Tài liệu Adaptive WCDMA (P16) pdf

16 Standards In this chapter we discuss the basic Code Division Multiple Access (CDMA) standards and give a brief history of the standard proposals. We present the main system parameters, which are essential for the understanding of the system concept (common air interface) of each standard. At this stage we use what we have learnt so far in this book to discuss the motivations behind the solutions. We believe that at the end of the book the reader should have the required knowledge to follow the closing discussion on the various choices for the different system parameters, and all the advantages and the drawbacks of these choices. 16.1 IS 95 STANDARD 16.1.1 Reverse link Available channels in the uplink are shown in Figure 16.1. A block diagram of a reverse channel data path is shown in Figure 16.2. Data and chip rates in different points in the system are indicated on the picture. The voice source is encoded by using variable rate codec with four possible rates of 1.2 to 9.6 kbps. This is the way to exploit voice activity factor. Prior to modulation, convolutional encoder and block interleaver are used. Modulation f or the reverse CDMA channel is 64-ary orthogonal signaling. One of the possible modulation symbols will be transmitted for each six-code symbol. Modulation symbol number = c 0 + 2c 1 + 4c 2 + 8c 3 + 16c 4 + 32c 5 (16.1) c 5 shall represent the last or the most recent and c 0 the first or the oldest binary valued (0 and 1) code symbol of each group of six code symbols that form a modulation symbol. One out of 64 Walsh symbols is transmitted for each different value of equation (16.1). Construction rules for Walsh functions are described in Chapter 2. On the basis of the chip rate 1.22881447 Mchips (indicated in Figure 16.2), the period of time required to transmit a single modulation symbol, referred to as a Walsh symbol interval, will be approximately Adaptive WCDMA: Theory And Practice. Savo G. Glisic Copyright ¶ 2003 John Wiley & Sons, Ltd. ISBN: 0-470-84825-1 566 STANDARDS • • • • • • • • • • • • • • • • • • • • • • • Reverse CDMA channels (1.23-MHz channel received by base station) Access Ch 1 Access Ch n Traffic Ch 1 Traffic Ch 55 User address long code PNs Figure 16.1 Example of logical reverse CDMA channels received at a base station. PN chip + I Q D I Q Long code mask Long code generator Zero-shift plot PN sequence I-channel 1.2288 MHz PN chip 1.2288 MHz Code symbol Code symbol Information bit 9.6 kbps 4.8 kbps 2.4 kbps 1.2 kbps Convolutional encoder and repetition r = 1/3 K = 9 Block interleaver 28.8 ksps 28.8 ksps 64-ary orthogonal modulator Walsh chip 307.2 kHz Zero-shift plot PN sequence Q-channel 1/2 PN chip delay = 406.9 ns FIR filter FIR filter D/A and filtering D/A and filtering I( t ) Q( t ) A cos(2p ft ) A sin(2p ft ) Figure 16.2 Reverse CDMA channel data path example. equal to 208.333 µs. The period of time associated with 164th of the modulation symbol is referred to as a Wals h chip and will be approximately equal to 3.2552083333 µs. The reverse traffic channel numerology is shown in Table 16.1. 16.1.2 Direct-sequence spreading The reverse traffic channel and the access channel will be combined with three differ- ent pseudonoise (PN) sequences. Data and PN sequence combination involves modulo-2 addition of the encoded, interleaved data stream with two PN code streams, each operating at 1.2288 MHz. The first sequence is referred to as the long code sequence. This sequence shall be a time shift of a sequence of length 2 42 –1 chips and shall be generated by a IS 95 STANDARD 567 Table 16.1 Reverse traffic channel numerology Data Rate (bps) Parameter 9600 4800 2400 1200 Units PN chip rate 1.2288 1.2288 1.2288 1.2288 Mcps Code rate 1/3 1/3 1/3 1/3 Bits/code sym TX duty cycle 100.0 50.0 25.0 12.5 % Code symbol rate 28 800 28 800 28 800 28 800 Sps Modulation 6 6 6 6 Code sym/ Walsh sym Walsh symbol rate 4800 4800 4800 4800 Sps Walsh chip rate 307.20 307.20 307.20 307.20 kcps Walsh symbol 208.33 208.33 208.33 208.33 µs PN chips/code 42.67 42.67 42.67 42.67 PN chip/ symbol code sym PN chips/Walsh 256 256 256 256 PN chip/ symbol Walsh sym PNchips/Walsh4444PNchip/ chip Walsh sym 1 39 8 4 