Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L69/00—Network arrangements, protocols or services independent of the application payload and not provided for in the other groups of this subclass
  • H04L69/04—Protocols for data compression, e.g. ROHC
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L69/00—Network arrangements, protocols or services independent of the application payload and not provided for in the other groups of this subclass
  • H04L69/22—Parsing or analysis of headers

Definitions

• the invention relates generally to packet channel communications and, more particularly, to header compression techniques for use in packet channel communications.
• header compression refers to the art of minimizing the necessary bandwidth for information carried in packet headers on a per hop basis over point-to-point links. Header compression is usually realized by sending static information only initially. Semi-static information is then transferred by sending only the change from the previous header. A full (uncompressed) header is sent occasionally in order to update the data bases of the header compression units.
• header compression is usually realized with a state machine.
• HC algorithms are conventionally used on a per hop basis, there is a possibility to use different HC algorithms on each hop, depending on the characteristic of the current link. This gives a possibility to optimize the performance, on a per hop basis, for links with a static characteristic in the time domain (e.g., a relatively constant error rate).
• Conventional HC algorithms do not, however, consider quality or error variations in time on the currently used link, and do not consider variations between links. So, if conventional HC algorithms are applied on links with quality or error variations in time, for example conventional wireless links, this can result in poor throughput due to too low robustness, or bandwidth waste due to too high robustness.
• the conventional HC algorithms consider each link independently of all other links. Although this model is adequate for wired channels where the use of one channel does not affect other similar channels, it does not adequately address wireless channels.
• the use of a wireless channel affects users of other wireless channels in terms of interference.
• HC algorithms according to the invention can adapt to the quality variations of the link as well as the system load. This can be done by interacting with the link on which the data is transmitted. Ideally, the level of compression can be optimized with respect to system load, and the amount of robustness can be optimized with respect to link quality.
• the invention provides a method for using an amount of bandwidth appropriate to transfer the desired information with sufficient quality.
• FIGURE 1 conceptually illustrates the operation of a header compression algorithm interacting with a radio network according to the invention.
• FIGURE 2 illustrates diagra matically a packet format that can be used with the invention.
• FIGURE 3 graphically illustrates an exemplary relationship between link quality and the amount of forward error correction associated with a packet according to the invention.
• FIGURE 3A graphically illustrates an exemplary relationship between link quality and the amount of header compression associated with a packet header according to the invention.
• FIGURE 4 illustrates graphically an exemplary relationship between system load and an average value of a combined amount of information included in a packet header and associated error correction bits according to the invention.
• FIGURE 4A illustrates graphically an exemplary relationship between system load and the amount of header compression associated with a packet header according to the invention.
• FIGURE 5 illustrates exemplary adaptive header compression and adaptive robustness operations according to the invention.
• FIGURE 6 illustrates diagrammatically the combining of two payloads into a single longer packet with a single compressed header in order to increase the level of header compression according to the invention.
• FIGURE 7 illustrates exemplary operations which can be performed in order to implement the payload combining illustrated in FIGURE 6.
• FIGURE 8 illustrates graphically, for a channel adaptive speech codec and a source adaptive speech codec, an exemplary relationship between the speech codec bit rate and the amount of forward error correction to be applied to a packet according to the invention.
• FIGURE 9 illustrates exemplary operations which can be used to implement the relationships of FIGURE 8.
• FIGURE 9A illustrates an exemplary alternative to the operations of FIGURE 9.
• FIGURE 10 illustrates pertinent portions of an exemplary embodiment of a radio communication station according to the invention.
• the header compression scheme may be more effective in terms of throughput and overall system capacity if it is interacting with the link in which the header compression algorithm is being used.
• the header compression scheme should then be robust to changes in the radio channel quality, while also avoiding unnecessary compression of the headers, for example in low load situations.
• Robustness for headers, payloads or both
• FEC forward error correction
• the amount of robustness can be based on the probability of erroneous packet transmission and/or based on the experienced link quality.
• the level (or amount) of header compression can be varied by, for example: (1) using a constant amount of compression for each compressed header, but varying the time intervals between transmission of full headers; (2) considering the compression of each header individually, and using an individually desired amount of compression for each header; or (3) a combination of (1) and (2).
