Next generation aeronautical communications: AeroMACS

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Chapter 2

Next generation aeronautical

communications: AeroMACS

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2.1 AeroMACS technology potentiality for ATS/AOC communications 23

2.1 AeroMACS technology potentiality for ATS/AOC

commu-nications

2.1.1 Future communications for next-generation air transportation

The highest concentration of sources, users, and stakeholders of information required for safe and regular flight operations occurs at the nation’s airports. Of all flight domains within the national airspace system (NAS), the airport domain is the one where aircraft are in closest proximity to each other and to a wide variety of service and operational support vehicles, personnel, and infrastructure. Air traffic controllers, aircraft pilots, airline operators, ramp operators, aircraft service providers, and security, emergency, construction, snow removal, and deicing personnel all contribute to the safe and efficient operation of flights. As the communications, navigation, and surveillance (CNS) facilities for air traffic management (ATM) and air traffic control (ATC) at an airport grow in number and complexity, the need for communications network connectivity and data capacity increases. Over time, CNS infrastructure ages and requires more extensive and expensive monitoring, maintenance, repair or replacement. Airport construction and unexpected equipment outages also require temporary communications alternatives. Some typical examples of airport infrastructure, aircraft, service vehicles, and operators are shown in Figure2.1.

Figure 2.1: Example of typical airport infrastructure

Capacity growth in the nation’s airports increases the total capacity of the NAS. But how can that growth occur while maintaining required safety, security, reliability, and diversity? A high-performance, cost-effective wireless communications network on the airport surface can provide part of the solution. AeroMACS is the best solution among some technology proposed for the future communications infrastructure (FCI) about future aeronautical air-to-ground

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(A/G) data communications capabilities.

AeroMACS is based on a specific commercial profile of the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard known as Wireless Worldwide Interoperability for Microwave Access or WiMAX (WiMax Forum). It offers the potential for broadband secure wireless mobile data communications capabilities to future air traffic controllers, pi-lots, airlines, and airport operators on the airport surface. The unprecedented connectivity, bandwidth, and security afforded by AeroMACS enhances the safety and regularity of flight operations in the future.

Potential AeroMACS configuration and applications

An AeroMACS based on the WiMAX standard for local area networks can potentially support a wide variety of voice, video, and data communications and information exchanges among mobile users at the airport. The airport CNS infrastructure supporting ATM and ATC on the airport surface can also benefit from secure wireless communications by improving availability and diversity. A wideband communications network can enable the sharing of graphical data and real-time video in order to significantly increase situational awareness, improve surface traffic movement to reduce congestion and delays, and help prevent runway incursions.

AeroMACS can provide temporary communications capabilities during construction or outages, and can reduce the cost of connectivity in comparison to underground cabling. A broadband wireless communications system like AeroMACS can enhance collaborative decision making, ease updating of large databases and loading of flight plans into the flight management system (FMS) avionics, and enable aircraft access to system wide information management (SWIM) services for delivery of time-critical advisory information to the cockpit.

Notional AeroMACS network configuration

In order to provide services to a potentially large number of mobile users and fixed assets, a standard WiMAX network architecture is proposed for AeroMACS. One or more base stations are required to provide coverage, availability, and security. Figure 2.2 on the next page

illustrates a notional AeroMACS network deployed at an airport. In this notional network configuration, air traffic control and management services can be physically isolated from airlines and airport/port authority services if required. However, WiMAX networks have the capability to integrate multiple services while preserving the desired security and quality of service.

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Figure 2.2: Notional AeroMACS network configuration and potential applications

Categories of potential AeroMACS services

The potential services and applications provided by AeroMACS can be grouped into three major categories:

• ATC/ATM and infrastructure • airline operations

• airport and/or port authority operations

Within these broad categories, the data communications services and applications can be described as either fixed or mobile, based on the mobility of the end user. However, only those services having direct impact on the safety and regularity of flight are candidates for provision by AeroMACS. Some examples of potential AeroMACS services and applications are listed in Table2.1.

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Table 2.1: Example of potential AeroMACS services and applications

FAA Air Traffic Control and Infrastructure Application Examples Selected air traffic control (ATC) and air traffic management (ATM)

• Surface communications, navigation, surveillance (CNS), weather sensors

Mobile Fixed Passenger and Cargo Airline Applications Examples

• Aeronautical operational control (AOC) • Advisory information

– Aeronautical information services (AIS) – Meteorological (MET) data services

– System wide information management (AAC) • Airline administrative communications (AAC)

Mobile

Mobile Airport Operator/Port Authority Applications Examples

• Security video

• Routine and emergency operations • Aircraft de-icing and snow removal

Fixed Mobile Mobile

Potential Air Traffic Applications

Many candidate mobile ATC/ATM applications are under consideration for future provision via AeroMACS. These include selected messages that are currently conveyed over the aircraft communications addressing and reporting system (ACARS) (e.g., pre-departure clearance (PDC)), selected controller pilot data link communications (CPDLC) messages (e.g., four-dimensional trajectory negotiations (4D-TRAD)), selected COCR services (e.g., surface in-formation guidance (D-SIG)), and other safety-critical applications (e.g., activate runway lighting systems from the cockpit (DLIGHTING)). Potential fixed infrastructure applications include communications (e.g., controller-to-pilot voice via remote transmit receiver (RTR)), navigation aids (e.g., instrument landing system data for glide slope and visibility data for runway visual range), and surveillance (e.g., airport surface movement detection and airport surveillance radar (ASR)). AeroMACS can also be used to convey electronic equipment performance data for remote maintenance and monitoring (RMM). Most of these existing applications are fixed point-to-point and use voice grade circuits. AeroMACS offers a flexible alternative to guided media (e.g., copper and fiber optic cable). However, separation of these services from the airline and airport services may required.

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Potential Airline and Advisory Applications

Mobile AIS/MET services can become significant drivers of AeroMACS design because of several high-volume data base synchronization services that would benefit from AeroMACS implementation. These include the AIS baseline synchronization service (e.g., uploading flight plans to the FMS and updating terrain and global positioning satellite (GPS) navigational databases and aerodrome charts to electronic flight bag (EFB)), data delivery to the cockpit (e.g., data link aeronautical update services (D-AUS), and airport/runway configuration infor-mation (D-OTIS)), and convective weather inforinfor-mation (e.g., graphical forecast meteorological information and graphical turbulence guidance (GTG) data and maps).

Passenger and cargo airlines provide another significant source of data and voice applications for potential integration over AeroMACS. These include ground operations and services (e.g., coordination of refueling and deicing operations), sharing of maintenance information (e.g., offload of flight operational quality assurance (FOQA) data), and aircraft and company operations (e.g., updates to flight operations manuals and weight and balance information required for takeoff).

