Source: https://patents.google.com/patent/US7227836?oq=6%2C240%2C376
Timestamp: 2018-02-24 12:09:39
Document Index: 163807325

Matched Legal Cases: ['Application No. 6833', 'Application No. 40167', 'art 50', 'art 50', 'art 10', 'art 10', 'application No. 61616', 'art 321', 'art 321', 'art 322', 'art 322', 'art 351', 'art 351', 'art 352', 'art 352', 'art 441', 'art 442', 'arts 441', 'art 441', 'art 442', 'art 471', 'art 471', 'art 472', 'art 472', 'art 321', 'art 321', 'art 322', 'art 322', 'arts 1021', 'arts 1021', 'arts 1026', 'arts 1021']

US7227836B2 - Rate control device and method for CDMA communication system - Google Patents
US7227836B2
US7227836B2 US10272143 US27214302A US7227836B2 US 7227836 B2 US7227836 B2 US 7227836B2 US 10272143 US10272143 US 10272143 US 27214302 A US27214302 A US 27214302A US 7227836 B2 US7227836 B2 US 7227836B2
US10272143
US20030128674A1 (en )
This application is a Divisional of parent application Ser. No. 09/260,213, filed on Mar. 1, 1999 now U.S. Pat. No. 6,700,881 which claims priority from Korean Patent Application No. 6833/1998 filed Mar. 2, 1998 and Korean Patent Application No. 40167/1998 filed Sep. 26, 1998.
A signal mapping part 50 maps binary data output from the mixer 40 into 4-level data by converting data “0” to “+1” and data “1” to “−1”. An orthogonal modulator 60 modulates data output from the signal mapping part 50 with an orthogonal code. A Walsh code can be used for the orthogonal code. In this case, Walsh codes of lengths 64, 128 and 256 bits can be used. A spreader 70 spreads the orthogonal modulation signal output from the orthogonal modulator 60 by combining it with spreading sequences. PN (Pseudo-random Noise) sequences can be used for the spreading sequences. Accordingly, a QPSK (Quadrature Phase Shift Keying) spreader can be used for the spreader 70. A gain controller 80 controls a gain of the spread signal input from the spreader 70 according to a gain control signal Gc.
In operation, when the convolutional encoder is used for the channel encoder and puncturing part 10, the coding rate is ⅓ and the constraint length, k=9, for an IS-95 system. Therefore, one input data bit is encoded into three encoded bits (i.e., three symbols) in the channel encoder and puncturing part 10 (which performs ⅓ rate convolutional encoding or ⅓ rate forward error correction (FEC)). Forward error correction is utilized to provide coding gain to a channel so as to compensate for an increase in a BER (Bit Error Rate) at a mobile station (for the case of a forward link) and a base station (for the case of a reverse link). An increase in the BER of a channel may arise as a result of the channel having a reduced SNR (Signal-to-Noise Ratio) due to an increase in signal path loss, noise and interference.
It is well known that CDMA communication systems cannot provide reliable communication service when a mobile station is located at an outer service area of the base station or is in a bad channel environment. In this case, it is preferable to change the coding rate to enhance the quality of the communication service in the bad channel environment. That is, when the channel SNR is reduced due to a bad channel environment or an increased distance between a mobile station and a base station, it is preferable to use a coding rate (or FEC rate) lower, ⅙ for example, than the present coding rate of ⅓.
In particular, when the distance between the base station and the mobile station increases, a reception device is very susceptible to path loss or noise on the link channel and interference, so that the channel SNR is reduced unless a transmission device increases the transmission power or performs a pertinent compensation. Therefore, when the traffic channel transmission device with the fixed channel structure of FIG. 1 experiences an increased BER (Bit Error Rate) due to a reduction in SNR, the base station increases a forward link traffic power in order to compensate for the increase in the BER. Therefore, it is preferable to use the FEC with a lower coding rate than the FEC in use. Given a ⅓ coding rate it has been shown that channel gain is lower by about 0.2–1 dB as compared with a ⅙ coding rate. For example, the forward reception power of a mobile station using the ⅓ coding rate is lower by about 1 dB than that of a mobile station using the ⅙ coding rate, when the mobile station is far from the base station or in a bad forward channel environment. Therefore, the base station should increase the forward link transmission power, resulting in a waste of transmission power and low communication performance.
Unlike the channel transmission device with the fixed channel structure of FIG. 1, a channel transmission/reception device for a 3rd generation multicarrier CDMA system as proposed in the TIA/EIA TR45.5 conference, includes a scheme for transmitting and receiving the respective channel data by distributing them to the multicarrier. For example, when three carriers are used and a rate ⅓ encoder is used, the multicarrier scheme encodes the respective input data bit into three encoded bits (i.e., symbols) using the rate ⅓ encoder and transmits the encoded bits using the three carriers after repetition and interleaving. This is well disclosed in Korean patent application No. 61616/1997 filed by the applicant of this invention. Here, the respective carriers each have a bandwidth of 1.2288 Mhz (hereinafter, referred to as 1.25 Mhz) which is identical to the IS-95 channel bandwidth. Therefore, the three carriers have a combined or collective bandwidth of 3.6864 Mhz, which is identical to three separate channel bandwidths.
