Wireless sound transmission system and method

Abstract

A system for providing sound to at least one user, having at least one audio signal source for providing audio signals; a transmission unit with a digital transmitter for wirelessly transmitting the audio signals as data packets; at least one receiver unit with at least one digital receiver for reception of the audio signals from the transmission unit; a mechanism for stimulating the hearing of the user(s) according to audio signals supplied from the receiver unit. The transmission unit transmits each data packet in a separate slot of a tdma frame at a different frequency in a frequency hopping sequence, in at least some of the slots, the audio signals are transmitted as audio data packets, the same audio packet being transmitted at least twice in the same tdma frame without expecting acknowledgement, and the tdma frames being structured for unidirectional broadcast transmission of the audio data packets.

Description

m=2¹⁶
r=s

Computation of f₀ Based on f_p
r=mod(17·r+c,m)
{circumflex over (r)}=(19·r)/2¹⁶
f₀=mod(f_p+11+{circumflex over (r)},40)

Computation of f₁, f₂, . . . , f₉ for Each f_i, iϵ{1:9}
r=mod(17·r+c,m)
{circumflex over (r)}=(19·r)/2¹⁶
f_i=mod(f_i-1+11+{circumflex over (r)},40)

The information necessary to compute the frequency-hopping sequence for the present frame is transmitted in the beacon packet in the first slot of the frame from the master device to the slave devices. The hopping sequence ID is not included in the beacon packet, but rather is transmitted in a pairing phase to the slave devices and is stored in each slave device. Once synchronized to the master device, the slave devices increment the sequence number automatically to calculate the frequency at which the beacon packet of the next frame is to be received.

The Hopping Sequence ID is chosen as an odd number between 1 and 65535 . . . . This number is chosen randomly by the network master (relay unit 15) and transmitted to the network slaves (transmission units 10 and receiver units 14) during pairing. This odd number is used as the additive term of the LCG. By selecting the hopping sequence ID randomly, it is provided that the hopping sequence is likely to be unique to the present network, so that there is only low cross-correlation with the hopping sequence of another network which may exist, for example, in the same building. In the unlikely event that two networks select the same hopping sequence ID and disturb each other, a new pairing process in one of the networks is likely to result in a different hopping sequence ID. The use of the frequency of the last slot of the previous frame in the hopping sequence algorithm ensures that there is always a minimum distance between two subsequent slots, namely also between the last slot of the previous frame and the first slot of the present frame.

Preferably, the frequency-hopping scheme is an adaptive frequency-hopping scheme, wherein packet error rate measurements are made for the used frequencies and wherein the master device may decide, based on such measurements, that a sub-set of the available frequencies should be declared as “bad frequencies” and should not be used any longer. If then, the frequency computation algorithm selects one of the bad frequencies, a frequency is pseudo-randomly selected instead, from a set of frequencies composed of all “good frequencies” at the exception of the good frequency used in the preceding slot. Removing the frequency used in the preceding slot from the set of potential replacement frequencies presents the advantage of avoiding the possibility of using the same frequency twice in consecutive slots.

FIG. 15 illustrates how synchronization between the master device (for example, the transmission unit 10) and the slave devices (for example, one of the receiver units 14) may be achieved.

The synchronization is passive in the sense that there is no feedback from the slave device to the master device during synchronization. Usually, the master device, e.g., the transmission unit 10, does not distinguish whether a certain one of the slaves, e.g., the receiver units 14, is in still a synchronization mode or already in a synchronized mode, so that the transmission operation of the master is always the same, i.e., the same algorithm for determining the hopping sequences is used and the same protocol is used, e.g., beacon packet in the first slot, audio data packets in some of the other slots (as long as audio signals are generated in/supplied to the transmission unit; the audio data packets are not shown in FIG. 15).