1 2 5 3 6 9 7 10 40 41 42 Modulo-2 addition lsb msb 42-Bit logic code matrix Long code sequence x 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 10 x 39 x 40 x 41 x 42 x 9 Figure 16.3 Long code generation and masking. linear generator using the following polynomial: p(x) = x 42 + x 35 + x 33 + x 31 + x 27 + x 26 + x 25 + x 22 + x 21 + x 19 + x 18 + x 17 + x 16 + x 10 + x 7 + x 6 + x 5 + x 3 + x 2 + x 1 + 1. The long code will be generated by masking the 42-bit state variables of the generator with a 42-bit mask. The actual PN sequence is generated by the modulo-2 addition of all 42 masked output bits of the sequence generator as shown in Figure 16.3. 16.1.3 Code mask The structure of the code mask is shown in Figure 16.4. The mask, used for the PN spreading, will vary depending on the channe l type on which the mobile station is com- municating. Access channel M 24 through M 41 shall be set to ‘1’. M 19 through M 23 shall 568 STANDARDS PCN 1 • • • • • • 41 41 41 40 39 0 01 00 0 32 31 24 23 19 18 16 15 9 8 0 0 0 Access channel long code mask 1 1 ACN REG_ZONE PILOT_PN PCN — Paging channel number ACN — Access channel number REG_ZONE — Registration zone for the forward CDMA channel PILOT_PN — PN offset for the forward CDMA channel Public long code mask ESN Private long code mask Private long code Figure 16.4 Long code mask format. be set to the access channel number chosen randomly. M 16 through M 18 shall be set to the code channel for the associated paging channel (i.e. the range shall be 1 through 7). M 9 through M 15 shall be set to the REG ZONE for the current base station (BS). M 0 through M 8 shall be set to the PILOT PN value for the CDMA channel. In the reverse traffic channel the mobile station shall use one of two long codes unique to that mobile station: a public long code unique to the mobile station’s electronic serial number (ESN) and a private long code unique for each mobile identification number (MIN). The public long code shall be as follows: M 32 through M 41 shall be set to ‘0’ and M 0 through M 31 shall be set to the mobile station’s ESN value. The second and third PN sequences are the I and Q ‘short codes’. The reverse access channel and the reverse traffic channel shall be offset quadrature phase shift keying (OQPSK) spread prior to actual transmission. This offset quadrature spreading on the reverse channel shall use the same I and Q PN codes as the forward I and Q PN codes. These codes are of length 2 15 . The reverse CDMA channel I and Q codes shall be the zero-time offset codes. The generating func tions for the I and Q short PN codes shall be as follows: P I (x) = x 15 + x 13 + x 9 + x 8 + x 7 + x 5 + 1 P Q (x) = x 15 + x 12 + x 11 + x 10 + x 6 + x 5 + x 4 + x 3 + 1 16.1.4 Data burst randomizer algorithm The data burst randomizer generates a masking stream of 0 s and 1 s that randomly mask out the redundant data generated by the code repetition. The masking stream pattern is determined by the frame data rate and by the block of 14 bits taken from the long code sequence. These mask bits are synchronized with the data flow and the data is selectively masked by these bits through the operation of the digital filter. The 1.2288-MHz-long IS 95 STANDARD 569 code sequence shall be input to a 14-bits shift register, which is shifted at 1.2288 MHz. The contents of this shift register shall be loaded into a 14-bit latch exactly one power control group (1.25 ms) before each reverse traffic channel frame boundary. b 0 b 1 b 2 b 3 b 4 b 5 b 6 b 7 b 8 b 9 b 10 b 11 b 12 b 13 The binary (0 and 1) contents of this latch shall be denoted as where b 0 shall represent the first bit to enter the shift register and b 13 shall represent the last (or most recent) bit to enter the sift register. Each 20-ms reverse traffic channel frame shall be divided into 16 equal length (i.e. 1.25 ms) power control groups numbered from 0 to 15. The data burst randomizer algorithm shall be as follows: Data rate selected: 9600 bps Frame transmission shall occur on power control groups numbered 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 Data rate selected: 4800 bps Frame transmission shall occur on power control groups numbered b 0 , 2 + b 1 , 