Method for communication below the noise-floor using a coded constellation

Abstract

A method at a transmitter that supports communication below a noise floor using a coded constellation, comprising encoding a first set of bits with a first encoding to obtain one or more first sets of encoded bits; encoding a second set of bits with a second encoding to obtain one or more second sets of encoded bits; concatenating the one or more first sets of encoded bits and the one or more second sets of encoded bits to obtain one or more transmit bit sequences; mapping the one or more transmit bit sequences to one or more transmit symbols from a set of symbols based on a modulation scheme; transmitting the one or more transmit symbols to a first receiver and a second receiver. The distance between the transmitter and the receiver is such large that the received signal which is below noise floor where SNR is below unity, and the first encoding is configured to enable reception of the first set of bits with a BER above a BER threshold for an SNR above an SNR threshold, wherein the SNR threshold is less than unity.

Description

[0001] - 1 -

[0002] METHOD FOR COMMUNICATION BELOW THE NOISE-FLOOR USING A CODED CONSTELLATION

[0003] Field of the Invention

[0004] The present invention generally relates to communication systems, and particularly to methods and systems for multiple access communications.

[0005] Background of the Invention

[0006] A Wireless Ad Hoc Network (WANET) is a decentralized wireless network without preexisting infrastructure, such as routers or wireless access points. Each device may forward traffic unrelated to its own use and, thus, function as a router. The determination of which devices forward data is made dynamically based on network connectivity and the routing algorithm used. Each device in a WANET may move independently in any direction, changing its connectivity to other devices. Consequently, the network connectivity between devices or the network topology of a WANET may change dynamically and randomly as devices move.

[0007] A management node is a device in a WANET that can be configured to manage the devices. This management may include authenticating devices, providing network configuration information to authenticated devices (e.g., frequency channels used by the network), providing control information to authenticated devices (e.g., scheduling information), and maintaining accurate routing information at authenticated devices.

[0008] One primary challenge in WANETs is ensuring that each device maintains connectivity with one or more management nodes as the network topology changes. This becomes harder as the scale of the WANET increases due to 1) an increased number of devices over a larger area to be provided with accurate routing information and; 2) an increased rate of change and variability of the network topology as the number of devices and coverage of the network increases.

[0009] The coverage or range of communication of the management node may be maximized by enabling communication below the noise floor, i.e., with received signal power levels that are less than noise power levels at the receiver, which result in Signal-To-Noise Ratio (SNR) values that are less than unity. Spread spectrum techniques are traditionally used to communicate below the noise floor. However, spread spectrum communication below the noise floor typically requires a transmission bandwidth that significantly exceeds the- 2 -

[0010] information bandwidth. This requires that every device on the network supports the maximum bandwidth requirement of the spread-spectrum technique at the minimum operating SNR of the network. Furthermore, every device must include an additional spread-spectrum transceiver. These two requirements imposed by using spread-spectrum significantly limit the type of devices that may connect to the WANET. For example, low- complexity devices like sensors may lack the required maximum bandwidth capability and an additional spread-spectrum transceiver.

[0011] It is therefore an object of the present invention to provide a low-complexity system and method for communication below the noise floor, which is bandwidth-efficient.

[0012] Other objects and advantages of the invention will become apparent as the description proceeds.

[0013] Summary of the Invention

[0014] A method at a transmitter that supports communication below a noise floor using a coded constellation, comprising:

[0015] a) encoding a first set of bits with a first encoding to obtain one or more first sets of encoded bits;

[0016] b) encoding a second set of bits with a second encoding to obtain one or more second sets of encoded bits;

[0017] c) concatenating the one or more first sets of encoded bits and the one or more second sets of encoded bits to obtain one or more transmit bit sequences;

[0018] d) mapping the one or more transmit bit sequences to one or more transmit symbols from a set of symbols based on a modulation scheme; and

[0019] e) transmitting the one or more transmit symbols to a first receiver and a second receiver,

[0020] wherein the distance between the transmitter and the receiver is such large that the received signal which is below noise floor where SNR is below unity, and

[0021] wherein the first encoding is configured to enable reception of the first set of bits with a BER above a BER threshold for an SNR above an SNR threshold, wherein the SNR threshold is less than unity.- 3 -

[0022] A transmitter that supports communication below a noise floor using a coded constellation comprising:

