1
ACP WG-F/19 WP03/
International Civil Aviation Organization
WORKING PAPER / ACP-WGF19/WP-03
AERONAUTICAL COMMUNICATIONS PANEL (ACP)
NINETEENTH MEETING OF WORKING GROUP F
Montréal, Canada 15 – 20 September 2008
Agenda Item3, 5 & 6WRC’11 Ag.It. 14 : Proposed future organization of the 960-977 MHz band forthe aeronautical future radio system , underthe AMACS/ LDACS2 . option
(Presented byEric Allaix)
SUMMARY. The aim of this paper is to proposean architecture (organisation of the band and radius of the cells) for an efficient future use of the 960-977 MHz band by the aeronautical FRS (future radio system ) in order to facilitate the band sharing studies called in by WRC’11 as well as by national considerations, such as compatibility studies with adjacent bands
This paper is presented in ICAO ACP/WGF, since it contains inputs to facilitate the studies of the L band (960-1164 MHz) sharing between the future aeronautical and existing systems operating in that band as well as with systems in adjacent bands.
It should also be presented to ICAO ACP/WG-T since it offers suggestions on this future system architecturewhich should be examined by that group’s experts
ACTION
It is proposed :
- to note this information;
- to take into considerationthese proposal in the future work on this topic;
- to bring it to the attention of ACP/WG T.
Introduction:
The aim of this paper is to propose an architecture(organisation of the band and radius of the cells) for an efficient future use of the 960-977 MHz band by the aeronautical FRS(future radio system )in order to obtainthe largest margin possiblein the budget link.
This paper focuses on the AMACS (L-DACS2)[ref. 1 ] systems with a channelization supporting the highest bit rate per cell (540 kbps for 400 KHzbandwidth occupancy) for air/ground, ground/air and air to air communications.
This paper is presented in ICAO ACP/WGF, since it contains inputs to facilitate the studies of the L band (960-1164 MHz) sharing between the future aeronautical and existing systems operating in that band as well as with systems in adjacent bands. It should also be presented to ICAO ACP/WG-T since it offers suggestions on this future system which should be examined by that group’s experts
Organisation of the band
The first step is to divide the band in three parts:
-one for the A/G and G/A communications in anTMAairspace,
-one for the air to air communications
-one for A/G and G/A en Route communications
In order to make the study take into account the worst case scenario, it is herein proposed to use the time division duplex (TDD) access.
The figure below shows the band partitioning proposed in order to limit risks of interference, under the LDACS-2/AMACS option.
Figure 1 –Band partitioning for aeronautical communications in the 960-977 MHz band
In some regions, notably ITU-R region 1, studies [ref 2] have shown potential interference between mobile base stations operating below 960 MHz band and DME in the band 960-1215 MHz. These interferences come from the aggregate interference created by the base stations transmitting as part of land mobile systems. The higher the aircraft flies, the higher is the aggregateinterferencedue to the increased number of the base stations seen by the aircraft.
The advantage of placingthe TMA communications in a in the adjacent mobile band is to optimize the C/I ratio as :
a)the distance between the aircraft and the ground is shorter, and.
b)the aggregate interference level is less on account of a smaller number of visible base stations
Locatingair-grounden-Route communicationsin the upper part of the band 960-977 MHz allows a largercell radiusfor the same transmission power for both ground and aircraft stations without, , any interference coming from mobile network, as established by the studies made in Europe in preparation to [ref2] report.
The sub-band thus allocated to air-air communication, between those of the other two usages- for the TMA and en-Route environmentcan beconsidered as an adjustable variable thatcan be used to meetTMA or en Route spectrum needs as necessary.
Definition of the cell radius
En route cells case
References [1] and [3] give the characteristics of the FRS. One particular parameter for the calculation of the link budget, reproduced hereafter for convenience sake, is the co-channel interference ratio, with interference coming from outer cells of same frequency, as illustrated in the figure below, also called self-noise. In order to minimize the impact of this parameter it is proposed to define the minimum cell radius for the en route network, such that the outer cell interference at the same frequency is blocked by the earth horizon (calculated with a 4/3 earth radius)
With the frequency plan described in the figure 2, extracted from ref [1] the distance from the interfered aircraftto its ground station is the wanted signal path dw = R.The distance from the interfered aircraftto its interferer on the same channel is the interfered signal path di = 4R.
