CHANNEL ESTIMATION, THROUGHPUT AND FAIRNESS FOR MULTI-USER, MULTIPLEINPUT, MULTIPLE-OUTPUT (MU- MIMO) SYSTEMS THROUGH DYNAMIC PORT ALLOCATION

Abstract

A method and system for improving channel estimation for multi-user, multiple-input, multiple-output (MU-MIMO) systems through dynamic DM-RS port allocation in a 5G New Radio network is provided. The method comprises of allocating, by a Scheduler aware UE port allocation unit, one or more MU-MIMO ports to a plurality of code division multiplexing (CDM) groups for a plurality of UE users, performing, by a code selection unit, a code selection based on a number of allocated MU-MIMO ports, determining, by a spreading factor unit, a spreading factor allocated for each of the MU-MIMO ports in each of the plurality of CDM groups, determining, by a signalling unit, a Downlink Control Information (DCI) signalling of a Partial Port Occupancy (P-Poi) transmission for each UE and obtaining, by a channel estimation unit, channel estimates at the receiver through VSFOCC de-spreading based on the P-POI assigned for each of the MU-MIMO ports.

Claims

1. A method for improving channel estimation for multi-user, multiple-input, multiple-output (MU-MIMO) systems through dynamic DM-RS port allocation in a 5G New Radio network, the method comprising: allocating (502), by a Scheduler aware UE port allocation unit, one or more MU-MIMO ports to a plurality of code division multiplexing (CDM) groups for a plurality of UE users; performing (504), by a code selection unit, a code selection based on a number of MU-MIMO ports allocated to the plurality of CDM groups; where a Code Division Multiplexing (CDM) group is a set of time-frequency resources where MU-MIMO ports are multiplexed using orthogonality of codes; determining (506), by a spreading factor unit, a spreading factor allocated for each of the MU-MIMO ports in each of the plurality of CDM groups; determining (508), by a signalling unit, a Downlink Control Information (DCI) signalling of a Partial Port Occupancy (P-Poi) transmission for each UE; and Obtaining (510), by a channel estimation unit, channel estimates at the receiver through VSFOCC de-spreading based on the P-POI assigned for each of the MU-MIMO ports.

2. The method of claim 1, further comprising: interpolating (512), by a linear or DFT interpolator, the obtained channel estimates to determine the channel over a number of Physical Resource blocks (N.sub.PRB); wherein the interpolation along with VSFOCC despreading increases the performance gain for channels.

3. The method of claim 1, wherein the Scheduling aware UE port mapping unit allots a plurality of spreading factors for the plurality of UE users based on a Modulation and Coding Scheme (MCS) information from a schedule unit.

4. The method of claim 1, wherein the code selection for each MU-MIMO port scheduled in the CDM group is assigned from an Orthogonal Variable Spreading Factor (OVSF tree) structure, where each MU-MIMO port present in a same CDM group are mapped to unique Orthogonal Cover Codes (OCC).

5. The method of claim 1, further comprising combining, by the channel estimator unit, least square estimation, and P-Poi information based de-spreading of the plurality of CDM groups to perform channel estimation.

6. The method of claim 1, further comprising: reducing an interpolation error of the channel estimates by increasing a number of unique channel estimates for partially loaded CDM groups through VSFOCC despreading.

7. A multi-user, multiple-input, multiple-output (MU-MIMO) system (100) to improve channel estimation in 5G New Radio Network, the system (100) comprises: a transmitter (102) comprising: a Scheduler aware UE port allocation unit (104) to allocate one or more MU-MIMO ports to a plurality of code division multiplexing (CDM) groups for a plurality of UE users; a code selection unit (106) to perform code selection according to a number of MU-MIMO ports assigned in the plurality of CDM groups, where a Code Division Multiplexing (CDM) group is a set of time-frequency resources where MU-MIMO ports are multiplexed using orthogonality of codes; a scheduler aware UE port mapping unit (108) to allot a reduced despreading factor for the users based on the Modulation and Coding Scheme (MCS) and a total number of scheduled user information received from the Scheduler aware UE port allocation unit; and a Spreading factor unit (110) to determine the spreading factor for the allocated one or more MU-MIMO ports in each of the plurality of CDM groups; a signalling unit (112) to transmit Downlink Control Information (DCI) Signalling of a Partial Port Occupancy (P-Poi) information for each User Equipment; and a receiver (114) comprising: a channel estimator unit (116) to perform channel estimation with VSFOCC de-spreading based on a Partial Port Occupancy (P-Poi) assigned for each of the MU-MIMO ports; and an interpolator (118) to interpolate the obtained channel estimates over a number of Physical Resource blocks, N.sub.PRB, wherein the interpolator (118) is one of a linear or DFT interpolator, where interpolation along with VSFOCC despreading increases performance gain for channels.

8. The system (100) of claim 7, wherein the Scheduling aware UE port mapping unit (108) allots a plurality of spreading factors for the plurality of UE users based on a Modulation and Coding Scheme (MCS) information from a schedule unit.

9. The system (100) of claim 7, wherein the code selection for each MU-MIMO port scheduled in the CDM group is assigned from an Orthogonal Variable Spreading Factor (OVSF tree) structure, where each MU-MIMO port present in a same CDM group are mapped to unique Orthogonal Cover Codes (OCC).

10. The system (100) of claim 7, wherein the channel estimator unit (116) further combines a least square estimation and P-Poi information based de-spreading of the plurality of CDM groups to perform channel estimation.

11. The system (100) of claim 7, wherein the interpolator is configured to reduce an interpolation error of the channel estimates by increasing a number of distinct channel estimates for partially loaded CDM groups through VSFOCC despreading.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The embodiments herein will be better understood from the following detailed description with reference to the drawings, in which:

[0018] FIG. 1 is a block diagram illustrating a system for improving channel estimation for multi-user, multiple-input, multiple-output (MU-MIMO) systems through dynamic port allocation, according to the embodiments herein;

[0019] FIG. 2 is a schematic representation of a demodulation reference signal (DM-RS) configuration, according to the embodiments herein;

[0020] FIG. 3 is an example illustration of a DMRS VSFOCC allocation for Type-2 Configuration, according to the embodiments herein;

[0021] FIG. 4 is a block diagram illustrating a Discrete Fourier Transform (DFT) Interpolation process, according to the embodiments herein;

[0022] FIG. 5 is a flow chart illustrating a method for improving channel estimation for multi-user, multiple-input, multiple-output (MU-MIMO) systems through dynamic port allocation, according to the embodiments herein; and

[0023] FIGS. 6A-6D are graphs illustrating the simulation results of four exemplary Mean Squared Error (MSE) for channel estimates, each pertaining to one of the four DM-RS configurations, according to the embodiments herein.