[0023] a) a first encoder configured to encode a first set of bits with a first encoding to obtain one or more first sets of encoded bits;

[0024] b) a second encoder configured to encode a second set of bits with a second encoding to obtain one or more second sets of encoded bits;

[0025] c) a bit sequence concatenation unit configured to concatenate the one or more first sets of encoded bits and the one or more second sets of encoded bits to obtain one or more transmit bit sequences; and

[0026] d) a modulator configured to map the transmit bit sequences to transmit symbols from a set of symbols based on a modulation scheme,

[0027] wherein the transmit symbols are transmitted to a first receiver and a second receiver, wherein a first distance between the transmitter and the first receiver is such large that the received signal which is below noise floor, where SNR is below unity, and

[0028] wherein the first encoding is configured to enable reception of the first set of bits with a BER above a BER threshold for an SNR above an SNR threshold, wherein the SNR threshold is less than unity.

[0029] A receiver that supports communication below a noise floor using a coded constellation, comprising:

[0030] a) in a first operational mode:

[0031] i) a deconcatenation unit in a first operational mode configured to map one or more first received symbols to one or more first sets of received encoded bits; and

[0032] ii) a first decoder in the first operational mode configured to decode the one or more first sets of received encoded bits to obtain a first set of decoded bits, and b) in a second operational mode:

[0033] i) a deconcatenation unit in the second operational mode configured to extract from the one or more received bit sequences one or more second sets of received encoded bits; and

[0034] ii) a second decoder in the second operational mode configured to decode the one or more second sets of received encoded bits to obtain a second set of decoded bits.-4 -

[0035] Brief Description of the Drawings

[0036] In the drawings:

[0037] FIG. 1 illustrates an example of a wireless communications subsystem that supports communication below a noise floor using a coded constellation, according to some embodiments of the invention;

[0038] FIG. 2 illustrates a block diagram of a transmitter subsystem that supports communication below a noise floor using a coded constellation, according to some embodiments of the invention;

[0039] FIG. 3 illustrates a block diagram of a receiver subsystem that supports communication below a noise floor using a coded constellation, according to some embodiments of the invention;

[0040] FIGS. 4A and 4B illustrate examples of symbol constellations that support communication below a noise floor using a coded constellation, according to some embodiments of the invention;

[0041] FIG. 5 is a flow chart generally illustrating a method at a transmitter subsystem that supports communication below a noise floor using a coded constellation, according to some embodiments of the invention;

[0042] FIG. 6 is a flow chart generally illustrating a method at a receiver subsystem in the first operational mode that supports communication below a noise floor using a coded constellation, according to some embodiments of the invention; and

[0043] FIG. 7 is a flow chart generally illustrating a method at a receiver subsystem in the second operational mode that supports communication below a noise floor using a coded constellation, according to some embodiments of the invention.

[0044] Detailed Description of the Invention

[0045] The present invention provides a method and system for communication below a noise floor using a coded constellation. According to some embodiments of the invention, a transmitter may transmit one or more bits to a first receiver and to a second receiver. The distance between the transmitter and the first receiver is such large that the received signal will be below noise floor, i.e., the SNR is below unity.

[0046] At the transmitter, a first set of bits for the first receiver may be encoded with a first encoding, and a second set of bits for the second transmitter may be encoded with a second encoding. The encoded bits may be combined and mapped to the one or more transmit-5 -

[0047] symbols using a modulation scheme with a defined constellation order, where the order may be greater than 2. The first encoding aims to guarantee high-quality reception at the first receiver of the first set of bits below the noise floor to maintain connectivity at long ranges. The first encoding may use a low-rate channel code. The second encoding may use a high-rate code.

[0048] FIG. 1 illustrates an example of a wireless communications subsystem 100 that supports communication below a noise floor using a coded constellation, according to some embodiments of the invention.

[0049] Wireless communications subsystem 100 may be a subsystem of a wireless communication network comprising a plurality of transmitters and receivers (e.g., a WANET). Wireless communications subsystem 100 may include a transmitter 110, a first receiver 120, and a second receiver 130. Transmitter 110 may transmit one or more bits to first receiver 120 and second receiver 130 over a wireless channel 70 and a wireless channel 80, respectively. A first distance 71 may separate between transmitter 110 and first receiver 120. A second distance 81 may separate between transmitter 110 and second receiver 130. First distance 71 may be substantially larger than second distance 81. First distance 71 may result in a received signal power level at first receiver 120 below a noise power level at first receiver 120, i.e., an SNR that is less than unity.