The forward link of the 3 G multicarrier system can employ an overlay method where it shares the same frequency band with the IS-95 forward channel. In this case, it may be interfered with the IS-95 system. In addition, it is preferable to use the coding rate lower than the present coding rate of ⅓, even when the channel SNR is reduced due to the bad channel environment or the increased distance between the mobile station and the base station.
A traffic channel transmission/reception device according to an embodiment of the present invention increases channel performance by decreasing the coding rate thereby causing an increase in the coding gain. The method has particular applicability for those situations where path loss or interference increases between a base station and a mobile station on a CDMA link channel. For example, when using a ⅙ coding rate rather than a conventional ⅓ coding rate, it is possible to improve performance against an increase in signal path loss, noise and interference. Therefore, in a relatively bad channel environment, it is more efficient to use the lower coding rate of ⅙ rather than the higher coding rate of ⅓.
An illustrative embodiment will be described which includes a method of improving a receiver's performance by channel encoding at two different rates as applied to a 3 G multicarrier CDMA system.
Although the present invention will be described as comprising two coding rates (i.e. ⅓ and ⅙), they are provided merely by way of example. It is to be appreciated that the use of other coding rates are well within the scope of the present invention. Moreover, for purposes of illustration, the traffic channel of the forward link may be characterized as comprising a base station as the transmission device and a mobile station as the reception device.
S_low_Th: is a PCB value accumulated for a particular duration;
FIG. 3 is a block diagram illustrating a structure of a forward link traffic channel transmission device including a rate ⅓ encoder and a rate ⅙ encoder according to an embodiment of the present invention.
The first encoder 311, upon reception of data input from the selector 301, encodes the input data into data symbols at a first coding rate (the ⅓ coding rate). That is, the first encoder 311 encodes one input data bit into three symbols. A convolutional encoder or a turbo encoder can be used for the first encoder 311. A first symbol repetition part 321 receives the data encoded at the first coding rate, and repeats the symbols output from the first encoder 311 as necessary so as to match the symbol rates of the data having different bit rates. A first interleaver 331 interleaves first encoded data output from the first symbol repetition part 321. A block interleaver can be used for the first interleaver 331.
The second encoder 312, upon reception of the data input from the selector 301, encodes and punctures the input data into data symbols at a second coding rate (the ⅙ coding rate). That is, the second encoder 312 encodes one input data bit into six symbols. A convolutional encoder or a turbo encoder can be used for the second encoder 312. A second symbol repetition part 322 receives the data encoded at the second coding rate, and repeats the symbols output from the second encoder 312 so as to match the symbol rates of the data having different bit rates. A second interleaver 332 interleaves second encoded data output from the second symbol repetition part 322. A block interleaver can be used for the second interleaver 332.
A long code generator 391 generates long codes for the user identification, which are uniquely assigned to the respective subscribers. A decimator 392 decimates the long codes so as to match a rate of the long codes to a rate of the symbols output from the interleavers 331 and 332. A selector 393 selectively outputs the decimated long code output from the decimator 392 to a mixer 341 or a mixer 342 according to the select signal Csel. The selector 393 switches the decimated long code to the first mixer 341 to select the ⅓ coding rate and to the second mixer 342 to select the /16 coding rate. The mixer 341 mixes the first encoded data output from the first interleaver 331 with the long code output from the selector 393. The second mixer 342 mixes the second encoded data output from the second interleaver 332 with the long code output from the selector 393.
A first signal mapping part 351 converts levels of the binary data output from the first mixer 341 by converting data “0” to “+1” and data “1” to “−1”. A first orthogonal modulator 361 includes a first orthogonal code generator (not shown) which generates a first orthogonal code for orthogonally modulating the first encoded data according to the orthogonal code number and length signals Wno and Wlength output from the decision block 213. The first orthogonal modulator 361 multiples the first orthogonal code generated according to the orthogonal code number and length signals Wno and Wlength by the data output from the first signal mapping part 351 to generate a first orthogonal modulation signal. Here, it is assumed that the Walsh code is used for the orthogonal code and a Walsh code of length 256 is used for the data encoded at the first coding rate of ⅓.
A second signal mapping part 352 converts levels of the binary data output from the second mixer 342 by converting data “0” to “+1” and data “1” to “−1”. A second orthogonal modulator 362 includes a second orthogonal code generator (not shown) which generates a second orthogonal code for orthogonally modulating the second encoded data according to the orthogonal code number and length signals Wno and Wlength output from the decision block 213. The second orthogonal modulator 362 multiples the second orthogonal code generated according to the orthogonal code number and length signals Wno and Wlength by the data output from the second signal mapping part 352 to generate a second orthogonal modulation signal. Here, it is assumed that the Walsh code is used for the orthogonal code and a Walsh code of length 128 is used for the data encoded at the second coding rate of ⅙.
FIG. 3 shows the transmission channel structure in which the forward link is switched to the first encoder 311 of the ⅓ FEC rate or the second encoder 312 of the ⅙ FEC rate in accordance with the channel environment. The data input path is switched to either the encoder 311 or the encoder 312 by the selector 301. Thus, the transmission data undergoes a different FEC rate according to the selected data path. That is, based on the select signal Csel output from the decision block 213, the selector 301 switches the input data to the first encoder 311 when the channel environment is good, and switches the input data to the second encoder 312 when channel environment is poor.
