DESC:FORM 2
THE PATENTS ACT, 1970
[39 of 1970]
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(Section 10; Rule 13)

METHOD FOR ENABLING CHANNEL RETENTION FOR CELLULAR COMMUNICATIONS ON UN-LICENSED TRANSMISSION BAND

SAMSUNG R&D INSTITUTE INDIA – BANGALORE Pvt. Ltd.
# 2870, ORION Building, Bagmane Constellation Business Park,
Outer Ring Road, Doddanakundi Circle,
Marathahalli Post,
Bangalore -560037, Karnataka, India
Indian Company

The following Specification particularly describes the invention and
the method it is being performed

RELATED APPLICATION
The present invention claims benefit of the Indian Provisional Application No. 4502/CHE/2014 titled "METHOD FOR ENABLING CHANNEL RETENTION FOR CELLULAR COMMUNICATIONS ON UN-LICENSED BAND” by Samsung R&D Institute India – Bangalore Private Limited, filed on 15th September 2014, which is herein incorporated in its entirety by reference for all purposes.

FIELD OF THE INVENTION

The present invention generally relates to broadband wireless access communications networks. More particularly embodiments of the present invention relates to licensed carrier assisted operation of cellular communications in unlicensed transmission spectrum.

BACKGROUND OF THE INVENTION

The cellular industry which was until now unassumingly built on the basic premise of operating over licensed spectrum is considering the usage of operation on unlicensed band in order to meet the surging traffic demands. The unlicensed bands are typically dominated by Wi-Fi and other technologies. 3GPP has already decided to customize LTE standards in the LTE Release 13 for operation on the unlicensed bands and to exist harmoniously with WiFi and other technologies. Unlicensed band is free to be used by any technology but is governed by few regulations (in most countries) like the requirement of “Listen Before Talk – LBT” which requires a transmitter to sense the channel for at least 20 us and if the channel is found to be free (not used by other devices) then it is allowed to transmit. Further the regulations allow for transmissions up to a maximum time limit and also provide means for giving fairness to the other devices/technologies. A typical example of LBT regulation can be referred to in European Union (EU) regulation for operation on unlicensed band as per the document “ETSI EN 301 893 v1.7.0 (2012-01)”.

Further, the EU regulation also classifies the equipment that can access the unlicensed spectrum into Frame Based Equipment (FBE) and Load Based Equipment (LBE). The FBE performs channel sensing periodically at the fixed time periods resembling the typical frame periods that is characteristic of most cellular systems, as illustrated in Figure 1. Figure 1 is a schematic diagram 100 illustrating channel sensing by the FBE, according to the existing art. The LBE can perform channel sensing at any time without any constraints as in FBE. The channel sensing mechanism which is designed to give fairness among the competing nodes for channel access is referred from “IEEE802.11-2007”. It is to be noted that IEEE802.11 (Wi-Fi), which is a popular technology for operating on the unlicensed spectrum, is based on LBE.

In the legacy 3GPP LTE system, the concept of carrier aggregation is used in which multiple carriers can be allocated to a multi-carrier capable UE in order to boost the data rates. One carrier is referred to as the Primary carrier and the other carriers are referred to as the secondary carriers. Figure 2 is a schematic diagram 200 illustrating a self-carrier and cross carrier based scheduling, according to a prior art illustration. According to the Figure 2, the two UE’s UE1 202 and UE2 204 are allocated with the primary carrier 206 and the secondary carrier 208. The sub-frame boundaries on the carriers are considered to be aligned. Further, the scheduling can be self-carrier based or cross carrier based. In the self-carrier mode, a Physical Downlink Control Channel (PDCCH) for a secondary carrier 208 is sent on the secondary carrier 208, while in the cross carrier mode, the resource allocation for all the secondary carriers 208 is contained in the PDCCH that is sent on the primary carrier 206.

In the context of using LTE on unlicensed spectrum, it has been foreseen and agreed by various industry partners in 3GPP that LBE is more favorable approach at least for the downlink transmission (from eNB to UEs) on the unlicensed channel. This can be further referred to in the 3GPP technical report “TR 36.889 v1.0.1”.

3GPP is designing LTE-LAA (LTE Licensed Assisted Access) for operation on unlicensed bands considering the requirement that LTE-LAA has to be fair in channel access across the technologies already in operation on unlicensed bands (like IEEE802.11). However, when the unlicensed carrier is to be used as a secondary carrier, considering that the frame structure of the LTE should be largely re-used, an issue of channel retention is foreseen which stems from the fact that the channel is to be retained after the channel is sensed to be available (as a result of LBT) till the upcoming sub-frame boundary when channel sensing is based on LBE. Figure 3 is a schematic diagram 300 illustrating implementation of an unlicensed carrier as a secondary carrier, according to a prior art illustration. The schematic diagram 300 comprises of a licensed carrier 306 and the unlicensed carrier 308 for transmission of packets for UE1 302 and UE2 304. Since the channel sensing for the unlicensed carrier 308 can be done at any time in LBE, if the channel is found to be available for use, then the channel needs to be retained until the start of the symbol boundary else other users of the unlicensed carrier (like Wi-Fi nodes) can usurp the channel. It is to be noted that if channel sensing is performed just before the start of the sub-frame boundary (for a duration as required by regulations – it is further referred to DIFS for example which is used in Wi-Fi for the same purpose), it drastically impacts the channel availability probability as non LTE-U users of the channel (like Wi-Fi), which do not work on fixed frame structures can sense and start transmission at any time.

During this retention duration, active communication with the intended receiver(s) is not possible as the PDCCH can only be sent at the start of the sub-frame in the legacy system. It is to be further noted that the retention duration is counted in the maximum channel occupancy duration which is the time the node can occupy the channel after successfully grabbing the channel as a result of channel sensing. Since no data communication can happen with the intended receiver during the retention duration, In view of the foregoing, there is a need to minimize the channel retention period in order to increase the unlicensed channel usage.

The above mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.

SUMMARY OF THE INVENTION
The various embodiments of the present invention disclose a method and system for reducing channel retention time on the unlicensed band transmission band. The method comprises of checking, by an eNodeB, if an unlicensed channel is free for data transmission, computing a channel retention time for which the unlicensed channel need to be retained before the data transmission is initiated, if the unlicensed channel is free for data transmission and transmitting a preservation signal on the unlicensed channel for the computed channel retention time.

According to an embodiment of the present invention, the time duration for which the unlicensed channel is to be retained is the time until the start of a subsequent sub-frame boundary. The eNB transmits the indication to the UE in at least one of a Physical Downlink Control Channel (PDCCH), a new Reference signal during a retention period or a reserved code of the Channel Reference Signal (CRS) pre-specified to the UE. According to another embodiment of the present invention, the unlicensed channel is time domain aligned at a sub-frame level with the start of the sub-frame on the licensed channel.

According to an embodiment of the present invention, the eNB transmits one of a Channel Reference Signal (CS) repetition of a PDCCH and a Random wideband Interference for the UE to retain the unlicensed channel until the start of the sub frame on the unlicensed channel. Here the channel retention time is a time duration upto a maximum of a sub-frame.