DETAILED DESCRIPTION OF THE DRAWINGS

[0024] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended the merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0025] As mentioned, there remains a need for a system and a method to enable improved Channel estimation quality for partially loaded DM-RS ports without compromising the estimation performance on the other ports. Referring now to the drawings, and more particularly to FIGS. 1 through 6D, where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.

[0026] FIG. 1 is a block diagram of a Multi-user, multiple-input, multiple-output (MU-MIMO) system enabling DM-RS port allocation to improve channel estimation, according to the embodiments of the present disclosure. The MU-MIMO system 100 includes a transmitter 102 and a receiver 114. The transmitter 102 comprises a Scheduler aware UE port allocation unit 104, a code selection unit 106, a scheduler-aware UE port mapping unit 108, a Spreading factor unit 110, and a signalling unit 112. The receiver 114 comprises a channel estimator unit 116 and an interpolator 118.

[0027] The Scheduler aware UE port allocation unit 104 allocates a specific number of MU-MIMO ports to a plurality of code division multiplexing (CDM) groups for a plurality of UE users. The port allocation can be made in multiple ways. The order in which the CDM group is filled varies for each case with the same number of ports getting advantage of MSE. E.g., If 10 ports are scheduled in total, the port allocation across three CDM groups in a double symbol Type 2 DM-RS can be (4,4,2) or (4,3,3), as both add up to 10. The order in the above 3-tuples does not matter. For example, (4,4,2) as described above can be treated as equivalent to (2,4,4) and (4,2,4). The key factor is the number of ports assigned in each group. The specific CDM group to which the ports are assigned doesn't matter, and all such mappings are equally valid. The objective of port allocation is to maximize the number of partially loaded CDM groups. To achieve this, ports can be mapped sequentially to CDM groups in an orderly fashion.

[0028] The code selection unit 106 is configured to perform code selection according to the number of ports assigned in the CDM group. A Code Division Multiplexing (CDM) group is a set of time-frequency resources where MU-MIMO ports are multiplexed using the orthogonality of codes. These codes are termed Orthogonal Cover Codes (OCC) in the context of 5G NR. The orthogonal codes are derived as shown below. The length of the code is controlled by the Spreading Factor (SF). The ‘child’ codes with a higher spreading factor are derived from a ‘parent’ code with a lower spreading factor, forming a tree structure. This tree connects orthogonal codes with various spreading factors. Hence, it is termed as Orthogonal Variable Spreading Factor (OVSF) code tree as shown below.

##STR00001##

[0029] In the code tree, the parent code (the one with a lower spreading factor) will be orthogonal to the child codes of the other parent code. The parent and child codes are of different lengths, so the orthogonality should be understood as follows. Here, each code C.sub.i can be represented as [C.sub.i1, C.sub.i2, . . . , C.sub.iSF]. The parent code C.sub.2 is orthogonal to the child code segments [C.sub.61, C.sub.62] and [C.sub.63, C.sub.64] and the child code segments [C.sub.71, C.sub.72] and [C.sub.73, C.sub.74]. Thus, if two ports are present in a CDM group (Here one CDM can support only 2 ports for a Single Symbol Type 1 DM-RS. As there are two CDM groups in a single symbol Type 1 DM-Rs, it supports a maximum of 4 ports), each code is taken from a different parent code. If three ports are present, two child codes of the same parent are chosen, and the third port is given the parent code of the other branch. Since the ports are already mapped to one unique code, code selection is equivalent to port selection.

[0030] In some embodiments, the OCC codes are spread across two subcarriers in one OFDM symbol. Thus, single symbol DM-RS can support two ports per CDM group denoted as P.sub.1, P.sub.2 using length-2 codes. Double symbol DM-RS can schedule four ports per CDM group, denoted as P.sub.1, P.sub.2, P.sub.3, and P.sub.4 using length-4 codes. Though the Type 1 and Type 2 patterns differ in the position of pilots, the CDM group size and the ports supported in a CDM group remain the same.

[0031] The port allocation strategy across CDM groups according to the embodiments of the present disclosure is shown in the following tables. Single symbol Type 1 DM-RS can support up to four ports. But if only three ports are required, two ports can be accommodated in CDM group 0 and the remaining port is placed in CDM group 1 as mentioned in Table 1.1 below. Since there is only one port in CDM group 1, there is no need for code orthogonality. Hence, in the receiver, the despreading factor can be viewed as one instead of two. This means that FD-CDM despreading is not required and there will be two distinct estimates per CDM group instead of one. Thus, the port in CDM group 1 will get twice the number of distinct channel estimates unlike the ports in CDM group 0. Note that the number of UEs allotted in all CDM groups is represented as (number of UEs in CDM 0, No. of UEs in CDM 1, No. of UEs in CDM 2). If there are 10 ports in the double symbol Type 2 configuration (table 1.4), the ports can be placed across CDM groups as (4,4,2) or (3,3,4). In both cases, two ports will get the advantage of getting more distinct channel estimates. From the above discussion, we can say that ports in partially filled CDM groups can use sequences with lower spreading factors from the code tree that can be exploited to get the MSE advantage. Thus, based on this constraint the possible port allocation for DM-RS configuration is as mentioned in Tables 1.1-1.4 below.

