PATENT DOCUMENT

Publication Number: US-11096076-B2
Application Number: US-201715827221-A
Country: US
Kind Code: B2

Title: Prioritized cell identification and measurement method

Abstract:
A prioritized cell identification and measurement method is disclosed. The method classifies frequency layers to be monitored and measured by an user equipment into normal- and reduced-performance groups. Several different embodiments are described. Where appropriate, the corresponding signaling design is also suggested. User equipment can adopt one or several of these embodiments, and can change configurations in a semi-static manner based on operating conditions.

Claims:
We claim: 
     
       1. An apparatus of a user equipment (UE) to operate in an evolved universal mobile telecommunication system terrestrial radio access (E-UTRAN) radio access technology (RAT), comprising:
 a processor; and 
 a memory coupled to the processor, the memory comprising instructions to be executed by the processor, wherein the instructions, when executed, cause the processor to:
 for each frequency layer associated with the UE of a total number, N freq , of frequency layers to be measured by the UE other than a primary frequency layer and one or more secondary frequency layers, assign that frequency layer to one of a group having normal performance or a group having reduced performance, wherein the number of frequency layers in the group having normal performance plus a number of frequency layers in the group having reduced performance is equal to N freq , wherein N freq  is an integer greater than eight, and wherein at least one of the group having normal performance or the group having reduced performance comprises at least one of an inter-frequency layer or an inter-RAT frequency layer; and 
 perform a configured measurement type on each frequency layer assigned to the group having normal performance. 
 
 
     
     
       2. The apparatus of  claim 1 , wherein N freq  is at least twelve. 
     
     
       3. The apparatus of  claim 1 , wherein the instructions, when executed, further cause the processor to determine a measurement gap repetition period (MGRP). 
     
     
       4. The apparatus of  claim 3 , wherein the MGRP is 40 milliseconds or 80 milliseconds. 
     
     
       5. The apparatus of  claim 3 , wherein the instructions when executed further cause the processor to perform the configured measurement type on the frequency layers, based at least in part on the MGRP. 
     
     
       6. The apparatus of  claim 1 , wherein the measurement type comprises at least one of a reference signal received power (RSRP) or a reference signal received quality (RSRQ). 
     
     
       7. The apparatus of  claim 3 , wherein the instructions, when executed, further cause the processor to determine a number of measurement gaps for the group having normal performance, based on the MGRP, N freq , and the number of frequency layers in the group having normal performance. 
     
     
       8. The apparatus of  claim 1 , wherein the instructions, when executed, further cause the processor to, for each frequency layer associated with the UE of the total number, N freq , of frequency layers to be measured by the UE other than the primary frequency layer and the one or more secondary frequency layers, assign that frequency layer to the group having normal performance. 
     
     
       9. A processor to operate in an evolved universal mobile telecommunication system terrestrial radio access (E-UTRAN) radio access technology (RAT), wherein the processor is configured to execute instructions provided thereto, and when executed cause the processor to:
 for each frequency layer associated with the processor of a total number, N freq , of frequency layers to be measured by the processor other than a primary frequency layer and one or more secondary frequency layers, assign that frequency layer to one of a group having normal performance or a group having reduced performance, wherein a number of frequency layers in the group having normal performance plus a number of frequency layers in the group having reduced performance is equal to N freq , wherein N freq  is an integer greater than eight, and wherein at least one of the group having normal performance or the group having reduced performance comprises at least one of an inter-frequency layer or an inter-RAT frequency layer; and 
 perform a configured measurement type on each frequency layer assigned to the group having normal performance. 
 
     
     
       10. The processor of  claim 9 , wherein N freq  is at least twelve. 
     
     
       11. The processor of  claim 9 , wherein the instructions, when executed, further cause the processor to determine a measurement gap repetition period (MGRP). 
     
     
       12. The processor of  claim 11 , wherein the MGRP is 40milliseconds or 80 milliseconds. 
     
     
       13. The processor of  claim 11 , wherein the processor is further configured to perform the configured measurement type on the frequency layers, based at least in part on the MGRP. 
     
     
       14. The processor of  claim 9 , wherein the measurement type comprises at least one of a reference signal received power (RSRP) or a reference signal received quality (RSRQ). 
     
     
       15. A method of operating an evolved universal mobile telecommunication system terrestrial radio access (E-UTRAN) radio access technology (RAT), comprising:
 for each frequency layer associated with a UE of a total number, N freq , of frequency layers to be measured by the UE other than a primary frequency layer and one or more secondary frequency layers, assigning that frequency layer to one of a group having normal performance or a group having reduced performance, wherein a number of frequency layers in the group having normal performance plus a number of frequency layers in the group having reduced performance is equal to N freq , wherein N freq  is an integer greater than eight, and wherein at least one of the group having normal performance or the group having reduced performance comprises at least one of an inter-frequency layer or an inter-RAT frequency layer; and 
 performing a configured measurement type on each frequency layer assigned to the group having normal performance. 
 
     
     
       16. The method of  claim 15 , wherein N freq  is at least twelve. 
     
     
       17. The method of  claim 15 , wherein the method further includes determining a measurement gap repetition period (MGRP). 
     
     
       18. The method of  claim 17 , wherein the MGRP is 40milliseconds or 80 milliseconds. 
     
     
       19. The method of  claim 17 , wherein the method further includes performing the configured measurement type on the frequency layers, based at least in part on the MGRP. 
     
     
       20. The method of  claim 15 , wherein the measurement type comprises at least one of a reference signal received power (RSRP) or a reference signal received quality (RSRQ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Provisional Patent Application, Ser. No. 61/990,647, filed on May 8, 2014, of PCT Patent Application, Ser. No. PCT/US2015/029953, filed on May 8, 2015, and of U.S. Pat. No. 9,843,956, issued on Dec. 12, 2017. 
    