Thus, the master device transmits a beacon packet in regular intervals, namely in the first slot of each TDMA frame (according to the example, a beacon packet is sent every 4 ms). The frequency at which the respective beacon packet is sent is calculated according to the same pseudo-random hopping-sequence algorithm which is used for transmitting audio packets in the synchronized state. The hopping sequence is long in the sense that it is much longer/larger than the number of frequency channels (for example, a sequence of the length 100 is likely to show a bad correlation with another sequence of the length 100, depending on the time shift). The slave device listens periodically for the first beacon packet for synchronization, i.e., it is operated in a duty cycling mode. The listening time period is longer than the duration of the beacon packet. Each listening period is done at a different frequency; for example, the first listening period may at the lowest frequency of the available band (i.e., the receiver listens in the lowest one of the frequency channels), and then the listening frequency is increased for each subsequent listening period (thereby going systematically through all frequency channels). After each listening period, the receiver goes back to sleep. The periodicity of the listening periods is chosen close to the beacon packet transmission periodicity (i.e., the frame length), but it is not exactly equal, in order to have a drift between the beacon packet transmission phase and the listening phase. Due to this drift, the listening phase is periodically in phase with the transmission of the beacon packet for a certain duration. When the beacon packet is transmitted at the same frequency as the one used presently for listening, synchronization is achieved and the receiver switches into the synchronized mode/state, wherein it can calculate the hopping sequence presently used by the transmission unit from the information included in the received beacon packet (i.e., the frame sequence number) and the hopping sequence ID stored in the receiver unit from the pairing phase. A more detailed explanation of this synchronization method is given below.

When a receiver is in the synchronization phase, it listens periodically with period T_ListenPeriod for a duration T_{ListenDuration} at a given frequency and then goes back to sleep. The frequency is changed for each listening phase starting with frequency number 0, and incrementing up to e.g., frequency 39. The beacon is transmitted on any of the 40 frequencies, following the pseudo-random frequency selection.

The period T_ListenPeriod is chosen to be close to the beacon transmission period T_BeaconPeriod but not to be exactly equal. The difference ΔT=|T_ListenPeriod−T_BeaconPeriod causes a drift between the beacon packet transmission phase and the listening phase. Due to this drift, the listening phase is periodically in phase with the transmission of the beacon packet for a certain duration. If the beacon packet is transmitted at the same frequency as the one used for listening, synchronization is achieved. This mechanism is illustrated in FIG. 15.

The values of parameters T_ListenPeriod, T_{ListenDuration} are to be chosen based on the beacon packet period T_BeaconPeriod and on the beacon packet duration T_{BeaconDuration}, as a trade-off between the synchronization delay and the synchronization power consumption.

With T_ListenPeriod=T_BeaconPeriod(1+θ), and ΔT=θT_BeaconPeriod is the shift in phase of the listening activity for every transmission of the beacon packet.

T_{ListenDuration} must be larger than T_{BeaconDuration} such that it is possible to receive a beacon packet. An additional margin ΔT is required such that the listen window is open for the duration of the beacon packet transmission, given the fact that the listen window is drifting compared to the transmission window. A larger margin than ΔT gives the opportunity for the reception of more than one beacon packet in a given transmission window.

The time interval between two in-phase periods will be

$\begin{array}{c}{T}_{\mathrm{InPhasePeriod}}=\frac{T_{\mathrm{BeaconPeriod}}{T}_{\mathrm{ListenPeriod}}}{\Delta T}\\ =\frac{T_{\mathrm{BeaconPeriod}}{T}_{\mathrm{ListenPeriod}}}{\theta T_{\mathrm{BeaconPeriod}}}\\ =\frac{T_{\mathrm{ListenPeriod}}}{\theta }\\ =T_{\mathrm{BeaconPeriod}}\frac{1+\theta }{\theta }\end{array}$

When the transmission and listening intervals are in phase, there will be enough time for a limited number of transmission trials, until the windows are out of phase again. The number of possible trials is given by

$N_{\mathrm{TrialInPhase}}=\lfloor \frac{T_{\mathrm{ListenDuration}}-T_{\mathrm{BeaconDuration}}}{\Delta T}\rfloor ,$

where └ ┘ means rounded to the nearest integer in a direction towards zero.

The average synchronization delay can then be computed with

${\stackrel{\_}{T}}_{\mathrm{Synchronization}}=\frac{T_{\mathrm{InPhasePeriod}}/N_{\mathrm{TrialsInPhase}}}{1/N_{\mathrm{Channels}}},$
when N_Channels=40, θ=0.01, T_BeaconPeriod=4 ms, T_{ListenDuration}=600 μs, T_{Synchronization}=1.6 s and the duty cycle will be, in this case,

$\eta =\frac{T_{\mathrm{ListenDuration}}}{T_{\mathrm{ListenPeriod}}}=\frac{600}{4000}=15\%.$

A further refinement can be obtained if a transmission unit has two radios, i.e., transmitters/transceivers. In such case, the two radios may be used to transmit the beacon messages in an inter-leaved manner, or in parallel and at different frequencies. This method would reduce the synchronization time required at the receiver side.

