technical comparison between 400 and 700 mhz
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Technical Comparison Between 400 and 700 MHzTRANSCRIPT
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FM49(13)028
FM 49 Radio Spectrum for BB PPDR
Oslo, 13 June - 14 June 2013
Date issued: 6 June 2013
Source:Cassidian, Alcatel-Lucent
Subject:Technical comparison between 400 and 700 MHz
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Proposal: FM PT49 is invited to consider this contribution as a contribution for report B, especially for the completion of the section dedicated to the technical comparison between the two options retained for BB PPDR WAN.Note that some alignments with existing and similar considerations into report A (now ECC report 199) may be necessary.
IntroductionThis contribution aims at delivering inputs for FM49 Report B, especially for the section dedicated to frequency options. At this stage of the contribution, it has to be noticed that some alignments with existing FM49 outcomes, especially with regards to the ECC Report 199 may be necessary.AssumptionsThis section introduces various link budgets assumptions to compare the coverage of 400 and 700 MHz cells using the LTE technology.Link Budget ParametersThe considered LTE system is using a 5 MHz channel width, i.e. 25 resource blocks (RBs) of 180 kHz each. The uplink transmission is limited to 5 resource blocks per user equipment (UE), which represents a reasonable trade-off between throughput, power spread and bandwidth noise increase.Base stations (BS) antenna gains have been retrieved from real products (Kathrein) relevant with the targeted mobile applications, especially regarding their capability to support MIMO transmission scheme for the two considered frequency bands (2 Tx antennas and 2 Rx antennas).User equipment has been considered as vehicle mounted equipment as this is representing significantly the PPDR usages. Considered car installation allows SIMO transmission scheme in uplink and MIMO transmission in downlink (1 Tx antenna and 2 Rx antennas). Antenna gains have been set to 2dBi, a typical value for car antennas in both 400 and 700 MHz ranges. By analogy with narrowband systems, UE transmission power has been set up at 5 W (37dBm) in order to allow significant uplink throughput. Please note that regulation considerations may lead to decrease such a transmission power as for Band 14 (US PPDR Frequency band, adjacent to commercial LTE band) where the maximum has been set at 31dBm (1.2W), or even at lower level. Ultimately, allowed maximum transmission power in 400 and 700MHz may be different depending on co-existing systems in adjacent bands.As LTE is designed to operate with a frequency re-use pattern of 1, extra-cell interferences are taken into account by considering a noise rise margin independent of the frequency band but linked to the network load, the SINR (Signal to Interference and Noise Ratio) targeted at the cell edge and the type of antenna configuration. In this paper, the noise rise has been set at 3 dB which represents a typical value for tri-sectorial roll-out.SINR has been set at -3.5 dB as coverage is clearly the design driver for PPDR but also to be consistent with the former noise rise assumption.To ease the comparison, no other margin as for confidence level has been considered. In this case, where maximum coverage is targeted, the LTE system is not limited by interferences but the effect of interferences is almost equivalent to the effect of noise at the edge of coverage.Last but not least, link budgets presented below are balanced link budgets. This has been achieved by limiting the transmission power of the Base Stations to 25 W whereas 60 W are reachable values at both 400 and 700 MHz. The impact of reducing Terminal maximum output power was also considered.