In addition, since the orthogonal code should be also changed according to the change of the FEC rate, it is necessary to select one of the orthogonal modulators 361 and 362 according to the change of the FEC rate. That is, when the first encoder 311 is selected to use the ⅓ FEC rate, the orthogonal code generator in the first orthogonal modulator 361 generates the orthogonal code of length 256 according to the orthogonal code number and length Wno and Wlength. Therefore, the orthogonal modulator 361 multiplies the signal encoded at the ⅓ FEC rate by the orthogonal code to generate the first orthogonal modulation signal, and the spreader 370 spreads the first orthogonal modulation signal using the PN sequences PNI and PNQ.
Furthermore, when the second encoder 312 is selected to use the ⅙ FEC rate, the orthogonal code generator in the second orthogonal modulator 362 generates the orthogonal code of length 128 according to the orthogonal code number and length Wno and Wlength. Therefore, the orthogonal modulator 362 multiplies the signal encoded at the ⅙ FEC rate by the orthogonal code to generate the second orthogonal modulation signal, and the spreader 370 spreads the second orthogonal modulation signal using the PN sequences PNI and PNQ.
As can be appreciated from the foregoing description, there is no change in structure of the spreader 370 for spreading the orthogonal modulation signal using the PN sequences. Accordingly, the ⅙ FEC rate scheme is identical in structure to the ⅓ FEC rate scheme, except for the encoder and interleaver. In particular, in the ⅙ FEC rate scheme, the bit rate of the final stage is increased from 576 to 1152 bits per frame. In addition, the interleaver size is also increased to twice its normal size.
The first orthogonal demodulator 431 includes a first orthogonal code generator for generating a first orthogonal code according to the orthogonal code number and length signals Wno and Wlength, output from the decision block 213. When connected to the selector 420, the first orthogonal demodulator 431 generates the first orthogonal code according to the orthogonal code number and length signals Wno and Wlength and multiplies the despread data by the first orthogonal code to output a first orthogonal demodulation signal. Here, it is assumed that a Walsh code is used for the orthogonal code and a Walsh code of length 256 is used for the data encoded at the ⅓ coding rate. A first signal demapping part 441 demaps the 4-level signal output from the first orthogonal demodulator 431 into binary data by converting data “+1” to “0” and data “−1” to “1”.
The second orthogonal demodulator 432 includes a second orthogonal code generator for generating a second orthogonal code according to the orthogonal code number and length signals Wno and Wlength output from the decision block 213. When connected to the selector 420, the second orthogonal demodulator 432 generates the second orthogonal code according to the orthogonal code number and length signals Wno and Wlength and multiplies the despread data by the second orthogonal code to output a second orthogonal demodulation signal. Here, it is assumed that a Walsh code is used for the orthogonal code and a Walsh code of length 128 is used for the data encoded at the ⅙ coding rate. A second signal demapping part 442 demaps the 4-level signal output from the second orthogonal demodulator 432 into binary data by converting data “+1” to “0” and data “−1” to “1”.
A long code generator 491 generates a long code identical to that generated at the transmitter. Here, the long codes are the user identification codes, and the different long codes are assigned to the respective subscribers. A decimator 492 decimates the long code so as to match a rate of the long code to a rate of the signals output from the signal demapping parts 441 and 442. A selector 493 switches the decimated long code output from the decimator 492 to a mixer 451 or a mixer 452 according to the select signal Csel. In other words, the selector 493 switches the decimated long code to the first mixer 451 to select the ⅓ coding rate, and switches the decimated long code to the second mixer 452 to select the ⅙ coding rate. The first mixer 451 mixes an output of the signal demapping part 441 with the long code to delete the long code contained in the received signal, and the second mixer 452 mixes an output of the signal demapping part 442 with the long code to delete the long code contained in the received signal.
A first deinterleaver 461 deinterleaves the received signal output from the first mixer 451 to rearrange the interleaved first encoded data into the original state. A first symbol extraction part 471 extracts the original encoded data by deleting the symbol-repeated encoded data from the output of the first deinterleaver 461. A first decoder 481 having a ⅓ decoding rate, decodes the encoded data output from the first symbol extraction part 471 into the original data.
A second deinterleaver 462 deinterleaves the received signal output from the second mixer 452 to rearrange the interleaved second encoded data into the original state. A second symbol extraction part 472 extracts the original encoded data by deleting the symbol-repeated encoded data from the output of the second deinterleaver 462. A second decoder 482 having a ⅙ decoding rate, decodes the encoded data output from the second symbol extraction part 472 into the original data.
As described above, the illustrative embodiment discloses a method of using the ⅙ FEC rate for the communication between base station and mobile station within a bad channel environment which has been degraded due to either a decrease of SNR or an increased BER in order to provide better link performance as compared with the case where the ⅓ FEC rate is used. In operation, a base station uses both the ⅓ FEC rate and the ⅙ FEC rate. In the case where only the ⅓ FEC rate is used, there are 256 available orthogonal codes of length 256. When only the ⅙. FEC rate is used there are 128 available orthogonal codes of length 128. However, when the two orthogonal code sets are both used, the use of a single orthogonal code of length 128 makes two of the corresponding orthogonal codes of length 256 unavailable. The use of one orthogonal code of length 256 makes one orthogonal code of length 128 unavailable. This is because there are orthogonal codes that are correlated between the two orthogonal code sets.
