KR200400912Y1 - Channel sounding for improved system performance - Google Patents

Abstract

The transmitter generates a low rate signal and transmits it to the target receiver. The target receiver generates and transmits a channel sounding response (CSR) upon receipt of this low rate signal. A CSR is a short burst that carries certain information, with a predefined transmission format. The transmitter then analyzes the CSR, determines the uplink channel response to approximate the downlink channel response, and determines appropriate transmission parameter settings based on this analysis and the downlink channel response estimate. The adjustment of the transmission parameter may be performed in either a medium access control (MAC) layer or a PHYs (PHYs) layer, or a combination of the two layers. The transmitter adjusts the transmission parameters, modulates the user data on the subcarriers according to the determined transmission parameter settings, and then transmits the user data to the receiver over the desired bandwidth portion. In a preferred embodiment, the transmitter generates a transmit format control (TFC) signal including the subcarrier modulation information and the determined transmission parameter setting and transmits it to the receiver.

Description

CHANNEL SOUNDING FOR IMPROVED SYSTEM PERFORMANCE} Integrated Circuits, Transmitters, and Receivers for Multiple Input / Output Orthogonal Frequency Division Multiplexed Wireless Communications Systems

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and apparatus for improving channel and system performance in a wireless communication system.

Orthogonal Frequency Division Multiplexing (OFDM) refers to a data transmission scheme in which user data is divided into small data streams, and the data streams are transmitted using subcarriers each composed of a bandwidth smaller than all of the available transmission bandwidths. The efficiency of OFDM is caused by the orthogonality of subcarriers. In other words, the subcarriers are selected so as not to interfere with each other during transmission, which is an efficient transmission scheme.

Multiple input / output (MIMO) refers to a wireless transmission / reception scheme in which a transmitter and a receiver employ a plurality of antennas for transmission and reception. MIMO systems increase throughput by using spatial diversity or spatial multiplexing options created by the presence of multiple antennas (multiple antennas).

Areas that continue to be attempted in OFDM-MIMO systems are system performance, i.e. capacity, reliability, and the like. For this purpose, for example, a plurality of techniques for improving channel capacity and / or reliability have been proposed. One example of such a technique is "water-filling," and another example is power control. Water filling and power control is used by the transmitter to determine channel conditions using feedback signals from the receiver in the system. Based on this estimate, the transmitter attempts to transmit user data in a way that optimizes channel performance in terms of channel conditions. Power control relies on transport channel knowledge through feedback signals to optimize channel performance, but the signaling overhead associated with these feedback signals is an important issue, limiting potential improvements in system performance. In addition, generating and transmitting feedback signals introduces time lag issues. In addition, this time delay also limits the potential improvement in system performance, which is a disadvantage of feedback signaling, particularly in systems with rapidly changing channel conditions, systems transmitting large amounts of data, and / or systems using large numbers of subcarriers. Stand out.

Accordingly, what is needed is a method and apparatus for efficiently estimating the current channel conditions used to improve overall system performance in an OFDM-MIMO system.

The present invention is a method and apparatus for improving the performance of a system in a multiple input / output (MIMO) orthogonal frequency division multiplexing (OFDM) wireless communication system. The transmitter generates a low rate signal and transmits it to the target receiver. The target receiver generates and transmits a channel sounding response (CSR) upon receipt of this low rate signal. A CSR is a short burst that carries certain information, with a predefined transmission format. The transmitter then analyzes the CSR, determines the uplink channel response to approximate the downlink channel response, and determines the appropriate transmission parameter settings based on this analysis and the downlink channel response estimate. The adjustment of the transmission parameter may be performed in either a medium access control (MAC) layer or a PHYs (PHYs) layer, or a combination of the two layers. The transmitter adjusts the transmission parameters, modulates the user data on the subcarriers according to the determined transmission parameter settings, and then transmits the user data to the receiver over the desired bandwidth portion. In a preferred embodiment, the transmitter generates a transmit format control (TFC) signal including the subcarrier modulation information and the determined transmission parameter setting and transmits it to the receiver.

