JP2010258541A - Multimedia video transmission system and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems wherein in a multimedia-broadcast-multicast service, when a high-quality multimedia stream signal is provided by a wireless WAN, (1) a packet loss occurs in the transmission of the wireless WAN, (2) a large amount of NAK occurs, if a retransmission request of the packet loss is performed, which a system cannot accommodate to, and (3) unbalance of a reception quality in an FEC occurs. <P>SOLUTION: (1) Within a node assembly constituting an ad-hoc network, nodes exchange packets received between wireless LANs, after a subset of different packets is received from a multimedia source. (2) Strain ratio based on a packet loss rate in each node is calculated, and a multimedia packet stream is transmitted at a source packet rate which makes the strain rate minimum. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to multicast transmission of high quality multimedia packet streams in wireless wide area networks.

  It is common to send multimedia stream signals from multimedia sources to a set of receiving nodes using a wireless wide area network (hereinafter referred to as wireless WAN). In this case, packet loss may occur during transmission over the wireless WAN. In order to cover this packet loss, if a retransmission request is made from each node by a feedback method, a large amount of NAK (negative ack) is transmitted, and the system may not be able to handle. In order to avoid this, forward error correction (FORWARD ERROR CORRECTION, hereinafter referred to as FEC) is often used. FEC does not retransmit data from the sending side, but instead sends FEC packets that can recover lost packets, and uses the FEC packets on the receiving side to repair lost packets during transmission. is there. In FEC, creating an FEC packet by linear combination of source packets is called “network coding”. For example, FEC is often used in communications for applications such as sending moving image or audio data. If the FEC is used, the receiving side does not need to wait for the data to be retransmitted, and the delay due to the error is reduced, so that the moving image can be displayed without delaying the display timing.

US application dated July 2, 2008, Appl No. 12/166998, title of invention: “Distribution Of Packets Among A Plurality Of Nodes”, inventor Gene Cheung

S. Raza, D. Li, C.-N. Chuah, and G. Cheung, “Cooperative peer-to-peer repair for wireless multimedia broadcast,” in IEEE International Conference on Multimedia and Expo, Beijing, China, July 2007. X. Liu, S. Raza, C.-N. Chuah, and G. Cheung, “Network coding based cooperative peer-to-peer repair in wireless ad-hoc networks,” in IEEE International Conference on Communications, Beijing, China, May 2008. X. Liu, G. Cheung, and C.-N. Chuah, “Rate-distortion optimized network coding for cooperative video stream repair in wireless peer-to-peer Networks,” in 1st IEEE Workshop on Mobile Video Delivery, NewportBeach, CA , June 2008. “Structured network coding and cooperative local peer-to-peer repair for MBMS video streaming,” in IEEE 2008 International Workshopon Multimedia Signal Processing, Cairns, Queensland, Australia, October 2008.

When transmitting a continuous high-quality multimedia stream signal over a wireless WAN in a transmission service such as 3G network multimedia broadcast / multicast service (MBMS), the following technologies There are some problems.
1. In transmission over the wireless WAN, temporary loss of the wireless link causes packet loss.
2. If a retransmission request is made in a feedback manner to cover packet loss, a large amount of NAK (negative ack) occurs, causing a problem that the system cannot cope.

As a result, since retransmission does not succeed, there is a problem in performing high-quality video multicast transmission in a feedback manner. In order to solve these problems, there is the aforementioned FEC. However, the conventional FEC has the following problems.
3. Since targeting the selected nth user, a user with a reception situation worse than the targeted nth user suffers from packet loss due to substantial channel loss. On the other hand, a user with better reception status receives data of channel encoding more than necessary.

