JP2009182650A - Wireless communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless communication apparatus performing handovers to different wireless communication networks without reducing reproduction quality and immediacy. <P>SOLUTION: When a handover is performed from a first wireless communication network 15 to a second wireless communication network 16, the preparation time until the handover, the communication quality after scheduling of handover execution, and respective delay times of the first wireless communication network 15 and second wireless communication network 16 are acquired by a handover control unit 36 in advance, and the reproduction speed of a running application is controlled on the basis of these pieces of acquired information and the amount of data in a jitter buffer 47 at the point of time when the start of the handover preparation is determined. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a radio communication apparatus capable of performing handover between different radio communication networks.

  In recent years, the Internet Engineering Task Force (IETF) has developed an IP mobility technology that enables seamless movement by enabling handover between a plurality of different wireless communication networks such as a mobile phone network and a wireless LAN in order to realize a ubiquitous environment. Is being considered. Specific protocols in this IP mobility technology include Mobile IPv4 and Mobile IPv6 (hereinafter collectively referred to as Mobile IP) that support movement of individual communication terminals, and support movement in units of networks. There is NEMO (Network Mobility).

  By the way, when an application having real-time characteristics such as VoIP (hereinafter, abbreviated as an application as appropriate) is executed via a wireless communication network, the allowable bandwidth of the wireless communication path changes depending on a propagation environment such as fading. Then, the arrival interval of packets received by the communication terminal also changes according to the change in the allowable bandwidth.

  For this reason, generally, a jitter buffer is provided in a communication terminal, and received packets are temporarily stored in the jitter buffer.Then, packets are read out from the jitter buffer at an interval according to the application and played back, thereby causing packet fluctuations. That is, a packet reproduction interval shift due to arrival interval shift (jitter) is absorbed to prevent a decrease in reproduction quality such as reproduction sound quality. Also, if the jitter is large and there are no packets in the jitter buffer and silence occurs, or if a large amount of packets are received in a short time and the packets do not fit in the jitter buffer, the playback speed is increased. It changes, discards received packets, and changes the size of the jitter buffer.

  On the other hand, the downlink absolute delay time of the packet received by the communication terminal, that is, the time (delay time) required until the packet transmitted from the partner communication terminal is received via the wireless communication network depends on the wireless communication network. Different. For this reason, in the case of a wireless communication apparatus in which a communication terminal moves, when handover is performed to a different wireless communication network, for example, if the downlink absolute delay time of the handover destination is longer than the downlink absolute delay time of the handover source, the difference As a result, a packet reception idle time is generated.

  In such a case, for example, when the packet reading interval from the jitter buffer is set to a constant interval according to the application and the packet is reproduced at a constant reproduction speed, the last packet received from the handover source wireless communication network is When the reception idle time is longer than the time required for reading from the jitter buffer (that is, the jitter buffer standard delay time), the packet in the jitter buffer is emptied for the longer time. As a result, since the packet is not played back at least during this time period, the sound becomes silent and the playback quality deteriorates.

  FIG. 14 is a diagram for explaining a control method of the jitter buffer in this case. FIG. 14A shows the number of packets received by the jitter buffer per unit time, and FIG. The packet playback speed (reading interval), FIG. 14C shows the number of packets in the jitter buffer. FIG. 15 shows the packet flow in this case, where “transmission” is the packet transmission timing by the counterpart communication terminal, “reception” is the reception timing of the packet received by the jitter buffer of the wireless communication device, “Reproduction” indicates packet reproduction timing (packet read timing from the jitter buffer) by the wireless communication apparatus. Here, in each of the handover source radio communication network A and the handover destination radio communication network B, it is shown that there is no fluctuation (shift in arrival interval) in the received packet.

  As apparent from FIGS. 14 and 15, the downlink absolute delay time TddnB in the handover destination radio communication network B is longer than the downlink absolute delay time TddnA in the handover source radio communication network A, and (TddnB−TddnA). Is longer than the jitter buffer standard delay time Tn received by the received packet when the standard number of packets is accumulated in the jitter buffer, the time of T = {(TddnB−TddnA) −Tn} is Packets are not played back. In addition, in this case, when a packet is received from the wireless communication network B that is the handover destination, the packet is immediately reproduced, so that jitter cannot be absorbed.

  For example, if the packet reception status is monitored and the packet cannot be received at a normal reception interval, reading of the packet from the jitter buffer, that is, the packet A jitter buffer control method for controlling the reproduction speed has been proposed (see, for example, Patent Document 1).

  FIG. 16 is a diagram for explaining the jitter buffer control method disclosed in Patent Document 1. FIGS. 16A to 16C are similar to FIGS. 14A to 14C, respectively. The number of received packets per unit time, the playback speed, and the number of packets in the jitter buffer are shown. FIG. 17 shows the packet flow in this case.

  In FIG. 16 and FIG. 17, the packet is received at the reception interval until then, as in the case of handover from the wireless communication network A having the downlink absolute delay time TddnA to the wireless communication network B having the downlink absolute delay time TddnB longer than TddnA. If the packet cannot be received, the playback speed of the packets in the jitter buffer is gradually reduced as the reception interval increases, and if the reception interval returns to normal after that, it depends on the number of packets in the jitter buffer. Thus, the playback speed is controlled to gradually increase to the normal playback speed.

JP 2006-238445 A

  However, in the jitter buffer control method disclosed in Patent Document 1, if a packet cannot be received at the previous reception interval, the playback speed of the packets currently accumulated in the jitter buffer is gradually decreased. It just controls it. For this reason, when the downlink absolute delay time TddnB at the handover destination is relatively long, there is a concern that the low speed change of the reproduction speed becomes large and the reproduction quality is deteriorated. Therefore, for example, in VoIP, the playback speed greatly changes from the original voice speed, so that the quality of the playback sound is greatly reduced, making it difficult for the user to hear.

  FIGS. 16 and 17 show examples of control in the case where the packet in the jitter buffer is empty and no silence is generated. However, how much the packet reception interval is actually free. Therefore, depending on the jitter buffer standard delay time Tn and the handover destination downlink absolute delay time TddnB, there is a concern that the packet in the jitter buffer becomes empty and silence may occur. Note that the jitter buffer standard delay time Tn may be increased in order to prevent the occurrence of silence or the like. However, for example, in VoIP, there is a delay in packet reproduction from the partner terminal. Therefore, the real-time property is lacking.

