CDMA Technology OverviewFebruary, Page 3-1 CDMA Technology Overview Lesson 4 - CDMA Reverse Channels

CDMA Technology OverviewFebruary, Page 3-2 Access Channels

CDMA Technology OverviewFebruary, Page 3-3 REG BTS Code Channels in the Reverse Direction There are two types of CDMA Reverse Channels: nTRAFFIC CHANNELS are used by individual users during their actual calls to transmit traffic to the BTS  a reverse traffic channel is defined by a user-specific public or private Long Code mask  there are as many reverse Traffic Channels as there are CDMA phones in the world nACCESS CHANNELS are used by mobile stations not yet in a call to transmit registration requests, call setup requests, page responses, order responses, and other signaling information  an access channel is defined by a user-independent public long code mask  Access channels are paired with Paging Channels. There can be up to 32 access channels per paging channel

CDMA Technology OverviewFebruary, Page 3-4 MTXBSCBTS (1 sector) Channel Element Access Channels Vocoder more Receiver, Sector X Channel Element Long Code Gen more User Long Code User Long Code User Long Code User Long Code User Long Code User Long Code Coding Process in the Reverse Direction A Reverse Channel is identified by: v its CDMA RF carrier Frequency v the unique Long Code PN Offset of the individual handset CDMA Frequency

CDMA Technology OverviewFebruary, Page 3-5 Access Channels nUsed by the mobile station to  Initiate communication with the base station  Respond to Paging Channel messages nHas a fixed data rate of 4800 bps nEach Access Channel is associated with only one Paging Channel nUp to 32 access channels (0-31) are supported per Paging Channel 4800 bps

CDMA Technology OverviewFebruary, Page 3-6 Access Channel Generation nMessage attempts are randomized to reduce probability of collision nTwo message types:  A response message (in response to a base station message)  A request message (sent autonomously by the mobile station) 28.8 ksps Convolutional Encoder & Repetition R = 1/ Mcps Access Channel Long Code Mask Long PN Code Generator 28.8 ksps Orthogonal Modulation kcps Mcps Q PN (No Offset) I PN (No Offset) D 1/2 PN Chip Delay Block Interleaver Access Channel Information (88 bits/Frame) 4.8 kpbs Direct Sequence Spreading

CDMA Technology OverviewFebruary, Page 3-7 Rate 1/3 Convolutional Encoder g0g0 g1g1 g2g2 Information bits (INPUT) Code Symbols (OUTPUT) Code Symbols (OUTPUT) Code Symbols (OUTPUT)

CDMA Technology OverviewFebruary, Page 3-8 Access Channel Block Interleaving n576 code symbols (288 x 2) are written sequentially by columns, then read by rows in a particular order (called “bit-reverse readout of the row addresses”) every 20 ms nBlock interleaving separates repeated symbols in two identical sets: one set is transmitted during the first 10 ms and the second set, with the repetitions, is transmitted during the second 10 ms  Improves survivability of symbol information  “Spreads” the effect of spurious interference and fast fading 28.8 ksps from Conv. Encoding & Symbol Repetition (2x) Input Array (Normal Sequence) 32 x 18 Output Array (Reordered Sequence) 32 x ksps to Orthogonal Modulation

CDMA Technology OverviewFebruary, Page 3-9 Access Channel Block Interleaving (4800 x 2 bps - Write Matrix)

CDMA Technology OverviewFebruary, Page 3-10 Access Channel Block Interleaving (4800 x 2 bps - Read Matrix)

CDMA Technology OverviewFebruary, Page 3-11 Access Channel Structure

CDMA Technology OverviewFebruary, Page 3-12 Access Channel Probing Access Probe 1 Access Probe 1 Access Probe 1 Access Probe 1 Access Probe 1 + NUM_STEP (16 max) System Time TARTTARTTARTTA PI IP (Initial Power) See previous figure ACCESS PROBE SEQUENCE Select Access Channel (RA) initialize transmit power

CDMA Technology OverviewFebruary, Page 3-13 Reverse Traffic Channels

CDMA Technology OverviewFebruary, Page 3-14 CDMA Reverse Traffic Channels nUsed when a call is in progress to send  Voice traffic from the subscriber  Response to commands/queries from the base station  Requests to the base station nSupports variable data rate operation for  8 Kbps vocoder  Rate Set , 4800, 2400 and 1200 bps  Multiplex Option 1  13 Kbps vocoder  Rate Set , 7200, 3600, 1800 bps  Multiplex Option 2

