Presentation is loading. Please wait.

Presentation is loading. Please wait.

Introduction Concepts of CDMA. Page 2 Cellular Access Methods Power Frequency Time FDMA Frequency PowerTime TDMA Frequency CDMA Power Time.

Similar presentations


Presentation on theme: "Introduction Concepts of CDMA. Page 2 Cellular Access Methods Power Frequency Time FDMA Frequency PowerTime TDMA Frequency CDMA Power Time."— Presentation transcript:

1 Introduction Concepts of CDMA

2 Page 2 Cellular Access Methods Power Frequency Time FDMA Frequency PowerTime TDMA Frequency CDMA Power Time

3 Page 3 CDMA Analogy

4 Page 4 CDMA is Also Full Duplex US Cellular Channel 384 Amplitude Frequency AMPS CDMA Frequency Amplitude Reverse Link Forward Link 45 MHz MHz MHz

5 Page 5 Cellular Frequency Reuse Patterns FDMA ReuseCDMA Reuse

6 Page 6 The CDMA Concept

7 Page 7 CDMA Paradigm Shift Multiple users on one frequency Channel is defined by code Capacity limit is soft

8 Page 8 Processing Gain AMPS = 1.5 MHz / 30 kHz = 50 Channels Capacity = 50 Channels / 7 ( 1/7 Frequency Reuse ) AMPS = 7 Calls ( Using 1.5 MHz BW ) CDMA = 42 Calls ( Using 1.5 MHz BW ) CDMA = ____________ X _____ X _____ X (0.67) (1,230,000 ) (1) (1) (9,600) (5.01) (.40) Capacity = _____________ X _____ X ____ X (Fr) (Data Rate) (S/N) (Vaf) (Chan BW) (1) (1) CDMA Capacity Gains

9 Page 9 CDMA Makes use of Diversity Spatial diversity Frequency diversity Time diversity

10 Page 10 CDMA Spatial Diversity Multiple antennas at base station Multiple base stations for soft handoff

11 Page 11 Spatial Diversity During Soft Handoff MTSO Vocoder / Selector Base Station 2 Base Station 1 Land Link

12 Page 12 CDMA Frequency Diversity Combats fading, caused by multipath Fading acts like notch filter to a wide spectrum signal May notch only part of signal Amplitude Frequency 1.25 MHz BW

13 Page 13 CDMA Time Diversity Uses rake receiver Data is interleaved Convolutional encoding Viterbi decoding

14 Page 14 The Rake Receiver Time Frequency Amplitude

15 Page 15 CDMA Reverse Link Power Control All mobiles are received at base station at equal power Two types of control: Open Loop Power Control Closed Loop Power Control

16 Page 16 Open Loop Power Control Assumes loss is similar on forward and reverse paths Receive Power + Transmit Power = -73 All powers in dBm Example: For a Received Power of -85 dBm (at the mobile) Transmit Power = (-73) - (-85) Transmit Power = +12 dBm

17 Page 17 Closed Loop Power Control Directed by base station Updated every 1.25 ms 1 dBm step size Corrects Open Loop Power Estimate

18 Page 18 CDMA Variable Rate Speech Coder 20 Millisecond blocks of speech Full data rate of 9600 bps Lowest rate (1/8) of 1200 bps Mobile transmits in bursts of 1.25 msec Base repeats bits and lowers power System capacity increases by 1/Voice Activity Factor

19 Page 19 CDMA Frame Formats bits in a ms frame bps Frame 8 Mixed Mode Bit Information Bits 1-bit Reserved Mixed Mode Bit Information Bits 2400 bps Frame 9600 bps Frame 4800 bps Frame 192 bits in a ms frame 96 bits in a ms frame 48 bits in a ms frame 1800 bps Frame 3600 bps Frame 7200 bps Frame bps Frame 288 bits in a ms frame 144 bits in a ms frame 72 bits in a ms frame 36 bits in a ms frame 1-bit Reserved 1-bit Reserved 1-bit Reserved Mixed Mode Bit Mixed Mode Bit Mixed Mode Bit Mixed Mode Bit Encoder Tail Bits CRC Encoder Tail Bits Encoder Tail Bits Encoder Tail Bits Information Bits Encoder Tail Bits Encoder Tail Bits Encoder Tail Bits Encoder Tail Bits CRC

20 Page 20 Mobile Power Bursting Each Frame is Divided into 16 Power Control Groups Each Power Control Group Contains 1536 Chips (represents 12 encoded voice bits) Average Power is Lowered 3 dB for Each Lower Data Rate CDMA Frame = 20 ms Full Rate Half Rate Quarter Rate Eighth Rate

21 Page 21 Walsh Codes W = W = W = 0 1 n n n n W W = 2n2n

22 Page 22 Forward Link Traffic Channel Physical Layer Walsh Cover I Short Code Q Short Code FIR Mbps Walsh Code Generator I Mbps Mbps Long Code 19.2 kbps Vocoded Speech data 20 ms blocks Interleaver Power Control Puncturing 19.2 kbps 800 bps P.C. MUX 9.6 kbps 19.2 kbps 3/4 rate 1/2 rate 14.4 kbps 19.2 kbps Convolutional Encoder Long Code Scrambling Short Code Scrambler Q

23 Page 23 Long Code Generation Modulo-2 Addition Long Code Output User Assigned Long Code Mask 42 bits Long Code Generator