  Further, the jitter buffer control method disclosed in Patent Document 1 does not consider the radio state of the handover destination. For this reason, even if the handover is executed, if the radio state of the handover destination is not good, there is a concern that the packet delay accumulates, the reproduction speed becomes slow after the handover, and the reproduction quality is lowered. .

  Accordingly, an object of the present invention made in view of such a point is to provide a wireless communication apparatus capable of performing handover to a different wireless communication network without deteriorating reproduction quality and real-time property.

The invention of a wireless communication device according to claim 1 that achieves the above object is as follows:
A wireless communication unit that performs wireless communication by connecting to a first wireless communication network and a second wireless communication network different from the first wireless communication network;
A jitter buffer and a jitter buffer monitoring unit that monitors a data amount of the jitter buffer, and an execution unit that executes an application of a real-time communication system via the wireless communication unit;
A communication quality acquisition unit configured to acquire communication quality of a radio link in the first radio communication network and the second radio communication network while executing the application while connected to the first radio communication network;
A determination unit that determines whether to start preparation for handover from the first wireless communication network to the second wireless communication network based on the communication quality acquired by the communication quality acquisition unit;
When the determination unit determines the start of handover preparation during the execution of the application, the handover preparation time is estimated until the handover is started based on the communication quality acquired by the communication quality acquisition unit, and the handover execution schedule is scheduled. An estimation unit for predicting the communication quality of the second wireless communication network later;
When the determination unit determines the start of handover preparation, a measurement unit that measures respective delay times in the first wireless communication network and the second wireless communication network;
The handover preparation time estimated by the estimation unit, the communication quality predicted by the estimation unit for the handover of the second radio communication network, and the first radio communication network and the second radio communication measured by the measurement unit Based on each delay time in the network and the amount of data in the jitter buffer by the jitter buffer monitoring unit at the time when the determination unit determines the start of handover preparation, the playback speed of the application by the execution unit is determined. A control unit to control;
It is characterized by providing.

The invention according to claim 2 is the wireless communication apparatus according to claim 1,
The control unit compares the delay time in the first wireless communication network with the delay time in the second wireless communication network, and the delay time in the second wireless communication network is the delay in the first wireless communication network. When the time is longer than the time by a predetermined time, the playback speed of the application by the execution unit is reduced.

The invention according to claim 3 is the wireless communication apparatus according to claim 2,
The control unit slows down the playback speed of the application by the execution unit after starting preparation for handover.

The invention according to claim 4 is the wireless communication apparatus according to claim 3,
The estimation unit predicts a transition until the throughput of the second wireless communication system reaches a required bandwidth threshold required for execution of the application, as the communication quality after the scheduled execution of the handover of the second wireless communication network,
The control unit, when the estimated throughput by the estimation unit has already reached the required bandwidth threshold at the time of scheduled handover execution, at the start of data reception from the second radio communication network, The playback speed of the application by the execution unit is controlled so that the amount of data becomes 0, and when the predicted throughput by the estimation unit has not reached the required bandwidth threshold at the scheduled handover execution time, the predicted throughput is When the required bandwidth threshold is reached, the playback speed of the application by the execution unit is controlled so that the data amount in the jitter buffer becomes zero.

The invention according to claim 5 is the wireless communication apparatus according to claim 3,
The estimation unit, based on the communication quality acquired at different times by the communication quality acquisition unit after the determination unit has determined the start of handover preparation, the corresponding first wireless communication network and the second wireless communication network When the predicted communication quality of the first wireless communication system exceeds the predicted communication quality of the second wireless communication system after a predetermined time exceeding the handover preparation time, , Notifying the controller of cancellation of the handover preparation,
The control unit, when receiving a notification of cancellation of the handover preparation from the estimation unit, controls to return the reproduction speed of the application by the execution unit to a normal reproduction speed.

  In the present invention, when handing over from the first wireless communication network to the second wireless communication network, the preparation time up to the handover, the respective delay times in the first wireless communication network and the second wireless communication network, and the handover in advance The amount of data in the jitter buffer at the time when the start of preparation is determined and the communication quality of the second wireless communication system that is the handover destination are acquired, and the playback speed of the application is controlled based on the acquired information. Thereby, for example, when the delay time of the second radio communication network of the handover destination is longer than the delay time of the first radio communication network of the handover source and the communication quality of the second radio communication system of the handover destination is not good In consideration of accumulation of delay time of received data after handover, data can be stored in the jitter buffer before handover. Therefore, before and after handover, the playback speed can be slowed down to increase the time that can be taken to absorb the delay time difference, and playback can be performed at a speed close to the standard playback speed, thus reducing the playback quality and real-time performance. Without this, handover from the first wireless communication network to the second wireless communication network becomes possible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of a communication network that can be used by a wireless communication apparatus according to an embodiment of the present invention. In FIG. 1, it is assumed that a wireless communication device 11 that is a mobile node makes a call with a partner communication terminal 12 that is an opposite node using VoIP that is a real-time communication application. The wireless communication device 11 can be handed over between the first wireless communication network 15 and the second wireless communication network 16. The first wireless communication network 15 and the second wireless communication network 16 are coupled to the Internet 18 via a packet network 17.

  Here, the first wireless communication network 15 is composed of, for example, a wireless LAN, and the second wireless communication network 16 is composed of, for example, a cdma2000 EV-DO mobile phone network, and the delay time (downward absolute delay in the first wireless communication network 15). (Time) is shorter than the delay time (downlink absolute delay time) in the second wireless communication network 16. In FIG. 1, reference numeral 15 a indicates an access point of the first wireless communication network 15, and reference numeral 16 a indicates a base station of the second wireless communication network 16.

  For example, the partner communication terminal 12 includes a personal computer to which a handset 12a is connected and a softphone is installed, and is connected to the Internet 18 through an Internet service provider (not shown).

