THE STRUCTURE AND GENERATION OF ROBUST WAVEFORMS FOR FM IN-BAND ON-CHANNEL DIGITAL BROADCASTING Paul J. Peyla

iBiquity Digital Corporation 8865 Stanford Blvd. 20 Independence Blvd. Columbia, MD 21045 Warren, NJ 07058

iBiquity Digital Corporation has developed a IBOC SERVICES AND PROTOCOLS digital broadcasting solution that permits a In order to provide broadcaster flexibility and smooth evolution from current analog FM radio enhance the listening experience, iBiquity’s FM to a fully digital in-band on-channel (IBOC) IBOC system supports a variety of digital system. The system delivers digital audio and program services. These include a main program data services to mobile, portable, and fixed service (MPS), personal data service (PDS), receivers from terrestrial transmitters in the station identification service (SIS), and auxiliary existing VHF radio band. Broadcasters may application service (AAS). continue to transmit analog FM simultaneously with the new, higher-quality and more robust The MPS delivers existing programming digital signals. This approach allows formats in digital audio, along with digital data broadcasters to convert from analog to digital that directly correlates with the audio radio while maintaining their current frequency programming. Whereas the MPS broadcasts a allocations. This paper describes the structure, traditional audio program to listeners, the PDS generation, and inherent flexibility of the enables listeners to select on-demand data transmitted FM IBOC waveforms. services, thereby providing personalized, user- valued information. The SIS provides the control

and identification information required to allow INTRODUCTION the listener to search and select IBOC digital radio stations and their supporting services. iBiquity’s FM IBOC solution affords Finally, the AAS allows a virtually unlimited broadcasters the ability to tailor their digital number of custom and specialized IBOC digital audio broadcasts to meet their own specific radio applications to co-exist concurrently. needs. During the transition period to digital, Auxiliary applications can be added at any time each station will have the opportunity to convert in the future. at its own pace – beginning with a hybrid analog/digital waveform, and eventually turning Simultaneous support of these services is off the analog and broadcasting an all digital provided via the layered protocol stack signal. illustrated in Figure 1. Source material (audio or data) moves down the protocol stack from layer To support a wide variety of program formats 5 to layer 1 at the transmitter, is broadcast over and broadcaster requirements, the FM IBOC the air, and is passed back up the protocol stack system was designed with a high degree of from layer 1 to layer 5 at the receiver. flexibility. Each waveform – whether hybrid or all digital – can be configured in a number of At the transmitter, layer 5 receives audio or ways by judiciously adjusting the throughput, data program content from the broadcaster. latency, and robustness of the audio and data Layer 4 provides content-specific source program content as it is converted into an IBOC encoding (such as audio compression), as well as waveform. station identification and control capabilities. Layer 3 ensures robust and efficient transfer of This paper describes the structure and layer 4 data, and layer 2 provides limited error generation of the FM IBOC waveforms, and detection, addressing, and multiplexing. presents the various configurations from which a broadcaster can choose in order to transmit digital audio or data in a manner that best supports his or her particular programming needs.

1 Layer 5 (Application) Station Identification Main Program Service Service Others TRANSMITTED WAVEFORMS AND L5 MPS L5 MPS Audio Data SIS Data (PDS,AAS) SPECTRA

Layer 4 (Encoding) The iBiquity FM IBOC design provides a L4 MPS L4 MPS L4 SIS Audio Data Data flexible means of transitioning to a digital Coding Formatting Formatting broadcast system by providing three new Layer 3 (Transport) waveform types: hybrid, extended hybrid, and all L3 MPS L3 SIS digital. The hybrid and extended hybrid types retain the analog FM signal, while the all digital Layer 2 (Service Mux) type does not. L2 Service Multiplexer In all waveforms, the digital signal is modulated using orthogonal frequency division Layer 1 (Physical) multiplexing (OFDM). In a single-carrier digital L1 Physical modulation scheme, the digital symbols are transmitted serially, with the spectrum of each symbol occupying the entire channel bandwidth during its appointed signaling interval. Figure 1 IBOC Protocol Stack Conversely, OFDM is a parallel modulation scheme in which the data stream simultaneously Layer 1 receives the formatted content from modulates a large number of orthogonal layer 2 and creates an FM IBOC waveform for subcarriers. Instead of a single, wideband carrier over-the-air transmission in the VHF band. Since at a high signaling rate, OFDM employs a large most of the signal processing required to number of narrowband subcarriers that are generate an FM IBOC waveform occurs in layer simultaneously transmitted at a much lower 1, it is the focus of this paper. composite symbol rate. The long symbol times Formatted program content is received from of OFDM provide superior robustness in the layer 2 in discrete transfer frames via multiple presence of multipath fading and interference.1 logical channels. A transfer frame is an ordered OFDM is also inherently flexible, readily collection of bits originating in layer 2, grouped allowing the mapping of specific logical for processing through a logical channel. A channels to different groups of subcarriers. logical channel is simply a signal path that The following sections describe the conducts transfer frames from layer 2 through transmitted spectrum for each of the three digital layer 1 with a specified grade of service. The waveform types. Each spectrum is divided into service mode defines the active logical channels several sidebands, which represent various and their associated transmission characteristics. OFDM subcarrier groupings. All spectra are This paper describes the FM IBOC system by illustrated at baseband, with an upper and lower introducing the following concepts: sideband centered around 0 Hz. • transmitted waveforms and spectra – Frequency partitions and spectral conventions describes the spectral structure of the The OFDM subcarriers are assembled into broadcast IBOC waveforms frequency partitions. Each frequency partition is • system configuration – describes the comprised of eighteen data subcarriers and one means by which a broadcaster can tailor reference subcarrier, as shown in Figure 2 a particular IBOC waveform to meet his (ordering A) and Figure 3 (ordering B). The or her specific needs position of the reference subcarrier (ordering A • logical channels – describes the or B) varies with the location of the frequency 2 conduits which carry the formatted partition within the spectrum. program content through layer 1, and For each frequency partition, data subcarriers their intended use d1 through d18 convey digital program content, • functional components – describes the while the reference subcarrier conveys system layer 1 processes used to convert logical control. OFDM subcarriers are numbered from 0 channels of formatted program content at the center frequency to ±546 at either end of to an FM IBOC waveform the channel frequency allocation.

