B-AMC Project Deliverable D1 - Eurocontrol

Unrestricted 1.2 R/0036/002 14 August 2007 Issue 1.0 Specific Context The project, of which this report is part, will evaluate the possibility of implementing a system using similar technology to B-VHF but in the Lband of 960 – 1164 MHz. The generic name given to the system is Broadband - Aeronautical Multi-Carrier Communication (B-AMC). At the project kick-off meeting, EUROCONTROL suggested that Work Package 1 (WP1) of this project should investigate three options with regard to the spectrum that could be used for the B-AMC technology. Those options, listed in the order of preference expressed by EUROCONTROL, are described below. 1.2.1 Option 1 Study the feasibility of utilising spectrum between successive Distance Measuring Equipment (DME) channels for B-AMC. This would allow for BAMC frequency planning that is ―independent‖ from DME planning. If ―enough‖ spectrum is available, the B-AMC would be deployed as an ―inlay‖ system in the L-band (960 - 1164 MHz). 1.2.2 Option 2 If option 1 proves to be not feasible, study the feasibility of assigning frequencies to B-AMC channels in areas where they are not used locally by DME. This would require the establishment of a relationship between potential B-AMC assignments and existing DME assignments. 1.2.3 Option 3 If neither option 1 nor option 2 proves to be feasible, investigate the feasibility of utilising the lower part of the band (960 – 978 MHz) for BAMC. In that case, inference with the Global System for Mobile Communications (GSM), which is operated in the lower adjacent band, would need to be considered. 1.3 Objectives of Work Package 1 The main objective of WP1 is to determine whether there is sufficient spectrum available in the 960 – 1164 MHz band to allow the proposed BAMC technology to operate without causing harmful interference to, or receiving harmful interference from, other systems in the band. To meet the above objective, it has been proposed that the following tasks are required: Inspect the characteristics (spectrum) of the DME signal-in-space for both uplink and downlink DME transmissions; Examine the current DME channel allocation plan and provide comment upon the expected future DME environment; B AMC Project Deliverable D1 Issue 1 0.doc 3 Unrestricted

Unrestricted R/0036/002 14 August 2007 Draft 1.0 Determine and quantify the amount of available spectrum for the BAMC system implementation assuming dense (worst-case) DME channel deployment; Identify the position (with respect to nominal DME channels) of any available spectrum blocks. B AMC Project Deliverable D1 Issue 1 0.doc 4 Unrestricted

Unrestricted 2 DME System Overview 2.1 Types of DME R/0036/002 14 August 2007 Issue 1.0 There are two types of DME, namely DME/N (where the N stands for narrow spectrum characteristics) and DME/P (where the P stands for precise distance measurement). DME/P is an integral part of the Microwave Landing System (MLS) for aircraft approach, landing and missed approach operations. Thus, DME/P must be capable of providing high accuracy range information in a potentially severe multipath environment such as that encountered during landing operations. The accuracy required (30 metres) for such operations is at least an order of magnitude better than that provided by DME/N systems. However, there are very few, if any, DME/Ps in operation. This is mainly because there are very few MLS in operation, and the DME/P was designed to work specifically with MLS. However, in the future we may see an expansion in the use of MLS, with possibly a corresponding increase in the use of DME/P. For this reason, it would be inappropriate to discount DME/P from this study at this time. When the standards for DME were written, they included provision for a DME/W system (where W stands for wide spectrum characteristics). However, in the latest version of the standards, all reference to DME/W has been removed. DME/W is no longer operated and as such can be discounted from this study. 2.2 Functional Overview The DME system comprises two main components; an interrogator and a transponder. The interrogator is located on the aircraft and the transponder is ground-based. The interrogator and transponder have similar main functional elements, each having an encoder, transmitter, receiver and decoder. A simplified process flow diagram for a DME system is given in Figure 2. B AMC Project Deliverable D1 Issue 1 0.doc 5 Unrestricted

Unrestricted R/0036/002 14 August 2007 Draft 1.0 Aircraft-Based Interrogator Decoder Output Receiver Calculation Encoder Ground-Based Transponder Transmitter Transmitter Encoder Receiver Decoder Figure 2: Simplified Process Flow Diagram for a DME System The purpose of the DME system is to calculate how far an aircraft is from a selected ground transponder. The interrogator interrogates a single transponder which then transmits a reply following a calibrated fixed time delay (shown in Table 1). The airborne unit then computes the slant range to that ground facility by measuring the elapsed time between the interrogation and the reception of the transponder reply. The measured range is then provided to the pilot and other aircraft systems, as required. Each interrogation consists of a pair of pulses. The spacing of the pulses defines the ‗code‘ of the channel, in accordance with Table 1. The code, along with the transmit frequency, defines the operating channel, thereby allowing the interrogations to be addressed to a specific ground facility. Similarly, the transponder reply consists of a pair of pulses with a code and frequency corresponding to the channel in use, thereby allowing the airborne unit to distinguish desired ground facility transmissions from those of other transponders operating on different channels that are within line-of-sight of the interrogator. The spacing of reply pulses is in accordance with Table 1. The reply frequency of the channel is different to the interrogation frequency, being offset by 63 MHz. B AMC Project Deliverable D1 Issue 1 0.doc 6 Unrestricted

