SYSTEM AND METHOD FOR OPTIMIZING DATA TRANSMISSION

OVER AN AIRLINK

Field of the Invention

The present invention is related to the field of data transmission in cellular networks. Specifically the invention relates to a system and method for optimizing the data transmission over an airlink.

Background of the Invention

Recently, the use of mobile devices over the world has increased dramatically. In every day life, people often use their mobile devices, such as PDAs (Personal Digital Assistants) and cellular phones instead of their PCs (Personal Computers). For example, more and more users play games on their mobile devices putting aside their PlayStations ^® , PCs and Laptops.

One of the problems faced by video data providers to a cellular system is caused by the quality of the airlink between their server and the end user's device. The video content is transmitted from the provider's server to the first base station in relatively large packets. At the base station the packets are fragmented into subpackets according to the size of the maximum transmission unit (MTU) of the system. The MTU for the system is dependent on many factors, some fixed and related to the system hardware and others highly variable, such as weather and distance between base station (stations) and the end device. The worse the conditions of the variable factors are, the shorter the subpacket that can be transmitted. Therefore the MTU for a cellular system does not have a fixed value. When the subpackets arrive at the end user's device they are reconstructed before being raised to the application layer for display to the user. Cellular systems operate with a Eeal Time Protocol (RTP), which is based on use of a UDP

protocol, which requires less processing and is much faster than the transmission control internet' protocol (TCP/IP). This is because according to the TCP/IP protocol if one. or the subpackets does not arrive at the end device, then instructions are sent back to the server of the service provider to resend the lost packet. In contrast to this attempt to resend lost data, for video streaming and similar applications there is simply no time to resend lost packets. Accordingly with the UDP protocol, if a subpacket is lost then a cyclic redundancy check (CRC) error is generated in the end user's device and the entire packet can not be reconstructed and therefore is dropped in its entirety from the data stream that is passed to the application level. If subpackets are lost very infrequently during the time the video is being played, then the loss of the associated packets goes unnoticed; however, if the loss of packets occurs frequently, then the quality of the presentation is severely affected. The term "quality of the airlink" is related to the severity of the variable factors that influence the size of the MTU.

It is known that in order to provide high presentation video quality and maximum efficiency of the system the MTU should be kept as large as possible. A major problem is that, the lower the quality of the airlink, the smaller the MTU, i.e. the smaller the subpacket size that can be sent from the base station to the end user's device. Therefore each original packet of a given size must be fragmented into more subpackets. The larger the number of subpackets being transmitted over the airlink the greater the chance that one of them will not arrive at its destination and therefore the chance that large amounts of information contained in the original packet will not be displayed on the end user's device.

It is an object of the present invention to present a method and system for overcoming this deficiency of the prior art by providing a method and system for optimizing the transmission of data over an airlink.

Further purposes and advantages of this invention will appear as the description proceeds.

Summary of the Invention

In a first aspect the invention is a system for optimizing data transmission over an airlink. The system comprises:

(a) a data provider server comprising a packet formation unit and a transmitter unit;

(b) a cellular services provider server linked via a communication link to the data provider server;

(c) an end user's device comprising a modem, an application layer, and an internal communication link; and

(d) one or more base stations defining the airlink between the transmitter unit and the modem.

The system of the invention is characterized in that the data provider server comprises a quality check unit, which determines the value of the maximum transmission unit (MTU) of the airlink and instructs the packet formation unit to divide the data into packets whose size is essentially equal to the MTU. The quality check unit can determine the MTU and update the length of the packet size either on command, periodically, or continuously.

The system of the invention is suitable for use when the data comprises video data and specifically when the video data, which may be a game, is streaming in real time to the end user.

In another aspect the invention is a method for optimizing data transmission over an airlink. The method of the invention comprises: (a) providing a system comprising:

(i) a data provider server comprising a packet formation unit and a transmitter unit and a quality check unit; (ii) a cellular services provider server linked via a communication link to the data provider server; (iii) an end user's device comprising a modem, an application layer, and an internal communication link; and (iv) one or more base stations defining the airlink between the transmission unit and the modem;

(b) activating the quality check unit to send a series of packets of varying size over the airlink to the modem;

(c) using signals returned from the modem over the airlink to the quality check unit to determine the maximum transmission unit (MTU) of the airlink; and

(d) instructing the packet formation unit to divide the data into packets whose size is essentially equal to the MTU.

According to the method of the invention, the quality check unit can determine the MTU and update the length of the packet size either on command, periodically, or continuously.

The method of the invention is suitable for use when the data comprises video data and specifically when the video data, which may be a game, is streaming in real time to the end user.

All the above and other characteristics and advantages of the invention will be further understood through the following illustrative and non-limitative description of preferred embodiments thereof, with reference to the appended drawings.

Brief Description of the Drawings

- Fig. 1 schematically shows the prior art system for transmitting data from the games provider to the end user device; and

- Fig. 2 schematically shows the system of the present invention for transmitting data from the games provider to the end user device.

Detailed Description of Preferred Embodiments

The present invention recognizes the fact that there it is not possible to entirely eliminate the occasional random loss of subpackets that are transmitted over an airlink between a video data provider server and the end user. As mentioned hereinabove, the loss of a subpacket is accompanied by the loss of the entire packet from which the subpacket originated. The method of the invention limits the amount of lost information by adjusting the size of the original packet to be equal to the MTU of the airlink. In this way the packets do not generally have to be fragmented and, if one packet is lost, only the information in that packet never arrives at the application level of the end user's device.

Although the following description is presented with specific reference to video data, it will be appreciated by the skilled person that any type of streaming video or other application including interactive games that can be, or is desired to be transmitted to a mobile device, will benefit from the present invention and is encompassed within it.

Fig. 1 schematically shows the prior art system for transmitting data from the video data provider 10 to the end user device 40 via the base station 20 of cellular services provider 30. End user device 40 is a mobile device, e.g. a PDA (Personal Digital Assistant) or a cellular phone. For convenience the server 12 of the video data provider 10 is shown in the figures as separate from the server 32 of cellular services provider 30 however this is not a

necessary configuration and the cellular services provider could also supply video data through its own server.

The user wishing to play a video connects to Video Data Server 12 and selects the desired video by means of his mobile device's keypad. During playing of the video, the data stream is processed by the packet formation unit 14, which divides the streaming information into packets 52 of a predetermined fixed size, which are transferred via data link 19 to transmitter 15 and then transmitted to base station 20. At the base station, each packet 52 is fragmented into a number of subpackets 52' depending upon the MTU of the airlink between base station 20 and end user device 40. The value of the MTU is determined by sending test signals either from the cellular services provider server 32 or a server located at the base station 20. In any case, subpackets 52' are relayed from base station 20 to modem 42. If all of the subpackets 52' associated with a given packet 52 arrive safely at modem 42 within the allotted time period, then entire packet 52 is reconstructed in the end user's device and transmitted via internal communications link 46 to the application layer 44 to be displayed to the user. Arrows 54 represent information and commands related to the video data, which are sent back and forth from device 40 to server 32 and vice versa. Arrow 50 represents a communication link between the cellular services provider server 32 and the video data provider server 12.

Fig. 2 schematically shows the system of the present invention for transmitting data from the games provider 10 to the end user device 40. Elements of the system of the present invention that are identical to those of the prior art shown in Fig. 1 are identified using the same reference numerals. The major difference between the present invention and the prior art is the addition of a quality check unit 16 to the video data server 12. Quality check unit 16 has two major functions: firstly it sends a stream of

packets 60 to modem 42 and receives returning signals 60' from the modem 42 and secondly, based on the information contained in packets 60' it determines the value of the packet size 62 to be formed by packet formation unit 14 and transmitted by transmitter unit 15 to base station 20.

The packets 60 sent by quality check unit 16 are not all the same, but are sent as a series of packets having gradually increasing (or decreasing) size. The signals 60' from the modem 42 are indicative of if a packet of a known size has been successfully transferred by the airlink from game server 12 via ground station 20, to modem 42 in its entirety in the allotted time period. The largest sized packet 60 that can be successfully transferred in the allotted time period at any given moment in time is the current MTU of the airlink. The quality check unit 16 transfers the determined value of the MTU to packet formation unit 14 via link 18, which transfers the packets 60 to transmitter 15 via link 19. Since video data server 12 adjusts the length of the packets and transmits the data as packets having length essentially equal to the MTU of the system, they will generally not be fragmented at the base station, except in rare instances when a sudden deterioration of the quality of the air link occurs before it is detected by the quality check unit.

Quality check unit 16 can be operated in several modes: on command, periodically, or continually. Closely spaced or continuous operation is preferred because this allows determination of the current MTU a parameter that can change rapidly under certain conditions, e.g. if the end user device is in a vehicle traveling at high speed. Thus the system of the invention allows for instantaneous updating of the packet size sent by the games server. This is important in real cellular networks, which unlike the schematic system shown in the figures, are comprised of a large network of base stations, which are combined in varying numbers and configurations to

define a continuously changing airlink by which the data is transferred from the games server to the end user.

Thus the system of the invention allows a method for optimizing the transmission of the data over the airlink by making the packet size transmitted by the server essentially equal to the real time value of the MTU of the airlink. The improvement over the prior art is in two areas. Firstly the time and processing power necessary to fragment and reconstruct the packets is saved and secondly, in the event that a packet is lost, the total amount of information that does not arrive at the application layer of the end user device is minimized, since the size of the packets 62 sent from the video server to the first base station according to the present invention will generally be much smaller than those in the prior art.

Theoretically the above advantages could be achieved by using the prior art method and arbitrarily limiting the size of the packets transmitted by packet formation and transmission unit 14. The problem with this approach is that in order to be sure that no fragmentation would take place, very short packets would be transmitted, which because of the space between packets would be very inefficient. Additionally considerably more processing capability would have to be provided at the end users device in order to recreate a coherent flow of the video data from a stream of small packets. As mentioned previously, the goal of optimal use of the airlink is achieved by using the largest packets that can pass through the airlink without having to be fragmented.

Although embodiments of the invention have been described by way of illustration, it will be understood that the invention may be carried out with many variations, modifications, and adaptations, without exceeding the scope of the claims.