CA2892255C - Deep and robust data communication - Google Patents

Abstract

In a data communication system an auxiliary communication signal is generated by applying On-Off Keying to a main communication signal of a wireless, optical or wireline communication system. The keying employs a gap position line-code by positioning silence intervals within the main communication signal, whereby the start- and end time of the interval depend on auxiliary data to be transmitted. During the positioned gap the main data that is transmitted over the communication signal is paused and the main communication signal is silenced. At the receiver, demodulation of the auxiliary channel is accomplished by detecting the power envelope of the received signal to determine the start- and end time of any gapping intervals, and the position of the interval is subsequently decoded to recover the auxiliary data. The auxiliary data stream is used as a more robust communication channel to overcome temporary heavy interference and fading during critical data transmissions, and it is used for wake-up calls and power management in the receiving device.

Description

TITLE OF THE INVENTION
Deep and Robust Data Communication NAME OF INVENTOR
Aryan Saed DESCRIPTION OF THE INVENTION
AREA OF INVENTION
[0001] The present invention applies to the area of data communications.
Specifically the invention is concerned with the modulation of signals, whereby the frequency, phase and/or amplitude of a signal are set by the data represented within it.

[0002] As is well known, data may be communicated by modulated waves. Such waves may be electromagnetic waves, typically at Radio Frequencies (RF) or at optical frequencies, they may be mechanical waves at sonic, subsonic and and ultrasonic frequencies, and/or they may comprise oscillations of voltage and/or current.

[0003] In prior art data modulation schemes and data division schemes, data may be parceled and allocated to streams (also called data channels) which are allocated to frequencies as in FDM
(Frequency Division Modulation) or OFDM (Orthogonal Frequency Division Modulation) schemes, or to time slots as in TDM (Time Division Modulation) schemes, or to orthogonal codes as in CDM
(Code Division Multiplexing), or a combination thereof.
DISCUSSION OF PRIOR ART

[0004] Main communications systems and protocols provide a distinct overhead or initialization channel so that transmitting stations and receiving stations can establish connections or communicate auxiliary data without disrupting their main payload channel.

[0005] Out-of-band signaling is commonly used for this purpose. Out-of-band signaling generally contains overhead & management data or synchronization signals separate from the main data. In some communication protocols, esp. optical networks, out-of-band signaling may refer to additional frame overhead embedded in the line data, thus requiring an increasing in the line rate to maintain a payload rate.

[0006] In computer peripheral protocols, out-of-band may refer to distinct and separate electrical connections or lanes that are used to send robust tones or patterns for device recognition and rate negotiation.
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[0007] High-speed interconnect protocols are commonly used between computers and other computing or storage devices. Examples of these protocols are PCIe (Peripheral Component Interconnect ¨
Express), Small Computer System Interface (SCSI), Serial Attached SCSI (SAS), and Serial ATA
(Serial Advanced Technology Attachment). During link initialization, it is common to transmit protocol primitives such as a fixed "ALIGN" bit-pattern and electrical idle, in an on/off manner, for speed negotiations, clock rate matching, and device recognition. Protocol primitives such as synchronization symbols or equalizer training symbols generally contain a repetitive pattern, resulting in a Power Spectral Density (PSD) profile that stands out from the rest of the signal that carries data.

[0008] Patent US 9270373, "Transporting Data And Auxiliary Signals Over An Optical Link" by Zbinden e.a. describes the controlled activation and deactivation of two or more optical channels of an optical link. Auxiliary signals are transmitted by selectively enabling and disabling two or more of the optical channels and in which one or more auxiliary signals are received by determining which ones of the optical channels have been enabled and which ones of the optical channels have been disabled.

[0009] Patent US 9712247 "Low Bit Rate Signaling With Optical IQ Modulators", by Duthel describes a low bit rate signaling data so that an optical receiver may identify the optical transmitter port to which it is connected, by decoding the average optical output power signal produced by the transmitter, and applying different transmit power levels, or different patterns of transmit power levels, for different channels.

[0010] Patent US 7283688 "Method, apparatus and system for minimally intrusive fiber identification"
by Frigo, and related publications, describe a detectable unique signature that is imparted on optical signals propagating through a subject optical fiber or optical fiber path. The signature comprises polarization (i.e., the direction of the oscillating electric field);
frequency; and amplitude (the electric field strength) or power (proportional to its square) and is subsequently detected to identify an optical fiber or path.