TABLE-US-00001 TABLE 1.1 SINGLE SYMBOL TYPE 1 Ports gaining No of Ports Allocation MSE ports CDM 0 CDM 1 advantage 1 1 1 2 1 1 2 3 2 1 1 4 2 2 0

TABLE-US-00002 TABLE 1.2 SINGLE SYMBOL TYPE 2 Ports gaining No of Ports Allocation MSE ports CDM 0 CDM 1 CDM 2 advantage 1 1 1 2 1 1 2 3 1 1 1 3 4 2 1 1 2 5 2 2 1 1 6 2 2 2 0

TABLE-US-00003 TABLE 1.3 DOUBLE SYMBOL TYPE 1 Ports Gaining No of Ports Allocation MSE ports CDM 0 CDM 1 Advantage 1 1 1 2 1 1 2 3 2 1 3 4 2 2 4 5 3 2 3 6 3 3 2 7 4 3 1 8 4 4 0

TABLE-US-00004 TABLE 1.4 DOUBLE SYMBOL TYPE 2 Ports gaining No of Ports Allocation MSE ports CDM 0 CDM 1 CDM 2 advantage 1 1 1 2 1 1 2 3 1 1 1 3 4 2 1 1 4 5 2 2 1 5 6 2 2 2 6 7 3 2 2 5 8 3 3 2 4 4 2 2 9 3 3 3 3 10 4 3 3 2 4 4 2 2 11 4 4 3 1 12 4 4 4 0

[0032] Here, the ordering of ports across CDM groups need not be the same as that shown in the table. Other orderings of ports are also possible.

[0033] Further, the pattern for filling the DM-RS CDM groups in the transmit side ensures maximum partially loaded groups. The Scheduler aware UE port mapping Unit 108 allots the reduced despreading factor for the users based on the Modulation and Coding Scheme (MCS) and a total number of scheduled user information received from the Scheduler aware UE port allocation unit 104. For example, In Type 1 Single Symbol DM-RS Configuration, four ports are possible. Suppose that 3 users are present and can only be scheduled with one layer each. Thus, three out of the possible four ports are occupied. Further, suppose that U.sub.1, U.sub.2, U.sub.3 have modulations 4QAM, 16QAM and 64QAM. Then, there are two possibilities. [0034] (i) To be fair, we can give U.sub.1 the MSE advantage, and hence promote it from 4QAM to 16QAM. [0035] (ii) Based on the sum-rate metric, we can give U.sub.3 the MSE advantage. This ensures BLER is lower for 64QAM since channel estimation errors lead to more errors in 4QAM than 64QAM. [0036] (iii) In this example, instead of improving the modulation, moving to a higher code rate can also achieve an improvement in the data transmission rate.

[0037] In some embodiments, the codes are selected for the ports scheduled in the CDM group from the OVSF tree. While the mapping of ports to the CDM group is important, assigning the appropriate codes from the OVSF tree is equally critical. The spreading factor unit 110 determines the spreading factor for the allocated one or more MU-MIMO ports in each of the plurality of CDM groups. The spreading factor allocation within a CDM group for all cases is mentioned in Table 2 below. Valid combinations of parent and child codes that ensure orthogonality should be selected. Otherwise, the orthogonality between sequences with lower SF and higher SF cannot be exploited. Each port in the DM-RS is multiplexed among time, frequency, and code. The ports present in the same CDM group are mapped to unique OCC codes, which vary according to the DM-RS configuration. The code to port mapping in the single symbol is done for (P.sub.1, P.sub.2) as (C.sub.2, C.sub.3) and the port mapping for (P.sub.1, P.sub.2, P.sub.3, P.sub.4) in the double symbol as (C.sub.4, C.sub.5, C.sub.6, C.sub.7). As discussed earlier, after selecting the number of ports in a CDM group, the code selection must be made. Hence each port is mapped to a unique OCC code. Choosing the port will indirectly assign the corresponding code. The port assignment is made following the concept of OVSF. The possible code mappings in a CDM group for all possible scenarios are shown in Table 2. In a scenario when three ports are present in a CDM group, there are three ways of allocating ports (Refer row 3 in Table 2). In which two codes are derived from the same parent and the third code belongs to a different parent. In a two-port case, each code must be taken from different parents. For that, four possible port-code assignment is available as shown in Table 2.

TABLE-US-00005 TABLE 2 VSFOCC Spreading Factor Allocation for a CDM Group Single Symbol DM-RS Double Symbol DM-RS No. of DCI Port SF at DCI Port SF at Ports Allocation Receiver Allocation Receiver 1 P.sub.1 or P.sub.2 1 P.sub.1 or P.sub.2 or 2 P.sub.3 or P.sub.4 2 (P.sub.1, P.sub.2) (2, 2) (P.sub.1, P.sub.2) or (2, 2) (P.sub.1, P.sub.4) or (P.sub.2, P.sub.3) or (P.sub.2, P.sub.4) 3 — — (P.sub.1, P.sub.2, P.sub.3) or (4, 4, 2) (P.sub.1, P.sub.3, P.sub.4) or (P.sub.1, P.sub.3, P.sub.4) 4 — — (P.sub.1, P.sub.2, P.sub.3, P.sub.4) (4, 4, 4, 4)

[0038] In some embodiments, the signalling module 112 transmits DCI Signalling of the Partial Port Occupancy (P-Poi) information for each User Equipment.

[0039] The receiver 114 herein comprises a channel estimator unit 116. The channel estimator unit 116 combines both Least Square (LS) estimation and P-Poi information-based despreading of the CDM groups. In partially filled CDM groups, the spreading factor for despreading will be lower. In the 5G-NR context this directly corresponds to skipping the FD-CDM despreading step in channel estimation for those ports. Generally, the despreading step can descend to a lower spreading factor in the OVSF tree. This leads to an increase (double channel estimates in 5G-NR context) in the number of distinct channel estimates on those ports.

[0040] In some embodiments, the channel estimator unit 116 performs channel estimation with VSFOCC despreading as follows. The received signal undergoes Cyclic Prefix (CP) removal and after taking FFT, the frequency domain data at the lth OFDM symbol can be written as,

[00001]$y=\underset{p=1}{\overset{P}{.Math.}}{X}^{\left(p\right)}{H}^{\left(p\right)}+Z$

where, Y is of size N×1. Also, X.sup.(p) is the diagonal matrix of size N×N having a.sub.k,l.sup.p as non-zero entries in the corresponding DM-RS positions or data from port p. Finally, H.sup.(p) is the N×1 channel vector between p.sup.th port and the receiver at l.sup.th symbol, and Z is N×1 zero-mean complex Gaussian noise, where Z˜N(0, σ.sub.n.sup.2I.sub.N), where σ.sub.n.sup.2 is the variance of noise.

