Patent Application
20160242039
The present invention generally relates to an approach for operating in an unlicensed band.
Cellular systems are often used for wireless broadband data, and for example 3rd Generation Partnership Project, 3GPP, Long Term Evolution, LTE, is a platform that meets that demand. Existing and new spectrum licensed for exclusive use by cellular technologies will remain fundamental for providing seamless coverage, achieving spectral efficiency, and ensuring the reliability through careful planning of cellular networks and deployment of high-quality network equipment and devices.
However, it is a desire to meet increasing demand for wireless bandwidth.
An object of the invention is to at least alleviate the above stated problem. The present invention is based on the understanding that additional bandwidth may be achieved by using unlicensed band, but that this implies certain operations for fair sharing of the unlicensed band. The inventors have found that embedding some information in a reservation signal may enable reducing power consumption for entities.
According to a first aspect, there is provided a method of operating a network node arranged for cellular communication. The network node is capable to operate according to a Radio Access Technology, RAT. The method comprises checking whether a channel in an unlicensed band is clear. If found that the channel is clear, the method proceeds with transmitting a reservation signal on the channel, transmitting data on the channel, and releasing the channel. The transmitting of the reservation signal further includes embedding information related to the transmitting entity and embedding information about scheduled recipient or recipients.
The transmitting of the reservation signal may include embedding information about a duration or end of intended transmission.
A duration of a transmission on the channel, including the time for checking whether the channel is clear, transmitting the reservation signal and transmitting the data, may correspond to a predetermined number of 3GPP LTE subframes. The predetermined number may be four.
The embedding of information related to the transmitting entity may include information about a cell the network node is operating, an operator operating the network node, or a network identity, or a combination thereof.
The embedding of information about scheduled recipient or recipients may include information about a station scheduled for data transmission, or a scheduling group of stations scheduled for the data transmission, or a combination thereof.
The embeddings of information in the reservation signal may include encoding according to a Physical Downlink Control CHannel, PDCCH, symbol mechanism utilizing a dedicated Downlink Control Information, DCI, format therefor.
The embeddings of information in the reservation signal may include utilizing a single PDCCH symbol repeated for a plurality of or all symbols of the reservation signal. The PDCCH symbol may be combined with reference signals for an arbitrary number of transmission ports.
The embeddings of information in the reservation signal may include encoding the information to be embedded according to a predetermined coding scheme, and mapping the encoded information to one or more symbols.
The embeddings of information in the reservation signal may include indexing the information to be embedded into an orthogonal cover code, multiplying a baseline reservation signal with the orthogonal cover code, and mapping the encoded information to one or more symbols.
The embeddings of information in the reservation signal may include assigning a time-domain signal for any permutation of the information to be embedded, wherein the time-domain signal is a Constant Amplitude Zero AutoCorrelation, CAZAC, sequence with different cyclic shifts or indices for the permutations, and mapping the time-domain signal to one or more symbols.
The embeddings of information in the reservation signal may include repeating the mapped symbol for a plurality of or all symbols of the reservation signal.
The RAT may be 3GPP Long Term Evolution, LTE.
According to a second aspect, there is provided a method of operating a transceiver station arranged for cellular communication. The transceiver station is capable to operate according to a Radio Access Technology, RAT. The method comprising receiving a signal on a channel in an unlicensed band, and determining whether the signal is according to the RAT. If the signal is according to the RAT, the method proceeds with decoding at least a part of the signal, determining whether the signal is of interest for the transceiver station, and if the signal is not of interest for the transceiver station, turning off a receiver of the transceiver station.
The determining whether the signal is of interest for the transceiver station may include determining whether the signal comprises information indicating that it is transmitted from a serving cell of the transceiver station, or the signal comprises information indicating that the transceiver station is an intended recipient, or a combination thereof. The information indicating that the signal is transmitted from a serving cell of the transceiver station may include information about a cell identity, an operator operating the network, or a network identity, or a combination thereof.