2 Reference Subcarrier 18 Data Subcarriers Besides the reference subcarriers resident within each frequency partition, depending on the service mode, up to five additional reference subcarriers are inserted into the spectrum at subcarrier numbers −546, −279, 0, 279, and 546. ce n 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 d d d d d d d d d 1 1 1 1 1 1 1 1 1 re d d d d d d d d d fe The overall effect is a regular distribution of e R Frequency reference subcarriers throughout the spectrum.

Figure 2 Frequency Partition – Ordering A For notational convenience, each reference subcarrier is assigned a unique identification number between 0 and 60. All lower sideband reference subcarriers are shown in Figure 4. All upper sideband reference subcarriers are shown in Figure 5. The figures indicate the relationship Reference Subcarrier between reference subcarrier numbers and 18 Data Subcarriers OFDM subcarrier numbers. Each spectrum described in the remaining subsections shows the subcarrier number and center frequency of certain key OFDM

0 1 2 3 4 5 6 7 8 e 1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 c d d d d d d d d d d d d d d d d d d n re subcarriers. The center frequency of a subcarrier fe e Frequency R is calculated by multiplying the subcarrier

number by the OFDM subcarrier spacing ∆f ≈ 363.373 Hz. The center of subcarrier 0 is located Figure 3 Frequency Partition – Ordering B at 0 Hz. In this context, center frequency is relative to the radio frequency (RF) allocated channel.

Lower Secondary Sideband

Lower Primary Sideband -527 -394 -375 -356 -337 -318 -299 -280 -546 -508 -489 -470 -451 -432 -413 OFDM -209 -279 -266 -247 -228 -190 -171 -152 -133 -114 -57 -38 -19 -95 -76 Subcarrier Numbers Frequency 0 1 2 3 4 5 6 7 8 9 10 11 12 13 1415 16 17 18 19 20 21 22 23 24 25 26 27 28 29 Reference Subcarrier Numbers

Figure 4 Lower Sideband Reference Subcarrier Spectral Mapping

Upper Primary Sideband

Upper Secondary Sideband

OFDM 356 508 527 546 280 299 318 337 375 394 413 432 451 470 489 Subcarrier 114 133 152 171 190 209 228 247 266 279 38 19 57 76 95 0 Numbers

Frequency 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 4546 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Reference Subcarrier Numbers

Figure 5 Upper Sideband Reference Subcarrier Spectral Mapping

3 Hybrid waveform In the hybrid waveform, the digital signal is The power spectral density of each OFDM transmitted in primary main (PM) sidebands on subcarrier in the PM sideband, relative to the either side of the analog FM signal, as shown in host analog power, is given in Table 1. A value Figure 6. The analog signal may be monophonic of 0 dB would produce a digital subcarrier whose or stereo, and may include SCA channels. Each power was equal to the total power in the PM sideband is comprised of ten frequency unmodulated analog FM carrier. The value was partitions, which are allocated among subcarriers chosen so that the total average power in a 356 through 545, or -356 through -545. primary main digital sideband (upper or lower) is Subcarriers 546 and -546, also included in the 23 dB below the total power in the unmodulated PM sidebands, are additional reference analog FM carrier. subcarriers. Table 1 summarizes the upper and lower primary main sidebands for the hybrid waveform.

Lower Digital Upper Digital Additional Additional Reference Sideband Sideband Reference Subcarrier Subcarrier Primary Primary

Main Main

Analog FM Signal 10 frequency 10 frequency partitions partitions

-198,402 Hz -129,361 Hz 129,361 Hz 198,402 Hz # -546 # -356 0 Hz # 356 # 546 # 0

Figure 6 Spectrum of the Hybrid Waveform

Table 1 Hybrid Waveform Spectral Summary center) center) Ordering Ordering Sideband Number of Comments Comments per subcarrier) (Hz from channel (Hz from channel dBc Subcarrier Range Subcarrier Range ( Frequency Partition Partition Frequency Frequency Partitions Partitions Frequency (Hz) Span Frequency Power Spectral Density Density Spectral Power Subcarrier Frequencies Subcarrier Frequencies

Includes Upper 356 129,361 additional Primary 10 A to to 69,041 -45.8 reference Main 546 198,402 subcarrier 546 Includes Lower -356 -129,361 additional Primary 10 B to to 69,041 -45.8 reference Main -546 -198,402 subcarrier -546

4 Extended hybrid waveform The extended hybrid waveform is created by The power spectral density of each OFDM adding OFDM subcarriers to the primary main subcarrier in the PM and PX sidebands, relative sidebands present in the hybrid waveform, as to the host analog power, is given in Table 2. shown in Figure 7. Depending on the service Like the hybrid waveform, the value was chosen mode, one, two, or four frequency partitions can so that the total average power in a primary main be added to the inner edge of each primary main sideband (upper or lower) is 23 dB below the sideband. This additional spectrum is termed the total power in the unmodulated analog FM primary extended (PX) sideband. Table 2 carrier. The level of the subcarriers in the PX summarizes the upper and lower primary sidebands is equal to the level of the subcarriers sidebands for the extended hybrid waveform. in the PM sidebands.

