Patent Publication Number: US-2016233904-A1

Title: System and Method for Full-Duplex Operation in a Wireless Communications System

Description:
This application is related to the following co-assigned patent application: Ser. No. 14/617,598, filed Feb. 9, 2015, attorney docket number HW 91018007US01, entitled “System and Method for Training Signals for Full-Duplex Communications Systems,” which application is hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to digital communications, and more particularly to a system and method for full-duplex operation in a wireless communications system. 
     BACKGROUND 
     Full-duplex is being considered as a radio access technology for Fifth Generation (5G) and beyond wireless communication systems. In full-duplex operation, a device simultaneously transmits and receives on the same channel. A significant challenge in a full-duplex communications system is interference at a device&#39;s receiver(s), where the interference comes directly from a transmitter(s) of the device. Such interference may be referred to as self-interference. As an example, for a Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) base station transceiver, the self-interference may be as much as 120 dB higher than the sensitivity level of the receiver(s) of the 3GPP LTE base station transceiver. 
     Therefore, there is a need for a frame structure for 3GPP LTE wireless communications systems, such as time division duplexed (TDD) wireless communications systems, that requires minimal changes to existing technical standards, and maintains compatibility with legacy hardware. 
     SUMMARY OF THE DISCLOSURE 
     Example embodiments of the present disclosure which provide a system and method for full-duplex operation in a wireless communications system. 
     In accordance with an example embodiment of the present disclosure, a method for operating a first device is provided. The method includes scheduling, by the first device, a first flexible allocation resource of a frame as a first resource for a second device served by the first device, scheduling, by the first device, a second flexible allocation resource of the frame as a second resource for a third device served by the first device, and generating, by the first device, the frame including the flexible allocation resources and a first half-duplex training period configured to convey a first training signal, where the first half-duplex training period and the first training signal facilitate an estimation of a channel impulse response (CIR) of a communications channel between a transmit antenna of the first device and a receive antenna of the first device. The method also includes transmitting, by the first device, the frame, and simultaneously receiving, by the first device, the frame. 
     In accordance with another example embodiment of the present disclosure, a first device is provided. The first device includes a processor, a transmitter operatively coupled to the processor, and a receiver operatively coupled to the processor. The processor schedules a first flexible allocation resource of a frame as a first resource for a second device served by the first device, schedules a second flexible allocation resource of the frame as a second resource for a third device served by the first device, and generates the frame including the flexible allocation resources and a first half-duplex training period configured to convey a first training signal, where the first half-duplex training period and the first training signal facilitate an estimation of a channel impulse response (CIR) of a communications channel between a transmit antenna of the first device and a receive antenna of the first device. The transmitter transmits the frame. The receiver simultaneously receives the frame. 
     In accordance with another example embodiment of the present disclosure, a communications system is provided. The communications system includes a plurality of user equipments, and a full-duplex device operatively coupled to the plurality of user equipments. The full-duplex device includes a processor, and a non-transitory computer readable storage medium storing programming for execution by the processor. The programming including instructions to schedule a first flexible allocation resource of a frame as a first resource for a second device served by the first device, schedule a second flexible allocation resource of the frame as a second resource for a third device served by the first device, generate the frame including the flexible allocation resources and a first half-duplex training period configured to convey a first training signal, where the first half-duplex training period and the first training signal facilitate an estimation of a channel impulse response (CIR) of a communications channel between a transmit antenna of the first device and a receive antenna of the first device, and simultaneously transmit and receive the frame. 
     One advantage of an embodiment is that the example embodiments are backwards compatible with legacy devices, enabling full-duplex compatible devices and legacy devices to coexist. 