The information indicating that the transceiver station is an intended recipient may include information about a station scheduled for data transmission, or a scheduling group of stations scheduled for the data transmission, or a combination thereof.
If the signal is not of interest for the transceiver station, the method may proceed with determining information about a duration or end of an intended transmission from the signal, and postponing turning on the receiver again until the intended transmission is ready. The determining of information about the duration or end of the intended transmission may comprise identifying the signal from information from the decoding to map to a predetermined duration or end of the intended transmission. The determining of information about the duration or end of the intended transmission may alternatively comprise reading explicit information about the duration or end of the intended transmission from the signal.
The RAT may be 3GPP Long Term Evolution, LTE.
According to a third aspect, there is provided a method of operating a network node arranged for cellular communication. The network node is capable to operate according to a Radio Access Technology, RAT. The method comprises receiving a signal on a channel in an unlicensed band, and determining whether the signal is according to the RAT. If the signal is according to the RAT, the method proceeds with decoding at least a part of the signal, determining whether the transmitting of the reservation signal includes embedded information about a duration or end of an intended transmission, and postponing monitoring of the channel again until the intended transmission is ready.
According to a fourth aspect, there is provided a network node arranged for cellular communication, wherein the network node is capable to operate according to a Radio Access Technology, RAT, and the network node comprises a transceiver and a controller, and is arranged to check whether a channel in an unlicensed band is clear, and if a signal is received on the channel determining whether the signal is according to the RAT, and if the signal is according to the RAT to decoding at least a part of the signal and determine whether the transmitting of the reservation signal includes embedded information about a duration or end of an intended transmission, wherein the network node is arranged to postpone monitoring of the channel again until the intended transmission is ready.
According to a fifth aspect, there is provided a network node arranged for cellular communication, wherein the network node is capable to operate according to a Radio Access Technology, RAT, and the network node comprises a transceiver and a controller, and is arranged to check whether a channel in an unlicensed band is clear, and if found that the channel is clear, the controller is arranged to cause the transceiver to transmit a reservation signal on the channel and transmit data on the channel, whereafter the controller is arranged to release the channel, wherein the reservation signal further includes embedded information related to the transmitting entity and embedded information about scheduled recipient or recipients.
The reservation signal may include embedded information about a duration or end of intended transmission.
A duration of a transmission on the channel, including the time for checking whether the channel is clear, transmitting the reservation channel and transmitting the data, may correspond to a predetermined number of 3GPP LTE subframes. The predetermined number may be four.
The embedded information related to the transmitting entity may include information about a cell the network node is operating, an operator operating the network node, or a network identity, or a combination thereof.
The embedded information about scheduled recipient or recipients may include information about a station scheduled for data transmission, or a scheduling group of stations scheduled for the data transmission, or a combination thereof.
The embedded information in the reservation signal may be encoded according to a Physical Downlink Control CHannel, PDCCH, symbol encoding utilizing a dedicated Downlink Control Information, DCI, format therefor.
The embedded information in the reservation signal may involve a single PDCCH symbol per subframe.
The embedded information in the reservation signal may involve a single PDCCH symbol repeated for a plurality of or all symbols of the reservation signal.
The PDCCH symbol may be combined with reference signals for an arbitrary number of transmission ports.
The embedded information in the reservation signal may include encoded information to be embedded according to a predetermined coding scheme mapped to one or more symbols.
The embedded information in the reservation signal may include indexed information to be embedded into an orthogonal cover code, wherein a baseline reservation signal multiplied with the orthogonal cover code, mapped to one or more symbols.
The embedded information in the reservation signal may include a time-domain signal assigned for any permutation of the information to be embedded, wherein the time-domain signal is a Constant Amplitude Zero AutoCorrelation, CAZAC, sequence with different cyclic shifts or indices for the permutations, mapped to one or more symbols.
The embedded information in the reservation signal may include the mapped symbol repeated for a plurality of or all symbols of the reservation signal.
The RAT may be 3GPP Long Term Evolution, LTE.