Additional Lower Digital Upper Digital Additional Reference Sideband Sideband Reference Subcarrier Subcarrier Primary Primary

Main Main Extended Extended

10 1, 2, or 4 1, 2, or 4 10 frequency Analog FM Signal frequency frequency partitions partitions partitions frequency partitions

-198,402 Hz -129,361 Hz (# -356) 129,361 Hz (# 356) 198,402 Hz (# -546) 0 Hz (# 0) (# 546) -122,457 Hz (# -337) 122,457 Hz (# 337)

-115,553 Hz (# -318) 115,553 Hz (# 318) -101,744 Hz (# -280) 101,744 Hz (# 280)

Figure 7 Spectrum of the Extended Hybrid Waveform

5

Table 2 Extended Hybrid Waveform Spectral Summary (Hz) Range center) center) Partition Ordering Ordering Sideband Partitions Number of Subcarrier Subcarrier Frequency Frequency Frequency Comments Comments subcarrier) from channel channel from Power Spectral Frequencies (Hz (Hz Frequencies Frequency Span Span Frequency Density (dBc per Density (dBc

Includes 356 129,361 additional Upper Primary 10 A to to 69,041 -45.8 reference Main 546 198,402 subcarrier 546 Includes -356 -129,361 additional Lower Primary 10 B to to 69,041 -45.8 reference Main -546 -198,402 subcarrier -546 Upper Primary 337 122,457 Extended 1 A to to 6,540 -45.8 none (1 frequency 355 128,997 partition) Lower Primary -337 -122,457 Extended 1 B to to 6,540 -45.8 none (1 frequency -355 -128,997 partition) Upper Primary 318 115,553 Extended 2 A to to 13,444 -45.8 none (2 frequency 355 128,997 partitions) Lower Primary -318 -115, 553 Extended 2 B to to 13,444 -45.8 none (2 frequency -355 -128,997 partitions) Upper Primary 280 101,744 Extended 4 A to to 27,253 -45.8 none (4 frequency 355 128,997 partitions) Lower Primary -280 -101, 744 Extended 4 B to to 27,253 -45.8 none (4 frequency -355 -128,997 partitions)

6

All digital waveform The all digital waveform is constructed by not contain frequency partitions as defined in disabling the analog signal, fully expanding the Figure 2 and Figure 3. bandwidth of the primary digital sidebands, and The total frequency span of the entire all adding lower-power secondary sidebands in the digital spectrum is 396,803 Hz. Table 3 spectrum vacated by the analog signal. The summarizes the upper and lower, primary and spectrum of the all digital waveform is shown in secondary sidebands for the all digital waveform. Figure 8. The power spectral density of each OFDM In addition to the ten main frequency subcarrier is given in Table 3. As with the hybrid partitions, all four extended frequency partitions and extended hybrid waveforms, the values are are present in each primary sideband of the all relative to the level of the unmodulated analog digital waveform. Each secondary sideband also FM carrier that is allocated for a particular has ten secondary main (SM) and four secondary broadcaster (even though the analog carrier is not extended (SX) frequency partitions. Unlike the transmitted in the all digital waveform). primary sidebands, however, the secondary main frequency partitions are mapped nearer to The primary sideband level sets the total channel center with the extended frequency average power in a primary digital subcarrier at partitions farther from the center. least 10 dB above the total power in a hybrid primary digital subcarrier. Any one of four Each secondary sideband also supports a power levels may be selected for application to small secondary protected (SP) region consisting the secondary sidebands. The four secondary of 12 OFDM subcarriers and reference subcarrier power levels set the power spectral density of the 279 or -279. The sidebands are referred to as secondary digital subcarriers (upper and lower) “protected” because they are located in the area in the range of 5 to 20 dB below the power of spectrum least likely to be affected by analog spectral density of the all digital primary or digital interference. An additional reference subcarriers. A single secondary power level is subcarrier is placed at the center of the channel evenly applied to all secondary sidebands. (0). Frequency partition ordering of the SP region does not apply since the SP region does

Lower Digital Sideband Upper Digital Sideband Additional Additional Reference Primary Secondary Secondary Primary Reference Subcarrier Subcarrier

Main Extended Extended Main

Protected Protected 10 frequency 4 4 10 frequency frequency Main Main frequency partitions partitions partitions Extended Extended partitions 12 subcarriers 12 subcarriers

4 4 frequency 10 frequency 10 frequency frequency partitions partitions partitions partitions

-198,402 Hz -129,361 Hz (# -356) -97,021 Hz 97,021 Hz 129,361 Hz (# 356) 198,402 Hz (# -546) (# -267) 0 Hz (# 267) (# 546) -101,744 Hz (# -280) -69,404 Hz (# 0) 69,404Hz 101,744 Hz (# 280) (# -191) (# 191)

Additional Additional -101,381 Hz 101,381 Hz Reference Reference (# -279) (# 279) Subcarrier Subcarrier

Figure 8 Spectrum of the All Digital Waveform

7 Table 3 All Digital Waveform Spectral Summary Power Range center) center) Density channel channel Spectral Spectral Partition (Hz from (dBc per Ordering Ordering Sideband Partitions Span (Hz) Number of Subcarrier Subcarrier Frequency Frequency Frequency Frequency Comments Comments subcarrier) subcarrier) Frequencies Frequencies

Includes Upper 356 129,361 additional Primary 10 A to to 69,041 -35.8 reference Main 546 198,402 subcarrier 546 Includes Lower -356 -129,361 additional Primary 10 B to to 69,041 -35.8 reference Main -546 -198,402 subcarrier -546 Upper 280 101,744 Primary 4 A to to 27,253 -35.8 none Extended 355 128,997 Lower -280 -101,744 Primary 4 B to to 27,253 -35.8 none Extended -355 -128,997 -40.8, Includes Upper 0 0 -45.8, additional Secondary 10 B to to 69,041 -50.8, reference Main 190 69,041 -55.8 subcarrier 0 -40.8, Lower -1 -363 -45.8, Secondary 10 A to to 68,678 none -50.8, Main -190 -69,041 -55.8 -40.8, Upper 191 69,404 -45.8, Secondary 4 B to to 27,253 none -50.8, Extended 266 96,657 -55.8 -40.8, Lower -191 -69,404 -45.8, Secondary 4 A to to 27,253 none -50.8, Extended -266 -96,657 -55.8 Includes -40.8, Upper 267 97,021 additional -45.8, Secondary N/A N/A to to 4,360 reference -50.8, Protected 279 101,381 subcarrier -55.8 279 Includes -40.8, Lower -267 -97,021 additional -45.8, Secondary N/A N/A to to 4,360 reference -50.8, Protected -279 -101,381 subcarrier -55.8 -279

