Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0015—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the adaptation strategy
  • H04L1/0016—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the adaptation strategy involving special memory structures, e.g. look-up tables
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0002—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate
  • H04L1/0003—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate by switching between different modulation schemes
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0009—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the channel coding
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0023—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the signalling
  • H04L1/0025—Transmission of mode-switching indication
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0023—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the signalling
  • H04L1/0026—Transmission of channel quality indication
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
  • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
  • H04L1/1812—Hybrid protocols; Hybrid automatic repeat request [HARQ]
  • H04L1/1819—Hybrid protocols; Hybrid automatic repeat request [HARQ] with retransmission of additional or different redundancy
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
  • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
  • H04L1/1829—Arrangements specially adapted for the receiver end
  • H04L1/1835—Buffer management
  • H04L1/1845—Combining techniques, e.g. code combining

Definitions

• the present invention generally relates to mode signalling in the field of communication systems and, more particularly, to mode signalling involving multiple modulation and coding schemes, link adaptation and incremental redundancy in digital communication systems.
• a corresponding minimum user bit rate is required.
• user bit rate corresponds to voice quality and/or data throughput, with a higher user bit rate producing better voice quality and/or higher data throughput.
• the total user bit rate is determined by a selected combination of techniques for speech coding, channel coding, modulation and resource allocation (e.g., for a TDMA system, the number of assignable time slots per call and for a CDMA system, the number of codes assigned to a call).
• GMSK Gaussian Minimum Shift Keying
• QPSK Quadrature Phase Shift Keying
• QAM Quadrature Amplitude Modulation
• each communication system operates using a single modulation scheme for transmission of information under all conditions.
• ETSI originally specified the GSM standard to communicate control, voice and data information over links using a GMSK modulation scheme to provide transmission and retransmission of information.
• modulation schemes may use a different number of values or levels to represent information symbols.
• the signal set i.e., amplitude coefficients, associated with QPSK, an exemplary lower level modulation (LLM) scheme, are illustrated in Figure 1(a).
• LLM lower level modulation
• 16QAM is a higher level modulation (HLM) scheme having the signal set depicted in Figure 1(b).
• the minimum Euclidean distance between the coefficients in the LLM scheme is greater than the minimum Euclidean distance between coefficients in the HLM scheme for the same average signal power, which makes it easier for receive signal processing to distinguish between modulation changes in the LLM scheme.
• LLM schemes are more robust with respect to noise and interference, i.e., require a lower carrier-to-interference (C/I) level to achieve acceptable received signal quality.
• HLM schemes provide greater user bit rates, e.g., 16QAM provides twice the user bit rate of QPSK, but require higher C/I levels.
• FEC forward error correction
• ARQ automatic retransmission request
• ARQ techniques involve analyzing received blocks of data for errors and requesting retransmission of blocks which contain errors.
• GPRS Generalized Packet Radio Service
• a logical link control (LLC) frame containing a frame header (FH), a pay load of information and a frame check sequence (FCS) is mapped into a plurality of radio link control (RLC) blocks, each of which include a block header (BH), information field, and block check sequence (BCS), which can be used by a receiver to check for errors in the information field.
• RLC blocks are further mapped into physical layer bursts, i.e., the radio signals which have been GMSK modulated onto the carrier wave for transmission.
• the information contained in each RLC block can be interleaved over four bursts (timeslots) for transmission.
• each RLC block When processed by a receiver, e.g., a receiver in a mobile radio telephone, each RLC block can, after demodulation, be evaluated for errors using the block check sequence and well known cyclic redundancy check techniques. If there are errors, then a request is sent back to the transmitting entity, e.g., a base station in a radiocommumcation system, denoting the block to be resent using predefined ARQ protocols.
• MCS modulation/coding schemes
• the originally selected FEC coding scheme is used for retransmission, i.e., this system employs fixed redundancy for retransmission purposes.
• the retransmitted block may be combined with the earlier transmitted version in a process commonly referred to as soft combining in an attempt to successfully decode the transmitted data.