[0011] In Pulse Position Modulation (PPM) of the prior art, data is communicated by transmitting a pulse in one of many temporal positions. This type of modulation is the basis of hydraulic semaphore systems where electrical or radio wave communications are not practical. For instance, in Measurement While Drilling (MWD), water or oil pressure fluctuations are employed to signal information about a drill unit deep underground to a driller above ground, where the information includes the reading of an analog sensor such as including the severity of vibration of a drill head, or battery life status, or a gyroscope position and magnetic heading for directional drilling. The position of the pulse is commonly a coded representation of the data to be communicated. PPM is also used for the control of actuators in Radio Controlled vehicles, where it is attractive due to its simplicity, since the position of the pulse relative to a predetermined range can be made analogous to a desired actuator setting relative to a maximum. To ease the symbol timing, Differential Pulse Position Modulation places each pulse relative to the previous, and the receiver measures the difference in the timing position of successive pulses. PPM is a sparse code, because the transmission is mostly idle: the time span during which a pulse. or "mark", occurs, during which typically a RF carrier or a high signal level is transmitted, is substantially less than the time spans during which its enveloping idle/quiet, or "space", occurs.

[0012] In wireless communications, overhead information is included in the communication data-frame that is sent between stations. The overhead is sometimes modulated at a lower order, so that it may be page 2 reliably decoded if the connection between the stations is poor, for instance due to interference, multi-path fading, or heavy signal attenuation. Examples are the headers employed in protocols for cellular communications, such as 4th Generation Long Term Evolution (LTE-4G), and wireless home networking protocols such as WiFi (IEEE 802.11a/b/n/g/ac). As part of cognitive radio protocols and wireless medium sharing and co-existence, devices may yield their transmission, using deliberate idles, back-offs, or gaps, in order to enable other wireless stations of the same or a different protocol to coexist within a same frequency channel or band. In wireless communications it is also common to include a random back-off transmission gap in the case of a Carrier Sense Multiple Access ¨ Collision Avoidance (CSMA-CA) scheme such as in Ethernet and WiFi, and in the case of a Time Domain Duplex communication there is commonly a Transmitter or Receiver Turn Around Gap (TTG, RTG) between Physical Layer frames, to allow switching of RF circuitry in cellular protocol devices. Most wireless communications protocols, including LTE and WiFi include preambles in their Physical Layer frames. These preambles contain pre-defined signatures with power spectral densities that stand out from the data portion of the frame, and they have good auto- and cross-correlation properties so that a receiver can recognize the beginning of a burst, perform timing and frequency synchronization and train its equalizers, even in communication channels that are noisy and that have heavy multi-path fading.

[0013] Publication Vvr0/2013/112983, "Dynamic Parameter Adjustment For LTE
Coexistence", by Bala e.a., describes the use of coexistence gaps to share a channel in a dynamic shared spectrum.
During negotiated transmission gaps, stations of one protocol, e.g. LTE, remain silent so that stations of a second protocol can communicate and coexist in the same frequency band or channel.
BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 illustrates a QPSK data transmission with 2 gaps.
Figure 2 shows the corresponding gapping signal which forms the auxiliary channel.
Figure 3 and 4 show an OFDM transmission with gaps.
DETAILED DESCRIPTION

[0015] In the present invention data may be parceled and allocated to one or more main data channels as in the prior art, and additionally to one or more auxiliary data channels.

[0016] Thc auxiliary channel may contain auxiliary data which would be transmitted at a lower average rate than the main data.

[0017] As a non limiting example, in the present invention a data burst comprised of 8 symbol slots contains 7 QPSK symbols and one gap symbol, for a total of 8 symbols. The position of the gap codes 3 bits, since there are 8 positions available for the gap. Each QPSK symbol contains 2 main bits. Thus each burst contains 3 bits of auxiliary data plus 14 bits of main data. The auxiliary data is transmitted at a rate of 3 bits per burst period. The main data is transmitted at a rate of 14 bits over the same burst period.

[0018] In accordance with the preferred embodiment, gapping involves idling (zeroing) the transmit signal over time periods as determined by the data in the auxiliary channel.
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[0019] A non-limiting example of such an idling scheme is OOK (On-Off Keying).
Thus, by sensing the power of the received signal, a receiver may decode the OOK back to corresponding auxiliary data values.

