Method, system and device for configuring uplink reference signal
Technical Field
The present invention relates to the field of communications technologies, and in particular, to a method, a system, and an apparatus for configuring an uplink reference signal of a long term evolution multi-carrier aggregation system.
Background
In a long term evolution broadband mobile communication system, such as an LTE-Advanced or IMT-Advanced system, a higher peak rate needs to be provided through a larger transmission bandwidth to meet the user's demand, but the expansion of the transmission bandwidth is limited by frequency resources owned by an operator. Since the frequency resources owned by the operator are limited, in order to meet the bandwidth requirement of the LTE-a system, it is necessary to aggregate a plurality of continuous or discontinuous LTE bands. In addition, the LTE-a system also needs to maintain good backward compatibility with the existing LTE (Long Term Evolution) system, and ensures that the LTE terminal can be smoothly accessed, so that each frequency band in the LTE-a system needs to be compatible with the LTE terminal to work. In the prior art, two ways may be adopted for aggregation, one way is to aggregate a plurality of continuous LTE carriers, and the other way is to aggregate a plurality of discontinuous LTE carriers, as shown in fig. 1, which is a schematic diagram of aggregating a plurality of discontinuous LTE carriers in the prior art.
The common consensus of the current carrier aggregation system design is that the design on each carrier should be consistent with LTE R8 as much as possible, so as to ensure that the terminal of LTE R8 can work normally on each component carrier. Because the uplink and downlink bandwidth requirements are different, more component carriers (e.g., 3 component carriers for downlink and 1 component carrier for uplink) for downlink will appear in the multi-carrier aggregation system than for uplink, and it is considered that for the LTE system, only one carrier of the multiple carriers of the carrier aggregation system can be accessed, so that it may appear that multiple UEs are on different downlink component carriers, but their uplink carriers are the same component carrier. In order to reduce the peak-to-average ratio of the downlink forming signal of the multi-carrier aggregation system, different downlink component carriers are configured with different Cell IDs (Cell identifiers). As shown in fig. 2, which is a schematic diagram of asymmetry of uplink and downlink frequency bands in the prior art, it can be seen that two different downlink component carriers (configured with different Cell IDs) correspond to the same uplink component carrier.
The prior art has a disadvantage that, because different downlink component carriers are configured with different Cell IDs, orthogonality of Uplink reference signals in the same Uplink component carrier corresponding to a UE (User Equipment) on different downlink component carriers is deteriorated, which affects performance of Channel estimation such as PUCCH (Physical Uplink Control Channel), SRS (Uplink pilot Signal), PUSCH (Physical Uplink Shared Channel), and the like. See the following analysis in particular:
currently, in LTE R8, uplink reference signal sequences group reference signal sequences with different lengths into one group, and 30 groups are set in total. UE according to Cell ID and time slot number (n) of the Cells) One of the reference signal sequence groups with a certain length is selected as an uplink reference signal sequence. Specifically, the formula is shown as follows:
u=(fgh(ns)+fss)mod 30
where u identifies the root sequence index of the uplink reference signal sequence (i.e., one of the 30 groups), fgh(ns) The identification root sequence index hops according to the time slot, mod is a modulo symbol:
wherein c (i) is a Gold sequence, the initial of whichHas a value of
Which is uniquely determined by the Cell ID, and the turn on of the group hopping of the sequence is indicated by higher layer signaling, wherein,
to round the symbol down.
Shift of sequence fssDifferent upstream channels are defined differently:
for the PUCCH channel:
for the PUSCH channel: <math>
<mrow>
<msubsup>
<mi>f</mi>
<mi>ss</mi>
<mi>PUSCH</mi>
</msubsup>
<mo>=</mo>
<mrow>
<mo>(</mo>
<msubsup>
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<mi>ss</mi>
<mi>PUCCH</mi>
</msubsup>
<mo>+</mo>
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<mi>Δ</mi>
<mi>ss</mi>
</msub>
<mo>)</mo>
</mrow>
<mi>mod</mi>
<mn>30</mn>
<mo>,</mo>
</mrow>
</math> wherein, DeltassE {0, 1.., 29} is given by higher layers.
