WO2009087546A2

WO2009087546A2 - Unequal error protection for wireless applications with cross layer design

Info

Publication number: WO2009087546A2
Application number: PCT/IB2008/055674
Authority: WO
Inventors: Wei Li; John Benko
Original assignee: France Telecom
Priority date: 2007-12-31
Filing date: 2008-12-15
Publication date: 2009-07-16
Also published as: WO2009087546A3

Abstract

Providing current transmission conditions from a data-link layer (or below) to an application layer, determining coding schemes, with différent coding schemes applied for encoding the data as determined by a threshold of transmission conditions, and transmitting the encoded data. The threshold of transmission conditions may correspond to the existing signal to noise ratio (SNR) in a transmission médium. One of the coding schemes may be a cross layer unequal error protection (UEP) coding scheme. The cross layer UEP may include adding error coding to both of the header and data packet portions of the data if the transmission conditions (eg. like the SNR) are below the threshold of transmission conditions.

Description

UNEQUAL ERROR PROTECTION FOR WIRELESS APPLICATIONS WITH CROSS LAYER DESIGN

FIELD OF THE PRESENT SYSTEM: The present system relates to a method, architecture, program and system for a cross-layer design that allows for better use of network resources .

BACKGROUND OF THE PRESENT SYSTEM: Currently, a layered architecture of communication or computer network protocols is widely used as being a good abstraction for network device functionality. While there are different expressions in the art of how many layers are utilized to describe the layers of communication protocol, there are seven (7) layers described in the Open Systems Interconnection Basic Reference Model (OSI Model) including from lowest to highest levels (with higher levels being closer to the user) , a physical layer, a data link layer including a Media Access Control (MAC) sublayer and a Logical Link Control (LLC) sublayer, a network layer, a transport layer, a session layer, a presentation layer and an application layer. Details of each layer are beyond the scope of the present system however, as may be readily appreciated, each layer is constructed to solve a set of problems involving the transmission of data, and provides a well-defined service to the upper layers based on using services provided from lower layers. Upper layers are logically closer to the user and deal with more abstract data, relying on lower layer protocols to translate data into forms that can eventually be physically transmitted. The motivation of such a layered architecture is to provide modularity and transparency between the layers to simplify the design of network protocols. Significant work has been done to develop efficient techniques for each layer of data transmission, such as for a wireless transmission, but most of the work is concentrated on optimizing each layer independent of other layers in the protocol stack. However, it is becoming increasingly clear that local optimization of layers does not lead to global optimization. Current cross-layer designs utilize fault tolerances in different data types to optimize data transmissions. This type of optimization is called Unequal Error Protection (UEP) and is based on a realization that different data types have different fault tolerances. For example, data transmissions, such as application downloads, usually require zero receive error rate with little restriction placed on transmission delays. On the other hand, real time video/voice streaming may tolerate a certain percentage of errors without apparent Quality of Service (QoS) loss or Mean Opinion Score (MOS - a measure of user-perceived performance) loss, however video/voice data has a much more strict limit on transmission delays. At the same time, a missed packet with video/voice streaming may cause more serious QoS loss compared to random error bits in the transmitted data. Current coding algorithms are designed for a data transmission system with a simple numerical error rate as design objective (DO) , which does not serve the purpose for real time video/voice transmissions . UEP algorithms are typically designed according to different systems and requirements. The traditional UEP Algorithms usually apply different kinds of coding algorithms to different kinds of data having different importance. For example, under traditional UEP algorithms, a header portion of a frame may get better coding than a data portion of the frame. While these types of UEP algorithms typically lead to lower packet drop rate, they do not consider the real time network transmission conditions and different requirements of different kinds of services. In fact, traditional UEP algorithms do not work ideally in all conditions such as when error rates in transmission are higher or lower than typical.

It is an object of the present system to overcome disadvantages and/or make improvements in the prior art.