[0020] In the preferred embodiment, when using 00K, the main data is transmitted during the On phase of the 00K. This phase may also be called the "Mark" phase. The signal transmitted in the ON
phase contains phase and/or amplitude signals modulated by the main data. The timing and thus temporal positioning of the OFF phase indicates the auxiliary data. The OFF
phase may be called the "Space" phase. Timing of the OFF phase may be relative to the start of a burst, or to the start or end of the previous OFF phase, or relative to other events embedded in the signal, or relative to an absolute timing reference such as a network referenced clock.

[0021] Thus the main data may be transmitted using schemes of prior art modulation, such as TDM
(Time Division Multiplexing), FDM (Frequency Division Multiplexing), OFDM
(Orthogonal Frequency Division Multiplexing), CDM (Code Division Multiplexing) etc... with prior art symbol modulation such as nPSK (Phase Shift Keying), PAM (Pulse Amplitude Modulation), QAM
(Quadrature Amplitude Modulation) etc.. The auxiliary data is transmitted by gapping the main data transmission at the transmitter. Since gapping occurs at the transmitter, no data is lost. Main data transmission may be suspended during a gap symbol and continued after the gap.

[0022] In the preferred embodiment, a gap location code is used to control the On/Off Keying. As a non-limiting example, a value of 0 to 15 is calculated from a group of 4 bits, each value uniquely mapping to one of the 4-bit permutations. A bit permutation "0000" yields a value of 0, "0001" yields a value of 1, "0010" a value of 2 etc.. in a binary fashion until "1111" which yields IS. Then this value, as determined by the permutation to be transmitted, determines the location of a gap in a transmission burst.

[0023] In accordance with the above non-limiting example, gapping is applied as follows to an OFDM
transmission. For binary auxiliary data "0011" symbol 3 of an OFDM burst transmission is idled. Thus, under poor channel conditions, when OFDM receptions of the main data channels are not successful, a power detector may be used to decode the auxiliary channel.

[0024] The present invention also provides for gapping with a higher indication order. It can be said that OOK entails gapping with a simple first order gap, an idle or zeroing.
Higher order indication may involve additionally adjusting the duration of the gap period depending on the data. For instance the location of a gap is determined by a 4 bit permutation of auxiliary data, as in the example above, and the length of the gap is determined by an additional bit of auxiliary data.

[0025] A single gap positioned in one of N slots entails a I in N code. The present invention may involve more than one gap per burst. Thus the auxiliary channel may employ M
gaps out of N slots, which entails an M in N code. The number of bits thus coded may be calculated as 1og2(N choose M).
For instance a 1 in 8 code encodes 8 values and thus 3 bits per burst, whereas a 2 in 8 code encodes 28 values and thus almost 5 bits.

[0026] In addition to setting the gap position based on the auxiliary data, also the duration of the gap may be set based on the auxiliary data, so that in combination more auxiliary data is transmitted in a page 4 burst.

[0027] Reception of auxiliary channel is thus valuable when reception of the main channel is not possible. This is useful in situations where the communications channel is temporarily faded or interfered and data rate adaptation to a more robust coding and modulation scheme has not yet been applied by the transmitter. Applications include Machine-to-Machine communications as part of the Internet-of-Things.

[0028] This is also useful in situations where acknowledgements or data rate feedback from the receiving station back to the transmitting station are temporarily or permanently not possible.
Applications include military probes and sensors, deep space communications, and telemetry for MWD
(Measurement While Drilling)

[0029] Figure 1 illustrates a data transmission in accordance with an embodiment of the present invention. The figure shows a QPSK (4-phase, quadrature phase shift keying) transmission of sinusoidal signal. As is well known in the art, a QPSK symbol is an oscillation at a specific frequency at one of 4 phases, each phase representing the value of one pair of data bits. The symbol period is 0.25s. The transmission begins with a 0.25s gap, which is an idle (zero, silent) transmission. Then follow 3 QPSK symbols, followed by another gap.