According to an embodiment of the present invention, the method further comprises of indicating, by the eNB, usage of self-scheduling on the unlicensed channel during the subsequent channel occupancy period when eNB gets the unlicensed channel, and switching, by the UE, the RF of the unlicensed channel to a low power mode by not actively monitoring the unlicensed channel.

According to an embodiment of the present invention, the method further comprises of indicating, by the eNB, to the UE an intent of using the unlicensed channel before performing a channel sensing and switching ON by the UE the unlicensed RF for reception on the unlicensed channel. The eNB transmits the indication to the UE as at least one of a unicast signal, a broadcast signal or a special code/index of a legacy reference signal RS or new RS.

Another embodiment of the present invention disclose a method of enabling channel retention for cellular communications on an unlicensed transmission band, the method comprises of assessing, by an eNodeB, presence of a clear channel indication, checking if an unlicensed channel is free for data transmission, computing a time duration for which the unlicensed channel need to be retained if the unlicensed channel is free for data transmission, transmitting a preservation signal to the unlicensed channel for the determined time duration, transmitting a Physical Downlink Control Channel (PDCCH) along with a PDCCH presence indicator to a User Equipment (UE) in a licensed channel, monitoring by the UE, presence of PDCCH on the unlicensed channel at the PDCCH start boundaries, checking if the PDCCH presence indicator is present or not, and decoding the PDCCH if the PDCCH presence indicator is present.

According to an embodiment of the present invention, the time duration for which the unlicensed channel is to be retained is the time until the start of a subsequent sub-frame boundary. The sub-frame boundary on the unlicensed channel starts at one of start of the sub frame on the licensed carrier aligned with the sub-frame boundary on the unlicensed channel, start at any OFDM symbol on the unlicensed channel and any pre-configured start boundaries in units of OFDM symbols. Here the unlicensed channel is time domain aligned at a sub-frame level with the start of the sub-frame on the licensed channel.

According to an embodiment of the present invention, the eNB transmits at least one of a repetition of a Cell Specific Reference Signal (CRS) or repetition of a PDCCH and a Random wideband Interference to retain the unlicensed channel until the start of the sub frame on the unlicensed channel. Further, the eNB transmits a reduced preservation signal on one of a fractional OFDM symbol if the channel retention duration is not an integral multiple of the OFDM symbol duration.

According to an embodiment of the present invention, the reduced preservation signal which is transmitted on the fractional OFDM symbol is generated by removing samples of a preservation signal which lie outside the fractional OFDM symbol.

According to an embodiment of the present invention, the channel retention time is a time duration upto a maximum of a sub-frame.

According to an embodiment of the present invention, the method further comprises of indicating, by the eNB, usage of self-scheduling on the unlicensed channel during the subsequent channel occupancy period when eNB gets the unlicensed channel.

According to an embodiment of the present invention, the method further comprises of indicating, by the eNB, to the UE an intent of using the unlicensed channel before performing a channel sensing; and switching ON by the UE the unlicensed RF for reception on the unlicensed channel unless the indication is received.

According to an embodiment of the present invention, the eNB transmits the indication to the UE as at least one of a unicast signal, a broadcast signal or a special code/index of a legacy reference signal RS or new RS.

According to another embodiment of the present invention, the method for enabling channel retention for cellular communications on an unlicensed transmission band comprises of checking, by an eNodeB, if an unlicensed channel is free for data transmission, computing a channel retention time for which the unlicensed channel need to be retained before the data transmission is initiated, if the unlicensed channel is free for data transmission, transmitting a preservation signal on the unlicensed channel for the computed channel retention time, informing to a User Equipment (UE) on a licensed channel, an indication regarding transmission status on the unlicensed channel from a subsequent sub-frame after acquiring the unlicensed channel and initiating, by the UE, signal reception on the unlicensed channel from the subsequent sub-frame based on the indication from the eNB.

According to an embodiment of the present invention, the eNB transmits the indication to the UE as at least one of a unicast signal, a broadcast signal or a special code/index of a legacy reference signal RS or new RS.

According to yet another embodiment of the present invention, the method of enabling channel retention for cellular communications on an unlicensed transmission band comprises of assessing, by an eNodeB, if an unlicensed channel is free for data transmission, computing a time duration for which the unlicensed channel need to be retained if the unlicensed channel is free for data transmission, transmitting a preservation signal to the unlicensed channel for the determined time duration, transmitting a Physical Downlink Control Channel (PDCCH) presence indicator to a User Equipment (UE) in a unlicensed channel at PDCCH start boundaries, monitoring by the UE, presence of the PDCCH presence indicator on the unlicensed channel at the PDCCH start boundaries, checking if the PDCCH presence indicator is present or not and switching to a micro-sleep if the PDCCH presence indicator is not present.

According to an embodiment of the present invention, the channel retention time is a maximum upto a duration of the PDCCH.

According to an embodiment of the present invention, the start of the sub-frame on the unlicensed channel occurs at pre-defined boundaries with respect to the sub-frame on the licensed channel, where the predefined boundaries can be pre-specified or are indicated to the UE in a broadcast or unicast manner.

According to an embodiment of the present invention, the eNB broadcasts the start boundaries to the UE in at least one of a new system information block, an unicast RRC signalling when the unlicensed channel is pre-configured or activated, a digit which indicates a gap between the start of the boundaries in a number of OFDM symbols units considering that the first OFDM symbol at the start of the sub-frame is the start boundary, exact OFDM symbol numbers which are the possible start boundaries of the PDCCH, a repetition period of the start of the sub-frame boundaries, a start offset in addition to repetition period of the start of the sub-frame boundaries and a PDCCH in a self-carrier scheduling mode.

According to an embodiment of the present invention, the eNB initiates transmission of preservation signal on the unlicensed channel, where the preservation signal is at least one of a legacy Reference Signal (RS), a repetition of PDCCH or a new wide band signal adapted for performing channel estimation and measurement of the unlicensed channel.

According to an embodiment of the present invention, an OFDM symbol at the start of the sub-frame on the unlicensed channel contains a PDCCH presence indicator.

Another embodiment of the present invention disclose a method of enabling channel retention for cellular communications on an unlicensed transmission band. The method comprises of assessing, by an eNodeB if an unlicensed channel is free for data transmission, computing a time duration for which the unlicensed channel need to be retained if the unlicensed channel is free for data transmission, transmitting a preservation signal to the unlicensed channel for the determined time duration, informing to a User Equipment (UE) on licensed channel for monitoring of unlicensed channel, transmitting data along with start preamble of the unlicensed channel to the UE, monitoring by the UE, presence of a Physical Downlink Control Channel (PDCCH) on the unlicensed channel at the PDCCH start boundaries, checking if a start preamble is present or not in the data transmitted from the eNB and decoding PDCCH and data if the start preamble is present.

According to an embodiment of the present invention, the time duration for which the unlicensed channel is to be retained is the time until the start of a subsequent sub-frame boundary.

