KR20080060526A - Method for clock synchronization of wireless home theater system - Google Patents

Abstract

A clock synchronization method of a wireless home theater system is provided to accurately compensate for a clock mismatch between a CP(Control Point) and a WS(Wireless Sink-device) by accurately calculating the clock error even when a communication conditions are poor. A signal transmission delay time(deltat) and a clock error(thetat) of a WS are calculated by a CP in a wireless home theater system for every predetermined period(S408). When predetermined numbers of the delay times and the clock errors are calculated, a clock error compensation value(sigmat) for the WS is calculated by using the delay times and the clock errors(S416). The calculated clock error compensation value is transmitted to the WS. The WS compensates for the clock error between the WS and the CP by using the clock error compensation value, which is transmitted from the CP.

Description

How to Synchronize Clocks in a Wireless Home Theater System {METHOD FOR CLOCK SYNCHRONIZATION OF WIRELESS HOME THEATER SYSTEM}

1 is a diagram illustrating a configuration of a wireless home theater system;

FIG. 2 is a diagram illustrating an embodiment of a data frame type that transmits and receives between a CP and a WS illustrated in FIG. 1;

3 is a diagram illustrating transmission and reception of a REQ frame and an RES frame between a CP and a WS; and

4 is a flowchart illustrating a clock synchronization method of a wireless home theater system according to the present invention.

The present invention relates to a clock synchronization method of a wireless home theater system, and more particularly, to synchronize a clock between a wireless signal source device and a sink device in consideration of degradation of a wireless communication environment occurring in a wireless home theater system. It is about a method.

Due to the development of A / V media and contents that can be found in the home represented by DVD, the speaker family is gradually evolving from stereo to surround and from surround to 5.1 channel, 6.1 channel, and 7.1 channel. Doing.

For 5.1 channels, including Woofers, look at Front Right, Front Left, Center, Woofer, Rear Right, and Rear. Left) is configured to provide maximum sound effect through six speakers.

Therefore, with the gradual evolution of the speaker family, the number of speakers provided in the home is increasing.

In addition, due to the increased bandwidth of the wireless transmission technology leading to Bluetooth, WLAN, and ultra-wideband (UWB) communication, high quality A / V signal wireless transmission is enabled.

Therefore, when wireless transmission is introduced into A / V products, complicated wiring and selection may naturally be solved, and thus the market expectation for wireless A / V products is also considerable. There are also experimental commercial products available from several major audio and speaker manufacturers.

However, the wireless A / V products on the market received considerable attention initially but did not usually lead to mass sales. This is because there is a disadvantage that does not provide the sound quality as expected.

Depending on the frequency of use of wireless A / V products, there is a problem such as noise generated by a cordless phone, a microwave oven, WLAN equipment, and the like, and above all, a delay occurs in A / V signal transmission by adding a wireless transmission process. There is a subtle time difference between the video output and the audio output, or between the wired speaker audio output and the wirelessly connected speaker audio output.

Therefore, there is a need to find a way to provide convenience of wireless connection while providing fidelity high sound quality as a wired connection desired by a user.

Therefore, an object of the present invention is to more precisely synchronize clocks between a wireless signal source device and a sink device in order to provide high fidelity sound quality of a wired connection desired by a user in a wireless home theater system. To provide a clock synchronization method that can be.

In order to achieve the above object, the clock synchronization method according to the present invention transmits a signal to a wireless sink device (WS) at a predetermined period in a control point (CP) in a wireless home theater system. Calculating a delay time δ _t and a clock error θ _t ; For calculating the signal transmission delay time (δ _t) and a clock error (θ _t) with respect to the wireless sink device by the number it puts the control point is set group, the calculated signal transmission delay time (δ _t) and the clock error calculating a clock error correction value (σ _t ) of the wireless sink device using (θ _t ); Transmitting, by the control point, the calculated clock error correction value (σ _t ) to the wireless sink device; And correcting, by the wireless sink device, the clock error with the control point through the clock error correction value σ _t transmitted from the control point.

Here, the calculation of the clock error correction value σ _{t of} the wireless sink device may include a signal transmission delay time δ _t and a clock error (? _T ) for the wireless sink device by a predetermined number W of the control point. when calculating θ _t ), calculating a weight value ω _t for each of the calculated clock errors θ _t through Equation 1 below; Calculating a clock error correction value σ _t of the wireless sink device by applying the calculated weight value ω _t and the clock error θ _t to the following Equation 2: It is characterized by consisting of;

Equation  One

Equation  2

t is a positive constant value starting from 0 representing the sequence number, and A is a positive constant value of any quantity.