From the above analysis, it can be seen that the selection of the uplink reference signal root sequence is only related to CellID. In LTE R8, it is guaranteed that UEs in the same uplink carrier use uplink reference signal root sequences in the same group to distinguish between UEs through cyclic shift, but in an uplink and downlink asymmetric multicarrier aggregation system, when Cell IDs on different downlink component carriers are different, uplink reference signal root sequences in multiple groups will appear in the corresponding same uplink component carrier. The orthogonality between reference signal root sequences in different groups is worse than the orthogonality between sequences of the same reference signal sequence generated by cyclic shift. Particularly for the PUCCH channel, the length of the reference signal sequence in the PUCCH is only 12, and if the reference signal sequence is the same root sequence, different cyclic shifts can also ensure complete orthogonality between the sequences, but if the reference signal sequence is different root sequences, the correlation performance between the reference signal sequences reaches 0.8, so that UEs cannot be distinguished, and the performance of the PUCCH is seriously affected.
Disclosure of Invention
The present invention is directed to at least solve one of the above technical drawbacks, and in particular, to solve a technical drawback in the prior art that orthogonality of uplink reference signals of different UEs cannot be guaranteed.
In order to achieve the above object, an aspect of the present invention provides a method for configuring an uplink reference signal, including: the base station judges whether asymmetric User Equipment (UE) exists in uplink member carriers of a multi-carrier aggregation system, wherein the asymmetric UE occupies the same uplink member carrier and different downlink member carriers; and if the asymmetric UE exists in the uplink member carrier wave, the base station indicates the sequence number of the uplink parameter signal root sequence to the asymmetric UE through signaling, and the asymmetric UE configures an uplink reference signal according to the signaling.
As an embodiment of the present invention, the indicating, by the base station to the asymmetric UE through signaling, the sequence number of the uplink parameter signal root sequence includes: the base station sends a uniform signaling CCI to the asymmetric UEUL RSAnd indicating the sequence number of the uplink parameter signal root sequence to the asymmetric UE.
As an embodiment of the invention, the unified signaling CCIUL RSIs 9 bits in length.
As an embodiment of the present invention, a formula of the asymmetric UE configuring the uplink reference signal according to the signaling is: u ═ fgh(ns)+fss) mod30, where u is the root sequence index of the uplink reference signal sequence, fgh(ns) Frequency hopping by time slot for root sequence index, fssIs a shift of the sequence.
As an embodiment of the present invention, the fgh(ns) Calculated by the following formula:
wherein c (i) is a Gold sequence, and the initial value of c (i) is
As an embodiment of the present invention, the fssRelated to an uplink channel, if the uplink channel is an uplink control channel PUCCH, the uplink control channel is a downlink control channel (PUCCH) If the uplink channel is an uplink shared channel (PUSCH), the method comprises the following steps <math>
<mrow>
<msubsup>
<mi>f</mi>
<mi>ss</mi>
<mi>PUSCH</mi>
</msubsup>
<mo>=</mo>
<mrow>
<mo>(</mo>
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<mi>f</mi>
<mi>ss</mi>
<mi>PUCCH</mi>
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<mi>ss</mi>
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</mrow>
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<mn>30</mn>
<mo>,</mo>
</mrow>
</math> Wherein, DeltassE {0, 1...., 29} is given by higher layers on the network side.
As an embodiment of the present invention, the indicating, by the base station to the asymmetric UE through signaling, the sequence number of the uplink parameter signal root sequence includes: said baseThe station respectively sends signaling indexes to the asymmetric UEUL RSSaid signaling IndexUL RSThe cell ID corresponding to the asymmetric UE is related, and the signaling Index corresponding to each asymmetric UEUL RSAnd the sum of the cell IDs is equal to the sum of the cell IDs so as to indicate the sequence number of the uplink parameter signal root sequence to the asymmetric UE, and the asymmetric UE indicates the sequence number of the uplink parameter signal root sequence according to the signaling IndexUL RSAnd configuring the uplink reference signal with the corresponding cell ID.
As an embodiment of the invention, the signaling IndexUL RSIs 5 bits in length.
