Patent Grant
8830985
This disclosure is generally related to high speed wireless packet-based networks and devices. In particular, this disclosure is related to interference between devices operating in a time division duplex (TDD) network and a frequency division duplex (FDD) network. Examples of TDD and FDD networks include networks operating on wireless technologies such as Worldwide Interoperability for Microwave Access (“WiMAX”) technologies and Long Term Evolution (LTE) technologies, or other “fourth generation” (4G) wireless technologies.
In many geographical regions, considering the nature of the regulatory environment and economic benefits, it may sometimes be advantageous to deploy dissimilar wireless networks to fully utilize a wireless operator's frequency spectrum including one or more paired frequency bands (i.e., frequency bands with separate carrier frequencies for uplink and downlink communications), and one or more unpaired bands (i.e., frequency bands in which both uplink and downlink communications are provided by the same carrier frequency). By deploying a FDD system using paired frequency spectrum allocations and a TDD system using stand-alone unpaired frequency allocations, wastage of valuable spectrum may be avoided.
However, when a TDD system operates on carrier frequencies adjacent to that of an FDD system, the possibility of severe interference may arise. In particular, severe interference may exist for the interference between base stations of the two networks, i.e., between TDD base station (BS) and FDD BS, and between TDD mobile station (e.g., WiMAX MS or LTE TDD user equipment (UE)) and FDD UE. For simplicity, the term “BS” is used throughout this disclosure to represent, for example, a TDD base station (e.g., a WiMAX base station or an “enhanced Node B” (eNB) as known in LTE TDD systems), as well as an FDD base station (e.g., LTE eNB). Also, throughout this disclosure, the term “MS” is used to represent a TDD wireless device, and the term “UE” is used to represent an FDD wireless device. Various methods, e.g. site-planning or special filters installed on base stations, may be employed to effectively mitigate the interference between base stations, e.g., the interference case of TDD BS-FDD BS, and interference between a base station and its associated mobile device(s), e.g., the interference cases of FDD UE-TDD BS and TDD MS-FDD BS. Yet, the interference between mobile devices each associated with a different base station, e.g., interference between TDD MS and FDD UE may be considered to be the most challenging case that poses a relatively greater risk for ensuring coexistence between dissimilar TDD and FDD networks.
Severe performance degradation may occur when a TDD MS and an FDD UE operating concurrently are located in a closed and small space, e.g., a café, a conference room, etc. Additionally, interference between the TDD MS and FDD UE may be severe when the MS and UE are located at an edge of a cellular region (or at a cell edge) which is served by co-located TDD and FDD base stations (i.e., base stations that are located with close geographical proximity and have respective coverage areas with significant overlap), or at the cell edge of two adjacent cells served by non co-located TDD and FDD base stations. In either of these cases, the interference problem between TDD MS and FDD UE is exacerbated, as the received downlink signal of FDD UE (or TDD MS) is typically quite weak, while the interfering TDD MS (or FDD UE) transmits an uplink signal typically at a level close to a maximum output power of the TDD MS (or FDD UE). From the perspective of user-perceived service quality, cell-edge mobile devices in high-density indoor environments, e.g. café, airport etc., are particularly vulnerable to severe performance degradation caused by TDD MS-FDD UE interference. This is because stationary mobiles in such environments are likely to transmit/receive persistently for long periods of time, which may result in prolonged service disruption due to strong interference. This persistent interference problem for indoor hotspot mobile devices could be better appreciated by comparing to that of outdoor mobile devices, which are likely to be mobile and therefore, may not stay in close proximity with each other for long periods of time. Thus, unlike the interference experienced by indoor hotspot wireless TDD or FDD devices, the interference and therefore, the performance degradation of outdoor TDD or FDD devices may be transient.
What is needed is a system and method to detect and mitigate interference between a TDD and an FDD network, particularly interference between mobile devices, e.g., interference caused at an FDD UE by a TDD MS, or interference caused at a TDD MS by an FDD UE operating in the TDD and FDD networks, respectively with adjacent and/or overlapping frequency bands.
This disclosure describes techniques for an FDD BS to detect a victim FDD UE in a network deployment scenario where spectrum (i.e., frequency) allocated to a TDD carrier is adjacent to a FDD downlink carrier. The interference may be detected at the FDD BS through a particular on-and-off interference pattern of interfering TDD MS. Once the identification of the victim FDD MS under TDD MS interference become known to the FDD BS, the interference may be avoided or alleviated by intelligent scheduling at the FDD BS. This disclosure also describes techniques including scheduling-based operations that may be performed in the FDD BS to prevent interference from a FDD UE to TDD MS.
The apparatus and method of this disclosure provide various features, functions, and capabilities as discussed more fully in the detailed description. For example, this disclosure provides a novel and useful system and method for use in a communications system, with particular application in wireless telecommunication systems such as those adhering to IEEE 802.16-2009 (fixed and mobile WiMAX), 3rd Generation Partnership Project (3GPP) Releases 8 and 9, and LTE-Advanced communication standard specifications and/or communication standards for EvDO, WiMAX, and LTE. However, this disclosure is not necessarily limited to use with such systems and methods. Also, the various embodiments disclosed herein generally may be realized by software enhancements to already existing FDD base stations, FDD wireless devices, TDD base stations and TDD wireless devices without requiring hardware modifications.
