KR20040069568A - Apparatus and method for transmitting packet data in a base station of mobile communication system - Google Patents

Abstract

Disclosed are a method and apparatus for transmitting a packet received from the base station controller by a base station to a terminal in a mobile communication system having a base station and a base station controller connected to the base station through an internet protocol network.

The present invention as described above is a process of detecting the reverse arrangement of the received packet by using the sequence number and the receiving order of the packet received in the current time interval, and if the reverse arrangement is detected, the received packet for a predetermined time period Storing in a predetermined queue, and compressing packets having consecutive sequence numbers among the packets stored in the queue and transmitting them to the terminal when the predetermined time interval elapses.

Description

Method and apparatus for transmitting packet in base station of mobile communication system {APPARATUS AND METHOD FOR TRANSMITTING PACKET DATA IN A BASE STATION OF MOBILE COMMUNICATION SYSTEM}

The present invention relates to a mobile communication system, and more particularly, to a method and apparatus for transmitting packet data between a base station and a base station controller when a base station and a base station controller constituting the mobile communication system are connected through an internet protocol network.

In the conventional ATM based base station system, since the base station control unit and the base station are directly connected through the E1 link, the frame delay problem is not seriously exposed. However, when the connection between the base station and the base station controller is an Internet Protocol (hereinafter referred to as 'IP') based network, traffic is transmitted through the User Data Protocol (UDP), which is a characteristic of the IP network. Depending on the characteristics of the best effort, delay and inverse arrangement of frame transmission may occur. Therefore, the voice call has a problem of poor call quality.

Services that require real time, such as voice calls, are particularly sensitive to packet delay. Therefore, the IP-based base station and base station control unit system needs to compensate for the delay time of the packet. In addition, a compensation technique considering compatibility with an existing terminal is required.

Accordingly, an object of the present invention is to provide a method and apparatus for solving the problem of packet de-arrangement in a base station system based on an IP network.

Another object of the present invention is to provide a method and apparatus for solving a packet delay problem in consideration of compatibility with an existing terminal in a base station system based on an IP network.

The present invention to achieve these objects

A mobile communication system having a base station and a base station control unit connected to the base station through an internet protocol network, the method for transmitting packets received from the base station control unit by the base station to the terminal,

Detecting the reverse arrangement of the received packets by using the sequence number and the reception order of the received packets in the current time interval, and if the reverse arrangement is detected, storing the received packets in a predetermined queue for a predetermined time interval. And, if the predetermined time period elapses, and compressing the packets having a consecutive sequence number of the packets stored in the queue and transmitting to the terminal.

In accordance with an embodiment of the present invention, a process of comparing a sequence number S of a packet received in a current time interval with a largest sequence number N of the sequence numbers of packets received up to a previous time interval, plus 1; Where S and N are integers,

If S is greater than N, adding S-1 to a predetermined wait set from sequence number N, storing the packet received in the current time interval in a predetermined queue, and storing the received sequence up to the previous time interval. And setting the largest sequence number among the numbers to S.

In addition, if S is less than the N, determining whether the S belongs to a preset waiting set, and if the S belongs to the waiting set, among the packets having a sequence number S, among the packets previously stored in a predetermined queue, The method may further include transmitting a packet having a sequence number consecutive with the S to the terminal in sequence number order.

And if S and N are equal, comparing the sum of packet lengths from packets having a sequence number closest to S to packets having a queue in a predetermined queue with a preset reference value; If the sum of the packet lengths is smaller than the reference value, transmitting the packet having the sequence number closest to S to the packet having the sequence number S to the terminal in sequence number order.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that those skilled in the art may better understand the detailed description of the invention that follows.

Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. Those skilled in the art should recognize that the disclosed concepts and specific embodiments of the invention may be readily used as a basis for modifying or designing other structures for achieving the same purposes of the present invention. Those skilled in the art should also recognize that structures equivalent to the invention do not depart from the spirit and scope of the broadest form of the invention.

1 is a view for explaining a packet transmission method according to the principles of the present invention;

2 shows a packet transmission apparatus according to an embodiment of the present invention;

3 is a flowchart illustrating a method of transmitting a packet in a base station according to an embodiment of the present invention.

DETAILED DESCRIPTION A detailed description of preferred embodiments of the present invention will now be described with reference to the accompanying drawings. It should be noted that reference numerals and like elements among the drawings are denoted by the same reference numerals and symbols as much as possible even though they are shown in different drawings. In the following description of the present invention, detailed descriptions of related known functions or configurations will be omitted when it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention.

