Patent Publication Number: US-11641227-B2

Title: Transmit antenna diversity wireless audio system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 17/208,841, filed on Mar. 22, 2021, which is a continuation of U.S. patent application Ser. No. 16/943,441, now U.S. Pat. No. 10,958,324, filed on Jul. 30, 2020, which claims the benefit of U.S. Provisional Patent Application No. 62/882,980, filed on Aug. 5, 2019. The contents of these applications are incorporated herein in their entireties. 
    
    
     TECHNICAL FIELD 
     This application generally relates to a wireless audio system that utilizes transmit antenna diversity. In particular, this application relates to a wireless audio system with a transmitter that applies multiple antenna diversity techniques for different signal types. 
     BACKGROUND 
     Audio production can involve the use of many components, including microphones, wireless audio transmitters, wireless audio receivers, recorders, and/or mixers for capturing, recording, and presenting the sound of productions, such as television programs, newscasts, movies, live events, and other types of productions. The microphones typically capture the sound of the production, which is wirelessly transmitted from the microphones and/or the wireless audio transmitters to the wireless audio receivers. The wireless audio receivers can be connected to a recorder and/or a mixer for recording and/or mixing the sound by a crew member, such as a production sound mixer. Electronic devices, such as computers and smartphones, may be connected to the recorder and/or mixer to allow the crew member to monitor audio levels and timecodes. 
     Wireless audio transmitters, wireless audio receivers, wireless microphones, and other portable wireless communication devices include antennas for transmitting and receiving radio frequency (RF) signals which contain digital or analog signals, such as modulated audio signals, data signals, and/or control signals. Users of portable wireless communication devices include stage performers, singers, actors, news reporters, and the like. 
     A wireless audio transmitter may transmit an RF signal that includes an audio signal to a wireless audio receiver. The wireless audio transmitter may be included in a wireless handheld microphone or body pack, for example, that is held or worn by the user and includes an integrated transmitter and antenna. As another example, the wireless audio transmitter may be included in an access point or other centralized unit. The wireless audio receiver may be portable, such as a wireless earphone, wireless conference unit, or body pack. When the RF signal is received at the wireless audio receiver, the RF signal may be degraded due to multipath fading caused by constructive interference and/or by other types of interference. This degradation may cause the RF signal to have a poor signal-to-noise ratio (SNR), which can result in bit errors that can cause audio artifacts and muting of the resulting output audio. However, muting the output audio is undesirable in many situations and environments, such as during professional stage productions and concerts. The effects of such multipath fading and interference are most prevalent in harsh RF environments where physical and electrical factors influence the transmission and reception of RF signals, e.g., movement of the microphone within the environment, other RF signals, operation in large venues, etc. 
     To alleviate issues with multipath fading of RF signals, wireless audio components may utilize frequency diversity and/or antenna diversity techniques. For example, wireless audio transmitters may utilize frequency diversity to simultaneously transmit on one antenna two RF signals of two separate frequencies in a combined RF signal, where the two RF signals both include the same audio signal. A wireless audio receiver may then use one or both of the underlying RF signals. As another example, wireless audio receivers may utilize antenna diversity to simultaneously receive RF signals from a wireless audio transmitter on multiple antennas. The received RF signals can be combined to produce a single audio output. 
     However, utilizing diversity on wireless audio receivers that are portable may be difficult and challenging, due to size and power constraints. For example, portable wireless audio receivers are typically small and battery-powered, so utilizing diversity techniques on such receivers may result in suboptimal antenna placements and/or unacceptable power dissipation. In addition, there may be significant costs and complexity when utilizing diversity techniques on multiple portable wireless audio receivers. 