    
     TECHNICAL FIELD 
     This application relates to measurements taken by user equipment operating under the long term evolution (LTE) standard. 
     BACKGROUND 
     The evolved packet core (EPC) is the core network of advanced mobile communications systems. The EPC allows different radio access technology (RATs) to operate in an integrated manner. These radio access technologies include first generation wireless local area networks (LANs), second generation (2G) systems, such as global system for mobile communication, or GSM, third generation systems (3G), such as the universal mobile telecommunication system (UMTS), and fourth generation systems (4G) such as long-term evolution (LTE). LTE is a specification promulgated by the 3 rd  Generation Partnership Project, hereinafter, “3GPP specification”. 
     Wireless mobile communication technology uses various standards and protocols to transmit data between a node (e.g., a transmission station or a transceiver node) and a wireless device (e.g., a mobile device). Some wireless devices communicate using orthogonal frequency-division multiple access (OFDMA) in a downlink (DL) transmission and single carrier frequency division multiple access (SC-FDMA) in an uplink (UL) transmission. Standards and protocols that use orthogonal frequency division multiplexing (OFDM) for signal transmission include the LTE (3GPP), the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard (e.g., 802.16e, 802.16m), which is commonly known to industry groups as WiMAX (worldwide interoperability for microwave access), and the IEEE 802.11 standard, which is commonly known to industry groups as WiFi. 
     In 3GPP radio access network (RAN) LTE systems, the node can be a combination of evolved universal terrestrial radio access network (E-UTRAN) NodeBs (also commonly denoted as evolved NodeBs, enhanced NodeBs, eNodeBs, or eNBs), and radio network controllers (RNCs). The eNBs communicate with a wireless device known as an user equipment (UE). The DL transmission can be a communication from the node (e.g., the eNB) to the wireless device (e.g., the UE), and the UL transmission can be a communication from the wireless device to the node. 
     A UE such as a cellphone can support multiple RATs, known as a multi-mode UE. Only one RAT is operable at a time in the multi-mode UE. A multi-mode UE  50  that is said to be “camped” on one RAT is utilizing only the technology of that RAT. The UE can be switched from one RAT to another, thus switching where the UE is camped. Thus, the multi-mode UE can be camped on LTE, get switched from the 4G RAT to the 3G RAT, and is thereafter camped on UMTS. 
     Under carrier aggregation, the UE can simultaneously communicate with two different RATs. Thus, the UE is able to concurrently utilize radio resources from multiple carrier frequencies. 
     In homogeneous networks, the eNB, also called a macro node or macro eNB, can provide basic wireless coverage to wireless devices in a cell. The cell can be the physical region or area inside which the wireless devices are operable to communicate with the macro eNB. Heterogeneous networks (HetNets) can be used to handle the increased traffic loads on the macro nodes due to the increased usage and functionality of wireless devices. HetNets can include a layer of planned high-power macro eNBs overlaid with layers of lower power nodes (small-eNBs, micro-eNBs, pico-eNBs, femto-eNBs, or home eNBs (HeNBs)) that can be deployed in a less well-planned or even entirely uncoordinated manner within the coverage area (cell) of a macro node. The lower power nodes (LPNs) can generally be referred to as “low power nodes”, small nodes, or small cells. 
     The macro node can be used for basic coverage. The low power nodes can be used to fill coverage holes, to improve capacity in hot zones or at the boundaries between the macro nodes&#39; coverage areas, and to improve indoor coverage where building structures impede signal transmission. Inter-cell interference coordination (ICIC) or enhanced ICIC (eICIC) can be used for resource coordination to reduce interference between the nodes, such as macro nodes and low power nodes, in a HetNet. 
     HetNets can use time-division duplexing (TDD) or frequency-division duplexing (FDD) for downlink or uplink transmissions. TDD is an application of time-division multiplexing (TDM) to separate downlink and uplink signals. In TDD, DL and UL signals can be carried on the same carrier frequency, where the DL signals use a different time interval from the UL signals. Thus, the DL signals and the UL signals do not generate interference with each other. TDM is a type of digital multiplexing in which two or more bit streams or signals, such as a DL or UL signal, are transferred apparently simultaneously as sub-channels in one communication channel, but are physically transmitted on different time resources. In FDD, a UL transmission and a DL transmission can operate using different frequency carriers. In FDD, interference can be avoided because the DL signals use a different frequency carrier from the UL signals. 
     Time-division duplexing (TDD) offers flexible deployments without requiring a pair of spectrum resources. Long-term evolution (LTE) TDD allows for asymmetric uplink-downlink (UL-DL) allocations. 
     As the UE operates in a wireless neighborhood, the channel conditions change. This can be due to movement by the UE, the presence of buildings and vehicles in the line of sight of the UE, and other conditions such as, for example, interference from neighboring stations, etc. Channel state information (CSI) is data about the channel conditions and is provided to the eNB by the UE during wireless communication. CSI includes channel quality information (CQI), pre-coding matrix indication, rank indication, and other characteristic information about the wireless channel. 
     The 3GPP organization includes several working groups dedicated to particular tasks under LTE. Radio access network 1 (RAN1) is responsible for defining the physical layer; RAN2 deals with radio interface protocols on top of the physical layer; RAN3 pertains to the overall UTRAN (EUTRAN) architecture; RAN4 is dedicated to the RF conformance aspects of UTRAN (EUTRAN), test specifications for radio network and terminal equipment regarding RF transmission and reception performance; and RAN5 pertains to radio interface conformance test specification, test specifications based on RAN4 specifications, and signaling procedures defined by other groups such as RAN2. 
     Under the LTE specification, the UE monitors a frequency (also known as a layer, frequency layer, carrier, or band) for the serving primary cell (pcell) of the UE as well as for a secondary cell (scell) of the UE. While being serviced by the pcell, the UE remains on the pcell frequency. The pcell frequency layer and the scell frequency layer are monitored at a first rate. 
     Additionally, the UE monitors other frequencies, including other RATs, at a second, lower rate, such that, if handover to a different frequency band (in the case of inter-RAT monitoring) or switching to a different RAT, such as USTM (3G) or WiFi (2G) becomes necessary, the UE knows the characteristics of these frequency layers. 
     Previously under LTE, the UE was expected to monitor eight or more frequency layers. Under recent RAN4 modifications (RAN4, release 12), the minimum number of frequency layers in EUTRAN to be monitored has increased from eight to thirteen. 
     Thus, there is a need for a cell identification and measurement method that addresses the RAN4 release 12 requirements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this document will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts throughout the various views, unless otherwise specified. 
         FIG. 1  is a simplified block diagram of a prioritized cell identification and measurement (PCIM) method, according to some embodiments; 
         FIG. 2  is a simplified diagram of a wireless network, according to some embodiments; 
         FIG. 3  is a simplified diagram of a heterogeneous wireless network for implementing the PCIM method of  FIG. 1 , according to some embodiments; 
         FIG. 4  is a diagram of a measurement gap repetition period used by the PCIM method of  FIG. 1 , according to some embodiments; 
         FIG. 5  is a flow diagram showing operations performed in a first embodiment of the PCIM method of  FIG. 1 , according to some embodiments; 
         FIG. 6  is a flow diagram showing operations performed in a second embodiment of the PCIM method of  FIG. 1 , according to some embodiments; 
         FIG. 7  is a flow diagram showing operations performed in a third embodiment of the PCIM method of  FIG. 1 , according to some embodiments; 
         FIG. 8  is a flow diagram showing operations performed in a fourth embodiment of the PCIM method of  FIG. 1 , according to some embodiments; 
         FIG. 9  is a flow diagram showing operations performed in a fifth embodiment of the PCIM method of  FIG. 1 , according to some embodiments; and 
         FIGS. 10A and 10B  are simplified system diagrams of a wireless neighborhood featuring an enhanced node B and an user equipment, both of which are implementing the PCIM method of  FIG. 1 , according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In accordance with the embodiments described herein, a prioritized cell identification and measurement, or PCIM, method is disclosed. The PCIM method classifies frequency layers to be monitored and measured by an user equipment into high- and reduced-performance groups. Several different embodiments are described. Where appropriate, the corresponding signaling design is also suggested. User equipment can adopt one or several of these embodiments, and can change configurations in a semi-static manner based on operating conditions. 
     In the following detailed description, reference is made to the accompanying drawings, which show by way of illustration specific embodiments in which the subject matter described herein can be practiced. However, it is to be understood that other embodiments will become apparent to those of ordinary skill in the art upon reading this disclosure. The following detailed description is, therefore, not to be construed in a limiting sense, as the scope of the subject matter is defined by the claims. 
       FIG. 1  is a conceptual diagram of a prioritized cell identification and measurement (PCIM) method  100 , according to some embodiments. The PCIM method  100  receives three parameters as input, a number of frequency layers being monitored, given as N freq , a number of measurement gaps, given as M inter , and a measurement gap repetition period (MGRP). The PCIM method  100  includes six possible embodiments, described herein. 