[system]
In order to solve the above problems, the present invention discloses the following means as a system.
A system including a multimedia source and a node set forming an ad hoc network that performs transmission and reception between nodes,
(1) The multimedia source includes the following means:
(A) Loss after packet stream is repaired by mutual exchange of packets generated based on received packets between nodes, and loss probability during transmission of packet stream from multimedia source to each node at each node Means to accept the input of probability,
(B) distortion based on a distortion reduction coefficient when encoding a given source packet, a loss probability at the time of packet stream transmission from the multimedia source to each node, and a loss probability after repair between nodes A means of determining the rate,
(C) means for determining a source packet rate that minimizes the distortion rate while changing the source packet rate under a given bandwidth limitation;
(D) means for transmitting a packet stream according to a source packet rate that minimizes the distortion rate; and
(2) The node set includes the following means:
(E) means for each node to receive the packet stream and repair a packet stream by exchanging packets generated based on received packets between the nodes;
(F) Means for each node to decode and reproduce the packet stream.

[Method]
In order to solve the above problems, the present invention discloses a method used in the following system.
A method of receiving and playing back a packet stream transmitted from a multimedia source at a node set forming an ad hoc network that transmits and receives between each node;
(A) The multimedia source is a packet obtained by mutual exchange of packets generated based on the loss probability at the time of packet stream transmission from the multimedia source to each node at each node and the received packets between the nodes. Accepting the input of loss probability after stream repair,
(B) Distortion reduction coefficient when a multimedia source encodes a given source packet, loss probability at the time of packet stream transmission from the multimedia source to each node, and loss probability after repair between nodes Obtaining a strain rate based on
(C) the multimedia source determines a source packet rate that minimizes the distortion rate while changing the source packet rate under a given bandwidth limit;
(D) a multimedia source transmits a packet stream according to a source packet rate that minimizes the distortion rate;
(E) Each node receives the packet stream, and repairs a packet stream by exchanging packets generated based on received packets between the nodes;
(F) Each node performs decoding and reproduces the packet stream.

[The invention's effect]
In the present invention, FEC is used to determine a source packet rate that minimizes a distortion rate in packet distribution from a multimedia source to a plurality of node sets, and the multimedia packet stream is obtained at the determined source packet rate. Send. Further, a system and method for performing the CPR on the transmitted packet stream in the node set and repairing the packet stream is disclosed. The present invention has two main effects as follows.
1. PSNR (Peak Signal to Noise Ratio) Improvement In the simulation experiment, compared to the conventional JSCC (Joint Source / Channel Coding) method, only the multimedia coding and the node set and the entire network coding optimized are performed. When the data restoration method (CPR) between nodes (between P2P) in wireless LAN was not performed, it was verified that PSNR was improved by 9.2 dB.
In addition, in the case of using the data restoration method (CPR) between nodes (between P2P), compared to the case where network coding is separately performed between the multimedia source and the node set, according to the present invention. It was verified that the PSNR was improved by 3.7 dB when optimization was performed for the multimedia source and the node set as a whole.
2. When a packet received from a multimedia source is transmitted to another node in the set, before forwarding, each node performs FEC and transmits to the other node, transmission from the multimedia source, and each node in the set Decoding is performed after repair of the packet is completed. As a result, in order to code with packets received from a multimedia source, even a node that receives an insufficient number of packets can immediately support packet repair (CPR) within the node set. I can do it.

1 is a schematic diagram of a system for implementing the present invention. It is a computer block diagram used by this invention. It is a figure which shows the data processing in the node set in this invention. It is a software block diagram of the multimedia source in this invention. It is a flowchart which shows the whole process in this invention. It is a flowchart which calculates | requires the loss rate in the node in this invention. It is a flowchart regarding restoration of a stream in the present invention. It is a software block diagram of the node in this invention. It is a figure which shows the experimental result in this invention.