As an embodiment of the present invention, the asymmetric UE is according to the signaling IndexUL RSThe formula for configuring the uplink reference signal with the corresponding cell ID is: u ═ fgh(ns)+fss) mod30, where u is the root sequence index of the uplink reference signal sequence, fgh(ns) Frequency hopping by time slot for root sequence index, fssIs a shift of the sequence.
As an embodiment of the present invention, the f
gh(n
s) Calculated by the following formula:
wherein c (i) is a Gold sequence, and the initial value of c (i) is
As an embodiment of the present invention, the fssRelated to the uplink channel, if the uplink channel is PUCCH, the uplink channel is a Physical Uplink Control Channel (PUCCH) If the uplink channel is PUSCH, the method comprises the following steps <math>
<mrow>
<msubsup>
<mi>f</mi>
<mi>ss</mi>
<mi>PUSCH</mi>
</msubsup>
<mo>=</mo>
<mrow>
<mo>(</mo>
<msubsup>
<mi>f</mi>
<mi>ss</mi>
<mi>PUCCH</mi>
</msubsup>
<mo>+</mo>
<msub>
<mi>Δ</mi>
<mi>ss</mi>
</msub>
<mo>)</mo>
</mrow>
<mi>mod</mi>
<mn>30</mn>
<mo>,</mo>
</mrow>
</math> Wherein, DeltassE {0, 1...., 29} is given by higher layers on the network side.
As an embodiment of the present invention, the indicating, by the base station to the asymmetric UE through signaling, the sequence number of the uplink parameter signal root sequence includes:
broadcasting Cell IDs of all downlink member carriers in broadcast information, directly selecting one Cell ID by a base station as the Cell ID adopted by the asymmetric UE when determining an uplink reference signal sequence, and informing the selected Cell ID to the asymmetric UE through signaling.
The invention also provides a system for configuring uplink reference signals, which comprises a base station and at least one UE (user equipment) served by the base station, wherein the base station is used for judging whether asymmetric UE exists in uplink member carriers of a multi-carrier aggregation system, the asymmetric UE is the UE occupying the same uplink member carriers and different downlink member carriers, and when the asymmetric UE is judged to exist, the serial number of an uplink parameter signal root sequence is indicated to the asymmetric UE through signaling; and the UE is used for receiving the signaling sent by the base station and configuring an uplink reference signal according to the signaling when the UE is the asymmetric UE.
As an embodiment of the invention, the signaling is a unified signaling CCIUL RS。
As an embodiment of the invention, the unified signaling CCIUL RSIs 9 bits in length.
As an embodiment of the present invention, the signaling is signaling indexes respectively sent by the base stationsUL RSSaid signaling IndexUL RSThe cell ID corresponding to the asymmetric UE is related, and the signaling Index corresponding to each asymmetric UEUL RSAnd the sum of cell IDs are all equal.
As an embodiment of the invention, the signaling IndexUL RSIs 5 bits in length.
The invention also provides a base station, which comprises a judging module and a signaling sending module, wherein the judging module is used for judging whether asymmetric UE exists in uplink member carriers of a multi-carrier aggregation system, wherein the asymmetric UE is UE occupying the same uplink member carriers and different downlink member carriers; the signaling sending module is configured to indicate a sequence number of an uplink parameter signal root sequence to the asymmetric UE through a signaling when the determining module determines that the asymmetric UE exists in the uplink component carrier, where the asymmetric UE configures an uplink reference signal according to the signaling.
The invention also provides UE, which comprises a signaling receiving module and an uplink reference signal configuration module, wherein the signaling receiving module is used for receiving a signaling sent by a base station when the UE is asymmetric UE, and the signaling is used for indicating the sequence number of an uplink parameter signal root sequence; the uplink reference signal configuration module is configured to configure an uplink reference signal according to the signaling received by the signaling receiving module.
As an embodiment of the invention, the signaling is a unified signaling CCIUL RS。
As an embodiment of the invention, the unified signaling CCIUL RSIs 9 bits in length.
As an embodiment of the present invention, a formula of the uplink reference signal configuration module configuring the uplink reference signal according to the signaling is as follows: u ═ fgh(ns)+fss) mod30, where u is the root sequence index of the uplink reference signal sequence, fgh(ns) Frequency hopping by time slot for root sequence index, fssIs a shift of the sequence.