       FIG. 2  is a simplified diagram of a wireless network  150 , consisting of a single macro eNB  20 A, a home eNB  20 B, and a pico eNB  20 C (collectively, “eNBs  20 ”). The wireless network  150  also features thirteen UEs  50 A- 50 P (collectively, “UEs  50 ”), many of which have established a connection to one of the eNBs  20  (indicated with arrows). Connections  40 A- 40 L are the frequency layers between the UEs  50  and their respective eNBs  20 , and are thus the serving frequency layers (collectively, “serving frequency layers  40 ”). 
     The macro eNB  20 A can serve as the serving base station (pcell) for several UEs  50 . In  FIG. 2 , the macro eNB  20 A is the pcell for UEs  50 A- 50 E with connections  40 A- 40 E, respectively. The home eNB  20 C is the pcell for UEs  50 F- 50 H, with connections  40 F- 40 H, respectively. The pico eNB  20 C is the pcell for UEs  50 J- 50 L, with connections  40 J- 40 L, respectively. 
     The home eNB  20 C or the pico eNB  20 C can further serve as the secondary base station (scell) for one or more UEs. In  FIG. 2 , the UE  50 C has pcell connection  40 C but also scell connection  70 A to the pico eNB  20 C. The UE  50 E has pcell connection  40 E but also scell connection  70 B to the home eNB  20 B (collectively, “secondary frequency layers  70 ”). 
     The UEs  50  are depicted in  FIG. 2  as cellular phones, but can also be laptop computers, tablets, smartphones, or other wireless devices. In addition to connection between a UE  50  and an eNB  20 , some UEs can communicate device-to-device within the wireless network  150 , and such communication can be in the form of unicast, broadcast, or multi-hop transmissions (not shown). 
     The PCIM method  100  includes embodiments to enable the UE in a 4G LTE wireless neighborhood or heterogeneous network to perform measurements of frequency layers (also referred to herein as frequencies, bands, connections, or carriers). Terms such as detect, identify, synchronize, monitor, and measure are used herein to describe what the UE is doing with the frequency layers. The terms “measure”, “measurement”, and “measuring” when used herein are meant to imply that the UE has already performed the necessary detection, identification, synchronization, and monitoring that would precede any possible measurement of the frequency layer being conducted. Some aspects of these operations are omitted herein, as they are outside the scope of this disclosure. 
     The frequency layers  40  and the secondary frequency layers  70  are monitored by the UEs  50  regularly, and are not the subject of the PCIM method  100 . Instead, the PCIM method  100  pertains to other frequency layers to measured, including both inter-frequency layers and inter-RAT frequency layers. The inter-frequency layers are the various frequency layers within the current RAT in which the UE  50  operates. As examples, in addition to monitoring pcell band  40 C and scell band  70 A, the UE  50 C in  FIG. 2  can detect and measure the frequency layer between itself and the home eNB  20 B; similarly, in addition to monitoring pcell band  40 E and scell band  70 B, the UE  50 E can detect and measure the frequency layer between itself and the pico eNB  20 C (not shown). 
     The inter-RAT measurements are the measurements outside the current RAT. Thus, for example, when the UE  50  is operating in the 4G RAT, an inter-RAT measurement would be a measurement of the 3G RAT (e.g., UMTS) or the 2G (WiFi) RAT, known as a wireless local area network (WLAN). 
       FIG. 3  is a simplified diagram of a HetNet  200 , which is also a wireless network. A single UE  50 D is depicted. The HetNet  200  includes physically or logically co-located LTE, UMTS, and WLAN cells. As before, there are three LTE-capable enhanced (4G) base stations, the macro eNB  20 A, the home eNB  20 B, and the pico eNB  20 C. 
     The cells are the coverage area of a given wireless base station. Whereas in a 4G network, the base station is an enhanced node B (eNB), in a 3G network, the base station is known as a cellular access point or a node B (NB). In the case of WiFi, the base station is known as an access point (AP). The cell coverage area of each base station is approximately shown as an oval shape. Macro eNB  20 A has cell area  60 A; similarly, home eNB  20 B has a cell area  60 B and pico eNB  20 C has a cell area  60 C. 
     Since the HetNet  200  is heterogeneous, it is expected to have cells that are not strictly part of the 4G LTE RAT.  FIG. 3  shows a 3G base station denoted node B (NB)  20 D, which covers a cell  60 D and a WiFi base station, AP  20 E, having WiFi cell  60 E (collectively, “cell area  60 ” or “cell  60 ”). 
     From the UE&#39;s perspective, the macro eNB  20 A is its primary base station (PSS) and the home eNB  20 B is its secondary base station (SSS). Thus, the pcell and scell frequency layers  40 A and  40 B, respectively, associated with the PSS and SSS are not the subject of the PCIM method  100 . 
     Instead,  FIG. 3  shows three frequency layers of interest. First, frequency layer  90 A is an inter-frequency layer. Like pcell frequency layer  40  and scell frequency layer  70 , frequency layer  90 A operates in the LTE 4G network and connects to an enhanced node B  20 C. Frequency layer  90 B, by contrast, is an inter-RAT frequency layer because it operates in a 3G network and connects to a (not enhanced) node B  20 D. Frequency layer  90 C is also an inter-RAT frequency layer because it operates in a WiFi network and connects to an AP  20 E. Frequency layer  90 D is a band between home eNB  20 B and UE  50 H, and is thus an inter-RAT frequency layer (with the characterization being from the perspective of the UE  50 D). Frequency layer  90 E is a device-to-device connection between UE  50 D and UE  50 H. Thus, both frequency layers that directly impact UE  50 D ( 90 A,  90 B,  90 C, and  90 E) as well as frequency layers that have nothing to do with the UE ( 90 D) are part of the measurable frequency layers that are being considered herein (collectively, “frequency layers to be measured  90 ” or simply “frequency layers  90 ”). In some embodiments, the measurable frequency layers are limited to those between a base station (nB, eNB, or AP) and a UE. In other embodiments, the measurable frequency layers include device-to-device bands, such as frequency layer  90 E. 
     When engaging in frequency layer detection (synchronization) and measurement, the UE  50 D can be said to be performing “cell identification”. Cell identification is thus just another way to describe the frequency layer measuring done by the UE. Thus, the method described herein is known as a prioritized cell identification and measurement, PCIM. 
     In discussing the PCIM method  100 , reference is made to the UE  50 , which can be any one of the UEs depicted in  FIG. 2 or 3 . The eNB  20  referenced in the description below may be any type of LTE-capable base station. The frequency layers to be measured are frequency layers  90 , as illustrated in  FIG. 3 , and not the scell  40  or pcell  70  frequency layers. 
     Based on the RAN4, release 12 requirements (referred to herein as “new RAN4”), both measurement and reporting delay conducted by the UE  50  is proportional to the number of monitored frequency layers  90 , except the serving frequency layers (e.g., pcell  40  and scell  70  frequency layers in  FIG. 3 ). Thus, when the minimum number of frequency layers  90  being monitored increases, an increased delay is expected. The inherent delay due to the increased number of frequency layers  90  to monitor can be problematic, especially when the mobility of the UE  50  is high. 
     From a throughput and power consumption perspective, an increased number of frequency layers to monitor unnecessarily results in higher power consumption and/or throughput loss (e.g., in non-DRX mode), under the new RAN4 procedure. DRX mode, short for discontinuous reception mode, is a power-saving feature of the UE in which the UE, while idle, listens for a paging message (such as incoming call, system information change, and so on), not at the default rate (every 1 ms), but instead at a reduced rate (e.g., every 60 ms), in order to mitigate loss of battery power in the UE. As a result, the challenge that comes with increasing the number of frequency layers to monitor includes how to re-balance the delay, measurement accuracy, and the measurement gap length per measurement gap repetition period (MGRP). 
       FIG. 4  is a simplified diagram showing a portion of a hypothetical wireless transmission  30 . A measurement gap length (MGL) of 6 milliseconds (ms) is shown, followed by a data transmission, then followed by another MGL of 6 ms, and so on. The transmission  30  of  FIG. 4  has a MGRP of 40 ms. Other transmissions can have a MGRP of 80 ms. The MGRP is the periodicity (density) of measurements being taken by the UE  50 . 
     In new RAN4, it has been agreed the performance requirements for increased frequency layer monitoring are divided into two performance groups, denoted as normal-performance and reduced-performance groups, respectively. Different performance requirements are to be defined by new RAN4 for the normal-performance group frequency layers and the reduced-performance group frequency layers. 
     In some embodiments, the PCIM method  100  satisfies two criteria: minimizing the overall measurement delay that results from the UE measuring more frequency layers  90  than in legacy UEs, and achieving backward compatible performance by the UE  50  relative to legacy UEs. As used herein, a legacy UE is an LTE UE that identifies and measures up to eight frequency layers, whereas the UE  50  identifies and measures up to thirteen frequency layers  90  (including the pcell band  40  and, if present, the scell band  70 ). The UE  50  described herein thus satisfies the new RAN4 requirements. 
     The minimum number of frequency layers  90  being monitored by the UE  50 , given by N freq , has increased from eight (legacy UE) to thirteen (new RAN4 requirement). Thus, for the new RAN4, N freq ≤13. A first normal-performance group, denoted g1, consists of a first number, N freq_g1  of frequency layers being monitored by the UE  50  (also known as the normal-performance group size). A second reduced-performance group, denoted g2, consists of a second number, N freq_g2  of frequency layers  90  being monitored by the UE (reduced-performance group size). 
     Without loss of generality, the maximum cell identification delay for inter-frequency measurements, given by T Identify_inter_g1  and T identify_inter_g2  for high- and reduced-performance groups, respectively is given as: 
     
       
         
           
             
               
                 
                   
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     Equations 1 a and 1 b (collectively, “equation 1”) represent the minimum requirement (maximum time) available to the UE  50  for measuring a frequency layer  90  for a first normal-performance group, g1, and a second reduced-performance group, g2, respectively. T Basic_Identify_Inter  is the maximum cell identification delay available to the legacy UE. M Inter_g1  and M Inter_g2  are the number of measurement gaps for the high- and reduced-performance groups, respectively; in other words, M Inter_g1  and M Inter_g2  are the number of measurement opportunities per 480 ms (the density of measurements being performed). (M Inter_g1  and M Inter_g2  are also know herein as the resource assignment for the high- and reduced-performance groups, respectively.)  FIG. 4 , above, illustrates the MGRP and MGP for LTE transmissions. 
     On average, M inter_g1  and M inter_g2  represent the number of measurement gaps assigned to the high- and reduced-performance groups, respectively, per 480 ms. Also, N freq_g1  and N freq_g2  represent the number of frequencies  90  being monitored in the high- and reduced-performance groups, respectively, excluding the pcell band  40 , such as the macro eNB  20 A, and the scell band  70 , such as the pico eNB  20 C ( FIG. 2 ), both of which are being monitored periodically by the UE  50 . 
     From Equation 1, it is shown that both the number of measurement gaps, M inter_g1  (M inter_g2 ) and the maximum cell identification delay, T Identify_inter_g1  (T identify_inter_g2 ) are proportional to the number of monitored frequency layers  90 , N freq_g1  (N freq_g2 ), except the frequency layers of the serving eNBs (pcell and scell). Thus, when the minimum number of frequency layers  90  being monitored, N freq , increases, an increased delay is expected. 
     In the LTE specification, the UE  50  typically has two different measurement opportunities. First, there are twelve measurement gaps per 480 ms; thus, every 40 ms there is one measurement gap and thus one measurement opportunity (480 ms/12=40 ms). Second, there are six measurement gaps per 480 ms; thus, every 80 ms there is one measurement gap/opportunity (480 ms/6=80 ms). Thus, M inter_g1  and M inter_g2  can be thought of as the measurement density for high- and reduced-performance groups, respectively. The MGRP shown in  FIG. 4  is the periodicity of the measuring performed by the UE  50 . 
     The measurements being taken by the UE  50  of the frequency layers are between the UE  50  and other entities in the wireless HetNet  200 , as illustrated in  FIG. 3 . Each measurement calculates some characteristic of the frequency layer  90 . Generally, this characteristic is the signal to interference plus noise ratio, or SINR. In the LTE environment, SINR is effectively obtained by measuring both reference signal received power (RSRP), which can be thought of as signal strength, and reference signal received quality (RSRQ), which is essentially the interference of the frequency layer  90 . 
     For RSRP and RSRQ measurements, the physical layer measurement periods, T measurement_period_Inter_FDD_g1  and T measurement_period_Inter_FDD_g2 , are defined for the high- and reduced-performance groups, respectively, given as: 
                     T     Measurement   ⁢           ⁢   _   ⁢           ⁢   Period   ⁢           ⁢   _   ⁢           ⁢   Inter   ⁢           ⁢   _   ⁢           ⁢   FDD   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   1       =     {             480   ·     480     MGRP   ·     M     Inter   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   1           ·     N     freq   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   1         ,       BW   measure     =     6   ⁢   RB                     240   ·     240     MGRP   ·     M     Inter   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   1           ·     N     freq   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   1         ,       BW   measure     =     50   ⁢   RB                         (     4   ⁢   a     )                 T     Measurement   ⁢           ⁢   _   ⁢           ⁢   Period   ⁢           ⁢   _   ⁢           ⁢   Inter   ⁢           ⁢   _   ⁢           ⁢   FDD   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   2       =     {             480   ·     480     MGRP   ·     M     Inter   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   2           ·     N     freq   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   2         ,       BW   measure     =     6   ⁢   RB                     240   ·     240     MGRP   ·     M     Inter   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   2           ·     N     freq   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   2         ,       BW   measure     =     50   ⁢   RB                         (     4   ⁢   b     )               
where BW measure measure denotes the measurement bandwidth and RB is the resource block. The smallest modulation structure in LTE is the resource element (RE), which is defined as one 15 kHz subcarrier having a width of one symbol. A resource block consists of twelve subcarriers multiplied by six (or seven) symbols.
 
     Assumptions 
     For each frequency layer  90  being monitored, the UE  50  first performs identification, then takes a measurement. Identification is also known as synchronization, in which the UE  50  detects the synchronization symbol for the frequency layer  90 . In LTE, the synchronization symbol is given as a primary synchronization symbol (PSS) or a secondary synchronization symbol (SSS). Only after synchronization occurs can the UE  50  perform measurements of the frequency layer  90 . 
     In some embodiments, the PCIM method  100  ensures that the frequency layers  90  being measured in the normal-performance group enjoy tighter requirements than the frequency layers in the reduced-performance group. As indicated above, T ldentiy_Inter_g1  and T Identify_Inter_g2  are time periods in which the UE  50  is able to identify the cell. Thus, a shorter time period is preferred. In some embodiments, a first assumption is given by the following formula:
 
 T   Identify_Inter_g1   ≤T   Identify_Inter_g2   (5)
 
Equation 5 indicates a preference for the UE  50  to identify the frequency layer  90  faster in the normal-performance group, g1, than in the reduced-performance group, g2.
 
     Recall also that T Measurement_Period_Inter_FDD_g1  and T Measurement_Period_Inter_FDD_g2  are time periods in which the UE  50  measures the characteristics (RSRP and RSRQ) of the identified frequency layers  90 . Again, a shorter time period is preferred. Thus, in some embodiments, a second assumption is given by the following formula:
 
 T   Measurement_Period_Inter_FDD_g1   ≤T   Measurement_Period_Inter_FDD_g2   (6)
 
     Equivalent Function 
     In some embodiments, using Equations 1-3, above, an equivalent function is given as: 
                           N     freq   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   1         M     Inter   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   1         ≤         N   freq     -     N     freq   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   1             480   MGRP     -     M     Inter   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   1             ⇒         N     freq   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   1         M     Inter   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   1         ≤       N   freq       480   MGRP           =         N   freq     ·   MGRP     480             (     7   ⁢   a     )               
Equation 7a can be restated as:
 
                       N     freq   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   1         M     Inter   ⁢           ⁢   _   ⁢           ⁢   g   ⁢           ⁢   1         ≤         N   freq     ·   MGRP     480             (   7   )               
Using Equations 2 and 3, as well as the assumptions given in Equations 5, 6, and 7, the following embodiments of the PCIM method  100  are described. Further, the network described herein is presumed to be a heterogeneous network, such as the HetNet network  200  of  FIG. 3 . Nevertheless, other wireless networks, such as homogeneous networks (consisting only of macro eNBs), that operate under the LTE specification may also employ the PCIM method  100 .
 
     Embodiment 1 
     The PCIM method  100  includes a first embodiment that can be employed when the operators and/or network vendors (e.g., AT&amp;T, Ericsson, or Huawai) define the number of frequency layers  90  to be monitored, given by N freq . In some embodiments, the serving eNB  20  defines the number of frequency layers  90  in the normal-performance group, given by N freq_g1 . Once the normal-performance group is known, the reduced-performance group is also known, since N freq_g2 =N freq −N freq_g1 . 
     In some embodiments, when the normal- and reduced-performance groups are defined, the size of the normal-performance group, N freq_g1 , and the assigned resources, M Inter_g1 , satisfies the constraint given in Equation 7, above. The number of frequency layers  90  in the normal-performance group, N freq_g1 , is divided by the number of measurement gaps in the normal-performance group, M Inter_g1 , and the result is less than or equal to the total number of frequency layers multiplied by MGRP/480. Equation 7 thus puts an upper bound on the size of the normal-performance group, N freq_g1 . 
     The PCIM method  100 , embodiment 1, is illustrated in the flow diagram of  FIG. 5 . The network operator defines the number of frequency layers  90  to be measured by the UE (block  302 ). The serving eNB  20  defines the number of frequency layers  90  in the normal-performance group (block  304 ). Equation 3 is used to derive the number of frequency layers  90  in the reduced-performance group (block  306 ). The periodicity of the measuring to be performed by the UE  50 , MGRP, is selected, either 40 ms or 80 ms (block  308 ). This selection is made by the UE  50 , by the pcell eNB  20 A, or by another network entity. 
     Once these values are ascertained, Equation 7 is used to derive the density of the measuring taking place for the normal-performance group (block  310 ). Finally, Equation 2 is used to derive the density of measurement for the reduced-performance group (block  312 ). The operations performed by the PCIM method  100 , embodiment 1, are complete. 
     The PCIM method  100  thus provides a design criterion to enable the eNB  20  to decide the size of the normal-performance group based on Equation 7 (with help from Equations 2 and 3). 
     Embodiment 2 
     In a second embodiment, to minimize the overall measurement delay, the PCIM method  100  assigns all frequency layers  90  to be monitored in a single group, with all resources being allocated to the same group. In some embodiments, this assignment is made by the eNB. In other embodiments, the assignment is made by the UE. This allows the UE  50  to prioritize one frequency layer over another frequency layer, for example. 
     In general, regardless of how normal-performance and reduced-performance groups are defined, it is desirable to reduce the overall measurement delay for each concerned inter-frequency and inter-RAT measurement. Timely measurement and reporting by the UE  50  not only facilitates network operation, but also reduces the probability of radio link failure (RLF), e.g., connection loss. This is especially the case when the serving cell coverage is weak. 
     The maximum cell identification delays for the high- and reduced-performance groups, respectively, are denoted as, T Identify_Inter_g1  and T Identify_Inter_g2 , the time periods in which the UE  50  is able to identify the cell (frequency layer  90 ). Mathematically, an overall measurement delay, T Identify_Inter_avg , an average for both groups g1 and g2, can be quantified as: 
     
       
         
           
             
               
                 
                   
                     T 
                     
                       Identify 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Inter 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       avg 
                     
                   
                   = 
                   
                     
                       
                         T 
                         
                           Identify 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           _ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           Inter 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           _ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           g 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                       · 
                       
                         
                           N 
                           
                             freq 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             _ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             g 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                         
                           N 
                           freq 
                         
                       
                     
                     + 
                     
                       
                         T 
                         
                           Identify 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           _ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           Inter 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           _ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           g 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                       · 
                       
                         
                           N 
                           
                             freq 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             _ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             g 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                         
                         
                           N 
                           freq 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     Recall also that the physical layer measurement periods for the high- and reduced-performance groups, respectively, denoted as, T Measurement_Period_Inter_FDD_g1  and T Measurement_Period_Inter_FDD_g2 , are time periods in which the UE  50  measures the characteristics (RSRP and RSRQ) of the identified frequency layers  90 . Mathematically, an overall physical layer measurement period, T Measurement_Period_Inter_FDD_g2 , an average for both groups g1 and g2, can be quantified as: 
     
       
         
           
             
               
                 
                   
                     T 
                     
                       Measurement 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Period 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Inter 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       FDD 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       ave 
                     
                   
                   = 
                   
                     
                       
                         T 
                         
                           Measurement 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           _ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           Period 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           _ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           Inter 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           _ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           FDD 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           _ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           g 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                       · 
                       
                         
                           N 
                           
                             freq 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             _ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             g 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                         
                           N 
                           freq 
                         
                       
                     
                     + 
                     
                       
                         T 
                         
                           Measurement 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           _ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           Period 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           _ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           Inter 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           _ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           FDD 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           _ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           g 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                       · 
                       
                         
                           N 
                           
                             freq 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             _ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             g 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                         
                         
                           N 
                           freq 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     Table 1 shows the results of several different normal-performance group sizes, N freq_g1 , and how the size of the normal-performance group makes a difference in terms of the measurement delay. Thus, assuming a total number of frequency layers, N freq , of 8, 9, 10, 11, and 12 are measured with alternating MGRPs sizes of 40 ms and 80 ms. Table 1 shows the relative measurement delay saving between the scenario when all carriers are normal-performance carriers and the scenario when the carriers are randomly assigned to either the normal-performance group or the reduced-performance group. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Normal-performance group size and assignment with 
               
               
                 minimized overall measurement delay 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 8 
                 9 
                 10 
                 11 
                 12 
               
            
           
           
               
               
            
               
                   
                 MGRP (ms) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 N freq   
                 40 
                 80 
                 40 
                 80 
                 40 
                 80 
                 40 
                 80 
                 40 
                 80 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 N freq _g1 
                 8 
                 8 
                 9 
                 9 
                 10 
                 10 
                 11 
                 11 
                 12 
                 12 
               
               
                 M Inter _g1 
                 12 
                 6 
                 12 
                 6 
                 12 
                 6 
                 12 
                 6 
                 12 
                 6 
               
               
                 %* 
                 72.5 
                 53.2 
                 74.0 
                 52.2 
                 75.4 
                 53.12 
                 77.1 
                 54.5 
                 71.0 
                 50 
               
               
                   
               
               
                 *N freq _g1 and M Inter _g1 are randomly selected with the constraint of 
               
               
                 
                   
                     
                       
                         
                           
                             N 
                             
                               freq 
                               ⁢ 
                               _ 
                               ⁢ 
                               g 
                               ⁢ 
                               1 
                             
                           
                           
                             M 
                             
                               Inter 
                               ⁢ 
                               _ 
                               ⁢ 
                               g 
                               ⁢ 
                               1 
                             
                           
                         
                         ≤ 
                         
                           
                             
                               N 
                               freq 
                             
                             · 
                             MGRP 
                           
                           480 
                         
                       
                     
                   
                 
               
            
           
         
       
     