• the level of compression can be based on one or more of the system load, the experienced link quality, and the amount of robustness, as described in more detail below.
• the radio access network provides conventional link quality and system load information to the HC algorithm. This is shown diagrammatically in FIGURE 1.
• the packets transmitted would ideally use exactly the amount of bandwidth needed for reaching a sufficient (desired) quality on each link.
• the level of header compression can be adapted to the system load situation which permits traffic to be adapted to the current system load. For example, during low system load, increased (e.g., out of charge) quality is possible.
• the header compression algorithm may have different targets (or objectives) depending on the system situation. At low load situations there is no need for a large degree of header compression, and quality can be optimized. Thus, any degradation of quality due to header compression is unnecessary and should be avoided. At high load situations, a minimum quality should be maintained, and header compression should be increased to gain capacity. Hence, quality (e.g., speech quality) may be traded for system capacity.
• FIGURE 2 illustrates an example of a voice over IP packet and the different parts it can include, namely a J-bit FEC portion, a K-bit header portion and an L-bit payload portion, for example a speech portion.
• the L-bit portion can be data other than speech data in some embodiments.
• the bit sizes of the different parts can be adapted to different system and link situations according to the invention.
• Link quality can comprehend many things but one basic exemplary meaning of link quality is bit error rate.
• Link quality can be represented by a number of different measurements, for example, one of the conventional measures shown below or any combination of them: mean bit error rate standard deviation of bit error rate - packet/block error rate
• the system load tells how much traffic a system is carrying and indicates, for example, if it is possible to add more traffic.
• System load can be measured in numerous ways, for example, by one of the conventional measures shown below or any combination of them:
• the number of spreading codes used (in a code limited CDMA system).
• the system load can be measured absolutely (for example 15 occupied channels) or relatively (for example 15 occupied channels of 20 possible channels).
• the system load measure can also represent, for example, a varying part of a cellular system, such as the load in one cell, i.e., how much traffic a specific cell is carrying, or the load in a cluster of cells.
• exemplary graphs are shown which indicate how the header compression algorithm can adapt to varying link quality (FIGURES 3 and 3A) and system load (FIGURES 4 and 4A) situations. These graphs can be seen as two-dimensional views of a more complex figure describing how the header compression algorithm adapts to both link quality and system load at the same time. Referencing FIGURE 3, when the link quality is poor, a larger amount of robustness, in this example more bits of forward error coding FEC (designated generally at J in
• FIGURES 2 and 3 can be added to protect the packet.
• a link with good quality is used, a smaller amount of robustness is adequate, so in this example the number of
• FEC bits, J can be decreased.
• FIGURE 3 A illustrates an example of how the amount of header compression can be adapted to link quality according to the invention.
• the header compression ratio (amount of header compression) in FIGURE 3 A is relatively small, and with good link quality the header compression ratio can be relatively large.
• the entity K_average represents the average bit rate used for sending header information. For each packet the size of the header is fixed, but when compressed headers are mixed with full headers in a stream of packets, or when headers compressed by different amounts are mixed in a stream of packets, a varying average header bit rate occurs. Thus, a varying header compression rate may be achieved. When the system load is low, there is no need to risk a degraded quality
• the header compression ratio can be relatively small, thus making K (see FIGURE 1) large.
• system capacity e.g., radio network capacity
• the header compression ratio should be as large as possible (to provide as much compression as possible) while still maintaining a minimum required quality.
• FIGURE 4A illustrates more generally how the amount of header compression can, in one example of the invention, be adapted according to the measured system load.
• FIGURE 4A shows relatively less header compression (a lower HC ratio) at low system loads, and relatively more header compression (a higher HC ratio) at higher system loads.
• the invention makes it possible to trade quality against capacity by suitably adapting the header compression scheme according to different targets, for example increased capacity or throughput.
• quality can be prioritized by using a relatively low HC ratio
• capacity can be prioritized by using a relatively higher HC ratio.
• Exemplary header compression and robustness adaptations such as described above are illustrated by the flow diagram of FIGURE 5.
• the system load and link quality (measured by and available from conventional wireless networks) are measured at 52.
• the robustness amount and header compression ratio are determined at 53, for example, using information as desired from any of the curves of FIGURES 3, 3 A, 4 and 4A. The information in these curves can be empirically determined based on the type of performance desired.
