US 20070071149 A1
Systems and methods are provided for enhancing signal quality at receivers in a wireless network. In one embodiment, an antenna is selected from a subset of antennas based on a signal quality parameter such as received signal power or signal-to-noise ratio (SNR). In another embodiment, multiple antennas are applied to independent signal processing paths for the respective antennas where output from the paths is then combined to enhance overall signal quality at the receiver.
1. A receiver processing method on a forward link of a multicast wireless network, comprising:
receiving a signal from at least two antennas across a wireless network;
processing the signal in at least two signal paths for the two antennas; and
combining the signals at an output from the signal paths to facilitate signal reception for a wireless device.
2. The method of
3. The method of
4. The method of
5. The method of
6. The method of
7. The method of
8. The method of
9. The method of
10. The method of
y i =c i,1 *r i,1 +c i,2 *r i,2,
where * denotes a complex conjugate.
11. The method of
12. A computer readable medium having computer executable instructions stored thereon to execute components of a wireless receiver, comprising:
receiving a signal from two or more antennas in a wireless receiver;
processing the signal in at least two signal chains in the wireless receiver; and
combining output from the two signal chains according to a maximum ratio signal between the two signal chains.
13. The computer readable medium of
14. The computer readable medium of
15. The computer readable medium of
16. The computer readable medium of
17. A wireless communications apparatus, comprising:
at least a first radio frequency processing channel to process a signal from at least one antenna from a subset of antennas;
at least a second radio frequency processing channel to process the signal from at least a second antenna from a subset of antennas;
a memory that includes a component to determine signal quality for the subset of antennas; and
a processor that facilitates signal processing for at least one wireless apparatus associated with the subset of antennas.
18. The apparatus of
19. The apparatus of
20. A wireless communications device, comprising:
means for receiving a signal at a wireless device from at least two signal sources;
means for processing the signal in a first signal chain;
means for processing the signal in a second signal chain; and
means for combining the first and the second signal chains.
21. The device of
22. The device of
23. The device of
24. The device of
25. The device of
26. The device of
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/721,373 filed on Sep. 27, 2005, entitled “SWITCHING DIVERSITY IN BROADCAST OFDM SYSTEMS BASED ON MULTIPLE RECEIVE ANTENNAS” the entirety of which is incorporated herein by reference.
The subject technology relates generally to communications systems and methods, and more particularly to systems and methods that enhance receiver performance in a wireless system by exploiting multiple antennas at the receiver.
One technology that has dominated wireless systems is Code Division Multiple Access (CDMA) digital wireless technology. In addition to CDMA, an air interface specification defines FLO (Forward Link Only) technology that has been developed by an industry-led group of wireless providers. In general, FLO has leveraged the most advantageous features of wireless technologies available and used the latest advances in coding and system design to consistently achieve the highest-quality performance. One goal is for FLO to be a globally adopted standard.
The FLO technology was designed in one case for a mobile multimedia environment and exhibits performance characteristics suited ideally for use on cellular handsets. It uses the latest advances in coding and interleaving to achieve the highest-quality reception at all times, both for real-time content streaming and other data services. FLO technology can provide robust mobile performance and high capacity without compromising power consumption. The technology also reduces the network cost of delivering multimedia content by dramatically decreasing the number of transmitters needed to be deployed. In addition, FLO technology-based multimedia multicasting complements wireless operators' cellular network data and voice services, delivering content to the same cellular handsets used on 3G networks.
The FLO wireless system has been designed to broadcast real time audio and video signals, apart from non-real time services to mobile users. The respective FLO transmission is carried out using tall and high power transmitters to ensure wide coverage in a given geographical area. In a broadcast Orthogonal Frequency Division Multiplexing (OFDM) system such as FLO, respective OFDM symbols are organized into frames having physical layer packets that are encoded with a Reed-Solomon (R-S) code and distributed across the frames to exploit time-diversity of a fading channel. Time diversity implies that several channel realizations are observed over the duration of each code block and hence, the packets can be recovered even if there was a deep fade during some of the packets. However, for very low speeds of a mobile handset or receiver (small Doppler spread), the channel coherence time is long compared to the time-span of a Reed-Solomon code block and thus, the channel evolves slowly. As a result, little time-diversity can be gained within a Reed-Solomon code block (for FLO, a Reed-Solomon code block spans across four frames. As a result, the duration of a Reed-Solomon code block is approximately 0.75 second). The prior approach was to use a single receive antenna on the handset. However, as the speed of the mobile handset (or Doppler spread) changes, especially for low Doppler spread scenarios, the performance of single receive antenna FLO receiver architectures can degrade.
