Method for reverse channel sounding in a communications system

• US 6,031,831 A
• Filed: 02/15/1996
• Issued: 02/29/2000
• Est. Priority Date: 02/15/1995
• Status: Expired due to Term

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Boscovic, Dragan, Aftelak, Andrew John, Wray, Antony John, Johnson, Christopher Philip, Tan Boon, Tiong, Gibbs, Jonathan Alastair
• Primary Examiner(s): TON, DANG T
• Application Number:
  US08/602,171
• Time in Patent Office: 1,475 Days
• Field of Search: 370/318, 370/320, 370/321, 370/324, 370/325, 370/328, 370/331, 370/330, 370/335, 370/337, 370/341, 370/342, 370/343, 370/344, 370/347, 370/350, 370/389, 370/395, 370/400 , 370/252, 370/251, 370/352, 370/254, 370/441, 370/442, 370/286, 455/33.1-33.4, 455/54.1-54.2, 455/51.1, 455/32.3, 455/38.1, 455/38.3, 375/200, 375/205
• US Class Current: 370/342
• CPC Class Codes: H04B 7/04 using two or more spaced independent antennas
• CPC Class Codes: H04W 52/362 Aspects of the step size
• CPC Class Codes: H04W 52/367 Power values between minimum and maximum limits, e.g. dynamic range

Abstract

A method is disclosed for determining current channel state information in a communications system having a first communications unit communicating to a second communications unit, wherein the first communications unit sends a channel sounding packet (32) to the second communications unit. The channel sounding packet (32) is sent a time period, t, prior to the transmission of a signal by the second communications unit to the first communications unit. The second communications unit receives the channel sounding packet (46) and processes the channel sounding packet to determine at least one channel characteristic. In response to receiving the channel sounding packet (46) the second communications unit appends frame code information (48) to the signal to be transmitted from the second communications unit to the first communications unit, to inform the first communications unit of the communications parameters that have been optimized.

Claims

1. A method of determining current channel state information in a radio communications system in order to optimize a transmission of an information signal, wherein the radio communications system includes a first communications unit and a second communications unit, the method comprising the steps of:

transmitting a channel sounding packet from the first communications unit to the second communications unit a time period, t, prior to transmission of the information signal by the second communications unit to the first communications unit;

receiving the channel sounding packet at the second communications unit;

processing the channel sounding packet at the second communications unit to determine at least one communication channel characteristic;

optimizing at least one communication parameter of the information signal based on the at least one communication channel characteristic; and

transmitting the optimized information signal from the second communications unit to the first communications unit wherein the information signal includes information indicating the at least one communication parameter that has been optimized by the second communications unit.

2. The method according to claim 1, wherein the step of transmitting the information signal includes:

appending frame code information to the information signal to be transmitted from the second communications unit; and

transmitting the information signal with the appended frame code information from the second communications unit to the first communications unit to inform the first communications unit of the at least one communication parameter that has been optimized.

3. The method according to claim 1, wherein optimizing of at least one of the communications parameter exceeds at least one of a predetermined communication parameter threshold level thereby initiating a hand-off process.

4. The method according to claim 2, wherein the step of appending frame code information to the information signal includes placing the frame code information in a header of a data packet of the information signal.

5. The method according to claim 1, wherein the time period, t, is selected from a group of switching time, frequency lock time, signal processing time, channel delay, and system delay.

6. The method according to claim 1, wherein the at least one communication parameter may include any of the following:

channel transmission rate, modulation type, modulation rate, channel coding rate, source coding rate, transmitter and/or receiver filter responses, packet length, transmitter signal power, adaptive power control levels, whether a channel equalizer is to be used, and which antennae are to be used when the radio communications system uses distributed antenna diversity.

7. The method according to claim 1, wherein the radio communications system operates on a frequency division multiple access (FDMA) time division duplex (TDD) scheme.

8. The method according to claim 1, wherein transmitting a channel sounding packet by the first communications unit includes transmitting a channel sounding packet bit to indicate when channel sounding packet information is being transmitted to the second communications unit.

9. The method according to claim 1, wherein the transmitting of the channel sounding packet by the first communications unit provides timing synchronization information for the second communications unit.

10. The method of determining current channel state information in a radio communications system according to claim 1, wherein the radio communications system is a code division multiple access radio communications system, the channel sounding packet is a channel sounding chip sequence and the information signal contains embedded information of the at least one optimized communication parameter.