Unrestricted Channel X Y Operating mode Time Delay (µs)1 Reply 1st pulse timing 2nd pulse timing DME/N 12 12 50 50 DME/P IA 12 12 50 - DME/P FA 18 12 56 - DME/N 36 30 56 50 DME/P IA 36 30 56 - DME/P FA 42 30 62 - - - - - DME/P IA 24 24 50 - DME/P FA 30 24 56 - - - - - DME/P IA 21 15 56 - DME/P FA 27 15 62 - DME/N Z Pulse pair spacing (µs) Interr. DME/N W R/0036/002 14 August 2007 Issue 1.0 Table 1: DME Channel Codes and Pulse Delays The DME interrogator and transponder are similar in that both must identify valid DME signals by using the three discriminates of pulse duration, frequency and code. The frequency and code of interrogations and replies define the operating channel. The pulse duration check is used to discriminate DME pulses from pulses from other sources. Figure 3 shows the timing of interrogation and reply cycles for X and Y channels. 1 When the DME is associated only with a VHF facility, the transponder fixed time delay is measured between the leading edge of the second pulse of the interrogation and the leading edge of the second pulse of the reply. When the DME is associated with an MLS facility, the transponder fixed time delay is measured between the leading edge of the first pulse of the interrogation and the leading edge of the first pulse of the reply. B AMC Project Deliverable D1 Issue 1 0.doc 7 Unrestricted

Unrestricted R/0036/002 14 August 2007 Draft 1.0 X-Channel Timing 12µs Interrogation SDES* SDES Decoder Delay Dead Time ( 60µs) 50µs Delay Time 12µs Reply Y-Channel Timing 36µs Interrogation SDES* SDES Decoder Delay Dead Time ( 60µs) 56µs Delay Time 30µs Reply *Short Distance Echo Suppression (SDES) is not implemented by all transponders and its duration, where implemented, may be different to that indicated in the diagram. Figure 3: Timing of Pertinent Events for X and Y-channel Operation W channels use the same frequencies as X channels and Z channels use the same frequencies as Y channels. For these same frequency / different code combinations, the same planning rules apply as for same frequency / same code assignments. The desired channel should always have an 8 dB advantage over all undesired channels. Note that W channels are not the same as DME/W. DME/W was a type of DME that is no longer operated. W channels, along with Z channels, are defined by the spacing between the pulses of interrogations and replies. These channels are assigned exclusively for use by DME/P systems. B AMC Project Deliverable D1 Issue 1 0.doc 8 Unrestricted

Unrestricted 3 R/0036/002 14 August 2007 Issue 1.0 DME Standards The standards and recommended practices for aeronautical radionavigation aids, including DME, are defined in ICAO Annex 10 Volume 1 [Reference B]. This section provides extracts from ICAO Annex 10 that are pertinent to this study. References to the sections from which the information was taken are shown in square brackets. 3.1.1 Characteristics of the Transmitted DME Signal 3.1.1.1 DME Pulse Shape and Spectrum Figure 4: DME Pulse Envelope B AMC Project Deliverable D1 Issue 1 0.doc 9 Unrestricted

Unrestricted R/0036/002 14 August 2007 Draft 1.0 Figure 5: DME Virtual Origin The following definitions [3.5.1] are used in the specification of the pulse shape and spectrum: Pulse rise time: The time as measured between the 10 and 90 per cent amplitude points on the leading edge of the pulse envelope, i.e. between points a and c on Figure 4. Pulse decay time: The time as measured between the 90 and 10 per cent amplitude points on the trailing edge of the pulse envelope, i.e. between points e and g on Figure 4. Pulse amplitude: The maximum voltage of the pulse envelope, i.e. point a in Figure 4. Pulse duration: The time interval between the 50 per cent amplitude point on leading and trailing edges of the pulse envelope, i.e. between points b and f on Figure 4. Virtual origin: The point at which the straight line through the 30 per cent and 5 per cent amplitude points on the pulse leading edge intersects the 0 per cent amplitude axis (see Figure 5). The following criteria apply to all radiated pulses: [3.5.4.1.3] B AMC Project Deliverable D1 Issue 1 0.doc 10 Unrestricted