4 + b 2 , 6 + b 3 , 8 + b 4 , 10 + b 5 , 12 + b 6 Data rate selected: 2400 bps Frame transmission shall occur on power control groups numbered b 0 if b 8 = 0, 2 + b 1 if b 8 = 1 4 + b 2 if b 9 = 0, 6 + b 3 if b 9 = 1 8 + b 4 if b 10 = 0, 10 + b 5 if b 10 = 1 12 + b 6 if b 11 = 0, 14 + b 7 if b 11 = 1 Data rate selected: 1200 bps Frame transmission shall occur on power control groups numbered b 0 if (b 8 = 0andb 12 = 0), 2 + b 1 if (b 8 = 1andb 12 = 0) 4 + b 2 if (b 9 = 0andb 12 = 1), 6 + b 3 if (b 9 = 1andb 12 = 1) 8 + b 4 if (b 10 = 0andb 13 = 0), 10 + b 5 if (b 10 = 1andb 13 = 0) 12 + b 6 if (b 11 = 0andb 13 = 1), 14 + b 7 if (b 11 = 1andb 13 = 1) An example is shown in Figure 16.5. 570 STANDARDS b 0 b 1 b 3 b 5 b 6 b 7 b 8 b 1 0 b 1 2 b 2 b 4 b 9 b 1 3 b 1 1 20 ms = 193 bits = 576 code symbols = 96 walsh symbols = 16 power control groups 1.25 ms = 12 bits = 36 code symbols = 6 Walsh symbols = 1 power control group Code symbols transmitted: Code symbols transmitted: Code symbols transmitted: Code symbols transmitted: Previous frame Previous frame Previous frame PN bits used for scrambling Sample masking streams shown are for the 14-bit PN sequence: ( b 0 , b 1 , …, b 13 ) = 0 0 1 0 1 1 0 1 1 0 0 1 0 0 PCG 15 PCG 14 Power control group number 1 33 65 97 … 481 513 545 2 34 66 98 … 452 514 546 1 17 33 49 … 241 257 273 2 18 34 50 … 242 258 274 1 9 17 25 … 121 129 137 2 10 18 26 … 122 130 138 1 5 9 13 … 61 65 69 2 6 10 14 … 62 66 70 Full rate 1/2 rate 1/4 rate 1/8 rate 121314150123456789101112 1413 15 121314150123456789101112 1413 15 121314150123456789101112 1413 15 121314150123456789101112 1413 15 Figure 16.5 Reverse CDMA channel variable data rate transmission example. 16.1.5 Reverse traffic channel frame quality indicator Each frame of the traffic channel shall include a frame quality indicator. For the default multiplex option’s 9600-bps and 4800-bps transmission rates, the frame quality indicator shall be a cyclic redundancy check (CRC). For the 9600-bps and 4800-bps rates, the frame quality indicator (CRC) shall be calculated on all bits within the frame, except the frame quality indicator (CRC) itself and the encoder tail bits. The 9600-bps transmission rate shall use a 12-bit frame quality indicator (CRC), which shall be transmitted within the 192-bit long frame. The generator polynomial for the 9600-bps rate g(x ) = x 12 + x 11 + x 10 + x 9 + x 8 + x 4 + x + 1 The 4800-bps transmission rate shall use a 8-bit CRC, which shall be transmitted within the 96-bit long frame. The generator polynomial for the 4800-bps rate g(x ) = x 8 + x 7 + x 4 + x 3 + x + 1 16.1.6 The CRCs procedure The circuit block diagrams for 9600 and 4800 bps are shown in Figures 16.6 and 16.7, respectively. Initially, all shift register elements shall be set to logical one and the switches shall be set in the up position. The register shall be clocked 172 times (for 192-bit frame) or 80 times (for 96-bit frame) with the traffic or the signaling bits and mode/format indicators as input. The switches shall be set in the down position, and the register shall be clocked an additional 12 times (for 192-bit frame) or 8 times (for 96-bit frame). IS 95 STANDARD 571 Denotes modulo-2 addition Up for first 172 bits Down for last 12 bits Output 0 0 Denotes one-bit storage element Input X 0 X 1 X 3 X 4 X 7 X 8 X 9 X 10 X 11 Figure 16.6 Reverse traffic channel frame quality indicator calculation at 9600-bps rate for the default multiplex option(1). Denotes modulo-2 addition Output 0 0 Denotes one-bit storage element Up for first 80 bits Down for last 8 bits Input X 0 X 1 X 2 X 3 X 4 X 5 X 6 X 7 Figure 16.7 Reverse traffic channel frame quality indicator calculation at 4800-bps rate for the default multiplex option(1). The 12 or 8 additional output bits shall be the check bits. The bits shall be transmitted in the order calculated. 