[0050] FIG. 2 illustrates a block diagram of a transmitter subsystem 200 that supports communication below a noise floor using a coded constellation, according to some embodiments of the invention.

[0051] FIG. 3 illustrates a block diagram of a receiver subsystem 300 that supports communication below a noise floor using a coded constellation, according to some embodiments of the invention.

[0052] FIGS. 4A and 4B illustrate examples of symbol constellations that support communication below a noise floor using a coded constellation, according to some embodiments of the invention.-6 -

[0053] Let β and γ be number of bits of the first set and the second set of encoded bits respectively.

[0054] By way of example, for β + γ = 6, the number of bits in a set from the one or more first sets of encoded bits may be 1 (β = 1), and the number of bits in a set from the one or more second sets of encoded bits may be 5 (γ = 5). For a transmission bandwidth (B) of 8 MHz, the first uncoded bit rate is R1= 8 Mbits / s. The second uncoded bit rate is R2= 40 Mbits / s.

[0055] The first bit rate and, consequently, the first code rate determine whether the BER of the first set of bits exceeds the BER threshold at the SNR threshold. For example, an SNR threshold of -8 dB may require the first bit rate (R1) to equal 64kbits / s for the BER to exceed a BER threshold of 10-3. This requires the first code rate to be less than or equal to 0.008. The first encoding may be repetition encoding, where the repetition number (number of repetitions) may be denoted as N. The repetition number N may be computed as follows: N = 2 × round(

[0056] ). Typically, the bit rate is given as a power of 2 (32, 64 , 128, etc.).

[0057]

[0058] However, sometimes B / R is not an integer, for example 8000 / 128=62.5. Therefore, rounding is used. In this case, at least 126 repetitions (i.e., N = 126) are needed for the first code rate to be less than or equal to 0.008 (the threshold used to detect the repetition code = N / 2). An SNR threshold of -5 dB may require the first bit rate (R1) to equal 128kbits / s for the BER to exceed a BER threshold of 10-3. This requires the first code rate to be less than or equal to 0.016. In this case, at least 62 repetitions (i.e., N = 62) are needed for the first code rate to be less than or equal to 0.016. An SNR threshold of -1.5 dB may require the first bit rate (R1) to equal 256kbits / s for the BER to exceed a BER threshold of 10-3. This requires the first code rate to be less than or equal to 0.032. In this case, at least 32 repetitions (i.e., n1= 32) are needed for the first code rate to be less than or equal to 0.032.

[0059] The number of bits in a set from the one or more first sets of encoded bits may be 2 (β = 2), and the number of bits in a set from the one or more second sets of encoded bits may be 4 (γ = 4). For a transmission bandwidth (B) of 8 MHz, the first uncoded bit rate is R1= 16 Mbits / s. The second uncoded bit rate is R2= 32 Mbits / s. An SNR threshold of -7.0 dB may require the first coded bit rate (R1) to equal 64kbits / s for the BER not to exceed a BER threshold of 10-3. This requires the first code rate to be less than or equal to 0.004. In this-7 -

[0060] case, at least 250 repetitions (i.e., N = 250) are needed for the first code rate to be less than or equal to 0.004. An SNR threshold of -3.5 dB may require the first coded bit rate (R1) to equal 128kbits / s for the BER not to exceed a BER threshold of 10-3. This requires the first code rate to be less than or equal to 0.008. In this case, at least 126 repetitions (i.e., N = 126) are needed for the first code rate to be less than or equal to 0.008. An SNR threshold of -1.0 dB may require the first coded bit rate (R1) to equal 256kbits / s for the BER not to exceed a BER threshold of 10-3. This requires the first code rate to be less than or equal to 0.016. In this case, at least 62 repetitions (i.e., N = 62) are needed for the first code rate to be less than or equal to 0.016.