     The last row of Table 1 shows the saved measurement delay compared to randomly picked frequencies to be monitored, N freq_g1 , and measurement gaps, M inter_g1 , where Equation 7 is assumed. A lower percentage number is preferred. Table 1 shows that, where the MGRP is 40 ms, the lowest percentage is 71% (when N freq_g1 =12) and when MGRP is 80 ms, the lowest percentage is 50% (also when N freq_g1 =12). Thus, in some embodiments, the measurement delay is minimized when all frequency layers  90  are assigned to a single group, e.g., the normal-performance group, and all resources are allocated to this group. 
     The PCIM method  100 , embodiment 2, is illustrated in the flow diagram of  FIG. 6 . All frequency layers to be measured are part of the normal-performance group (block  402 ). This may be done by the UE  50  or by the eNB  20 . The reduced-performance group is empty (block  404 ). The periodicity of the measuring to be performed by the UE  50 , MGRP, is selected by the UE, either 40 ms or 80 ms (block  406 ). Equation 7 is used to derive the density of the measuring taking place for the normal-performance group (block  408 ). The operations performed by the PCIM method  100 , embodiment 2, are complete. 
     Embodiment 3 
     The PCIM method  100  also considers backward compatible performance of the UE  50 . Embodiment 3 is enables the normal-performance group, g1, to at least achieve the legacy system performance in terms of the measurement delay. Legacy UEs have fewer frequency layers (e.g., N freq =8) to monitor than the UE  50  (e.g., N freq =13), so the measurement delay is likely to be lower for the legacy UE. 
     To achieve backward compatible performances, one of the two following selections are available in embodiment 3:
         Mode 1: the normal-performance group, g1, consists of 4 frequencies with 7 measurement gaps assigned within 480 ms when MGRP=40 ms   Mode 2: the normal-performance group, g1, consists of 5 frequencies with 4 measurement gaps assigned within 480 ms when MGRP=80 ms       

     If these numbers are plugged into Equation 7, the following is obtained for mode 1: 4/7≤1; in mode 2: 5/4≤2. Both equations are true. Thus, both modes 1 and 2 in Embodiment 3 satisfy Equation 7. 
     Core and performance backward compatibility is important for both UE  50  implementation and network operation perspectives. The existing inter-frequency/inter-RAT measurement delay requirements have been developed since RAN4 Release 8. Their robustness and sustainability have been well approved in the field. Therefore, in some embodiments, it is desirable to make sure some, if not all, of the monitored frequencies, e.g. the normal performance carriers, 90 can achieve the existing minimum performance requirements, as compared to legacy UE performance, even when the number of frequencies to monitor is significantly increased. One of the two selections can be preferred, for example, when the UE  50  is moving at high speed (such as when operated in a train or other vehicle) and/or when the serving cell coverage is poor. Correspondingly, in some embodiments, the following formula shows how to make sure the normal performance carriers can achieve the legacy performance requirement: 
     
       
         
           
             
               
                 
                   
                     T 
                     
                       Identify 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Inter 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       g 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                   
                   = 
                   
                     
                       
                         
                           
                             T 
                             
                               Basic 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               _ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               Indentify 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               _ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               Inter 
                             
                           
                           · 
                           
                             480 
                             
                               5 
                               · 
                               
                                 M 
                                 
                                   Inter 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   _ 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   g 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   1 
                                 
                               
                             
                           
                           · 
                           
                             N 
                             
                               freq 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               _ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               g 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                             
                           
                         
                         ≈ 
                         
                           
                             T 
                             
                               Basic 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               _ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               Indentify 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               _ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               Inter 
                             
                           
                           · 
                           
                             480 
                             
                               T 
                               
                                 Inter 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                           
                           · 
                           7 
                         
                       
                       ⇒ 
                       
                         
                           
                             N 
                             
                               freq 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               _ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               g 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                             
                           
                           
                             M 
                             
                               Inter 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               _ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               g 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                             
                           
                         
                         ≈ 
                         
                           
                             7 
                             · 
                             MGRP 
                           
                           480 
                         
                       
                     
                     = 
                     
                       { 
                       
                         
                           
                             
                               
                                 7 
                                 / 
                                 12 
                               
                               , 
                               
                                 MGRP 
                                 = 
                                 
                                   40 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   ms 
                                 
                               
                             
                           
                         
                         
                           
                             
                               
                                 7 
                                 / 
                                 6 
                               
                               , 
                               
                                 MGRP 
                                 = 
                                 
                                   80 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   ms 
                                 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
     When MGRP=40 ms, the following (N freq_g1 , M Inter_g1 ) pair can approximately achieve the existing minimum requirements: 
                     TABLE 2                  Normal-performance group characteristics when MGRP = 40 ms       to achieve backward compatibility                         N freq     —     g1                                                               1   2   3   4   4   4   5   5   6   6                                                                     M Inter     —     g1     2   3   4   5   6   7   8   9   10   11                    
One of the entries in Table 2, (N freq_g1 =4, M Inter_g1 =7) is mode 1.
 
     Similarly, when MGRP=80 ms, the following (N freq_g1 , M Inter_g1 ) pair can approximately achieve the existing minimum requirements: 
                     TABLE 3               Normal-performance group characteristics when       MGRP = 80 ms to achieve backward compatibility                                                                N freq     —     g1     2   4   5   6   7           M Inter     —     g1     2   3   4   5   6                        
One of the entries in Table 3, (N freq_g1 =5, M Inter_g1 =4) is mode 2.
 
     In addition to the normal-performance group performance, it is also desirable to maximize the normal-performance group size, such that the UE  50  can promptly measure and report more frequencies  90  in the normal-performance group. Meanwhile, it is also important to maintain the overall measurement delay as well. As a result, in some embodiments, the corresponding group and resource assignments are recommended. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Recommended group and resource assigments to 
               
               
                 maintain backward compatibility 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 relative 
                 relative 
               
               
                   
                   
                   
                   
                 measurement 
                 measurement 
               
               
                  N freq   
                 MGRP (ms) 
                  N freq _g1 
                  M Inter _g1 
                 
                   
                     
                       
                         delay 
                         ⁢ 
                         
                           
                             T 
                             
                               
                                 Identify 
                                 ⁢ 
                                 _ 
                                 ⁢ 
                                 Inter 
                               
                               ⁢ 
                               
                                 _ 
                                 ⁢ 
                                 g 
                                 ⁢ 
                                 1 
                               
                             
                           
                           
                             T 
                             
                               
                                 Identify 
                                 ⁢ 
                                 _ 
                                 ⁢ 
                                 Inter 
                               
                               ⁢ 
                               
                                 _ 
                                 ⁢ 
                                 g 
                                 ⁢ 
                                 2 
                               
                             
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         delay 
                         ⁢ 
                         
                           
                             T 
                             
                               
                                 Identify 
                                 ⁢ 
                                 _ 
                                 ⁢ 
                                 Inter 
                               
                               ⁢ 
                               
                                 _ 
                                 ⁢ 
                                 g 
                                 ⁢ 
                                 1 
                               
                             
                           
                           
                             T 
                             
                               
                                 Identify 
                                 ⁢ 
                                 _ 
                                 ⁢ 
                                 Inter 
                               
                               ⁢ 
                               
                                 _ 
                                 ⁢ 
                                 r 
                                 ⁢ 
                                 11 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 8 
                 40 
                 4 
                 7 
                 0.36 
                 1.07 
               
               
                 9 
                   
                   
                   
                 0.41 
                   
               
               
                 10 
                   
                   
                   
                 0.48 
                   
               
               
                 11 
                   
                   
                   
                 0.54 
                   
               
               
                 12 
                   
                   
                   
                 0.71 
                   
               
               
                 8 
                 80 
                 5 
                 4 
                 0.36 
                 1.07 
               
               
                 9 
                   
                   
                   
                 0.42 
                   
               
               
                 10 
                   
                   
                   
                 0.50 
                   
               
               
                 11 
                   
                   
                   
                 0.62 
                   
               
               
