Channel sounding for improved system performance
A transmitter generates and transmits a low rate signal to its intended receiver. Upon receiving the low rate signal, the intended receiver generates and transmits a channel sounding response (CSR), said CSR being a short burst having a predefined transmit format and carrying predetermined information. The transmitter then analyzes the CSR and determines uplink channel response, estimates downlink channel response, and determines appropriate transmit parameter settings based on the analysis and downlink response estimate. Adjustment of the transmit parameters can be made in either the MAC or PHY layer or in a combination of both. After adjusting its transmit parameters and modulating sub-carriers with user-data according to the determined transmit settings, the transmitter transmits the user-data to the receiver on a preferred portion of bandwidth. In a preferred embodiment, the transmitter also generates and transmits a transmit format control (TFC) signal containing the determined transmit parameter settings, including sub-carrier modulation information, to the receiver.
1. A wireless communications method for a base station, the method comprising:
transmitting a channel sounding request to a wireless transmit/receive unit (WTRU), wherein the channel sounding request includes channel sounding instructions;
receiving a predefined channel sounding response (CSR) responsive to the channel sounding request, wherein the CSR is defined in terms of a number of symbols, size and symbol amplitude;
analyzing the CSR to estimate an uplink (UL) channel via measuring the amplitude and phase of subcarriers of the CSR at a plurality of antennas;
determining transmit parameter settings based on the estimated UL channel including modulation and coding parameters for each of a plurality of subcarriers to be transmitted on using at least one of the plurality of antennas;
adjusting transmit parameters and modulating a plurality of sub-carriers with data according to the determined transmit parameter settings; and
transmitting the data using the adjusted transmit parameters and transmitting an indicator that indicates at least one of the adjusted transmit parameters.
2. The method of claim 1 , wherein the channel sounding request is a data packet header including source and destination information.
3. The method of claim 1 , wherein the data is modulated to the sub-carriers using a channel capacity optimization technique.
4. The method of claim 3 , wherein the channel capacity optimization technique is water-filling.
5. The method of claim 1 , wherein the data is modulated to the sub-carriers using a channel reliability optimization technique.
6. The method of claim 5 , wherein the channel reliability optimization technique is power control.
7. The method of claim 1 , further comprising saving the determined transmit parameter settings and transmitting subsequent data according to the saved transmit parameter settings.
8. The method of claim 1 , further comprising generating a transmit format control (TFC) signal, the TFC signal comprising the determined transmit parameter settings.
9. The method of claim 1 , wherein adjusting the transmit parameters occurs in a medium access control (MAC) layer of a transmitter.
10. The method of claim 1 , wherein adjusting the transmit parameters occurs in a physical (PHY) layer of a transmitter.
11. The method of claim 1 , wherein adjusting the transmit parameters occurs in a combination of a MAC layer and a PHY layer of a transmitter.
12. The method of claim 1 wherein the uplink channel is a multiple input multiple output (MIMO) channel.
13. The method of claim 1 wherein the adjusted transmit parameters include at least the plurality of sub-carriers on which the data are being transmitted.
14. A base station for use in wireless communications comprising:
a transmitter configured to transmit a channel sounding request including channel sounding instructions;
a receiver; and
at least one transmit/receive antenna configured to receive and transmit communication signals;
wherein the receiver is configured to receive a predefined channel sounding response (CSR) in response to the channel sounding request, wherein the CSR is defined in terms of a number of symbols, size and symbol amplitude, and wherein the transmitter is further configured to analyze the CSR to estimate an uplink (UL) channel via measuring the amplitude and phase of subcarriers of the CSR at a plurality of antennas, determine transmit parameter settings based on the estimated UL channel including modulation and coding parameters for each of a plurality of subcarriers to be transmitted on using at least one of the plurality of antennas, adjust transmit parameters and modulate a plurality of sub-carriers with data according to the determined transmit parameter settings, transmit the data using the adjusted transmit parameters, and transmit an indicator that indicates at least one of the adjusted transmit parameters.
15. The base station of claim 14 , further comprising a memory component configured to store determined transmit parameter settings for use in transmitting subsequent data according to the stored transmit parameter settings.
16. The base station of claim 15 , further comprising a TFC processor configured to generate local TFC signals and process received TFC signals, wherein the local TFC signals comprise the determined transmit parameter settings.
17. The base station of claim 16 , further comprising:
a signal monitoring processor configured to monitor CSR signals;
a receiver comprising a signal analyzer configured to assess channel conditions of a communication link; and
a second memory component configured to maintain a history of the channel conditions.
18. The base station of claim 14 , wherein the transmitter is configured to generate a channel sounding request comprising a data packet header including source and destination information.
19. The base station of claim 14 wherein the transmit parameters are adjusted in a MAC layer, in a PHY layer, or in a combination of the two.
20. The base station of claim 14 wherein the uplink channel is a multiple input multiple output (MIMO) channel.
21. The base station of claim 14 wherein the adjusted transmit parameters include at least the plurality of sub-carriers on which the data are being transmitted.