  Further, SIP (Session Initiation Protocol) servers 21 and 22 for controlling communication are connected to the packet network 17 and the Internet 18, respectively. Further, a home agent (HA) 23 is connected to the Internet 18 for transferring a received packet addressed to the wireless communication device 11 to a wireless communication network to which the wireless communication device 11 is connected.

  In the communication network shown in FIG. 1, the home address used in the wireless communication network to which the wireless communication device 11 originally belongs is registered in the HA 23, and the care-of address of the wireless communication network 16 that is the handover destination is set at the time of handover. Registration enables handover between different wireless communication networks. Note that such IP mobility technology is well known in the above-described mobile IP and NEMO, and thus detailed description thereof is omitted here.

  In the present embodiment, it is assumed that the wireless communication network to which the wireless communication device 11 originally belongs is the first wireless communication network 15 and is handed over from the first wireless communication network 15 to the second wireless communication network 16.

  FIG. 2 is a functional block diagram showing a schematic configuration of radio communication apparatus 11 according to the present embodiment shown in FIG. The wireless communication device 11 executes a first wireless I / F (interface) 31 corresponding to the first wireless communication network 15, a second wireless I / F 32 corresponding to the second wireless communication network 16, and a VoIP application. The wireless information of the telephone function unit 33, the communication processing unit 34 that controls connection to the first wireless communication network 15 and the second wireless communication network 16, and the wireless information of the first wireless communication network 15 and the second wireless communication network 16 is acquired. A wireless information acquisition unit 35; and a handover control unit 36 that controls a handover between the first wireless communication network 15 and the second wireless communication network 16.

  The communication processing unit 34 constitutes a wireless communication unit that performs wireless communication. Between the telephone function unit 33 and the counterpart communication terminal 12, the first wireless communication network 15 or the second wireless communication network 16 is used. While making a call, the connection of the first wireless I / F 31 or the second wireless I / F 32 is controlled so as to communicate with the HA 23 under the control of the handover control unit 36.

  The wireless information acquisition unit 35 acquires the communication quality of the corresponding first wireless communication network 15 and second wireless communication network 16 from the first wireless I / F 31 and the second wireless I / F 32 as wireless information, The acquired communication quality is supplied to the handover control unit 36. Here, as the communication quality, for example, an RSSI (Received Signal Strength Indicator) representing a radio state is acquired. Therefore, in the present embodiment, the radio information acquisition unit 35 constitutes a communication quality acquisition unit that acquires the communication quality of the radio link.

  Based on the communication quality from the radio information acquisition unit 35, the handover control unit 36 determines whether to schedule handover, that is, whether to start preparation for handover, and after determining the handover schedule, Handover information including whether or not to cancel the scheduled handover is generated, and handover is controlled based on the handover information.

  FIG. 3 is a functional block diagram showing a schematic configuration of the telephone function unit 33 of the wireless communication apparatus 11 shown in FIG. The telephone function unit 33 is composed of, for example, a soft phone, and has a button input unit 41, a screen display unit 42, a microphone 43, an encoder 44, a packet transmission unit 45, a packet reception unit 46, a jitter buffer, as in the configuration of a known soft phone. 47, a decoder 48, a speaker 49, a jitter buffer monitoring unit 50, a jitter buffer control unit 51, a SIP control unit 52, and an overall control unit 53 for controlling the overall operation.

  The overall control unit 53 acquires user operation information via the button input unit 41 and the screen display unit 42, and controls the overall operation based on the acquired information. The SIP control unit 52 controls SIP procedures for starting and ending a call. During a call, the audio data acquired from the microphone 43 is encoded by the encoder 44, and the encoded data is put into a packet from the packet transmission unit 45 and transmitted to the partner communication terminal 12 via the communication processing unit 34.

  Further, the packet from the partner communication terminal 12 received by the packet receiving unit 46 via the communication processing unit 34 is once fetched into the jitter buffer 47 and then read, and the read packet is decoded by the decoder 48 in the payload portion, Output as reproduced sound from the speaker 49. The reception status of packets in the jitter buffer 47 and the number of packets (data amount) in the jitter buffer 47 are monitored by the jitter buffer monitoring unit 50. Based on the monitoring result, the jitter buffer control unit 51 Controls the reading speed of the packet from the jitter buffer 47 and processing such as discarding the received packet.

  In the present embodiment, the telephone function unit 33 is further provided with a handover information acquisition unit 55 and a playback speed calculation unit 56. The handover information acquisition unit 55 acquires the required bandwidth threshold of the softphone (application) from the overall control unit 53 and supplies it to the handover control unit 36 at the start of the call, and also receives handover information from the handover control unit 36 during the call. When the handover information is acquired at regular intervals and the handover information is acquired, the acquired handover information is supplied to the reproduction speed calculation unit 56.

  Based on the handover information acquired from the handover information acquisition unit 55, the playback speed calculation unit 56 determines the packet reading speed of the jitter buffer 47, that is, the playback speed of the received packet (in this embodiment, the playback speed of the VoIP application). It is determined whether or not to control. As a result, when controlling, the reproduction speed calculation unit 56 calculates the reproduction speed of the received packet based on the acquired required handover information and the monitoring result of the jitter buffer 47 by the jitter buffer monitoring unit 50. The calculation result is supplied to the jitter buffer control unit 51. Thereby, the jitter buffer control unit 51 controls reading of the received packet from the jitter buffer 47 so that the reproduction speed of the received packet becomes the reproduction speed calculated by the reproduction speed calculation unit 56. Therefore, in the present embodiment, the telephone function unit 33 constitutes an execution unit that executes a real-time communication system application and a control unit that controls the playback speed of the application.

  Hereinafter, the operation of radio communication apparatus 11 according to the present embodiment will be described. First, the operation of the handover control unit 36 will be mainly described.