8 Noise and emissions limits All FM IBOC transmissions will remain MS4 configure the secondary sidebands in the all within the FCC emissions mask in accordance digital waveform. The allowable service modes with CFR Title 47 §73.317, as summarized in for each FM IBOC waveform type are Table 4.3 Measurements of the analog signal are summarized in Table 5. made at the antenna input by averaging the Table 5 Allowable Service Modes for FM IBOC power spectral density in a 1-kHz bandwidth Waveforms over a 10-second segment of time. Table 4 FCC RF Spectral Emissions Mask Primary Secondary Waveform Service Service Modes Modes Offset from Power Spectral Density Carrier Relative to Unmodulated Hybrid MP1 None Frequency Analog FM Carrier Extended MP2 – MP7 None (kHz) (dBc/kHz) Hybrid 120 to 240 -25 All Digital MP5 – MP7 MS1 – MS4 240 to 600 -35 All waveforms require the definition of a -80, or -43 - (10 · log10 [power in watts]), primary and a secondary service mode. If whichever is less, where secondary sidebands are not present (as in the greater than 600 [power in watts] refers to hybrid or extended hybrid waveform), the the total unmodulated secondary service mode is set to “None.” transmitter output carrier Service modes MP1 through MP4 are invalid for power the all digital waveform. Only primary service modes MP5 through MP7 may be paired with secondary service modes MS1 through MS4 SYSTEM CONFIGURATION when broadcasting the all digital waveform. Any combination of these primary and secondary The FM IBOC transmission system is service modes is allowable. configured through primary and secondary service modes, analog diversity delay, and Table 5 indicates that there are up to 19 sideband power levels. The system configuration possible combinations of service modes, thereby determines how the various logical channels are providing ample flexibility to the broadcaster. combined to generate the transmitted waveform. The actual configuration of logical channels by service mode, the assignment of program content Service modes to the active logical channels, and the subsequent The service modes dictate the performance mapping of the logical channels to the and configuration of the logical channels, which appropriate digital sidebands is detailed in later carry program content through layer 1. There are sections. two types of service modes: primary service Analog diversity delay modes, which configure primary logical channels, and secondary service modes, which To provide robust reception during outages configure secondary logical channels. The seven typical of a mobile environment, the FM IBOC primary service modes are MP1, MP2, MP3, system applies time diversity between MP4, MP5, MP6, and MP7. The four secondary independent analog and digital transmissions of service modes are MS1, MS2, MS3, and MS4. the same audio source. In addition, a blend function allows graceful audio degradation of the Service mode MP1 is used to broadcast the digital signal as the receiver nears the edge of a hybrid waveform. Service modes MP2 through station’s coverage. The FM IBOC system can MP4 increase the capacity of the hybrid provide this capability by delaying the analog waveform by adding one, two, or four extended transmission by several seconds relative to the frequency partitions to each primary sideband. digital audio transmission. When the digital Service modes MP5 through MP7 employ all signal is corrupted, the receiver blends to analog primary extended frequency partitions, and are which, by virtue of its time diversity with the used to broadcast the extended hybrid or all digital signal, does not experience the outage.4 digital waveform. Service modes MS1 through

9 To support this feature, in service modes block-oriented operations of layer 1 (such as MP1 through MP4, the analog audio is delayed interleaving) require that it process data in in an upper protocol layer by a fixed duration to discrete transfer frames, rather than continuous realize time diversity with the digital audio. streams. As a result, throughput is calculated as When the system is transmitting the extended the product of transfer frame size and transfer hybrid waveform in service modes MP5 – MP7, frame rate. Spectral mapping and channel code or the all digital waveform, the analog diversity rate determine the throughput of a logical delay is automatically set to zero. channel, since spectral mapping limits capacity and coding overhead limits information Sideband power levels throughput. The levels of the primary and secondary Latency. Latency is the delay that a logical sidebands are independently scaled. Primary channel imposes on a transfer frame as it sideband power levels are fixed, and depend on traverses layer 1. The latency of a logical the transmitted waveform. Hybrid and extended channel is defined as the sum of its interleaver hybrid waveforms have a different primary depth and diversity delay. It does not include power level than all digital waveforms. processing delay or delays through higher One of four secondary sideband power levels protocol layers. must be selected for application to each of the The interleaver depth determines the amount secondary sidebands. They allow the power of delay imposed on a logical channel by its spectral density of the secondary digital interleaver. Diversity delay is also applied to subcarriers to lie 5, 10, 15, or 20 dB below the some logical channels to improve robustness. power spectral density of the all digital primary For example, in some service modes, logical subcarriers. channel P1 presents dual processing paths; one LOGICAL CHANNELS path is delayed and the other is not. A logical channel is a signal path that Robustness. Robustness is the ability of a conducts program content through layer 1 with a logical channel to withstand channel specific grade of service, as determined by the impairments such as noise, interference, and service mode. There are ten logical channels, fading. There are eleven relative levels of although not all are used in every service mode. robustness in the FM IBOC system. A robustness The variety of logical channels reflects the of 1 indicates a very high level of resistance to inherent flexibility of the system. channel impairments, while an 11 indicates a lower tolerance for channel-induced errors. There are four primary logical channels, denoted as P1, P2, P3, and PIDS. There are six Spectral mapping, channel code rate, secondary logical channels that are used only interleaver depth, and diversity delay determine with the all digital waveform. They are denoted the robustness of a logical channel. Spectral as S1, S2, S3, S4, S5, and SIDS. Logical mapping affects robustness by setting the relative channels P1 through P3 and S1 through S5 are power level, spectral interference protection, and designed to convey digital audio and data, while frequency diversity of a logical channel. Channel the PIDS and SIDS logical channels are designed coding increases robustness by introducing to carry IBOC data service (IDS) information. redundancy into the logical channel. Interleaver depth influences performance in multipath The performance of each logical channel is fading. Finally, some logical channels in certain completely described through three service modes delay transfer frames by a fixed characterization parameters: throughput, latency, duration to realize time diversity. This diversity and robustness. The service mode sets these delay also affects robustness, since it mitigates characterization parameters by defining the the effects of the mobile radio channel. spectral mapping, interleaver depth, diversity delay, and channel encoding for each active Assignment of characterization parameters logical channel. Table 6 through Table 16 show the active Characterization parameters logical channels and their characterization parameters – throughput, latency, and relative Throughput. Throughput defines the layer 1 robustness – for a given service mode. A audio or data capacity of a logical channel, broadcaster might use these tables as a basis of excluding upper layer framing overhead. The comparison when selecting a service mode.