In one embodiment, a method of detecting and mitigating interference between a wireless time division duplex (TDD) communications device and a wireless frequency division duplex (FDD) communications device includes processing, e.g., using a processor operatively associated with a FDD base station, quality-indicator reports received from the FDD device indicating quality of a reception of one or more FDD data packets at the FDD device. Based on the processing of the quality-indicator reports, it may be determined whether the reception at the FDD device has experienced interference from the TDD device. For example, based on a transmission rate of FDD data packets from the FDD base station to the FDD device, the processing of the quality-indicator reports may be completed based on a frame structure parameter to determine interference at the FDD device. The frame structure parameter may be associated with a frame configuration of TDD frames in a TDD network. Alternatively, a period of receiving quality-indicator reports at the FDD base station may be selected such that, e.g., the reports are received more frequently than before the start of the interference detection process. Further, the processing of the reports may include determining an actual quality-indicator report pattern for a set of periodically-received quality-indicator reports. The actual quality-indicator report pattern may indicate whether the reception at the FDD device has experienced interference from the TDD device.
If it is determined that the reception at the FDD device has experienced interference from the TDD device, one or more configuration adjustments may be made in the FDD network. For example, a downlink configuration adjustment may be made at the FDD base station such that the FDD base station is configured to transmit FDD data packets to the FDD device during an interference-free time interval associated with TDD frames. Additionally, or alternatively, the FDD base station may be configured such that the FDD base station transmits FDD data packets to the FDD device on a reduced-interference frequency. The reduced-interference frequency may be selected from within a FDD downlink frequency used, e.g., for communication between the FDD base station and the FDD device. The FDD downlink frequency band may include first and second frequencies, such that the first frequency is adjacent to a TDD transmission frequency band, and the reduced-interference frequency may be selected such that it is closer to the second frequency than the first frequency. Selection of different configuration adjustments may be determined based on whether a data-quality requirement, e.g., a Quality of Service (QoS) requirement, of the FDD device has been met.
In another embodiment, a method of detecting and mitigating interference between a wireless frequency division duplex (FDD) communications device in communication with an FDD base station and a wireless time division duplex (TDD) communications device includes determining, using a processor operatively associated with a FDD base station, if a monitored value of an operational parameter of the FDD device is within a fixed range of a maximum value of the operational parameter. If it is determined that the monitored value of the operational parameter of the FDD device is within the fixed range of the maximum value of the operational parameter, one or more configuration adjustments may be made in the FDD network. For example, an uplink configuration may be selected such that the FDD base station is configured to receive FDD data packets from the FDD device on a reduced-interference frequency. The reduced-interference frequency may be selected from within an FDD uplink frequency band. An FDD uplink frequency band may include first and second frequencies, such that the first frequency is adjacent to a TDD transmission frequency band, and the reduced-interference frequency may be either closer to the second frequency than the first frequency, or the reduced-interference frequency may be at a center of the FDD uplink frequency band. Additionally, or alternatively, if a frame configuration of TDD frames including a TDD downlink time interval is known at the FDD base station, the FDD base station may be configured such that the FDD device does not transmit data packets to the FDD base station during the TDD downlink time interval.
In another embodiment, an apparatus capable of operating in a wireless network and detecting and mitigating interference between wireless devices includes a transceiver, a memory device, a channel-quality module, and a configuration-adjustment module. The transceiver may be configured to exchange FDD data packets with a wireless frequency division duplex (FDD) communications device. The memory device may be configured to store quality-indicator reports indicating a reception quality of one or more FDD data packets received at the FDD device. The channel-quality module may be configured to process of the quality-indicator reports, and based on the processing, determine whether the reception at the FDD device has experienced interference from the TDD device. For example, based on a transmission rate of FDD data packets from the FDD base station to the FDD device, the channel-quality module may process the quality-indicator reports based on a frame structure parameter and thereby determine interference at the FDD device. The frame structure parameter may be associated with a frame configuration of TDD frames in a TDD network. Alternatively, a period of receiving quality-indicator reports at the FDD base station may be selected such that, e.g., the reports are received (and stored in the memory) more frequently than before the start of the interference detection process. Further, the channel-quality module may process the set of the periodically-received quality-indicator reports, and communicate the processed set to a pattern-analysis module. The pattern-analysis module may determine an actual quality-indicator report pattern for the processed set of periodically-received quality-indicator reports. The actual quality-indicator report pattern may indicate whether the reception at the FDD device has experienced interference from the TDD device.