     A further advantage of an embodiment is that the example embodiments require small changes to existing technical standards, which will simplify acceptance and implementation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
         FIG. 1  illustrates an example communications system according to example embodiments described herein; 
         FIG. 2  illustrates an example full-duplex device according to example embodiments described herein; 
         FIG. 3 a    illustrates a diagram of an example overview of 3GPP LTE TDD uplink-downlink configurations according to example embodiments described herein; 
         FIG. 3 b    illustrates an example sequence of subframes of a frame for a 3GPP LTE TDD compliant communications system according to example embodiments described herein; 
         FIG. 4 a    illustrates example subframe structures for different UE types according to example embodiments described herein; 
         FIG. 4 b    illustrates an example full-duplex subframe structure according to example embodiments described herein; 
         FIG. 4 c    illustrates an example sequence of subframes of a frame for a communications system supporting full-duplex operation according to example embodiments described herein; 
         FIG. 5  illustrates a flow diagram of example operations occurring in a full-duplex device transmits a frame that includes assistance in performing self-interference cancellation according to example embodiments described herein; 
         FIG. 6  illustrates an example special subframe with an extended half-duplex pilot signal (or training signal) according to example embodiments described herein; 
         FIG. 7  illustrates an example full-duplex frame structure with an extended TP special subframe according to example embodiments described herein; 
         FIG. 8  illustrates a diagram of an example overview of full-duplex frame configurations derived from 3GPP LTE TDD uplink-downlink frame configurations according to example embodiments described herein; 
         FIG. 9  illustrates a flow diagram of example operations occurring at a device operating in full-duplex mode according to example embodiments described herein; and 
         FIG. 10  illustrates an example communications device according to example embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The operating of the current example embodiments and the structure thereof are discussed in detail below. It should be appreciated, however, that the present disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific structures of the disclosure and ways to operate the disclosure, and do not limit the scope of the disclosure. 
     One embodiment of the disclosure relates to full-duplex operation in a wireless communications system. For example, a device schedules a first flexible allocation resource of a frame as a first resource for a second device served by the first device, schedules a second flexible allocation resource of the frame as a second resource for a third device served by the first device, and generates the frame including the flexible allocation resources and a first half-duplex training period configured to convey a first training signal, where the first half-duplex training period and the first training signal facilitate an estimation of a channel impulse response (CM) of a communications channel between a transmit antenna of the first device and a receive antenna of the first device. The device also transmits the frame, and simultaneously receives the frame. 
     The present disclosure will be described with respect to example embodiments in a specific context, namely Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) TDD compliant communications systems that support full-duplex operations. The disclosure may be applied to standards compliant communications systems, such as those that are compliant with 3GPP LTE frequency division duplexed (FDD), IEEE 802.11, and the like, technical standards, and non-standards compliant communications systems, that support full-duplex operations. 
       FIG. 1  illustrates an example communications system  100 . Communications system  100  includes an eNB  105 . eNB  105  may serve user equipment (UE), such as UE  110 , UE  112 , and UE  114 . In general, eNB  105  may operate as an intermediary for the UEs, receiving transmissions to and from the UEs and then forwarding the transmissions to their intended destination. Communications system  100  may also include a relay node (RN)  120  that uses some bandwidth donated by eNB  105  to serve UEs, such as UE  116 . RN  120  may help to improve coverage, data rate, as well as overall communications system performance, by utilizing some network resources donated by eNB  105 . eNBs may also be commonly referred to as base stations, NodeBs, controllers, access points, base station transceiver, and the like, while UEs may also be commonly referred to as stations, mobiles, mobile stations, terminals, users, subscribers, and the like. 
     While it is understood that communications systems may employ multiple eNBs capable of communicating with a number of UEs, only one eNB, one RN, and a number of UEs are illustrated for simplicity. 