A mobile communication system having a base station and a base station control unit connected to the base station through an internet protocol network, the present invention relates to a method for transmitting packets received from the base station control unit by the base station to the terminal. In particular, the present invention is applied to the case where the packets are a packet requiring a large amount of real-time transmission, for example, a voice packet.

The principle of the present invention is to detect the reverse arrangement of the packet in the transmission of the packet between the base station and the base station control unit, determining whether there is a margin in the data rate when the reverse arrangement is detected, and if there is a margin, queuing for the portion where delay is expected. Then, it compresses the part selectively and instantaneously and transmits it to the destination node at high speed. Therefore, the base station or base station control unit detects the order of the received packet, and if the order is reversed, buffers it and retransmits it.

Here, the inverse arrangement of packets means a case in which the sequence numbers of the received packets and the reception order do not match.

In general, channels of a mobile communication system may operate at a full rate or a partial rate for a given rate. In the case of the file transfer protocol, the transmission rate is close to the maximum transmission rate, but services such as web services and voice calls can be transmitted at the partial transmission rate. Therefore, using the average data rate compared to the maximum data rate at a given time Ti, the free space that the system can buffer is calculated. Here, the average rate refers to the average of the partial rate at which each packet is transmitted. Such free space can be obtained by Equation 1 below.

L_i = │Rmax / Ravg│

If L_i is larger than 1 in Equation 1, since there is enough free space, buffering by 1 / L_i is possible. If a packet delay occurs, discontinuity with the previous packet sequence is detected by checking the time stamp and sequence number of the received packet at that time. In this case, if a packet having a previous sequence number is waited and sent together, reverse arrangement due to packet delay can be prevented. Here, a reference time for waiting for a packet having a previous sequence number is required. Assuming that each slot is one packet frame in FIG. 1, the reference time must satisfy a time interval smaller than 1 / L_i. In order to transmit a delayed packet under such a condition, a packet having a continuity among the previously arrived sequence numbers larger than the current packet may be compressed. Referring to FIG. 1, a packet having a sequence number j-1 (hereinafter, referred to as a j-1 packet) is received, and since j + 1 packet is received thereafter, the j + 1 packet is stored in a reception queue. In order, j + 2, j, j + 4, j + 5 and j + 3 packets are received and stored in the receive queue. At the time when the reference time interval elapses, the packets stored in the reception queue are queued according to sequence numbers, and are compressed and transmitted at a predetermined transmission rate. Queuing here means that packets are rearranged in sequence number order.

If the condition based on 1 / L_i is not satisfied, the packet is treated as a loss so that other packets do not continuously delay.

For the forward link, the supported data rates are 1/2, 1/4, and 1/8. Therefore, the forward link can theoretically handle up to eight frames of delay at one time. In the case of the reverse link, the delayed packet performs queuing according to the execution speed of the vocoder.

Hereinafter, a method for detecting a sequence of received packets will be described.

The base station and the base station controller maintain the following variables to detect the sequence of received packets.

N _RX : the largest sequence number among the sequence numbers of recently received packets.

-W [MAX_NUM_OF_OOS] or waiting set W: The sequence number of packets waiting to be received for the currently received packets to be in-order. The system must be able to store MAX_NUM_OF_OOS as much as . The concept corresponding to the in-order is out-of-sequence and is defined as follows.

In-order: when there are exactly j-i-1 received packets between received packets having a sequence i and j (i <j)

Out-of-sequence: a sequence number that violates the in-order condition among the sequence numbers of the received packets. In other words, if the out-of-sequence number is i, it is the sequence number of a packet for any integer k that has not yet been received at the time i + k is received and has not been removed from the system queue.

Here, assuming that a packet having a sequence number i is Pi, Pi assumes that time information to be transmitted is also included in the packet. _{P i-3, P i-} 2, P i-1 P i + 1, if the packet is received in the order of _{P i + 2, P i +} 3, P i + 1 is out of the received time-of- The sequence is detected and packets received after P _{i + 1} are queued to wait for Pi. At this time, when P _{i + k} (k: positive integer) is received, the following variables are defined to determine transmission of this packet.

Max Information Bit in Unit duration (Ψ_max): The maximum number of bits that can be transmitted during a specified unit duration. The specified time period can be set to 5ms, 10ms, 20ms, etc.

Len (Px): Number of information bits included in a packet Px having a sequence number x.

B (Px): The upper limit of the transmission time that must be observed to ensure the quality of service (QoS) of packet Px with sequence number x.

Since B (x) depends on the performance and algorithm of the vocoder, it is simply assumed that the time the packet is received + y (y is a constant).