According to an embodiment of the present invention, the signal transmission occurs at a boundary where the unlicensed channel and the licensed channel are aligned at an OFDM symbol level.

According to an embodiment of the present invention, the eNB transmits the PDCCH in a cross-carrier scheduling mode on the licensed channel for the upcoming data transmission on the unlicensed channel.The eNB transmits the indication to the UE in at least one of a (E) PDCCH, a new reference signal during retention period or a special reserved code of the channel reference signal. Here the start preamble is a PDCCH presence indicator.

According to an embodiment of the present invention, the method further comprises of transmitting, by the eNB, one of a channel release command to the UE when the eNB intends to release the unlicensed channel and switching OFF by the UE the unlicensed RF for reception on the unlicensed channel when the indication is received.

The foregoing has outlined, in general, the various aspects of the invention and is to serve as an aid to better understanding the more complete detailed description which is to follow. In reference to such, there is to be a clear understanding that the present invention is not limited to the method or application of use described and illustrated herein. It is intended that any other advantages and objects of the present invention that become apparent or obvious from the detailed description or illustrations contained herein are within the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS
The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:

Figure 1 is a schematic diagram illustrating channel sensing by the FBE, according to the existing art.

Figure 2 is a schematic diagram illustrating a self-carrier and cross carrier based scheduling, according to a prior art illustration.

Figure 3 is a schematic diagram illustrating implementation of an unlicensed carrier as a secondary carrier, according to a prior art illustration.

Figure 4A is schematic diagram illustrating transmission of the signal on the unlicensed carrier for channel estimation and measurement of the unlicensed channel, according to another embodiment of the present invention.

Figure 4B is a flow chart illustrating transmission of the signal on the unlicensed carrier for channel estimation and measurement of the unlicensed channel, according to an embodiment of the present invention.

Figure 4C is a schematic diagram illustrating transmission of the signal on the unlicensed carrier for channel estimation and measurement of the unlicensed channel, according to another embodiment of the present invention.

Figure 4D is a schematic diagram illustrating transmission of the signal on the unlicensed carrier for channel estimation and measurement of the unlicensed channel, according to yet an embodiment of the present invention.

Figure 5A is a schematic diagram illustrating transmission of the signal on the unlicensed carrier for channel estimation and measurement of the unlicensed channel, according to another embodiment of the present invention.

Figure 5B is a flow chart illustrating a method of monitoring of unlicensed channel from a UE, according to an embodiment of the present invention.

Figure 5C is a flow chart illustrating a method of signaling UE with intent of using the unlicensed channel before performing channel sensing by the eNodeB, according to an embodiment of the present invention.

Figure 6A is a flow diagram illustrating signaling sub-frame boundaries between an eNodeB and a UE, according to an embodiment of the present invention.

Figure 6B is a schematic diagram illustrating transmission of the signal on the unlicensed carrier for channel estimation and measurement of the unlicensed channel, according to another embodiment of the present invention.

Figure 6C is a flow chart illustrating a method of transmitting signal on the unlicensed carrier for channel estimation and measurement of the unlicensed channel, according to yet another embodiment of the present invention.

Figure 7A is a schematic diagram illustrating enabling channel retention for cellular communications on an unlicensed transmission band, according to yet another embodiment of the present invention.

Figure 7B is a flow chart illustrating a method for enabling channel retention for cellular communications on an unlicensed transmission band, according to another embodiment of the present invention.

Figure 7C is a schematic diagram illustrating enabling channel retention for cellular communications on an unlicensed transmission band, according to yet another embodiment of the present invention.

Figure 8 is a schematic diagram illustrating enabling channel retention for cellular communications on an unlicensed transmission band, according to yet another embodiment of the present invention.

Although specific features of the present invention are shown in some drawings and not in others, this is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The various embodiments of the present invention disclose a method and system for reducing channel retention time and also provide multiple options for the signal which can be used for the preservation/retention of the channel on the unlicensed band. In the following detailed description of the embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.

The specification may refer to “an”, “one” or “some” embodiment(s) in several locations. This does not necessarily imply that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.

As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes”, “comprises”, “including” and/or “comprising” when used in this specification, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations and arrangements of one or more of the associated listed items.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

According to an embodiment herein, the terms unlicensed carrier and unlicensed channel are used interchangeably throughout the document.

The present invention provides various method and system for reducing channel retention time of the channel on the unlicensed band. Figure 4A is a schematic diagram illustrating transmission of the signal on the unlicensed carrier for channel estimation and measurement of the unlicensed channel, according to another embodiment of the present invention. The schematic diagram 400 comprises of UE1 402, UE2 404, a licensed carrier 406 and an unlicensed carrier 408. According to the Figure 4A, the unlicensed carrier 408 is considered to be time domain aligned at a sub-frame level with the start of the sub-frame on the licensed carrier 406. The PDCCH is considered to be sent at the start of the sub-frame in cross carrier scheduling mode. The channel retention time is up to a maximum of one sub-frame. In order to retain the channel, the LTE-U eNB needs to transmit on the unlicensed carrier 408, wherein the transmission can be either a legacy Reference Signal RS, such as, but not limited to, CRS, PRS, PSS, SSS, DRS, and the like or it can be composed of repetition of PDCCH or a new wide band signal can be designed that can further aid the channel estimation and measurement of the unlicensed carrier 408. The channel retention reference signal is further referred to as CR-RS. If the legacy signals are used as CR-RS, the entire duration of CR-RS, which is computed as the time difference from the end of channel sensing till the start of the subsequent sub-frame boundary, is constituted of continuous repetitions of the considered legacy signals. For example, CRS can be repeated for every symbol in the entire channel retention duration. In yet another embodiment of the present invention, any signal, which may be amplified noise as well, can be transmitted by the transmitter as the CR-RS.

Figure 4B is a schematic flow diagram 410 illustrating transmission of the signal on the unlicensed channel for channel estimation and measurement of the unlicensed channel, according to an embodiment of the present invention. The flow diagram 410 illustrates communication between an eNodeB 412 and a UE 414 for enabling channel retention on the unlicensed channel. According to the flow diagram 410, at step 416, the eNodeB 412 performs a clear channel assessment to identify whether the unlicensed channel is free and available for data transmission or is occupied by any other UE. At step 418, the eNodeB checks whether the unlicensed channel/ channel is free or not. If the eNodeB identifies that the unlicensed channel is free, then the eNodeB 412 moves to step 420, otherwise the step 416 is repeated again to perform assessment of the clear channel. In an embodiment of the present invention, the eNodeB 412 can perform assessment of the clear channel periodically, upon receiving signal from the UE 414 upon freeing the signal, or based on any of the known scenario, without departing from the scope of the invention.

At step 420, the eNodeB 412 computes the channel retention time for which the unlicensed channel needs to be preserved for data transmission of the UE 414. At step 422, the eNodeB 412 transmits the preservation signal to the UE 414 indicating that the unlicensed channel is preserved for the computed channel time duration. At step 424, the UE 414 starts the reception on the unlicensed channel from the start of the next sub-frame.