Unrestricted R/0036/002 14 August 2007 Issue 1.0 For DME/N, pulse rise time shall not exceed 3 microseconds. Pulse duration shall be 3.5 microseconds plus or minus 0.5 microseconds. Pulse decay time shall nominally be 2.5 microseconds but shall not exceed 3.5 microseconds. The instantaneous amplitude of the pulse shall not, at any instant between the point of the leading edge which is 95 per cent of maximum amplitude and the point of the trailing edge which is 95 per cent of the maximum amplitude, fall below a value which is 95 per cent of the maximum voltage amplitude of the pulse. To ensure proper operation of the thresholding techniques, the instantaneous magnitude of any pulse turn-on transients which occur in time prior to the virtual origin shall be less than one per cent of the pulse peak amplitude. Initiation of the turn-on process shall not commence sooner than 1 microsecond prior to the virtual origin. For DME/P, pulse rise time shall not exceed 1.6 microseconds. For the Final Approach (FA) mode, the pulse shall have a partial rise time of 0.25 plus or minus 0.05 microseconds. With respect to the FA mode and accuracy standard 1, the slope of the pulse in the partial rise time shall not vary by more than plus or minus 20 per cent. For accuracy standard 2, the slope shall not vary by more than plus or minus 10 per cent. Recommendation.— Pulse rise time should not exceed 1.2 microseconds. The following applies to the transponder reply signal: [3.5.4.1.3] The spectrum of the pulse modulated signal shall be such that during the pulse, the effective radiated power contained in a 0.5 MHz band centred on frequencies 0.8 MHz above and 0.8 MHz below the nominal channel frequency in each case, shall not exceed 200 mW, and the effective radiated power contained in a 0.5 MHz band centred on frequencies 2 MHz above and 2 MHz below the nominal channel frequency in each case, shall not exceed 2 mW. The effective radiated power contained within any 0.5 MHz band shall decrease monotonically as the band centre frequency moves away from the nominal channel frequency. The following applies to the interrogation signal: [3.5.5.1.3] The spectrum of the pulse modulated signal shall be such that at least 90 per cent of the energy in each pulse shall be within 0.5 MHz in a band centred on the nominal channel frequency. B AMC Project Deliverable D1 Issue 1 0.doc 11 Unrestricted

Unrestricted R/0036/002 14 August 2007 Draft 1.0 The following guidance material relating to the pulse spectrum measurement is provided: [Attachment C Section 7.1.11] The effective radiated power contained in the 0.5 MHz measurement frequency bands [around the first and second adjacent channels] can be calculated by integrating the power spectral density in the frequency domain or, equivalently, by integrating the instantaneous power per unit time in the time domain using the appropriate analogue or digital signal processing techniques. If the integration is performed in the frequency domain then the resolution bandwidth of the spectrum analyser must be commensurate with the 5 per cent duration interval of the DME pulse. If the integration is performed in the time domain at the output of a 0.5 MHz five pole (or more) filter then the time sample rate must be commensurate with the pulse spectrum width. 3.1.1.2 Transponder Peak Power Output [3.5.4.1.5.2] For DME/N, the peak equivalent isotropically radiated power shall not be less than that required to ensure a peak pulse power density of minus 89 dBW/m2 under all operational weather conditions, at any point within the specified coverage. Recommendation.— The peak effective radiated power should not be less than that required to ensure a peak pulse power density of approximately minus 83 dBW/m2 at the maximum specified service range and level. [3.5.4.1.5.3] For DME/P, the peak equivalent isotropically radiated power shall not be less than that required to ensure the following peak pulse power densities under all operational weather conditions: a) b) c) d) 3.1.2 minus 89 dBW/m2 at any point within the coverage specified in 3.5.3.1.2, at ranges greater than 13 km (7 NM) from the transponder antenna; minus 75 dBW/m2 at any point within the coverage specified in 3.5.3.1.2, at ranges less than 13 km (7 NM) from the transponder antenna; minus 70 dBW/m2 at the MLS approach reference datum; minus 79 dBW/m2 at 2.5 m (8 ft) above the runway surface, at the MLS datum point, or at the farthest point on the runway centre line which is in line of sight of the DME transponder antenna. Characteristics of the DME Receiver The standards specified in ICAO Annex 10 refer almost exclusively to intra-system performance. Therefore, the standards do not specify the requirements for receiver performance in the presence of non-DME signals. For example, in the section titled ―Protection against interference‖ [3.5.4.2.10], which is actually a recommendation and not mandatory, it is simply stated that ―Protection against interference outside the DME B AMC Project Deliverable D1 Issue 1 0.doc 12 Unrestricted

Unrestricted R/0036/002 14 August 2007 Issue 1.0 frequency band should be adequate for the sites at which the transponders will be used‖. However, the following extracts from ICAO Annex 10 are provided since they describe the characteristics of the transponder and interrogator receivers. 3.1.2.1 Transponder Sensitivity [3.5.4.2.3] In the absence of all interrogation pulse pairs, with the exception of those necessary to perform the sensitivity measurement, interrogation pulse pairs with the correct spacing and nominal frequency shall trigger the transponder if the peak power density at the transponder antenna is at least: a) b) c) minus 103 dBW/m2 for DME/N; minus 86 dBW/m2 for DME/P Initial Approach (IA) mode; minus 75 d

Study the feasibility of utilising spectrum between successive Distance Measuring Equipment (DME) channels for B-AMC. This would allow for B-AMC frequency planning that is ―independent‖ from DME planning. If ―enough‖ spectrum is available, the B-AMC would be deployed as an ―inlay‖ system in the L-band (960 - 1164 MHz).