[0041] The despreading and Least Squares (LS) channel estimate at q'th subcarrier index for the port p is given by,

[00002]${\hat{H}}^p\left(q^{\prime }\right)=\frac{1}{\mathrm{SF}}\left(\underset{i\in l}{.Math.}\underset{j\in k^{\prime }}{.Math.}{Y}_{k,i}^{\prime }{w}_f\left(j\right)w_t\left(i\right)r\star \left(2n+j\right)\right)$

[0042] Further, the estimated locations are formulated as,

[00003]$q^{\prime }=\{\begin{array}{cc}4n+\Delta ,& \mathrm{Configuration}\mathrm{Type}1\\ 6n+\Delta ,& \mathrm{Configuration}\mathrm{Type}2\end{array}$

[0043] For the VSFOCC allocation according to the embodiments herein, the modified estimate allocation in the frequency axis is given by,

[00004]$q^{\prime }=\{\begin{array}{cc}4n+2k^{\prime }+\Delta ,& \mathrm{Configuration}\mathrm{Type}1\\ 6n+k^{\prime }+\Delta ,& \mathrm{Configuration}\mathrm{Type}2\end{array}$

[0044] The total number of estimates in the allotted PRBs, N.sub.e depends on the spreading factor as,

[00005]$N_e=\{\begin{array}{cc}\frac{6N_{\mathrm{PRB}}}{\mathrm{SF}},& \mathrm{Configuration}\mathrm{Type}1\\ \frac{4N_{\mathrm{PRB}}}{\mathrm{SF}},& \mathrm{Configuration}\mathrm{Type}2\end{array}$

[0045] where Ĥ.sub.p is the N.sub.e×1 estimate vector. Y.sub.j,i′ is the (j, i).sup.th element from the received grid of a slot after removing guard subcarriers from Y. SF values are assigned as mentioned in Table 2.

[0046] The channel estimates obtained from above are interpolated using an interpolator 118, where the interpolator may be a liner or DFT interpolator, to estimate the channel over N.sub.PRB subcarriers. The DFT-based channel interpolation exploits the property of having more CFR estimates than the CP length. Thus, the channel taps are resolved without losing much information. However, for banded allocation where the number of pilots could be less than the CP length, the multipath components cannot then be adequately resolved in the time domain. Denoising this CIR with poor resolution induces a loss in performance. The linear or DFT interpolator 118 is configured to reduce an interpolation error of the channel estimates by increasing a number of distinct channel estimates for partially loaded CDM groups through VSFOCC despreading.

[0047] FIG. 2 is a schematic representation of a demodulation reference signal (DM-RS) configuration, according to the embodiments herein. The DM-RS in 5G NR uses Orthogonal Cover Codes (OCC) to introduce the orthogonality across the MU-MIMO ports. These DM-RS for Physical Downlink Shared Channel or Physical Uplink Shared Channel (PDSCH or PUSCH) has the flexibility to support a wide range of configurations. In single symbol DM-RS, Code Division Multiplexing (CDM) is only over the frequency domain (FD-CDM) occupying two Resource Elements (REs). In double symbol DM-RS, CDM utilizes four REs over both the time and frequency domains (FD+TD CDM). Based on the position of DM-RS pilots in frequency, they can be further classified into two types. While Type 1 DM-RS occupies alternate subcarriers, Type 2 has two pairs of two consecutive subcarriers in a Physical Resource Block (PRB), where both pairs are four subcarriers apart. Hence, Type 1 has two CDM groups, and Type 2 has three CDM groups as shown in FIG. 2.

[0048] FIG. 3 is an example illustration of a DMRS VSFOCC allocation for Type-2 Configuration, according to the embodiments herein. The lower spreading factor based despreading doubles the number of distinct channel estimates at the receiver. In Multi-User MIMO (MU-MIMO) antenna systems, multiple users are served in the same set of physical resource blocks. The example embodiment according to FIG. 3 considers a MU-MIMO scenario employing Type 2 configuration with P=10 users 902a-902j, where each user (902a-902j) is allotted with a single layer. One possible allocation to get the maximum number of estimates in {CDM 0, CDM 1, CDM 2} is {(P.sub.1, P.sub.2, P.sub.3, P.sub.4), (P.sub.1, P.sub.2, P.sub.3, P.sub.4), (P.sub.1, P.sub.4)} with Spreading Factor (SF) assigned as {(4, 4, 4, 4), (4, 4, 4, 4), (2, 2)}. The receiver views this allocation as shown in FIG. 9. From the allocation, it can be observed that CDM group 2 is partially filled. So, length-2 OCC codes are sufficient to bring the orthogonality between the ports. Hence, the despreading needs to be done only in the time domain. As a result, ports P.sub.1 and P.sub.4 in CDM group 2 will get twice the distinct estimates as compared to other ports. However, in order to achieve this, those two ports must be chosen such that the ports are mapped to the codes derived from different parents.

[0049] FIG. 4 is a block diagram illustrating a Discrete Fourier Transform (DFT) Interpolation process, according to the embodiments herein. The CFR estimates obtained from Channel Estimation with VSFOCC Despreading are interpolated to estimate the channel over N.sub.PRB subcarriers. The DFT-based channel interpolation has the advantage of more CFR estimates than the predefined cyclic prefix (CP) length. Thus, the channel taps are resolved without losing much information. Hence, time-domain denoising can be done without changing the sampling frequency. However, for banded allocation where the number of pilots could be less than the CP length, the multipath components cannot then be adequately de-noised in the time domain, inducing loss in performance.

[0050] According to the embodiments herein, the DFT interpolator 402 is selected according to the following two scenarios: [0051] i) Ne≥Ncp: In this case, Ne-point IDFT and DFT can be employed to get the interpolated CFR. [0052] ii) Ne<Ncp: In this case, the channel information will be lost, if N-point IDFT is not used. As there will not be enough samples in the time domain, this leads to poor resolution of the channel. Thus, the N-DFT is most suitable for DFT-based channel estimators.

[0053] FIG. 5 is a flow chart illustrating a method for improving channel estimation for multi-user, multiple-input, multiple-output (MU-MIMO) systems through dynamic port allocation, according to the embodiments herein. At step 502, MU-MIMO ports are allocated across multiple Code Division Multiplexing groups for all users or UE layers (Scheduling Aware). At step 504, code selection according to the number of ports in the CDM group level is performed. At step 506, the spreading factor allocated for all the ports is determined. At step 508, DCI signaling of the Partial Port Occupancy (P-Poi) transmission for each UE is determined. At step 510, the receiver obtains the channel estimates by performing channel estimation with VSFOCC despreading based on the assigned spreading factor. The channel estimation herein combines least squares (LS) and despreading interpolation methods. At step 512, the channel estimates obtained at the receiver are interpolated to estimate the channel over a number of Physical Resource block, N.sub.PRB, subcarriers.