• the header compression ratio can be determined as a function of one or more of link quality (see FIGURE 3 A), system load (see FIGURE
• the robustness adaptation at FIGURE 3 when link quality conditions degrade, if the robustness adaptation at FIGURE 3 is adequate to provide desired results, then there may be no need to decrease the amount of header compression in response to the degradation in link quality, even though FIGURE 3 A might otherwise indicate a decrease in the amount of header compression.
• the amount of header compression could be decreased in order to compensate for the inadequacy of the robustness adaptation. In this latter example, the amount of header compression could still decrease less in response to the link quality degradation than would otherwise be indicated by FIGURE 3 A, due to the presence of at least some (although inadequate) robustness adaptation.
• the compression ratio from 53 can be applied to the header in conventional fashion, and the robustness amount from 53 can be applied to the header and/or payload in conventional fashion.
• the worst case for any radio network is when the system load is high and the link quality is poor. In this situation, which is relatively common, any ability to increase system capacity, for instance by reducing the relative system load while maintaining the absolute system load, is desirable.
• the amount of header compression in such situations could be further increased by combining two or more payloads, for example the speech frames of FIGURE 6, in one packet with a single compressed header 61.
• the compressed header 61 can be produced, for example, by compressing the uncompressed header 62, or by compressing the uncompressed header 63. In another embodiment, the uncompressed headers 62 and 63 can both be compressed at the same time to produce the single compressed header 61.
• sending the two payloads in a single packet with the compressed header 61 permits the two payloads to be transmitted with less overall header overhead than would be required if the headers 62 and 63 were compressed individually and the two payloads were transmitted in separate packets with their respective compressed headers.
• the overall header compression ratio can thereby be increased at the cost of an increased delay. System capacity is therefore traded off against delay. To find the proper trade-off between capacity and delay, this trade-off can be made adaptive with respect to system load.
• FIGURE 7 is an example of operations that can be performed according to the invention in the high load, low quality situations described above. If the link quality is below a threshold TH Q at 71 , and if the system load is above a threshold TH L at 72, then the procedure discussed above relative to FIGURE 6 is performed at 73. The operations in FIGURE 7 can, as shown, be performed between operations 53 and 54 of FIGURE 5.
• the speech codec may adapt to the channel conditions (conventional adaptive multi-rate speech coding). For example, when there is congestion, the speech codec may decrease the bit rate and transmit almost the same speech information with fewer bits, thereby increasing the amount of information per packet.
• the speech codec may also adapt to the speech source behavior, for example, decreasing the bit rate when there is less speech information to transmit. In this case the amount of information per packet is decreased.
• the header compression algorithm can adapt to changes in the speech codec bit rate. This is illustrated in the example of
• FIGURE 8 For a channel adaptive speech codec (solid line in FIGURE 8), the robustness (e.g., the amount of forward error correction coding in FIGURE 8) for each speech packet can be advantageously increased as the speech codec bit rate decreases, because there is more speech information per bit in the reduced packets, making loss of a packet more costly. For a source adaptive speech codec (broken line in FIGURE 8), the robustness for each speech packet can be advantageously decreased with the codec bit rate, because there is less speech information in the reduced packets, so the loss of a packet may have only a small impact on speech quality.
• the curves shown in FIGURE 8 can be determined empirically based on the type of performance desired.
• FIGURE 9 illustrates example operations that can be performed to implement the adaptive control of robustness (e.g., FEC) shown in FIGURE 8. If the codec bit rate is lowered below a threshold TH BR at 91, then the amount of robustness is increased at 94 if the codec mode is channel adaptive at 92. If the codec mode is source adaptive at 92, then the amount of robustness is decreased at 93.
• the operations of FIGURE 9 can, as shown, be performed between operations 53 and 54 of FIGURE 5.
• FIGURE 9A illustrates an alternative to the embodiment of FIGURE 9.
• the amount of header compression can be increased at 93 A instead of or in combination with the decreasing of robustness, and at 94A the amount of header compression can be decreased instead of or in combination with the increasing of the robustness.
• the amount of header compression may not need to be decreased at 94A.