10 Table 6 Logical Channels - Service Mode MP1 Table 12 Logical Channels – Service Mode MP7

Logical Throughput Latency Relative Logical Throughput Latency Relative Channel (kbps) (seconds) Robustness Channel (kbps) (seconds) Robustness P1 98.4 1.49 2 P1 24.8 0.19 4 PIDS 0.9 0.09 3 P2 98.4 1.49 2 P3 24.8 0.19 4 Table 7 Logical Channels - Service Mode MP2 PIDS 0.9 0.09 3

Logical Throughput Latency Relative Table 13 Logical Channels – Service Mode MS1 Channel (kbps) (seconds) Robustness

P1 98.4 1.49 2 Logical Throughput Latency Relative P3 12.4 0.19 4 Channel (kbps) (seconds) Robustness PIDS 0.9 0.09 3 S4 98.4 0.19 7

S5 5.5 0.09 6 Table 8 Logical Channels - Service Mode MP3 SIDS 0.9 0.09 8

Logical Throughput Latency Relative Table 14 Logical Channels – Service Mode MS2 Channel (kbps) (seconds) Robustness P1 98.4 1.49 2 Logical Throughput Latency Relative P3 24.8 0.19 4 Channel (kbps) (seconds) Robustness PIDS 0.9 0.09 3 S1 24.8 4.64 5

S2 73.6 1.49 9 Table 9 Logical Channels – Service Mode MP4 S3 24.8 0.19 11 S5 5.5 0.09 6 Logical Throughput Latency Relative SIDS 0.9 0.09 10 Channel (kbps) (seconds) Robustness P1 98.4 1.49 2 Table 15 Logical Channels – Service Mode MS3 P3 49.6 0.19 4 PIDS 0.9 0.09 3 Logical Throughput Latency Relative Channel (kbps) (seconds) Robustness Table 10 Logical Channels - Service Mode MP5 S1 49.6 4.64 5 S2 48.8 1.49 9 Logical Throughput Latency Relative S5 5.5 0.09 6 Channel (kbps) (seconds) Robustness SIDS 0.9 0.09 10 P1 24.8 4.64 1 P2 73.6 1.49 2 Table 16 Logical Channels – Service Mode MS4 P3 24.8 0.19 4 PIDS 0.9 0.09 3 Logical Throughput Latency Relative Channel (kbps) (seconds) Robustness

Table 11 Logical Channels - Service Mode MP6 S1 24.8 0.19 11 S2 98.4 1.49 9 Logical Throughput Latency Relative S3 24.8 0.19 11 Channel (kbps) (seconds) Robustness S5 5.5 0.09 6 P1 49.6 4.64 1 SIDS 0.9 0.09 10 P2 48.8 1.49 2 PIDS 0.9 0.09 3

11 Spectral mapping mode MP1, the P1 and PIDS logical channels carry MPS audio and SIS data on each primary For a given service mode, each logical main sideband. In addition, the P3 logical channel is assigned to a group of OFDM channel is designed to carry additional data subcarriers or frequency partitions. This spectral services, such as MPS, PDS, or AAS data, on the mapping contributes to the throughput and primary extended sidebands. Identical program robustness of the logical channel. material is carried on each sideband, so that the Since this is a digital system, the various alternate sideband would be available if the other logical channels are simply conduits for the sideband were corrupted. delivery of bits; the content of the bits is immaterial. However, the service modes were designed with specific services in mind for the Lower Sideband Upper Sideband active logical channels. As a result, although not Primary Primary strictly required, the recommended use of the Main Main Extended Extended

1 1 logical channels is described along with the 10 frequency partitions frequency frequency 10 frequency partitions partition partition Analog FM Signal spectral mapping in the following sections. PIDS PIDS P3 P3 P1 P1 Primary spectral mapping. The following sections illustrate the assignment of primary -198,402 Hz -129,361 Hz 129,361 Hz 198,402 Hz 0 Hz 122,457 Hz logical channels to the primary sidebands, and -122,457 Hz describe the intended application of the logical channels for each primary service mode. Figure 10 Spectral Mapping – Service Mode MP2 Service mode MP1 spectral mapping. The assignment of logical channels to OFDM Service mode MP3 spectral mapping. The subcarriers in service mode MP1 is shown in assignment of logical channels to OFDM Figure 9. Both the P1 and PIDS logical channels subcarriers in service mode MP3 is shown in are mapped to the upper and lower primary main Figure 11. The transmitted spectrum in service sidebands. In service mode MP1, the P1 logical mode MP3 is identical to service mode MP1, channel is designed to carry the MPS audio, with the addition of two extended frequency while the PIDS logical channel would carry SIS partitions to each primary sideband. As in data. Identical program material is carried on service mode MP1, the P1 and PIDS logical each sideband (upper and lower), so that the channels carry MPS audio and SIS data on each alternate sideband would be available if the other primary main sideband. In addition, the P3 sideband were corrupted. logical channel is designed to carry additional data services, such as MPS, PDS, or AAS data, on the primary extended sidebands. Identical program material is carried on each sideband, so that the alternate sideband would be available if the other sideband were corrupted. Lower Sideband Upper Sideband Primary Primary