In another embodiment, an apparatus capable of operating in a wireless network, and detecting and mitigating interference between wireless devices includes a transceiver, a parameter-monitoring module, a memory device, and a configuration-adjustment module. The transceiver may be configured to exchange FDD data packets with a wireless frequency division duplex (FDD) communications device over a FDD network. The parameter-monitoring module may determine if a monitored value of an operational parameter of the FDD device is within a fixed range of a maximum value of the operational parameter. The memory device may be configured to store the monitored value of the operational parameter of the FDD device, and frame information including a TDD downlink time interval associated with TDD frames. The configuration-adjustment module, responsive to a determination that the monitored value is within the fixed range of the maximum value of the operational parameter, may configure the transceiver in one or more ways. For example, the transceiver may be configured such that the transceiver receives FDD data packets from the FDD device on a reduced-interference frequency selected from within an FDD uplink frequency band. The FDD uplink frequency band may include first and second frequencies, such that the first frequency is adjacent to a TDD transmission frequency band of a TDD network, and the reduced-interference frequency is selected such that it is either closer to the second frequency than the first frequency, or the reduced-interference frequency is at a center of the FDD uplink frequency band. Additionally, or alternatively, the FDD device may not transmit data packets to the transceiver during the TDD downlink time interval.
In another embodiment, a method of detecting and mitigating interference between a first TDD device operational with a first TDD base station and a second TDD device operational with a second TDD base station, includes processing quality-indicator reports received from the second TDD device indicating a reception quality of one or more TDD data packets at the second TDD device. The processing may indicate whether the reception at the second TDD device has experienced interference from the first TDD device, and if the interference at the second device is determined, a downlink configuration of the second TDD base station may be adjusted to mitigate interference from the first TDD device.
In another embodiment, a method of detecting and mitigating interference between a first TDD device in communication with a first TDD base station and a second TDD device in communication with a second TDD base station, includes determining whether a monitored value of an operational parameter (e.g., power) of the first TDD device is within a fixed range of a maximum value of the operational parameter. If the monitored value of the operational parameter is within the fixed range, the first TDD base station may be configured such that the first TDD base station receives data packets from the first TDD device on a reduced-interference frequency selected from within a first TDD frequency band that is associated with the first TDD base station. Additionally, or alternatively, the first TDD base station may be configured such that the first TDD device does not transmit data packets to the first TDD base station during a TDD downlink time interval associated with a frame configuration of the second TDD base station.
In the discussion of various embodiments and aspects of the apparatus and method of this disclosure, examples of a processor may include any one or more of, for instance, a personal computer, portable computer, personal digital assistant (PDA), workstation, web-enabled mobile phone, WAP device, web-to-voice device, or other device. Further, examples of TDD and FDD networks may include networks operating on WiMAX technology or LTE technology. Also, examples of TDD and FDD devices described in this disclosure may include single mode devices operating under WiMAX or LTE technology, or multimode or dual mode 3G/4G devices, e.g., CDMA EvDO/WiMAX, W-CDMA HSPA/WiMAX, CDMA EvDO/LTE or W-CDMA HSPA/WiMAX devices. Such wireless devices may include wireless phone handsets, smart phones, modems, laptop computers with embedded dual-mode functionality, mobile Internet devices such as used for video streaming, and other user equipment (UE), for example.
Those with skill in the art will appreciate that the inventive concept described herein may work with various system configurations. In addition, various embodiments of this disclosure may be made in hardware, firmware, software, or any suitable combination thereof. Aspects of this disclosure may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device, or a signal transmission medium), and may include a machine-readable transmission medium or a machine-readable storage medium. For example, a machine-readable storage medium may include read only memory, random access memory, magnetic disk storage media, optical storage media, flash memory devices, and others. Further, firmware, software, routines, or instructions may be described herein in terms of specific exemplary embodiments that may perform certain actions. However, it will be apparent that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, or instructions.
In
In one or more embodiments, interference detection and mitigation techniques described herein are implemented in one or more base stations, e.g., FDD (or LTE) BS 130, 132, each including one or more components or modules to carry out some or all of the functions described herein.
Also, although not specifically illustrated, it should be understood that, in various embodiments, one or more of devices 135, 137, 140, 142 are configured to operate in accordance with WiMAX and LTE standards, respectively, and may include a 4G transceiver operatively coupled with one or more antennas, one or more processors, a baseband processing module, a parameter-monitoring module, memory, input/output controller, and other peripherals which may be used to carry out some or all of the functionality described herein. The processor(s) may be configured to execute various functionality associated with processing of information received and/or transmitted from the antennas including, but not limited to, processing data packets received from the associated base station and periodic channel quality reports for the base station. The baseband processing module, e.g., operatively connected with the processor(s), may be configured to convert radio frequency (RF) signals from the associated base station to baseband signals. The parameter monitoring module may provide values of one or more operational parameters, e.g. power, of the mobile device. The memory may be configured to store various data and program instructions, e.g., data packets or frames, monitored operational-parameter values, etc. The input/output controller may operate in conjunction with a user interface of the device to allow display of information to a user, for example, as well as to receive input from the user using conventional input/output devices, among other purposes. If any of devices 135, 137, 140, 142 is a dual-mode/multimode device, e.g. configured to operate in both 3G EvDO/HSPA and 4G WiMAX/LTE modes, the device may include an additional 3G transceiver which, along with the 4G transceiver, supports the communication in both 3G and 4G modes. One or more of these wireless devices may be pre-provisioned with an optional GPS receiver which may be used in various ways, e.g., to provide a common time reference source to synchronize the start timings of TDD and FDD frames.