Discussion on Diversity gains The question of diversity gain at terminal side has arisen in former FM49 contributions and discussions. For a vehicle installation the system benefits from full diversity gains since, in this case, the two receiving antennas can be sufficiently separated to ensure a good decorrelation of the fading observed on each of them. The question is more complex in the case of a handheld, i.e. a Smartphone-like PPDR terminal.Two different types of diversity can be considered. The first one is the space diversity where antennas are separated in distance (at least 1 lambda); the signals seen on each antenna are experiencing different and independent fading conditions. The second one is the polarization diversity; since the signals during the reflections on obstacles are depolarized, the orientation of the received wave is changed in a random manner. This creates behaviour of the fading that is independent in two orthogonal directions (let say vertical one and horizontal one). So if the antennas of the terminal are orthogonal, then there is a gain of polarization diversity.Space diversity is due to the fact that a terminal is operating in an environment of interference fringes which are created by reflection on the obstacles surrounding the terminal. The characteristics of these interference fringes are quite complex, and for a supposed regular distribution of obstacles around the terminal, a moving terminal is experiencing a Rayleigh fading. In order to estimate the correlation of the fading received by the 2 antennas, we use the formula of the correlation of the fading, depending on the delay of reception between the 2 antennas. The diversity correlation is derived from this correlation formula. The correlation depends only on the distance between the antennas and the wavelength. The methods to determine the correlation level between the two antennas is provided in Annex 1 to this contribution.It can be observed from the considerations provided in Annex that, in the range of interest, i.e. for a BER before channel decoding between 1% and 10%, that at 700 MHz there is a relative decorrelation gain compared to 400 MHz of approximately 0.5 to 1dB. After channel decoding but also considering that LTE is using advanced repetition mechanism, the relative gain is expected to be similar. Moreover this gain will impact the available throughput at a given distance. This impact is expected to represent approximately 7% difference for the throughput.In addition to this space diversity gain, there is polarization diversity gain. This gain appears if the two antennas are, at least partly, orthogonal. This can be the case for example with patch antennas. This polarization diversity gain adds to the antenna gain. The polarization diversity gain is not dependant with the frequency. It depends on the geometry of the antennas.To summarize, space diversity gain difference can be neglected (very limited impact on available throughput) whereas polarisation diversity gain is not going to be considered into the following sections as providing similar gains at 400 and 700 MHz for smartphones.Link Budgets400 MHz Downlink Link BudgetTransmitter
BS Tx Power (2 PA)47dBm
BS Antenna Gain14.5dBi
BS Cable Loss2dB
EIRP59.5dBm
Receiver
UE Antenna Gain2dBi
UE Cable Loss2dB
Thermal Noise-174dBm/Hz
UE Noise Figure7dB
Total Thermal Noise (25 RB)-100.5dBm
Target SINR-3.5dB
System Gain 163.5 dB
Margin
Noise Rise3dB
Path Loss 160.5dB
400 MHz Uplink Link BudgetTransmitter
UE Tx Power (1 PA)37dBm
UE Antenna Gain 2dBi
UE Cable Loss2dB
EIRP37dBm
Receiver
BS Antenna Gain14.5dBi
BS Cable Loss2dB
Thermal Noise-174dBm/Hz
BS Noise Figure4dB
Total Thermal Noise (5RB)-115.5dBm
SINR Target-3.5dB
System Gain163dB
Margin
Noise Rise3dB
Path Loss 160dB
700 MHz Downlink Link BudgetTransmitter
BS Tx Power (2 PA)47dBm
BS Antenna Gain17.7dBi
BS Cable Loss2dB
EIRP62.7dBm
Receiver
UE Antenna Gain2dBi
UE Cable Loss2dB
Thermal Noise-174dBm/Hz
UE Noise Figure7dB
Total Thermal Noise (25 RB)-100.5dBm
SINR Target-3.5dB
System Gain 166.7 dB
Margin
Noise Rise3dB
Path Loss 163.7dB
700 MHz Uplink Link BudgetTransmitter
UE Tx Power (1 PA)37dBm
UE Antenna Gain 2dBi
UE Cable Loss2dB
EIRP37dBm
Receiver
BS Antenna Gain17.7dBi
BS Cable Loss2dB
Thermal Noise-174dBm/Hz
BS Noise Figure4dB
Total Thermal Noise (5RB)-115.5dBm
SINR Target-3.5dB
System Gain166.7dB
Margin
Noise Rise3dB
Path Loss 163.7dB