Hereinafter, a wireless transmit / receive unit (WTRU) includes but is not limited to a user device, mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment. In the description herein, a base station includes, but is not limited to, a Node B, a site controller, an access point, or any other type of interfacing device in a wireless environment.

In a preferred embodiment, channel sounding pulses are used to improve channel and system performance in an orthogonal frequency division multiplexing (OFDM) system using multiple input / output (MIMO) devices. The MIMO OFDM transmitter can use this channel sounding pulse to access, for example, the current channel state, so that it can specify the format of the transmission data packet that optimizes throughput in terms of this current channel state.

According to the present invention, the MIMO OFDM transmitter generates a low rate signal such as a channel sounding pulse request (CSRq) and transmits it to the target receiver. The receiver generates a channel sounding response (CSR) upon receipt of this channel sounding pulse request and transmits it to the requesting transmitter. This CSR is preferably a short burst that formats certain transmission parameters to ensure reception success in a given particular system configuration and environment. The CSR contains information known to the transmitter. The transmitter processes the information upon reception of the CSR to determine the state of the current channel. Based on this determination, the transmitter modulates the user data on the subcarrier and uses one of a variety of channel optimization techniques, including water filling and power control, to determine channel capacity, reliability, and / or other performance characteristics of the channel required by the user. Adjust the transmission parameters to maximize By evaluating channel conditions using CSR pulses rather than using conventional feedback signals, the transmitter formats and transmits data packets that optimize channel performance without incurring both the time delay and overhead of conventional channel enhancement methods. can do.

Referring to FIG. 1, a channel sounding scheme for improving system performance in a MIMO OFDM wireless communication system is shown in a flowchart 100. Prior to transmitting the data, the transmitter generates a channel sounding response request in the form of a low rate signal and transmits it to the receiver (step 102). This channel sounding response request is preferably a low data rate signal such as a data packet header that includes information about the source (i.e. transmitter) and the destination (i.e. target receiver). The receiver receives and processes the low rate signal (step 104) and then generates and transmits a predefined channel sounding response (CSR), preferably in a short burst or pulse, to the transmitter (step 106). The CSR is predefined by size, number of symbols, amplitude, and the like, to ensure successful reception at the transmitter with a particular system configuration and / or the allocated resources of the receiver. The CSR contains information that the transmitter can use to evaluate the current channel condition.

The transmitter receives the CSR, processes the information transmitted as part of the CSR (step 108), and uses this to measure the characteristics of the current channel state (step 110). This characteristic measurement step includes measuring the amplitude, phase, and quality of each subcarrier received at each antenna to determine the uplink channel response and estimating the downlink channel response. For example, if the error rate is high on a particular subcarrier, the transmitter will not modulate data on that subcarrier. Conversely, if a transmitter arrives at a relatively low error rate for a particular subcarrier, the transmitter will modulate that subcarrier with more user data.

Once the channel condition is known in the uplink and estimates for the downlink are made (step 110), the transmitter can set the appropriate set of transmission parameters (e.g., antenna selection, antenna power, bandwidth selection, carrier power, carrier coding, carrier modulation, etc.). Is determined (step 112), the appropriate transmission parameters are adjusted (step 114) and, accordingly, modulated to the corresponding subcarrier using water filling, power control or similar techniques (step 116). It should be noted that the adjustment of the transmission parameters may be performed at the MAC layer, may be performed at the physical layer, or may be performed at a combination of the two layers. The formatted data packet is transmitted to the receiver on the selected portion of bandwidth (step 118). Optionally, the transmitter can track channel performance estimates based on current and previous CSR measurements (step 112a) to predict future channel conditions and use them to optimize channel performance in future data transmissions. It is possible.

It is to be understood that the overall channel performance of the communication link remains relatively fixed, although certain subcarrier and / or antenna pairs may change very rapidly. This is especially true if the communication link has sufficient bandwidth and spatial diversity. Thus, by leaving only the encoding parameters adjustable and fixing the data packet transmission size, it can be performed in near real time based on the received CSR. The complexity of the MAC layer can be greatly simplified when transmitting data packets with a fixed size. However, the complexity required at the physical layer becomes even greater, especially when the configuration for determining and implementing the final encoding scheme is done at the physical layer.

The transmitter generates a transmission format control (TFC) signal and optionally transmits it to the receiver before, after or simultaneously with transmitting the formatted data packet (step 118) (step 120). This TFC signal contains information related to the transmission parameter settings and specifies which subcarriers have been modulated in which modulation schemes (eg, QPSK, 16QAM, 256QAM, etc.) and / or which coding scheme and data rate has been used. Providing this kind of information to the receiver as part of the TFC signal simplifies the overall decoding complexity of the receiver. Alternatively, if the TFC signal is not generated or is not successfully received by the receiver, the receiver determines the TFC information through a trial and error method, hereinafter referred to as "blind TFC detection". do.

To further improve overall system performance, the transmitter and / or receiver monitor the CSR signal emitted by other receivers in the system, evaluate the communication link between itself and the receiver emitting the CSR, and then The history may be maintained and used for future communication with the other receiver.

2, there is shown a MIMO OFDM transmitter 202 and a receiver 204 constructed in accordance with the present invention. The transmitter 202 includes a channel sounding processor for generating a low rate sounding request signal, processing the received channel sounding response signal, and preferably for evaluating the channel state of the communication link between its own transmitter and receiver. 201). In addition, the transmitter 202 may transmit the MAC layer processor 203 for setting data transmission parameters such as data rate, coding scheme, packet format, and the like between subcarriers and transmit antennas 207 according to parameter settings of the MAC layer processor 203. ₁ , 207 ₂ ,... 207 _n ) MAC layer processor (205) according to the transmission parameter settings of the physical (PHY) layer processor 205, or optionally the PHY layer processor 205 for spreading the data bits. 203 and optional transmission format control (TFC) processor 206 for processing information from PHY layer processor 205, optional signal monitoring processor 208 for monitoring CSR signals transmitted between different transceiver pairs. Optional memory 210 for maintaining a history of channel status and determined transmission parameters, and a plurality of transmit and receive antennas 207 ₁ , 207 ₂ ,... 207 _n .

A plurality of transmit / receive antennas 209 ₁ , 209 ₂ ,... 209 _n ), process low rate channel sounding requests, generate channel sounding response (CSR) signals, and preferably other transmitters and / or receivers Included in the receiver 204 is a channel sounding processor 211 that evaluates the channel state of the communication link between and. In addition, the receiver 204 processes the received TFC information, and the optional TFC processor 213 for determining the TFC information through the blind TFC detection method, the data received according to the information provided by the TFC processor 213 Based on a data packet processor 215 for decoding and demodulating packets, an optional signal monitoring processor 217 for monitoring CSR signals transmitted from other receivers, a memory 219 for maintaining channel state history, and a channel state history. And an optional processor 221 for adjusting the transmission parameters.

For brevity and merely illustrative purposes, the transmitter 202 and receiver 204 shown in FIG. 2 will now be described as separate devices operating independently in a MIMO OFDM system. However, as shown in FIG. 3, the transmitter and receiver 202, 204 are preferably configured to coexist as interrelated elements of a single MIMO OFDM network device, such as a base station or WTRU. The MIMO OFDM wireless communication system 300 of FIG. 3 includes a base station 301, a WTRU 302, and a wireless network controller (RNC) 250 controlling the base station 301, which communicate over an air interface. As shown in the figure, both the base station 301 and the WTRU include a transmitter 202-receiver 204 pair configured according to the present invention.

2, at the transmitter 202, a low rate channel sounding request signal is generated at the channel sounding processor 201 prior to processing the transmission data stream Tx. This channel sounding request signal is then transmitted to the transmit antennas 207 ₁ , 207 ₂ ,... 207 _n and transmitted to the receiver 204 via the air interface. Upon receiving the low rate channel sounding request, the receiver 204 processes the channel sounding request to generate a channel sounding response (CSR) in the channel sounding processor 211. As mentioned above, the CSR is preferably a short burst formatted to ensure reception at the transmitter 202 and includes information known to the transmitter 202, which is used to evaluate the current channel condition. Once generated, the CSR is sent to the antennas 209 ₁ , 209 ₂ ,... 209 _n of the receiver, and sent to the transmitter 202.

The CSR is then received at the transmitter 202 and processed at the transmitter's channel sounding processor 201. Channel sounding processor 201 analyzes the information transmitted as part of the CSR, uses this information to measure the characteristics of the current channel state in the uplink, and estimates the downlink channel response. This channel characteristic measurement information is then transmitted to the MAC layer processor 203 and / or PHY layer processor 205, where the channel characteristic measurement information is assigned to subchannel assignment, transmit antenna assignment, subcarrier transmit power, transmit antenna power, It is used to set data transmission parameters including subcarrier coding, bandwidth selection, and the like. Optionally, in connection with selecting the desired bandwidth portion at the time of transmission, the transmitter 202 may include a separate processor (not shown) configured to operate as a bandwidth selection unit. The PHY layer processor 205 then formats the transmitted data packet using channel capacity optimization techniques such as water filling, channel reliability optimization techniques or any other channel performance optimization technique in accordance with the transmission parameter settings, and the user data. Is modulated onto various subcarriers (not shown), and then the modulated subcarriers are mapped to the transmit / receive antennas 207 ₁ , 207 ₂ , ... 207 _n . The formatted data packet is forwarded to the transmit / receive antennas 207 ₁ , 207 ₂ ,... 207 _n and sent to the receiver 204 using the desired bandwidth portion. Optionally, the transmitter 202 maintains a channel state estimate history for use in optimizing and transmitting future data packets.

Before, after, or at the same time as the transmission of the formatted data packet, the optional TFC processor 206 generates a TFC signal via a transmit / receive antenna 207 ₁ , 207 ₂ , ... 207 _n and over the air interface. To send. This TFC signal indicates the transmission parameter setting of the data packet transmitted to the receiver 204, at the same time the position (i.e., which subcarrier the data carrier is being transmitted on), the coding scheme applied to the transmission data packet, and It includes information identifying the modulation scheme (eg, QPSK, 16 QAM, etc.).

When the TFC signal has been sent, the receiver 204 receives the TFC signal and processes it in the optional TFC processor 213. The TFC processor 213 extracts the format and modulation information from the TFC signal and sends it to the data packet processor 215 for use in decoding and demodulation. In addition, if the TFC signal was not successfully detected at the receiver 204, the TFC processor 213 collects available TFC information using a process of blind RFC detection.

To further improve system capacity and efficiency, the transmitter 202 and receiver 204 monitor their CSR collected from other receivers (not shown) using their respective signal monitoring processors 208 and 217. After that, the channel state with the other receiver may be evaluated and estimated. Each channel sounding processor 201, 211 at its transmitter 202 and receiver 204 may be configured to perform this channel estimation and estimation. In the alternative, the transmitter 202 and the receiver 204 are each configured to function as signal analyzers for evaluating uplink channel conditions and additional processors configured to function as estimators for estimating downlink channel conditions based on the channel estimates. (Not shown) may be included. This channel state information is used by both the transmitter 202 and the receiver 204 so that the channel state history is maintained for use in determining transmission parameters in future communication with the receiver. This channel state history can be stored in each memory element 210, 219.

According to the present invention, the transmitter 202 is configured to transmit data set by the PHY layer processor 205 and / or MAC layer processor 203 to continuously transmit data even in a time period in which a future CSR indicates a channel state change. This transmission parameter setpoint can be reused, preferably stored in an optional memory element 210. Alternatively, the transmitter 202 predicts when a change in channel state occurs, and accordingly transmits using historical results from a previously received CSR stored in an optional memory element 210 or an auxiliary memory element (not shown). You can adjust the parameters. Similarly, receiver 204 may maintain a channel state history of its optional memory element 219 for use in adjusting transmission parameters via its optional adjustment processor 221.

Although not specifically mentioned, the frequency at which the transmitter requires channel sounding information from the receiver depends on a variety of factors. Examples of such factors include, but are not limited to, system configuration, the number of subcarriers, the number of spatial channels, the state variation nature of the communication link, the communication environment, and the like. In a general sense, the transmitter must request the CSR very frequently to maintain accurate knowledge of the channel. As an example, the transmitter can begin by requesting a CSR at predetermined time intervals. As the transmitter begins to accumulate CSR data, the transmitter can use this data to estimate the channel state change rate and correspondingly request the CSR according to the change frequency.

The present invention can be implemented in any type of wireless communication system as desired. For example, the present invention can be implemented in an 802 type system, UMTS-FDD, UMTS-TDD, TDSCDMA, CDMA 2000, OFDM-MIMO or other type of wireless communication system. The invention can also be implemented in the form of integrated circuits such as ASICs, multiple integrated circuits, logical programmable gate arrays (LPGAs), multiple LPGAs, discrete components or combinations of integrated circuits, LPGAs, discrete components, and the like.

Although the present invention has been described with reference to various embodiments, those skilled in the art will recognize that other variations are possible within the scope of the invention as outlined in the claims of the invention. In addition, although the features and elements of the present invention have been described in various embodiments in particular combinations, they may be used with or without other features and elements of the present invention (without other features and elements of the preferred embodiments).

As described above, according to the present invention, by efficiently estimating the current channel state, the overall system performance can be improved in the OFDM-MIMO system.

1 is a flow diagram illustrating a channel sounding scheme for improving system performance in a multiple input / output (MIMO) orthogonal frequency division multiplexing (OFDM) communication system.

2 illustrates a MIMO OFDM transmitter-receiver pair configured to improve system performance using channel sounding pulses.

3 illustrates a MIMO OFDM wireless communication system in which each of a base station and a wireless transmit / receive unit (WTRU) comprise a transmitter-receiver pair in accordance with the present invention.

<Explanation of symbols for the main parts of the drawings>

201: sender channel sounding processor

202 transmitter

203: MAC layer processor

204: receiver

205: PHY layer processor

206: transmitting side TFC processor

208: sender signal monitoring processor

210: sender memory

211: receiving channel sounding memory

213: Receive Side TFC Processor

215: data packet processor

217: Receive side signal monitoring processor

219: receiving channel sounding processor

250: radio network controller (RNC)

301: base station

302: wireless transmit / receive unit (WTRU)

Claims (12)

An integrated circuit for use in a multiple input / output (MIMO) orthogonal frequency division multiplexing (OFDM) wireless communication system, (a) a channel sounding processor that processes a received low rate signal to produce a channel sounding response (CSR) signal, wherein the CSR signal has a predefined transmission format and is a short burst that carries predetermined information In channel sounding processor, (b) a plurality of transmit and receive antennas for receiving the low rate signal and transmitting the response CSR signal; (c) an integrated circuit for a MIMO OFDM wireless communication system comprising a data packet processor for processing subcarriers encoded with user data. A transmitter for use in a multiple input / output (MIMO) orthogonal frequency division multiplexing (OFDM) wireless communication system, A signal monitoring processor coupled to a plurality of transmit / receive antennas via a MIMO antenna interface and configured to monitor channel sounding responses transmitted in the MIMO OFDM communication system; Coupled to the signal monitoring processor and the MIMO antenna interface, generate a low rate signal, analyze a channel sounding response, determine an uplink channel state based on the channel sounding response analysis, and determine the determined uplink A channel sounding processor that estimates the downlink channel state based on the channel state; A memory element coupled to the channel sounding processor and configured to store the received channel sounding response, the determined uplink channel state information, and the estimated downlink channel state information; A MAC layer coupled to the memory element and an input for receiving user data and configured to determine and adjust transmission parameter settings based on an estimated downlink channel condition provided by the memory element for use in transmitting the user data Processor, A PHY layer processor coupled to the MAC layer processor, the memory element, and the MIMO antenna interface, and configured to modulate the user data into a subcarrier according to the determined set value received from the MAC layer processor; A TFC processor coupled to the MAC layer processor, the PHY layer processor and the MIMO antenna interface, the TFC processor configured to generate a transport format control (TFC) signal including determined transmission parameter settings provided by the MAC layer processor and the PHY layer processor Wow, A plurality of transmit / receive antennas coupled to the transmitter via the MIMO antenna interface and configured to receive a channel sounding response and to transmit a modulated subcarrier provided by the PHY layer processor and a TFC signal provided by the TFC processor. Transmitter for OFDM wireless communication system. 3. The transmitter of claim 2 further comprising an estimator coupled to the channel sounding processor and configured to estimate a downlink channel state based on the determined uplink channel state. 4. The system of claim 3 further comprising a bandwidth selection processor coupled to the estimator and the PHY layer processor and configured to select a portion of the bandwidth to transmit data based on the estimated downlink channel conditions. Transmitter. 5. The method of claim 4, coupled to the MAC layer processor and the memory element to adjust transmission parameters based on the stored estimated downlink channel state information to communicate with receivers and other transmitters using coordinated transmission parameters. A transmitter for a MIMO OFDM wireless communication system further comprising a processor for adjustment.  6. The transmitter of claim 5 wherein the determined transmission parameter setting stored in the memory element is used to transmit subsequent user data. 7. The transmitter of claim 6 wherein the transmitter is a wireless transmit / receive unit (WTRU). 7. The transmitter of claim 6 wherein the transmitter is a base station. A receiver for use in a multiple input / output (MIMO) orthogonal frequency division multiplexing (OFDM) wireless communication system, A signal monitoring processor coupled to the plurality of transmit and receive antennas via a MIMO antenna interface, the signal monitoring processor being configured to monitor channel sounding responses transmitted from other receivers in the MIMO OFDM communication system; Is coupled to the signal monitoring processor and the MIMO antenna interface, processes the received low rate signal, and response channel sounding response—the channel sounding response is a short burst, with each burst having a predefined transmission format and A channel sounding processor for generating information, determining an uplink channel state, and estimating a downlink channel state based on the determined uplink channel state; A memory element coupled to the channel sounding processor and configured to store a received low rate signal, a monitored channel sounding response, determined uplink channel state information, and estimated downlink channel state information; A TFC processor coupled to the memory element and the MIMO antenna interface and configured to process a received TFC signal, the TFC signal comprising subcarrier modulation information and including transmission parameter settings of a received data packet; A data packet processor coupled to the MIMO antenna interface and the TFC processor and configured to decode and demodulate user data encoded subcarriers received through the plurality of antennas based on information provided by the TFC processor; A coordination processor coupled to the memory element and the MIMO antenna interface, for determining and adjusting transmission parameters based on stored channel state information; A plurality of transmit / receive antennas coupled to the receiver via the MIMO antenna interface, the transmit / receive antennas configured to receive low rate signals and monitored channel sounding responses and to transmit the generated channel sounding responses. receiving set. 10. The receiver of claim 9 further comprising an estimator coupled to the channel sounding processor and configured to estimate a channel condition based on the monitored channel sounding response. 11. The receiver of claim 10 wherein the receiver is a WTRU. 11. The receiver of claim 10 wherein the receiver is a base station.