(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2005/0243774 A1
`Choi et al.
`(43) Pub. Date:
`Nov. 3, 2005
`
`US 2005O243774A1
`
`(54) REPETITION CODING FOR A WIRELESS
`SYSTEM
`(75) Inventors: Won-Joon Choi, Sunnyvale, CA (US);
`Qinfang Sun, Cupertino, CA (US);
`Jeffrey M. Gilbert, Sunnyvale, CA
`(US)
`Correspondence Address:
`VAN PELT, YI & JAMES LLP
`10050 N. FOOTHILL BLVD #200
`CUPERTINO, CA 95.014 (US)
`(73) Assignee: Atheros Communications, Inc.
`(21) Appl. No.:
`10/666,952
`
`(22) Filed:
`
`Sep. 17, 2003
`
`Publication Classification
`
`(51) Int. Cl. ............................................. H04B 71216
`(52) U.S. Cl. .............................................................. 370/335
`
`(57)
`
`ABSTRACT
`
`A System and method are disclosed for transmitting data
`over a wireleSS channel. In Some embodiments, transmitting
`data includes receiving convolutionally encoded data and
`enhancing the transmission of the data by further repetition
`encoding the data.
`
`TRANSMTTER
`202
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`204
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`2O6
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`208
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`210
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`CONVOLUONAL
`NCODER
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`802.11a
`INTERLEAVER
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`RTITION
`ENCOOER
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`PSEUDORANDOM
`MASK
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`DELL-1008
`10,079,707
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`

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`Patent Application Publication Nov. 3, 2005 Sheet 1 of 5
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`Patent Application Publication
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`Patent Application Publication Nov. 3, 2005 Sheet 4 of 5
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`Patent Application Publication Nov. 3, 2005 Sheet 5 of 5
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`US 2005/0243774 A1
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`

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`US 2005/0243774 A1
`
`Nov. 3, 2005
`
`REPETITION CODING FOR AWIRELESS
`SYSTEM
`
`FIELD OF THE INVENTION
`0001. The present invention relates generally to a data
`transmission Scheme for a wireleSS communication System.
`More Specifically, a repetition coding Scheme for a wireleSS
`System is disclosed.
`
`BACKGROUND OF THE INVENTION
`0002 The IEEE 802.11a, 802.11b, and 802.11g stan
`dards, which are hereby incorporated by reference, Specify
`wireleSS communications Systems in bands at 2.4 GHz and
`5 GHz. The combination of the 802.11a and 802.11g stan
`dards, written as the 802.11a/gstandard, will be referred to
`repeatedly herein for the purpose of example. It should be
`noted that the techniques described are also applicable to the
`802.11b standard where appropriate. It would be useful if
`alternate Systems could be developed for communication
`over an extended range or in noisy environments. Such
`communication is collectively referred to herein as extended
`range communication. The IEEE 802.11a/g Standard Speci
`fies a robust data encoding Scheme that includes error
`correction. However, for extended range communication, a
`more robust data transmission Scheme at reduced data rates
`is required.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0003. The present invention will be readily understood by
`the following detailed description in conjunction with the
`accompanying drawings, wherein like reference numerals
`designate like Structural elements, and in which:
`0004 FIG. 1A is a diagram illustrating the data portion
`of a regular 802.11a/g OFDM packet.
`0005 FIG. 1B is a diagram illustrating the data portion
`of a modified 802.11a/g OFDM packet where each symbol
`is repeated twice (r=2).
`0006 FIG. 2A is a diagram illustrating a transmitter
`System with a repetition encoder placed after the output of
`an interleaver such as the one specified in the IEEE
`802.11a/g Specification.
`0007 FIG. 2B is a diagram illustrating a receiver system
`for receiving a signal transmitted by the transmitter System
`depicted in FIG. 2A.