Main Main

10 frequency partitions 10 frequency partitions Analog FM Signal PIDS PIDS

P1 P1 Lower Sideband Upper Sideband Primary Primary

Main -198,402 Hz -129,361 Hz 129,361 Hz 198,402 Hz Main 0 Hz Extended Extended 2 2 10 frequency partitions frequency frequency 10 frequency partitions partitions partitions Analog FM Signal PIDS PIDS P3 P3 Figure 9 Spectral Mapping – Service Mode MP1 P1 P1

-198,402 Hz -129,361 Hz 129,361 Hz 198,402 Hz

Service mode MP2 spectral mapping. The -122,457 Hz 0 Hz 122,457 Hz assignment of logical channels to OFDM -115,553 Hz 115,553 Hz subcarriers in service mode MP2 is shown in Figure 10. The transmitted spectrum in service Figure 11 Spectral Mapping – Service Mode MP3 mode MP2 is identical to service mode MP1, with the addition of a single extended frequency partition to each primary sideband. As in service

12 Service mode MP4 spectral mapping. The same P1 logical channel is diversity delayed and assignment of logical channels to OFDM separately mapped to the inner two extended subcarriers in service mode MP4 is shown in frequency partitions of each primary sideband. Figure 12. The transmitted spectrum in service At the receiver, the two P1 channels are mode MP4 is identical to service mode MP1, combined to form a more robust backup core with the addition of all four extended frequency audio stream. partitions to each primary sideband. As in service mode MP1, the P1 and PIDS logical channels carry MPS audio and SIS data on each primary main sideband. In addition, the P3 Lower Sideband Upper Sideband logical channel is designed to carry additional Primary Primary data services, such as MPS, PDS, or AAS data, Main Main Extended Extended

4 4 on the primary extended sidebands. Identical 10 frequency partitions frequency Analog FM Signal frequency 10 frequency partitions partitions partitions program material is carried on each sideband, so PIDS PIDS P3 P1 P1 P3 that the alternate sideband would be available if P1 and P2 (Not present in All Digital waveform) P1 and P2 the other sideband were corrupted. -198,402 Hz -129,361 Hz 129,361 Hz 198,402 Hz

-115,553 Hz 0 Hz 115,553 Hz -101,744 Hz 101,744 Hz

Lower Sideband Upper Sideband Figure 13 Spectral Mapping – Service Mode MP5 Primary Primary

Main Main Extended Extended

4 4 In hybrid and extended hybrid waveforms, 10 frequency partitions frequency frequency 10 frequency partitions partitions Analog FM Signal partitions PIDS PIDS the analog host provides fast tuning and a P3 P3 P1 P1 diversity-delayed backup channel for graceful degradation of audio near the edge of coverage. -198,402 Hz -129,361 Hz 129,361 Hz 198,402 Hz -115,553 Hz 0 Hz 115,553 Hz In the all digital waveform, the analog host no -101,744 Hz 101,744 Hz longer exists. In this case, the robust P1 logical channel, carrying core audio, acts as the backup Figure 12 Spectral Mapping – Service Mode MP4 for graceful audio degradation and fast tuning (since it is lightly interleaved). When the Service modes MP1 through MP4 provide enhanced audio is not available, the receiver essentially the same program services, with reverts to the backup core audio stream. varying data capacity via the P3 logical channel on the primary extended sidebands. The P3 logical channel also carries additional data services, such as MPS, PDS, or AAS data, Service Mode MP5 Spectral Mapping. The on the primary extended sidebands. As in service assignment of logical channels to OFDM modes MP1-MP4, the PIDS logical channel subcarriers in service mode MP5 is shown in carries SIS data over the primary main Figure 13. The transmitted spectrum is identical sidebands. Again, identical program material is in service modes MP4 and MP5. However, the carried on each sideband, so that the alternate spectral mapping in service mode MP5 allows sideband would be available if the other sideband operation as either an extended hybrid or all were corrupted. digital waveform. Service Mode MP6 Spectral Mapping. The In service mode MP5, the MPS audio is assignment of logical channels to OFDM divided into core and enhanced audio streams. subcarriers in service mode MP6 is shown in The core audio is a stand-alone, low bitrate (~25 Figure 14. The transmitted spectrum is identical kbps), backup audio stream. When the core audio to service mode MP5. However, in service mode is combined with enhanced audio, the result is a MP6, the size of the core audio stream is doubled virtual-CD quality (~98 kbps) audio stream. The to a higher quality ~50 kbps. As a result, all four enhanced audio is not autonomous; it can only be frequency partitions in the primary extended used in combination with the core audio stream. sideband are required to carry the backup core In service mode MP5, the core MPS audio audio, and capacity is no longer available for stream is carried by the P1 logical channel, and data. Thus, the increased data capacity in service the enhanced audio is carried by the P2 logical mode MP5 is traded for core audio quality in channel. Both P1 and P2 are mapped together in service mode MP6. the primary main sidebands. In addition, the

13 As in service mode MP5, the P3 logical channel carries additional data services, such as Lower Sideband Upper Sideband MPS, PDS, or AAS data, on the primary Primary Primary

Main Main extended sidebands. The PIDS logical channel Extended Extended 4 4 also carries SIS data over the primary main 10 frequency partitions frequency Analog FM Signal frequency 10 frequency partitions partitions partitions

PIDS PIDS sidebands. As always, identical program material P1 (Not present in All Digital waveform) P1 P1 and P2 P1 and P2 is carried on each sideband, so that the alternate sideband would be available if the other sideband