[System-wide configuration]
The best mode of the present invention will be described below. FIG. 1 is a diagram showing a hardware configuration of the entire system. The system 100 disclosed herein includes a multimedia source 110 and a node set 120. The multimedia source 110 transmits the multimedia stream to the node set 120 over the wireless WAN. The node set 120 includes a plurality of nodes, and each node receives a multimedia stream. Examples of the node include, but are not limited to, a personal computer, a notebook personal computer, a PDA (Persona Data Assistant), and a mobile phone terminal. Here, each node forms an ad hoc network in which nodes transmit and receive each other. An ad hoc network is a network composed of only nodes that do not require an access point and can be connected wirelessly.

[Computer internal hardware configuration diagram]
FIG. 2 shows a computer internal hardware configuration diagram of the transmitting-side multimedia source 110 and each node AD 122a of the node set 120 that implements the present invention. These apparatuses using a computer have a processor 302, and a program executed in the present invention is executed. Data and commands are sent from the processor 302 through the communication bus 304. The computer 300 also has a main memory 306 typified by RAM, where program code is executed. The secondary memory 308 includes, for example, one or more hard disks 310 or a removable storage drive 312 such as a flexible disk drive, a magnetic tape drive, and a CD disk drive. Here, the program code for implementing the present invention is stored.

  User I / O devices include a keyboard 316, a mouse 318, a display 320, and the like. Display adapter 322 interfaces communication bus 304 and display 320, receives data from processor 302 and converts it to display commands for display 320. Further, the processor 302 communicates with, for example, the Internet and a LAN through the network adapter 324.

[Node hardware configuration]
FIG. 3 is a block diagram of the hardware configuration of the receiving side node of the present invention. Multimedia source 110 transmits packet stream 132 to node set 120. As an example, a case where the node A 122a receives these signals will be described. The node A 122 a receives the packet stream at the wireless WAN interface 152 and stores the data in the data store 154. Here, it should be noted that the received packet stream often cannot receive all packet streams due to transmission loss from the multimedia source. In addition, the data is subjected to network coding based on the received packet stream transmitted to the controller 158 to create an FEC packet. The received source packet and the created FEC packet are transmitted to the wireless LAN interface 156, and from there to the other node N122n in the node set.

[Repair stream with CPR]
In many cases, the packet stream 132 received from the multimedia source 110 by the node N 122n cannot receive all the packet streams. The node N122n uses the packet stream received from the node A to repair the multimedia stream received by the node N122n from the multimedia source. Thus, in the case of transmitting a packet stream from a multimedia source to a node set consisting of a plurality of nodes, the packet received by itself in the node set that has received these is transmitted to other nodes in the node set, Each node in the set takes in packets that it has not received and repairs the packet stream. This is called CPR (Corporate Peer-to-Peer Repair) in this specification.

[Node software configuration]
FIG. 8 is a diagram illustrating a software configuration of the node. The following software modules are included. A transmission / reception unit 252, an ad hoc network generation unit 254, a packet data analysis unit 256, a stream data analysis unit 258, a received packet store unit 260, a stream restoration unit 262, a decoding unit 264, a stream reproduction unit 268, and a network encoding unit 266 are included. .
Here, the transmission / reception unit 252 receives packet data stream data from the multimedia source 110 and receives packet data from other nodes, and transmits packet data received by itself to other nodes. The packet loss rate received by itself and the packet loss rate after stream restoration by CPR are transmitted.

The ad hoc network generation unit 254 will be described. In the present invention, an ad hoc network is configured within a node set in order to exchange packets with each other within the node set. For this purpose, the ad hoc network generator forms an ad hoc network with other nodes in the node set.

The packet data analysis unit 256 analyzes whether or not a packet transmitted from another node has been normally received. The normally received packet is sent to the stream repair unit 262.

The stream data analysis unit 258 analyzes whether the multimedia stream transmitted from the multimedia source 110 has been received correctly. The correctly received part is sent to the reception packet store unit 260. Also, if necessary, the loss rate of the stream at the time of reception is calculated and sent to the transmission / reception unit 252.

The reception packet store unit 260 stores stream packets that are correctly received.