Potential Airport Operator Applications

The airport or port authority operations provide the final category of potential applications for AeroMACS. These are dominated by video applications required for safety services (e.g., fixed surveillance cameras and in-vehicle and portable mobile cameras for live video feeds and voice communications with central control during snow removal, de-icing, security, fire and rescue operations). Finally, AeroMACS can also help ensure compliance with regulations for safety self-inspection (e.g., reporting status of airport runway and taxiway lights and monitoring and maintenance of navigational aids and time critical airfield signage).

Many of these services and applications are currently provided to mobile users through a mix of VHF voice and data links, land mobile radio services, and commercial local area wire-less networks. The fixed communications services and applications at airports are typically implemented via buried copper and fiber optic cables. AeroMACS offers the potential for integration of multiple services into a common broadband wireless network that also securely isolates the applications from each other.

The deployment of AeroMACS infrastructure at an airport to enable the migration or augmentation of one of more existing services opens the potential for many additional services, especially those that require wider bandwidth, such as graphical information delivery and video services.

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2.2 Propagation channel model in airport environment

The development of technologies presented in 2.1 needs not only an appropriate hardware equipment design but also a realistic model of the enviroment in which it operates, in this case an airport area (aeronautical channel). The complexity of this environment, characterized by a high mobility of its “users”, necessitates, as known, a statistical approach.

Until a few years ago, the attention was focused on ground-air links, characterized by the existence of a direct path (line-of-sight, LOS) between transmitter and receiver, thus omitting ground communications inside the airport area. Here we can find big and small buildings, different types of vehicle and many other structures, each of them representing, for the purpose of statistically analyzing the propagation channel, a reflector or a scatterer. The considered environment could therefore present prevalent LOS areas and NLOS (non-line-of-sight) areas. A significant example of this situation is given in Figure 2.3, that represents the situation noticed at Franz Josef Strauss International Airport in Munich [1]. Different identified areas are described in Table 2.2 on the next page.

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2.2 Propagation channel model in airport environment 29

Table 2.2: Munich Airport – Area arrangement considered for the statistical evaluation.

A poor reflection due to main buildings, a lot of small objects (vehicles, esca-lators), LOS always present

B1 and B2 a wall behind a moving vehicle, significant reflection

C1 and C2 buildings between transmitter and receiver, diffraction phenomena and spo-radic shadowing

D1 and D2 high distance and wide open spaces behind a moving vehicle

E total absence of LOS

It is plain by this results that the considered propagation channel is non-stationary as well as frequency selective. It is however possible to introduce a substantial simplification: if we consider a receiver moving at a speed of 30 Km/h a data frame of 5 ms corresponds to a 4 cm change in position, that is less than a wavelength for 5 GHz systems. Due to this assumption we can use a Wide Sense Stationary Uncorrelated Scattering (WSSUS) channel characterization [1]: Uncorrelated Scattering (US) assumes that channel taps with different propagation delays are uncorrelated and Wide Sense Stationary (WSS) assumes that channel taps are stationary in time. In general, a time-varying multipath channel satisfies these assumptions only in a small area. A WSSUS channel model is fully described by the Power Delay Profile (PDP) and the Doppler Power Profile (DPP) of each tap.

A WSSUS channel model for airport environment is analyzed in [1]. The multipath phe-nomenon is implemented as a tapped delay line (TDL) with a number of taps Ntequal to the

number of received components (Figure2.4).

Each tap is characterized by an amplitude Ak, a delay τk= kTc and underlies an

indepen-dent fading process ak(nTc), with Tc being the sampling period of the received signal, nTc

represents the nth

time sample and k = 0, . . . , Nt− 1. The received signal y(nTc) results from

the sum of all the tap components, obtained by multiplying the delayed transmitted signal x(nTc) by the weighted fading coefficients:

y(nTc) = Nt−1

X

k=0

Ak· αk(nTc) · x(nTc− τk). (2.1)

The tap fading coefficients αk(nTc) are a realization of a complex Gaussian process, i.e.

exhibit a Rayleigh distributed amplitude. The time variance of a tap coefficient is given by the spread of its Doppler Power Spectrum (DPS).

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Figure 2.4: Tapped Delay Line – Multipath implementation

The fading process can be modeled by the sum of sinusoids [4]. Assuming that the kth

tap is composed of NS0 scatterers, i.e. the DPS can be modeled by NS0 independent Gaussian

distributions, the corresponding complex fading coefficient αk is given by

αk(nTc) = ak,1(nT c) + j · αk,2(nT c) (2.2) with αk,l(nTc) = NS0 X β=0 NH−1 X i=0

ci,k(β)· cos(2πfi,k(β)nTc+ θi,k(β)). (2.3)

The real and imaginary part of the complex Gaussian random processes, αk,l with l = 1, 2,

are uncorrelated. Each scatterer is obtained from a sum of NH harmonic components,

characterized by an amplitude ci,k(β), a phase θi,k(β) and a Doppler frequency fi,k(β). The

phases θi,k(β) are random variables uniformly distributed in [0, 2π]. The frequencies fi,k(β)

are given by fi,k(β)= fDk(β)+ υi,k(β), where fDk(β) represents the Doppler shift of the βth

scatterer of kth

tap and υi,k(β) models the Doppler spread.

A good approximation for the Doppler Spectrum is obtained in [1] with a low number of harmonics NH, with amplitudes calculated from the power spectral density Sαα(f ):

ci,k(β)= 2

q

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2.2 Propagation channel model in airport environment 31 with Sαα(fi,k(β)) = 1 q 2πσ2_k exp (fi,k−fDk) 2 2σ2 k ! . (2.5)

For each scatterer, is choosen the fixed frequency quantity ∆fDk as a function of the Doppler

spread σk2, ∆fDk(β)= 4σk

(β)

NH and the discrete Doppler frequencies fi,k

(β) _{can be calculated} by fi,k(β)= fDk(β)+ i −N₂H · ∆fDk(β). (2.6)

In the area with the LOS, first tap is given as a mixture of a direct path and a number of paths with |τi − τ0| ≤ Tc/2. If the receiver moves, the reflected paths will cause a Doppler

spread due to a different angle of incidence. The LOS fading can be modeled by

α0(nTc) = c0· expj 2πfD0nTc + NH

X

i=1

ci,0· expj 2π(fD0+ υi,0)nTc+ θi,0 . (2.7)

It is also set υi,0 = (i−N₂H)·_N4σ_H0. The linear Rice factor models the ratio R = c02/2PN_i=1Hci,02.