[0061] Returning to Fig. 2, bit sequence concatenation unit 230 may concatenate a first set of encoded bits from the one or more first sets of encoded bits and a second set of encoded bits from the one or more second sets of encoded bits to obtain a transmit bit sequence. The transmit bit sequence may be transmitted in a transmission time interval. Modulator 240 maps the transmit bit sequence to a transmit symbol (TS) 250 from a set of symbols based on a modulation scheme (e.g., quadrature amplitude modulation or QAM). The modulation order may denote a defined number of symbols in the set of symbols. The modulation order may be a number greater than 2, usually 2α, where α = β + γ is a number for bits per symbol (e.g., 64). Let M denote the modulation order; then M = 2β+γ.

[0062] Each symbol from the set of symbols may be encoded as a unique combination of an amplitude and a phase of a carrier. A unique constellation point on a symbol constellation may represent each symbol from the set of symbols. Transmit symbol 250 may be transmitted (e.g., using a radio frequency frontend) over a first wireless channel (e.g., first wireless channel 70) to a first receiver (e.g., first receiver 120) and a second wireless channel (e.g., second wireless channel 71) to a second receiver (e.g., second receiver 130) in the transmission time interval.

[0063] Fig. 3 illustrates the implementation of receiver subsystem 300 while functioning as a receiver, according to an embodiment of the invention. Receiver subsystem 300 has two receiving modes: the first receiving mode is suitable for long distance (SNR<1) and the second receiving mode is suitable for short distance (SNR>1). In the first receiving mode, switch 301 it controlled to be in state 1. In the second receiving mode, switch 301 it-8 -

[0064] controlled to be in state 2. For example, if the transmitted constellation is 16-QAM (using 4 bits), all four bits are received by the demodulator 302. For β = 1 and γ = 3, one bit will be assigned to the receiver subsystem 300 located at long distance, and three bits will be assigned to the receiver subsystem 300 located at short distance.

[0065] A bit sequence deconcatenation unit 303 takes the left half bits of the transmitted 16-QAM symbols constellation, in which all the first bits are "0". In the right half bits of the transmitted 16-QAM symbols constellation, all the first bits are "1". Therefore, at state 1 (when receiver subsystem 300 is at long distance), the first decoder 304a considers the bits at the left half as b = "0" and the bits at the right half as b±= "1". At this state, all symbol bits b2— b4are ignored by the second decoder 304b.

[0066] At state 2 (when receiver subsystem 300 is at short distance), the second decoder 304b considers only three bits b2, b3, b4at the left half or right half depending if the first bit at the left half as "0" or the first bit at the right half as "1". At this state, all bits are ignored by the first decoder 304a. Therefore, at state 2, the second decoder 304b considers only the three bits b2,b3,b4.

[0067] According to one embodiment, the demodulator 302 may include a channel equalizer to compensate for one or more characteristics (e.g., phase-shift) of the wireless channel, as well as a maximum likelihood detector.

[0068] When the receiver subsystem 300 is far from the transmitter which results with SNR below 1, the first mode is used (state 1). In what follows, the first decoder uses first one (for 16-QAM) or one or two bits (for 64-QAM) of the received encoded bits.

[0069] When the first encoding is a repetition encoding, the receiver subsystem 300 which is in state 1, uses a majority rule to detect the information bits.

[0070] When the device is close to the transmitter which results with SNR above 1, the second mode (state 2) is used. The encoding of the second mode may be any kind commonly used like convolutional, LDPC or no encoding, while the second decoder 304b matches the encoder used.-9 -

[0071] First, decoder 304a may combine the one or more first sets of received encoded bits to obtain a set of decision values. Each bit from a set of the one or more first sets of received encoded bits corresponds to one decision value from the set of decision values. No bits from a set of the one or more first sets of received encoded bits correspond to the same decision value from the set of decision values. A decision value from the set of decision values is based on adding values of bits from the one or more first sets of received encoded bits that correspond to the decision value. First decoder 304a may determine first set of decoded bits 451 based on the set of decision values. A value of each bit of first set of decoded bits 451 is determined to be a first value (e.g., "1") based on a corresponding decision value in the set of decision values exceeding a decision threshold. A value of each bit of first set of decoded bits 451 is determined to be a second value (e.g., "0") based on the corresponding decision value in the set of decision values not exceeding a decision threshold.

