The present invention generally relates to transfer of voice over IP (VoIP) data on radio links. The invention relates particularly, though not exclusively, to semi-persistent scheduling of VoIP data on radio links between mobile stations and base stations in an Evolved Universal Terrestrial Radio Access (EUTRA) network.
VoIP is seen to be potentially one of the major applications in EUTRA systems, which systems are being designed as part of the Long-Term Evolution (LTE) within the 3rd Generation Partnership Project (3GPP). Regarding this, many system parameters of EUTRA are being optimized for VoIP. The EUTRA is based in Orthogonal Frequency Division Multiple Access (OFDMA), wherein a given amount of sub-carriers is allocated to users for predetermined periods of time. These sub-carriers allocated for predetermined periods are typically denoted as physical resource blocks (PRBs), with time and frequency dimensions. Allocation of PRBs is handled by a scheduling function at a 3GPP base station (so-called eNodeB).
Various contributions have addressed different aspects of VoIP on top of EUTRA. The EUTRA has limited resources for Open Systems Interconnection Basic Reference Model Layer 1 (OSI L1 or L1 in short) signalling and it is generally desired to spare those resources where possible. In so-called persistent scheduling, VoIP traffic is treated as circuit switched data so that VoIP packets on each data channel have dedicated scheduled slots. If no data needs to be conveyed in a particular slot, no other data can be scheduled therein. The persistent model is very simple in terms of directing the scheduling but this advantage is outweighed by the need to reserve roughly half of the radio resource unnecessarily.
Seeking to improve the persistent model, various contributions tie signalling overhead with scheduling flexibility in order to find most balanced working point for VoIP traffic on top of EUTRA system. Semi-persistent scheduling of VoIP traffic is one of the most promising techniques. OSI L3 RRC signalling or radio resource control plane signalling is typically used to define initial transmissions (normal repeated VoIP packets that carry voice data) for a recipient terminal.
On the start of the voice spurt, the quality of a radio channel used is determined based on say 20 ms period and correspondingly radio transmission parameters such as used radio channel parameters like frequency and time slot are defined and signalled to the recipient terminal for use throughout the starting voice spurt.
Each talk spurt usually lasts for several seconds. Talk spurt length is usually modelled as a negative exponential distribution with low bound as shown in
In VoIP, speech is typically encoded and later decoded using encoders and decoders optimised for speech. Speech has substantial amount of redundancy that may be compressed with so-called inter-coding, where previously encoded data is used in encoding subsequent data packets. Inter-coding greatly compresses voice data by making use of its inherent redundancy. However, the major compression ability comes at the cost that losing a single packet may prevent decoding of all subsequent packets. Hence, if applied to EUTRA VoIP where the semi-persistent models define transmission parameters for the whole voice spurt based on a very brief sample at the start of the spurt, there is a great risk that deteriorating radio channel will lead into major degradation in reconstructed voice quality at the recipient terminal.
Presents proposals for enhancing scheduling of VoIP data packets in the EUTRA make different compromises between layer 1 and 2 signalling, scheduling complexity and traffic channel use efficiency. It is desired to reach alternative solution that spares layer 1 and layer 2 signalling without an undue cost on traffic channel efficiency.
According to a first aspect of the invention there is provided a method comprising:
Advantageously, the scheduling of the radio link may be adapted during the transferring of VoIP data packets of a given voice spurt. Hence, diversity and robustness of transfer may be enhanced in comparison to maintaining the radio link unchanged throughout each voice spurt.
The inventors have realised that the conditions may rapidly change during the voice spurt. While radio transmission parameters defined for the transmissions carrying the serial VoIP data packets are originally optimised based on a small portion of each talk spurt, the changing of the scheduling of the use of radio resources during the voice spurt increases flexibility and efficiency of scheduling of VoIP data traffic. The method of the first aspect may thus significantly enhance the performance of semi-persistent VoIP scheduling.
The radio link may be a link between a base station and mobile station of a telecommunications network.