Exemplary TDD-WiMAX and FDD-LTE frame structures are discussed below to show the distinctive pattern of interference created from a TDD (or WiMAX) device to an FDD (or LTE) device. The frame structures may be exploited to detect the interference cases of MS-to-UE (i.e., scenario 1) in a wireless system including both TDD and FDD networks. WiMAX is a TDD-based 4G wireless system that may be configured to operate in various modes, each of which, among other factors, may specify a particular frame configuration for WiMAX frames including downlink time interval and uplink time interval for WiMAX frames (or data packets). For example, in one or more modes, WiMAX network may operate on a 5 ms transmit-to-receive switch point periodicity. Table 1 summarizes a number of different modes available in a WiMAX network. Mode with frame configuration “(29, 18)” is a default WiMAX mode, and is used in this disclosure to describe WiMAX (or TDD) operations. However, other WiMAX modes may be used without altering the system configuration shown in
An exemplary FDD-LTE frame structure or configuration 300 is shown in
When an LTE UE e.g., FDD device 140, is under persistent interference from WiMAX MS, e.g., TDD device 135, a received signal quality of the LTE UE may exhibit a distinctive repetitive pattern with a periodicity equal to or at least directly related to a time interval covered by a WiMAX frame. For example, LTE UE's received signal quality may show a pattern with 5 ms periodicity due to the duty cycle of interfering WiMAX MS uplink transmission.
In 3GPP LTE standards, Reference Signal Received Power (RSRP) is an indicator of the desired signal strength for the downlink connection, i.e., the transmission of data packets from the base station to the wireless device. RSRP is defined as the linear average over the power contributions of the Resource Elements (REs) which carry cell-specific reference signal (RS) within the considered measurement frequency bandwidth for a specific cell. To take the interference level into account, an LTE UE may also compute Reference Signal Received Quality (RSRQ) that is defined as, RSRQ=N×RSRP/RSSI, where N is the number of Resource Blocks (RBs) of the LTE carrier Received Signal Strength Indication (RSSI) measurement bandwidth. For the calculation of the ratio, RSRQ, the measurements for both RSRP and RSSI are made over the same set of resource blocks. RSRQ may therefore capture the combined effect of (wanted) signal strength and (unwanted) interference level, and may be interpreted as an indicator for Signal to Interference and Noise Ratio (SINR) at the LTE UE receiver.
As shown in
Turning to interference scenario 2 shown in
Refer to
In one or more embodiments, one or more modules of the apparatus 200, or other components that the module may be connected with (but are not shown in any of the figures) may include one or more processors and/or individual memory modules, to perform the functions and processes described herein. Also, although the modules in
As would be understood by a person with skill in the art, the functional block diagram of
Transceiver 215 may be operatively connected to antenna 210 to exchange data packets with one or more wireless devices. For example, if apparatus 200 is configured as an FDD base station (e.g., FDD BS 130 or 132) to be operational in an FDD network, transceiver 215 may be configured to communicate FDD data packets with an FDD device (e.g., FDD device 140 or 142). Further, transceiver 215 may be coupled with or may include a baseband processing module (not shown) which may be configured to convert radio frequency (RF) signals received from transceiver 215 to baseband signals. In some embodiments, transceiver 215 of FDD BS 130 transmits packets to FDD device 140 using a frequency from FDD downlink frequency band 115. Similarly, transceiver 215 of FDD BS 132 may receive packets from FDD device 142 using a frequency from FDD uplink frequency band 120.
Memory 220 may be configured to store various data and program instructions to facilitate the interference detection and mitigation operations of one or more modules of (or associated with) apparatus 200. For example, memory 220 may store reports indicating reception quality of data packets at an FDD device (e.g., device 140) associated with apparatus 200. Additionally, or alternatively, memory 220 may store threshold values and/or real-time values for various operational parameters (e.g., device power, service level, network load or traffic, frequency band information, TDD or FDD frame configuration, number of transmitted or received data packets, outputs generated by the modules, etc.) of the TDD or FDD wireless network within which apparatus 200 is operating.
Input/output controller 255 may operate in conjunction with user interface 260 to allow display of information to a user, for example, as well as to receive input from the user using conventional input/output devices, among other purposes.
Scenario 1: TDD MS to FDD UE Interference Case
In some embodiments, to determine interference between wireless devices (e.g., between TDD device 135 and FDD device 140), channel-quality module 245 (arranged in, e.g., BS 130) is coupled to memory 220 and is configured to process the quality-indicator reports received by apparatus 200 from FDD device 140. As a result of such processing, channel-quality module 245 may determine whether or not FDD device 140 has experienced interference from TDD device 135. The quality-indicator reports from FDD device 140 may include values of one or more various parameters such as Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), Channel Quality Information (CQI), Acknowledgement (ACK) or Non-acknowledgement (NACK) signals, etc.