SUMMARY OF THE PRESENT SYSTEM:

The present system includes a method, architecture, system and device for encoding data, including providing current transmission conditions from a data-link layer (or below) to an application layer, determining coding schemes, with a different number of coding schemes to be applied for encoding the data as determined by a threshold of transmission conditions, and transmitting the encoded data. The threshold of transmission conditions may correspond to a signal to noise ratio (SNR) of a transmission medium. One of the coding schemes may be a cross layer unequal error protection (UEP) coding scheme. The cross layer UEP may include adding error coding to both of the header and data packet portions of the data if the transmission conditions are below the threshold of transmission conditions.

The transmission conditions may include an identification of a data type of the data. The transmission conditions may include an identification of quality of service (QoS) requirements of the data. In one embodiment, the threshold of transmission conditions may include first and second thresholds, wherein one of the coding schemes is applied when transmission conditions are below the first threshold, wherein a second coding scheme is applied when transmission conditions are between the first and second thresholds, and wherein a third coding scheme is applied when transmission conditions are above the second threshold.

BRIEF DESCRIPTION OF THE DRAWINGS:

The invention is explained in further detail, and by way of example, with reference to the accompanying drawings wherein: FIG. 1 shows a simulation of error coding schemes based in accordance with an embodiment of the present system;

FIG. 2 shows a process flow diagram in accordance with an embodiment of the present system; and

FIG. 3 shows a system including an encoder operationally coupled to a decoder in accordance with an embodiment of the present system.

DETAILED DESCRIPTION OF THE PRESENT SYSTEM:

The following are descriptions of illustrative embodiments that when taken in conjunction with the following drawings will demonstrate the above noted features and advantages, as well as further ones. In the following description, for purposes of explanation rather than limitation, illustrative details are set forth such as architecture, interfaces, techniques, etc. However, it will be apparent to those of ordinary skill in the art that other embodiments that depart from these details would still be understood to be within the scope of the appended claims. Moreover, for the purpose of clarity, detailed descriptions of well known devices, circuits, techniques, architectures and methods are omitted so as not to obscure the description of the present system. It should be expressly understood that the drawings are included for illustrative purposes and do not represent the scope of the present system.

The method, architecture, and system described herein address problems in prior art systems. In accordance with an embodiment of the present system, method, architecture, and device, when the transmission medium is operating better, as for example signified by a low error rate in transmitted data, a requirement for embedding error coding into a data transmission is determined by the present system to be low and therefore an embodiment of the present system reduces coding at these times. In accordance with the present system, knowledge about error rates available from lower layers is utilized to adjust data coding at higher layers. For example, in accordance with an embodiment of the present system, when data error rates,

(e.g., such as expressed as a signal to noise ration (SNR) of data received that is error free divided by the total error received) , are better than a given threshold, no additional error correction coding is embedded into the transmitted data. In this way, when error rates are low, a data channel utilized for transmitting data may transmit more data since less additional error coding is applied.

The present system operates on a principle that network protocols and designs should be engineered by optimizing across the network layers and taking into consideration different characteristics of different types of applications and data. The present design methodology is referred to as cross-layer design. Cross-layer design allows a better use of network resources by optimizing across the boundaries of traditional network layers. Cross -layer design is based on an information exchange and joint optimization over two or more network layers. The Applicant's have recognized that a cross-layer design may yield significantly improved performance by exploiting a tight coupling between the layers in data transmission systems, such as wireless systems.

FIG. 1 shows a simulation of error coding schemes based on a third generation (3G) code division multiple access (CDMA) system, such as a cellular telephone 3G system. To facilitate the simulation, a static usage scenario is presumed (e.g., no Doppler effect) including a block Rayleigh fading channel simulation with close loop power control. The Rayleigh fading channel is widely used as a general fading channel model for mobile and/or wireless communication, and the Doppler Effect with a moving speeds of less than 50 km/hour may be considered negligible. In FIG. 1, three schemes are compared. First is a constant 5/6 convolution coding equal error protection (EEP) scheme (labeled No UEP) . Second is an Unequal Error Protection (UEP) convolution coding scheme in accordance with prior systems, with 7/8 rate coding for payload data and ³A rate coding for frame headers, and an unlimited buffer size (e.g., excluding an effect of overflow) . The third is a cross layer UEP algorithm in accordance with the present system (labeled "UEP + xlayer design" ) having similar code rates as the UEP for SNR >10 dB, and for SNR < 10 dB having ³A rate coding for payload data and ¹A rate coding frame header, and an unlimited buffer size. In the simulation, if the error rate is larger than 10% or there are one or more errors in a packet header after decoding a packet, an assumption is made that this packet is dropped. Accordingly, FIG. 1 provides a measure of a probability that a packet loss will occur for giving transmission operating conditions and different encoding schemes.