According to another scenario of the present invention, the retention duration may not be an integral multiple of the Orthogonal Frequency Division Multiplexing (OFDM) symbol duration, as described in Figure 4C.

Figure 4C is a schematic diagram 430 illustrating transmission of the signal on the unlicensed channel for channel estimation and measurement of the unlicensed channel, according to an embodiment of the present invention. According to the diagram 430, the channel retention duration may not be an integral multiple of the OFDM symbol duration and hence the CR-RS for the reduced OFDM symbol needs to be defined.. One method of construction of the reduced CR-RS can be to chop the RF samples corresponding to a symbol which do not fall within the reduced symbol. The full OFDM symbol transmission can be started from the subsequent OFDM symbol boundary following the end of channel sensing. The reduced OFDM symbol can be considered from the end of channel sensing till the start of the subsequent OFDM symbol boundary. In another embodiment of the present invention, the CR-RS is not considered for reduced OFDM symbol, which implies that no transmission is done from the end of channel sensing until the start of the subsequent OFDM symbol boundary for retaining of the channel during the reduced OFDM symbol duration. However in the subsequent full OFDM symbols, the CR-RS is transmitted during the channel retention duration.

In another embodiment of the present invention, after the channel sensing if the LTE-U eNB is able to get the channel, the eNodeB can indicate to the UE on the licensed channel that it will start the transmission on the unlicensed channel from the next sub-frame, as described in Figure 4D. Figure 4D is a schematic diagram 440 illustrating transmission of the signal on the unlicensed channel for channel estimation and measurement of the unlicensed channel, according to yet another embodiment of the present invention. According to the schematic diagram 440, upon receiving the information from the eNodeB that the eNodeB can start transmission on the unlicensed channel from the next sub-frame, the UE can start reception on the unlicensed channel from the next sub-frame else the UE can keep the RF of the unlicensed channel in low power mode by not actively monitoring the unlicensed channel unnecessarily. The indication can be sent in the Enhanced Physical Downlink Control Channel (E) PDCCH if possible or as a new RS during the retention period or a special reserved code of the CRS can be used to signal that the eNB has been able to grab the unlicensed channel. If a special code/index of an existing/legacy RS is to be used as the said indicator then it needs to be pre-specified or broadcasted or configured to the UE so that the UE is aware of the specific indicator for the said purpose.

According to another embodiment, the unlicensed channel can be considered to be time domain aligned at a sub-frame level with the start of the sub-frame on the primary carrier. According to the present embodiment, the PDCCH is considered to be sent at the start of the sub-frame in self-carrier scheduling mode. The channel retention time is up to a maximum of one sub-frame. In order to retain the channel, the LTE-U eNB needs to transmit on the unlicensed channel, wherein the transmission can be either a legacy Reference Signal (RS), such as, but not limited to CRS, PRS, PSS, SSS, DRS and the like, or it can be composed of repetition of PDCCH or a new wide band signal can be designed that can further aid the channel estimation and measurement of the unlicensed channel. Figure 5A is a schematic diagram 500 illustrating transmission of the signal on the unlicensed channel for channel estimation and measurement of the unlicensed channel, according to another embodiment of the present invention. According to the diagram 500, the channel retention RS is further referred to as CR-RS. If the legacy signals are used as CR-RS, the entire duration of CR-RS, which is computed as the time difference from the end of channel sensing till the start of the subsequent sub-frame boundary, is constituted of continuous repetitions of the considered legacy signals. For example, CRS can be repeated for every symbol in the entire channel retention duration. In yet another embodiment, any signal (which may be amplified noise as well) can be transmitted by the transmitter as the CR-RS. The other embodiments as mentioned for the cross carrier scheduling case above are applicable for this scenario as well.

In one embodiment of the present invention, after the channel sensing if the LTE-U eNB is able to get the channel, it can indicate to the UE on the licensed channel that it will start the transmission on the unlicensed channel from the next sub-frame. The eNB can also indicate that Self-Scheduling will be used on the unlicensed channel during the upcoming channel occupancy period. The UE on receiving this information can start reception on the unlicensed channel from the next sub-frame else the UE can keep the RF of the unlicensed channel in low power mode by not actively monitoring the unlicensed channel unnecessarily. The indication can be sent in the (E) PDCCH if possible or as a new RS during the retention period or a special reserved code of the CRS can be used to signal that the eNB has been able to grab the unlicensed channel. If a special code/index of an existing/legacy RS is to be used as the said indicator then it needs to be pre-specified or broadcasted or configured to the UE so that the UE is aware of the specific indicator for the said purpose. In one exemplification of the said embodiments, one CRS code per cell can indicate no unlicensed channel usage in subsequent sub-frame while another can indicate unlicensed channel usage in subsequent sub-frame with cross carrier scheduling while yet another can indicate unlicensed channel usage in subsequent sub-frame with self-carrier scheduling.

Figure 5B is a schematic flow diagram 510 illustrating monitoring of unlicensed channel from a UE, according to an embodiment of the present invention. The flow diagram illustrates an eNodeB 512 and the UE 514, wherein the UE 514 monitors the unlicensed channel for data transmission. According to the flow diagram 510, at step 516, the eNodeB 512 checks whether the clear channel assessment is successful or not. If yes, then at step 518, the eNodeB 512 transmits the CRS index to the UE 514 indicating the unlicensed channel occupancy and/ or scheduling type information of the same. If no, then the eNodeB 512 keeps on performing clear channel assessment. The clear channel assessment performed by the eNodeB is clearly described in the herein above mentioned embodiments, and therefore not described again to avoid repetition.

Upon receiving the CRS index from the eNodeB 512, at step 520, the UE 514 checks if the CRS index denotes usage of the unlicensed channel. If yes, then at step 522, the UE 514 monitors the unlicensed channel from the next sub-frame. If no, then the method moves to step 524, wherein the UE 514 does not monitor the unlicensed channel for the next sub-frame.

In another embodiment of the present invention, the eNodeB can signal its intent of using the unlicensed channel to the UE in advance, which can be even before performing channel sensing, so that the UE can switch ON its unlicensed RF and be ready for reception on unlicensed carrier. The signaling can be in unicast or broadcast manner at any of the physical layer (PHY), medium access control (MAC) layer or radio resource control (RRC) level. For example, the (E) PDCCH can be used for this purpose. A new DCI needs to be created or a reserved field in an existing DCI can be used for this purpose. Alternatively, a special code/index of an existing/new RS can be used to signal the start implicitly.

Figure 5C is a schematic flow diagram 530 illustrating the eNodeB 532 signaling intent of using the unlicensed channel to the UE 534 in advance before performing channel sensing, according to an embodiment of the present invention. According to the flow diagram 530, at step 536, the eNodeB 532 transmits CRS index to the UE 534, wherein the CRS index denotes unlicensed channel occupancy and/ or scheduling type. In an embodiment of the present invention, the CRS index can be of the type CRS1 that denotes intention to use unlicensed channel. In another embodiment of the present invention, the CRS index can be of the type CRS2 that denotes the any other type of access intention, without departing from the scope of the invention.