  The handover control unit 36 determines the handover schedule or cancels the determined handover schedule based on the communication qualities acquired from the first radio I / F 31 and the second radio I / F 32, respectively. For example, when a call is made by forming a wireless link with the first wireless communication network 15, the communication quality acquired from the first wireless I / F 31 is equal to or lower than the handover schedule determination threshold, and at that time, the second wireless When the communication quality acquired from the I / F 32 is equal to or higher than the communication quality acquired from the first radio I / F 31, the handover control unit 36 performs a predetermined handover based on the communication quality acquired from the first radio I / F 31. When the preparation time Tb elapses, the handover schedule is determined so that the handover to the second wireless communication network 16 is performed, that is, the start of handover preparation is determined.

  In addition, when the communication quality acquired from the first radio I / F 31 becomes equal to or lower than the handover schedule determination threshold, the communication quality acquired from the second radio I / F 32 reaches the communication quality acquired from the first radio I / F 31. If not, the subsequent communication quality in the first wireless communication network 15 and the second wireless communication network 16 is predicted based on the respective communication qualities, and the predicted communication quality of the second wireless communication network 16 is the first wireless communication network. When a handover preparation time Tb that is equal to or higher than the communication quality of the communication network 15 has elapsed, the start of handover preparation is determined so that the handover to the second wireless communication network 16 is performed. The communication quality of the second wireless communication network 16 that is not used for a call is acquired (measured) by receiving broadcast information transmitted from the base station 16a, for example.

  When the handover control unit 36 determines the handover schedule, the handover preparation time Tb until the start of the handover, the handover destination throughput after the handover preparation time Tb (after the handover execution schedule), the wireless communication network currently used (here, , The handover source downlink absolute delay time Tddn1 in the first radio communication network 15) and the handover destination downlink absolute delay time Tddn2 in the handover destination radio communication network (here, the second radio communication network 16) are obtained, and these information are obtained. The required handover information is supplied to the telephone function unit 33 together with information indicating that there is a handover schedule.

  Next, a method for acquiring the handover preparation time Tb, the handover destination throughput, the handover source downlink absolute delay time Tddn1, and the handover destination downlink absolute delay time Tddn2 by the handover control unit 36 will be described.

(How to obtain handover preparation time Tb)
As described above, the handover preparation time Tb is the time when the communication quality of the handover destination is equal to or higher than the communication quality of the handover source when the communication quality of the handover source becomes equal to or less than the handover schedule determination threshold ((a) first handover) Preparation time acquisition method) and when the communication quality of the handover source does not reach the communication quality of the handover source at the time when the communication quality of the handover source falls below the handover schedule determination threshold ((b) the second handover preparation time The acquisition method differs depending on the acquisition method.

(A) First handover preparation time acquisition method In this case, for example, as shown in FIGS. 4A and 4B, based on the rate of change ΔRs (slope) of the radio state (Rs) that determines the communication quality Thus, the handover preparation time Tb is calculated. Here, the rate of change ΔRs is obtained by measuring as a rate of change of unit time (Δt) when the radio state falls below the handover schedule determination threshold and determining the handover schedule, or when the handover schedule is determined. In addition, in the present embodiment, from the point in time when the handover is scheduled to be determined in the present call, it is possible to measure and acquire using a wireless state a predetermined time before (for example, 2 seconds before). An average rate of change ΔRsrms per unit time until a predetermined time is acquired.

For this reason, the handover control unit 36 calculates the change rate ΔRs (t) of the unit time (Δt) of the radio state in the currently used radio communication network at a predetermined timing according to the following equation (1). A plurality of change rates ΔRs (t) up to the previous time are held in the memory, and when a handover schedule is determined, an average change rate ΔRsrms up to a predetermined time held at that time is calculated. Here, it is assumed that the wireless state is gradually getting worse.
[Equation 1]
ΔRs (t) = | {Rs (t) −Rs (t−Δt)} / Δt | (1)

  Thereafter, the handover control unit 36 determines whether or not the calculated change rate average value ΔRsrms is smaller than a preset change rate threshold value Rsref. As a result, in the case of ΔRsrms ≦ Rsref, that is, when the wireless state changes slowly, as shown in FIG. 4A, the handover preparation time Tb is set to a preset standard time Tref (for example, 5 sec). To do.

  On the other hand, when ΔRsrms> Rsref, that is, when the radio state changes rapidly, for example, Tb = Tref (Rsref / ΔRsrms) is calculated, and the higher the change rate ΔRsrms, the greater the handover preparation time Tb. Is set shorter than the standard time Tref. FIG. 4B shows a case where ΔRsrms> Rsref and the handover preparation time Tb is set to approximately half the standard time Tref (2.5 sec).

(B) Second handover preparation time acquisition method In this case, as shown in FIG. 5, when the communication quality of the handover source falls below the handover schedule determination threshold, the average rate of change ΔRsrms of the handover source is calculated. Then, the subsequent communication quality is predicted, and the change rate average value ΔRsrms is calculated for the handover destination to predict the subsequent communication quality. As a result, the handover preparation time Tb is acquired from the time when the communication quality of the handover source becomes equal to or less than the handover schedule determination threshold to the time when the predicted communication quality of the handover destination becomes equal to or higher than the predicted communication quality of the handover source.

(Handover destination throughput acquisition method)
The handover destination throughput predicts a transition (each predicted throughput and its period) from when the handover is scheduled to be executed until the throughput of the second wireless communication network 16 reaches the required bandwidth threshold of the application acquired from the telephone function unit 33. For this reason, the handover control unit 36 stores in advance a conversion table of communication quality (wireless state) and throughput as shown in FIG. 6, for example. For example, based on the communication quality after the scheduled handover execution predicted from the change rate average value ΔRsrms at the scheduled handover decision time, the handover control unit 36 determines from the conversion table in FIG. The transition until the throughput of 16 reaches the required bandwidth threshold of the application is predicted.

  Here, for example, as shown in FIGS. 4 (a) and 4 (b), when the predicted throughput of the handover destination is equal to or greater than the required bandwidth threshold of the application at the time of scheduled execution of the handover, the predicted throughput and period 0 are set as the telephone number. It supplies to the function part 33. On the other hand, as shown in FIG. 5, when the estimated throughput of the handover destination does not reach the required bandwidth threshold of the app at the scheduled handover execution time, the prediction until the predicted throughput satisfies the required bandwidth threshold of the app .., Tm corresponding to each predicted throughput in the region S indicated by hatching in FIG. 5 and the periods T1, T2,. To supply.