     Other techniques for alleviating issues with multipath fading of RF signals may have undesirable side effects. For example, the transmit power of a wireless audio transmitter may be increased to account for a large fading margin. However, the overall spectral efficiency may be negatively impacted due to intermodulation products when the transmit power is increased. Furthermore, the physical design of the transmitter and/or governmental regulations may limit how much the transmit power may be increased. In addition, increased transmit power does not resolve error floors that are caused by frequency-selective fading. As another example, antennas may be designed to the focus transmitted signal energy from wireless audio transmitters to wireless audio receivers. However, such antennas may be excessively directional, which can affect the coverage of the wireless audio transmitters. As a further example, in certain applications (e.g., wireless in-ear personal monitors) ad hoc signal splitting techniques may be utilized in an attempt to improve diversity performance. However, such techniques can create phase cancellation issues that may result in degraded and unreliable performance. 
     Accordingly, there is an opportunity for a wireless audio system that utilizes transmit antenna diversity that addresses these concerns. More particularly, there is an opportunity for a wireless audio system with a transmitter using multiple antenna diversity techniques for different signal types that can provide optimal multipath performance and improved spectral efficiency. 
     SUMMARY 
     The invention is intended to solve the above-noted problems by providing a wireless audio system that utilizes transmit antenna diversity that is designed to, among other things: (1) simultaneously apply different transmit diversity techniques depending on the type of signal being transmitted, such as data/control symbols, pilot symbols, and synchronization signals; (2) utilize embedded orthogonal pilot symbols for independent channel estimation and coherent demodulation while maintaining optimal data rates; and (3) be flexibly encoded and/or routed to multiple antennas for increased coverage and/or capacity. 
     In an embodiment, a wireless audio transmitter includes a mode selection interface for enabling a user to select one of a plurality of modes of the wireless audio transmitter; a plurality of antennas configured to each transmit an audio signal; an encoder in communication with the mode selection interface, where the encoder is configured to receive (i) a data symbol comprising audio data signals and control signals and (ii) a pilot symbol; a synchronization transformer; and the plurality of converters each in communication with the encoder, the synchronization transformer, and one of the plurality of antennas. The encoder may be further configured to when in a first mode, receive and route the data symbol and the pilot symbol to each of a plurality of converters; and when in a second mode, receive and encode the data symbol and the pilot symbol based on a first diversity technique, and route the encoded data symbol and the encoded pilot symbol to one or more subsets of the plurality of converters. 
     The synchronization transformer may be configured to receive and transform a synchronization signal based on a second diversity technique. Each of the converters may be configured to when in the first mode, combine the data symbol, the pilot symbol, and the transformed synchronization signal into the audio signal to be transmitted on one of the plurality of antennas; and when in the second mode, combine the encoded data symbol, the encoded pilot symbol, and the transformed synchronization signal into the audio signal to be transmitted on one of the plurality of antennas. 
     In another embodiment, a method for wirelessly transmitting an audio signal using a wireless audio transmitter may include receiving, from a mode selection interface, a selection of one of a plurality of modes of the wireless audio transmitter; receiving, at an encoder, (i) a data symbol comprising audio data signals and control signals and (ii) a pilot symbol; when the selection is of a first mode, routing the data symbol and the pilot symbol to each of a plurality of converters, using the encoder; and when the selection is of a second mode, encoding the data symbol and the pilot symbol based on a first diversity technique, using the encoder, and routing the encoded data symbol and the encoded pilot symbol to one or more subsets of the plurality of converters, using the encoder. The method may further include receiving, at a synchronization transformer, a synchronization signal; transforming the synchronization signal based on a second diversity technique, using the synchronization transformer; when the selection is of the first mode, combining the data symbol, the pilot symbol, and the transformed synchronization signal into the audio signal to be transmitted on one of the plurality of antennas, using each of the plurality of converters; and when the selection is of the second mode, combining the encoded data symbol, the encoded pilot symbol, and the transformed synchronization signal into the audio signal to be transmitted on one of the plurality of antennas, using the one or more subsets of the plurality of converters. 