Figure 2– Co-channel interference in a 12 channels re-use pattern
It.Nr / Item / value / Unit / Uplink (To a/c) / Dnlink (fr. a/c) / Comments1 / Transmitter's output: 100 on-ground & 50 W on-board aircraft / dBW / 20,0 / 17,0
2 / cable/guideanddiplexer insertion losses / 2,0 / 3,0
3 / Antenna gain, on-ground and on a/c / dBi / 8,0 / 0,0
4 / Transmitted EIRP / dbW / 26,0 / 14,0
5 / Carrier frequency in MHZ / 968
6 / Free space propagation losses at range of, in NM / 70 / -134,4 / -134,4
7 / Receivingantenna gain / dBi / 0,0 / 8,0
8 / Polarisation losses / dB / 0,0 / 0,0
9 / cable/guideanddiplexer insertion losses / dB / 3,0 / 2,0
10 / C, received carrier level / dBW / -111,4 / -114,4
11 / Receiver noise factor / dB / 7,0 / 7,0 / assumed value
12 / No , receiver noise density / dBW/Hz / -194,0 / -195,0
13 / C/No, thermal / dB-Hz / 82,6 / 80,6
14 / Transmit & receivebandwidth, in KHz / 400
15 / C/Ic co-channel interference ratio / dB / 12,0 / 12,0
16 / Associated Interference / dBW / -123,4 / -126,4 / 20log[4/1];(10)- [C/I]
17 / Io : equivalent interference density / dBW/Hz / -179,4 / -182,4 / (15)- 10log{(14)*1000}
18 / Resulting Io+No / dBW/Hz / -179,3 / -182,2 / 10log{10^(12)/10+10^(16)/10}
19 / Delta No due to Io, / dB / 14,7 / 12,8 / (17)-(12)
20 / Ground Multipath loss, / dB / 5,0 / 5,0 / From Annex 10, DME guidance section
21 / RSS'ingof Delta No andGM loss / dB / 15,5 / 13,7
22 / Resulting C/(No+Io) / dB HZ / 67,0 / 66,8 / (13)-(20)
23 / Assumed Eb/No / 3,0 / dB / @BER 10 E-4
24 / Gross (transmit ) rate, Kbps / 540,0
24 / FEC rate, / 0,77 / Inferred from ref [4]
25 / Datarate , in Kbps / 416
26 / Required C/No / dBHz / 59,2 / 59,2 / (22)+10log{(24)*1000}
27 / Margin, / dB / 7,9 / 7,7 / (21)-(25)
Table 1 : Typical AMACS/LDACS2 link budget with70 NM cell rangerepresentativeof an en-route situation
The distance to the radio horizon from a station in an aircraft isgiven by the formula, quoted in Annex 10, Vol. 5 :
(1)
where D= distance in nautical miles;
h= height of the aircraft station above earth;
Typically, the highest level for an aircraft in en-route phase is about 45,000 feet. In that case by applyingthe above equation the distance of the radio horizon equals 261 NM.
Figure 2givesthe interfered pathdistance as di = 4R, hence the C/I ratio computed as 20 Log(4/1).
So by imposing a minimum size of about 70 NM for each cell radius (dw) in the en-routecellular network,corresponding to an unwanted or interfered path di greater that the radio horizonwe ensure that no interfering co-channel will occur , i.e. the C/I ratiobecomes infinite.Usingthe above link analysis and replacing the 12 dB C/Ivalue of row 15 in the table above by say 60 dB - representative of an infinite C/I ratio for practical calculation purpose-improves the budget link margin (row 27)byabout 10.5and 8,7dB, in the up- and downlinksrespectively. Beyond that distancethesame reused frequencyinterferenceatrange 4x dwcan be safely assumed as being nil, sincebeyond the radio horizonwith a significant margin. And theup and downlinkmargins become:
Uplink (To a/c) Margin / Dnlink (fr. a/c) MarginCommunicationrange R (cell size)in NM / 150 / 11,8 / 9,8
200 / 9,3 / 7,3
250 / 7,3 / 5,3
Note: 1° ) The calculation of improvement in the link margin is done for an FRS cell radius of 70 NM, because it is the smallest cell sizefor which same frequencycells could potentially interfere., since the undesiredsignal at range diisjustabove the radio horizon for an aircraftat flight level of 45,000 feet
2°)the overall margin improvementis less thatthe expected reduction of overallnoisesince it is calculated asa change tothe ratio C/(total noise), obtained by RSS’ing the negative impact of a 5 dB ground multipath error on Cand the positive impact of the sum No+Io going down to No.