24 Page 24 Forward Link Channel Format Walsh Code 32 Walsh Code 0 Pilot Channel Sync Channel Walsh Codes 1 to 7 Walsh Codes 8-31, Traffic Channels 1 up to 55 Channels All 0's 19.2 kbps kbps I Convert to I/Q & PN Spreading Convert to I/Q & PN Spreading Convert to I/Q & PN Spreading FIR LP Filter & D/A Conversion FIR LP Filter & D/A Conversion FIR LP Filter & D/A Conversion FIR LP Filter & D/A Conversion Q 4.8 kbps I Data Q Data Paging Channels 1 up to 7 Channels 19.2 kbps kbps Convert to I/Q & PN Spreading

25 Page 25 Interleaver I Short Code Q Short Code Mbps I Q kbps t/2 1/2 Chip Delay 28.8 kbp s 20 ms blocks Vocoded Speech Data 64-ary Modulator Mbps 1 of 64 Walsh Codes Long Code Mbps FIR Walsh Code 1 Walsh Code 2 Walsh Code 0 Walsh Code 62 Walsh Code 63 Walsh Code 61 Convolutional Encoder 9.6 kbp s 28.8 kbp s 1/3 rate 1/2 rate 14.4 kbp s 28.8 kbp s Long Code Modulator Short Code Scrambler Reverse Link Traffic Channel Physical Layer

26 Page 26 CDMA Modulation Formats I Q I Q Base Station Transmitter Mobile Station Transmitter Filtered QPSKFiltered Offset QPSK

27 Page 27 Ten Minutes in the Life of a CDMA Mobile Phone System access Continue travel Initiate Soft Handoff Terminate Soft Handoff End call Turn-on System access Travel Idle State Hand-Off Initiate call

28 Page 28 CDMA Turn On Process Find all receivable pilot signals Choose strongest one Establish Frequency and PN Time Reference (Base station I.D.) Demodulate sync channel Establish system time Determine paging channel Long Code Mask

29 Page 29 CDMA Service Options Service Options Are: 1- Voice Using 9600 bps IS-96-A Vocoder 2- Rate Set 1 Loopback (9600 bps) 3- Voice Using 9600 bps (EVRC) 4- Asynchronous Data Service (circuit switched) 5- Group 3 Fax 6- Short Message Service (9600 bps) 7- Internet Standard PPP Packet Data 8- CDPD Over PPP Packet Data 9- Rate Set 2 Loopback (14400 bps) 14-Short Message Service (14400 bps) 32,768- Voice Using bps (CDG )

30 Page 30 CDMA Protocol Stacks IS -95 Rev 0 Original System-never actually deployed ARIB T53 Japan CDMA System Cellular Protocol IS -95 Rev A Backwards compatible with IS-95. First Deployed Protocol TBS- 74 Cellular Protocol that adds Channel Support J-STD-008 Not Backwards Compatible, PCS only Protocol EIA/TIA-95 Rev B Combines TSB-74 & J-STD-008 for a Universal Protocol

31 Page 31 Sync Channel Message Contains the Following Data: Base Station Protocol Revision Min Protocol Revision Supported SID, NID of Cellular System Pilot PN Offset of Base Station Long Code State System Time Leap Seconds From Start of System Time Local Time Offset from System Time Daylight Savings Time Flag Paging Channel Data Rate Channel Number SYNC

32 Page 32 Paging Channel Messages –Overhead Messages System Parameters Access Parameters CDMA Channel List Extended System Parameters Extended Neighbor List –Other Messages Order Channel Assignment Data Burst –More Messages Authentication SSD Update Feature Notification Status Request Service Redirection General Page Global Service Redirection TMSI Assignment J-STD-008 Paging Messages

33 Page 33 CDMA Idle State Handoff No Call in progress Mobile Listens to new Cell Move Registration Location if entering a new zone

34 Page 34 CDMA Call Initiation Dial numbers, then press send Mobile transmits on a special channel called the Access Channel The Access Probe uses Long Code Mask based on: Access & Paging Channel Numbers Base station ID Pilot PN offset

35 Page 35 CDMA Call Completion Base answers Access Probe using the Channel Assignment Message Mobile goes to a Traffic Channel based on the Channel Assignment Message information Base station begins to transmit and receive traffic channel

36 Page 36 CDMA Soft Handoff Initiation Mobile finds second Pilot of sufficient power (exceeds T_add Threshold) Mobile sends Pilot strength message to first Base station Base station notifies MTSO MTSO requests New Walsh Assignment from second Base station If available, New Walsh Channel Info is relayed to first Base station

37 Page 37 CDMA Soft Handoff Completion First Base station orders Soft Handoff with New Walsh Assignment MTSO sends Land Link to second Base Station Mobile receives Power from two Base Stations MTSO chooses better quality frame every 20 milliseconds

38 Page 38 Ending CDMA Soft Handoff First BS Pilot Power Goes low at Mobile Station (drops below T_drop) Mobile sends Pilot Strength Message First Base station stops transmitting and frees up Channel Traffic channel continues on Base station Two

39 Page 39 CDMA End of Call Mobile or land initiated Mobile and Base stop transmission Land connection broken

40 Page 40 CDMA Conclusions New access method Code based Designed for use in interfering environment Uses multipath to advantage Has high capacity 6 to 20 times analog CDMA


Download ppt "Introduction Concepts of CDMA. Page 2 Cellular Access Methods Power Frequency Time FDMA Frequency PowerTime TDMA Frequency CDMA Power Time."

Similar presentations


Ads by Google