The control point calculating the signal transmission delay time δ _t and the clock error θ _t for the wireless sink device may include the signal transmission delay time for the wireless sink device every predetermined period. δ _t ) and time information T _{0 when} a REQ frame is transmitted to the wireless sink device to calculate a clock error θ _t , time information T ₁ when the wireless sink device receives the REQ frame, and Confirming, by the wireless sink device, time information (T ₂ ) of transmitting the RES frame, and time information (T ₃ ) of receiving the RES frame from the wireless sink device; And applying the checked time information (T _{0 ,} T _{1 ,} T _{2 ,} T ₃ ) to the following Equations 3 and 4, and a signal transmission delay time δ _t for the wireless sink device. Computing the clock error (θ _t ), respectively.

Equation  3

Equation  4

In the clock synchronization method according to the present invention, before the control point calculates a signal transmission delay time (δ _t ) and a clock error (θ _t ) for the wireless sink device at predetermined periods, And transmitting the INIT frame to the wireless sink device to initialize the internal clock counter value of the sink device to zero.

The control point transmits the calculated clock error correction value σ _t to the wireless sink device, wherein the control point transmits a signal transmission delay time δ _t and a clock error θ _t for the wireless sink device. ), The calculated clock error correction value (σ _t ) may be included in the REQ frame transmitted to the wireless sink device at predetermined intervals, and then transmitted to the wireless sink device.

Hereinafter, with reference to the accompanying drawings will be described the present invention in more detail. However, in the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, detailed description thereof will be omitted.

1 is a diagram illustrating a configuration of a wireless home theater system, and FIG. 1 illustrates a wireless home theater system having a video display device and a 5.1-channel speaker configuration, and two rear speakers consisting of wireless speakers.

That is, 5.1-channel speaker configuration Front Right (Front Right, FR), Front Left (Front Left, FL), Center Speaker (CS), Woofer (W), Rear Light (Rear Right, RR), And six left rear speakers (RL), and the RR and RL speakers are wireless speakers that receive audio signals through wireless communication.

In the wireless home theater system, one control point (hereinafter, referred to as 'CP') exists. CP is a wireless source device that receives A / V signals and transmits them to a video display device and a speaker connected wirelessly or wired, and performs wired / wireless communication with an external video display device and a speaker. Transmit the V signal.

Thus, the CP is connected to one or more wireless sink devices (hereinafter referred to as WSs), which are wireless video display devices or wireless speakers existing in a wireless home theater system, perform wireless communication with the WS, and transmit audio to the WS side. Or transmits a video signal.

The present invention allows the clock synchronization operation between the CP and the WS to implement the Hi-Fi wireless home theater system.

In order to perform a clock synchronization operation between the CP and the WS, the present invention is first configured to periodically send and receive a specific type of data frame between the CP and the WS, and to perform a clock synchronization operation between the CP and the WS. The data frame has a form as shown in FIG.

FIG. 2 is a diagram illustrating an embodiment of a data frame type that transmits and receives between a CP and a WS illustrated in FIG. 1.

As shown, the data frame transmitted and received for clock synchronization between the CP and WS is composed of a header section and a data section, and the header section includes preamble information, destination information, and source. Header information including information and frame type information. The data section includes three time stamp information sections capable of transmitting time stamp information (Timestamp # 0, Timestamp # 1, and Timestamp # 2), which are time information at which the data frame is transmitted or received.

Here, the preamble information in the header information is bit string data having a length of 16 bits to be distinguished from other types of data.

The destination information means an identification address value of a CP or WS that will receive a data frame, and the source information means an identification address value of a CP or WS that transmits a data frame.

Address Meaning Misc. 0x00 Control Point (CP) 0x01-0x3e Wireless Subsystem (WS) 0x3f Broadcast Address Destination only

[Table 1] is an example in which the field lengths of the destination information and the source information are 6 bits, and each address value represented by the 6-bit bit value is assigned to the CP and the WS.

So, if 0x00 address value is designated as CP address value and 0x3f with 6 bit value is all 1 as broadcast address value, the actual number of addresses assigned to WS is 62 from 0x01 to 0x3e. do. As a result, the number of WSs that the CP can control is limited to 62.

The source information may not use a 0x3f value that is a broadcast address.