[0030] Figure 2 shows the corresponding gapping signal which forms the auxiliary channel. A signal level of 0 denotes a gap. Thus gaps are located at several positions: a first at Os to 0.25s, a second gap at Is to 1.25s, a third at 1.5s to 1.75s, a fourth at 5.25s to 5.5s. The first and third may be used for synchronization and may be used to separate the second and fourth gaps as auxiliary data from a data TYPE indicator (spanning 4 symbol slots from 0.5s to 1.5s) and a data VALUE
indicator (spanning 16 slots form 2s to 6s) in a TYPE/VALUE field of a data structure for the auxiliary channel. The gap for TYPE is in slot 2 indicating the data type the field (e.g. a temperature reading) , and the gap for VALUE is in slot 13, indicating the temperature value of the reading.

[0031] Figure 3 and 4 show an OFDM transmission with gaps. Figure 4 shows two bursts of an OFDM
main communication signal and figure 3 shows an on-off signal to highlight the position of gaps in accordance with the present invention: where the on-off signal is "high" the OFDM main communication signal is being transmitted, and where the on-off signal is "low" the OFDM main communication signal is ceased. The first burst occurs from 0.5 to 2.5s, then there is a 0.5s separation, followed by the second burst which occurs from 3s to 5s. Here, the OFDM symbol period is 0.25s for both bursts, and both bursts are 8 symbols (2s) in length. In accordance with one aspect of the invention, each symbol in a burst is assigned a unique index: the first symbol has index 0, the second symbol has index 1 etc.. until the last symbol which has index 7. From the auxiliary data, portions of 3 bits of auxiliary data are transmitted in subsequent bursts, by uniquely selecting one of the 8 symbols to represent the 3 bits in a burst. This is easily accomplished by calculating a 3 bit binary value from the 3 auxiliary bits and selecting the corresponding symbol. The gap of the first burst occurs from ls to 1.25s, which is in the 3 symbol (having symbol index 2) of the burst, which corresponds to a bit permutation of "010" for the transmitted portion of auxiliary data. Thus, each burst contains a gap, and the location of the gap within the burst represents the value of a portion of transmitted auxiliary data.
Analogously, the gap of the second burst occurs from 4.25s to 4.5s, which is in the 6th symbol (having symbol index 5) of the burst, which corresponds to a bit permutation of -101"
for the transmitted portion of auxiliary data. It should be clear to a person skilled in the art that the selection of the symbol page 5 period, the length of the burst, and the type of symbol are examples to illustrate the transmission of auxiliary data by transmitting gaps in lieu of modulation symbols of the main signal.

[0032] In alternative embodiments, the symbols contain higher order modulated signals, such as OFDM symbols. Moreover, the symbols may occupy only a sub-band (a sub-division) of the transmission frequency band width. For instance, in a sonic transmission over a pressure wave channel that is 10KHz wide, symbols may occupy a sub-band that is 500Hz wide, centered at 1KHz.

[0033] In alternative embodiments the gap may constitute a transmission of a tone, or other signal at a frequency generally outside the frequency band of the data symbols. This may allow transmission of data in a different frequency sub-band of the communication channel. For instance, where data symbols occupy a sub-band that is 500Hz wide centered at 1KHz, during the gap data symbols are transmitted in a different sub-band that is 500Hz wide centered at 2KHz.

[0034] The aforementioned gapping with optional sub-banding per the present invention applies equally to RF signals. For instance a 20MHz WiFi transmission may be divided into an upper 10MHz and a lower 10MHz, and auxiliary signaling occurs by switching transmissions between the two.

[0035] In alternative embodiments the gap may have a duration of multiple whole symbols (e.g. one of 2 or 3 symbol periods etc..) or a fractions of a symbol (e.g. one of 0.5 or 0.25 or 0.75symbo1 period), or a combination of the two (e.g. one of 1 or 1.25 or 1.5 or 1.75 Symbols). The set of allowable durations may be adjusted based on the receiver requirements and the communication channel conditions such as distortion, noise and interference. Generally, the worse the channel conditions are, the longer of a gap may be required to reliably distinguish between a gap symbol and an ordinary modulated symbol.