Setting c02+PNi=1Hci,02= 1, we obtain NH X i=1 ci,02 = 1 1 + 2R and c0 = r 2R 1 + 2R. (2.8)

Applying the same calculation for tap amplitudes, where Ak, k = 0, . . . , Nt − 1, are

determined by the PDP and the ratio A02/PNk=1t−1Ak2 by the K factor, we obtain

A0 = r K 1 + K and Nt X k=1 Ak2= 1 1 + K (2.9)

where the K factor is defined by

K = log P PLOS

m6=LOSPm

!

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Considering a threshold of -35 dB below the LOS tap, the maximum evaluated delay is 3µs. Regarding B = 10M Hz, this delay correspond to the maximum number of 30 taps, whereas according to experimental results the main received power is contained in the first L = 13 taps, i.e. roughly 1.2µs. Since the number of uncorrelated multipath components is smaller than L, it is sufficient to model the channel with a smaller number of taps, adequately distributed between τ0 = 0 and τmax= 3µs. According to the observations it is assumed that

the multipath propagation can be realistically modeled with up to 8 paths with delays τk=1...8

generated from the uniform distribution in interval [0.1, 1.2]µs and 3 single paths with delays τk=9...11 generated from the uniform distribution in interval [1.3, 3]µs. Hence, with the LOS

tap at τ0 = 0, the maximum number of taps considered for channel modeling is Nt= 12. The

random generation of the path delay according to this scenario can be used also for the NLOS case. Figure 2.5 shows two different PDPs for LOS and NLOS cases.

Figure 2.5: Proposed PDPs for LOS and NLOS areas ([1])

2.3 Specific of AeroMACS (IEEE 802.16e-based) Physical Layer

As we announced in the introduction, in this thesis we have treated the physical layer of 802.16 standard (WiMAX) considering as given the higher levels parameters. We considered a particular configuration among the all possible ones like number of subcarriers, frequency of bandwidth signal, OFDMA frame structure, duplexing method, channel coding parameters, etc.. Report the entire physical layer of WiMAX standard would be excessive, so we shall report only the interested part about our solution and some general information so that you may understand how level two stack must be implemented. Parameters that are higher than physical layer won’t be explained. For a complete realization and comprehension of the standard see [2].

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2.3 Specific of AeroMACS (IEEE 802.16e-based) Physical Layer 33

Introduction

The WirelessMAN-OFDMA PHY, based on OFDM modulation, is designed for NLOS op-eration in the frequency bands below 11 GHz. Due to the longer wavelength, compared with upper frequency permitted (until 60 GHz), LOS is not necessary and multipath may be significant. The ability to support near-LOS and non-LOS (NLOS) scenarios requires additional PHY functionality, such as the support of advanced power management techniques, interference mitigation/coexistence, and multiple antennas. Wherease these facilities, this design may works both in licensed bands and license-exempt bands. Infact, into the environ-ment there are additional interference and co-existence issues, whereas regulatory constraints limit the allowed radiated power. In addition to the features described above, the PHY and MAC introduce mechanisms to facilitate the detection and avoidance of interference and the prevention of harmful interference into other users including specific spectrum users identified by regulation. This includes a mechanism for regulatory compliance called dynamic frequency selection (DFS).

For the licensed bands channel bandwidths allowed shall be limited to the regulatory provi-sioned bandwidth divided by any power of 2 no less than 1.0 MHz. The OFDMA PHY mode based on at least one of the FFT sizes 2048 (backward compatible to IEEE Std 802.16-2004), 1024, 512, and 128 shall be supported. This facilitates support of the various channel bandwidths. The MS may implement a scanning and search mechanism to detect the DL signal when performing initial network entry, and this may include dynamic detection of the FFT size and the channel bandwith employed by the BS.

2.3.1 OFDMA symbol description, symbol parameters and transmitted

signal

Time domain description

Inverse-Fourier-transforming creates the OFDMA waveform; this time duration is referred to as the useful symbol time Tb. A copy of the last Tg of the useful symbol period, termed CP,

is used to face the multipath, while maintaining the orthogonality of the tones. Figure2.6 on the next pageillustrates this structure. The transmitter energy increases with the length of the guard time while the receiver energy remains the same (the cyclic extension is discarded), so there is a 10 log(1 − Tg/(Tb + Tg))/ log(10) dB loss in Eb/N0. Using a cyclic extension,

the samples required for performing the FFT at the receiver can be taken anywhere over the length of the extended symbol. This provides multipath immunity as well as a tolerance for symbol time synchronization errors.

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Figure 2.6: OFDM symbol time structure

On initialization, an SS should search all possible values of CP until it finds the CP being used by the BS.The SS shall use the same CP on the UL. Once a specific CP duration has been selected by the BS for operation on the DL, it should not be changed. Changing the CP would force all the SSs to resynchronize to the BS.

Frequency domain description

The frequency domain description includes the basic structure of an OFDMA symbol. An OFDMA symbol is made up of subcarriers, the number of which determines the FFT size used. There are several subcarrier types, as follows:

• Data subcarriers: for data transmission

• Pilot subcarriers: for various estimation purposes

• Null carrier: no transmission at all, for guard bands and DC carrier

The purpose of the guard bands is to enable the signal to naturally decay and create the FFT “brick wall” shaping.

In the OFDMA mode, the active subcarriers are divided into subsets of subcarriers, each subset is named a subchannel. In the DL, a subchannel may be intended for different (groups of) receivers; in the UL, a transmitter may be assigned one or more subchannels, several transmitters may transmit simultaneously. The subcarriers forming one subchannel may, but need not be adjacent. The concept is shown in Figure 2.7 on the facing page.

The symbol is divided into logical subchannels to support scalability, multiple access, and advanced antenna array processing capabilities.

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Figure 2.7: OFDM frequency description

Primitive parameters

The following four primitive parameters characterize the OFDMA symbol:

BW : The nominal channel bandwidth.

Nused: Number of used subcarriers (which includes the DC subcarrier).

n: Sampling factor. This parameter, in conjunction with BW and Nused determines

the subcarrier spacing and the useful symbol time. This value is set as follows: for channel bandwidths multiple of 1.75 MHz, then n = 8/7; else, for channel bandwidths that are a multiple of any of 1.25, 1.5, 2, or 2.75 MHz, then n = 28/25; else, for channel bandwidths not otherwise specified, then n = 8/7.

G: This is the ratio of CP time to “useful” time. The following values shall be supported: 1/32, 1/16, 1/8, and 1/4.