When all of the users have a ⅓ rate FEC, the maximum number of users can be 256, however the maximum number of users will be 128 if all the users have a ⅙ FEC rate. For this reason, use of the selectable ⅙ FEC rate is restricted since it decreases the system capacity (i.e., the number of users). It is possible to limit the number of forward channels using the ⅙ FEC rate by allowing use of the ⅙ rate encoder to the forward link hating a high signal path loss, a high signal transmission power or a high BER. In addition, since use of one orthogonal code of length 128 precludes the use of two orthogonal codes of length 256, the number of link channels using the rate ⅙ encoder is limited as long as it is possible to assign a sufficient number of orthogonal codes the mobile stations. When utilizing the method of present invention the base station should be designed to switchably use both the rate ⅓ encoder and the rate ⅙ encoder. The base station could order a mobile station in a certain condition to switch from the ⅓ FEC rate to the ⅙ FEC rate, and could order another mobile station in a certain other condition, described below, to switch from the ⅙ FEC rate to the ⅓ FEC rate.
Moreover, in some cases, it is also possible to initially select one of the ⅓ FEC rate and the ⅙ FEC rate at the beginning of a channel setup process. Also, the base station may allow a mobile station requesting the high forward traffic channel transmission power to preferentially use the ⅙ FEC rate as long as available orthogonal codes can be assigned without establishing the conditions required to determine whether to permit a rate change to either the ⅓ FEC rate or the ⅙ FEC rate. Other possible setting conditions (i.e., energy per chip: Ec, or chip energy to interference ratio: Ec/Io) can be determined depending on the received power of the forward pilot channel, and the signal path loss, fading and signal transmission power of the forward link or the reverse link.
The following is a description and explanation of the present invention directed with specific reference to orthogonal code assignment. Since the orthogonal codes are generated through the Hadamard transform, there exist non-orthogonal codes between a 2N*2N orthogonal code set and a 2(N+1)*2(N+1) orthogonal code set. Therefore, for a base station allowing 2 sets of different orthogonal codes (e.g., an orthogonal code set of length 2*N and 2*(N+1)), orthogonal codes among the 2N*2N orthogonal code set to a forward channel, careful selection is necessary in order to maintain the orthogonality with the existing assigned orthogonal code of length 2(N+1). This means that the base station should examine the non-orthogonality between every orthogonal code of length 2N for a new assignment and all the existing assigned orthogonal codes of length 2(N+1).
FIGS. 5 and 6 illustrate a method for switching the coding rate to the ⅓ FEC rate or the ⅙ FEC rate for the forward link of a 3 G CDMA system.
FIG. 5 illustrates a method in which the base station allows the mobile station to request the second encoder 312 of the ⅙ FEC rate through the paging and access channels during the call setup. A description will be provided below directed to the operation of selecting the ⅙ FEC rate for the forward link from the start of the call through the access channel and the paging channel at the call setup stage,
FIG. 6 illustrates a method in which the base station allows the mobile station to change the coding rate in the middle of a call. A description will be provided below directed to an operation of switching from the ⅓ FEC rate to the ⅙ FEC rate during the call processing in the IS-95B system.
Table 2B shows the channel assignment message for ASSIGN_MODE=“000”,
Table 2C shows the channel assignment message for ASSIGN_MODE=“001”,
Table 2D shows the channel assignment message for ASSIGN_MODE=“010”,
Table 2E shows the channel assignment message for ASSIGN_MODE=“011”,
Table 2F shows the channel assignment message for ASSIGN_MODE=“100”,
Table 2G shows the channel assignment message for ASSIGN_MODE=“101”.
MSG_TYPE (“00000100”) 8
ACK_TYPE 3
MSID_TYPE 3
MSID_LEN 4
MSID 8 × MSID_LEN
AUTH_MODE 2
AUTHR 0 or 18
RANDC 0 or 8
COUNT 0 or 6
MSG_TYPE (“00001000”) 8
ASSIGN_MODE 3
ADD_RECORD_LEN 3
Additional Record Fields 8 × ADD_RECORD_LEN
ENCODER_RATE 2
RESERVED 0–5 (as needed)
if ASSIGN_MODE = “000”, the additional record fields shall be:
CODE_CHAN 8
CDMA_FREQ 0 or 11
FRAME_OFFSET 4
ENCRYPT_MODE 2
if ASSIGN_MODE = “001”, the additional record fields shall be:
if ASSIGN_MODE = “010”, the additional record fields shall be:
ANALOG_SYS 1
USE_ANALOG_SYS 1
if ASSIGN_MODE = “011”, the additional record fields shall be:
ANALOG_CHAN 11
AN_CHAN_TYPE 2
DSCC_MSB 1
if ASSIGN_MODE = “100”, the additional record fields shall be:
RESERVED 74
DEFAULT_CONFIG 3
GRANTED_MODE 2
BAND_CLASS 0 or 5
if ASSIGN_MODE = “101”, the additional record fields shall be:
Referring to FIG. 6, during an active state where a call is connected between the base station and the mobile station, the base station examines the channel environment with the mobile station by estimating, for example, the RSSI. In step 611, the base station estimates the RSSI, selects a coding rate lower than the present coding rate when the RSSI is lower than a threshold value R_low_th, and selects a coding rate higher than the present coding rate when the RSSI is higher than a threshold value R_high_th.