At step 538, the UE 534 starts monitoring the unlicensed channel based on the CRS index received from the eNodeB 532. At step 540, the eNodeB 532 checks whether the clear channel assessment is successful or not. If yes, then the eNodeB 532 uses the CRS1, or the eNodeB 532 uses the CRS2. Further at step 542, the UE 534 checks whether the CRS index denotes usage of the unlicensed channel. If yes, then at step 544, the UE 534 monitors the unlicensed channel from the next sub-frame. If no, then the method moves to step 546, wherein the UE 534 does not monitor the unlicensed channel for the next sub-frame.

According to an embodiment of the present invention, a method for enabling channel retention for cellular communications on an unlicensed transmission band is disclosed. The method discloses communication between an eNodeB and a UE, wherein the method includes the eNodeB assessing presence of a clear channel indication. The UE can be in need of the channel for transfer of data/ control packets. The eNodeB can assess the availability of the clear channel. The assessment of clear channel by the eNodeB is described in the herein above mentioned embodiment, and therefore not described herein again to avoid repetition.

Further, the method comprises step of checking if an unlicensed channel is free for data transmission. Upon identifying that the channel indication is clear for accessing, the eNodeB can further check whether the unlicensed channel that are available for the data transmission are free or not. In an embodiment of the present invention, the eNodeB can use any of the known channels checking mechanism, without departing from the scope of the invention.

Further, the method comprises step of computing a channel retention time for which the unlicensed channel need to be retained if the unlicensed channel is free for data transmission. The step of computing channel retention time is described in the herein above mentioned embodiments and therefore not described herein again to avoid repetition. Further, the method comprises step of transmitting a preservation signal to the unlicensed channel for the computed channel retention time. The method of transmitting preservation signal is also described in the herein above mentioned embodiments and therefore not described herein again to avoid repetition. In an embodiment of the present invention, the channel retention time is a maximum up to a duration of the PDCCH.

Further the method comprises step of transmitting a Physical Downlink Control Channel (PDCCH) along with a PDCCH presence indicator to a User Equipment (UE) in a licensed channel. The PDCCH along with the PDCCH presence indicator can be transmitted by the eNodeB to the UE for accessing the unlicensed channel on the licensed channel.

Further, the method comprises step of the UE monitoring presence of PDCCH on the unlicensed channel at the PDCCH start boundaries. The UE monitors the start of the PDCCH sub-frame boundaries on the unlicensed channels upon receiving the PDCCH and/or the PDCCH presence indicators from the eNodeB. In an embodiment of the present invention, the start of the sub-frame on the unlicensed channel occurs at pre-defined boundaries with respect to the sub-frame on the licensed channel, where the predefined boundaries can be pre-specified or are indicated to the UE in a broadcast or unicast manner.

In an embodiment of the present invention, the eNB broadcasts the start boundaries to the UE in at least one of, but not limited to, a new system information block, an unicast RRC signaling when the unlicensed channel is pre-configured or activated, a digit which indicates a gap between the start of the boundaries in a number of OFDM symbols units considering that the first OFDM symbol at the start of the sub-frame is the start boundary, exact OFDM symbol numbers which are the possible start boundaries of the PDCCH, a repetition period of the start of the sub-frame boundaries, a start offset in addition to repetition period of the start of the sub-frame boundaries, a PDCCH in a self-carrier scheduling mode, and the like, without departing from the scope of the invention.

In another embodiment of the present invention, the eNB initiates signal transmission on the unlicensed channel, where the signal transmission is at least one of, but not limited to, a legacy Reference Signal (RS), a repetition of PDCCH, a new wide band signal adapted for performing channel estimation and measurement of the unlicensed channel, and the like.

Further, the method comprises step of checking if the PDCCH presence indicator is present or not. The UE, upon monitoring the presence of the PDCCH at the start of the sub-frame of the PDCCH start boundaries on the unlicensed channel, also checks for the PDCCH presence indicators. In an embodiment of the present invention, the OFDM symbol at the start of the sub-frame on the unlicensed channel contains a PDCCH presence indicator, if a self-carrier scheduling mode is configured for the UE. In another embodiment of the present invention, the OFDM symbol at the start of the sub-frame on the unlicensed channel contains a sub-frame indicator indicating if the eNB was able to grab the unlicensed channel for transmission.

Further, the method comprises step of decoding the PDCCH, if the PDCCH presence indicator is present. If the UE identifies the presence of the PDCCH presence indicator at the start boundary on the unlicensed channel, the UE decodes the PDCCH. In an embodiment of the present invention, the UE on decoding the PDCCH presence indicator shifts to a micro-sleep mode until the next sub-frame start opportunity, if the PDCCH presence indicator indicates the absence of the PDCCH.

According to the current embodiment of the present invention, the start of the sub-frame on the unlicensed channel is not aligned to the start of the sub-frame on the licensed channel but it can only occur at pre-defined boundaries within the sub-frame. One example can be that the said pre-defined boundaries are spaced apart by the duration of PDCCH which is 2 or 3 symbols. It is to be noted that the OFDM symbols on the licensed and unlicensed channel may or may not be aligned in time. However, for the sake of further discussion, the symbols boundaries are considered to be aligned between the licensed and unlicensed channels. The pre-defined boundaries for the start of the sub-frame on the unlicensed channel with respect to the licensed channel can be pre-specified or are indicated to the UE in a broadcast or unicast manner. The eNB can broadcast the possible start boundaries in any of the system information. For example a new system information block can be created to signal information about the unlicensed channel. Alternatively, the possible start boundaries can be sent to the UE in unicast RRC signaling message. For example, when the unlicensed channel is configured or activated.

In one embodiment of the present invention, the possible start boundaries can be signaled using just one number which indicates the gap between the start of the boundaries in number of OFDM symbols units considering that the first OFDM symbol at the start of the sub-frame always is one of the possible start boundaries. For example the repetition period of the start boundaries can be indicated as 2 which implies that 1, 3, 5, 7, 9, 11, 13 are possible symbol start boundaries within a sub-frame.

In another embodiment, the exact OFDM symbol numbers can be indicated to the UE which are the possible start boundaries of the PDCCH. For example, the start boundaries can be 1, 3, 5, 9, 11th OFDM symbols wherein 1st denotes the first OFDM symbol of the sub-frame. In yet another embodiment a start offset can be given in addition to the repetition period of the start of the sub-frame boundaries. For example, start offset of 3 and repetition period of 4 indicates 4, 8, 12 are symbols that are possible sub-frame start boundaries. The signaling method is further illustrated in Figure 6A. In one of the embodiment the PDCCH is sent in self-carrier scheduling mode as in prior embodiments.

Figure 6A is a schematic flow diagram 600 illustrating signaling possible sub-frame boundaries between an eNodeB 602 and a UE 604, according to an embodiment of the present invention. According to the flow diagram 600, at step 606, the eNodeB 602 transmits possible sub-frame start boundaries on an unlicensed channel, wherein the possible sub-frame start boundaries can comprise of information such as, but not limited to, repetition period, start offset, exact symbol numbers and the like. Based on the received information from the eNodeB 602, at step 608, the UE 604 monitors the only start boundaries for start of the sub-frame.