According to a sixth aspect, there is provided a transceiver station arranged for cellular communication, wherein the transceiver station is capable to operate according to a Radio Access Technology, RAT, and the transceiver station comprises a transceiver and a controller, and is arranged to receive a signal on a channel in an unlicensed band and determine whether the signal is according to the RAT, and if the signal is according to the RAT, the transceiver station is arranged to decode at least a part of the signal and determine whether the signal is of interest for the transceiver station, wherein if the signal is not of interest for the transceiver station, the controller is arranged to turn off a receiver of the transceiver.
The determination whether the signal is of interest for the transceiver station may be based on whether the signal comprises information indicating that it is transmitted from a serving cell of the transceiver station, or the signal comprises information indicating that the transceiver station is an intended recipient, or a combination thereof. The information indicating that the signal is transmitted from a serving cell of the transceiver station may include information about a cell identity, an operator operating the network, or a network identity, or a combination thereof.
The information indicating that the transceiver station is an intended recipient may include information about a station scheduled for data transmission, or a scheduling group of stations scheduled for the data transmission, or a combination thereof.
The controller may be arranged to, if the signal is not of interest for the transceiver station, determine information about a duration or end of an intended transmission from the signal, and postpone controlling of turning on the receiver again until the intended transmission is ready.
The RAT may be 3GPP Long Term Evolution, LTE.
According to a seventh aspect, there is provided a computer program comprising instructions which, when executed on one or more processors of a network node, causes the network node to perform the method according to any one of the first or third aspects.
According to an eighth aspect, there is provided a computer program comprising instructions which, when executed on one or more processors of a transceiver station, causes the transceiver station to perform the method according to the second aspect.
Other objectives, features and advantages of the present invention will appear from the following detailed disclosure, from the attached dependent claims as well as from the drawings. Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the [element, device, component, means, step, etc]” are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.
The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings.
A number of abbreviations are used in this disclosure. Some of them are listed below, and others are explained as they appear in the text.
LAA Licensed Assisted Access
RS Reservation Signal
SG Scheduling group
LTE Long Term Evolution
UE User Equipment
LBT Listen Before Talk
SCell Secondary Cell
PCell Primary Cell
DFS Dynamic Frequency Selection
To meet ever increasing data traffic demand from users and, in particular, in concentrated high traffic buildings or hot spots, more mobile broadband bandwidth may be needed. Given the large amount of spectrum available in unlicensed bands, unlicensed spectrum may be considered as a complementary tool to augment service. While unlicensed spectrum may not match some qualities of the licensed regime, solutions that allow an efficient use of it as a complement to licensed deployments have the potential to bring value to the cellular operators.
Some of the examples given in this disclosure are made in light of the 3GPP LTE system. The invention may of course also be used for other systems in a similar way. For the understanding of some terms and principles referred to in some of the examples, a brief explanation of some features of the 3GPP LTE will be given.
LTE uses OFDM in the downlink and DFT-spread OFDM in the uplink. The basic LTE downlink physical resource can thus be seen as a time-frequency grid as illustrated in
Furthermore, the resource allocation in LTE is typically described in terms of resource blocks, where a resource block corresponds to one slot, with a duration of 0.5 ms, in the time domain and 12 contiguous subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth.
Downlink and uplink transmissions are dynamically scheduled, i.e. in each subframe the base station transmits control information about to or from which terminals data is transmitted and upon which resource blocks the data is transmitted.
The control information to a given terminal is transmitted using one or multiple physical downlink control channels (PDCCH). A PDCCH is transmitted in the control region consisting of the first n=1, 2, 3 or 4 OFDM symbols in each subframe where n is the Control Format Indicator (CFI). Typically the control region consists of many PDCCH carrying control information to multiple terminals simultaneously. A downlink system with 3 OFDM symbols allocated for control signalling (for example the PDCCH) is illustrated in
After channel coding, scrambling, modulation and interleaving of the control information, the modulated symbols are mapped to the resource elements in the control region. To multiplex multiple PDCCH onto the control region, control channel elements (CCE) has been defined, where each CCE maps to 36 resource elements. One PDCCH can, depending on the information payload size and the required level of channel coding protection, comprise 1, 2, 4 or 8 CCEs, and the number is denoted as the CCE aggregation level (AL). By choosing the aggregation level, link-adaptation of the PDCCH is obtained. In total there are NCCE CCEs available for all the PDCCH to be transmitted in the subframe and the number NCCE varies from subframe to subframe depending on the number of control symbols n.