`0008 FIG. 3A is a diagram illustrating a transmitter
`System with a repetition encoder placed before the input of
`an interleaver designed to handle repetition coded bits Such
`as the one described below
`0009 FIG. 3B is a diagram illustrating a receiver system
`for receiving a signal transmitted by the transmitter System
`depicted in FIG. 3A.
`0010 FIGS. 4A-4C are tables illustrating an interleaver.
`DETAILED DESCRIPTION
`0011. It should be appreciated that the present invention
`can be implemented in numerous ways, including as a
`
`process, an apparatus, a System, or a computer readable
`medium Such as a computer readable Storage medium or a
`computer network wherein program instructions are Sent
`over optical or electronic communication linkS. It should be
`noted that the order of the Steps of disclosed processes may
`be altered within the scope of the invention.
`0012. A detailed description of one or more preferred
`embodiments of the invention is provided below along with
`accompanying figures that illustrate by way of example the
`principles of the invention. While the invention is described
`in connection with Such embodiments, it should be under
`stood that the invention is not limited to any embodiment.
`On the contrary, the scope of the invention is limited only by
`the appended claims and the invention encompasses numer
`ous alternatives, modifications and equivalents. For the
`purpose of example, numerous Specific details are Set forth
`in the following description in order to provide a thorough
`understanding of the present invention. The present inven
`tion may be practiced according to the claims without Some
`or all of these Specific details. For the purpose of clarity,
`technical material that is known in the technical fields
`related to the invention has not been described in detail So
`that the present invention is not unnecessarily obscured.
`0013 In a typical system as described below, bits repre
`Senting a set of data that is to be communicated are convo
`lutionally encoded or otherwise transformed into values.
`Various types of modulation may be used such as BPSK,
`QPSK, 16QAM or 32OAM. In the case of BPSK, which is
`described further herein, each BPSK symbol may have one
`of two values and each BPSK symbol corresponds to one bit.
`An OFDM symbol includes 48 values that are transmitted on
`different Subchannels. To provide extended range, each
`value that is Sent is repeated Several times by the transmitter.
`In one embodiment, the bits are convolutionally encoded
`using the same encoding Scheme as the encoding Scheme
`specified for the IEEE 802.11a/g standard. Each encoded
`value is repeated and transmitted. Preferably, the values are
`repeated in the frequency domain, but the values may also
`be repeated in the time domain. In Some embodiments, the
`repetition coding is implemented before interleaving and a
`Specially designed interleaver is used to handle repeated
`values. In addition, a pseudorandom code may be Superim
`posed on the OFDM symbols to lower the peak to average
`ratio of the transmitted Signal.
`0014. The receiver combines each of the signals that
`correspond to the repetition coded values and then uses the
`combined Signal to recover the values. In embodiments
`where the values are combined in the frequency domain, the
`Signals are combined coherently with correction made for
`different subchannel transfer functions and phase shift
`errors. For the purpose of this description and the claims,
`“coherently” combining should not be interpreted to mean
`that the Signals are perfectly coherently combined, but only
`that Some phase correction is implemented. The Signals from
`different Subchannels are weighted according to the quality
`of each Subchannel. A combined Subchannel weighting is
`provided to a Viterbi detector to facilitate the determination
`of the most likely transmitted Sequence.
`
`

`

`US 2005/0243774 A1
`
`Nov. 3, 2005
`
`0.015 Using the modulation and encoding scheme incor
`porated in the IEEE 802.11a/g Standard, the required signal
`to noise ratio decreases linearly with data rate assuming the
`Same modulation technique and base code rate are not
`changed and repetition coding is used. Some further gains
`could be achieved through the use of a better code or outer
`code. However, in a dual mode System that is capable of
`implementing both the IEEE 802.11a/g standard and an
`extended range mode, the complexity introduced by those
`techniques may not be worth the limited gains that could be
`achieved. Implementing repetition of values is in compari
`Son Simpler and more efficient in many cases.