The base station may be an enhanced node b (eNB) in the Evolved Universal Terrestrial Radio Access (EUTRA). The eNB may comprise a scheduler that is configured to define physical resource blocks (PRBs) for use in transmission of VoIP data packets between the base station and the mobile station.
The changing of the schedule may comprise any of:
A series of initial VoIP data packets may be scheduled at the start of a voice spurt and the scheduling may be communicated from the base station to the mobile station. An initial VoIP data packet refers to a data packet that is sent as a member of a train of planned packets which convey audio coding data each for an interval of one or more speech coding frames. If an initial VoIP data packet is lost, a retransmission or generally corrective VoIP packet may be sent as a remedy for a lost VoIP data packet.
Advantageously, the scheduling of initial VoIP data packets may be changed during the period of the voice spurt and indicated to the recipient typically without new physical messaging by using otherwise unnecessary padding bits, because the data link layer (OSI model layer 2) messages on the radio link are commonly padded with redundant bits.
The changing of the schedule may be responsive to a change in the quality of the radio link. Advantageously, it may be possible to improve quality of radio interface during the period of the voice spurt to avoid severe impairment of voice quality. Moreover, the scheduling may be adapted by changing one recipient to use another channel that is not necessarily better in order to free resources on its channel for other use such as for another VoIP recipient. This may be useful if the same radio channel provides drastically different a reception quality for two mobile stations or terminals and by changing channel allocation neither recipient is substantially harmed but one is significantly helped.
The changing of the scheduling of the transmission of the serial VoIP data packets may be identified by means of predetermined bit patterns. The bit patterns may be defined to identify maintaining present channel, moving to a preceding or next channel as defined by channel number or frequency, for instance. Such use of bit pattern may operate with merely two padding bits. If more padding bits are available, further transmission parameters may be defined such as modulation and coding scheme (MCS) and Number of Physical Resource Block (PRB).
The identifying of the changing of the scheduling of the transmission of the serial VoIP data packets may be provided in the padding bits of two or more different VoIP data packets in order to provide interference resilience.
The changing of the scheduling of the transmission of the serial VoIP data packets may take place at predetermined intervals. The predetermined intervals may be set by the sender, by the scheduler or by any network entity based on input from the scheduler and/or the sender. The intervals may range from 0.2 to 3 seconds, suitably from 0.5 to 1 second inclusive of these exemplary bounds. For instance, 0.5 second would correspond to 25 VoIP packets each corresponding to 20 ms of speech (or other audio content as the case may be with VoIP).
The mobile station may further be configured to perform blind detection of the change in the scheduling if scheduling signalling is lost as may happen in some cases. The blind detection is the simpler the fewer different channels there are to test.
Further advantageously, the method may further include changing physical radio resources used in the radio interface in transmission of given serial VoIP data packets based on signalling provided to the recipient in the data link layer padding bits.
The radio link may be a link between a mobile station and a base station and the changing of the schedule may comprise changing any of:
The changing of a channel may involve changing from one channel to another or changing properties such as a bit rate or transmission power of a given channel.
The scheduling information may comprise any of:
The coding mode may be conveniently changed particularly if adaptive multi-rate coding is used in audio coding of the VoIP data packets. By reducing coding bit rate necessary data transmission rate can be responsively reduced, which is particularly useful in interference-limited communication technologies such as the Code Division Multiple Access (CDMA).
The causing of the change in the schedule may comprise causing of sending to a network entity a request or status indication configured to cause the network entity to change the schedule; and the scheduling information may be configured to carry said request or status indication. According to a second aspect of the invention, there is provided a method comprising:
Advantageously, after the schedule is changed, VoIP data packets may be received using the radio link resources according to the new schedule until a next change in the schedule takes place.
According to a third aspect of the invention there is provided an apparatus comprising:
According to a fourth aspect of the invention there is provided an apparatus comprising:
According to a fifth aspect of the invention, there is provided a computer program embodied in a computer readable memory medium, the computer program comprising computer executable program code configured to enable a telecommunications apparatus to perform:
According to a sixth aspect of the invention, there is provided a computer program embodied in a computer readable memory medium, the computer program comprising computer executable program code configured to enable a telecommunications apparatus to perform:
According to a seventh aspect of the invention, there is provided an apparatus comprising:
The memory medium may be a digital data storage such as a data disc or diskette, optical storage, magnetic storage, holographic storage, phase-change storage (PCM) or opto-magnetic storage. The memory medium may be formed into a device without other substantial functions than storing memory or it may be formed as part of a device with other functions, including but not limited to a memory of a computer, a chip set, and a sub assembly of an electronic device.