[0036] In alternative embodiments, the auxiliary data channel which determines the position of the gap may instead determine the start time of a burst rather than the location of a gap within it. As a non-limiting example, instead of transmitting a gap in slot 5 to represent a data value of 5, the spacing between two bursts is set to 5 gap periods. Thus a data value in the range 0 to 7 (8 values, 3 bits) may be communicated in the auxiliary channel by spacing two bursts respectively in the amount of 0 to 7 gap periods. Alternatively a fixed base spacing of for instance 2 gap periods may be included thus spacing two bursts respectively in the amount of 2 to 9 gap periods thus providing a minimum of 2 gap periods regardless the auxiliary data.

[0037] In alternative embodiments a burst or portion thereof is transmitted at a predetermined set of frequencies, and a different burst or a different portion thereof is transmitted at a different predetermined set of frequencies. The choice between the first set and second set is determined by the auxiliary channel data. As a non-limiting example, an auxiliary data sequence of "101" may imply the transmission using frequency sets A, B then A. A first burst is transmitted at frequencies of set A, the following burst is transmitted at frequencies of set B, and the third burst is transmitted at frequencies of set A.

[0038] As non limiting examples, these frequency sets may be odd/even groupings of OFDM
subcarriers, or High/Low FDM frequency sub-bands.

[0039] A receiver in accordance with the present invention includes a detector to determine the length and or location of the gaps at specified and predetermined frequencies. This may be accomplished by page 6 comparing the received signal within the transmission sub-band against a suitable OOK threshold. The threshold is ideally placed between the expected receive power for symbol periods that contain symbol signals, and the expected receive power in idle symbols. The latter power level is chiefly determined by receiver "background" noise and/or interference when there is no transmission.
The threshold may be adapted during reception based on fluctuating receive signal, noise and interference power levels.
The receiver may measure the receive power using a band pass filter or equivalent, in digital and/or analog form, to minimise out-of-band noise, signals and interference.
Alternatively the output of an FFT operation commonly used in OFDM demodulators may be used to determine the power level of an individual symbol.

[0040] Thus the present invention provides a more robust auxiliary channel for a more reliable transfer of critical data on top of the main data.

[0041] Applications of the present invention include but are not limited to:
I. Communication of signals in temporarily heavy fading RF channels (wireless links), where user safety demands the reliable communication of critical data as in vehicle-to-vehicle communications, robot communications, and machine-to-machine communications.
2. Communication of signals in temporarily heavily distorted and disturbed sonic (acoustic) channels in production tubing (pipe) or drill pipe in oil & gas exploration and exploitation 3. Communication of deep space signals by optical means such as laser, or RF
4. Areas where bi-directional communications used for acknowledgements and rate adaptation are expensive or slow, and a robust uni-directional backup channel is required, such as in uplink -only drilling applications, or in downlink-only space applications or in broadcast-only multi-user applications.
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Claims (29)

1. A method for transmitting auxiliary data in a transmitter of a first communication device to a receiver in a second communication device, the transmitter having a modulator, the method comprising:
a) receiving main data at a first input of the modulator, and generating in the modulator, from the main data, a main communication signal, wherein the main communication signal comprises one or more modulation symbols, wherein one or more of the modulation symbols each have an individual symbol time instance, b) receiving the auxiliary data at a second input of the modulator, wherein the auxiliary data has a permutation of auxiliary bit values;
c) associating one or more of the symbol time instances with the permutation of auxiliary bit values;
d) performing a transmission of the main communication signal;
e) transmitting a gap by ceasing the transmission of the main communication signal at one of the one or more associated symbol time instances, wherein the gap has a gap duration, and whereby a time instance of the gap depends at least on the permutation of auxiliary bit values;
0 after the gap duration, resuming the transmission of the main communication signal;

2. The method of claim 1, whereby the symbol time instance of one of the modulation symbols equals a start time of the one of the modulation symbols;

3. The method of claim 1, whereby the symbol time instance of one of the modulation symbols equals an end time of the one of the modulation symbols;

4. The method of claim 1, wherein the modulation symbols comprise K symbol periods, and wherein the auxiliary data comprises N bits, and wherein K=2AN (K equals 2 to the power N), and wherein the page 8 associating comprises:
a) assigning to each of the K symbol periods a unique index value ranging from 0 to K-1 (K minus one);
b) calculating a binary value from the permutation of auxiliary bit values, the binary value ranging from 0 to K-1 (K minus one);
c) selecting from the K symbol periods a symbol period having the unique index value that equals the binary value.