[0072] By way of example, at transmitter subsystem 200, first encoder 220 may implement repetition encoding. The repetition number may be 2, which means two transmission time intervals are required to transmit a single first set of bits. Second encoder 221 may implement a second encoding with a second code rate of unity (i.e., no encoding), which means one transmission time interval is required to transmit a single second set of bits. In a first transmission time interval from the two transmission time intervals, the first set of bits may be {0} and the second set of bits may be {0,0,1, 0,0}. In a second transmission time interval from the two transmission time intervals, due to the repetition encoding, the first set of bits is the same as in the first transmission time interval {0}. In the second transmission time interval, due to the second code rate of unity, the second set of bits may differ from that in the first transmission time interval and may be {1, 0, 1, 0, 0}.

[0073] In the first transmission time interval, bit sequence concatenation unit 230 may concatenate the first set of encoded bits {0} and the second set of encoded bits {0, 0, 1, 0, 0} to obtain a transmit bit sequence {0, 0, 0, 1, 0, 0}. In the second transmission time interval, bit sequence concatenation unit 230 may concatenate the first set of encoded bits {0} and the second set of encoded bits {1, 0, 1, 0, 0} to obtain a transmit bit sequence {0, 1, 0, 1, 0, 0}.

[0074] In the first transmission time interval, modulator 240 may map the transmit bit sequence {0, 0, 0, 1, 0, 0} to a transmit symbol 411 based on a QAM scheme. In the second- 10-

[0075] transmission time interval, modulator 240 may map the transmit bit sequence {0, 1, 0, 1, 0, 0} to a transmit symbol 412 based on a QAM scheme.

[0076] The QAM scheme may have a modulation order of 64. Transmit symbol 411 and transmit symbol 412 may have constellation points on a 64-QAM symbol constellation 400a (e.g., as shown in FIG. 4A). A transmit symbol may have a constellation point on a part 410 of 64-QAM symbol constellation 400a when the first set of encoded bits is {0} regardless of the second set of encoded bits, e.g., transmit symbol 411 and transmit symbol 412 (as shown in FIG. 4A). A transmit symbol may have a constellation point on a part 420 of 64-QAM symbol constellation 400a when the first set of encoded bits is {1} regardless of the second set of encoded bits, e.g., transmit symbol 421 (as shown in FIG. 4A).

[0077] In the first transmission time interval, transmit symbol 411 may be transmitted over the first wireless channel (e.g., first wireless channel 70) to the first receiver (e.g., first receiver 120) and the second wireless channel (e.g., second wireless channel 71) to the second receiver (e.g., second receiver 130). In the second transmission time interval, transmit symbol 412 may be transmitted over the first wireless channel (e.g., first wireless channel 70) to the first receiver (e.g., first receiver 120) and the second wireless channel (e.g., second wireless channel 71) to the second receiver (e.g., second receiver 130).

[0078] The receiver subsystem 300 may receive two first received symbols. A first symbol of the two first received symbols may be received in the first transmission time interval, the second symbol of the two first received symbols may be received in the second transmission time interval. The first symbol may be based on transmit symbol 411 and characteristics (e.g., attenuation and phase-shift) of the first wireless channel. The second symbol may be based on transmit symbol 412 and characteristics (e.g., attenuation and phase-shift) of the first wireless channel.

[0079] First decoder 304a may combine the two first sets of the received encoded bits to obtain a set of decision values, based on a majority rule. For repetition number of 2, the decision values are given in the Table 1 below:

[0080] Table 1- 11 -

[0081] two

[0082] first 00 01 10 11

[0083] sets

[0084] decision 0 0 0 1

[0085]

[0086] First, decoder 304a may combine the two first sets of received encoded bits to obtain a set of decision values. Each decision value from the set of decision values is based on adding values of corresponding bits from first set {0} and second bit {0} to obtain the set of decision values {0}. In the example of Table 1, for the two first sets of received encoded bits {0,0}, {0,1} and {1,0}, the corresponding decision value is {0}. For the two first sets of received encoded bits {1,1}, the corresponding decision value is {1}.

[0087] The second decoder 304b may receive any symbol indicated in 400a. If the first bit of the transmit symbol is {0}, then the received symbols are from the left side of the 400a, namely 410. If the first bit of the transmit symbol is {1}, then the received symbols are from the right side of the 400a, namely 420.