As an embodiment of the present invention, the f
gh(n
s) Calculated by the following formula:
wherein c (i) is a Gold sequence, and the initial value of c (i) is
As an embodiment of the present invention, the fssRelated to an uplink channel, if the uplink channel is an uplink control channel PUCCH, the uplink control channel is a downlink control channel (PUCCH) If the uplink channel is an uplink shared channel (PUSCH), the method comprises the following steps <math>
<mrow>
<msubsup>
<mi>f</mi>
<mi>ss</mi>
<mi>PUSCH</mi>
</msubsup>
<mo>=</mo>
<mrow>
<mo>(</mo>
<msubsup>
<mi>f</mi>
<mi>ss</mi>
<mi>PUCCH</mi>
</msubsup>
<mo>+</mo>
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<mi>Δ</mi>
<mi>ss</mi>
</msub>
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</mrow>
<mi>mod</mi>
<mn>30</mn>
<mo>,</mo>
</mrow>
</math> Wherein, DeltassE {0, 1...., 29} is given by higher layers on the network side.
As an originalIn an embodiment of the present invention, the signaling is signaling indexes respectively sent by the base stationsUL RSSaid signaling IndexUL RSThe cell ID corresponding to the asymmetric UE is related, and the signaling Index corresponding to each asymmetric UEUL RSAnd the sum of cell IDs are all equal.
As an embodiment of the invention, the signaling IndexUL RSIs 5 bits in length.
As an embodiment of the present invention, a formula of the uplink reference signal configuration module configuring the uplink reference signal according to the signaling is as follows: u ═ fgh(ns)+fss) mod30, where u is the root sequence index of the uplink reference signal sequence, fgh(ns) Frequency hopping by time slot for root sequence index, fssIs a shift of the sequence.
As an embodiment of the present invention, the f
gh(n
s) Calculated by the following formula:
wherein c (i) is a Gold sequence, and the initial value of c (i) is
As an embodiment of the present invention, the fssRelated to the uplink channel, if the uplink channel is PUCCH, the uplink channel is a Physical Uplink Control Channel (PUCCH)
If the uplink channel is PUSCH, the method comprises the following steps <math>
<mrow>
<msubsup>
<mi>f</mi>
<mi>ss</mi>
<mi>PUSCH</mi>
</msubsup>
<mo>=</mo>
<mrow>
<mo>(</mo>
<msubsup>
<mi>f</mi>
<mi>ss</mi>
<mi>PUCCH</mi>
</msubsup>
<mo>+</mo>
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<mi>ss</mi>
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<mi>mod</mi>
<mn>30</mn>
<mo>,</mo>
</mrow>
</math> Wherein, DeltassE {0, 1...., 29} is given by higher layers on the network side.
The invention explicitly indicates the reference signal sequence in the uplink member carrier through the signaling, can avoid the interference among UE (user equipment) caused by using different Cell IDs (identities) for the downlink member carrier, ensures the orthogonality among the uplink reference signal sequences, and improves the performances of PUCCH (physical uplink control channel), SRS (sounding reference signal), PUSCH (physical uplink shared channel) channel estimation and the like. Meanwhile, the compatibility of the LTE-A and the LTE system is considered, and the system performance is optimized to a greater extent.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The foregoing and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
fig. 1 is a diagram illustrating aggregation of multiple discontinuous LTE carriers in the prior art;
fig. 2 is a diagram illustrating asymmetry of uplink and downlink bands in the prior art;
fig. 3 is a flowchart of a method for configuring an uplink reference signal according to a first embodiment of the present invention;
fig. 4 is a flowchart of a method for configuring an uplink reference signal according to a second embodiment of the present invention;
fig. 5 is a structural diagram of a configuration system of an uplink reference signal according to an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative only and should not be construed as limiting the invention.
The invention mainly aims to clearly indicate the reference signal sequence in the uplink member carrier through signaling, thereby avoiding the interference among the UE caused by the downlink member carrier using different Cell IDs and ensuring the orthogonality among the uplink reference signal sequences. As embodiments of the present invention, the present invention proposes various signaling modes, and specifically, refer to the following description.