5. The method of claim 1, wherein the main communication signal is a radio-frequency signal.

6. The method of claim 1, wherein the main communication signal is an acoustic signal.

7. The method of claim 1, wherein the main communication signal is an electrical signal.

8. The method of claim 1, wherein the main communication signal is an optical signal.

9. The method of claim 1, wherein the modulator generates the main communication signal from the main data using Orthogonal Frequency Division Multiplexing (OFDM).

10. The method of claim 1, wherein the gap duration is of a fixed amount.

11. The method of claim I, wherein the aap duration is of a configurable amount.

12. The method of claim 1, wherein the gap duration is of a variable amount, and wherein the permutation of auxiliary bit values determines, through the association, the gap duration.

13. The method of claim 1, wherein the ceasing and the resuming are performed by on-off keying of the main communication signal, and wherein the temporal location of an off-phase of the on-off keying is based on the auxiliary bit values.

14. The method of claim 1, with additionally transmitting a second signal during at least a portion of the gap duration, wherein the main communication signal has a main frequency spectrum, and wherein the second signal has a second frequency spectrum that is substantially different from the main frequency spectrum.
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15. The method of claim 14, wherein the second signal comprises a second communication signal for transmission of second data.

16. The method of claim I, wherein the auxiliary data comprises a duplicate of a portion of the main data.

17. A method for receiving auxiliary data sent from a transmitter of a data communication system, wherein the transmitter transmits a main communication signal comprising one or more modulation symbols, wherein the modulation symbols each have an individual symbol time instance, wherein the auxiliary data has a permutation of auxiliary bit values, wherein the permutation of auxiliary bit values selects, through an association, one or more of the symbol time instances, wherein the transmitter transmits a gap by ceasing the transmission of the main communication si2nal at one of the determined symbol time instances, wherein the gap has a gap duration, the method comprising the steps of:
a) in a receiver receiving the main communication signal as a received signal from the transmitter, the received signal having at least one received gap;
b) applying a detector to the received signal, and determining with the detector a time instance of the received gap;
c) determining the permutation of auxiliary bit values at least from the time instance of the received gap and through a reverse of the association.

18. The method of claim 17, wherein the permutation of auxiliary bit values also determines the gap duration through the association, with the additional steps of:
page 10 a) determining with the detector a duration of the received gap;
b) determining the permutation of auxiliary bit values at least from the duration of the received gap and through a reverse of the association.

19. The method of claim 17, wherein the main communication signal is a radio-frequency signal.

20. The method of claim 17, wherein the main communication signal is an acoustic signal.

21. The method of claim 17, wherein the main communication signal is an electrical signal.

22. The method of claim 17, wherein the main communication signal is an optical signal.

23. The method of claim 17, wherein the main communication signal comprises Orthogonal Frequency Division Multiplexing (OFDM).

24. The method of claim 17, wherein the modulation symbols comprise K symbol periods, and wherein the auxiliary data comprises N bits, and wherein K=2.LAMBDA.N (K equals 2 to the power N), with the additional steps of a) assigning to each of the K symbol periods a unique index value ranging from 0 to K-1 (K minus one):
b) selecting from the K symbol periods a symbol period that corresponds to the time instance of the received gap;
c) determining the unique index value of the symbol period selected in step b) d) calculating a permutation of the N bits, wherein the permutation has a binary value that corresponds to the unique index value determined in step c)

25. The method of claim 17, wherein the transmitter additionally transmits a second signal during at least a portion of the gap duration, wherein the main communication signal has a main frequency spectrum, wherein the second signal has a second frequency spectrum that is substantially different from the main page 11 frequency spectrum, and wherein the detector is frequency selective and distinguishes between the main frequency spectrum and the second frequency spectrum.

26. The method of claim 17, wherein the receiver comprises a demodulator for the main communications signal, and wherein the auxiliary data comprises a control message to activate the demodulator for the main communications signal.

27. The method of claim 17, wherein the main communication signal has a main frequency spectrum, and wherein the detector comprises spectral filtering with a pass band that substantially matches the main frequency spectrum.

28. The method of claim 25, wherein the detector comprises spectral filtering with a pass band that substantially matches the second frequency spectrum

29 The method of claim 17, wherein the detector distinguishes between a first level of the received signal during the modulation symbols and a second level of the received signal during the received gap page 12