Layered modulation for machine type communication (MTC) transmissions from multiple transceiver stations

A first transceiver station broadcasts information to machine type communication (MTC) devices in the coverage area of the transceiver station using layered modulation where MTC devices receiving the broadcast above a signal quality threshold can recover the MTC information by applying a high modulation order. MTC devices receiving the broadcast below the quality threshold, recover a portion of the MTC information by applying a lower modulation order and recover the remaining portion of the MTC information transmitted from a second transceiver.

RELATED PATENT APPLICATIONS

The present application is related to PCT Patent Application No. PCT/US2017/051003, entitled “LAYERED MODULATION FOR MACHINE TYPE COMMUNICATION (MTC) TRANSMISSIONS”, and PCT Patent Application No. PCT/US2017/051009, entitled “LAYERED MODULATION WITH MULTIPLE CODING RATES FOR MACHINE TYPE COMMUNICATION (MTC) TRANSMISSIONS”, both filed concurrently with this application, assigned to the assignee hereof, and hereby expressly incorporated by reference herein.

FIELD

This invention generally relates to wireless communications and more particularly to devices and methods for transmitting information to machine type communication (MTC) devices using layered modulation from multiple transceiver stations.

BACKGROUND

Machine type communication (MTC) is a form of data communication which involves one or more entities that do not necessarily need human interaction. Depending on the particular implementation, an MTC device may communicate with one or more servers or with other devices. The network operator provides network connectivity to MTC server(s) regardless of whether the MTC server is controlled by the network operator. An MTC device is typically a user equipment (UE) device that is equipped for Machine Type Communication and communicates through a public land mobile network (PLMN) with MTC Server(s) and/or other MTC Device(s). In some situations, an MTC device might also communicate locally through a hardwired or wireless connection with other entities.

MTC devices are increasingly being used in a variety of applications. Examples of some of the general areas of use include security, tracking, health, payment, remote diagnostics, metering and consumer electronics. Some of the many specific applications include surveillance system control, control of physical access (e.g. to buildings), fleet management, order management, asset tracking, navigation, traffic information, road tolling, point of sales, vending machines, gaming machines, vital signs monitoring, web access telemedicine points, remote maintenance and control of sensors, lighting, pumps, valves, and elevators, vehicle diagnostics, metering of power, gas, water and heating, grid control, and management and control of digital photo frames, cameras and eBooks.

SUMMARY

A first transceiver station broadcasts information to machine type communication (MTC) devices in the coverage area of the transceiver station using layered modulation where MTC devices receiving the broadcast above a signal quality threshold can recover the MTC information by applying a high modulation order. MTC devices receiving the broadcast below the quality threshold, recover a portion of the MTC information by applying a lower modulation order and recover the remaining portion of the MTC information transmitted from a second transceiver.

DETAILED DESCRIPTION

As mentioned above, MTC devices are increasingly being used for numerous applications where the MTC devices exchange information with other devices and servers. The network facilitating communication with the MTC devices must handle the increased traffic due to the numerous MTC devices while accommodating the particular requirements and limitations of the MTC devices. One important consideration includes minimizing the power consumption of the MTC device. As a result, it is advantageous to minimize the time that the MTC device transmits and receives data. In addition, in some situations, it is critical that the information be received uninterrupted at the MTC device. For example, firmware updates should not be interrupted.

Communication systems employ a variety of transmission techniques to maximize efficiency of network resources. One example includes broadcasting information to multiple devices simultaneously rather than establishing a dedicated channel to each of the devices. The same information may be broadcasted from several base stations to devices in multiple service areas. In other situations, however, the information is broadcasted in a single service area or cell. In systems operating in accordance with at least some revisions of The Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) specification, this broadcast is typically referred to as a single cell—point to multipoint (SC-PTM) transmission and is performed using Multimedia Broadcast Multicast Services (MBMS). For SC-PTM transmission of MBMS in accordance with 3GPP specifications, MBMS is transmitted in the coverage of a single cell where one Single Cell-Multicast Control Channel (SC-MCCH) and one or more single cell—multicast traffic channel(s) SC-MTCH(s) are mapped on a Downlink Shared Channel (DL-SCH). For conventional SC-PTM, the base station (eNB) and the core network (CN) schedule the SC-PTM transmissions. In particular, the SC-MCCH and SC-MTCH transmissions are each indicated by a logical channel specific Radio Network Temporary Identifier (RNTI) on the Physical Downlink Shared Channel (PDSCH). There is a one-to-one mapping between Temporary Mobile Group Identity (TMGI) and G-RNTI used for the reception of the DL-SCH to which a SC-MTCH is mapped. As with all existing broadcast mechanisms, including SC-PTM, the broadcast is not guaranteed to reach all UE devices within a cell. With conventional techniques, the broadcast multicast or Single-cell Point-to-Multipoint (SC-PTM) transmissions are designed to meet a target number of UE devices to be able to decode the data packets successfully. In most cases the broadcast transmissions are designed to provide a Block Error Rate less than one percent (BLER <1%) for 95% of the UE devices in the cell.