By way of example, Table 3 represents the service configuration for the case where the two coding rates of ⅓ and ⅙ are used. In this example, if the mobile station includes at least two encoders having different coding rates and the orthogonal code length is changed according to the coding rates, the lengths of the ENCODER_RATE field and the CODE_CHAN field of Table 3 are also changed to accomodate all the cases, and the RECORD_LEN values of Tables 4, 5 and 6 are also adjusted.
Type-Specific Field Length [bits]
MSG_TYPE (“00010010”) 8
SERV_REQ_SEQ 3
REQ_PURPOSE 4
MSG_TYPE (“00010011”) 8
RESP_PURPOSE 4
MSG_TYPE (“00010100”) 8
SERV_CON_SEQ 3
SERV_REQ_SEQ 4
As used in the examples above, 256 orthogonal codes of length 256 bits are used for the ⅓ coding rate and 128 orthogonal codes of length 128 bits are used for the ⅙ coding rate. Here, since the orthogonal codes of length 256 are created by applying the Hadamard transform to the orthogonal codes of length 128, one orthogonal code of length 128 does not satisfy orthogonality with two orthogonal codes of length 256, losing the orthogonality between the channels. Therefore, assignment of one orthogonal code of length 128 decreases the available number of orthogonal codes of length 256 by two. Alternately, assignment of one orthogonal code of length 256 makes one orthogonal code of length 128 unusable. The base station continuously monitors the assigned orthogonal codes of length 128 and 256 to assign the new orthogonal codes so as to avoid the non-orthogonality with the previously assigned orthogonal codes.
The present embodiment assumes that coding rate and the length of the corresponding orthogonal codes are simultaneously changed in accordance with the channel environment. However, it is also possible to independently change the coding rate and the length of the orthogonal code. Furthermore, the present embodiment assigns the longer orthogonal code when the coding rate is increased (e.g., from ⅙ to ⅓), and assigns the shorter orthogonal code when the coding rate is decreased (e.g., from ⅓ to ⅙), thereby maintaining the same chip rate irrespective of the change in the rate. However, it is also possible to change the coding rate and the orthogonal code without maintaining the same chip rate during the channel communication between the base station and the mobile station.
However, when there are available orthogonal codes of length N, the available orthogonal codes are written in a search list W(k), in step 915. The search list W(k) stores information about the unused orthogonal codes in the form of w(k,i) as follows:
W ⁡ ( k ) = [ w ⁡ ( k , l 1 ) w ⁡ ( k , l 2 ) w ⁡ ( k , l 3 ) ⋮ w ⁡ ( k , l N ) ]
where 0≦11<12<13 . . . N−1
After that, in step 917, a search procedure 1 is performed on the search list to search those orthogonal codes which are non-orthogonal with orthogonal codes in use whose length is longer than 2k, and to extract those orthogonal codes from the search list W(k). That is, in the search procedure 1, the orthogonal codes not satisfying the orthogonality with the orthogonal codes presently in use among the orthogonal codes of length longer than 2k are deleted from the search list W(k). Stated more precisely, the orthogonal codes that are not orthogonal with the orthogonal codes w(k+j,i) (where j≧1, i=0, 1, 2, . . . , 2k+1−1), are deleted from the search list W(k). Variable j is incremented by one to increase the length of the orthogonal code. The search and extraction procedure is repeated for all the orthogonal codes of length 2K+J with all the orthogonal codes in the list W(k). The search procedure 1 performed in step 917 is defined as:
1. set j←1
2. while k+j≦maximum
2.1 find Walsh code(s) w(k,i) in the list W(k), which is (are) not orthogonal with w(k+j,i) in use can be equal to a subset of
{i=0, 1, 2, . . . , 2k+j−1}
2.2 extract the Walsh codes w(k+i) which satisfy 2.1 from search Walsh code list W(k)
2.3 set j←j+1
2. while k−j≧1
2.1 find Walsh code(s) w(k,i) in the list W(k), which is (are) not orthogonal with w(k−j,i) in use can be equal to a subset of
{i=0, 1, 2, . . . , 2k−j−1}
w(5,10)=BB, w(5,11)=CC, w(5,12)=DD, w(5,26)=B B, w(5,27)=C C, w(5,28)=D D, w(6,11)=CCCC, w(6,26)=B BB B, w(6,27)=C CC C, w(6,28)=D DD D, w(6,43)=CC CC, w(6,58)=B BBB, w(6,59)=C CCC and w(6,60)=D DDD.
k = 4 k = 5 k = 6
w(6,11) = CCCC
w(5,10) = BB w(6,26) = B BB B
w(4,10) = B w(5,11) = CC w(6,27) = C CC C
w(4,11) = C w(5,12) = DD w(6,28) = D DD D
w(4,12) = D w(5,26) = B
w(6,43) = CC CC
w(5,27) = C
w(6,58) = B BBB
w(5,28) = D
w(6,59) = C CCC
w(6,60) = D DDD
If the orthogonal code w(5,10) is not in use then the elements of the search list W(k) after performing the search procedure 1 are w(5,10), w(5,11), w(5,26) and w(5,27), therefore the search list W(k) has no orthogonal code satisfying step 921. Then, the search procedure 2 is performed in step 923. In the search procedure 2, for those orthogonal codes of length 2k−1 (i.e., k−1=4) in the search list W(k), those which are not orthogonal with the orthogonal codes presently in use are deleted from the search list W(k). Since the orthogonal code w(4,11)=C is in use, the orthogonal codes w(5,11)=CC and w(5,27)=C C are deleted from the search list W(k). As a result, the orthogonal codes stored in the search list W(k) are W(k=5)={w(5,10), w(5,26)}, which satisfies the condition of step 925. Thus, in step 927, the orthogonal codes w(5,10) and w(5,26) are assigned as the available orthogonal codes.