CDMA Technology OverviewFebruary, Page 3-15 Reverse Traffic Channel Generation 9600 bps 4800 bps 2400 bps 1200 bps or bps 7200 bps 3600 bps 1800 bps 28.8 ksps R = 1/ Mcps User Address Mask Long PN Code Generator 28.8 ksps Orthogonal Modulation Data Burst Randomizer kcps Mcps Q PN (no offset) I PN (no offset) D 1/2 PN Chip Delay Direct Sequence Spreading R = 1/2 Convolutional Encoder & Repetition Block Interleaver

CDMA Technology OverviewFebruary, Page 3-16 Reverse Traffic Channel Frame Structure Transmission Rate Total Erasure InformationCRCTail Bits — — —40— —16— Number of Bits per Frame Rate Set

CDMA Technology OverviewFebruary, Page 3-17 Reverse Traffic Channel Convolutional Encoding & Symbol Repetition nConvolutional encoding:  Results in 3 code symbols out for each bit in, at Rate Set 1, and in 2 code symbols out for each bit in, at Rate Set 2  Also allows for reduction in transmit power  Reduces overall noise & increases capacity nSymbol repetition maintains a constant 28.8 ksps output to block interleaver PCM Voice Convolutional Encoding Code Symbol Repetition Block Interleaving Orthogonal Modulation Data Burst Randomizer Direct Sequence Spreading Quadrature Spreading Baseband Filtering Vocoder Processing Baseband Traffic to RF Section Variable Rate Output from Vocoder R=1/3 K=9 Convolutional Encoder R=1/2 K= ksps to Block Interleaver 28.8 ksps (No repetition) 14.4 ksps (2 X repetition) 7.2 ksps (4 X repetition) 3.6 ksps (8 X repetition) 28.8 ksps (No repetition) 14.4 ksps (2 X repetition) 7.2 ksps (4 X repetition) 3.6 ksps (8 X repetition) Symbol Repetition 9.6 kbps 4.8 kbps 2.4 kbps 1.2 kbps 14.4 kbps 7.2 kbps 3.6 kbps 1.8 kbps

CDMA Technology OverviewFebruary, Page 3-18 Reverse Traffic Channel Block Interleaving n20 ms symbol blocks are sequentially reordered nCombats the effects of fast fading nSeparates repeated symbols at 4800 bps and below  Improves survivability of symbol data  “Spreads” the effect of spurious interference PCM Voice Convolutional Encoding Code Symbol Repetition Block Interleaving Vocoder Processing Baseband Traffic to RF Section Orthogonal Modulation Data Burst Randomizer Direct Sequence Spreading Quadrature Spreading Baseband Filtering 28.8 ksps From Coding & Symbol Repetition Output Array (Reordered Sequence) 32 x ksps to Orthogonal Modulation Input Array (Normal Sequence) 32 x 18

CDMA Technology OverviewFebruary, Page 3-19 Lesson Review 1.The two types of CDMA Reverse Channels are Traffic Channels and Access Channels. [True/False] True 2.Short PN sequences are used to achieve _____________________. Phase Modulation 3.How many access channels are supported by a single paging channel? 32 (0 - 31) 4.When generating the Access Channel, why are message attempts randomized? To reduce the probability of collision 5.What is the access channel preamble? A frame comprised of 96 zeroes that aids the base station in acquiring access channel transmission.

CDMA Technology OverviewFebruary, Page 3-20 Lesson Review, cont’d 6.All Access Channels associated with a particular Paging Channel a. have the same slot size b. do not have the same slot size c. all slots begin at the same time d. all slots do not begin at the same time e. a and c f. a and d g. none of the above a and c 7.Why is the Reverse Traffic Channel preamble transmitted by the mobile to the base station? To help the base station acquire the Reverse Traffic Channel 8.The pilot PN sequences are offset relative to system time, not mobile station time. Why? The mobile draws its time reference from the earliest usable pilot component it receives. 9.What is used in the reverse path: direct sequence spreading or data scrambling? Direct sequence spreading

CDMA Technology OverviewFebruary, Page 3-21