• Another proposed hybrid ARQ scheme sometimes referred to as incremental redundancy or type-II hybrid ARQ, provides for additional redundant bits to be transmitted if the originally transmitted block cannot be decoded.
• This scheme is conceptually illustrated in Figure 3.
• three decoding attempts are made by the receiver.
• the receiver attempts to decode the originally received data block (with or without redundancy).
• the receiver receives additional redundant bits Rl , which it uses in conjunction with the originally transmitted data block to attempt decoding.
• the receiver obtains another block of redundant information R2, which it uses in conjunction with the originally received data block and the block of redundant bits Rl to attempt decoding for a third time. This process can be repeated until successful decoding is achieved.
• incremental redundancy does not require that link quality estimates be transmitted or used.
• one problem with this technique is the large memory requirement associated with storing the data block (and possibly additional blocks of redundant bits) until a successful decode occurs, which storage is needed since the subsequently transmitted redundancy blocks (e.g., Rl and R2) cannot be independently decoded to give the same performance as if combined decoding was used.
• the storage requirements are further increased if the receiver stores a multi-bit soft value associated with each received bit, the soft values indicating a confidence level associated with the decoding of the received bit.
• many variations and combinations of these techniques are possible. For example, it is possible to combine link adaptation with incremental redundancy.
• the MCS of the first transmission can be varied, e.g., such that the first transmission is made using some channel coding or not the least robust modulation.
• the MCS can be changed for many reasons, e.g., to reduce the number of retransmissions or delay or to dynamically adapt to changes in memory requirements.
• MCS changes may or may not be based solely on reported link quality estimates. For example, when incremental redundancy is used and the receiver has limited memory it may be beneficial to increase the robustness of the MCS even though (in a system with unlimited memory) it would decrease throughput.
• the number of required retransmissions for successful incremental redundancy combination will be higher. This, in turn, requires a lot of memory. If the receiver runs out of memory, it will begin to discard received blocks that have previously been stored for later incremental redundancy combination. Since the information transmitted using the relatively unrobust MCS probably relies in part upon incremental redundancy combining to achieve acceptable decoding performance, the result may be significantly degradation in received signal quality.
• control of MCS changes may reside with the receiving entity 42 as shown in Figure 4(b). Then, the receiving entity 42 makes quality measurements on the forward link as in Figure 4(a). However, instead of transmitting the quality measurements to the transmitting entity 40, the receiving entity determines if any MCS changes are desirable and forwards such information to the transmitting entity on the reverse link 46.
• the conventional MCS choice information transmitted on the reverse link 46 applied only to originally transmitted blocks.
• a message can be transmitted between two entities which informs a transmitting entity whether a receiving entity currently prefers incremental redundancy. For example, if the receiving entity is ninning out of memory in which to store blocks for incremental redundancy combining, then the receiving entity can signal the transmitting entity using this message. The transmitting entity can, in turn, factor this information into its choice of MCS for subsequent transmissions.
• another message can be transmitted which informs the transmitting entity whether the receiving entity currently prefers resegementation of retransmitted blocks. If so, then the transmitter may adjust the MCS of retransmitted blocks relative to the MCS used to originally transmit the block which is being retransmitted. Otherwise, if the receiving entity informs the transmitting entity that resegmentation is not preferred, then the transmitting entity can retransmit blocks using the original MCS.
• the resegmentation message is transmitted in control blocks on the dowlink, while the incremental redundancy message is transmitted in control blocks on the uplink.
• FIG. 1(a) and FIG.1(b) are diagrams of modulation constellations for QPSK and 16QAM modulation schemes, respectively;
• FIG. 2 depicts information mapping in a conventional system operating in accordance with GSM
• FIG. 3 illustrates a conventional variable redundancy technique
• FIGS. 4(a) and 4(b) depict conventional control signalling techinques associated with link adaptation techniques
• FIG. 5(a) is a block diagram of a GSM communication system which advantageously uses the present invention.
