Wireless audio transmission system and method
A system and method transmit a data stream from a source to a destination over a communication channel. A transmitter includes devices for processing inputs to assemble data packets for the data stream, and a multiplexer for assembling a data frame to be transmitted over the communication channel, in which each data frame has at least one fixed slot. The multiplexer sets at least one freely allocatable time slot in each data frame. Retransmission control devices connected to the multiplexer retransmit a specific data packet which is not properly received by the destination, using one of the freely allocatable slots.
1. A method for transmitting at least one data stream from a source to at least one destination over a communication channel, wherein the at least one data stream comprises a sequence of a plurality of data packets, and wherein the method comprises:
transmitting the at least one data stream over the communication channel using a signal comprising data frames according to a protocol, wherein each data frame comprises N fixed slots with a single negative acknowledge sub-slot following each of the N fixed slots, and at least one freely allocatable slot, wherein each freely allocatable slot comprises N negative acknowledge sub-slots following the freely allocatable slot for indicating in which of the N fixed slots a specific data packet was not received; and
retransmitting a specific data packet, which is not properly received by the at least one destination, from the source using one of the at least one freely allocatable slot, wherein the specific data packet is transmitted uncompressed in the step of transmitting, and compressed in the step of retransmitting.
2. The method according to claim 1 , where the step of retransmitting comprises retransmitting the specific data packet for a specific data stream in the fixed slot of that specific data stream in a next data frame.
3. The method according to claim 1 , wherein each data frame comprises a down-link part and an up-link part, each having at least one fixed slot and at least one freely allocatable slot.
4. The method according to claim 1 , wherein a data packet has a predefined duration, the predefined duration being small compared to non-transmitting gaps of possible interfering sources.
5. The method according to claim 4 , further comprising detecting the non-transmitting gaps by carrier sense/detect techniques, and synchronizing the data stream transmission to the detected non-transmitting gaps.
6. The method according to claim 1 , further comprising receiving acknowledgement of a received data packet from the at least one destination, and retransmitting a not properly received data packet within the same data frame.
7. The method according to claim 6 , wherein the acknowledgment comprises a pseudo-noise code.
8. The method according to claim 1 , further comprising allocating at least one freely allocatable slot to transmit a control data message.
9. The method according to claim 8 , further comprising using a back-off mechanism for transmitting the control data message for multiple access.
10. The method according to claim 1 , further comprising applying antenna and/or frequency diversity.
11. The method according to claim 1 , further comprising:
converting received data packets into an audio signal;
replacing a missing data packet with an earlier received data packet; and
smoothing a transition between the earlier received data packet and the replaced data packet.
12. The method according to claim 11 , wherein the step of smoothing comprises using a raised cosine filter function to smooth the transition between the earlier received data packet and the replaced data packet.
13. The method according to claim 1 , further comprising scrambling a retransmitted data packet before retransmission using a pseudo-randomly varying scrambling technique, and descrambling the retransmitted data packet upon reception.
14. The method according to claim 13 , further comprising integrating multiple retransmitted data packets.
15. The method according to claim 1 , further comprising the source increasing its transmission power upon determination that a data packet is not properly received by the destination.
16. The method according to claim 1 , further comprising the source comparing a received signal strength to a threshold value, and either: (a) decreasing its transmission power by a predefined step if the threshold value is exceeded, or (b) increasing its transmission power by a predefined step otherwise.
17. The method according to claim 16 , wherein the threshold value is adaptively controlled by an outer control loop.
18. The method according to claim 1 , wherein a data packet comprises one or more of a preamble, a header, at least one packet of control message data, and at least one packet of application data from at least one input.
19. A transmitter arrangement for use in a system for transmitting at least one data stream from a source to at least one destination over a communication channel, the transmitter arrangement comprising:
input processing means for assembling data packets for each of the at least one data stream
a multiplexer arranged to receive data packets from the input processing means for each of the at least one data stream, wherein the multiplexer is configured to assemble a plurality of data frames to be transmitted over the communication channel, wherein each data frame comprises N fixed slots with a single negative acknowledge sub-slot following each of the N fixed slots, and at least one freely allocatable slot wherein each freely allocatable slot comprises N negative acknowledge sub-slots following the freely allocatable slot for indicating in which of the N fixed slots a specific data packet was not received;
retransmission control means connected to the multiplexer and configured to retransmit a specific data packet, which is not properly received by the at least one destination, using one of the at least one freely allocatable slot; and
a compressor connected to the retransmission control means to enable the specific data packet to be transmitted uncompressed in a first transmission, and compressed in at least one of the retransmissions.
20. The transmitter arrangement according to claim 19 , wherein at least one of the multiplexer and the retransmission control means are further configured to execute a method in which the specific data packet for a specific data stream is retransmitted in the fixed slot of that specific data stream in a next data frame.
21. The transmitter arrangement according to claim 19 , further comprising a scrambler for scrambling a retransmitted data packet before retransmission using a pseudo-randomly varying scrambling technique.
22. The transmitter arrangement according to claim 19 , further comprising a modulator.
23. A receiver arrangement for receiving at least one data stream transmitted by the transmitter arrangement according to claim 19 .
24. The receiver arrangement according to claim 23 , comprising audio processing electronics.
25. The receiver arrangement according to claim 23 , further comprising a descrambler for descrambling a retransmitted data packet upon reception.
26. The receiver arrangement according to claim 25 , further comprising a pre-detection accumulator for integrating multiple retransmitted data packets.