-198,402 Hz -129,361 Hz 129,361 Hz 198,402 Hz

-115,553 Hz 0 Hz 115,553 Hz were corrupted. -101,744 Hz 101,744 Hz Secondary spectral mapping. The Figure 14 Spectral Mapping – Service Mode MP6 following sections illustrate the assignment of secondary logical channels to the secondary In service mode MP6, the core MPS audio sidebands, and describe the intended application stream is carried by the P1 logical channel, and of the logical channels for each secondary the enhanced audio is carried by the P2 logical service mode. Secondary sidebands are present channel. Both P1 and P2 are mapped together in only in the all digital waveform. the primary main sidebands. In addition, the Only the secondary sidebands are presented same P1 logical channel is diversity delayed and in the following subsections; the added presence separately mapped to all four extended frequency of primary digital sidebands in service modes partitions of each primary sideband. The PIDS MP5, MP6, or MP7 is implied. logical channel also carries SIS data over the primary main sidebands. Identical program Service Mode MS1 Spectral Mapping. The material is carried on each sideband, so that the assignment of logical channels to OFDM alternate sideband would be available if the other subcarriers in service mode MS1 is shown in sideband were corrupted. Figure 16. Service mode MS1 is intended for the transmission of secondary broadband data. Service Mode MP7 Spectral Mapping. The assignment of logical channels to OFDM subcarriers in service mode MP7 is shown in Lower Sideband Upper Sideband Secondary Secondary Figure 15. The transmitted spectrum is identical to service modes MP5 and MP6. However, service mode MP7 provides enhanced data Protected Protected capacity by reducing the amount of spectrum Main Main Extended Extended devoted to audio programming. SIDS SIDS S S 12 5 5 12 subcarriers S4 S4 subcarriers

4 10 frequency 10 frequency 4 frequency frequency -101,381 Hz partitions partitions partitions partitions 101,381 Hz

-97,021 Hz -69,404 Hz 0 Hz 69,404 Hz 97,021 Hz Lower Sideband Upper Sideband Primary Primary

Main Main Extended Extended Figure 16 Spectral Mapping – Service Mode MS1 4 4 10 frequency partitions frequency Analog FM Signal frequency 10 frequency partitions partitions partitions

PIDS PIDS P3 P1 (Not present in All Digital waveform) P1 P3 P2 P2 In service mode MS1, logical channel S4 carries MPS, PDS, or AAS data over the

-198,402 Hz -129,361 Hz 129,361 Hz 198,402 Hz secondary main and extended sidebands. In -115,553 Hz 0 Hz 115,553 Hz -101,744 Hz 101,744 Hz addition, the SIDS logical channel also carries SIS data over the secondary main and extended Figure 15 Spectral Mapping – Service Mode MP7 sidebands. Finally, the S5 logical channel carries MPS, PDS, or AAS data over the secondary In service mode MP7, MPS audio is carried protected sidebands. by the P1 logical channel, which is mapped to As with the primary sidebands, identical the inner two extended frequency partitions of program material is carried on each secondary each primary sideband. Logical channel P2 sideband (upper and lower), so that the alternate carries MPS, PDS, or AAS data over the primary sideband would be available if the other sideband main sidebands. were corrupted.

14 Service Mode MS2 Spectral Mapping. The Lower Sideband Upper Sideband assignment of logical channels to OFDM Secondary Secondary subcarriers in service mode MS2 is shown in

Figure 17. Service mode MS2 is the secondary Protected Protected equivalent of primary service mode MP5. Main Main Extended Extended SIDS SIDS S S1 S1 S 12 5 5 12 subcarriers S1 and S2 S1 and S2 Lower Sideband Upper Sideband subcarriers Secondary Secondary 4 10 frequency 10 frequency 4 frequency frequency -101,381 Hz partitions partitions partitions partitions 101,381 Hz

-97,021 Hz -69,404 Hz 0 Hz 69,404 Hz 97,021 Hz

Protected Protected Main Main Extended Extended Figure 18 Spectral Mapping – Service Mode MS3 SIDS SIDS S S1 S3 S3 S1 S 12 5 5 12 Both S1 and S2 are mapped together in the subcarriers S1 and S2 S1 and S2 subcarriers

4 10 frequency 10 frequency 4 secondary main sidebands. In addition, the same frequency partitions partitions frequency -101,381 Hz partitions partitions 101,381 Hz S1 logical channel is diversity delayed and -97,021 Hz -69,404 Hz 0 Hz 69,404 Hz 97,021 Hz separately mapped to all four extended frequency

partitions of each secondary sideband. The SIDS logical channel also carries SIS data over the secondary main sidebands. Finally, the S5 Figure 17 Spectral Mapping – Service Mode MS2 logical channel carries MPS, PDS, or AAS data over the secondary protected sidebands. Identical In service mode MS2, the S1 and S2 logical program material is carried on each sideband, so channels might carry core and enhanced that the alternate sideband would be available if auxiliary audio (such as surround sound), the other sideband were corrupted. intended to enhance the MPS audio broadcast on the primary sidebands. Both S1 and S2 are Service Mode MS4 Spectral Mapping. The mapped together in the secondary main assignment of logical channels to OFDM sidebands. In addition, the same S1 logical subcarriers in service mode MS4 is shown in channel is diversity delayed and separately Figure 19. Service mode MS4 is the secondary mapped to the outer two extended frequency equivalent of primary service mode MP7. It is partitions of each secondary sideband. intended for broadcast of a single, low-bitrate audio stream, with the remaining capacity The S3 logical channel carries additional data reserved for data services. services, such as MPS, PDS, or AAS data, on the secondary extended sidebands. The SIDS logical channel also carries SIS data over the secondary main sidebands. Finally, the S5 logical channel Lower Sideband Upper Sideband carries MPS, PDS, or AAS data over the Secondary Secondary secondary protected sidebands. Identical program material is carried on each secondary Protected Protected sideband, so that the alternate sideband would be Main Main available if the other sideband were corrupted. Extended Extended SIDS SIDS S S1 S3 S3 S1 S Service Mode MS3 Spectral Mapping. The 12 5 5 12 subcarriers S2 S2 subcarriers assignment of logical channels to OFDM 4 10 frequency 10 frequency 4 frequency partitions partitions frequency subcarriers in service mode MS3 is shown in -101,381 Hz partitions partitions 101,381 Hz Figure 18. Service mode MS3 is the secondary -97,021 Hz -69,404 Hz 0 Hz 69,404 Hz 97,021 Hz equivalent of primary service mode MP6. Figure 19 Spectral Mapping – Service Mode MS4