[0054] FIGS. 6a-6d are graphs illustrating the simulation results of four exemplary Mean Squared Error (MSE) for channel estimates, each pertaining to one of the four DM-RS configurations, according to the embodiments herein. In some embodiments, the simulations are used to evaluate the Mean Square Error (MSE) of the various channel estimation schemes. The channel model used is TDL-C, which follows Rayleigh fading. The MSE results obtained are averaged over 1000 realizations of the channel. The simulation parameters are given in the Table 3 below. Perfect timing and frequency synchronization is assumed at the receiver.

TABLE-US-00006 TABLE 3 Simulation parameters System Bandwidth 50 MHZ FFT Size N 2048 Subcarrier Spacing 30 kHz Symbol duration 33.33 μs Allocated PRBs N.sub.PRB  12 Cyclic Prefix duration 2.34 μs Power Delay Profile TDL-C Delay spread 1.95 μs Maximum Doppler spread 50 Hz

[0055] The simulation results compare the MSE results of CFR estimates between a port and the UE with the standard specified OCC and the VSFOCC method according to the present disclosure under the same channel conditions. The VSFOCC method doubles the number of estimates for partially loaded CDM groups, thus leading to a decrease in interpolation error. This reduction in interpolation error shows up as an MSE gain in higher SNRs for channels with moderate to high delay spread. The UE receives pilots from all ports and estimates the channel from the scheduled port. The simulation results for four scenarios, each pertaining to one of the four DM-RS configurations, are shown.

[0056] FIG. 6a is a graph 602 illustrating the MSE of a port using VSFOCC with P=3, according to a first example scenario. In a single symbol, DM-RS with P=3; VSFOCC is applied to the Port 1, and the MSE is compared between existing OCC and the method disclosed in the present disclosure as shown in FIG. 10a. From the result, it can be seen that Ne-point DFT interpolators are not suitable even for minimum users because of the poor resolution of channel taps. Hence, only N-point DFT interpolator is used for the remaining cases. The MSE values of all ports with N-DFT interpolation following OCC and VSFOCC are shown in Table 4. The MSE of Port 1 is improved, whereas the others remain the same.

TABLE-US-00007 TABLE 4 MSE Comparison of all ports MSE in dB at SNR = 20 dB Port OCC VSFOCC Port 1 −24.51 −27.21 Port 2 −23.03 −23.03 Port 3 −22.97 −22.97

[0057] FIG. 6b is a graph 604 illustrating MSE of a port using VSFOCC with P=5 according to a second example scenario. With P=5, the ports are scheduled in {CDM 0, CDM 1, CDM 2} as {(P.sub.1, P.sub.2), (P.sub.1, P.sub.2), (P.sub.2)} in Type 2 configuration. The port in CDM group 2 is assigned with a variable spreading factor (SF=1) instead of two. The performance of that port with VSFOCC is better than the existing Walsh spreading. The results can be seen in FIG. 6b.

[0058] FIG. 6c is a graph 606 illustrating MSE of one of the ports using VSFOCC with P=10 according to a third example scenario. In this scenario, different number of ports are considered in the double symbol Type 2 configuration. The number of ports considered, P=10 are scheduled. With the different number of ports in the double symbol Type 2 configuration allocation, two ports get an advantage over OCC. The MSE graph of one of the ports is shown in FIG. 6c.

[0059] FIG. 6d is a graph 608 illustrating MSE of one of the ports using VSFOCC with P=12 according to a third example scenario. When entire DM-RS resources are allocated with P=12, the OCC allocation and VSFOCC are identical. The MSE result showing the similar performance between OCC and VSFOCC for one of the ports is shown in FIG. 6d.

[0060] The embodiments herein provide uniformly better MSE for Type 1 configuration, and it provides better MSE from medium to moderate SNRs for Type 2. As VSFOCC reduces the spreading factor, noise averaging reduces, which in turn directly impacts the linear interpolation performance.

[0061] In some aspects, the embodiments of the present disclosure improve mean squared error of channel estimates because of the increase in the number of distinct channel estimates in certain ports. The improved mean squared error can translate to a lower block error rate and hence provide a higher throughput. Further, it does not require any changes in the complexity of the transmitter or receiver.

[0062] The different allocation strategies give slightly different MSE performances. The example case of MSE performance for 10 UEs with two different allocation strategies in Type 2 double symbol configuration is tabulated below.

TABLE-US-00008 Allocation (CDM0, MSE MSE CDM1, SNR = 27 dB Improvement SNR = 30 dB Improvement CDM2) OCC VSFOCC (dB) OCC VSFOCC (dB) (3, 3, 2) −28.6 −30.6 2 −29.6 −31.6 2 −28.8 −30.4 1.6 −29.2 −31.4 2.2 −28.2 −30.4 2.2 −28.8 −31.2 2.4 −29.1 −30.9 1.8 −29.6 −32.1 2.5 Average 1.9 2.275 MSE Improvement (4, 2, 2) −28.9 −30.7 1.8 −29.5 −31.8 2.3 −28.5 −30.1 1.6 −29.3 −31.5 2.2 −29 −30.8 1.8 −29.7 −31.9 2.2 −28.6 −30.2 1.6 −29.3 −31.2 1.9 Average 1.7 2.15 MSE Improvement

[0063] In some embodiments, additional DMRS port combinations are added in the DCI to increase the possibilities for the port combinations to enable the optimal channel estimation in partial port occupancy. Following modifications are proposed for Table 7.3.1.1.2-8 through Table 7.3.1.1.2-23 in 38.212. Some tables may require additional bits. [0064] (i) Modifications to Table 7.3.1.1.2-8: Antenna port(s), transform precoder is disabled, dmrs-Type=1, maxLength=1, rank=1

TABLE-US-00009 Number of DMRS CDM DMRS Value group(s) without data port(s) 0 1 0 1 1 1 2 2 0 3 2 1 4 2 2 5 2 3 6-7 Reserved Reserved 6 1 2 7 1 3 [0065] (ii) Modifications to Table 7.3.1.1.2-9: Antenna port(s), transform precoder is disabled, dmrs-Type=1, maxLength=1, rank=2