     A half-duplex device is capable of only transmitting or receiving at any given time, frequency, and/or space that it is allowed to communicate. In general, half-duplex devices do not have to worry about self-interference. In other words, since receivers of a half-duplex device are not being used at the same time, frequency, and/or space as transmitters of the half-duplex device, the receivers do not have to worry about interference caused by the transmitters. A full-duplex device is capable of transmitting and receiving at any given time, frequency, and/or space that it is allowed to communicate. Full-duplex devices may have built-in mechanisms to compensate for the self-interference. A full-duplex device may also operate as a half-duplex device. 
       FIG. 2  illustrates an example full-duplex device  200 . Full-duplex device  200  may be an eNB capable of full-duplex operation. Full-duplex device  200  may also be a UE capable of full-duplex operation. Full-duplex device  200  may include one or more transmit antenna  205  and one or more receive antenna  210 . Since in most implementations, transmit antenna  205  are relatively close to, collocated with, or shared with receive antenna  210 , signals transmitted using transmit antenna  205  may appear at receive antenna  210  at significantly higher power levels than transmissions made by remotely located devices that are transmitting to full-duplex device  200 . Although full-duplex device  200  is shown in  FIG. 2  as having collocated or shared transmit antenna  205  and receive antenna  210 , alternative implementations of full-duplex device  200  may have remotely located transmit antenna  205  and/or receive antenna  210 . As an illustrative example, an alternate full-duplex device may include multiple remote antennas serving as transmit antennas and/or receive antennas. Therefore, the illustration of full-duplex device  200  having co-located antennas should not be construed as being limiting to either the scope or the spirit of the example embodiments. 
       FIG. 3 a    illustrates a diagram  300  of an example overview of 3GPP LTE TDD uplink-downlink configurations. Diagram  300  displays uplink and downlink assignments for subframes for a variety of different configurations of a 3GPP LTE TDD compliant communications system. In general, a frame of a 3GPP LTE TDD compliant communications system is partitioned into 10 subframes, numbered from 0 to 9. Some of the subframes may be used only for downlink communications (denoted D for either a normal downlink subframe or a downlink pilot time slot (DwPTS) in a special subframe), while some of the other subframes may be used only for uplink communications (denoted U for either a normal uplink subframe or a uplink pilot time slot (UpPTS) in a special subframe). Although the discussion focuses on 3GPP LTE TDD, the example embodiments presented herein are also operable with 3GPP LTE FDD, as well as other technical standards, such as IEEE 802.11, WiMAX, and the like. Therefore, the discussion should not be construed as being limiting to either the scope or the spirit of the example embodiments. 
     As shown in  FIG. 3 a   , the shaded subframes indicate subframes that, in a 3GPP LTE TDD half-duplex communications system, may be used for both uplink and downlink communications. The subframes that are usable for both uplink and downlink communications (i.e., the shaded subframes) may be referred to special subframes and include subframe #1 in all of the illustrated configurations, as well as subframe #6 in configurations 0, 1, 2, and 6. In half-duplex devices, when switching from uplink operation to downlink operation (and vice versa), a period is sometimes needed to allow for the circuitry of the half-duplex devices to be re-configured, as well as to provide sufficient spacing to help align timing and reduce interference between the signals. In 3GPP LTE, the period is referred to as a guard period (GP). In 3GPP LTE TDD compliant communications systems, the special subframes include a downlink portion (a DwPTS) followed by a GP followed by an uplink portion (an UpPTS). 
       FIG. 3 b    illustrates an example sequence of subframes  350  of a frame for a 3GPP LTE TDD compliant communications system. Sequence of subframes  350  may be representative of subframes for a 3GPP LTE TDD compliant communications system utilizing configurations 0, 1, 2, and 6. Sequence of subframes  350  includes a first special subframe  355  comprising a DwPTS portion  357 , a GP portion  359 , and an UpPTS portion  361 . Sequence of subframes  350  also includes a second special subframe  365 . For 3GPP LTE TDD compliant communications systems utilizing configurations 3, 4, and 5, a representative sequence of subframes may be similar, but with an exception that there is only a single special subframe per frame. Table 1 illustrates a number of samples available in the three portions of a special subframe for different 3GPP LTE TDD subframe configurations. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Samples for Subframe Configurations. 
               