Value Frame type 0 INIT One REQ 2 RES To 15 Reserved

Table 2 shows an example of a data frame type represented by each value of frame type information having a 4-bit field length.

Looking at the value '0' of the frame type information means an INIT frame.

The INIT frame is a data frame transmitted by the CP to the WS when the CP is powered on. The WS receiving the INIT frame initializes its clock counter value to zero.

The value '1' of the frame type information means a REQ frame.

The REQ frame is a data frame transmitted by the CP to the WS, and is a data frame used by the CP to calculate a signal transmission delay time and a clock error value with the WS and to correct a clock error occurring in the WS.

The value '2' of the frame type information means the RES frame.

The RES frame is a data frame transmitted by the WS to the CP. The RES frame is a data frame used by the CP together with the REQ frame to calculate a signal transmission delay time to the WS and a clock error value with the WS.

The timestamp information transmitted in the data section of the data frame shown in FIG. 2 is a 32-bit value representing time in seconds.

Time stamp information transmitted in the data section of the data frame will be described with reference to FIG. 3.

3 is a diagram illustrating transmission and reception of a REQ frame and an RES frame between a CP and a WS.

When the CP transmits a REQ frame to the WS, the CP records a timestamp # 0 (T ₀ ) value, which is time information for transmitting the REQ frame, in the data section of the REQ frame and transmits it. Then, the WS receiving the REQ frame from the CP adds and records a time stamp # 1 (T ₁ ) value, which is time information of receiving the REQ frame, to the data section of the received REQ frame.

WS converts the frame type information of the REQ frame received from the CP into RES frame type information to change the received REQ frame into an RES frame, and then is time information for transmitting RES frames in the data section of the RES frame. Add stamp # 2 (T ₂ ) value to record and send RES frame to CP.

The CP receives the RES frame from the WS, checks the value of time stamp # 3 (T ₃ ), which is the time information when the RES frame was received, and in addition, T _O , T ₁ , and T ₂ recorded in the RES frame. Check all the values.

Here, the time stamp # 0 (T ₀ ) value, which is the time information when the CP transmits the REQ frame, and the time stamp # 3 (T ₃ ) value, which is the time information when the RES frame is received, are clock counters provided in the CP at the corresponding time. The counting value of. The value of time stamp # 1 (T ₁ ), which is the time information when the WS receives the REQ frame, and the value of time stamp # 2 (T ₂ ), which is the time information when the RES frame is transmitted, are respectively determined by the clock counters provided in the WS at that time. It means counting value.

Each CP and WS has a clock oscillator for generating a clock of the same frequency and a clock counter for counting clocks generated by the clock oscillator in order to perform synchronization work with each other. The CP controls the operation of the WS based on the value counted by the clock counter so that the WS outputs a signal that is synchronized and transmitted at the time designated by the CP.

However, even if the clock oscillation element included in each CP and WS is a clock oscillation element generating a clock of the same frequency, the clock oscillation element may not operate normally due to the influence of an external environment, and thus may generate clocks at different frequencies. Therefore, the values counted by the clock counters included in each CP and WS have errors with each other, and the CP tries to synchronize the signal output from the WS at a predetermined time point based on the value counted by the clock counter, but the WS has its own. When the time specified by the CP is determined according to the counted clock counter, the CP and the WS are not synchronized in outputting the signal.

Accordingly, in the present invention, the CP transmits a REQ frame to the WS, receives a RES frame from the WS, and checks values of T ₀ , T ₁ , T _2, and T ₃ to correct a clock error with the WS. CP applies the values of T ₀ , T ₁ , T _2, and T ₃ to Equation 1 and Equation 2 below, and transmits a delay time (δ _t ) to the WS and a clock counter counting value to the WS. Is calculated, that is, clock error θ _t .

Where t is a positive constant value starting from 0 representing the sequence number.

4 is a flowchart illustrating a clock synchronization method of a wireless home theater system according to the present invention. Referring to FIG. 4, a clock synchronization method between a CP and a WS in a wireless home theater system will be described in more detail.

When the power is turned on, the CP initializes its clock counter value to 0, and designates the t value as 0 and the clock error correction value σ _t of the WS as 0 (S400).

After performing the initialization process as described above, the CP transmits an INIT frame for initializing the clock counter value of the WS to 0 (S402).