`0016. The repetition code can be implemented either in
`the time domain or in the frequency domain. For time
`domain repetition, the OFDM symbols in the time domain
`(after the IFFT operation) are repeated a desired number of
`times, depending on the data rate. This Scheme has an
`advantage in efficiency Since just one guard interval is
`required for r-repeated OFDM symbols in the time domain.
`0017 FIG. 1A is a diagram illustrating the data portion
`of a regular 802.11a/g OFDM packet. Each OFDM symbol
`102 is separated by a guard band 104. FIG. 1B is a diagram
`illustrating the data portion of a modified 802.11a/g OFDM
`packet where each Symbol is repeated twice (r=2). Each set
`of repeated Symbols 112 is separated by a single guard band
`104. There is no need for a guard band between the repeated
`symbols.
`0018. The OFDM symbols can also be repeated in the
`frequency domain (before the IFFT). The disadvantage of
`this Scheme is that one guard interval has to be inserted
`between every OFDM symbol in the time-domain since the
`OFDM symbols with frequency-domain repetition are not
`periodic. However, repetition in the frequency domain can
`achieve better multipath performance if the repetition pat
`tern is configured in the frequency-domain to achieve fre
`quency diversity.
`0019. In a typical environment where signals are reflected
`one or more times between the transmitter and the receiver,
`it is possible that certain reflections and direct Signals will
`tend to cancel out at the receiver because the phase differ
`ence between the paths could be close to 180 degrees. For
`different frequencies, the phase difference between the paths
`will be different and So Spreading the repeated values among
`different frequencies to achieve frequency diversity ensures
`that at least Some of the values will arrive at the receiver with
`Sufficient signal Strength to be combined and read. To
`maximize the benefit of frequency diversity, it is preferable
`to repeat values acroSS Subchannels that are as widely spaced
`as is practicable, Since the phase difference between adjacent
`Subchannels is Small.
`0020 FIG. 2A is a diagram illustrating a transmitter
`System with a repetition encoder placed after the output of
`an interleaver such as the one specified in the IEEE
`802.11a/g specification. In this example system, BPSK
`modulation is implemented and the repetition encoder and
`the interleaver are described as operating on bits, which is
`equivalent to operating on the corresponding values. In other
`embodiments, other modulation Schemes may be used and
`values may be repeated and interleaved. The interleaver is
`included in the IEEE 802.11a/g transmitter specification for
`
`the purpose of changing the order of the bits Sent to remove
`correlation among consecutive bits introduced by the con
`volutional encoder. Incoming data is convolutionally
`encoded by convolutional encoder 202. The output of con
`volutional encoder 202 is interleaved by IEEE 802.11a/g
`interleaver 204. Repetition encoder 206 repeats the bits and
`pseudorandom mask combiner 208 combines the output of
`repetition encoder 206 with a pseudorandom mask for the
`purpose of reducing the peak to average ratio of the Signal,
`as is described below. The signal is then processed by IFFT
`processor 210 before being transmitted.
`0021
`FIG. 2B is a diagram illustrating a receiver system
`for receiving a signal transmitted by the transmitter System
`depicted in FIG. 2A. The received signal is processed by
`FFT processor 220. The output of FFT processor 220 is input
`to mask remover 218 which removes the pseudorandom
`mask. Data combiner 216 combines the repetition encoded
`data into a stream of nonrepetitive data. The operation of
`data combiner 216 is described in further detail below. IEEE
`802.11a/g deinterleaver 214 deinterleaves the data and Vit
`erbi decoder 212 determines the most likely Sequence of
`data that was input to the transmission System originally.
`0022. The system depicted in FIGS. 2A and 2B can use
`the same interleaver and deinterleaver as the regular
`802.11a/g System, and also has flexibility in designing the
`repetition pattern Since the repetition coder is placed right
`before the IFFT block. However, it has certain disadvan
`tages. Data padding is required at the transmitter and data
`buffering is required at the receiver. Bits have to be padded
`according to the number of bytes to be sent and the data rate.