As illustrated in FIG. 16, by using two spaced-apart antennas 38A, 38B multi-path fading resulting from destructive interference between several copies of the same signal travelling due to multiple reflections along different signal paths with different lengths (for example, direct signal and signal reflected once), can be mitigated, since the interference conditions are different at different positions, i.e., if destructive interference occurs at the position of one of the antennas, it is likely that no destructive interference occurs at the position of the other antenna. In other words, if the two antennas are sufficiently spaced apart, the fading events are uncorrelated on both antennas.

The present invention may utilize this effect by applying a packet level diversity scheme in the receiver unit. When a data packet has been received by the receiver 58A, it will be verified by using the CRC and it will be buffered in the buffer 59A. In addition, an interrupt request is sent from the receiver 59A to the processing unit 74, in order to indicate that a packet has been received. The other receiver 58B acts in parallel accordingly: when it receives a data packet, it verifies the data packet and buffers it in the buffer 59B and sends an interrupt request to the processing unit 74.

When the processing unit 74 receives such an interrupt request, it reads the data packet from one of the two buffers 59A, 59B (usually, there is a default setting as to from which one of the buffers the processing unit 74 will try to read the data packet first) and flushes the other one of the buffers 59A, 59B, if the data packet was obtained correctly (rather than using interrupt requests, the respective buffer 59A, 59B could be checked at the end of the last reception slot; i.e., the receivers could operated via polling rather than via interrupts). However, if it is not possible to read the data packet from the default one of the buffers (usually because the respective antenna 38A, 38B suffered from severe multi-path fading at the reception time), the processing unit 74 tries to read the data packet from the other one of the buffers and, if it is successful in reading the data packet, it flushes the buffer of the other.

An example of this method is illustrated in FIG. 17, wherein it is assumed that the third transmission of the data packet “A” from the transmission unit 10 fails at the antenna 38A allocated to the receiver 58A so that, in this case, the processing unit 74 reads the data packet from the buffer 59B of the receiver 58B rather than from the buffer 59A of the receiver 58A (which, in the example, is the default receiver). Typically, such packet level diversity is applied not only to the audio data packets, but also to the other data packets, such as the beacon packet.

However, it is noted that such packet level diversity is not applicable to ear level receiver units since, due to the small size of ear level receiver units, there is usually not enough space for the required spatial separation of the two antennas required for the above-described packet level diversity scheme.

While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto, and is susceptible to numerous changes and modifications as known to those skilled in the art. Therefore, this invention is not limited to the details shown and described herein, and includes all such changes and modifications as encompassed by the scope of the appended claims.

Claims

1. A system for providing sound to at least one user, comprising:

at least one audio signal source for providing audio signals;

a transmission unit comprising a digital transmitter for applying a digital modulation scheme in order configured to transmit the audio signals as data packets from the audio signal source via a wireless digital audio link;

at least one receiver unit for reception of configured to receive audio signals from the transmission unit via the digital audio link, comprising at least one digital receiver;

means for stimulating hearing of at least one user according to audio signals supplied from the receiver unit;

wherein the transmission unit is adapted configured to transmit each data packet in a separate slot of a tdma frame at a different frequency according to a frequency hopping sequence,

wherein, in at least some of the slots, the audio signals are to be transmitted as audio data packets, wherein a same audio packet is to be transmitted at least twice in a same tdma frame, without expecting acknowledgement messages from the at least one receiver unit,

wherein the tdma frames are structured for unidirectional broadcast transmission of the audio data packets, without individually addressing the at least one receiver unit, and

wherein each audio data packet comprises a start frame delimiter, audio data and a frame check sequence, and wherein each digital receiver of the at least one receiver unit is adapted configured to verify each received data packet by using the frame check sequence and to use the audio data of the first verified version of each data packet as the signal to be supplied to the stimulation means while not using the audio data of other versions.

2. The system of claim 1, wherein the same audio packet is to be transmitted at least twice in subsequent slots.

3. The system of claim 1, wherein each receiver of the at least one receiver unit is adapted to sleep at least during times when no data packets are to be expected.