Derived parameters

NFFT: Smallest power of two greater than N_used

Sampling frequency: Fs = f loor(n · BW/8000) · 8000

Subcarrier spacing: ∆f = Fs/NF F T

Useful symbol time: Tb= 1/∆f

CP time: Tg= G · Tb

OFDMA symbol time: Ts= Tb+ Tg

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Transmitted signal

Equation (2.11) specifies the transmitted signal voltage to the antenna, as a function of time, during any OFDMA symbol.

s(t) = Re ( ej2πfct (Nused−1)/2 X k=−(Nused−1)/2 k6=0 ck· ej2πk∆f (t−Tg) ) (2.11) where

t: is the time, elapsed since the beginning of the subject OFDMA symbol, with 0 6 t 6 Ts

ck: is a complex number; the data to be transmitted on the subcarrier whose frequency

offset index is k, during the subject OFDMA symbol. It specifies a point in a QAM constellation

Tb: is the guard time

Ts: is the OFDMA symbol duration, including guard time

∆f : is the subcarrier frequency spacing

2.3.2 OFDMA basic terms definition

Slot and data region

A slot in the OFDMA PHY requires both a time and subchannel dimension for completeness (subchannels are defined in subsection 2.3.5 on page 48) and is the minimum possible data allocation unit. The definition of an OFDMA slot depends on the OFDMA symbol structure, which varies for UL and DL, for FUSC (Full Usage of SubCarriers) and PUSC (Partial Usage of SubCarriers), and for the distributed subcarrier permutations and the adjacent subcarrier permutation.

• For DL FUSC and DL optional FUSC, one slot is one subchannel by one OFDMA symbol.

• For DL PUSC, one slot is one subchannel by two OFDMA symbols.

In OFDMA, a data region is a two-dimensional allocation of a group of contiguous sub-channels, in a group of contiguous OFDMA symbols. All the allocations refer to logical subchannels. A two-dimensional allocation may be visualized as a rectangle, such as the 4 × 3 rectangle shown in Figure 2.8 on the facing page.

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Figure 2.8: Example of a data region that defines an OFDMA allocation

Segment

A segment is a subdivision of the set of available OFDMA subchannels (that may include all available subchannels). One segment is used for deploying a single instance of the MAC.

Permutation zone

Permutation zone is a number of contiguous OFDMA symbols, in the DL or the UL, that use the same permutation formula. The DL subframe or the UL subframe may contain more than one permutation zone.

OFDMA data mapping

MAC data shall be processed as described in subsection 2.3.8 and shall be mapped to an OFDMA data region for DL and UL using the algorithms defined below. UL mapping will be omitted.

1. Segment the data into blocks sized to fit into one OFDMA slot.

2. Each slot shall span one subchannels in the subchannel axis and one or more OFDMA symbols in the time axis, as per the slot definition (see Figure2.9for an example). Map the slots so that the lowest numbered slot occupies the lowest numbered subchannel in the lowest numbered OFDMA symbol.

3. Continue the mapping so that the OFDMA subchannel index is increased. When the edge of the data region is reached, continue the mapping from the lowest numbered OFDMA subchannel in the next available symbol.

The subchannels referred to in this subclause are logical subchannels, before subchannel renumbering in the DL. Figure2.9illustrate the order in which OFDMA slots are mapped to subchannels and OFDMA symbols.

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Figure 2.9: Example of mapping OFDMA slots to subchannels and symbols in the DL (in PUSC mode)

2.3.3 Frame structure

In licensed bands, the duplexing method shall be either FDD or TDD. FDD SSs may be full-duplex (FDD) or half-full-duplex (H-FDD). The FDD BS shall support both SS types concurrently. In license-exempt bands,the duplexing method shall be TDD.

TDD Frame structure

When implementing a TDD system, the frame structure is built from BS and SS transmissions. Each frame in the DL transmission begins with a preamble followed by a DL transmission period and an UL transmission period. In each frame, the TTG and RTG shall be inserted between the DL and UL and at the end of each subframe, to allow the BS to turn around. Figure 2.10 shows an example of an OFDMA frame (with only mandatory zone) in TDD mode.

OFDMA Frame Parameters and Operations

Subchannel allocation in the DL may be performed in the following ways: PUSC where some of the subchannels are allocated to the transmitter and FUSC where all subchannels are

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Figure 2.10: Example of OFDMA frame (with only mandatory zone) in TDD mode

allocated to the transmitter. The FCH shall be transmitted using QPSK rate 1/2 with four repetitions using the mandatory coding scheme (i.e., the FCH information shall be sent on four subchannels with successive logical subchannel numbers) in a PUSC zone. The FCH contains the DL frame prefix as described on the next page, and specifies the length of the DL-MAP message that immediately follows the DL frame prefix and the repetition coding used for the DL-MAP message. The transitions between modulations and coding take place on slot boundaries in time domain (except in AAS zone) and on subchannels within an OFDMA symbol in frequency domain.

The OFDMA frame may include multiple zones (such as PUSC, FUSC, PUSC with all subchannels, optional FUSC, AMC, TUSC1, and TUSC2), the transition between zones is indicated in the DL-Map by specific entry. No DL-MAP or UL-MAP allocations can span over multiple zones. Figure 2.11 on the following page depicts the OFDMA TDD frame with multiple zones. The PHY parameters may change from one zone to the next. More than one DL or UL zone may be defined for each configuration (e.g., permutation, STC mode, PermBase, etc). For example, zones may be used for defining partitions in time for an FDD/H-FDD system.

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Figure 2.11: Illustration of OFDMA TDD frame with multiple zones

The following restrictions apply to DL allocations. These are not all ones precisely:

• The maximum number of DL zones is 8 in one DL subframe.

• For each SS, the maximum number of bursts to decode in one DL subframe is 64. If the BS allocates more bursts or zones, then the SS is required to decode the first bursts/zones until the limit is reached.

DL frame prefix

The DL_Frame_Prefix is a data structure transmitted at the beginning of each frame and contains information regarding the current frame and is mapped to the FCH. Table2.3defines the structure of DL_Frame_Prefix except for the case of 128-FFT.

Table 2.3: OFDMA DL Frame Prefix format for all FFT sizes except 128

Syntax Size Notes

(bit) DL_Frame_Prefix_Format() {

Used subchannel bitmap 6

Bit 0: Subchannel group 0 Bit 1: Subchannel group 1 Bit 2: Subchannel group 2 Bit 3: Subchannel group 3 Bit 4: Subchannel group 4 Bit 5: Subchannel group 5 Reserved 1 Shall be set to zero

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Table 2.3: OFDMA DL Frame Prefix format for all FFT sizes except 128

Syntax Size Notes

(bit)

Repetition_Coding_indication 2

0b00: No repetition coding on DL-MAP 0b01: Repetition coding of 2 used on DL-MAP 0b10: Repetition coding of 4 used on DL-MAP 0b11: Repetition coding of 6 used on DL-MAP

Repetition_Coding_indication 2

0b000: CC encoding used on DL-MAP 0b001: BTC encoding used on DL-MAP 0b010: CTC encoding used on DL-MAP 0b011: ZT CC encoding used on DL-MAP 0b100: CC encoding with optional interleaver 0b101: LDPC encoding used on DL-MAP 0b110 to 0b111: Reserved

DL-Map_Length 8

Reserved 4 shall be set to zero }

Used subchannel bitmap:

A bitmap indicating which groups of subchannel are used on the first PUSC zone and on PUSC zones in which ’Use All SC’ field is set to ’0’ in STC_DL_Zone_IE(). A value of ’1’ means used by this segment, and ’0’ means not used by this segment.