Annex 2 proposes additional 700 MHz link budget for 31 and 27 dBm UE transmission power.DiscussionNumber of sitesThe tables above illustrates that the path loss difference between 400 MHz and 700 MHz is in the range of 3.5 dB (considering 5W user equipments) where as the attenuation difference is in the range of 6 dB referring to Okumura-Hata model. It remains 2.5dB in favor of 400 MHz.As a consequence, the coverage of a given area is going to require 40% more sites at 700 MHz than at 400 MHz considering that the propagation attenuation is following a d-3.5 rule.Considering omnidirectional antenna which is making sense for rural roll-out, path losses are similar and even in favor of 400 MHz as the current choice of omnidirectional antenna at 700 MHz is really limited. Under those assumptions (similar path losses), the coverage of a given area will require 2.2 time more sites at 700 MHz than at 400 MHz.If the UE transmission power is limited to 31 dBm in 700 MHz band (analogy with US Band14), the difference between the two frequency bands is increasing from 2.5dB to 8.5dB, i.e. requiring more than 3 time more sites at 700 MHz. Limitation to UE transmission power at the level used into carrier networks (23 dBm) will lead to an even higher ratio (in the range of 9). Handheld considerationsConcerning handhelds, their coverage will be much more limited due to their lower transmitted power. One can expect only to have coverage in dense or very dense areas for handhelds.It can be noticed that, in dense areas where the design is capacity driven, the limiting factor is not noise but interference. Then there is, in this case, no real difference between 700 MHz and 400 MHz. It can be noted that even higher frequencies would also be acceptable for such limited coverage.SummaryAs long as the network design is driven by coverage, the 400 MHz band is keeping the advantage of a better propagation compared to the 700 MHz band. As a consequence the 400 MHz is clearly the best option to leverage existing sites and avoid costly additional site constructions.In this case the key element is clearly the transmitted power of the user equipment; under realistic conditions (UE power limited to 31dBm at 700 MHz), this would lead to 3 time more sites with 700MHz..When the deployment is driven by capacity, i.e. in very dense areas, the frequency is not the main determining factor.
Annex - 1Determination of Handheld Terminals Antennas correlation
It is well-known that the correlation between antennas is expressed by the formula:
,where d is the distance between the 2 antennas, is the wavelength, and J0 is the Bessel function of the first kind and of zeroth order.
The following figure shows the value of the correlation as a function of the ratio :
In a Smartphone-like PPDR terminal, the maximum distance we can expect between 2 equal gain antennas, in the best conditions, would be around 6 cm.It can be observed that, at 450 MHz, the wavelength is 66.67 cm. This gives a ratio of the distance between antennas and the wavelength of 9 %. The corresponding correlation factor () is 0.92.At 750 MHz, the wavelength is 40 cm. This gives a ratio of the distance between antennas and the wavelength of 15%. The corresponding correlation factor () is 0.82.When two antennas are partially correlated (the fading that they receive are partially correlated), they are equivalent to two antennas fully decorrelated but not having the same gain. The gain of the equivalent (and decorrelated) antennas are respectively:
,where the gain of the original antennas is supposed to be 0 dBi.So, at 450 MHz, the two antennas are equivalent to two decorrelated antennas with respective gains: 2.66 dB and -8.14 dB.Similarly, at 750 MHz, the two antennas are equivalent to two decorrelated antennas with respective gains: 2.23 dB and -4,84 dB.The comparison of the space diversity effect created with the two antennas at 450 MHz and at 750 MHz is shown in the next figure. This figure shows the performance in term of Bit Error Rate (BER), before channel decoding, in a single path Rayleigh fading propagation case.
It can be observed that, in the range of interest, i.e. for a BER before channel decoding between 1% and 10%, that at 750 MHz there is a relative gain compared to 450 MHz of 0.5 to 1dB. After channel decoding but also considering that LTE is using advanced repetition mechanism, the relative gain is expected to be similar. Moreover this gain will impact the available throughput at a given distance. This impact is expected to represent approximately 7% difference for the throughput.
Annex - 2Additional 700 MHz Downlink Link BudgetTransmitter
UE Tx Power (1 PA)373123dBm
UE Antenna Gain 2dBi
UE Cable Loss2dB
EIRP373123dBm
Receiver
BS Antenna Gain17.7dBi
BS Cable Loss2dB
Thermal Noise-174dBm/Hz
BS Noise Figure4dB
Thermal Noise (5RB)-115.5dBm
SINR Target-3.5dB
System Gain166.7160.7152.7dB
Margin
Noise Rise3dB
Path Loss 163.7157.7149.7dB
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