If higher robustness is needed (e.g., for firmware downloads where none of the data can be dropped for the download to be successful), and if the worst-channel condition information is available (e.g., with Channel State Information (CSI) feedback) then one of the viable solutions is for the base station to transmit the data robust enough to overcome those channel conditions. This may lead to increased use of resources, however, if broadcast data needs to be transmitted at lower MCS (to allow cell edge UEs to receive the broadcast successfully). Alternatively, higher power broadcast transmissions may be used, but resulting in increased interference to neighboring eNBs.

Other approaches for higher broadcast robustness are based on the use of Hybrid Automatic Repeat Request (HARQ) feedback from the receivers which were unable to decode the data successfully. The base station can then apply link-adaptation for the retransmissions. However, several factors need to be considered. If HARQ retransmissions or any type of feedback is needed from the UE it will be necessary for the MTC device to transmit feedback information to the eNB. This is not desirable for MTC devices, since the main criteria for the MTC UE device includes reducing power consumption. However, unlike other non-MTC applications, latency is generally not an issue for MTC UEs. Therefore, solutions for higher robustness could be achieved at the expense of higher latency.

Assuming feedback is not provided to the base station (eNB), it will be necessary for the eNB to decide how the SC-PTM transmissions should be configured. In particular, depending on the intended coverage of the SC-PTM transmissions, the base station (eNB) needs to decide the Modulation and Coding Scheme (MCS) configuration used for the transmissions. With higher MCS, more traffic data can be sent in a shorter duration giving MTC UEs more time to sleep and conserve power, while lower MCS configuration allows better penetration into all coverage areas but at a much lower data rate requirement more power consumption from MTC device.

With conventional techniques, SC-PTM transmission is only transmitted at a particular modulation order, one that will typically cover up to 90 percent of devices in its cell. Although a lower modulation order may be used to increase the percentage of coverage, devices that can successfully receive the data packet at a higher modulation order will need to stay awake longer since the same data packet will need to be transmitted over multiple transmissions at the lower modulation order. In other words, majority of the devices will suffer (power-consumption-wise) for the benefit of the few devices that cannot receive the packet at the higher modulation order. Under the conventional techniques, a device that cannot receive SC-PTM has the option to obtain the same data packets over Unicast service. However, unicast service is not preferable for a MTC device due to higher power consumption since HARQ feedback is assumed. Furthermore, additional power will be consumed if the MTC device needs to transition to the connected mode to receive the unicast service and the MTC device was originally in the Idle mode (to conserve power). Note that SC-PTM can be received while the MTC device is in the Idle mode. This is also undesirable from a network resource perspective as the main objective of SC-PTM is to be able to broadcast information to many devices that are interested in the same contents without the need to for Unicast delivery. As discussed below, these considerations are addressed by applying layered modulation to broadcasted MTC information from a first transceiver station that allows an MTC device in lower signal quality area of the first transceiver to recover a portion of the MTC information using a lower modulation order and to recover the remaining portion of MTC information from a second transceiver station.

FIG. 1is a block diagram of a communication system100including a first transceiver station102and a second transceiver station104providing MTC information106to MTC devices108,110within the service areas of the transceiver stations102,104. The transceiver stations108,110can be any type of base station, access point, radio head, eNodeB, standalone relay station, base station with relay functionality, or other device capable of transmitting signals within a geographical service area. Two examples are discussed below where, in one example, both transceiver stations102,104are base stations. In another example, the first transceiver station102is a base station such as an eNodeB and the second transceiver station104is a relay station. Other types and combinations of transceiver stations may be used.

The MTC devices108,110are devices that employ machine type communication (MTC) and are otherwise user equipment (UE) devices operating on the communication system100. For the examples herein, the communication system100operates in accordance with at least one revision of a 3GPP communication specification although the principles and techniques discussed may be applied to other types of systems in some circumstances. The transceiver stations broadcast MTC information106within the cells using Multimedia Broadcast Multicast Services (MBMS) techniques for the example. Accordingly, the broadcast transmissions are SC-PTM transmissions. For the example ofFIG. 1, the MTC information106is broadcast from the first transceiver station102using layered modulation in a first transmission112and at least some of the MTC information114is transmitted from the second transceiver station104in a second transmission116.

