noise Figure
7 dB
Height (Base Station)
7 m
Height (Mobile User)
1.5 m
DL interference topology with one single cell of interference
Propagation exponent are g=2.1 for 28 GHz,
and g=2.3 for 40 GHz, 60 GHz and 73 GHz
CNIR and Physical Throughput (Rb)
For the shortest Rs (R = 25 m), the highest MCS are used in a large percentage of the cell coverage areas, for the longest coverage distances the highest MCS is only used for less than 10 or 20 % of the cell are.
Areas of the coverage rings where a given value of physical throughput
Variation of the CNIR and throughput with d for 28 GHz, 38 GHz, 60 GHz, 73 GHz, for R= 25m, 50m for Xσ =0
Normalized transmitter power as a function of cell radius
Variation of the CNIR and throughput with d for 28 GHz, 38 GHz, 60 GHz, 73 GHz, for R= 25m, for Xσ ≠0
Implicit formulation that maps the CNIR into the values of the Rb through the corresponding MCS, where the index J represents the MCS index
Analysis of PHY Troughout and System Capacity with LTE parameters adapted to Millimetre Waves
Conclusion - High bit/data rates can be supported in small cells with short-range coverage while assuming the MCSs from LTE-A. The carrier-to-noise-interference ratio C/I is increasing with R and is clearly higher when the co-channel reuse factor D/R raises from 4 to 6, and from 6 to 8.
For Xs = 0, at 28 GHz, although lower system capacity is achieved for very short coverage distances, of the order of m, in comparison to the GHz frequency bands, the supported throughput increases for longer coverage ranges, and is clearly more favourable for the lowest frequency band.
3D view graph for the supported throughput mapped into MCS (with 29 levels, in the zz axis), for Xσ=0, 28 GHz, R = m and m 1 ≤ d ≤ R.
Supported throughput for 28 GHz, 38 GHz, 60 GHz, 73 GHz for R=500 m, for Xσ = 0 and Xσ ≠ 0
Supported throughput higher for 28 GHz. 60 GHz frequency band only performs better than the 73 GHz band for Rs up to circa 100 m. Reduction of the coverage at 60 GHz due to the O2 attenuation.
Performance of the PHY throughput (Rb) mapped into MCS (with 29 levels, in the zz axis); cell radii in yy axis, normalized in the xx axis.
These surfaces shown decrease in the MCSs while the distance varies inside the cell, faster for longer Rs.
The supported throughput is higher for the 28 GHz frequency band compared to other frequencies.
For Xs ≠ 0, the behavior is similar to the previous ones.
Results are clearly more optimistic for X = 0 compared to the case X ≠ 0 (when the fading margin is considered for coverage purposes)
This research is supported by CREaTION, COST CA 15104, ECOOP and Bolsa BID/ICI-FE/Santander Universidades-UBI/2017.
Encontro com a Ciência e Tecnologia em Portugal, 3 a 5 de julho 2017.