(Acquisition method of absolute delay time Tddn1, Tddn2)
The handover source downlink absolute delay time Tddn1 and the handover destination downlink absolute delay time Tddn2 are acquired by, for example, any one of first to fourth absolute delay time acquisition methods described below. In the present embodiment, since the network between the counterpart communication terminal (CN) 12 and the HA 23 is not switched, the absolute delay time between them is not considered.

(A) First Absolute Delay Time Acquisition Method After the handover schedule is determined in the handover control unit 36, the telephone function unit 33 and / or the communication processing unit 34 are controlled to synchronize the wireless communication device 11 with the HA 23. Is requested to transmit a measurement packet having a transmission time stamp, whereby the HA 23 causes the measurement packet to be transmitted to both the first wireless communication network 15 and the second wireless communication network 16. The wireless communication device 11 receives the measurement packet transmitted from the HA 23 via the corresponding first wireless I / F 31 and second wireless I / F 32, respectively, and based on the reception time and the time stamp of the measurement packet. Then, the downstream absolute delay times Tddn1 and Tddn2 of the corresponding network are measured. When the absolute downlink delay time of the handover source wireless communication network can be measured from the received packet during a call, transmission of the measurement packet to the wireless communication network can be omitted.

(B) Second Absolute Delay Time Acquisition Method Once the handover control unit 36 determines the handover schedule, the telephone function unit 33 and / or the communication processing unit 34 are controlled to synchronize the wireless communication apparatus 11 with the HA 23. As a result, the measurement packet is transmitted from the HA 23 to both the first wireless communication network 15 and the second wireless communication network 16 as in the first absolute delay time acquisition method. Then, the downlink absolute delay times Tddn1 and Tddn2 of the corresponding network are measured.

(C) Third Absolute Delay Time Acquisition Method When the handover control unit 36 determines a handover schedule, the telephone function unit 33 and / or the communication processing unit 34 are controlled so that the wireless communication device 11 and the wireless communication device 11 Sending measurement packets such as PING and RTCP from both the first wireless communication network 15 and the second wireless communication network 16 to the time-synchronized HA 23, receiving the reply, and sending the corresponding network Downlink absolute delay times Tddn1 and Tddn2 are measured.

(D) Fourth Absolute Delay Time Acquisition Method When the handover control unit 36 determines a handover schedule, the absolute delay time of each wireless communication network is acquired using a handover technique studied in IEEE 802.21. The illustration is given below.
A method for obtaining the absolute delay time (Tddn1) of the first wireless communication network 15 will be described below.
The wireless communication device 11 acquires the next value stored in the first information server of the first wireless communication network 15.
From the measurement server that operates to measure the delay time (for example, connected to the backbone network of the Internet 18) to the current access point 15a connected through the first wireless communication network 15 Standard value of one-way delay time (Tn3)
Standard value of the upper and lower delay times between the access point 15a and the terminal connected to the access point 15a (downward: Trdn3, upstream: Trup3)
Further, the wireless communication device 11 transmits a measurement packet such as PING to the HA 23, receives the reply, and measures the round-trip delay time Trt1 between the wireless communication device 11 and the HA 23.
Then, the absolute delay time Tddn1 of the first wireless communication network 15 is calculated from these values according to the following equation (2). However, since the one-way delay time between the access point 15a and the HA 23 cannot be acquired, this one-way delay time is approximated by adding Tn3 and {Trt1- (Tn3 + Trdn3 + Tn3 + Trup3)} / 2. .
[Equation 2]
Tddn1 = Tn3 + Trdn3 + {Trt1- (Tn3 + Trdn3 + Tn3 + Trup3)} / 2 (2)

Next, a method for obtaining the absolute delay time (Tddn2) of the second wireless communication network 16 that is the handover destination will be described below.
The wireless communication device 11 obtains the next value stored in the second information server connected to the second wireless communication network 16 that is the handover destination via the first information server of the first wireless communication network 15. To do. Note that the location information of the wireless communication device 11 acquired by the wireless communication device 11 or the access point 15a is transmitted to the second information server.
Standard value (Tn4) of one-way delay time between the base station 16a expected to be connected to the wireless communication device 11 and the measurement server
Standard value of the upper and lower delay times between the base station 16a and the terminal connected to it (downward: Trdn4, upstream: Trup4)
Then, from these values, the absolute delay time Tddn2 of the second wireless communication network 16 is calculated according to the following equation (3). However, since the one-way delay time between the base station 16a and the HA 23 cannot be acquired, this one-way delay time is approximated by adding Tn4 and {Trt1- (Tn3 + Trdn3 + Tn3 + Trup3)} / 2. .
[Equation 3]
Tddn2 = Tn4 + Trdn4 + {Trt1- (Tn3 + Trdn3 + Tn3 + Trup3)} / 2 (3)

  As described above, the handover control unit 36 acquires the handover preparation time Tb, the handover destination throughput, the handover source downlink absolute delay time Tddn1, and the handover destination downlink absolute delay time Tddn2, and uses the acquired information as the telephone function unit. 33.

  Further, when the handover control unit 36 determines the handover schedule, the handover control unit 36 controls the communication processing unit 34 to connect the second wireless I / F 32 to the second wireless communication network 16. Thereafter, when the handover preparation time Tb elapses, the handover control unit 36 transmits a Registration Request (Binding Update in NEMO) to the HA 23 via the second wireless communication network 16 that is the handover destination, and the handover destination to the HA 23. Register the care of address.

  At that time, the handover control unit 36 sets 8 bits of the Registration Request Field of the Registration Request message in the communication processing unit 34 (in NEMO, multiple care of address is used), and the first radio communication network 15 also uses the second radio. The communication network 16 can also communicate.

  After that, when receiving the Registration Reply (Binding Acknowledge in NEMO), which is the handover completion information returned from the HA 23, the handover control unit 36 cancels the registration of the care-of address of the first wireless communication network 15 that is the handover source, and connects After that, the communication processing unit 34 is controlled to continue the VoIP application via the second wireless communication network 16 that is the handover destination, and the received handover completion information is supplied to the telephone function unit 33.