     In a further embodiment, a wireless audio system may include an audio source; a wireless audio transmitter in communication with the audio source; and a wireless audio receiver in wireless communication with the wireless audio transmitter. The audio source may be configured to generate one or more audio source signals each comprising a data symbol comprising audio data signals and control signals. The wireless audio transmitter may include a plurality of antennas configured to each transmit an audio signal; an encoder in communication with the audio source, and configured to receive and encode the data symbol and a pilot symbol based on a first diversity technique; a synchronization transformer in communication with the audio source, and configured to receive and transform a synchronization signal based on a second diversity technique; and a plurality of converters each in communication with the encoder, the synchronization transformer, and one of the plurality of antennas, where each of the plurality of converters is configured to combine the encoded data symbol, the encoded pilot symbol, and the transformed synchronization signal into the audio signal to be transmitted on one of the plurality of antennas. The wireless audio receiver may be configured to receive the audio signal on at least one receiving antenna. 
     These and other embodiments, and various permutations and aspects, will become apparent and be more fully understood from the following detailed description and accompanying drawings, which set forth illustrative embodiments that are indicative of the various ways in which the principles of the invention may be employed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of a wireless audio system utilizing transmit antenna diversity, in accordance with some embodiments. 
         FIG.  2    is a schematic diagram of a portion of a wireless audio transmitter utilizing two antennas for transmit diversity, in accordance with some embodiments. 
         FIG.  3    is a schematic diagram of a portion of a wireless audio transmitter utilizing four antennas for transmit diversity, in accordance with some embodiments. 
         FIG.  4    is a flowchart illustrating operations for wirelessly transmitting an audio signal using a wireless audio transmitter utilizing transmit antenna diversity, in accordance with some embodiments. 
         FIG.  5    is a table showing encoding of data symbols and pilot symbols using space-time block coding for use in a wireless audio transmitter utilizing two antennas for transmit diversity, in accordance with some embodiments. 
         FIG.  6    is an exemplary graph showing the performance of a wireless audio system utilizing two antennas for transmit diversity, in accordance with some embodiments. 
         FIGS.  7 A,  7 B,  8 A,  8 B, and  9    are exemplary depictions of the encoding and/or routing of audio channels to converters and antennas in different modes of a wireless audio transmitter, in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The description that follows describes, illustrates and exemplifies one or more particular embodiments of the invention in accordance with its principles. This description is not provided to limit the invention to the embodiments described herein, but rather to explain and teach the principles of the invention in such a way to enable one of ordinary skill in the art to understand these principles and, with that understanding, be able to apply them to practice not only the embodiments described herein, but also other embodiments that may come to mind in accordance with these principles. The scope of the invention is intended to cover all such embodiments that may fall within the scope of the appended claims, either literally or under the doctrine of equivalents. 
     It should be noted that in the description and drawings, like or substantially similar elements may be labeled with the same reference numerals. However, sometimes these elements may be labeled with differing numbers, such as, for example, in cases where such labeling facilitates a more clear description. Additionally, the drawings set forth herein are not necessarily drawn to scale, and in some instances proportions may have been exaggerated to more clearly depict certain features. Such labeling and drawing practices do not necessarily implicate an underlying substantive purpose. As stated above, the specification is intended to be taken as a whole and interpreted in accordance with the principles of the invention as taught herein and understood to one of ordinary skill in the art. 
     The wireless audio system described herein can utilize transmit antenna diversity by including a transmitter that uses multiple antenna diversity techniques for different signal types, in order to attain optimal multipath performance and improved spectral efficiency. The different signal types may include, for example, data symbols including audio data signals and control signals, pilot symbols, and a synchronization signal. The wireless audio transmitter may use orthogonal pilot symbols for independent channel estimation and coherent demodulation. The data rate of the wireless audio system with transmit antenna diversity may be consistent and maintained, as compared to systems with a non-diversity wireless audio transmitter. The number of antennas utilized by the wireless audio transmitter may be selectable, extensible, and scalable to attain greater coverage and/or capacity. In addition, the wireless audio system may still be able to operate with reduced range and/or performance, even if a particular transmit path fails. Performance of the wireless audio system may be more robust in both single zones (e.g., a stage) and in multiple zones (e.g., a stage and backstage). 