TABLE-US-00010 Number of DMRS CDM DMRS Value group(s) without data port(s) 0 1 0, 1 1 2 0, 1 2 2 2, 3 3 2 0, 2 4-7 Reserved Reserved 4 2 0, 3 5 2 1, 2 6 2 1, 3 7 1 2, 3 [0066] (iii) Modifications to Table 7.3.1.1.2-10: Antenna port(s), transform precoder is disabled, dmrs-Type=1, maxLength=1, rank=3

TABLE-US-00011 Number of DMRS CDM DMRS Value group(s) without data port(s) 0 2 0-2 2-7 Reserved Reserved 2 2 0, 1, 3 3 2 0, 2, 3 4 2 1, 2, 3 [0067] (iv) Modifications to Table 7.3.1.1.2-11: Antenna port(s), transform precoder is disabled, dmrs-Type=1, maxLength=1, rank=4

TABLE-US-00012 Number of DMRS CDM DMRS Value group(s) without data port(s) 0 2 0-3 2-7 Reserved Reserved [0068] (v) Modifications to Table 7.3.1.1.2-12: Antenna port(s), transform precoder is disabled, dmrs-Type=1, maxLength=2, rank=1

TABLE-US-00013 Number of DMRS CDM DMRS Number of front- Value group(s) without data port(s) load symbols 0 1 0 1 1 1 1 1 2 2 0 1 3 2 1 1 4 2 2 1 5 2 3 1 6 2 0 2 7 2 1 2 8 2 2 2 9 2 3 2 10 2 4 2 11 2 5 2 12 2 6 2 13 2 7 2 14-15 Reserved Reserved Reserved [0069] (vi) Modifications to Table 7.3.1.1.2-13: Antenna port(s), transform precoder is disabled, dmrs-Type=1, maxLength=2, rank=2

TABLE-US-00014 Number of DMRS CDM DMRS Number of front- Value group(s) without data port(s) load symbols 0 1 0, 1 1 1 2 0, 1 1 2 2 2, 3 1 3 2 0, 2 1 4 2 0, 1 2 5 2 2, 3 2 6 2 4, 5 2 7 2 6, 7 2 8 2 0, 4 2 9 2 2, 6 2 2 1, 4 2 0, 5 2 1, 5 2 2, 7 2 3, 6 2 3, 7 [0070] (vii) Modifications to Table 7.3.1.1.2-14: Antenna port(s), transform precoder is disabled, dmrs-Type=1, maxLength=2, rank=3

TABLE-US-00015 Number of DMRS CDM DMRS Number of front- Value group(s) without data port(s) load symbols 0 2 0-2 1 1 2 0, 1, 4 2 2 2 2, 3, 6 2 2 1, 4, 5 2 3, 6, 7 2 0, 4, 5 2 2, 6, 7 2 0, 1, 5 2 2, 3, 7 [0071] (viii) Modifications to Table 7.3.1.1.2-15: Antenna port(s), transform precoder is disabled, dmrs-Type=1, maxLength=2, rank=4

TABLE-US-00016 Number of DMRS DMRS Number of front- Value group(s) without data port(s) load symbols 0 2 0-3 1 1 2 0, 1, 4, 5 2 2 2 2, 3, 6, 7 2 3 2 0, 2, 4, 6 2 4-15 Reserved Reserved Reserved [0072] (ix) Modifications to Table 7.3.1.1.2-16: Antenna port(s), transform precoder is disabled, dmrs-Type=2, maxLength=1, rank=1

TABLE-US-00017 Number of DMRS CDM group(s) DMRS Value without data port(s) 0 1 0 1 1 1 2 2 0 3 2 1 4 2 2 5 2 3 6 3 0 7 3 1 8 3 2 9 3 3 10 3 4 11 3 5 12-15 Reserved Reserved [0073] (x) Modifications to Table 7.3.1.1.2-17: Antenna port(s), transform precoder is disabled, dmrs-Type=2, maxLength=1, rank=2

TABLE-US-00018 Number of DMRS CDM group(s) DMRS Value without data port(s) 0 1 0, 1 1 2 0, 1 2 2 2, 3 3 3 0, 1 4 3 2, 3 5 3 4, 5 6 2 0, 2 2 0, 3 2 1, 2 2 1, 3 3 2, 4 3 2, 5 3 3, 4 3 3, 5 3 0, 4 3 0, 5 3 1, 4 3 1, 5 [0074] (xi) Modifications to Table 7.3.1.1.2-18: Antenna port(s), transform precoder is disabled, dmrs-Type=2, maxLength=1, rank=3

TABLE-US-00019 Number of DMRS CDM group(s) DMRS Value without data port(s) 0 2 0-2 1 3 0-2 2 3 3-5 3 3 2, 4, 5 3 2-4 3 2, 3, 5 2/3 0, 1, 3 2/3 1-3 2/3 0, 2, 3 [0075] (xii) Modifications to Table 7.3.1.1.2-19: Antenna port(s), transform precoder is disabled, dmrs-Type=2, maxLength=1, rank=4

TABLE-US-00020 Number of DMRS CDM group(s) DMRS Value without data port(s) 0 2 0-3 1 3 0-3 3 2-5 [0076] (xiii) Modifications to Table 7.3.1.1.2-20: Antenna port(s), transform precoder is disabled, dmrs-Type=2, maxLength=2, rank=1

TABLE-US-00021 Number of DMRS CDM DMRS Number of front- Value group(s) without data port(s) load symbols 0 1 0 1 1 1 1 1 2 2 0 1 3 2 1 1 4 2 2 1 5 2 3 1 6 3 0 1 7 3 1 1 8 3 2 1 9 3 3 1 10 3 4 1 11 3 5 1 12 3 0 2 13 3 1 2 14 3 2 2 15 3 3 2 16 3 4 2 17 3 5 2 18 3 6 2 19 3 7 2 20 3 8 2 21 3 9 2 22 3 10 2 23 3 11 2 24 1 0 2 25 1 1 2 26 1 6 2 27 1 7 2 28-31 Reserved Reserved Reserved [0077] (xiv) Modifications to Table 7.3.1.1.2-21: Antenna port(s), transform precoder is disabled, dmrs-Type=2, maxLength=2, rank=2