  Further, when the handover control unit 36 determines the handover schedule, the handover control unit 36 also monitors the communication quality of the first wireless communication network 15 and the second wireless communication network 16 and predicts the subsequent communication quality at regular intervals. To do. As a result, for example, as shown in FIG. 7, the prediction of the first wireless communication network 15 that is the handover source after a certain time or more has passed beyond the handover preparation time Tb than the predicted communication quality of the second wireless communication network 16. When the situation that the communication quality is improved (exceeds) continues for a predetermined period or longer, the decision of the handover schedule is canceled and the fact is supplied to the telephone function unit 33.

  Therefore, in the present embodiment, the handover control unit 36 determines whether or not to start handover preparation, estimates the handover preparation time, predicts the handover destination communication quality after the handover is scheduled, and performs handover. An estimation unit that cancels the schedule and a measurement unit that measures the respective delay times in the first wireless communication network 15 and the second wireless communication network 16 are configured.

  Next, the operation of the telephone function unit 33 will be described. FIG. 8 is a sequence diagram showing the operation of the main part of the telephone function unit 33. The handover information acquisition unit 55 of the telephone function unit 33 acquires the required bandwidth threshold of the softphone (application) from the overall control unit 53 and supplies it to the handover control unit 36 at the start of a call. In addition, during a call, the handover information acquisition unit 55 monitors the handover information from the handover control unit 36 at regular intervals. If the handover information acquisition unit 55 acquires information indicating that there is a handover schedule, the handover information acquisition unit 55 further receives a request from the handover control unit 36. The handover preparation time Tb, the handover destination throughput, the handover source downlink absolute delay time Tddn1, and the handover destination downlink absolute delay time Tddn2 are acquired, and the obtained required handover information is supplied to the reproduction speed calculation unit 56. .

  Based on the required handover information acquired from the handover information acquisition unit 55, the playback speed calculation unit 56 and the downlink absolute delay time (Tddn2) of the second radio communication network 16 and the downlink absolute delay time ( A difference Ta (Ta = Tddn2−Tddn1) from Tddn1) is calculated, and it is determined whether or not a predetermined value (> 0) is exceeded.

Here, when the delay time difference Ta exceeds a predetermined value, that is, when the delay time of the second radio communication network 16 as the handover destination is later than the delay time of the first radio communication network 15 as the handover source, Based on the acquired required handover information and the monitoring result of the jitter buffer 47 by the jitter buffer monitoring unit 50, the playback speed calculation unit 56 calculates the playback speed V of the received packet of the jitter buffer 47 from the following equation (4). Calculate In the equation (4), Vn represents a standard reproduction speed, and Tc represents a time corresponding to the number of packets (data amount) in the jitter buffer 47 at the time when information indicating that a handover is scheduled is received. The reproduction speeds V and Vn are expressed as a time ratio (time / time), for example, Vn = 1.
[Equation 4]
V = (Tc + Tb × Vn + V1 × T1 + V2 × T2 + ... + Vm × Tm) / (Tb + Ta + T1 + T2 + ... + Tm) (4)

Here, for example, as shown in FIGS. 4A and 4B, when the predicted throughput of the handover destination is equal to or higher than the required bandwidth threshold of the application at the time of scheduled handover execution, the predicted throughput and period 0 are the handover control. In this case, the periods T1, T2,..., Tm are 0 in the above equation (4). Accordingly, the reproduction speed V in this case is calculated by the following (5), and the number of packets in the jitter buffer 47 becomes 0 at the start of reception of packets from the handover destination.
[Equation 5]
V = (Tc + Tb × Vn) / (Tb + Ta) (5)

  On the other hand, when the predicted throughput of the handover destination after the scheduled execution of the handover does not satisfy the required bandwidth threshold of the application, it corresponds to the predicted throughput V1, V2,. Periods T1, T2,..., Tm are acquired from the handover control unit 36. Therefore, in this case, the playback speed V is calculated by the above equation (4), and the number of packets in the jitter buffer 47 becomes zero when the predicted throughput satisfies the required bandwidth threshold of the application.

  The reproduction speed V calculated by the reproduction speed calculation unit 56 is supplied to the jitter buffer control unit 51, so that the received packet is reproduced from the jitter buffer 47 so as to reproduce at a reproduction speed V lower than the standard reproduction speed Vn. Controls reading of received packets.

  Here, the playback speed control of the received packet by the jitter buffer control unit 51 is executed by, for example, one of the first playback speed control method and the second playback speed control method described below.

(A) First playback speed control method TRn is a packet reading interval from the jitter buffer 47 with respect to the standard playback speed Vn, and TR is a packet reading interval from the jitter buffer 47 corresponding to the calculated playback speed V. TR = TRn / V. For example, when the playback speed V is 80% (k = 0.8) of the standard playback speed Vn in the case of a VoIP application that reads and plays back packets in the jitter buffer 47 at 20 msec intervals at the standard playback speed Vn. The packet reading interval TR from the jitter buffer 47 is TR = 20 / 0.8 (msec).

(B) Second Playback Speed Control Method When playback speed control for handover is started, the time stamp of the packet (first packet) played back immediately after that is recorded in combination with the playback time. Subsequent packets are read from the jitter buffer 47 and reproduced at time Tv shown by the following equation (6). In Equation (6), TD is a delay time, and the initial value is 0.
[Equation 6]
Tv = (packet time stamp−first packet time stamp) + (first packet playback time + TD) (6)

  For example, when reading a packet from the jitter buffer 47, the [{Vn / (Vn-V)}-1] -th read packet is copied and stored in the memory in the decoder 48, and the copy source packet is reproduced. After that, the copied packet is read out and reproduced at the next reproduction timing. For example, when the playback speed V is 80% of the standard playback speed Vn, as shown in FIG. 9, the sequential four packets P1 to P4 in the jitter buffer 47 are sequentially read and played back, The fourth packet P4 is copied, and the copied packet P4 ′ is reproduced at the next reproduction timing after reproducing the copy source packet P4. Thereafter, when reading the packet P5 from the jitter buffer 47, the TD of the above equation (6) is increased by the reproduction interval time by copying. If the [{Vn / (Vn−V)} − 1] -th packet to be read has not arrived or is discarded and is not in the jitter buffer 47, the packet at the next reproduction timing is The same processing is performed.