4. The system of claim 3, wherein each receiver of the at least one receiver unit is adapted to wake up a given guard time period before expected arrival of an audio packet different from the previous audio packet.

5. The system of claim 4, wherein each receiver of the at least one receiver unit is adapted to wake up at a given guard time period before expected arrival of the repetition of the previous audio packet, if a start frame delimiter has not been received or if the previous audio packet could not be verified.

6. The system of claim 5, wherein each receiver of the at least one receiver unit is adapted to go to sleep again after a given timeout period after an expected end of transmission of the audio packet, if no audio packet has been received.

7. The system of claim 6, wherein each receiver is adapted to go to sleep again after a given timeout period after an expected end of transmission of the start frame delimiter of the audio packet, if a start frame delimiter has not been received.

8. The system of claim 1, wherein, in a first slot of each frame, a beacon packet is to be transmitted which contains information for hopping frequency synchronization.

9. A system for providing sound to at least one user, the system comprising:

at least one an audio signal source for providing audio signals;

a transmission unit comprising a digital transmitter for applying a digital modulation scheme in order configured to transmit the audio signals as data packets from the audio signal source via a wireless digital audio link;

at least one a receiver unit configured for reception of audio signals the data packets from the transmission unit via the digital audio link, comprising at least one wherein the receiver unit includes a digital receiver;

means for stimulating hearing of at least one providing at least portions of the audio signals to a user according to audio signals supplied from the receiver unit;,

wherein the transmission unit is adapted to configured to transmit each data packet in a separate slot of a tdma time-slotted frame at a different frequency according to a frequency hopping sequence,

wherein, in at least some of the slots, the audio signals data packets are to be transmitted as audio data packets, and

wherein a same each audio data packet is to be transmitted at least twice in a the same tdma time-slotted frame, without expecting acknowledgement messages from the at least one receiverunit,

wherein, in a first slot of each frame, a beacon packet to be transmitted is provided which contains data necessary for synchronizing the network, and

wherein each receiver of the at least one receiver unit is adapted to wake up a given guard time period before expected arrival of the beacon packet of certain ones of the frames, while sleeping during expected transmission of the beacon packet of the other frames.

10. The system of claim 9, wherein each receiver of the at least one the receiver unit is adapted to wake up at a given guard time period before expected arrival of beacon packets of frames having a sequence number which fulfills a given condition with regard to an address of the respective receiver unit having a sequence number which fulfills a given condition with regard to periodicity.

11. The system of claim 10, wherein the at least one receiver unit comprise is a first receiver unit and the system further comprises a plurality of receiver units, and wherein the transmission unit is adapted to send a message to a specific one of the receiver units by including the message into the beacon packet of a frame having a sequence number for which the given condition is fulfilled with regard to an address of the a respective receiver unit.

12. A system for providing sound to at least one user, comprising:

at least one audio signal source for providing audio signals;

a transmission unit comprising a digital transmitter for applying a digital modulation scheme in order to transmit the audio signals as data packets from the audio signal source via a wireless digital audio link;

at least one receiver unit for reception of audio signals from the transmission unit via the digital audio link, comprising at least one digital receiver;

means for stimulating hearing of at least one user according to audio signals supplied from the receiver unit;

wherein the transmission unit is adapted to transmit each data packet in a separate slot of a tdma frame at a different frequency according to a frequency hopping sequence,

wherein, in at least some of the slots, the audio signals are to be transmitted as audio data packets, wherein a same audio packet is to be transmitted at least twice in a same tdma frame, without expecting acknowledgement messages from the at least one receiver unit,

wherein, in a first slot of each frame, a beacon packet to be transmitted is provided which contains data necessary for synchronizing the network, and

wherein the at least one receiver unit comprise a plurality of receiver units, and wherein each receiver unit is adapted to wake up at a given guard time period before expected arrival of the beacon packet of frames having a sequence number fulfilling a certain global condition, in order to have all receiver units periodically listen to a same beacon packet.

13. The system of claim 8, wherein the transmission unit is adapted to receive in a second slot of each frame a control data packet from the receiver units requested by the transmission unit.

14. The system of claim 8, wherein a first slot of each frame is for multiplexing a beacon packet to be sent by the transmission unit and a control data packet to be received from the at least one receiver unit as requested by the transmission unit.