The following presents a simplified summary of various embodiments in order to provide a basic understanding of some aspects of the embodiments. This summary is not an extensive overview. It is not intended to identify key/critical elements or to delineate the scope of the embodiments disclosed herein. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.
Systems and methods are provided to facilitate receiver performance in a broadcast wireless network by employing multiple antennas at the receiver that cooperate to enhance signal quality in the receiver. In one embodiment, at least two antennas are employed at the receiver, where the antennas are monitored and switching components are utilized to select an antenna from a subset of antennas. The selected antenna from the subset generally provides the strongest signal power, highest signal-to-noise ratio (SNR), or other signal quality parameter at the receiver thus enhancing the quality of signal to be processed at the receiver. In another embodiment, a dual-track (or multi-track) approach is applied where multiple antennas are adapted to separate receiver processing paths. Respective output from the paths is then combined in what is referred to as a maximum ratio combining technique to enhance overall signal quality at the receiver.
To the accomplishment of the foregoing and related ends, certain illustrative embodiments are described herein in connection with the following description and the annexed drawings. These aspects are indicative of various ways in which the embodiments may be practiced, all of which are intended to be covered.
Systems and methods are provided for enhancing signal quality at receivers in a wireless network. In one embodiment, an antenna is selected from a subset of antennas based on a signal quality parameter such as received signal power or signal-to-noise ratio (SNR). In another embodiment, multiple antennas are applied to independent signal processing paths for the respective antennas where output from the paths is then combined to enhance overall signal quality at the receiver. By employing multiple receive antennas, and selecting from a subset of antennas or providing independent processing paths for the antennas, signal quality and hence performance of the receiver can be improved in the wireless network.
As used in this application, the terms “component,” “network,” “system,” and the like are intended to refer to a computer-related entity, either hardware, a combination of hardware and software, software, or software in execution. For example, a component may be, but is not limited to being, a process running on a processor, a processor, an object, an executable, a thread of execution, a program, and/or a computer. By way of illustration, both an application running on a communications device and the device can be a component. One or more components may reside within a process and/or thread of execution and a component may be localized on one computer and/or distributed between two or more computers. Also, these components can execute from various computer readable media having various data structures stored thereon. The components may communicate over local and/or remote processes such as in accordance with a signal having one or more data packets (e.g., data from one component interacting with another component in a local system, distributed system, and/or across a wired or wireless network such as the Internet).
With respect to the first receiver configuration 120, by employing two or more diversity antennas and switching to the antenna with stronger Received Signal Strength Indication (RSSI) or higher Signal-to-Noise Ratio (SNR), the configuration 120 exploits antenna diversity and improves receiver performance. In one example, this is beneficial for slow fading channels to compensate for the lack of time-diversity. Due to the bursting nature of Forward Link Only (FLO) transmissions, the RSSI measurement, SNR calculation (or other parameter measurement) and antenna selection is performed before the start of Multicast Logical Channel (MLC) processing. Thus, decoding of respective OFDM symbols of interest are generally not affected. The added power consumption for RSSI measurement or SNR calculation and antenna selection is also fairly insignificant. In the presence of antenna differential, switching diversity can be turned off at high Doppler spread so that performance in this scenario should not be impacted. The RSSI can be calculated based on Low Noise Amplifier (LNA) state information and the Automatic Gain control (AGC) loop accumulator values in a straightforward manner.
