Device and method for bi-orthogonal code hopping multiple access communication

0001The present invention relates to a transmitter/receiver and a transmitting/receiving method in a spread spectrum multiple access communications system, and in particular, to a transmitter/receiver and a transmitting/receiving method using bi-directional orthogonal code hopping (BDOCH) in a spread spectrum multiple access communications system.

0002FIGs. 1 and 2 are block diagrams of a transmitter and a receiver using a conventional orthogonal code in a multiple access communications system, respectively. FIG. 3 illustrate the waveforms of the signals in the transmitter and the receiver of FIGs. 1 and 2 in the multiple access communications system.

0003Referring to FIG. 1, the transmitter includes orthogonal code generators (OCGs) 10 as many as channels, for providing different orthogonal codes to information data inputs 0-m on channels. Here, the orthogonal codes may be Walsh, Hadamard, or Gold codes. Each of a plurality of mixers 11 corresponding in number to the number of information data inputs mixes respective information data with an orthogonal code generated from a respective OCG 10. An adder 12 adds mixed data received from the mixers 11. A pseudo noise sequence generator (PNSG) 13 generates a PN sequence for use in producing a spread spectrum signal. A mixer 14 mixes the output of the adder 12 with the PN sequence, thereby generating the spread spectrum signal. A modulator 15 modulates the signal received from the mixer 14 to an RF (Radio Frequency) signal. A power amplifier 16 amplifies the power of the RF signal received from the modulator 15 and outputs the amplified signal via an antenna 17.

0004Referring to FIG. 2, the receiver has a receiving amplifier 21 for amplifying an RF signal received via an antenna 20. A demodulator 22 demodulates the signal received from the receiving amplifier 21. A PNSG 23 generates a PN sequence for use in despreading a spread spectrum signal. A mixer 24 mixes the output of the demodulator 22 with the PN sequence, thereby generating a despread signal. OCGs 28 are as many as channels and generate different orthogonal codes. The orthogonal codes may be Walsh, Hadamard, or Gold codes. Mixers 25 corresponding in number to the number of channels, each mix respective channel data with an orthogonal code generated from a respective OCG 28. Integrators 26 integrate the data received from the mixers 25 to output the respective channel information data 0-m.

0005The transmitter and receiver of FIGs. 1 and 2 are operated as shown in FIG. 3. It is assumed that input information data is provided on two channels ch1 and ch2 and orthogonal codes are Walsh codes given by <tables id="tabl0001" num="0001"><table frame="all"><title>(Table 1)</title><tgroup cols="2" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">W(0)</entry><entry namest="col2" nameend="col2" align="left">+1 +1 +1 +1</entry></row><row><entry namest="col1" nameend="col1" align="left">W(1)</entry><entry namest="col2" nameend="col2" align="left">+1 -1 +1 -1</entry></row><row><entry namest="col1" nameend="col1" align="left">W(2)</entry><entry namest="col2" nameend="col2" align="left">+1 +1 -1 -1</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">W(3)</entry><entry namest="col2" nameend="col2" align="left">+1 -1 -1 +1</entry></row></tbody></tgroup></table></tables>

0006Referring to FIGs. 1 and 3, and table 1, information data 0 and 1 on the channels ch1 and ch2 are signals 311 and 312, respectively. A mixer 11 mixes the information data 0 with the Walsh code w(0) and generates a signal 313 (ch1xW(0)), and a mixer 11 mixes the information data 1 with the Walsh code W(1) and generates a signal 314 (ch2xW(1)). The adder 12 adds the signals 313 and 314 and generates a signal 315 (ch1xW(0)+ch2xW(1)). The mixer 14 spreads the signal 315 with a PN sequence, and the modulator 15 modulates the spread signal to an RF signal.

0007Referring to FIGs. 2 and 3, and table 1, the mixer 24 mixes the RF signal, received via the receiving amplifier 21 and the demodulator 22 from the transmitter, with a PN sequence, and outputs the despread signal 315 (ch1xW(0)+ch2xW(1)). Then, the mixer 25 for recovering the output of the channel ch1 mixes the signal 315 with the Walsh code W(0) and outputs a signal 321 ({ch1xW(0)+ch2xW(1)}xW(0)), and the integrator 26 for the channel ch1 integrates the signal 321 and recovers the information data 0 of the channel 1, that is, a signal 322. The mixer 25 for recovering the output of the channel ch2 mixes the signal 315 with the Walsh code W(1) and generates a signal 323 (ch1xW(0)+ch2xW(1)}xW(1)), and the integrator 26 for the channel ch2 integrates the signal 323 and recovers the information data 1 of the channel ch2, that is, a signal 324.