                 12 
                   
                   
                   
                 0.83 
               
               
                   
               
            
           
         
       
     
     Table 4 is based on Tables 2 and 3. The number of frequency layers  90  to be measured, N freq , is between eight and twelve (first column). A relative measurement delay, T Identify_Inter_g1 /T Identify_Inter_g2 , is taken for the first backward compatible selection of four frequency layers  90  in the normal-performance group, seven measurement gaps, and an MGRP of 40 ms, resulting in the first five values shown in column 5. Similarly, the relative measurement delay is taken for the second backward compatible selection of five frequency layers  90  in the normal-performance group, four measurement gaps, and an MGRP of 80 ms, resulting in the second five values shown in column 5. Column 6 includes relative measurement delays as between the normal-performance group and a legacy cell identification delay, given by T Identify_Inter_r11 . 
     The PCIM method  100 , embodiment 3, is illustrated in the flow diagram of  FIG. 7 . A selection between mode 1 and mode 2 is made (block  502 ). Where mode 1 is selected, the number of frequency layers  90  in the normal-performance group is four (block  504 ), the number of measurement gaps in the normal-performance group is seven (block  506 ) per 480 ms, and the MGRP is 40 ms (block  508 ). The UE  50  thus has the relevant information to enable frequency layer measurements to be performed so as to achieve backwards compatibility. 
     Where mode 2 is instead selected, the number of frequency layers  90  in the normal-performance group is five (block  510 ), the number of measurement gaps in the normal-performance group is four (block  512 ) per 480 ms, and the MGRP is 40 ms (block  514 ). The UE  50  thus has the relevant information to enable frequency layer measurements to be performed so as to achieve backwards compatibility. By having two available modes in this embodiment, the system design of the UE  50  can be greatly simplified. 
     Embodiment 4 
     Theoretically, in addressing the increase in the number of frequency layers being monitored by the UE, the eNB  20  can provide a variety of different instructions to the UE  50 , such as the size (N freq_g1 ) of the normal-performance group, g1, the MGRP, and the number of measurement gaps, M Inter_g1  and M Inter_g2 , for each group, g1 and g2. Because of this variety, in Embodiment 4, the PCIM method  100  proposes one of three modes, discernable by a signal or bit, with each mode specifying a group size and resource assignment combination. 
     From a UE  50  implementation perspective, it is desirable to limit the variation of group size (N freq_g1 ) and its resource assignment (M inter_g1 ). For different group size and resource assignment combinations, a different algorithm can be used, for example, for performing the measurements. Thus, a leaner UE  50  with fewer resources can benefit from a signal that indicates one of just two possible modes. 
     Table 5 shows a first mode (mode 3) in which all frequency layers are assigned to the normal-performance group and the number of measurement gaps, M inter_g1  for the normal-performance group per 480 ms is 480/MGRP. Thus, if the MGRP is 40 ms, M inter_g1  is 12 and if the MGRP is 80 ms, M inter_g1  is 6. The reduced-performance group, g2, has no frequency layers. A signal or bit indicates to the UE  50  that mode 3 has been selected. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Mode 3 group size and resource assignment 
               
            
           
           
               
               
               
            
               
                   
                 normal-performance 
                 reduced-performance 
               
               
                   
                 group, g1 
                 group, g2 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                 group size, N freq     —     g1   
                 N freq   
                 0 
               
               
                 resource assignment, 
                 480/MGRP 
                 0 
               
               
                 M inter     —     g1   
               
               
                   
               
            
           
         
       
     
     Table 6 shows second and third modes, indicated as mode 4 and mode 5. In mode 4, the MGRP is 40 ms. In mode 4, the group size for the normal-performance group, N freq_g1 , is four and thus the group size for the reduced-performance group is derived from this. The resource assignment (the number of measurement gaps) for the normal-performance group, M inter_g1 , is seven and, for the reduced-performance group, the resource assignment, M inter_g2 , is five. In Mode 5, the group size for the normal-performance group, N freq_g1 , is seven and thus the group size for the reduced-performance group is derived from this. The resource assignment for the normal-performance group, M inter_g1 , is four and, for the reduced-performance group, the resource assignment, M inter_g2 , is two. In modes 4 and 5, the normal-performance group size is fixed while the total number of frequency layers remains variable. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Group size and resource assignments for modes 4 and 5 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                 normal- 
                 reduced- 
               
               
                   
                   
                   
                 performance 
                 performance 
               
               
                   
                 Mode 
                 MGRP 
                 group, g1 
                 group, g2 
               
               
                   
                   
               
               
                   
                 4 
                 40 ms 
                 N freq     —     g1  = 4 
                 N freq     —     g2  = N freq  − 4 
               
               
                   
                   
                   
                 M inter     —     g1  = 7 
                 M inter     —     g2  = 5 
               
               
                   
                 5 
                 80 ms 
                 N freq     —     g1  = 5 
                 N freq     —     g2  = N freq  − 5 
               
               
                   
                   
                   
                 M inter     —     g1  = 4 
                 M inter     —     g2  = 2 
               
               
                   
                   
               
            
           
         
       
     
     In some embodiments, Modes 4 and 5 are designed to fix the size of the normal-performance group, regardless of how many frequency layers are to be monitored. The UE  50  has the Table 6 to reference when mode selection is made. When a signal is received (or a predefined bit is set), the UE  50  knows to operate according to Mode 3 (Table 5). When the signal is not received (or the bit is cleared), the UE  50  references Table 6 and operates according to either Mode 4 or Mode 5. 
     The PCIM method  100 , embodiment 4, is illustrated in the flow diagram of  FIG. 8 . A signal received or a bit set indicates Mode 3, while the signal not received or the bit cleared indicates Mode 4 or 5 (block  602 ). If Mode 3 is indicated, then all frequency layers are assigned to the normal-performance group (block  604 ), the resource assignment is set at 480/MGRP (block  606 ), and this enables the UE  50  to decide the MGRP to use (e.g., 40 ms or 80 ms) (block  608 ). 
     If the signal is not received or the bit cleared, Mode 4 or 5 is indicated. If the UE  50  decides to use an MGRP=40 ms, this indicates Mode 4 (block  610 ). From Table 6, the number of frequencies in the normal-performance group is 4 (block  612 ) and the resource assignment for the normal-performance group is 7 (block  614 ). If the UE  50  decides to use an MGRP of 80 ms, this indicates Mode 5. From Table 6, the number of frequencies in the normal-performance group is 5 (block  616 ) and the resource assignment for the normal-performance group is 4 (block  618 ). By having three available modes in this embodiment, the system design of the UE  50  can be greatly simplified. 
     Embodiment 5 
     Recall that the UE  50  receives a list of frequency layers to measure from the network. For example, the network can send to the UE  50  a list of ten frequency layers, band 1-band 10, but they can be sent in order of priority, say, band 7, band 3, band 4, band 8, band 2, band 1, band 10, band 9, band 5, and band 6. In some embodiments, an index to that list, given by N freq_g1  is sent and the index implicitly tells the UE  50  which frequency layers are in the normal-performance group, with the remaining entries belonging to the reduced-performance group. 
     For example, if the index is on the third entry in the list, the UE  50  automatically knows that bands 7, 3, and 4 are in the normal-performance group while bands 8, 2, 1, 10, 9, 5, and 6 are in the reduced-performance group. 
     Further, in some embodiments, a one-bit signal indicates to the UE  50  the group size, N freq_g1 , and the resource assignment, M inter_g1 , combination. In a first mode, Mode 6, there is only one group, the normal-performance group, g1. Otherwise, either Mode 7 or Mode 8 applies, with the group size N freq_g1 , and the resource assignment, M inter_g1 , for the normal-performance group being fixed. For both modes 7 and 8, Table 6 provides the group size and resource assignment values, based on the MGRP. 
     In summary, Embodiment 5 provides the following:
         A single measurement list is provided to the UE:
           No explicit normal-performance and reduced-performance groups are separately provided to the UE   
           The frequencies in the measurement list are prioritized in decreasing order   A one-bit signaling is introduced to indicate to the UE  50  the group size and resource assignment combination mode:
           In mode 6: there is only one group (i.e., normal-performance group)   In modes 7 and 8: the size and resource assignment for the normal-performance group is fixed. The exact values depend on the MGRP, given in Table 6   
               