       FIG.  1    is a schematic diagram of an exemplary wireless audio system  100  utilizing transmit antenna diversity. The system  100  may include a wireless audio transmitter  110  having antennas  112   a ,  112   b  for transmission of radio frequency (RF) signals, and wireless audio receivers  150   a ,  150   b ,  150   c  having respective antennas  152   a ,  152   b ,  152   c  for receiving the RF signals. The transmitter  110  may utilize antenna diversity due to the multiple antennas  112   a ,  112   b , and as described in more detail below. Antenna diversity can include using physically separated antennas (i.e., antennas positioned apart in space), for example. It is contemplated and possible for the transmitter  110  to have more than two antennas, and for there to be any number of receivers  150 . The transmitter  110  may be an access point or other centralized unit, in some embodiments. The receivers  150   a ,  150   b ,  150   c  may be portable wireless audio receivers, in some embodiments, such as a wireless earphone, wireless conference unit, or body pack. 
     In embodiments, the system  100  may be an OFDM (orthogonal frequency-division multiplexing) wideband audio system that allows various types of traffic to be carried on individual subcarriers and multiplexed together into a single wideband carrier. In other embodiments, the system  100  may be a narrowband audio system, e.g., personal monitoring systems. The RF signals transmitted by the transmitter  110  and received by the receivers  150  may include data symbols having audio data signals and control signals, pilot symbols, and/or synchronization signals, for example. A data symbol may be a QPSK/QAM-modulated subcarrier that can carry the audio data signals and/or control signals, in some embodiments. The pilot symbols may be known symbols that can enable channel estimation and coherent demodulation of the signals at the receivers  150 . 
     As described in more detail below, the data symbols and pilot symbols may be mapped to multiple antennas using space-time block coding (STBC), in some embodiments. Encoding the data symbols and pilot symbols using STBC involves processing a block of symbols and transmitting them multiple times across multiple antennas. In other embodiments, the data symbols and pilot symbols may be transformed using other appropriate techniques. 
     The synchronization signals may be transmitted from the transmitter  110  so that the receivers  150  can acquire the frequency and/or timing references of the system  100 . The transmitter  110  and the receivers  150  generally need to be synchronized with one another so that the data symbols and pilot symbols may be properly transmitted and received. For example, the frequency and phase of the local oscillators of the receivers  150  may need to be synchronized with that of the transmitter  110 . As described in more detail below, round-robin switched diversity or cyclic delay diversity (CDD) techniques may be applied to the synchronization signal. Accordingly, the data symbol, the pilot symbol, and the synchronization signal may utilize different antenna diversity techniques. 
     The system  100  may also include an audio source  120  in communication with the transmitter  110 . The audio source  120  may generate one or more audio source signals including the data symbol that has audio data signals and control signals. The transmitter  110  may modulate the data symbol from the audio source  120 , and insert the pilot symbols and synchronization symbols prior to transmission of the RF signal(s) on the antennas  112   a ,  112   b.    
       FIG.  2    is a schematic diagram of a portion of a wireless audio transmitter  210  utilizing two antennas  212   a ,  212   b  for transmit diversity. For simplicity,  FIG.  2    does not show other components of the transmitter  210 , such as modulators, analog to digital converters, digital to analog converters, codecs, etc. The transmitter  210  may transmit RF signals containing data symbols, pilot symbols, and/or synchronization signals for reception by one or more receivers, such as the receivers  150  in the wireless audio system  100  of  FIG.  1   . Various components included in the wireless audio transmitter  210  may be implemented using software executable by one or more servers or computers, such as a computing device with a processor and memory, and/or by hardware (e.g., discrete logic circuits, application specific integrated circuits (ASIC), programmable gate arrays (PGA), field programmable gate arrays (FPGA), etc.). 