For example, with a center frequency of 2.6 GHz, the coherence time of 3 km/h pedestrian user is about 30 ms. However, channel-quality module 245 at FDD base station 130, by processing RSRQ or CQI reports, may determine that the interference caused by stationary TDD (e.g., WiMAX) device 135 jumps (labeled as 502) or drops (labeled as 504) abruptly every 2 or 3 ms with respect to a threshold 506 of an acceptable level of RSRQ (or with respect to an acceptable-interference threshold or criterion) when TDD device 135 switches between transmit and receive modes in every TDD frame of duration equal to 5 ms. Consequently, FDD device 140 may observe an abrupt change of RSRQ and, therefore, may determine TDD device interference, even though its RSRP remains relatively unchanged. In other words, the estimated coherence time, based on the rate of change of RSRP values, may be much larger than what is estimated based on RSRQ values.
With regard to differentiating between interference between TDD and FDD devices and interference at an FDD device from other sources, it may be worth noting that LTE and WiMAX systems, each of which are based on OFDM, may have no intra-cell interference. Accordingly, the only determination FDD (LTE) BS 130 has to make in order to detect external TDD interference from TDD (WiMAX) device 135 is to discriminate between inter-sector downlink interference. In some embodiments, it may be easier for FDD BS 130 to detect the interference using, e.g., interference pattern detection in LTE systems than in other cellular systems such as CDMA, which may suffer from intra-sector interference problem. For a stationary or slowly moving FDD device not suffering from TDD device interference, the interference may mostly result from adjacent FDD base stations' downlink transmission. Such interference may be calculated from downlink (DL) transmission rate or load (i.e., from an FDD base station to its associated FDD device(s)) of the interfering FDD base stations, and the channel paths between the affected FDD device and the interfering FDD base stations. Taking into account the semi-static nature of DL loads (i.e., DL load of an FDD base station may not change rapidly, e.g., in a millisecond scale, as the load is equal to the sum of intended traffic stream of many active wireless FDD devices in the coverage area of the FDD base station), and large channel coherence time, the interference level of a stationary FDD device may be reasonably assumed to remain relatively unchanged across multiple FDD frames or data packets. Thus, it may be reasonably concluded that interference from the neighboring FDD base station is unlikely to cause abrupt RSRQ change of the FDD device. Additionally, or alternatively, information related to transmission rate or load of the adjacent FDD base station may be made available to the FDD base station serving the affected FDD device using, e.g., X2 interface. The load information may enable the serving FDD base station to determine whether the abrupt change of interference (in terms of RSRQ values) is caused by the change of loads of adjacent FDD base stations or some other sources.
For example, in a well-designed FDD LTE network, FDD LTE device(s) operating on the edge of the cell (or coverage area) of the FDD base station may be able to achieve a guaranteed minimum throughput most of the time. However, if an FDD BS receives and processes reports indicating a service disruption for one of the FDD devices which are in communication with the FDD BS, e.g., by either receiving a predetermined number of consecutive NACKs or very low values of CQI, the FDD base station may take actions to find out the cause of service disruption. For example, in some embodiments, for FDD BS 130 being aware of neighboring or co-located TDD BS 125 operating on adjacent carrier frequencies (from within TDD frequency band 110), FDD BS 130 may utilize channel-quality module 245, alone or in combination with other modules, to initialize an interference detection mechanism for determining whether FDD device 140 is experiencing interference from TDD device 135.
The following review of CQI feedback mechanisms in an LTE wireless system is provided to understand the use of CQI reports as quality-indicator reports for interference detection and mitigation operations described herein. A variety of CQI feedback schemes are known to be part of the LTE standard. For example, an LTE UE (e.g., device 140) may be configured, using Radio Resource Control (RRC) signaling, to periodically provide CQI reports to the LTE BS (e.g., BS 130) over the PUCCH (Physical Uplink Control Channel), when the LTE UE is not scheduled for data transmission. In some embodiments, periodic CQI reports over multiple FDD LTE frames may be required by the FDD LTE BS 130 to decide with reasonable confidence whether the interference at FDD LTE device 140 is due to TDD device 135 (which is in close proximity). Both wideband and LTE UE-selected subband CQI feedback schemes may be utilized for periodic CQI reporting. Also, a period of the CQI reports may be selected by an operator of apparatus 200, or may be dynamically configured within apparatus 200. For example, the CQI report period may be configured equal to 2, 5, 10, 16, 20, 32, 40, 64, 80, or 160 ms. For the wideband CQI reporting, FDD LTE device 140 may send a single wideband CQI report corresponding to the entire FDD channel bandwidth. In the case of the LTE UE-selected subband CQI reporting, FDD LTE device 140 may send a CQI report for each subband. As another CQI reporting option, FDD LTE device 140 may provide non-periodic CQI reports with other multiplexed data transmission over PUSCH (Physical Uplink Shared Channel). Furthermore, FDD LTE BS 130 may instruct FDD LTE UE 140 to provide on-demand, non-periodic CQI reports that are carried on the PUSCH.