     The PCIM method  100 , embodiment 5, is illustrated in the flow diagram of  FIG. 9 . A measurement list consisting of a prioritized list of frequency layers to be measured is supplied to the UE  50  (block  702 ). An index into the measurement list, N freq_g1 , indicates which of the frequency layers is part of the normal-performance group (block  704 ). If a signal is received or a bit is set, the UE  50  performs the measurements in Mode 6 (block  706 ), in which there is no reduced-performance group (block  708 ), and both the MGRP (block  710 ) and the resource assignment (block  712 ) are designated by the UE  50 . 
     If instead the signal is not received or the bit is cleared (block  706 ), the UE  50  operates according to Table 6, above, in either Mode 7 or Mode 8. If the MGRP is not 40 ms (block  714 ), the UE  50  operates in Mode 7. The number of frequency layers in the normal-performance group is five (block  716 ) and the resource assignment is four (block  718 ). Otherwise, the MGRP is 40 ms (block  714 ) and the number of frequency layers in the normal-performance group is four (block  720 ) and the resource assignment is seven (block  722 ). By having three available modes in this embodiment, the system design of the UE  50  can be greatly simplified. 
     Embodiment 6 
     Embodiment 6 is well-suited to situations in which the UE  50  is moving at high speeds. In Embodiment 6, the UE  50  is able to dynamically change the high- and reduced-performance group designations. If moving at high speeds, the UE  50  can move the frequency layers and measurement requirements to the reduced-performance group. By adapting the assignment of frequency layers according to the UE speed, the measurement delay at the normal-performance group becomes manageable, in some embodiments. For example, in a situation where the UE  50  is moving at high speeds, such as on a high-speed train, the measurements are needed faster than for a UE sitting in an idle position. Thus, the size of the normal-performance group can be purposely reduced under this circumstance. 
     In some embodiments, the UE  50  can have the capability to implement any or all of the embodiments described herein. In other embodiments, the UE  50  is limited in capability to very few of the above embodiments. Practically speaking, the UE  50  is likely to adopt one of the embodiments at an initialization stage, and thereafter does not change. There can be circumstances, however, when it makes sense for the UE  50  to change its configuration, such as in Embodiment 6 when the UE  50  is moving at high speeds. In any case, if made by the UE, any change in configuration is semi-static, in some embodiments, as there is signaling overhead associated with such a change. 
       FIGS. 10A and 10B  are simplified block diagrams of a wireless neighborhood  800  including the eNB  20  and the UE  50 , both of which are transceivers. The eNB  20  and the UE  50  employ the above-described PCIM method  100 , according to some embodiments. In this example, the eNB  20  operates as a transmitter and the UE  50  operates as a receiver.  FIG. 10A  shows a software-based version of the eNB  20  and the UE  50  while  FIG. 10B  shows an ASIC-based version. 
     Looking first at  FIG. 10A , each device includes an antenna  154 , a front-end  132 , a radio  136 , a baseband digital signal processor (DSP)  138 , and a medium access controller (MAC)  130 . Although both devices have the hardware shown in each device, the eNB  20  is shown having a power amplifier  146  in its front-end  132  while the UE  50  includes a low noise amplifier  148  in its front-end. The eNB  20  includes a digital-to-analog converter (DAC)  134  while the UE  50  includes an analog-to-digital converter (ADC)  142 . The UE  50  can be virtually any wireless device, such as a laptop computer, a cellular phone, or other wireless system, and can operate as a transmitter (transmit mode) or as a receiver (receive mode). 
     The MAC  130  includes an embedded central processing unit (CPU)  124  and a data memory  120 , such that the PCIM method  100 , some portion of which is software-based, in some embodiments, can be loaded into the memory and executed by the CPU. The depiction of  FIG. 10A  is a simplified representation of the MAC  130 , and other devices, circuits, and logic elements that can be part of the MAC are omitted. 
     The MAC  130  interfaces with logic devices that are commonly found in transmitters and receivers: the front-end  132 , the DAC  134 , the ADC  142 , the radio  136 , and the DSP  138 . The devices  132 ,  134 ,  136 ,  138 , and  142  are also known herein as target modules. The target modules, as well as the logic devices within the MAC  130 , can consist of hardware, software, or a combination of hardware and software components. 
     The target modules are commonly found in most transmitters and receivers. The FE  132  is connected to the antenna  154 , and includes a power amplifier (PA) (for the transmitter), a low noise amplifier (LNA) (for the receiver), and an antenna switch (not shown), for switching between transmitter and receiver modes. The DAC  134  is used to convert the digital signal coming from the DSP  138  to an analog signal prior to transmission via the radio (transmitter); conversely, the ADC  142  is used to convert the analog signal coming from the radio to a digital signal before processing by the DSP  138  (receiver). At the eNB  20 , the radio  136  transfers the signal from base-band to the carrier frequency; at the UE  50 , the radio  136  transfers the signal from carrier frequency to base-band. At the UE  50 , the DSP  138  demodulates the OFDM signal from the ADC  142 , for processing by the MAC  130 . At the eNB  20 , the DSP  138  modulates the MAC data into an OFDM signal in base-band frequency, and sends the resulting signal to the DAC  134 . 
     A typical transmit operation occurs as follows: at the eNB  20 , the MAC  130  sends a packet to the DSP  138 . The DSP  138  converts the packet into a digital OFDM signal and sends it to the DAC  134 . The DAC  134  converts the signal into an analog signal, and sends the signal to the radio  136 . The radio  136  modulates the base-band signal to the carrier frequency and sends the signal to the power amplifier  146  of the front-end  132 , which amplifies the signal to be suitable for over-air transmission via the antenna  154 . 
     At the UE  50 , the signal is received by the antenna  154 . The weak analog signal is received into the low noise amplifier  148  of the front-end  132 , sending the amplified analog signal to the radio  136 , which filters the signal according to the selected frequency band and demodulates the carrier frequency signal into a base-band signal. The radio  136  sends the analog signal to the ADC  142 , which converts the analog signal to a digital signal, suitable for processing by the DSP  138 . The DSP  138  demodulates the OFDM signal and converts the signal to MAC  130  packet bytes. Other operations, such as encryption and decryption of the packets, are not shown. Where the transmission is successful, the packet received by the MAC  130  in the UE  50  is the same as the packet transmitted by the MAC  130  in the eNB  20 . 
     In other embodiments, as depicted in  FIG. 10B , the eNB  20  and the UE  50  do not include a CPU  124  in the MAC  130 . Instead, an application-specific integrated circuit (ASIC)  190  can drive the PCIM method  100  as a state machine implemented using logic registers ( 192 ). The ASIC solution of  FIG. 10B  can be preferred over the MAC-based implementation of  FIG. 10A , for example, in systems in which low power consumption is important. 
     While the application has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of the invention.

Metadata:
Filing Date: 20171130
Publication Date: 20210817
Grant Date: 20210817
Priority Date: 20140508
Inventors: TANG, YANG
HUANG, RUI
YIU, Candy
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W24/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W24/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W24/02", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W24/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0048", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/0453", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W24/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W24/02", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W24/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W24/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W72/0453", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0048", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W24/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0048", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 54393058