     An embodiment of a process  400  for wirelessly transmitting an audio signal using a wireless audio transmitter utilizing transmit antenna diversity is shown in  FIG.  4   . The process  400  may be performed by the transmitter  210 . One or more processors and/or other processing components (e.g., analog to digital converters, encryption chips, etc.) within or external to the transmitter  210  may perform any, some, or all of the steps of the process  400 . One or more other types of components (e.g., memory, input and/or output devices, transmitters, receivers, buffers, drivers, discrete components, etc.) may also be utilized in conjunction with the processors and/or other processing components to perform any, some, or all of the steps of the process  400 . 
     The transmitter  210  may generate a signal that includes data symbols, pilot symbols, and a synchronization signal for transmission on the antennas  212   a ,  212   b . The data symbols may include audio data signals and/or control signals. The control signals may include system messaging and other information. The encoder  214  may have multiple modes of operation that allow the data symbols and pilot symbols to be encoded and/or routed to be ultimately transmitted on the antennas  212   a ,  212   b . A selection of the mode of the encoder  214  and transmitter  210  may be received at step  402 , such as from a user interface. The data symbols and pilot symbols may be received by an encoder  214  at step  404 . 
     Synchronization signals may be in the frequency domain or time domain, and be transformed using cyclic delay diversity (CDD) techniques for transmission on the antennas  212   a ,  212   b . The synchronization signals may be received by a synchronization transformer  218  at step  406 . CDD may be applied to the synchronization signals so that nulls do not occur in the radiation pattern of the antennas  212   a ,  212   b . In particular, at step  408 , a phase ramp 
             e     -       j   ⁢   2   ⁢   π   ⁢   m     N             
may be applied by the synchronization transformer  218  to transform the synchronization signals in the frequency domain, or the synchronization signals can be transformed by the synchronization transformer  218  using a cyclic delay in the time domain. Accordingly, the first antenna  212   a  may transmit an original copy of the synchronization signals, while the second antenna  212   b  may transmit a cyclic shifted version of the synchronization signals. It should be understood that the two antennas  212   a ,  212   b  illustrated in  FIG.  2    are merely exemplary. In some embodiments, the synchronization signals may be transformed by the synchronization transformer  218  in a round-robin switched diversity scheme.
 
     The data symbols and pilot symbols (whether encoded or not) and the synchronization signals may be combined by converters  216   a ,  216   b , depending on the selected mode at step  410 . For example, in a first mode of the transmitter  210 , the data symbols and pilot symbols may not be encoded by the encoder  214  and are routed to the converters  216   a ,  216   b  at step  412 . The converters  216   a ,  216   b  may then combine the data symbol, the pilot symbol, and the transformed synchronization signal into an audio signal that is transmitted on the antennas  212   a ,  212   b  as an RF signal at step  414 . In another example, in a second mode of the transmitter  210 , the data symbols and pilot symbols may be encoded by the encoder  214  at step  416  and routed to the converters  216   a ,  216   b  at step  418 . The converters  216   a ,  216   b  may combine the encoded data symbol, the encoded pilot symbol, and the transformed synchronization signal into an audio signal that is transmitted on the antennas  212   a ,  212   b  at step  420 . 
     In embodiments, the transmitter  210  may be an OFDM wideband transmitter, and the data symbols and pilot symbols may be in the frequency domain and be mapped by space-time block coding (STBC) in the encoder  214 . The data symbols may be QPSK/QAM-modulated subcarriers. As shown in the table of  FIG.  5   , the encoder  214  may process a pair of symbols for transmission on two antennas  212   a ,  212   b . For example, when the input symbol pair for the data subcarrier is s n,0 , s n,1 , then the first antenna  212   a  may transmit the same symbol pair s n,0 , s n,1 , while the second antenna  212   b  may transmit the symbol pair s* n,0 , −s* n,1  (i.e., the complex conjugate of the input symbol pair). In particular, the encoder  214  may receive and encode the input symbol pair using STBC, as is known in the art, to generate the symbols for transmission on the antennas  212   a ,  212   b . In embodiments, the code may be a rate-1 STBC (known from Alamouti) or another appropriate code. 