TMA cells case
In order to optimize the frequency reutilization, it is proposed to limit the size of the TMA’s network cells to a maximum radius of 50 NM.
It has to be noted that the operationaltransition from the TMA to the en -Route network, with two different sets of frequencies,has to be done between the levels 200 and 240.
It was already demonstrated that a cellular scheme will provide the adequate configuration to the airspace controlled by ATC. The size of the cell should (and could) be modulated according to the traffic. As a first assessment, three operational environments should be distinguished:
- En-Route low density cells, with a range of about the optical range 250NM. For lower airspace of the same type smaller cells could be used taking into account the line of sight coverage limitations
- En-Route High Density cells, with a minimum range of about 70 NM
- TMA cells, with a range of maximumrange of 50NM modulated by the size of the airport
Taking into account these different constraints the future architecture could be represented in Europe by the following figure:
Figure 3 – example of such cellular deployment over the ECAC area
Discussion:
Imposingsystem architecturecell size constraint of70 NM min for en-Route and 50 NM max for TMA networksneeds to be validated with respect to FRS loadingrequirements in terms of peak instantaneous aircraftcount(PIAC) and cell communication volume in kbps. Reference in this matter is the ICAO/ACP COCR(communication operatingconcepts and requirements) phase 2 (see ref [4]), as quotedin reference [5]:
-Recognizinga cell peak aircraft loading is reached whenan COCR identified “large”en-Route airspace can be entirely contained ina single cell , the maximumPIAC to be served by the FRSis 204. Using COCR phase 2 scenarios ref[5] has determined that the cell communication load is about 190 Kbps . This is a prioricompatible with the TDD architecture assumed in this paper noting that with an FEC rate efficiency of 0.77 and 540 Kbps gross communication rate (with 400 KHz spectrum occupancy per cell frequency) this leads toa maximum of user’s rate of 416 kbps, to be shared between the up and downlink communication traffic.
-The ability todesign a TMA cellular networkwith max cell size of 50 NM in region like Europecentral core area (and possibly the US North-Eastern seaboard area)will depend on the feasibility todistribute each of the 12 frequencies of the cells pattern to neighboring TMAs, while avoiding any two adjacent cellsusing the same frequency.
-Assignment to TMA cell of a size less that 50 NM will impose transitioning from the TMA to the en-Route frequency sets ata lower flight levels than the 20,000 feet mentionned above
Conclusion
This paper show two ways to optimize the use of the lower part (960-1164 Mhz) of the DME band allocated to the AM(R)S at the last WRC.:
i) sub-banding the available band between 960 and 977 MHzinto TMA , en-Route and air-aircellular network assignment
ii) imposing a min size of 70 NM for the en-Route and a maximum size of 50NMfor the TMA network
Underthe assumption that suchsystem architecture choiceswill bevalidated ,, these elements will hopefully help to achieve the different studiesthe aviation community has to complete at national and ICAOlevelssome withinthe framework of WRC’11 A.I. 1.4.
References:
- AMACS presentation,ACP/WG-T-1-WP07
- ECC Report 96 : compatibility between UMTS 900/1800and systems operating in adjacent bands
- ACP-WGF18/WP-13 :Heuristic assessment of the compatibility between the aeronautical FRS and radionavigation DME/TACAN in the band 960-1164 MHz
- Communications Operating Concept and Requirements for the Future Radio System, Eurocontrol, v2, January 2007., also available at :
- ACP-WGT-1 WP08 AMACS performance anlysis V1_0