16.1.7 Base station Transmitter Each BS within a given system shall use the same CDMA frequency assignments for each of the CDMA channels. The channel structure is shown in Figures 16.8 and 16.9. Variable data rate transmission The forward traffic channel shall support variable data rate operation. Four data rates are supported: 9600, 4800, 2400 and 1200 bps. The data rate shall be selectable on a frame-by-frame (i.e. 20-ms) basis without consideration for the rate in the previous or subsequent frames. Although the data rate may vary on a 20-ms basis, the modulation 572 STANDARDS W1 W33 Up to Forward CDMA channel (1.23-MHz channel transmitted by base station) Pilot chan Sync chan Paging Ch 1 Paging Ch 7 Traffic Ch 1 Traffic Ch N Traffic Ch 24 Traffic Ch 25 Traffic Ch 55 W0 W32 W7 W8 Up to Up to W31 W63 W = Walsh symbol number Traffic data Mobile power control subchannel Figure 16.8 Example of a forward CDMA channel transmitted by a base station. symbol rate is kept constant by code repetition at 19.2 kilo-symbols per second (ksps). The modulation symbols that are transmitted at the lower data rates shall be transmitted using lower energy, as shown in Table 16.2. Note that all the symbols in the interleaver block are from the same frame. Thus they are all transmitted a t the same energy. Power control bits are always transmitted with energy E b . Pilot channel The pilot channel is transmitted at all times by the BS on each active forward CDMA channel. It is an unmodulated spread spectrum signal that is used by a mobile station operating within the geographic coverage area of the base station. It is used by the mobile station to acquire synchronization with the pilot PN sequence, to provide a phase reference and to provide sync channel frame timing. The acquisition of the pilot channel pilot PN sequence is the first step in the process of the mobile station acquiring the system timing or reacquiring the system timing. Code for the pilot channel shall be a quadrature sequence of length 2 15 (i.e. 32768 PN chips in length). Code polynomial P I (x) = x 15 + x 13 + x 9 + x 8 + x 7 + x 5 + 1 P Q (x) = x 15 + x 12 + x 11 + x 10 + x 6 + x 5 + x 4 + x 3 + 1 for the in-phase (I) sequence and for the quadrature (Q) phase sequence is used. The length of these sequences is 2 15 –1. I n order to generate a pilot PN sequence of length 2 15 ,a binary 1 is inserted in the sequence generator output after the contiguous succession of 14 binary 0 outputs (that occurs only once per period of the sequence). The chip rate for the pilot PN sequence shall be 1.2288 Mcps. The pilot PN sequence period is 26.666 ms. Exactly 75 pilot PN sequence repetitions occur every 2 s. IS 95 STANDARD 573 bit + Wp cover + + + + + + + 19.2 Power 19.2 MHz MHz Symbol W32 1.2288 scrambling MHz + W0 MHz Symbol ksps ksps 1.2288 1.2288 1.2288 control WI WJ + + + + + + + + + + I-channel pilot PN sequence Pilot channel: all O´s Sync channel data 1200 bps Convolutional encoder and repetition Convolutional encoder and repetition Convolutional encoder and repetition Convolutional encoder and repetition Block interleaver Block interleaver Block interleaver Block interleaver 4800 sps Repeat four times 19.2 ksps 19.2 ksps Long generator Long generator Long code generator Symbol scrambling Symbol cover Q-channel pilot PN sequence M u x M u x Symbol cover Power control bit Symbol cover Paging channel p Long code mask User i long code mask User j long code mask Modulo-2 addition Paging channel data 9.6 kbps 4.8 kbps 2.4 kbps 9.6 kbps 4.8 kbps 2.4 kbps 1.2 kbps Forward traffic channel data 9.6 kbps 4.8 kbps 2.4 kbps 1.2 kbps Forward traffic channel data Figure 16.9 Forward CDMA channel structure. Pilot channel index Each BS shall use a time offset of the pilot P N sequence to identify its forward CDMA channel. Time offsets may be reused within a CDMA cellular system, so long as the coverage area of the BS emitting a given pilot P N sequence time offset does not overlap the coverage area of another BS using the same pilot PN sequence time offset. Distinct pilot channels shall be designated by an index identifying an offset value from a zero offset pilot PN sequence (in increments of 64 PN chips). The zero offset pilot PN sequence 574 STANDARDS Table 16.2 Transmitted symbol energy versus data rate Data rate (bps) Energy per modulation symbol 9600 E S = E b /2 4800 E S = E b /4 2400 E S = E b /8 1200 E S = E b /16 shall be such that the start of the sequence shall be output at the beginning of every even second in time, referenced to system time. The start of the