As shown, the UEP scheme in accordance with the present system (hereinafter, cross layer UEP) has better performance (less packet loss) than "No UEP" prior systems at an SNR below thirty (30) dB . Further, the cross layer UEP encoding scheme in accordance with the present system, has better performance than prior UEP systems, for example with a SNR below 1OdB. However, when the channel condition is very good (e.g., SNR is large, such as above 30) a difference between each of the schemes is small. As may be readily appreciated, in accordance with the present system, by providing higher coding layers, such as an application layer, with error rates available from lower layers, such as a Media Access Control (MAC) sublayer, different thresholds may be set for different types of data to determine which coding scheme to apply in coding the data for transmission. By only introducing additional coding, such as error coding

(Forward Error Correction, Backward Error Correction, etc.) at times when a benefit may be appreciated, such as when there is a decrease in SNR, higher (payload) data rates may be provided. For example, less resources may be put on channel coding (e.g., by introduction of weaker error correction coding schemes) so that the payload data- rate may be higher at times when the SNR is higher than 1OdB, for example when standard UEP may be provided in place of a cross layer

UEP operating in accordance with the present system. At SNR levels lower than 1OdB, cross layer UEP may provide a performance improvement, for example of up to 7dB with % coding rate with stronger error correction ability for headers while ³A coding rate for the information bit, which provides less error correcting ability but more throughput . In accordance with a further embodiment, a second threshold level of the SNR may be utilized to determine when to stop utilization of standard UEP, such as for example at a SNR of 30 or higher as shown in FIG. 1. In accordance with an algorithm in accordance with the present system, the algorithm may find one, two or more threshold points for selecting specific coding schemes to be applied to encoding data. The thresholds may change based on differences in data types that are transmitted. For example, additional coding may be performed for a packet header of a video data packet when a SNR level is below a threshold (e.g., below 10 dB) such that packet delivery is more likely even if data portions of the packet may contain errors. As may be appreciated, since video transmissions are tolerant of errors in the data as long as multiple frames are not lost in transmission, the present system of providing more coding in the header at times of a decrease in the SNR levels reduces a likelihood of frame loss at a risk of increased errors in the data. In this way, a likelihood of delay in the video data transmission may be reduced from a coding scheme wherein the header and data portion of a packet are coded similarly.

In accordance with the present system, when a similar level of SNR is provided for a data packet, such as related to a file download, further coding may be provided in a data portion as well as the header portion to ensure that packets received are error free at a risk of an increase in transmission delay. Further differentiation in coding schemes and thresholds may be applied for different transmission types. For example, different coding schemes and thresholds may be applied for different types of wireless networks, for different transmission power levels, etc. For example, for a cellular system, downlink voice transmission may have good performance if the signal to noise ratio is higher than 20 dB, in this case very light channel coding may be applied. However, if the signal to noise ratio is lower than 20 dB, strong error control coding may be needed and applied. Different data sub-types even within a given data type may also elicit different coding and threshold treatment in accordance with the present system. For example, a High Definition (HD) data type (e.g., HDTV) may receive higher coding in one or more of the header and data portion of a packet resulting in a more robust data transmission (e.g., more reliably received) than a Standard Definition (SD) data type.