According to the above definitions and assumptions, the operation to be performed by the system when P _{i + k} (k is a positive constant) is as follows.

Case 1: If the sequence number of the currently received packet is P _{i + k} and the previous out-of-sequence start packet (P _{i + 1} ) to the current packet is in-order and the condition of Equation 2 is In this case, the packet waiting for out-of-sequence resolution is treated as a loss and the packet from P _{i + 1} to P _{i + k} is compressed.

In Equation 1, α is a margin value determined by an operator.

Case 2; If the sequence number of the received packet is Pi (that is, Pi∈W), the packet is transmitted from i to the maximum value j (j <N _RX ) satisfying the in-order. In this case, when gating of each packet is referred to as G _k , the gating rate G _TX is expressed by Equation 3 below. Here, the gating rate means a frame rate at which the received packet is actually transmitted.

Where B (Px) is 1.

Case 3: If the sequence number of the received packet is greater than N _RX +1, another out-of-sequence occurs, so the sequence number is included in the set W.

In this case, the operations according to 1,2,3 are performed, and the states of the packets are checked and arranged at the end of each time interval for the packets stored by the current out-of-sequence. If the current time is Ti, first of all, if B (Px) of the packet Pxs in the queue is equal to or larger than Ti, obtain the minimum j satisfying Equation (4) below and transmit the Pj to Pk packets Packets smaller than j are removed from the queue. If the removed sequence number is in the set W, the sequence number is also removed from W.

As described above, when a plurality of packets are combined and transmitted in G _TX , the configuration of a 20ms frame follows the method proposed in IS-2000.

If retransmission is caused by delay of packets, the sum of gating rates of each packet must be less than 1 to adjust G _TX . That is, when the size of a packet that can be transmitted during one frame slot is P_frame, the sum of the packets to be retransmitted is expressed by Equation 5 below.

In Equation 5, P_t _i becomes the size of each subpacket, and accordingly, a gating rate to be used for transmission can be determined. If the above conditions are met, packets whose order is reversed by delay may be transmitted to the terminal through the forward wireless link. One more thing to consider is that for real-time packets, their arrival times must be constant. However, if one frame slot is a small frame such as a 5ms, 10ms or 20ms frame, the perceived call quality is guaranteed if the average transmission data rate within a certain period is guaranteed rather than the instant arrival time. If the time period is larger than the length of the frame slot, the average transmission rate during the period (T) when transmitted without delay is called M_norm, and the transmission data rate when transmitted by normal transmission or compression in one period is called R_i. It can be assumed that Equation 6 below is satisfied.

Therefore, the present invention can guarantee the quality of service without reversal or loss of packet order due to packet delay within a relatively large period.

2 is a diagram illustrating a packet transmission apparatus according to an embodiment of the present invention.

Here, the packet transmission device is provided in the base station.

Referring to FIG. 2, the reception queue 210 stores a packet received through the IP network 200. The sequence controller 220 manages the sequence number of the received packet and is responsible for detecting an out-of-sequence. When the out-of-sequence is detected, the sequence controller 220 detects the packet and stores the packet having the sequence number after the corresponding sequence in the reception queue 210. In addition, when the in-order packet is received, the packet multiplexer 240 directly transmits the received packet. A time stamp is recorded for the out-of-sequence detected packet, and then the sum of the lengths of the received in-order packets increases beyond the length to be transmitted at the full rate or exceeds the predetermined time interval. In this case, it no longer waits for a packet to make this sequence in-order, but transmits it in length.

The timing controller 230 provides a time signal at 1.25 ms and 20 ms intervals to the packet multiplexer 240 and the reception queue 210.

The packet multiplexer 240 generates and transmits a 20ms packet by using the packet stored in the reception queue 210 and the time information provided from the timing controller 230. If a packet having a length corresponding to the full rate is not received, a frame is transmitted using 20ms frame gating.

3 is a flowchart illustrating a method of transmitting a packet in a base station according to an embodiment of the present invention. The operation of FIG. 3 is performed by the sequence controller 220 shown in FIG. Hereinafter, a description will be given with reference to FIGS. 2 and 3.

In step 300, when the packet having the sequence number S is received, in step 310, a value obtained by adding 1 to the largest sequence number N among the sequence numbers of the packets received up to the previous time interval is compared.

If S is greater than N + 1, in step 320, S-1 to S-1 is added to a predetermined wait set W. In operation 323, the received packet is stored in a predetermined queue. In order to perform the same operation on the packet received in the next time interval, the process returns to step 310.

