Concatenated encoding and decoding for multilayer communication protocol

CONCATENATED ENCODING AND DECODING FOR MULTILAYER COMMUNICATION PROTOCOL

<b>background</b>

<b>Field</b>

The present invention relates to a communication system. More particularly, the present invention relates to systems and methods for reducing decoding complexity in communication systems.

<b>background</b>

Communication systems have been developed to be able to transmit information signals from a sending station to a physically separate receiving station. In transmitting an information signal from an originating station through a communication channel, the information signal is first converted into a suitable form for effective transmission through the communication channel. Transformation, or modulation, of an information signal involves changing the parameters of the carrier wave according to the information signal so that the spectrum of the final modulated carrier wave is confined within the communication channel bandwidth. At the receiving station, the original information signal is copied from a modulated carrier wave received over a communication channel. In general, this replication is achieved by using the inverse of the modulation process used by the originating station.

Modulation also facilitates multiple-access, ie, simultaneous transmission/reception, of multiple signals over a common communication channel. A multiple-access communication system includes a plurality of subscriber units requesting intermittent service of relatively short duration rather than continuous access to a common communication channel. Several multiple-access techniques are known in the art, such as time division multiple-access (TDMA), frequency division multiple-access (FDMA), and amplitude modulation multiple-access (AM). Another form of multiple-access technology is code division multiple-according to "TIA/EIA/IS-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wide-Band Spread Spectrum Cellular System", hereinafter referred to as the IS-95 standard. Access (CDMA) is a spread spectrum system. U.S. Patent No. 4,901,307 entitled "SPREAD SPECTRUM MULTIPLE-ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS," and "SYSTEM AND METHOD FOR GENERATING," covering the use of CDMA technology in multiple-access communication systems. VAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM," is disclosed in US Pat. No. 5,103,459.

Multiple-access communication systems may be wireless or wired and may carry voice and/or data. An example of a communication system that carries both voice and data is a system conforming to the IS-95 standard that specifies transmission of voice and data over a communication channel. A method of transmitting data in a fixed-size code channel frame is described in detail in US Pat. No. 5,504,773, entitled "METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION," assigned to the assignee of the present invention. According to the IS-95 standard, data or voice is partitioned into 20 millisecond wide code channel frames with data rates as high as 14.4 Kbps. Another example of a communication system carrying both voice and data is described in the documents 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (W-CDMA standard), or "TR-45.5 Physical Layer for cdma2000 Spread Spectrum Systems." It is a communication system conforming to the "3rd Generation Partnership Project" (3GPP), included in a set of documents including "Standard" (IS-2000 standard).

An example of a data-only communication system is a high data rate (HDR) communication system conforming to the TIA/EIA/IS-856 industry standard, hereinafter referred to as the IS-856 standard. This HDR system is based on the communication system disclosed in co-pending Application No. 08/963,386 entitled "METHOD AND APPARATUS FOR HIGH RATE PACKET DATA TRANSMISSION", filed on November 3, 1997, assigned to the assignee of the present invention. do. The HDR communication system defines a set of data rates ranging from 38.4 Kbps to 2.4 Mbps at which an access point (AP) may transmit data to a subscriber station (access terminal (AT)). Because APs are similar to base stations, the terminology for cells and sectors is the same as for voice systems.

In a multiple-access communication system, communication between users is carried out through one or more base stations. A first user on a first subscriber station communicates with a second user on a second subscriber station by transmitting data over a reverse link to a base station. A base station may receive the data and route the data to another base station. The data is transmitted to the second subscriber-station via the forward link of the same base station, or a different base station. The forward link refers to transmissions from the base station to the subscriber station, and the reverse link refers to transmissions from the subscriber station to the base station. Similarly, communication may be conducted between a first user for a first subscriber station and a second user for a terrestrial station. The base station receives data from the user over the reverse link and routes the data to the second user over the public switched telephone network (PSTN). In many communication systems, for example IS-95, W-CDMA, IS-2000, separate frequencies are assigned to the forward link and the reverse link.