Example one
As shown in fig. 3, which is a flowchart of a method for configuring an uplink reference signal according to an embodiment of the present invention, in this embodiment, signaling sent by a base station to all asymmetric UEs on the same uplink component carrier is the same, that is, unified signaling, and the length of the signaling may refer to the length of a current Cell ID, and is preferably 9 bits. The method specifically comprises the following steps:
step S301, the base station determines whether there is an asymmetric UE in the uplink component carriers of the multi-carrier aggregation system, where the asymmetric UE is a UE that occupies the same uplink component carrier and different downlink component carriers.
Step S302, if the asymmetric UE exists in the uplink member carrier wave, the base station passes the uniform signaling CCIUL RSAnd indicating the sequence number of the uplink parameter signal root sequence to the asymmetric UE. Said unified signalling CCIUL RSReference may be made to the length setting of the current Cell ID, which may preferably be 9 bits. Since the Cell ID is 504 data at present, the closest 9-bit signaling (0-511, 512 data can be provided) can be selected. Of course, signaling of more than 9 bits, such as 10 bits, may also be selected.
Step S303, the asymmetric UE according to the unified signaling CCIUL RSAnd configuring the uplink reference signal. It can be seen that in this embodiment all asymmetric UEs receive a uniform signaling CCIUL RSThe base station and the UE are the same, so that the UE can use the uplink reference signal root sequence in the same group, and the defect of poor orthogonality is avoided. In addition, for the embodiment, the original calculation formula does not need to be changed, and only CCI is neededUL RSReplace the original Cell ID (N)ID cell) And (4) finishing.
Specifically, it can be calculated by the following formula:
u=(fgh(ns)+fss)mod 30
where u is the root sequence index of the uplink reference signal sequence, fgh(ns) Frequency hopping is performed for the root sequence index by time slot,
wherein c (i) is a Gold sequence, and the initial value of c (i) is
The initial value of c (i) can be determined by the unified signaling CCI
UL RSAnd (4) uniquely determining.
Wherein the shift of the sequence is fssDifferent upstream channels are defined differently:
if the uplink channel is PUCCH, then
If the uplink channel is PUSCH, then <math>
<mrow>
<msubsup>
<mi>f</mi>
<mi>ss</mi>
<mi>PUSCH</mi>
</msubsup>
<mo>=</mo>
<mrow>
<mo>(</mo>
<msubsup>
<mi>f</mi>
<mi>ss</mi>
<mi>PUCCH</mi>
</msubsup>
<mo>+</mo>
<msub>
<mi>Δ</mi>
<mi>ss</mi>
</msub>
<mo>)</mo>
</mrow>
<mi>mod</mi>
<mn>30</mn>
<mo>,</mo>
</mrow>
</math> Wherein, DeltassE {0, 1...., 29} is given by higher layers on the network side.
Example two
As shown in fig. 4, a flowchart of a method for configuring an uplink reference signal according to a second embodiment of the present invention is shown, in which a base station sends signaling indexes to asymmetric UEs on the same uplink component carrier respectivelyUL RSThe signaling IndexUL RSCell ID associated with asymmetric UE, and signaling Index corresponding to each asymmetric UEUL RSAnd the sum of cell IDs (N)ID cell+IndexUL RS) The two sequences are equal to each other, so that the UE can use the uplink reference signal root sequence in the same group. The length of the signaling is preferably 5 bits. The method specifically comprises the following steps:
step S401, the base station determines whether there is an asymmetric UE in the uplink component carriers of the multi-carrier aggregation system, where the asymmetric UE is a UE that occupies the same uplink component carrier and different downlink component carriers.
Step S402, if the asymmetric UE exists in the uplink member carrier wave, the base station sends signaling indexes to the asymmetric UE respectivelyUL RSA sequence number for indicating a root sequence of an uplink parameter signal, wherein the signaling IndexUL RSCell ID associated with asymmetric UE, and signaling Index corresponding to each asymmetric UEUL RSAnd the sum of cell IDs (N)ID cell+IndexUL RS) The two sequences are equal to each other, so that the UE can use the uplink reference signal root sequence in the same group. As a preferred embodiment of the present invention, the signaling IndexUL RSIs 5 bits in length.