In step 310, if S is less than the N + 1, in step 330, it is determined whether the S belongs to the preset waiting set W. If the S does not belong to the waiting set W, this means that a packet having a sequence number consecutive with the sequence number S is not stored in the queue, and the received packet is stored in the reception queue 210 in step 335.

If the S belongs to the standby set, in step 333, the packet having the sequence number S to the packet having the sequence number consecutive to the S among the packets previously stored in a predetermined queue are transmitted to the terminal in sequence number order. do. That is, packets from the sequence S to the maximum sequence number j satisfying the above in-order are transmitted at a gating rate G _k . Thereafter, the process returns to step 310 to perform the same operation on the next time interval packet.

In the comparison of step 310, if S and N + 1 are the same, in step 340, it is determined whether the waiting set W is zero. If the waiting set W is 0, the packet received in the current time interval is a packet that does not cause an inverse array problem. In step 343, the packet is transmitted to the terminal according to the corresponding gating rate. If the wait set W is not 0 in step 340, there is a packet waiting for the packet received in the current time interval. In step 345, a sequence number j closest to the S among the packets waiting in a predetermined queue is waited. Extract from set W. In operation 350, the sum of packet lengths from the packet having the sequence number j to the packet having the sequence number S is compared with a preset reference value. Herein, the preset reference value is determined by Equation 2 to Equation 4.

If the sum of the packet lengths is greater than the reference value, in step 365, the packet received in the current time interval is stored in the reception queue 210.

If the sum of the packet lengths is smaller than the reference value, in step 355, packets from the sequence number j to the packets with the sequence number S are compressed in sequence order and transmitted at a gating rate G _k .

Thereafter, in step 360, the value of N is increased by 1 and the process returns to step 310 to perform the same operation on the packet received in the next time interval.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, the present invention has the advantage of solving the problem of packet rearrangement in the base station system based on the IP network. In addition, the present invention has the advantage of solving the packet delay problem in the base station system based on the IP network.

Claims (7)

A mobile communication system having a base station and a base station control unit connected to the base station through an internet protocol network, the method for transmitting packets received from the base station control unit by the base station to the terminal, Detecting an inverse arrangement of the received packet using a sequence number and a reception order of the received packet in a current time interval; If the reversed arrangement is detected, storing the received packet in a predetermined queue for a predetermined time period; And when the predetermined time interval elapses, compressing the packets having consecutive sequence numbers among the packets stored in the queue and transmitting the compressed packets to the terminal. In the mobile communication system having a base station and a base station control unit connected to the base station through an internet protocol network, a method for transmitting a packet received from the base station control unit by the base station to a predetermined terminal, Comparing the sequence number S of the packet received in the current time interval with the largest sequence number N of the sequence numbers of the packets received up to the previous time interval plus one, where S and N are integers, If S is greater than (N + 1), adding S-1 to a predetermined wait set from sequence number N, and And storing the packet received in the current time interval in a predetermined queue and setting the largest sequence number of the sequence numbers of the packets received up to the previous time interval to S. The method of claim 2, If S is smaller than (N + 1), determining whether S belongs to a preset waiting set; If the S belongs to the standby set, transmitting a packet having a sequence number S to a packet having a sequence number consecutive to the S among packets stored in a predetermined queue to the terminal in sequence number order. Said method comprising: a. The method of claim 2, If the S and the (N + 1) is the same, comparing the sum of the packet length from the packet having the sequence number closest to the S to the packet having the sequence number S among the packets waiting in a predetermined queue with a preset reference value and, If the sum of the packet lengths is smaller than the reference value, transmitting a packet having a sequence number closest to S to a packet having a sequence number S to the terminal in sequence number order; Way. The method of claim 4, wherein after transmitting the packets to the terminal, And increasing the largest sequence number of the sequence numbers of the packets received by the previous time interval by one. The method of claim 4, wherein If the sum of the packet lengths is greater than the reference value, storing the packet having the sequence number S in a predetermined queue. In a mobile communication system having a base station and a base station control unit connected to the base station through an internet protocol network, the base station apparatus for transmitting packets received from the base station control unit to the terminal, A receive queue that stores received packets When the reverse sequence of the received packet is detected using the sequence number and the reception order of the received packet in the current time interval, the received packet is stored in the reception queue for a predetermined time interval, and when the predetermined time interval has elapsed, A sequence control unit for rearranging packets stored in the reception queue according to sequence numbers; And a packet multiplex for generating a frame to be transmitted using the rearranged packets and time information provided from a timing controller.