TABLE-US-00022 Number of DMRS CDM Number group(s) of front- without DMRS load Additional Value data port(s) symbols Comments 0 1 0, 1 1 1 2 0, 1 1 2 2 2, 3 1 3 3 0, 1 1 4 3 2, 3 1 5 3 4, 5 1 6 2 0, 2 1 7 3 0, 1 2 8 3 2, 3 2 9 3 4, 5 2 10 3 6, 7 2 11 3 8, 9 2 12 3 10, 11 2 13 1 0, 1 2 14 1 6, 7 2 15 2 0, 1 2 16 2 2, 3 2 17 2 6, 7 2 18 2 8, 9 2 19 3 0, 6 Use Reserved field 20 3 0, 7 Use Reserved field 21 3 1, 6 Use Reserved field 22 3 1, 7 Use Reserved field 23 3 2, 8 Use Reserved field 24 3 2, 9 Use Reserved field 25 3 3, 8 Use Reserved field 26 3 3, 9 Use Reserved field 27 3  4, 10 Use Reserved field 28 3  4, 11 Use Reserved field 29 3  5, 10 Use Reserved field 30 3  5, 11 Use Reserved field 31 3 0, 3 Use Reserved field 32 3 0, 8 Reserve field exhausted, need additional bits for indication 33 3 0, 9 Reserve field exhausted, need additional bits for indication 34 3 1, 2 Reserve field exhausted, need additional bits for indication 35 3 1, 3 Reserve field exhausted, need additional bits for indication 36 3 1, 8 Reserve field exhausted, need additional bits for indication 37 3 1, 9 Reserve field exhausted, need additional bits for indication 38 3 2, 6 Reserve field exhausted, need additional bits for indication 39 3 3, 6 Reserve field exhausted, need additional bits for indication 40 3 6, 8 Reserve field exhausted, need additional bits for indication 41 3 6, 9 Reserve field exhausted, need additional bits for indication 42 3 2, 7 Reserve field exhausted, need additional bits for indication 43 3 3, 7 Reserve field exhausted, need additional bits for indication 44 3 7, 8 Reserve field exhausted, need additional bits for indication 45 3 7, 9 Reserve field exhausted, need additional bits for indication 46 3 0, 4 Reserve field exhausted, need additional bits for indication 47 3 0, 5 Reserve field exhausted, need additional bits for indication 48 3  0, 10 Reserve field exhausted, need additional bits for indication 49 3  0, 11 Reserve field exhausted, need additional bits for indication 50 3 1, 4 Reserve field exhausted, need additional bits for indication 51 3 1, 5 Reserve field exhausted, need additional bits for indication 52 3  1, 10 Reserve field exhausted, need additional bits for indication 53 3  1, 11 Reserve field exhausted, need additional bits for indication 54 3 4, 6 Reserve field exhausted, need additional bits for indication 55 3 5, 6 Reserve field exhausted, need additional bits for indication 56 3  6, 10 Reserve field exhausted, need additional bits for indication 57 3  6, 11 Reserve field exhausted, need additional bits for indication 58 3 4, 7 Reserve field exhausted, need additional bits for indication 59 3 5, 7 Reserve field exhausted, need additional bits for indication 60 3  7, 10 Reserve field exhausted, need additional bits for indication 61 3  7, 11 Reserve field exhausted, need additional bits for indication 62 3 2, 4 Reserve field exhausted, need additional bits for indication 63 3 2, 5 Reserve field exhausted, need additional bits for indication 64 3  2, 10 Reserve field exhausted, need additional bits for indication 65 3  2, 11 Reserve field exhausted, need additional bits for indication 66 3 3, 4 Reserve field exhausted, need additional bits for indication 67 3  3, 10 Reserve field exhausted, need additional bits for indication 68 3 2, 5 Reserve field exhausted, need additional bits for indication 69 3  3, 11 Reserve field exhausted, need additional bits for indication 70 3 4, 8 Reserve field exhausted, need additional bits for indication 71 3 5, 8 Reserve field exhausted, need additional bits for indication 72 3  8, 10 Reserve field exhausted, need additional bits for indication 73 3  8, 11 Reserve field exhausted, need additional bits for indication 74 3 4, 9 Reserve field exhausted, need additional bits for indication 75 3 5, 9 Reserve field exhausted, need additional bits for indication 76 3  9, 10 Reserve field exhausted, need additional bits for indication 77 3  9, 11 Reserve field exhausted, need additional bits for indication
Modifications to Table 7.3.1.1.2-22: Antenna port(s), transform precoder is disabled, dmrs-Type=2, maxLength=2, rank=3