The MTC information106is directed to multiple MTC devices such as the MTC devices108,110. For the example ofFIG. 1, two MTC devices108,110are shown although many situations may include numerous MTC devices. For the example, a first MTC device108receives the signals transmitted from the first transceiver station102at a first signal quality level and a second MTC device110receives the signals transmitted from the second transceiver station104at second signal quality lower than the first signal quality. The difference in signal quality may be due to a variety of conditions such a noise, signal attenuation due to propagation loss, obstacles in the signal path and receiver quality. For example, the first MTC device108may be closer to the first transceiver station102than the second MTC device110and may therefore receive signals at a higher strength.

For the example ofFIG. 1, the first transceiver station102broadcasts all of the MTC information106using layered modulation such that all of the MTC information106can be recovered by a MTC device using a high modulation order to demodulate the transmission and such that some of the MTC information can be recovered by a MTC device using a low modulation order lower than the high modulation order. The high modulation order can be used to successfully demodulate the signal when the signal quality of the received transmission is above a signal quality threshold.

Since the transmission112from the first transceiver station102includes all of the MTC information106in the example, the MTC information106can be recovered with successful demodulation of only the transmission112from the first transceiver station102. In order to recover all bits of the MTC information from the transmission112, however, the receiving MTC device must apply a higher modulation order to demodulate the transmission. A lower modulation order can be applied to recover a portion of the MTC information118contained in the transmission112.

For the example ofFIG. 1, the second MTC device110receives signals from the first transceiver station102below the signal quality threshold that allows demodulation of the transmission112using the higher modulation order. The second MTC device110, however, applies the low modulation order to demodulate the transmission112and recovers a portion of the MTC information118. The remaining portion of the MTC information114is received from the second transceiver station104. The remaining portion of MTC information114may be transmitted at the low modulation order or the high modulation order depending on the implementation and/or circumstances. The remaining portion114may be transmitted as part of transmission that includes all of the MTC information or may be transmitted without other MTC information. For example, where the second transceiver station104is a base station broadcasting MTC information within its cell, the MTC information may be transmitted with layered modulation such that the remaining portion114can be recovered using the low modulation order.

Generally, using the higher modulation order will require fewer transmissions leading to less processing time than demodulating a higher number of transmissions at a lower modulation order to receive the same information. As a result, using a higher modulation order typically reduces the power consumption of the MTC device because the device spends less time receiving the transmissions and the time saved is used for sleep mode or in some other less active state. Although for the example all of the information is transmitted in a transmission from the first transceiver station, other techniques can be used where the information is received over some number of transmissions where the number of transmissions required to retrieve all of the information is less using higher modulation orders than the number required to receive the information using lower modulation orders.

Therefore, the first MTC device108demodulates the transmission112from the first transceiver station102using the high modulation order to recover the MTC information106with minimum power consumption by receiving the MTC information106within a minimized reception time period. The second MTC device110cannot use the high modulation order for demodulating the transmission112and uses the low modulation order to demodulate the layered modulation transmission112to receive a portion of the MTC information118. The MTC device110recovers the remaining portion of the MTC information114by demodulating the signal116transmitted form the second transceiver station104. The second MCT device110, therefore, recovers all of the MTC information from information in multiple transmissions112,116from multiple transceiver stations102,104.

FIG. 2is a block diagram of the communication system100for an example where the first transceiver102is a first base station202and the second transceiver104is a second base station204. For the example ofFIG. 2, the first transceiver station102and the second transceiver station104are base stations such as eNBs, eNodeBs, access points, or any other devices performing similar tasks. Each base station202,204provides wireless service within a geographical service area where the two areas at least partially overlap with each other. The second MTC device110can receive signals from both base stations202,204. For the example ofFIG. 2, all of the MTC information106is included in the first transmission112from the first base station202and all of the MTC information106is included in the second transmission116from the second base station204. As discussed below, however, the sequence of bits of the MTC information is different between the two transmissions112,116. Each base station broadcasts the MTC information106using layered modulation where a MTC device that receives a transmission above a signal quality threshold can recover the MTC information106demodulating the transmission using the high modulation order. Therefore, the first MTC device108can recover all of the MTC information106from the first transmission112using the high modulation order. A third MTC device206that receives the second transmission116from the second base station104above the signal quality threshold can also recover the MTC information106by using the high modulation order to demodulate the second transmission116. For the example ofFIG. 2, the second MTC device110does not receive either of the transmissions112,116at a sufficiently high quality to allow demodulation of either transmission112,116using the high modulation order. However, the second MTC device110recovers all of the MTC information106by using the low modulation order to recover a portion of the MTC information118from the first transmission112and to recover the remaining portion of the MTC information114from the second transmission116from the second base station204.