[0088] In the first transmission time interval, bit sequence deconcatenation unit 303 may extract from the first sequence 411 {0, 0, 0, 1, 0, 0} a second set of received encoded bits {0, 0, 1, 0, 0}. When the second code rate is unity (i.e., no encoding), second decoder 304b may decode the second set of received encoded bits {0, 0, 1, 0, 0} to obtain a second set of decoded bits {0, 0, 1, 0, 0}, which is identical with the second set of bits transmitted in the first transmission time interval.

[0089] In the second transmission time interval, bit sequence deconcatenation unit 303 may extract from the second sequence 412 {0, 1, 0, 1, 0, 0} a second set of received encoded bits {1, 0, 1, 0, 0}. When the second code rate is unity (i.e., no encoding), second decoder 304b may decode the second set of received encoded bits {1, 0, 1, 0, 0} to obtain a second set of decoded bits {1, 0, 1, 0, 0}, which is identical with the second set of bits transmitted the second transmission time interval.

[0090] In another example, in the first transmission time interval, the first set of bits may be {0, 0} and the second set of bits may be {0, 1, 0, 0}, 431. In the second transmission time interval,- 12-

[0091] due to the repetition encoding, the first set of bits is the same as in the first transmission time interval {0, 0}. In the second transmission time interval, due to the second code rate of unity, the second set of bits may differ from that in the first transmission time interval and may be {0, 1, 1, 0}, 432.

[0092] First encoder 220 may encode the first set of bits 210, to obtain the first set of encoded bits. Second encoder 221 may encode the second set of bits 220, to obtain the second set of encoded bits. In the first transmission time interval, the first set of encoded bits may be {0, 0} and the second set of bits may be {0, 1, 0, 0}. In the second transmission time interval, due to the repetition encoding, the first set of encoded bits is the same as in the first transmission time interval and is {0, 0}. In the second transmission time interval, due to the second code rate of unity, the second set of encoded bits equals the second set of bits in the second transmission interval {0, 1, 1, 0}.

[0093] In the first transmission time interval, bit sequence concatenation unit 230 may concatenate the first set of encoded bits {0,0} and the second set of encoded bits {0, 1, 0, 0} to obtain a transmit bit sequence {0, 0, 0, 1, 0, 0}. In the second transmission time interval, bit sequence concatenation unit 230 may concatenate the first set of encoded bits {0, 0} and the second set of encoded bits {0, 1, 1, 0} to obtain a transmit bit sequence {0, 0, 0, 1, 1, 0}.

[0094] In the first transmission time interval, modulator 240 may map the transmit bit sequence {0, 0, 0, 1, 0, 0} to a transmit symbol 431 based on a QAM scheme. In the second transmission time interval, modulator 240 may map the transmit bit sequence {0, 0, 0, 1, 1, 0} to a transmit symbol 432 based on a QAM scheme.

[0095] Transmit symbol 431 and transmit symbol 432 may have constellation points on a 64-QAM symbol constellation 400b (e.g., as shown in FIG. 4B). A transmit symbol may have a constellation point on a part 430 of 64-QAM symbol constellation 400b when the first set of encoded bits is {0,0} regardless of the second set of encoded bits, e.g., transmit symbol 431, and transmit symbol 432 (as shown in FIG. 4B). A transmit symbol may have a constellation point on a part 440 of 64-QAM symbol constellation 400b when the first set of encoded bits is {0, 1} regardless of the second set of encoded bits, e.g., transmit symbol 441 (as shown in FIG. 4B). A transmit symbol may have a constellation point on a part 450 of 64-QAM symbol constellation 400b when the first set of encoded bits is {1, 1} regardless of the- 13-

[0096] second set of encoded bits, e.g., transmit symbol 451 (as shown in FIG. 4B). A transmit symbol may have a constellation point on a part 460 of 64-QAM symbol constellation 400b when the first set of encoded bits is {1, 0} regardless of the second set of encoded bits, e.g., transmit symbol 461 (as shown in FIG. 4B).

[0097] In the first transmission time interval, transmit symbol 431 may be transmitted over the first wireless channel (e.g., first wireless channel 70) to the first receiver (e.g., first receiver 120) and the second wireless channel (e.g., second wireless channel 71) to the second receiver (e.g., second receiver 130). In the second transmission time interval, transmit symbol 432 may be transmitted over the first wireless channel (e.g., first wireless channel 70) to the first receiver (e.g., first receiver 120) and the second wireless channel (e.g., second wireless channel 71) to the second receiver (e.g., second receiver 130).