It is noted that in one approach, an algorithm can be employed to estimate noise variance at the receiver. The base-band composite received power which includes power from both signal and noise is also computed. The ratio of the composite received power to the estimated noise variance is taken and serves as an indication of the received SNR. The antenna with higher received SNR is selected and used for data reception of the current frame. Another switching technique can be to select the antenna independently at each sub-carrier (or combine the two observations). However, this can increase receiver complexity, since it may employ a second set of RF chains, having two FFT blocks at the base-band and the per sub-carrier antenna selection logic.
It is noted that in another approach, an antenna switching scheme can be based on effective SNR. The effective SNR is an indication of received signal quality when the channel realization varies across a code word (due to time-variation or frequency variation or both). The effective SNR can be a monotonous function of the average constrained capacity. For an OFDM symbol, the average constrained capacity for a set of subcarriers with a common modulation scheme m is calculated as the following:
where Hi,k is a channel estimate for subcarrier k of OFDM symbol i, and σ2 is the variance of the additive noise/interference. The constrained capacity function φm(.) generally depends on the modulation scheme m, e.g., QPSK, 16QAM, and so forth. The average constrained capacity is a monotonous function of the effective SNR, with higher effective SNR representing higher average constrained capacity. Therefore, antenna selection can be determined by the average constrained capacity. In this scheme, the average constrained capacity can be calculated for the preamble symbols reserved for antenna selection for both antennas based on the channel estimate and noise variance estimate according Equation (1). The antenna with higher average constrained capacity (hence higher effective SNR) can be selected and used for data reception. For the case in which the subcarriers for the OFDM symbol of interest are modulated by different modulation schemes, one possibility of the antenna selection is based on the average constrained capacity of the subcarriers with the lowest modulation size. In this case, the summation in Equation (1) should be over the subcarriers with the lowest modulation size.
In addition to switching diversity provided at 120 between antennas in the subset 110, a maximum ratio combining (MRC) technique for a FLO-like broadcast OFDM system is provided at the configuration 160. Being different from the switching diversity scheme which selects the antenna with stronger RSSI or higher SNR for reception and demodulation based on the overall received power at each antenna at 120, maximum ratio combining combines received signals from the designated antennas in the subset 110 independently at each sub-carrier post Fast Fourier Transform (FFT) processing. An example diagram of an MRC in a FLO-like OFDM system is illustrated in
As noted above, one approach for signal processing is to have at least two separate antennas on a receiver handset. For simplicity, the following discussion is related to having two receive antennas, however it is to be appreciated that the systems and methods described herein can be readily generalized to more than two receive antennas in the subset 110. In addition, though the system 100 is motivated in part by the desire to improve performance at low Doppler spreads, it is not generally coupled to Reed-Solomon (R-S) coding and facilitates signal performance even when such coding is absent. For FLO-like OFDM broadcast systems, typically a fraction of the frame duration is used to transmit packets of interest to the receiver. These packets could correspond to particular content being broadcast, and multiple content channels can be multiplexed into the respective frame. These set of packets of interest can be referred to as an MLC (Multicast Logical Channel). To reduce power consumption, the receiver is typically operating during the OFDM symbols of interest and a small number of preamble and post-amble symbols for the frame.
Typically, before the start of an MLC of a current frame, the AGC 254 powers up and a first antenna 210 is connected to the RF chain. At the end of the AGC acquisition period, based on the information of the current LNA gain state and the AGC loop accumulator, a received signal strength indication (RSSI) of the first antenna is calculated at 264. Then, a second antenna is selected by the switch 260 and connected to the RF chain. After the AGC acquisition period for the second antenna elapses, its RSSI is calculated at 264 and compared with that of the first antenna 210. The antenna with higher RSSI is selected and used for data reception of the current frame. Therefore, at least two AGC acquisition periods of OFDM symbols can be employed to perform a decision on antenna selection prior to the subsequent preamble and MLC symbols. To reduce receiver power consumption, during AGC acquisition and RSSI measurement, successive blocks of AGC can be turned off. An alternative embodiment is to have two sets of RF chains and A/D, DC, and DGVA blocks implemented so that AGC acquisition and RSSI calculation for both antennas can proceed concurrently as described below with respect to
For the system 200, antenna switching is generally not allowed during the data demodulation of a frame. That is, antenna selection is made once per frame. An alternative method is to have other or higher antenna switching rates such as once per MLC assuming a suitable gap between MLCs for antenna selection. This can also include switching during an MLC provided that time-averaging of the channel estimates is disabled. For very slow antenna selection rates, lesser diversity is realized in fading channels since the selected antenna may not remain the best antenna as the channel changes. Very high antenna switching rates could help in continuing to provide antenna diversity at higher Doppler spreads. However, switching an antenna during MLC demodulation could disrupt the base-band receiver operations such as AGC and channel estimation averaging. Switching at high rate can also increase the receiver power consumption. As can be appreciated, the system 200 can be employed as part of a wireless communications device. This can include means for monitoring a subset of antennas at a wireless device (e.g., RSSI component 264), means for selecting one antenna from the subset of antennas (e.g., Antenna analog switch 260); and means for processing a signal from the selected antenna (e.g., RF filter, low noise amplifier (LNA) 224, mixer 230, analog base-band low-pass filter 234, an A/D converter 240, a digital filter 244, a DC correction component 250, and an automatic gain control (AGC) 254).