Figure 6B is a schematic diagram 610 illustrating transmission of the signal on the unlicensed channel for channel estimation and measurement of the unlicensed channel, according to another embodiment of the present invention. According to the diagram 610, the UE scans for the PDCCH only at the specified start boundary opportunities. If no PDCCH is present at the specified start boundary, then the UE can go to sleep till the next PDCCH occurring boundary. However, it is to be noted that RF of the recipient (UE) needs to be in ON state to capture the received signal until the processing for the detection of the PDCCH is completed. The channel retention time is maximum up to duration of PDCCH. In order to retain the channel, the LTE-U eNB needs to transmit on the unlicensed channel, wherein the transmission can be either a legacy Reference Signal (RS), such as, but not limited to, Cell-specific reference signal (CRS), Position Reference Signals (PRS), Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS), and the like or it can be composed of repetition of PDCCH or a new wide band signal can be designed that can further aid the channel estimation and measurement of the unlicensed channel as in the above mentioned embodiments, without departing from the scope of the invention.

Figure 6C is a schematic flow diagram 620 illustrating transmission of the signal on the unlicensed channel for channel estimation and measurement of the unlicensed channel, according to yet another embodiment of the present invention. According to the flow diagram 620, at step 626, an eNodeB 622 performs clear channel assessment of an unlicensed channel for a UE 624 so that the UE 624 can obtain the unlicensed channel for data transmission. At step 628, the eNodeB checks if the unlicensed channel is free or not. If yes, then at step 630, the eNodeB 622 calculates channel retention time for the unlicensed channel based on the time till next PDCCH start boundary of the UE 624 so that the unlicensed channel can be provided to the UE 624 for data transmission.

At step 632, the eNodeB 622 transmits preservation signal to the UE 624 indicating the determined channel retention time. Further, at step 634, the eNodeB 622 transmits PDCCH along with the PDCCH presence indicator to the UE 624. At step 636, the UE 624 continuously monitors for the PDCCH on the unlicensed channel at the PDCCH boundaries. At step 638, the UE 624 checks for the presence of the PDCCH presence indicator at the start boundaries of the unlicensed channel. If the PDCCH presence is present at the start boundary, then, at step 640, the UE 624 decodes the PDCCH for data transmission on the unlicensed channel. If no, then the UE 624 continues with step 636 to monitor for the PDCCH on the unlicensed channel at the PDCCH boundaries.

According to another embodiment of the present invention, if the self-carrier scheduling mode is configured, the OFDM symbol at the start of the sub-frame start opportunities can contain a PDCCH presence indication. The UE on decoding the PDCCH presence indicator can go to micro-sleep till the next sub-frame start opportunity if the PDCCH presence indicator indicates the absence of the PDCCH and thereby leads to enhanced power savings. The PDCCH presence indicator can be designed to be easily decodable for example a pre-defined pair of PN codes wherein one code indicates presence while the other code represents absence of the PDCCH. Alternatively they can be pre-specified as in preceding embodiments. In one variant of the said embodiment, no extra indication is required to signal the absence of PDCCH.

In another embodiment of the present invention, the OFDM symbol at the start of the sub-frame on unlicensed channel can contain a sub-frame start indicator which indicates if the eNB was able to grab the channel and the transmission is actually being started. This is can be independent of the self or cross carrier scheduling modes. The sub-frame start indicator can be designed to be easily decodable for example a special PN code can indicate the start of the sub-frame. The UE can chose to enter micro-sleep till the next possible start boundary if the start indicator was not found at a possible start boundary.

According to yet another embodiment of the present invention, a method for enabling channel retention for cellular communications on an unlicensed transmission band is disclosed. The method discloses communication between an eNodeB and a UE, wherein the method includes the eNodeB assessing presence of a clear channel indication. The UE can be in need of the channel for transfer of data/ control packets. The eNodeB can assess the availability of the clear channel. The assessment of clear channel by the eNodeB is described in the herein above mentioned embodiment, and therefore not described herein again to avoid repetition.

Further, the method comprises step of checking if an unlicensed channel is free for data transmission. Upon identifying that the channel indication is clear for accessing, the eNodeB can further check whether the unlicensed channel that are available for the data transmission are free or not. In an embodiment of the present invention, the eNodeB can use any of the known channels checking mechanism, without departing from the scope of the invention.

Further, the method comprises step of computing a channel retention time for which the unlicensed channel need to be retained if the unlicensed channel is free for data transmission. The step of computing channel retention time is described in the herein above mentioned embodiments and therefore not described herein again to avoid repetition. Further, the method comprises step of transmitting a preservation signal to the unlicensed channel for the computed channel retention time. The method of transmitting preservation signal is also described in the herein above mentioned embodiments and therefore not described herein again to avoid repetition. In an embodiment of the present invention, the time duration for which the unlicensed channel is to be retained is the time until the start of a subsequent sub-frame boundary. In another embodiment of the present invention, the signal transmission occurs at a boundary where the unlicensed channel and the licensed channel are aligned at an OFDM symbol level.

Further, the method comprises of informing to a User Equipment (UE) on licensed channel for monitoring of unlicensed channel. The eNodeB, along with transmitting preservation signal to the UE, communicates the UE on the licensed channel and informs to monitor the unlicensed channel. In another embodiment of the present invention, the eNodeB transmits the PDCCH to the UE in a cross-carrier scheduling mode on the licensed channel for the upcoming data transmission on the unlicensed channel.

Further, the method comprises step of transmitting data along with start preamble of the unlicensed channel to the UE. Upon informing the UE on the licensed channel to monitor the unlicensed channel, the eNodeB transmits data to the UE along with start boundary preamble of the unlicensed channel. In an embodiment of the present invention, the eNodeB transmits the PDCCH in a cross-carrier scheduling mode on the licensed channel for the upcoming data transmission on the unlicensed channel.

In another embodiment of the present invention, the eNB transmits the indication to the UE in at least one of, but not limited to, a (E) PDCCH, a new reference signal during retention period, a special reserved code of the channel reference signal and the like. In another embodiment of the present invention, the start preamble is a PDCCH presence indicator, as described in the above mentioned embodiments.

Further, the method comprises of the UE monitoring presence of PDCCH on the unlicensed channel at the PDCCH start boundaries. The UE monitors the start of the PDCCH sub-frame boundaries on the unlicensed channels upon receiving the PDCCH and the PDCCH presence indicators from the eNodeB.

Further, the method comprises step of checking if a start preamble is present or not in the data transmitted from the eNodeB or not. The UE, upon monitoring the presence of PDCCH on the unlicensed channel, also checks for the presence of the start preamble on the unlicensed channel.

Further, the method comprises step of decoding the PDCCH and data, if the start preamble is present. If the UE identifies the presence of the start preamble on the unlicensed channel, then the UE decodes the PDCCH along with data. In another embodiment of the present invention, the eNodeB transmits one of a channel deactivation command to the UE when the eNB intends to release the unlicensed channel.

