Communication system and its method

In a communication system including a plurality of pairs of a transmitting device 2 and a receiving device 3, the transmission performance in the pairs is to be improved. The transmitting device 2-k transmits a transmission signal sk(t) to the receiving device 3-k a plurality of number of times. The receiving device 3-k updates the weight matrix Wk and the hopping pattern Pk used by the FIR filter which performs filtering on the transmission signal rk(t) at a predetermined time interval. The receiving device 3-k transmits the updated hopping pattern Pk to the transmitting device 2-k. The transmitting device 2-k receives the hopping pattern Pk to be used for subsequent spread spectrum.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. national stage application claiming the benefit of International Application No. PCT/JP2008/062753, filed on Jul. 15, 2008, which claims the benefit of Japanese Application No. 2007-341948, filed on Dec. 25, 2007, the entire contents of which are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to a communication system and its method for transmitting data in a spread spectrum system using frequency hopping.

BACKGROUND ART

For example, Non-Patent Document 1 discloses a communication system configured such that any two communication devices are taken from a large number of communication devices to make a plurality of pairs of communication devices, each pair capable of transmitting data in an asynchronous DS-CDMA (Direct-Sequence Code Division Multiple Access) system.

Non-Patent Document 2 discloses a communication system where a receiving device feeds back a hopping pattern to a transmitting device.

Non-Patent Document 3 discloses an initial value of the hopping pattern P.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

Against the above background, the communication system and its method according to the present application has been made, and one of the embodiments is a communication system (1) including a plurality of pairs of a transmitting device (2) and a receiving device (3), wherein in each of the pairs, the transmitting device has signal transmission units (222,224,226, and244) which, based on a spread pattern (hopping pattern Pk) which includes a plurality of first elements (weights) defined with respect to components of a predetermined first number (M) of first domains (frequency domains) and components of a predetermined second number (L) of second domains (time domains) and spreads transmission data (message symbol bk) to the components of the first domains and the components of the second domains, sequentially spreads the transmission data to the components of the first domains and the components of the second domains every predetermined time interval (Tc, and Ts) and transmits the transmission data as a transmission signal (sk); and update units (240and242) which, based on the spread pattern received from the receiving device, update the spread pattern used to spread the transmission data; and the receiving device has receiving units (208,210,212) which receive the transmission signal; expansion units (400,402,404,424, and440) which sequentially expand the received transmission signal (s′k) into a plurality of second elements defined with respect to components of the first domains whose number is equal to or greater than the first number and components of the second domains whose number is a third number (L+α) which is greater than the second number at each of the time intervals; processing units (410,414,428,442,444) which sequentially perform a process using a plurality of first coefficients defined for each of the second elements on the second elements obtained as a result of the expansion at each of the time intervals; a generation unit (344) which generates the spread pattern using the processed second elements and a plurality of second coefficients constituting a part of the first coefficients; and a pattern transmission unit (346) which transmits the generated spread pattern to the transmitting device.

It should be noted that the above description contains reference numerals to clarity the correspondence between the present specification and the accompanying drawings, which is not intended to limit the technical scope of the present invention.

SUMMARY

An embodiment of the communication system according to the present invention includes a large number of communication devices and uses any plurality of pairs of the communication devices (e.g., a pair of two communication devices) to transmit a transmission signal obtained by spreading transmission data based on a hopping pattern represented in a matrix form, at the same time in parallel between the pairs of communication devices.

The plurality of pairs of communication devices can share the same path with each other. Thus, a pair of communication devices receives a transmission signal from another pair of communication devices, which decreases the transmission quality of the transmission signal in the pair communication devices.

In a pair of communication devices, one communication device (transmitting device) mainly transmits a transmission signal and the other communication device (receiving device) receives the transmission signal. It should be noted that the transmitting device and the receiving device may be of a completely different configuration or of the same configuration.

The receiving device receives a transmission signal, expands the received transmission signal into a matrix of components of a frequency domain and components of a time domain, multiplies each of the expanded matrix elements by a coefficient (first coefficient) for filtering, adds them in a row direction and in a column direction, and then outputs them as the filtering results.

The first coefficient uses the first coefficient as an element and can be expressed in a matrix larger in the row direction and in the column direction or in any one of the directions than that of the frequency hopping pattern.

The receiving device uses the above filtering results to update the matrix of the first coefficients so as to improve the quality of the transmission data decoded from the transmission signal.

Further, the receiving device extracts the second coefficients corresponding to the hopping pattern from the updated matrix of the first coefficients and transmits them to the transmitting device.

The transmitting device uses a new hopping pattern transmitted from the receiving device, generates a transmission signal with a transmission performance better than that before the new hopping pattern is used, and transmits the signal to the receiving device.

Thus, while transmission and feedback of transmission signals are repeated between the transmitting device and the receiving device belonging to the same pair of communication devices, the signal transmission performance therebetween is gradually improved.

The technical advantages of the present invention and other technical advantages should be readily apparent to those skilled in the art by reading the detailed description of the embodiments illustrated in the accompanying drawings.

The accompanying drawings are incorporated in the present specification to constitute a part thereof, illustrate embodiments of the present invention, and serve to explain the embodiments as well as the principle of the present invention.

The drawings referred to in the present specification should not be understood to be drawn in a certain scale unless otherwise noted.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention are illustrated in the accompanying drawings.

The present invention is described in connection with the embodiments, but it should be understood by those skilled in the art that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed.

On the contrary, the present invention is intended to cover the explicit spirit as defined by the appended claims as well as all alternatives, modifications, and equivalents falling within the scope of the invention as defined by the appended claims.

Moreover, the present invention is described specifically as well as in detail to the level that those skilled in the art can sufficiently understand the appended claims.

However, as will be apparent to those skilled in the art, the present invention may be made without following all the descriptions described specifically as well as in detail herein.

It should be noted that known methods, procedures, components, and circuits may not be described in detail for a simplified description of the embodiments of the present invention.

However, it should be noted that these terms and other similar terms should each be associated with an appropriate physical quantity and thus should be understood as a convenient label assigned to the corresponding quantity.