Repetition_Coding_Indication:

Indicates the repetition code used for the DL-MAP. Repetition code may be 0 (no additional repetition), 1 (one additional repetition), 2 (three additional repetitions) or 3 (five additional repetitions).

Coding_Indication:

Indicates the FEC encoding code used for the DL-MAP. The DL-MAP shall be trans-mitted with QPSK modulation at FEC rate 1/2. The BS shall ensure that DL-MAP (and other MAC messages required for SS operation) are sent with the mandatory coding scheme often enough to ensure uninterrupted operation of SS supporting only the mandatory coding scheme.

DL-Map_Length:

Defines the length in slots of the burst which contains only DL-MAP message or compressed DL-MAP message and compressed UL_MAP, if it is appended, that follows immediately the DL frame prefix after repetition code is applied.

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The subchannel index of the six subchannel groups is shown in Table 2.4. Before being mapped to the FCH, the 24-bit DL frame prefix shall be duplicated to form a 48-bit block, which is the minimal FEC block size.

Table 2.4: Subchannel index of the six subchannel groups

FFT size # Subchannel # Subchannel FFT size # Subchannel # Subchannel

group range group range

2048 0 0-11 512 0 0-4 1 12-19 1 N/A 2 20-31 2 5-9 3 32-39 3 N/A 4 40-51 4 10-14 5 52-59 5 N/A 1024 0 0-5 128 0 0 1 6-9 1 N/A 2 10-15 2 1 3 16-19 3 N/A 4 20-25 4 2 5 26-29 5 N/A

Subchannels allocation for FCH and DL-MAP and logical subchannel numbering

In PUSC, any segment used shall be allocated at least the same number of subchannels as in subchannel group #0. For FFT sizes other than 128, the first 4 slots in the DL part of the segment contain the FCH as defined on page 38. These slots contain 48 bits modulated by QPSK with coding rate 1/2 and repetition coding of 4. The basic allocated subchannel sets for segments 0, 1, and 2 are subchannel group #0, #2, and #4, respectively. Figure 2.12 on the facing page depicts this structure.

After decoding the DL_Frame_Prefix message within the FCH, the SS has the knowledge of how many and which subchannels are allocated to the PUSC segment. In order to observe the allocation of the subchannels in the DL as a contiguous allocation block, the subchannels shall be renumbered. For the first PUSC zone, the renumbering shall start from the FCH subchannels (renumbered to values 0. . . 11) and then continue numbering the subchannels in a cyclic manner to the last allocated subchannel and from the first allocated subchannel to the FCH subchannels. Figure 2.13 on the next pagegives an example of such renumbering for segment 1. For other PUSC zones in which the Use All SC field is set to 1 or that are defined by AAS_DL_IE() renumbering shall be performed starting from

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Figure 2.12: FCH subchannel allocation for all 3 segments

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subchannel (Nsubchannels/3)×PRBS_ID, where PRBS ID is specified in the STC DL Zone

IE or AAS_DL_IE(). For other PUSC zones in which the Use All SC field is set to 0, the renumbering shall be the same as in the first PUSC zone.

The DL-MAP of each segment shall be mapped to the slots allocated to the segment in a frequency-first order, starting from the slot after the FCH (subchannel 4 in the first symbol, after renumbering) and continuing to the next symbols if necessary. The FCH of segments that have no subchannels allocated (unused segments) shall not be transmitted, and the respective slots may be used for transmission of MAP and/or data of other segments.

2.3.4 Map message fields and IEs

DL-MAP message

The MAP message defines the access to the DL information. If the length of the DL-MAP message is a nonintegral number of bytes, the LEN field in the MAC header (a part of the MAC PDU) is rounded up to the next integral number of bytes. The message shall be padded to match this length, but the SS shall disregard the 4 pad bits. DL-MAP message field contains fixed and variable entries in number other than in dimension.

Fixed entries are:

PHY Synchronization:

The PHY synchronization entry and the used encoding is dependent on the PHY specification used.

Padding Nibble:

Padding to reach byte boundary.

Variable entries are:

DL-MAP IE():

Might be more than one DL-MAP IE() entry and it specifies the definition of DL subframe pattern as described on page 46.

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DL-MAP PHY Synchronization field

The format of the PHY Synchronization field of the DL-MAP message is given in Table2.5. The frame duration codes are given in Table 2.6. The frame number is incremented by one each frame and eventually wraps around to zero.

Table 2.5: OFDMA PHY Synchronization Field

Syntax Sizes Notes (bit)

PHY_synchronization_field() {

Frame Duration Code 8

Frame Number 24

}

A BS shall generate DL-MAP messages including all of the following parameters:

Frame number :

The frame number is incremented by 1 mod 224 _{each frame.}

Frame duration code:

The frame duration code values are specified in Table 2.6.

Table 2.6: OFDMA frame duration (Tf ms) codes

Code Frame duration

Frame per second (N) (ms) 0 Reserved N/A 1 2 500 2 2.5 400 3 4 250 4 5 200 5 8 125 6 10 100 7 12.5 80 9 20 50 9-255 Reserved

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Frame duration codes

Table 2.6 defines the various frame durations that are allowed. The frame durations defined in the table indicate the periodicity of the DL frame start preamble in both FDD and TDD cases.

Note that the frame durations indicated in Table 2.6 typically are not integer multiples of one OFDMA symbol duration. Therefore some time padding may be necessary between the last useful OFDMA symbol of a frame and the beginning of the next frame. In addition, in the TDD case, note that the RTG and TTG guard intervals shall be included in a frame. Both RTG and TTG shall be no less than 5µs in duration.

DL-MAP IE Format

The OFDMA DL-MAP IE defines a two-dimensional allocation pattern as defined in Table2.7. It doesn’t treat the overall field shown in the original OFDMA DL-MAP IE pattern, but only the ones that we used in our work.

Table 2.7: OFDMA DL-MAP IE format

Syntax Sizes Notes

(bit) DL-MAP_IE() {

DIUC 4

CID 16

OFDMA Symbol Offset 8 Subchannel Offset 6

Boosting 3

000: Normal (not boosted); 001: +6dB; 010: -6dB; 011: +9dB; 100: +3dB; 101: -3dB; 110: -9dB; 111: -12dB;

No. OFDMA Symbols 7 No. Subchannel 6

Repetition Coding Indication 2

0b00: No repetition coding 0b01: Repetition coding of 2 used 0b10: Repetition coding of 4 used 0b11: Repetition coding of 6 used }

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DIUC :

DIUC used for the burst.