`The number of padded bits is determined by how many bits
`one OFDM symbol can carry. Since the 802.11a/g inter
`leaver works with 48 coded bits for BPSK modulation, bits
`need to be padded to make the number of coded bits a
`multiple of 48. Since the repetition coder is placed after the
`interleaver, it may be necessary to pad the data by adding
`unnecessary bits for lower data rates than 6 Mbps.
`0023 For example, one OFDM symbol would carry
`exactly 1 uncoded repeated bit at a data rate of '4 Mbps.
`Since the OFDM symbol could be generated from that one
`bit, there would never be a need to add extra uncoded bits
`and So padding would not be necessary in principle. How
`ever, due to the Special Structure of the 802.11a/g interleaver,
`several bits would need to be padded to make the number of
`coded bits a multiple of 48 before the interleaver. The
`padded bits convey no information and add to the overhead
`of the transmission, making it more inefficient.
`0024. On the other hand, if the repetition encoder is
`placed after the interleaver, the repetition coded bits gener
`ated from the 48 interleaved bits are distributed over mul
`tiple OFDM symbols. Therefore, the receiver would need to
`process the multiple OFDM symbols before deinterleaving
`the data could be performed. Therefore, additional buffers
`would be necessary to Store frequency-domain data.
`0025 The system can be improved and the need for data
`padding at the transmitter and data buffering at the receiver
`can be eliminated by redesigning the interleaver So that it
`operates on bits output from the repetition encoder.
`0026 FIG. 3A is a diagram illustrating a transmitter
`System with a repetition encoder placed before the input of
`an interleaver designed to handle repetition coded bits Such
`
`

`

`US 2005/0243774 A1
`
`Nov. 3, 2005
`
`as the one described below. Incoming data is convolutionally
`encoded by convolutional encoder 302. The output of con
`volutional encoder 302 is repetition coded by repetition
`encoder 304. Interleaver 306 interleaves the repetition coded
`bits. Interleaver 306 is designed so that data padding is not
`required and So that for lower repetition levels, the bits are
`interleaved So as to Separate repeated bits. Pseudorandom
`mask combiner 308 combines the output of Interleaver 306
`with a pseudorandom mask for the purpose of reducing the
`peak to average ratio of the Signal, as is described below. The
`signal is then processed by IFFT processor 310 before being
`transmitted.
`0.027
`FIG. 3B is a diagram illustrating a receiver system
`for receiving a signal transmitted by the transmitter System
`depicted in FIG. 3A. The received signal is processed by
`FFT processor 320. The output of FFT processor 320 is input
`to mask remover 318 which removes the pseudorandom
`mask. Deinterleaver 316 deinterleaves the data. Data com
`biner 314 combines the repetition encoded data into a stream
`of nonrepetitive data. The operation of data combiner 314 is
`described in further detail below. Viterbi decoder 312 deter
`mines the most likely Sequence of data that was input to the
`transmission System originally.
`0028 Interleaver 306 is preferably designed such that the
`same (repeated) data are transmitted well separated in the
`frequency domain to achieve full frequency diversity. For
`example, a repetition pattern in the frequency domain for in
`1 Mbps mode in one embodiment would repeat each bit 6
`times. Denoting data in the frequency domain as d, d, . .
`., ds, the repeated Sequence of data is given by:
`d1 d1 d1 d1 d1 d1 d2 d2 d2 d2 d2 d2 ... disds disds disds
`0029. The same data are placed in a group fashion
`because it is easy to combine those data at the receiver. Note
`that the repeated data can be combined only after r (6 in this
`example) data are available.
`0030 The repetition pattern in the above example does
`not provide the greatest possible frequency diversity since
`the Spacing between the same data transmitted on adjacent
`Subchannels may not be large enough and the Subchannels
`corresponding to the Same data are not completely indepen
`dent. Greater frequency diversity would be desirable espe
`cially for multipath channels with large delay spreads.