Various embodiments of the present invention have been illustrated only with reference to certain aspects of the invention. It should be appreciated that corresponding embodiments may apply to other aspects as well.
The invention will be described, by way of example only, with reference to the accompanying drawings, in which:
In the following description, like numbers denote like elements.
The processor 31,41 in any one of the scheduler, sender or recipient MS may be a master control unit MCU. Alternatively, the processor may be a microprocessor, a digital signal processor, an application specific integrated circuit, a field programmable gate array, a microcontroller or a combination of such elements.
The rescheduling of initial VoIP data packets and scheduling of retransmissions are further explained in connection with
The period between initial transmissions is typically 20 millisecond (ms). The interval in which re-scheduling of initial transmissions is performed is a value subject to optimising the operation of the network. In an embodiment of the invention, the re-scheduling interval is partly or entirely determined by the terminal 25. The interval is typically between 0.5 s and 2 s. There is a trade-off between better adaptation to changes in radio connection quality and load with shorter interval and smaller signalling overhead caused by re-scheduling with longer interval. In an embodiment of the invention, the interval is further adapted so that major changes in the quality of connection trigger shortened or longer intervals depending on whether the connection has deteriorated or enhanced, respectively.
The reserved combination of the padding bits may indicate altering the re-scheduling interval in one embodiment and additionally changing to a higher or lower PRB in another embodiment. The altering of the re-scheduling interval may be such that in the absence of retransmissions, the re-scheduling interval is increased according to a predetermined scheme for new retransmission intervals and after a given number of retransmissions within one re-scheduling interval, the reserved combination is applied to indicate that the re-scheduling interval shall be shortened.
The first alternative embodiment for the use of padding bits 703-1 may be seen to instruct the terminal the PRBs used for initial transmissions in the next re-scheduling interval on the downlink that is for VoIP data packets from the eNB 23 to the terminal 25.
In the second alternative embodiment for the use of the padding bits 703-2, the terminal 25 is informed both on the amount of PRBs used in the following re-scheduling interval and whether the resources allocated for the following re-scheduling interval should use the same, higher or lower PRB. Further, among the options for the resource use in the following re-scheduling interval there is provided a combination of a sub-set of the padding bits 703-2 indicative of a reserved combination. The reserved combination may be used for corresponding function as was explained in connection with the first alternative embodiment for the use of the padding bits 703-1.
In a further embodiment of the invention, the terminal 25 is capable of adjusting audio transfer on the uplink to the eNB 23 using L2 padding bits in uplink VoIP data packets.
It should be appreciated that the process of
The padding bits 1003 in
The embodiments presented in the foregoing are generally effective and efficient and they may enable improving frequency diversity usage during relatively long talk spurts. However, sometimes, the voice talk-spurts may be relatively short and the channel condition may remain constant or change insignificantly during several sequential talk-spurts. For instance, the mobile station 25 may stay in one place or move relatively slowly (e.g. walking speed) and the speech may contain numerous short spurts short talk spurts such as commands or instructions so that there are many short pauses. If explicit persistent allocation signalling is sent regardless of whether the allocated resources are changed among the consecutive talk spurt, same explicit signalling has to be repeated thereby causing unnecessary signalling. Even if the amount required by the signalling may be greatly reduced from prior known techniques, it is yet desirable to improve radio resource usage and/or at least provide other alternatives. To this end, different embodiments of the invention seek to avoid repeated explicit signalling.
In one alternative, in-band signalling in downlink a VoIP data packet is used to instruct the mobile station 25 to adhere to its previous allocation. In another alternative, silent control is applied such that when an e-NB receives “resource request” signalling from the mobile station 25 at the start of a talk spurt but sends no reply, then UE expects that it should use previous resources for this spurt. If the resource allocation should be changed, the e-NB sends explicit signalling to respectively instruct the mobile station 25 for use in a commencing talk spurt.