The stream restoration unit 262 confirms the missing packet among the stream packets sent from the received packet store unit 260, determines whether or not the packet can be restored using the packet data sent from the packet data analysis unit 256, If repair is possible, repair. Further, if necessary, the loss rate of the restored stream is calculated and sent to the transmission / reception unit 252.

The decoding unit 264 decodes the repaired stream data.

The stream reproduction unit 268 reproduces the decoded packet stream.

The network encoding unit 266 further performs encoding using the normally received packet sent from the reception packet store unit 260 and sends the packet to the transmission / reception unit 252.

[Configuration diagram of multimedia source]
FIG. 4 is a software configuration diagram of the multimedia source 110.
The multimedia source 110 includes a data transmission / reception unit 162, a packet loss rate input unit 164, a node packet loss rate calculation unit 166, a distortion rate calculation unit 168, a network code calculation unit 170, a multimedia packet stream generation unit 172, and multimedia data management. Section 174 and multimedia data storage section 176.

The data transmission / reception unit 162 receives data relating to transmission to the multimedia stream to the node set and packet loss from each node. If the data is known, the data is input from the packet loss rate input unit 164 to the multimedia source. The node packet loss rate calculation unit 166 calculates a loss rate at the time of receiving a multimedia stream transmitted from each node and a loss rate of the multimedia stream after CPR repair.

The strain rate calculation unit 168 calculates the strain rate according to the definition of the strain rate described later.

The network code calculation unit 170 calculates the distortion rate for the distortion rate calculated by the distortion rate calculation unit 168 while changing R _s (source packet rate) and obtains R _s that minimizes the distortion rate. To decide.

The multimedia data storage unit 176 stores a multimedia packet data stream to be transmitted. These data are sent to the multimedia data management unit 174.

The multimedia data management unit 174 manages the multimedia data storage unit 176 and sends the data sent from the multimedia data storage unit 176 to the multimedia packet data stream generation unit 172.

The multimedia packet data stream generation unit 172 generates a multimedia packet data stream according to the network code determined by the network code calculation unit 170.

[FEC]
In the present invention, network coding is performed in the case of transmission from a multimedia source to a node set and in the case of packet stream restoration by CPR in the node set. FEC is a method of transmitting an FEC packet that can recover a lost packet instead of retransmitting data from the transmitting side, and recovering the lost packet during transmission using the FEC packet on the receiving side. . In FEC, when an FEC packet is created, creation by linear combination of source packets is called network coding.

(1) FEC when sending multimedia source
Here, a case where five packets are transmitted from a multimedia source will be described as an example. Assume that three of the five packets are source packets (s1, s2, s3) and two are FEC packets (c4, c5).
The packet PC (S) generated by the multimedia source is defined as follows.
PC (S) = {s1, s2, s3, a4, a5}
Here, c4 and c5 can be expressed as follows.
a4 = α1 · s1 + α2 · s2 + α3 · s3
a5 = β1 · s1 + β2 · s2 + β3 · s3
Here, α1, α2, α3, β1, β2, and β3 are randomly generated multipliers that are transmitted together with a4 and a5. If any three of the five packets are received on the receiving side, the number of unknown packets is three and the number of equations is three, so that a solution can be obtained. That is, the transmitted stream packet can be reproduced on the receiving side.

(2) FEC in node set
(2-1) FEC at node A
For example, assume that node A has received three of the aforementioned packets as follows. It is assumed that the received packet PR (SA) at node A = {s1, s3, c4}. Here, since three independent packets have been received, it can be decoded into source packets at this point by solving the equations. That is, the source packet PS = {s1, s2, s3} can be reproduced.

FEC packet created at node A The following FEC packet is generated by linear combination of packets PR (SA) = {s1, s3, c4} received at node A.

b1 = γ1 · s1 + γ2 · s3 + γ3 · a4
Node A transmits this FEC packet (b1) to other packets in the set. For example, the data is transmitted to the node B.