0008When the transmitter simultaneously transmits multiple channels in the conventional spread spectrum multiple access communications system, each channel should be distinguished by a different orthogonal code. That is, each channel is assigned a unique orthogonal code taken from a set of orthogonal codes to distinguish channels from one another. This spread spectrum multiple access system requires orthogonal codes as many as channels and suffers from non-uniform power density distribution on the frequency spectrum.

0009The object of the present invention is to provide a spread spectrum multiple access communication device and method which overcomes the above-mentioned shortcomings of the conventional systems and provides improved communication security.

0010To achieve the above object, there is provided a communication device using bi-orthogonal code hopping multiple access (BOCHMA) with the features of claim 1.

0011The object is also solved by a communication method according to claim 6.

0012The invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which: <ul id="ul0001" list-style="none" compact="compact"><li>FIG. 1 is a block diagram of a transmitter in a conventional spread spectrum multiple access communications system using an orthogonal code;</li><li>FIG. 2 is a block diagram of a receiver in the conventional spread spectrum multiple access communications system using an orthogonal code;</li><li>FIG. 3 illustrates the waveforms of signals, referred to for describing characteristics of the conventional spread spectrum multiple access communications system using an orthogonal code;</li><li>FIG. 4 is a block diagram of a transmitter in a spread spectrum multiple access communications system using bi-orthogonal code hopping according to an embodiment of the present invention;</li><li>FIG. 5 is a block diagram of a receiver in the spread spectrum multiple access communications system using bi-orthogonal code hopping according to the embodiment of the present invention;</li><li>FIG. 6 illustrates Walsh codes as orthogonal codes for bi-orthogonal code hopping;</li><li>FIG. 7 illustrates Hadamard codes as orthogonal codes for bi-orthogonal code hopping; and</li><li>FIG. 8 illustrates the waveforms of signals in the spread spectrum multiple access communications system using bi-orthogonal code hopping according to the embodiment of the present invention.</li></ul>

0013Use of orthogonal code hopping multiple access (OCHMA) allows each channel to be multiplied not by a fixed orthogonal code but by different orthogonal codes according to a hopping pattern, with mutual orthogonality maintained. If a signal spread by the orthogonal code hopping is not multiplied by a PN sequence or a wiretapper acquires the PN sequence of a base station and removes the PN sequence from a signal spread by the orthogonal code hopping and multiplied by the PN sequence, the OCHMA has the following problem.

0014When a wiretapper knows the size and kind of orthogonal codes used in a transmitter and the starting and ending points of each orthogonal code, the wiretapper can find out encoded channel data before it is multiplied by an orthogonal code just by checking particular chips of the orthogonal code despite orthogonal code hopping, as long as the wiretapper can accurately decipher each orthogonal code to the chip though an orthogonal code hopping pattern is not known.

0015Walsh and Hadamard codes are constructed as shown in tables 2 and 3, respectively. <tables id="tabl0002" num="0002"><table frame="all"><title>(Table 2)</title><tgroup cols="2" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">W0</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> +1 +1 +1 +1 +1 +1 +1</entry></row><row><entry namest="col1" nameend="col1" align="left">W1</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> -1 +1 -1 +1 -1 +1 -1</entry></row><row><entry namest="col1" nameend="col1" align="left">W2</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> +1 -1 -1 +1 +1 -1 -1</entry></row><row><entry namest="col1" nameend="col1" align="left">W3</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> -1 -1 +1 +1 -1 -1 +1</entry></row><row><entry namest="col1" nameend="col1" align="left">W4</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> +1 +1 +1 -1 -1 -1 -1</entry></row><row><entry namest="col1" nameend="col1" align="left">W5</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> -1 +1 -1 -1 +1 -1 +1</entry></row><row><entry namest="col1" nameend="col1" align="left">W6</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> +1 -1 -1 -1 -1 +1 +1</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">W7</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> -1 -1 +1 -1 +1 +1 -1</entry></row></tbody></tgroup></table></tables><tables id="tabl0003" num="0003"><table frame="all"><title>(Table 3)</title><tgroup cols="2" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">H0</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1</entry></row><row><entry namest="col1" nameend="col1" align="left">H1</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> +1 +1 +1 -1 -1 +1 -1 -1 +1 -1 -1</entry></row><row><entry namest="col1" nameend="col1" align="left">H2</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> +1 +1 -1 -1 +1 -1 -1 +1 -1 -1 +1</entry></row><row><entry namest="col1" nameend="col1" align="left">H3</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> -1 +1 -1 +1 -1 -1 -1 -1 +1 +1 +1</entry></row><row><entry namest="col1" nameend="col1" align="left">H4</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> +1 -1 -1 +1 -1 -1 +1 +1 +1 -1 -1</entry></row><row><entry namest="col1" nameend="col1" align="left">H5</entry><entry namest="col2" nameend="col2" align="left"><b>-1</b> +1 +1 -1 +1 -1 +1 +1 -1 -1 -1 +1</entry></row><row><entry namest="col1" nameend="col1" align="left">H6</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> -1 +1 +1 +1 +1 -1 +1 -1 -1 -1 -1</entry></row><row><entry namest="col1" nameend="col1" align="left">H7</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> +1 -1 +1 -1 -1 -1 +1 -1 -1 +1 +1</entry></row><row><entry namest="col1" nameend="col1" align="left">H8</entry><entry namest="col2" nameend="col2" align="left"><b>-1</b> +1 +1 -1 -1 +1 -1 +1 -1 +1 +1 -1</entry></row><row><entry namest="col1" nameend="col1" align="left">H9</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> -1 +1 -1 -1 -1 +1 +1 +1 -1 +1 -1</entry></row><row><entry namest="col1" nameend="col1" align="left">H10</entry><entry namest="col2" nameend="col2" align="left"><b>+1</b> +1 -1 -1 +1 +1 +1 -1 -1 -1 +1 -1</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">H11</entry><entry namest="col2" nameend="col2" align="left"><b>-1</b> +1 +1 +1 +1 -1 -1 -1 +1 -1 +1 -1</entry></row></tbody></tgroup></table></tables>