CID:

The connection identifier that represents the assignment of the IE to a broadcast, multicast, or unicast address.

OFDMA Symbol offset:

The offset of the OFDMA symbol in which the burst starts, measured in OFDMA symbols from the DL symbol in which the preamble is transmitted with the symbol immediately following the preamble being offset 1. The symbol offset shall follow the normal slot allocation within a zone so that the difference between OFDMA symbol offsets for all bursts within a zone is a multiple of the slot length in symbols.

Subchannel offset:

The lowest index OFDMA subchannel used for carrying the burst, starting from sub-channel 0.

Boosting:

Power boost applied to the allocation’s data subcarriers. The field shall be zero in an AAS zone with AMC permutation or in a zone with AMC or PUSC-ASCA permutation using dedicated pilots.

No. OFDMA Symbols:

The number of OFDMA symbols that are used (fully or partially) to carry the DL PHY burst. The value of the field shall be a multiple of the slot length in symbols.

No. of subchannels:

The number of subchannels with subsequent indexes, used to carry the burst.

Repetition Coding Indication:

Indicates the repetition code used inside the allocated burst. Repetition shall be used only for DIUC indicating QPSK modulation.

Within the OFDMA DL-MAP IE a SS will find the number of the burst in the downlink subframe, their location and their dimension, shown by the above field. In this way, a SS will be able to recognize if a burst carries system information or data information, and if it’s directed to itself.

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Figure 2.14: DL trasmission basic structure

2.3.5 OFDMA subcarriers allocation

For OFDMA, Fs = f loor(n · BW/8000) · 8000 where n is the sampling factor which is

dependent on bandwidth. Subtracting the guard tones from NF F T, one obtains the set of

“used” subcarriers N_used. For both UL and DL, these used subcarriers are allocated to pilot subcarriers and data subcarriers. However, there is a difference between the different possible zones. For FUSC and PUSC, in the DL, the pilot tones are allocated first; what remains are data subcarriers, which are divided into subchannels that are used exclusively for data. Thus, in FUSC, there is one set of common pilot subcarriers, and in PUSC of the DL, there is one set of common pilot subcarriers in each major group.

Downlink (DL)

The DL can be divided into a three-segment structure. A preamble begins the transmission. This preamble uses one of the three carrier-sets specified in the next paragraph. Figure 2.14

illustrates the DL transmission basic structure.

Preamble

The first symbol of the DL transmission is the preamble. For each FFT size, three different preamble carriersets are defined, differing in the allocation of subcarriers. Those subcarriers are modulated using a boosted BPSK modulation with a specific pseudo-noise (PN) code. The preamble carrier-sets are defined using Equation (2.12).

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Figure 2.15: Basic structure of DL preamble, 2048-FFT

where

P reambleCarrierSetn: specifies all subcarriers allocated to the specific preamble

n: is the designating number of the preamble carrier-set indexed 0, 1, and 2

k : is a running index. 0-567 for 2K-FFT, 0-283 for 1024-FFT, 0-142 for 512-FFT, and 0-35 for 128-FFT

Each segment uses a preamble composed of a single carrier-set in the following manner: • Segment 0 uses preamble carrier-set 0.

• Segment 1 uses preamble carrier-set 1. • Segment 2 uses preamble carrier-set 2.

In the case of segment 0, the DC carrier will not be modulated at all, and the appropriate PN will be discarded. Therefore, the DC carrier shall always be zeroed. Each segment eventually modulates each third subcarrier. As an example, Figure2.15depicts the preamble of segment 1 in the case of the 2048-FFT. In this figure, subcarrier 0 corresponds to the first subcarrier used in the preamble symbol.

For 512-FFT size, the PN series modulating the preamble carrier-set is defined in Table2.8. The series modulated depends on the segment used and IDcell parameter. The defined series shall be mapped onto the preamble subcarriers in ascending order. The value of the PN is obtained by converting the series to a binary series (Wk) and mapping the PN starting from

the MSB of each symbol to the LSB (0 mapped to +1 and 1 mapped to -1). For example, for Index = 0 and Segment = 0, Wk = 110000010010..., and the mapping shall follow: -1 -1 +1

+1 +1 +1 +1 -1 +1 +1 -1 +1. . . ).

In 512-FFT case, the final bit of the 144-bit series shown in each row of the table shall be discarded, so that the series used is 143 bits long. For the preamble symbol, there will be 42 guard band subcarriers on the left (lower-frequency) side and 41 guard band subcarriers on the right (higher-frequency) side of the spectrum. The modulation used on the preamble is defined on page59. For a complete description of all preamble modulations see [2].

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Table 2.8: Preamble modulation series per segment and IDcell for the 512-FFT mode

Index IDcell Segment Series to modulate (in hexadecimal format)

0 0 0 0x66C9CB4D1C8F31D60F5795886EE02FFF6BE4 1 1 0 0xD8C30DA58B5ED71056C5D79032B80E05522C .. . ... ... ... 44 12 1 0x8447E25CA9A0EE1CFB9FADB6C42B8F565B3C 45 13 1 0x757C45DA8F140FB6E71024294B2439CDACFC .. . ... ... ... 112 16 1 0x46CE626ACD894F9650E6B7C3F9E3BFAE5B08 113 17 2 0xC59B894FBF170F44F4816750280AB8CB4E48

2.3.6 Symbol structure for PUSC

The symbol structure is constructed using pilots, data, and zero subcarriers. The symbol is first divided into basic clusters and zero carriers are allocated. Pilots and data carriers are allocated within each cluster. Table 2.9 summarizes the parameters of the symbol structure.

Table 2.9: 512-FFT OFDMA downlink carrier allocations on PUSC zone

Syntax Sizes Notes

Number od DC Subcarriers 1 Index 256 Number of Guard Subcarriers. Left 46

Number of Guard Subcarriers. Right 45 Number of Used Subcarriers (Nused)

including all possible allocated pilots and the DC subcarrier.

421 Number of all subcarrier used within a symbol.

Renumbering sequence 12,13,26,9,5,15,21,6,28,4,2,7,10,18,29, 17,16,3,20,24,14,8,23,1,25,27,22,19,11,0

Used to renumber clusters before allocation to subchannels Number of carriers per cluster 14

Number of clusters 30 Number of data subcarriers in each symbol per subchannel

24

Number of subchannels 15 PermutazionBase5 (for 5 subchannels) 4,2,3,1,0

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Figure 2.16: Cluster structure

Figure 2.16 depicts the cluster structure. It shows subcarriers from left to right in order of increasing subcarrier index. For the purpose of determining PUSC pilot location, odd and even symbols are counted from the beginning of the current zone. The first symbol in the zone is even. The preamble shall not be counted as part of the first zone.