(2-2) FEC at Node B
It is assumed that data transmitted from node A to node B is PC (AB) = {b1}. The received packet of the packet transmitted from the node A at the node B is PR (AB) = {b1}.

(2-3) Received packet at Node B Node B also has a packet received from a multi-channel source. Assume that Node B has received two packets from a multi-channel source and that they are PR (SB) = {s1, s2}.
PR (AB) = {b1}
PR (SB) = {s1, s2}
From these information, in packet B, since there are three equations for three variables, a solution can be obtained, and as a result, s3 can be reproduced from s1, s2, and b1. I can do it.

  Details of the processing flow of the present invention will be described below. The present invention obtains a source packet rate that minimizes a distortion rate in packet transmission from a multimedia source (transmitter) to a node set of an ad hoc network connected by a wireless LAN, and further according to the source packet rate. A method / system for transmitting a multimedia packet stream,

[Overall process flow]
FIG. 5 shows the overall processing flow of the present invention.
(A) The multimedia source is a packet obtained by mutual exchange of packets generated based on a loss probability at the time of packet stream transmission from the multimedia source to each node at each node and a received packet between the nodes. Receiving an input of loss probability after stream repair (410);
(B) Distortion reduction coefficient when a multimedia source encodes a given source packet, loss probability at the time of packet stream transmission from the multimedia source to each node, and loss probability after repair between nodes Determining a strain rate based on (430),
(C) the multimedia source determines a source packet rate that minimizes the distortion rate while changing the source packet rate under a given bandwidth limit (440);
(D) the multimedia source transmits a packet stream according to a source packet rate that minimizes the distortion rate (450);
(E) Each node receives the packet stream, and repairs a packet stream by exchanging packets generated based on received packets between the nodes (460).
(F) Each node performs decoding and reproduces the packet stream (470).

Hereinafter, details of the processing flow will be described in order from (A) to (F).
[Details of step (A)]
(A) The multimedia source is a packet obtained by mutual exchange of packets generated based on a loss probability at the time of packet stream transmission from the multimedia source to each node at each node and a received packet between the nodes. Accepting the input of loss probability after stream repair.
The loss probability at the time of packet stream transmission at each node and the loss probability after repairing the packet stream by mutual exchange of packets generated based on the received packets between the nodes determine the “distortion rate” described later. Is necessary. If the data is known, the data is input from the packet loss rate input unit 164 to the multimedia source.

[Measurement of packet loss rate]
Below, the loss rate at the time of packet stream transmission at each node and the loss rate after repairing the packet stream by mutual exchange of packets generated based on received packets between nodes are measured from the actual nodes. FIG. 6 shows a flow in the case of obtaining by this.
(A) the multimedia source sends a packet stream to the node set (412);
At this time, since the loss rate at each node at the time of reception in the node set is obtained, it is not necessary to perform FEC.
(B) Each node receives the packet stream and obtains a packet loss rate at the time of reception (414),
Each node in the node set receives a packet stream from the multimedia source. In the case of a wireless WAN, it is well known that packet loss may occur during transmission due to temporary wireless link interruptions. Here, each node obtains the packet loss rate when the packet stream is received.
(C) Each node exchanges packets received between the nodes and repairs the packet stream (416),

(D) Each node decodes the repaired packet stream (418),
(E) Each node transmits the loss rate at the time of receiving the packet stream of each node and the loss rate after repair by exchanging packets between the nodes to the multimedia source (420).
Each node obtains a packet loss rate at the time of packet stream reception and after stream restoration by packet exchange between nodes, and transmits the data to the multimedia source.
As described above, the loss probability at the time of packet stream transmission of each node and the loss probability after repair between the nodes are transmitted to the multimedia source.