0016Referring to tables 2 and 3, orthogonal codes of a length N can be generated so that the same numbered chips in the orthogonal codes have the same value, like the +1s marked bold at the first chips in table 2. In the case of the different signs of the first chips as marked bold in table 3, the signs can be changed to be equal by multiplying the chips of the underlined orthogonal codes by -1 and thus changing the sign of each chip, while maintaining mutual orthogonality of the codes given by<maths id="math0001" num="(1)"><math display="block"><mrow><mfrac><mrow><mtext>1</mtext></mrow><mrow><mtext mathvariant="italic">N</mtext></mrow></mfrac><mtext></mtext><apply><sum /><lowlimit><mtext mathvariant="italic">n</mtext><mtext>=1</mtext></lowlimit><uplimit><mtext mathvariant="italic">N</mtext></uplimit><mrow><mtext></mtext><msub><mrow><mtext mathvariant="italic">a</mtext></mrow><mrow><mtext mathvariant="italic">i</mtext></mrow></msub><mtext>(</mtext><mtext mathvariant="italic">n</mtext><mtext>)</mtext><msub><mrow><mtext mathvariant="italic">a</mtext></mrow><mrow><mtext mathvariant="italic">j</mtext></mrow></msub><mtext>(</mtext><mtext mathvariant="italic">n</mtext><mtext>)</mtext></mrow></apply><mtext> = </mtext><mfenced open="[" close="]"><mrow><mtable><mtr><mtd><mtext mathvariant="italic">O</mtext><mtext>(</mtext><mtext mathvariant="italic">i</mtext><mtext>≠</mtext><mtext mathvariant="italic">j</mtext><mtext>)</mtext></mtd></mtr><mtr><mtd><mtext>1(</mtext><mtext mathvariant="italic">i</mtext><mtext>=</mtext><mtext mathvariant="italic">j</mtext><mtext>)</mtext></mtd></mtr></mtable></mrow></mfenced></mrow></math><img file="EP0902549A2_D0001.tif" /></maths>

0017In the above case, the orthogonal codes can be deciphered just by determining the signs of the first chips. Therefore, it is desirable to form orthogonal code pairs, in which each orthogonal code has different values at any chip from the other code of its pair.

0018In an embodiment of the present invention, a communication device and method using bi-orthogonal code hopping will be provided to offer communication security in any situation.

0019FIG. 4 is a block diagram of a transmitter in a communication device using bi-orthogonal code hopping according to the embodiment of the present invention.

0020Referring to FIG. 4, a hopping controller 400 generates hopping control signals for hopping orthogonal codes selected from a set of orthogonal codes according to a predetermined pattern for respective channels. The hopping control signals correspond in number to the number of the transmission channels and are composed of hopping code generating signals and hopping code selecting signals for hopping bi-orthogonal codes taken from a set of bi-orthogonal codes according to a preset pattern for each channel. The number of the digital signal sources 410 is also equal to that of the channels.