TABLE-US-00023 Number of DMRS CDM Number group(s) of front- without DMRS load Additional Value data port(s) symbols Comments 0 2 0-2 1 1 3 0-2 1 2 3 3-5 1 3 3 0, 1, 6 2 4 3 2, 3, 8 2 5 3  4, 5, 10 2 6 3 2, 3, 6, 7 Use Reserved field 7 3 6, 7, 8, 9 Use Reserved field 8 3 2, 3, 4, 5 Use Reserved field 9 3 2, 3, 10, 11 Use Reserved field 10 3 4, 5, 8, 9 Use Reserved field 11 3 8, 9, 10, 11 Use Reserved field 12 3 0, 1, 4, 5 Use Reserved field 13 3 0, 1, 10, 11 Use Reserved field 14 3 4, 5, 6, 7 Use Reserved field 15 3 6, 7, 10, 11 Use Reserved field 16 3 6, 7, 9 Use Reserved field 17 3 0, 2, 3 Use Reserved field 18 3 01-Mar Use Reserved field 19 3 2, 3, 6 Use Reserved field 20 3 2, 3, 7 Use Reserved field 21 3 0, 3, 8 Use Reserved field 22 3 1, 3, 8 Use Reserved field 23 3 3, 6, 8 Use Reserved field 24 3 3, 7, 8 Use Reserved field 25 3 0, 8, 9 Use Reserved field 26 3 1, 8, 9 Use Reserved field 27 3 6, 8, 9 Use Reserved field 28 3 07-Sep Use Reserved field 29 3 0, 1, 4 Use Reserved field 30 3 0, 1, 5 Use Reserved field 31 3  0, 1, 10 Use Reserved field 32 3  0, 1, 11 Reserve field exhausted, need additional bits for indication 33 3 1, 4, 6 Reserve field exhausted, need additional bits for indication 34 3 1, 5, 6 Reserve field exhausted, need additional bits for indication 35 3  1, 6, 10 Reserve field exhausted, need additional bits for indication 36 3  1, 6, 11 Reserve field exhausted, need additional bits for indication 37 3 4, 6, 7 Reserve field exhausted, need additional bits for indication 38 3 05-Jul Reserve field exhausted, need additional bits for indication 39 3  6, 7, 10 Reserve field exhausted, need additional bits for indication 40 3  6, 7, 11 Reserve field exhausted, need additional bits for indication 41 3 0, 4, 5 Reserve field exhausted, need additional bits for indication 42 3 1, 4, 5 Reserve field exhausted, need additional bits for indication 43 3 04-Jun Reserve field exhausted, need additional bits for indication 44 3 4, 5, 7 Reserve field exhausted, need additional bits for indication 45 3  0, 5, 10 Reserve field exhausted, need additional bits for indication 46 3  1, 5, 10 Reserve field exhausted, need additional bits for indication 47 3  5, 6, 10 Reserve field exhausted, need additional bits for indication 48 3  5, 7, 10 Reserve field exhausted, need additional bits for indication 49 3 0, 10, 11 Reserve field exhausted, need additional bits for indication 50 3 1, 10, 11 Reserve field exhausted, need additional bits for indication 51 3 6, 10, 11 Reserve field exhausted, need additional bits for indication 52 3 7, 10, 11 Reserve field exhausted, need additional bits for indication 53 3 02-Apr Reserve field exhausted, need additional bits for indication 54 3 2, 3, 5 Reserve field exhausted, need additional bits for indication 55 3  2, 3, 10 Reserve field exhausted, need additional bits for indication 56 3  2, 3, 11 Reserve field exhausted, need additional bits for indication 57 3 3, 4, 8 Reserve field exhausted, need additional bits for indication 58 3 3, 5, 8 Reserve field exhausted, need additional bits for indication 59 3  3, 8, 10 Reserve field exhausted, need additional bits for indication 60 3  3, 8, 11 Reserve field exhausted, need additional bits for indication 61 3 4, 8, 9 Reserve field exhausted, need additional bits for indication 62 3 5, 8, 9 Reserve field exhausted, need additional bits for indication 63 3 08-Oct Reserve field exhausted, need additional bits for indication 64 3  8, 9, 11 Reserve field exhausted, need additional bits for indication 65 3 2, 4, 5 Reserve field exhausted, need additional bits for indication 66 3 3, 4, 5 Reserve field exhausted, need additional bits for indication 67 3 4, 5, 8 Reserve field exhausted, need additional bits for indication 68 3 4, 5, 9 Reserve field exhausted, need additional bits for indication 69 3  2, 5, 10 Reserve field exhausted, need additional bits for indication 70 3  3, 5, 10 Reserve field exhausted, need additional bits for indication 71 3  5, 8, 10 Reserve field exhausted, need additional bits for indication 72 3  5, 9, 10 Reserve field exhausted, need additional bits for indication 73 3 2, 10, 11 Reserve field exhausted, need additional bits for indication 74 3 3, 10, 11 Reserve field exhausted, need additional bits for indication 75 3 8, 10, 11 Reserve field exhausted, need additional bits for indication 76 3 09-Nov Reserve field exhausted, need additional bits for indication 77 3 0, 1, 7 Reserve field exhausted, need additional bits for indication 78 3 1, 6, 7 Reserve field exhausted, need additional bits for indication 79 3 0, 6, 7 Reserve field exhausted, need additional bits for indication 80 3 2, 3, 8 Reserve field exhausted, need additional bits for indication 81 3 2, 3, 9 Reserve field exhausted, need additional bits for indication 82 3 3, 8, 9 Reserve field exhausted, need additional bits for indication 83 3 2, 8, 9 Reserve field exhausted, need additional bits for indication 84 3  4, 5, 11 Reserve field exhausted, need additional bits for indication 85 3 5, 10, 11 Reserve field exhausted, need additional bits for indication 86 3 4, 10, 11 Reserve field exhausted, need additional bits for indication [0078] (xv) Modifications to Table 7.3.1.1.2-23: Antenna port(s), transform precoder is disabled, dmrs-Type=2, maxLength=2, rank=4

TABLE-US-00024 Number of DMRS CDM DMRS Number of front- Value group(s) without data port(s) load symbols 0 2 0-3 1 1 3 0-3 1 2 3 0, 1, 6, 7 2 3 3 2, 3, 8, 9 2 4 3 4, 5, 10, 11 2 3 0, 1, 8, 9 3 2, 3, 6, 7 3 6, 7, 8, 9 3 2, 3, 4, 5 3 2, 3, 10, 11 3 4, 5, 8, 9 3 8, 9, 10, 11 3 0, 1, 4, 5 3 0, 1, 10, 11 3 4, 5, 6, 7 3 6, 7, 10, 11

[0079] In some aspects, the port allocation can be made in multiple ways. The order in which the CDM group filled varies for each case with the same number of ports getting the advantage of MSE. For e.g., If 10 ports are scheduled in total, the port allocation across three CDM groups in a double symbol type 2 DM-RS can be (4,4,2) or (4,3,3), as both add up to 10. The order in the above 3-tuples do not matter. For example, (4,4,2) as the above can be treated as equivalent to (2,4,4) and (4,2,4). key factor is the number of ports in each group. The specific CDM group it is assigned to doesn't matter, and all possible permutations are covered.

[0080] For the purposes of the embodiments of the present disclosure, the following abbreviations apply:

TABLE-US-00025 Abbreviations Description PDU Protocol Data Unit MCS Modulation & Coding Scheme P-Poi Partial Port Occupancy Information VSFOCC Variable Spreading Factor Orthogonal Cover Codes DM-RS Demodulation Reference Signal OVSF Orthogonal Variable Spreading Factor MSE Mean Squared Error OCC Orthogonal Cover Codes PDSCH Physical Downlink Shared Channel PDCCH Physical Downlink Control Channel DCI Downlink Control Information CDM Code Division Multiplexing MU-MIMO Multi-User Multiple Input Multiple Output

[0081] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification.