METHOD FOR TRANSMITTING PACKET IN WIRELESS TELECOMMUNICATION TERMINAL

Technical Field

[1] The present invention relates to a method for transmitting packets in a wireless telecommunication terminal; and, more particularly, to a packet transmitting method for transmitting packets to a base station by controlling a transmission interval on a slot basis according to a channel environment in a wireless telecommunication terminal using a slotted Aloha random access control method and an automatic repeat request (ARQ) error correction method.

[2]

Background Art

[3] A wireless telecommunication terminal of the present invention means a mobile wireless telecommunication terminal which can transmit/receive speech, text and image data through wireless telecommunication such as a mobile communication terminal, a Personal Communication Service (PCS) terminal, a Personal Digital Assistant (PDA), a smart phone, an International Mobile Telecommunication-2000 (IMT-2000) terminal, and a wireless Local Area Network (LAN) terminal.

[4] Also, a wireless telecommunication system of the present invention includes a geostationary orbit (GEO) satellite communication system, which transmits an upward link packet by integrating a slotted Aloha random access control method and an automatic repeat request (ARQ) error correction method and has long round trip time, and a terrestrial mobile communication system forming a cell based on a base station. Herein, each system includes a wireless telecommunication terminal operated in a method corresponding to the system.

[5] A third-generation mobile communication system such as a Wideband-Code

Division Multiple Access (W-CDMA) system of the Third- Generation Partnership Proj ect (3GPP) and Code Division Multiple Access (CDMA) 2000 system of the Third- Generation Partnership Project 2 (3GPP2) for providing diverse multimedia services including a speech service and a packet service provides a method forming a wireless link by integrating a wireless link forming method of a circuit switching method and a packet switching method, which is suitable for a packet service. Herein, when the wireless link is formed by the packet switching method, there is a random access control method by which a user terminal, i.e., the wireless telecommunication terminal, transmits the packet to the base station.

[6] The random access control method is a technology included in a 2 ⁿ layer of seven

layers in Open System Interconnection (OSI), and controls that many users access to one media. Examples of the random access control include Aloha, slotted Aloha, reserved Aloha, Carrier Sensing Multiple Access/Collision Detection (CSMA/CD), and Carrier Sensing Multiple Access/Collision Avoidance (CSMA/CA) are included and they are selectively used based on the characteristics of each system.

[7] Meanwhile, a method for resolving the problem of a transmission error along with the random access control method includes Forward Error Correction (FEC) and the ARQ. The FEC is a method for helping error correction on a receiving part by using an error correction code and the ARQ is a method that a transmitting part retransmits an erroneous packet.

[8] The ARQ error correction method includes stop and wait ARQ, go back n ARQ, selective ARQ and hybrid ARQ. The FEC or the ARQ error correction method is also selectively used based on the characteristics of each system.

[9] Meanwhile, a user terminal uses the slotted Aloha random access control method in a third-generation (3G) mobile communication system to transmit a packet to the base station, and uses the stop and wait ARQ method to remove an error caused in a reception packet.

[10] Since round trip time between the user terminal and the base station is not long in the terrestrial mobile communication system, the service can be provided through the simple slotted Aloha random access control method and the stop and wait ARQ method.

[11] When a region controlled by the base station controls a wide region, are generally used since Carrier Sensing (CS) is basically not possible. Herein, when the round trip time is long, the selective ARQ error correction method is used in addition to the slotted Aloha random access control method or the reserved Aloha random access control method.

[12] The wireless telecommunication terminal continuously transmits packets to be transmitted to the base station in the wireless telecommunication system integrating the conventional slotted Aloha random access control method and ARQ error correction method.

[13] As shown in Fig. 1, since the base station receives packets from other wireless telecommunication terminals and packets from the wireless telecommunication terminals collide with each other, there is a problem that a probability of normal packet reception is very low.

[14] When the above method is described in detail with reference to Fig. 1, a first wireless telecommunication terminal continuously transmits Pl-I, P 1-2 and P 1-3 packets to the base station.

[15] Also, a second wireless telecommunication terminal continuously transmits P2-1,

P2-2, P2-3 and P2-4 packets to the base station at a transmission time of the P 1-2 packet of a first wireless telecommunication terminal.

[16] Also, a third wireless telecommunication terminal continuously transmits P3-1,

P3-2 and P3-3 packets to the base station at transmission time of the P2-3 packet of the second wireless telecommunication terminal.

[17] Therefore, it can be seen that there is a problem that the packets collide with each due to same packet transmission time and only the Pl-I packet and the P3-3 packet are normally received from the first wireless telecommunication terminal and from the third wireless telecommunication terminal, respectively.

[18]

Disclosure of Invention Technical Problem

[19] It is, therefore, an object of the present invention to provide a packet transmitting method for decreasing a packet collision probability between packets transmitted from other wireless telecommunication terminals and increasing packet transmission efficiency by controlling a packet transmission interval in a wireless telecommunication terminal according to a channel environment when the packet is transmitted from the wireless telecommunication terminal, which uses a slotted Aloha random access control method and an automatic repeat request (ARQ) error correction method, to a base station.

[20] Other objects and advantages of the invention will be understood by the following description and become more apparent from the embodiments in accordance with the present invention, which is set forth hereinafter. It will be also apparent that objects and aspects of the invention can be embodied easily by the means defined in the claims and combinations thereof.

[21]

Technical Solution

[22] In accordance with one aspect of the present invention, there is provided a method for transmitting packets in a wireless telecommunication terminal, including the steps of: a) storing upward link transmission packets in an automatic repeat request (ARQ) buffer; b) transmitting the packets stored in the ARQ buffer at a first slot interval; c) performing packet retransmission or additional packet transmission based on feedback information for the transmitted packets; and d) transmitting additional upward link transmission packets at a second slot interval when abnormal feedback information is received for the transmitted packets predetermined times consecutively.

[23]

Advantageous Effects

[24] The present invention can decrease a packet collision probability between packets transmitted from other wireless telecommunication terminals and increase packet transmission efficiency by controlling a packet transmission interval based on a channel environment when the packet is transmitted from the wireless telecommunication terminal, which uses a slotted Aloha random access control method and an automatic repeat request (ARQ) error correction method, to a base station.

Brief Description of the Drawings

[25] The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:

[26] Fig. 1 is a diagram showing a packet transmission result in a conventional wireless telecommunication terminal;

[27] Fig. 2 is a diagram showing a wireless telecommunication system to which the present invention is applied;

[28] Fig. 3 is a diagram showing a packet transmission process in a conventional wireless telecommunication terminal in accordance with an embodiment of the present invention;

[29] Fig. 4 is a diagram describing a packet transmission result in the wireless telecommunication terminal in accordance with the embodiment of the present invention;

[30] Fig. 5 is a flowchart describing a packet transmitting method in a wireless telecommunication terminal in accordance with an embodiment of the present invention; and

[31] Fig. 6 is a flowchart showing a packet transmission process when the terminal is operated in a delay transmission mode in accordance with an embodiment of the present invention. Best Mode for Carrying Out the Invention

[32] Other objects and advantages of the present invention will become apparent from the following description of the embodiments with reference to the accompanying drawings. Therefore, those skilled in the art that the present invention is included can embody the technological concept and scope of the invention easily. In addition, if it is considered that detailed description on prior art may blur the points of the present invention, the detailed description will not be provided herein. The preferred embodiments of the present invention will be described in detail hereinafter with reference to the attached drawings.

[33] Fig. 2 is a diagram showing a wireless telecommunication system to which the present invention is applied.

[34] As shown in Fig. 2, the wireless telecommunication system of the present invention includes a base station 21, e.g., a satellite, for receiving packets from a plurality of

wireless telecommunication terminals 22 through an upward link channel and the wireless telecommunication terminals 22 for transmitting packets to the base station 21 by controlling a transmission interval of the packets, i.e., a slot basis based on a channel environment.

[35] Herein, when a packet transmitting process in a wireless telecommunication terminal 22 is described in detail with reference to Fig. 3, the wireless telecommunication terminal 22 using a slotted Aloha random access control method and an ARQ error correction method includes an ARQ buffer such as a selective ARQ buffer having a predetermined packet size, e.g., 5 packets. Herein, the wireless telecommunication terminal 22 can transmit the packets as many as they can be stored in the ARQ buffer without feedback information from the base station.

[36] Subsequently, the wireless telecommunication terminal 22 transmits packets 1 to 5 to the base station 21, e.g., a satellite. When feedback information from the satellite 21 is normal, i.e., ACK, the packet is deleted from the ARQ buffer, and when the feedback information is abnormal, i.e., NACK, the packet is retransmitted after waiting for a predetermined waiting time. Herein, when there are more packets to be transmitted to the base station in the upper layer, the wireless telecommunication terminal 22 stores the packets in the ARQ buffer for transmission.

[37] Meanwhile, when the number of the packets stored in the ARQ buffer is more than two, a packet collision probability can be calculated to consider how sequential packet transmission affects the packet collision probability to continuously transmit the packet.

[38] Since an event that each wireless telecommunication terminal transmits the packet is an independent event, the packet collision probability can be obtained by subtracting a probability that all wireless telecommunication terminals do not transmit packets, and a probability that only one wireless telecommunication terminal transmits packets from the entire probability, i.e., 1. That is described in Equation 1.

[39]

[40]

\ - (i - py - p(\ - pγ- ¹

Eq. 1 [41] [42] where P denotes a probability that the wireless telecommunication terminals transmit packets; and N denotes the number of the wireless telecommunication terminals. [43] When a probability that a wireless telecommunication terminal transmitting one

packet transmits a packet in the next slot is an independent event, a probability that packets collide twice consecutively can be obtained by multiplying the probabilities.

Thus, it becomes a square of the probability that the first packet collision event occurs.

This is as shown in Equation 2. [44] [45]

[l - (l - py - p(i - p)* ^Λ γ

Eq. 2

[46]

[47]

[48] However, when a packet is actually transmitted from the wireless telecommunication terminal, a plurality of Media Access Control (MAC) layer packets should be transmitted to transmit the packet generated in an application layer. Accordingly, a probability that the wireless telecommunication terminal transmitting one packet is to transmit a packet in the next slot becomes not an independent event but a dependent event.

[49] Therefore, the probability that packet collision occurs twice consecutively is described as the following Equation 3.

[50]

[51]

[l - (\ - P) ^{N m} (l - P'r - {(N - m)P(l -P) ^{N l m} - (l - P'y +m -P'(l -P) ^{N m} {l -P') ^{m l} }/N] X (I - (I -PY -P(l - P) ^{N 1} )

Eq. 3 [52] [53] where

P' is a probability that the wireless telecommunication terminal transmitting a packet in a previous slot will again transmit a packet in the current slot; and m is the number of the wireless telecommunication terminals transmitting packets in the previous slot. Herein, since

P' has a larger value than the P, a probability of the Equation 3 is smaller than a probability of the Equation 2. However, when

, the probability of the Equation 3 is the same as the probability of the Equation 2. [54] Therefore, when continuous packets are transmitted by satisfying that

, the present invention has the

P' have a similar probability to the Equation 2.

[55] Fig. 4 is a diagram describing a packet transmission result in the wireless telecommunication terminal in accordance with the embodiment of the present invention.

[56] As shown in Fig. 4, when there are a plurality of packets to be transmitted, a slot to be transmitted in the next packet is arbitrarily determined after one packet is transmitted instead of continuously transmitting the packets.

[57] Herein, a slot to be transmitted in the next packet is determined by selecting a certain value between 1 and a value dividing an average round trip time T, which is formed on a slot basis, by a size B of an ARQ buffer, which is formed on a slot basis. That is, the slot to be transmitted in the next packet is determined by selecting a certain integer value between 1 and T/B.

[58] The packets are transmitted at a low packet collision probability by making

P ¹ and P be close to independent events from each other. [59] In Fig. 4, a first wireless telecommunication terminal transmits Pl-I, Pl-2 and Pl-3 packets to the base station at a predetermined slot interval. [60] Also, a second wireless telecommunication terminal transmits P2-1, P2-2, P2-3 and

P2-4 packets to the base station at a predetermined slot interval. [61] Also, a third wireless telecommunication terminal transmits P3-1, P3-2s and P3-3 packets to the base station at a predetermined slot interval. [62] Herein, although the satellite do not receive the Pl-I and P3-3 packets due to the collision of the Pl-I packet from the first wireless telecommunication terminal and the

P3-3 packet from the third wireless telecommunication terminal, the satellite normally receives the other packets.

[63] Fig. 5 is a flowchart describing a packet transmitting method in a wireless telecommunication terminal in accordance with an embodiment of the present invention. [64] It is checked at step S501 whether packets to be transmitted to the base station exist in the upper layer, i.e., a layer on top of the MAC. When there is no packet to be transmitted, the logic flow ends. [65] As a check result of the step S501, when there are packets to be transmitted, it is checked how many packets there are to be transmitted in the MAC, and the packets to be transmitted are inputted into the ARQ buffer sequentially at step S502.

[66] At step S503, one packet is transmitted based on the sequence the packets are inputted into the ARQ buffer.

[67] It is checked at step S504 whether there are remaining packets to be transmitted in the ARQ buffer.

[68] As a check result of the step S504, when there are packets to be transmitted, one packet after a predetermined number R of the slots is transmitted to the base station at step S505, and the logic flow goes to the step S504. Herein, R is a certain integer value between 1 and TVB.

[69] As a check result of the step S504, when there is no packet to be transmitted, feedback information from the base station is checked at step S506.

[70] When it is turned out at the step S506, the feedback information is an ACK signal indicating that the base station has normally received the feedback information, it is checked at step S507 whether there are packets to be additionally transmitted exist in the upper layer. When there are the packets to be additionally transmitted, packets receiving the ACK are removed from the ARQ buffer and the packets to be additionally transmitted are inputted into the ARQ buffer at step S508. Subsequently, the logic flow goes to the step S503.

[71] Meanwhile, as a check result of the step S507, when there is no packet to be transmitted in the upper layer, it is checked at step S509 whether there are packets to be transmitted in the ARQ buffer. When there are packets to be transmitted, the logic flow goes to the step S506. When there is no packet to be transmitted in the ARQ buffer, the logic flow ends. Herein, transmission completion means a condition that feedback information, i.e., the ACK signal or the NACK signal, is transmitted from the base station with respect to the packet transmitted to the base station.

[72] Meanwhile, when it is turned out at the step S506 that the feedback information is a

NACK signal indicating that the base station does not normally receive the packets, the packet having an error is retransmitted after waiting for a predetermined time, i.e., after random backoff, through the slot Aloha method at step S510.

[73] It is checked at step S511 whether the NACK signals are transmitted from the base station in predetermined times consecutively. Herein, the predetermined number may be three times.

[74] As a check result of the step S511, when the NACK signals are not transmitted from the base station consecutively predetermined times, the logic flow goes to the step S506. When the NACK signals are transmitted consecutively predetermined times, the logic flow goes to a delay transmission mode.

[75] Herein, the delay transmission mode will be described in detail with reference to

Fig. 6.

[76] As shown in Fig. 6, it is checked whether packets to be transmitted exist in the

ARQ buffer when the wireless telecommunication terminal enters the delay transmission mode at step S610.

[77] As a check result of the step S610, when there are packets to be transmitted, one packet after an

R' slot is transmitted at step S620 and the logic flow goes to the step S610. Herein,

R ¹ is a certain integer between k*T/2B and k*T/B, and the k is a certain integer, which is determined according to the system.

[78] Meanwhile, when it is turned out that there is no packet to be transmitted in the step

S610, feedback information from the base station is checked at step S630.

[79] When it is turned out at the step S630 that the feedback information is an ACK signal indicating that the base station has received the packets normally, it is checked at step S640 whether there are packets to be additionally transmitted in the upper layer. When there are packets to be additionally transmitted, the packets with the ACKs are removed from the ARQ buffer, and the packets to be additionally transmitted are inputted into the ARQ buffer at step S650. Thus, one packet after the

R' slots is transmitted at step S660.

[80] When it is turned out at the step S630 that the feedback information is a NACK signal indicating that the base station has not received the packets normally, a packet with an error is retransmitted after random backoff.

[81] It is checked at step S670 whether the transmitted packet have got the ACKs without a predetermined number of NACKs. Herein, the predetermined number means the size of the ARQ buffer, i.e., the number of packets.

[82] When it is turned out that the wireless telecommunication terminal has received receives the ACKs for the transmitted packets without the predetermined number of NACKs, the logic flow goes to the step S504 of Fig. 5 after ending the delay transmission mode and subsequent processes are performed. When the wireless telecommunication terminal does not receive ACKs for the packets, the logic flow goes to the step S610 and subsequent processes are performed.

[83] When it is turned out at the step S640 that there is no packet to be transmitted in the upper layer, it is checked at step S680 whether there are packets to be transmitted in the ARQ buffer. When there are packets to be transmitted in the ARQ buffer, the logic flow goes to the step S630. Otherwise, the logic flow ends. Herein, transmission completion means a condition that the feedback information, i.e., the ACK signal or the NACK signal, is transmitted from the base station with respect to the packet

transmitted to the base station.

[84] In short, Fig. 6 shows a process for preventing packets from wireless telecommunication terminals from colliding with each other by entering the delay transmission mode and transmitting the packets at an interval of

R' slots when the packets are not normally transmitted although the packets are transmitted at the interval of R slots. Herein, the

R' slot interval is longer than the R slot interval. It means that the transmission time interval between packets becomes longer.

[85] When a channel environment is improved later and the wireless telecommunication terminal receives the ACKs for the transmitted packets without the predetermined number of NACKs, it transmits packets at the R slot interval again.

[86] Meanwhile, when the wireless telecommunication terminal of the present invention is operated in the delay transmission mode and receives NACKs three times consecutively, it can modify the k value into a larger value. Therefore, when the wireless telecommunication terminal receives three NACKs in series in the delay transmission mode, the k value becomes larger and the transmission rate can fall down to a level similar to the transmission rate of the stop and wait ARQ method where only one packet is transmitted for round trip time. Herein, when the K value is larger than the round trip time, the present invention can be operated in the stop and wait ARQ method to prevent the K value from infinitely getting larger.

[87] As described in detail, the technology of the present invention can be realized as a program and stored in a computer-readable recording medium, such as CD-ROM, RAM, ROM, a floppy disk, a hard disk and a magneto-optical disk. Since the process can be easily implemented by those skilled in the art, further description will not be provided herein.

[88] The present application contains subject matter related to Korean patent application

No. 2005-0019695, filed in the Korean Intellectual Property Office on March 9, 2005, the entire contents of which are incorporated herein by reference.

[89] While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.