The aforementioned wireless communication service is an example of a point-to-point communication service. Conversely, the broadcast service provides a point-to-multipoint communication service. The basic model of a broadcast system consists of a user's broadcast net served by one or more central stations that transmit specific content, for example news, movies, sporting events, and information with the user's preferences. Each broadcast net user's subscriber-station monitors a common broadcast forward link signal. Because the central office firmly determines the content, users generally do not communicate back. Examples of common use of a broadcast service communication system include TV broadcast, radio broadcast, and the like. Generally, these communication systems are highly specialized, purpose-built communication systems. With recent developments in wireless cellular telephone systems, there has been an interest in using the existing infrastructure of point-to-point cellular telephone systems primarily for broadcast services. (As used herein, the term "cellular" system includes communication systems that use both cellular and PCS frequencies.)

Information signals exchanged between terminals of a communication system often consist of a plurality of packets. To illustrate this, a packet is a group of bytes containing data (payload) and control elements arranged in a specific format. The control element includes, for example, a preamble and a quality matrix. Quality matrices include, for example, cyclic redundancy checks (CRC), parity bit(s), and other types of matrices known to those skilled in the art. The packet is then formatted to fit the frame according to the communication channel structure. A properly modulated frame traveling between an originating terminal and a destination terminal is affected by the characteristics of the communication channel, such as signal-to-noise ratio, fading, time variation, and other characteristics. These characteristics affect different modulated signals in different communication channels. As a result, transmission of a modulated signal over a wireless communication channel requires different considerations than transmission of a modulated signal over a wired communication channel, for example, a coaxial cable or an optical cable. In addition to selecting the appropriate modulation for a particular communication channel, other methods of protecting information signals have been explored. Such methods include, for example, encoding, symbol repetition, interleaving, and other methods known to those skilled in the art. However, these methods increase overhead. Therefore, an engineering trade-off must be made between the reliability of information signal transmission and the amount of overhead. Even with the protection of the information signal described above, the state of the communication channel may deteriorate to the point where the receiving station cannot decode (erasate) any packets. In data-only communication systems that allow feedback communication from a receiving terminal to an originating terminal, one cue uses an automatic retransmission request (ARQ) made by the receiving station to retransmit undecoded packets to the calling station. However, under certain conditions, ARQ may overload the communication system. Also, as described with respect to the broadcast communication system, the subscriber cannot communicate back to the base station. As a result, other means of information protection are desirable.

Co-pending Application No. 09/933,912 entitled "METHOD AND SYSTEM FOR UTILIZATION OF AN OUTER DECODER IN A BROADCAST SERVICES COMMUNICATION SYSTEM," assigned to the assignee of the present invention, and filed on Aug. The use of an external decoder is discussed in detail in Fig. As described in co-pending application No. 09/933,912, first, a bit stream of information to be transmitted is encoded by an outer decoder, and then the encoded stream is encoded by an inner encoder. As shown in FIG. 1 , a bit stream 102 of information to be transmitted, originating from a higher layer, is provided to a transmit buffer 104 . The transmit buffer is shown in more detail in FIG. 2 . Referring to FIG. 2, bits fill the systematic portion 204(1) of the transmit buffer 104 (of FIG. 1) from left to right, row by row. The systematic portion 204 ( 1 ) includes k rows 208 of length L . Referring again to FIG. 1 , when the systematic part 204( 4 ) (of FIG. 2 ) is filled, the outer block encoder 106 , Activated to perform column-wise encoding to create an (nk) additional row 210 (in FIG. 2 ) of parity bits. This column-wise operation is performed column-by-column for binary outer code, ie, m=1. For non-binary codes, ie, m > 1, all m adjacent columns in a row are treated as m-bit symbols. The m-bit symbols along the top k rows are read by the outer encoder to produce nk m-bit symbols that populate the lower nk rows of these columns.