As NCCE varies from subframe to subframe, the terminal needs to blindly determine the position and the number of CCEs used for its PDCCH which can he a computationally intensive decoding task. Therefore, some restrictions in the number of possible blind decodings a terminal needs to go through have been introduced. For instance, the CCEs are numbered and CCE aggregation levels of size K can only start on CCE numbers evenly divisible by K, as illustrated in
The set of CCE where a terminal needs to blindly decode and search for a valid PDCCH are called search spaces. This is the set of CCEs on an AL a terminal should monitor for scheduling assignments or other control information. In each subframe and on each AL, a terminal will attempt to decode all the PDCCHs that can be formed from the CCEs in its search space. If the CRC checks, then the content of the PDCCH is assumed to be valid for the terminal and it further processes the received information. Often will two or more terminals have overlapping search spaces and the network has to select one of them for scheduling of the control channel. When this happens, the non-scheduled terminal is said to be blocked. The search spaces vary pseudo-randomly from subframe to subframe to minimize this blocking probability.
A search space is further divided to a common and a terminal specific part. In the common search space, the PDCCH containing information to all or a group of terminals is transmitted (paging, system information etc). If carrier aggregation is used, a terminal will find the common search space present on the primary component carrier (PCC) only. The common search space is restricted to aggregation levels 4 and 8 to give sufficient channel code protection for all terminals in the cell (since it is a broadcast channel, link adaptation can not be used). The m8 and m4 first PDCCH (with lowest CCE number) in an AL of 8 or 4 respectively belong to the common search space. For efficient use of the CCEs in the system, the remaining search space is terminal specific at each aggregation level.
A CCE comprises 36 QPSK modulated symbols that map to the 36 resource elements (REs) unique for this CCE. To maximize the diversity and interference randomization, interleaving of all the CCEs is used before a cell specific cyclic shift and mapping to REs. This may include structuring all PDCCHs into CCE, scrambling and modulating, possibly layer mapping for transmit diversity, interleaving based on quadruplex, cyclically shiftning based on cell identity and mapping to resource element groups. Note that in most cases are some CCEs empty due to the PDCCH location restriction to terminal search spaces and aggregation levels. The empty CCEs are included in the interleaving process and mapping to RE as any other PDCCH to maintain the search space structure. Empty CCE are set to zero power and this power can instead be used by non-empty CCEs to further enhance the PDCCH transmission.
Furthermore, to enable the use of 4 antenna TX diversity, a group of 4 adjacent QPSK symbols in a CCE is mapped to 4 adjacent RE, denoted a RE group (REG). Hence, the CCE interleaving is quadruplex (group of 4) based and mapping process has a granularity of 1 REG and one CCE corresponds to 9 REGs (=36 RE).
There will also in general be a collection of REG that remains as leftovers after the set of size NCCE CCEs has been determined (although the leftover REGs are always fewer than 36 RE) since the number of REGs available for PDCCH in the system bandwidth is in general not an even multiple of 9 REGs. These leftover REGs are in LTE unused by the system.
The information carried on the PDCCH is called downlink control information (DCI). Depending on the configured transmission mode (a UE is configured in one uplink and one downlink transmission mode), and the purpose of the message, the content of the DCI varies. As an example, an uplink MIMO transmission is scheduled using DCI format 4 and contains the necessary information about where the UE shall transmit the uplink data, i.e. the resource block assignment, which precoding matrix to use, which reference signal to use, etc. The corresponding downlink DCI format is format 2C. The size of each DCI format depends on the system bandwidth and reaches in this example 66 bits for DCI format 2C.