As will be apparent from the above discussion that unless otherwise noted, throughout the present invention, the description containing the terms such as “spread” and “transmit” should be understood to mean an operation and a process executed by a specific use of a computer hardware resource or a dedicated hardware resource.

First, a communication system1according to an embodiment of the present invention will be described.

FIG. 1illustrates the communication system1according to an embodiment of the present invention.

As illustrated inFIG. 1, the communication system1includes a K (two or more integer) number of transmitting devices (TX)2-1to2-K and a K number of receiving devices (RX)3-1to3-K each of which is fixed or semifixed in one place or mobile.

In the following description, when any one of the plurality of components such as transmitting devices2-1to2-K is specified without identifying a specific one, the one may be written simply as the transmitting device2for simplicity.

Hereinafter, the same reference numeral or reference character denotes substantially the same component throughout the figures.

Note that the transmitting device2and the receiving device3may be of the same configuration, but are distinguished from each other in the following description for the purpose of substantiating and clarifying the description.

As described above, the communication system1is configured such that one transmitting device2may transmit a transmission signal to a plurality of receiving devices3, a plurality of transmitting devices2may each transmit a transmission signal to one receiving device3, and a plurality of transmitting devices2may each transmit a transmission signal to a plurality of receiving devices3.

However, in the following description, for the purpose of substantiating and clarifying the description, the communication system1is configured as a specific example such that one transmitting device2-k(K≧k≧1) and one receiving device3-kare paired and a transmission signal is transmitted only between the transmitting device2-kand the receiving device3-kincluded in each of the plurality of pairs; and based on a frequency hopping pattern, spread spectrum is performed on the transmission signal sk(t) expressed in the low-pass equivalent.

FIG. 2illustrates modeled transmission signals s′k(t) received by the receiving device3-kof the communication system1illustrated inFIG. 1and the hopping pattern fed back from the receiving device3-kto the transmitting device2-k.

The communication system1allows a path to be shared by not only a pair of the transmitting device2-kand the receiving device3-kbut also other pairs.

In this case, as illustrated inFIG. 2, the receiving device3-kreceives not only the transmission signal sk(t) from the transmitting device2-kincluded in the same pair but also transmission signals s′k(t) including the transmission signals from the transmitting devices2-1to2-(k−1) and2-(k+1) to2-K included in other pairs.

In other words, the communication system1allows the receiving device3-kto be constantly susceptible to interference from each of the transmitting devices2-k′ belonging to other pairs.

Even in such a circumstance, the receiving device3-kof the communication system1sequentially updates a weight matrix (Wk) expressed in complex weights wk, m, andl(M≧m≧1 and L+α≧l≧1, where α is an integer equal to or greater than 0 and l is a process for each chip time length Tc) used for filtering so as to improve receiving performance of the transmission signal sk(t) received from the transmitting device2-kbelonging the same pair.

Further, the receiving device3-kfeeds back a part of the elements of the updated weight matrix (Wk) to the transmitting device2-kas a hopping pattern Pkand causes the transmitting device2-kto update the hopping pattern used for spectrum spreading so that the transmission signal sk(t) itself can be subject to spectrum spreading using a pattern suitable for passing through the path illustrated inFIG. 2.

FIG. 3illustrates a hardware configuration of the transmitting device2and the receiving device3illustrated inFIG. 1.

As illustrated inFIG. 3, the transmitting device2and the receiving device3are used by being connected to a computer (PC) or a network (not illustrated) such as a LAN where a message symbol (transmission data) bk(n: n denotes the sequence of message symbols) in a QPSK (quadrature phase-shift keying) system is outputted to the transmitting device2or the message symbol bk(n) is inputted from the receiving device3.

The transmitting device2and the receiving device3include an interface (IF) circuit200, a digital signal processor (DSP)202, a memory204for the DSP202, a digital/analog (D/A) converter206, a radio frequency (RF) circuit208, an antenna210, an analog/digital (A/D) converter212, a CPU214, and a memory216for the CPU214, and a user interface (UI) device218interfacing between the transmitting device2or the receiving device3and the user.

The transmitting device2and the receiving device3include a component such as a cell phone configured to be able to transmit voice and data in the CDMA system or a radio LAN device serving as a computer allowing software to perform signal processing, radio communication and information processing.

Note that in the following description, for the purpose of substantiating and clarifying the description, it is assumed as a specify example that the transmitting device2and the receiving device3allow software to perform signal processing and information processing.

However, the transmitting device2and the receiving device3may be configured to allow embedded hardware to perform signal processing and information processing depending on the configuration, application, and performance requirement thereof.

Moreover, the transmitting device2and the receiving device3do not necessarily use both the DSP202and the CPU214, but may use either any one depending on the configuration, application, and performance requirement thereof.

In the transmitting device2-kand the receiving device3-k, the IF200provides a function to input and output the message symbol bk(n) between the computer or the network and the transmitting device2and the receiving device3.

The DSP202executes a signal processing program stored in the memory204to perform spread spectrum on a message symbol bk(n) inputted from the IF200or a message symbol bk(n) generated from the voice inputted through a microphone (not illustrated) of the UI218, and outputs it to the D/A206.

The D/A206converts the digital message symbol bk(n) undergoing spread spectrum to an analog baseband or a transmission signal sk(t) with an intermediate frequency of the frequency which can be processed by the DSP202or the CPU214, and outputs it to the RF208.

The RF208converts the transmission signal sk(t) to a transmission signal sk(t) of a frequency used for signal transmission between the transmitting device2and the receiving device3and transmits the signal to the path through the antenna210.

Then, the RF208receives the transmission signal sk(t) from the transmitting device2or the receiving device3of the communication party, converts the signal to a transmission signal sk(t) of a baseband or an intermediate frequency, and outputs the signal to the A/D212.

The A/D212converts the analog transmission signal sk(t) to a digital transmission signal sk(t) and outputs the signal to the DSP202.

The CPU214executes a program stored in the memory216to control the operation of the transmitting device2and the receiving device3, for example, according to the user operation to the UI218.

In addition, the CPU214performs processes of setting and updating the weight used for filtering the transmission signal sk(t) received by the DSP202.

Moreover, the CPU214controls the UI218to present the user with information and the like.