• FIG. 5(b) is a block diagram used to describe an exemplary GPRS optimization for the GSM system of FIG. 5(a);
• FIGS. 6(a)-6(d) describe exemplary embodiments of the present invention including a message field which indicates whether or not incremental redundancy is currently employed at a receiving entity;
• FIGS. 6(e)-6(h) depict exemplary embodiments of the present invention including a message field which indicates whether or not resegmentation of retransmitted blocks is to be performed;
• Figure 7 is a table illustrating exemplary relationships between the MCS for an originally transmitted block and a corresponding, retransmitted block;
• Figure 8 is an exemplary EGPRS embodiment of the present invention.
• TDMA time division multiple access
• CDMA code division multiple access
• ETSI European Telecommunication Standard Institute
• a communication system 10 according to an exemplary GSM embodiment of the present invention is depicted.
• the system 10 is designed as a hierarchical network with multiple levels for managing calls. Using a set of uplink and downlink frequencies, mobile stations 12 operating within the system 10 participate in calls using time slots allocated to them on these frequencies.
• a group of Mobile Switching Centers (MSCs) 14 are responsible for the routing of calls from an originator to a destination. In particular, these entities are responsible for setup, control and termination of calls.
• MSCs Mobile Switching Centers
• One of the MSCs 14, known as the gateway MSC handles communication with a Public Switched Telephone Network (PSTN) 18, or other public and private networks.
• PSTN Public Switched Telephone Network
• each of the MSCs 14 are connected to a group of base station controllers (BSCs) 16.
• BSCs base station controllers
• the BSC 16 communicates with a MSC 14 under a standard interface known as the A-interface, which is based on the Mobile Application Part of CCITT Signaling System No. 7.
• each of the BSCs 16 controls a group of base transceiver stations (BTSs) 20.
• Each BTS 20 includes a number of TRXs (not shown) that use the uplink and downlink RF channels to serve a particular common geographical area, such as one or more communication cells 21.
• the BTSs 20 primarily provide the RF links for the transmission and reception of data bursts to and from the mobile stations 12 within their designated cell. When used to convey packet data, these channels are frequently referred to as packet data channels (PDCHs).
• PDCHs packet data channels
• a number of BTSs 20 are incorporated into a radio base station (RBS) 22.
• RBS radio base station
• the RBS 22 may be, for example, configured according to a family of RBS-2000 products, which products are offered by Ardaktiebolaget L M Ericsson, the assignee of the present invention.
• RBS-2000 products which products are offered by Telefonaktiebolaget L M Ericsson, the assignee of the present invention.
• the interested reader is referred to U.S. Patent Application Serial No. 08/921,319, entitled "A Link Adaptation Method For Links using Modulation Schemes That Have Different Symbol Rates", to Magnus Frodigh et al., the disclosure of which is expressly incorporated here by reference.
• An advantage of introducing a packet data protocol in cellular systems is the ability to support high data rate transmissions and at the same time achieve a flexibility and efficient utilization of the radio frequency bandwidth over the radio interface.
• the concept of GPRS is designed for so-called "multislot operations" where a single user is allowed to occupy more than one transmission resource simultaneously.
• FIG. 5(b) An overview of the GPRS network architecture is illustrated in Figure 5(b). Since GPRS is an optimization of GSM, many of the network nodes/entities are similar to those described above with respect to Figure 5(a).
• Information packets from external networks will enter the GPRS network at a GGSN (Gateway GPRS Service Node) 100.
• the packet is then routed from the GGSN via a backbone network, 120, to a SGSN (Serving GPRS Support Node) 140, that is serving the area in which the addressed GPRS mobile resides. From the SGSN 140 the packets are routed to the correct BSS (Base Station System) 160, in a dedicated GPRS transmission.
• BSS Base Station System
• the BSS includes a plurality of base transceiver stations (BTS), only one of which, BTS 180, is shown and a base station controller (BSC) 200.
• BTS base transceiver stations
• BSC base station controller
• the interface between the BTSs and the BSCs are referred to as the A-bis interface.
• the BSC is a GSM specific denotation and for other exemplary systems the term Radio Network Control (RNC) is used for a node having similar functionality as that of a BSC.
