Electrical computers and digital processing systems: multicomput – Computer network managing – Network resource allocating
Reexamination Certificate
1998-08-07
2002-03-26
Follansbee, John A. (Department: 2154)
Electrical computers and digital processing systems: multicomput
Computer network managing
Network resource allocating
C709S241000, C709S241000, C709S201000, C709S225000, C709S229000, C714S746000, C714S748000
Reexamination Certificate
active
06363425
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for communicating forward error correction (FEC) encoded packet information in a digital telecommunications system, wherein the amount of communication resources is variable for each transmission of information and wherein erroneously received packets may be selectively re-transmitted. Through the inventive method the estimated total time for communicating packets from a transmitting party to a receiving party is minimised.
The invention is also directed to an arrangement for performing the above mentioned method.
The invention is particularly suitable for use in a GPRS system (GPRS=General Packet Radio Service), standardised within GSM (GSM=Global System for Mobile telecommunication).
STATE OF THE ART
A packet is defined as an amount of information, which can be sent from a transmitting party to a receiving party over one or more communication resources. A communication resource is typically a channel and may, for instance, be a particular carrier frequency in a FDMA system (FDMA=Frequency Division Multiple Access), a particular time slot in a TDMA system (TDMA =Time Division Multiple Access), a particular code or signature sequence in a CDMA system (CDMA=Code Division Multiple Access), a particular sub-channel carrier in an OFDM system (OFDM=Orthogonal Frequency Division Multiplex) or a certain wavelength in a WDMA system (Wavelength Division Multiple Access). Normally, each packet is segmented into a number of data blocks. A very short packet may be fitted into a single data block, but in most cases a packet corresponds to two or more data blocks.
A packet can further be defined differently on different logical levels in a telecommunications system. Hence, what is one packet on a first logical level may be considered to be several packets on a second logical level. For instance in GPRS higher level packets are usually split into two or more so called LLC frames (LLC=Link Layer Control) before transmission across the air interface. With regard to this invention such LLC frames and corresponding sub-packets are likewise considered as packets.
Moreover, before a data block is sent, redundancy symbols may be included in the data block. The redundancy symbols are correlated with the payload information in the data block, so that a limited deterioration of the data during the transmission may be corrected by the receiving party. The process of adding redundancy symbols is called forward error correction coding and is carried out in accordance with a coding scheme.
The more redundancy symbols that are included, the more transmission deterioration can be tolerated. However, the size of a data block is constant. Thus, a large amount of redundancy results in many data blocks, which of course, gives a longer transmission time than if no redundancy symbols had been added. On the other hand, a small amount of redundancy increases the probability for data block re-transmissions, due to the occurrence of unrecoverable errors during the transmission. A large number of such re-transmissions definitely leads to a long total transmission time for the information contained in the packet.
From the document U.S. Pat. No. 5,526,399 is known as method for transmitting information in a radio communications system, whereby a combination of Forward Error Correction (FEC) and Automatic Repeat reQuest (ARQ) can be used to achieve a good transmission efficiency. The number of repeat communication requests per time interval is monitored and if this number is greater than a first value, then the amount of forward error correction is increased. If instead the number of repeat communication requests per time interval is smaller than a second value the amount of forward error correction is decreased.
A method for non-transparent data transmission is disclosed in WO, A1, 96/36146. The document describes how channel coding is employed on information, which is transmitted from a first to a second party. The quality of the non-transparent connection is monitored and if the quality drops to a certain level, then the channel coding is changed to a more efficient one. In order to compensate for a lower transmission rate per channel for the payload information, during the use of the more efficient channel coding, the allocated channel capacity is simultaneously increased.
The document U.S. Pat. No. 4,939,731 discloses another example of a method, in which an increasing number of repeat communication requests is overcome by expanding the amount of redundancy in each data block in relation to the payload information. Here however, there is no compensation for the lowered payload transmission rate.
In the article “Performance of the Burst-Level ARQ Error Protection Scheme in an Indoor Mobile Radio Environment”, IEEE Transactions on Vehicular Technology, No. 1, March 1994, pp 1412-1416, E. Malkamäki presents a burst-level ARQ scheme as an alternative to conventional FEC-encoding for speech transmission, where redundancy is sent only when required.
All these methods, in one way or another, adaptively set the relationship between the amount of forward error correction and the number of data block re-transmissions per time interval in order to achieve an efficient transfer of information from a transmitting party to a receiving party.
Nevertheless, none of the previously known methods a priori aims at minimising the total transmission time for the information. Instead, each method tentatively varies the amount of forward error correction to a level, which for the moment gives a satisfying throughput of the payload information.
DISCLOSURE OF THE INVENTION
An object of the present invention is thus to minimise the average transmission time for payload information in a telecommunications system.
Another object of the invention is to utilise the air interface of a radio communications system as efficiently as possible, when communicating packet information in such a system.
A further object of the invention is to provide a reliable transmission of packet information in an environment, where the transmission conditions are unstable.
These objects are met by the present invention by a priori minimising the estimated transmission time for each packet communicated through the system. Generally, the available communication resources have quite varying transmission quality. It is therefore important to make a wise selection from these resources. Depending on how many communication resources that have sufficiently high transmission quality and the quality variance between these resources, one particular coding scheme is the optimal scheme to use. Thus, it is crucial which coding scheme that is chosen in combination with the allocated communication resources. Moreover, the distribution of encoded data blocks over the allocated communication resources is a parameter, which must be optimised.
According to one embodiment of the present invention there is provided a method for communicating packet information in a digital telecommunications system. The method presupposes that the amount of communication resources is variable for each packet and that the system operates in accordance with a protocol, which admits selective re-transmission of erroneously received packets. Furthermore, it must be possible to forward error correction encode the payload information via one of at least two different coding schemes, before sending the information to a receiving party.
The method finds, for each packet and set of available communication resources, a combination of a coding scheme and a subset of resources, which minimises an estimated transmission time for the information contained in the packet. By transmission time is meant, the time from start of transmission of an initial data block in the packet, to reception of a positive acknowledgement message for the packet, i.e. including any possible intermediate delays and waiting times. Naturally, the choice of coding scheme and subset of resources may also be based upon additional premises, on
H{umlaut over (oo)}k Mikael
Nyström Johan
El-Hady Nabil
Follansbee John A.
Telefonaktiebolaget L M Ericsson
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