FIG. 4illustrates a configuration of a transmitting program20executed by the transmitting device2-kand the receiving device3-killustrated inFIG. 1.

FIG. 5illustrates a configuration of a symbol and a chip used by the transmitting device2and the receiving device3.

As illustrated inFIG. 4, the transmitting program22includes a timing control unit220, first and second multiplication units222and226, a delay unit224, a hopping pattern (Pk) receiving unit240, a hopping pattern setting unit242and a frequency synthesizer (FS) unit244.

The transmitting program20is supplied to the transmitting device2and the receiving device3, for example, via a storage medium or the network; is loaded in the memory204for the DSP or loaded in the memory216for the CPU illustrated inFIG. 3; and is executed by specifically using a hardware resource of the transmitting device2and the receiving device3under an OS such as ITRON executed by the DSP202or the CPU214(the same is applied to the each of the following programs).

The transmitting program22uses the above units to perform spread spectrum on the message symbol bk(n) inputted through the network or the like according to the hopping pattern to generate the transmission signal sk(t) and outputs the signal to the D/A206.

In the transmitting program22executed by the transmitting device2-k, the timing control unit220controls the timing of the operation of each component of the transmitting program22so as to be synchronized with the message symbol bk(n) and the chip illustrated inFIG. 5.

The delay unit224gives a delay Tsof one message symbol to the multiplication result dk(n−1) of an (n−1)-th message symbol bk(n−1) outputted from the first multiplication unit222.

When an n-th message symbol bk(n) is inputted to the first multiplication unit222, the delay unit224outputs the delayed multiplication result to the first multiplication unit222as delay data dk(n−1).

The first multiplication unit222multiplies the inputted n-th message symbol bk(n) by the delay data dk(n−1) inputted from the delay unit224and outputs the multiplication result dk(n) to the delay unit224and the second multiplication unit226.

Note that as discussed later as the performance evaluation of the communication system1, the weight adjustment (training) of the filter unit4is performed using known data (pilot) preliminarily stored in the transmitting device2and the filter unit4, the above described process (differential encoding) by the delay unit224and the first multiplication unit222is not required.

In this case, the transmitting device2outputs the message symbol bk(n) itself to the multiplication unit226as the multiplication result dk(n).

The hopping pattern receiving unit240receives a hopping pattern Pkused for spread spectrum of the message symbol bk(n) by frequency hopping (FH) from the receiving device3via the antenna210, the RF208, the A/D212, and the receiving program30(described later by referring toFIGS. 6 to 8) executed by the transmitting device2-k, and outputs it to the hopping pattern receiving unit240.

The hopping pattern Pkcan be expressed in an M×L matrix as shown in the following expression 1, where the column component includes the number of components corresponding to the code length L (an L number of components of the time domain; L denotes an integer of 2 or more) per chip and the row component includes the M number (M denotes an integer of 2 or more) of elements of the frequency domain contained in a signature wave signal ck(t) generated by the frequency synthesizer unit244.

The hopping pattern setting unit242replaces an old hopping pattern Pkwhich has been used so far with a new hopping pattern Pkinputted from the hopping pattern receiving unit240to update the hopping pattern.

In addition, the hopping pattern setting unit242outputs the updated hopping pattern Pkto the frequency synthesizer unit244.

The frequency synthesizer unit244generates a signature wave signal ck(t) of a frequency based on the hopping pattern Pkinputted from the hopping pattern setting unit242and outputs the signal to the second multiplication unit226.

The second multiplication unit226operates as a quadrature modulator, performs complex multiplication on the multiplication result bk(n) inputted from the first multiplication unit222and the signature wave signal ck(t) for spreading spectrum and outputs the signal to the D/A206(FIG. 3) as digital data indicating the transmission signal sk(t).

The D/A206converts the digital data indicating the transmission signal sk(t) to an analog transmission signal sk(t), which is converted to a frequency used for transmission between the transmitting device2and the receiving device3by the RF208. Then, the frequency undergoes power amplification before being transmitted to each communication party through the antenna210.

FIG. 6illustrates a configuration of a receiving program30executed by the transmitting device2-kand the receiving device3-killustrated inFIG. 1.

FIG. 7illustrates a configuration of a filter unit4of the receiving program30illustrated inFIG. 6.

FIG. 8illustrates a configuration of the coefficient multiplication unit44illustrated inFIG. 7.

As illustrated inFIG. 6, the receiving program30includes a timing control unit300, a filter unit4, a decoding unit32, and an updating unit34.

The decoding unit32includes an addition unit (Σ)320, a demodulation unit322, a delay unit324, and a multiplication unit326.

The updating unit34includes a received signal matrix (Rk(n)) generation unit340, a weight (Wk) updating unit342, a hopping pattern (Pk) generation unit344, and a hopping pattern (Pk) transmission unit346.

As illustrated inFIG. 7, the filter unit4illustrated inFIG. 7includes an M number of function generation units400-1to400-M each corresponding to an element of the frequency domain of the hopping pattern Pk; multiplication units402-1to402-M, low pass filter (LPF) units404-1to404-M, selection units406-1to406-M, and414, a selection control unit408, a coefficient setting unit410, a weighting unit420including a hopping pattern corresponding portion422containing an M×L number of elements each corresponding to a hopping pattern Pk, and a total sum calculation unit (Σ)412, which constitute an FIR filter.

Note that in the following description, for the purpose of clarifying the description, the reference numeral or reference character may be followed by ( ) such as (1,1), and thus the reference numeral or reference character may be different between the following description and the corresponding drawing.

Of the components of the above weighting unit420, the hopping pattern corresponding portion422corresponds to each of the M×L number of delay units424-(1,1) to424-(M, L), coefficient multiplication units426-(1,1) to426-(M, L), and addition units428-(1,1) to428-(M, L).

It should be noted that apparently the technical scope of the present invention also covers the communication system1including a modified receiving program30which further increases each component of the weighting unit420such that the M×(L+α) number of delay units424, coefficient multiplication units44or the M×(L+α−1) number of addition units are increased to the (M+1)×(L+α) number or the (M+1)×(L+α−1) number thereof, or further increase the number of each component of the weighting unit420.

