P-PERSISTENT CARRIER SENSE MULTIPLE ACCESS (CSMA) FOR NON-PACKETIZED WIRELESS DIGITAL VOICE NETWORKS

• US 20080013564A1
• Filed: 07/13/2006
• Published: 01/17/2008
• Est. Priority Date: 07/13/2006
• Status: Active Grant

• Current Assignee: Harris Global Communications, Inc. (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: KOSKI, Eric
• Granted Patent: US 7,826,474 B2
• Time in Patent Office: Days
• US Class Current: 370/445
• CPC Class Codes: H04W 74/0833 Random access procedures, e.g. with 4-step access

Abstract

A communications system includes a plurality of radios that form a CSMA wireless communications network to communicate none-packetized digital voice with each other. Each radio is operative for dividing the period following the end of a received transmission into a sequence of time slots, each having a duration at least equal to an effective end-to-end traffic latency. In each time slot, the radio decides randomly with probability p whether to start transmitting on the channel in that slot, provided that a new transmission has not been detected on the channel prior to the start of the slot.

Claims

1. A communications system, comprising:

a plurality of radios that form a CSMA wireless communications network and communicate non-packetized digital voice with each other;

each radio being operative for dividing the period following the end of a received transmission into a sequence of time slots, and in each time slot, deciding randomly or pseudo-randomly with probability p whether to start transmitting on the channel in that slot, provided that a new transmission has not been detected on the channel prior to the start of the slot.

2. The communications system according to claim 1, wherein a radio comprises a transmit key switch such that upon the operator'"'"'s depressing said transmit key switch, said radio is operative for either commencing transmission once a chosen time slot is reached, or aborting transmission and processing an incoming new transmission if the transmission arrives earlier than the chosen time slot.

3. The communications system according to claim 1, wherein each slot in the sequence of slots has a duration at least equal to an effective end-to-end traffic latency which includes some or all of transmit latency, maximum propagation time, and latency of traffic detection by a receiver, so as to permit a transmission commenced in slot n to be detected prior to a start of slot n+1.

4. The communications system according to claim 1, wherein at least one of said radios adapts a probability p based on one or more of at least traffic loading, number of stations, priority of traffic and durations of past transmissions.

5. The communications system according to claim 1, wherein at least one of said radios is operative for determining a first transmission time slot for a transmission that starts at a beginning of a time slot.

6. The communications system according to claim 1, wherein slot transmission probabilities (p) for successive transmission time slots are adjusted to compensate for a probability distribution of key switch actuation over time.

7. The communications system according to claim 1, wherein at least one of said radios is operative for inferring whether collisions are likely from patterns in a temporal sequence of past transmissions on a communications channel.

8. The communications system according to claim 7, wherein a radio is operative for determining whether to apply a p-persistence on each occasion on which a voice transmission ends and a communications channel becomes free.

9. A method for communicating digital voice, which comprises:

receiving within a radio a non-packetized digital voice communications signal over a CSMA wireless communications channel;

dividing the period following the end of a received transmission into a sequence of time slots; and

in each time slot, deciding randomly or pseudo-randomly with probability p whether to start transmitting on the channel in that slot, provided that a new transmission has not been detected on the channel prior to the start of the slot.

10. The method according to claim 9, which further comprises the operator'"'"'s pressing and holding a transmit key switch at a radio to transmit, and the radio'"'"'s either commencing transmission once a chosen time slot is reached, or aborting a transmission and processing an incoming new transmission if the transmission arrives earlier than the chosen time slot.

11. The method according to claim 9, which further comprises choosing a slot duration in the sequence of the slots at least equal to an effective end-to-end traffic latency which includes some or all of transmit latency, maximum propagation time, and latency of traffic detection by a receiver, so as to permit a transmission commenced in slot n to be detected prior to a start of slot n+1.

12. The method according to claim 9, which further comprises adapting the probability p based on one or more of at least traffic loading, number of stations, priority of traffic and durations of past transmissions.

13. The method according to claim 9, which further comprises determining a first transmission time slot in which a radio is allowed to transmit and forcing transmissions to start at a beginning of a time slot.

14. The method according to claim 9, which further comprises adjusting slot transmission probabilities (p) for successive transmission time slots to compensate for a probability distribution of key switch actuation over time.

15. The method according to claim 9, which further comprises inferring whether collisions are likely from patterns in a temporal sequence of past transmissions on a communications channel.

16. The method according to claim 15, which further comprises determining whether to apply p-persistence on each occasion on which a voice transmission ends and a communications channel becomes free.

17. The method according to claim 16, which further comprises applying p-persistence only when collisions are likely to occur so as to reduce overhead during transmission scenarios when collisions are unlikely.

18. The method according to claim 9, which further comprises processing information within a transmission to determine if a collision is likely to occur, and if so, applying p-persistence.

19. The method according to claim 18, wherein said information comprises one or more of at least voice information, and a data tag appended to a voice transmission.

20. The method according to claim 18, wherein an operator indicates to the radio whether a collision is likely to occur following a transmission, and incorporating this information into a voice transmission so that it can be used by receiving radios to decide whether or not to apply p-persistence following the transmission.

21. The method according to claim 20, wherein the operator so indicates by at least one of operating a switch or other control mechanism other than the key switch before, during, or after the voice transmission, and depressing of a key switch a predetermined number of times.

22. The method according to claim 18, which further comprises receiving a voice communications signal at one of plurality of mobile wireless communications devices that operate as a p-persistent CSMA wireless communications network.

23. A method for communicating digital voice, which comprises:

receiving within a radio a non-packetized digital voice communications over a CSMA wireless communications channel;

determining at the radio the start time of a sequence of transmit time slots;

determining which of the transmit time slots in the sequence of transmit time slots is a first slot in which the radio can transmit; and

if a key switch at the radio is depressed before a start of a time slot in which the radio can transmit, playing an audible signal as a hold-off tone at the radio and informing an operator that the radio must wait before transmitting, and when a next time slot arrives in which the radio can transmit, the audible signal is removed and the radio starts to transmit, and if a key switch is depressed after a start of the time slot, then waiting for a start of a next time slot to transmit.

24. The method according to claim 23, which further comprises playing a received voice signal if a radio receives an incoming voice signal before the radio starts to transmit in response to actuation of a key switch.

25. The method according to claim 23, which further comprises the operator'"'"'s pressing and holding a transmit key switch at a radio to transmit, and the radio'"'"'s either commencing transmission once a chosen time slot is reached, or aborting transmission and processing an incoming transmission if one arrives earlier than the chosen time slot.

26. The method according to claim 23, which further comprises choosing a slot duration at least equal to an effective latency end-to-end traffic latency which includes some or all of transmit latency, a maximum propagation time, and latency of traffic detection by a receiver, so as to permit a transmission commenced in slot n to be detected prior to a start of slot n+1.

27. The method according to claim 23, which further comprises adapting the probability p based on one or more of at least traffic loading, number of stations, priority of traffic and durations of past transmissions.

28. The method according to claim 23, which further comprises adjusting slot transmission probabilities (p) for successive transmission time slots to compensate for a probability distribution of key switch actuation over time.

29. The method according to claim 23, which further comprises inferring whether collisions are likely from patterns in a temporal sequence of past transmissions on a communications channel, and applying p-persistence only when such patterns indicate that collisions would otherwise be likely to occur.