     The pilot symbols may be known symbols for use in channel estimation and coherent demodulation of the signals at the receivers. In embodiments, the pilot symbols may be orthogonal sequences. As shown in the table of  FIG.  5   , the STBC encoder  214  may process a pair of values of +1 for the pilot symbols, and generate an orthogonal pilot pattern on the antennas  212   a ,  212   b . For example, when the input symbol pair for the pilot symbol is +1, +1, then the first antenna  212   a  may transmit the same symbol pair +1, +1, while the second antenna  212   b  may transmit the symbol pair +1, −1. In embodiments, the pilot symbols may be orthogonal in code, rather than in time or frequency. This may ensure that there is no reduction in capacity since there are unique pilots on multiple antennas. In addition, in embodiments, the pilot symbols may use the same STBC mapping as for the data symbols, which may assist in reducing the complexity of implementation. 
     One or more receivers, such as the receivers  150   a ,  150   b ,  150   c , may receive the RF signal transmitted from the transmitter  210  that includes the audio signal on their respective antennas, such as antennas  152   a ,  152   b ,  152   c . The receivers may demodulate, convert, and/or process the received RF signal to generate an analog or digital output audio signal, as is known in the art. In particular, the receivers may decode the data symbols and pilot symbols based on how they were encoded, e.g., Alamouti rate-1 STBC. In embodiments, the receivers may each have multiple antennas in a spatial diversity scheme that simultaneously receive the transmitted RF signals from the transmitter  210 . When both the transmitters and receivers have spatial diversity, multiple-input multiple-output (MIMO) techniques could be utilized. For example, the use of MIMO can result in increased diversity gain for fading mitigation due to lower bit error rates in fading environments. As another example, the use of MIMO can result in higher throughput due to spatial multiplexing, i.e., more bits per frequency. 
     It can be seen in the exemplary graph of  FIG.  6    that the performance of the wireless audio system  100  with two antenna diversity is improved over the performance of a single antenna wireless audio system. In particular,  FIG.  6    shows the data bit error rate (BER) performance of the wireless audio system  100  with two antenna diversity (the dashed line) as compared to that of a single antenna wireless audio system (the solid line). Accordingly, at low bit error rates, e.g., less than 10 −5 , the wireless audio system  100  with two antenna diversity performs approximately 5 dB better. It should be noted that the graph of  FIG.  6    reflects that the combined transmission power of the wireless audio system  100  with two antenna diversity is equal to the transmission power of the signal antenna wireless audio system. 
       FIG.  3    is a schematic diagram of a portion of an OFDM wideband wireless audio transmitter  310  utilizing four antennas  312   a ,  312   b ,  312   c ,  312   d  for transmit diversity. For simplicity,  FIG.  3    does not show other components of the transmitter  310 , such as modulators, analog to digital converters, digital to analog converters, codecs, etc. The transmitter  310  may transmit RF signals containing data symbols, pilot symbols, and/or synchronization signals for reception by one or more receivers, such as the receivers  150  in the wireless audio system  100  of  FIG.  1   . Various components included in the wireless audio transmitter  310  may be implemented using software executable by one or more servers or computers, such as a computing device with a processor and memory, and/or by hardware (e.g., discrete logic circuits, application specific integrated circuits (ASIC), programmable gate arrays (PGA), field programmable gate arrays (FPGA), etc.). 