  As described above, the reproduction speed control of the received packet by the jitter buffer control unit 51 is executed. Thereafter, when the handover information acquisition unit 55 acquires the handover completion information from the handover control unit 36, the playback speed calculation unit 56 acquires the packet reception interval time from the jitter buffer monitoring unit 50 at regular intervals, and acquires the received reception. An average value of the interval time in a predetermined time is calculated, and it is monitored whether or not a difference between the calculated packet reception interval average value and a standard reception interval in the VoIP application is within a threshold value.

  As a result, if it falls within the threshold value, the playback speed calculation unit 56 determines that the packet from the handover destination has been received, and determines the number of packets (data amount) in the jitter buffer 47 at that time as the jitter buffer. It is acquired from the monitoring unit 50, and it is determined whether or not the acquired number of packets exceeds a predetermined amount.

  As a result, when the number of packets in the jitter buffer 47 does not exceed the predetermined amount, the normal reproduction speed after t = (Tn−Tc) / (Vn−V), when the number of packets exceeds the predetermined amount. The jitter buffer control unit 51 is instructed to return to the control. Here, Tn is a jitter buffer standard delay time corresponding to the standard number of packets in the jitter buffer 47. On the other hand, when the number of packets in the jitter buffer 47 exceeds a predetermined amount, the jitter buffer control unit 51 is instructed to return to normal playback speed control. That is, when the playback speed calculation unit 56 determines that a packet from the handover destination has been received, the jitter buffer control unit 51 returns the standard playback speed Vn to the standard playback speed Vn when the number of packets in the jitter buffer 47 exceeds a predetermined amount. The reading of the jitter buffer 47 is controlled.

  10 and 11 are diagrams showing an example of control of the jitter buffer 47 according to the present embodiment. FIG. 10 shows a control example based on the reproduction speed V of the above equation (5), and FIG. 11 shows a control example based on the reproduction speed V of the above equation (4). In each figure, (a) is the number of packets received by the jitter buffer 47 per unit time, (b) is the playback speed (reading interval) of packets from the jitter buffer 47, and (c) is the jitter buffer 47. Indicates the number of packets.

  As can be seen from FIG. 10, when the estimated throughput of the handover destination is equal to or greater than the required bandwidth threshold of the application at the scheduled handover execution time, the number of packets in the jitter buffer 47 is 0 at the start of packet reception from the handover destination. Thus, the playback speed V of the application becomes slower than the standard playback speed Vn from the notification point of the handover schedule. Therefore, since the difference in absolute delay time from the handover destination can be absorbed over a long time, the playback speed V can be made closer to the standard playback speed Vn.

  As is apparent from FIG. 11, when the predicted throughput of the handover destination does not reach the required bandwidth threshold of the application at the scheduled handover execution time, when the predicted throughput reaches the required bandwidth threshold of the application, the jitter buffer The playback speed V of the application becomes slower than the standard playback speed Vn from the time when the handover schedule is notified so that the number of packets in 47 is zero. Therefore, in this case, since the radio state of the handover destination is poor, the difference in absolute delay time from the handover destination is absorbed over a longer time than in the case of FIG. Similarly to the above, the decrease in the playback speed V from the standard playback speed Vn can be reduced. As a result, handover from the first wireless communication network 15 to the second wireless communication network 16 having a longer absolute delay time is possible without degrading the reproduction quality and real-time property.

  Next, the operation when the telephone function unit 33 acquires handover schedule information and starts controlling playback speed and then acquires handover schedule cancellation information will be described with reference to the sequence shown in FIG. . In this case, when the playback speed calculation unit 56 acquires the cancellation information of the handover schedule from the handover information acquisition unit 55, first, the playback speed calculation unit 56 acquires the number of packets in the jitter buffer 47 at that time from the jitter buffer monitoring unit 50, Determine whether is standard.

As a result, if the number of packets in the jitter buffer 47 is below the standard, the playback speed calculation unit 56 returns the playback speed control of the jitter buffer 47 to the normal playback speed control with respect to the jitter buffer control unit 51. Instruct. On the other hand, if the number of packets in the jitter buffer 47 exceeds the standard, playback is performed at a predetermined speed Vf faster than the standard playback speed Vn, and after a time t calculated by the following equation (7), the normal playback speed The jitter buffer control unit 51 is instructed to return to the control. In the equation (7), the predetermined speed Vf is reproduction speed / standard reproduction speed Vn × 100, which is a ratio to the standard reproduction speed Vn. Further, when reproducing at such a fast predetermined speed Vf, the packet reading interval (extraction interval) from the jitter buffer 47 is set to Ti / Vf (Ti: standard reading interval, Vf: ratio to the standard reproducing speed Vn). ) And shorten it.
[Equation 7]
t = (Tn-Tc) / (Vn-Vf) (7)

  FIG. 13 is a diagram illustrating a control example of the jitter buffer 47 when the number of packets in the jitter buffer 47 exceeds the standard when the handover schedule is canceled in the present embodiment. In FIG. 13, (a) is the number of packets received by the jitter buffer 47 per unit time, (b) is the reproduction speed (reading interval) of packets from the jitter buffer 47, and (c) is in the jitter buffer 47. Indicates the number of packets.

  As described above, in this embodiment, when a handover is performed from the first wireless communication network 15 having a short absolute delay time Tddn1 to the second wireless communication network 16 having a long absolute delay time Tddn2, the handover is scheduled in advance. The handover destination throughput is predicted, and the reproduction speed from the handover schedule determination time is calculated in consideration of the predicted throughput. Therefore, the first radio communication network 15 that is the handover source and the handover destination are compared to the conventional cases shown in FIGS. 16 and 17, not only when the radio state after the handover execution is good but also when the radio state is not good. By increasing the time that can be taken to absorb the delay time difference with the second wireless communication network 16, the application can be played back at a constant playback speed that is closer to the standard playback speed. Thus, handover from the first wireless communication network 15 to the second wireless communication network 16 can be performed without reducing the performance.