The first alternative for avoiding repeated explicit signalling is next described in more detail. Let us assume that there is on-going downlink and uplink data transmission. The eNB 23 then receives a the “Resource Request” from the mobile station 25 for coming talk-spurt. The eNB 23 decides to maintain the uplink resources (such as frequency and MCS). The eNB 23 sends an indication of resource continuance to the mobile station 25 by using padding bits or puncture bits in the downlink VoIP data packets (both new transmission and retransmission of DL packets are applicable)
The other alternative for avoiding repeated explicit signalling is next described in more detail. This embodiment is particularly useful when there is no on-going downlink data transmission into which the in-band signalling could be included. In order to avoid introducing explicit new signalling when the resource allocation for the uplink is maintained, the eNB 23 may interpret lack of explicit signalling as an indirect or silent control to maintain the resource allocation used in previous talk spurt. Only if the eNB 23 changes the resource allocation for the mobile station 25, the eNB 23 uses control signalling. Hence, no additional signalling or padding bits are needed in this method.
It is appreciated that relying to correct interpretation to missing signal, possibly of a single bit, may be exposed to errors in case that the signalling is somehow lost on the radio link. Even though the likelihood of such an error is low, typically about 1%, further measures may be taken in order to avoid adverse consequences from the error. For instance, a timer can be used to cause the mobile station 25 to wait for a predetermined time for explicit control signalling and if none is received then the mobile station 25 starts transmitting next talk-spurt using the previous resource allocation used by its previous talk-spurt. The timer may be started when the mobile station 25 sends a resource allocation request for a new talk spurt.
In
On start of the next talk spurt, the mobile station 25 sends a new request 122 as was also drawn for the preceding spurts, but in this case, the eNB 23 desires to change the resource allocation and sends a normal resource grant message 126. As there is no ongoing downlink transfer at this moment of time, the resource grant message 126 is sent as a separate message to the mobile station 25.
A normally skilled person appreciates that for cases when there are many frequent short-duration talk-spurts in speech that is being transmitted, the embodiments described in the foregoing may avoid unnecessary signalling and/or reduce resource allocation/grant signalling cost. Compared to a case where explicit control signalling is sent even when the resources for next talk-spurt need not be changed, substantial reduction in the signalling may be attained as shown in
It should be appreciated that whilst in the foregoing the uplink was used as an example, the first and other alternative embodiments apply equally for instructing the mobile station 25 on resource allocation for the downlink.
In
wherein N is the number of continuous talk-spurt. In equation 1, old signalling number may thus equal to N units of signalling, as each talk-spurt needs one signalling. New signalling amount is then 1+(N−1)*(1−X), because the first talk-spurt always needs one signalling unit and then the remaining number of talk-spurts less the first one use signalling units in extent (1−X).
The foregoing description has provided by way of non-limiting examples of particular implementations and embodiments of the invention a full and informative description of the best mode presently contemplated by the inventors for carrying out the invention. It is however clear to a person skilled in the art that the invention is not restricted to details of the embodiments presented above, but that it can be implemented in other embodiments using equivalent means without deviating from the characteristics of the invention. For instance, an EUTRA access network has been used as an example network in which different embodiments of the invention may be used, but it should be understood that the invention may find use in any types of radio systems such as IEEE 802.11 (WLAN), IEEE 802.16 (WiMAX), or ITU IMT-2000 (CDMA-2000).
Furthermore, some of the features of the above-disclosed embodiments of this invention may be used to advantage without the corresponding use of other features. As such, the foregoing description shall be considered as merely illustrative of the principles of the present invention, and not in limitation thereof. Hence, the scope of the invention is only restricted by the appended patent claims.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FI2007/050551 | 10/10/2007 | WO | 00 | 1/20/2010 |
Number | Date | Country | |
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Parent | 11881484 | Jul 2007 | US |
Child | 12669946 | US |