FIG. 3is a block diagram of the system100ofFIG. 2where the two base stations transmit encoded bits representing the MTC information to the MTC devices. Each base station202,204encodes and sequences the MTC information106into at least one sequence of coded bits, modulates the sequence of coded bits with layered modulation and transmits the modulated sequence. For the example, the sequence of bits in the transmission116from the second base station204is different from the sequence of bits in the first transmission112from the first base station202. In some situations, a base station encodes and sequences the MTC information106into two sequences of coded bits, modulates the two sequences with layered modulation, and transmits each modulated sequence as a first transmission and second transmission. Such a technique is discussed in PCT Patent Application No. PCT/US2017/051003, entitled “LAYERED MODULATION FOR MACHINE TYPE COMMUNICATION (MTC) TRANSMISSIONS”, filed concurrently with this application and hereby incorporated by reference in its entirety, herein. Such techniques allow multiple MTC devices in the service area of the base station to receive all of the MTC information in a single transmission using the high modulation order or to receive the MTC information over multiple transmissions using a lower modulation order. Therefore, in some situations, each base station202,204encodes and sequences the MTC information106into two sequences of coded bits, modulates the two sequences with layered modulation, and transmits each modulated sequence as different transmissions to broadcast the information as two transmissions. As mentioned above, for the example, each base station at least broadcasts one transmission. Accordingly, in the interest of brevity and simplicity, multiple transmissions from the base stations is discussed below after the discussion of a single transmission from each base station202,204.

Each base station includes an encoder306,307that encodes the MTC information106into a number of coded bits308,309. The resulting coded bits308,309are used to generate sequences of coded bits. The sequencer310in the first base station202generates a first sequence of coded bits312based on the MTC information coded bits308and the sequencer311in the second base station204generates a second sequence of coded bits314based on the MTC information coded bits309. For the example, the first sequence of coded bits312is the same as the sequence of the coded bits308and the second sequence of coded bits314is the coded bits308,309with the two most significant bits (MSBs) of each set of four coded bits being replaced with the least significant bits (LSBs) of the set. For example, if the coded bits308,309are represented with CNCN-1CN-2CN-3. . . C3C2C1C0,then the first sequence of coded bits312is the same and the second sequence of coded bits314are represented as CN-2CN-3CNCN-1. . . C1C0C3C2.Numerous other sequencing techniques can be used. In another situation, for example, the second sequence of coded bits314may be the reverse of the first sequence of coded bits312.

The modulator316in the first base station202receives the sequence of coded bits312and applies layered modulation to generate a modulated signal318that contains all of the MTC information106. The modulator317in the second base station204receives the sequence of coded bits314and applies layered modulation to generate a modulated signal320that contains all of the MTC information106. For the example, the layered modulation includes two modulation orders including a high modulation order and a low modulation order. The terms “high” and “low” are used to designate the relative level of modulation order between the two orders. Therefore, the high modulation order has a higher order than the low modulation order although both can be higher or lower relative to other modulation orders. Examples of suitable modulation orders include quadrature amplitude modulation with different constellation sizes such as 4-QAM and 16-QAM modulation techniques. As is known, 4-QAM is a quadrature amplitude modulation scheme where the data is represented by a single symbol in each of four quadrants of a phase-amplitude representation. For 16-QAM, data is represented by four different symbols in each quadrant. As a result, 16-QAM allows for transmission of more data over time than 4-QAM but requires the receiver to be able to distinguish between smaller differences between phase and amplitude to identify symbols than 4-QAM. Each modulation order requires a minimum signal quality of the received signal at the receiver in order to adequately demodulate the signals and recover the data. Therefore, a received signal must meet a minimum signal quality threshold in order for the receiver to receive a 16-QAM signal. If the signal is transmitted at a higher modulation order while keeping the mean energy the same as the signal transmitted at a lower modulation order, the constellation points of the higher modulation order must be closer together. As a result, assuming the noise and interference level stays the same, it will be more difficult for the receiver to correctly demodulate the signal at higher modulation order.