            
           
           
               
               
            
               
                 Number of  
                 Special Subframe Configuration 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Samples 
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 DwPTS 
                 7680 
                 20480 
                 23040 
                 25600 
                 7680 
                 20480 
                 23040 
                 12800 
               
               
                 UpPTS 
                 2560 
                 2560 
                 2560  
                 2560  
                 5120 
                 5120 
                 5120 
                 5120 
               
               
                 GP 
                 20480  
                 7680 
                 5120 
                 2560 
                 17920  
                 5120 
                 2560  
                 12800 
               
               
                   
               
            
           
         
       
     
     As discussed previously, self-interference is a significant hindrance to full-duplex operation. Self-interference cancellation may be used to remove the contribution of the self-interference at the receiver of the full-duplex device. 
     According to an example embodiment, existing subframe configurations are reused to help maintain compatibility with legacy devices and to minimize changes to existing technical standards. Maintaining compatibility with legacy devices and minimizing changes to existing technical standards may help to simplify acceptance of full-duplex devices and minimize expenditures in implementing full-duplex communications systems. 
       FIG. 4 a    illustrates example subframe structures  400  for different UE types. Subframe structures  400 , as shown in  FIG. 4 a   , are based on subframe configuration 3 of a 3GPP LTE TDD compliant communications system. The subframes shown in  FIG. 4 a    are of illustrative purposes only, and other subframe structures are possible. A first example subframe structure  405  is for a legacy UE and follows configuration 3 without modification. A second example subframe structure  415  may support a full-duplex aware UE, which knows that full-duplex operation is present in the communications system, but is not capable of full-duplex operation. A third example subframe structure  425  may support a full-duplex UE, which is capable of full-duplex operation. Second example subframe structure  415  and third example subframe structure  425  also support situations where neither UL nor DL operations are scheduled with such subframes being labeled X (for example, subframe 4 in second example subframe structure  415  and subframe 5 in third example subframe structure  425 ). 
     According to an example embodiment, a full-duplex device transmits a training signal (or pilot signal) in the GP of the special subframes to allow the full-duplex device to estimate a channel impulse response (CIR) of a communications channel from the transmit antenna to the receive antenna of the full-duplex device. When the GP includes the training signal (or pilot signal), the GP may be referred to as a training period (TP). In general, the GP when capable of carrying the training signal (or pilot signal) may be referred to as a GP/TP. The GP/TP may be a half-duplex period during which the full-duplex device transmits the training signal (or pilot signal) and transmissions from other devices served by the full-duplex device are not scheduled. The CIR may be used to cancel the self-interference in the received signal. The transmission of the training signal (or pilot signal) helps to ensure that the estimated CIR is not influenced by other signals received by the receive antenna, e.g., uplink transmissions received by the receive antenna. The presence of at least one GP/TP per frame (with subframe configurations 3, 4, and 5, while configurations 0, 1, 2, and 6 have two GP/TP per frame) allows the full-duplex device to regularly perform CIR estimation to help ensure that it is able to maintain an accurate estimate of the self-interference. Examples of training signal (or pilot signal) that may be used for CIR estimation are discussed in detail in co-assigned patent application entitled “System and Method for Training Signals for Full-Duplex Communications Systems”, attorney docket number HW 91018007US01, which is here incorporated herein by reference. 
       FIG. 4 b    illustrates an example full-duplex subframe structure  450 . Full-duplex subframe structure  450  is based on subframe configuration 3 of a 3GPP LTE TDD compliant communications system and is capable of supporting the three example subframe structures shown in  FIG. 4 a   . Subframes 0 and 2 of full-duplex subframe structure  450  may be used for downlink transmissions and uplink transmissions, respectively. Subframe 1 of full-duplex subframe structure  450  may be a special subframe including a DwPTS portion  455 , a GP/TP  460 , and an UpPTS portion  465 . GP/TP  460  may serve several purposes. From the perspective of a legacy UE or a full-duplex aware UE, GP/TP  460  may serve as a GP between DwPTS portion  455  and UpPTS portion  465 . However, when full-duplex subframe structure  450  is used in conjunction with a full-duplex eNB, GP/TP  460  may be used to allow full-duplex devices (a full-duplex eNB in this example) to perform CIR estimation in accordance with a half-duplex pilot signal (or training signal) transmitted in GP/TP  460 . The length of GP/TP  460  may be adjusted using special subframe configurations. As an illustrative example, as indicated in Table 1, the number of samples in a GP/TP (e.g., GP/TP  460 ) changes with the subframe configuration. Hence, it may possible to select a subframe configuration that supports a required GP/TP length. 