2.3.7 DL subchannels subcarriers allocation in PUSC

The carrier allocation to subchannels is performed using the following procedure:

1. Dividing the subcarriers into the number of clusters (Ncluster) physical clusters

con-taining 14 adjacent subcarriers each (starting from carrier 0). The number of clusters, Ncluster, must be compliant to Figure 2.16.

2. Renumber the physical clusters into logical clusters according to Equation (2.13).

LogicalCluster = RenumberingSequence(((P hysicalCluster)

+ 13 · DL_PermBase)modNcluster)

(2.13)

3. Allocate logical clusters to groups. For 512-FFT, dividing the clusters into three major groups (labeled 0, 2 and 4), group 0 includes clusters 0-9, group 2 includes clusters 10-19, and group 4 includes clusters 20-29. These groups may be allocated to segments. If a segment is being used, then at least one group shall be allocated to it (by default, group 0 is allocated to sector 0, group 2 is allocated to sector 1, and group 4 is allocated to sector 2).

4. Allocating subcarriers to subchannel in each major group is performed separately for each OFDMA symbol by first allocating the pilot carriers within each cluster and then

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taking all remaining data carriers within the symbol and using the same procedure de-scribed in the section below. For 512-FFT use the parameters from Table2.9 on page 50, with basic permutation sequence 5 for even-numbered major groups, to partition the subcarriers into subchannels containing 24 data subcarriers in each symbol.

Partitioning of data subcarriers into subchannels in DL

After mapping all pilots, the remainder of the used subcarriers are used to define the data subchannels. To allocate the data subchannels, the remaining subcarriers are partitioned into groups of contiguous subcarriers. Each subchannel consists of one subcarrier from each of these groups. The number of groups is therefore equal to the number of subcarriers per subchannel, and it is denoted Nsubchannels. The number of the subcarriers in a group is equal

to the number of subchannels, and it is denoted Nsubchannels. The number of data subcarriers

is thus equal to Nsubcarriers× Nsubchannels.

The exact partitioning into subchannels is according to Equation (2.14), called a permuta-tion formula.

subcarrier(k, s) =Nsubchannels· nk+

ps[nkmodNsubchannels] + DL_PermBasemodNsubchannels

(2.14)

where

subcarrier(k,s): is the subcarrier index of subcarrier k in subchannel s

s: is the index number of a subchannel, from the set [0. . . Nsubchannels -1]

nk: is (k + 13 · s)modNsubcarriers where k is the subcarrier-in-subchannel index

from the set [0. . . Nsubcarriers -1]

Nsubchannels: is the number of subchannels (for PUSC, use number of subchannels in

the currently partitioned major group)

ps[j]: is the series obtained by rotating basic permutation sequence cyclically to

the left s times

DL_PermBase: is an integer ranging from 0 to 31, which is set to preamble IDCell in the first zone and determined by the DL-MAP for other zones

On initialization, an SS shall search for the DL preamble. After finding the preamble, the user shall know the IDcell used for the data subchannels.

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2.3.8 Channel coding

Channel coding procedures including randomization (see page 53), FEC encoding (see page

54), bit interleaving (see page56), repetition (see page59), and modulation (see page57) are shown in Figure2.17. Repetition shall be applied only to QPSK modulation.

Figure 2.17: Channel Coding chain

Randomization

Data randomization is performed on all data transmitted on the DL and UL, except the FCH. The randomization is initialized on each FEC block. If the amount of data to transmit does not fit exactly the amount of data allocated, padding of 0xFF (1 only) shall be added to the end of the transmission block up to the amount of data allocated. Here, the amount of data allocated means the amount of data that corresponds to the amount of ⌊Ns/R⌋ slots, where

Ns is the number of the slots allocated for the data burst and r is the repetition factor used.

The PRBS generator shall be 1 + X14 + X15, as shown in Figure 2.18. Each data byte to be transmitted shall enter sequentially into the randomizer, MSB first. Preambles are not randomized. The seed value shall be used to calculate the randomization bits, which are combined in an XOR operation with the serialized bit stream of each FEC block. The randomizer sequence is applied only to information bits. The bit issued from the randomizer shall be applied to the encoder. The randomizer is initialized with the vector [LSB] 0 1 1 0 1 1 1 0 0 0 1 0 1 0 1 [MSB].

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Encoding

The ecoding method used as the mandatory scheme shall be the tail-biting convolutional coding (CC), and the optional modes Block Turbo Coding (BTC) and Convolutional Turbo codes (CTC) shall be also supported.

The encoding block size shall depend on the number of slots allocated and the modulation specified for the current transmission. Concatenation of a number of slots shall be performed in order to make larger blocks of coding where it is possible, with the limitation of not exceeding the largest supported block size for the applied modulation and coding.

Table2.11 on the next pagespecifies the concatenation of slots for different allocations and modulations. The parameters in Table 2.10 and Table 2.11 shall apply to the CC encoding scheme and the BTC encoding scheme. For the CTC encoding scheme and LDPC encoding scheme, the concatenation rule is defined in different and shall be omitted. For any modulation and FEC rate, given an allocation of n slots, the following parameters are defined:

j : is parameter dependent on the modulation and FEC rate

n: is floor (number of allocated slots · STC rate/(repetition factor · number of STC layers)) k : is floor(n/j)

m: is n modulo j.

Table 2.10shows the rules used for slot concatenation.

Table 2.10: Slots concatenation rule

Number of slots Slot concatenated

n 6 j 1 block of n slots n > j if(n mod j = 0) k blocks of j slots else (k -1) blocks of j slots

1 block of ceil ((m + j )/2) slots 1 block of floor ((m + j )/2) slots

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Table 2.11: Encoding slot concatenation for different allocations and modulations

Modulation and rate j QPSK-1/2 j = 6 QPSK-3/4 j = 4 16-QAM-1/2 j = 3 16-QAM-3/4 j = 2 16-QAM-1/2 j = 2 16-QAM-2/3 j = 1 16-QAM-3/4 j = 1 Convolutional coding (CC)

Each FEC block is encoded by the binary convolutional encoder, which shall have native rate of 1/2, a constraint length equal to K = 7, and shall use the following generator polynomials codes to derive its two code bits:

G1= 171OCT F OR X

G2= 133OCT F OR Y

(2.15)

The generator is depicted in Figure2.19.