`Interleaver 306, therefore, is designed to spread the repeated
`data in the frequency domain to achieve frequency diversity
`as much as is practical.
`0031. In one embodiment, the interleaver is designed to
`optimize the frequency diversity provided by the interleaver
`for data rates faster than 1 Mbps (repetition number<=6).
`For lower data rates /2 and 4 Mbps, there is enough
`repetition that Sufficient Subchannels are covered to provide
`frequency diversity even if adjacent Subchannels are used. In
`the preferred interleaver described below, repeated bits are
`Separated at least by 8 Subchannels and consecutive coded
`bits from the convolutional encoder are Separated at least by
`3 Subchannels. The interleaver is designed according to the
`following Steps:
`0032 1. A 6x8 table is generated as shown in FIG. 4A
`to satisfy the first rule which specifies that bits are
`Separated at least by 8. Subchannels.
`
`0033 2. As shown in FIG. 4B, the columns are
`Swapped to meet the Second rule which specifies that
`consecutive coded bits are separated at least by 3
`Subchannels.
`0034) 3. As shown in FIG. 4C, separation between
`repeated bits is increased by Swapping rows. In the
`example shown, repeated bits are separated by at least
`16 bins for 3 Mbps (Repetition number=2 for 3 Mbps
`So each bit is repeated once.)
`0035. For the example interleaver shown, if the input to
`the interleaver is {1, 2, 3, . . . , 48, then the output would
`be: {1, 19, 37, 7, 25, 43, 13, 31, 4, 22, 40, 10, 28,46, 16,34,
`2, 20, 38, 8, 26, 44, 14, 32, 5, 23, 41, 11, 29, 47, 17, 35, 3,
`21, 39, 9, 27, 45, 15, 33, 6, 24, 42, 12, 30, 48, 18, 36.
`0036 Repetition of the values in the frequency domain
`tends to generate a peak in the time domain, especially for
`very low data rates (i.e., for large repetition numbers). The
`large peak-to-average ratio (PAR) causes problems for the
`System, especially the transmit power amplifier. This prob
`lem can be ameliorated by Scrambling or masking the values
`transmitted on different frequencies So that they are not all
`the Same. AS long as the masking Scheme is known, the
`Scrambling can be undone at the receiver. In one embodi
`ment, the frequency-domain data is multiplied by the long
`symbol of 802.11a/g, which was carefully designed in terms
`of PAR. As can be seen in FIG. 2, the mask operation is
`performed right before the IFFT operation. In general, any
`masking Sequence can be used that causeS repeated values to
`differ enough that the PAR is suitably reduced. For example,
`a pseudorandom code is used in Some embodiments.
`0037. At the receiver, decoding includes: (1) mask
`removal, (2) deinterleaving, (3) data combining, (4) channel
`correction, (5) Viterbi decoding. It should be noted that in
`Some embodiments, the order of the StepS may be changed
`as is appropriate.
`0038. In embodiments using frequency repetition, the
`transmitter preferably masks the frequency-domain Signal to
`reduce the peak-to-average ratio (PAR) in the time-domain.
`The receiver removes the mask imposed by the transmitter.
`If, as in the example above, the mask used by the transmitter
`consists of +/-1S, then the mask is removed by changing the
`signs of the FFT outputs in the receiver. After the mask is
`removed, the data is deinterleaved according to the inter
`leaving pattern at the transmitter.
`0039 The repeated signal is combined in the frequency
`domain at the receiver to increase the SNR of the repeated
`signal over the SNR had the signal not been repeated. The
`SNR is increased by multiplying the complex conjugate of
`the channel response as follows.
`
`jeSc
`
`jeSc
`
`0040) where Y is the signal in subchannel j, H, is the
`response of Subchannelj, Y is the combined signal, H is the
`combined channel, and S is the set of indices corresponding
`to the frequency Subchannels that contain the same data.