Note that the delay units424-m, lto (m, L+α) and the register units440-m,1to (m, L+α) illustrated inFIG. 7serve as L+α stages of shift registers which shift complex data received from the previous stage to the following stage every Tc.

The receiving program30executed by the receiving device3-kuses the above components to receive a transmission signal from the transmitting devices2-1to2-K via the antenna210, the RF208, and the A/D212(FIG. 3), and decodes a message symbol b′k(n) from the digital-converted transmission signal s′k(t) to output the message symbol to the network or the like.

In addition, the receiving program30updates the weight matrix (Wk) expressed in an M×(L+α) matrix used by the filter unit4by repeating the update a predetermined number of times so as to decode the message symbol b′k(n) corresponding to the message symbol bk(n) in the transmitting device2-kbelonging to the same pairs with excellent performance from the transmission signal s′k(t) received from the transmitting devices2-1to2-K.

Of the updated weight matrices Wk, the receiving program30transmits (feeds back) the element corresponding to the hopping pattern corresponding portion422to the transmitting device2-kvia the D/A206, the RF208and the antenna210as illustrated inFIG. 2so as to update the hopping pattern Pk.

That is, the hopping pattern Pkis defined as complex conjugates wk, m, lof numbers w*k, m, lmultiplied by a (first to M-th row)×(first to L-th column) of elements starting with the element inputted to the filter unit4early in the weight matrices Wk(* preceded by a symbol denotes a complex conjugate number indicated by the symbol).

It should be noted that the technical scope of the present invention also covers the communication system1including a modified receiving program30which associates the hopping pattern Pkwith an element of a weight matrix Wkdifferent from the above in the time axis direction.

As illustrated inFIGS. 6 to 8, in the receiving program30executed by the receiving device3-k, the timing control unit300controls the timing of the operation of each component of the receiving program30so as to be synchronized with the message symbol bk(n) and the chip illustrated inFIG. 5.

The selection control unit408controls the timing of the selection of each of the selection units406and414.

The digital message symbol r(t) is inputted to the multiplication units402-1to402-M of the filter unit4of the receiving program30.

Each function generation unit400-mgenerates a function e−j2πζmt, and outputs the function to the multiplication unit402-m.

Note that in the function e−j2πζmt, j is (−1)1/2, and ζm(Hz) denotes a frequency of the m-th tone of the spectrum spread transmission signal such as ζm=(m−1)/Tc(Hz).

Each multiplication unit402-moperates as a quadrature modulator and performs complex multiplication on the transmission signal r(t) inputted from the A/D212(FIG. 3) and the function e−j2πζmtinputted from the function generation unit400-mto output the complex multiplication result r(t)e−j2πζmtto the LPF404-m.

Each LPF404-mis implemented, for example, by an integrator which integrates the multiplication result r(t) e−j2πζmtinputted from the multiplication unit402-ifrom the time nTs+(l−1)Tc+τk, k, 1to the time nTs+lTc+τk, k, 1.

In this case, each LPF404-mpasses the frequency component rk, m, l(n) of an m-th tone of an 1-th chip for the purpose of decoding an n-th message symbol bk(n) and outputs frequency component to the selection unit406-m.

In a timing (t=Ts+lTc+τk, k, 1) when each LPF unit404-mcompletes integration, the selection unit406-m, according to the control of the selection control unit408, selects the frequency component rk, m, l(n) inputted from the LPF404-mand outputs the frequency component to the delay unit424-m,1and the received signal matrix generation unit340.

When the frequency component rk, m, L+α(n) of an m-th tone is inputted from each selection unit406-m, the delay unit424-(m, L+α) continuously outputs the frequency component rk, m, L+α(n) of an (L+α−1) th chip giving a delay of Tcto each register440-m, L+α and stores the frequency component therein.

Note that likewise, other delay units424also continuously each output the frequency component rk, m, lto the corresponding register440. The operation of the filter unit4is stabilized by continuously outputting a value to each register440during the time period of Tc.

Moreover, each delay unit424-(m, L+α) sequentially gives a delay of Tcto the frequency component rk, m, L+α(n) inputted from each selection unit406-mat a cycle of Tcand outputs the result to each delay unit424-(m, L+α−1) at the following stage.

When each of the (L+α−1) to second frequency component rk, m, L+α−1(n) to rk, m, 2(n) is inputted from each of the delay units424-(m, L+α) to424-(m,3) at the previous stage, each of the delay units424-(m, L+α−1) to424-(m,2) outputs the (L+α−2) to first frequency component rk, m, L+α−2(n) to rk, m, 1(n) giving a delay of Tcat the previous stage to the register440-m, land stores it therein.

In addition, each of the delay units424-(m, L+α−1) to424-(m,2) sequentially gives a delay of Tcto the (L+α) to third frequency component rk, m, L+α(n) to rk, m, 3(n) inputted from each of the delay units424-(m, L+α) to424-(m,3) at the previous stage at a cycle of Tcand outputs the result to each of the delay units424-(m, L+α−2) to424-(m,1) at the following stage.

When each second frequency component rk, m, 2(n) is inputted from each delay unit424-(m,2) at the previous stage, each delay unit424-(m,1) outputs the first frequency component rk, m, 1(n) giving a delay of Tcat the previous stage to each register440-m,1and stores the frequency component therein.

Each register440-m, lholds the frequency component rk, m, 1(n) inputted from the delay unit424-m, land outputs the frequency component to each multiplication unit442-m, l.

Each coefficient storage unit444-m, lholds each element m, l (weight wk, m, l) of the weight matrix (Wk) set by the weight updating unit342(FIG. 6) and outputs the element to each multiplication unit442-m, l.

Each multiplication unit442-(m, L+α) performs complex multiplication on each of the frequency components rk, m, L+α(n) inputted from the registers440-(m, L+α), the weight wk, m, L+α, and the complex conjugate number w*k, m, L+αand outputs the multiplication results to each addition unit428-(m, L+α−1).

Each of the multiplication units442-(m, L+α−1) to442-(m,1) performs complex multiplication on each of the frequency components rk, m, L+α(n) to rk, m, 1(n), the weights wk, m, L+αto wk, m, 2, and the complex conjugate numbers w*k, m, L+αto W*k, m, land outputs the multiplication results to the respective addition units428-(m, L+α−1) to424-(m,1).