     Remaining subframes of full-duplex subframe structure  450  may be utilized in a flexible (F) manner, meaning that each subframe may be used for downlink transmissions and/or uplink transmissions. In other words, one or more uplink transmissions and/or one or more downlink transmissions may be scheduled for each subframe. The scheduling for the subframes that may be used in a flexible manner may be optimized based on a number of criterion (criteria), such as maximum capacity, interference constraints, and the like. From a UE&#39;s perspective, the UE may need to be able to prepare an uplink transmission or a downlink reception based on scheduling assignments received on a control channel or higher layer signaling (such as radio resource control (RRC) signaling). 
       FIG. 4 c    illustrates an example sequence of subframes  475  of a frame for a communications system supporting full-duplex operation. Sequence of subframes  475  may be representative of subframes for a communications system supporting full-duplex operation utilizing extensions to 3GPP LTE TDD compliant communications system utilizing configurations 0, 1, 2, and 6. Sequence of subframes  475  includes a first special subframe  480  comprising a DwPTS portion, a GP/TP portion, and an UpPTS portion. Sequence of subframes  475  also includes a second special subframe  485 . For communications system supporting full-duplex operation utilizing extensions to 3GPP LTE TDD compliant communications system utilizing configurations 3, 4, and 5, a representative sequence of subframes may be similar, but with an exception that there is only a single special subframe per frame. 
     According to an example embodiment, a full-duplex device generates a special subframe including a half-duplex pilot signal in the GP/TP of the special subframe and transmits the special subframe. 
       FIG. 5  illustrates a flow diagram of example operations  500  occurring in a full-duplex device transmits a frame that includes assistance in performing self-interference cancellation. Operations  500  may be indicative of operations occurring in a full-duplex device, such as an eNB, as the full-duplex device transmits a frame that includes assistance in performing self-interference cancellation. 
     Operations  500  may begin with the full-duplex device scheduling transmission opportunities (both downlink and uplink transmissions) (block  505 ). The full-duplex device may schedule downlink transmissions to UEs as well as uplink transmissions for UEs on the same or different subframe and frequency band. If the full-duplex device is scheduling transmissions for legacy UEs, the full-duplex device may follow subframe configurations compatible with the legacy UEs, such as the 3GPP LTE TDD subframe configurations discussed previously and upon which the full-duplex subframes are based. If the full-duplex device is scheduling transmissions for full-duplex UEs and/or full-duplex aware UEs, the full-duplex device may follow the flexible subframe configurations compatible with the full-duplex UEs and/or the full-duplex aware UEs. 
     The full-duplex device may generate a frame in accordance with the schedule transmission opportunities (block  510 ). The frame may include a GP/TP that comprises a training signal (or equivalently, pilot signal) to help the full-duplex device perform CIR estimation for self-interference cancellation purposes. The frame may follow the format of example frames discussed herein. Alternatively, the frame may follow the format of other frames not discussed herein as long as the frame includes a training period that may be allocated in a manner similar to or different from the GP/TP in the 3GPP LTE TDD example presented herein. The full-duplex device may transmit and receive the frame (block  515 ). 
     According to an example embodiment, it is possible to extend the length of the training signal (or pilot signal) to be longer than a GP/TP portion(s) that is limited due to restrictions imposed by the special frame configurations and the minimization of overhead of full-duplex operation. Since the training signal (or pilot signal) is transmitted by the full-duplex device, it may be possible to schedule and use a subset of portions of a special subframe dedicated for downlink transmissions to also carry the training signal (or pilot signal). The overhead of full-duplex is increased in this case due to the additional use of the system resources (a portion of the downlink portion of the special subframe(s)). More generally, any portion of the system resource (e.g., uplink and/or downlink) may be reserved and used for a training period transmitting pilot signal for full-duplex operations. It is noted that the portion of the special subframe dedicated for downlink transmission may be used for downlink transmissions when the special subframe is being used for legacy UE communications, while when full-duplex UE and/or full-duplex aware UE is available and requests for communications, the portion of the special subframe may be configured for flexible (F) communications. 
       FIG. 6  illustrates an example special subframe  600  with an extended half-duplex pilot signal (or training signal). Special subframe  600  includes a DwPTS portion  605 , a GP/TP  610 , and an UpPTS portion  615 . In situations where a longer training signal (or pilot signal) is warranted, but legacy compatibility is needed, a subset of DwPTS portion  605  may be reserved by a scheduler and used to carry the training signal (or pilot signal). As shown in  FIG. 6 , a part of DwPTS portion  605  (SYM 2 /TP  620  and SYM 3 /TP  622 ) is used to carry the training signal (or pilot signal), yielding an extended TP. Although shown in  FIG. 6  as being contiguous, the subset of DwPTS portion  605  used to carry the training signal (or pilot signal) may have to be contiguous with GP/TP  610 . As an illustrative example, parts of DwPTS portion  605  not reserved for control signaling (including but not limited to SYM 3   624 , SYM 5   626 , and SYM 6   628 , as well as SYM 2 /TP  620  and SYM 3 /TP  622 ) may be used to carry the training signal (or pilot signal). Furthermore, in frames with multiple special subframes, all of the special subframes may have extended TPs, a subset of the special subframes may have extended TPs, or none of the special subframes may have extended TPs. 