The term “rate” used in connection with FIGS. 7A, 7B and 8 refers to the coding rate and/or the length of the orthogonal code. A “first rate change condition” means a condition for switching from the higher rate to the lower rate, and a “second rate change condition” means a condition for switching from the lower rate to the higher rate. For example, the first rate change condition for changing the higher rate to the lower rate means that the channel environment is changed from, for example, a state where the ⅓ coding rate and the orthogonal code of length 256 are used to a state where the ⅙ coding rate and the orthogonal code of length 128 are used. Likewise, the second rate change condition for changing the lower rate to the higher rate means that the channel environment is changed from, for example, a state where the ⅙ coding rate and the orthogonal code of length 128 are used to a state where the ⅓ coding rate and the orthogonal code of length 256 are used. In the present embodiment, when the higher coding rate is used, the longer orthogonal code is assigned, and when the lower coding rate is used, the shorter orthogonal code is assigned, to maintain a constant data rate.
1 ( Tx ⁢ ⁢ power ⁢ ⁢ to ⁢ ⁢ the ⁢ ⁢ MS ) ≥ ( total ⁢ ⁢ available ⁢ ⁢ at ⁢ ⁢ BS ⁢ ⁢ for ⁢ ⁢ all forward ⁢ ⁢ link ⁢ ⁢ in ⁢ ⁢ the ⁢ ⁢ same ⁢ ⁢ FA ) - ( power ⁢ ⁢ margin ) number ⁢ ⁢ of ⁢ ⁢ MSs ⁢ ⁢ in ⁢ ⁢ service ⁢ ⁢ in ⁢ ⁢ the ⁢ ⁢ same ⁢ ⁢ FA
2 (average reverse link received signal strength (i.e., RSSI) for a
particular duration) ≦ Thrssi − σrssi
3 (average reverse link SNR for a particular duration) ≦ Thsnr − σsnr
4 any available orthogonal code?
by the number of mobile stations in service in the same area. The second condition (2) is satisfied when an average reverse link received signal strength (i.e., RSSI or Ec/Io of the forward pilot channel), is used in the above case for a particular duration is lower than or equal to a value obtained by subtracting a standard deviation of the RSSI, σrssi from a threshold RSSI, Thrssi. Condition 3 is satisfied when an average reverse link SNR for a particular duration is lower than or equal to a value obtained by subtracting a standard deviation of the SNR, σsnr from a threshold SNR, Thsnr. Condition 4 is satisfied when there are available orthogonal codes among the orthogonal codes of the requested length. Here, the orthogonal codes are searched for and extracted based on the procedure of FIG. 9. That is, as the result of the search, even though there may exist available orthogonal codes, they are considered as unavailable orthogonal codes when they do not satisfy orthogonality with the other orthogonal codes in use. That is, the orthogonal codes satisfying condition 4 should have a length corresponding to the requested coding rate and have orthogonality with the forward channel for the other mobile stations.
Accordingly, when the first rate change condition is satisfied in step 715, the base station sends to the mobile station information about the requested coding rate and the assigned orthogonal code together with the response message, in step 717. For example, when the ⅓ coding rate is presently used, it can be changed to the ⅙ coding rate, and when the ½ coding rate is presently used, it can be change to ¼ coding rate. In this case, the shorter orthogonal codes are assigned which have the orthogonality with the orthogonal codes used for the other forward link channels. The decision block 213 includes a table for storing the orthogonal codes previously set by the Hadamard transform, and assigns the orthogonal codes by selecting from the table the orthogonal codes having orthogonality with other orthogonal codes based on the procedure of FIG. 9. After sending the changed coding rate and the orthogonal information, the decision block 213 of the base station outputs the coding select signal Csel and the orthogonal code number and length signals Wno and Wlength for changing the present rate to the requested lower rate in step 719, thereby to change the coding rate and the orthogonal code of the channel encoder in the base station.
1 (Tx power to the MS) ≦ (average Tx power to all MSs) −
σpwr
2 (average reverse link received signal strength (i.e., RSSI)
for a particular duration) ≧ Thrssi + σrssi
3 (average reverse link SNR for a particular duration) ≧
Thsnr + σsnr
In Table 10, condition 1 is satisfied when transmission power to the mobile station is lower than or equal to a value obtained by subtracting a standard deviation, σpwr, of the average transmission power for the respective forward traffic channels from an average transmission power to all mobile stations. Condition 2 is satisfied when an average reverse link received signal strength (i.e., RSSI or Ec/Io of the forward pilot channel) for a particular duration is higher than or equal to a value obtained by adding the standard deviation of the RSSI, σrssi, to the threshold RSSI, Thrssi. Condition 3 is satisfied when an average reverse link SNR for a particular duration is higher than or equal to a value obtained by adding the standard deviation of the SNR, σsnr, to the threshold SNR, Thsnr.