Each of the addition units428-(m, L+α−1) to428-(m,2) performs complex addition on the multiplication results inputted from the respective multiplication units442-(m, L+α−1) to442-(m,2) and the addition results inputted from the respective addition units428-(m, L+α) to (m,3), and outputs the addition results to the respective addition units428-(m, L+α−2) to428-(m,1).

The addition unit428-(m,1) performs complex addition on the multiplication results inputted from the multiplication unit442-(m,1) and the addition results inputted from the addition unit428-(m,2) and outputs the addition results to the total sum calculation unit412.

The total sum calculation unit412calculates the total sum of the addition results inputted from the addition unit428-(m,1) and outputs the complex filter output data d′k(n) to the selection unit414.

The selection unit414selects the filter output data d′k(n) calculated by the total sum calculation unit412, and outputs the data to the demodulation unit322(FIG. 6).

The received signal matrix generation unit340generates an (L+α)×M of received signal matrices Rk(n) from all frequency components for decoding an n-th symbol outputted from each LPF404-m, namely, the frequency components rk, m, 1(n) to rk, m, L(n) and a part of the frequency components rk, m, l(n+1) (in the case of L>α, the frequency components rk, m, 1(n+1) to rk, m, α(n+1) is also written as the frequency components rk, m, L+1(n) to rk, m, L+α(n)), and outputs received signal matrices Rk(n) to the weight updating unit342.

The weight updating unit342processes the received signal matrix Rk(n) inputted from the received signal matrix generation unit340, for example, using an N-LMS (normalized least mean square) algorithm.

The weight updating unit342uses the above processing results and the error data ek(n) inputted from the addition unit320to optimize the weight wk, m, 1contained in the weight matrix (Wk) so as to decode the message symbol bk(n) from the transmission signal rk(t) received from the transmitting device2-kwith better performance.

The hopping pattern generation unit344extracts a portion corresponding to the hopping pattern corresponding portion422from the weight wk, m, lupdated by the weight updating unit342to generate a hopping pattern Pkcontaining the weight wk, m, 1to wk, m, Land outputs the pattern to the hopping pattern transmission unit346.

The hopping pattern transmission unit346outputs the message symbol bk(n) indicating the hopping pattern Pkinputted from the hopping pattern generation unit344to the transmitting program22(FIG. 4) executed by the receiving device3-kso as to be transmitted to the transmitting device2-kvia the A/D212, the RF208and the antenna210.

The demodulation unit322performs a process using a signum function (sgn(x); also called a code function) on the filter output data d′k(n) received from the filter unit4to obtain the complex reference data d″kas the processing result, and outputs the reference data to the delay unit324and the multiplication unit326.

Note that the signum function sgn(x) is defined such that if x is positive (x>0), +1 is returned; if x is negative (x<0), −1 is returned; and if x=0, 0, +1 or −1 is appropriately returned;

Note that generally x is unlikely to be 0 due to noise, there no practical need to define the value returned by the signum function in the case of x=0.

The delay unit324delays, by Ts, the reference data d″k(n) outputted from the demodulation unit322and outputs the reference data to the multiplication unit326.

Note that as discussed later as the performance evaluation of the communication system1, the weight adjustment (training) of the filter unit4is performed using known data (pilot) preliminarily stored in the transmitting device2and the filter unit4, the above described process (differential decoding) by the above described demodulation unit322and the delay unit324is not required.

In this case, in the receiving device3, the reference data d″k(n) is assumed to be the demodulated message symbol bk(n).

The multiplication unit326multiplies the reference data d″k(n) inputted from the demodulation unit322and the reference data d″k(n−1) delayed by the delay unit324to decode the message symbol bk(n) and outputs the message symbol bk(n) to a network or the like connected to the receiving device3-k.

The addition unit320subtracts the filter output data d′k(n) outputted from the processing result data filter unit4from the reference data d″k(n) outputted from the demodulation unit322to generate the error data ek(n) and outputs the error data ek(n) to the weight updating unit342.

Hereinafter, the communication between the transmitting device2-kand the receiving device3-kwhich transmit the message symbol bk(n) to each other as a pair of communication devices in the communication system1(FIG. 1) will be described.

First, the process in the transmitting device2-kwill be described.

In the transmitting device2-k, the multiplication unit222of the transmitting program22(FIG. 4) receives the message symbol bk(n) from the network or the like.

The multiplication unit222and the delay unit224processes the inputted message symbol bk(n) to generate a differentially encoded complex symbol dk(n) and outputs the symbol dk(n) to the delay unit224.

The differentially encoded complex symbol dk(n) is defined as dk(n)=bk(n) dk(n−1) using an n-th inputted message symbol bk(n) and an (n−1)-th generated differentially encoded complex symbol dk(n−1).

Meanwhile, the hopping pattern setting unit242sets an initial value of the hopping pattern Pkor the hopping pattern Pkupdated by the receiving device3-kof the communication party and received by the hopping pattern receiving unit240, to the frequency synthesizer unit244.

The frequency synthesizer unit244uses the set hopping pattern Pkto generate a signature waveform signal ck(t) defined in the following expression 2 and outputs the signal ck(t) to the multiplication unit226.

In the expression 2, Tcdenotes the time length of the chip illustrated inFIG. 5and defined as Tc>t>0; and αk, 1(t) defines an 1-th chip waveform defined as the following expression 3.

In the expression 3, the rectangular function g(t) is defined as the following expression 4.

Meanwhile, as described above, the frequency hopping pattern Pkused to spread spectrum of the message symbol bk(n) in the transmitting device2-kcan be defined as an M×L matrix shown in the following expression 5.

Note that in the expression 5, L denotes the number of chips contained in one message symbol illustrated inFIG. 5; and M denotes the number of tones used for frequency hopping.

The multiplication unit226multiplies the signature waveform signal ck(t) inputted from the hopping pattern setting unit242and the differentially encoded complex symbol dk(n) inputted from the multiplication unit222to generate the transmission signal sk(t) defined in the following expression 6 as the multiplication result and outputs the transmission signal sk(t) to the D/A206.

The D/A206, the RF208, and the antenna210(FIG. 3) transmit the inputted transmission signal sk(t) to the receiving device3-kof the communication party.

Note that in the expression 6, Tsdenotes the code time length of the message symbol bk(n) illustrated inFIG. 5and defined as LTs=Tc.

Moreover, the expression 6 indicates differentially encoded complex symbol dk(n)=bk(n)·dk(n−1) and a differentially encoded complex symbol transmitted during nTs>t>(n−1)Ts.

As described above, the message symbol bk(n) is generated, for example, assuming that a QPSK modulation system is used.

Next, a non-target signal received by the transmitting device2-killustratedFIG. 1and the like will be described.

In the communication system1, a transmission signal is transmitted independently to each pair of communication devices.

In this case, the receiving device3-kreceives transmission signals from the transmitting devices2-1to2-(k−1),2-(k+1) to2-K as illustrated inFIG. 2.

In other words, the receiving device3-kreceives not only a transmission signal from the receiving device3-kof the communication party but also unwanted signals and noise from the transmitting devices2-k′ of other pairs.

Note that inFIG. 2, hk′, k(t) denotes a complex impulse response function which the path from the transmitting device2-k′ to the receiving device3-kgives to a transmission signal from the transmitting device2-k′ to the receiving device3-k, and is defined in the following expression 7.

In addition, inFIG. 2, AWGN denotes additive white Gaussian noise which the receiving device3-kreceives together with the transmission signals.

Note that in the expression 7, hk′, idenotes a complex gain constant defined in an i-th transmission channel; and τk′, k, i(Tc>τk′, k, i>0) denotes a delay defined in an i-th transmission channel.

In addition, in the expression 7, hk′, kdenotes the number of paths contained in the path from the transmitting device2-kto the receiving device3-k.

The transmission signal rk(t) received by the receiving device3-kis formulated by the following expressions 8-1 and 8-2.

Next, the process in the receiving device3-kwill be described.

In the receiving device3-k, the RF208(FIG. 3) receives a transmission signal rk(t) shown in the expressions 8-1 and 8-2 via the antenna210, converts the transmission signal to a transmission signal sk(t) of a baseband or an intermediate frequency which can be processed by the DSP202and the like, and outputs the transmission signal sk(t) to the A/D212.

The A/D212converts the transmission signal rk(t) inputted from the RF208to a digital transmission signal rk(t) and outputs the transmission signal rk(t) to the DSP202and the like.

The receiving program30(FIGS. 6 to 8) is executed in the DSP202and the like in the receiving device3-k.

In the filter unit4of the receiving program30, the multiplication unit402-mmultiplies the inputted transmission signal rk(t) by a function e−j2πηmtand outputs the multiplication result r(t)e−j2πηmtto the LPF404-m.

Each LPF404-msequentially integrates the multiplication result r(t)e−j2πζmtduring nTs+(l−1)Tc+τk′, k, ito nTs+lTc+τk′, k, ias shown in the following expressions 9-1 and 9-2, and outputs the result to the weighting unit420.

As a result of integration by the LPF404-m, as shown in the following expressions 9-1 and 9-2, an m-th tone of component contained in the transmission signal rk(t) is separated individually.

Note that as described above, the expressions 9-1 and 9-2 assume L+α≧l≧1, ζm(Hz) denotes an m-th tone frequency in the spectrum spread transmission signal, and is defined as ζm=(m−1)/Tc(Hz).

The received signal matrix generation unit340generates a received signal matrix Rk(n) defined in the following expression 10 from the frequency component rk, m, 1(n), rk, 1(n+1) obtained in the time length t (nTs+(L+α)Tc+τk′, k, i>t>nTs+τk′, k, i).

Meanwhile, the filter output data d′k(n) outputted from the filter unit4is defined in the following expression 11.

Note that in the expression 11, H denotes a complex conjugate and a transposition of the matrix; and tr denotes a trace of the matrix.
[Expression 11]
d′k(n)=tr└wkH(n)Rk(n)┘  (11)

The demodulation unit322performs a process using a signum function on the filter output data d′k(n) as shown in the following expression 12 to generate reference data d″k(n).

Note that in the expression 12, sgn denotes a signum function, Re[x] denotes a real number component of a complex number x, and Im[x] denotes a imaginary number component of the complex number x.
[Expression 12]
d″k(n)=sgn[Re[{circumflex over (d)}k(n)]]+j sgn[Im[{circumflex over (d)}k(n)]]  (12)

The multiplication unit326performs complex multiplication on an n-th reference data d″k(n) and an (n−1)-th reference data d″k(n) as shown in the following expressions 13-1 to 13-3 to obtain the message symbol b′k(n).

The addition unit320subtracts the filter output data d′k(n) outputted from the filter unit4from the reference data d″k(n) outputted from the demodulation unit322to generate the error data ek(n) defined in the following expression 14 and outputs the error data ek(n) to the weight updating unit342.

As will be apparent from the generation method, the error data ek(n) indicates the difference between the reference data d″k(n) and the filter output data d′k. The weight updating unit342updates and optimizes the weight so as to minimize the value of the error data ek(n), namely, so that the value of the reference data d″k(n) comes close to the value of the filter output data d′k.
[Expression 14]
ek(n)={tilde over (d)}k(n)−tr└wkH(n)Rk(n)┘  (14)

The weight updating unit342is defined in the following expression 15; uses the received signal matrix Rk(n) and the error data ek(n) to update the weight matrix Wk(n) used by the filter unit4to process an n-th message symbol bk(n) as shown in the following expression 16; generates a weight matrix Wk(n+1) used to process an (n+1) th or later message symbol bk; and outputs the weight matrix to the coefficient setting unit410of the filter unit4and hopping pattern generation unit344.

Note that ∥Rk(n)∥Fin the expression 15 denotes a Frobenius norm of the received signal matrix Rk(n) defined in the following expression 17.

Each time the weight updating unit342updates the weight matrix Wk(n+1), the coefficient setting unit410sets the element m, l(weight wk, m, 1(n)) of a new weight matrix Wk(n+1) to each coefficient storage unit444-m, lof the coefficient multiplication units44-(m,1), for example, at the boundary of a message symbol inputted to the filter unit4.

Note that as the initial value of the weight matrix Wk, for example, the weight matrix Wk(0) defined in the following expression 18 is used.

Note that in the expression 18, T denotes a transposition of the matrix and 0α×MT denotes a zero matrix with a size of α×M.
[Expression 18]
Wk(0)=└PkT(0)Oα×MT┘T(18)

The filter unit4uses the weight matrix Wk(n+1) updated as described above to perform filtering on the next (n+1) th transmission signal rk(t). The decoding unit32processes the filter output data d′k(n+1) outputted from the filter unit4to decode the message symbol b′k(n) corresponding to the message symbol bk(n) processed by the transmitting program22executed in the transmitting device2-k.

[Feedback of Hopping Pattern Pk]

Hereinafter, the feedback process of the hopping pattern Pkfrom the receiving device3-kto the transmitting device2-kwill be described.

The hopping pattern generation unit344of the receiving program30executed in the receiving device3-kextracts a part of the weight matrix Wkinputted from the weight updating unit342corresponding to the hopping pattern corresponding portion422(FIG. 7) as shown in the expressions 19-1 and 19-2 to generate an new hopping pattern Pk(λ) and outputs the hopping pattern Pk(λ) to the hopping pattern transmission unit346.

Note that the expressions 19-1 and 19-2 exemplifies that the hopping pattern Pk(λ) is fed back from the receiving device3-kto the transmitting device2-kat the time t=λTf+Δk+αTc+τk, k, 1.

In the expressions 19-1 and 19-2, λ is defined as Nf≧λ≧1; Nfdenotes the number of times the feedback is repeated; Tfdenotes a time interval of the feedback; Δk(Tf≧Δk≧0) denotes an offset time preliminarily determined for feedback timing.

Note that in the expressions 19-1 and 19-2, a transmission delay from the receiving device3-kto the transmitting device2-kis ignored.

Moreover, in the expressions 19-1 and 19-2, the symbol shown in the following expression 20 is defined in the following expression 21.

In the expression 21, {q} denotes a maximum positive integer equal to or less than q.
[Expression 20]
{circumflex over (n)}k(20)
[Expression 21]
{circumflex over (n)}kΔ{(λTf+Δk+αTc+τk,k,1)/Ts}  (21)

The hopping pattern transmission unit346transmits the new hopping pattern Pk(λ) inputted from the hopping pattern generation unit344to the transmitting device2-kvia the A/D212, the RF208and the antenna210(FIG. 3) as illustrated inFIG. 2.

In the transmitting program22executed in the transmitting device2-k, the hopping pattern receiving unit240receives the hopping pattern Pk(λ) from the receiving device3-kand outputs the hopping pattern Pk(λ) to the hopping pattern setting unit242.

The hopping pattern setting unit242sets the hopping pattern Pk(λ) to the frequency synthesizer unit244, which generates the signature wave signal ck(t) based on the hopping pattern Pk(λ) and performs spread spectrum on the message symbol bk(n).

Note that the initial value Pk(0) of the hopping pattern Pkset by the frequency synthesizer unit244is sequentially optimized by updating the hopping pattern Pkdescribed above, and thus, for example, may be a value preliminarily determined by experiment or may be a random value.

In the above configured communication system1, the data transmission between the transmitting device2-kand the receiving device3-kcan minimize the ISI (intersymbol interference) and the MAI (multiple access interference).

Moreover, the update of the hopping pattern Pkof the transmitting device2-kallows the reference data d″k(n) to achieve the MMSE (minimum mean-squared error) due to the update.

Therefore, according to the update of the hopping pattern Pkdescribed above, data transmission with an extremely small bit error rate (BER) can be provided between the transmitting device2-kand the receiving device3-k.

Hereinafter, the overall operation of the data transmission between the transmitting device2-kand the receiving device3-k, the feedback of the hopping pattern Pk, and the update thereof will be described.

FIG. 9illustrates a communication sequence diagram illustrating the data transmission and the feedback (S10) of the hopping pattern Pkbetween the transmitting device2-kand the receiving device3-killustrated inFIG. 1and the like.

In step100-1(S100-1), the transmitting device2-ktransmits a transmission signal sk(t) to the receiving device3-ka plurality of number of times.

In step102-1(S102-1), the receiving device3-kupdates the weight matrix Wkand the hopping pattern Pkat the time intervals described by referring to the expressions 19-1 and 19-2.

In step104-1(S104-1), the receiving device3-ktransmits or feeds back the updated hopping pattern Pkto the transmitting device2-k.

In step106-1(S106-1), the transmitting device2-kupdates the hopping pattern Pkby replacing the previous hopping pattern Pkwith the new hopping pattern Pkreceived from the receiving device3-kand uses the updated hopping pattern Pkfor spread spectrum.

The above described process is repeated, for example, an Nfnumber of times between the transmitting device2-kand the receiving device3-k.

Hereinafter, a variation of the communication system1(FIG. 1, etc.) will be described.

The description has been made such that the feedback of the hopping pattern Pkand the update thereof are repeated an Nfnumber of times between the transmitting device2-kand the receiving device3-k. However, for example, the number of times of the feedback and the update is not limited but the feedback and the update may be performed at a constant time interval or at random times.

Moreover, as illustrated by dotted lines inFIG. 6, the receiving program30may be configured such that a quality measurement unit360which measures the signal intensity or the SN (signal noise) ratio of the transmission signal rk(t) is added to the receiving program30, and when the transmission signal quality becomes lower than a specified level, the updating unit34performs the feedback and the update of the hopping pattern Pkto improve the transmission signal quality.

Moreover, if the message symbol bk(n) contains an error detection code, as illustrated by dotted lines inFIG. 6, the receiving program30may be configured such that an error rate measurement unit362which measures the error rate of the message symbol b′k(n) obtained by decoding is added to the receiving program30, and when the error rate of the message data b′k(n) reaches or exceeds a specified level, the updating unit34performs the feedback and the update of the hopping pattern Pkto reduce the error rate.

Moreover, the description has been made such that in the communication system1, the transmitting device2and the receiving device3use frequency hopping to spread spectrum of the message symbol bk(n). However, for example, the communication system1may be configured such that the transmitting device2and the receiving device3use a hopping pattern made of two time domains or frequency components to perform the update and the feedback of the hopping pattern.

Moreover, the description has been made such that in the communication system1, the weight matrix Wkis optimized by the N-LMS algorithm to update the hopping pattern Pk, but the update optimization algorithm may be appropriately changed to another algorithm depending on the configuration and the application of the communication system1and the performance of the DSP202.

EMBODIMENTS

Hereinafter, an embodiment of the communication system according to the present invention will be specifically described by focusing how the communication system1can improve the transmission performance between the transmitting device2-kand the receiving device3-k.

First, as the initial value of the hopping pattern Pk, a hopping pattern Pk(0) with L=7, M=8 using frequency hopping codes proposed in Non-Patent Document 3 and an M number of Gold sequences with a length of L are used.

The frequency hopping code ykof the hopping pattern Pk(0) is defined in the following expressions 22-1 and 22-2.
[Expression 22]
yK=xk·β⊕γk·1  (22-1)
=[yk,1yk,2. . . yk,L]T(22-2)

In the expression 22, β=[β0, β1, β2, . . . , βL-1]; β denotes an initial element of GF (M=23); xk, γkδ GF(23); and l denotes a column vector with an 1 number of elements in all and having a length of L.

In the expression 22, the symbol and “•” shown in the expression 23 denote addition and multiplication with respect to GF(23) respectively.
[Expression 23]
⊕  (23)

The value of xk, ykwith respect to a k-th signal is obtained by (k−1)=yk+xk. The element vk, l, mof (l, m) of an L×M matrix Vkis defined in the following expression 24.

Here, when an M number of diagonal matrix sets Z0, Z1, . . . ZM-1each containing an M number of Gold sequences on the diagonal line thereof are defined, the initial hopping pattern Pk(0) is defined as Pk(0)=ZxkVk.

FIG. 10illustrates a model of a path for evaluating the performance of the communication system1.

Further, in order to evaluate the performance of the communication system1, as illustrated inFIG. 10, a six-path model indicating exponential decay performance is assumed (Ik′, k=6 for every k, k′).

The path delays τk′, k, iare τk′, k, i+1−τk′, k, i=(L+1)Tc/16 (for ≈Ts/16; L=7). τk′, k, 1for all k′, k and θk, k, i+1for all k′, k, i are statistically independent of each other and are uniformly distributed random variables in the interval of [0,T) and [0,2π).

Note that for simplifying the assumption, as described above, the amplitude attenuation is assumed to be the same −3 dB for all k′, k, and τk′, k, 1, θk, k, i+1is assumed to be independent for all k′, k, i, which provides a very strict path condition in the communication system1.

The communication system1requires an initial training period from when the transmitting device2feeds back a part of weight matrix (Wk) to the receiving device3as the hopping pattern Pkto when the transmitting device2is ready to generate an appropriate signature waveform signal ck(t) according to the actual path condition.

The communication system1assumes that the initial training period is t<(Nf+1)Tf+Δk+τk, k, 1as described above.

The steady bit error rate (BER) in the communication system1shown below is obtained after the initial training period, and during the steady period, the weight matrix Wkis updated only on the receiving device3-kside, but the hopping pattern Pkis not fed back to the transmitting device2-k.

Moreover, the reference data d″kused to update the weight matrix Wkis assumed to be d″k=dkduring the initial training period, which means that a pilot data symbol used during the initial training period is stored in the transmitting device2and the stored pilot data symbol is used during the initial training period.

The BER performance slightly depends on a randomly selected value τk′, k, 1, θk, k, i+1, and thus points in the graphs in the following drawings are each an average of the values obtained by five simulations.

The simulation conditions including the above assumptions are listed in the following Table 1.

Hereinafter, the results obtained by evaluating the performance of the communication system1by computer simulation will be described.

The computer simulation is used to compare the BER performance of the communication system1with the BER performance of a communication system which adopts the DS-CDMA using a conventional Gold sequence, uses a matched filter, and uses or does not use a RAKE combining method, and the BER performance of a communication system adopting the FCSS/CDMA system.

FIG. 11is a graph of the BER performance with respect to the number of active transmission signals sk(t) in the communication system1.

FIG. 12is a graph of the BER performance with respect to Eb/Nofor K=32.

FIGS. 13A to 13Deach are a graph illustrating an initial hopping pattern, the updated hopping pattern, and the corresponding power spectra.

Note that inFIG. 13, the tone level pk, l, mis indicated by the absolute value |pk, l, m|.

As will be understood fromFIG. 11, in the communication systems each adopting a conventional DS-CDMA system, as the number of active transmission signals sk(t) increases, the BER increases rapidly.

In contrast to this, in the communication system1with α=7 and Nf=10, as the number of active transmission signals sk(t) increases, the error rate increases most gradually.

Moreover, as will be understood fromFIG. 12, in comparison with the system adopting the FCSS/DS-CDMA (α=31 and Nf=10), in the communication system1(α=7 and Nf=10), a gain of 0.3 dB is obtained when the BER is 10−3.

Moreover, as will be understood fromFIG. 13C, the initial value Pk(0) of the hopping pattern contains one tone for each chip, but the updated hopping pattern contains a plurality of tones for each chip.

The above embodiments are provided for illustration and explanation purposes, and do not cover all embodiments of the present invention.

Moreover, the above embodiments are not intended to limit the technical scope of the present invention to the particular forms disclosed, and various modifications and variations can be made by referring to the particular forms disclosed.

Further, the above embodiments are selected and described so as to describe the principle and actual applications of the present invention in the most appropriate manner. Therefore, based on the particular forms disclosed in the above embodiments, those skilled in the art can use the present invention and the embodiments thereof by making various modifications to be suitable for every possible actual application.

Further, the technical scope of the present invention is intended to be defined by the description and the equivalents.

DESCRIPTION OF SYMBOLS

INDUSTRIAL APPLICABILITY

The present invention can be used for data transmission by spread spectrum.