[0098] The receiver subsystem 300 may receive two first received symbols. A first symbol of the two first received symbols may be received in the first transmission time interval, and a second symbol of the two first received symbols may be received in the second transmission time interval. The first symbol may be based on transmit symbol 431 and characteristics (e.g., attenuation and phase-shift) of the first wireless channel. The second symbol may be based on transmit symbol 432 and characteristics (e.g., attenuation and phase-shift) of the first wireless channel.

[0099] First decoder 304a may combine the two first sets of the received encoded bits to obtain a set of decision values based on majority rule. For repetition number of 2 the decision values are given in Table 2 below:

[0100] Table 2

[0101] three 00 00 00 00 11 11 11 11 first sets 00 01 10 11 00 01 10 11

[0102] decision 00 00 00 00 00 01 10 11

[0103]

[0104] Table 2 gives an example how the majority rule is applied.- 14-

[0105] In the example of Table 1, for the three first sets of received encoded bits {0,0}, {0,0};{0,0}, {0,1 };{0,0}, {1,0}; {0,0}, {1,1}; and {1,1}, {0,0}, the corresponding decision value is {0,0}. For the three first sets of received encoded bits {1,1}, {0,1}, the corresponding decision value is {0,1}. For the three first sets of received encoded bits {1,1}, {1,0}, the corresponding decision value is {1,0}. For the three first sets of received encoded bits {1,1}, {1,1}, the corresponding decision value is {1,1}.

[0106] The second decoder 304b may receive any symbol indicated in 400b. If the first two bits of the transmit symbol are {0,0}, then the received symbols are from the 430 section of the 400b. If the first two bit of the transmit symbol are {0,1}, then the received symbols are from the 440 section of the 400b. If the first two bit of the transmit symbol are {1,1}, then the received symbols are from the 450 section of the 400b. If the first two bit of the transmit symbol are {1,0}, then the received symbols are from the 460 section of the 400b.

[0107] In the first transmission time interval, bit sequence deconcatenation unit 303 may extract from the first sequence {0, 0, 0, 1, 0, 0} a second set of received encoded bits {0, 1, 0, 0}. When the second code rate is unity (i.e., no encoding), second decoder 304b may decode the second set of received encoded bits {0, 1, 0, 0} to obtain a second set of decoded bits {0, 1, 0, 0}, which is identical with the second set of bits.

[0108] In the second transmission time interval, bit sequence deconcatenation unit 303 may extract from the second sequence {0, 0, 0, 1, 1, 0} a second set of received encoded bits {0, 1, 1, 0}. When the second code rate is unity (i.e., no encoding), second decoder 304b may decode the second set of received encoded bits {0, 1, 1, 0} to obtain a second set of decoded bits {0, 1, 1, 0}, which is identical with the second set of bits.

[0109] Reference is now made to FIG. 5, which is a flow chart generally illustrating a method 500 at a transmitter subsystem that supports communication below a noise floor using a coded constellation, according to some embodiments of the invention.

[0110] Transmitter subsystem 200 may implement the steps of method 500. At step 510, a first set of bits may be encoded with a first encoding to obtain one or more first sets of encoded bits (e.g., using first encoder 220 as described hereinabove). At step 520, a second set of bits- 15-

[0111] may be encoded with a second encoding to obtain one or more second sets of encoded bits (e.g., using second encoder 221 as described hereinabove). At step 530, the first set of bits and the second set of bits may be concatenated to obtain one or more transmit bit sequences (e.g., using bit sequence concatenation unit 230 as described hereinabove). At step 540, the transmit bit sequence may be mapped to one or more transmit symbols (e.g., using modulator 240 as described hereinabove). At step 550, the one or more transmit symbols may be transmitted (e.g., using a radio frequency front end).

[0112] Reference is now made to FIG. 6, which is a flow chart generally illustrating a method 600 at a receiver subsystem in the first operational mode that supports communication below a noise floor using a coded constellation, according to some embodiments of the invention.

[0113] Receiver subsystem 300 may implement the steps of method 600 in the first operational mode (State 1). At step 610, one or more first received symbols may be received (e.g., using a radio frequency front end). At step 620, the one or more first received symbols may be mapped to one or more first sets of received encoded bits (e.g., using first demodulator 302 as described hereinabove). At step 630, the one or more first sets of received encoded bits may be decoded to obtain a first set of decoded bits (e.g., using first decoder 304a as described hereinabove).