     Similar to the transmitter  210  in  FIG.  2   , the transmitter  310  may generate a signal that includes data symbols, pilot symbols, and a synchronization signal for transmission on the antennas  312   a ,  312   b ,  312   c ,  312   d . The data symbols may include audio data signals and/or control signals. The control signals may include system messaging and other information. The data symbols and pilot symbols in the transmitter  310  may be in the frequency domain, and be mapped by a space-time-block coding (STBC) encoder  314 . In embodiments, the STBC encoder  314  may utilize Alamouti rate-1 STBC, a quasi-orthogonal rate-1 STBC (known from Jafarkhani), an orthogonal rate-3/4 STBC (known from Ganesan), or other appropriate codes. The synchronization signal may be in the frequency domain or the time domain, and be transformed using cyclic delay diversity (CDD) techniques for transmission on the antennas  312   a ,  312   b ,  312   c ,  312   d . Alternatively, the synchronization signal may be transmitted in a round-robin switched diversity scheme on the antennas  312   a ,  312   b ,  312   c ,  312   d . A detailed description is omitted of the functionality of the synchronization transformer  318  of  FIG.  3    that is the same or similar as the synchronization transformer  218  of  FIG.  2   . 
     The embodiment of the process  400  shown in  FIG.  4    may also be performed by the transmitter  310 . One or more processors and/or other processing components (e.g., analog to digital converters, encryption chips, etc.) within or external to the transmitter  310  may perform any, some, or all of the steps of the process  400 . One or more other types of components (e.g., memory, input and/or output devices, transmitters, receivers, buffers, drivers, discrete components, etc.) may also be utilized in conjunction with the processors and/or other processing components to perform any, some, or all of the steps of the process  400 . 
     The STBC encoder  314  may have multiple modes of operation that allow the data symbols and pilot symbols to be encoded and/or routed to be ultimately transmitted on the antennas  312   a ,  312   b ,  312   c ,  312   d . A selection of the mode of the STBC encoder  314  and transmitter  310  may be received at step  402 , such as from a user interface. The selected mode may determine the type of mapping (if any) and the routing performed by the STBC encoder  314 . In embodiments, the transmitter  310  may have three modes, while in other embodiments, the transmitter  310  may have another number of modes. The number of modes of the transmitter  310  may be dependent on the number of antennas, the number of coverage zones, and/or the number of audio channels. 
     A first mode of the transmitter  310  may cause the STBC encoder  314  to receive (step  404 ) and route (step  412 ) the data symbols and pilot symbols to converters  316   a ,  316   b ,  316   c ,  316   d  in respective communication with the antennas  312   a ,  312   b ,  312   c ,  312   d , without any STBC mapping. This mode may route up to N audio channels to N coverage zones, where N is equal to the number of antennas. As such, for the transmitter  310 , up to four audio channels can be routed to four coverage zones. For example, in this mode, the STBC encoder  314  may route one audio channel (i.e., one stream of data symbols and pilot symbols) to four single-antenna coverage zones, such as depicted in  FIG.  7 A . This mode may enable coverage of multiple zones, such as along a parade route. As another example, in this mode, the STBC encoder  314  may route four unique audio channels (i.e., four separate streams of data symbols and pilot symbols) to four respective single-antenna coverage zones, such as depicted in  FIG.  7 B . 
     A second mode of the transmitter  310  may cause the STBC encoder  314  to receive (step  404 ) and encode (step  416 ) the data symbols and pilot symbols with 2-branch STBC mapping. The encoded data symbols and pilot symbols may be routed (step  418 ) to converters  316   a ,  316   b ,  316   c ,  316   d  in respective communication with the antennas  312   a ,  312   b ,  312   c ,  312   d . This mode may encode and route up to N/2 audio channels to N/2 coverage zones, e.g., for the transmitter  310 , up to two audio channels can be encoded and routed to two coverage zones. For example, in this mode, the STBC encoder  314  may encode and route one audio channel (i.e., one stream of data symbols and pilot symbols) to two coverage zones each having two antennas, such as depicted in  FIG.  8 A . In particular, one coverage zone may be covered by antennas  312   a ,  312   b  and the other coverage zone may be covered by antennas  312   c ,  312   d . As another example, in this mode, the STBC encoder  314  may encode and route two unique audio channels (i.e., two separate streams of data symbols and pilot symbols) to two respective coverage zones each having two antennas, such as depicted in  FIG.  8 B . 