       FIG. 7  illustrates an example full-duplex frame structure  700  with an extended TP special subframe. Full-duplex subframe structure  700  is based on subframe configuration 0, 1, 2, or 6 of a 3GPP LTE TDD compliant communications system. Subframes 0 and 2 of full-duplex subframe structure  700  may be used for flexible transmission (i.e., downlink transmissions and uplink transmissions). Subframe 1 of full-duplex subframe structure  700  may be a special subframe including a first portion  705  supporting flexible transmission and/or extended TP, a second portion  710  supporting GP/TP, and third portion  715  supporting flexible transmission. Subframe 6 of full-duplex subframe structure  700  may be another subframe with the same or different configuration from subframe 1. 
       FIG. 8  illustrates a diagram  800  of an example overview of full-duplex frame configurations derived from 3GPP LTE TDD uplink-downlink frame configurations. Diagram  800  displays transmission assignments for different full-duplex frame configurations that are derived from 3GPP LTE TDD uplink-downlink frame configurations. For each full-duplex frame configuration, an original 3GPP LTE TDD uplink-downlink frame configuration is shown above a corresponding full-duplex frame configuration. 
       FIG. 9  illustrates a flow diagram of example operations  900  occurring at a device operating in full-duplex mode. Operations  900  may be indicative of operations occurring at a device, such as an eNB capable of full-duplex operation or a full-duplex UE, as the device operates in full-duplex mode. 
     Operations  900  may begin with the device transmitting a training signal for full-duplex CIR estimation (block  905 ). The half-duplex training signal may be transmitted in packets as described in the example embodiments presented herein. As an illustrative example, the training signal may be transmitted in GP/TP portions of special subframes of packets. As another illustrative example, the training signal may be transmitted in parts of downlink portions of special subframes of packets, as well as in GP/TP portions of the special subframes. The device may measure self-interference in accordance with the training signal, as well as estimate CIR (block  910 ). The device may send and/or receive (block  915 ). The device may cancel interference present in the received signals by using the estimated CIR (block  920 ). 
       FIG. 10  illustrates an example communications device  1000 . Communications device  1000  may be an implementation of a device operating in a full-duplex mode, such as an eNB capable of full-duplex operation or a full-duplex UE. Communications device  1000  may be used to implement various ones of the embodiments discussed herein. As shown in  FIG. 10 , a transmitter  1005  is configured to transmit packets, half-duplex training signals, and the like. Communications device  1000  also includes a receiver  1010  that is configured to receive packets, and the like. 
     A training signal generating unit  1020  is configured to generate training signals used in CIR estimation. A frame generating unit  1022  is configured to generate frames and subframes, such as full-duplex frames and subframes, as discussed herein. Frame generating unit  10222  is configured to place signals, such as training signals, as well as signals transmitted by communications device  1000 , in the frames and subframes. A measuring/estimating unit  1024  is configured to measure self-interference in accordance with the training signals transmitted by communications device  1000 . Measuring/estimating unit  1024  is configured to use the measurements of the training signals to estimate CIR. An interference cancelling unit  1026  is configured to cancel self-interference in received signals from transmissions made by communications device  1000  using the estimated CIR. Interference in received signals from transmissions made by other communications devices may be canceled or suppressed by other conventional units, such as a modulator, a demodulator, an encoder and a decoder (not shown in  FIG. 10 ) in the transmitter  1005  and the receiver  1010  in  FIG. 10 . A memory  1030  is configured to store packets, training signals, generated frames and subframes, measurements, estimated CIR, received signals, self-interference, and the like. 
     The elements of communications device  1000  may be implemented as specific hardware logic blocks. In an alternative, the elements of communications device  1000  may be implemented as software executing in a processor, controller, application specific integrated circuit, or so on. In yet another alternative, the elements of communications device  1000  may be implemented as a combination of software and/or hardware. 
     As an example, receiver  1010  and transmitter  1005  may be implemented as a specific hardware block, while training signal generating unit  1015 , frame generating unit  1022 , measuring/estimating unit  1024 , and interference cancelling unit  1026  may be software modules executing in a microprocessor (such as processor  1015 ) or a custom circuit or a custom compiled logic array of a field programmable logic array. Training signal generating unit  1015 , frame generating unit  1022 , measuring/estimating unit  1024 , and interference cancelling unit  1026  may be modules stored in memory  1030 . 
     Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims.