WiCoRe, UT-Dallas IS-95 Overview

WiCoRe, UT-Dallas CDMA Overview l Code Division Multiple Access (CDMA) is a radically new concept in wireless communications. It has gained widespread international acceptance by cellular radio system operators as an upgrade that will dramatically increase both their system capacity and the service quality. system capacity and the service quality. l CDMA is a form of spread-spectrum, a family of digital communication techniques that have been used in military applications for many years. –Use of noise-like carrier waves –Bandwidths much wider than the bandwidth of traditional narrow band signal.

WiCoRe, UT-Dallas CDMA Overview (Cont.) l Originally there were two motivations –Either to resist enemy efforts to jam the communications (anti-jam, or AJ). Or to hide the fact that communication was even taking place, sometimes called low probability of intercept (LPI). –It has a history that goes back to the early days of World War II. –CDMA for civilian mobile radio applications is was proposed theoretically in the late 1940's. –Commercial applications became possible because of two evolutionary developments of Integrated Circuit and effective access method.

WiCoRe, UT-Dallas Market Coverage CDMA

WiCoRe, UT-Dallas Network Architecture l Five Levels –Mobile Station (MS) –Base Station System(BSS) –Switching System(SS) –Global Positioning System –Control Network (HLR, VLR, EIR, AuC). Switching System Base Station Base Station Public Network GPS HLR VLR EIR AuC

WiCoRe, UT-Dallas Logical Architecture l Logical Channels –Pilot Channel –Sync Channel –Paging Channel –Access Channel Switching System Base Station Base Station Public Network GPS

WiCoRe, UT-Dallas Services & Capabilities l Multiple Access using the same Frequency band for multiple users. l Simplicity in Frequceny Planning and efficiency. Reuse factor of one with no cell sectorizaation. l Comprehensive telephone services (voice, text, and low speed data communication). Compatible with other protocols ISDN TIME FREQUENCY CODE CDMA:Spread Spectrum User n User 2 User 1

WiCoRe, UT-Dallas Services & Capabilities l CDMA frequency based is the same as AMPS l Channel Bandwidth is 1.25MHz l Modulation is based on QPSK and OQPSK l Channel Bite Rate is based on Mb/s l Channel data rate from 1200 b/s to 9600 b/s l Channel uplink frequency is 824 to 849MHz; down link is between 869 to 894 MHz; with frequency spacing of 45 MHz. l Simplicity in Frequceny Planning and efficiency. One (1) reuse factor with no cell sectorizaation. l Challenge is SIR… need to add more details here. l Compherise telephone services (voice, text, and low speed data communication). Compatible with other protocol sISDN

WiCoRe, UT-Dallas Channel Structure

WiCoRe, UT-Dallas Radio Link Overview  Channel Structure –Forward Channel –Reverse Channel  Different modulation techniques for uplink and down link  Two Stage Modulation  Variable Bit Rate  Reuse Factor of 1

WiCoRe, UT-Dallas Bandwidth  Bandwidth of a CDMA channel is 1.23MHz which is equivalent to 41 contiguous AMPS Channels or about 20 AMPS channels per CDMA carrier  Can be used along side AMPS sharing the same FCC assigned spectrum by giving CDMA a section of the frequency

WiCoRe, UT-Dallas Processing Gain  Early Implementations use R=9600 b/s for a Processing gain of 128 ch/b  Later Implementations use R=14400 b/s for a processing gain of 85.3 ch/b G = Processing Gain W = Switching Rate Ch/s R = Source Information Rate b/s

WiCoRe, UT-Dallas Spectrum Efficiency  C = Conversation/base station  29.8 conversations/cell ≤ C ≤ 111 conversations per cell

WiCoRe, UT-Dallas PN Sequence  Signal is spread using a pseudorandom noise sequence  Low cross correlation  Feedback shift register with 42 stages  Long code repeats after ch or 41.4 days

WiCoRe, UT-Dallas Reverse Channel

WiCoRe, UT-Dallas Reverse Channel Modulation  Offset Quadrature Phase Shift Keying (OQPSK)  Modulates in-phase and quadrature components of the carrier-frequency  Modulates at 1,228,800 ch/s and has a periodicity of 2 15 chips  Terminal synchronizes to base station sync channel

WiCoRe, UT-Dallas Data Rates Reverse Channel  Frame Length 20 ms Data Rate R b/s 1,2002,4004,8009,600 Information Rate R I b/s Information bits per frame (IBPF) Parity bits per frame (PBPF) Data bits per frame (IBPF+PBPF+8) Coded bits per frame (CBPF) Repetitions8421 Total bits per frame (BPF)

WiCoRe, UT-Dallas Reverse Channel Digital Modulation Rate 1/3RepeatInterleave 20 ms Walsh Modulator Digital Modulator Random Number Generator 42-Stage Shift Register Channel Identifier (42 bits) Digital Logic Convolutional Code variable rate 28,800 b/s 307,200 b/s Long Code Digital Carrier Long Code Mask Mch/s Mch/s

WiCoRe, UT-Dallas OQPSK Digital Modulator Mixer + + Delay (1/2 Chip) Mch/s In-Phase Quadrature Radio Carrier Radio Signal Q-Channel Binary sequence Period =2/75 seconds I-Channel Binary sequence Period = 2/75 seconds

WiCoRe, UT-Dallas Forward Channel

WiCoRe, UT-Dallas Forward Link Radio Transmission Overview  1 Physical channel contains 64 chips  Quadrature Phase Shift Keying (QPSK)  Each basestation has 64 physical channels (One Row of Walsh Hadamard Matrix) numbered 0 to 63  Base station reduces power to maintain energy per bit when operating at lower bit rates

WiCoRe, UT-Dallas Data Rates Forward Channel  Frame Length 20 ms Data Rate R b/s 1,2002,4004,8009,600 Information Rate R I b/s Information bits per frame (IBPF) Parity bits per frame (PBPF) Data bits per frame (IBPF+PBPF+8) Coded bits per frame (CBPF) Repetitions8421 Total bits per frame (BPF)

WiCoRe, UT-Dallas Forward Channel Digital Modulation (Paging and Forward Traffic) Rate 1/2RepeatInterleave 384 bits 20 ms Decimate 64:1 Digital Modulator Random Number Generator 42-Stage Shift Register Channel Identifier (42 bits) Digital Logic Convolutional Code variable rate 19.2 kb/s 19.2 kb/s Long Code Digital Carrier Long Code Mask Mch/s Mch/s x 19.2 kb/s pseudorandom scrambling 64-bit carrier

WiCoRe, UT-Dallas Forward Channel Digital Modulation (Sync) Rate 1/2Repeat 2:1 Interleave 128 bits ms Repeat 4:1 Digital Modulator Convolutional Code 1,200 b/s 4,800 b/s 19.2 kb/s Mch/s 64-bit carrier Walsh 32 2,400 b/s 4,800 b/s

WiCoRe, UT-Dallas Forward Radio Modulation Digital Modulator Mixer Mch/s In-Phase Quadrature Radio Carrier Radio Signal Q-Channel Binary sequence Period =2/75 seconds I-Channel Binary sequence Period = 2/75 seconds Base Station Time Delay PN_OFFSET Base Station Time Delay PN_OFFSET

WiCoRe, UT-Dallas CDMA Logical Channels Pilot Forward Access Sync Variable-Bit-Rate User Information Paging Signaling Messages Power Control Variable-Bit-Rate User Information Reverse Signaling Messages Traffic

WiCoRe, UT-Dallas Logical Channels Forward Link

WiCoRe, UT-Dallas Pilot  Transmit a continuous sequence of 0s  Rate Mch/s  Used as references of carrier phase and timing  Also, used for Handoff signal indications

WiCoRe, UT-Dallas Sync  Rate = 1,200 b/s ; Digital Carrier Walsh 32  Transmits one Message –System Time –Time delay found in Pseudorandom sequence –Identifiers  Base station  Network

WiCoRe, UT-Dallas Paging Channel  Up to 7 paging channels  Walsh 1 to Walsh 7  Rate – 4,800 b/s or 9,600 b/s  Sleep mode