Step S403, signaling Index according to which asymmetric UEUL RSAnd configuring the uplink reference signal. Specifically, it can be calculated by the following formula:
u=(fgh(ns)+fss)mod 30
where u is the root sequence index of the uplink reference signal sequence, fgh(ns) Frequency hopping is performed for the root sequence index by time slot,
wherein c (i) is a Gold sequence, and the initial value of c (i) is
The initial value of c (i) may be selected from N
ID cellAnd (4) uniquely determining.
Wherein the shift of the sequence is fssDifferent upstream channels are defined differently:
if the uplink channel is PUCCH, then
If the uplink channel is PUSCH, then <math>
<mrow>
<msubsup>
<mi>f</mi>
<mi>ss</mi>
<mi>PUSCH</mi>
</msubsup>
<mo>=</mo>
<mrow>
<mo>(</mo>
<msubsup>
<mi>f</mi>
<mi>ss</mi>
<mi>PUCCH</mi>
</msubsup>
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<mi>ss</mi>
</msub>
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</mrow>
<mi>mod</mi>
<mn>30</mn>
<mo>,</mo>
</mrow>
</math> Wherein, DeltassE {0, 1...., 29} is given by higher layers on the network side.
In the third embodiment, the first step is that,
if Cell IDs of all downlink component carriers are broadcast in the broadcast information, the base station may directly select one of the Cell IDs as a Cell ID used by the asymmetric UE when determining the uplink reference signal sequence, and notify the selected Cell ID to the UE through a signaling.
As shown in fig. 5, a configuration system structure diagram of an uplink reference signal according to an embodiment of the present invention includes a base station 100 and at least one UE200 served by the base station 100. The base station 100 is configured to determine whether an asymmetric UE exists in uplink component carriers of the multi-carrier aggregation system, where the asymmetric UE is a UE that occupies the same uplink component carrier and occupies different downlink component carriers, and indicate a sequence number of an uplink parameter signal root sequence to the asymmetric UE through a signaling when it is determined that the asymmetric UE exists. The UE200 is configured to receive a signaling sent by the base station 100 when the UE200 is an asymmetric UE, and configure an uplink reference signal according to the signaling.
The base station 100 includes a determining module 110 and a signaling sending module 120. The determining module 110 is configured to determine whether an asymmetric UE exists in uplink component carriers of the multi-carrier aggregation system, where the asymmetric UE is the UE200 that occupies the same uplink component carrier and different downlink component carriers. The signaling sending module 120 is configured to indicate, through a signaling, a sequence number of an uplink parameter signal root sequence to the asymmetric UE when the determining module 110 determines that the asymmetric UE exists in the uplink component carrier.
The UE200 includes a signaling receiving module 210 and an uplink reference signal configuration module 220. The signaling receiving module 210 is configured to receive a signaling sent by the base station 100 when the UE200 is an asymmetric UE, where the signaling is used to indicate a sequence number of an uplink parameter signal root sequence. The uplink reference signal configuring module 220 is configured to configure an uplink reference signal according to the signaling received by the signaling receiving module 210.
As an embodiment of the invention, the signaling may be a unified signaling CCIUL RSPreferably, it is 9 bits in length. The uplink reference signal configuration module is based on the unified signaling CCIUL RSThe configuration of the uplink reference signal may refer to the first embodiment, and is not described herein again.
As an embodiment of the present invention, the signaling may be a signaling Index respectively transmitted by the base station 100UL RSSignaling IndexUL RSCell ID associated with asymmetric UE, and signaling Index corresponding to each asymmetric UEUL RSAnd the sum of cell IDs are all equal. The length thereof is preferably 5 bits. Similarly, the uplink reference signal configuration module is according to the signaling IndexUL RSFor the configuration of the uplink reference signal, reference may be made to embodiment two, and details are not described herein again.
The invention explicitly indicates the reference signal sequence in the uplink member carrier through the signaling, can avoid the interference among UE (user equipment) caused by using different Cell IDs (identities) for the downlink member carrier, ensures the orthogonality among the uplink reference signal sequences, and improves the performances of PUCCH (physical uplink control channel), SRS (sounding reference signal), PUSCH (physical uplink shared channel) channel estimation and the like. Meanwhile, the compatibility of the LTE-A and the LTE system is considered, and the system performance is optimized to a greater extent.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.