JP2003516091A - Estimation of relative speed using TPC command - Google Patents

Abstract

(57) Abstract: Rayleigh fading of a wireless channel in a system having a transmitter and a receiver communicating over a wireless channel, wherein the signal transmission power of the transmitter is adjusted to compensate for fading dips in the channel The rate and the relative speed between the transmitter and the receiver are estimated by efficiently monitoring the adjustment or variation of the transmitter signal transmission power or amplitude. According to an exemplary embodiment of the present invention, this is a TPC (Transmission Power Control) command that causes the transmitter to adjust its signal transmission power to deal with Rayleigh fading in the wireless channel, ie, a fading dip. It is performed by monitoring. Since the TPC command causes the transmitter to adjust its signal transmission power to compensate for the fading dip, the fading dip, and thus the fading rate and the relative speed between the transmitter and the receiver, are determined by the TPC command. It can be determined by monitoring the variation of the signal transmission power represented.

Description

Detailed Description of the Invention

[0001] Technical Field of the Invention The present invention relates to wireless communications, and more particularly to estimate the speed of the mobile station relative to the transmitter in a mobile communication system.

[0002] In the prior art mobile communication system, in order to enhance the ability of a receiver to receive signals by radio channel, be or model to accurately estimate the radio channel often necessary.

FIG. 1 shows a typical radio channel known in the art. In particular, transmitter 102 transmits a signal over radio channel 104, which is subject to AWGN (additive white Gaussian noise), as represented by element 106. The signal is then received by receiver 108.

Wireless channels are often subject to multipath propagation, which involves reflection paths from large objects whose path between the transmitter and receiver is large, resulting in a series of reflections from the transmitter. It occurs when the transmitted signal travels through different paths of different lengths before it reaches the receiver. Thus, when a series of signals gather, there is a phase difference between them due to the different path lengths. This can increase Rayleigh fading, where portions of the transmitted signal and their reflected waves combine to increase or decrease depending on their phase. In this way, the combined signal received at the receiver appears to vary randomly in amplitude and phase, as it consists of many small reflected waves of the transmitted signal that travel on different paths to the receiver. Therefore, even when the transmitter outputs a transmission signal with constant power or amplitude, the amplitude or power of the transmission signal at the receiver can change due to Rayleigh fading.

The combined signal received by the receiver is generally modeled or represented by the following equation as having a Rayleigh probability distribution.

[0006]

[Equation 1]

In other words, the Rayleigh distribution has an obstruction in the linear path between the receiver and the transmitter, so that the signal transmitted from the transmitter is reflected by different paths to the receiver. Of the signal components in the Rayleigh fading channel within the envelope of the RMS value of the signal transmitted from the transmitter to the receiver when it arrives at the receiver in a multipath format, with different parts or components of the signal Represents the distribution. The Rayleigh distribution represents an envelope because the in-phase and quadrature components of the signal are essentially Gaussian, due to the large number of out-of-phase multipath components or parts. Therefore, the signal envelope, which is the square root of the sum of the squares of the in-phase and quadrature components, follows the Rayleigh distribution.

Whether the portions of the transmitted signal from the transmitter are combined to increase / decrease at the receiver depends on the particular location of the obstructing / reflecting object at the receiver, transmitter and its surroundings. Depends on. Thus, if the receiver changes position with respect to the transmitter and its surroundings, the signal will move between differently combined positions. In other words, as the receiver moves, the signals are combined in an alternating fashion such that they increase at the receiver and then decrease, resulting in a periodic decrease in the amplitude of the received signal, Then go back to the previous level in a series of "fading dips (fa
ding dip) ”. The period of these fading dips, or in other words the number of fading dips per unit time, is commonly referred to as the "fading rate" of the radio channel.

The fading rate corresponds to the speed of the receiver relative to the transmitter, so that as the speed of the receiver increases, the fading rate also increases. Thus, the fading rate is equivalent to the "Doppler spread" of the Rayleigh fading radio channel given by:

[0010]

[Equation 2]

Where F _d = Doppler spread, V = speed of receiver with respect to transmitter, F _c = frequency of transmitted signal from transmitter, c = speed of light (3 × 10 ⁸ m / sec), is there.

For example, if the receiver speed is 50 km / h and the transmitted signal frequency is 2 GHz, the Doppler spread is about 185 Hz. Therefore, the fading rate is 18
5 Hz, which means that the amplitude of the transmitted signal at the receiver periodically drops or decreases 185 times per second and then recovers. Conversely, if the frequency of the transmitted signal and the fading rate are known, this equation can be used to determine the relative velocity of the receiver.

The relative velocity between the receiver and the transmitter is proportional to the bandwidth of the Rayleigh distribution, which is related to the characteristic value of the wireless channel, such as the statistical characteristic value of the second moment of the wireless channel. The exchange or communication between transmitter and receiver can be improved considerably if the characteristic values of the radio channel are known. In other words, the relative speed between the transmitter and the receiver determines or influences the characteristics of the radio channel that are effective in enhancing the communication between the transmitter and the receiver. As a result, it is important to accurately determine the relative speed between the receiver and transmitter, for example between mobile stations (MS) and base stations (BS) in a mobile communication network. The relative speed between receiver and transmitter is usually estimated by examining the fading characteristics of the radio channel as seen by the receiver, for example by the Doppler spread equation given above.

Due to the high chip rates in mobile communication systems that use CDMA (Code Division Multiple Access), the receivers of such systems typically use to reduce or counter the effects of fading dips in the radio channel. Has power control. The control of the power of the signal broadcast by the transmitter is generally based on the SIR (Signal to Interference Ratio) estimation of the receiver. SIR
Is generally estimated using pilot techniques, such as pilot signals or channels, data, or a combination of pilot techniques and data. The receiver notifies or directs the transmitter using an estimate of the SIR to reduce or increase the power with which the transmitter broadcasts a signal to the receiver. In essence, the transmitter modifies the power to broadcast the signal to compensate for Rayleigh fading. Thus, the power or amplitude of the broadcast signal at the transmitter is modified so that the power or amplitude of the broadcast signal from the transmitter at the receiver is effectively constant, which results in a constant SIR at the receiver. Keep on.

FIG. 2 shows an exemplary procedure known in the art, where the SIR is estimated using data and / or pilot techniques, as shown at step 202. When control proceeds from step 202 to step 204, the SIR is compared against the reference value. When control proceeds from step 204 to step 206, the TPC command is sent based on the comparison in step 204 to inform the transmitter how much power or amplitude of the signal the transmitter is transmitting to the receiver. Is formed and transmitted to the transmitter.

Communication between the receiver and transmitter (eg, mobile station and base station) regarding the power of the signal transmitted from the transmitter is typically performed using TPC commands.

FIG. 3 shows a typical configuration of data transmitted in the downlink from the network to the mobile station in a W-CDMA (Wideband Code Division Multiple Access) system. Specifically, superframe 302 includes 72 frames, such as frame 304. Each frame contains 15 slots, such as slot 306.
Each slot contains symbols including pilot symbols and TPC symbols. The number of symbols of each type and the total number of symbols in the slot are calculated by CDMA.
It is determined by the diffusion coefficient used for diffusion. For example, as shown in slot 306, each slot may include a total of 20 symbols including four pilot symbols 308 and one TPC symbol 310.

The transmit power control rate applied to the transmitter limits the maximum rate of fading that the transmitter can effectively compensate. For example, in W-CDMA (wideband code division multiple access) with a power control rate of 1500 Hz, fading dips can be effectively addressed using TPC commands when the mobile station moves at a speed of less than 30 km / h. . Power control typically works best against fading when the relative speed is low relative to the power control rate. It determines how quickly the power control rate allows the transmitter to react and change its broadcast output power to handle fading dips at the receiver, and between the receiver and transmitter. This is because the relative speed of s determines the frequency of fading dips at the receiver. As the relative speed increases and thus the fading rate increases, the power control to effectively deal with fading.
The rate also needs to be raised. In other words, the high fading rate due to the high relative speed of the receiver can theoretically be effectively dealt with using the TPC command if the power control rate is increased appropriately.

However, the relative speed between the receiver and transmitter is usually estimated by examining the fading characteristics of the radio channel as seen by the receiver. Therefore, TP
When the C command is effectively used to address Rayleigh fading as seen by the receiver, this technique of estimating relative speed is inaccurate because compensation eliminates the fading as seen by the receiver. In other words, the speed estimation inaccuracy increases with the effectiveness of the power control. When the speed is low relative to the power control rate, the power control will effectively eliminate fading, so the speed estimate will be inaccurate.

Therefore, there is a need to accurately estimate the relative speed between transmitters and receivers such as mobile stations and base stations while reducing or eliminating fading.

SUMMARY OF THE INVENTION In accordance with a representative embodiment of the present invention, a system having a transmitter and a receiver communicating over a wireless channel and compensating for fading at the receiver comprises Rayleigh fading or Doppler spread and relative velocity between transmitter and receiver effectively monitor variations in signal power or amplitude at the transmitter instead of variations in power or quality of the signal received at the receiver. It is estimated by This is the TPC command or TPC sent by the receiver to cause the transmitter to adjust the signal transmit power so that the signal has a valid constant power level or signal quality when received at the receiver. This is done by monitoring the change in signal broadcast power represented by the command.

The patterns of TPC commands (or the changes in the power they represent) correspond to fading dips in the channel, so the time to find out how many fading dips are occurring during that time. TP over the interval
C commands can be monitored. As a result, the TPC command, or the change in the signal broadcast power represented by the TPC command, is related to the fading rate and the relative speed between the receiver and transmitter using the Doppler spreading technique described above for that fading rate. It can also be used to accurately estimate and.

Other objects and advantages of the present invention will become apparent to those skilled in the art by reading the following description of the preferred embodiments with reference to the accompanying drawings. Similar elements are designated with the same reference numbers in the figures.

Description of the Preferred Embodiments In accordance with an exemplary embodiment of the present invention, a transmitter and receiver communicating over a wireless channel, the signal transmission power or amplitude emanating from the transmitter being the fading dip in the channel. In a system that is tuned to compensate for, the Rayleigh fading rate of the radio channel and the relative speed between the transmitter and receiver effectively adjust or vary the transmitter signal transmission power or amplitude. Estimated by monitoring.

The receiver controls and adjusts the transmit power of the transmitter to compensate for Rayleigh fading, a fading dip in the radio channel, which results in a constant signal power or quality being provided to the receiver. It For example, the receiver may allow the transmitter to adjust the signal transmission power to handle fading dips,
TPC (Transmit Power Control) commands can be sent to the transmitter. Fading rate (fading dips per unit time) because the fluctuations in the transmission power correspond to and represent fading dips in the channel
Or, Doppler spread can be determined by monitoring TPC commands.
In other words, fading rate or Doppler spread can be used to accurately estimate the relative speed between the receiver and transmitter using the Doppler spread technique described above for fading rate.

FIG. 4 shows an example of a series of TPC commands and corresponding signal transmission powers, which represents a fading dip. The X-axis is the time axis for binary TPC commands (“u” = up, “d” = down) that increase or decrease the signal transmission power of the transmitter. The signal transmission power is represented on the Y axis. In this example,
A slot structure as shown in FIG. 3 is used and each slot that the receiver sends to the transmitter contains a TPC command. The frequency of the TPC command can be 1500 Hz in a WCDMA system, for example. Typical signal power increments and frequencies for other typical TPC commands are well known in the art and will not be described in further detail here.

As can be seen from time interval A, the TPC command instructs the transmitter to effectively maintain a steady state of signal transmission power. In time interval B, the overall result is an increase in signal transmission power, and in time interval C, the TPC command issued from the receiver to the transmitter reduces the signal transmission power of the transmitter to a steady state level.
In the time period D, the TPC command instructs to efficiently maintain the stable state of the signal transmission power. Thus, FIG. 4 shows the fading dips of the signal occurring in the channel during the time intervals over time intervals B and C.

Slight noise or fluctuations in the rate of change of signal power during the fall are also seen in the middle part in time interval B, here before the next TPC command continues to increase the signal transmit power. One of the TPC commands is temporarily reducing the signal transmission power. In addition, it may be necessary to represent different rate changes in signal power using a mixture of "up" and "down" binary TPC commands. For example, up-up-up-down-up-up-
The up-down TPC sequence represents higher rate changes than the up-up-down-up-up-down series. Those skilled in the art will appreciate that fading noise can be accommodated by changing the signal transmission power over time, even if there are variations in the signal transmission power caused by factors other than noise and fading dips
It will be appreciated that known signal processing techniques can be readily used to accurately identify dips.

FIG. 5 illustrates a method of using TPC commands to estimate the relative speed between a receiver and a transmitter, according to an exemplary embodiment of the invention. Step 502
First, the TPC commands are monitored, as indicated by. Control passes from step 502 to step 504 to identify, based on the monitored TPC commands, some signal transmission power level variations corresponding to fading dips in the wireless channel between the transmitter and receiver. . The time frame in which the identified variation occurs is also identified to determine the rate or frequency of the identified variation. This rate is the estimated fading rate or Doppler spread.

Control proceeds from step 504 to step 506, and the estimated fading
Based on the rate or Doppler spread, the speed of the receiver with respect to the transmitter is estimated. In particular, this rate can be estimated by substituting the estimated fading rate and the known carrier frequency of the signal transmitted by the transmitter into the Doppler spread equation described above.

Control passes from step 506 to step 508, where the estimated relative velocity of the receiver to the transmitter is used to estimate or characterize the characteristic value of the wireless channel. Control proceeds from step 508 to step 510, where the characteristic value of the wireless channel is used to maintain or improve the quality of communication between the receiver and transmitter over the wireless channel. From step 510, control proceeds to step 502,
The processing cycle is repeated.

According to an exemplary embodiment of the invention, monitoring and analysis of TPC commands for determining fading rate and relative speed between mobile station and base station may be performed within the mobile station. According to another exemplary embodiment of the present invention, monitoring and analysis of TPC commands to determine fading rate and relative speed between mobile station and base station may be performed within the receiver. Alternatively, the analysis and measurements may be performed within the communication system or at any suitable location or locations associated with the system.

Those skilled in the art will appreciate that the communication between the mobile station and the base station is usually bi-directional, so that the mobile station can act both as a transmitter and as a receiver, and the base station also acts as a transmitter. It will be appreciated that it can work both as a receiver. Therefore, the principles described herein may be applied in various ways iteratively to both mobile stations and base stations, as well as other transceivers.

Those skilled in the art will appreciate that TPCs with varying magnitudes of available power increments, including for example zero.
It will be appreciated that the present invention is also applicable to systems having different or widely available sets of TPC commands, including commands.

Another mechanism that represents fluctuations in signal transmission power at a transmitter corresponding to fading dip is also a fading dip or fading of a radio channel.
It can be used or monitored to determine the rate and the relative speed between the receiver and transmitter.

Those skilled in the art can implement the present invention in other specific forms without departing from the spirit or essential characteristics of the present invention, and the present invention is not limited to the specific exemplary embodiments described herein. You will also understand that. The exemplary embodiments described herein are illustrative in all senses and not limiting. It is to be understood that the scope of the invention is determined by the appended claims rather than the above description, and that variations and equivalents that are intended to be included within the scope are encompassed by the invention.

[Brief description of drawings]

[Figure 1]   It is a figure which shows the wireless communication in a prior art.

[Fig. 2]   It is a figure which shows the typical transmission power control procedure by a prior art.

FIG. 3 is a diagram showing a typical structure of data transmitted by downlink from a network to a mobile station in a W-CDMA (Wireless Code Division Multiple Access) system.

FIG. 4 is a diagram showing an example of a series of TPC commands corresponding to fading dip.

[Figure 5]   FIG. 6 is a diagram showing a process according to an exemplary embodiment of the present invention.

[Procedure for Amendment] Submission for translation of Article 34 Amendment of Patent Cooperation Treaty

[Submission date] December 27, 2001 (2001.12.27)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 10

[Correction method] Change

[Contents of correction]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0002

[Correction method] Change

[Contents of correction]

Prior Art PC, which was internationally published on March 11, 1999 as WO 99/12275.
T international application PCT / US98 / 17911 describes an adaptive power control method in a wireless communication system. Communication within this system is
It is performed using both the pilot channel configuration and the traffic channel configuration. Specifically, the base station uses traffic and pilot channels for both forward and reverse transmissions. The transmission of traffic and pilot channels from the base station occurs as follows: the remote unit uses the traffic channel during the time interval during which it actively communicates with the base station, and the remote unit Actively monitoring the pilot channel for use in coherent demodulation of the channel's data. In addition, the base station actively monitors the speed of the remote unit. The base station determines an appropriate transmission power based on the system state, and optimally adjusts the transmission power of the pilot channel based on the system state. In particular, the transmit power of the pilot channel is adjusted independently of the transmit power of the traffic channel and is based on the speed of the remote unit. In mobile communication systems, it is often necessary to accurately estimate or model the radio channel in order to enhance the receiver's ability to receive signals over the radio channel.

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Claims (10)

[Claims] 1. A method for estimating the relative velocity between a transmitter and a receiver in a radio channel with Rayleigh fading, the signal being transmitted to the transmitter to address Rayleigh fading in the radio channel. Monitoring a TPC (transmission power control) command for instructing to change the transmission power; estimating a Rayleigh fading rate of the radio channel based on the monitored TPC command; Estimating the speed of the receiver with respect to the transmitter based on a Rayleigh fading rate. 2. The TPC command is monitored for a time interval, and the step of estimating the Rayleigh fading rate identifies a series of TPC commands corresponding to a fading dip in the channel; and the time interval. Estimating the Rayleigh fading rate based on a number of fading dips represented by the identified series of TPC commands occurring within. The method described in. 3. The method of claim 1, wherein the transmitter is a mobile station in a mobile communication network. 4. The method of claim 1, wherein the transmitter is a base station in a mobile communication network. 5. The method of claim 1, wherein the receiver is a mobile station in a mobile communication network. 6. The method of claim 1, wherein the receiver is a base station in a mobile communication network. 7. Characterizing a characteristic value of the wireless channel based on the estimated relative speed; and between the transmitter and the receiver based on the characterized characteristic value of the wireless channel. The method of claim 1, further comprising improving the quality of wireless communication. 8. The method of claim 1, wherein a plurality of said steps are performed by a receiver. 9. A method of estimating the relative speed between a transmitter and a receiver in a radio channel with Rayleigh fading, the method comprising: monitoring variations in the signal transmission power emitted from the transmitter. Obtaining a variation corresponding to a fading dip in the radio channel, estimating a Rayleigh fading rate of the radio channel based on the obtained fading dip, and the estimated Rayleigh fading rate Estimating the speed of the receiver relative to the front transmitter based on Eq. 10. The variation is monitored indirectly by monitoring a TPC (Transmit Power Control) command that directs the transmitter to change its signal transmit power. The method described in.