• RNC Radio Network Control
• a GPRS register will hold all GPRS subscription data.
• the GPRS register may, or may not, be integrated with the HLR (Home Location Register) 220 of the GSM system. Subscriber data may be interchanged between the SGSN and the MSC/VLR 240 to ensure service interaction, such as restricted roaming.
• the access network interface between the BSC 200 and MSC/VLR 240 is a standard interface known as the A-interface, which is based on the Mobile Application Part of CCITT Signaling System No. 7.
• the MSC/VLR 240 also provides access to the land-line system via PSTN 260.
• one or more additional overhead messages can be provided in the signalling between the receiving entity 600 (e.g., RBS 180 or MS 210) and the transmitting entity 610 (e.g., MS 210 or RBS 180).
• These messages referred to as LA/IR and RSEG/NRSEG in Figures 6(a)-6(h) are shown as portions of control blocks which are transmitted periodically from each entity (or upon request) and which also include other messages, e.g., acknowledgement reports.
• the LA/IR message provides an explicit request of the preferred operating mode, i.e., either link adaptation or incremental redundancy.
• This message can be included in a control block in addition to the link quality measurements or MCS command described above with respect to Figures 4(a) or 4(b). This information can then be used by the other entity when selecting from two predetermined rules or rule sets for changing the MCS.
• the receiving entity 600 transmits the LA/IR message field on link 620 (along with link quality measurements(LQM)) with a value which indicates that incremental redundancy is preferred, this implies that it currently has adequate memory capacity to continue to store blocks to support incremental redundancy combining.
• This informs the transmitting entity 610 that it can employ an MCS rule or rule set that makes, for example, aggressive (i.e., less robust) MCS choices, taking the link quality estimate report which is also transmitted to the transmitting entity 610 into account.
• the LA/IR message may instead have a value which indicates that link adaptation is preferred by receiving entity 600.
• transmitting entity 600 may then switch to a second MCS rule or rule set that makes more conservative (i.e., more robust) MCS choices, based on the link quality estimates, to ensure that the receiver achieves sufficient performance without the incremental redundancy combining.
• the receiving entity 600 can transmit the LA/IR message with a value indicating that incremental redundancy is preferred.
• the controlling entity i.e., the receiver 600 in this example
• the MCS as signaled in the MCS command which is transmitted along with the LA/IR message
• the non-controlling party will note that IR combining is being performed and, therefore, shall provide retransmissions using the same MCS as the initial transmissions.
• the MCS identified in the MCS command should be used.
• the receiving entity 600 can transmit the LA/IR message with a value indicating that incremental redundancy is not available at the receiving entity as seen in Figure 6(d).
• the non-controlling party will note that incremental redundancy combining is not being performed and, therefore, shall preferably provide retransmissions using the same, or close to the same, MCS as is currently employed for new block transmissions. Again, for the new transmissions, the MCS identified in the MCS command should be used.
• receiving entity 600 can also inform transmitting entity 610 whether or not retransmissions should be made with resegmented blocks, i.e., whether the MCS for retransmissions should be the same or different than the MCS for new block transmissions, using the RSEG/NRSEG message.
• the RSEG/NRSEG message can be transmitted with either link quality measurements or MCS commands.
• the transmitting entity 600 will know that a more (or less) robust MCS can be selected for retransmitting not acknowledged blocks than was used to originally transmit those blocks to receiving entity 600.
• the original MCS can be varied based on the link quality measurements reported on link 630, taking into account that a more robust MCS has been requested for the retransmissions (which fact may be used by transmitting entity 610 to increase the MCS for original transmissions as well).
• the transmitting entity 610 will perform retransmissions with the same MCS as the initial transmissions. This may also be taken as an indication by transmitting entity 600 that the prevailing MCS can continue to be used for new block transmissions, based also on the link quality measurements.
• the RSEG/NRSEG message can also be transmitted with MCS commands instead of link quality measurements.
• MCS commands instead of link quality measurements.