As in service mode MS2, the S1 and S2 In service mode MS4, the low-bitrate audio is logical channels might carry core and enhanced carried by the S1 logical channel, which is auxiliary audio (such as surround sound), mapped to the outer two extended frequency intended to enhance the MPS audio broadcast on partitions of each secondary sideband. Logical the primary sidebands. However, in service channel S2 carries MPS, PDS, or AAS data over mode MS3, the size of S1 is doubled, and the secondary main sidebands. capacity is no longer available for S3 data.

15 As in service mode MS2, the S3 logical impairments. The size of the logical channel channel carries additional data services, such as transfer frames is increased in inverse proportion MPS, PDS, or AAS data, on the secondary to the code rate. The encoding techniques are extended sidebands. The SIDS logical channel configurable by service mode. Diversity delay is also carries SIS data over the secondary main also imposed on selected logical channels. sidebands. As always, identical program material Interleaving is carried on each sideband, so that the alternate sideband would be available if the other sideband Interleaving re-orders the transmitted bits to were corrupted. disperse burst errors typical of a fading channel. The FM IBOC waveform is interleaved in both

time and frequency. The custom interleaving FUNCTIONAL COMPONENTS techniques are tailored to the VHF Rayleigh fading environment and are configurable by The conversion of audio and data program service mode. content into the FM IBOC waveform is accomplished by the layered protocol stack. In this process, the logical channels lose their Source material is received from the broadcaster identities. The interleaver output is structured in in layer 5, source encoded in layer 4, a matrix format; each matrix is comprised of one multiplexed into logical channels in layers 3 and or more logical channels, and is associated with a 2, and formatted for over-the-air broadcast in particular portion of the transmitted spectrum. layer 1. System control processing This section includes a high-level description This function generates a matrix of system of each layer 1 functional block, and the control data sequences, which includes control associated signal flow. Figure 20 is a functional and status (such as service mode), for broadcast block diagram of layer 1 processing. on the reference subcarriers. Scrambling OFDM subcarrier mapping This function randomizes the digital data in This function assigns the interleaver matrices each logical channel to mitigate signal and the system control data matrix to the OFDM periodicities, which could cause undesired subcarriers. One row of each active interleaver emissions and degraded reception. matrix is processed every OFDM symbol time to Channel encoding produce one output vector X, which is a frequency-domain representation of the signal. A digital signal, when passed through an RF The mapping is specifically tailored to the non- transmission channel, is likely to encounter uniform interference environment and is a various impairments, including noise, fading, function of the service mode. and interference. Digital systems employ error correction techniques to correct bit errors caused OFDM signal generation by these impairments. Forward error correction This function generates the digital portion of (FEC) algorithms improve signal robustness by the time-domain FM IBOC waveform. The input adding error correction bits to the signal prior to vectors are transformed into a shaped time- transmission. These FEC bits are used by the domain baseband pulse, y (t), defining one receiver to correct bit errors and regenerate the n OFDM symbol. transmitted bitstream. Transmission subsystem FEC codes are typically specified by their coding rate, which is simply the number of This function formats the baseband information bits divided by the total number of waveform for transmission through the VHF transmitted bits. For example, in a rate 1/2 code, channel. Major subfunctions include symbol half of the bits carry information, and the other concatenation and frequency up-conversion. In half carry the FEC overhead. addition, when transmitting the hybrid or extended hybrid waveforms, this function The channel encoding function uses modulates the analog source and combines it convolutional encoding to add redundancy to the with the digital signal to form a composite digital data in each logical channel, in order to signal, s(t), ready for transmission. improve its reliability in the presence of channel

16 Analog, SCA Layer 2 Sources PIDS SIDS P1 P2 P3 S1 S2 S3 S4 S5 Control/Status

Scrambling

Channel Encoding Control/Status

System Control Interleaving Processing

C

o

n

t

r

o

l

/

S

t

a

t

u

s

OFDM Subcarrier Mapping

X

OFDM Signal Generation

yn(t)

Baseband Transmission Subsystem

s(t)

Figure 20 Layer 1 Functional Block Diagram

ACKNOWLEDGEMENTS [2] B.W. Kroeger, D.M. Cammarata, “Robust Modem and Coding The author wishes to acknowledge the Techniques for FM Hybrid IBOC contributions of Brian Kroeger, Jeff Baird, DAB,” IEEE Transactions on Denise Cammarata, Harvey Chalmers, Ashruf Broadcasting, vol. 43, no. 4, pp. 412- El-Dinary, Rick Martinson, Stephen Mattson, 420, Dec. 1997 Glynn Walden, and all other members of the [3] Federal Communications Commission, iBiquity Digital Corporation FM technical team. Code of Federal Regulations, Title 47,

Part 73

REFERENCES [4] “Petition for Rulemaking to the United States Federal Communications [1] R.W. Chang, “High-speed multichannel Commission for In-Band On-Channel data transmission with bandlimited Digital Audio Broadcasting,” Appendix orthogonal signals,” Bell sys. Tech. J., C, p. 7, USA Digital Radio Corporation, vol. 45, pp. 1775-1796, Dec. 1966 October 7, 1998

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