Figure 2.19: Convolutional encoder of rate 1/2

The puncturing patterns and serialization order that shall be used to realize different code rates are defined in Table 2.12: “1” means a transmitted bit and “0” denotes a removed bit, whereas X and Y are in reference to Figure 2.19.

Each FEC block is encoded by a tail-biting convolutional encoder, which is achieved by initializing the encoders memory with the last data bits of the FEC block being encoded (the packet data bits numbered bn−5...bn).

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Table 2.12: Convolutional code with puncturing configuration Code rates Rate 1/2 2/3 3/4 df ree 10 6 5 X 1 10 101 Y 1 11 110 XY X1Y1 X1Y1Y2 X1Y1Y2X2

Table 2.13: Useful data payload for a FEC Block

QPSK 16 QAM 64 QAM

Encoding rate R=1/2 R=3/4 R=1/2 R=3/4 R=1/2 R=2/3 R=3/4

Data payload (bytes) 6 9 12 12 18 18 18 18 24 24 24 27 27 30 36 36 36 36 36

Table 2.13defines the basic sizes of the useful data payloads to be encoded in relation with the selected modulation type and encoding rate and concatenation rule.

Interleaving

All encoded data bits shall be interleaved by a block interleaver with a block size corresponding to the number of coded bits per the encoded block size Ncbps. The interleaver is defined by a

two-step permutation. The first ensures that adjacent coded bits are mapped onto nonadjacent subcarriers. The second permutation insures that adjacent coded bits are mapped alternately onto less or more significant bits of the constellation, thus avoiding long runs of lowly reliable bits. Let Ncpcbe the number of coded bits per subcarrier, i.e., 2, 4, or 6 for QPSK, 16-QAM,

or 64-QAM, respectively. Let s = Ncpc/2. Within a block of Ncbps bits at transmission,

let k be the index of the coded bit before the first permutation, mk be the index of that

coded bit after the first and before the second permutation and let jk be the index after

the second permutation, just prior to modulation mapping, and d be the modulo used for the permutation. The first permutation is defined by Equation (2.16a), and the second by Equation (2.16b).

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mk= (Ncbps/d) · kmod(d)+ f loor(k/d) (2.16a)

jk= s · f loor(mk/s) + (mk+ Ncbps− f loor(d · mk/Ncbps))mod(s) (2.16b)

k = 0, 1, ..., Ncbps− 1 d = 16

The de-interleaver, which performs the inverse operation, is also defined by two permuta-tions. Within a received block of Ncbpsbits, let j be the index of a received bit before the first

permutation; mj be the index of that bit after the first and before the second permutation;

and let kj be the index of that bit after the second permutation, just prior to delivering the

block to the decoder. The first permutation is defined by Equation (2.17a) and the second by Equation (2.17b)

mj = s · f loor(j/s) + (j + f loor(d · j/Ncbps))mod(s) (2.17a)

kj = d · mj− (Ncbps− 1) · f loor(d · mj/Ncbps) (2.17b)

j = 0, 1, ..., Ncbps− 1 d = 16

The first permutation in the de-interleaver is the inverse of the second permutation in the interleaver, and conversely.

Modulation

Subcarrier randomization

The PRBS generator depicted hereafter shall be used to produce a sequence, wk see

Fig-ure2.20. The polynomial for the PRBS generator shall be X11+ X9+ 1. The value of the pilot modulation, on subcarrier k, shall be derived from wk. The initialization vector of the

PRBS generator for both UL and DL shall be designated b10..b0 so that

b0..b4 : 5 LSBs of IDcell as indicated by the frame preamble in the first DL zone. b0 is MSB and b4 is LSB.

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Figure 2.20: PRBS generator for pilot modulation

b5..b6 : Set to the segment number + 1 as indicated by the frame preamble in the first DL zone. b5 is MSB and b6 is LSB.

b7..b10 : 0b1111 (all ones) in the downlink. b7 is MSB and b10 is LSB.

Data modulation

After the repetition block, the data bits are entered serially to the constellation mapper. Gray-mapped QPSK and 16-QAM shall be supported, whereas the support of 64-QAM is optional. The constellations shall be normalized by multiplying the constellation point with the factor c to achieve equal average power. c factor for the constellation is respectively:

• c = 1/√2 for QPSK • c = 1/√10 for 16QAM • c = 1/√42 for 64QAM

Per-allocation adaptive modulation and coding shall be supported in the DL. Each m interleaved bits (M = 2,4,6) shall be mapped to the constellation bits b(M - 1) - b0 in MSB-first order (i.e., the MSB-first bit shall be mapped to the higher index bit in the constellation). The constellation-mapped data shall be subsequently modulated onto the allocated data subcarriers. Before mapping the data to the physical subcarriers (i.e., after applying the subcarrier permutation), each subcarrier shall be multiplied by the factor 2 · (1/2 − wk)

according to the subcarrier physical index, k.

In the DL, data subcarriers that belong to slots that are not allocated in the DL-MAP shall not be transmitted (zero energy). In other, such subcarriers that belong to the allocated slots for a burst but are not modulated shall not be transmitted (zero energy).

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Pilot modulation

In the DL PUSC, each pilot shall be transmitted with a boosting of 2.5 dB over the average non-boosted power of each data tone. These pilot subcarriers shall be modulated according to Equation (2.18). Re{ck} = 8 3 1 2− wk Im{ck} = 0 (2.18)

In the DL PUSC all pilots of the segment shall be modulated, regardless of whether all the subchannels are allocated in the DL-MAP.

Preamble pilot modulation

The pilots in the DL preamble shall follow the instructions on page48, and shall be modulated according to Equation (2.19):

Re{P reambleP ilotModulation} = 4 ·√2 · 1₂− wk

Im{P reambleP ilotModulation} = 0

(2.19)

Repetition

Repetition coding can be used to further increase signal margin over the modulation and FEC mechanisms. In the case of repetition coding, r = 2, 4, or 6, the number of allocated slots (Ns) shall be a whole multiple of the repetition factor r for UL. For the DL, the number of

the allocated slots (Ns) shall be in the range of [RxK, RxK + (R − 1)] where k is the number

of the required slots before applying the repetition scheme. For example, when the required number of slots before the repetition is 10(= k ) and the repetition of r = 6 shall be applied for the burst transmission, then the number of the allocated slots (Ns) for the burst can be

from 60 slots to 65 slots.

The binary data that fits into a region that is repetition coded is reduced by a factor R compared to a nonrepeated region of the (⌊Ns/R⌋)/R slots with the same size and FEC code

type. After FEC and bitinterleaving, the data is segmented into slots, and each group of bits designated to fit in a slot shall be repeated r times to form r contiguous slots following the normal slot ordering that is used for data mapping. This repetition scheme applies only to QPSK modulation.