[Details of step to repair packet stream]
Here, the step (d) in which each node exchanges packets received between the nodes and repairs the packet stream (418) will be described in detail as follows. A flowchart in this case is shown in FIG.
(D-1) a step in which one node transmits the received packet to another node (510);
One node transmits the received packet to all other nodes in the node set. Here, based on the linear combination of packets received by one node, FEC packets are generated and transmitted.
(D-2) a step in which another node receives a packet transmitted from one node (512),
Here, even if there is a packet that the other node does not receive, the node does not send a retransmission request for the packet to the multimedia source. This is because a NAK (Negative Acknowledgment) problem occurs when a retransmission request is transmitted.

(D-3) A step of repairing a packet stream when another node has a missing packet stream received from a multimedia source and can be repaired using a packet transmitted from one node. (514, 516),
At this time, without decoding the received packet, the packet stream is repaired using the source packet received from the multimedia source and the FEC packet received from one node.
(D-4) Step (518) of repeating (d-1) to (d-3) for a predetermined time period,
(D-5) decoding the repaired stream (520),
Decoding is performed after a series of streams have been repaired.
As described above, the packet stream received from the multimedia source is repaired while performing CPR in the node set.

[Details of Step (B)]
(B) Distortion reduction coefficient when a multimedia source encodes a given source packet, loss rate at the time of packet stream transmission from the multimedia source to each node, and loss rate after repair between nodes Determining a strain rate based on (430),
(1) Calculation of distortion rate Actually, loss occurs at the time of transmission from the multimedia source to each node, and loss at the time of transmission between the nodes. Does not have.
Therefore, the distortion reduction rate d (R _s ) obtained as a function of Rs, the loss probability (l ′ _col ) when each node transmits a packet from the multimedia source to each node, and the loss after repair between the nodes of each node Based on the probability Q, the strain rate is calculated.
(2) Definition of strain rate The strain rate is defined below.

(Formula 1)
Distortion rate = f {d (R _s ), l ′ _col , Q}
= {D−d (R _s ) * (1−P _grp (R _s , R _c ))} R _s + R _c = <C
Here, D is an initial value of distortion, and is an overall distortion rate when a packet is not received at each node. R _s is the source packet rate, and R _c is the FEC packet rate.
d (R _s ) is a distortion reduction rate when a given GOP sequence is quantized with a predetermined number of bits, and is proportional to R _s . Here, GOP refers to a group of frame data necessary for efficiently managing one frame (frame) as a minimum unit in a compression codec used when recording a video stream. The d (R _s) in turn to reduce every one packet R _s, obtained by experiment R _s for the evaluation function minimizes while monitoring the change in the evaluation function for the strain rate. C is the full bandwidth of the wireless WAN available for transmission.

[Group loss probability]
P _grp (R _s , R _c ) is a “group loss probability” based on R _s and R _c , and is a probability that CPR cannot be recovered when R _c or more packets are lost. P _grp (R _s , R _c ) can also be obtained by giving a loss rate (l ′ _col ) in packet delivery to each node and a loss rate Q after repair between nodes of each node. _{Incidentally, P grp (R s, R} c) detailed definition of, described in detail in _{[P grp (R s, R} c) detailed definition of 'below.

[Details of Step (C)]
(C) the multimedia source determines a source packet rate that minimizes the distortion rate while changing the source packet rate under a given bandwidth limit (440);
Find the source packet rate that minimizes the distortion factor.
In order to obtain the optimum R _s and R _c that minimize (Equation 1), as an example, the present invention discloses the following search method, but the search method is not limited to this.
(A) determining the initial value _{R s} of _{R s.}
(B) The value of R _s , that is, the number of packets of R _s is sequentially decreased by 1 to obtain the value of Equation (1).
(C) Repeat (b) so that the value of (Equation 1) is minimized.
Thus, the value of R _s that minimizes (Equation 1) can be obtained.

[Details of Step (D)]
(D) the multimedia source transmits a packet stream according to a source packet rate that minimizes the distortion rate (450);
At this time, transmission is performed while performing net coding based on the obtained source packet rate.

[Details of Step (E)]
(E) Each node receives the packet stream, and repairs a packet stream by exchanging packets generated based on received packets between the nodes (460);
Also at this time, each node transmits to other nodes while performing network coding.

[Details of Step (F)]
(F) Each node reproduces the packet stream by decoding (470).
Here, in the present invention, decoding is performed after the restoration of the stream data is completed as follows.
Thereby, it is possible to reproduce a multimedia packet data stream having a minimum distortion rate.

[Definition of probability P _grp (R _s , R _c ) that packet cannot be recovered]
The probability P _grp (R _s , R _c ) that the packet cannot be recovered is given by the following equation.

(Formula 2)

Here, l _avg is the average value of the packet loss probability l _m of each node when each node receives a multimedia source. (Here, m = 1 to N, where N represents the number of all nodes.) P _col is the probability that the set cannot be fully recovered when i packets are lost. In other words,
(I) when a single packet is correctly delivered over the wireless WAN, or
(ii) The probability that a single packet can be recovered when a single packet is not delivered correctly over the wireless WAN and is delivered correctly within the set and consequently repaired by CPR within the set.

P _col (i, R _c ) is defined by the following equation.

(Formula 3)

P _isuf (i, R _c ) is an “unsatisfactory set probability”, and Q (i), which is a probability that the minimum packets necessary for repair by CPR are not complete, is a CPR loss probability, Loss probability depending on the number of FEC packets.
Insufficient probability _P isuf (i, _{R c)} of the set can be represented by equation (4).

(Formula 4)

Here, (Equation 4) is a probability that only j packets are received through the set among i packets lost at the node, and other packets are lost within the set. Therefore, if it is less than this value, the entire packet group cannot be recovered. l ′ _col is an aggregate packet loss probability, which is a loss probability at the time of transmission from the multimedia source to each node.

(Formula 5)

It is. Here, l _m (m = 1 to N, N is the number of all nodes) is a packet loss probability when each node receives the multimedia source, and ρ is a spatial correlation factor. . This is a value related to whether or not the same signal is received at each node when a multimedia signal is received. This is related to the distance between the nodes. In this embodiment, ρ = 1.
Thereby, the distortion rate is based on the loss rate (l ′ _col ) at the time of transmission from the multimedia source to each node and the loss rate (Q (i)) depending on the number of FEC packets at each node. I understand that.

[Experimental result]
With the source packet obtained by the method disclosed in the present invention, it is possible to reduce the distortion rate in the case where transmission is performed from the multimedia source to each node and the lost packet is repaired at each node.
The experimental examples disclosed in the present invention using the JSCC method and CPR at the same time, the experimental examples using only CPR, and the experimental examples when CPR is not used are shown below. 9A shows the case of the HM packet loss model, and FIG. 9B shows the case of the HT packet loss model.

110: Multimedia source 120: Node set 122a: Node A
122n: Other node N
132: Packet stream 158: Controller 154: Data store 156: WLAN interface 300: Computer 302: Processor 304: Communication bus 306: Main memory 308: Secondary memory 310: Hard disk 316: Keyboard 318: Mouse 320: Display

Claims (8)