11. The method according to claim 10, wherein optimization of the at least one communication parameter exceeds at least one of a predetermined communications parameter threshold level, thereby initiating a hand-off process.

12. The method according to claim 10, wherein the time period, t, is selected from a group of switching time, frequency lock time, signal processing time, channel delay, and system delay.

13. The method according to claim 10, wherein the at least one communication parameter includes any of the following:

channel transmission rate, modulation format, channel coding rate, source coding rate, pre-filtering characteristics, packet length, transmitter signal power and power control level.

14. The method according to claim 10, wherein the step of transmitting a channel sounding chip sequence by the first communications unit includes transmitting a channel sounding chip sequence bit to indicate when a channel sounding chip sequence is being transmitted from the first communications unit to the second communications unit.

15. The method according to claim 10, wherein the step of transmitting the channel sounding chip sequence from the first communications unit also provides timing synchronization information for the second communications unit.

16. The method according to claim 10, wherein the radio communications system further includes at least one third communications unit for communicating with the first communications unit, the method further comprising the steps of:

receiving a second channel sounding chip sequence from the first communications unit at the at least one third communications unit, at a simultaneous time to the second communications unit receiving the first channel sounding chip sequence, the second channel sounding chip sequence being of a different orthogonal code to the first channel sounding chip sequence;

processing the second channel sounding chip sequence at the at least one third communications unit to determine at least one second channel characteristic;

optimising at least one communication parameter of the third communications unit based on the at least one second channel characteristic; and

transmitting a second information signal from the at least one third communications unit to the first communications unit, wherein the second information signal contains embedded information of the at least one optimized communication parameter of the third communications unit.

17. A method for adapting at least one communication parameter of a communications unit, in accordance with current communication channel information obtained from a reverse channel sounding technique, wherein a first communications unit communicates to a second communications unit on a communication channel of a first time-discontinuous radio communications system, the method comprising the steps of:

transmitting channel sounding information, from the second communications unit to the first communications unit, a time period, t, prior to transmission of an information signal from the second communications unit to the first communications unit;

receiving the channel sounding information at the first communications unit and processing the channel sounding information to determine a current state of the communication channel;

assessing whether at least one communication parameter of the information signal needs to be optimized in accordance with the processed channel sounding information; and

optimizing at least one communication parameter when the state of the communication channel requires.

18. The method for adapting at least one communication parameter of a communications unit, in accordance with claim 17, further comprising the steps of:

transmitting the information signal from the first communications unit to the second communications unit, wherein the information signal includes information indicative of the at least one optimized communication parameter;

receiving the information signal containing the at least one optimized communication parameter at the second communications unit;

processing the information signal to obtain the information indicating the at least one optimized communication parameter; and

adapting a receiver demodulation process of the second communications unit to receive the information signal from the first communications unit.

19. A method for determining whether hand-off is required from a first time-discontinuous radio communications system to a second time-discontinuous radio communications system, wherein the first time-discontinuous radio communications system includes a first communications unit communicating to a second communications unit on a communication channel using a reverse channel sounding technique to assess a current state of at least one channel characteristic of the communication channel, the method comprising the steps of:

transmitting channel sounding information, from the first communications unit to the second communications unit, a time period, t, prior to transmission of an information signal from the first communications unit to the second communications unit;

receiving the channel sounding information at the second communications unit and processing the channel sounding information to determine the current state of the communication channel;

optimising at least one communication parameter of the second communications unit according to the received channel sounding information;

comparing the at least one optimised communication parameter with at least one of a predetermined communication parameter threshold level;

monitoring, at the second communications unit when the predetermined communication parameter threshold level is exceeded, channel sounding information of the second time-discontinuous radio communication system, to determine whether communication to and from the second communications unit would benefit from handing-off to the second time-discontinuous radio communication system; and

initiating a hand-off procedure at the second communications unit when the communication to and from the second communications unit would benefit from handing-off to the second time-discontinuous radio communication system.