External encoders include, for example, systematic Reed-Solomon (RS) encoders. Referring again to FIG. 1 , the contents of the transmit buffer 104 are provided to the physical layer 108 . At the physical layer 108, individual frames are encoded by an inner encoder (not shown) to generate encoded frames. The structure of the internal decoder is well known to those skilled in the art. The buffer's systematic and parity rows may be interlaced during transmission to reduce the chance of multiple systematic rows being erased when the total number of inner code erasures exceeds the correction capability of the outer code. The frame is further processed according to a selected modulation scheme, for example, cdma2000, WCDMA, UMTS, and other modulation schemes known to those skilled in the art. The processed frame is then transmitted over the communication channel 110 .

The transmitted frame is received at a receiving station and provided to the physical layer 112 . In the physical layer 112, individual frames are demodulated and provided to an inner decoder (not shown). The inner decoder decodes each frame, and if decoding is successful, outputs a correctly decoded frame, and if decoding is unsuccessful, declares an erase. The success or failure of decoding must be determined with high accuracy and is achieved, for example, by including a long (eg 16-bit) cyclic redundancy check (CRC) after the outer encoding and before the inner encoding. The contained CRC obtained from the decoded frame is compared with the CRC calculated from the bits of the decoded frame, and if the two CRCs are equal, the decoding declares success.

If the inner decoder cannot decode the frame, the decoder declares an erase and provides an indication of a lost frame to the outer block decoder 116 . Processing continues until there are correctly received and passed parity frames in the parity portion 114(2) of the receive buffer 114 as there are the same number of erased systematic frames. The receiver stops receiving any remaining frames and an external decoder (not shown) is activated to recover the erased systematic frame. The recovered systematic frame is passed to the upper layer.

It is well known in the art that decoding/error correction computational complexity increases with the value of the number of rows in transmit buffer 104 . Since the decoding/error correction computational complexity affects power consumption as well as hardware complexity at the receiving terminal, a need exists for a method and system.

<b>summary</b>

Embodiments disclosed herein can be performed by encoding systematic bits in each of a plurality of buffers having an outer code, multiplexing the contents of the plurality of buffers, and encoding the multiplexed content with an inner code to provide a set of frames. The above needs are addressed by providing a system and method for implementing the method.

In another aspect of the invention, the received set of frames is decoded by an internal decoder, the correctly decoded frames are de-multiplexed into a plurality of buffers, and the contents of each buffer are further processed. If the systematic portion of the buffer has been decoded correctly, processing includes providing the contents of the systematic portion to a higher layer. Alternatively, if it is determined that decoding of the buffer contents by the external decoder has recovered the systematic part, then the external decoder is activated and the recovered content along with the correctly received content of the systematic part is presented to a higher layer.

<b>Brief description of the drawing</b>

1 is a diagram showing a conventional physical layer processing.

Fig. 2 is a diagram showing a transmission buffer.

3 is a diagram showing physical layer processing according to an embodiment of the present invention.

<b>details</b>

<b>Justice</b>

In this specification, the word "exemplary" is used in the sense of "which may be used as an example, instance, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or useful over other embodiments.

In this specification, the term point-to-point is used to mean communication between two subscriber stations over a dedicated communication channel.

In this specification, the term broadcast communication or point-to-multipoint communication is used to mean a communication in which a plurality of subscriber stations receive a communication from one source.

In this specification, the term packet is used to mean a group of bits that contain data (payload) and control elements, and are arranged in a specific format. Control elements include, for example, preambles, quality matrices, and others known to those skilled in the art. Quality matrices include, for example, cyclic redundancy checks (CRC), parity bits, and others known to those skilled in the art.

In this specification, the term access network is used to mean a collection of a base station (BS) and a controller of one or more base stations. An access network transmits data packets between multiple subscriber stations. The access network may be connected to additional networks outside the access network, such as a corporate intranet or the Internet, and may transmit data packets between each access terminal and the external network.

In this specification, the term base station is used to mean the hardware with which the subscriber station communicates. A cell refers to a hardware or geographic coverage area depending on the context in which the term is used. A sector is a partition of a cell. Because a sector has the properties of a cell, the description of a cell is easily extended to a sector.

In this specification, the term subscriber station is used to mean the hardware with which the access network communicates. A subscriber station may be mobile or stationary. A subscriber station may be any data device that communicates, for example, over a wireless channel or over a wired channel using optical fiber or coaxial cable. A subscriber station may be any number of types of devices including but not limited to PC cards, compact flash, external or internal modems, or wireless or wireline telephones. A subscriber station that is establishing an active traffic channel connection with a base station may be said to be in a connection establishment state. A subscriber station that has established an active traffic channel connection with a base station is called an active subscriber station and is said to be in a traffic state.

In this specification, the term physical channel is used to mean a communication route through which signals described in terms of modulation characteristics and coding propagate.

In this specification, the term logical channel is used to mean a communication route within the protocol layer of a base station or subscriber station.

In the present invention, the term communication channel/link is used to mean a physical channel or a logical channel depending on the context.

In this specification, the term reverse communication channel/link is used to mean a communication channel/link through which a subscriber station transmits a signal to a base station.

In this specification, a forward channel/link is used to mean a communication channel/link through which a base station transmits a signal to a subscriber station.

In this specification, the term soft hand-off is used to mean communication between a subscriber station and two or more sectors, where each sector belongs to a different cell. Reverse link communications are received by all sectors, and forward link communications are carried simultaneously on the forward links of two or more sectors.

In this specification, the term softer hand-off is used to mean communication between a subscriber station and two or more sectors, where each sector belongs to the same cell. Reverse link communications are received by all sectors, and forward link communications are carried simultaneously on one of the forward links of two or more sectors.

In this specification, the term erasure is used to mean a message recognition failure.

In this specification, the term dedicated channel is used to mean a channel that is modulated by information specific to an individual subscriber station.

In this specification, the term common channel is used to mean a channel modulated by information shared between all subscriber stations.

In this specification, the term physical layer is used to mean a part of a communication protocol between an originating terminal and a receiving terminal capable of responding to transmission and reception of data. The physical layer corresponds to layer 1 in the international standard configuration model for open system-to-system connections.

In this specification, the term upper layer(s) is used to mean a part of a communication protocol between a calling terminal and a receiving terminal on top of the physical layer. The upper layers correspond to layers 2 to 7 in the international standard configuration model for open system-to-system connections.

<b>Explanation</b>

According to an embodiment of the present invention, as shown in FIG. 3 , a bit stream 302 of information to be transmitted, originating from an upper layer, is de-multiplexed and provided to a transmit buffer 304(i). Bits fill the systematic portion 306(1) of the transmit buffer 304(1) from left to right, row by row. The systematic portion 306(1) includes k rows of length L. In one embodiment, the length L of the buffer matches the length of the radio frame with no overhead (eg, CRC to aid the inner decoder and tail bits for the inner encoder). When the systematic portion 306(1) of the transmit buffer 304(1) is filled, the procedure is repeated for the remaining transmit buffers 304(2) - 304(p). When the systematic portion 306(i) of the transmit buffer 304(i) is filled, the outer block encoder 310(i) performs column-wise encoding of bits in the systematic portion 306(i)). to generate (nk) additional rows of parity bit 308(i). These column-wise operations are performed column-by-column for the binary outer code, ie, m=1. For non-binary codes, ie, m>1, all m adjacent columns in a row are treated as m-bit symbols. The m-bit symbols along the top k rows are read by the outer encoder to produce nk m-bit symbols that populate the corresponding lower nk rows of these columns.

In another embodiment, the length L of the buffer is equal to the number of bits of the no-overhead radio frame divided by m, which is the dimension of the outer encoder code. In this embodiment, the first m rows from transmit buffer 304(i) are transmitted in the first radio frame, and the second m rows of bits are transmitted in the second radio frame, until the entire buffer is transmitted. is sent When the systematic portion 306(1) of the transmit buffer 304(1) is filled, the procedure is repeated for the remaining transmit buffers 304(2) - 304(p). When the systematic portion 306(i) of the transmit buffer 304(i) is filled, the outer block encoder 310(i) performs column-wise encoding of bits in the systematic portion 304(i)). to generate m(nk) additional rows of parity bit 308(i). These column-wise operations are performed column-by-column for binary outer code, ie, m=1. For a non-binary code, ie, m>1, every m-row of a column forms an m-bit symbol. The k symbols from the top k rows in a column are read by an outer encoder to produce (nk) m-bit symbols that populate the corresponding lower m(nk) rows of this column.

In one embodiment, external encoder 310(i) comprises a systematic Reed-Solomon (RS) encoder. The contents of transmit buffer 304(i) are then provided to multiplexer 312. The multiplexer 312 cycles through the transmit buffers 304(1) - 304(p) so that a block of bits containing a predetermined number of bits is transmitted from the previous buffer 304(i-1) and then continues Select the transmit buffer 304(1). In one embodiment, the predetermined number of bits in the block is equal to L. This method seeks to evenly distribute the corruption of data caused by the interference of the physical channel 316 between the buffers 304(i). However, it will be understood by those skilled in the art that other multiplexing methods are equally applicable and may be utilized without departing from the spirit or scope of the present invention. The multiplexed block of bits is provided to the physical layer 314 of the originating terminal. At the physical layer 314 , additional overhead bits (eg, CRC check) are added to each bit block, and the resulting structure is encoded by an inner encoder (not shown) that generates an encoded frame. The structures of the external and internal encoders and multiplexers may be, for example, those of FIG. 3 . The frame is further processed according to the selected modulation scheme. In one embodiment, processing is performed according to the IS-2000 standard. The processed frame is then transmitted over communication channel 316 .

The transmitted frame is received at a receiving station (not shown) and provided to a physical layer 318 at the receiving station. At the physical layer 318, individual frames are demodulated and provided to an inner decoder (not shown). In one embodiment, the inner decoder decodes each frame and, if decoding is successful, outputs a correctly decoded frame, or declares an erase if decoding fails. The success or failure of decoding must be determined with high accuracy. In one embodiment, accuracy is achieved by including a long (eg, 16-bit) cyclic redundancy check (CRC) in the frame after the outer encoding and before the inner encoding, as described above. However, one of ordinary skill in the art will recognize that other mechanisms for indicating frame quality may be used. The contained CRC obtained from the decoded frame is compared with the CRC calculated from the bits of the decoded frame, and if the two CRCs are equal, the decoding is declared successful. Other processing in the physical layer continues depending on the result of the inner decoder decision.

The correctly decoded frame is provided to a de-multiplexer 320 that distributes the correctly decoded frame among the receive buffers 322(i), using a method opposite to the method used for multiplexing. The systematic from the systematic portion 324(i) of the receive buffer 322(i) if all k frames are correctly decoded by the internal decoder for that particular receive buffer 322(i). The frame is provided on the upper layer.

If the inner decoder is unable to decode the frame, the decoder declares an erase and provides an indication to the de-multiplexer 324 that the frame has been lost. De-multiplexer 324 provides information to an outer block decoder 328(i) communicatively coupled to receive buffer 322(i) to which the frame belongs. Correctly received parity frames accumulated in systematic frame and systematic part 324(i) and parity part 326(i) of receive buffer 322(i) are sufficient, or receive buffer 322(i) ) is filled, the process continues. An external decoder (not shown) is then activated to recover the erased systematic frame. The recovered systematic frame is provided to the upper layer.

According to one embodiment, if the total number of frames correctly received in the receive buffer 322(i) is less than k, the external decoder is not activated because there is no guarantee that the decoding is successful. A correctly received systematic frame with identification of lost bits is provided to the upper layer. In another embodiment, the receiver uses the decoded bits from the internal decoder (which cannot be trusted as indicated by the failed CRC check) to recover the bits for the systematic bits. According to one embodiment, the receiver decodes the unreliable bit from the internal decoder and finds the most probable codeword. In another embodiment, the receiver forms a sub-buffer with k rows using a measure of the signal quality of the erased frame in the buffer to select the erroneously received frame with the highest signal-to-noise ratio. Then, the receiver performs bit flipping (at the same time changing the bit value of 0 to the bit value of 1 in the column and vice versa) and checks whether bit flipping generates a codeword. In one embodiment, bit flipping is performed first for the least reliable bit and continues with the bit in order of increasing reliability of the bit. The reliability of bits is determined by an internal decoding matrix, e.g., similar to the Yamamoto matrix, signal-to-noise and interference ratio during a frame, re-encoded symbol error rate, re-encoded energy matrix, and other matrices known to those skilled in the art. , or may be determined according to the combination of matrices. If no codeword is found, bit flipping continues through all remaining columns for all unreliable rows. If no codeword is found, bit flipping is performed until a codeword is found or all combinations are exhausted, with an incremented number of bits flipped (i.e., up to the maximum number of bits, 2 bits at a time, then 3 change the bit). In another embodiment, the CRC from the unreliable row is used to check the overall success of decoding in this situation. If the CRCs from all rows match, the frame is provided to the upper layer, and if not, only bits from the reliable row are provided to the upper layer.

In another embodiment, to improve the reliability of decoding, demodulation and inner decoding are performed on the k or more correctly received frames in the buffer. According to another embodiment, demodulation and internal decoding are performed for every frame in the buffer. In all embodiments, outer decoding is performed for k (or km) rows with the highest quality. Quality is an internal decoding matrix, e.g., similar to the Yamamoto matrix, signal-to-noise and interference ratio during a frame, re-encoded symbol error rate, re-encoded energy matrix, and other matrices known to those skilled in the art, or It may be determined according to the combination of matrices. The use of quality metrics for quality estimation is described in U.S. Patent Nos. 5,751,725, entitled "METHOD AND APPARATUS FOR DETERMINING THE RATE OF RECEIVED DATA IN A VARIABLE RATE COMMUNICATIONS SYSTEM," and "METHOD AND APPARATUS," all assigned to the assignee of the present invention. FOR DETERMINING DATA RATE OF TRANSMITTED VARIABLE RATE DATA IN A COMMUNICATIONS RECEIVER."

Those skilled in the art will appreciate that the number of transmit buffers 304 and thus receive buffers 322 is a compromise between processing overhead and the amount of potential data loss. A small value of k resulting in more transmit/receive buffers results in increased processing overhead. On the other hand, a large value of k resulting in fewer transmit/receive buffers results in an increase in the transmit buffer size, discarding large blocks when the contents of the transmit buffer cannot be recovered due to (nk) or more row erasures. make it Also, a large buffer size increases the memory request at the receiving terminal.

Those of skill in the art will appreciate that information and signals may be represented using any of a variety of different technologies. For example, data, instructions, instructions, information, signals, bits, symbols, and chips to which reference may be made throughout the above detailed description may include voltages, currents, electromagnetic waves, magnetic fields or particles, optics or particles, or any combination thereof. may be expressed as

Those of skill in the art will appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations thereof. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Such functionality is implemented as hardware or software depending on the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but should not be interpreted as causing a departure from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein include general purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), and circuits designed to perform the functionality described herein. It may be implemented and implemented as a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or combinations thereof. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, eg, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors coupled with a DSP core, or other configuration.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be included directly in hardware, a software module executed by a processor, or a combination thereof. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. . An exemplary storage medium is coupled to the processor, the processor capable of reading information from, and writing information to, the storage medium. Alternatively, the storage medium may be integral to the processor. A processor and storage medium may be integral to the processor. The ASIC may reside in the user terminal. Alternatively, the processor and storage medium may reside as separate components of the user terminal.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Portions of the disclosure of this patent document contain material subject to copyright protection. The copyright owner has no objection to facsimile reproduction by way of patent documents or patent disclosures, as indicated in the Patent and Trademark Office patent files, but retains all copyrights.