Figure 7A is schematic diagram 700 illustrating enabling channel retention for cellular communications on an unlicensed transmission band, according to yet another embodiment of the present invention. According to the diagram 700,a, the start of the sub-frame on the unlicensed channel is not aligned to the start of the sub-frame on the licensed channel, but it can start at any symbol boundary, wherein the unlicensed channel and the licensed channels are aligned at the OFDM symbol level. It is to be noted that the OFDM symbols on the licensed and the unlicensed channel may or may not be aligned in time. The PDCCH is sent in the cross carrier scheduling mode on the licensed channel for the upcoming data transmission on the unlicensed channel. The start of the transmission on the unlicensed band is not known and hence the UE continuously scans the unlicensed channel for the start of the transmission wherein the start of the transmission is characterized by a preamble/RS which is further referred to as the Start Preamble as in preceding embodiments.

Figure 7B is a schematic flow diagram 710 illustrating a method for enabling channel retention for cellular communications on an unlicensed transmission band, according to yet another embodiment of the present invention. According to the flow diagram 710, at step 716, an eNodeB 712 performs clear channel assessment of an unlicensed channel for a UE 714 so that the UE 714 can obtain the unlicensed channel for data transmission. At step 718, the eNodeB checks if the unlicensed channel is free or not. If yes, then at step 720, the eNodeB 712 calculates channel retention time for the unlicensed channel based on the time till next symbol start boundary of the UE 714 so that the unlicensed channel can be provided to the UE 714 for data transmission.

At step 722, the eNodeB 712 transmits preservation signal to the UE 714 indicating the determined channel retention time. Further, at step 724, the eNodeB 712 transmits information to the UE 714 on licensed channel for monitoring of the unlicensed channel. At step 726, the eNodeB further transmits data along with start preamble on the unlicensed channel. At step 728, the UE 714 continuously monitors for the PDCCH on the unlicensed channel at the start preamble. At step 730, the UE 714 checks for the presence of the start preamble on the unlicensed channel. If the start preamble is present on the unlicensed channel, then, at step 732, the UE 714 decodes the PDCCH and data for data transmission on the unlicensed channel. If no, then the UE 714 continues with step 728 to monitor for the PDCCH on the unlicensed channel.

In another embodiment of the present invention, after the channel sensing if the LTE-U eNB is able to get the channel, it can indicate to the UE on the licensed channel that it will start the transmission on the unlicensed channel from the next sub-frame. The eNB can also indicate that Self-Scheduling will be used on the unlicensed channel during the upcoming channel occupancy period. The UE on receiving this information can start reception on the unlicensed channel from the next sub-frame start boundary or as indicated by a start offset else the UE can keep the RF of the unlicensed channel in low power mode by not actively monitoring the unlicensed channel unnecessarily. The indication can be sent in the (E) PDCCH, if possible or as a new RS during the retention period or a special reserved code of the CRS can be used to signal that the eNB has been able to grab the unlicensed channel. If a special code/index of an existing/legacy RS is to be used as the said indicator then it needs to be pre-specified or broadcasted or configured to the UE so that the UE is aware of the specific indicator for the said purpose.

It is to be noted that it is less complex to gather and correlate the Start Preamble as compared to decoding the PDCCH in the abovementioned embodiment of the present invention. Furthermore, in one variant of the above embodiment, the PDCCH corresponding to the sub-frames apart from the first sub-frame (in the channel occupany duration of the unlicensed channel) can contain PDCCH in self-scheduling mode. Figure 7C is schematic diagram 740 illustrating enabling channel retention for cellular communications on an unlicensed transmission band, according to yet another embodiment of the present invention. According to the diagram 740, the PDCCH corresponding to the first sub-frame of the channel occupancy duration indicates resources for the entire channel occupancy duration. Further if the LTE-U eNB decides to release the unlicensed channel (for example, if all the data is completed for all the related UEs) then the LTE-U eNB can send a channel deactivation command on the licensed channel or the same can be indicated in the PDCCH which is sent in the licensed or the unlicensed channel. In one variant PDCCH presence indicator can act as the Start Preamble.

Figure 8 is a schematic diagram 800 illustrating enabling channel retention for cellular communications on an unlicensed transmission band, according to yet another embodiment of the present invention. According to the diagram 800, the start of the sub-frame on the unlicensed channel can is not aligned to the start of the sub-frame on the licensed channel but it can start at any symbol boundary wherein the unlicensed channel and the licensed channels are aligned at the OFDM symbol level. The PDCCH is sent in the self-carrier scheduling mode on the unlicensed channel. The start of the transmission on the unlicensed band is not known and hence the UE continuously scans the unlicensed channel for the start of the transmission. After the channel sensing if the LTE-U eNB is able to get the channel, it can indicate to the UE on the licensed channel that it will start the transmission on the unlicensed channel. The UE on receiving this information can start reception on the unlicensed channel immediately (after accounting for the RF switching ON time).

In the following detailed description of the embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.

,CLAIMS:
CLAIMS
We Claim:
1. A method of enabling channel retention for cellular communications on an unlicensed transmission band, the method comprises of:
checking, by an eNodeB, if an unlicensed channel is free for data transmission;
computing a channel retention time for which the unlicensed channel need to be retained before the data transmission is initiated, if the unlicensed channel is free for data transmission; and
transmitting a preservation signal on the unlicensed channel for the computed channel retention time.

2. The method of claim 1, wherein the time duration for which the unlicensed channel is to be retained is the time until the start of a subsequent sub-frame boundary.

3. The method of claim 2, wherein the sub-frame boundary on the unlicensed channel starts at one of:
start of the subframe on the licensed carrier aligned with the sub-frame boundary on the unlicenced channel;
start at any OFDM symbol on the unlicensed channel; and
any pre-configured start boundaries in units of OFDM symbols.

4. The method of claim1, wherein the unlicensed channel is time domain aligned at a sub-frame level with the start of the sub-frame on the licensed channel.

5. The method of claim 1, wherein the eNB transmits at least one of a repetition of a Cell Specific Reference Signal (CRS) or repetition of a PDCCH and a Random wideband Interference to retain the unlicensed channel until the start of the sub frame on the unlicensed channel.

6. The method of claim 1, wherein the eNB transmits a reduced preservation signal on one of a fractional OFDM symbol if the channel retention duration is not an integral multiple of the OFDM symbol duration.

7. The methods of claim 6, wherein the reduced preservation signal which is transmitted on the fractional OFDM symbol is generated by removing samples of a preservation signal which lie outside the fractional OFDM symbol.

8. The method of claim 1, wherein the channel retention time is a time duration upto a maximum of a sub-frame.

9. The method of claim 1, further comprising:
indicating, by the eNB, usage of self-scheduling on the unlicensed channel during the subsequent channel occupancy period when eNB gets the unlicensed channel.

10. The method of claim 1 further comprising:
indicating, by the eNB, to the UE an intent of using the unlicensed channel before performing a channel sensing; and
switching ON by the UE the unlicensed RF for reception on the unlicensed channel unless the indication is received.