Accordingly, when the second rate change condition is satisfied in step 721, the base station sends to the mobile station the information about the requested coding rate and the assigned orthogonal code together with the response message, in step 717. For example, when the present coding rate is ⅙, the FEC rate can be changed to the ⅓, and when the present coding rate ¼, it can be change to ½. In this case, as the coding rate is increased, the longer orthogonal codes can be assigned which have the orthogonality with the orthogonal codes used for the other forward link channels. After sending the changed coding rate and orthogonal code, the decision block 213 of the base station outputs the coding select signal Csel and the orthogonal code number and length signals Wno and Wlength for changing the present rate to the requested higher rate in step 719, thereby to change the coding rate and the orthogonal code of the channel encoder in the base station.
1 (average Tx power for a particular duration) ≧ Thpwr + σpwr
2 (average forward link received signal strength (i.e., RSSI or
forward pilot Ec/Io) for a particular duration) ≦ Thrssi − σrssi
3 (average forward traffic channel SNR for a particular
duration) ≦ Thsnr − σsnr
In Table 11, condition 1 is satisfied when an average reverse transmission power for a particular duration is higher than or equal to a value obtained by adding a standard deviation σpwr to a threshold power Thpwr. Condition 2 is satisfied when an average received forward link RSSI (forward pilot Ec/Io may also be used) for a particular duration is lower than or equal to a value obtained by subtracting a standard deviation σrssi from a threshold RSSI Thrssi. A condition 3 is satisfied when an average received forward link SNR for a particular duration is lower than or equal to a value obtained by subtracting a standard deviation σsnr from a threshold SNR Thsnr.
However, when the received rate change request message represents the change to the higher rate in step 813, the decision block 213 of the mobile station examines in step 821 whether a second rate change condition is satisfied or not. Here, the second rate change condition where the mobile station changes the present rate to the higher rate, represents a condition in which at least two of the conditions in the following Table 12 are satisfied.
1 (average reverse Tx power for a particular duration) ≦
Thpwr − σpwr
2 (average forward link received signal strength (i.e., RSSI
or Ec/Io of the forward pilot) for a particular duration) ≧
Thrssi + σrssi
In Table 12, the condition 1 is satisfied when an average reverse transmission power for a particular duration is lower than or equal to a value obtained by subtracting a standard deviation, σpwr, of the reverse link from a threshold power Thpwr. Condition 2 is satisfied when an average received forward link signal strength (i.e., RSSI or pilot Ec/Io) for a particular duration is higher than or equal to a value obtained by adding a standard deviation of the RSSI, σrssi, to a threshold RSSI Thrssi. Condition 3 is satisfied when an average received forward traffic channel SNR for a particular duration is higher than or equal to a value obtained by adding a standard deviation of the SNR, σsnr, to a threshold SNR Thsnr.
Accordingly, when the second rate change condition is satisfied in step 821, the mobile station sends to the base station the requested coding rate and the assigned orthogonal code together with a response message in step 817. For example, when the present coding rate is ⅙, it can be changed to ⅓, and when the present coding rate is ¼, it can be changed to ½. Further, the longer orthogonal code can be assigned after the searching process as described in FIG. 9. After sending the changed coding rate and orthogonal code, the decision block 213 of the mobile station outputs the coding select signal Csel and the orthogonal code number and length signals Wno and Wlength for selecting the requested higher rate to change the coding rate of the encoder and the orthogonal code in step 819, thereby to perform the communication service at the changed rate.
However, when the rate change request message received from the base station does not satisfies both the first and second rate change conditions, the decision block 213 of the mobile station perceives this in step 815 or 821, and sends to the mobile station a response message representing impossibility of changing the coding rate and the orthogonal code in step 823, terminating the procedure.
FIG. 10 illustrates a multicarrier transmission device according to another embodiment of the present invention. It is assumed that the forward traffic channel transmission device uses 3 carriers, and includes a rate ⅓ encoder, a rate 16 encoder and a plurality of orthogonal modulators for independently modulating the signals according to the three carriers.
The first encoder 311, upon reception of the data input from the selector 301, encodes and punctures the input data into data symbols at the ⅓ coding rate (the first coding rate). That is, the first encoder 311 encodes one input data bit into three symbols. A convolutional encoder or a turbo encoder can be used for the first encoder 311. A first symbol repetition part 321 receives the data encoded at the first coding rate, and repeats the symbols output from the first encoder 311 so as to match the symbol rates of the data having different bit rates. A first interleaver 331 interleaves first encoded data output from the first symbol repetition part 321. A block interleaver can be used for the first interleaver 331.
The second encoder 312, upon reception of the data input from the selector 301, encodes and punctures the input data into data symbols at the coding rate ⅙ (the second coding rate). That is, the second encoder 312 encodes one input data bit into six symbols. A convolutional encoder or a turbo encoder can be used for the second encoder 312. A second symbol repetition part 322 receives the data encoded at the second coding rate, and repeats the symbols output from the second encoder 312 so as to match the symbol rates of the data having different bit rates. A second interleaver 332 interleaves second encoded data output from the second symbol repetition part 322. A block interleaver can be used for the second interleaver 332.