A system including a multimedia source and a node set forming an ad hoc network that performs transmission and reception between nodes,
The multimedia source includes the following means:
(A) Loss after packet stream is repaired by mutual exchange of packets generated based on received packets between nodes, and loss probability during transmission of packet stream from multimedia source to each node at each node Means to accept the input of probability,
(B) distortion based on a distortion reduction coefficient when encoding a given source packet, a loss probability at the time of packet stream transmission from the multimedia source to each node, and a loss probability after repair between nodes A means of determining the rate,
(C) means for determining a source packet rate that minimizes the distortion rate while changing the source packet rate under a given bandwidth limitation;
(D) means for transmitting a packet stream according to a source packet rate that minimizes the distortion rate; and
The node set includes the following means:
(E) means for each node to receive the packet stream and repair a packet stream by mutual exchange of packets generated based on the received packets between the nodes;
(F) means for each node to decode and reproduce the packet stream;
Having a system. The system of claim 1, further comprising:
The multimedia source includes the following means:
(A) means for the multimedia source to send a packet stream to the node set;
Each of the nodes includes the following means:
(B) means for each node to receive the packet stream and obtain a packet loss rate at the time of reception;
(C) means for each node to exchange packets received between the nodes and repair the packet stream;
(D) means for each node to decode the repaired packet stream;
(E) Means for each node to transmit the loss rate at the time of receiving the packet stream of each node and the loss rate after repair between the nodes to the multimedia source. The system according to claim 1 or 2, wherein means for repairing a packet stream by mutual exchange of packets generated based on received packets between the nodes further includes the following means:
(A) means for repairing a packet stream when another node has a missing packet stream received from a multimedia source and can be repaired using a packet transmitted from the one node;
(B) Means for repeating (a) for a predetermined time. The system according to claims 1 to 3, wherein the distortion rate is given by the following equation:
Distortion rate = {D−d (R _s ) * (1−P _grp (R _s , R _c ))}
Here, R _s is the source packet rate, and R _c is the FEC packet rate. D is a distortion rate when no packet is received. d (R _s ) is a distortion reduction coefficient when the source packet is encoded with a predetermined number of bits, and is a function of R _s . P _grp (R _s , R _c ) is a group loss probability based on the packet loss probability of multimedia packets at each node and the loss probability after repair between the nodes of each node. A method of receiving and playing back a packet stream transmitted from a multimedia source at a node set forming an ad hoc network that transmits and receives between each node;
(A) The multimedia source is a packet obtained by mutual exchange of packets generated based on the loss probability at the time of packet stream transmission from the multimedia source to each node at each node and the received packets between the nodes. Accepting the input of loss probability after stream repair,
(B) Distortion reduction coefficient when a multimedia source encodes a given source packet, loss probability at the time of packet stream transmission from the multimedia source to each node, and loss probability after repair between nodes Obtaining a strain rate based on
(C) the multimedia source determines a source packet rate that minimizes the distortion rate while changing the source packet rate under a given bandwidth limit;
(D) a multimedia source transmits a packet stream according to a source packet rate that minimizes the distortion rate;
(E) Each node receives the packet stream, and repairs a packet stream by exchanging packets generated based on received packets between the nodes;
(F) Each node performs decoding and reproduces the packet stream. 6. The method of claim 5, wherein the receiving step further comprises the following steps:
(A) a multimedia source sends a packet stream to a set of nodes;
(B) Each node receives the packet stream and obtains a packet loss rate at the time of reception;
(C) each node exchanging received packets between the nodes and repairing the packet stream;
(D) a step in which each node decodes the repaired packet stream;
(E) Each node transmits the loss rate at the time of receiving the packet stream of each node and the loss rate after repair between the nodes to the multimedia source. The method according to claim 5 and 6, wherein the step of repairing a packet stream by exchanging packets generated based on received packets between the nodes further includes the following steps:
(A) repairing the packet stream when another node is missing in the packet stream received from the multimedia source and can be repaired using the packet transmitted from the one node;
(B) A step of repeating (a) for a predetermined time. The method according to claims 5 to 7, wherein the strain rate is given by the following equation:
Distortion rate = {D−d (R _s ) * (1−P _grp (R _s , R _c ))}
Here, R _s is the source packet rate, and R _c is the FEC packet rate. D is a distortion rate when no packet is received. d (R _s ) is a distortion reduction coefficient when the source packet is encoded with a predetermined number of bits, and is a function of R _s . P _grp (R _s , R _c ) is a group loss probability based on the packet loss probability of multimedia packets at each node and the loss probability after repair between the nodes of each node.

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