For example, Licensed-Assisted Access, LAA, technologies has been studied in 3GPP, wherein an LAA framework is suggested to build on the carrier aggregation solutions to access additional bandwidth in the unlicensed band. For example, it is suggested that the LTE network can configure a User Equipment, UE, to aggregate additional secondary cells, SCells, (Cf. primary cells, PCells, which use a licensed spectrum) which are using the frequency carriers in the unlicensed band. The PCell may retain the exchange of essential control messages and also provide always-available robust spectrum for real-time or high-value traffic. The PCell may also provide mobility handling and management for the UE via the high-quality licensed band LTE radio access network with wide coverage. The aggregated SCells in the unlicensed band, when available, can be utilized as bandwidth booster to serve, e.g., best effort traffic. The LAA SCell may operate in downlink, DL, only mode or operate with both uplink, UL, and DL traffic.
The unlicensed spectrum in general allows non-exclusive use. Given the widespread deployment and usage of other technologies in unlicensed spectrum for wireless communications, it is envisioned that cellular systems such as the LTE would have to coexist with existing and future uses of unlicensed spectrum. Some regulatory regime adopts a technology-neutral coexistence policy. For operating a cellular system such as the LTE in unlicensed spectrum, an approach is to check whether an unlicensed channel is unused before commencing a transmission, often referred to as listen-before-talk, LBT.
The LBT procedure is defined as a mechanism by which equipment applies a clear channel assessment, CCA, check before using the channel. The CCA utilizes at least energy detection to determine the presence or absence of other signals on a channel in order to determine if a channel is occupied or clear, respectively. Some national or regional regulations mandate the usage of LBT in the unlicensed bands. Apart from regulatory requirements, carrier sensing via LBT will lead to fair sharing of the unlicensed spectrum and hence it is considered to be an important feature for fair and friendly operation in the unlicensed spectrum.
Since the UE could be scheduled a data burst that starts at any of the sub-frame borders, the UE needs to receive and process every sub-frame to determine whether it was a valid transmission from it's serving cell to itself or if it was any other transmission. Because of this continuous reception and processing at the UE, the power consumption may be high.
Several operators may simultaneously use the unlicensed spectrum and they may or may not synchronize their transmissions.
A cellular network operating in the unlicensed band may enable UEs, and also other network nodes to save energy by providing additional information embedded in for example the reservation signal, from which the UEs may gain knowledge that no transmission is intended for them during the upcoming transmission, or the other network nodes may gain knowledge that the channel will be occupied during the upcoming transmission. They may thus save energy by omitting monitoring activities during the upcoming transmission.
Consider a receiving station, e.g. a UE capable of communicating according to the LTE, starting its receiver a few symbols before a subframe boundary.
Note that if information about which UEs that are scheduled is embedded in the form scheduling groups, the design could allow that only a few of the UEs in a scheduling group actually are scheduled. Those UEs belonging to a scheduling group indicated in the received reservation signal would of course keep their receivers on and not save power, but there would still be a potential for power-save for those UEs belonging to other scheduling groups.
The proposed design of reservation signal allows the UE to save power by only turning on for a few symbols, say 2-5 symbols, out of a total data burst with a length in the order of 14*4 symbols whenever it is not scheduled. The receiver could therefore in an extreme case be turned off for in the order of 90% of the time compared to existing solutions. Upon the start of scheduling of an upcoming data-transmission in a LAA system, a scheduling algorithm residing in a network node determines which UE will, or may be, scheduled in either the upcoming sub-frame, or the upcoming set of sub-frames contained in the upcoming transmission. The following information may then be prepared to be transmitted in a signalling message from the network node to the UE:
A two-dimensional bitmap indicating which UE:s or scheduling groups, that will or may be scheduled per each potential sub-frame in the upcoming transmission.
A real number, or an index from a predetermined set of configurable alternatives, indicating the length, e.g. in sub-frames, of the upcoming transmission. Alternatively the transmission length is implicitly deduced from the size of the two-dimensional bitmap in case its size is designed to be dynamically changing with the transmission length.