A long code generator 391 generates long codes for the user identification, which are differently assigned to the respective subscribers. A decimator 392 decimates the long codes so as to match a rate of the long codes to a rate of the symbols output from the interleavers 331 and 332. A selector 393 selectively outputs the decimated long code output from the decimator 392 to a mixer 341 or a mixer 342 according to the encoder select signal Csel. The selector 393 switches the decimated long code to the first mixer 341 to select the ⅓ coding rate and to the second mixer 342 to select the ⅙ coding rate. The mixer 341 mixes the first encoded data output from the first interleaver 331 with the long code output from the selector 393. The second mixer 342 mixes the second encoded data output from the second interleaver 332 with the long code output from the selector 393.
A first demultiplexer 1011 demultiplexes data output from the first mixer 341 to the respective carriers in sequence. Signal mapping parts 1021–1023 map levels of the binary data output from the first demultiplexer 1011 by converting data “0” to “+1” and data “1” to “−1”. Orthogonal modulators 1031–1033, in the same number as that of the carriers, each include a first orthogonal code generator (not shown) which generate a first orthogonal code for orthogonally modulating the first encoded data according to the orthogonal code number and length Wno and Wlength output from the decision block 213. The orthogonal modulators 1031–1033 multiply the first orthogonal code generated according to the orthogonal code number and length Wno and Wlength by the data output from the signal mapping parts 1021–1023, respectively, to generate a first orthogonal modulation signal. Here, it is assumed that the Walsh code is used for the orthogonal code and a Walsh code of length 256 is used for the data encoded at the first coding rate of ⅓.
A second demultiplexer 1012 demultiplexes data output from the second mixer 342 to the respective carriers in sequence. Signal mapping parts 1026–1028 map levels of the binary data output from the second demultiplexer 1012 by converting data “0” to “+1” and data “1” to “−1”. Orthogonal modulators 1036–1038, in the same number as that of the carriers, each include a second orthogonal code generators (not shown) which generate a second orthogonal code for orthogonally modulating the second encoded data according to the orthogonal code number and length Wno and Wlength output from the decision block 213. The orthogonal modulators 1036–1038 multiply the second orthogonal code generated according to the orthogonal code number and length Wno and Wlength by the data output from the signal mapping parts 1021–1023, respectively, to generate second orthogonal modulation signals. Here, it is assumed that the Walsh code is used for the orthogonal code and a Walsh code of length 128 is used for the data encoded at the second coding rate of ⅙.
Spreaders 1041–1043 combine the first and second orthogonal modulation signals output from the orthogonal modulators 1031–1033 and second orthogonal modulators 1036–1038 with the received spreading sequence to spread transmission signals. Here, the PN sequence can be used for the spreading sequence and the QPSK spreaders can be used for the spreaders. Gain controllers 1051–1053 control gains of the spread signals input from the spreaders 1041–1043 according to gain control signals G1–G3. The respective gain controllers 1051–1053 output different carriers.
1. A channel communication method for a CDMA communication system, comprising the steps of:
selecting a length of an orthogonal code corresponding to a coding rate, and selecting unused orthogonal codes among orthogonal codes having the selected length;
examining non-orthogonality between the selected orthogonal codes and orthogonal codes longer than the selected orthogonal codes and between the selected orthogonal codes and orthogonal codes shorter than the selected orthogonal codes, and excluding orthogonal codes not satisfying orthogonality therebetween from the selected orthogonal codes; and
assigning one of the orthogonal codes remaining after exclusion to spread encoded data.
2. A channel communication method for a CDMA communication system, comprising the steps of:
selecting a length of an orthogonal code corresponding to a coding rate, and selecting unused orthogonal codes among the orthogonal codes having the selected length;
examining non-orthogonality between the selected orthogonal codes and orthogonal codes longer than the selected orthogonal codes and excluding orthogonal codes not satisfying orthogonality therebetween;
determining whether complementary orthogonal codes of the orthogonal codes remaining after exclusion are in use; and
assigning one of the orthogonal codes whose complementary orthogonal codes are in use to spread encoded data.
3. The channel communication method as claimed in claim 2, wherein said complementary orthogonal codes are determined by (i+n/2)mod N, (where i is an orthogonal code number and N is an orthogonal code length).
4. The channel communication method as claimed in claim 2, further comprising the steps of:
when the complementary orthogonal codes corresponding to the orthogonal codes remaining after exclusion are all not in use, examining non-orthogonality between the remaining orthogonal codes and orthogonal codes shorter than the remaining orthogonal codes and excluding the orthogonal codes not satisfying orthogonality therebetween; and
assigning one of the orthogonal codes remaining after the exclusion.
US10272143 1998-03-02 2002-10-16 Rate control device and method for CDMA communication system Active 2021-10-17 US7227836B2 (en)
KR19980006833 1998-03-02
KR6833/1998 1998-03-02
KR19980040167 1998-09-26
KR40167/1998 1998-09-26
US09260213 US6700881B1 (en) 1998-03-02 1999-03-01 Rate control device and method for CDMA communication system
US10272143 US7227836B2 (en) 1998-03-02 2002-10-16 Rate control device and method for CDMA communication system
US09260213 Division US6700881B1 (en) 1998-03-02 1999-03-01 Rate control device and method for CDMA communication system
US20030128674A1 true US20030128674A1 (en) 2003-07-10
US7227836B2 true US7227836B2 (en) 2007-06-05
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US09260213 Active US6700881B1 (en) 1998-03-02 1999-03-01 Rate control device and method for CDMA communication system
US10272143 Active 2021-10-17 US7227836B2 (en) 1998-03-02 2002-10-16 Rate control device and method for CDMA communication system
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