     A third mode of the transmitter  310  may cause the STBC encoder  314  to receive (step  404 ) and encode (step  416 ) the data symbols and pilot symbols with 4-branch STBC mapping. The encoded data symbols and pilot symbols may be routed (step  418 ) to converters  316   a ,  316   b ,  316   c ,  316   d  in respective communication with the antennas  312   a ,  312   b ,  312   c ,  312   d . This mode may encode and route up to N/4 audio channels to N/4 coverage zones, e.g., for the transmitter  310 , up to one audio channel can be encoded and routed to one coverage zone. For example, in this mode, the STBC encoder  314  may encode and route one audio channel (i.e., one stream of data symbols and pilot symbols) to one coverage zone that has four antennas, such as depicted in  FIG.  9   . 
     The converters  316   a ,  316   b ,  316   c ,  316   d  may combine the data symbols, pilot symbols, and the synchronization signals, such as in the first mode described above where there is no encoding (step  414 ); or combine the encoded data symbols, encoded pilot symbols, and the synchronization signals, such as in the second and third modes described above (step  420 ). The converters  316   a ,  316   b ,  316   c ,  316   d  may generate an audio signal that is transmitted on the antennas  312   a ,  312   b ,  312   c ,  312   d , respectively. 
     Each of the converters  316   a ,  316   b ,  316   c ,  316   d  may include inverse fast Fourier transforms (IFFTs)  320   a ,  320   b ,  320   c ,  320   d  to convert the data symbols and pilot symbols into the time domain. The output of the synchronization transformer  318 , i.e., the transformed synchronization signal, may also be communicated to the IFFTs  320   a ,  320   b ,  320   c ,  320   d . The outputs of the respective IFFTs  320   a ,  320   b ,  320   c ,  320   d  may be converted by parallel to serial converters  322   a ,  322   b ,  322   c ,  322   d . In order to transmit the audio signal on the antennas  312   a ,  312   b ,  312   c ,  312   d , a cyclic delay  324   a ,  324   b ,  324   c ,  324   d  may be applied to the output of the parallel to serial converters  322   a ,  322   b ,  322   c ,  322   d . Each cyclic delay may result in a unique time shift on each antenna. In particular, the output of the parallel to serial converters  322   a ,  322   b ,  322   c ,  322   d  may include data symbols, pilot symbols, and synchronization signals in the time domain, i.e., after conversion by the IFFTs  320   a ,  320   b ,  320   c ,  320   d . As discussed previously, the data symbols and pilot symbols may have been encoded in certain modes, and may not have been encoded in other modes. 
     One or more receivers, such as the receivers  150   a ,  150   b ,  150   c , may receive the RF signal transmitted from the transmitter  310  that includes the audio signal on their respective antennas, such as antennas  152   a ,  152   b ,  152   c . The receivers may demodulate, convert, and/or process the received RF signal to generate an analog or digital output audio signal, as is known in the art. In particular, the receivers may decode the data symbols and pilot symbols based on how they were encoded, e.g., Alamouti rate-1 STBC, quasi-orthogonal Jafarkhani rate-1 STBC, orthogonal Ganesan rate-3/4 STBC. In embodiments, the receivers may each have multiple antennas in a spatial diversity scheme that simultaneously receive the transmitted RF signals from the transmitter  310 . 
     Any process descriptions or blocks in figures should be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps in the process, and alternate implementations are included within the scope of the embodiments of the invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those having ordinary skill in the art. 
     This disclosure is intended to explain how to fashion and use various embodiments in accordance with the technology rather than to limit the true, intended, and fair scope and spirit thereof. The foregoing description is not intended to be exhaustive or to be limited to the precise forms disclosed. Modifications or variations are possible in light of the above teachings. The embodiment(s) were chosen and described to provide the best illustration of the principle of the described technology and its practical application, and to enable one of ordinary skill in the art to utilize the technology in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the embodiments as determined by the appended claims, as may be amended during the pendency of this application for patent, and all equivalents thereof, when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.