15. A system for providing sound to at least one user, comprising:

at least one audio signal source for providing audio signals;

a transmission unit comprising a digital transmitter for applying a digital modulation scheme in order to transmit the audio signals as data packets from the audio signal source via a wireless digital audio link;

at least one receiver unit for reception of audio signals from the transmission unit via the digital audio link, comprising at least one digital receiver;

means for stimulating hearing of at least one user according to audio signals supplied from the receiver unit;

wherein the transmission unit is adapted to transmit each data packet in a separate slot of a tdma frame at a different frequency according to a frequency hopping sequence,

wherein, in at least some of the slots, the audio signals are to be transmitted as audio data packets, wherein a same audio packet is to be transmitted at least twice in a same tdma frame, without expecting acknowledgement messages from the at least one receiver unit,

wherein, in a first slot of each frame, a beacon packet to be transmitted is provided which contains data necessary for synchronizing the network, and

wherein the at least one receiver unit comprise a plurality of receiver units, and wherein each beacon packet includes at least one item of information relevant for an audio stream from the group of items comprising a description of encoding format, a description of audio content, a gain parameter, surrounding noise level; information relevant for multi-talker network operation, and control data for all or a specific one of the receiver units.

16. The system of claim 1, wherein the transmission unit is adapted to encode the audio data using ADPCM.

17. The system of claim 1, wherein the audio signal source is a microphone arrangement integrated into or connected to the transmission unit for capturing a speaker's voice.

18. The system of claim 17, wherein the transmission unit comprises an audio signal processing unit for processing the audio signals captured by the microphone arrangement prior to being transmitted.

19. The system of claim 1, wherein the transmission unit is adapted to establish the digital audio link at a carrier frequency in a 2.4 GHz ISM band.

20. The system of claim 1, wherein the transmission unit is adapted to be connected to an external audio device from the group of external audio devices comprising a mobile phone, an FM radio, a music player, a telephone and a TV device, as the audio signal source.

21. The system of claim 1, wherein the transmission unit is adapted to be connected via a digital audio link to an external transmission unit comprising a microphone for capturing a speaker's voice as the audio signal source.

22. The system of claim 1, wherein the at least one receiver unit comprise a plurality of receiver units, and wherein at least one of the receiver units is connected to or integrated into an ear-worn device, comprising the stimulation means.

23. The system of claim 1, wherein the at least one receiver unit comprise a plurality of receiver units, and wherein at least one of the receiver units is a neck-worn device comprising a transmitter for transmitting audio signals via an inductive link to an ear-worn device, comprising the stimulation means.

24. The system of claim 1, wherein the at least one receiver unit comprise a plurality of receiver units, and wherein the at least one receiver unit is connected to or integrated within at least one audience loudspeaker serving as the stimulation means.

25. A system for providing sound to at least one user, comprising:

at least one audio signal source for providing audio signals;

a transmission unit comprising a digital transmitter for applying a digital modulation scheme in order to transmit the audio signals as data packets from the audio signal source via a wireless digital audio link;

at least one receiver unit for reception of audio signals from the transmission unit via the digital audio link, comprising at least one digital receiver;

means for stimulating hearing of at least one user according to audio signals supplied from the receiver unit;

wherein the transmission unit is adapted to transmit each data packet in a separate slot of a tdma frame at a different frequency according to a frequency hopping sequence,

wherein in at least some of the slots, the audio signals are to be transmitted as audio data packets, wherein a same audio packet is to be transmitted at least twice in a same tdma frame, without expecting acknowledgement messages from the at least one receiver unit,

wherein the tdma frames are structured for unidirectional broadcast transmission of the audio data packets, without individually addressing the at least one receiver unit, and

wherein the at least one receiver unit comprise a plurality of receiver units, and wherein at least one of the receiver units is a neck-worn device comprising a transmitter for transmitting audio signals via an inductive link to an ear-worn device, comprising the stimulation means, and

wherein the at least one receiver unit comprise a plurality of receiver units, wherein each receiver unit comprises at least two digital receivers, each being connected to a common processing unit and an antenna and including a demodulator and a buffer, wherein each receiver is for receiving, verifying and buffering each of the audio data packets, wherein each receiver unit is adapted to send an interrupt request from at least one of the receivers to the processing unit to indicate when a packet has been received, and wherein the processing unit is adapted to read an audio data packet from a buffer of one of the receivers and, if the packet has been correctly received by that receiver, to flush the buffer of the other receivers and, if the packet has not been correctly received by that receiver, to read the audio data packet from the buffer of another one of the receivers.