A real number indicating an operator id, so as to aid the UE in distinguishing which operator the transmitting network node belongs to.
For example, consider the following assumptions:
> Assume nrof_SE Scheduling Identities (UE:s or groups of UE:s) can be scheduled
—Assume to use a bit-map type of addressing, i.e. Nrof SE bits required to make it flexible to address one or many scheduling identities per transmission time interval, TTI.
—Assume support for nrof_operators operator ID:s
—Assume the operator to be semi-static.
> Assume nrof_bits_operatorID bits required for identifying the operator.
> Assume nrof_tl_alternatives transmission length alternatives e.g. 4, 6, or 8 sub-frames, and max_transmission_length to be the alternative with the highest value, i.e. the longest duration.
the message would then for example comprise of the following information entities,
Scheduling information bitmap (nrof_SE* max_transmission_length)
Transmission length (log2(tl_alternatives) bits)
Operator ID (nrof_bits_operator ID bits).
From this, a number of variants of solutions may be provided. For example, the message bits may be encoded using existing PDCCH processing, as described above, but using a new DCI format that only contains the information mentioned above. Another example is that a single PDCCH symbol is used (CFI=1). This single symbol may comprise one or more PDCCH transmissions that can be combined with reference signals for an arbitrary number of transmission ports. The single symbol can further be transmitted every OFDM symbol from the point in time that LBT succeeds at the eNodeB transmitter, serving to both reserve the channel as well as info in the UEs about upcoming scheduling so that UEs not scheduled can turn off their receivers and save power. Another example is that the message bits are encoded using a generic coding scheme such as time/frequency block coding, convolutional coding, etc., and then mapped to resource elements in a single LTE symbol which is repeated from the point in time that LBT succeeds at the eNodeB. Still another example is that any baseline reservation signal is multiplied with an orthogonal cover code with a length long enough to index the different permutations that convey the information, prior to being mapped to resource elements in a single LTE symbol which is repeated from the point in time that LBT succeeds at the eNodeB. Further still another example is that the information is conveyed by assigning a time-domain signal to each permutation of the information bits such as e.g. a constant amplitude zero autocorrelation (CAZAC) sequence such as a Zadoff-Chu sequence with different cyclic shifts and q index. The UE can decode the message e.g. by performing time-domain correlation with each pre-defined signal alternative.
The embeddings of information in the reservation signal may include encoding the information to be embedded according to a predetermined coding scheme and mapping the encoded information to one or more symbols.
The embeddings of information in the reservation signal may include indexing the information to be embedded into an orthogonal cover code, multiplying a baseline reservation signal with the orthogonal cover code, and mapping the encoded information to one or more symbols.
The embeddings of information in the reservation signal may include assigning a time-domain signal for any permutation of the information to be embedded, wherein the time-domain signal is a Constant Amplitude Zero AutoCorrelation, CAZAC, sequence with different cyclic shifts or indices for the permutations, and mapping the time-domain signal to one or more symbols.
The embeddings of information in the reservation signal may include repeating the mapped symbol for a plurality of or all symbols of the reservation signal.
The determination 1008 whether the signal is of interest for the transceiver station includes for example determining whether the signal comprises information indicating that it is transmitted from a serving cell of the transceiver station, and/or the signal comprises information indicating that the transceiver station is an intended recipient. The information indicating that the signal is transmitted from a serving cell of the transceiver station may for example include information about a cell identity, an operator operating the network, a network identity, etc. The information indicating that the transceiver station is an intended recipient may for example include information about a station scheduled for data transmission, a scheduling group of stations scheduled for the data transmission, etc.
The methods according to the present invention are suitable for implementation with aid of processing means, such as computers and/or processors, especially for the case where the network node or transceiver station is controlled by a processor. Therefore, there is provided computer programs, comprising instructions arranged to cause the processing means, processor, or computer to perform the steps of any of the methods according to any of the embodiments described above. The computer programs preferably comprises program code which is stored on a computer readable medium 1400, as illustrated in
The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/053340 | 2/17/2015 | WO | 00 |