zero offset pilot PN sequence for either the I or the Q sequence shall be defined as the state of the sequence generator for which the previous 15 outputs were ‘0’. Five hundred and eleven unique values shall be possible for the pilot PN sequence offset (the offset index of ‘111 111 111’ binary shall be reserved). The pilot P N sequence offset shall be denoted as a 9-bit binary pilot PN sequence index for a given BS. The timing offset for a given pilot PN sequence shall be equal to the offset index value multiplied by 64 multiplied by the pilot channel chip period (= 813.802 ns). For example, if the pilot PN sequence offset index is 15 (decimal), the pilot PN sequence offset will be 15 × 64 × 813.802 ns = 781.1 µs. In this case the pilot PN sequence will start 781.1 µs after the start of every even second of the system time. The same pilot PN sequence offset shall be used on all CDMA frequency a ssignments for a given BS. The sync channel shall be an encoded, interleaved, modulated direct-sequence spread spectrum signal that is used by mobile stations operating within the geographic coverage area of that BS (a cell or a sector within a cell) to acquire synchronization to the long code sequence and to acquire system timing. Sync channel acquisition is the second step that the mobile station takes in acquiring the system. Forward traffic channel data scrambler The forward traffic channel data shall be scrambled by an additional modulo-2 addition operation prior to transmission. This data scrambling shall be performed on the data output from the block interleaver at the 19 200-cps rate. The data scrambling shall be accomplished by performing the modulo-2 addition of the interleaver output symbol with the binary value of the PN chip that is valid at the start of the transmission period for that symbol as shown in Figure 16.10. This sequence generator shall operate at 1.2288- MHz clock rate although only one output of 64 shall be used for data scrambling (i.e. at a 19 200-cps rate). The PN sequence used for data scrambling shall be the decimated version of the sequence used by the mobile station for direct-sequence spreading of the reverse traffic channel (either the public long code or the private long code). [...]... Gain GF PNI Long code PNQ Walsh (+ + − −) Figure 16.14 The uplink dedicated channel structure signal for coherent detection when adaptive antennas are not employed The pilot channel is similar to IS-95 (i.e it is composed of a long PN code and Walsh sequence number 0) When adaptive antennas are used, auxiliary pilot is used as a reference signal for coherent detection Code-multiplexed auxiliary pilots... ms and interleaving can be over 5, 10 or 20 ms IS-665 W-CDMA has open and closed loop power control The closed loop power control uses variable step sizes of 0.5, 1, 2 and 4 dB, which are adaptively controlled IS-665 WCDMA supports the use of interference cancellation So, even this standard was transparent to the use of the technology described in Chapters 14 and 15 The basic system parameters are summarized... principle for packet data transmission Instead of fixed transmission power, it increases the transmission power for the random access burst after an unsuccessful access attempt This is an additional form of adaptive CDMA network described in Chapter 12 When the mobile station has been allocated a traffic channel, it can transmit without scheduling up to a predefined bit rate If the transmission rate exceeds... channels are transmitted with the multicode principle The variable spreading factor scheme is used for higher data rates in the supplemental channel Similar to wideband code division multiple access (WCDMA) , complex spreading is used In the uplink, it is used with dual-channel modulation Multirate The fundamental and supplemental channels can have different coding and interleaving schemes In the downlink, . modulation symbol, referred to as a Walsh symbol interval, will be approximately Adaptive WCDMA: Theory And Practice. Savo G. Glisic Copyright ¶ 2003 John Wiley. when adaptive antennas are not employed. The pilot channel is similar to IS-95 (i.e. it is composed of a long PN code and Walsh sequence number 0). When adaptive