  In addition, this invention is not limited only to the said embodiment, Many deformation | transformation or a change is possible. For example, the present invention is not limited to the case of executing a VoIP application, but can be effectively applied to the case of executing a real-time communication application such as streaming reproduction of multimedia data such as video and music. In this case, the application execution unit may be configured by a multimedia function unit having a similar jitter buffer control function instead of the telephone function unit.

It is a figure which shows schematic structure of the communication network which can use the radio | wireless communication apparatus which concerns on one embodiment of this invention. It is a block diagram which shows schematic structure of the radio | wireless communication apparatus shown in FIG. It is a functional block diagram which shows schematic structure of the telephone function part of the radio | wireless communication apparatus shown in FIG. FIG. 3 is a diagram for explaining a first handover preparation time acquisition method by a handover control unit shown in FIG. 2. FIG. 4 is a diagram for explaining a second handover preparation time acquisition method by the handover control unit shown in FIG. 2. FIG. 3 is a diagram illustrating an example of a conversion table between communication quality (wireless state) and throughput stored in a handover control unit illustrated in FIG. 2. It is a figure which shows the radio | wireless state of an example of the handover origin in the case of canceling a handover schedule, and a handover destination. It is a sequence diagram which shows operation | movement of the principal part of the telephone function part shown in FIG. 3 in the case of performing a handover schedule. FIG. 4 is a diagram for explaining an example of a reception packet reproduction rate control method by a jitter buffer control unit shown in FIG. 3. It is a figure which shows the example of 1 control of the jitter buffer in the telephone function part shown in FIG. 3 in the case of performing a handover schedule. It is a figure which shows the other example of control of the jitter buffer in the telephone function part shown in FIG. 3 in the case of performing a handover schedule. FIG. 4 is a sequence diagram showing an operation of a main part of the telephone function unit shown in FIG. 3 when canceling a handover schedule. It is a figure which shows the example of 1 control of the jitter buffer in the telephone function part shown in FIG. 3 in the case of canceling a handover schedule. It is a figure for demonstrating an example of the control method of the conventional jitter buffer. It is a figure which shows the flow of the packet by the control method shown in FIG. It is a figure for demonstrating the other example of the control method of the conventional jitter buffer. It is a figure which shows the flow of the packet by the control method shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Wireless communication apparatus 12 Partner communication terminal 12a Handset 15 1st wireless communication network 15a Access point 16 2nd wireless communication network 16a Base station 17 Packet network 18 Internet 21,22 SIP server 23 Home agent (HA)
31 First wireless I / F
32 Second wireless I / F
33 Telephone Function Unit 34 Communication Processing Unit 35 Radio Information Acquisition Unit 36 Handover Control Unit 47 Jitter Buffer 50 Jitter Buffer Monitoring Unit 51 Jitter Buffer Control Unit 55 Handover Information Acquisition Unit 56 Playback Speed Calculation Unit

Claims (5)

A wireless communication unit that performs wireless communication by connecting to a first wireless communication network and a second wireless communication network different from the first wireless communication network;
A jitter buffer and a jitter buffer monitoring unit that monitors a data amount of the jitter buffer, and an execution unit that executes an application of a real-time communication system via the wireless communication unit;
A communication quality acquisition unit configured to acquire communication quality of a radio link in the first radio communication network and the second radio communication network while executing the application while connected to the first radio communication network;
A determination unit that determines whether to start preparation for handover from the first wireless communication network to the second wireless communication network based on the communication quality acquired by the communication quality acquisition unit;
When the determination unit determines the start of handover preparation during the execution of the application, the handover preparation time is estimated until the handover is started based on the communication quality acquired by the communication quality acquisition unit, and the handover execution schedule is scheduled. An estimation unit for predicting the communication quality of the second wireless communication network later;
When the determination unit determines the start of handover preparation, a measurement unit that measures respective delay times in the first wireless communication network and the second wireless communication network;
The handover preparation time estimated by the estimation unit, the communication quality predicted by the estimation unit for the handover of the second radio communication network, and the first radio communication network and the second radio communication measured by the measurement unit Based on each delay time in the network and the amount of data in the jitter buffer by the jitter buffer monitoring unit at the time when the determination unit determines the start of handover preparation, the playback speed of the application by the execution unit is determined. A control unit to control;
A wireless communication apparatus comprising:   The control unit compares the delay time in the first wireless communication network with the delay time in the second wireless communication network, and the delay time in the second wireless communication network is the delay in the first wireless communication network. The wireless communication apparatus according to claim 1, wherein when the execution unit is longer than the time by a predetermined time, the playback speed of the application by the execution unit is slowed down.   The wireless communication apparatus according to claim 2, wherein the control unit slows down a reproduction speed of the application by the execution unit after starting preparation for handover. The estimation unit predicts a transition until the throughput of the second wireless communication system reaches a required bandwidth threshold required for execution of the application, as the communication quality after the scheduled execution of the handover of the second wireless communication network,
The control unit, when the estimated throughput by the estimation unit has already reached the required bandwidth threshold at the time of scheduled handover execution, at the start of data reception from the second radio communication network, The playback speed of the application by the execution unit is controlled so that the amount of data becomes 0, and when the predicted throughput by the estimation unit has not reached the required bandwidth threshold at the scheduled handover execution time, the predicted throughput is 4. The wireless communication apparatus according to claim 3, wherein the playback speed of the application by the execution unit is controlled so that the data amount in the jitter buffer becomes zero when the required bandwidth threshold is reached. The estimation unit, based on the communication quality acquired at different times by the communication quality acquisition unit after the determination unit has determined the start of handover preparation, the corresponding first wireless communication network and the second wireless communication network When the predicted communication quality of the first wireless communication system exceeds the predicted communication quality of the second wireless communication system after a predetermined time exceeding the handover preparation time, , Notifying the controller of cancellation of the handover preparation,
4. The control unit according to claim 3, wherein when the notification of cancellation of the handover preparation is received from the estimation unit, the control unit controls the playback speed of the application by the execution unit to return to a normal playback speed. The wireless communication device described.

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