By providing an application layer with error rate information available from a data layer, such as a MAC layer, an algorithm in accordance with the present system may adjust a coding scheme applied to data packets. For example, the MAC layer may provide an average and maximum data rate to an application layer, so the application layer may arrange the data rate accordingly for different applications based on the applications tolerance of errors in data and delays in transmission. Further, by providing information such as data type, QoS requirements, etc. , further modifications to coding schemes and thresholds may be applied in accordance with the present system. For example, for data/file transmission, longer delay may be tolerated but usually no errors may be accepted. So for data, high performance error control coding may be applied in accordance with an embodiment of the present system. For real time video data transmissions, information has to be transferred within the video timing, so if high performance error control coding is needed, to keep the required date rate, more channel resources (such as bandwidth) may be allocated to the application in accordance with an embodiment. These adjustments need to be decided by the applications in real time depend on the inputs from lower layers, such as from a MAC layer. Further, a system in accordance with an embodiment of the present system, usually does not require any review until a change in the channel/network condition makes it necessary to make adjustments to help ensure the best application performance and optimum network throughput and quality of service. As may be readily appreciated, by adjusting a coding scheme applied to data transmissions when the network condition is really bad, by for example, applying more high performance error control coding as needed or by adjusting the cross layer design algorithm selected at given threshold levels, an encoding scheme is provided that may adapt to current network conditions .

FIG. 2 shows a process flow diagram 200 in accordance with an embodiment of the present system. The process starts during act 210 wherein an encoder receives a data packet intended for transmission over a transmission medium, such as a wireless transmission medium, during act 220, the encoder queries the data layer and/or any other layer lower than the application layer, for current transmission error rate information such as data packet error rate, retransmission rate, data collision rate and data packet type. In another embodiment, the data layer may simply provide this information to the application layer upon arrival of the data packet. Additional information may also be provided to the application layer such as QoS requirements, etc. During act 230, the application layer determines two or more (different) encoding schemes including threshold error rates for applying each of the two or more encoding schemes based on the data received from the data layer. For example, the encoder may determine the encoding scheme including thresholds for transmission conditions based on information from the data-link layers (and/or below) , as well as the application layer (in terms of packet type) . In accordance with an embodiment of the present system, the two or more encoding schemes and/or thresholds may be predetermined. In an embodiment wherein one or more of the encoding schemes and thresholds are predetermined, the current network conditions, such as error rates, etc., are compared to the (predetermined) thresholds to determine a currently suitable encoding scheme.

Thereafter, utilizing the determined encoding schemes and current error rates and thresholds, data is encoded during act 240 and transmitted over a transmission medium. In one embodiment, based on current transmission conditions, coding schemes of packets (data and header) may be determined and packets may be accordingly encoded and transmitted over the transmission medium. In accordance with an embodiment of the present system wherein more than one transmission medium may be available for data transmissions, the present system may determine which transmission medium to utilize for transmission of the encoded data packet. The transmission mediums may include different data channels (e.g., transmission frequencies for a wireless transmission medium) as well as a change in the transmission medium type. For example, in a system wherein more than one transmission medium is available to the encoder, a selection of the transmission medium may be made in accordance with an embodiment of the present system.

The data packet is received by the decoder and the data packet is decoded during act 250. The data packet may thereafter be rendered and/or stored during act 260. In one embodiment in accordance with the present system the encoded data may be stored prior to rendering for later rendering. Naturally the process may be repeated during data transmission (e.g. , transmission of one or more subsequent data packets) to detect any changes in transmission conditions during data transmission (e.g., repeat of act 220-260) . When data transmission is completed, the process may end during act 270 wherein the encoder/decoder awaits receipt of a next data packet and/or next data transmission. In accordance with the present system, one or more thresholds of SNR values may be utilized for selecting amongst two or more different packet encoding schemes. For example, with a SNR level above a threshold level, simple channel coding may be applied to packet headers. In the same embodiment, if the SNR is below the threshold level, a strong channel coding may be utilized for both the header and the payload of the packet. In other words, the coding scheme may be adapted according to the information from different layers, different service requirements (e.g., QoS) and depending on the transmission medium capabilities. In accordance with the present system, cross-layer designs may be utilized to yield significantly improved performance by exploiting a tight coupling between the layers in wireless systems. FIG. 3 shows a system 300 including an encoder 302 operationally coupled to a decoder 312 in accordance with an embodiment of the present system. For example, the encoder 302 may include a processor 310 operationally coupled to a memory 320, a data input 330 and a data output 340. The data input 330 may be coupled to one or more transmission mediums and/or data storage devices. The data output 340 may be coupled to one or more transmission mediums, such as a wired and/or wireless transmission medium. Similarly, the decoder 312 may include a processor 350 operationally coupled to a memory 360, a data input 370 and a data output 380. The data input 370 and the data output 380 are coupled to a transmission medium, such as a wired and/or wireless transmission medium. The data output 340 of the encoder 302 is operationally coupled to the data input 370 of the decoder 312. In accordance with the present system, the operational coupling may include one or more of a wired and wireless communication medium. In accordance with a further embodiment of the present system, the data output 380 may be operationally coupled to an output device 390, such as a data storage device and/or a data rendering device.

The memories 320, 360 may be any type of device for storing application data as well as other data related to the described operation. The application data and other data are received by the processors for configuring the processors to perform operation acts in accordance with the present system. The operation acts may include receiving data from data inputs, determining network transmission conditions as well as data type from a data layer, determining two or more suitable coding/decoding schemes for the data including threshold conditions for application of each of the two or more coding schemes. Clearly the processors 310, 350 and the memories 320, 360 may all or partly be a portion of a communication system such as a wireless communication system.

The methods of the present system are particularly suited to be carried out by a computer software program, such program containing modules corresponding to one or more of the individual steps or acts described and/or envisioned by the present system. Such program may of course be embodied in a computer-readable medium, such as an integrated chip, a peripheral device or memory, such as a memory coupled to one or more of the processors. The memories 320, 360 configure corresponding processors 310, 350 to implement the methods, operational acts, and functions disclosed herein. The memories may be distributed, for example between the clients and/or servers, or local, and one or more of the processors 310, 350, where additional processors maybe provided, may also be distributed or may be singular. The memories may be implemented as electrical, magnetic or optical memory, or any combination of these or other types of storage devices. Moreover, the term "memory" should be construed broadly enough to encompass any information able to be read from or written to an address in an addressable space accessible by one or more of the processors 310, 350. With this definition, information accessible through a communication network is still within the memory, for instance, because one or more of the processors 310, 350 may retrieve the information from the network for operation in accordance with the present system.

The processors 310, 350 are operable for determining a suitable encoding/decoding scheme and for performing the suitable encoding/decoding and executing instructions stored in a corresponding memory. The processors may be application-specific or general-use integrated circuit (s) . Further, the processors may be dedicated processors for performing in accordance with the present system or may be general -purpose processors wherein only one of many functions operates for performing in accordance with the present system. The processors may operate utilizing a program portion, multiple program segments, or may be a hardware device utilizing a dedicated or multi-purpose integrated circuit.

Further variations of the present system would readily occur to a person of ordinary skill in the art and are encompassed by the following claims. In accordance with the present system, different operating condition thresholds, such as SNR thresholds/ranges may be utilized to determine different types of encoding schemes to aid in optimizing overall network performance. The present system may be readily applied for all types of transmission mediums including wireless transmission mediums, for example based on transmission standards such as IEEE 802.11, 802.15 and 802.16 wireless transmission standards.

Finally, the above-discussion is intended to be merely illustrative of the present system and should not be construed as limiting the appended claims to any particular embodiment or group of embodiments. Thus, while the present system has been described with reference to exemplary embodiments, it should also be appreciated that numerous modifications and alternative embodiments may be devised by those having ordinary skill in the art without departing from the broader and intended spirit and scope of the present system as set forth in the claims that follow. In addition, the section headings included herein are intended to facilitate a review but are not intended to limit the scope of the present system. Accordingly, the specification and drawings are to be regarded in an illustrative manner and are not intended to limit the scope of the appended claims.

In interpreting the appended claims, it should be understood that : a) the word "comprising" does not exclude the presence of other elements or acts than those listed in a given claim; b) the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements; c) any reference signs in the claims do not limit their scope; d) several "means" may be represented by the same item or hardware or software implemented structure or function; e) any of the disclosed elements may be comprised of hardware portions (e.g., including discrete and integrated electronic circuitry) , software portions (e.g. , computer programming) , and any combination thereof; f ) hardware portions may be comprised of one or both of analog and digital portions; g) any of the disclosed devices or portions thereof may be combined together or separated into further portions unless specifically stated otherwise; h) no specific sequence of acts or steps is intended to be required unless specifically indicated; and i) the term "plurality of" an element includes two or more of the claimed element, and does not imply any particular range of number of elements; that is, a plurality of elements may be as few as two elements, and may include an immeasurable number of elements.

Claims

Claims What is claimed is:

1. A method of encoding data, the method comprising acts of: providing current transmission conditions from a data layer to an application layer; determining a plurality of coding schemes, with a different one of the plurality of coding schemes to be applied for encoding the data as determined by a threshold of transmission conditions; and transmitting the encoded data.

2. The method of claim 1, wherein the threshold of transmission conditions corresponds to a signal to noise ratio (SNR) of a transmission medium.

3. The method of claim 1, wherein one of the plurality of coding schemes is a cross layer unequal error protection (UEP) coding scheme.

4. The method of claim 3, wherein the cross layer UEP includes adding error correction coding to both of the header and data packet portions of the data if the transmission conditions are below the threshold of transmission conditions.

5. The method of claim 1, wherein the transmission conditions includes an identification of a data type of the data.

6. The method of claim 1, wherein the transmission conditions includes an identification of quality of service (QoS) requirements of the data.

7. The method of claim 1, wherein the threshold of transmission conditions comprises first and second thresholds, wherein a first one of the plurality of coding schemes is applied when transmission conditions are below the first threshold, wherein a second one of the plurality of coding schemes is applied when transmission conditions are between the first and second thresholds, and wherein a third one of the plurality of coding schemes is applied when transmission conditions are above the second threshold.

8. An application embodied on a computer readable medium arranged to encode and transmit data, the application comprising: a portion configured to operate as an application layer of a transmission medium and to receive current transmission conditions from a data layer; a portion configured to apply one of a plurality of coding schemes based on the current transmission conditions, with a different one of the plurality of coding schemes applied for encoding the data as determined by a threshold of transmission conditions; and a portion configured to transmit the encoded data.

9. The application of claim 8, wherein the threshold of transmission conditions corresponds to a signal to noise ratio (SNR) of the transmission medium.

10. The application of claim 8, wherein one of the plurality of coding schemes is a cross layer unequal error protection (UEP) coding scheme .

11. The application of claim 10, wherein the cross layer UEP includes adding error coding to both of the header and data packet portions of the data if the transmission conditions are below the threshold of transmission conditions.

12. The application of claim 8, wherein the transmission conditions includes an identification of a data type of the data.

13. The application of claim 8, wherein the transmission conditions includes an identification of quality of service (QoS) requirements of the data.

14. The application of claim 8, wherein the threshold of transmission conditions comprises first and second thresholds, wherein the portion configured to apply one of the plurality of coding schemes is configured to apply a first one of the plurality of coding schemes when transmission conditions are below the first threshold, is configured to apply a second one of the plurality of coding schemes when transmission conditions are between the first and second thresholds, and is configured to apply a third one of the plurality of coding schemes when transmission conditions are above the second threshold.

15. An encoder configured to encode data, the encoder comprising: a memory; and a processor operationally coupled to the memory, wherein the processor is configured by the memory to: operate as an application layer of a transmission medium and to receive current transmission conditions from a data layer; apply one of a plurality of coding schemes based on the current transmission conditions, with a different one of the plurality of coding schemes applied for encoding the data as determined by a threshold of transmission conditions; and transmit the encoded data.

16. The encoder of claim 15, wherein the threshold of transmission conditions corresponds to a signal to noise ratio (SNR) of the transmission medium.

17. The encoder of claim 15, wherein one of the plurality of coding schemes is a cross layer unequal error protection (UEP) coding scheme.

18. The encoder of claim 17, wherein the cross layer UEP includes adding error coding to both of the header and data packet portions of the data if the transmission conditions are below the threshold of transmission conditions.

19. The encoder of 15, wherein the transmission conditions includes an identification of a data type of the data.

20. The encoder of 15, wherein the threshold of transmission conditions comprises first and second thresholds, wherein the processor is configured to apply a first one of the plurality of coding schemes when transmission conditions are below the first threshold, wherein the processor is configured to apply a second one of the plurality of coding schemes when transmission conditions are between the first and second thresholds, and wherein the processor is configured to apply a third one of the plurality of coding schemes when transmission conditions are above the second threshold.