• the transmitting entity 610 if the RSEG value is transmitted, then the transmitting entity 610 will use a more robust MCS to retransmit a resegmented version of unacknowledged blocks. The MCS for originally transmitted blocks is then dictated by the MCS command.
• the transmitting entity will use the same MCS value for retransmitted blocks and will use the MCS indicated in the MCS command for new transmissions.
• LA/IR and RSEG/NRSEG messages may be provided together on both links, separately on either link or in any other combination desirable.
• LA/IR and RSEG/NRSEG messages may be provided together on both links, separately on either link or in any other combination desirable.
• EGPRS Enhanced GPRS
• MCS-1 most robust
• MCS-8 most robust
• the network will control he MCS choices, i.e., the mobile station reports downlink quality estimates in the uplink, and the network gives uplink MCS commands to the mobile station in the downlink.
• Block acknowledgments are signaled in both links in so-called Control Blocks.
• the above mentioned quality reports and MCS commands are included in these Control Blocks.
• EGPRS allow changes of the MCSs for retransmissions with certain constraints as seen in Figure 7. For new block transmissions, any MCS can be used.
• the messages described above according to the present invention can be used as follows.
• the downlink quality estimate is signaled.
• the inventive LA/IR message is introduced, for example by using an additional bit flag in the control word.
• the network's interpretation is that if the IR value is signaled, incremental redundancy operation is possible for the mobile station 800 and the network (as represented by RBS 810)can be very aggressive when choosing an MCS, since it can rely on the fact that the mobile station 800 uses IR combining.
• the control blocks include an MCS command is signaled, which tells the mobile station 800 which MCS (e.g., of those shown in Figure 7) should be used for transmitting uplink RLC blocks.
• the RSEG/NRSEG message can also be added to the downlink control blocks, e.g., using a bit flag.
• an NRSEG value can be interpreted by the mobile station 800 as meaning retransmissions by the mobile station use the same MCSs as the initial transmissions of those blocks.
• a RSEG value should be interpreted by mobile station 800 as meaning that blocks to be retransmitted should be resegmented and transmitted using different (e.g. , more robust) MCSs than the initial MCSs of those blocks.
• the specific MCS to use for retransmissions can be determined by a predetermined rule stored in the mobile station.
• This rule could be, purely for example, that: "Resegment to the same MCS as the MCS commanded for new transmissions, if possible. If not possible, resegment to the least robust MCS that is more robust than the commanded MCS. If still not possible, resegment to the most robust MCS as possible. " This would mean that in some cases, the MCS for retransmissions is less robust than the MCS for the original transmission.
• Another rule could be the same as above with the addition that "If the MCS determined according to the above rule is less robust than the initial one, use the initial one instead". This way the MCS can only be more robust (or the same) for the retransmissions.
• the MCS for retransmissions without losing old IR information.
• those transitions could be allowed, even if resegmentation is not allowed for other retransmissions.
• NRSEG can be indicated in the downlink control block
• retransmissions for blocks originally transmitted -lousing MCS-8 or MCS-7 can be performed using MCS-6 or MCS-5, respectively, if the ordered MCS is lower or equal to MCS-8 or MCS-7, respectively.
• the NRSEG value can be controlling.
• the RSEG/NRSEG flag can be extended to two bits, one indicating the RSEG/NRSEG value and one indicating whether NRSEG is valid for all MCSs.
• the present invention provides for increase flexibility of the modulation and coding scheme choices in systems using link adaptation and Incremental Redundancy. Moreover, the strategy for the link adaptation algorithm will be more sensitive to whether incremental redundancy can should be used at each moment, and does not have to sacrifice performance in either case.
• the link adaptation protocol will be more robust to memory problems in the receivers, i.e., when there is no or little memory available for incremental redundancy operation, this is taken into account in the algorithms.
• the present invention also makes it more likely that protocol stalling and unnecessarily large performance degradations can be avoided.

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• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Detection And Prevention Of Errors In Transmission (AREA)
• Mobile Radio Communication Systems (AREA)
• Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
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• 1999
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