0021In each of code hoppers 420 equal in number to that of the digital signal sources, an OCG 421 generates an orthogonal code OC(Hx) (x is a channel number) corresponding to a hopping code generating signal for a channel received from the hopping controller 400. A multiplier 422 multiplies the orthogonal code OC(Hx) by -1 and generates a code /OC(Hx) being the complement of OC(Hx). A switch 423 selectively outputs the orthogonal code OC(Hx) or /OC(Hx) according to a hopping code selecting signal received from the hopping controller 400. A mixer 424 mixes a digital signal source 410 with the orthogonal code received from the switch 423.

0022An adder 430 adds up the signals received from each of the code hoppers 420. A spreader 440 includes a PNSG 441 for generating a PN sequence with which to spread a transmission signal, and a mixer 442 for mixing the output of the adder 430 with the PN sequence. A transmitting unit 450 includes a modulator, a filter, and an amplifier, for outputting the transmission signal as an RF signal.

0023FIG. 5 is a block diagram of a receiver in the communications system using bi-orthogonal code hopping according to the embodiment of the present invention.

0024Referring to FIG. 5, a receiving unit 510 includes a demodulator, a filter, and an amplifier, for outputting an input RF signal as a baseband signal. A despreader 520 has a PNSG 521 for generating a PN sequence with which to despread the received spread signal, and a mixer 522 for mixing the output of the receiving unit 510 with the PN sequence and generates a despread signal.

0025A hopping controller 500 generates hopping control signals for providing orthogonal codes according to a predetermined hopping rule to recover the digital signals on the channels. The hopping control signals are equal in number to that of the transmission channels and composed of hopping code generating signals and hopping code selecting signals for hopping bi-orthogonal codes taken from a set of bi-orthogonal codes according to a preset pattern for each channel. The hopping control signals are the same as those generated from the hopping controller 400 in the transmitter. That is, the hopping controllers 400 and 500 generate the same hopping control signal for a particular channel.

0026In each of code hoppers 530 equal in number to that of digital signal destinations 540, an OCG 531 generates an orthogonal code OC(Hx) corresponding to a hopping code generating signal for a channel received from the hopping controller 500. A multiplier 532 multiplies the orthogonal code OC(Hx) by -1 and generates a code /OC(Hx) being the complement of OC(Hx). A switch 533 selectively outputs the orthogonal code OC(Hx) or /OC(Hx) according to a hopping code selecting signal received from the hopping controller 500. A mixer 534 mixes the output of the despreader 520 with the orthogonal code received from the switch 533. An integrator 535 integrates the output of the mixer 534, thereby recovering the digital signals and outputting them to their respective digital signal destinations 540.

0027The transmitter of FIG. 4 simultaneously transmits a plurality of digital signals on a single communication channel and the receiver of FIG. 5 selects a desired signal from a plurality of input signals. In the embodiment of the present invention, the transmitter and receiver use hopping patterns of bi-orthogonal codes to distinguish channels from one another. With a set of orthogonal codes used in OCHMA given as {OC(1), OC(2), OC(3), ..., OC(N)}, a set of bi-orthogonal codes is {OC(1), /OC(1), OC(2), /OC(2), OC(3), /OC(3), ..., OC(N), /OC(N)} with respect to the orthogonal code set, where /OC(N) denotes the complement of OC(N), that is, an inverted output corresponding to OC(N).

0028The transmitter of FIG. 4 is provided with the code hoppers 420 equal in number to that of the channels, and each code hopper 420 multiplies the digital signal source of a respective channel by orthogonal codes generated and selected by hopping control signals received from the hopping controller 400, thereby distinguishing the channels from another. Orthogonal codes generated from a code hopper 530 in the receiver of Fig. 5 are identical to those multiplied by a respective channel for transmission. That is, the hopping controllers 400 and 500 generate the same hopping control signals for one and the same channel.

0029FIGs. 6 and 7 illustrate exemplary orthogonal codes generated in the code hoppers 420. From the orthogonal codes shown in FIGs. 6 and 7, orthogonal codes to be mixed are selected by means of the same hopping control signal output from the hopping controllers 400 and 500 based on a predetermination made between the transmitter and the receiver. Here, two hopping patterns used in the transmitter should not include the same orthogonal code at a particular time to prevent their collision.

0030FIG. 8 illustrates the waveforms of signals, referred to for describing the operational characteristics of the communication device using BOCHMA. It is assumed that input information data is provided on two channels ch1 and ch2 and Walsh codes as constructed below are used here as orthogonal codes. <tables id="tabl0004" num="0004"><table frame="all"><title>(Table 4)</title><tgroup cols="4" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">W0</entry><entry namest="col2" nameend="col2" align="left">+1 +1 +1 +1</entry><entry namest="col3" nameend="col3" align="left">/W0</entry><entry namest="col4" nameend="col4" align="left">-1 -1 -1 -1</entry></row><row><entry namest="col1" nameend="col1" align="left">W1</entry><entry namest="col2" nameend="col2" align="left">+1 -1 +1 -1</entry><entry namest="col3" nameend="col3" align="left">/W1</entry><entry namest="col4" nameend="col4" align="left">-1 +1 -1 +1</entry></row><row><entry namest="col1" nameend="col1" align="left">W2</entry><entry namest="col2" nameend="col2" align="left">+1 +1 -1 -1</entry><entry namest="col3" nameend="col3" align="left">/W2</entry><entry namest="col4" nameend="col4" align="left">-1 -1 +1 +1</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">W3</entry><entry namest="col2" nameend="col2" align="left">+1 -1 -1 +1</entry><entry namest="col3" nameend="col3" align="left">/W3</entry><entry namest="col4" nameend="col4" align="left">-1 +1 +1 -1</entry></row></tbody></tgroup></table></tables>

0031Referring to FIGs. 4 and 5, and table 4, information data 0 on the channel ch1 and information data 1 on the channel ch2 are signals 811 and 812, respectively. Orthogonal codes for the channel ch1 are hopped in the order of W(0), W(1), /W(3), and W(2), and those for the channel ch2 are hopped in the order of W(1), /W(2), W(2), and W(1). Here, an orthogonal code can occur twice for a channel. The hopping controller 400 outputs hopping control signals for generating and selecting the bi-orthogonal codes designated as above.

0032Then, the code hopper 420 for the channel ch1 receives hopping code generating signals in the order of W(0), W(1), W(3), and W(2) from the hopping controller 400, and hopping code selecting signals for switching in the order of 1101. The OCG 421 in the code hopper 420 generates the orthogonal codes W(0), W(1), W(3), and W(2) and the switch 423 selects the output of the multiplier 422 at the location of the orthogonal code W(3). Therefore, the mixer 424 receives a hopped orthogonal code H0 including W(0), W(1), /W(3), and W(2). On the other hand, the code hopper 420 for the channel ch2 receives hopping code generating signals in the order of W(1), W(2), W(2), and W(1) from the hopping controller 400, and hopping code selecting signals for switching in the order of 1011. The OCG 421 in the code hopper 420 generates the orthogonal codes W(1), W(2), W(2), and W(1) and the switch 423 selects the output of the multiplier 422 at the location of the former of the orthogonal codes W(2). Therefore, the mixer 424 receives a hopped orthogonal code H1 including W(1), /W(2), /W(2), and W(1).

0033Then, the mixer 424 mixes the information data 0 with the hopped orthogonal code H0 and generates a signal 813 (ch1xH0). It also mixes the information data 1 with the hopped orthogonal code H1 and generates a signal 814 (ch2xH1). The adder 430 adds the signals 813 and 814 and generates a signal 815 (ch1xH0+ch2xH1). The mixer 442 mixes the signal 815 with a PN sequence and the transmitting unit 450 converts the spread signal received from the mixer 442 to an RF signal for transmission.

0034The spectrum despreader 520 mixes the RF signal received from the transmitter via the receiving unit 510 with the PN sequence, and generates the despread signal 815 (ch1xH0+ch2xH1). It is to be noted that the hopping controller 500 should generate the same hopping control signals as from the hopping controller 400. That is, the transmitter and receiver use the same bi-orthogonal codes for a channel.

0035Thus, the switch 533 for the channel ch1 outputs the hopped orthogonal code H0, and the switch 533 for the channel ch2 outputs the hopped orthogonal code H1. Then, the mixer 534 for the channel ch1 mixes the hopped orthogonal code H0 with the signal 815 received from the despreader 520, and generates a signal 821 ((ch1xH0+ch2xH1)xH0). The integrator 535 for the channel ch1 integrates the signal 821 and recovers the information data 822 of the channel ch1. The mixer 534 for the channel ch2 mixes the hopped orthogonal code H1 with the signal 815 received from the despreader 520, and generates a signal 823 ((ch1xH0+ch2xH1)xH1). The integrator 535 for the channel ch2 integrates the signal 823 and recovers the information data 824 of the channel ch2.

0036As described above, BOCHMA produces two kinds of selectable codes with the same spreading gain with respect to each orthogonal code, thereby preventing wiretapping and improving communication security.