Other components in the switching system 200 can include an automatic frequency control (AFC) 270 that receives input from the DGVA 254. Output from the AFC 270 then feeds a sample buffer 272, a Fast Fourier Transform (FFT) component 274, and a de-channelization component 276. A timing component 278 and a channel estimation component 280 can be employed as feedback elements. Other components in the switching system 200 can include a decoding metric generator 282, a de-interleaving component 284, a descrambling component 286, and a turbo decoder 288.
The first switching processing option 310 may be of generally more interest when there is differential between two or more antennas. For FLO systems, the primary antenna may have a gain that is approximately 5 dB higher than the secondary antenna. The gain on the second antenna could be lesser because it is tuned to operate in different frequency band (e.g., CDMA) or due to form factor considerations, for example. By having the switching block always on, for high Doppler spread there is a possibility that the secondary antenna is chosen during RSSI measurement while it turns out that the primary antenna has stronger received power during most of the MLC of interest. As a result, turning on the switching block only for low vehicular speed (small Doppler spread) can be beneficial. A method can be adopted to estimate the Doppler spread based on channel estimates of adjacent OFDM symbols. Thus, the switching diversity block is turned on only when the channel time correlation is higher than a pre-determined threshold. It is noted that a second antenna if employed can be mounted internally due to form factor considerations.
The receiver chains 410 and 414 operate concurrently during demodulation of MLC symbols of interest as well as demodulation of preamble and post-amble symbols. Signal received on the antennas 416 and 418 are processed by the receiver chains 410 and 414 separately up to the output of an FFT and channel estimation blocks at 480 and 482 respectively. The FFT output and channel estimate of the receiver chains are then combined at 466 (Maximal Ratio Combining (MRC) block) on a per sub-carrier basis to maximize signal-to-noise ratio and sent to successive blocks for decoding at 468-476. Each receiver chain maintains its own LNA gain state, DVGA gain, DC correction, frequency and time tracking, for example.
At the FFT output at 480 and 482 respectively, let the received signal on the i-th sub-carrier be ri,1 and ri,2 for receiver chain #1 and #2, respectively, and the frequency-domain channel estimate of sub-carrier i be ci,1 and ci,2 for receiver chain #1 and #2, respectively. The MRC block 466 combines the output of the two receiver chains for the i-th sub-carrier as following:
The FLO air interface specification typically does not specify the upper layers to allow for design flexibility in support of various applications and services. These layers are shown to provide context. The Stream Layer includes multiplexes up to three upper layer flows into one logical channel, binding of upper layer packets to streams for each logical channel, and provides packetization and residual error handling functions. Features of the Medium Access Control (MAC) Layer includes controls access to the physical layer, performs the mapping between logical channels and physical channels, multiplexes logical channels for transmission over the physical channel, de-multiplexes logical channels at the mobile device, and/or enforces Quality of Service (QOS) requirements. Features of Physical Layer include providing channel structure for the forward link, and defining frequency, modulation, and encoding requirements
In general, FLO technology utilizes Orthogonal Frequency Division Multiplexing (OFDM), which is also utilized by Digital Audio Broadcasting (DAB), Terrestrial Digital Video Broadcasting (DVB-T), and Terrestrial Integrated Services Digital Broadcasting (ISDB-T). Generally, OFDM technology can achieve high spectral efficiency while effectively meeting mobility requirements in a large cell SFN. Also, OFDM can handle long delays from multiple transmitters with a suitable length of cyclic prefix; a guard interval added to the front of the symbol (which is a copy of the last portion of the data symbol) to facilitate orthogonality and mitigate inter-carrier interference. As long as the length of this interval is greater than the maximum channel delay, reflections of previous symbols are removed and the orthogonality is preserved.
Typically, each super frame consists of 200 OFDM symbols per MHz of allocated bandwidth (1200 symbols for 6 MHz), and each symbol contains 7 interlaces of active sub-carriers. Each interlace is uniformly distributed in frequency, so that it achieves the full frequency diversity within the available bandwidth. These interlaces are assigned to logical channels that vary in terms of duration and number of actual interlaces used. This provides flexibility in the time diversity achieved by any given data source. Lower data rate channels can be assigned fewer interlaces to improve time diversity, while higher data rate channels utilize more interlaces to minimize the radio's on-time and reduce power consumption.
The acquisition time for both low and high data rate channels is generally the same. Thus, frequency and time diversity can be maintained without compromising acquisition time. Most often, FLO logical channels are used to carry real-time (live streaming) content at variable rates to obtain statistical multiplexing gains possible with variable rate codecs (Compressor and Decompressor in one). Each logical channel can have different coding rates and modulation to support various reliability and quality of service requirements for different applications. The FLO multiplexing scheme enables device receivers to demodulate the content of the single logical channel it is interested in to minimize power consumption. Mobile devices can demodulate multiple logical channels concurrently to enable video and associated audio to be sent on different channels.
Error correction and coding techniques can also be employed. Generally, FLO incorporates a turbo inner code13 and a Reed Solomon (RS) 14 outer code. Typically, the turbo code packet contains a Cyclic Redundancy Check (CRC). The RS code need not be calculated for data that is correctly received, which, under favorable signal conditions, results in additional power savings. Another aspect is that the FLO air interface is designed to support frequency bandwidths of 5, 6, 7, and 8 MHz. A highly desirable service offering can be achieved with a single Radio Frequency channel.
Proceeding to 710, an antenna subset is selected. As previously noted, at least two antennas are typically employed for the antenna subset but more than two antennas are possible. Based on a desired receiver configuration, two processing paths are possible for the determined antenna subset at 714 and 718. If the process path 718 is selected, signals from the antenna subset 710 are monitored measured or sampled for various signal parameters such as received signal strength or signal-to-noise ratio. At 730, based on the measurements at 720, an antenna is selected from the subset for receiving a wireless signal. As previously noted, switching decisions can be performed at different times and under differing situations. For instance, in some cases, switching decisions may be performed during specified times such as during detected movement of a receiver. In other cases, monitoring and switching of antennas may be performed at regular intervals such as between super frames or between super frame subsets. At 740, signals from the selected antenna are processed through the respective receiver. This can include amplifying, mixing, digital or analog conversions, filtering, gain controlling, FFT computations, channel estimations, buffering, decoding, descrambling, and so forth.
If the path at 718 is taken in the process 700, a separate signal processing path can be assigned for each antenna employed by the receiver at 750. Such processing paths for the respective antennas can include filters, mixers, amplifiers, gain controllers, buffers, timing components, FFT components, and channel estimation components, for example. At 760, outputs from the individual processing paths are combined. Such combining can include analog processes, digital processes, or a combination thereof and include processes such as maximal ratio combining, for example. At 770, the combined signals from the respective antenna subset and signal processing paths are further processed in a wireless receiver. Such processing can include de-channelization, decoding, de-interleaving, descrambling, and so forth.
User device 800 can additionally comprise memory 808 that is operatively coupled to processor 806 and that stores information related to calculated ranks for user device 800, a rank calculation protocol, lookup table(s) comprising information related thereto, and any other suitable information for supporting list-sphere decoding to calculate rank in a non-linear receiver in a wireless communication system as described herein. Memory 808 can additionally store protocols associated rank calculation, matrix generation, etc., such that user device 800 can employ stored protocols and/or algorithms to achieve rank determination in a non-linear receiver as described herein.
It will be appreciated that the data store (e.g., memories) components described herein can be either volatile memory or nonvolatile memory, or can include both volatile and nonvolatile memory. By way of illustration, and not limitation, nonvolatile memory can include read only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM), which acts as external cache memory. By way of illustration and not limitation, RAM is available in many forms such as synchronous RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), Synchlink DRAM (SLDRAM), and direct Rambus RAM (DRRAM). The memory 808 of the subject systems and methods is intended to comprise, without being limited to, these and any other suitable types of memory. User device 800 further comprises a background monitor 814 for processing FLO data, a symbol modulator 814 and a transmitter 816 that transmits the modulated signal.
A modulator 922 can multiplex a signal for transmission by a transmitter 924 through transmit antenna 908 to user devices 904. FLO channel component 918 can append information to a signal related to an updated data stream for a given transmission stream for communication with a user device 904, which can be transmitted to user device 904 to provide an indication that a new optimum channel has been identified and acknowledged. In this manner, base station 902 can interact with a user device 904 that provides FLO information and employs a decoding protocol in conjunction with a non-linear receiver, such as an ML-MIMO receiver, and so forth.
Referring now to
TMTR 1020 receives and converts the stream of symbols into one or more analog signals and further conditions (e.g., amplifies, filters, and frequency up converts) the analog signals to generate a downlink signal suitable for transmission over the wireless channel. The downlink signal is then transmitted through an antenna 1025 to the terminals. At terminal 1030, an antenna 1035 receives the downlink signal and provides a received signal to a receiver unit (RCVR) 1040. Receiver unit 1040 conditions (e.g., filters, amplifies, and frequency down converts) the received signal and digitizes the conditioned signal to obtain samples. A symbol demodulator 1045 demodulates and provides received pilot symbols to a processor 1050 for channel estimation. Symbol demodulator 1045 further receives a frequency response estimate for the downlink from processor 1050, performs data demodulation on the received data symbols to obtain data symbol estimates (which are estimates of the transmitted data symbols), and provides the data symbol estimates to an RX data processor 1055, which demodulates (i.e., symbol de-maps), de-interleaves, and decodes the data symbol estimates to recover the transmitted traffic data. The processing by symbol demodulator 1045 and RX data processor 1055 is complementary to the processing by symbol modulator 1015 and TX data processor 1010, respectively, at access point 1005. Other components that may be provided include a TX data processor 1060, a symbol modulator 1065, a transmitter unit 1070, a receiver unit 1075, a symbol demodulator 1080, an RX data processor 1085, and a processor 1090.
Processors 1090 and 1050 direct (e.g., control, coordinate, manage, etc.) operation at access point 1005 and terminal 1030, respectively. Respective processors 1090 and 1050 can be associated with memory units (not shown) that store program codes and data. Processors 1090 and 1050 can also perform computations to derive frequency and impulse response estimates for the uplink and downlink, respectively.
For a multiple-access system (e.g., FDMA, OFDMA, CDMA, TDMA, etc.), multiple terminals can transmit concurrently on the uplink. For such a system, the pilot subbands may be shared among different terminals. The channel estimation techniques may be used in cases where the pilot subbands for each terminal span the entire operating band (possibly except for the band edges). Such a pilot subband structure would be desirable to obtain frequency diversity for each terminal. The techniques described herein may be implemented by various means. For example, these techniques may be implemented in hardware, software, or a combination thereof. For a hardware implementation, the processing units used for channel estimation may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. With software, implementation can be through modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in memory unit and executed by the processors 1090 and 1050.
For a software implementation, the techniques described herein may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in memory units and executed by processors. The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.
What has been described above includes exemplary embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the embodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations are possible. Accordingly, these embodiments are intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term “includes” is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is interpreted when employed as a transitional word in a claim.