• the robustness adaptation at 94A is insufficient, or if no robustness adaptation is provided at 94A, then the amount of header compression can be decreased as necessary to compensate for the inadequate (or non-existent) robustness adaptation.
• the amount of header compression can be increased at 93 A by an amount depending on the robustness adaptation (if any).
• FIGURE 10 illustrates pertinent portions of exemplary embodiments of a wireless communication station according to the invention.
• the wireless communication station of FIGURE 10 can be, for example, a mobile radio transceiver such as a cellular telephone, or a fixed-site radio transceiver.
• the communication station includes a communication port 101 for providing substantive information (for example speech information) to a packet unit 102.
• the communication port 101 also provides header information to a header unit 103.
• the header unit 103 produces headers from the header information provided by communication port 101, including adaptively compressing the headers according to the above-described techniques of the invention.
• the header unit 103 provides the outgoing headers to the packet unit 102.
• the header unit also selectively provides a COMBINE signal to direct the packet unit to combine two or more payloads into a packet with a single compressed header (see
• FIGURES 6 and 7 are identical to FIGURES 6 and 7).
• the packet unit 102 includes an input for receiving link quality information 107, as described above.
• the packet unit 102 can use, for example, information from the curve of FIGURE 3 to determine the desired amount of robustness to be used for each packet's header, payload or both.
• the packet unit 102 can use conventional techniques to provide the desired amount of robustness, for example, to determine the appropriate FEC bits based on the desired amount of FEC bits, or to determine a transmission power level corresponding to the desired amount of robustness.
• the packet unit 102 can use conventional techniques to combine the FEC bits together with the header bits and the substantive information bits (i.e., payload bits) to form an outgoing packet such as illustrated generally in FIGURE 2.
• the header unit 103 receives as control inputs link quality information 107, system load information 108 and error probability information 109 as described above. Such information is routinely provided by conventional radio communication networks.
• the header unit 103 can also receive as a control input information indicative of the robustness amount, as determined by the packet unit 102.
• the header unit 103 also receives, from the codec (not shown) of the communication station, a control input including information at 110 such as bit rate and adaptation mode, the latter of which can indicate, for example, whether the codec is operating in a channel adaptive mode or a source adaptive mode as described above.
• the aforementioned control inputs are used by the header unit 103 to provide adaptive header compression, for example in the fashion described in detail above with respect to FIGURES 1-9.
• the packet unit 102 can also receive as a control input the codec information at 110, which can be used by the packet unit to provide robustness adaptation as illustrated in FIGURES 8-9A above.
• the packet unit 102 forwards the assembled packet to a radio unit 104 which transmits the packet over a radio link 105 to a receiving station (not shown) which can have, for example, robustness and header compression functionality analogous to the communication station of FIGURE 10 for purposes of receiving packets transmitted by the communication station of FIGURE 10.
• a receiving station could receive the control inputs 107-110 used in FIGURE 10 and, for example, apply appropriate error correction and header decompression techniques to the incoming packets.
• the header unit 103 can use the received link quality information 107, system load information 108 and codec information 110 to access lookup tables 106 provided in the header unit.
• the tables 106 can include, for example, stored information corresponding to the information depicted graphically in FIGURES 3-4A and 8, thereby permitting the header unit to perform the above- described adaptive robustness and header compression operations.
• the packet unit 102 can, in some embodiments, include similar lookup tables (not shown) with which to implement the exemplary robustness adaptations described above with respect to
• FIGURES 3 and 8-9A are identical to FIGURES 3 and 8-9A.

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• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Data Exchanges In Wide-Area Networks (AREA)
• Mobile Radio Communication Systems (AREA)
• Detection And Prevention Of Errors In Transmission (AREA)
• Communication Control (AREA)

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• 2000
  • 2000-02-21 JP JP2000601803A patent/JP2002538672A/ja active Pending
  • 2000-02-21 CN CN00806841.0A patent/CN1349702A/zh active Pending
  • 2000-02-21 WO PCT/SE2000/000344 patent/WO2000051307A1/en not_active Application Discontinuation
  • 2000-02-21 EP EP00913203A patent/EP1157519A1/en not_active Withdrawn
  • 2000-02-21 AU AU34679/00A patent/AU3467900A/en not_active Abandoned

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