11. The method of claim 10, wherein the eNB transmits the indication to the UE as at least one of a unicast signal, a broadcast signal or a special code/index of a legacy reference signal RS or new RS.

12. A method of enabling channel retention for cellular communications on an unlicensed transmission band, the method comprises of:
checking, by an eNodeB, if an unlicensed channel is free for data transmission;
computing a channel retention time for which the unlicensed channel need to be retained before the data transmission is initiated, if the unlicensed channel is free for data transmission;
transmitting a preservation signal on the unlicensed channel for the computed channel retention time;
informing to a User Equipment (UE) on a licensed channel, an indication regarding transmission status on the unlicensed channel from a subsequent sub-frame after acquiring the unlicensed channel; and
initiating, by the UE, signal reception on the unlicensed channel from the subsequent sub-frame based on the indication from the eNB.

13. The method of claim 11, wherein the eNB transmits the indication to the UE in at least one of a PDCCH, a new Reference signal during a retention period or a reserved code of a Channel Reference Signal (CRS) pre-specified to the UE.

14. The method of claim 11 wherein, the CRS index indicates the unlicensed channel status for the subsequent subframe such that a pair of CRS is pre-configured to the UE, one indicating the channel status as acquired while the other indicating the channel status as not acquired.

15. The method of claim 11 wherein, the indication to the UE indicates the channel status for the subsequent channel occupancy duration.

16. The method of claim 11, wherein the time duration for which the unlicensed channel is to be retained is the time until the start of a subsequent sub-frame boundary.

17. The method of claim 16, wherein the sub-frame boundary on the unlicensed channel starts at one of:
start of the subframe on the licensed carrier aligned with the sub-frame boundary on the unlicenced channel;
start at any OFDM symbol on the unlicensed channel; and
any pre-configured start boundaries in units of OFDM symbols.

18. The method of claim 11, wherein the unlicensed channel is time domain aligned at a sub-frame level with the start of the sub-frame on the licensed channel.

19. The method of claim 11, wherein the eNB transmits at least one of a repetition of a Cell Specific Reference Signal (CRS) or repetition of a PDCCH and a Random wideband Interference to retain the unlicensed channel until the start of the sub frame on the unlicensed channel.

20. The method of claim 11, wherein the eNB transmits a reduced preservation signal on one of a fractional OFDM symbol if the channel retention duration is not an integral multiple of the OFDM symbol duration.

21. The methods of claim 20, wherein the reduced preservation signal transmitted on the fractional OFDM symbol is generated by dividing the samples of a preservation signal which lie outside the fractional OFDM symbol.

22. The method of claim 11, further comprising:
indicating, by the eNB, usage of self-scheduling on the unlicensed channel during the subsequent channel occupancy period when eNB gets the unlicensed channel.

23. The method of claim 11 further comprising:
indicating, by the eNB, to the UE an intent of using the unlicensed channel before performing a channel sensing; and
switching ON by the UE the unlicensed RF for reception on the unlicensed channel unless the indication is received.

24. The method of claim 11, wherein the eNB transmits the indication to the UE as at least one of a unicast signal, a broadcast signal or a special code/index of a legacy reference signal RS or new RS.

25. A method of enabling channel retention for cellular communications on an unlicensed transmission band, the method comprises of:
assessing, by an eNodeB, if an unlicensed channel is free for data transmission;
computing a time duration for which the unlicensed channel need to be retained if the unlicensed channel is free for data transmission;
transmitting a preservation signal to the unlicensed channel for the determined time duration;
transmitting a Physical Downlink Control Channel (PDCCH) presence indicator to a User Equipment (UE) in a unlicensed channel at PDCCH start boundaries;
monitoring by the UE, presence of the PDCCH presence indicator on the unlicensed channel at the PDCCH start boundaries;
checking if the PDCCH presence indicator is present or not; and
switching to a micro-sleep if the PDCCH presence indicator is not present.

26. The method of claim 25, wherein the channel retention time is a maximum upto a duration of the PDCCH.

27. The method of claim 25, wherein the start of the sub-frame on the unlicensed channel occurs at pre-defined boundaries with respect to the sub-frame on the licensed channel, where the predefined boundaries can be pre-specified or are indicated to the UE in a broadcast or unicast manner.

28. The method of claim 25, wherein the eNB broadcasts the start boundaries to the UE in at least one of:
a new system information block;
an unicast RRC signalling when the unlicensed channel is pre-configured or activated;
a digit which indicates a gap between the start of the boundaries in a number of OFDM symbols units considering that the first OFDM symbol at the start of the sub-frame is the start boundary;
exact OFDM symbol numbers which are the possible start boundaries of the PDCCH;
a repetition period of the start of the sub-frame boundaries;
a start offset in addition to repetition period of the start of the sub-frame boundaries;
a PDCCH in a self-carrier scheduling mode.

29. The method of claim 25, wherein the eNB initiates transmission of preservation signal on the unlicensed channel, where the preservation signal is at least one of:
a legacy Reference Signal (RS);
a repetition of PDCCH; or
a new wide band signal adapted for performing channel estimation and measurement of the unlicensed channel.

30. The method of claim 25, wherein an OFDM symbol at the start of the sub-frame on the unlicensed channel contains a PDCCH presence indicator

31. A method of enabling channel retention for cellular communications on an unlicensed transmission band, the method comprises of:
assessing, by an eNodeB if an unlicensed channel is free for data transmission;
computing a time duration for which the unlicensed channel need to be retained if the unlicensed channel is free for data transmission;
transmitting a preservation signal to the unlicensed channel for the determined time duration;
informing to a User Equipment (UE) on licensed channel for monitoring of unlicensed channel;
transmitting data along with start preamble of the unlicensed channel to the UE;
monitoring by the UE, presence of a Physical Downlink Control Channel (PDCCH) on the unlicensed channel at the PDCCH start boundaries;
checking if a start preamble is present or not in the data transmitted from the eNB; and
decoding PDCCH and data if the start preamble is present.

32. The method of claim 31, wherein the time duration for which the unlicensed channel is to be retained is the time until the start of a subsequent sub-frame boundary.

33. The method of claim 31, wherein the signal transmission occurs at a boundary where the unlicensed channel and the licensed channel are aligned at an OFDM symbol level.

34. The method of claim 31, wherein the eNB transmits the PDCCH in a cross-carrier scheduling mode on the licensed channel for the upcoming data transmission on the unlicensed channel.

35. The method of claim 31, wherein the eNB transmits the indication to the UE in at least one of :
a (E) PDCCH;
a new reference signal during retention period; or
a special reserved code of the channel reference signal.

36. The method of claim 31, wherein the start preamble is a PDCCH presence indicator.

37. The method of claim 31, further comprising:
transmitting, by the eNB, one of a channel release command to the UE when the eNB intends to release the unlicensed channel; and
switching OF by the UE the unlicensed RF for reception on the unlicensed channel when the indication is received.

Dated this the 7th day of September 2015
Signature

KEERTHI J S
Patent agent
Agent for the applicant