20. A method for performing a communication hand-off from a code division multiple access radio communications system, having a first communications unit communicating to a second communications unit, to a time-discontinuous radio communications system having a third communications unit, wherein both radio communication systems use a reverse channel sounding technique to obtain a current assessment of at least one channel characteristic of a communications link, the method comprising the steps of:

entering a time-discontinuous mode of operation for communications between the first communications unit and the second communications unit in the code division multiple access radio communications system, once hand-off to the time-discontinuous radio communications system is desired;

monitoring channel sounding transmissions of the time-discontinuous radio communications system by the first communications unit during periods of non-transmission on the code division multiple access radio communications system;

commencing communications between the first communications unit and the third communications unit on the time-discontinuous radio communications system according to the channel sounding information and timing parameters of the time-discontinuous radio communications system;

continuing communications from the first communications unit to both the second communications unit in the time-discontinuous mode and to the third communications unit in alternative time periods in a time-discontinuous mode until full hand-off to the second time-discontinuous radio communications system can be completed; and

communicating from the first communications to the third communications unit in normal time-discontinuous mode of operation when hand-off is completed.

21. The method for performing a communication hand-off from a code division multiple access radio communications system, according to claim 20, the method further comprising the steps of:

registering by the first communications unit with the time-discontinuous radio communications system; and

adjusting a power control level for communicating on the code division multiple access radio communications system according to a rate of transmissions in the time-discontinuous mode.

22. The method for performing a communication hand-off from a code division multiple access radio communications system, according to claim 20, wherein the time-discontinuous radio communications system is a second code division multiple access radio communications system, the method further comprising the steps of:

transmitting from the first communications unit to the third communications unit information containing embedded data obtained from the channel sounding process detailing at least one communication parameter being used by the first communications unit in the transmission;

receiving the information, at the third communications unit;

optimising at least one communication parameter at the third communications unit according to the embedded data of the received information;

wherein the steps of continuing and communicating include;

continuing communications from the first communications unit to the second communications unit on the code division multiple access radio communications system and alternatively from the first communications unit to the third communications unit on the second code division multiple access radio communications system in a time-discontinuous mode until a full hand-off can be completed; and

communicating from the first communications unit to the third communications unit in a normal time-continuous mode of operation when hand-off is completed.

23. A method for performing a communication hand-off from a time division multiple access radio communications system, having a first communications unit communicating to a second communications unit, to a time-discontinuous radio communications system having a third communications unit, wherein both radio communication systems use a reverse channel sounding technique to obtain a current assessment of at least one channel characteristic of a communications link, the method comprising the steps of:

monitoring reverse channel sounding transmissions of the time-discontinuous radio communications system by the first communications unit, during periods of non-transmission between the first communications unit and the second communications unit on the time division multiple access radio communications system;

determining whether the first communications unit would benefit from a hand-off to the time-discontinuous radio communications system using information from the reverse channel sounding transmissions of the time-discontinuous radio communications system;

commencing communications between the first communications unit and the third communications unit on the time-discontinuous radio communications system according to the channel sounding information and timing parameters monitored on the time-discontinuous radio communications system, and so as not to interfere with communications from the first communications unit to the second communications unit on the time division multiple access radio communications system;

continuing communications from the first communications unit to both the second communications unit and to the third communications unit in the time-discontinuous mode until full hand-off from the Time division multiple access communications system to the time-discontinuous communications system can be completed; and

transmitting from the first communications unit only to the third communications unit when hand-off is completed.

24. The method for performing a communication hand-off from a time division multiple access radio communications system according to claim 23 wherein the time-discontinuous communications system is a code division multiple access radio communications system, the method further comprising the steps of:

determining, at the first communications unit, a number of sub-frames per frame on which to communicate with the third communications unit on the code division multiple access radio communications system, using the monitored channel sounding information;

registering, by the first communications unit with the code division multiple access radio communications system;

informing the third communications unit to enter a time-discontinuous mode of operation indicating the number of sub-frames and timing parameters to be used for transmissions from the first communications unit to the third communications unit so as not to interfere with transmissions from the first communications unit to the second communications unit; and

adjusting a power control level for communications between the first communications unit and the third communications unit according to the number of sub-frames to be used for the transmissions.

25. The method for performing a communication hand-off from a time division multiple access radio communications system according to claim 23, wherein the time-discontinuous communications system is a second time division multiple access radio communications system, the method further comprising the step of:

registering, by the first communications unit with the second time division multiple access radio communications system; and

transmitting from the first communications unit to the third communications unit information containing data obtained from the channel sounding process detailing at least one optimised communication parameter for subsequent communications between the first communications unit and the third communications unit.