In general, FDD BS 130 may formulate the detection of interference from TDD device 135 as a statistical hypothesis testing problem, with the following hypotheses:
In some embodiments, channel-quality module 245 is coupled with operation-monitoring module 235, such that a decision to start the processing of quality-indicator reports and the type of processing to be carried out at channel-quality module 245 is related to an outcome provided by operation-monitoring module 235. For example, channel-quality module 245 may process the quality-indicator reports responsive to a determination by operation-monitoring module 235 that a triggering event in the FDD network has occurred. The triggering event may include a service disruption event between FDD BS 130 (or transceiver 215) and FDD device 140, e.g., occurring for a particular continuous time period. The service disruption event may be defined as FDD BS 130 experiencing an increase in the probability of not receiving ACK signals indicating correct reception of data packets at FDD device 140. Typically, the probability of not receiving an ACK signal for initial downlink transmission is around 10% (or 0.1) or may be some other value as configured by FDD BS 130. In the case where there's a sudden increase in NACK signals for downlink transmission due to abrupt change of channel condition, the probability of not receiving an ACK signal may be lowered by FDD BS 130 power control mechanism to the pre-configured or known targeted probability equal to around 10%. Furthermore, such a disrupting channel condition may not be persistent. However, during a service disruption, the probability of not receiving an ACK signal may be much higher and may also be persistent as the mechanism, e.g. power control mechanism, may be ineffective for combating interference from TDD mobile devices, e.g., TDD device 135.
In some embodiments, to minimize the processing burden at FDD BS 130, channel-quality module 245 may start processing the quality-indicator reports after it is determined (e.g., by operation-monitoring module 235) that a transmission power of FDD device 140 is greater than a transmission power threshold. For example, such decision may be based on an observation that the TDD-to-FDD interference is most likely to happen when FDD device 140 is at a cell-edge or indoor, and is transmitting close to a level which is greater than a power threshold and/or at about maximum transmit power level. The power threshold used here may be pre-selected or configured depending on various factors, such as number of users in the cell covered by FDD BS 130, average load per user, etc.
In some embodiments, channel-quality module 245 processes the quality-indicator reports using more than one technique, and selects a particular processing technique based on a determination (made, e.g., by operation-monitoring module 235) whether a rate of transmission of FDD data packets from FDD BS 130 to FDD device 140 (i.e., FDD DL rate) is less than or greater than a load threshold. The load threshold may be calculated based at least on a rate of transmission of TDD data packets from TDD BS 125 to TDD device 135 (i.e., TDD DL rate) or a TDD frame configuration at TDD BS 125. For example, the load threshold for FDD BS 130 may be set as equal to (or less than) the TDD DL rate, or to a load level that may be accommodated by the interference-free interval that is associated with or inherently provided by the TDD frame configuration. Accordingly, the load threshold may be a certain percentage (less than 100%) of the FDD DL rate. The percentage value may be determined based on a ratio of downlink (DL) time interval and uplink (UL) time interval of TDD data packets or frames exchanged between TDD BS 125 and TDD device 135. For example, as shown in
In some embodiments, if FDD DL rate is less than the load threshold, channel-quality module 245 may analyze whether the reception quality (in terms of, e.g. CQI reports, RSRQ) at FDD device 140 has met an acceptable-interference threshold, as shown in
Additionally, or alternatively in the case where FDD DL rate is greater than the load threshold, FDD BS 130 may configure FDD device 140 such that FDD device 140 periodically provides the CQI reports as the quality-indicator reports (which are stored in memory 220) with the period being configurable, as discussed above. In one embodiment, the period of CQI reports is selected or configured such that the CQI reports are received at FDD BS 130 more frequently than before the start of the interference detection at FDD BS 130. For example, for one FDD LTE frame of duration 10 ms, FDD device 140 may be configured to provide five CQI reports with 2 ms periodic CQI reporting. As discussed above, either wideband or sub-band CQI reporting may be used, according to network implementation. However, it is noted that sub-band CQI reports near channel border 160 (i.e., frequencies common to both TDD and FDD frequency bands) may be more accurate than wideband CQI reports in terms of the interference level from TDD device 135 uplink transmit power leakage, since TDD device 135 interference may be strongest near the channel border.
Channel-quality module 245 may then process one or more periodically-received CQI reports for one or more FDD data packets, and provide the processed report(s) to pattern-analysis module 225 to ascertain an actual CQI (or quality-indicator) report pattern in the processed report(s) for each FDD data packet. The actual CQI report pattern, which may be a result of TDD DL/UL duty cycle of TDD frames, may be further processed (as described later) to determine that FDD device 140 has experienced interference from TDD device 135. Additionally, pattern-analysis module 225 may be configured to determine an expected CQI (or quality-indicator) report pattern of FDD device 140 based on a frame configuration of TDD frames. The expected CQI pattern over one FDD LTE radio frame (e.g., I=[1 1 0 1 0]) is given in Table 2 below. Here, “1” in the actual or expected pattern indicates that FDD device 140 is experiencing interference, and “0” indicates no interference at FDD device 140.
Based the actual and expected CQI pattern, the interference detection problem may be formulated as a sequence-detection problem in apparatus 200. Accordingly, correlation module 240 of apparatus 200 may be configured to correlate the actual CQI report pattern with the expected CQI report pattern to determine if FDD device 140 has experienced interference. In some embodiments, correlation module 240 may calculate a correlation value representing a correlation between the expected CQI report pattern and the actual CQI report pattern, calculate an average correlation value for a sequence of actual CQI report patterns corresponding to multiple FDD frames, and compare the average correlation value with a predetermined threshold value to determine if the reception at FDD device 140 has experienced interference from TDD device 135.
As discussed above, the expected CQI pattern in accordance with the exemplary TDD frame configuration 410 shown in
Based on the correlation of the actual and expected. CQI patterns, if the interference at FDD device 140 is confirmed, channel-quality module 245 may place identifying information of FDD device 140 in the list of FDD devices including FDD devices 140 affected by TDD device interference. Further, clean-slot module 252 may determine an interference-free time interval, which may be used by configuration-adjustment module 230 to adjust a downlink configuration of FDD device 140. The interference-time interval may or may not be aligned with DL time interval 417 of TDD frame structure 410. Configuration-adjustment module 230 may configure transceiver 215 such that transceiver 215 transmits FDD data packets to FDD device 140 during the interference-free time interval.
Additionally, or alternatively, configuration-adjustment module 230 may adjust the downlink configuration of transceiver 215 such that transceiver 215, responsive to a determination (by, e.g., channel-quality module 245) that a data-quality requirement of the FDD device has not been met, transmits FDD data packets to FDD device 140 on a reduced-interference frequency. The reduced-interference frequency may be selected from within FDD downlink frequency band 115 that includes first and second frequencies. The first frequency may be adjacent to TDD transmission frequency band 110 (i.e., may be equal to a frequency at an edge of the TDD band 110), and the reduced-interference frequency may be closer to the second frequency than the first frequency. In other words, the reduced-interference frequency may be from within the half of FDD band 115 which is farther away from channel border 160 of TDD band 110 and FDD band 115. Such selection of reduced-interference frequency may ensure that FDD device 140 is away from severe interfering power of TDD device 135 operating on an interfering frequency from TDD band 110. Moreover, if FDD device 140 is operational with an application with a strict data-quality requirement, including a Quality of Service (QoS) requirement, FDD device 140 may not afford to wait for the next available interference-free time interval for transmission and, in such cases, FDD device 140 may be configured to transmit on a reduced-interference frequency with no guarantee of availability of an interference-free time interval. The application with a QoS requirement may include an application with a delay constraint (e.g., a Voice over IP (VoIP) application), an application with a minimum data rate constraint (e.g., a video streaming application), or an application with a minimum jitter constraint (e.g., a real-time multimedia application).
Additionally, or as an alternative, configuration-adjustment module 230 may perform other adjustments or modification in the operation of apparatus 200 to address any interference issue. For example, configuration adjustment module may increase DL transmission power level, change modulation and/or channel coding scheme, switch Multiple Input Multiple Output (MIMO) mode for higher diversity, etc.
Furthermore, in general, the number of FDD devices 140 suffering from TDD interference is small compared to the total number of active FDD devices in a cell of the FDD network. Accordingly, the probability of the affected FDD devices 140 requiring higher DL capacity than the DL capacity offered in the interference-free interval (e.g., three out of every five subframes, as shown in and described with respect to
Turning now to
At step 605, it may be determined, e.g., by operation-monitoring module 235, whether a triggering event in the FDD network has occurred, which may be an indicator to initiate interference detection, e.g., at FDD BS 130. The event may include a service disruption event between FDD BS 130 (or transceiver 215) and FDD device 140, e.g., occurring for a particular continuous time period. If the occurrence of the triggering event has been confirmed, processing of the quality-indicator (e.g., CQI) reports received from FDD device 140 at FDD BS 130 (or specifically, at transceiver 215) for interference detection may be carried out using more than one technique. Accordingly, a particular processing technique may be selected, at step 610, based on a determination (made, e.g., by operation-monitoring module 235) whether an FDD DL rate is less than a load threshold. As discussed above, the load threshold may be calculated based on, among other factors, a TDD DL rate (e.g., equal to the TDD DL rate or a certain percentage of the FDD DL rate).
If the response is “N” (i.e., label 611) at step 610, indicating that FDD DL rate is greater than the load threshold, a detailed interference detection technique including processing of the quality-indicator (CQI) reports by channel-quality module 245 may be initiated. For example, at step 615, FDD BS 130 may configure FDD device 140 such that FDD device 140 periodically provides the CQI reports with the period selected such that the CQI reports are received at FDD BS 130 more frequently than before the start of the interference detection. For example, the period of CQI reporting may be selected as 2 ms, which, considering the FDD (LTE) frame structure of 10 ms as shown in
At step 620, it is determined if Nmonitored
At step 630, the actual quality-indicator report pattern may be correlated with the expected quality-indicator report pattern to determine the correlation value, β and Nmonitored
If the response of step 620 is “N” (label 621), the final correlation value, β from step 630 is averaged over the total number of frames, Nreqd
Referring to step 610, if the response is “Y” (label 612), a simpler processing of CQI reports is carried out by, e.g., channel-quality module 245. For example, at step 645, an interference-free time interval may be determined based on the frame configuration of TDD frames. As discussed above, the interference-free time interval may correspond to DL time interval of TDD frames, and FDD device 140 may be scheduled to receive FDD data packets from FDD BS 130 during the interference-free time interval. At step 650, it may be determined whether the reception quality at FDD device 140 for data packets received during the interference-free time interval has met (or exceeded) an acceptable-interference criterion (or threshold). If the response is “N” (i.e., label 651), at step 640, it is determined that degradation or interference at FDD device 140 is not caused by TDD device 135. However, if the response is “Y” (i.e., label 652), FDD device 140 may be directly placed in the list at step 655.