`
`

`

`US 2005/0243774 A1
`
`Nov. 3, 2005
`
`0041. The channel effect is preferably removed before the
`data is input to the Viterbi decoder so that the Viterbi
`decoder is able to use the same Soft decision unit regardless
`of the actual channel response. In the extended-range mode,
`the combined channel is used in the channel correction unit.
`0042. The frequency-domain signals are weighted for
`calculating the path-metrics in the Soft-decision Viterbi
`decoder, and the optimal weights are determined by the
`corresponding SNR.
`0043. The resulting SNR for the combined signal
`becomes:
`
`jeSc.
`
`0044) where E is the signal power, and o, is the noise
`power for the subchannel j. The combined SNR is used to
`evaluate the Viterbi weights.
`004.5 The 802.11a/gstandard specifies that there are four
`pilot signals included in each OFDM symbol for the purpose
`of estimating timing offset and frequency offset and tracking
`phase noise in 802.11a/g Signals. The 802.11a/g System
`assumes that these 4 pilots are reliable enough to estimate
`the phase information. That assumption may not be true for
`a System with a very low SNR. The redundancy that exists
`in the frequency-domain Signal is exploited to help the pilots
`to estimate and track phase.
`0046) The phase information is estimated from the fre
`quency domain data as follows:
`0047 1. The repeated signals are combined in the fre
`quency domain to increase the SNR, with a channel estimate
`determined from a preamble Sequence of long Symbols and
`an estimated slope, which captures the effect of timing
`offset.
`2. Hard decisions are made for each of the com
`0.048
`bined signals after removing the phase offset estimated from
`the previous Symbol.
`0049. 3. The combined signals are multiplied by their
`own hard decisions. The average of the hard-decision cor
`rected Signal is used to evaluate an angle to estimate the
`phase offset for the current symbol.
`0050. A filter is applied to the estimated phase offset to
`reduce the effect of noise. In one embodiment, a nonlinear
`median filter is used. The nonlinear median filter effectively
`detects and corrects an abrupt change in the phase offset,
`which could be caused by hard decision errors.
`0051. An encoding and decoding scheme for a wireless
`System has been disclosed. Preferably, repetition coding in
`the frequency domain is used. An interleaver that provides
`frequency diversity has been described. In various embodi
`ments, the described techniques may be combined or used
`Separately according to specific System requirements.
`0.052 Although the foregoing invention has been
`described in Some detail for purposes of clarity of under
`Standing, it will be apparent that certain changes and modi
`fications may be practiced within the Scope of the appended
`
`claims. It should be noted that there are many alternative
`ways of implementing both the proceSS and apparatus of the
`present invention. Accordingly, the present embodiments are
`to be considered as illustrative and not restrictive, and the
`invention is not to be limited to the details given herein, but
`may be modified within the Scope and equivalents of the
`appended claims.
`What is claimed is:
`1. A method of transmitting data over a wireleSS channel
`comprising:
`receiving convolutionally encoded data, and
`enhancing the transmission of the data by further repeti
`tion encoding the data.
`2. A method of transmitting data over a wireleSS channel
`as recited in claim 1 wherein the data is repeated in the
`frequency domain.
`3. A method of transmitting data over a wireleSS channel
`as recited in claim 1 wherein the data is repeated in the time
`domain.
`4. A method of transmitting data over a wireleSS channel
`as recited in claim 2 further including masking the data to
`reduce its peak to average ratio.
`5. A method of transmitting data over a wireleSS channel
`as recited in claim 1 further including masking the data by
`applying a pseudorandom Sequence.
`6. A method of transmitting data over a wireleSS channel
`as recited in claim 1 wherein the data is encoded using an
`IEEE802.11a/g encoder.
`7. A method of transmitting data over a wireleSS channel
`as recited in claim 1 wherein the data is interleaved after
`repetition encoding whereby a need to pad the data prior to
`interleaving is reduced.
`8. A method of receiving data over a wireleSS channel
`comprising:
`receiving convolutionally encoded and repetition encoded
`data;
`combining the repetition encoded data to produce com
`bined data; and
`decoding the combined data.
`9. A method of receiving data over a wireleSS channel as
`recited in claim 8 wherein the combined data is decoded
`using a Viterbi decoder.
`10. A method of receiving data over a wireleSS channel as
`recited in claim 8 wherein the repetition encoded data is
`repeated in the time domain.
`11. A method of receiving data over a wireleSS channel as
`recited in claim 8 wherein the repetition encoded data is
`repeated in the frequency domain.
`12. A method of receiving data over a wireleSS channel as
`recited in claim 8 wherein the received data is further
`encoded by a pseudorandom mask, further including remov
`ing the pseudorandom mask.
`13. A method of receiving data over a wireleSS channel as
`recited in claim 8 wherein the convolutional encoding
`conforms to the IEEE 802.11a/g standard convolutional
`encoding.
`14. A method of receiving data over a wireleSS channel as
`recited in claim 8 further including deinterleaving the data
`before combining the data.
`15. A method of receiving data over a wireleSS channel as
`recited in claim 8 wherein the repetition encoded data is
`
`

`

`US 2005/0243774 A1
`
`Nov. 3, 2005
`
`repeated in the frequency domain on Subchannels, and
`wherein combining the repetition encoded data to produce
`combined data includes compensating for the effect of each
`Subchannel.
`16. A method of receiving data over a wireleSS channel as
`recited in claim 8 wherein the repetition encoded data is
`repeated in the frequency domain on Subchannels and
`wherein combining the repetition encoded data to produce
`combined data includes weighting data received on different
`Subchannels according to the quality of the Subchannels.
`17. A method of receiving data over a wireleSS channel as
`recited in claim 8 wherein the repetition encoded data is
`repeated in the frequency domain on Subchannels and
`wherein an aggregate channel quality estimation is made for
`bits included in the combined data and wherein the aggre
`gate channel quality estimation is used by the Viterbi to
`determine a maximum likely transmitted data Sequence.
`18. A method of receiving data over a wireleSS channel as
`recited in claim 8 further including estimating a phase offset
`using the received repetition encoded data.
`19. A method of receiving data over a wireless channel as
`recited in claim 8 further including estimating a phase offset
`using the received repetition encoded data by making a hard
`decision and determining a hard decision corrected Signal.
`20. A method of receiving data over a wireleSS channel as
`recited in claim 8 further including:
`estimating a phase offset using the received repetition
`encoded data by making a hard decision and determin
`ing a hard decision corrected Signals, and
`filtering the estimated phase offset using a median filter.
`21. A System for encoding data for transmission over a
`wireleSS channel comprising:
`
`a convolutional encoder configured to convolutionally
`encode data; and
`a repetition encoder configured to enhance the transmis
`sion of the convolutionally encoded data by further
`repetition encoding the data.
`22. A System for encoding data as recited in claim 21
`further including an interleaver.
`23. A System for encoding data as recited in claim 21
`further including a masking processor configured to Super
`impose a pseudorandom mask on the repetition coded data.
`24. A System for receiving data over a wireleSS channel
`comprising:
`a receiver configured to receive convolutionally encoded
`and repetition encoded data;
`a data combiner configured to combine the repetition
`encoded data to produce combined data; and
`a decoder configured to decode the combined data.
`25. A System for receiving data as recited in claim 24
`further including a deinterleaver configured to deinterleave
`the combined data.
`26. A System for receiving data as recited in claim 24
`wherein the decoder is a Viterbi decoder.
`27. A System for receiving data as recited in claim 24
`further including a mask remover.
`A System for receiving data as recited in claim 24 further
`including a phase offset processor configured to deter
`mine a phase offset by making a hard decision and
`determining a hard decision corrected Signals.
`
`