After transmitting the INIT frame to the WS, the CP transmits a REQ frame to the WS to calculate a signal transmission delay time δ _t and a clock error θ _t with the WS (S404). At this time, the CP records time information for transmitting the REQ frame in the first time stamp information (T0) section in the data section of the REQ frame. The CP transmits a REQ frame by recording a clock error correction value σ _{t in} the second timestamp information T1 section in which information is not yet recorded.

The WS receiving the REQ frame from the CP checks the clock error correction value (σ _t ) recorded in the second timestamp information (T1) section of the REQ frame, and checks the second timestamp information (T1) section of the REQ frame. Instead of the clock error correction value? _T recorded by the CP, the time information on which the REQ frame is received is recorded.

The WS performs an operation of correcting a clock error with the CP in addition to its clock counter value through the checked clock error correction value σ _t . In this case, since the clock error correction value σ _t is 0, the WS clock counter value No correction is made.

The WS changes the frame type information in the REQ frame to the RES frame type information, and then records the time information for transmitting the RES frame in the third timestamp information (T2) section and transmits the RES frame to the CP.

The CP receives the RES frame transmitted from the WS (S406), and records the T3 value which is time information when the RES frame is received. The CP checks the time stamp information T ₀ , T ₁ , and T ₂ recorded in the first, second, and third time stamp information intervals of the RES frame. The signal transmission delay time δ _t and the clock error θ _t with the WS are calculated through S (S408).

CP increases the value of t by 1 (S410), and if the value of t is smaller than the preset reference value (W), the clock error correction value (σ _t ) for WS is continuously set to 0 and the above process is performed. Repeatedly performed (S412, S414). The CP then collects the signal transmission delay time (δ _t ) and the clock error (θ _t ) with the WS, calculated from the point t from 0 to the value W-1, and the collected W The clock error correction value σ _t for correcting the clock error of the WS is calculated using the signal transmission delay time δ _t and the clock error θ _t (S416).

In general, the clock error θ _t calculated for each t-th may include an error according to a wireless communication state between the CP and the WS. Therefore, when a situation in which the wireless environment is not good due to a temporary external influence occurs, the clock error θ _t may be calculated as a clock error larger or smaller than the clock error generated between the actual CP and the WS.

As described above, the temporary deterioration of the state of the wireless environment between the CP and the WS does not accurately calculate the clock error generated between the CP and the WS, and also tends to cause a large transmission delay time δ _t between the CP and the WS.

Therefore, in the present invention, considering that the accuracy of the clock error θ _t calculated in CP is inversely proportional to the signal transmission delay time δ _t between CP and WS, the transmission delay time δ between CP and WS for each t-th _t ) is also calculated, and a weight value ω _t is calculated in consideration of the accuracy of each clock error θ _t according to the calculated transmission delay time δ _t .

Equation 3 calculates a weight value ω _t for a clock error for each t-th.

Where A is a positive constant value and the weight value ω _t for each t th clock error is calculated by dividing the case where t is zero and the case where t is greater than zero.

As can be seen from Equation 3, the weight value ω _t for each t-th clock error is inversely proportional to the transmission delay time δ _t . If t is greater than 0, the weight value ω _t for the clock error considering the variation in delay time between t-1 th transmission delay time δ _t-1 and t time delay time δ _t . Calculate

The CP calculates a weight value ω _t for each t-th clock error, and then calculates a clock error correction value σ _t for correcting the clock error of the WS through Equation 4 below.

The clock error correction value σ _t for correcting the clock error of the WS according to the present invention is a weight value ω for each clock error θ _{t for} each of the W clock errors calculated previously as shown in Equation 4. _t ) is given and averaged.

The CP records the clock error correction value (σ _t ) calculated through Equation 4 in the second timestamp information interval in the REQ frame and transmits the same to the WS, and the WS is recorded in the REQ frame transmitted by the CP. The counting value is corrected by adding the clock error correction value? _T to the value counted by the own clock counter.

Through the above operation until the power of the CP is turned off, the WS can reduce the clock error occurring with the CP, thereby minimizing the clock error between the CP and the WS and allowing clock synchronization with each other (S418).

Meanwhile, in the present invention, when the power of the CP is turned on and enters a synchronization period (SYNC PERIOD) with the WS, a REQ frame is transmitted to each WS at a relatively short time interval during the synchronization period. When the synchronization period ends, the REQ frame transmission period is differently set to transmit the REQ frame to each WS at a relatively long time interval.