Referring to
Scenario 2: FDD UE to TDD MS Interference Case
Referring to
In some embodiments, for determining interference in scenario 2, parameter-monitoring module 230 may be configured to monitor an operational parameter of interfering FDD device 142, and determine whether the monitored parameter is within a fixed range of a maximum value of the operational parameter to confirm FDD-TDD device interference. In some embodiments, the operational parameter includes a transmit power level at which FDD device 142 is transmitting FDD data packets or frames to FDD BS 132. For example, if FDD device 142 has a maximum power level equal to about 23 dBm, a fixed range for monitoring purposes may include power values, e.g., from 13 dBm to 23 dBm or may be a smaller range. However, the link budget and overall cell coverage for FDD BS 132 may be reduced if the range includes power level values too far from the maximum value. In other words, the fixed range may be so chosen such that the parameter monitoring involving the fixed range provides enough protection to nearby TDD mobile devices so as not to unnecessarily sacrifice the link budget. To have an exact value of a power threshold, instead of a fixed range for interference detection, may require, among other things, study of RF characteristics of both FDD 142 and TDD 137 devices, FDD and TDD network deployment details, and mobile subscriber geographical distribution. In other words, the fixed power range or power threshold may be implemented as a configurable parameter, and be fine-tuned during the deployment based on the above-mentioned network characteristics.
Accordingly, if it is determined that FDD device 142 is causing interference to TDD device 137, configuration-adjustment module 230 may configure transceiver 215 such that transceiver 215 receives FDD data packets from FDD device 142 on a reduced-interference frequency selected from within FDD UL band 120. The reduced-interference frequency may be selected such that it is either the frequency at the center of the FDD UL band 120, or is from within the half of FDD band 120 which is farther away from channel border 160 of bands 112 and 120. Additionally, or as an alternative, if FDD BS 132 has knowledge of a TDD frame structure including TDD DL time interval (as described earlier), transceiver 215 and/or FDD device 142 may be configured such that device 142 does not transmit data packets to transceiver 215 during the TDD downlink time interval.
Generalization for TDD UE-FDD UE Interference
While the system and techniques in this disclosure are described for interference scenarios between TDD devices (e.g., WiMAX MS) and FDD devices (e.g., LTE UE), the above-discussed interference determination and mitigation techniques may be generalized to apply for scenario related to interference between TDD-LTE and FDD-LTE devices (i.e., both the interfering and affected wireless devices are operating on LTE networks, albeit on TDD and FDD schemes, respectively). Accordingly, instead of using TDD WiMAX frame structure 410 shown in
Furthermore, in some embodiments, the above-discussed interference detection and mitigation techniques are applicable for wireless system involving interference between two TDD wireless devices each operating with a different TDD (LTE or WiMAX) network. For example, instead of operating on FDD scheme, devices 140, 142 and base stations 130, 132 may be operating on TDD scheme with corresponding TDD frequency bands, such that interference is caused between TDD device 135 and TDD device 140, and between TDD device 137 and TDD device 142.
Further, the above processes may be implemented as computer instructions embodied on a physical, tangible computer-readable medium which, when executed by a processor in or associated with FDD and TDD base stations 125, 127, 130, 132, or in devices 135, 137, 140, 142, carries out the functionality of the embodiments described above.
In addition, over-the-air provisioning of software updates and/or data updates from a base station to a wireless device may be made along the lines of the embodiments discussed above.
Those with skill in the art will appreciate that the inventive concept described herein may work with various system configurations. In addition, various embodiments of this disclosure may be made in hardware, firmware, software, or any suitable combination thereof. As discussed above, various aspects of this disclosure may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable storage medium may include read only memory, random access memory, magnetic disk storage media, optical storage media, flash memory devices, and others. Further, firmware, software, routines, or instructions may be described herein in terms of specific exemplary embodiments that may perform certain actions. However, it will be apparent that such descriptions are merely for convenience, and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, or instructions.
Various embodiments may be described herein as including a particular feature, structure, or characteristic, but every aspect or embodiment may not necessarily include the particular feature, structure, or characteristic. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it will be understood that such feature, structure, or characteristic may be included in connection with other embodiments, whether or not explicitly described. Thus, various changes and modifications may be made to this disclosure without departing from the scope or spirit of the inventive concept described herein. As such, the specification and drawings should be regarded as examples only, and the scope of the inventive concept to be determined solely by the appended claims.
This application is a divisional of U.S. patent application Ser. No. 12/896,494, filed Oct. 1, 2010, the contents of which are hereby incorporated by reference herein in their entirety.
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| Child | 13660545 | US |