26. A method for providing sound, the method comprising:

transmitting an audio signal as audio data packets from a transmission unit via a wireless digital audio link;

receiving, at a receiver unit, the audio data packets from the transmission unit via the digital audio link,

wherein the receiver unit includes a digital receiver,

wherein the transmission unit transmits each audio data packet twice in separate slots of a time-slotted frame at different frequencies according to a frequency hopping sequence, and

wherein transmissions of the twice transmitted audio data packets are executed unconditionally, irrespective of whether the receiver unit has correctly received one of the transmissions of the audio data packets.

27. The method of claim 26, wherein each frame comprises a start frame delimiter, the two audio data packets, and a frame check sequence, and wherein the digital receiver of the receiver unit verifies each received data packet by using a frame check sequence.

28. The method of claim 26, wherein the receiver unit is electronically coupled to or integrated in a hearing aid, headphone, or earphone.

29. A method for providing sound, the method comprising:

receiving an audio signal;

converting the audio signal to digital audio packets;

transmitting wirelessly the digital audio packets to a receiver unit,

wherein the transmitting further includes transmitting a first digital audio packet on a first frequency in a first time slot of a time-slotted frame,

wherein the transmitting further includes transmitting a second digital audio packet on a second frequency in a second time slot of the time-slotted frame, and

wherein the first digital audio packet and the second digital audio packet include the same audio information and are transmitted in subsequent slots of the time-slotted frame.

30. The method of claim 29, the method further comprising:

determining an expected arrival time when the first digital audio packet is expected to arrive;

determining a time when the receiver unit will start listening by subtracting a guard period from the expected arrival time; and

in response to determining the time when the receiver unit will start listening, waking up the receiver unit to start listening at the time.

31. The method of claim 29, the method further comprising:

determining that the first digital audio packet has been correctly received;

in response to determining the first digital audio packet has been correctly received, sleeping during the transmission of the second digital audio packet.

32. The method of claim 29, the method further comprising:

in response to determining the first digital audio packet was not received, switching the receiver unit to receive the second digital audio packet on the second frequency and waiting for the second digital packet.

33. The method of claim 29, wherein the receiver unit is electronically coupled to or integrated into a hearing aid or headphone.

34. The method of claim 29, wherein the time-slotted frame includes a zero time slot, wherein the zero time slot includes a beacon packet, and wherein the beacon packet includes data for synchronizing.

35. A non-transitory computer-readable medium storing instructions, which when executed by a device, cause the device to perform operations for providing audio to multiple receivers, the operations comprising:

receive an audio signal;

convert the audio signal to digital audio packets;

transmit wirelessly the digital audio packets to a receiver unit,

wherein the transmitting further includes transmitting a first digital audio packet on a first frequency in a first time slot of a time-slotted frame,

wherein the transmitting further includes transmitting a second digital audio packet on a second frequency in a second time slot of the time-slotted frame, and

wherein the first digital audio packet and the second digital audio packet include the same audio information and are transmitted in subsequent slots of the time-slotted frame.

36. The non-transitory computer readable medium of claim 35, the operations further comprising:

determine an expected arrival time when the first digital audio packet is expected to arrive;

determine a time when the receiver unit will start listening by subtracting a guard period from the expected arrival time; and

in response to determining the time when the receiver unit will start listening, wake up the receiver unit to start listening at the time.

37. The non-transitory computer readable medium of claim 35, the operations further comprising:

determine that the first digital audio packet has been correctly received;

in response to determining the first digital audio packet has been correctly received, sleep during the transmission of the second digital audio packet.

38. The non-transitory computer readable medium of claim 35, the operations further comprising:

in response to determining the first digital audio packet was not received, switch the receiver unit to receive the second digital audio packet on the second frequency and wait for the second digital packet.

39. The non-transitory computer readable medium of claim 35, wherein the receiver unit is electronically coupled to or integrated in a hearing aid, earphone, or headphone.

40. The method of claim 26, wherein the transmission unit transmits each audio data packet three times in separate slots of the time-slotted frame.