As such, transmitting a REQ frame to each of the WSs at short time intervals during the synchronization period is intended to more quickly correct a clock error between the initial CP and the WS. The transmission of REQ frames is designed to periodically compensate for clock errors while minimizing the impact on signal traffic between the CP and the WS so that the WS can provide high fidelity sound quality over the wired connection desired by the user.

Although the present invention has been described in detail with reference to exemplary embodiments above, those skilled in the art to which the present invention pertains can make various modifications to the above-described embodiments without departing from the scope of the present invention. I will understand. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims below and equivalents thereof.

The present invention is to solve the problem that the clock synchronization between the CP (Control Point) and WS (Wireless Sink_device) in the wireless home theater system is not synchronized with the video display device or wired speaker and signal output is not synchronized It allows you to periodically calculate and compensate for clock errors that occur between WSs.

According to the present invention, even when environmental degradation occurs in a wireless communication, the clock error generated between the CP and the WS is calculated relatively accurately, thereby allowing the clock error occurring between the CP and the WS to be more accurately corrected.

Therefore, the present invention enables more accurate clock synchronization between the CP and the WS in the wireless home theater system, thereby providing a high fidelity sound quality as the wired connection desired by the user.

Claims (6)

Computing a signal transmission delay time (δ _t ) and a clock error (θ _t ) for a wireless sink device (WS) at a predetermined period of a control point (CP) in a wireless home theater system ; For calculating the signal transmission delay time (δ _t) and a clock error (θ _t) with respect to the wireless sink device by the number it puts the control point is set group, the calculated signal transmission delay time (δ _t) and the clock error calculating a clock error correction value (σ _t ) of the wireless sink device using (θ _t ); Transmitting, by the control point, the calculated clock error correction value (σ _t ) to the wireless sink device; And And correcting, by the wireless sink device, a clock error with the control point through a clock error correction value (σ _t ) transmitted from the control point. According to claim 1, Calculating the clock error correction value (σ _t ) of the wireless sink device, When the signal transmission delay time δ _t and the clock error θ _t for the wireless sink device are calculated by the predetermined number W of the control point, the calculated clock error θ _t is calculated. Calculating a weight value ω _t through Equation 1 below; And Calculating a clock error correction value (σ _t ) of the wireless sink device by applying the calculated weight value (ω _t ) and the clock error (θ _t ) to the following Equation 2 for each clock error; Clock synchronization method of a wireless home theater system, characterized in that consisting of. Equation  One

Equation  2

Where t is a positive constant value starting from 0 representing the sequence number, and A is a positive constant value of any quantity. According to claim 1, The control point calculates a signal transmission delay time δ _t and a clock error θ _t for the wireless sink device, Time information T _{0 at} which the control point transmits a REQ frame to the wireless sink device to calculate a signal transmission delay time δ _t and a clock error θ _t for the wireless sink device at predetermined intervals, the wireless sink device, the time information receiving the REQ frame (T _1), the wireless sink device RES time information by transmitting the frame (T _2), and time information by receiving the RES frame from the wireless sink device ( Identifying T ₃ ); And The signal transmission delay time (δ _t ) and the clock for the wireless sink apparatus are applied to the confirmed time information (T _{0 ,} T _{1 ,} T _{2 ,} T ₃ ) to Equations 3 and 4 below. Computing the error (θ _t ) respectively; Clock synchronization method of a wireless home theater system, characterized in that consisting of. Equation  3

Equation  4

According to claim 1, Before the control point calculates a signal transmission delay time δ _t and a clock error θ _t for the wireless sink device at predetermined periods, And transmitting, by the control point, an INIT frame for initializing the internal clock counter value of the wireless sink device to 0 to the wireless sink device. The method of claim 3, wherein The control point transmits the calculated clock error correction value σ _t to the wireless sink device, The calculated clock error correction in the REQ frame that the control point transmits to the wireless sink every predetermined period to calculate the signal transmission delay time δ _t and clock error θ _t for the wireless sink. value by including the (σ _t) how clock synchronization of wireless home theater system, characterized in that the transmission to the wireless sink device. The method of claim 3, wherein The predetermined period for the control point to transmit a REQ frame to the wireless sink device, Characterized in that the predetermined period for transmitting the REQ frame during the synchronization period (SYNC PERIOD) with the wireless sink device is shorter than the predetermined period for transmitting the REQ frame during the communication period with the wireless sink device. A clock synchronization method of a wireless home theater system.

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