WiCoRe, UT-Dallas Traffic Channels  Carries voice, control, and power data  Physical channel can change when moving through new cells

WiCoRe, UT-Dallas Logical Channels Reverse Link

WiCoRe, UT-Dallas Access Channels  A terminal without a call in progress uses the access channels to communicate with the base station  Originate call, respond to paging message, register location  Transmission rate is 4800 b/s  88bit or 20 ms frames  Message length of 4-26 frames  Terminal will wait for acknowledgement and retransmit if necessary

WiCoRe, UT-Dallas Traffic Channels  Carries both voice, control

WiCoRe, UT-Dallas Messages Traffic Channel  Call Management Messages  Authentication and Privacy Messages  Radio Resource Management Messages  Mobility Management Messages  Operation, Administration, and Maintnence Messages

WiCoRe, UT-Dallas Messages Paging/Access Channel  Broadcast Messages  Call Management Messages  Authentication and Privacy Messages  Mobility Management Messages  Operations, Administration, and Maintenance Messages

WiCoRe, UT-Dallas QCELP  Qualcomm Code Excited Linear Prediction  20ms speech frames  Variable bit rate speech encoder  4 bit rates; 8,000 4,000 2,000 and 800 b/s

WiCoRe, UT-Dallas Network Operations Radio Resources Management -Power Control -Handoffs Mobility Management Authentication and Security Operations and Maintenance

WiCoRe, UT-Dallas Radio Resources Management A CDMA system has to maintain a narrow range of received power levels. Strong received signals interfere excessively with weaker signals. For power control, IS-95 uses: Open-loop operations Closed-loop operations

WiCoRe, UT-Dallas Power Control Open-loop power control: Mobile unit measures strength of received pilot signal. -Strong signal = close to base station *Mobile transmits at low power. -Weak signal = far from base station *Mobile transmits at high power. -The power level of all received signals at the base station should be equal. P open (dBm) = -P receive (dBm) + P target (dB) P target (dB) = -73 dB + P control (dB)

WiCoRe, UT-Dallas Power Control Closed-loop power control: P transmit (dBm) = P open (dBm) + P closed (dB) -P closed (dB) = P closed (dB) + 1 dB, 0 received* -P closed (dB) = P closed (dB) - 1 dB, 1 received* * Base station transmits either 0 or 1 in power control subchannel, based on received power level at base station.

WiCoRe, UT-Dallas Soft Handoff As mobile moves from cell to cell, it communicates with both cells. Handoffs are mobile initiated and switch controlled. The switch makes handoff decisions and assigns new physical channels. Handoffs use the correlators of the RAKE receiver to communicate with multiple base stations at once.

WiCoRe, UT-Dallas Soft Handoff Same Frequency Band Soft Handoff Region Base station lists: Active list Candidate list Neighbor list Remaining list Base stations are assigned to a list based on signal strength.

WiCoRe, UT-Dallas Switch Old Base Mobile New Base conversation neighbor > threshold Pilot Strength Measurement select channel at new base new active set Handoff Direction program correlators Handoff Complete conversation select signalactive < threshold Pilot Strength Measurement Handoff Direction release correlators conversation Handoff Complete Soft Handoff Flow chart of a soft handoff:

WiCoRe, UT-Dallas Other Handoffs Analog Handoff -Moving to region without CDMA Hard Handoff -Change frequency band -Change switch

WiCoRe, UT-Dallas Mobility Management The mobile sends registration messages to the system. Registration messages help the system to locate the mobile when a call is directed to the mobile.

WiCoRe, UT-Dallas Authentication and Security Authentication and security in IS-95 are the same as in GSM. Added security feature for IS-95: Private Long Code Mask

WiCoRe, UT-Dallas Operations and Maintenance Signals in all cells cover a bandwidth of 1.23 MHz: System is vulnerable to malfunctions in mobile units. - A mobile unit radiating excessive power causes interference to other users. System prevents malfunctioning units from accessing the system.

WiCoRe, UT-Dallas IS-95 Conclusions Uses CDMA technology: Reduces cell reuse factor Efficient bandwidth use -PN sequences to spread signal Soft handoffs