The transmitter322in the first base station202transmits the first modulated signal318as the first transmission112within the service area of the first base station202. The transmitter323in the second base station204transmits the second modulated signal320as the second transmission116within the service area of the second base station204. The two signals are therefore broadcasted in the corresponding cell of each base station. As discussed above, MBMS techniques can be used to broadcast the transmissions112,116. For the example, the signals are transmitted using SC-PTM techniques in accordance with at least one revision of the 3GPP communication specification but with the additional features discussed herein. In some situations, the two transmissions112,116are transmitted at the same time over two different channels. In the example forFIG. 3, however, the signals are transmitted at different times. In some situations, the signals are transmitted over the same channel at the same time. The traffic channel of SC-PTM is transmitted on PDSCH while the traffic channel for MBMS is transmitted over a MBSFN channel.

The lines representing the transmissions inFIG. 3are shown with heavier lines to the first MTC device108and the third MTC device206heavier than the lines to the second MTC device110to indicate that the signals are being received at a higher quality at the first and third MTC devices108,206than at the second MTC device110. For the example, signal quality of the received transmission at the first MTC device108is sufficiently high to allow the first MTC device108to demodulate the first transmission112at the high modulation order (e.g., 16-QAM). For the example, signal quality of the received transmission at the third MTC device206is sufficiently high to allow the third MTC device206to demodulate the second transmission116at the high modulation order. The signal quality of the received transmissions at the second MTC device106is not sufficient to allow the second MTC device110to demodulate either transmission112,116at the high modulation order (e.g., 16-QAM). The signal quality, however, is adequate for the second MTC device110to demodulate the transmissions at the low modulation order (e.g., 4-QAM). As a result, the first MTC device108and the third MTC device206can recover all of the MTC information106by applying the high modulation order to only one transmission. The second MTC device110, however, applies the low modulation order to both transmissions112,116to recover the MTC information106. As a result, the first MTC device108and the third MTC device206will be in active mode for less time receiving the transmissions and will be in sleep mode longer thereby conserving power. As discussed above, this technique allows a greater number of MTC devices in the cell to receive the MTC information while allowing some MTC devices to conserve power by using the high modulation order to receive the MTC information.

In some situations, the sequences of coded bits are predetermined and static. In other circumstances, however, the sequence of the bits in one or more of the transmissions112,116, is dynamically changing or otherwise not known by the MTC devices108,110,206. As a result, at least one of the base stations202,204provides the ordering of the sequence(s) to the second MTC device110. An example of suitable technique includes transmitting the sequence information324in a control signal such as a part of the control information provided in the SC-MCCH for SC-PTM and in the MCCH for MBSFN. For the example, the control channels are transmitted at a lower modulation order such that all UE devices are able to obtain the information throughout the cell coverage area. An example of another suitable technique for transmitting the sequence information includes broadcasting the information over a system broadcast message in a semi-static manner.

The technique discussed above can be generalized for layered modulation where the modulation order of the base component is represented by 2pand the modulation order enhanced component is 2r. For the generalization, r and p are integers and r is greater than p. For the examples herein, r is also an integer multiple of p although systems can be implemented without this constraint in some circumstances. The number of retransmissions is equal to differences in the exponent of the order of the enhanced modulator and the exponent of the base modulation minus one. Therefore, if 2pis the base modulator order and 2ris the enhanced modulator order, then the number of retransmission is (r−p)/p and the total of number of transmissions (n) is equal to (r−p)/p+1. For example, for the situation where 4-QAM and 16-QAM are used, r is 4 and p is 2 and the number of retransmissions is (4−2)/2=1. The total number of transmissions is equal to (4−2)/2+1=2, n=2. In another example, where the enhanced modulator is 64-QAM and the base modulator is 4-QAM, r=6 and p=2 and the number of retransmissions is (6−2)/2=2.

In some situations, as mentioned above, one or both base station202,204can transmit multiple layered transmissions that include the MTC information206. For example, the sequencer310in the first base station202may generate the second sequence of coded bits314in addition to the first sequence of coded bits312. The second sequence of coded bits314is modulated with layered modulation to generate another second modulated signal325. The second modulated signal325is transmitted within the service area of the first base station202by the transmitter322. For this example, the second modulated signal325contains the same information and sequence of coded bits at the second modulated signal320. Since, however, the base stations202,204are neighboring base stations, the two signals are transmitted within different channels to avoid interference. MTC devices within the service area of the first base station202that cannot receive the transmissions from the base station202above the signal quality threshold, may be able to demodulate both transmissions using the low modulation order to recover a portion of the MTC information from each transmission.

The second base station204can also transmit multiple layered modulation transmissions such that devices receiving signals below the signal quality threshold can recover the MTC information. For example, the sequencer311in the second base station204may generate the first sequence of coded bits312in addition to the second sequence of coded bits314. The first sequence of coded bits312is modulated with layered modulation to generate another first modulated signal327. The first modulated signal327is transmitted within the service area of the second base station204by the transmitter323. For this example, the second modulated signal327contains the same information and sequence of coded bits at the first modulated signal318. Since, however, the base stations202,204are neighboring base stations, the two signals are transmitted within different channels to avoid interference.

The various functions and operations of the blocks described with reference to the base stations202,204may be implemented in any number of devices, circuits, electronics, code, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single block may be implemented over several devices. For example, the functions of the encoder306, and sequencer310may be performed by a single signal processing device328in some circumstances. Similarly, the functions of the encoder307, and sequencer311may be performed by a single signal processing device329in some circumstances.

FIG. 4is a block diagram of the system100for an example where the first transceiver station102is a base station402and the second transceiver station104is a relay station404. The relay station404may be a standalone relay station with limited functionality or may be a base station with relay functionality. In many cases the relay station may be a UE with limited battery life. The relay station404at least has the capability of forwarding signals from a base station to one or more UE devices including MTC devices. In typical situations, the relay station404also forwards uplink signals from UE devices to the base station.

For the example ofFIG. 4, the base station402broadcasts a layered modulation signal including the MTC information106and the relay station404transmits at least a portion of the MTC information in a second transmission116wherein the MTC information is received from the base station402in the first transmission112. As discussed above in regard to other examples, a device using the high modulation order to demodulate the first transmission112can be recover all of the MTC information106. As a result, the MTC devices, such as the first MTC device108, receiving the first transmission above a signal quality threshold can use the high modulation order to demodulate the first transmission and recover the MTC information. The relay station404also receives the first transmission112above the signal quality threshold in the example. Accordingly, the relay station404receives the first transmission112and recovers all of the MTC information106.

The second MTC device110, however, receives the first transmission112below the signal quality threshold and recovers a portion of the MTC information118by demodulating the first transmission112using the low modulation order. When the second MTC device110receives the first transmission112it has the option to indicate to the relay station404whether the first transmission112was received above or below the signal quality threshold. The indication may be in the form of an SNR value or it may be just a 1-bit indication and the need for this indication may be configurable by the relay station404or the base station402. If the relay station404received the indication from the MTC device110that the first transmission112is received above the signal quality threshold then the relay station404may refrain from sending the second transmission114to conserve power. In the present example, the relay station404transmits the remaining portion of the MTC information114in the second transmission116to the second MTC device110allowing the second MTC device to combine the portion118received from the base station402and the remaining portion114received from the relay station404to recover all of the MTC information106.

Any of several techniques can be used by the relay station404for transmission of the second transmission116where the selected technique may depend on the particular situation. In a first example of relay transmission, the relay station404transmits a layered modulation signal that includes all of the MTC information106. MTC devices receiving the second transmission116above the signal quality threshold can recover all of the MTC information by demodulating the second transmission using the high modulation order. MTC devices receiving the second transmission below the threshold can recover the remaining portion of MTC information114using the low modulation order to demodulate the second transmission signal. Typically, the sequence of bits in the second transmission is different than the sequence of bits in the first transmission and, for the example, the sequence in the second transmission is the same as the sequence used by the base station402for transmitting a second transmission. Therefore, for the first example of relay transmission, the second MTC device110can use the high modulation order to receive all of the MTC information from the relay station or can use the lower modulation order to receive the remaining portion of the MTC information not received from the base station in the first transmission112.

In a second relay transmission example, the relay station404only transmits the remaining portion of the MTC information114that was not received by the second MTC device110from the base station. For the second relay transmission example, the relay station404transmits the remaining portion114at the lower modulation order. Accordingly, for this situation, the second MTC device110can recover the remaining portion114using the low modulation order on the second transmission116. Since the second transmission116, in this situation, includes only the remaining portion of the MTC information114, the transmission116is shorter than a transmission that includes all of the MTC information106.

In a third relay transmission example, the relay station404transmits only the remaining portion114using the high modulation order. Accordingly, the transmission in this situation is shorter than the second transmission in the second relay transmission example.

In a fourth relay transmission example, the relay station determines the appropriate modulation order to apply the second transmission and transmits only the remaining portion. The modulation may be selected from the high modulation order and the low modulation order or may be another modulation order. Based on the channel quality feedback from the MTC devices, the relay station may determine what is the best MCS. In another approach, the base station such as an anchor base station, informs the relay station what MCS to use. The anchor base stations typically have good data regarding the channel conditions of the served MTC devices. This information can be delivered either by a unicast transmission to the relay station or on a SIB message. In situations where device to device (D2D) relays stations (ProSe Relays) are implemented, the discovery procedure may be used by the relay station to determine how far the MTC device is located while the connection is established for one-to-one communication

FIG. 5is a block diagram of the system100ofFIG. 4where the base station402and the relay station404transmit encoded bits representing the MTC information106to the MTC devices108,110. The base station402and the relay station404each encode and sequence the MTC information106into at least one sequence of coded bits, modulate the sequence of coded bits with layered modulation and transmit the modulated sequence. The relay station404receives the first sequence of bits405from the base station402and generates the second sequence of coded bits412which is transmitted to the MTC device110.

The base station402operates similarly to the base station202inFIG. 2andFIG. 3except that, for the example ofFIG. 5, the base station402sequences the coded bits308to create a sequence405that includes nulls where the base station402does not include information. As a result, transmissions from the relay station404and the base station402within the same channel will not interfere with each other. For the example, the base station402generates at least one sequence of bits of the MTC information that is broadcasted using layered modulation within the service area. In some situations, as discussed above, the base station402may also generate a second sequence of bits that is broadcasted allowing MTC devices within the service area to use the lower modulation order to recover the MTC information from the two transmissions. In some situations, the base station402may determine whether to transmit the second sequence or to have the relay station404transmit the second sequence. Such a determination may be based on serval factors and typically depends on the MTC devices requiring the information and the availability and relative positions of relay stations in the area.

A receiver406in the relay station404receives the first transmission112from the base station402that includes the MTC information106. The demodulator408used the high modulation order to recover the coded bits308of the MTC information106. The sequencer410in the relay station404generates a second sequence of bits412based on the coded bits308recovered from the received first transmission112. For the example, the second sequence of bits412also includes nulls where no information is included. Therefore, for the example ofFIG. 5, the first sequence of coded bits405is generically represented as null null CN CN-1 CN-2 . . . null null C7 C6 C5 C4 null null C3 C2 C1 C0 and the second sequence of coded bits is represented as CN CN-1 null null . . . null null C7 C6 null null null null C3 C2 null null null null. The second sequence of bits412is modulated by the modulator414to form the second modulated signal416which is transmitted as the second transmission116by the transmitter418. The modulator414may use the low modulation order, the high modulation or another modulation order to generate the second modulated signal416. For the example, the second transmission116includes only the remaining portion of MTC information114. In some situations, however, the relay station404can retransmit all of the MTC information106using layered modulation techniques. As an alternative to including nulls in the sequence, the base station can transmit the whole sequence without the nulls and the relay station waits for the base station to finish the transmission before transmitting the second transmission.

In the example ofFIG. 5, the second MTC device110recovers a portion of the MTC information118from the first transmission112from the base station402using the low modulation order and recovers the remaining portion of the MTC information114from the second transmission from the relay station404using the low modulation order. In other examples, the remaining portion may be transmitted at a higher modulation order and the second MTC device can recover the remaining portion in less time. For instance, the relay station404transmits the second sequence as CN CN-1 CN-4 CN-5 null null . . . C7 C6 C3 C2 null null null null null null null null in another example.

For the example, the sequence information324is provided to the MTC device110. In some situations, the base station402may provide the sequence information324using the techniques described above. In other situations, the relay station may provide at least a portion of the sequence information. For example, the base station402may provide sequence information related to the first and second transmissions. The relay station404may provide additional or updated sequence information for the second sequence. Such a situation may occur, where the relay station dynamically determines a modulation order for transmission and modifies the bit sequence. In such situations, however, control signal overhead may be increased.

FIG. 6is a flow chart of an example of a method of broadcasting MTC information103from two transceiver stations. The steps ofFIG. 6can be performed in a different order than shown and some steps may be combined into a single step. Additional steps may be performed and some steps may be omitted.

At step602, the sequence information324is transmitted to the MTC devices in the cell. The sequence information324indicates the sequence order of bits in one or more transmissions. The first transceiver102such as a base station broadcasts the sequence information324as control information over SC-MCCH, MCCH, or System information. In some circumstances, the second transceiver104transmits the sequence information324.

At step604, a first sequence of coded bits is generated based on the coded bits308representing the MTC information. A sequencer at the first transceiver station102generates the first sequence of coded bits from the encoded bits representing the MTC information106. For the example, the sequence of bits represents all the MTC information and is different from the other sequences.

At step606, a second sequence of bits is generated based on the coded bits representing the MTC information. A sequencer in the second transceiver station generates the second sequence of coded bits. As described above, the first sequence of bits is the original sequence of coded bits for the example and the second sequence may include swapping MSBs with LSBs in sets of bits forming the sequence. The second sequence of bits may include all of the MTC information bits106or may include only the remaining portion not yet recovered by a MTC device110. Where the second transceiver is a relay station, the first sequence of coded nits and the second sequence of coded bits include nulls. In some circumstances, the relay station receives an indication from the MTC devices that the first sequence was received above the signal threshold. In this case the relay station may refrain from transmitting the second sequence to conserve power.

At step608, layered modulation is applied to the first sequence of bits to generate a first modulated signal. The modulator in the first transceiver modulates the first sequence of coded bits such that a portion may be recovered by applying a low modulation order and all the MTC information can be received by using a high modulation order to demodulate the first modulated signal.

AT step610, the second transceiver modulates the second sequence of coded bits to generate the second modulated signal. In some circumstances, layered modulation can be sued to modulate the sequence of coded bits that represent all of the MTC information106. For example, where both transceiver stations are base stations with overlapping service areas, each base station may serve MTC devices that cannot receive transmissions as a sufficient quality to demodulate the signals using the high modulation order. By receiving multiple transmissions with layered modulation from the serving base station, a MTC device can recover all of the MTC information106. In other circumstances, the transceiver station104may use only the high modulation order to modulate the sequence of coded bits representing only the remaining portion of MTC information114. For example, where the second transceiver station104is a relay station404, the relay station404may receive all of the MTC information from the first transmission, generate a second sequence of bits that includes only the remaining portion of MTC information and modulate the sequence with the high modulation order. This may be particularly useful where the targeted MTC device110is receiving signals from the relay station at above the signal quality threshold and the reception time can be minimized by using the high modulation order. In still other circumstances, the second transceiver station may apply the low modulation order or another modulation order to modulate the second sequence of coded nits representing only the remaining portion of the MTC information not recovered by the targeted MTC device110. These techniques may be useful where the second transceiver station is a relay station and the MTC device is not receiving signals from the relay station above a signal quality threshold.

At step612, the first transceiver station broadcasts the MTC information in the first transmission. As described above the signal is modulated using layered modulation such that MTC devices receiving the transmission above a signal quality threshold can demodulate the transmission to recover all of the MTC information included in the transmission using a high modulation order. Other MTC devices can recover a portion of the MTC information by applying a lower modulation order to demodulate the first transmission.

In one scenario, as discussed above, the transmission may include 16-QAM modulation and 4-QAM modulation such that the MTC information is recoverable by a MTC device by applying 16-QAM demodulation to the transmissions and the portion of MTC information is recoverable by another MTC device by applying 4-QAM to the transmission.

At step614, the second transceiver station transmits the remaining portion of the MTC information not recovered by the second MTC device form the first transmission. The second transmission is transmitted such that the second device can recover the remaining portion of the MTC information. By combining the portion received in the first transmission and the remaining portion received in the second transmission, the MTC device110recovers all of the MTC information106.

FIG. 7is a flow chart of a method of receiving MTC information at a MTC device. The steps ofFIG. 7can be performed in a different order than shown and some steps may be combined into a single step. Additional steps may be performed and some steps may be omitted. For the example, the method is performed by a MTC UE device such as the MTC device108or the MTC device110.

At step702, sequence information is received from the either the first transceiver station, the second transceiver station, or both.

At step704, the MTC device received the first transmission from the first transceiver station.

At step706, it is determined where the signal quality of the first transmission received from the first transceiver station is above a threshold. The threshold is the minimum quality that allows the MTC device to successfully demodulate the transmission using the high modulation order. The threshold may be, or may be based on any combination of a signal to noise ratio (SNR), signal-to-noise-plus-interference ratio (SNIR). Reference Signal Received Quality (RSRQ) Reference Signal Received Power (RSRP)or any other suitable parameter that allows the MTC device to determine if the higher modulation order can be used.

If the signal quality is above the threshold, the method continues at step708where the first transmission is demodulated using the high modulation order (e.g., 16-QAM). The MTC device has the option to inform the second transceiver station if the signal quality is above the threshold. Otherwise, the method continues at step710.

At step710, the first transmission is demodulated using the low modulation order to recover the portion of MTC information. When using the lower modulation order, the MTC device retrieves some of the coded bits from the transmission to recover the portion of MTC information.

At step712, the MTC device received the second transmission from the second transceiver station.

At step714, the MTC device demodulates the second transmission to recover the remaining portion of the MTC information. The MTC device uses the sequence information to recover the appropriate bits.

At step716, the MTC device combined the portion of MTC information received in the first transmission with the remining portion of MTC information received in the second transmission to recover all of the MTC information106.

Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. The above description is illustrative and not restrictive. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.