[0114] Reference is now made to Fig. 7, which is a flow chart generally illustrating a method 700 at a receiver subsystem in the first operational mode that supports communication below a noise floor using a coded constellation, according to some embodiments of the invention.

[0115] Receiver subsystem 300 may implement the steps of method 700 in the second operational mode (e.g., as depicted in FIG. 3). At step 710, one or more second received symbols may be received (e.g., using a radio frequency front end). At step 720, the one or more second received symbols may be mapped to one or more received bit sequences. At step 730, one or more second sets of received encoded bits may be extracted from the one or more received bit sequences (e.g., using bit sequence deconcatenation unit 303 as described hereinabove). At step 740, the one or more second sets of received encoded bits may be decoded to obtain a second set of decoded bits.The above examples and description have of course been provided only for the purpose of illustrations, and are not intended to limit the invention in any way. As will be appreciated by the skilled person, the invention can be carried out in a great variety of ways, employing more than one technique from those described above, all without exceeding the scope of the invention.

Claims

- 17 -Claims1. A method at a transmitter that supports communication below a noise floor using a coded constellation, comprising:a) encoding a first set of bits with a first encoder to obtain one or more first sets of encoded bits;b) encoding a second set of bits with a second encoder to obtain one or more second sets of encoded bits;c) concatenating the one or more first sets of encoded bits and the one or more second sets of encoded bits to obtain one or more transmit bit sequences;d) mapping the one or more transmit bit sequences to one or more transmit symbols from a set of symbols based on a modulation scheme; ande) transmitting the one or more transmit symbols to a first receiver and a second receiver,wherein the distance between the transmitter and the receiver is sufficiently large such that the received signal which is below noise floor where SNR is below unity, andwherein the first encoding is configured to enable reception of the first set of bits with a BER above a BER threshold for an SNR above an SNR threshold, wherein the SNR threshold is less than unity.

2. A method according to claim 1, wherein the first encoding uses a lower-rate channel code.

3. A method according to claim 1, wherein the second encoding may use a higher-rate code.

4. A transmitter according to claim 1, wherein each symbol from the set of symbols is encoded as a unique combination of amplitude and phase of a carrier.

5. A transmitter that supports communication below a noise floor using a coded constellation comprising:a) a first encoder configured to encode a first set of bits with a first encoding to obtain one or more first sets of encoded bits;b) a second encoder configured to encode a second set of bits with a second encoding to obtain one or more second sets of encoded bits;- 18 -c) a bit sequence concatenation unit configured to concatenate the one or more first sets of encoded bits and the one or more second sets of encoded bits to obtain one or more transmit bit sequences; andd) a modulator configured to map the transmit bit sequences to transmit symbols from a set of symbols based on a modulation scheme,wherein the transmit symbols are transmitted to a first receiver and a second receiver, wherein a first distance between the transmitter and the first receiver is sufficiently large such that the received signal which is below noise floor, where SNR is below unity, and wherein the first encoding is configured to enable reception of the first set of bits with a BER above a BER threshold for an SNR above an SNR threshold, wherein the SNR threshold is less than unity.

6. A transmitter according to claim 5, wherein the encoded bits are combined and mapped to the one or more transmit symbols using a modulation scheme with a defined constellation order.

7. A transmitter according to claim 5, wherein each symbol from the set of symbols is encoded as a unique combination of amplitude and phase of a carrier.

8. A transmitter according to claim 5, wherein in a first or second transmission time intervals, the modulator map the transmit bit sequence to a transmit symbol, based on a QAM scheme.

9. A receiver that supports communication below a noise floor using a coded constellation, comprising:a) in a first operational mode:i) a deconcatenation unit in a first operational mode configured to map one or more first received symbols to one or more first sets of received encoded bits; andii) a first decoder in the first operational mode configured to decode the one or more first sets of received encoded bits to obtain a first set of decoded bits, and b) in a second operational mode:- 19 -i) a deconcatenation unit in the second operational mode configured to extract from the one or more received bit sequences one or more second sets of received encoded bits; andii) a second decoder in the second operational mode configured to decode the one or more second sets of received encoded bits to obtain a second set of decoded bits.

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